JP4106210B2 - Optical semiconductor device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical semiconductor device, and more particularly to a semiconductor laser used as a signal source for optical communication and a pumping light source for a fiber amplifier.
[0002]
[Prior art]
FIG. 29 shows a semiconductor laser module in which a semiconductor laser 510 and an optical fiber 520 are combined, which is indicated as a whole by 500. The semiconductor laser module 500 has a structure in which the light 530 emitted from the front end surface 511 of the semiconductor laser 510 is resonated between the rear end surface 512 of the semiconductor laser 510 and the diffraction grating 521 provided in the optical fiber 520. . Therefore, when light is emitted from the semiconductor laser 510, it is necessary to reduce reflection at the front end face 511 as much as possible.
[0003]
Such a structure for reducing the reflectance at the end face is described in, for example, Japanese Patent No. 3040273. FIG. 30 is a perspective view of a super luminescence diode (hereinafter referred to as “SLD”) described in the publication, which is generally indicated by 600. The SLD 600 includes a GaAs substrate 601. On the GaAs substrate 601, an AlGaAs cladding layer 603, an AlGaAs active layer 604, AlGaAs guide layers 605 and 606, an AlGaAs cladding layer 609, and a GaAs contact layer 610 are stacked via a GaAs buffer layer 602. Further, a current blocking layer 607 and a protective layer 608 are provided so as to sandwich the window portion 607a.
[0004]
FIG. 31 shows an equivalent refractive index distribution when the SLD 600 of FIG. 30 is viewed from above. As shown in FIG. 31, the cladding region 614 and the active region 620 having a higher refractive index than the cladding region 614 form an optical waveguide. The active region 620 is bent at the bent portion 621 and intersects the rear end surface 622 substantially perpendicularly, while the front end surface 623 intersects with the normal direction of the front end surface 623 by an inclination angle θ. Further, by setting the inclination angle θ to 3 ° or more, the substantial reflectance at the front end face 623 is reduced to suppress laser oscillation. In addition, by setting the inclination angle θ to 15 ° or less, total reflection with respect to the front end surface 623 is prevented.
[0005]
[Problems to be solved by the invention]
However, in the SLD 600, since the inclination angle θ of the active region (stripe) 620 is 3 ° or more and 15 ° C. or less, the light emitted from the front end surface 623 is approximately 9 ° to 45 ° with respect to the normal line of the front end surface 623. It will tilt about °. For this reason, as in the case of the semiconductor laser module 500 of FIG. 29, when the outgoing light is incident on the optical fiber, it is very difficult to align the optical axis with the optical fiber.
Further, as the inclination angle θ is increased, the amount of light reflected by the front end face 623 and absorbed inside the SLD 600 is increased, and the loss is increased.
Furthermore, at the bent portion 621, light escapes out of the active region 620, causing radiation loss.
[0006]
Accordingly, an object of the present invention is to provide an optical semiconductor element in which the inclination angle θ at the front end face is small and the effective reflectance at the front end face is reduced. It is another object of the present invention to provide a semiconductor element with reduced radiation loss at the bent portion of the optical waveguide.
[0007]
[Means for Solving the Problems]
Therefore, as a result of intensive studies, the inventors have found that a low reflectance can be realized even when the inclination angle θ is made smaller by combining the inclination of the optical waveguide on the front end face and the antireflection film covering the front end face. The present invention has been completed.
[0008]
That is, according to the present invention, at least a first conductivity type cladding layer, an active layer, and a second conductivity type cladding layer are stacked, a ridge structure is provided in a part of the second conductivity type cladding layer, and the stacking direction is An active region, a clad region sandwiching the active region from both sides, an optical waveguide having a constant width in the direction perpendicular to the optical axis, and the optical waveguide, An optical semiconductor element including a front end face and a rear end face provided in parallel to each other including an end portion of a waveguide, wherein the active region includes a linear first active region and a linear second active region. A reflection surface that is directly connected at a predetermined bending angle and totally reflects light propagating through the active region at the bending portion, and the optical axis of the optical waveguide is a method of the front end surface at the front end surface. Inclined at an inclination angle of less than 3 ° with respect to the line, and at the rear end face Becomes perpendicular to the rear surface, further, an optical semiconductor element characterized in that the front end face is covered with an anti-reflection film.
In this way, by combining the optical waveguide having the inclination angle θ and the antireflection film, the front end face has 1% or less, particularly 0.1% or less, even though the inclination angle θ is less than 3 °. Effective reflectance can be obtained. As a result, good resonance can be obtained when a resonator is formed by combining an optical semiconductor element and a diffraction grating.
In addition, by providing such a reflection surface to substantially totally reflect light propagating in the active region, it is possible to reduce radiation loss at the bent portion of the active region.
[0009]
The inclination angle is preferably about 1.5 ° or less.
As described above, when the inclination angle is reduced, the outgoing light is emitted in a direction substantially perpendicular to the front end face, and therefore the connection between the optical semiconductor element and the optical fiber can be easily performed.
[0010]
It is preferable that the reflection surface is a flat surface formed so as to cut out a part of the active region.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Embodiment 1 FIG.
FIGS. 1A and 1B show a semiconductor laser represented as a whole by 200 according to the first embodiment. FIG. 1A is a cross-sectional view, and FIG. (A) is sectional drawing at the time of seeing in the II direction of (b).
