JP7295739B2 - Semiconductor laser element and chip-on-submount - Google Patents

Description

The present invention relates to a semiconductor laser device and a chip-on-submount.

Semiconductor laser devices are widely used as laser light sources for optical communication applications, industrial processing applications, and the like. In optical communication applications, it is necessary to propagate laser light over long distances (e.g., several hundred kilometers) through optical fibers, and single-mode laser light is generally used to suppress degradation of optical signal quality. is. On the other hand, industrial processing applications, for example, require higher output than laser light for optical communication applications. However, since it is not necessary to propagate long distances, multimode laser light, which is advantageous for high power, is generally used. Edge-emitting semiconductor laser devices that oscillate and emit multimode laser light employ a configuration in which the width of the waveguide is widened to allow oscillation and waveguiding of multiple modes of laser light within the waveguide. ing. A semiconductor laser device having such a configuration may hereinafter be referred to as a multimode semiconductor laser device as appropriate. Here, multimode means that a plurality of transverse modes exist.

In a multimode semiconductor laser device, for example, in order to effectively couple light to an optical element such as a multimode optical fiber, the horizontal radiation angle (hereinafter sometimes referred to as FFPh) of the laser light emitted from the light emitting end face is ) should be kept small.

On the other hand, multimode semiconductor laser devices are also required to have high optical output power and electrical-to-optical conversion efficiency. The electrical-optical conversion efficiency is a value obtained by dividing the optical output of a multimode semiconductor laser device by the power input to the multimode semiconductor laser device.

The optical output can be increased by increasing the injection current value to the multimode semiconductor laser device. However, in general, FFPh increases as the injection current value increases. In recent years, in particular, multimode semiconductor laser devices have come to be used in a high current injection region of, for example, 15 A or more in order to increase the optical output. It is required. Therefore, it is important to suppress the increase of FFPh especially in the high current injection region.

Patent Literature 1 discloses a configuration that employs a split electrode structure that is divided into a plurality of parts between a light emitting end face and a rear end face. According to the disclosed configuration, it is possible to realize a high-output semiconductor laser device that performs stable multimode laser oscillation by increasing the injected current density in the electrode closer to the light emitting facet. .

WO2005/062433

However, the divided electrode structure disclosed in Patent Document 1 has problems that its fabrication is difficult and laser oscillation control is complicated. Therefore, in a multimode semiconductor laser device, it is desired to increase the optical output power and the electrical-to-optical conversion efficiency and to suppress the increase in FFPh with a simple structure, especially in the high current injection region.

SUMMARY OF THE INVENTION The present invention has been made in view of the above, and provides a semiconductor laser element and a chip-on-submount that have a simple configuration, have high optical output power and high electrical-to-optical conversion efficiency, and suppress an increase in FFPh. intended to

In order to solve the above-described problems and achieve the object, a semiconductor laser device according to an aspect of the present invention includes a light emitting facet, a rear facet facing the light emitting facet, and the light emitting facet and the rear facet. and a current injection region for injecting a current into the waveguide region, wherein the difference between the width of the waveguide region and the width of the current injection region is 1/2 is the coverage width, the minimum value of the coverage width in the light emitting side region located on the light emitting end face side of the center line in the extending direction is the first coverage width, and the rear end face side of the center line is the minimum value of the coverage width When the maximum value of the coverage width in the rear side region located in is defined as a second coverage width, the first coverage width is narrower than the second coverage width, and the area of the current injection region in the light emission side region is When the current injection area on the light emission side and the area of the current injection region in the rear region are defined as the rear current injection area, the current injection area on the light emission side is greater than 100% and 200% of the current injection area on the rear side. It is below.

The coverage width may be constant or increased from the light exit facet toward the rear facet.

There may be a portion where the coverage width increases discontinuously from the light emitting facet toward the rear facet.

The first coverage width may be 5 μm or less.

The light emitting side current injection area may be larger than 100% and 175% or less of the rear side current injection area.

The light emitting side current injection area may be larger than 100% and 160% or less of the rear side current injection area.

The light emitting side current injection area may be larger than 100% and 150% or less of the rear side current injection area.

The light emitting side current injection area may be 105% or more and 148% or less of the rear side current injection area.

The light emitting side current injection area may be 113% or more and 145% or less of the rear side current injection area.

A semiconductor laser device according to an aspect of the present invention includes a light emitting facet, a rear facet facing the light emitting facet, and a multimode waveguide region extending in the extending direction between the light emitting facet and the rear facet. and a current injection region for injecting a current into the waveguide region, and the coverage width is defined as a half of the difference between the width of the waveguide region and the width of the current injection region. There are one or more locations where the coverage width is constant or increases from the light emitting end face toward the rear end face and the coverage width changes discontinuously.

A chip-on-submount according to an aspect of the present invention includes the semiconductor laser element and a submount on which the semiconductor laser element is mounted.

The semiconductor laser element may be mounted on the submount in a junction-down state.

Advantageous Effects of Invention According to the present invention, it is possible to realize a semiconductor laser device with a simple structure, high optical output power and high electrical-to-optical conversion efficiency, and in which an increase in FFPh is suppressed.

