JPH11274638A - Grating coupled surface emitting laser - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To increase light extraction efficiency by a diffraction grating, and to achieve higher output and lower threshold. SOLUTION: An active layer 314 is formed by cladding layers 313, 31.
A waveguide layer 315 having a diffraction grating 316 is provided in the form of a stripe inside a double hetero structure sandwiched between the layers 7, and a light is emitted in a direction perpendicular to the waveguide region. DBR reflection layers 312 and 318 are provided above and below the terrorist structure to amplify the light emitted from the diffraction grating, and the thickness of the lower DBR is varied in the stripe direction. The resonator length has a position dependency.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a surface emitting laser, and more particularly to a grating-coupled surface emitting laser that extracts output light in a direction perpendicular to the direction of a resonator by using a second or higher order diffraction grating.

[0002]

2. Description of the Related Art In recent years, with the aim of realizing an optical subscriber system, research on reducing the cost of an optical transmission / reception terminal device has been actively pursued. In order to reduce the cost of the optical transmission / reception terminal device, it is necessary to reduce the number of components by directly optically coupling a semiconductor laser serving as a transmission light source and an optical fiber without using a lens. However, the coupling efficiency is extremely low between the conventional waveguide semiconductor laser and the optical fiber because the spot size is greatly different. In a semiconductor laser in which a spot size conversion waveguide is integrated, high optical coupling efficiency can be obtained, but a margin for alignment between the semiconductor laser and the optical fiber is insufficient.

On the other hand, with the increase in the amount of transmitted information, various optical devices for information processing have been actively developed. Above all, attention has been paid to a surface-emitting type optical element in order to facilitate parallel processing. In particular, a high performance surface emitting laser having a sub-milliamp oscillation threshold has been developed in the short wavelength band. This type of surface light emitting element also has a feature that optical coupling is easy because the beam radiation angle is relatively small.

However, in a long wavelength band useful for optical communication, there is no material system having a large difference in refractive index, so that a mirror having a high reflectivity cannot be formed, or there is a large amount of non-light-emitting components inherent to the material. Due to the limitations, there is no report of a good surface emitting laser. Therefore, the emergence of a surface emitting laser having excellent characteristics such as an edge emitting laser used for optical communication and optical interconnection is desired.

Although a grating-coupled surface emitting laser has been studied, this laser has a problem that the emitted radiation mode light has two peaks in the waveguide direction. In order to improve this, it has been proposed to incorporate a plurality of phase shift structures into the waveguide. However, in this case, the emission pattern of the radiation mode light has a rectangular shape from the shape of the electrode stripe, and is far from the Gaussian distribution, which is the eigenmode of the fiber. It was small.

In order to improve this, the light emission output pattern of the radiation mode in the waveguide direction is changed to a Gaussian distribution by a phase shift structure of a substantially symmetric distribution in which the phase is gradually shifted over a region longer than the period of the diffraction grating. A device to bring it closer has been devised. However, in the grating-coupled surface emitting laser, in addition to the problem of the emission output pattern described above, since the extraction of the radiation mode by the diffraction grating is also a loss, there is a problem that the extraction effect by the diffraction grating cannot be enhanced. I have.

[0007]

As described above, conventionally, a surface emitting laser has been studied as a transmission light source of an optical transmission / reception terminal device of an optical subscriber system, but this type of surface emitting laser has a large beam diameter. However, there is a problem that the oscillation threshold becomes high in a long wavelength band and the optical output becomes weak. In a grating-coupled surface emitting laser,
In addition to being unable to increase the extraction efficiency by diffraction,
Since the emitted light is reduced in reflection by the layered structure of the waveguide region, or the two emitted lights interfere with each other and are weakened, there has been a problem that a high output and a low threshold cannot be achieved.

The present invention has been made in consideration of the above circumstances, and an object of the present invention is to increase the light extraction efficiency by a diffraction grating and to achieve a higher output and a lower threshold. It is to provide a grating type surface emitting laser which can be measured.