As shown in FIG. 1A, the semiconductor laser 200 includes an n-GaAs substrate 1. A buffer layer 2 including a superlattice buffer is provided on the n-GaAs substrate 1. On the buffer layer 2, an InGaAs quantum well active layer 15 sandwiched from above and below by n-AlGaAs cladding layers 3 and 7 and n-AlGaAs grating guide layers 4 and 6 is provided. The n-AlGaAs cladding layer 7 has a ridge portion 7a. On the n-AlGaAs cladding layer 7, Si ₃ N ₄ An insulating film 9 is provided, and a p-GaAs cap layer 10 is provided on the ridge portion 7a. Furthermore, a p-side electrode 11 made of, for example, Ti—Pt—Au is formed on the bottom surface, and an n-side electrode 12 made of, for example, Ge—Au—Ni is formed on the top surface.
[0012]
As shown in FIG. 1B, the semiconductor laser 200 has a front end face 110 and a rear end face 120. An antireflection film 20 is provided on the front end face 110, and a reflective film 21 is provided on the rear end face 120, respectively. ing. The ridge portion 7a is formed of two straight portions 7c and 7d having a bent portion 7b. The ridge portion 7c is inclined by the inclination angle θ with respect to the normal direction of the front end face 110. The inclination angle θ is less than 3 °, preferably less than 1.5 °. On the other hand, the rear end surface 120 and the ridge portion 7a intersect substantially vertically.
[0013]
FIG. 2 shows an equivalent refractive index distribution when the semiconductor laser 200 shown in FIG. As shown in FIG. 1B, an optical waveguide is formed by the cladding region 5 and the active region 30 having a refractive index higher than that of the cladding region 5 (the same applies to the following semiconductor lasers). Further, by forming the bent ridge portion 7a as shown in FIG. 1B, the active region (stripe) 30 is formed from two straight portions 31 and 32 which are bent and connected at the bent portion 33. .
On the front end face 110, the optical axis 40 (active region) of the optical waveguide is inclined by an inclination angle θ from the normal direction of the front end face 110. The inclination angle θ is substantially less than 3 °, and is preferably 1.5 ° or less. On the other hand, on the rear end face 120, the optical axis 40 of the optical waveguide is substantially perpendicular to the rear end face 110.
[0014]
An antireflection film 20 is formed on the front end face 110. The antireflection film 20 is made of, for example, alumina (Al ₂ O ₃ ) / (4n) thickness (n is the refractive index of alumina) is used.
On the other hand, on the rear end surface 120, for example, SiO ₂ / A-Si / SiO ₂ A reflective film 21 made of a multilayer film as described above is formed.
Also in the following embodiments, the antireflection film 20 and the reflection film 21 are films having such a structure.
[0015]
FIG. 3 shows the inclination angle dependency of the end face reflectance when the end face is not coated, that is, when the cleaved face is used as the end face. In determining the tilt dependence, Marcuse's method (D. Marcuse, “Reflection loss of laser mode from tilted end mirror,” IEEE J. Lightwave Technol., Vol. 7, No. 2, pp. 336-339, 1989 Reference) was used. In FIG. 3, the horizontal axis represents the inclination angle θ of the optical axis of the optical waveguide from the normal direction of the end face, and the vertical axis represents the reflectance at the end face. Where the wavelength of light (λ), wave number in vacuum (k ₀ ), Equivalent refractive index of semiconductor laser (n _eff ), The refractive index of the active region 30 (n _a ), The refractive index of the cladding region 5 (n _c ) And the width (2T) of the stripe (active region) were 0.98 μm, 2π / λ, 3.37232, 3.37232, 3.36950, and 3.5 μm, respectively.
As can be seen from FIG. 3, when the tilt angle θ is increased, the reflectance decreases monotonously. For example, the reflectance when the tilt angle θ is 1 ° and 1.5 ° is 1 / 2.54 and 1 / 7.21 times that when the tilt angle θ is not tilted (when the tilt angle θ is 0). , About 12% and about 4%, respectively. However, in order to make the reflectance as low as 1% or less, the inclination angle θ needs to be 2 ° or more. This is because the end surface is a cleaved surface, and therefore, the Fresnel reflectivity (about 30%) determined by the boundary between the semiconductor crystal and air exists on the end surface.
[0016]
On the other hand, in the semiconductor laser 200 according to the present embodiment, the front end face 110 has, for example, an alumina layer (Al) with a film thickness λ / (4n) (where n is the refractive index of alumina). ₂ O ₃ ) Is formed, the effective reflectivity at the front end face 110 is reduced while the inclination angle θ is reduced.
[0017]
FIG. 4 shows the inclination angle dependency of the effective reflectance at the cleavage end face. (A) is a case where an antireflection film is not formed, and (b) is a case where an antireflection film is formed. When the tilt angle θ is 0, the effective reflectance when the antireflection film is not formed (FIG. 4A) is about 30%, which is the value of the Fresnel reflectance, but when the antireflection film is formed (FIG. 4). 4 (a)) can be reduced to 2.4%.
Therefore, when the inclination angle θ is 1.0 °, the reflectance is about 0.8%, and when the inclination angle θ is 1.5 °, the reflectance is about 0.3%. Furthermore, a reflectance of about 0.1% or less can be realized by bringing the inclination angle θ close to 3.0 °.
[0018]
As described above, in the semiconductor laser 200 according to the first embodiment, the optical axis 40 of the optical waveguide is inclined by the predetermined inclination angle θ from the normal direction of the front end face 110 and the antireflection film is formed on the front end face 110. By forming 20, a low reflectance of 0.4% or less, particularly 0.1% or less, can be realized with a small inclination angle θ of less than 3 ° or even 1.5 ° or less.
[0019]
On the rear end surface 120, for example, SiO ₂ / A-Si / SiO ₂ A reflective film 21 having a high reflectance composed of a multilayer film as described above is formed. As a result, the reflectance at the rear end face 120 is about 98%, which greatly exceeds the Fresnel reflectance (about 30%), and a high reflectance can be realized. For this reason, a high-power semiconductor laser can be realized.
