JP2006216722A - Modulator-integrated surface emitting laser - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a modulator-integrated surface emitting laser which is remarkably increased in temperature range in which a good modulation characteristic is available. <P>SOLUTION: The modulator-integrated surface emitting laser 1 comprises an active layer 6 for exciting laser light, an absorption-type light modulation layer 8 which performs modulation using a change in light absorption factor due to application of voltage, and a wavelength variable resonator 17 wherein light resonates between two light reflection layers 4 and 12 with the active layer 6 and the light modulation layer 8 put in-between and the resonant wavelength can be changed depending on the temperature. The temperature dependency of the resonant wavelength of the wavelength variable resonator 17 and that of the band gap energy of the light modulation layer 8 are nearly the same. A portion for supporting part of one of the two light reflection layers 4 and 12 which constitutes an optical reflector 12R of the wavelength variable resonator 17 has a cantilever beam 18 structure consisting of two semiconductor layers 12 and 13 having a different coefficient of thermal expansion. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a modulator integrated surface emitting laser. More specifically, the present invention relates to a modulator integrated surface emitting laser in which an absorption type modulator is integrated in a wavelength tunable resonator of a surface emitting laser.

  A surface emitting laser in which a modulator is integrated in a resonator has already been developed. In particular, among surface-emitting lasers in which an optical modulation layer is integrated in a resonator, those using the electric field dependence of absorption in the quantum well layer as an optical modulation layer are attracting attention as devices capable of ultra-high-speed modulation at a low voltage. Has been. (For example, see Non-Patent Document 1)

  With regard to such a surface emitting laser, Koyama et al. Have adopted a cantilever structure made of two types of semiconductors having different compositions as the support part of one of the two reflecting mirrors of the surface emitting laser. We realized a surface emitting laser whose cavity length automatically changes with the designed temperature coefficient when the temperature changes. (See Non-Patent Documents 2 and 3)

  FIG. 5 shows the configuration of the wavelength tunable resonator 21. There are two distributed Bragg reflectors (hereinafter referred to as DBR reflectors) 22R, 23R as light reflectors, and two DBR reflectors 22R, 23R and a portion sandwiched between them are resonators. 21, the distance between the two DBR reflecting mirrors 22R and 23R becomes the resonator length, and the resonance wavelength is determined. A thermal stress layer 24 is laminated on the upper DBR reflecting mirror 23, and the cantilever 25 supports the thermal stress layer 24. The cantilever beam 25 includes a DBR reflector layer 23 and a thermal stress layer 24 having the same film configuration as the DBR reflector 23R. The upper DBR reflector 23 is formed at the tip of the cantilever beam 25. Since the thermal expansion coefficients of the DBR reflecting mirror layer 23 and the thermal stress layer 24 are different, the cantilever 25 is warped when the temperature is changed, the resonator length is changed, and the resonance wavelength is changed. If the thermal expansion coefficient of the thermal stress layer 24 ′ is larger than the thermal expansion coefficient of the DBR reflector layer 23, the cantilever beam 25 warps downward, the resonance wavelength changes to the short wavelength side, and the thermal expansion of the thermal stress layer 24. If the coefficient is smaller than the thermal expansion coefficient of the DBR reflector layer 23, the cantilever beam 25 warps upward, and the resonance wavelength changes to the long wavelength side. The reflecting mirror layer 22 has the same film configuration as the reflecting mirror 22R.

  FIG. 6 shows a change in resonance wavelength due to a change in temperature. The horizontal axis indicates the temperature change (K), and the vertical axis indicates the wavelength change (nm). The amount of wavelength change also depends on the film thickness of the thermal stress layer 24 and the length of the beam, but in FIG. 6, when the thermal stress layer 24 is a GaAs layer (film thickness 500 nm, beam length 140 μm) due to an increase in temperature. When the resonance wavelength is on the short wavelength side and the thermal stress layer 24 ′ is a Ga0.2Al0.8As layer (film thickness 1250 nm, beam length 140 μm), the resonance wavelength changes to the long wavelength side.

