JP6834368B2 - Surface emitting laser element, atomic oscillator - Google Patents

Description

The present invention relates to a surface emitting laser device and an atomic oscillator.

A Vertical Cavity Surface Emitting LASER (VCSEL) is a semiconductor laser that emits light in the direction perpendicular to the substrate surface, and is cheaper, consumes less power, and is smaller than an end face emitting semiconductor laser. It has features such as high performance and easy two-dimensional integration.

The surface emitting laser has a resonator structure including a resonator region including an active layer and an upper reflector and a lower reflector provided above and below the resonator region (see, for example, Patent Document 1). The resonator region is formed with a predetermined optical film thickness at which light having a wavelength λ resonates in the resonator region in order to obtain light having an oscillation wavelength λ.

The upper and lower reflectors are formed by alternately laminating materials having different refractive indexes, that is, low refractive index materials and high refractive index materials, so that high reflectance can be obtained at wavelength λ. , The low refractive index material and the high refractive index material are formed so that the optical film thickness is λ / 4.

The surface emitting laser can be produced by using a metal organic chemical vapor deposition (MOCVD) method, a molecular beam epitaxy (MBE) method, or the like.

However, in the manufacturing process of the surface emitting laser, the crystals produced by the crystal growth method such as the MOCVD method or the MBE method have different growth rates in the surface of the substrate wafer due to the partial difference in the flow velocity and temperature of the raw material gas. , A film thickness distribution occurs in the surface of the substrate wafer.

Since the resonance wavelength of the surface emitting laser is determined by the film thickness distribution, in the surface emitting laser that requires a pinpoint oscillation wavelength, when the film thickness distribution occurs in the surface of the substrate wafer, it is transmitted from one substrate wafer. The number of wafers that can be obtained is reduced, and the yield with respect to the oscillation wavelength is reduced.

The present invention has been made in view of the above, and an object of the present invention is to provide a surface emitting laser element capable of improving the yield with respect to an oscillation wavelength.

The main surface emitting laser element includes a lower Bragg reflector formed on a substrate, a resonator including an active layer formed on the lower Bragg reflector, and an upper Bragg formed on the resonator. The upper Bragg reflecting mirror includes a reflecting mirror, and the upper Bragg reflecting mirror is formed by a first upper Bragg reflecting mirror and a second upper Bragg reflecting mirror which is a wavelength adjustment region from the substrate side, and is formed by the second upper Bragg reflecting mirror. It is a requirement that the optical film thickness Dp of each layer of the mirror satisfies the formula (1) or the formula (2).

但し、式（１）及び式（２）において、λは面発光レーザ素子の発振波長、ｍは５＋０．５（ｐ−１）を満たす値（ｐ：自然数）である。

However, in the equations (1) and (2), λ is the oscillation wavelength of the surface emitting laser element, and m is a value (p: natural number) satisfying 5 + 0.5 (p-1).

According to the disclosed technique, it is possible to provide a surface emitting laser element capable of improving the yield with respect to the oscillation wavelength.

It is a top view which illustrates the surface emitting laser element which concerns on 1st Embodiment. It is a partial cross-sectional view which illustrates the surface emitting laser element which concerns on 1st Embodiment. It is a figure which shows the concept which changes the distribution of the resonance wavelength in the wafer plane in 1st Embodiment. It is a figure explaining the adjustable wavelength range in 1st Embodiment. It is a figure explaining the manufacturing method of the surface emitting laser element which concerns on 1st Embodiment. It is a figure which illustrates the adjustable range of the optical film thickness of each layer of the 2nd upper DBR. It is a top view which illustrates the surface emitting laser element which concerns on 2nd Embodiment. It is a partial cross-sectional view which illustrates the surface emitting laser element which concerns on 2nd Embodiment. It is a schematic diagram of the layer structure of the wavelength adjustment region and the vertical mode of a standing wave which concerns on 2nd Embodiment. It is a figure which shows the concept which changes the distribution of the resonance wavelength in the wafer plane in the 2nd Embodiment. It is a figure explaining the adjustable wavelength range in 2nd Embodiment. It is a schematic diagram of the layer structure of the wavelength adjustment region and the vertical mode of a standing wave which concerns on 3rd Embodiment. It is a figure explaining the adjustable wavelength range in 3rd Embodiment. It is a figure which shows the concept which changes the distribution of the resonance wavelength in the wafer plane in 4th Embodiment. It is a schematic diagram which illustrates the atomic oscillator which concerns on 6th Embodiment. It is explanatory drawing of the atomic energy level related to CPT. It is explanatory drawing of the output wavelength at the time of surface emission laser modulation. It is a correlation diagram of a modulation frequency and a transmitted light amount.

Hereinafter, modes for carrying out the invention will be described with reference to the drawings. In each drawing, the same components may be designated by the same reference numerals and duplicate description may be omitted.

<First Embodiment>
(Outline of surface emitting laser element)
FIG. 1 is a plan view illustrating the surface emitting laser element according to the first embodiment. FIG. 2 is a partial cross-sectional view illustrating the surface emitting laser element according to the first embodiment, and shows a cross section taken along the line AA of FIG. Note that FIG. 1 has been simplified for the purpose of explaining the present embodiment, and the description of the contact layer and the like has been omitted for convenience.

As shown in FIGS. 1 and 2, the surface emitting laser element 10 includes one surface emitting laser 11. The surface emitting laser 11 has a mesa structure. The shape of the mesa structure viewed from the upper part of the surface emitting laser element 10 may be circular, oval, square, rectangular, or the like. The surface emitting laser element 10 emits laser light on the opposite side of the substrate 101 (in the direction of arrow L in FIG. 2).

The surface emitting laser element 10 is formed on, for example, a semiconductor chip of about 300 μm square, and the surface emitting laser 11 formed on the semiconductor chip is connected to the electrode pad 12. The wavelength (oscillation wavelength) of the laser light emitted from the surface emitting laser 11 is λ.

In the surface emitting laser element 10, a lower Bragg reflector 102 (hereinafter referred to as a lower DBR 102) is formed on the substrate 101. DBR is an abbreviation for Distributed Bragg Reflector.

As the substrate 101, for example, an n-GaAs substrate can be used. The lower DBR 102 is formed by alternately laminating semiconductor materials having different refractive indexes. Specifically, in the lower DBR102, for example, _{the optical film thickness of each of the n-Al 0.16} Ga _0.84 As high refractive index layer and the n-AlAs low refractive index layer is λ / 4. It can be formed by laminating 33.5 pairs as described above.

On the lower DBR 102, an active layer 104 made of a GaInAs quantum well layer / AlGaAs barrier layer is formed via a lower spacer layer 103 made of AlGaInP. An upper spacer layer 105 made of AlGaInP is formed on the active layer 104. The lower spacer layer 103, the active layer 104, and the upper spacer layer 105 form a resonator region having an optical film thickness of one wavelength.

An upper Bragg reflector 160 (hereinafter referred to as an upper DBR 160) is formed on the upper spacer layer 105. The upper DBR 160 includes a first upper Bragg reflector 106 (hereinafter referred to as a first upper DBR 106) and a second upper Bragg reflector 107 (hereinafter referred to as a second upper DBR 107).

The first upper DBR 106 is formed by alternately laminating semiconductor materials having different refractive indexes. Specifically, the first upper DBR 106 includes, for example, a p-Al _0.16 Ga _0.84 As high refractive index layer and an n-Al _0.9 Ga _0.1 As low refractive index layer. It can be formed by laminating 6 pairs so that the optical film thickness of the above is λ / 4.

