WO2006011370A1

WO2006011370A1 - Polarization modulating laser device

Info

Publication number: WO2006011370A1
Application number: PCT/JP2005/013032
Authority: WO
Inventors: Shigeru Koumoto; Shigeo Sugou
Original assignee: Nec Corporation
Priority date: 2004-07-30
Filing date: 2005-07-14
Publication date: 2006-02-02
Also published as: JPWO2006011370A1; JP4946439B2

Abstract

A polarization modulation laser device which outputs a laser beam having stable output intensity on a low-threshold current with high efficiency and can be easily fabricated . The polarization modulation laser device comprises a quantum line absorption modulation layer (4) (first polarization control structure) for fixing the polarization direction of the laser beam to a first polarization direction by means of electrical means and a rectangular post structure (second polarization control structure) for controlling the polarization direction of the laser beam to a direction other than the first polarization direction. The quantum line absorption modulation layer (4) includes an absorption modulation structure for varying the light absorption coefficient to the laser beam by means of electrical means. The quantum line absorption modulation layer (4) has an anisotropic light absorption coefficient in the plane perpendicular to the output direction of the laser beam of the absorption modulation structure. In the polarization modulating laser device, the absorption modulation structure of the quantum line absorption modulation layer (4) is electrically isolated form the quantum well active layer (9) (layer containing a gain medium).

Description

Specification

Polarization modulation laser device

Technical field

TECHNICAL FIELD [0001] The present invention relates to a laser device, and more particularly to a polarization-modulated laser device that can modulate the polarization direction of laser light at high speed.

Background art

[0002] With the development of technology in recent years, a practical surface-emitting laser device has been developed, and its application to various optical communication applications is being studied. The surface emitting laser is easier to integrate than the conventional edge emitting laser, and has advantages such as low power consumption and low cost. In addition, due to such characteristics, surface emitting lasers are positioned as important light emitting elements even in optical interconnection, which is optical communication between computer boards or chips. In particular, in inter-chip optical communication, it is necessary to mount an optical transmission module densely in a small area, so it is considered essential to use a surface-emitting laser with low power consumption characteristics. When surface-emitting lasers are used for optical interconnection, it is required to further expand the modulation band without reducing power consumption and optical output.

[0003] When surface emitting lasers are classified according to the modulation method of laser light intensity, they are classified into a direct current modulation type and a modulator integrated type. In a direct current modulation surface emitting laser, the amount of injected current is greatly changed, so that the optical density and carrier density in the laser optical resonator vary greatly. As a result, the modulation bandwidth is limited in the direct current modulation type surface emitting laser.

Japanese Examined Patent Publication No. 7-93473 (see paragraph 0004) describes a modulator integrated surface emitting laser having an absorption modulator by applying an electric field outside an optical resonator. However, this modulator-integrated surface-emitting laser element does not vary greatly in the optical density and carrier density in the optical resonator, but in order to obtain a sufficient extinction ratio, the thickness, absorption layer, or many Since a large number of absorption layers is required, a large modulation voltage is required.

In order to avoid the problem that a large modulation voltage is required, Japanese Patent Laid-Open No. 5-152674 (see paragraph 0005) describes an optical resonator structure in an absorption modulator provided outside the optical resonator. There is described a surface emitting semiconductor laser provided with a structure to increase the effective light absorption amount and to achieve a low voltage operation of the optical modulator. However, since this surface emitting semiconductor laser employs a composite resonator structure, the laser oscillation itself becomes unstable.

There are also polarization-modulated surface-emitting lasers that switch the polarization direction of a laser beam in accordance with an input signal, in contrast to an intensity-modulated surface-emitting laser such as a direct current modulation type or a modulator integrated type. The polarization-modulated surface-emitting laser has a larger amount of injected current than that of a direct-current-modulated surface-emitting laser or a modulator-integrated surface-emitting laser in which an absorption modulator is provided outside or inside the resonator. The optical density and carrier density in the laser resonator where the change of the laser beam is small can be made almost constant. Therefore, if a polarization-modulated surface emitting laser is used, a higher modulation speed can be obtained as compared with the case where an intensity-modulated surface emitting laser is used. In other words, if a polarization-modulated surface emitting laser is used, the three characteristics of low current or low voltage modulation, high-speed modulation, and stable laser oscillation can be realized simultaneously.

