JP3387751B2 - Semiconductor laser capable of polarization modulation and method of manufacturing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor optical device such as a polarization-modulatable semiconductor laser used for optical communication and optical information processing, and a manufacturing method thereof.

[0002]

2. Description of the Related Art Optical communication technology using optical devices such as semiconductor lasers has solved many problems today. However, the phenomenon called so-called chirping, in which the fluctuation of the refractive index due to the carrier non-uniform distribution during high-speed intensity modulation distorts the waveform of the output light, has not always been solved. A mainstream method currently used to solve this is to drive a semiconductor laser by CW (continuous operation) and perform intensity modulation by an external semiconductor optical modulator. However, recent studies have revealed that even this method has a limit in reducing chirping.

On the other hand, a polarization modulation laser that switches the plane of polarization of laser light according to a signal makes the optical density and carrier density in the resonator almost constant during modulation, as compared with a normal intensity modulation laser. Therefore, the chirping is small and the modulation speed and the transmission distance can be improved. Regarding the polarization modulation laser, for example, Japanese Patent Publication No.
There are semiconductor laser devices disclosed in Japanese Patent No. 68111 and Japanese Patent Laid-Open No. 7-235718. This semiconductor laser device is composed of two semiconductor lasers connected in series or in parallel, one of which mainly generates or amplifies a wave of a specific polarization state (TE or TM polarization), and the other mainly of another polarization state ( Waves of TM or TE polarization) are generated or amplified. Then, at that time, a light wave amplified or generated by one of the two semiconductor lasers and a light wave amplified or generated by the other semiconductor laser can be superimposed on each other.

FIG. 30 is a schematic diagram for explaining the structure of a conventional example. This semiconductor laser is composed of two different semiconductor lasers connected in series. The first semiconductor laser is T
The second semiconductor laser has a gain region 1103a in which the gain for the E mode is always higher than that for the TM mode, the second semiconductor laser has a gain region 1103b having the opposite gain characteristic, and each semiconductor laser has its own gain spectrum. Is characterized by having distributed reflectors 1107a and 1107b such as a grating having a Bragg wavelength in the vicinity of the peak wavelength. The operating principle is that carriers are independently injected into the first semiconductor laser region and the second semiconductor laser region so that the TE mode and the TM mode have the same threshold gain. The polarization switching of the TE mode and the TM mode is performed by slightly modulating the number of injected carriers of. Compared with a normal intensity-modulated laser, the light density and the carrier density in the resonator can be made almost constant during modulation, so chirping is small and the modulation speed and transmission distance can be improved. Has been done. In FIG. 29, 1101 is a substrate, 1102 is a lower clad layer, 1104 is an optical guide layer, 1105 is an upper clad layer, 1106 is a contact layer, 1109a,
Reference numerals 1109b and 1110 are electrodes, and 1111 is an antireflection film.

Although a specific manufacturing method of this semiconductor laser has not been proposed at all, the following method can be considered from known manufacturing methods of other devices. 1) A method of manufacturing a TE mode semiconductor laser region and a TM mode semiconductor laser region by selective growth twice. 2) A method of producing a TE / TM mode semiconductor laser region by growth without a selective mask twice and selective etching twice. 3) A method of producing a TE mode semiconductor laser region and a TM mode semiconductor laser region by one-time growth utilizing the area dependency of the selective mask region.

[0006]

However, the above-mentioned conventional example has the following problems. (1) In the conventional example, since the device for controlling the wavelength fluctuation at the time of high-speed modulation has not been devised, not only is the transmission capacity limited, but it is also unsuitable as a light source for wavelength division multiplexing communication.

(2) No specific design guideline and manufacturing method for two types of semiconductor lasers having different polarization directions are shown. As an example of the manufacturing method, a method of manufacturing on the same substrate by using a selective growth method such as MOCVD can be considered, but it is very difficult to optimize each semiconductor laser independently. For example, in the first method, abnormal growth is likely to occur at the selective mask edge, and it is extremely difficult to secure the controllability or crystal quality equivalent to the first time by the pattern effect in the second growth. The second
In the method (1), the controllability of the selective etching is difficult, and abnormal growth easily occurs at the boundary portion, which deteriorates the device manufacturing yield. Although the third method has a small manufacturing problem, it has a drawback that the device structure that can be manufactured is limited and the device cannot be optimized. In any case, at present, it can be said that there is no method capable of reliably realizing the above-mentioned conventional polarization-modulated laser.

(3) The polarization modulation possible range is narrow. The two semiconductor lasers that compose this structure are DFB lasers, respectively, but when the compound resonator configuration is adopted, a simple DFB laser is used.
Rather, the other resonator sometimes acts as a DBR and sometimes as a Fabry-Perot resonator. Therefore, the phase condition is not simple, unlike when the DFB is used alone. Therefore, the operation range in which the polarization modulation is possible becomes extremely small only by the optical coupling.

(4) The manufacturing method for forming an array is difficult. Arraying of semiconductor lasers is indispensable for optical communication, especially for optical interconnect and wavelength division multiplexing communication, but it is more difficult to fabricate arraying of semiconductor lasers.
Naturally, the implementation method is not considered in the conventional example. In particular, it becomes more difficult for the array to make the gain peak wavelength and the Bragg wavelength substantially match.

Therefore, an object of the present invention is to solve the structural and manufacturing problems of the conventional polarization modulation semiconductor laser, and to optimize the TE mode semiconductor laser structure and the TM mode semiconductor laser that can be optimized substantially independently. Using a semiconductor laser structure, wavelength control is performed (wavelength stability is ensured) and a semiconductor laser having a wide polarization modulation operation range and a relatively low cost, a manufacturing method thereof,
An object of the present invention is to provide an apparatus, a system and the like using the semiconductor laser.

[0011]

FIG. 1 schematically shows the principle of a representative example of the present invention. In FIG. 1, 1 is a first semiconductor laser structure, 2 is a second semiconductor laser structure,
Reference numeral 3 represents a void (gap) formed between the two and / or a filler filled therein. The semiconductor laser structures 1 and 2 are individually tuned by using the first resonator 7 as the TM.
While the mode (or the TE mode) is excited by the TE mode (or the TM mode) in the second resonator 8, the first and second resonators are optically coupled to each other. Besides, the TE mode and the TM mode are excited by the composite resonator including the third resonator 9. For this purpose, the TM mode of the first semiconductor laser structure 1 is coupled with the TM mode of the second semiconductor laser structure 2, and similarly, the TE mode of the second semiconductor laser structure 2 is the first semiconductor laser structure 1.
It is necessary to combine the TE mode with. This means that the propagation constants of TE modes and TM modes of the first semiconductor laser structure 1 and the second semiconductor laser structure 2 are substantially equal to each other. Achieving this is not technically difficult.

An important point of the present invention is that the first, second and third
A carrier I ₁ injected into the TE semiconductor laser structure and the TM semiconductor laser structure with the threshold gains of the TE mode and the TM mode allowed in the composite resonator including the resonator of
The point is that they can be made almost equal by controlling I ₂ . If this state can be realized, then by slightly controlling the phase condition or the like with the modulation current or voltage, oscillation occurs in the polarization mode with the smaller threshold value, and polarization modulation can be performed.