[0020]
Next, a method for manufacturing the semiconductor laser 200 will be briefly described. The semiconductor laser 200 is formed on the GaAs substrate 1 from the buffer layer 2 to the AlGaAs cladding layer 7 using the same manufacturing process as that of a normal semiconductor laser.
Subsequently, the AlGaAs cladding layer 7 is etched to form a ridge portion 7a. In this step, the AlGaAs cladding layer 7 is etched so that the ridge portion 7a has a shape as shown in FIG. For the etching, a dry etching method is preferably used.
Subsequently, in the same process as in the prior art, Si ₃ N ₄ The semiconductor laser 200 is completed by forming the film 9, the electrodes 11, 12 and the like.
[0021]
In the semiconductor laser 200 according to the present embodiment, the substantial reflectance at the front end face can be reduced while the inclination angle θ from the normal direction of the front end face is suppressed to less than 3 °. For this reason, when the resonator is formed by combining the semiconductor laser 200 and the diffraction grating, good resonance can be obtained. For example, when a resonator using a fiber grating is manufactured, it is possible to provide a semiconductor laser having a stable wavelength and a high output.
[0022]
Further, since the inclination angle θ of the optical waveguide is less than 3 °, the angle formed by the normal line of the front end surface and the light emitted from the front end surface is also 10 ° or less, preferably 5 ° or less. Therefore, the connection (optical axis alignment) between the semiconductor laser 200 and the optical fiber is facilitated.
[0023]
Further, the ratio of light reflected from the front end face and absorbed outside the active region is reduced, and loss at the front end face can be reduced. Therefore, a highly efficient semiconductor laser with a low threshold current can be provided.
[0024]
Embodiment 2. FIG.
FIG. 5 shows the distribution of the equivalent refractive index of the semiconductor laser according to the present embodiment, the whole being represented by 210. FIG. 5 shows the distribution of the equivalent refractive index when viewed in the same direction as FIG. 2, and in FIG. 5, the same reference numerals as those in FIG. 2 indicate the same or corresponding parts. Note that the distribution of the equivalent refractive index of the semiconductor laser shown below is all the distribution when viewed in the same direction as in FIG.
In the semiconductor laser 210, the bent active region 30 is provided in the cladding region 5, similarly to the semiconductor laser 200 described above. However, the inclination angle θ at which the optical axis of the optical waveguide is inclined from the normal direction of the front end face 110 may be 3 ° or more.
The active region 30 includes a bent portion 33 in which a substantially straight first active region 31 and a second active region 32 are bent and connected at a predetermined bending angle, and the bending angle is smaller than 180 °. A local waveguide region 50 having a refractive index higher than that of the cladding region 5 is provided adjacent to the bent portion 33 in the cladding region 5. Note that the bending angle refers to an angle between the first active region 31 and the second active region 32.
[0025]
In the active region 30 having the bent portion 33, the light distribution is biased toward the outside of the bent portion 33 (the side where the bent angle is larger than 180 °), and light is emitted. For this reason, when the active region 30 having the bent portion 33 is applied to a semiconductor laser, a radiation loss due to the radiation of the light occurs. As a result, the threshold current of the semiconductor laser is increased and the light emission efficiency is decreased.
[0026]
On the other hand, in the semiconductor laser 210 according to the second embodiment, the local waveguide region 50 having a refractive index higher than that of the cladding region 5 is provided adjacent to the cladding region 5 having a bending angle smaller than 180 °. Thus, the light passing through the active region 30 is attracted to the local waveguide region 50 side. As a result, the light emitted to the outside from the active region 30 is reduced in the bent portion 33, and the radiation loss in the bent portion 33 can be reduced.
[0027]
As shown in FIG. 1, the active region 30 can be formed in the cladding region 5 by providing a ridge portion 7 a above the active region 30, but the ridge portion 7 a is also provided above the region that becomes the local waveguide region 50. As a result, the local waveguide region 50 adjacent to the active region 30 can be formed in the cladding region 5. The shape of the local waveguide region 50 can be controlled by changing the shape of the ridge portion 7a formed above.
[0028]
Next, in order to clarify the effect of the present invention, BPM (Beam Propagation Method, MD Feit and JA Fleck, Jr., “Computation of mode properties in optical fiber waveguides by a propagating beam method,” Appl. Opt., vol. 19, no. 7, pp. 1154-1164, 1980).
[0029]
FIG. 6 shows the distribution of the equivalent refractive index of the semiconductor laser 211 used for the analysis by the BPM method, and has almost the same structure as FIG.
The resonator length L of the semiconductor laser 211 is 1500 μm. The active region 30 includes a substantially straight first active region 31 and a second active region 32, and has a bent portion 33 at a substantially central portion. Further, a substantially triangular local waveguide region 50 is provided adjacent to the bent portion 33. The length of the local waveguide region 50 is Lz in both directions from the bent portion 33, and the width 2T of the active region (stripe) 30 is 3.5 μm. In addition, the inclination angle is θ, the refractive index of the active region 30 is 3.37232, the refractive index of the cladding region 5 on both sides thereof is 3.36950, and the wavelength λ of light passing through the active region 30 is 0.98 μm. The refractive index of the local waveguide region 50 is the same as the refractive index of the active region 30.
[0030]
The effect of providing the local waveguide region 50 is that when the fundamental mode light incident on the active region 30 from the rear end surface 120 passes through the bent portion 33 and reaches the front end surface 110, the fundamental mode of the inclined waveguide region 50 is obtained. The degree of coupling efficiency is evaluated by the coupling efficiency.