S. F. Lim, J .; A. Huggings, L.M. P. Chen, G.G. S. Li, W.L. Yuen, K .; Y. Lau and C.M. J. et al. Chang-Hasnain, “Modulation of a Vertical-Cavity Surface-Emitting Laser Usage an Intracavity Quantum-Well Absorber”, IEEE Photonics Tech. Letts. , Vol. 10, no. 3, pp. 319-321, Mar. 1998 T.A. Amano, F.M. Koyama, T .; Hino, M.M. Arai and A.A. Matsutani, “Design and Fabrication of GaAs-AlGaAs Micromachined Tunable Filter With Thermal Strain Control”, J. Am. Lightwave Tech. vol. 21, no. 3, pp. 596-601, Mar. 2003 T.A. Amano, F.M. Koyama, M .; Arai and A.A. Matsutani, “Micromachined GaAs / AlGaAs Resonant-Cavity Light Emitter with Small Temperature Dependence of Emission Wavelength”, Jpn. J. et al. Appl. Phys. , Vol 42, pp. L1377-L1379, Nov. 2003.

  The problem with this modulator integrated surface emitting laser is that the temperature range where a sufficient extinction ratio can be obtained is as narrow as + -5 to 10 degrees, and in order to operate stably, temperature stabilization by a Peltier element or the like is required. It was. This has led to an increase in the size of the device and an increase in power consumption, which has been a major problem in optical interconnections in which a large number of channels are simultaneously used in parallel. The reason for this narrow temperature range will be described next.

  In order to realize effective light modulation with a conventional modulator integrated surface emitting laser, it is necessary to match the absorption edge wavelength of the quantum well layer, which is an absorption layer (light modulation layer), with the oscillation wavelength of the laser. The absorption type light modulation layer absorbs light having an energy higher than the energy difference between the quantum levels of the quantum wells. The energy difference between the quantum levels is the sum of the band gap energy and the quantum level energy in the conduction band and valence band. The wavelength corresponding to this energy difference is the absorption edge wavelength. In a state where no voltage is applied to the light modulation layer, the resonance wavelength of the resonator is set to a wavelength of light that is slightly longer than the absorption edge wavelength (low energy) and has a small absorption. When a voltage is applied to the light modulation layer, the band gap energy is effectively reduced, light of the set resonance wavelength is absorbed, and the amount of absorption changes according to the applied voltage, allowing amplitude modulation. It is. Therefore, effective modulation is performed when the oscillation wavelength of the laser light is slightly longer than the absorption edge wavelength that is amplitude-modulated. The oscillation wavelength of the surface emitting laser, that is, the resonance wavelength is determined by the optical length of the resonator in consideration of the refractive index. On the other hand, the absorption edge wavelength is determined by the band gap energy of the material of the quantum well layer. Therefore, if the temperature dependence of the optical length of the resonator and the temperature dependence of the band gap energy are different, even if the relationship between the optical length and the band gap energy is adjusted to an optimum condition at a certain temperature, There is a problem that the above relationship deviates from the optimum condition and efficient modulation is not applied.

  This is because the optical length of the resonator changes by about 0.1 nm / ° C. when converted to a wavelength reflecting the temperature dependence of the refractive index, whereas the absorption edge wavelength changes by the temperature dependence of the energy gap. This is due to a change of about 0.4 nm / ° C. when converted to wavelength. That is, in the conventional modulator integrated surface emitting laser, the temperature dependence of the oscillation wavelength determined by the optical length of the resonator and the absorption edge wavelength determined by the band gap energy of the modulator is different by about four times. Even if a good modulation characteristic is obtained at a certain temperature, the modulation characteristic deteriorates when the temperature changes, and there is a problem that the temperature range in which an efficient modulation operation can be performed is extremely narrow.

  An object of the present invention is to provide a modulator integrated surface emitting laser having an expanded temperature range in which good modulation characteristics can be obtained.

  In order to solve the above-mentioned problem, a modulator integrated surface emitting laser 1 according to claim 1 includes an active layer 6 that excites laser light and a light absorption coefficient due to voltage application, as shown in FIGS. Wavelength at which the resonance wavelength is variable depending on the temperature, with the light resonating between the absorption light modulation layer 8 that modulates using the change and the two light reflection layers 4 and 12 sandwiching the active layer 6 and the light modulation layer 8 The variable resonator 17 is provided, and the temperature dependency of the resonance wavelength of the wavelength variable resonator 17 and the temperature dependency of the band gap energy of the light modulation layer 8 are substantially equal.