Japanese Laid-Open Patent Publication No. 10-261842 (see paragraphs 0007-0011 and FIG. 2) describes a surface-type optical device using a polarization-modulated surface-emitting laser. With reference to FIGS. 1A and 1B, the structure of this polarization-modulated surface-emitting laser device will be described.

FIG. 1A is a cross-sectional view showing the structure of a polarization-modulated surface-emitting laser device described in Japanese Patent Application Laid-Open No. 10-261842. As shown in FIG. 1A, the polarization-modulated surface-emitting laser device includes a first n-clad layer 202, a first quantum wire active layer 203, a p-clad layer 204, and a second quantum layer on an n-type substrate 201. The thin-wire active layer 205, the second n-cladding layer 206, the contact layer 207, and the first dielectric multilayer mirror 208 are sequentially formed. On the opposite side of the first n-clad layer 202 from the n-type substrate 201, the second dielectric multilayer mirror 209 is in contact with the first n-clad layer 202 through the n-type substrate 201. Formed!

In addition, the polarization-modulated surface-emitting laser device is in contact with the p-electrode 211 force contact layer 207 so as to be in contact with the first n-electrode 210 force p-cladding layer 204 so as to contact the n-type substrate 201 A second n-electrode 212 is formed respectively.

FIG. 1B is a perspective view showing the structure of the quantum wire active layer of the polarization modulation surface emitting laser device shown in FIG. 1A. As shown in FIG. 1B, in the polarization-modulated surface emitting laser device, the first quantum wire active layer 203 and the second quantum wire active layer 205 are perpendicular to each other. It is arranged in a direction.

In the polarization-modulated surface-emitting laser device shown in FIGS. 1A and 1B, a laser resonator is formed by two dielectric multilayer mirrors 208 and 209. When operating this polarization-modulated surface emitting laser device, currents are allowed to flow independently between the first n-electrode 210 and p-electrode 211 and between the second n-electrode 212 and p-electrode 211, respectively. Thus, the gains of the first quantum wire active layer 203 and the second quantum wire active layer 205 can be independently controlled. In this case, the gain at the band edge of the quantum wire is maximized for linearly polarized light parallel to the quantum wire.

In addition, in the polarization-modulated surface emitting laser device shown in FIGS. 1A and 1B, the DC bias currents of the two quantum wire active layers 203 and 205 are adjusted, and the laser modulation current is changed to the first quantum wire active layer. Either 203 or the second quantum wire active layer 205 is implanted, or both the two quantum wire active layers 203 and 205 are implanted. By doing so, a laser beam polarized in parallel to the quantum wire of the first quantum wire active layer 203 and a laser beam polarized in parallel to the quantum wire of the second quantum wire active layer 205 orthogonal to the first quantum wire active layer 203 Thus, the polarization direction of the laser beam is modulated.

[0013] Japanese Unexamined Patent Publication No. 6-232501 (see paragraphs 0012-0016 and FIG. 3) describes a polarization switching laser using a polarization-modulated surface emitting laser. FIG. 2 is a cross-sectional view showing the structure of a polarization-modulated surface-emitting laser device described in JP-A-6-232501. As shown in FIG. 2, the polarization-modulated surface emitting laser device includes a first p-type Bragg reflection mirror 301, an i-AlGaAs layer 302, a fractional layer superlattice 303, an n + -AlGaAs layer, and an i-A1 GaAs layer. And an n-contact Z high-resistance layer 304 composed of an n + -AlGaAs layer, a variable optical path length medium 305, and a second p-type Bragg reflection mirror 306 are sequentially formed.

[0014] The fractional layer superlattice 303 has a structure in which an A10.5GaO.5AsZGaAs superlattice is erected perpendicularly to the Bragg reflection mirror surface. As electrodes, a first p-electrode 307 is formed so as to be in contact with the first p-type Bragg reflection mirror 301, and a second p-electrode 308 is formed so as to be in contact with the second p-type Bragg reflection mirror 306. . An n electrode (not shown) is formed so as to be in contact with the two n + —AlGa As layers of the n contact Z high resistance layer 304.