[0031]
FIG. 7 shows the relationship between the length Lz of the local waveguide region 50 and the coupling efficiency. The inclination angle θ (the inclination of the optical axis of the optical waveguide from the normal direction of the front end face) is 0.5 °. 1.0 ° and 1.5 °. It can be seen that when the length Lz of the local waveguide region 50 is increased, the coupling efficiency is higher than when there is no local waveguide region 50 (Lz = 0). This is because the radiation loss is reduced due to the presence of the local waveguide region 50.
As shown in FIG. 7, when the length Lz of the local waveguide region 50 is approximately 200 μm or more, good coupling efficiency can be obtained at the inclination angles θ of 0.5 °, 1.0 °, and 1.5 °. Recognize.
[0032]
FIG. 8 shows an equivalent refractive index distribution of another semiconductor laser according to the present embodiment, which is represented as a whole by 212. The semiconductor laser 212 is formed by forming the antireflection film 20 and the reflection film 21 so as to cover the front end face 110 and the rear end face 120 of the semiconductor laser 211 described above.
[0033]
Thus, by forming the antireflection film 20 and the reflection film 21 on the respective end faces, the reflectance at the front end face 110 is reduced even when the inclination angle θ of the optical axis of the optical waveguide is made smaller than 3 °. be able to. In addition, by including the local waveguide region 50, radiation loss caused by the active region 30 having the bent portion 33 can be reduced.
[0034]
Embodiment 3 FIG.
FIG. 9 shows an equivalent refractive index distribution of the semiconductor laser according to the present embodiment as a whole represented by 213. In FIG. 9, the same reference numerals as those in FIG. 2 denote the same or corresponding parts.
In the semiconductor laser 213, the active region 30 bent in the same manner as the semiconductor laser 200 described above is provided in the cladding region 5. However, the inclination angle θ at which the optical axis of the optical waveguide (that is, the direction in which the active region 30 is formed) is inclined from the normal direction of the front end face 110 may be 3 ° or more.
Furthermore, a local reflection enhancement region 60 is provided along the active region 30 on the side where the bending angle at the bent portion 33 of the active region 30 is larger than 180 °. The refractive index of the local reflection enhancement region 60 is lower than that of the surrounding cladding region 5.
[0035]
The local reflection enhancement region 60 is formed by reducing the equivalent refractive index below the removed portion by removing the cladding layer 7 and the like above the active layer 15 by etching. That is, in the bent portion of the ridge portion 7a, the region adjacent to the ridge portion 7a is removed by etching, whereby the local reflection enhancement region 60 is formed.
[0036]
As described above, when the active region 30 has the bent portion 33, light is emitted to the outside of the active region 30 at the bent portion 33, and radiation loss occurs.
On the other hand, in the semiconductor laser 213 according to the present embodiment, the local reflection enhancement region 60 having a refractive index lower than that of the surrounding cladding region 5 is provided along the active region 30, so that The difference in refractive index is increased. As a result, the amount of light emitted from the active region 30 to the local reflection enhancement region 60 is suppressed at the bent portion 33, and radiation loss can be reduced. This makes it possible to realize a semiconductor laser 213 with a low threshold current and high emission efficiency.
[0037]
FIG. 10 shows an equivalent refractive index distribution of another semiconductor laser according to the present embodiment, which is represented entirely by 214. The semiconductor laser 214 is formed by forming the antireflection film 20 and the reflection film 21 so as to cover the front end face 110 and the rear end face 120 of the semiconductor laser 213 described above.
[0038]
Thus, by forming the antireflection film 20 and the reflection film 21 on the respective end faces, the reflectance at the front end face 110 is reduced even when the inclination angle θ of the optical axis of the optical waveguide is made smaller than 3 °. be able to. In addition, by including the local reflection enhancement region 60, radiation loss due to the active region 30 having the bent portion 33 can be reduced.
[0039]
FIG. 11 shows an equivalent refractive index distribution of another semiconductor laser according to the present embodiment, the whole being represented by 215. The semiconductor laser 215 has a structure in which the above-described semiconductor laser 213 further includes a local waveguide region 50. That is, adjacent to the bent portion 33 of the active region 30, the local waveguide region 50 is provided on the side where the bending angle is smaller than 180 °, and the local reflection enhancement region 60 is provided on the side where the bending angle is larger than 180 °.
[0040]
As described above, in the semiconductor laser 215, the active region 30 having the inclination angle θ from the normal direction of the front end surface 110 can reduce the reflectance of light emitted from the front end surface 110, and the bent portion of the active region 30 can be reduced. By having the local waveguide region 50 and the local reflection enhancement region 60 in 33, radiation loss due to the active region 30 having the bent portion 33 can be reduced.
[0041]
FIG. 12 shows an equivalent refractive index distribution of another semiconductor laser according to the present embodiment, the whole being represented by 216. The semiconductor laser 216 has a structure in which the above-described semiconductor laser 215 further includes an antireflection film 20 and a reflection film 21 that cover the front end face 110 and the rear end face 120.
That is, the local waveguide region 50 and the local reflection enhancement region 60 are provided adjacent to the bent portion 33 of the active region 30, and the reflection film 20 and the antireflection film 21 are provided so as to cover the end surfaces 110 and 120. It has been.
[0042]
As described above, since the semiconductor laser 216 has the active region 30 having the inclination angle θ from the normal direction of the front end surface 110, the reflectance of the light emitted from the front end surface 110 can be reduced, and the bent portion of the active region 30 can be reduced. By having the local waveguide region 50 and the local reflection enhancement region 60 in 33, radiation loss due to the active region 30 having the bent portion 33 can be reduced.