[0009]

(Structure) In order to solve the above-mentioned problem, the present invention employs the following structure.
That is, the present invention relates to a grating-coupled surface emitting laser having a diffraction grating of a second or higher order with respect to guided light in at least a part of a waveguide region and extracting light in a direction perpendicular to the waveguide region. And reflecting mirrors provided above and below the waveguide region to amplify the light emitted from the diffraction grating.

Here, preferred embodiments of the present invention include the following. (1) At least one of the reflecting mirrors has a wavelength dependency or a reflection phase position dependency. (2) At least one of the reflecting mirrors has a position dependence on the resonator length in the resonator constituted by the reflecting mirror. (3) The waveguide region has an active layer sandwiched between cladding layers. It is provided in the form of a stripe inside the double hetero structure, and the reflecting mirrors are provided as DBR (distributed Bragg reflection) layers above and below the outside of the double hetero structure. (4) In (3), at least one of the reflection layers is formed so as to have a different thickness in the stripe direction of the waveguide region. λ / 4n (n: effective refractive index of the reflective layer). (5) In (3), at least one of the cladding layers is formed so as to have a different thickness in the stripe direction of the waveguide region. Satisfies the resonance condition of

(6) The waveguide region is provided in the form of a stripe inside a double hetero structure in which an active layer is sandwiched between cladding layers, and at least one of the reflecting mirrors is provided outside the laser device body including the double hetero structure. It is provided in. (7) In (6), the reflector provided outside the laser element body is arranged at an angle to the stripe direction of the waveguide region, and the resonator length between the reflectors at the center of the stripe from which light is to be extracted. Satisfies the resonance condition of the oscillation wavelength.

(8) In (3) to (5), electrodes are provided on the upper and lower surfaces of the laser element body including the double heterostructure, and a circular opening is provided on the electrode on the light extraction side. That you are.

According to the present invention, the light diffracted by the diffraction grating and traveling in the direction perpendicular to the waveguide region is once returned to the light emitting region (active layer) by the reflectors provided above and below the waveguide region. Can be done. As a result, the light can be further increased, and the Q value of the laser itself can be increased, so that a lower threshold and higher output can be achieved.

[0014] Further, by giving at least one of the reflecting mirrors a wavelength dependency or a position dependency of a reflection phase, or by giving a resonator length in a resonator constituted by the reflecting mirror a position dependency. The shape of the emitted light can be shaped and controlled. Therefore, it is possible to control the beam shape. For example, by making the light emission output pattern close to a Gaussian distribution, it is possible to efficiently couple light to an optical fiber or the like.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to the illustrated embodiments. (First Embodiment) FIG. 1 is a sectional view showing a schematic structure of a grating-coupled surface emitting semiconductor laser according to a first embodiment of the present invention.

In the figure, reference numeral 111 denotes an n-type InP substrate. On this substrate 111, an n-type InGaAsP / InP reflective layer (DBR) 112, an n-type InP cladding layer 113 having a thickness of 1.0 μm, and a 0.1. 1 μm InGaAsP active layer 114 (1.55 μm composition) 114 and 0.1 μm thick I
An nGaAsP waveguide layer 115 is grown and formed in the above order, and a second-order diffraction grating 116 having a period of 480 nm is formed on the waveguide layer 115. Further, the waveguide layer 115 is formed in a stripe shape by etching a part thereof.

Waveguide layer 115 and exposed active layer 114
On top, the p-type InP cladding layer 117 and the p-type InGa
AsP / InP reflective layer (DBR) 118, and further p ⁺
A type InGaAsP contact layer 119 is grown and formed in the above order. A p-side electrode 120 having a partial opening is formed on the contact layer 119, and an n-side electrode 121 is formed on the back surface of the substrate 111. Further, the rear surface of the substrate 111 is provided with a frosted glass-like process 122 in order to prevent light emitted to the substrate side from being reflected by the electrode 121 and becoming return light. The p-side electrode 120
The opening formed in the hole is for extracting light, and may be determined according to a required output light pattern, and may be, for example, circular.