  Here, the active layer 6 and the light modulation layer 8 do not necessarily have to be inside the wavelength tunable resonator 17, and some of them may protrude outside. Also, the light reflecting layers 4 and 12 need not all be the light reflecting mirrors 4R and 12R of the resonator 17, but may have a portion protruding outside. The region of the wavelength tunable resonator 17 is a portion where light and current spread, and is a region sandwiched between the light reflecting layers 4 and 12 including the space 11 region, which is somewhat wider than the openings of the oxidized constricting layers 5 and 7. Part. With this configuration, the temperature dependence of the wavelength tunable resonator 17 and the temperature dependence of the band gap energy of the light modulation layer 8 are substantially equal. Therefore, the modulator integrated surface light emission that expands the temperature range in which good modulation characteristics can be obtained. A laser can be provided.

  Further, the invention according to claim 2 is the modulator integrated surface emitting laser according to claim 1, comprising, for example, one of the two light reflecting layers 4R and 12R as shown in FIGS. The cantilever 18 is formed of two semiconductor layers 12 and 13 having different thermal expansion coefficients that support the portion constituting the light reflecting mirror 12R of the wavelength tunable resonator 17.

  Here, the light reflecting mirrors 4R and 12R are mainly the portions that function as the reflecting mirrors of the wavelength variable resonator 17 in the light reflecting mirror layers 4 and 12, but are not limited to this portion, and have a predetermined shape (see FIG. 1 includes a peripheral portion formed integrally with this portion. Since the boundary of the wavelength tunable resonator 17 is not always clear, it is formed wider with a margin than the part that actually functions as a reflecting mirror. Further, when such a peripheral part is quite wide, it is a part facing the paired light reflecting mirrors. Further, the light reflecting mirror 12R may be a part of the cantilever 18 and the cantilever 18 may support other portions together with the light reflecting mirror 12R. Moreover, the material may be the same or different in the portion of the light reflecting mirror 12R of the cantilever 18 and the portion that supports it. Even if the portion of the cantilever 18 that supports the light reflecting mirror 12R is made of three or more semiconductor layers, if the thermal expansion coefficients of the two or more semiconductor layers are different, distortion due to thermal stress occurs. In this case, it is assumed that they are included in two semiconductor layers having different thermal expansion coefficients. With this configuration, when the temperature changes, the cantilever 18 warps due to thermal stress, the resonator length between the two light reflecting mirrors 4R and 12R of the wavelength tunable resonator 17 changes, and the resonance wavelength changes. Therefore, it is possible to obtain a structure suitable for a modulator integrated surface emitting laser with an expanded temperature range in which good modulation characteristics can be obtained.

  Further, according to a third aspect of the present invention, in the modulator integrated surface emitting laser according to the first or second aspect, for example, as shown in FIGS. This is a distributed Bragg reflector in which two films having different lengths and a thickness substantially equal to ¼ of the resonance wavelength are alternately laminated.

  If comprised in this way, the resonance characteristic of the wavelength variable resonator 17 can be improved.

  According to the present invention, in the modulator-integrated surface-emitting laser, the temperature change of the absorption wavelength of the quantum well absorption layer and the temperature change of the oscillation wavelength of the surface-emitting laser can be substantially matched, so that good modulation characteristics can be obtained. The temperature range that can be expanded. For example, the operating temperature range of a conventional modulator integrated surface emitting laser is about a specified temperature + -5 to 10 ° C., but according to the present invention, the operating temperature range is +30 to 40 ° C. or higher. Can be expanded. This eliminates the need for temperature stabilization by a Peltier element or the like, which is very advantageous in terms of low power consumption, miniaturization, and cost reduction.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 shows a configuration example of a modulator integrated surface emitting laser according to a first embodiment of the present invention. Three-dimensional coordinates are represented by XYZ. Moreover, the side view seen from the X direction is shown in FIG. 2, and the side view seen from the Y direction is shown in FIG. The modulator integrated surface emitting laser 1 is formed by laminating a number of semiconductor thin films on a GaAs substrate 2 and using a semiconductor microfabrication technique.

  1 to 3, a first n-type DBR reflecting mirror layer 4 is formed on a substrate 2 as a light reflecting layer via a buffer layer 3, and a first oxidized constricting layer 5 and an active layer are partially formed on the first n-type DBR reflecting mirror layer 4. The layer 6, the second oxide constriction layer 7, and the p-type contact layer 19 are formed in a trapezoidal shape, and a light modulation layer (absorption layer) 8 is further formed thereon, and an intermediate n-type DBR reflector layer as a light reflection layer 9 is formed in a trapezoidal shape that is long in one direction. A spacer layer 10 is formed on one end of the base that is long in one direction, and a space (air layer) is formed on the other most part. A cantilever 18 comprising a second n-type DBR reflector layer 12 as a light reflecting layer and a thermal stress layer 13 is extended from the spacer layer 10 with a space 11 on the intermediate n-type DBR reflector layer 9 interposed therebetween. Is formed.