In particular, by providing the antireflection film 20, a low reflectance can be obtained at the front end face 110 even when the inclination angle θ is smaller than 3 °.
[0043]
Embodiment 4 FIG.
FIG. 13 shows an equivalent refractive index distribution of the semiconductor laser according to the present embodiment, the whole being represented by 220. In FIG. 13, the same reference numerals as those in FIG. 2 denote the same or corresponding parts.
In the semiconductor laser 220, the bent active region 30 is provided in the cladding region 5 as in the above-described semiconductor laser 200. The inclination angle θ at which the optical axis of the optical waveguide is inclined from the normal direction of the front end face 110 may be 3 ° or more.
The active region 30 includes a bent portion 33 in which a substantially straight first active region 31 and a second active region 32 are bent and connected at a predetermined bending angle. Further, the active region 30 on the side where the bending angle is larger than 180 ° is cut off at an angle φ (φ is an angle between the high axis of the optical waveguide 30 and the cut surface 70) to form the cut surface 70. That is, in the bent portion 33, the active region 30 is cut at a cutting angle inclined by an angle φ from the optical axis direction to form a cut surface 70.
[0044]
In the semiconductor laser 220, the active region 30 is inclined by the inclination angle θ from the normal direction of the front end face 110 and is substantially perpendicular to the rear end face 120. The active region 30 has a structure bent at the bent portion 33. In such a structure, the front end surface 110 can have a low reflectance and the rear end surface 120 can have a high reflectance, but on the other hand, a light radiation loss occurs in the bent portion 33.
In the semiconductor laser 220, a cut surface 70 is provided at the bent portion 33 of the active region 30 in order to reduce such radiation loss.
[0045]
In the semiconductor laser 220, as shown in FIG. 13, in the linear active region 30 (the first active region 31 and the second active region 32), the waveguide mode has a propagation constant β from the rear end surface 120 toward the front end surface 110. Go ahead.
In this case, the angle φ at which the active region 30 is cut off is
[0046]
(Β / k ₀ ) · Sin ((π / 2) −φ) = n _cl (1)
Where k ₀ (= 2π / λ, where λ is the wavelength): Wave number in vacuum
n _cl : Refractive index of the cladding region around the active region
[0047]
Is satisfied, the traveling wave is totally reflected at the cut surface 70 of the bent portion 33 and is not emitted outside the active region 300.
Thus, by providing the cut surface 70 having the cut angle φ, radiation loss at the bent portion 33 of the active region 30 can be significantly reduced.
[0048]
For example, the width 2T of the active region (stripe) 30 is 3.5 μm, the refractive index of the active region 30 is 3.37232, the refractive index of the cladding region 5 around the active region 30 is 3.36950, and the wavelength λ is 0.98 μm. , Β / k of the basic mode ₀ Is 3.37131, and the cut-off angle φ required for the light passing through the active region 30 to be totally reflected by the bent portion 33 is 1.88 °.
[0049]
Such an active region 30 having a cut surface 70 cut at a predetermined cut angle φ can be produced by forming a ridge portion 7a formed above the clad region 5 into a shape cut at a cut angle φ. .
[0050]
As described above, in the semiconductor laser 220 according to the present embodiment, the active region 30 is cut at the bent portion 33 of the active region 30 at a cut angle inclined by the predetermined angle φ from the optical axis direction, and the cut surface 70 is formed. As a result, the light passing through the active region 30 can be totally reflected by the cut surface 70.
As a result, it is possible to provide a semiconductor laser having a low threshold current by reducing the radiation loss of light at the bent portion 33 of the active region 30.
[0051]
FIG. 14 shows an equivalent refractive index distribution of another semiconductor laser according to the present embodiment, the whole being represented by 221. The semiconductor laser 221 has a structure in which the above-described semiconductor laser 220 further includes an antireflection film 20 and a reflection film 21 that cover the front end face 110 and the rear end face 120.
As described above, the semiconductor laser 221 having the cut surface 70 can reduce radiation loss at the bent portion 33 of the active region 30. Furthermore, by providing the antireflection film 20 on the front end face 110, the reflectance at the front end face 110 can be reduced. In particular, even when the inclination angle θ is smaller than 3 °, a low reflectance can be realized. Further, by having the reflective film 21, a high-power semiconductor laser 221 can be realized.
[0052]
FIG. 15 shows an equivalent refractive index distribution of another semiconductor laser according to the present embodiment, the whole being represented by 222. The semiconductor laser 222 has a structure in which the above-described semiconductor laser 220 further includes a local waveguide region 50.
In the semiconductor laser 222, since the active region 30 has the cut surface 70 cut out at a predetermined angle φ, the light is totally reflected by the cut surface 70. For example, the width 2T of the active region (stripe) 30 is 3.5 μm, the refractive index of the active region 30 is 3.37232, the refractive index of the cladding region 5 around the active region 30 is 3.36950, and the wavelength λ is 1.3 μm. Then, in the above equation (1), β / k of the fundamental mode ₀ Is 3.37097, and the cutting angle φ is 1.69 °.
[0053]
As described above, in the semiconductor laser 222 according to the present embodiment, the cut surface 70 is formed in the bent portion 33 of the active region 30, whereby the light passing through the active region 30 can be totally reflected by the cut surface 70. . Also, by having the local waveguide region 50, the emission of light to the outside can be suppressed. As a result, a radiation loss of light at the bent portion 33 of the active region 30 can be reduced, and a highly efficient semiconductor laser with a low threshold current can be provided.