The respective components of the present invention will be described below in accordance with the claims. The first invention for achieving the above object is the first invention.
And a composite resonator type semiconductor laser in which two different semiconductor laser structures having both a second polarization mode and at least an active layer and a waveguide layer (or an optical guide layer) are arranged in series in the waveguide direction. And the first semiconductor laser structure is
Of the active region and the distributed feedback resonator or the distributed Bragg reflective resonator, the gain of which is superior to the gain of the second polarized mode, and the second semiconductor laser structure has the second polarized laser. An active region having a gain for a wave mode superior to a gain for a first polarization mode and a distributed feedback resonator, a distributed Bragg reflection resonator, or a Fabry-Perot resonator, and the first semiconductor laser structure and the first semiconductor laser structure. The second semiconductor laser structure is configured such that the propagation constants of the first polarization mode and the second polarization mode are substantially equal to each other, and the first semiconductor laser structure and the second semiconductor laser structure are Are arranged with a gap in the waveguide direction, and the Bragg wavelength of the distributed feedback resonator or distributed Bragg reflection resonator is near the peak wavelength of the gain spectrum of the semiconductor laser structure. The oscillation mode is switched between the first polarization mode and the second polarization mode by modulating carriers injected into at least one of the first and second semiconductor laser structures. This is a semiconductor laser capable of polarization modulation (corresponding to claim 1).

In the above structure, if both TE mode and TM mode are set to DFB or DBR mode, the wavelength can be stabilized even at the time of modulation, and the threshold gain with which both can oscillate simultaneously can be set.

If the TE Fabry-Perot mode is used for one side and the DFB or DBR mode is used for the other side, it is possible to set a threshold gain at which both can simultaneously oscillate, which makes it easier to fabricate and mount the device, and to use the composite resonator. The polarization modulation operating range can be further widened. In this case, only the stable TM mode may be used as the signal light. According to the first invention, in realizing a semiconductor laser capable of polarization modulation in this manner, design guidelines for improving controllability of semiconductor laser fabrication and improving an operation range in which polarization modulation is possible are provided. To be

A second aspect of the present invention for attaining the above object is the first and second semiconductor laser structures, each of which has a substrate and a laminated structure independently formed thereon. It is characterized in that it is arranged on a support base with a gap in the waveguide direction (corresponding to claim 2).

According to the second invention, the semiconductor laser structure for TE and the semiconductor laser structure for TM can be manufactured independently, and the degree of freedom in design is further increased. In addition, the optical axis between the two laser structures can be surely adjusted.

A third aspect of the present invention for attaining the above object is the first and second semiconductor laser structures, wherein at least an active layer and a waveguide layer are separately formed on the same substrate. The laminated structures on the same substrate are arranged with a gap in the waveguide direction (corresponding to claim 3).

A fourth invention for attaining the above object is characterized in that the gap between the first and second semiconductor laser structures is filled with a filler to form a phase adjustment region ( (Corresponding to claim 4). This adjusts the phase and ensures polarization modulation by the composite resonator.

A fifth aspect of the invention for attaining the above object is that the substance filled in the gap is a material whose refractive index can be electrically controlled, and is an optical element for modulating the optical length of the phase adjusting region. A long modulation means is provided (corresponding to claim 5). As a result, the phase adjustment can be made variable, and the operating range of polarization modulation by the composite resonator can be further widened.

A sixth invention for attaining the above object is characterized in that the second semiconductor laser structure has a distributed feedback resonator or a distributed Bragg reflection resonator (corresponding to claim 6). ).

A seventh aspect of the invention for achieving the above object is that the opposing end faces of the first and second semiconductor laser structures are formed obliquely with respect to the waveguide direction with a gap therebetween. It is characterized (corresponding to claim 7). As a result, when both semiconductor laser structures are DFB or DBR lasers, the influence of end facet reflection is suppressed and polarization modulation by the compound resonator is ensured.

An eighth invention for attaining the above object is characterized in that the second semiconductor laser structure has a Fabry-Perot type resonator (corresponding to claim 8).

A ninth invention for achieving the above object is the first semiconductor laser structure, which is a DFB or DBR laser among the end faces facing each other with a gap between the first and second semiconductor laser structures. Is formed obliquely with respect to the waveguide direction (corresponding to claim 9). Thus, when one semiconductor laser structure is a DFB or DBR laser and the other semiconductor laser structure is a Fabry-Perot type, the influence of end facet reflection is suppressed and polarization modulation by the compound resonator is ensured.

The tenth invention for achieving the above object is as follows:
An AR coat is applied to the end faces of the first and second semiconductor laser structures facing each other so as to be non-reflecting (corresponding to claim 10). This suppresses the influence of end face reflection and ensures polarization modulation by the composite resonator. In addition, adverse effects due to end face reflection or phase of the semiconductor laser are suppressed, the characteristics of the semiconductor laser are averaged, and the yield is improved.

The eleventh invention for achieving the above object is as follows:
At least one of the active layers of the first and second semiconductor laser structures has a quantum well structure or a strained quantum well structure (corresponding to claim 11). As a result, the threshold gains of the TE mode and the TM mode can be easily counterbalanced, and the polarization modulation operation can be surely realized.

A twelfth invention for achieving the above object is
A composite resonator type semiconductor laser array in which two different semiconductor laser arrays having both a first and a second polarization mode are arranged in series in the waveguide direction, the composite resonator type semiconductor laser array having a plurality of first semiconductor laser structures. The first semiconductor laser array is formed by arranging a plurality of the first semiconductor laser structures on the same substrate in parallel to the waveguide direction, and the gain peak for the first polarization mode can be changed by the carrier injection amount. Each first semiconductor laser structure including an active region is provided with a distributed Bragg reflector or a distributed Bragg reflector having a Bragg wavelength set near the different gain peak. A second semiconductor laser array including a plurality of second semiconductor laser structures as many as the semiconductor laser structure has the second semiconductor laser structure arranged in the same manner as the first semiconductor laser structure. Ri, gain for the second polarization mode comprises a dominant common active region than the gain for the first polarization mode, for individual second semiconductor laser structure,
The first semiconductor laser structure and the second semiconductor laser structure forming a pair, which have Fabry-Perot resonators, have propagation constants between the first polarization mode and the second polarization mode, respectively. The first semiconductor laser array and the second semiconductor laser array are arranged to be substantially equal to each other, and are arranged with a gap in the waveguide direction.
Of the semiconductor laser structure, the carrier wave injected into at least one of the semiconductor laser structures is modulated to switch the oscillation mode between the first polarization mode and the second polarization mode. A semiconductor laser array (corresponding to claim 12).

With this structure, since the structure of the second semiconductor laser structure of the Fabry-Perot resonator type can be simplified, arraying of the multi-wavelength semiconductor laser structure becomes easy. Further, the second semiconductor laser structure of the Fabry-Perot type can be flexibly designed according to the first semiconductor laser structure of the DFB or DBR type, and the quality of the oscillation light of the mode which is slightly superior to that of the second semiconductor laser structure can be obtained. Even at the expense of, the oscillation light of the dominant mode in the first semiconductor laser structure can be surely used in the polarization modulation operation.