The thickness of the cladding layer of the vertical resonator formed by the two DBRs 112 and 118 is adjusted so as to satisfy the resonance condition with respect to the wavelength of light vertically extracted by the diffraction grating 116. Further, the reflectance of the DBR 118 on the light extraction side is changed to the other DBR 1
If the reflectance is smaller than 12, the improvement of the extraction efficiency can be expected. Further, in addition to the configuration of FIG. 1, by partially changing the period of the diffraction grating 116 or partially adjusting the phase by providing a phase shift unit, the light emission output pattern can be made closer to a Gaussian distribution.

As described above, according to the present embodiment, the DBRs 113 and 11 are disposed above and below the double hetero structure including the waveguide region.
8, the diffracted radiated light from the diffraction grating 116 is once fed back to the active layer 114 and amplified, so that the optical output can be increased and the Q value of the laser can be increased. The threshold can also be reduced.

(Second Embodiment) FIG. 2 shows a second embodiment of the present invention.
FIG. 2 is a cross-sectional view illustrating a schematic configuration of a grating-coupled surface emitting semiconductor laser according to the first embodiment. Note that 211 to 221 in FIG. 2 correspond to 111 to 121 in FIG.

This embodiment is also a grating-coupling type surface emitting semiconductor laser having a reflector similarly to the first embodiment, and is different from the first embodiment in that an external mirror 224 is used instead of the DBR 118. That is. That is, the external mirror 224 is located above the opening of the p-side electrode 220.
Is arranged. The external mirror 224 is formed, for example, by laminating a dielectric multilayer film on the surface of a glass substrate or by vapor-depositing metal (for example, gold). Also,
An AR (Anti-reflection) coat 22 for efficiently extracting outgoing light is provided in an opening formed in the p-side electrode 220.
5 are formed.

With such a configuration, a resonator is formed between the DBR 212 and the external mirror 224, and the diffracted radiation can be once fed back to the active layer 214 and amplified. The same effects as in the embodiment can be obtained.

(Third Embodiment) FIG. 3 shows a third embodiment of the present invention.
FIG. 3 is a cross-sectional view illustrating a schematic structure of a grating-coupled surface emitting semiconductor laser according to the embodiment. Note that 311 to 321 in FIG. 3 correspond to 111 to 121 in FIG.

This embodiment is different from the first embodiment described above in that the lower DBR 312 has a wedge shape,
That is, the reflectance has a wavelength dependency. That is, the lower DBR 312 is formed such that the left side is thinner and the right side is thicker along the stripe direction of the waveguide layer 315, and the thickness of the central portion (the center of the opening of the p-side electrode 320) is λ with respect to the oscillation wavelength λ. / 4n (n: effective refractive index of the DBR 312). That is, the lower DBR 312 is set so that the reflection at the light extraction portion becomes the largest with respect to the oscillation wavelength λ.

With such a configuration, the DBR 312,
318 allows the diffracted radiation to be fed back to the active layer 314 and amplified, and furthermore, the DBRs 312 and 3
Light can be extracted only from a portion satisfying the resonance conditions in the vertical resonator formed by 18, and the shape of the emitted light can be controlled. Specifically, a light emission output pattern close to a Gaussian distribution can be obtained, and the coupling efficiency with an optical fiber can be improved.

Note that instead of changing the thickness of the lower DBR 312 in the stripe direction of the waveguide layer 315, the upper DBR
The same effect can be obtained by changing the thickness of 318. Further, both thicknesses of the DBRs 312 and 318 may be changed.

(Fourth Embodiment) FIG. 4 shows a fourth embodiment of the present invention.
FIG. 3 is a cross-sectional view illustrating a schematic structure of a grating-coupled surface emitting semiconductor laser according to the embodiment. Note that 411 to 421 in FIG. 4 correspond to 111 to 121 in FIG.