[0054]
FIG. 16 shows an equivalent refractive index distribution of another semiconductor laser according to the present embodiment, the whole being represented by 223. The semiconductor laser 223 has a structure in which the above-described semiconductor laser 222 further includes an antireflection film 20 and a reflection film 21.
[0055]
As described above, in the semiconductor laser 223 according to the present embodiment, the cutout surface 70 and the local waveguide region 50 are included in the bent portion 33 of the active region 30, so that the radiation loss of light in the bent portion 33 of the active region 30. Thus, a semiconductor laser having a low threshold current can be provided.
Furthermore, by providing the antireflection film 20 on the front end face 110, the reflectance at the front end face 110 can be reduced. In particular, even when the inclination angle θ is smaller than 3 °, a low reflectance can be realized. In addition, by providing the reflective film 21 on the rear end surface 120, it is possible to increase the output of the semiconductor laser.
[0056]
Embodiment 5. FIG.
FIG. 17 shows an equivalent refractive index distribution of the semiconductor laser according to the present embodiment, the whole being represented by 230. In FIG. 17, the same reference numerals as those in FIG. 2 denote the same or corresponding parts.
In the semiconductor laser 230, the bent active region 30 is provided in the cladding region 5, similarly to the semiconductor laser 200 described above. However, the inclination angle θ at which the optical axis of the optical waveguide is inclined from the normal direction of the front end face 110 may be 3 ° or more.
The active region 30 includes a bent portion 33 in which a substantially straight first active region 31 and a second active region 32 are bent and connected at a predetermined bending angle. Further, a high refractive index region 80 having a higher refractive index than that of the cladding region 5 is provided along the active region 30 on the front end face 110. The high refractive index region 80 is provided in the cladding region 5 on the side where the angle between the front end face 110 and the optical axis of the active region 30 is larger than 90 °.
The refractive index of the high refractive index region 80 is preferably the same as the refractive index of the active region 30.
[0057]
In general, light is attracted to a region having a high refractive index. Accordingly, as shown in FIG. 17, in the vicinity of the front end face 110, the high refractive index region 80 having a refractive index larger than that of the cladding region 5 is on the side where the intersection angle between the front end face 110 and the optical axis of the active region 30 is larger than 90 °. Is provided, the light passing through the active region 30 is drawn toward the high refractive index region 80 side. For this reason, the light reflected by the front end face 110 becomes difficult to be coupled to the active region (stripes) 30, and the substantial reflectance of the front end face 110 can be reduced.
[0058]
Such a high refractive index region 80 can be produced by forming the ridge portion 7 a formed above the active layer 15 also above the high refractive index region 80.
[0059]
FIG. 18 shows an equivalent refractive index distribution of another semiconductor laser according to the present embodiment, the whole being represented by 231. The semiconductor laser 231 has a structure in which the above-described semiconductor laser 230 further includes an antireflection film 20 and a reflection film 21.
[0060]
Thus, in the semiconductor laser 231 according to the present embodiment, the reflectance of the front end face 110 can be reduced by having the high refractive index region 80. Furthermore, the reflectance at the front end face 110 can also be reduced by providing the antireflection film 20 on the front end face 110. In particular, even when the inclination angle θ is smaller than 3 °, a low reflectance can be realized.
[0061]
FIG. 19 shows an equivalent refractive index distribution of another semiconductor laser according to the present embodiment, the whole being represented by 232. The semiconductor laser 232 has a structure in which the above-described semiconductor laser 230 further includes a local waveguide region 50.
[0062]
Thus, in the semiconductor laser 232 according to the present embodiment, the reflectance at the front end face 110 can be reduced by having the high refractive index region 80. Further, by having the local waveguide region 50, it is possible to suppress the emission of light to the outside. As a result, a radiation loss of light at the bent portion 33 of the active region 30 can be reduced, and a highly efficient semiconductor laser with a low threshold current can be provided.
[0063]
FIG. 20 shows an equivalent refractive index distribution of another semiconductor laser according to the present embodiment, the whole being represented by 233. The semiconductor laser 233 has a structure in which the above-described semiconductor laser 232 further includes an antireflection film 20 and a reflection film 21 on the end faces 110 and 120.
[0064]
In the semiconductor laser 233, the reflectance of the front end face 110 can be reduced by having the high refractive index region 80. Also, by having the local waveguide region 50, the emission of light to the outside can be suppressed.
Furthermore, by having the antireflection film 20, the reflectance at the front end face 110 can be reduced. In particular, even when the inclination angle θ is smaller than 3 °, a low reflectance can be realized. Further, by providing the reflective film 21, the output of the semiconductor laser can be increased.
[0065]
FIG. 21 shows an equivalent refractive index distribution of another semiconductor laser according to the present embodiment, the whole being represented by 234. The semiconductor laser 234 has a structure in which the above-described semiconductor laser 230 further includes a local reflection enhancement region 60.
[0066]
In the semiconductor laser 234, the reflectance of the front end face 110 can be reduced by having the high refractive index region 80. Also, by having the local reflection enhancement region 60, it is possible to suppress the emission of light to the outside.
Therefore, it is possible to provide a semiconductor laser having a low reflectance at the front end face 110 and a reduced radiation loss at the bent portion 33 of the active region 30.
[0067]
FIG. 22 shows an equivalent refractive index distribution of another semiconductor laser according to the present embodiment, the whole being represented by 235. The semiconductor laser 235 has a structure in which the above-described semiconductor laser 234 further includes the antireflection film 20 and the reflection film 21 on the end faces 110 and 120.