A thirteenth invention for achieving the above object is as follows:
The gap between the first and second semiconductor laser arrays is filled with a filling material to form a phase adjustment region (corresponding to claim 13). This adjusts the phase and ensures the polarization modulation operation by each set of composite resonators.

The fourteenth invention for achieving the above object is to:
The substance filled in the gap is a material whose refractive index can be electrically controlled, and an optical length modulation means for modulating the optical length of the phase adjusting region is provided (claim 14). Corresponding to). As a result, the phase adjustment can be made variable, and the operating range of polarization modulation by the composite resonators of each set can be further widened.

A fifteenth invention for achieving the above object is to:
A method of making a semiconductor laser as described above, comprising:
Process for producing the semiconductor laser structure, the process for producing the second semiconductor laser structure independently of this process, and the process for serially connecting the first and second semiconductor laser structures optically in series in the waveguide direction. A method of manufacturing a semiconductor laser capable of polarization modulation, comprising the step of disposing a gap on the same support base (corresponding to claim 15).

According to this, the TE semiconductor laser structure and the TM semiconductor laser structure can be manufactured independently, and the optical axis can be adjusted surely. Further, in realizing a semiconductor laser capable of polarization modulation, it is possible to provide a manufacturing method and a phase control method for mounting with higher accuracy.

A sixteenth invention for achieving the above object is as follows:
The step of arranging the first and second semiconductor laser structures in series in the waveguide direction with a gap on the same support so as to optically couple the first and second semiconductor laser structures, includes disposing the first semiconductor laser structure on the support. After fixing the second semiconductor laser structure, the second semiconductor laser structure is caused to emit light, and at the same time, the first semiconductor laser structure is made to function as a photodetector to receive the light of the second semiconductor laser structure to position the second semiconductor laser structure. And a fixing step (corresponding to claim 16).

As a result, the two semiconductor laser structures can be aligned more easily.

A seventeenth invention for achieving the above object is as follows:
The step of arranging the first and second semiconductor laser structures in series in the waveguide direction with a gap on the same support so as to optically couple the markers and the semiconductor laser structure. The method further comprises the step of adjusting the marker formed on the substrate to a desired positional relationship and disposing and fixing the semiconductor laser structure (corresponding to claim 17).

As a result, the alignment can be easily performed and the optical axis can be surely adjusted.

The eighteenth invention for achieving the above object is as follows:
The step of arranging the first and second semiconductor laser structures in series in the waveguide direction so as to optically couple with each other on the same support base with a gap is the semiconductor laser mounting surface formed on the support base. The method further comprises disposing the semiconductor laser structure by abutting a side surface of the semiconductor laser structure on a vertically upright plane (corresponding to claim 18).

With this, alignment can be easily performed.

The nineteenth invention for achieving the above object is as follows:
The method further comprises the step of filling the gap with a substance having a desired refractive index (corresponding to claim 19). The phase can be adjusted even if a gap is left between the two semiconductor laser structures, but the phase can be adjusted more flexibly by filling with a substance having a desired refractive index.

A twentieth invention for achieving the above object is to:
A method of manufacturing a semiconductor laser as described above, comprising the steps of manufacturing a first semiconductor laser structure on a semiconductor substrate,
Producing a second semiconductor laser structure on the substrate;
And a step of forming a gap at a boundary portion between the first and second semiconductor laser structures, which is a method of manufacturing a semiconductor laser capable of polarization modulation (corresponding to claim 20).

According to this, by removing the abnormal structure produced in the manufacturing process at the boundary between the two semiconductor laser structures and providing a gap that can serve as the phase adjusting section there, the structural principle resulting from the abnormal structure is obtained. And solve manufacturing problems at the same time.

The twenty-first invention for achieving the above object is as follows:
The step of fabricating the first semiconductor laser structure may include forming a first semiconductor laser structure only on a region of the first semiconductor laser structure on the semiconductor substrate.
Laminating the active layer and the first optical waveguide layer, the first optical waveguide layer having a pitch controlled to have a Bragg wavelength near the gain peak of the first active layer. A step of forming a grating, and a step of manufacturing the second semiconductor laser structure includes a step of forming a second semiconductor laser structure on the semiconductor substrate.
The step of laminating the second active layer and the second optical waveguide layer only in the region of the semiconductor laser structure, and the Bragg wavelength is provided in the second optical waveguide layer in the vicinity of the gain peak of the second active layer. And a step of forming a second grating having a pitch controlled so as to have, the step of forming the first semiconductor laser structure and the step of forming the second semiconductor laser structure are both the first step. First with grating formed
And a common clad layer and a contact layer are collectively laminated on the second optical waveguide layer on which the second grating is formed (corresponding to claim 21). .

A twenty-second invention for achieving the above object is as follows:
The step of producing the first semiconductor laser structure and the step of producing the second semiconductor laser structure both include a step of laminating a first cladding layer, an active layer, and an optical waveguide layer on the entire surface of the semiconductor substrate; The optical waveguide layer in the region of the second semiconductor laser structure is left as it is, and the pitch is set so as to have a Bragg wavelength near the gain peak of the active layer only on the optical waveguide layer in the region of the first semiconductor laser structure. It is characterized by including a step of forming a controlled grating and a step of stacking a common second cladding layer and a common contact layer all over the optical waveguide layer (corresponding to claim 22).

The twenty-third invention for achieving the above object is as follows:
The step of forming a gap at the boundary between the first and second semiconductor laser structures includes the step of simultaneously forming a slit-shaped gap and a ridge waveguide at the boundary between the regions of the first and second semiconductor laser structures. Is included (claim 2
Corresponding to 3).

A twenty-fourth invention for achieving the above object is as follows:
The method further comprises the step of filling the gap with a substance having a desired refractive index (corresponding to claim 24).

The twenty-fifth aspect of the invention for achieving the above object is to provide a polarized light such as a polarizer for selecting and outputting only one polarized wave in the output section of the semiconductor laser capable of polarization modulation of the above invention. The optical transmission device is provided with a selection unit (corresponding to claim 25). With this configuration, it is possible to realize an optical transmitter that outputs an optical signal with a small modulation power, a narrow occupied wavelength width, and a large extinction ratio.

The twenty-sixth invention for achieving the above object is as follows:
The semiconductor laser capable of polarization modulation described above, a polarization selecting means for transmitting one polarized light of the output light from the semiconductor laser, and a polarization state of the output light of the semiconductor laser are switched according to an input signal. Control the semiconductor laser for
An optical transceiver having a control circuit for driving and a receiving means for receiving an input signal (claim 26).
Corresponding to). The same effect as that of the optical transmitter of the twenty-fifth invention is exhibited.

The twenty-seventh invention for achieving the above object is as follows:
A light source device comprising the above-mentioned polarization-modulated semiconductor laser and a polarization selection means for extracting only one of two polarization modes, TE and TM, of light emitted from the polarization-modulated semiconductor laser. It is characterized by (corresponding to claim 27). The same effect as that of the optical transmitter of the twenty-fifth invention is exhibited.

A twenty-eighth invention for achieving the above object is an optical transmission system or an optical communication system including a transmitter using the semiconductor laser of the present invention (corresponding to claim 28). ). As a result, an intensity-modulated signal with little output power fluctuation and little chirping can be obtained even at the time of high-speed modulation, and the receiving side only needs to receive the intensity-modulated signal, so that a conventional simple receiver is used.