In the polarization modulation surface emitting laser device shown in FIG. 2, two Bragg reflection mirrors 301 and 306 are used. As a result, a laser resonator is formed. The optical path length variable medium 305 is a medium whose refractive index changes when an electric field is applied. For example, i-AlGaAs is used as the optical path length variable medium 305.

When operating the polarization-modulated surface-emitting laser device shown in FIG. 2, the forward direction is between the p electrode 307 and the n contact Z high resistance layer 304 and the n + —AlGaAs layer on the fractional superlattice 303 side. By applying a bias voltage 310, a laser can be oscillated by supplying a DC bias current. In this case, a modulation bias voltage 309 is applied between the p-electrode 308 and the n + -AlGaAs layer on the optical path length variable medium 305 side of the n-contact Z high-resistance layer 304. By doing so, the resonance peak wavelength of the laser resonator can be varied.

[0017] The gain peak wavelength for linearly polarized light perpendicular to the superlattice layer surface of the fractional layer superlattice 303 is relatively shorter than the gain peak wavelength for linearly polarized light parallel to the superlattice layer. Therefore, when the resonance peak wavelength is changed to the relatively short wavelength side, the polarization modulation surface emitting laser device emits laser light having a polarization perpendicular to the superlattice layer surface of the fractional layer superlattice 303. Further, when the resonance peak wavelength is changed to the relatively long wavelength side, the polarization modulation surface emitting laser device emits laser light having a polarization parallel to the superlattice layer surface of the fractional layer superlattice 303. In this way, the polarization direction of the laser light is modulated by changing the resonance peak wavelength.

Disclosure of the invention

[0018] In the case of using the polarization-modulated surface-emitting laser device described in JP-A-10-261842 or JP-A-6-232501, in-plane polarization anisotropy is necessary to obtain the optical gain of the active layer. It is. In order to concretely realize such an active layer having anisotropy, a quantum wire with a minimum in-plane structure dimension on the order of 10 nm, a fractional layer superlattice, an in-plane shape anisotropy Dots or the like are used. However, it is generally difficult to form such a quantum microstructure with high quality and high density, and to realize surface emitting laser performance equivalent to that of a quantum well. Therefore, the polarization-modulated surface-emitting laser device described in Japanese Patent Laid-Open Nos. 10-261842 and 6-232501 has a high-performance surface emission that outputs high-efficiency laser light with a practical low threshold current. It is difficult to realize a laser.

Therefore, the present invention has been made to solve the above-described problems, and is easy to manufacture. However, an object of the present invention is to provide a polarization-modulated surface-emitting laser device that can output laser light with low threshold current and high efficiency and stable output intensity.

A polarization-modulated laser device according to the present invention is a polarization-modulated laser device that modulates and outputs laser light, and is realized by a first reflection mirror (for example, an n-type Bragg reflection mirror 2 shown in FIG. 3). And a layer including a gain medium for obtaining optical gain (for example, realized by the quantum well active layer 9 shown in FIG. 3), and a second reflecting mirror (for example, P-type shown in FIG. 3). A laser beam oscillated by a layer including a resonator and a gain medium formed by the first reflecting mirror and the second reflecting mirror, and the first reflecting mirror or An output unit (for example, realized by the aperture 14 shown in FIG. 3) that outputs in a direction perpendicular to the surface of the second reflecting mirror and an output laser beam in the first polarization direction by electrical means. First polarization control structure to be fixed (For example, realized by the quantum wire absorption modulation layer 4 shown in FIG. 3) and the second polarization control structure for directing the output laser light in a second polarization direction different from the first polarization direction (For example, it is realized by forming a portion where the quantum well active layer 9, the p-type AlGaAs layer 12 and the p-type Bragg reflection mirror 13 shown in FIG. 3 are stacked in a predetermined post structure). The first polarization control structure includes an absorption modulation structure (for example, realized by a quantum wire, a quantum dot, or a fractional layer superlattice) that changes an optical absorption coefficient for laser light by an electric means, and absorbs modulation. The structure has optical anisotropy in the light absorption coefficient in a plane parallel to the plane perpendicular to the laser beam output direction, and the absorption modulation structure and the layer containing the gain medium are electrically separated. And!

In addition, the absorption modulation structure may change the light absorption coefficient with respect to the laser beam by applying an electric field as an electrical means.

