Laser module, laser module control method and control device

Abstract

This laser module (1) comprises a semiconductor laser (11) that oscillates using one circularly polarized light among right circularly polarized light and left circularly polarized light, and a quarter wavelength plate (15) that is disposed on the emission surface side of the semiconductor laser, wherein the semiconductor laser is driven by current that is higher than the threshold current of the one circularly polarized light and is lower than the threshold current of the other circularly polarized light. The semiconductor laser is provided with an n-type cladding layer, an active layer, and a p-type cladding layer. The semiconductor laser is further provided with an n-type electrode and a p-type electrode, and at least one among the n-type electrode and the p-type electrode is a ferromagnet electrode.　As a result, the present invention can provide a low-cost laser module that is capable of limiting the impact of optical feedback.

Description

[Technical Field]

[0001] The present invention relates to a laser module capable of suppressing the influence of returning light, a method for controlling the laser module, and a control device. [Background technology]

[0002] Semiconductor lasers are widely used in the field of optical communications. In optical communications systems, laser light from a semiconductor laser is incident on (coupled with) an optical fiber and propagates through the optical fiber as signal light.

[0003] In some cases, the laser light from the semiconductor laser is reflected by the end face of the optical fiber and enters the semiconductor laser again as returned light. Even if the intensity of this returned light is slightly lower than that of the emitted light, it is amplified by stimulated emission and causes noise and mode instability.

[0004] To prevent the effects of this returning light, an optical isolator that combines a linear polarizer and a Faraday rotator is used (see, for example, Patent Document 1). The optical isolator can convert the returning light into TM mode by rotating the light emitted from a laser oscillating in TE mode by 45° on both the outgoing and return paths. The returning light in TM mode is absorbed by the linear polarizer inside the optical isolator, suppressing noise and mode instability caused by the returning light. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-099503 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the Faraday rotators used in optical isolators are expensive, which poses a problem in reducing costs. Because expensive materials such as YIG (yttrium iron garnet) are used for Faraday rotators, it is difficult to reduce costs through device design. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems, a laser module according to the present invention includes a semiconductor laser that oscillates with either right-handed circularly polarized light or left-handed circularly polarized light, and a quarter-wave plate that is disposed on an emission surface side of the semiconductor laser, the semiconductor laser comprises, in order, an n-type cladding layer, an active layer, and a p-type cladding layer, an n-type electrode electrically connected to the n-type cladding layer, and a p-type electrode electrically connected to the p-type cladding layer; The semiconductor laser is driven by a current that is higher than the threshold current for one of the circularly polarized light beams and lower than the threshold current for the other circularly polarized light beam. At least one of the n-type electrode and the p-type electrode is a ferromagnetic electrode. It is characterized by the following.

[0008] The present invention also provides a method for controlling a laser module, the laser module including a semiconductor laser that oscillates with either right-handed circularly polarized light or left-handed circularly polarized light, and a quarter-wave plate disposed on the emission surface side of the semiconductor laser. The semiconductor laser comprises, in this order, an n-type cladding layer, an active layer, and a p-type cladding layer, an n-type electrode electrically connected to the n-type cladding layer, and a p-type electrode electrically connected to the p-type cladding layer, and at least one of the n-type electrode and the p-type electrode is a ferromagnetic electrode. a control method for a laser module, the method comprising: injecting a current into the semiconductor laser that is higher than a threshold current for one of the circularly polarized light beams and lower than a threshold current for the other circularly polarized light beam.

[0009] The laser module control device according to the present invention includes a semiconductor laser that oscillates with either right-handed circularly polarized light or left-handed circularly polarized light, and a quarter-wave plate disposed on the emission surface side of the semiconductor laser. The semiconductor laser comprises, in this order, an n-type cladding layer, an active layer, and a p-type cladding layer, an n-type electrode electrically connected to the n-type cladding layer, and a p-type electrode electrically connected to the p-type cladding layer, and at least one of the n-type electrode and the p-type electrode is a ferromagnetic electrode. a device for controlling a laser module including a semiconductor laser, the device injecting a current into the semiconductor laser that is higher than a threshold current for one circularly polarized light and lower than a threshold current for the other circularly polarized light; Characterized by . [Effects of the Invention]