One of the low refractive index layers of the first upper DBR 106 is formed by a current constriction layer 108 made of AlAs. The peripheral portion of the current constriction layer 108 is selectively oxidized to form a selective oxidation region 108a, and the central portion is formed with an unoxidized current constriction region 108b.

A second upper DBR 107 is formed on the first upper DBR 106. The second upper DBR 107 includes, for example, a p-Al _0.16 Ga _0.84 As high refractive index layer and a p-Al _0.9 Ga _0.1 As low refractive index layer, respectively. Can be formed by laminating 18 pairs so that the value is different from λ / 4. The technical significance of setting the optical film thickness of each layer constituting the second upper DBR 107 to a value different from λ / 4 will be described later.

A contact layer 109 is formed on the second upper DBR 107. The contact layer 109 can be formed from, for example, p-GaAs.

An upper electrode 111 serving as a p-side electrode is formed on the contact layer 109. The upper electrode 111 is connected to the electrode pad 12. Further, a lower electrode 112 serving as an n-side electrode is formed on the back surface of the substrate 101.

Here, the technical significance of setting the optical film thickness of each layer constituting the second upper DBR 107 to a value different from λ / 4 will be described.

In the surface emitting laser element 10, the resonance wavelength determined by the film thickness distribution in the wafer surface during crystal growth may deviate from the desired resonance wavelength, or the region where the desired resonance wavelength is achieved may be small. is there. In such a case, it is preferable to expand the in-plane region of the wafer having a desired resonance wavelength from the viewpoint of improving the yield.

Therefore, in the surface emitting laser element 10, the in-plane region of the wafer having a desired resonance wavelength is formed by changing the optical film thickness of each layer constituting the second upper DBR 107 to a value different from λ / 4. It is expanding. That is, in the surface emitting laser element 10, the second upper DBR 107 is the wavelength adjustment region.

FIG. 3 is a diagram showing a concept of changing the distribution of resonance wavelengths in the wafer plane in the first embodiment. In FIG. 3, r on the horizontal axis indicates a predetermined radial direction in the wafer surface, and λ on the vertical axis indicates a wavelength. _{When the distribution D 1} of the resonance wavelength in the wafer surface deviates from the desired wavelength range R, the optical film thickness Dp of each layer constituting the second upper DBR 107 is a value different from λ / 4. by changing, it is possible to change the distribution D ₂ of the resonant wavelength in the wafer plane. Thereby, the in-plane region E of the wafer having a desired resonance wavelength can be expanded.

_{For example, when the resonance Dip wavelength λ dip} after crystal growth up to the first upper DBR 106 is a short wavelength with respect to the desired oscillation wavelength λ, the optical film thickness of each layer constituting the second upper DBR 107 By making Dp thicker than λ / 4, the in-plane region E of the wafer having a desired resonance wavelength can be expanded.

_{Further, when the resonance dip} wavelength λ dip after crystal growth up to the first upper DBR 106 is a long wavelength with respect to the desired oscillation wavelength λ, the optical film thickness of each layer constituting the second upper DBR 107 is formed. By making Dp thinner than λ / 4, the in-plane region E of the wafer having a desired resonance wavelength can be expanded.

However, if the optical film thickness Dp is significantly changed, the oscillation threshold current value of the surface emitting laser 11 changes significantly, which greatly changes the laser characteristics with respect to the design value. Therefore, the range in which the optical film thickness Dp is changed is set. Need to be specified. This will be described with reference to FIG.

FIG. 4 is a diagram illustrating an adjustable wavelength range in the first embodiment, in which the adjusted wavelength Δλ and the oscillation threshold current Is, which are the differences between _{the resonant dip wavelength λ dip and the desired oscillation wavelength λ.} The optical film thickness Dp dependence is illustrated. In FIG. 4, the triangle is the oscillation threshold current Is, and the black circle is the adjustment wavelength Δλ.

As shown in FIG. 4, the amount of change in the oscillation threshold current Is is about 0.1 mA between 0.247λ <optical film thickness Dp <0.255λ shown by the two vertical two-dot chain lines. The wavelength shift amount with respect to this current value is estimated to be about 0.05 nm.

That is, when 0.247λ <optical film thickness Dp <0.255λ, the influence of the wavelength shift due to the current is sufficiently small with respect to the change in the oscillation wavelength λ due to the change in the optical film thickness Dp, and the oscillation wavelength is increased. Does not have a significant effect.

Therefore, if 0.247λ <optical film thickness Dp <0.255λ, the resonance wavelength can be adjusted at ± 0.75 nm without significantly changing the laser characteristics with respect to the design value.

That is, when the number of pairs of the high refractive index layer and the low refractive index layer in the first upper DBR 106 is 6, 0.247λ <optical film thickness Dp <0.25λ or 0.25λ <optical film. By adjusting the optical film thickness Dp so as to satisfy the thickness Dp <0.255λ, a desired oscillation wavelength λ can be obtained without significantly affecting the characteristics.

(Manufacturing method of surface emitting laser element)
Next, a method of manufacturing the surface emitting laser element 10 including a wavelength adjusting step (a step of adjusting the optical film thickness of each layer in the wavelength adjusting region) will be described.

First, as shown in step S100 of FIG. 5, the wavelength adjustment region (second upper DBR107) is laminated up to the lower layer on the substrate 101. Specifically, a lower DBR 102 made of a semiconductor material, a lower spacer layer 103, an active layer 104, an upper spacer layer 105, and a first upper DBR 106 are laminated on a substrate 101 made of n-GaAs.

Those in which a plurality of layers are laminated on the substrate 101 in this way may be referred to as a "laminated body" for convenience below. The laminate can be formed by, for example, an organometallic vapor phase growth (MOCVD) method. Further, it may be carried out by using a molecular beam epitaxy (MBE) method or the like.

Next, as shown in step S110 of FIG. 5, reflection spectroscopy measurement in the wafer plane is performed, and the deviation between the desired wavelength and the resonance wavelength is calculated. Then, as shown in step S120 of FIG. 5, the film thickness of the second upper DBR 107, which is the wavelength adjustment region, is determined, and the second upper DBR 107 and the contact layer 109 are recrystallized.

_{Specifically, when the resonance Dip wavelength λ dip} after crystal growth up to the first upper DBR 106 is a short wavelength with respect to the desired oscillation wavelength λ, the optical film thickness of the second upper DBR 107 is λ /. Feedback is given to the growth time at the time of recrystallization growth so as to increase the thickness from 4.

On the other hand, when the resonance Dip wavelength λ _dip after crystal growth up to the first upper DBR 106 is a long wavelength with respect to the desired oscillation wavelength λ, the optical film thickness of the second upper DBR 107 is thinner than λ / 4. The feedback is given to the growth time at the time of recrystallization growth.

For example, 0.247λ <optical film thickness Dp <0.25λ, based on the relationship between the adjustment wavelength Δλ shown in FIG. 4 and the optical film thickness Dp of each layer constituting the second upper DBR107. Alternatively, the optical film thickness Dp can be determined within the range of 0.25λ <optical film thickness Dp <0.255λ.

Next, as shown in step S130 of FIG. 5, the steps after the production of the wavelength adjustment region are executed. Specifically, after forming the second upper DBR 107, the semiconductor layer around the region to be the surface emitting laser 11 is removed by etching to at least the depth at which the side surface of the current constriction layer 108 appears to form a mesa structure. .. A dry etching method can be used for etching when forming the mesa structure. The mesa structure may be formed so that the shape seen from the upper part is circular, or may be formed so as to have an elliptical shape, a square shape, a rectangular shape, or the like.