[0022] The second polarization control structure has an optical waveguide (for example, a portion where the quantum well active layer 9, the p-type AlGaAs layer 12, and the p-type Bragg reflection mirror 13 shown in FIG. The optical waveguide has a rectangular cross section in a plane perpendicular to the traveling direction of the laser light, and the long side of the rectangular shape is realized by forming a post structure having an elliptical cross sectional shape). The long side direction in which the optical waveguide loss on the side is larger than the optical waveguide loss on the short side may be arranged in a direction not parallel to the first polarization direction! /. [0023] The absorption modulation structure may have a minimum dimension of 50 nm or less in a plane parallel to a plane perpendicular to the laser light output direction.

[0024] Further, the absorption modulation structure may include a quantum wire, a quantum dot, or a fractional layer superlattice.

[0025] The first reflection mirror and the second reflection mirror have a multilayer film structure, and the absorption modulation structure included in the layer including the gain medium and the first polarization control structure is a semiconductor layer. In the polarization modulation laser device, a first reflection mirror, a second reflection mirror, a layer including a gain medium, and an absorption modulation structure may be laminated on a substrate.

[0026] The first reflection mirror and the second reflection mirror may have a semiconductor multilayer structure.

[0027] The substrate on which the first reflection mirror, the second reflection mirror, the layer including the gain medium, and the absorption modulation structure are stacked may be a semiconductor substrate.

The polarization modulation laser device according to the present invention includes an absorption modulation structure that changes an optical absorption coefficient for laser light by an electric means inside a laser resonator having an active medium sandwiched between two reflection mirrors. It has been. The polarization modulation laser device modulates the polarization of the laser light by modulating the light absorption coefficient of the absorption modulation structure. In this case, a structure having anisotropy in the light absorption coefficient in a plane parallel to the plane perpendicular to the output direction of the laser beam is used as the absorption modulation structure. For example, quantum wires are used as the absorption modulation structure.

[0029] With the above configuration, the polarization-modulated laser device generates laser light by the two reflection mirrors and the active medium sandwiched between the two reflection mirrors. If the other laser components of the polarization modulation laser apparatus have no optical anisotropy with respect to the laser light, the polarization direction of the generated laser light is determined by applying an electric field to the absorption modulation structure. The first polarization direction with the smallest absorption coefficient is fixed.

However, with only the above configuration, there is a possibility that the polarization direction when no electric field is applied coincides with the polarization direction when an electric field is applied. In view of this, the polarization modulation laser device according to the present invention provides the second laser structure that controls the laser beam in a polarization direction different from the direction in which the polarization direction is fixed when an electric field is applied, in the above laser structure when no electric field is applied. Polarization control structure Introduce construction. For example, the polarization modulation laser device has a rectangular cross-sectional shape as the second polarization control structure, and the optical waveguide loss on the long side of the cross section is appropriately larger than the optical waveguide loss on the short side. Includes an optical waveguide arranged in a direction not parallel to the first polarization direction.

[0031] By introducing the second polarization control structure, the polarization modulation laser apparatus has a specific polarization fixed direction that becomes the polarization direction only when an electric field is applied to the absorption modulation structure. Can do. In this case, the polarization fixing direction is determined by the relationship between the first polarization direction and the polarization control characteristics of the second polarization control structure. Therefore, when the second polarization control structure is introduced, the polarization fixing direction when the electric field is applied tl to the absorption modulation structure is the same as the first polarization direction when the second polarization control structure is not introduced. Not necessarily the same.

In the polarization modulation laser device according to the present invention, since the active medium and the absorption modulation structure are electrically separated, even if a modulation voltage is applied to the absorption modulation layer, the number of carriers in the active medium varies. Can be kept low. Therefore, it is possible to reduce the fluctuation of the average output intensity of the laser beam.

[0033] According to the present invention, as a gain medium of the laser of the polarization modulation laser apparatus, a generally used high-quality and easily formed material and structure such as a multiple quantum well are used. The polarization modulation laser device also includes an absorption modulation structure that does not need to be of higher quality than the active layer. Further, the layer including the gain medium and the absorption modulation structure are electrically separated, so that the carrier fluctuation in the gain medium can be suppressed to a low level. Therefore, while the polarization modulation laser device can be easily manufactured, the polarization modulation laser device can output a laser beam having a low threshold current and a high efficiency and a stable output intensity.