FIG. 1 is a schematic diagram of a semiconductor laser device according to Embodiment 1. FIG. FIG. 2 is a sectional view taken along line II--II of FIG. FIG. 3 is a diagram showing the relationship between So/Sr and the change in optical output for Examples and Comparative Examples. FIG. 4 is a diagram showing the relationship between So/Sr and changes in electrical-to-optical conversion efficiency for Examples and Comparative Examples. FIG. 5 is a diagram showing the relationship between So/Sr and changes in FFPh for Examples and Comparative Examples. FIG. 6 is a schematic diagram of a semiconductor laser device according to Embodiment 2. FIG. FIG. 7 is a schematic diagram of a semiconductor laser bar device according to Embodiment 3. FIG. FIG. 8 is a schematic diagram of a chip-on-submount according to Embodiment 4. FIG.

Embodiments will be described below with reference to the drawings. In addition, this invention is not limited by this embodiment. In addition, in the description of the drawings, the same or corresponding elements are given the same reference numerals as appropriate. Also, it should be noted that the drawings are schematic, and the relationship of dimensions of each element, the ratio of each element, and the like may differ from reality. Even between the drawings, there are cases where portions with different dimensional relationships and ratios are included. Also, in the drawings, directions may be described using the XYZ orthogonal axes.

(Embodiment 1)
FIG. 1 is a schematic diagram of a semiconductor laser device according to Embodiment 1. FIG. FIG. 2 is a sectional view taken along line II--II of FIG.

The semiconductor laser device 1 includes a light emitting facet Eo, a rear facet Er, a waveguide region Awg, and a current injection region Aci.

The semiconductor laser element 1 is an edge-emitting type laser element, and emits a laser beam oscillated by the semiconductor laser element 1 from the light emitting end face Eo. The rear end surface Er is a surface facing the light emitting end surface Eo in the Z direction in the figure. The rear facet Er is provided with a high reflectance reflecting film having a reflectance of 90% or more, for example, 95% at the wavelength of the laser light. A low-reflectance reflective film having a reflectance lower than that of the high-reflectance reflective film at the wavelength of the laser beam, for example, 0.1% to 7%, is provided on the light emitting facet Eo. A laser resonator is formed by the light emitting facet Eo and the rear facet Er. In the figure, L is the distance between the light emitting facet Eo and the rear facet Er, which is also called the laser cavity length. Although L is not particularly limited, it is, for example, 800 μm to 6 mm, and may be 3 mm to 5 mm.

The waveguide region Awg is a multimode waveguide region extending in the extension direction between the light emitting facet Eo and the rear facet Er. Here, the stretching direction is a direction parallel to the Z direction. The optical axis of the waveguide region Awg is parallel to the extending direction. The waveguide region Awg has a width in the X direction for guiding the laser light oscillated by the semiconductor laser element 1 in multimode. The multimode waveguide region is a region in which the laser light emitted by the semiconductor laser device 1 is guided in multimode. Moreover, the waveguide region Awg includes an active layer as a laser amplification medium, emits light by injecting a current, and exhibits a light amplification effect.

The current injection region Aci is a region for injecting current into the waveguide region Awg.

The current injection region Aci and waveguide region Awg will be described in more detail with reference to FIG. A semiconductor laser device 1 has a ridge structure R. As shown in FIG. A semiconductor laser device 1 includes a substrate 2 made of n-type GaAs, a lower electrode 3 provided on the back surface of the substrate 2, a semiconductor lamination portion 4 formed on the substrate 2, a passivation film 5, and an upper electrode 6. , is equipped with

When a current is injected by applying a voltage between the lower electrode 3 and the upper electrode 6, the semiconductor laser element 1 oscillates and outputs laser light from the light emitting facet Eo.

The semiconductor lamination portion 4 includes an n-type buffer layer 7, an n-type cladding layer 8, an n-type guide layer 9, an active layer 10, a p-type guide layer 11, a p-type cladding layer 12, and a A p-type contact layer 13 is included.

The n-type buffer layer 7 is made of GaAs and is a buffer layer for growing a laminated structure of high-quality epitaxial layers on the substrate 2 . The n-type cladding layer 8 and the n-type guide layer 9 are made of AlGaAs whose refractive index and thickness are set so as to realize a desired optical confinement state in the stacking direction. The Al composition of the n-type guide layer 9 is, for example, 15% or more and less than 40%. Also, the n-type cladding layer 8 has a smaller refractive index than the n-type guide layer 9 . Also, the thickness of the n-type guide layer 9 is preferably 50 nm or more, for example, about 1000 nm. The thickness of the n-type cladding layer 8 is preferably about 1 μm to 3 μm. These n-type semiconductor layers may also contain, for example, silicon (Si) as an n-type dopant.

The active layer 10 comprises a lower barrier layer, a quantum well layer and an upper barrier layer and has a single quantum well (SQW) structure. The lower barrier layer and the upper barrier layer have a barrier function for confining carriers in the quantum well layer, and are made of high-purity AlGaAs that is not intentionally doped. The quantum well layers consist of high-purity InGaAs with no intentional doping. The In composition and film thickness of the quantum well layer and the composition of the lower barrier layer and the upper barrier layer are set according to the desired emission center wavelength (eg, 900 nm to 1080 nm). The structure of the active layer 10 may be a multiple quantum well (MQW) structure in which a laminated structure of quantum well layers and barrier layers formed above and below the quantum well layers is repeated by a desired number. In some cases, donors and acceptors are intentionally added to the quantum well layer, the lower barrier layer and the upper barrier layer.