After forming the mesa structure, the current constriction layer 108 is oxidized from the periphery of the mesa structure by performing heat treatment in steam, and the selective oxidation region 108a (oxidized region) in the peripheral portion and the central portion are oxidized. It forms with no current constriction region 108b. That is, the current constriction layer 108 is composed of an oxidized selective oxidation region 108a and an unoxidized current constriction region 108b, and has a current constriction structure.

After that, a protective film 170 made of SiN or the like is formed on the outside of the mesa structure of the surface emitting laser 11. Then, the protective film 170 on the contact layer 109 is removed, and an upper electrode 111 serving as a p-side electrode is formed on the contact layer 109. Then, a lower electrode 112 serving as an n-side electrode is formed on the back surface of the substrate 101. Through the above steps, the surface emitting laser element 10 is completed.

The above constitutes the second upper DBR 107 when 6 pairs of the high refractive index layer and the low refractive index layer are laminated so that the optical film thickness of each layer is λ / 4. This is an example of obtaining a desired oscillation wavelength λ by adjusting the optical film thickness Dp of each layer. However, since the number of pairs of the high refractive index layer and the low refractive index layer in the first upper DBR 106 is not limited to 6, the number of pairs of the high refractive index layer and the low refractive index layer in the first upper DBR 106 is generally used. The case of refraction will be described below.

When the number of pairs of the high refractive index layer and the low refractive index layer in the first upper DBR 106 is m, the optical film thickness Dp of each layer constituting the second upper DBR 107 is calculated by the following formula (1). ) Or the desired oscillation wavelength λ can be obtained by adjusting within the range of the equation (2). In addition, in equations (1) and (2), the range of the optical film thickness Dp of each layer constituting the second upper DBR 107 in which the amount of change in the oscillation threshold current value is 0.1 mA or less is defined as the range of the optical film thickness Dp. The number of pairs of the upper DBR 106 of 1 is obtained as a variable m.

但し、式（１）及び式（２）において、λは面発光レーザ素子の発振波長、ｍは５＋０．５（ｐ−１）を満たす値（ｐ：自然数）である。ここで、ｍが整数でない場合（ｍ＝５．５、６．５、・・・）を含むのは、高屈折率層の数と低屈折率層の数が異なる場合があるからである。

However, in the equations (1) and (2), λ is the oscillation wavelength of the surface emitting laser element, and m is a value (p: natural number) satisfying 5 + 0.5 (p-1). Here, the case where m is not an integer (m = 5.5, 6.5, ...) Is included because the number of high refractive index layers and the number of low refractive index layers may be different.

As shown in equations (1) and (2), even if the first upper DBR 106 and the second upper DBR 107 are moved to arbitrary positions above 5 pairs, the variable m is the number of pairs of the first upper DBR 106. The optical film thickness Dp of each layer of the second upper DBR 107 whose wavelength can be adjusted can be described as.

FIG. 6 shows an adjustable range of the optical film thickness of each layer of the second upper DBR 107. In FIG. 6, the vertical axis is the optical film thickness Dp of each layer of the second upper DBR 107, and the horizontal axis is the position within the upper DBR 160 of the interface between the first upper DBR 106 and the second upper DBR 107 (first upper DBR 106). The number of pairs is m).

As shown in FIG. 6, the range of the film thickness to be restricted changes depending on where the boundary between the first upper DBR 106 and the second upper DBR 107 is placed. The wavelength closer to the substrate 101 side (resonator region) can be moved significantly with a smaller amount of change in film thickness. However, the more the optical film thickness of each layer is deviated from λ / 4 in an attempt to largely adjust the wavelength, the lower the characteristics (increase in the threshold current value). In the film thickness range satisfying the formula (1) or the formula (2) (that is, the adjustable film thickness range shown by the broken line in FIG. 6), the wavelength can be adjusted without significantly deteriorating the characteristics as in FIG. is there. In the case of FIG. 6, the resonance wavelength can be adjusted in the range of ± 0.75 nm without significantly deteriorating the characteristics.

The reason why only m = 5 (5 pairs) or more is targeted in the equations (1) and (2) is as follows. An object of the present invention is to grow once up to the first upper DBR106 at the stage of crystal growth when manufacturing a surface emitting laser element _{, calculate the deviation of the resonance Dip wavelength λ dip} , and correct the calculated deviation. The optical film thickness of the wavelength adjustment layer is adjusted. At this time, if about 5 pairs of the first upper DBR 106 are not stacked, the contribution of the first upper DBR 106 becomes small. Therefore, in the formulas (1) and (2), m = 5 (5 pairs) or more is limited.

As described above, in the surface emitting laser element 10 according to the first embodiment, the second upper DBR107 is provided on the first upper DBR106, and the second upper DBR107 is provided so that a desired oscillation wavelength λ can be obtained. The optical film thickness Dp of each layer constituting the above is adjusted within the range of the formula (1) or the formula (2).

As a result, even when the film thickness fluctuates in the wafer surface during crystal growth and the desired oscillation wavelength λ and the resonance wavelength deviate from each other, the desired oscillation wavelength λ can be adjusted. As a result, the yield of the surface-emitting laser element with respect to the oscillation wavelength λ is improved (that is, it is possible to maximize the region in the wafer surface where the desired oscillation wavelength λ can be achieved), and the cost of the surface-emitting laser element 10 is low. Can be realized.

<Second Embodiment>
In the second embodiment, an example in which the oscillation wavelength λ is adjusted by a method different from that of the first embodiment is shown. In the second embodiment, the description of the same components as those in the above-described embodiment may be omitted.

(Outline of surface emitting laser element)
FIG. 7 is a plan view illustrating the surface emitting laser element according to the second embodiment. FIG. 8 is a partial cross-sectional view illustrating the surface emitting laser element according to the second embodiment, and shows a cross section taken along the line BB of FIG. Note that FIG. 7 has been simplified for the purpose of explaining the present embodiment, and the description of the contact layer and the like is omitted for convenience.

As shown in FIGS. 7 and 8, the surface emitting laser element 20 includes one surface emitting laser 21. The surface emitting laser 21 is connected to the electrode pad 22. The wavelength (oscillation wavelength) of the laser light emitted from the surface emitting laser 21 is λ.

The surface emitting laser element 20 is different from the surface emitting laser element 10 (see FIG. 2 and the like) in that a second upper DBR 107 is formed on the first upper DBR 106 via a wavelength adjustment region 150. .. Further, in the surface emitting laser element 20, the second upper DBR107 is not in the wavelength adjustment region, and the second upper DBR107 is, for example, p-Al _0.16 Ga _0.84 As high refractive index layer and p-Al _{0. .9} Ga _0.1 As low refractive index layer is formed by laminating 18 pairs so that the optical film thickness of each layer is λ / 4.

FIG. 9 is a schematic view of the layer structure of the wavelength adjustment region and the vertical mode of the standing wave according to the second embodiment.

As shown in FIG. 9, the wavelength adjustment region 150 is configured by laminating a first phase adjustment layer 151, a wavelength adjustment layer 153, and a second phase adjustment layer 152 from the first upper DBR106 side. .. Further, the wavelength adjustment layer 153 is configured by laminating a first adjustment layer 153a, a second adjustment layer 153b, and a third adjustment layer 153c from the first phase adjustment layer 151 side.

In the surface emitting laser element 20, as an example, the first phase adjusting layer 151 and the second phase adjusting layer 152 are formed of a p—Al _0.16 Ga _0.84 As high refractive index layer. The first phase adjusting layer 151 and the second phase adjusting layer 152 may be formed of a semiconductor material other than AlGaAs.