  The second n-type DBR reflecting mirror layer 12 is a second n-type DBR reflecting mirror 12R at the tip of the cantilever 18 and, of the first n-type DBR reflecting mirror layer 4, the second n-type DBR reflecting mirror layer 12R is used. A portion (opposite portion) immediately below the type DBR reflecting mirror 12R is the first n-type DBR reflecting mirror 4R. The light reflecting mirrors 4R and 12R are mainly the portions that function as the reflecting mirrors in the light reflecting mirror layers 4 and 12, but are not limited to this portion, and are integrated with this portion in a predetermined shape (circular in FIG. 1). It is assumed that the peripheral part formed automatically is included. Since the boundary of the wavelength tunable resonator 17 is not always clear, it is formed wider with a margin than the part that actually functions as a reflecting mirror. Further, when such a peripheral part is quite wide, it is a part facing the paired light reflecting mirrors. 1 to 3, the circular portion of the second n-type DBR reflector layer 12 can be said to be a portion formed integrally with this portion in a predetermined shape, and the first portion directly below the portion is formed. The n-type DBR reflecting mirror layer 4 is a portion facing the paired light reflecting mirrors, and corresponds to the first and second n-type DBR reflecting mirrors 4R and 12R, respectively. As for the intermediate n-type DBR reflector 9R, a portion of the intermediate n-type DBR reflector layer 9 in which a rectangular portion under the second n-type DBR reflector 12R is integrally formed with this portion in a predetermined shape It corresponds to.

  The first n-type DBR reflecting mirror 4R and the second n-type DBR reflecting mirror 12R include the space 11, the first oxidized constricting layer 5, the active layer 6, the second oxidized constricting layer 7, A resonator 17 is configured with a p-type contact layer 19, a light modulation layer 8, and an intermediate n-type DBR reflecting mirror 9 </ b> R (hereinafter referred to as a space). Correctly, since the main optical path is the portion of the first oxidized constricting layer 5 and the portion of the second oxidized constricting layer 7 which are in contact with the upper and lower portions, the central portion of the resonator is included. The part where the current spreads functions as the resonator 17. The portion functioning as the resonator 17 is a region of the resonator 17, a region sandwiched between the light reflecting layers 4 and 12 including the space 11 region, and a portion somewhat wider than the opening of the oxide constriction layers 5 and 7. Yes, schematically shown in FIG. Accordingly, the resonator 17 includes the first oxidized constricting layer 5, the active layer 6, the second oxidized constricting layer 7, and the p-type contact layer from the first n-type DBR reflecting mirror 4R formed and fixed on the substrate 2. 19, a light modulation layer 8, a lower part to the intermediate n-type DBR reflecting mirror 9R, an upper part composed of the second n-type DBR reflecting mirror 12R, and a space (air layer) 11 therebetween.

  The cantilever 18 supports the upper portion of the resonator 17, and the spacer layer 10 supports the cantilever 18. The cantilever 18 includes a second n-type DBR reflector layer 12 and a thermal stress layer 13, and the two semiconductor layers 12 and 13 have different thermal expansion coefficients. Note that the second n-type DBR reflector 12R and the thermal stress layer 13 thereon are part of the cantilever 18.

Further, n _A electrode 14 is formed on the exposed portion of the first n-type DBR reflector layer 4 (connected to the n region of the active layer 6), p regions and the light modulating layer of p-type contact layer 19 (active layer 6 8 p electrode 15 on the exposed portion of the p connected to region) is formed of, n _B electrode 16 is formed on the exposed portion of the intermediate n-type DBR reflector layer 9 (connected to the n region of the light modulation layer 8) . The n _A electrode 14 and the p electrode 15 are electrodes for applying a forward voltage to the active layer 6 to excite the laser beam, and the p electrode 15 and the n _B electrode 16 are a reverse voltage applied to the light modulation layer 8. This is an electrode for applying amplitude to modulate the amplitude.