The p-type guide layer 11 and the p-type clad layer 12 are paired with the above-described n-type clad layer 8 and n-type guide layer 9, and have a refractive index, a thickness, and a thickness so as to realize a desired optical confinement state in the stacking direction. is made of AlGaAs. The p-type cladding layer 12 has a smaller refractive index than the p-type guide layer 11 . The Al composition of the p-type cladding layer 12 is set slightly larger than that of the n-type cladding layer 8 in order to shift the light field in the layer toward the n-type cladding layer 8 to reduce the waveguide loss. The Al composition of the p-type guide layer 11 is set smaller than the Al composition of the p-type cladding layer 12 . Moreover, the thickness of the p-type guide layer 11 is preferably 50 nm or more, for example, about 1000 nm. The thickness of the p-type cladding layer 12 is preferably about 1 μm to 3 μm. Also, these p-type semiconductor layers may contain carbon (C) as a p-type dopant. The C concentration of the p-type guide layer 11 is set to, for example, 0.1 to 1.0×10 ¹⁷ cm ₋₃ , preferably about 0.5 to 1.0×10 ¹⁷ cm ⁻³ . The C concentration of the p-type cladding layer 12 is set at, for example, 1.0×10 ¹⁷ cm ⁻³ or higher.

The p-type contact layer 13 is made of GaAs heavily doped with Zn or C. The projecting portion of the p-type cladding layer 12 and the p-type contact layer 13 form a ridge structure R. As shown in FIG. The width of the ridge structure R in the X direction is substantially constant along the Z direction (see FIG. 1). The ridge structure R has a function of confining light in the X direction and constitutes a waveguide structure.

The passivation film 5 is an insulating film made of SiNx, for example, and is formed so as to cover the p-type cladding layer 12 and the p-type contact layer 13 . The passivation film 5 has an opening 5a provided at the position of the ridge structure R. As shown in FIG. The upper electrode 6 is in ohmic contact with the p-type contact layer 13 via the opening 5a.

Inside the semiconductor laser device 1, light exists mainly in the regions of the n-type guide layer 9, the active layer 10, and the p-type guide layer 11 in the Y direction. Also, the light mainly exists in the region immediately below the ridge structure R in the X direction. Therefore, the region immediately below the ridge structure R in the n-type guide layer 9, active layer 10, and p-type guide layer 11 can be called a waveguide region Awg.

In addition, since a current is injected from the upper electrode 6 into the active layer 10 through the p-type contact layer 13 which is in ohmic contact via the opening 5a, the region of the p-type contact layer 13 corresponding to the opening 5a is It can be called a current injection region Aci.

Therefore, in the case of the semiconductor laser device 1, the width of the waveguide region Awg can be considered as the width of the ridge structure R in the X direction. Also, the width of the current injection region Aci can be considered as the width of the opening 5a in the X direction.

Here, as in the following formula, 1/2 of the difference between the width of the waveguide region Awg and the width of the current injection region Aci is defined as the coverage width.
Coverage width=(Width of waveguide region Awg−Width of current injection region Aci)/2
Note that the coverage width on both sides in the width direction of the current injection region Aci does not necessarily have to be the same width. width is preferred. In this embodiment, it is assumed that both sides have the same coverage width.

Further, in the waveguide region Awg, a region positioned closer to the light emitting end face Eo than the center line CL in the extending direction (Z direction) is defined as a light emitting side region Ao. Also, in the waveguide region Awg, a region located on the rear end face Er side of the center line CL in the extending direction is referred to as a rear region Ar. The lengths in the extending direction of the light emitting side area Ao and the rear side area Ar are both L/2.

Here, in the semiconductor laser device 1, the waveguide region Awg has a constant width along the Z direction. On the other hand, the current injection region Aci includes a portion whose width is constant from the light emitting facet Eo toward the rear facet Er and a portion whose width gradually decreases. Specifically, the current injection region Aci has a constant width over the length L1 from the light emitting end face Eo, but the width gradually decreases at the changing portion P1 existing in the light emitting side region Ao, and further, the width Constant width across L2. Then, the width gradually decreases at the changing portion P2 existing in the rear region Ar, and is constant over the length L3, and reaches the rear end face Er. Also, in the semiconductor laser device 1, L1+L2+L3 is assumed to be substantially equal to L.

Therefore, assuming that the minimum coverage width in the light emitting side area Ao is the first coverage width, the first coverage width is the width Wo at the position from the light emitting end surface Eo to the length L1. If the maximum value of the coverage width in the rear area Ar is the second coverage width, the second coverage width is Wr at the position from the rear end face Er to the length L3. At this time, the first coverage width Wo is narrower than the second coverage width Wr. Also, the coverage width is constant or increases from the light emitting end face Eo to the rear end face Er, and the increase is discontinuous. The changing portions P1 and P2 are examples of portions where the coverage width increases discontinuously from the light emitting end face Eo toward the rear end face Er.

Further, let the area of the current injection region Aci in the light emission side region Ao be the light emission side current injection area So, and let the area of the current injection region Aci in the rear side region Ar be the rear side current injection area Sr.