In the second upper DBR 107, the layer in contact with the second phase adjusting layer 152 is a p-Al _0.9 Ga _0.1 As low refractive index layer. That is, the second phase adjusting layer 152 is formed of a material having a higher refractive index than the material of the lowermost layer of the second upper DBR 107 in contact with the second phase adjusting layer 152.

The wavelength adjustment layer 153 is a form in which three semiconductor material films having different refractive indexes are alternately laminated, and from the substrate 101 side, the first adjustment layer 153a, the second adjustment layer 153b, and the third adjustment layer 153c. Is. However, as will be described later, the surface emitting laser element 20 may not have the wavelength adjusting layer 153 depending on the wavelength at the time of crystal growth.

The first adjusting layer 153a and the third adjusting layer 153c are formed of GaInP as an example, and the second adjusting layer 153b is formed of GaAsP as an example. The material forming the first adjusting layer 153a, the third adjusting layer 153c, and the second adjusting layer 153b may be the opposite. Further, the first adjusting layer 153a, the third adjusting layer 153c, and the second adjusting layer 153b may be formed of another semiconductor material.

The film thickness of the wavelength adjustment region 150 is 3λ / 4, the standing wave at the interface between the first upper DBR 106 and the wavelength adjustment region 150 is a node, and the vicinity of the center of the wavelength adjustment layer 153 is also a node. There is.

In the present embodiment, in order to achieve a desired oscillation wavelength, the resonance wavelength can be changed by 1 nm by changing the number of layers of the wavelength adjustment layer 153 one by one, and the layer of the wavelength adjustment layer 153. The 3 nm resonance wavelength can be adjusted by changing the number.

Specifically, in the in-wafer in-plane region having a desired resonance wavelength during crystal growth, the wavelength adjustment region 150 includes the first phase adjustment layer 151, the first adjustment layer 153a, the second adjustment layer 153b, and the third. It is composed of an adjusting layer 153c and a second phase adjusting layer 152, and emits light having a desired wavelength.

In the in-wafer region having a resonance wavelength 1 nm longer than the desired wavelength during crystal growth, the wavelength adjustment region 150 includes the first phase adjustment layer 151, the first adjustment layer 153a, the second adjustment layer 153b, and the first. It is composed of two phase adjusting layers 152, and light having a desired wavelength is emitted.

In the in-wafer in-plane region having a resonance wavelength 2 nm longer than the desired wavelength during crystal growth, the wavelength adjustment region 150 is formed from the first phase adjustment layer 151, the first adjustment layer 153a, and the second phase adjustment layer 152. Therefore, light of a desired wavelength is emitted.

In the in-wafer in-plane region having a resonance wavelength 3 nm longer than the desired wavelength during crystal growth, the wavelength adjustment region 150 is composed of a first phase adjustment layer 151 and a second phase adjustment layer 152, and light having a desired wavelength is emitted. It is emitted.

In this way, by changing the number of layers of the wavelength adjusting layer 153, it is possible to cancel the wafer in-plane film thickness distribution for 3 nm and expand the wafer in-plane region having a resonance Dip wavelength close to a desired wavelength.

In the present embodiment, the wavelength adjusting layer 153 has three adjusting layers, but the present invention is not limited to this, and the number of adjusting layers may be more or less than three. Further, in the present embodiment, the film thickness of the wavelength adjusting layer 153 is designed so that the wavelength can be adjusted by 1 nm for each adjusting layer, but the film thickness of the adjusting layer is thick even if it is thinner than this. However, the film thickness of the adjusting layer can be appropriately determined according to the required wavelength accuracy.

In the present embodiment, the wavelength can be adjusted in the range of 3 nm by arbitrarily changing the number of layers of the wavelength adjusting layer 153. However, when the desired wavelength deviates from the wavelength range of 3 nm that can be adjusted by the number of layers of the wavelength adjusting layer 153 at the stage of crystal growth up to the wavelength adjusting layer 153, or even if the wavelength is adjusted, it is desired in the wafer surface. There may be few regions where wavelengths can be achieved. Therefore, the resonance wavelength of the entire wafer surface can be adjusted by arbitrarily changing the film thickness of the second phase adjusting layer as described below.

In this method, since the wavelength can be adjusted by changing the film thickness of only the second phase adjusting layer 152, it is easy to control the film thickness. Further, since the amount of change from the original film thickness design value of the entire layer structure is small, it is easy to obtain desired laser characteristics.

FIG. 10 is a diagram showing a concept of changing the distribution of resonance wavelengths in the wafer plane in the second embodiment. In FIG. 10, r on the horizontal axis indicates a predetermined radial direction in the wafer surface, and λ on the vertical axis indicates a wavelength. _{As shown in FIG. 10, the resonance wavelength distribution D 2} in the wafer surface, which is made uniform by canceling _{the wafer in-plane film thickness distribution D 1} for 3 nm by adjusting the wavelength adjusting layer 153, is from the desired wavelength range R. If you are out, by arbitrarily changing the thickness of the second phase adjusting layer 152, it is possible to change the distribution D ₃ of the resonance wavelength in the wafer plane. Thereby, the in-plane region E of the wafer having a desired resonance wavelength can be expanded.

(Manufacturing method of surface emitting laser element)
First, on a substrate 101 made of n-GaAs, a lower DBR 102 made of a semiconductor material, a lower spacer layer 103, an active layer 104, an upper spacer layer 105, a first upper DBR 106, and a part of a wavelength adjustment region 150. The phase adjustment layer 151 and the wavelength adjustment layer 153 of No. 1 are laminated and formed.

Next, reflection spectroscopy measurement in the wafer surface is performed, the deviation between the resonant Dip wavelength and the desired wavelength is calculated, and the number of adjustment layers to be changed in the wavelength adjustment layer 153 is determined.

Below, the wavelength adjustment region 150, the first adjustment layer 153a, the second adjustment layer 153b, and the third adjustment layer 153c surface emitting laser is formed 20 _1, and the first adjustment layer 153a and the second the surface emitting laser 2 of the adjustment layer 153b is formed 20 _2, the first adjustment layer 153a only the surface emitting laser is formed 20 _3, one of the adjustment layer is also not formed a surface emitting laser 20 ₄ wafers A method of forming each wavelength adjustment region 150 will be described by taking the case of forming in the plane as an example. Further, here, as an example, it is assumed that the first adjusting layer 153a is formed of GaInP, the second adjusting layer 153b is formed of GaAsP, and the third adjusting layer 153c is formed of GaInP.

First, a resist pattern in a region where the surface emitting laser 20 ₁ is formed. Specifically, a photoresist is applied onto the third adjustment layer 153c in the wavelength adjustment region 150, the exposure by the exposure device, by performing development, the resist pattern only in a region where the surface emitting laser 20 ₁ is formed Form.

Next, the third adjusting layer 153c in the region where the resist pattern is not formed is removed by wet etching. Specifically, since the third adjusting layer 153c is formed of GaInP, wet etching is performed with a mixed solution of hydrochloric acid and water (hereinafter, may be referred to as a first etching solution).

Thus, the surface emitting laser ₂₀ 2 where the resist pattern is not formed, 20 _3, and only the third adjustment layer 153c is removed in a 20 _{region 4} is formed to expose the surface of the second adjustment layer 153b be able to.

The first etching solution can etch GaInP forming the third adjusting layer 153c, but can hardly etch GaAsP forming the second adjusting layer 153b. After that, the resist pattern is removed with an organic solvent or the like.

Next, a photoresist is applied to the third adjustment layer 153c and the second adjustment layer 153b on the exposure by the exposure device, by performing development, the area where the surface emitting laser 20 ₁ and 20 ₂ are formed only on Form a resist pattern.