Brief Description of Drawings

FIG. 1A is an explanatory view showing an example of the structure of a conventional polarization modulation surface emitting laser device.

FIG. 1B is an explanatory diagram showing an example of the structure of a conventional polarization modulation surface emitting laser device.

FIG. 2 is a cross-sectional view showing another structural example of a conventional polarization modulation surface emitting laser device.

FIG. 3A is an explanatory view showing an example of the structure of a polarization modulation laser device according to the present invention.

FIG. 3B is an explanatory diagram showing an example of the structure of the polarization modulation laser device according to the present invention.

Explanation of symbols High-resistance GaAs substrate n-type Bragg reflection mirror First n-clad layer Quantum wire absorption modulation layer Barrier layer

First p-clad layer High-resistance AlGaAs layer Second n-clad layer Quantum well active layer Second p-clad layer High-resistance layer

p-type AlGaAs layer p-type Bragg reflector mirror aperture

17 p electrode

18 n electrode

1 n-type substrate

2 First n-clad layer 3 First quantum wire active layer 4 P-clad layer

5 Second quantum wire active layer 6 Second n-clad layer 7 Contact layer

8 1st dielectric multilayer mirror 9 2nd dielectric multilayer mirror 0 1st n electrode

1 rho electrode

2 Second n-electrode 301 First p-type Bragg reflector mirror

302 i— AlGaAs layer

303 fractional superlattice

304 n contact Z high resistance layer

305 Optical path length variable medium

306 Second p-type Bragg reflector mirror

307 p electrode

308 p electrode

309 Bias voltage

310 Bias voltage

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described with reference to the drawings. 3A and 3B are diagrams for explaining an example of the structure of the polarization modulation laser device according to the present invention. FIG. 3A is a cross-sectional view showing an example of the structure of the polarization modulation laser device. In the present embodiment, a case where the polarization modulation laser device is a polarization modulation surface emitting laser device will be described.

[0037] As shown in FIG. 3A, the polarization modulation laser device includes a high-resistance GaAs substrate 1, an n-type Bragg reflection mirror 2, a first n-cladding layer 3, a quantum wire absorption modulation layer 4, a barrier layer 5, 1 p-cladding layer 6, high-resistance AlGaAs layer 7, second n-cladding layer 8, quantum well active layer 9, second p-cladding layer 10, p-type AlGaAs layer 12, and p-type Bragg reflector 13 were stacked Includes structure.

[0038] The p-type Bragg reflecting mirror 13 includes an opening 14 that emits laser light. The portion where the quantum well active layer 9, the p-type AlGaAs layer 12 and the p-type Bragg reflector 13 are stacked is processed into a rectangular shape when viewed from the opening 14 side (X direction shown in FIG. 3A). . In the following, the shape of the portion where the quantum well active layer 9, the p-type AlGaAs layer 12, and the p-type Bragg reflection mirror 13 are stacked, as viewed from the opening 14 side, is a rectangular post. Also called. In the present embodiment, the portion where the quantum well active layer 9, the p-type AlGaAs layer 12, and the p-type Bragg reflector 13 are stacked has a rectangular cross-sectional shape, so that the optical waveguide on the long side of the cross-section is provided. An optical waveguide whose loss is appropriately larger than the optical waveguide loss on the short side is formed. A high resistance layer 11 is formed outside the p-type AlGaAs layer 12. [0039] In addition, the polarization-modulated laser device includes, as electrodes, a P-electrode 15 provided in contact with the surface of the p-type Bragg reflector 13 and a ring-shaped n provided in contact with the second n-cladding layer 8. Electrode 16, ring-shaped p-electrode 17 provided in contact with first p-cladding layer 6, and ring-shaped n-electrode 18 provided in contact with first n-cladding layer 3 in total Includes electrodes.

FIG. 3B is a plan view of the polarization-modulated laser device shown in FIG. 3A as viewed from the opening 14 side (X direction shown in FIG. 3A). Fig. 3B shows a rectangular boosted structure in which a quantum well active layer 9, a p-type AlGaAs layer 12 and a p-type Bragg reflector 13 processed into a rectangular shape are stacked, and a quantum wire absorption modulation layer 4 The relationship of the direction is shown. The vertical and horizontal dimensions of the rectangle of the rectangular post are, for example, about 6 microns x 4 microns.