The twenty-ninth invention for achieving the above object is as follows:
The optical transmitter or the transmitter / receiver can transmit optical signals of a plurality of different wavelengths, and forms a wavelength multiplexing type network (corresponding to claim 29).

The thirtieth invention for achieving the above object is as follows:
A light source device comprising the polarization modulation semiconductor laser described above and polarization selection means for extracting only one of two polarization modes of TE and TM from the light emitted from the polarization modulation semiconductor laser is used. , By superimposing a current modulated according to a transmission signal on a predetermined bias current and supplying the current to the polarization modulation semiconductor laser, the signal light intensity-modulated according to the transmission signal is taken out from the polarization selecting unit, It is an optical communication method for transmitting this signal light toward the optical receiving side (corresponding to claim 30).

[0052]

DETAILED DESCRIPTION OF THE INVENTION

(First Embodiment) FIG. 2 is a view best showing the present embodiment, in which 1 is a first semiconductor laser, 2 is a second semiconductor laser, 3 is a filling material for voids, 4 is a heat sink, and 5 is a marker. Is. Although not shown here, the semiconductor laser is mounted on the heat sink 4 arranged on the subcarrier. It may be placed directly on the subcarrier.

First, a method of manufacturing a semiconductor laser will be described. FIG. 3 is a sectional view in the direction including the oscillation axis of the first semiconductor laser 1, and FIG. 4 is a sectional view in the vertical direction thereof. For example, on an n-type (100) InP substrate 101,
MOCVD method (Metal Organic Chem
ical Vapor Deposition) and CB
E method (Chemical Beam Epitaxy)
After stacking the n-InP clad layer 102, the undoped active layer 103, and the p-InGaAsP optical guide layer 104 using, a phase shift grating 108 having a pitch of 325 nm and a depth of 50 nm is formed, and the p-InP clad layer 105, A p-InGaAs contact layer (cap layer) 106 is laminated. Reference numeral 115 denotes an antireflection (AR) coat for reducing the reflection on the end surface, which is formed on both end surfaces.

FIG. 5 shows a band diagram of the active layer 103 (SCH layers are formed on both upper and lower sides thereof). 121 is a tensile strained InGaAs well layer (strain rate is -9%, thickness is 9 nm), and 122 is unstrained InGaAs.
P barrier layer (band gap 0.99 eV, thickness 10 n
m) and the number of wells was 5.

As shown in FIG. 4, a ridge structure having a width of 2.5 μm is used for controlling the transverse mode. In FIG. 4, reference numeral 111 is a ridge type optical waveguide, and 112 is an insulating film such as a SiO _x film for preventing a current from flowing to portions other than the ridge portion.
Further, 109 is a positive electrode formed on the surface side of the substrate (the positive electrode 109 includes two electrodes 109a, 1a in the resonance direction as shown in FIG. 3).
09b), 110 is a negative electrode on the substrate side. In the present embodiment, an example in which the positive electrode 109 is divided into two parts (this makes it possible to adjust the injection carrier distribution and widen the polarization modulation operation range), but a single electrode may also be used. In FIG. 4, the projecting laminated structure on both sides of the ridge-type optical waveguide 111 is not required in terms of function,
It is only formed as a result of the etching process for forming the ridge type optical waveguide 111.

As a result of applying the tensile strain multiple quantum structure to the active layer 103 and setting the Bragg wavelength in the vicinity of the gain peak wavelength (depending on the setting of the pitch of the grating 108), the TM gain always exceeds the TE gain.
It always oscillates in the DFB mode of TM polarization. In this embodiment, the grating 10 is formed after the active layer 103 is grown.
No. 8 is formed because it is considered that the fabrication accuracy of the grating is higher than that of the current technology with respect to the wavelength controllability of crystal growth (that is, the active layer is grown and the gain peak is increased). Since it is better to determine the pitch of the grating and so on after the wavelength is decided), if both can be manufactured with high accuracy, the grating may be formed directly on the substrate and then the active layer etc. may be grown. . This also applies to the following examples.

Next, the second semiconductor laser manufacturing method will be described. In the present embodiment, the second semiconductor laser 2 is controlled in layer thickness and composition in order to make the TE mode and the propagation constant of the first semiconductor laser 1 substantially equal, but basically, the structure other than the active layer is used. May be substantially the same as the first semiconductor laser 1. The lateral mode control of the second semiconductor laser 2 also uses the ridge structure, but the width thereof does not necessarily have to be the same as that of the first semiconductor laser 1. When the widths of the ridge structures are different, other structural parameters may be changed accordingly so that the propagation constants of both lasers 1 and 2 become equal.

The band diagram structure of the active layer of the second semiconductor laser 2 is shown in FIG. 6 (SC is provided on both sides of the active layer.
H layer is formed). 123 is unstrained InGaAs
Well layer (thickness: 7.5 nm), 124 is unstrained InGaA
sP barrier layer (band gap 0.99 eV, thickness 10 n
m) and the number of wells was 5. As a result, the transition between heavy holes and electrons becomes dominant, so that TE gain is always TM.
Since the Bragg wavelength is set higher than the gain and near the peak wavelength of the TE gain, it always oscillates in the TE polarization DFB mode.

It is desirable that the two types of semiconductor lasers 1 and 2 should be paired with each other except polarization, in order to facilitate the formation of a compound resonator. For example, the threshold current value and efficiency can be adjusted by the cavity length and end face reflectance of each laser. In order to make the DFB mode dominant, it is desirable that the end faces facing each other have a reflectance as low as possible. As described above, it is a major feature of the present invention that the structures of the first and second semiconductor lasers can be easily and independently controlled or selected.

Next, a method of mounting the two semiconductor lasers 1 and 2 on the heat sink 4 will be described with reference to FIG.
For example, the first semiconductor laser 1 is die-bonded to a desired position indicated by the marker 5 by episide down. The second semiconductor laser 2 performs position adjustment by causing the first semiconductor laser 1 to function as a waveguide type photodetector while oscillating by pulse current driving. Second
After the position adjustment of the semiconductor laser 2 is completed, before the die bonding, the first semiconductor laser 1 is reversely pulse-driven, and the second semiconductor laser 2 is operated as a photodetector to confirm that it can receive light. And then bond. As a result, the two semiconductor lasers 1 and 2 are
It is fixed on the heat sink 4 in an optimal optical coupling state. Even if the optical power coupling efficiency is high, the size of the air gap 3 generated between the two semiconductor lasers 1 and 2 is difficult to control, and the phases are shifted, so that polarization modulation is less likely to occur (either TE mode or TM mode). It only works). At this time, the phase (optical length) of competing light waves is adjusted by filling a void 3 formed between the two semiconductor lasers 1 and 2 with a filler 3 such as gel or polymer capable of controlling the refractive index, and the yield is improved. It becomes possible to apply polarization modulation.
Further, instead of gel or polymer, liquid crystal is filled in the voids 3, electrodes are formed on the liquid crystal, and a voltage is applied, whereby the refractive index or the transmittance of the liquid crystal (the transmittance is the absorptivity if the expression is changed. In view of the complex refractive index, the refractive index and the transmittance are equal to each other, and the polarization modulation can be applied with good yield even by adjusting the transmittance).