The semiconductor laser device 1 configured as described above has a simple configuration, and has high optical output power and high electrical-to-optical conversion efficiency, and suppresses an increase in FFPh.

A specific description will be given below. Inside the waveguide region Awg of the edge-emitting semiconductor laser device 1 having the light emitting facet Eo with a low reflectance and the rear facet Er with a high reflectance, the light intensity and carrier density depend on the extension direction (both in the cavity length direction). may be described). The light intensity is higher on the side of the light exit facet Eo than on the side of the rear facet Er. On the other hand, the carrier density is lower on the side of the light emitting facet Eo than on the side of the rear facet Er. This is because higher optical power consumes more carriers. In addition, due to such distributions of light intensity and carrier density in the cavity length direction, heat generation and gain in the waveguide region Awg also have distributions in the optical waveguide direction. The amount of heat generated on the side of the light emitting end surface Eo is greater than that on the side of the rear end surface Er. On the other hand, the gain is lower on the side of the light exit facet Eo than on the side of the rear facet Er. The light emitting side area Ao can also be called a heat dominated area. The rear region Ar can also be called a carrier-dominant region.

In the semiconductor laser device 1, since the first coverage width Wo is narrower than the second coverage width Wr, the current injection region Aci is wider in the light emission side region Ao on the side of the light emission facet Eo than in the rear region Ar on the side of the rear facet Er. Wide. As a result, more current can be injected in the light emitting side region Ao where carrier consumption is high, so the light output can be increased.

In addition, since the width of the current injection region Aci in the light emitting side region Ao is wide, heat dissipation via the upper electrode 6 is more effectively generated in the light emitting side region Ao. In other words, the light output side area Ao has improved heat dissipation, and the overflow of carriers due to heat is suppressed, so that the light output can be further increased.

Furthermore, since heat dissipation is improved in the light emitting side area Ao, the degree of the thermal lens effect in the light emitting side area Ao is suppressed, so an increase in FFPh is suppressed. Specifically, for example, in a high current injection region of 15 A or more, the thermal lens effect due to heat generation becomes significant, and the thermal lens effect may increase FFPh. In order to suppress the thermal lens effect and reduce FFPh, it is not necessary to improve the overall heat dissipation in the resonator length direction of the waveguide region Awg. It was found for the first time by the inventors of the present invention that a sufficient effect can be obtained by improving it. In other words, it has been found that the effect of reducing FFPh can be obtained by making the first coverage width Wo narrower than the second coverage width Wr.

Furthermore, since the second coverage width Wr is wider than the first coverage width Wo , the high-order mode oscillation gain, which is higher in the rear area Ar than in the light emitting side area Ao, is effectively reduced. . Therefore, the increase in FFPh is further suppressed. In a multimode semiconductor laser device, a higher-order mode radiates at a wider angle, that is, contributes more to an increase in FFPh. Therefore, it is important for reducing FFPh that the second coverage width Wr is wider than the first coverage width Wo to suppress laser oscillation in higher-order modes and to reduce the number of oscillation modes.

For example, in order to suppress higher-order mode laser oscillation on the rear facet Er side, it is desirable that a region with a wide coverage width exist on the rear facet Er side for a certain length in the cavity length direction. At the same time, in order to increase the current injection in the light emitting side region Ao where carrier consumption is high and to increase the light output, the wide current injection region on the side of the light emitting facet Eo should extend in the cavity length direction to some extent. It is desirable that only the length exists. Based on the above, the present inventors have determined that the light emitting side current injection area So, which is the area of the current injection region Aci in the light emitting side region Ao, and the rear current injection area So, which is the area of the current injection region Aci in the rear region Ar. It has been found for the first time that the area ratio to the injection area Sr is important for improving the light output and electricity-to-light conversion efficiency and suppressing the increase in FFPh.

Furthermore, it is preferable for reducing FFPh to make the width of the current injection region Aci as close as possible to the width of the waveguide region Awg by reducing the coverage width in the light emitting side region Ao. For example, it is preferable to set the first coverage width Wo to 5 μm or less.

(Preferred range of So/Sr)
In the semiconductor laser device 1, it is preferable that the light emitting side current injection area So is larger than 100% and 200% or less of the rear side current injection area Sr. A preferable range of the area ratio between the light emitting side current injection area So and the rear side current injection area Sr will be described below.

A semiconductor laser device having the same configuration as the semiconductor laser device 1 of the example, and a semiconductor laser device of a comparative example having the same configuration as the semiconductor laser device of the example except that the coverage width is constant at 10 μm along the cavity length direction. was fabricated, and the light output, light-electric conversion efficiency, and FFPh were measured. The cavity length (L in FIG. 1) of each semiconductor laser element was set to 4500 μm. Also, for the semiconductor laser device of the example, the first coverage width Wo was set to 5 μm, and the second coverage width Wr was set to 25 μm. Also, the lengths of regions with different coverage widths (L1, L2, and L3 in FIG. 1) were set to different values in each example.

A current value of 10A, 15A or 20A was injected into each semiconductor laser element. If the current value is 10A, an optical output of about 9W can be obtained, for example.