In the present embodiment, the quantum wire absorption modulation layer 4 is disposed between the two Bragg reflection mirrors 2 and 1 3 at a position where the light intensity becomes maximum. The absorption modulation structure of the quantum wire absorption modulation layer 4 has a minimum dimension of 50 nm or less in a plane parallel to a plane perpendicular to the traveling direction of the laser beam. For example, the thin wire width of the quantum wire that is an absorption modulation structure is lOnm, and as shown in FIG. 3B, in the quantum wire absorption modulation layer 4, the extension direction of the quantum wire is parallel to the long-side direction of the rectangle post rectangle. It is arranged to be.

Next, the operation of the polarization modulation laser device of the present embodiment will be described. In the polarization modulation laser device having the structure shown in FIG. 3A, the quantum well active layer 9 emits light by applying a DC noise voltage as a forward bias between the p-electrode 15 and the n-electrode 16. The n-type Bragg reflection mirror 2 and the p-type black reflection mirror 13 form a resonator, and the polarization modulation laser device oscillates when a current exceeding the oscillation threshold current is applied.

Further, by applying a reverse voltage Vm between the p electrode 17 and the n electrode 18, the polarization modulation laser device changes the light absorption coefficient of the quantum wire absorption modulation layer 4 with respect to the laser light. In this embodiment, the quantum wire absorption modulation layer 4 has a shape, size, and composition so that the light absorption coefficient with respect to the laser light becomes almost 0 when Vm = 0, and light absorption occurs when Vm ≠ 0. It has been adjusted.

[0044] For example, when Vm = 0, the polarization direction of the laser light is parallel to the long side of the rectangular post. become. This is because the waveguide loss is the smallest in this polarization direction. When Vm ≠ 0, the absorption coefficient in the extension direction of the quantum wire absorption modulation layer 4 is maximized, and the absorption coefficient in the direction perpendicular to the quantum wire is minimized. Therefore, when Vm ≠ 0, the polarization direction of the laser light is parallel to the short side direction of the rectangular post. In this case, when the polarization parallel to the long side of the rectangular post and the polarization parallel to the short side are compared, the difference in loss and threshold current with respect to the polarization is small. Therefore, the modulation voltage Vm can be small, and the light density and carrier density in the laser resonator hardly change! Therefore, a large polarization modulation speed can be obtained.

[0045] By operating as described above, the polarization-modulated laser device emits polarization-modulated laser light. Further, by arranging a polarizer above the opening 14, the laser beam polarized and modulated by the polarization modulation laser device can be extracted as an intensity-modulated laser beam. In this case, depending on how the polarizers are arranged, either laser light having a polarization parallel to the long side of the rectangular post or laser light having a polarization parallel to the short side is appropriately selected and taken out. Can do.

[0046] As described above, according to the present embodiment, in the polarization modulation laser device, as a gain medium of the laser of the quantum well active layer 9, for example, a multi-quantum well or the like, which is generally used, can be easily formed with high quality. Materials and structures can be used. According to the present embodiment, the polarization modulation laser device includes the quantum wire absorption modulation layer 4 as the absorption modulation structure. In general, it is necessary to use a quantum wire having a minimum dimension of lOnm order as an absorption modulation structure having optical anisotropy, but according to the present embodiment, the quantum wire absorption modulation layer 4 is not an active layer. The quantum wire absorption modulation layer 4 does not have to be of high quality. Therefore, according to the present embodiment, when the polarization modulation laser device is applied to a semiconductor surface emitting laser, it is possible to realize a polarization modulation surface emitting laser device that is easy to manufacture and that has a low threshold current and high efficiency.

Furthermore, according to the present embodiment, the active medium of the quantum well active layer 9 and the absorption modulation structure of the quantum wire absorption modulation layer 4 are electrically separated. For this reason, even when a modulation voltage is applied to the absorption modulation layer, the variation in the number of carriers in the active medium can be suppressed low, and the variation in the average output intensity of the laser light can be reduced. Therefore, polarization modulation with stable output intensity Laser light can be obtained. Therefore, while the polarization modulation laser device can be easily manufactured, the polarization modulation laser device can output a laser beam having a low threshold current and high efficiency and stable output intensity.