[0068]
In the semiconductor laser 235, the reflectance of the front end face 110 can be reduced by having the high refractive index region 80. Also, by having the local reflection enhancement region 60, it is possible to suppress the emission of light to the outside. Furthermore, by having the antireflection film 20, the reflectance at the front end face 110 can be further reduced. Further, by providing the reflective film 21, the output of the semiconductor laser can be increased.
Therefore, it is possible to provide a high-power semiconductor laser having a low reflectance at the front end face 110 and a reduced radiation loss at the bent portion 33 of the active region 30.
[0069]
FIG. 23 shows an equivalent refractive index distribution of another semiconductor laser according to the present embodiment, the whole being represented by 236. The semiconductor laser 236 has a structure in which the above-described semiconductor laser 230 has both the local waveguide region 50 and the local reflection enhancement region 60.
[0070]
In the semiconductor laser 236, the reflectance of the front end face 110 can be reduced by having the high refractive index region 80. Further, by having both the local waveguide region 50 and the local reflection enhancement region 60, the radiation loss at the bent portion 33 can be greatly reduced.
Therefore, it is possible to provide a semiconductor laser having a low reflectance at the front end face 110 and a reduced radiation loss at the bent portion 33 of the active region 30.
[0071]
FIG. 24 shows an equivalent refractive index distribution of another semiconductor laser according to the present embodiment, the whole of which is represented by 237. The semiconductor laser 237 has a structure in which the above-described semiconductor laser 236 further includes the antireflection film 20 and the reflection film 21 on the end surfaces 110 and 120.
[0072]
In the semiconductor laser 237, the reflectance of the front end face 110 can be further reduced by having the high refractive index region 80 and the antireflection film 20. Further, by having both the local waveguide region 50 and the local reflection enhancement region 60, the radiation loss at the bent portion 33 can be greatly reduced. Further, by providing the reflective film 21 on the rear end face 120, it becomes possible to increase the output of the semiconductor laser.
Therefore, it is possible to provide a high-power semiconductor laser having a low reflectance at the front end face 110 and a reduced radiation loss at the bent portion 33 of the active region 30.
[0073]
FIG. 25 shows an equivalent refractive index distribution of another semiconductor laser according to the present embodiment, the whole being represented by 238. The semiconductor laser 238 has a structure in which the semiconductor laser 230 described above has a cut surface 70.
[0074]
In the semiconductor laser 238, the reflectance of the front end face 110 can be reduced by having the high refractive index region 80. Further, by having the cut surface 70, radiation loss at the bent portion 33 can be reduced.
Therefore, it is possible to provide a semiconductor laser having a low reflectance at the front end face 110 and a reduced radiation loss at the bent portion 33 of the active region 30.
[0075]
FIG. 26 shows an equivalent refractive index distribution of another semiconductor laser according to the present embodiment, the whole being represented by 239. The semiconductor laser 239 has a structure in which the above-described semiconductor laser 238 further includes the antireflection film 20 and the reflection film 21 on the end faces 110 and 120.
[0076]
In the semiconductor laser 239, the reflectance of the front end face 110 can be significantly reduced by having the high refractive index region 80 and the antireflection film 20. Further, by having the cut surface 70, radiation loss at the bent portion 33 can be reduced. Further, by providing the reflective film 21 on the rear end face 120, it becomes possible to increase the output of the semiconductor laser.
Therefore, it is possible to provide a high-power semiconductor laser having a low reflectance at the front end face 110 and a reduced radiation loss at the bent portion 33 of the active region 30.
[0077]
FIG. 27 shows an equivalent refractive index distribution of another semiconductor laser according to the present embodiment, the whole being represented by 240. The semiconductor laser 240 has a structure in which the above-described semiconductor laser 230 further has a local waveguide region 50 and a cut surface 70 at the bent portion 33.
[0078]
In such a semiconductor laser 240, by having the high refractive index region 80, the reflectance of the front end face 110 can be reduced. In addition, by having the local waveguide region 50 and the cut surface 70 in the bent portion 33, radiation loss at the bent portion 33 can be significantly reduced.
Therefore, it is possible to provide a conductor laser having a low reflectance at the front end face 110 and a reduced radiation loss at the bent portion 33 of the active region 30.
[0079]
FIG. 28 shows an equivalent refractive index distribution of another semiconductor laser according to the present embodiment, the whole being represented by 241. The semiconductor laser 241 has a structure in which the above-described semiconductor laser 240 further includes the antireflection film 20 and the reflection film 21 on the end faces 110 and 120.
[0080]
In the semiconductor laser 241, since the antireflection film 20 and the high refractive index region 80 are provided, the reflectance of the front end face 110 can be significantly reduced. In addition, by having the local waveguide region 50 and the cut surface 70 in the bent portion 33, radiation loss at the bent portion 33 can be significantly reduced. Furthermore, by providing the reflective film 21 on the rear end face 120, it is possible to increase the output of the semiconductor laser.
Therefore, it is possible to provide a high-power semiconductor laser having a low reflectance at the front end face 110 and a reduced radiation loss at the bent portion 33 of the active region 30.
[0081]
In the first to fifth embodiments, the case where the InGaAs layer is used as the active layer 15 has been described. However, the GaAs layer can be used as the active layer.
[0082]
Further, other semiconductor materials may be used for the substrate or the like. For example, an InGaAsP / InP semiconductor laser using an InP substrate may be used.
[0083]
In the above embodiment, the ridge type semiconductor laser has been described. However, the present invention can also be applied to other refractive index waveguide type semiconductor lasers such as a buried type semiconductor laser. In such a buried semiconductor laser, buried layers are formed on both sides (the y-axis direction side in FIG. 1) of the active layer 15, and the local waveguide region 50, the local reflection enhancement region 60, and the high refractive index region 80 are formed in the buried layer. Is formed.