[0010] According to the present invention, it is possible to provide an inexpensive laser module, a method for controlling a laser module, and a control device that can suppress the influence of returning light. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic diagram showing the configuration of a laser module according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a diagram for explaining the operation of the laser module according to the first embodiment of the present invention. [Figure 3] FIG. 3 is a diagram for explaining the operation of the laser module according to the first embodiment of the present invention. [Figure 4] FIG. 4 is a flowchart illustrating a method for controlling the laser module according to the first embodiment of the present invention. [Figure 5A] FIG. 5A is a diagram for explaining the effect of the laser module according to the first embodiment of the present invention. [Figure 5B] FIG. 5B is a diagram for explaining the effect of the laser module according to the first embodiment of the present invention. [Figure 6A] FIG. 6A is a diagram for explaining the effect of the laser module according to the first embodiment of the present invention. [Figure 6B] FIG. 6B is a diagram for explaining the effect of the laser module according to the first embodiment of the present invention. [Figure 7] FIG. 7 is a schematic diagram showing the configuration of a laser module according to a first embodiment of the present invention. [Figure 8] FIG. 8 is a schematic diagram showing the configuration of a laser module according to a second embodiment of the present invention. [Figure 9] FIG. 9 is a schematic diagram showing the configuration of a laser module according to a third embodiment of the present invention. [Figure 10] FIG. 10 is a diagram illustrating an example of the configuration of a computer according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] First Embodiment A laser module according to a first embodiment of the present invention will be described with reference to FIGS. 1 to 6B.

[0013] <Laser module configuration> As shown in FIG. 1, the laser module 1 according to this embodiment includes a semiconductor laser 11 and a quarter-wave plate 15.

[0014] The emitted light 5 from the semiconductor laser 11 is reflected by the external reflecting mirror 4 and enters the semiconductor laser 11 as return light 6. Here, the reflection by the external reflecting mirror 4 corresponds to, for example, reflection from an end face of an optical fiber or various optical components in normal optical communications.

[0015] Furthermore, a control device 16 supplies current to the semiconductor laser 11 .

[0016] The semiconductor laser 11 is a spin laser and includes a semiconductor layer structure 12, a p-type electrode 13, and an n-type electrode .

[0017] In the semiconductor laser 11, either the p-type electrode 13 or the n-type electrode 14 is a ferromagnetic electrode. The ferromagnetic electrode is made of a ferromagnetic material magnetized in the same direction as the light emission direction. However, both electrodes may be ferromagnetic electrodes.

[0018] Light 5 emitted from the semiconductor laser 11 passes through the quarter-wave plate 15. Furthermore, light reflected by the external reflecting mirror 4 (for example, an end face of an optical fiber or various optical components) passes through the quarter-wave plate 15 as returned light 6 and enters the semiconductor laser 11.

[0019] <Basic operation of semiconductor laser> The basic operation of the semiconductor laser (spin laser) 11 in this embodiment will be described below.

[0020] The spin laser 11 utilizes the phenomenon that the spin (up / down) of electrons corresponds to the direction (right / left) of circularly polarized light emitted by recombination. That is, by injecting a spin-polarized current into the semiconductor laser 11, circularly polarized light is emitted from the active layer in the semiconductor layer structure 12.

[0021] The spin laser 11 is superior to conventional semiconductor lasers in that it can reduce the threshold current (M. Holub, et al., “Electrical Spin Injection and Threshold Reduction in a Semiconductor Laser,” Physical Review Letters, 98, 146603 (2007)).

[0022] This reduction in threshold current is due to the phenomenon that by controlling the spin direction injected into the laser, only circularly polarized light with either right-handed or left-handed directional polarization can be lased. That is, when the current injected into the semiconductor laser is increased, only circularly polarized light with the direction corresponding to the majority spin dominantly lases at low currents, while circularly polarized light with the direction corresponding to the minority spin does not lases but only emits light by spontaneous emission.

[0023] Let I be the current injected into the spin laser 11 and P be the spin polarization of the injected electrons. Then, the current I + and a current I with minority spin - can be written as equation (1), respectively.

[0024]

number

[0025] If spin relaxation is not taken into account, the threshold current when a current without spin polarization is injected is I th Then, the threshold current I for oscillation due to the charge of the majority spin is th1 and the threshold current I for the charge-driven oscillation of the minority spin th2 can be written as equation (2), respectively.

[0026]

number

[0027] The light intensity-current characteristics at this time are shown in FIG.

[0028] For example, if |P|>0, then I th1 th Therefore, the threshold current of the spin laser 11 is reduced compared to that of the conventional laser. th2 In smaller areas, only circularly polarized light in one direction oscillates.