10 A is a standard current value used in conventional multimode semiconductor laser devices. Also, 15 A and 20 A are current values whose use in multimode semiconductor laser devices has recently begun to be examined. In order to increase the output power of a multimode semiconductor laser device, it is necessary to use a current value of 15A, 18A, or even 20A or more. It should be noted that the current value described here is the maximum current value that can be used in the target semiconductor laser device. Even if the target semiconductor laser device has a maximum usable current value of, for example, 18 A, the actual injected current may be less than 18 A under conditions of use that require only a small optical output. Of course. However, since the FFPh of the multimode semiconductor laser device increases with the current, it is important to consider the maximum current value that can be used in the semiconductor laser device when designing.

Also, each semiconductor laser element was mounted on a submount (to be described later) in a junction-down state, and a current was injected.

Calculate the ratio (L1/(L1+L2+L3)) [%] of the length L1 of the region of the first coverage width Wo of 5 μm to the total length (L1+L2+L3) of the current injection region Aci for the semiconductor laser devices of the example and the comparative example. bottom. Also, the ratio (L2/(L1+L2+L3)) [%] of the length L2 of the coverage width region of 10 μm to L1+L2+L3 was calculated. Also, the ratio (L3/(L1+L2+L3)) [%] of the length L3 of the region of the second coverage width Wr of 25 μm to L1+L2+L3 was calculated. Then, the relationship between these ratios and So/Sr was calculated. Table 1 shows the results. The ratio of So/Sr is 100% in the semiconductor laser device of the comparative example, and 101% to 140.7% in the semiconductor laser device of the example.

FIG. 3 is a diagram showing the relationship between So/Sr and the change in optical output for Examples and Comparative Examples. FIG. 4 is a diagram showing the relationship between So/Sr and changes in electrical-to-optical conversion efficiency for Examples and Comparative Examples. FIG. 5 is a diagram showing the relationship between So/Sr and changes in FFPh for Examples and Comparative Examples. The changes in optical output, FFPh, and electrical-to-optical conversion efficiency are all indicated by the amounts of change from the values in the comparative example. The dashed-dotted line, solid line, or broken line are eye guides based on measurement points indicated by circles, squares, or triangles at current values of 10 A, 15 A, and 20 A, respectively.

As can be seen from FIGS. 3, 4, and 5, as the So/Sr ratio increases from 100%, the optical output and electrical-to-optical conversion efficiency increase and FFPh decreases. The reasons for such an increase in optical output, an increase in the electrical-to-optical conversion efficiency, or a decrease in FFPh are that more current can be injected in the light emitting side region Ao where carriers are rapidly consumed, and heat dissipation can be achieved in the light emitting side region Ao. It is possible to suppress the overflow of carriers due to heat by improving the efficiency, suppress the degree of the thermal lens effect in the light emitting side region Ao, and effectively reduce the high-order mode oscillation gain. This is considered to be due to the effect of Further, the amount of increase in light output, the amount of increase in electrical-to-light conversion efficiency, and the amount of decrease in FFPh sharply increase as the current value increases, and the above effects are more pronounced as the current is injected higher. It was confirmed that Also, the above effect was exhibited even when the ratio of So/Sr was slightly increased by 1% from 100% to 101%, and the effect was more effective when the ratio was increased by 5% to 105%, which was more effective than expected. For example, when the ratio of So/Sr is 101%, the electric-light conversion efficiency increases by 0.9% at a current value of 20A. Further, when the ratio of So/Sr was 105%, the electrical-to-optical conversion efficiency further increased to 1.4%, and the increase in optical output and the decrease in FFPh were also sufficient. Therefore, So/Sr may be 101% or more or 105% or more.

However, when the length L3 of the region of the second coverage width Wr increases beyond a certain level, So/Sr increases, but the total area of the current injection region Aci decreases, so the voltage for current injection rises. As a result, the electrical-to-optical conversion efficiency decreases. Furthermore, when the heat generation in the rear region Ar becomes unignorable, the luminous efficiency of the active layer 10 decreases and the light output decreases, or the effect of reducing the high-order mode oscillation gain fades and the FFPh increases. . Furthermore, when the length L1 of the region of the first coverage width Wo increases to a certain extent, So/Sr increases, but it becomes difficult to deviate the carrier distribution toward the light emitting facet Eo, resulting in light output and electrical-to-light conversion efficiency. decreases. It was also confirmed that the decrease in optical output and electricity-to-light conversion efficiency and the increase in FFPh along with the increase in So/Sr were steeper as the current value increased.

From the above, as shown in FIGS. 3, 4, and 5, as the So/Sr increases from 100%, the optical output and the electrical-to-optical conversion efficiency increase, and the FFPh decreases, but increases beyond a certain level. It is believed that the light output and electrical-to-light conversion efficiency will then decrease and the FFPh will increase. That is, it was confirmed that there is an optimum range for So/Sr. Since the effect of the voltage rise described above appears immediately when So/Sr increases from 100%, it is believed that the peak of the electrical-to-optical conversion efficiency appears at a value of So/Sr closer to 100% than the optical output or FFPh. be done.

As the eye guides of FIGS. 3, 4 and 5 show, it is preferable that So/Sr is greater than 100% and less than or equal to 200% at a current value of 10 A or less. Further, at 15 A or less, if So/Sr is greater than 100% and less than or equal to 175%, optical output, electrical-to-optical conversion efficiency and FFPh are simultaneously improved over the comparative example, which is preferable. Further, at 20 A or less, if So/Sr is greater than 100% and less than or equal to 150%, optical output, electrical-to-optical conversion efficiency and FFPh are simultaneously improved over the comparative example, which is preferable.