Next, the second adjusting layer 153b in the region where the resist pattern is not formed is removed by wet etching. Specifically, since the second adjusting layer 153b is formed of GaAsP, wet etching is performed with a mixed solution of sulfuric acid, hydrogen peroxide, and water (hereinafter, may be referred to as a second etching solution). ..

Thus, only the second adjustment layer 153b is removed in the region where the surface emitting laser 20 ₃ and 20 ₄ where the resist pattern is not formed is formed, it is possible to expose the surface of the first adjustment layer 153a.

The second etching solution can etch GaAsP forming the second adjusting layer 153b, but can hardly etch GaInP forming the first adjusting layer 153a. After that, the resist pattern is removed with an organic solvent or the like.

Next, a photoresist is applied on the third adjusting layer 153c, the second adjusting layer 153b, and the first adjusting layer 153a, and the surface emitting lasers 20 ₁ and 20 are exposed and developed by an exposure apparatus. _2, and 20 ₃ to form a resist pattern only in the region is formed.

Next, the first adjusting layer 153a in the region where the resist pattern is not formed is removed by wet etching. Specifically, since the first adjusting layer 153a is formed of GaInP, wet etching is performed with the first etching solution.

Accordingly, only to remove the first adjustment layer 153a of the surface emitting laser 20 ₄ where the resist pattern is not formed, it is possible to expose the surface of the first phase adjusting layer 151. After that, the resist pattern is removed with an organic solvent or the like.

Next, the second phase adjusting layer 152, the second upper DBR 107, and the contact layer 109 are recrystallized and grown. As a result, the wavelength adjustment region 150 and the second upper DBR 107 in the surface emitting laser according to the present embodiment can be formed. Thereafter, by singulating a surface emitting laser 20 _1-emitting laser 20 _4, a plurality of surface emitting laser layer number of the wavelength adjustment layer 153 in consideration of the deviation of the desired wavelength and the resonant Dip wavelength is adjusted The element 20 is formed.

In the present embodiment, since the first adjusting layer 153a, the second adjusting layer 153b, and the third adjusting layer 153c forming the wavelength adjusting layer 153 do not contain Al, they are oxidized after etching. It is difficult to maintain a clean surface condition even after etching.

That is, since Al is extremely easily corroded, when any of the first adjusting layer 153a, the second adjusting layer 153b, and the third adjusting layer 153c is formed from the material containing Al, wet etching or the like is performed. Later surface conditions will be poor. Therefore, even if the second upper DBR 107 is formed on this, it may be peeled off or the thickness may be uneven.

However, in the surface emitting laser element 20, since the wavelength adjusting layer 153 is formed of a material that does not contain Al, corrosion of Al or the like does not occur, and such a problem does not occur.

Further, in the present embodiment, the wavelength adjustment layer 153 in the wavelength adjustment region 150 is formed by alternately forming GaAsP and GaInP. Then, when performing wet etching, etching is performed using two types of etching solutions, one of which can be etched with each other but the other cannot be etched.

By performing etching using these two types of etching solutions, the surface after etching becomes flat, and it is possible to form a predetermined thickness without over-etching. As a result, the surface emitting laser element 20 having stable characteristics can be obtained.

In the above example, the case where the adjustment layer constituting the wavelength adjustment layer 153 is a combination of GaAsP and GaInP has been described. However, the adjustment layer constituting the wavelength adjustment layer 153 may be a combination of other semiconductor materials which are materials that do not contain Al, have different etching solutions, and have a bandgap energy larger than the oscillation wavelength.

For example, when the oscillation wavelength is 894.6 nm, examples of such a combination of semiconductor materials include GaInAsP / GaInP, GaAs / GaInP, GaAs / GaInAsP, GaAsP / GaInAsP, and the like. Further, N and Sb may be added such as GaAsN / GaInP, GaInNAs / GaInP, GaAsSb / GaInP and the like.

Next, the optical film thickness of the second phase adjusting layer 152 in the surface emitting laser element 20 will be described in detail. As described above, by changing the number of layers of the wavelength adjusting layer 153, it is possible to cancel the film thickness distribution in the wafer surface and obtain a uniform wavelength, but the adjustable wavelength range is the wavelength adjusting layer 153. In this embodiment, the film thickness distribution is up to 3 nm, depending on the number of layers. Therefore, in the crystal growth up to the wavelength adjustment layer 153, the desired wavelength may deviate from the wavelength range that can be adjusted by the wavelength adjustment layer 153, or even if the desired wavelength is adjusted, the in-plane region of the wafer that achieves the required specifications may be small. ..

Therefore, after the wavelength adjustment layer 153 is formed, reflection spectroscopy measurement in the wafer surface is performed to calculate the deviation between the resonant Dip wavelength and the desired wavelength. Then, the resonance wavelength can be adjusted to a desired wavelength by changing the film thickness of the second phase adjusting layer 152 so as to compensate for the calculated deviation.

_{Specifically, when the uniform resonance dip} wavelength λ dip after adjusting the number of adjustment layers of the wavelength adjustment layer 153 is a short wavelength with respect to the desired oscillation wavelength λ, the second phase adjustment layer 152 Feedback is given to the growth time during recrystallization so as to increase the film thickness.

On the other hand, when the uniform resonance Dip wavelength λ _dip after forming the wavelength adjustment layer 153 is a long wavelength with respect to the desired oscillation wavelength λ, the film thickness of the second phase adjustment layer 152 is reduced so as to be thin. Feedback is given to the growth time during recrystallization growth.

By the way, in the wavelength adjustment by changing the film thickness of the second phase adjusting layer 152, the wavelength can be adjusted by changing only the film thickness of one layer of the second phase adjusting layer 152. Therefore, the number of layers for which the film thickness is changed can be reduced as compared with the case where the optical film thickness of each layer of the second upper DBR 107 is changed from λ / 4. This means that there is little variation from the laser characteristics obtained from the initial design value, and it is effective to adjust the wavelength only by changing the optical film thickness of the second phase adjustment layer 152.

FIG. 11 is a diagram illustrating an adjustable wavelength range in the second embodiment, in which the first phase adjusting layer 151 and the second phase adjusting layer 152 have p-Al _0.16 Ga _0.84 As. In the case of a high refractive index layer, the dependence of the adjustment wavelength Δλ, which is the difference between the resonance Dip wavelength and the desired oscillation wavelength λ, and the optical film thickness d of the second phase adjustment layer 152 of the oscillation threshold current Is Illustrate. In FIG. 11, the triangle is the oscillation threshold current Is, and the black circle is the adjustment wavelength Δλ.

As shown in FIG. 11, assuming that the optical film thickness d'per one adjusting layer of the wavelength adjusting layer 153, the number of layers n (positive integer) of the wavelength adjusting layer 153, and the film thickness D of the wavelength adjusting region 150, Regarding the optical film thickness d of the second phase adjusting layer 152, the amount of change in the oscillation threshold current Is is about 0 in the range represented by the equation (3) (the range indicated by the two vertical two-point chain lines). It is about 1 mA, and the wavelength shift amount with respect to this current value is estimated to be about 0.05 nm.

In FIG. 11, the horizontal axis is the optical film thickness d (λ) of the second phase adjusting layer 152, but “0” on the horizontal axis indicates “1/2 (D−nd')”. There is. For example, in FIG. 11, the 0.05 portion means d = 0.05λ + 1/2 (D−nd ′).