[0029] Circular polarization degree P C is a parameter that represents the physical state of circularly polarized light and indicates the purity of circular polarization, and P C =(S + -S - ) / (S + +S - ) where S + and S - are the circular polarization intensities of the oscillating light due to the charge of the majority spin and the minority spin, respectively.

[0030] Figure 3 shows the degree of circular polarization P C In the state where only one type of circularly polarized light (right-handed or left-handed) is oscillating as described above, the degree of circular polarization is about 1, and laser light with pure one type of circular polarization (right-handed or left-handed) is obtained.

[0031] By increasing the injection current, the degree of circular polarization approaches 0.5, where both circularly polarized light beams lased.

[0032] <Laser module control method> A method for controlling the laser module 1 according to this embodiment will be described below. The method for controlling the laser module 1 according to this embodiment is executed by the control device 16.

[0033] ​In the laser module 1 according to this embodiment, the semiconductor laser 11 has a spin polarization in the ferromagnetic electrode P and a threshold current of the semiconductor laser 11 in a state where the ferromagnetic electrode is not magnetized I. th Then, the value of the current I injected into the semiconductor laser 11 is I th / (1+|P|) <I<I th Drives in the range of / (1-|P|).

[0034] Since electrons in a magnetized ferromagnetic material are spin-polarized, the electron spins injected from the ferromagnetic material into the active layer of the semiconductor laser 11 are also polarized, resulting in a difference in the intensity of the emitted circularly polarized light (right-handed / left-handed).

[0035] Furthermore, as mentioned above, if spin relaxation is not taken into consideration, the value of the injected current I is I th / (1+|P|) <I<I th Because the laser is driven in the range of / (1-|P|), only the circularly polarized light produced by the majority carriers is lasing, and the minority carriers hardly contribute to stimulated emission.

[0036] FIG. 4 shows a flowchart of a method for controlling the laser module 1.

[0037] First, the threshold current (I th1 ) is determined (step S1). th1 is acquired in advance by driving the semiconductor laser 11 and measuring it, and is stored in the storage unit of the control device 16.

[0038] Next, the threshold current of the other circularly polarized light (I th2 ) is determined (step S2). th2 is acquired in advance by driving the semiconductor laser 11 and measuring it, and is stored in the storage unit of the control device 16.

[0039] Finally, remembered I th1 , I th2 Based on I th1 Higher I th2A lower drive current is injected into the semiconductor laser 11 (step S3).

[0040] <Effects> The effects of the laser module 1 according to this embodiment will be described below.

[0041] In a typical laser module, an optical isolator combining a linear polarizer and a Faraday rotator is used to transmit the linearly polarized light emitted from a semiconductor laser oscillating in TE mode, rotate it by 45° using the Faraday rotator, and then rotate the returned light by another 45°, for a total rotation of 90°.

[0042] As a result, the returning light becomes TM mode and is absorbed by the linear polarizer in the optical isolator, preventing it from entering the laser, thereby suppressing noise and mode instability due to the returning light.

[0043] Thus, a typical laser module requires a Faraday rotator to rotate the linearly polarized light.

[0044] In the laser module 1 according to this embodiment, the semiconductor laser 11 oscillates with circularly polarized light. th / (1+|P|) <I<I th It is driven in the range of / (1-|P|) and oscillates with either right-handed or left-handed circular polarization (for example, right-handed).

[0045] 1, for one of the circularly polarized laser beams (for example, clockwise), the return beam 6 passes twice through the quarter-wave plate 15 arranged in the emission direction. Passing twice through the quarter-wave plate 15 is equivalent to passing through a half-wave plate, and the direction of the circularly polarized light that passes through the half-wave plate is reversed. For example, if clockwise circularly polarized light is oscillated, the return beam 6 will be counterclockwise.

[0046] As a result, the semiconductor laser 11 does not oscillate with left-handed circularly polarized light, and the return light 6 is not amplified by stimulated emission. Therefore, in the laser module 1, noise due to the return light 6 can be suppressed.

[0047] In this way, the laser module according to this embodiment is configured with a semiconductor laser that oscillates with circularly polarized light and a quarter-wave plate, making it possible to suppress noise caused by returned light without using a Faraday rotator.

[0048] The effects of the laser module 1 according to this embodiment will be described with reference to the calculation results of the dynamic characteristics shown in FIGS. 5A to 6B.