Moreover, the maximum value of So/Sr, which is suitable for simultaneously improving the light output, the electrical-to-light conversion efficiency, and FFPh over the comparative example, decreases linearly with the current value. Therefore, the preferred maximum value of So/Sr at which the light output, the electrical-to-light conversion efficiency and FFPh are simultaneously improved over the comparative example at a current value of 18 A, for example, is the preferred maximum value of So/Sr at 15 A and 20 A. can be easily inferred from Specifically, at 18 A or less, if So/Sr is greater than 100% and less than or equal to 160%, light output, electrical-to-light conversion efficiency and FFPh are simultaneously improved over the comparative example, which is preferable.

Further, when the So/Sr ratio is 105% or more and 148% or less, the light output, the electric-light conversion efficiency and the FFPh are simultaneously improved over the comparative example at 20 A or less, and at the conventional standard current value It is preferable because FFPh decreases by 0.4 degrees or more from the comparative example over a range of 10 A to 15 A to 20 A, which can be said to be a high current injection region. Furthermore, when So/Sr is 113% or more and 145% or less, the optical output, electrical-optical conversion efficiency and FFPh are simultaneously improved at 20A or less than the comparative example, and FFPh is compared from 10A to 20A. It is preferable because it is reduced by 0.6 degrees or more than the example.

(Embodiment 2)
FIG. 6 is a schematic diagram of a semiconductor laser device according to Embodiment 2. FIG.

The semiconductor laser element 1A includes a light emitting facet EAo, a rear facet EAr, a waveguide region AAwg, and a current injection region AAci.

The semiconductor laser element 1A is an edge-emitting type laser element having a ridge structure similar to the semiconductor laser element 1 according to the first embodiment, and emits a laser beam oscillated by the semiconductor laser element 1A from the light emitting end surface EAo. . The rear end surface EAr is a surface facing the light emitting end surface EAo in the Z direction in the figure. A high reflectance reflective film having a high reflectance at the wavelength of the laser light is provided on the rear facet EAr. A low-reflectance reflective film having a lower reflectance than the high-reflectance reflective film at the wavelength of the laser light is provided on the light emitting end surface EAo. A laser resonator is formed by the light emitting facet EAo and the rear facet EAr. In the figure, L is the laser cavity length.

The waveguide region AAwg is a multimode waveguide region extending in the extending direction between the light emitting facet EAo and the rear facet EAr. The optical axis of the waveguide region AAwg is parallel to the extending direction. The waveguide region AAwg has a width in the X direction for guiding the laser light oscillated by the semiconductor laser element 1A in multimode. Also, the waveguide region AAwg includes an active layer as a laser amplification medium, emits light by injecting a current, and exhibits a light amplification effect.

The current injection region AAci is a region for injecting current into the waveguide region AAwg. The semiconductor laser device 1A has a cross-sectional structure similar to that of the semiconductor laser device 1. FIG. Since the current injection region AAci and the waveguide region AAwg are the same as the current injection region Aci and the waveguide region Awg of the semiconductor laser device 1, description thereof will be omitted.

In the semiconductor laser device 1A, the coverage width is defined as half the difference between the width of the waveguide region AAwg and the width of the current injection region AAci. The coverage width on both sides in the width direction of the current injection region AAci does not necessarily have to be the same width. It is preferable to be In this embodiment, it is assumed that both sides have the same coverage width.

Also, in the waveguide region AAwg, a region positioned closer to the light emitting end surface EAo than the center line CL in the extending direction (Z direction) is referred to as a light emitting side region AAo. Further, in the waveguide region AAwg, a region located on the rear end surface EAr side of the center line CL in the extending direction is referred to as a rear region AAr. The lengths of the light emitting area AAo and the rear area AAr are both L/2.

Here, in the semiconductor laser device 1A, the width of the waveguide region AAwg is constant along the Z direction. On the other hand, the current injection region AAci has a fixed portion and three portions where the width varies discontinuously from the light emitting end surface EAo toward the rear end surface EAr. Specifically, the current injection region AAci has a constant width over the length LA1 from the light emitting end surface EAo, but the width gradually decreases at the changing portion PA1 existing in the light emitting side region AAo, and further the length Constant width across LA2. The width gradually decreases at the transition portion PA2 existing in the rear region AAr, and is constant over the length LA3. Then, the width decreases discontinuously at the transition portion PA3 existing in the rear area AAr, is constant over the length LA4, and reaches the rear end surface EAr. Here, as shown in the drawing, when the changing portion PA3 is enlarged, the changing portion PA3 consists of two portions where the width changes discontinuously and a portion where the width continuously decreases between the two portions. It is configured. The length of the continuously decreasing portion is minute compared to the laser cavity length L, for example 0.001L to 0.01L (that is, 0.1% to 1% of L). With such a continuous change, there is less possibility that the reliability of the semiconductor laser device 1A will be lowered due to the electric field concentration at the end points.