This embodiment is different from the first embodiment in that the thickness of the lower cladding layer 413 is varied along the stripe direction of the waveguide 415, and the thickness of the lower cladding layer 413 is determined by the vertical cavity length composed of the DBRs 412 and 418. It has dependencies. That is, the lower cladding layer 413 is
Along the stripe direction, the left side is thinner and the right side is thicker. And the distance between DBR412 and 418 is
The optimum resonator length is at the center (the center of the opening of the electrode 420).

With such a configuration, the DBR 412,
Light can be extracted only from the portion of the vertical resonator formed by 418 that satisfies the resonance condition,
Control of the emitted light becomes possible. That is, since the central portion has the optimum resonator length, it approaches a Gaussian distribution where the light intensity increases at the central portion. Therefore, the same effect as in the third embodiment can be obtained.

The same effect can be obtained by changing the thickness of the upper cladding layer 417 instead of changing the thickness of the lower cladding layer 413 in the stripe direction of the waveguide layer 415. Further, both thicknesses of the cladding layers 413 and 415 may be changed.

(Fifth Embodiment) FIG. 5 shows a fifth embodiment of the present invention.
FIG. 3 is a cross-sectional view illustrating a schematic structure of a grating-coupled surface emitting semiconductor laser according to the embodiment. Note that 511 to 521 in FIG. 5 correspond to 111 to 121 in FIG.

This embodiment is different from the second embodiment in that the external mirror 524 is tilted,
The point is that the resonance condition of the resonator formed by 512 changes depending on the axial direction.

With such a configuration, light can be extracted only from the portion satisfying the resonance condition in the vertical resonator formed by the DBR 512 and the external mirror 524. Therefore, it becomes possible to control the shape of the emitted light,
The same effects as in the fourth embodiment can be obtained.

Instead of tilting the external mirror 524, the thickness of the lower cladding layer 513 is changed so that the lower DBR 5
12 may be inclined. In addition, external mirror 5
24 and the lower DBR 512 may be tilted.

(Sixth Embodiment) FIG. 6 shows a sixth embodiment of the present invention.
FIG. 3 is a diagram showing a schematic configuration of a grating-coupled surface emitting dye laser according to the embodiment.

In the figure, reference numeral 1 denotes a dye cell for holding an organic dye Na-fluorescein dissolved in ethanol as a solvent. The dye cell 1 is excited by an argon ion laser 2. The excitation light 3 from the laser 2 is split into two light beams 5, 6 by a half mirror 4, and the respective light beams 5, 6 are incident on the upper surface of the dye cell 1 at an appropriate incident angle θ by total reflection mirrors 7, 8. Is done.

The two light beams 5 and 6 incident on the upper surface of the dye cell 1 interfere with each other, and form a light stripe pattern defined by the incident angle θ and the excitation wavelength on the dye cell surface. Therefore, the organic dye is excited in a striped manner, and even if the organic dye is not provided with a laser resonator mirror, the striped excitation forms a diffraction grating having a complex refractive index (gain). Enables laser oscillation. The oscillation wavelength is determined by the period of the diffraction grating, which can be adjusted by the incident angle θ. In the case of this dye cell 1, 5
Green laser light of 30 to 560 nm can be obtained.

In such a dye cell 1, the incident angle θ can be adjusted so that the diffraction grating forms a secondary diffraction grating with respect to the oscillation wavelength. Laser light can be extracted in a direction perpendicular to the axial direction (axial direction of the diffraction grating). At this time, by arranging the reflecting mirrors 9 and 10 so as to sandwich the dye cell 1, the laser light extracted in the vertical direction is once applied.
It can be returned to the cell 1.

Therefore, similarly to the first embodiment, the light in the vertical direction can be amplified to increase the light output, and the same effect as that of the first embodiment can be obtained. In the same manner as described in the second to fifth embodiments, the light emission is achieved by changing the distance (resonator length) between the reflecting mirrors 9 and 10 and the thickness of the reflecting mirrors 9 and 10 in the horizontal direction. It is also possible to control the output pattern.