[0049] The dynamic characteristics of the light intensity of the laser module 1 according to this embodiment are calculated by equations (3) and (4). Table 1 shows constants (parameters) in equations (3) and (4).

[0050]

number

[0051]

number

[0052] [Table 1]

[0053] Equations (3) and (4) represent the spin-up and spin-down electron densities N ± and the electric field E of right-handed and left-handed circularly polarized light ± is a rate equation that takes into account the electron spin direction, the circular polarization of the outgoing light, and the returning light. Here, + indicates upspin and right-handed circular polarization, and - indicates downspin and left-handed circular polarization. The returning light is also considered to be circularly polarized in the opposite direction to the outgoing light.

[0054] Here, I± is the spin injection current, where + indicates spin up and - indicates spin down.

[0055] Equation (4) is the rate equation for spin lasers (N. Yokota, et al., “Lasing Polarization Characteristics in 1.55-um Spin-Injected VCSELs,” IEEE PHOTONICS TECHNOLOGY LETTERS, 29(9), 711 (2017).) with a third term added to represent the effect of optical feedback (birefringence and circular dichroism are ignored).

[0056] Furthermore, when the quarter-wave plate 15 is used, the formula can be expressed by adding the contribution of left-handed or right-handed returned light to the formula for right-handed or left-handed circularly polarized light, respectively. That is, E - It is calculated using

[0057] On the other hand, when the quarter-wave plate 15 is not provided, the formula can be expressed by adding a term for clockwise or counterclockwise returned light to the formula for clockwise or counterclockwise circularly polarized light, respectively. That is, E is added to the electric field of the circularly polarized light in the third term of formula (4). + It is calculated using

[0058] 5A and 5B show the calculation results of the dynamic characteristics of the light intensity of the laser module 1 when the quarter-wave plate 15 is included and when the quarter-wave plate 15 is not included, respectively. Here, the light intensity |E + | 2 is shown by a solid line, and the left-handed circularly polarized light intensity |E - | 2 is shown by a dotted line.

[0059] Here, the injected current is set to a range that oscillates only circularly polarized light in one direction (clockwise), i.e., I th / (1+|P|) <I<I thThe spin polarization is set constant at / (1-|P|). In this way, one circularly polarized light (right-handed) oscillates dominantly.

[0060] Without the quarter-wave plate 15, the light intensity |E + | 2 Even though a constant current is injected, the optical intensity fluctuates greatly due to the influence of the feedback light. - | 2 is almost 0 (zero) because right-handed circularly polarized light does not oscillate.

[0061] In this case, one (right-handed) circularly polarized light emitted from the semiconductor laser 11 is reflected externally and returns to the semiconductor laser 11 in the same polarization state, thereby varying the intensity of the dominantly oscillating one (right-handed) circularly polarized light.

[0062] This fluctuation in light intensity deteriorates the stable operation of the semiconductor laser 11. Conventional laser modules require an optical isolator using YIG or the like to suppress this fluctuation in light intensity and ensure the stability of the semiconductor laser operation.

[0063] On the other hand, when the quarter-wave plate 15 is provided, as shown in FIG. 5A, the light intensity |E + | 2 The variation is very small.

[0064] In this case, when one (right-handed) circularly polarized light emitted from the semiconductor laser 11 is reflected externally and returns to the semiconductor laser 11 through the quarter-wave plate 15, the one (right-handed) circularly polarized light is inverted and becomes left-handed, resulting in a polarization state opposite to the one (right-handed) circularly polarized light, and therefore does not fluctuate the intensity of the one (right-handed) circularly polarized light that is dominantly oscillated.

[0065] In this way, in the laser module 1, by combining the semiconductor laser 11 that oscillates with one circularly polarized light and the quarter-wave plate 15, it is possible to suppress fluctuations in light intensity.

[0066] 6A and 6B show the injection current I th2 If you drive less than th2 Calculation results of the dynamic characteristics of the light intensity of the laser module 1 having the quarter-wave plate 15 when driven at a higher current are shown.

[0067] Here, the dynamic characteristics of the optical intensity are expressed as the injection current I + and I - As a sum of I + and I - It is calculated assuming the ratio to be constant.

[0068] The injection current into the semiconductor laser 11 is I th2 When driven with a higher current, as shown in Figure 6B, oscillation occurs not only in one (right-handed) circularly polarized light due to the majority carriers, but also in the other (left-handed) circularly polarized light due to the minority carriers, resulting in oscillation in both circular polarizations.