  In the present embodiment, the substrate and each layer are formed as follows, for example. An n-type GaAs substrate is used as the substrate 1, and a MOCVD (metalorganic chemical vapor deposition) method can be used for crystal growth of a multilayer semiconductor thin film thereon. The buffer layer 3 is a layer for adjusting the crystal lattice of a thin film formed thereon, and an n-type GaAs layer is formed to a thickness of 500 nm.

  As the first n-type DBR reflector layer 4, 28 pairs of combinations of two layers of an n-type Al0.90Ga0.10As layer 80 nm and an n-type Al0.16Ga0.84As layer 70 nm are stacked. The DBR reflector layer is a layer for forming a DBR reflector. The DBR reflector is a multi-layered reflector in which two semiconductor layers are alternately stacked. The two DBR reflectors form an optical resonator, and the reflectors have a multi-layered structure so that the wavelength of the reflected light is aligned and resonant. The characteristic is improved (the Q value is increased). The first n-type DBR reflecting mirror 4R and the second n-type DBR reflecting mirror 12R constitute a wavelength variable resonator 17, and only the light resonating between the two DBR reflecting mirrors 4R and 12R is amplified. Then, the light passes through the first n-type DBR reflecting mirror 4R or the second n-type DBR reflecting mirror 12R and is output to the outside. Further, the first n-type DBR reflector 4R and the second n-type DBR reflector 12R are formed by alternately stacking two films having optical lengths that are substantially equal to ¼ of the resonance wavelength and having different refractive indexes. This is a laminated DBR reflector, whereby the resonance characteristics of the resonator 17 can be improved. Further, the first n-type DBR reflecting mirror 4R and the intermediate n-type DBR reflecting mirror 9R constitute an auxiliary resonator that reciprocates part of the light with the active layer 6 interposed therebetween, thereby oscillating in the active layer 6. It is easy to do.

  An n-type Al0.98Ga0.02AS layer 30 nm is formed on the n-type Al0.90Ga0.10As layer 55 nm as the first oxide constriction layer 5. The oxide constriction layers 5 and 7 are layers for efficiently concentrating current to the central portion of the resonator 17 and efficiently oscillating. The portions that transmit light and current are opened, and the other portions are insulating oxide films. And The opening is an n-type semiconductor layer. Three pairs of two combinations of a GaAs layer 10 nm and an In0.2Ga0.8As layer 8 nm are stacked on the non-doped Al0.6Ga0.4As layer 113 nm as the active layer 6, and the GaAs layer 10 nm and the Al0.6Ga0.4As layer are formed thereon. 113 nm is formed. The active layer 6 has a quantum well structure, and the injected carriers are recombined to emit light corresponding to the sum of the band gap energy and quantum level energy of the quantum well. A p-type Al 0.98 Ga 0.02 AS layer 30 nm is formed on the p-type Al 0.90 Ga 0.10 As layer 55 nm as the second oxide constriction layer 7. The opening is a p-type semiconductor layer, and the other part is an insulating oxide film. The oxidation constriction layer may be a single layer, but here the efficiency is improved by using two layers. A p-type GaAs layer having a thickness of 110 nm is formed as the p-type contact layer 19 on the second oxide constriction layer 7.

  The light modulation layer 8 has a layer structure in which an In0.2Ga0.8As layer 8 nm is sandwiched between approximately 140 nm of two Al0.6Ga0.4As layers 140 nm. An absorption light modulation layer is employed as the light modulation layer 8. Therefore, the light modulation layer 8 is also an absorption layer, and absorbs light having energy higher than the energy difference between quantum levels of the quantum well. That is, the wavelength corresponding to the sum of the band gap energy and the quantum level energy is the absorption edge wavelength. In a state where no voltage is applied to the light modulation layer 8, the resonance wavelength of the resonator is set to a wavelength slightly longer (low energy) than the absorption edge wavelength, and is set to the wavelength of light with small absorption. When a reverse voltage is applied to the light modulation layer 8, the band gap energy is effectively reduced, light having a set resonance wavelength is absorbed, and the amount of absorption changes according to the applied voltage. Is possible.