Therefore, the first coverage width WAo is the minimum coverage width in the light emitting area AAo, and the maximum coverage width WAr is the rear area AAr. The first coverage width WAo is narrower than the second coverage width WAr. Also, the coverage width is constant or increases from the light emitting end surface EAo to the rear end surface EAr, and the increase is discontinuous.

Furthermore, when the area of the current injection region AAci in the light emission side region AAo is the light emission side current injection area SAo, and the area of the current injection region AAci in the rear region AAr is the rear side current injection area SAr, for example, SAo is It is greater than 100% and 200% or less of SAr.

As with the semiconductor laser device 1, the semiconductor laser device 1A configured as described above has a simple configuration, and has high optical output power and high electrical-to-optical conversion efficiency, and suppresses an increase in FFPh.

In both semiconductor laser elements 1 and 1A, the coverage width is constant or increases from the light emitting facet toward the rear facet, and there are one or more places where the coverage width changes discontinuously. . As a result, with a simple configuration, the optical output and the electrical-to-optical conversion efficiency are high, and an increase in FFPh is suppressed.

In the semiconductor laser devices 1 and 1A, there are two or three locations where the coverage width changes discontinuously. The fact that the coverage width increases constantly or discontinuously from the light emitting facet toward the rear facet and that the region where the coverage width is constant has a certain length contributes to heat dissipation and the asymmetry of current injection in the direction of the cavity. This is preferable in terms of simultaneously realizing the distribution and the effect of suppressing higher-order mode oscillation on the rear end face side. In addition, the number of locations where the coverage width changes discontinuously is preferably one or more, and the number of locations is not limited, but two to four locations are preferable in order to secure the length of the region where the coverage width is constant.

In the semiconductor laser device according to the embodiment, the width of the waveguide region may be constant in the optical axis direction as in the semiconductor laser devices 1 and 1A, or may vary continuously like a straight line or a curved line. However, it may change discontinuously like a step. Therefore, the waveguide region may be of a flare type having a wider width on the light emitting end surface side. Further, it is preferable that the width of the waveguide region is monotonically increasing or monotonously decreasing and that it is continuous, since the structure is simple and the manufacturing is easy. In any case of the waveguide region, the optical axis is preferably parallel to the stretching direction in order to more effectively suppress the increase in FFPh.

When the laser light emitted from the semiconductor laser element is coupled to the optical fiber, the width of the waveguide region (waveguide width) at the light emitting end face must be within ±50 μm with respect to the core diameter of the optical fiber. If there is, it is preferable from the viewpoint of optical coupling. The waveguide width is, for example, in the range of 80 μm to 250 μm, more preferably in the range of 100 μm to 200 μm. Unlike a semiconductor laser device that oscillates in a single mode or a multimode semiconductor laser device with a waveguide width of about 50 μm, the multimode semiconductor laser device described here with a wider waveguide width is allowed by the waveguide structure. The number of modes that can be used increases. Therefore, as in the present invention, it becomes more important to consider suppression of an increase in FFPh while considering reduction in the number of modes.

Also, the current non-injection region may be provided between the waveguide region and the light emitting facet and/or between the waveguide region and the rear facet. This can improve the reliability of the semiconductor laser device. Here, the current non-injection region refers to a region into which no current is injected. A region defining the coverage width is a current non-injection region in which no current is injected into the waveguide region Awg.

Also, the semiconductor laser elements 1 and 1A can be manufactured using a known semiconductor process. For example, in the semiconductor laser device 1, the current injection region can be formed by forming the opening 5a in the passivation film 5 by photolithography and etching, and forming the upper electrode 6 by vacuum deposition or sputtering. . As a method for forming the current non-injection region, there is a method in which the passivation film 5 is not removed, a method in which a part of the p-type contact layer 13 is removed, and a portion where the passivation film 5 is removed is formed into Schottky contact with the p-type contact layer 13. For example, there is a method of forming an electrode that

The waveguide structure of the semiconductor laser elements 1 and 1A is realized by a ridge structure, but is not limited to this, and adopts a waveguide structure such as a SAS structure (Self-Aligned Structure) or a BH structure (Buried-Hetero Structure). It is also possible to Alternatively, a technique of forming a waveguide by mixing quantum wells may be employed. Although the above embodiment is an example of a refractive index waveguide type semiconductor laser device, it is not limited to a refractive index waveguide type semiconductor laser device and may be a gain waveguide type semiconductor laser device. Further, in the case of a waveguide region having a ridge structure, even if there is a portion of the semiconductor layer having substantially the same height as the ridge structure outside the ridge structure, the function as a waveguide does not change. Also, the width of the waveguide region can be appropriately defined according to the waveguide structure. For example, in the case of a semiconductor laser device having a waveguide structure of the BH structure, the width of the waveguide region can be considered as the width of the waveguide, which constitutes the BH structure, for example, the active layer.

(Embodiment 3)
FIG. 7 is a schematic diagram of a semiconductor laser bar device according to Embodiment 3. FIG. The semiconductor laser bar device 100 is a semiconductor laser device having a configuration in which a plurality of semiconductor laser devices 1 are arranged in parallel, and includes a plurality of waveguide regions and a plurality of current injection regions. The semiconductor laser bar device 100 can be produced, for example, by forming a plurality of semiconductor laser devices 1 on a semiconductor substrate and cutting it so that the desired number of semiconductor laser devices 1 are included. The semiconductor laser bar device 100 is a semiconductor laser bar device that has a simple configuration, has high optical output power and high electrical-to-optical conversion efficiency, and suppresses an increase in FFPh.