[0069] Here, the intensity of one (right-handed) circularly polarized light and the other (left-handed) circularly polarized light increase, causing the light intensities of each to fluctuate significantly. At this time, the light intensity of one (right-handed) circularly polarized light is greater than that of the other (left-handed) circularly polarized light, and oscillation with one (right-handed) circularly polarized light is dominant.

[0070] In this case, when the other (left-handed) circularly polarized light returns to the semiconductor laser 11 through the quarter-wave plate 15, the other (left-handed) circularly polarized light is inverted and becomes right-handed, becoming in the same polarization state as the one (right-handed) circularly polarized light, thereby varying the intensity of the one (right-handed) circularly polarized light that oscillates dominantly.

[0071] Furthermore, when one (right-handed) circularly polarized light returns to the semiconductor laser 11 through the quarter-wave plate 15, the one (right-handed) circularly polarized light is inverted and becomes left-handed, becoming in the same polarization state as the other (left-handed) circularly polarized light, thereby varying the intensity of the other (left-handed) circularly polarized light.

[0072] Therefore, even in a configuration with the quarter-wave plate 15, the influence of noise due to the returned light becomes large, causing fluctuations in the light intensity.

[0073] On the other hand, when the injection current to the semiconductor laser 11 is I th2 When driven below this, the light intensity |E + | 2 The variation in the injection current is very small. th2 By driving the light source at a frequency less than 1000 kHz, fluctuations in light intensity can be suppressed.

[0074] Thus, the injected current is I th2 When driven at a frequency lower than this, the other (left-handed) circularly polarized light does not oscillate, and therefore the intensity of the dominantly oscillating (right-handed) circularly polarized light does not fluctuate.

[0075] According to the laser module of this embodiment, fluctuations in laser light intensity can be stably suppressed without using an optical isolator using YIG or the like, and the cost of the laser module can be reduced.

[0076] In this embodiment, a semiconductor laser (spin laser) is injected with a current I th2 Although an example has been shown in which the laser is driven at less than 1000 Hz to oscillate with clockwise circularly polarized light, the same effect can be achieved by oscillating with counterclockwise circularly polarized light.

[0077] <First Example> A laser module according to a first embodiment of the present invention will be described with reference to FIG.

[0078] 7, the laser module according to this embodiment includes a semiconductor laser 11 and a quarter-wave plate 15. It also includes a control device 16 that drives the semiconductor laser 11.

[0079] The semiconductor laser 11 comprises, in order, a p-type GaAs substrate 120, a p-type AlGaAs cladding layer 121 (layer thickness: for example, about 1 μm), a GaAs active layer 122 (layer thickness: for example, about 500 nm), and an n-type AlGaAs cladding layer 123 (layer thickness: for example, about 1 μm), and has an emission wavelength of 850 nm.

[0080] Furthermore, a p-type electrode 13 is formed on the back surface of the p-type GaAs substrate 120. Here, the p-type electrode 13 may be formed so as to be electrically connected to the p-type AlGaAs cladding layer 121. For example, when the p-type AlGaAs cladding layer 121 is formed on a semi-insulating GaAs substrate, the p-type electrode 13 may be formed on the p-type AlGaAs cladding layer 121.

[0081] A laminated metal film of Ti and Au or a laminated metal film of Ti, Pt, and Au, which has low electrical resistance, is used for the p-type electrode 13. Other metal materials that can achieve low electrical resistance may also be used for the p-type electrode 13. The thickness of the p-type electrode 13 is, for example, about 100 nm to 1 μm.

[0082] Furthermore, an n-type electrode 14 is formed on the surface of the n-type AlGaAs cladding layer 123. Here, the n-type electrode 14 may be formed so as to be electrically connected to the n-type AlGaAs cladding layer 123.

[0083] The n-type electrode 14 is formed by MBE, sputtering, or the like using Fe, which is a ferromagnetic material at room temperature. Here, Co or an alloy such as CoFeB may also be used for the n-type electrode 14. The thickness of the n-type electrode 14 is, for example, about 100 nm to 1 μm.

[0084] When the semiconductor laser 11 of the laser module 10 is driven without magnetizing the Fe ferromagnetic electrode (n-type electrode) 14, it oscillates at a threshold current of 10 mA, just like a conventional semiconductor laser. Furthermore, the light intensity fluctuates significantly due to the influence of feedback light.