Next, the operation method of the first embodiment will be described. FIG. 7 shows the distribution of polarization modes when currents (I ₁ and I ₂ , respectively) are independently applied to the first and second semiconductor lasers ₁ and ₂ . The boundary line AB indicates that the threshold gains of the TE mode and the TM mode are almost equal,
By using this line as a bias point (for example, point M or point N) and superposing the modulation signal, the so-called polarization modulation in which the oscillation polarization mode is switched is realized. For example, when the bias point is M, an example in which the modulation signal is placed only on I ₁ is set, and when the bias point is N, I ₁ and I _{2 are set.}
An example in which the modulation current is placed in the reverse phase is shown in FIG. When the positive electrodes 109a and 109b of the first semiconductor laser 1 are divided into two, the carriers can be non-uniformly injected into the respective electrodes to finely adjust the phase, thereby enabling the polarization modulation region. Can be further expanded.

The advantages of this embodiment can be summarized as follows. (1) The semiconductor laser for TE and the semiconductor laser for TM can be optimized independently. (2) Appropriate LDs can be selected from a plurality of semiconductor lasers of the same type to construct this structure. (3) Both have good line width and the like, so that both TE mode light and TM mode light can be used for optical communication. (4) Even if the phases do not match, the phase adjustment is easy by adjusting the voids and the filler.

In this embodiment, the lateral mode control of the two semiconductor lasers 1 and 2 is performed by the ridge structure. However, the lateral confinement is not limited to the ridge structure and may be another structure such as a buried structure used in the conventional semiconductor laser.

(Second Embodiment) Next, an example of a polarization modulation semiconductor laser which can be manufactured more easily than the first embodiment will be described.

The second embodiment (1) selects a DFB semiconductor laser and a Fabry-Perot resonator semiconductor laser as a combination of two semiconductor lasers. (2) Heat sink (or support for subcarrier)
A heat sink (or a support for a subcarrier) having a surface perpendicular to the laser fixing surface is used as the shape. 2 is different from the first embodiment.

First, a method of manufacturing a laser will be described. The first DFB semiconductor laser may have basically the same structure as the first semiconductor laser or the second semiconductor laser of the first embodiment. FIG. 9 is a sectional view showing the oscillation axis of the second Fabry-Perot semiconductor laser, and FIG. 10 is a vertical sectional view thereof. The manufacturing method is, for example, n-type (100) InP.
On the substrate 131, the n-InP clad layer 132, the undoped active layer 133, the n-InGaAsP light guide layer 13 are formed.
4, p-InP clad layer 135 and p-InP contact layer 136 are laminated. The structure of the active layer 133 is the same as that of the first embodiment here.

The lateral mode control is not intentionally performed. For example, only the electrode stripe 139 having a width of 50 μm is formed. As a result, the second semiconductor laser always oscillates in the TE mode, but because of the absence of the grating and the transverse mode control mechanism, unlike the case of the first embodiment, the second Fabry-Perot mode oscillation is always performed.

It is desirable that the end faces of the first and second semiconductor lasers facing each other have a reflectance as low as possible. Therefore, as shown in FIGS. 3 and 9, the AR coat 1
15, 142 are formed on both end faces of the laser. Further, since the widths of the first and second semiconductor lasers are set to be substantially equal to each other and the side surface is brought into contact with the vertical surface of the heat sink 4, it is desirable to provide a surface close to the cleavage, when manufacturing.

Next, a method of mounting the two semiconductor lasers on the support base such as heat sinks and sub-carriers will be described with reference to FIG. 8, a semiconductor laser fixing surface (here, a pattern electrode 6 (only the laser 1 side is shown) is formed on the heat sink 4 and is connected to the electrodes of the semiconductor lasers 1 and 2. (Not shown, but the same is true in FIG. 2)), and a vertical surface 10 is formed, and the semiconductor lasers 1 and 2 are positioned by abutting the side surfaces of the chips against the vertical surface 10.

In the case of the present embodiment, it is not necessary to intentionally perform active alignment (alignment using the method of oscillating and detecting) as in the first embodiment. Sufficient accuracy can be obtained by previously setting markers (not shown) on the heat sink 4 and the laser chips 1 and 2 and performing alignment (passive alignment). That is, in the case of the present embodiment, the alignment of the optical waveguides of the two semiconductor lasers 1 and 2 is performed only with the positional accuracy in the direction perpendicular to the cleavage plane. This is because the semiconductor laser having a wide electrode stripe structure is used as the second semiconductor laser 2 so that the degree of freedom in aligning the optical axis in the lateral direction is increased. If necessary, the same active alignment as in the first embodiment may be partially performed.

Thus, the Fabry-Perot semiconductor laser 2
It is very easy to adjust the optical axis because
This is a major feature of this embodiment.

Next, the driving method will be described. Figure 11
Represents the distribution of oscillation polarization modes when currents are independently applied to the first and second semiconductor lasers 1 and 2. The boundary line A-B indicates that the threshold gains of the TE mode and the TM mode are substantially equal, and if the modulation signal is superposed on this line as a bias point (for example, the point M or the point N), the polarization mode is changed. Switching, so-called polarization modulation, is realized. Compared with the first embodiment, the Fabry-Perot resonator semiconductor laser is used for one of the lasers, and this is a major feature that the bias region capable of polarization modulation is wide. this is,
This means that the control range of light output and oscillation wavelength is wide.
The operation of this embodiment is essentially the same as the operation of the fourth embodiment described later, so please refer to the description thereof.

The advantages of this second embodiment are as follows. (1) For example, a TE mode laser can be a very simple electrode stripe laser and is therefore low in cost. (2) About two types of semiconductor lasers, a plurality of arbitrary L
An appropriate LD can be selected from D. (3) Since the Fabry-Perot resonator semiconductor laser is used for one side, the optical axes of the two semiconductor lasers can be easily aligned. (4) Even if the phases do not match, phase matching is easy by filling the voids with the filler 3 whose refractive index can be controlled. (5) The Fabry-Perot resonator semiconductor laser has a wide operating range of polarization modulation because the operating conditions are not severe.

(Third Embodiment) FIG. 12 is a schematic diagram of the third embodiment. In FIG. 12, 1 is a first semiconductor laser, 2 is a second semiconductor laser, and 3 is a void and / or a filler. FIG. 13 is a sectional view in the direction including the oscillation axes of the first and second semiconductor lasers 1 and 2, and FIG. 14 is a sectional view in the vertical direction thereof.

First, the manufacturing method will be described. Figure 15
Represents the manufacturing process of this embodiment. For example, after slightly forming the n-InP clad layer 161 as a buffer layer on the n-type (100) InP substrate 161, an AND active layer 163a and p-InGaAsP are formed only in the first semiconductor laser region by using the selective mask 174a. The light guide layer 164a is laminated. The growth method at this time is MOCVD.
Method and CBE method are suitable. At this time, abnormal growth easily occurs in the vicinity of the mask edge portion, but this may be left as it is.

Instead of this process, first, the entire surface of the substrate 161 is grown without a selective mask and then the first selective etching is performed.
Areas other than the semiconductor laser area may be removed.