  Three pairs of combinations of a p-type Al0.16Ga0.84As layer 70 nm and a p-type Al09.90Ga0.10As layer 80 nm are laminated as the intermediate n-type DBR reflector layer 9. Although the intermediate n-type DBR reflecting mirror 9R is not essential, it is installed in the middle of the first and second n-type DBR reflecting mirrors 4R and 12R forming the resonator, and the active layer 6 is arranged as the first n-type DBR reflecting mirror. By sandwiching between 4R and the intermediate n-type DBR reflecting mirror 9R, light is partially reflected by the intermediate n-type DBR reflecting mirror 9R toward the active layer 6, thereby making it easy to oscillate and lowering the oscillation threshold. Since the intermediate n-type DBR reflecting mirror 9R has a small number of layers, it reflects a part of the resonance wave and transmits a part thereof. If the reflectivity of the intermediate n-type DBR reflector 9R is increased, the resonance power of the outer wavelength tunable resonator 17 is decreased, and if the reflectivity is decreased, the laser operation itself becomes difficult, so the reflectivity is about 60 to 90%. Is appropriate. The optical length between the first and second n-type DBR reflecting mirrors 4R and 12R and the optical length between the first n-type DBR reflecting mirror 4R and the intermediate n-type DBR reflecting mirror 9R are both 1 / resonance wavelength. It is almost equal to an integer multiple of 2.

  As the spacer layer 10, an Al0.6Ga0.4As layer is formed at 1600 nm. The distance of the space between the intermediate n-type DBR reflector layer 9 and the second n-type DBR reflector layer 12 is determined by the thickness of the spacer layer 10, whereby the first n-type DBR reflector 4R and the second n-type DBR reflector mirror 12 The optical length of the resonator 17 composed of the n-type DBR reflecting mirror 12R (space or the like as an optical path) is determined, and the resonance wavelength is determined. As the second n-type DBR reflector layer 12, 33 pairs of an n-type Al0.90Ga0.10As layer of 80 nm and an n-type Al0.16Ga0.84As layer of 70 nm are stacked. An Al0.48Ga0.52As layer having a thickness of 500 nm is formed as the thermal stress layer 13.

After these multiple films are laminated, the 60 μm square base including the active layer 6, the 30 μm square base including the light modulation layer 8, and the base (1600 nm) to be left as the spacer layer 10 by photolithography and dry etching. Form. Next, by chemical etching, the space (air layer) 11 is formed by removing the portion under the second n-type DBR reflector 12R, leaving only the spacer layer 10 on the table. Next, the shapes of the second n-type DBR reflector layer 12 and the thermal stress layer 13 are adjusted to the shapes shown in FIGS. 1 to 3 by photolithography and dry etching. Then, a p electrode 15 with a conductive film such as AuZn-Au, forming an _{n A} electrode 14, _{n B} electrode 16 with a conductive film such as AuNi-Au or AuGe-Au.

  The n-type DBR reflector layer 12 (GaAs / GaAlAs semiconductor multilayer reflector layer) and the thermal stress layer 13 constitute a cantilever 18 and the first n-type DBR reflector 4R (GaAlAs / GaAlAs semiconductor multilayer reflector). ) And the second n-type DBR reflecting mirror 12R constitute a resonator 17 with a space (air layer) 11 or the like interposed therebetween. That is, the upper part of the resonator 17 is formed at the tip of the cantilever 18. Only the light resonated between the upper and lower DBR reflecting mirrors 4R, 12R is transmitted through the resonator 17 and output from the second n-type DBR reflecting mirror 12R or output from the first n-type DBR reflecting mirror 4R through the substrate 2. The In the present embodiment, since the second n-type DBR reflector layer 12 has a larger number of layers than the first n-type DBR reflector layer 4, it is output to the first n-type DBR reflector 4R side. . The thermal stress layer 13 is made of a mixed crystal semiconductor of GaAs or AlAs that can be epitaxially grown in the DBR material system.

  Due to the difference in thermal expansion coefficient between the thermal stress layer 13 and the second n-type DBR reflector layer 12, the cantilever 18 is displaced by stress when the temperature changes. When the thermal stress layer 13 is a GaAs layer, the GaAs layer has a larger thermal expansion coefficient than the second n-type DBR reflector layer 12, and the cantilever 18 is warped so as to be lowered toward the substrate when the temperature rises. When the stress layer 13 is an AlAs layer, the AlAs layer has a smaller thermal expansion coefficient than that of the second n-type DBR reflector layer 12, and when the temperature rises, the cantilever 18 rises to the opposite side of the substrate. Warp like so. By changing the temperature in this manner, the position of the cantilever 18 is displaced in the vertical direction, and the resonator length of the resonator 17 is changed.