The present invention is not limited to the above embodiments. In the embodiment, InP is used as a material system.
Although a system was used, instead of this, for example, GaAs or In
GaAlP-based, GaN-based, and other optical materials may be used. Further, the diffraction area and the light emitting area may be different areas. Further, in the embodiment, the structure in which light is extracted to the surface side (the side opposite to the substrate) is described as an example. However, a structure in which light is extracted from the substrate side by turning the element upside down may be used.

In the sixth embodiment, Na-fluorescein is used as the organic dye, and an argon ion laser is used as the excitation light source. However, other combinations may be used. In addition, various modifications can be made without departing from the scope of the present invention.

[0042]

As described in detail above, according to the present invention, it is possible to improve the light output and further reduce the threshold. As a result, performance enhancements such as higher output and lower threshold of grating-coupled surface-emitting lasers, which are key devices in optical network equipment and optical information processing systems used in optical subscriber systems, and have a large alignment tolerance with optical fibers Is easily realized, and its usefulness is enormous.

Further, by changing the resonance condition in the vertical direction in the axial direction, the beam shape can be controlled and a narrow beam can be easily realized, and its usefulness is enormous.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a schematic structure of a grading-coupling type surface emitting semiconductor laser according to a first embodiment.

FIG. 2 is a sectional view showing a schematic structure of a grading-coupling type surface emitting semiconductor laser according to a second embodiment;

FIG. 3 is a cross-sectional view illustrating a schematic structure of a grading-coupling type surface emitting semiconductor laser according to a third embodiment.

FIG. 4 is a sectional view showing a schematic structure of a grading-coupling type surface emitting semiconductor laser according to a fourth embodiment;

FIG. 5 is a sectional view showing a schematic structure of a grading-coupling type surface emitting semiconductor laser according to a fifth embodiment;

FIG. 6 is a diagram showing a schematic configuration of a surface emitting dye laser according to a sixth embodiment.

[Explanation of symbols]

111, ..., 511 ... n-type InP substrate 112, ..., 512 ... n-type InGaAsP / InP reflective layer (DBR) 113, ..., 513 ... n-type InP cladding layer 114, ..., 514 ... InGaAsP active layer 115, ..., 515... InGaAsP waveguide layer 116, 516... Second-order diffraction grating 117, 517, p-type InP cladding layer 118, 318, 418 p-type InGaAsP / InP
Reflective layer (DBR) 119, 519, p ⁺ -type contact layer 120, 520, p-side electrode 121, 521, n-side electrode 224, 524 external mirror 225 AR coating

Claims (5)

[Claims] 1. A grating-coupled surface-emitting laser having a diffraction grating of a second or higher order with respect to guided light in at least a part of a waveguide region and extracting light in a direction perpendicular to the waveguide region. A grating-coupled surface-emitting laser, wherein reflection mirrors are provided above and below the waveguide region to amplify light emitted from the diffraction grating. 2. A method according to claim 1, wherein at least one of said reflecting mirrors has a wavelength dependency or a position dependency of a reflection phase, or a resonator length in a resonator constituted by said reflecting mirror has a position dependency. The grating-coupled surface emitting laser according to claim 1, wherein: 3. The waveguide region is provided in the form of a stripe inside a double hetero structure in which an active layer is sandwiched by cladding layers, and the reflecting mirrors are provided as reflection layers above and below the double hetero structure. The grating type surface emitting laser according to claim 1, wherein the surface emitting laser is provided. 4. At least one of the reflection layers is formed so as to have a different thickness in the stripe direction of the waveguide region. The grating type surface emitting laser according to claim 3, wherein / 4n (n: refractive index of the reflective layer) is set. 5. The semiconductor device according to claim 1, wherein at least one of said cladding layers is formed so as to have a different thickness in a stripe direction of said waveguide region. The grating type surface emitting laser according to claim 3, wherein the resonance condition is satisfied.