[0085] On the other hand, when the semiconductor laser 11 of the laser module 10 is driven in a state where the ferromagnetic electrode (n-type electrode) 14, which is made of Fe, is magnetized, the spin polarization of Fe is about 0.4 (S.V. Karthik, et. al., “Spin polarization of Co-Fe alloys estimated by point contact Andreev reflection and tunneling magnetoresistance,” Applied Physics Letters, 105, 07C916 (2009)). Therefore, the threshold current I th1 and the threshold current I for circularly polarized light in the other direction. th2 are I th1 =I th / (1 + |P|) = 7.1mA, I th2 =I th / (1-|P|)=16.7mA.

[0086] Here, a magnetic field (magnetic field strength: for example, 1 to 10 tesla) is applied to the laser module 10 to magnetize the Fe (ferromagnetic electrode 14) in one direction (e.g., corresponding to upward spin) parallel to the direction of emission of the laser light, and the Fe is used as a ferromagnetic electrode of the permanent magnet. Here, the Fe (ferromagnetic electrode 14) may be magnetized in the opposite direction (e.g., corresponding to downward spin) to the one direction parallel to the direction of emission of the laser light.

[0087] Therefore, the semiconductor laser 11 of the laser module 10 is I th1 (7.1mA) higher than I th2 When driven at a current lower than (16.7 mA), for example 10 mA, good characteristics with very little fluctuation in light intensity are obtained, as shown in FIGS. 5A and 6A.

[0088] According to the laser module of this embodiment, fluctuations in laser light intensity can be stably suppressed without using an optical isolator using YIG or the like, and the cost of the laser module can be reduced.

[0089] <Second Example> The laser module according to the second embodiment of the present invention will be described with reference to FIG. 8.

[0090] As shown in FIG. 8, the semiconductor laser 21 in the laser module 20 according to this embodiment includes an insulating tunnel layer 211 between the n-type clad layer 123 and the ferromagnetic electrode (n-type electrode) 14. Other configurations are the same as those in the first embodiment.

[0091] The insulating tunnel layer 211 is MgO which is an insulator and is formed by MBE, sputtering, or the like. The thickness of the insulating tunnel layer 211 is, for example, about 1 to 20 nm. The insulating tunnel layer 211 can suppress the spin relaxation that occurs when injecting spin-polarized electrons from the ferromagnetic electrode 14 into the laser. (W. H. Butler, et al., “Spin-dependent tunneling conductance of Fe|MgO|Fe sandwiches,” Physical Review B 63, 054416 (2001).). As the insulating tunnel layer 211, Al2O3 or the like may be used in addition to MgO.

[0092] The oscillation threshold value of circular polarization by majority / minority carriers becomes the value calculated by Equation (2) when spin relaxation can be ignored. However, in an actual device, the spin of the current injected into the active layer with respect to the spin polarization rate of the ferromagnetic material becomes x times (0 < x < 1) due to relaxation. Therefore, the range of the current in which circular polarization in only one direction oscillates is I th / (1 + x|P|) < I < I th / (1 - x|P|), and compared with the case where spin relaxation can be ignored, the range of the current in which the effect of the present invention can be expected is limited.

[0093] According to the laser module of this embodiment, since the spin relaxation of spin-polarized electrons can be suppressed, the limitation of the current range due to spin relaxation can be suppressed, and driving with suppressed fluctuation of light intensity in a wider current range becomes possible.

[0094] In this embodiment, the n-type electrode is a ferromagnetic electrode, but the p-type electrode may be a ferromagnetic electrode. In this case, the insulating tunnel layer is disposed between the ferromagnetic electrode (p-type electrode) and the p-type cladding layer.

[0095] <Third Example> A laser module according to a third embodiment of the present invention will be described with reference to FIG.

[0096] 9, the semiconductor laser 31 in the laser module 30 according to this embodiment has a layered structure composed of an n-type AlGaAs cladding layer 323, a GaAs active layer 322, and a p-type AlGaAs cladding layer 321 on a semi-insulating GaAs substrate 320, and has a ferromagnetic electrode (n-type electrode) 34 on the side of the layered structure on the n-type AlGaAs cladding layer 323. Also, a p-type electrode 33 is provided on the surface of the p-type AlGaAs cladding layer 321.