Using such a cantilever 18 (cantilever) structure, the temperature coefficient of the change in the oscillation wavelength due to the change in the resonator length and the temperature coefficient of the change in the absorption edge wavelength due to the change in the band gap energy of the quantum well are matched. It is possible. For example, by devising such as increasing the thickness of the Ga _0.2 Al _0.8 As layer or slightly increasing the length of the cantilever 18, and by designing accurately to match the temperature coefficient of both Thus, it is possible to provide a modulator integrated surface emitting laser 1 that can realize an appropriate combination of the wavelength tunable resonator 17 and the light modulation layer 8 and expand a temperature range in which good modulation characteristics can be obtained.

  In the present embodiment, the Al composition of the thermal stress layer 13 is 0.48, the thickness of the thermal stress layer 13 is 500 nm, and the length of the cantilever 18 (up to the tip) is 250 μm. At this time, since the thermal expansion coefficient of the thermal stress layer 13 is smaller than the average thermal expansion coefficient of the second DBR reflector layer 12 immediately below the thermal stress layer 13, when the ambient temperature rises, the cantilever 18 is Warp upward. That is, the resonator length (optical length) of the resonator 17 formed between the first n-type DBR reflecting mirror 4R and the second n-type DBR reflecting mirror 12R becomes longer as the temperature rises, and as a result, the oscillation wavelength becomes longer. . As a result of selecting about 0.98 μm as the resonance wavelength and setting the parameters as described above, the wavelength change was 0.4 nm per 1 ° C. temperature rise. This wavelength change rate is substantially equal to the wavelength change rate of the optimum operating wavelength (absorption edge wavelength) of the light modulation layer 8 due to the band gap of the InGaAs light modulation layer 8 shrinking with temperature. As a result, this device showed excellent modulation characteristics such as an on / off ratio of modulated light of 10 dB or more over a wide temperature range from 0 ° C. to 80 ° C. As a result, even if the temperature changes, the relative relationship between the absorption edge wavelength and the oscillation wavelength of the quantum well hardly changes, and stable modulation characteristics can be expected. That is, it is possible to realize a modulator integrated surface emitting laser that greatly expands the temperature range in which good modulation characteristics can be obtained.

  In addition, in order to use a conventional modulator integrated surface emitting laser in such a wide temperature range, a temperature control element such as a Peltier element must be used together, the device shape becomes larger, and the power consumption increases significantly. As a result, the application to optical interconnections that use a large number of elements in parallel has been greatly restricted. However, according to this embodiment, a small and low power consumption device can be realized. Thus, the restriction in application to the optical interconnection or the like is removed.

  Next, a modulator integrated surface emitting laser according to a second embodiment of the present invention will be described. In the first embodiment, an example in which there are three DBR reflectors and two oxidized constricting layers has been described. However, in this embodiment, two DBR reflectors and two oxidized constricting layers are used. is there. That is, from the first embodiment, the intermediate n-type DBR reflector layer 9 and the first oxidized constricting layer 5 are removed, and the light reflector of the wavelength tunable resonator 17 is changed to the first n-type DBR reflector 4R. And the second n-type DBR reflecting mirror 12R. In this case, the resonance wavelength is determined from the optical lengths of the first n-type DBR reflector 4R and the second n-type DBR reflector 12R including the space 11. Therefore, by increasing the distance between the optical path of the intermediate n-type DBR reflecting mirror 9R and the first oxidized constricting layer 5 and the space 11, adjusting the film thickness of the thermal stress layer 13, the length of the cantilever 18 and the like, It is possible to make the temperature coefficient of the change of the oscillation wavelength due to the change of the resonator length coincide with the temperature coefficient of the change of the absorption edge wavelength due to the change of the band gap energy of the quantum well. For example, an m × n sample is prototyped using the thickness of the thermal stress layer 13 and the length of the cantilever 18 as parameters, and the temperature coefficient of change in oscillation wavelength and the temperature coefficient of change in band gap energy are the closest. Both temperature coefficients may be made to coincide with each other through an experiment, for example, by readjusting the parameters in the vicinity of the combination.

  Next, a modulator integrated surface emitting laser according to a third embodiment of the present invention will be described. In the first and second embodiments, as the cantilever 18 that holds the light reflector whose warpage changes with temperature change, the thermal stress layer 13 is formed on the lower side with a layer having the same composition as one of the DBR reflector layers 12. Two layers were combined on the top. In order to obtain the same effect, only the portion of the cantilever 18 that supports the DBR reflector 12R of the resonator 17 is supported by using two semiconductor layers having different thermal expansion coefficients, for example, a combination of an AlGaAs layer and a GaAs layer. The DBR reflecting mirror 12R of the vessel 17 may be laminated separately. In this structure, the DBR reflector 12R may be a movable reflector by forming a dielectric multilayer film on the tip of the cantilever 18 by vapor deposition or the like instead of a semiconductor.