(Embodiment 4)
FIG. 8 is a schematic diagram of a chip-on-submount according to Embodiment 4. FIG. The chip-on-submount 200 includes the semiconductor laser device 1 according to Embodiment 1 and a submount 201 on which the semiconductor laser device 1 is mounted.

The submount 201 includes a ceramic substrate 202 made of AlN or the like, and metal films 203 , 204 and 205 made of Au or the like formed on the main surface of the ceramic substrate 202 . Metal films 204 and 205 are formed on the same main surface and are insulated from each other. Semiconductor laser element 1 is bonded to metal film 204 of submount 201 with solder 206 .

The semiconductor laser element 1 is mounted on the submount 201 in a junction-down state. That is, the semiconductor laser element 1 does not have the substrate 2 interposed between it and the active layer 10 , and the upper electrode 6 closer to the active layer 10 is joined to the submount 201 . As a result, the heat generated in the active layer 10 is preferably radiated to the submount 201 . The lower electrode 3 is electrically connected to the metal film 205 by a bonding wire 207 made of Au or the like. As a result, a current is injected into the semiconductor laser device 1 through the metal films 204 and 205 .

In the chip-on-submount 200, the semiconductor laser element 1 is mounted on the submount 201 in a junction-down state, but may be mounted in a junction-up state. In the junction-up state, it is preferable to provide the upper electrode 6 with a heat dissipation structure.

In addition, the present invention is not limited by the above-described embodiment. The present invention also includes a configuration obtained by appropriately combining the respective constituent elements described above. For example, the present invention also includes a semiconductor laser bar element including the semiconductor laser element 1A and a chip-on-submount provided with the semiconductor laser element 1A. Further effects and modifications can be easily derived by those skilled in the art. Therefore, broader aspects of the present invention are not limited to the above embodiments, and various modifications are possible.

1, 1A semiconductor laser element 2 substrate 3 lower electrode 4 semiconductor lamination portion 5 passivation film 5a opening 6 upper electrode 7 n-type buffer layer 8 n-type clad layer 9 n-type guide layer 10 active layer 11 p-type guide layer 12 p-type Cladding layer 13 p-type contact layer 100 semiconductor laser bar element 200 chip-on submount 201 submount 202 ceramics substrate 203, 204, 205 metal film 206 solder 207 bonding wires Aci, AAci current injection regions Ao, AAo light emission side regions Ar, AAr Rear area Awg, AAwg Waveguide area CL Center line Eo, EAo Light emission facet Er, EAr Rear facet P1, P2, PA1, PA2, PA3 Change portion R Ridge structure So, SAo Light emission side current injection area Sr, SAr Rear side current injection area Wo, WAo first coverage width Wr, WAr second coverage width

Claims (10)

a light emitting end surface;
a rear end surface facing the light emitting end surface;
a multimode waveguide region extending in the extension direction between the light emitting facet and the rear facet;
a current injection region for injecting current into the waveguide region;
with
A half of the difference between the width of the waveguide region and the width of the current injection region is defined as the coverage width, and the coverage width in the light emitting side region located closer to the light emitting facet than the center line in the extending direction is the coverage width. The first coverage width is the second coverage width, where the minimum value is the first coverage width and the maximum value of the coverage width in the rear region located on the rear end surface side of the center line is the second coverage width. When the area of the current injection region in the light emission side region is defined as the light emission side current injection area, and the area of the current injection region in the rear side region is defined as the rear side current injection area, the light emission side is narrower. A current injection area is greater than 100% and 200% or less of the rear-side current injection area,
the width of the current injection region decreases from the light emitting facet toward the rear facet, and is narrower on the rear facet side than on the light emitting facet side;
Carrier density is lower on the light emitting facet side than on the rear facet side, heat generation is greater on the light emitting facet side than on the rear facet side, and gain is greater on the light emitting facet side than on the rear facet side. A semiconductor laser device characterized by being lower than a rear facet side. 2. The semiconductor laser device according to claim 1, wherein there is a portion where the coverage width increases discontinuously from the light emitting facet toward the rear facet. 3. The semiconductor laser device according to claim 1 , wherein said first coverage width is 5 [mu]m or less. 4. The semiconductor laser device according to claim 1, wherein said light emitting side current injection area is more than 100% and 175 % or less of said rear side current injection area. 4. The semiconductor laser device according to claim 1, wherein said light emitting side current injection area is larger than 100% and 160% or less of said rear side current injection area. 4. The semiconductor laser device according to claim 1, wherein said light emitting side current injection area is more than 100% and 150% or less of said rear side current injection area. 4. The semiconductor laser device according to claim 1, wherein said light emitting side current injection area is 105% or more and 148 % or less of said rear side current injection area. 4. The semiconductor laser device according to claim 1, wherein the light emitting side current injection area is 113% or more and 145 % or less of the rear side current injection area. a semiconductor laser device according to any one of claims 1 to 8 ;
a submount on which the semiconductor laser element is mounted;
A chip-on-submount comprising: 10. The chip-on-submount according to claim 9 , wherein said semiconductor laser element is mounted on said submount in a junction-down state.

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