In this embodiment, the case where the quantum wire absorption modulation layer 4 including quantum wires is used as the absorption modulation structure has been described. However, the in-plane parallel to the surface perpendicular to the laser light output direction is described. Other structures may be used as long as they have anisotropy in the light absorption coefficient. For example, as an absorption modulation structure, a fractional layer superlattice may be used, and in-plane shapes and quantum dots with anisotropic strain distribution may be used.

[0049] In addition, the structure in which the polarization direction can be controlled when Vm = 0 is not limited to the rectangular post structure, but an elliptical post (ie, quantum well active layer 9, p-type A1 GaAs if the shape has no central symmetry. Other post structures such as the layer 12 and the p-type Bragg reflection mirror 13 may be laminated and the portion may have an elliptical cross-sectional shape. Further, the height of the rectangular post is not limited to the case shown in the present embodiment. For example, instead of making all the parts of the quantum well active layer 9, the p-type AlGaAs layer 12 and the p-type Bragg reflection mirror 13 rectangular, the part up to the middle of the p-type Bragg reflection mirror 13 is rectangular. Post height may be adjusted

[0050] Further, as a structure capable of controlling the polarization direction when Vm = 0, a substrate having absorption anisotropy in a plane typified by (311) B surface or (311) A surface is used. A structure having a post shape formed thereon may be used. Further, a structure using an in-plane anisotropic electrode, a high resistance layer, or an active layer may be used. Further, a structure provided with an absorption modulation structure that is electrically separated from the quantum wire absorption modulation layer 4 may be used. If such an anisotropic substrate, electrode, high resistance layer or active layer is used, or a structure with another absorption modulation structure is provided, the post shape is made cylindrical and external optics such as laser light and fiber are used. The coupling rate with the system can be increased.

[0051] The quantum wire absorption modulation layer 4 may have a spontaneous internal electric field. By doing so, the polarization-modulated laser device can perform a modulation operation so that the absorption coefficient is large when Vm = 0 and the absorption coefficient is small when V ≠ 0.

[0052] As shown in the present embodiment, the quantum wire absorption modulation layer 4 includes two blocks. Although it is preferable to arrange at a position where the light intensity is maximum between the lag reflecting mirrors 2 and 13, it may be arranged at another position. For example, the quantum wire absorption modulation layer 4 may be arranged inside the n-type Bragg reflection mirror 2 or the p-type Bragg reflection mirror 13!

[0053] If the quantum wire absorption modulation layer 4 and the quantum well active layer 9 can be separated in a direct current, the high resistance AlGaAs layer 7 may be an n-type or p-type semiconductor layer, or an n-type layer. It is also possible to eliminate the high-resistance AlGaAs layer 7 that can be a stacked structure of n-type and p-type layers (underlying n-type) or an insulating layer. In this case, for example, an Fe-doped AlGaAs layer can be used as the high-resistance AlGaAs layer 7. Instead of the Fe-doped AlGaAs layer, as the high-resistance AlGaAs layer 7, for example, an insulating layer formed by oxidizing an AlAs layer or an A1-rich AlGaAs layer may be used.

In the present embodiment, the high-resistance GaAs substrate 1 is used as the substrate, but an n-type substrate may be used as the substrate. In addition, a p-type substrate may be used as a substrate on the condition that appropriate substitution is performed for the conductivity type of the semiconductor layer on the substrate. If a conductive substrate is used as the substrate, the n-electrode 18 may be formed on the back surface of the substrate.

[0055] Further, if the material that realizes the characteristics of the quantum well active layer 9, the quantum wire absorption modulation layer 4, and the Bragg reflection mirrors 2 and 13 shown in the present embodiment, the quantum well active layer 9, the quantum well active layer 9, Various materials can be used as the material of the thin wire absorption modulation layer 4 and the Bragg reflection mirrors 2 and 13. For example, the n-type Bragg reflection mirror 2 and the p-type Bragg reflection mirror 13 may be configured to have a multilayer film structure such as a semiconductor multilayer film structure. For example, the quantum well active layer 9 and the quantum wire absorption modulation layer 4 may be configured as a semiconductor layer.