[0097] In the semiconductor laser 31, spin-polarized electrons are injected into the active layer 322 from the ferromagnetic electrode (n-type electrode) 34 through the n-type AlGaAs cladding layer 323. As a result, laser oscillation occurs as in the first embodiment, and the laser module 30 exhibits excellent characteristics with very little fluctuation in light intensity.

[0098] The laser module according to this embodiment has the same effects as the first embodiment.

[0099] FIG. 10 shows an example of the computer configuration of the laser module control device 16 according to the embodiment of the present invention. The laser module control device 16 can be realized by a computer including a CPU (Central Processing Unit) 43, a storage device (storage section) 42, and an interface device 41, and a program that controls these hardware resources. The semiconductor laser 11 is connected to the interface device 41. The CPU 43 executes the laser module control method according to the embodiment of the present invention in accordance with the laser module control program stored in the storage device 42. In this way, the laser module control program causes the laser module control device to function.

[0100] In the laser module control device 16 according to the embodiment of the present invention, a computer may be provided inside the device, or at least a part of the computer's functions may be realized using an external computer. The storage unit may also use a storage medium 45 external to the device, and the laser module control program stored in the storage medium 45 may be read and executed. Examples of the storage medium 45 include various magnetic recording media, magneto-optical recording media, CD-ROMs, CD-Rs, and various memories. The laser module control program may also be supplied to the computer via a communication line such as the Internet.

[0101] In the laser module according to the embodiment of the present invention, an example has been shown in which it is applied to a GaAs-based laser, but it may also be applied to an InP-based laser or the like.

[0102] In the embodiments of the present invention, examples of the structure, dimensions, materials, etc. of each component in the laser module, the laser module control method, and the configuration of the control device are shown, but the present invention is not limited to these examples. Anything that can demonstrate the function and effect of the laser module can be used. [Industrial Applicability]

[0103] The present invention relates to a laser module, and can be applied to an optical communication system. [Explanation of symbols]

[0104] 1 laser module 11 Semiconductor laser 15 1 / 4 wave plate

Claims

1. a semiconductor laser that oscillates with either right-handed circularly polarized light or left-handed circularly polarized light; a quarter-wave plate disposed on the emission surface side of the semiconductor laser; Equipped with The semiconductor laser is In order, an n-type cladding layer; an active layer; a p-type cladding layer; Equipped with an n-type electrode electrically connected to the n-type cladding layer; a p-type electrode electrically connected to the p-type cladding layer; Equipped with the semiconductor laser is driven by a current higher than a threshold current for one of the circularly polarized light beams and lower than a threshold current for the other circularly polarized light beam; At least one of the n-type electrode and the p-type electrode is a ferromagnetic electrode. A laser module characterized by:

2. The ferromagnetic electrode is magnetized in a direction parallel to the direction of the emitted light from the semiconductor laser.

2. The laser module according to claim 1.

3. an insulating tunnel layer disposed between the n-type electrode and the n-type clad layer when the one electrode is the n-type electrode, and disposed between the p-type electrode and the p-type clad layer when the one electrode is the p-type electrode; The laser module according to claim 1 or 2, comprising:

4. The present invention comprises a semiconductor laser that oscillates with either right-handed circularly polarized light or left-handed circularly polarized light, and a quarter-wave plate disposed on the side of the emission surface of the semiconductor laser, 1. A method for controlling a laser module comprising, in order, an n-type cladding layer, an active layer, and a p-type cladding layer, an n-type electrode electrically connected to the n-type cladding layer, and a p-type electrode electrically connected to the p-type cladding layer, wherein at least one of the n-type electrode and the p-type electrode is a ferromagnetic electrode, A current higher than the threshold current of one of the circularly polarized light beams and lower than the threshold current of the other circularly polarized light beam is injected into the semiconductor laser. A method for controlling a laser module.

5. An apparatus for controlling a laser module, comprising: a semiconductor laser that oscillates with either right-handed circularly polarized light or left-handed circularly polarized light; and a quarter-wave plate disposed on an emission surface side of the semiconductor laser, the semiconductor laser comprising, in order, an n-type cladding layer, an active layer, and a p-type cladding layer, an n-type electrode electrically connected to the n-type cladding layer, and a p-type electrode electrically connected to the p-type cladding layer, and at least one of the n-type electrode and the p-type electrode is a ferromagnetic electrode, A current higher than the threshold current of one of the circularly polarized light beams and lower than the threshold current of the other circularly polarized light beam is injected into the semiconductor laser. A laser module control device comprising:

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