第２の位相調整層１５２の光学的膜厚ｄが式（３）で表される範囲では、第２の位相調整層の膜厚ｄの変更による発振波長λの変化に対して、電流による波長シフトの影響は十分に小さく、発振波長に大きく影響しない。

In the range where the optical film thickness d of the second phase adjustment layer 152 is represented by the equation (3), the wavelength due to the current is in response to the change in the oscillation wavelength λ due to the change in the film thickness d of the second phase adjustment layer. The effect of shift is small enough and does not significantly affect the oscillation wavelength.

Therefore, if the optical film thickness d of the second phase adjusting layer 152 is within the range represented by the equation (3), the resonance wavelength is adjusted at ± 2.4 nm without significantly changing the laser characteristics with respect to the design value. It is possible to do.

If this is generalized, the range of the optical film thickness d of the adjustable second phase adjusting layer 152 can be expressed by the equation (4). In the equation (4), N is a positive integer, but it is desirable that N is small in consideration of adverse effects such as an increase in the oscillation threshold current value due to the influence of light absorption.

ところで、波長調整領域１５０を共振器内に形成することも可能である。その場合、共振器に近いことから、波長調整層１５３の膜厚が本実施の形態より薄くても、大きく波長範囲を変えることが可能である。層構造に対して大きな変化を与えずに、発振波長を大きく変える必要がある場合は、波長調整領域１５０を共振器に近づけていくことで、対応可能である。

By the way, it is also possible to form the wavelength adjustment region 150 in the resonator. In that case, since it is close to a resonator, the wavelength range can be significantly changed even if the film thickness of the wavelength adjusting layer 153 is thinner than that of the present embodiment. When it is necessary to change the oscillation wavelength significantly without giving a large change to the layer structure, it can be dealt with by moving the wavelength adjustment region 150 closer to the resonator.

As described above, in the surface emitting laser element 20 according to the second embodiment, a desired oscillation wavelength λ can be obtained for a uniform resonance Dip wavelength λdip after adjusting the number of adjustment layers of the wavelength adjustment layer 153. , The optical film thickness d of the second phase adjusting layer 152 is adjusted within the range of the equation (4).

As a result, even when the desired oscillation wavelength λ and the resonance wavelength deviate from each other, the desired oscillation wavelength λ can be adjusted. As a result, the yield of the surface-emitting laser element with respect to the oscillation wavelength λ is improved (that is, it is possible to maximize the region in the wafer surface where the desired oscillation wavelength λ can be achieved), and the cost of the surface-emitting laser element 20 is low. Can be realized.

<Third embodiment>
In the third embodiment, another example in which the oscillation wavelength λ is adjusted by a method different from that of the first embodiment is shown. In the third embodiment, the description of the same components as those in the above-described embodiment may be omitted.

The layer structure of the surface emitting laser element according to the third embodiment includes the number of pairs of the first upper DBR106, the composition and film thickness of the first phase adjusting layer 151 and the second phase adjusting layer 152, and the second. Except for the number of pairs of the upper DBR 107, it is the same as the surface emitting laser element 20 according to the second embodiment.

In the surface emitting laser element according to the third embodiment, the first upper DBR 106 has a p-Al _0.16 Ga _0.84 As high refractive index layer and a p-Al _0.9 Ga _0.1 As low refraction. The rate layer is formed by laminating 6.5 pairs so that each layer is λ / 4. The layer of the first upper DBR 106 in contact with the first phase adjusting layer 151 is a p-Al _0.16 Ga _0.84 As high refractive index layer.

FIG. 12 is a schematic view of the layer structure of the wavelength adjustment region and the longitudinal mode of the standing wave according to the third embodiment. In the surface emitting laser device according to the third embodiment, the wavelength adjustment region 150 is formed on the first upper DBR 106. The wavelength adjustment region 150 includes a first phase adjustment layer 151, a first adjustment layer 153a, a second adjustment layer 153b, and a third adjustment layer 153c, which _{are composed of a p-Al 0.9} Ga _{0.1 As low refractive index layer.} , P—Al _0.9 Ga _0.1 As A second phase adjusting layer 152 made of a low refractive index layer is formed. That is, the second phase adjusting layer 152 is formed of a material having a refractive index lower than that of the material of the lowermost layer of the second upper DBR 107 in contact with the second phase adjusting layer 152.

The film thickness of the wavelength adjustment region 150 is 3λ / 4, the standing wave at the interface between the first upper DBR 106 and the wavelength adjustment region 150 is antinode, and the vicinity of the center of the wavelength adjustment layer 153 is a node. There is. As in the second embodiment, the formed surface emitting laser element cancels the film thickness distribution in the wafer surface and has a wavelength for each position in the wafer surface so as to obtain a desired resonance wavelength. A part of the adjustment region 150 has been removed.

In the present embodiment, as in the second embodiment, by changing the number of layers of the wavelength adjustment layer 153, the in-wafer film thickness distribution for 3 nm is canceled, and the resonance Dip wavelength close to the desired oscillation wavelength is obtained. Enlarge the in-plane area of the wafer with. After that, reflection spectroscopy measurement is performed, and the film thickness of the second phase adjusting layer 152 is arbitrarily changed so as to compensate for the deviation between the resonance Dip wavelength and the desired oscillation wavelength.

In the present embodiment as well, as in the second embodiment, the in-plane region of the wafer having a uniform resonant Dip wavelength expanded by changing the number of layers of the wavelength adjusting layer 153 is formed in the second phase adjusting layer 152. By changing the film thickness of the wafer, the in-plane region of the wafer having the desired resonant Dip wavelength is adjusted to be maximized.

FIG. 13 is a diagram illustrating an adjustable wavelength range in the third embodiment, in which the first phase adjusting layer 151 and the second phase adjusting layer 152 are p-Al _0.9 Ga _0.1 As. In the case of a low refractive index layer, the dependence of the adjustment wavelength Δλ, which is the difference between the resonance Dip wavelength and the desired oscillation wavelength λ, and the optical film thickness d of the second phase adjustment layer 152 of the oscillation threshold current Is Illustrate. In FIG. 13, the triangle is the oscillation threshold current Is, and the black circle is the adjustment wavelength Δλ.

As shown in FIG. 13, assuming that the optical film thickness d'per one adjusting layer of the wavelength adjusting layer 153, the number of layers n (positive integer) of the wavelength adjusting layer 153, and the film thickness D of the wavelength adjusting region 150, In the range represented by the equation (5) (the range indicated by the two vertical two-point chain lines), the change amount of the oscillation threshold current Is is about 0 for the optical film thickness d of the second phase adjusting layer 152. It is about 1 mA, and the wavelength shift amount with respect to this current value is estimated to be about 0.05 nm.

In FIG. 13, the horizontal axis is the optical film thickness d (λ) of the second phase adjusting layer 152, but “0” on the horizontal axis indicates “1/2 (D−nd')”. There is. For example, in FIG. 13, the 0.05 portion means d = 0.05λ + 1/2 (D−nd ′).

第２の位相調整層１５２の光学的膜厚ｄが式（５）で表される範囲では、第２の位相調整層の膜厚ｄの変更による発振波長λの変化に対して、電流による波長シフトの影響は十分に小さく、発振波長に大きく影響しない。

In the range where the optical film thickness d of the second phase adjustment layer 152 is represented by the equation (5), the wavelength due to the current is in response to the change in the oscillation wavelength λ due to the change in the film thickness d of the second phase adjustment layer. The effect of shift is small enough and does not significantly affect the oscillation wavelength.

Therefore, if the optical film thickness d of the second phase adjusting layer 152 is within the range represented by the equation (5), the resonance wavelength is adjusted at ± 2.2 nm without significantly changing the laser characteristics with respect to the design value. It is possible to do.