A band diagram of the active layer 163a is shown in FIG. 181 is a tensile strained InGaAs well layer (strain rate of −0.9%, thickness 9 nm), and 182 is a strainless InGaAsP barrier layer (bandgap of 0.99e).
V, thickness 10 nm), and the number of wells was 3. The gain spectrum of the active layer 163a can be predicted from the photoluminescence measurement and the equivalent refractive index. In the case of this embodiment,
The grating pitch is chosen to be 235 nm, as it is predicted that there will be a gain peak near 1.53 μm and the equivalent refractive index in the final device form was calculated to be 3.25. Therefore, a phase shift grating 167a having a pitch of 235 nm and a depth of 50 nm is formed on the light guide layer 164a (see FIG. 15A).

Next, after the selection mask 174a is removed and a new selection mask 174b is formed so as to cover the first semiconductor laser region, the second active layer 163b and the second light guide layer 164b are selectively formed. Grows (see FIG. 15 (b)). In this case as well, abnormal growth easily occurs near the edges, but this may be maintained. The band diagram of the second active layer 163b is the same as that shown in FIG. Similar to the first semiconductor laser region, here, the pitch is 231 nm and the depth is 5
The 0 nm grating 167b is used as the second light guide layer 1
It was formed on 64b (see FIG. 15 (b)).

After removing the selective mask 174b, the p-InP clad layer 165 and the p-InGaA are formed on the entire wafer.
The s contact layer 166 is laminated (FIG. 15C).

The subsequent process is a characteristic part of this embodiment. The abnormal growth portion at the boundary between the two semiconductor laser regions is removed in a slit shape (FIG. 15D). This time,
The depth of the slit was set to reach the n-InP clad layer 162, and the slit pattern was inclined with respect to the waveguide direction as indicated by 3 in FIG. This is to avoid reflection at the voids as much as possible. This step may be performed by the usual MOCVD method and dry etching,
RIBE (Reacti) coupled with CBE device in high vacuum
The reliability is further increased by continuously performing the exposure without exposing to the atmosphere with a ve Ion Beam Etching) device or the like. This step is the same as the next ridge waveguide fabrication step (see FIG.
(See 4)). Further, if the end face of the void portion 3 is AR-coated, the influence of reflection will be further reduced.

Next, a ridge waveguide structure having a width of 2.5 μm was formed for controlling the transverse mode. In FIG. 14, 17
Reference numeral 2 is a ridge type optical waveguide, and 173 is an insulating film such as a SiO ₂ film for preventing a current from flowing other than in the ridge portion. Electrode 16
9a, 169b and 170 are formed, AR coating 171 is applied to both end surfaces, and finally, a filler 1 having a desired refractive index.
This example is completed by filling the voids with 68 (FIG. 1).
5 (e)).

Also in this embodiment, the grating is formed after growing the active layer, which is the same as that described in the first embodiment.

Next, the driving method of this embodiment will be described. As a result of applying the tensile strain multiple quantum structure to the first active layer 163a and setting the Bragg wavelength by the grating 167a in the vicinity of the gain peak wavelength, the TM gain always exceeds the TE gain. It always oscillates in the DFB mode of TM polarization. On the other hand, in the second semiconductor laser 2, the TE gain always exceeds the TM gain, and the Bragg wavelength by the grating 167b is set in the vicinity of the peak wavelength of the TE gain. Therefore, the second semiconductor laser 2 always oscillates in the TE polarization DFB mode. In this embodiment,
Since the first semiconductor laser 1 and the second semiconductor laser 2 use optical waveguides having almost the same structure except for the active layer, the propagation constants of both TE mode and TM mode are set close to each other. Therefore, by controlling the number of carriers injected into the first and second semiconductor lasers, the gratings 167a,
The TE mode and TM mode of the Bragg wavelength of 167b can be set so as to have the lowest threshold gain.

However, for both semiconductor lasers 1 and 2, the other resonator causes the phase to be disturbed, so that it may not be possible to oscillate at the Bragg wavelength unless the phase is adjusted. At this time, the phase 3 of the competing light waves (optical length) is adjusted by filling the gap 3 formed between the two semiconductor lasers 1 and 2 with a filling material 168 such as gel or polymer capable of controlling the refractive index to improve the yield. It becomes possible to apply polarization modulation. Further, instead of gel or polymer, the voids may be filled with liquid crystal to form electrodes, and a voltage may be applied to change the refractive index or the transmittance. this is,
This is the same as the above embodiment. Further, after the void 3 is formed, a semiconductor such as InP is continuously epitaxially grown, then an electrode is formed, and the carrier injection amount can be varied to adjust the phase.

FIG. 7 also shows the distribution of polarization modes when currents (I ₁ and I ₂ , respectively) are independently applied to the first and second semiconductor lasers of this embodiment. The description is as described in the first embodiment.

In the present embodiment, the first and second semiconductor lasers are not formed completely independently but are formed partially in common, and the abnormal growth portion of the boundary portion by the manufacturing method is formed with a slit having a sufficient width. The first is that it has a configuration of removing.
Different from the embodiment. The advantages of this embodiment are summarized as follows according to the difference. (1) Waveguide portion which is the central portion of the semiconductor laser for TE and T
The waveguide portion, which is the central portion of the M semiconductor laser, can be optimized independently. (2) Both have good line width and the like, so that both TE mode light and TM mode light can be used for optical communication. (4) It is easy to adjust the phase even if the phases do not match.

(Fourth Embodiment) Next, an example in which a polarization modulation semiconductor laser is manufactured more easily than in the third embodiment will be described. FIG. 17 is a schematic diagram of the fourth embodiment. This embodiment is largely different from the third embodiment in that one of the two semiconductor lasers has a Fabry-Perot resonator.

FIG. 18 is a schematic diagram for explaining the manufacturing process of the fourth embodiment. For example, on an n-type (100) InP substrate 201, an n-InP clad layer 202, an undoped active layer 203, a p-InGaAsP optical guide layer 204.
Are stacked. The growth method at this time is MOCVD or CBE.
The law is appropriate.

A band diagram of the active layer 203 is shown in FIG.
9 shows. 221 is a tensile strained InGaAs first well layer (strain rate: −0.9%, thickness: 9 nm), and 222 is a non-strained InGaAsP barrier layer (bandgap: 0.99e).
V, thickness 10 nm), 223 is a strain-free InGaAsP second well layer (bandgap 0.75 eV, thickness 10 n)
m).

Using the selective mask 214, only the light guide layer 204 in the first semiconductor laser region has a pitch 235n.
A phase shift grating 207 having an m and a depth of 50 nm was formed (see FIG. 18A). In the case of this embodiment, 1.
The grating pitch was selected to be 235 nm because it was predicted that there was a TM mode gain peak near 53 μm and the equivalent refractive index in the final device form was predicted to be 3.25. Next, the selection mask 214 is removed (see FIG.
(B)), p-InP clad layer 20 over the entire wafer surface
5 and the p-InGaAs contact layer 206 are laminated (FIG. 18C).