  FIG. 4 shows a modulator integrated surface emitting laser device in which modulator integrated surface emitting lasers are arranged in an array as a fourth embodiment of the present invention. A 4 × 4 laser array 31 is arranged on a substrate 32, and a laser beam 34 is emitted from a 3 × 3 light emitting laser 33 among them. Each light emitting laser 33 uses the modulator integrated surface emitting laser according to the first embodiment. In this case, since the oscillation frequencies of the respective light emitting lasers 33 are equal, it can be used for parallel processing, time series use, high power use, and the like. Note that the oscillation frequency of each laser beam 34 may be changed so that it can be used in a wide frequency band as a whole, such as for wavelength multiplexing communications.

  Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and it is obvious that various modifications can be made to the embodiments.

  For example, the active layer may be a buried type in order to increase the utilization efficiency of laser light, or may be an active layer having a quantum dot structure for power saving. Also, the resonance wavelength can be selected between 0.4 μm and 1.6 μm, for example. In this embodiment, an example of a DBR reflecting mirror has been described as the light reflecting mirror, but a single-layer reflecting mirror may be used. In the present embodiment, an example of one or two oxidized constricting layers has been described. The formation of the thin film is not limited to the MOCVD method, and a CBE (Chemical Beam Epitaxy) method may be used. In addition, the matching temperature coefficient value can be arbitrarily selected, and the logarithm of two types of layers such as the reflecting mirror layer, the composition and thickness of the thin film, the arrangement of the stage and the electrode, and the like are various.

  The present invention is used for obtaining laser light having a wide operating temperature range.

It is a figure which shows the structural example of the modulator integrated surface emitting laser by the 1st Embodiment of this invention. It is the side view which looked at the modulator integrated surface emitting laser of FIG. 1 from the X direction. It is the side view which looked at the modulator integrated surface emitting laser of FIG. 1 from the Y direction. It is the figure which has arrange | positioned the modulator integrated surface emitting laser by this invention in the array form. It is a figure which shows the structural example of the conventional modulator integrated surface emitting laser. It is a figure which shows the change of the resonant wavelength by the change of temperature.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Modulator integrated surface emitting laser 2 Substrate 3 Buffer layer 4 1st n-type DBR reflecting mirror layer (light reflecting layer)
4R 1st n-type DBR reflector 5 1st oxidation confinement layer 6 Active layer 7 2nd oxidation confinement layer 8 Light modulation layer 9 Intermediate n-type DBR reflection mirror layer (light reflection layer)
9R Intermediate n-type DBR reflector 10 Spacer layer 11 Space 12 Second n-type DBR reflector layer (light reflecting layer)
12R Second n-type DBR reflector 13 Thermal stress layer 14 n _A electrode 15 p electrode 16 n _B electrode 17 Wavelength variable resonator 18 Cantilever 19 p-type contact layer 21 Wavelength variable resonators 22 and 23 DBR reflector layer 22R, 23R DBR reflectors 24, 24 'Thermal stress layer 25 Cantilever 31 Laser array 32 Substrate 33 Surface emitting laser 34 Laser light

Claims (3)

An active layer for exciting laser light;
An absorptive light modulation layer that modulates light absorption coefficient by applying voltage;
A wavelength tunable resonator in which light resonates between two light reflection layers sandwiching the active layer and the light modulation layer, and the resonance wavelength is variable depending on temperature;
The temperature dependence of the resonance wavelength of the wavelength tunable resonator is substantially equal to the temperature dependence of the band gap energy of the light modulation layer;
Modulator integrated surface emitting laser. A cantilever beam comprising one of the two light reflecting layers and comprising two semiconductor layers having different thermal expansion coefficients that support a portion constituting the light reflecting mirror of the wavelength tunable resonator;
The modulator integrated surface emitting laser according to claim 1. The two light reflecting layers are distributed Bragg reflectors in which an optical length is approximately equal to ¼ of the resonance wavelength and two films having different refractive indexes are alternately laminated.
The modulator integrated surface emitting laser according to claim 1.

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