If this is generalized, the range of the optical film thickness d of the adjustable second phase adjusting layer 152 can be expressed by the equation (6). In the formula (6), N is a positive integer, but it is desirable that N is small in consideration of adverse effects such as an increase in the oscillation threshold current value due to the influence of light absorption.

このように、第３の実施の形態に係る面発光レーザ素子では、波長調整層１５３の調整層の数を調整後の均一な共振Ｄｉｐ波長λｄｉｐについて、所望の発振波長λが得られるように、第２の位相調整層１５２の光学的膜厚ｄを式（６）の範囲内で調整する。

As described above, in the surface emitting laser element according to the third embodiment, a desired oscillation wavelength λ can be obtained for a uniform resonance Dip wavelength λdip after adjusting the number of adjustment layers of the wavelength adjustment layer 153. The optical film thickness d of the second phase adjusting layer 152 is adjusted within the range of the equation (6).

As a result, even when the desired oscillation wavelength λ and the resonance wavelength deviate from each other, the desired oscillation wavelength λ can be adjusted. As a result, the yield of the surface emitting laser element with respect to the oscillation wavelength λ is improved (that is, it is possible to maximize the region in the wafer surface where the desired oscillation wavelength λ can be achieved), and the cost of the surface emitting laser element is reduced. Can be realized.

<Fourth Embodiment>
The fourth embodiment shows another example in which the oscillation wavelength λ is adjusted by a method different from that of the first embodiment. In the fourth embodiment, the description of the same components as those in the above-described embodiment may be omitted.

The layer structure of the surface emitting laser element according to the fourth embodiment is the same as that of the second embodiment except for the film thickness of each layer of the second upper DBR107. That is, in the surface emitting laser element according to the fourth embodiment, a second upper DBR107 which is a wavelength adjustment region is formed in the upper DBR160, and a wavelength adjustment region including a wavelength adjustment layer and a phase adjustment layer is further provided. 150 is formed.

When the film thickness distribution in the wafer surface is out of the adjustable wavelength range due to an arbitrary change in the number of layers of the wavelength adjusting layer 153 and the film thickness of the second phase adjusting layer 152, the first embodiment Similarly, the wavelength can be adjusted by arbitrarily changing the film thickness of each layer of the second upper DBR.

FIG. 14 is a diagram showing a concept of changing the distribution of resonance wavelengths in the wafer plane in the fourth embodiment. In FIG. 14, r on the horizontal axis indicates a predetermined radial direction in the wafer surface, and λ on the vertical axis indicates a wavelength. _{As shown in FIG. 14, the resonance wavelength distribution D 2} in the wafer surface, which cancels out the wafer in-plane film thickness distribution D ₁ for 3 nm by adjusting the wavelength adjustment layer 153 and becomes uniform, is from the desired wavelength range R. If you are out, the thickness of the second phase adjusting layer 152 by arbitrarily altered within the scope of formula (4) can be changed in the distribution D ₃ of the resonance wavelength in the wafer plane ( Adjustment range: ± 2.4 nm).

Further, by adjusting the optical thickness Dp of each of the layers constituting the second upper DBR107 within the scope of formula (1) or Formula (2), the distribution D ₄ of the resonant wavelength in the wafer surface It can be changed (adjustment range: ± 0.75 nm). That is, the oscillation wavelength can be adjusted to a desired wavelength within ± 3.15 nm without significantly changing the oscillation threshold current.

<Fifth Embodiment>
In the fifth embodiment, another example in which the oscillation wavelength λ is adjusted by a method different from that of the first embodiment is shown. In the fifth embodiment, the description of the same components as those in the above-described embodiment may be omitted.

The layer structure of the surface emitting laser element according to the fifth embodiment is the same as that of the third embodiment except for the film thickness of each layer of the second upper DBR107. That is, in the surface emitting laser element according to the fifth embodiment, a second upper DBR107 which is a wavelength adjustment region is formed in the upper DBR160, and a wavelength adjustment region including a wavelength adjustment layer and a phase adjustment layer is further provided. 150 is formed.

When the film thickness distribution in the wafer surface is out of the adjustable wavelength range due to an arbitrary change in the number of layers of the wavelength adjusting layer 153 and the film thickness of the second phase adjusting layer 152, the first embodiment Similarly, the wavelength can be adjusted by arbitrarily changing the film thickness of each layer of the second upper DBR.

_{Similar to FIG. 14, the resonance wavelength distribution D 2} in the wafer surface, which is made uniform by canceling _{the wafer in-plane film thickness distribution D 1} for 3 nm by adjusting the wavelength adjustment layer 153, deviates from the desired wavelength range R. If it is, the thickness of the second phase adjusting layer 152 by arbitrarily altered within the scope of formula (6) can be changed in the distribution D ₃ of the resonance wavelength in the wafer plane (adjustment Range: ± 2.2 nm).

Further, by adjusting the optical thickness Dp of each of the layers constituting the second upper DBR107 within the scope of formula (1) or Formula (2), the distribution D ₄ of the resonant wavelength in the wafer surface It can be changed (adjustment range: ± 0.75 nm). That is, the oscillation wavelength can be adjusted to a desired wavelength within ± 2.95 nm without significantly changing the oscillation threshold current.

<Sixth Embodiment>
The sixth embodiment shows an atomic oscillator using the surface emitting laser element according to the first embodiment. In the sixth embodiment, the description of the same components as those in the above-described embodiment may be omitted.

FIG. 15 is a schematic diagram illustrating an atomic oscillator according to the sixth embodiment. The atomic oscillator 400 shown in FIG. 15 is a CPT type small atomic oscillator, and has a light source 410, a collimating lens 420, a λ / 4 wave plate 430, an alkali metal cell 440, a photodetector 450, and a modulator 460. ..

The atomic oscillator 400 has two different wavelengths of light emitted from the surface emitting laser, which are incident on the alkali metal cell 440, and thus has light absorption characteristics due to the quantum interference effect of two types of resonance light. It is an atomic oscillator that controls the oscillation frequency.

The surface emitting laser element 10 according to the first embodiment is used as the light source 410. However, although an example in which the surface emitting laser element 10 is used will be described in the following description, the surface emitting laser element according to the second to fifth embodiments may be used instead of the surface emitting laser element 10 according to the first embodiment. Good.

The alkali metal cell 440 is filled with Cs (cesium) atomic gas as an alkali metal, and the transition of the D1 line is used. A photodiode is used in the photodetector 450.

In the atomic oscillator 400, the light emitted from the light source 410 is applied to the alkali metal cell 440 filled with the cesium atomic gas to excite the electrons in the cesium atom. The light transmitted through the alkali metal cell 440 is detected by the photodetector 450, the signal detected by the photodetector 450 is fed back to the modulator 460, and the modulator 460 modulates the surface emitting laser element 10 in the light source 410.

FIG. 16 shows the structure of the atomic energy level associated with CPT. It utilizes the fact that the light absorption rate decreases when electrons are simultaneously excited from two ground levels to the excited levels. As the surface emitting laser constituting the surface emitting laser element 10, an element having a carrier wavelength close to 894.6 nm is used. The wavelength of the carrier wave can be tuned by changing the temperature or output of the surface emitting laser. Specifically, the temperature dependence of the wavelength can be adjusted at about 0.05 nm / ° C.

As shown in FIG. 17, by applying modulation, side bands are generated on both sides of the carrier wave, and the frequency difference is modulated at 4.6 GHz so as to match the natural frequency of 9.2 GHz of the Cs atom. ..