[0056] For example, using GaAs or InGaAs as the material of the quantum well active layer 9, the laser device may be configured in a near-infrared surface emitting laser structure, or in a visible surface emitting laser structure such as InGaP or AlGalnP. It may be configured. Also, a long wave surface emitting laser structure may be configured by using an active layer such as InGaAsP or InAlGaAs on an InP substrate or GaAsSb, GalnNAs or InAs quantum dots on a GaAs substrate. Alternatively, a surface emitting laser structure for blue or ultraviolet light may be configured by using a material such as GaN or ZnSe. In addition, use a Si-based or Si compound-based material or an organic material for the active layer to form a surface-emitting laser structure.

[0057] Further, depending on the active layer material used for the quantum well active layer 9, the quantum wire absorption modulation layer 4 The material and composition of the absorption modulation structure, such as the Bragg reflection mirrors 2 and 13, may be appropriately selected from the same compound semiconductor, dielectric, elemental semiconductor, and organic material as the quantum well active layer 9. The quantum well active layer 9, quantum wire absorption modulation layer 4, and Bragg reflection mirrors 2 and 13 may be selected and set as appropriate depending on the structural thickness and the number of in-plane Z layers.

Further, in the present embodiment, the case where the polarization modulation laser device is a surface emitting laser device has been described, but the configuration of the polarization modulation laser device shown in the present embodiment is other than the surface emitting laser device. The present invention can also be applied to the case where the laser apparatus of the form performs polarization modulation. Industrial applicability

[0059] The present invention can be applied to a use of a polarization-modulated laser device that emits laser light by surface emission, polarization-modulates and outputs the laser light. In particular, by using the polarization-modulated laser device according to the present invention, the polarization-modulated laser device can output a laser beam having a low threshold current, a high efficiency, and a stable output intensity, while making the polarization-modulated laser device easy. it can.

Claims

The scope of the claims

[1] A polarization-modulated laser device that modulates and outputs a laser beam,

A first reflecting mirror;

A layer containing a gain medium to obtain optical gain;

A second reflecting mirror;

Laser light oscillated by a resonator formed by the first reflecting mirror and the second reflecting mirror and a layer including the gain medium is transmitted to the first reflecting mirror or the second reflecting mirror. An output unit that outputs in a direction perpendicular to the surface;

A first polarization control structure for fixing the output laser beam in a first polarization direction by an electrical means;

A second polarization control structure for directing the output laser light in a second polarization direction different from the first polarization direction;

The first polarization control structure includes an absorption modulation structure that changes a light absorption coefficient for the laser light by an electric means,

The absorption modulation structure has optical anisotropy in a light absorption coefficient in a plane parallel to a plane perpendicular to the output direction of the laser beam,

The polarization modulation laser apparatus, wherein the absorption modulation structure and the layer including the gain medium are electrically separated.

2. The polarization modulation laser device according to claim 1, wherein the absorption modulation structure changes an optical absorption coefficient with respect to the laser light by applying an electric field as an electrical means.

[3] The second polarization control structure includes an optical waveguide,

The optical waveguide has a rectangular cross section perpendicular to the traveling direction of the laser light, and the long side direction in which the optical waveguide loss on the long side of the rectangle is larger than the optical waveguide loss on the short side is The polarization-modulated laser device according to claim 1 or 2, wherein the polarization-modulated laser device is disposed in a direction not parallel to the first polarization direction.

[4] The polarization according to any one of claims 1 to 3, wherein the absorption modulation structure has a minimum dimension of 50 nm or less in a plane parallel to a plane perpendicular to the output direction of the laser beam. Modulation laser device.

[5] The polarization-modulated laser device according to any one of claims 1 to 4, wherein the absorption modulation structure includes a quantum wire, a quantum dot, or a fractional layer superlattice.

[6] The first reflecting mirror and the second reflecting mirror have a multilayer structure,

The layer including the gain medium and the absorption modulation structure included in the first polarization control structure are semiconductor layers, the first reflecting mirror, the second reflecting mirror, the layer including the gain medium, and the absorption The polarization-modulated laser device according to claim 1, wherein the modulation structure is laminated on a substrate.

7. The polarization-modulated laser device according to claim 6, wherein the first reflection mirror and the second reflection mirror have a semiconductor multilayer film structure.

8. The polarization modulation laser device according to claim 6, wherein the substrate on which the first reflection mirror, the second reflection mirror, the layer including the gain medium, and the absorption modulation structure are stacked is a semiconductor substrate.