The subsequent process is a characteristic part of this embodiment. A boundary portion between the two semiconductor laser regions is removed in a slit shape (FIG. 18D). At this time, the depth of the slit is set to reach the n-Inp cladding layer 202, and the gap pattern 3 is set to the first semiconductor laser 1 as shown in FIG.
The end face side of the second semiconductor laser 2 is oblique to the waveguide direction, and the second semiconductor laser 2 side is perpendicular to the waveguide direction. This is for the first DFB semiconductor laser 1 to avoid reflection at the air gap as much as possible, and for the Fabry-Perot resonator to be formed in the second Fabry-Perot semiconductor laser region. This step may be performed by the usual MOCVD method and dry etching, but C
By performing the BE and RIBE devices continuously in a high-vacuum combined process device without exposing them to the atmosphere,
The reliability is further increased. Here, the substance 2 that fills the voids
When InP or the like is selected as 08, epitaxial selective growth may be continued (FIG. 18E). InP
It is also possible to adjust the phase by epitaxially growing a semiconductor such as the above and then forming an electrode and varying the carrier injection amount.

Next, a ridge structure having a width of 2.5 μm was formed for controlling the transverse mode. This step is exactly the same as in the third embodiment (see FIG. 14). Also, 219a and 219
Reference numeral b denotes a positive electrode on the substrate surface side of the first and second semiconductor lasers 1 and 2, and 220 denotes a negative electrode. Electrodes 219 and 22
This example is completed by forming 0 and filling the filling material 208 having a desired refractive index (FIG. 18E).

Next, the driving method will be described. Figure 20
Shows the injection carrier density dependence of the gain spectrum of the active layer 203 having an asymmetric double well structure including two different well layers. In FIG. 20A, when the injection density is low, the filling efficiency of the first tensile strained quantum well layer 221 on the n-side is high, so that e-lh transition (transition between light holes and electrons) is dominant. The TM mode gain always exceeds the TE mode gain. Therefore, the T of the grating 207 of the first DFB semiconductor laser is near the peak wavelength of the TM gain.
It has set the Bragg wavelength λ ^TM _B of M-mode, and,
If the entire resonator loss is controlled so that the threshold gain is obtained at that wavelength, the TM polarization always oscillates in the DFB mode (in FIG. 20, λ ^TM _B and λ ^TE _B are the TM mode and the T mode, respectively).
The Bragg wavelength of E mode is shown).

On the other hand, in FIG. 20B, when the injection current is high, the carrier filling efficiency of the second unstrained quantum well 223 on the p-side is high, so that the e-hh transition (transition between heavy holes and electrons). ) Becomes dominant, and TE mode gain always exceeds TM gain. Here, if the pitch of the grating 207 and the resonator loss are controlled as described above, it is possible to oscillate in the DFB mode of TE polarization. However, tuning two sets of gain spectrum and Bragg wavelength at the same time (that is, at this time, having the TE mode Bragg wavelength λ ^TE _B of the grating 207 of the first DFB semiconductor laser in the vicinity of the peak wavelength of TE gain). Coming) requires high precision design technology and manufacturing technology. In this embodiment, this problem is solved by using a Fabry-Perot resonator for the second semiconductor laser 2. As a result, when a certain carrier density is reached, oscillation occurs in any Fabry-Perot mode. At this time, since the TE mode does not control the wavelength, it oscillates in several multi-axis modes as shown in FIG. Even in such a case, when it is used for communication, it is sufficient if at least either TE or TM can be used, so there is no problem.

However, for both semiconductor lasers, the other resonator causes the phase to be disturbed, so it may not be possible to oscillate at the Bragg wavelength unless the phase is adjusted. At this time, the phase (optical length) of competing light waves is obtained by filling a void 208 formed between the two semiconductor lasers 1 and 2 with a filler 208 such as gel or polymer whose refractive index can be controlled.
It is possible to adjust the polarization ratio and apply polarization modulation with good yield.

In this embodiment, the same active layer 203 is used for the first and second semiconductor lasers 1 and 2, but this is to simplify the manufacturing method. As in the third embodiment, active layers are separately stacked, one of which is a DFB resonator,
The other may be a Fabry-Perot resonator. Although this method makes the manufacturing method a little complicated, it has an advantage that the operation range in which polarization modulation is possible is further widened as compared with the fourth embodiment.

The advantages of this embodiment are as follows. (1) Since the active layer is manufactured at once, the manufacturing is easy. (2) Since one of the semiconductor lasers may be a very simple electrode stripe laser having no grating, it is easy to manufacture. (3) Phase matching is easy even if the phases may not match. (4) The polarization modulation operation range is wide.

(Fifth Embodiment) Next, a multi-wavelength polarization modulation semiconductor laser array according to a fifth embodiment, in which the oscillation wavelengths of the respective semiconductor lasers are different, will be described. FIG. 21 is a plan view thereof. In FIG. 21, 301 is a TM mode semiconductor laser array, 302 is a TE mode semiconductor laser array,
Reference numeral 303 denotes a DBR region of each laser of the TM mode semiconductor laser array 301, 304 denotes a TM gain region of each laser of the TM mode semiconductor laser array 301, and 305 a TE gain region.
The TE gain region, 306, of each laser of the mode semiconductor laser array 302 is an air gap and / or a filling material.

The design guidelines for this example are as follows. (1) The first semiconductor laser array 301 has a common active layer in which TM gain is dominant and a distributed Bragg reflector (DBR) having different Bragg wavelengths. (2) The second semiconductor laser array 302 has a common active layer in which TE gain is dominant and a Fabry-Perot resonator. (3) The threshold gain (resonator loss) of each laser of the first semiconductor laser array 301 is set to the active region 304 and the DBR.
Adjustment is performed by changing the size of the area 303. (4) The individual lasers of the second semiconductor laser array have the same structure and a common threshold gain.

First, a method of manufacturing the first semiconductor laser array 302 will be described. FIG. 22 is a cross-sectional view of the first semiconductor laser array 301 in the direction including the oscillation axis. The vertical sectional view is almost the same as that of the third embodiment (FIG. 14).
reference).

Since this manufacturing method is similar to that of the third embodiment, it will be described with reference to FIG. For example, n-type (100)
After stacking the n-InP cladding layer 312 on the InP substrate 311, an undoped active layer 313a and a p-InGaAsP optical guide are formed only in the first semiconductor laser region using a selective mask (corresponding to 174a in FIG. 15). Layer 31
4a is laminated. The growth method at this time is MOCVD or C
The BE method or the like is suitable. At this time, abnormal growth easily occurs in the vicinity of the mask edge portion, but this may be left as it is. Active layer 313
The band diagram of a is shown in FIG. 371 is
Tensile strain InGaAs first well layer (strain rate -0.9
%, Thickness 9 nm), 372 is an unstrained InGaAsP barrier layer (band gap 0.99 eV, thickness 10 nm), 3
73 is the tensile strained InGaAsP second well layer (strain rate-
0.7%, band gap 0.8 eV, thickness 10 n
m)).

Only in the DBR region on the light guide layer 314a, 10 grating (depth 50 nm) regions 317 are pitched from 325 nm to 0.4 nm in the lateral direction (vertical direction in FIG. 21) at 100 μm intervals. Formed. In FIG. 15A, the grating is formed on the entire surface of the optical guide layer 164a, but in the present embodiment, the grating is not formed in the TM gain region. This DBR
The lengths of the region and the TM gain region in the resonance direction gradually differ on the array as shown in FIG. This is because, as will be described later, there is a difference in the threshold gain of each semiconductor laser.