As shown in FIG. 18, the laser beam passing through the excited Cs gas becomes maximum when the sideband frequency difference matches the natural frequency difference of the Cs atom. Therefore, the modulation frequency of the surface emitting laser element 10 in the light source 410 is adjusted by feeding back in the modulator 460 so that the output of the photodetector 450 holds the maximum value.

Since the natural frequency of the atom is extremely stable, the modulation frequency becomes a stable value, and this information is taken out as an output. When the wavelength is 894.6 nm, a light source having a wavelength in the range of ± 1 nm is required. That is, a light source having a wavelength in the range of 893.6 nm to 895.6 nm is required.

Since the atomic oscillator 400 uses the surface emitting laser element 10 having a high yield with respect to the oscillation wavelength, the atomic oscillator 400 can be manufactured and provided at low cost. Further, when the surface emitting laser element in the third embodiment and the fourth embodiment is used, it is possible to provide an atomic oscillator 400 having a longer life. This is because the surface emitting laser element of the third and fourth embodiments has a smaller change in the layer structure than the surface emitting laser element of the first embodiment, and the wavelength can be finely adjusted. In other words, since the adjustment accuracy to the desired wavelength is high, the oscillation threshold current is the smallest, and the operation as the atomic oscillator 400 can be realized with the least load and low power consumption.

In this embodiment, Cs is used as the alkali metal, and a surface emitting laser having a wavelength of 894.6 nm is used to use the transition of the D1 line. However, when the D2 line of Cs is used, it is 852.3 nm. A surface emitting laser can be used.

Further, Rb (rubidium) can be used as the alkali metal, and a 795.0 nm surface emitting laser can be used when the D1 line is used, and a 780.2 nm surface emitting laser can be used when the D2 line is used.

The material composition of the active layer and the like can be designed according to the wavelength. When Rb is used, the modulation frequency is 3.4 GHz for 87 Rb and 1.5 GHz for 85 Rb. Even at these wavelengths, a light source having a wavelength in the range of ± 1 nm is required. That is, when using the Cs D2 line, a light source having a wavelength in the range of 851.3 nm to 853.3 nm is required. Further, when using the D1 line of Rb, a light source having a wavelength in the range of 794.0 nm to 796.0 nm is required. Further, when using the D2 line of Rb, a light source having a wavelength in the range of 779.2 nm to 781.2 nm is required.

Although the preferred embodiment has been described in detail above, it is not limited to the above-described embodiment, and various modifications and substitutions are made to the above-described embodiment without departing from the scope of claims. Can be added.

For example, in the sixth embodiment, the case where the surface emitting laser element is used for the atomic oscillator has been described, but the surface emitting laser element according to the first to fifth embodiments is a predetermined surface emitting laser element such as a gas sensor. It can be used for other devices and the like that require light of a wavelength. In this case, the same effect can be obtained in these devices and the like by using the surface emitting laser light having a predetermined wavelength according to the application.

10, 20-sided emission laser element 11, 21 Surface-emitting laser 12, 22 Electrode pad 101 Substrate 102 Lower DBR
103 Lower spacer layer 104 Active layer 105 Upper spacer layer 106 First upper DBR
107 Second upper DBR
108 Current constriction layer 108a Selective oxidation region 108b Current constriction region 109 Contact layer 111 Upper electrode 112 Lower electrode 160 Upper DBR
170 Protective film 150 Wavelength adjustment region 151 First phase adjustment layer 152 Second phase adjustment layer 153 Wavelength adjustment layer 153a First adjustment layer 153b Second adjustment layer 153c Third adjustment layer 400 Atomic oscillator 410 Light source 420 Collimating Lens 430 λ / 4 wave plate 440 Alkali metal cell 450 Optical detector 460 Modulator

Japanese Unexamined Patent Publication No. 2008-53353

Claims (7)

The lower Bragg reflector formed on the substrate and
A resonator containing an active layer formed on the lower Bragg reflector and
Including an upper Bragg reflector formed on the resonator.
The upper Bragg reflector is formed of a first upper Bragg reflector and a second upper Bragg reflector which is a wavelength adjustment region from the substrate side.
A surface emitting laser element characterized in that the optical film thickness Dp of each layer of the second upper Bragg reflector satisfies the formula (1) or the formula (2).

However, in the equations (1) and (2), λ is the oscillation wavelength of the surface emitting laser element, and m is a value (p: natural number) satisfying 5 + 0.5 (p-1). A second wavelength adjustment region provided with a wavelength adjustment layer and a phase adjustment layer is formed in the upper Bragg reflector.
The phase adjusting layer is formed of a material having a higher refractive index than the material of the upper Bragg reflector in contact with the phase adjusting layer.
The surface emitting laser element according to claim 1, wherein the optical film thickness d of the phase adjusting layer satisfies the equation (4).

However, in the formula (4), d'is the optical film thickness per wavelength adjusting layer, n is the number of wavelength adjusting layers (positive integer), D is the film thickness of the wavelength adjusting region, and N is positive. Is an integer of. A second wavelength adjustment region provided with a wavelength adjustment layer and a phase adjustment layer is formed in the upper Bragg reflector.
The phase adjusting layer is formed of a material having a refractive index lower than that of the material of the upper Bragg reflector in contact with the phase adjusting layer.
The surface emitting laser element according to claim 1, wherein the optical film thickness d of the phase adjusting layer satisfies the equation (6).

However, in the formula (6), d'is the optical film thickness per wavelength adjusting layer, n is the number of wavelength adjusting layers (positive integer), D is the film thickness of the wavelength adjusting region, and N is positive. Is an integer of. The lower Bragg reflector formed on the substrate and
A resonator containing an active layer formed on the lower Bragg reflector and
Including an upper Bragg reflector formed on the resonator.
A wavelength adjustment region having a wavelength adjustment layer and a phase adjustment layer is formed in the upper Bragg reflector.
The phase adjusting layer is formed of a material having a higher refractive index than the material of the upper Bragg reflector in contact with the phase adjusting layer.
A surface emitting laser element characterized in that the optical film thickness d of the phase adjusting layer satisfies the equation (4).

However, in the formula (4), d'is the optical film thickness per wavelength adjusting layer, n is the number of wavelength adjusting layers (positive integer), D is the film thickness of the wavelength adjusting region, and N is positive. Is an integer of. The lower Bragg reflector formed on the substrate and
A resonator containing an active layer formed on the lower Bragg reflector and
Including an upper Bragg reflector formed on the resonator.
A wavelength adjustment region having a wavelength adjustment layer and a phase adjustment layer is formed in the upper Bragg reflector.
The phase adjusting layer is formed of a material having a refractive index lower than that of the material of the upper Bragg reflector in contact with the phase adjusting layer.
A surface emitting laser element characterized in that the optical film thickness d of the phase adjusting layer satisfies the equation (6).

However, in the formula (6), d'is the optical film thickness per wavelength adjusting layer, n is the number of wavelength adjusting layers (positive integer), D is the film thickness of the wavelength adjusting region, and N is positive. Is an integer of. The surface emitting laser element according to any one of claims 1 to 5.
An alkali metal cell containing an alkali metal and
It has a photodetector that detects the light transmitted through the alkali metal cell among the light emitted from the surface emitting laser element to the alkali metal cell.
Of the light including the sideband emitted from the surface emitting laser element, two different wavelengths of light are incident on the alkali metal cell, so that the oscillation frequency is increased by the light absorption characteristic due to the quantum interference effect of the two types of resonance light. An atomic oscillator characterized by being controlled. The atomic oscillator according to claim 6, wherein the alkali metal is rubidium or cesium.

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