[0084]
Furthermore, it can be applied not only to a semiconductor laser but also to other optical semiconductor elements such as a super luminescence diode.
[0085]
【The invention's effect】
As is clear from the above description, in the optical semiconductor element according to the present invention, the substantial reflectance at the front end face can be reduced.
[0086]
In particular, the reflectance at the front end face can be 1% or less, and further 0.1% or less, while suppressing the inclination angle θ of the optical axis of the optical waveguide from the normal direction of the front end face to less than 3 °.
[0087]
In the optical semiconductor device according to the present invention, it is possible to reduce the radiation loss at the bent portion of the active region (stripe) constituting the optical waveguide.
[Brief description of the drawings]
1A and 1B are a cross-sectional view and a top view of an optical semiconductor device according to a first embodiment of the present invention.
FIG. 2 is an equivalent refractive index distribution of the optical semiconductor element according to the first embodiment of the present invention.
FIG. 3 shows the relationship between the inclination angle θ of the optical waveguide and the reflectance at the front end face.
FIG. 4 is a relationship between the inclination angle θ of the optical waveguide and the reflectance at the front end face.
FIG. 5 is an equivalent refractive index distribution of the optical semiconductor element according to the second embodiment of the present invention.
FIG. 6 is an equivalent refractive index distribution of another optical semiconductor element according to the second embodiment of the present invention.
FIG. 7 shows the relationship between the local waveguide region length and the coupling efficiency.
FIG. 8 is an equivalent refractive index distribution of another optical semiconductor element according to the second embodiment of the present invention;
FIG. 9 is an equivalent refractive index distribution of the optical semiconductor element according to the third embodiment of the present invention.
FIG. 10 is an equivalent refractive index distribution of another optical semiconductor element according to the third embodiment of the present invention.
FIG. 11 is an equivalent refractive index distribution of another optical semiconductor element according to the third embodiment of the present invention.
FIG. 12 is an equivalent refractive index distribution of another optical semiconductor device according to the third embodiment of the present invention;
FIG. 13 is an equivalent refractive index distribution of the optical semiconductor device according to the fourth embodiment of the present invention.
FIG. 14 is an equivalent refractive index distribution of another optical semiconductor element according to the fourth embodiment of the present invention;
FIG. 15 is an equivalent refractive index distribution of another optical semiconductor element according to the fourth embodiment of the present invention;
FIG. 16 is an equivalent refractive index distribution of another optical semiconductor device according to the fourth embodiment of the present invention;
FIG. 17 is an equivalent refractive index distribution of the optical semiconductor device according to the fifth embodiment of the present invention;
FIG. 18 is an equivalent refractive index distribution of another optical semiconductor element according to the fifth embodiment of the present invention;
FIG. 19 is an equivalent refractive index distribution of another optical semiconductor element according to the fifth embodiment of the present invention;
FIG. 20 is an equivalent refractive index distribution of another optical semiconductor element according to the fifth embodiment of the present invention;
FIG. 21 is an equivalent refractive index distribution of another optical semiconductor element according to the fifth embodiment of the present invention;
FIG. 22 is an equivalent refractive index distribution of another optical semiconductor element according to the fifth embodiment of the present invention;
FIG. 23 is an equivalent refractive index distribution of another optical semiconductor element according to the fifth embodiment of the present invention;
24 is an equivalent refractive index distribution of another optical semiconductor element according to the fifth embodiment of the present invention; FIG.
FIG. 25 is an equivalent refractive index distribution of another optical semiconductor element according to the fifth embodiment of the present invention;
FIG. 26 is an equivalent refractive index distribution of another optical semiconductor element according to the fifth embodiment of the present invention;
FIG. 27 is an equivalent refractive index distribution of another optical semiconductor element according to the fifth embodiment of the present invention;
FIG. 28 is an equivalent refractive index distribution of another optical semiconductor element according to the fifth embodiment of the present invention;
FIG. 29 shows a conventional semiconductor laser module.
FIG. 30 is a perspective view of a conventional super luminescence diode.
FIG. 31 is a distribution of equivalent refractive index of a conventional super luminescence diode.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 5 Cladding area | region, 20 Antireflection film | membrane, 21 Reflective film | membrane, 30 Active area | region (stripe), 31 1st active area | region, 32 2nd active area | region, 33 Bending part, 40 Optical axis, 110 Front end surface, 120 Rear end surface, 200 Semiconductor laser.

Claims (3)

At least a first conductivity type cladding layer, an active layer, and a second conductivity type cladding layer are stacked, a ridge structure is provided in a part of the second conductivity type cladding layer, and in a plane perpendicular to the stacking direction, An active region, a cladding region sandwiching the active region from both sides, an optical waveguide composed of the active region and the cladding region and having a constant width in a direction perpendicular to the optical axis, and an end of the optical waveguide An optical semiconductor element including a front end face and a rear end face provided in parallel to each other,
In the active region, a linear first active region and a linear second active region are directly connected at a predetermined bending angle, and light propagating through the active region is totally reflected by the bent portion. Including a reflective surface
The optical axis of the optical waveguide is inclined at an inclination angle of less than 3 ° with respect to the normal line of the front end surface at the front end surface, and is perpendicular to the rear end surface at the rear end surface. An optical semiconductor element covered with an antireflection film.   The optical semiconductor element according to claim 1, wherein the inclination angle is 1.5 ° or less.   The optical semiconductor element according to claim 1, wherein the reflection surface is a flat surface formed so as to cut out a part of the active region.

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