Next, the selection mask is removed, and a new selection mask (corresponding to 174b in FIG. 15) is formed so as to cover the first semiconductor laser region, and then n is slightly formed as a buffer layer. A second active layer 313b and a second light guide layer 314 on the InP clad layer 312.
b is selectively grown. In this case as well, abnormal growth easily occurs near the edges, but this may be maintained. Second active layer 313b
It is desirable that the structure (1) has a large TE gain and a flat gain spectrum. Here, an undoped InGaAsP layer (wavelength 1.53 μm, thickness 500 nm) was used.

After removing the selective mask (corresponding to 174b in FIG. 15), the p-InP cladding layer 315 and the p-InGaAs contact layer 316 are laminated on the entire wafer.

The subsequent steps are also characteristic parts of this embodiment. The boundary portion between the two semiconductor laser array regions is removed in a slit shape (see FIG. 15D). At this time, the depth is set to reach the n-InP cladding layer 312, and the gap pattern is set so that the end face side of the first semiconductor laser array 301 is inclined with respect to the waveguide direction. The end face side of is perpendicular to the waveguiding direction (in FIG. 21, this oblique end face is drawn straight). This is for the first semiconductor laser array to avoid reflection at the void portion 318 as much as possible, and for the Fabry-Perot resonator to be formed in the second semiconductor laser array region. This step may be performed by the usual MOCVD method and dry etching, but the reliability can be further improved by performing it continuously without exposing it to the atmosphere by a composite process apparatus in which the CBE apparatus and the RIBE apparatus are coupled in high vacuum. Increase.

As shown in FIG. 21, the transverse mode waveguide is 10
A plurality of ridge waveguides each having a width of 10 μm were formed in the TM semiconductor laser array region 301 at a pitch of 0 μm. The second semiconductor laser arrays 302 all have an electrode stripe structure with a width of 10 μm in order to have the same threshold gain. Finally, electrodes 319a to 319d and 320 are provided so that carriers can be independently injected into the DBR region, the TM gain region, the phase adjustment region and the TE gain region.
Reference numeral 321 is an AR film provided on the end surface of the DBR laser.

As a result of using the asymmetric strained quantum well structure for the active layer 313a, the gain spectrum thereof is significantly different from that of the normal strainless multi-weight well active layer. First, by introducing tensile strain in the two well layers 371 and 373, transition between electrons and light holes (e-lh) becomes dominant, and the TM mode gain always gives the TE mode gain at the peak wavelength. Surpass. Secondly, since the well layer thickness and composition are asymmetrical, the ground level is different for each well layer, and the gain spectrum changes greatly depending on the carrier injection amount. FIG. 24 schematically shows a typical TM mode gain spectrum of the semiconductor laser array of the present embodiment with the injected carrier density as a parameter. The peak size increases as the carrier injection amount increases, and the peak position shifts to the shorter wavelength side. Therefore, it is necessary to set the Bragg wavelength of each semiconductor laser (by setting the period of the grating 317 or the like) at the positions of arrows (λ ₁ , λ ₂ , λ ₃ ...) In FIG. 24 to control the magnitude of loss. Thus, it is possible to obtain the semiconductor laser array 301 having different wavelengths, high wavelength stability, and constantly oscillating in the TM mode. As the method of controlling the loss, in the present embodiment, a method of decreasing the gain region as the threshold gain is larger was used (FIG. 21).
reference). Although this embodiment is not a pure frame DBR laser because it includes the active layer 313a in the DBR region, both wavelength and threshold gain can be controlled by controlling the amount of current in the gain region and the DBR region. In this embodiment, this structure is adopted because of ease of fabrication, but it is of course possible to use a normal DBR laser having a DBR region without gain.

On the other hand, the TE mode semiconductor laser array 3
No. 02 uses the Fabry-Perot resonator and the bulk active layer 313b having a wide gain spectrum, so that it oscillates in the Fabry-Perot mode and in the multimode. Therefore, unless the wavelength range of the TM mode DBR laser array is extremely wide, the TM of each TM mode DBR laser is always
It is possible to oscillate in a Fabry-Perot mode with TE polarization equal to the threshold gain of the mode. The conditions therefor are milder than in the case of the first embodiment. This means that the operation area in which polarization modulation is possible becomes wider.
When the wavelength range of the TM mode DBR laser array 301 is wide, it can be dealt with by applying an asymmetric compression strain quantum well structure or the like to the active layer of the TE mode Fabry-Perot semiconductor laser array 302.

However, for both semiconductor lasers, since the other resonator causes the phase to be disturbed, it may not be possible to oscillate at the Bragg wavelength unless the phase is adjusted. At this time, the phase (optical length) of competing light waves is adjusted by filling a gap 318 formed between the two semiconductor lasers with a filler such as gel or polymer capable of controlling the refractive index, and polarization modulation is performed with good yield. It becomes possible to call.
Further, as described in the above embodiment, it is possible to change the refractive index or the transmittance by applying a voltage by filling an electrode with a liquid crystal in a space instead of the gel or the polymer. Furthermore, after forming this void, a semiconductor such as InP is continuously epitaxially grown, and then an electrode is formed.
It is also possible to adjust the phase by changing the carrier injection amount.

The advantages of this embodiment are as follows. (1) A semiconductor laser array capable of multi-wavelength polarization modulation can be easily realized. (2) For example, a TE mode laser is low in cost because a very simple electrode stripe laser array may be used. (3) Phase control is easy even if the phases may not match. (4) The operating range in which polarization modulation is possible is wide.

(Sixth Embodiment) FIG. 25 shows an embodiment in which the semiconductor laser of the present invention is applied to an optical transmitter for optical communication. In FIG. 25, 331 is a control circuit, 332 is the semiconductor laser of the present invention shown in the above embodiment, 333 is a polarizer, and 33
Reference numeral 4 is an optical coupling means for coupling the light propagating in the space to an optical fiber, 335 is an optical fiber, 336 is an electric signal sent from a terminal, 337 is a control circuit 331, and a semiconductor laser 332 is driven. Drive signal sent for, 3
38 is an optical signal output by driving the semiconductor laser 332 according to the drive signal 337, and the 339 is adjusted so as to extract only one of two orthogonal polarization states of the optical signal 338. The optical signal that has passed through the polarizer 333,
340 is an optical signal transmitted through the optical fiber 335,
1 is an optical transmitter using the semiconductor laser 332 of the present invention. In this embodiment, the optical transmitter 341 has a control circuit 33.
1, semiconductor laser 332, polarizer 333, optical coupling means 3
34, an optical fiber 335, and the like.

Next, the transmission operation of the optical transmitter 341 of this embodiment will be described. When the electric signal 336 from the end is input to the control circuit 331, the semiconductor laser 33 of the present invention
The drive signal 337 is sent to the No. 2. The semiconductor laser 332, to which the drive signal 337 is input, outputs an optical signal 338 whose polarization state changes according to the drive signal 337. The optical signal 338 is the optical signal 339 of one polarization in the polarizer 333.
And further coupled to the optical fiber 335 by the optical coupling means 334. In this way, the intensity-modulated optical signal 340 is transmitted for communication. In this case, since the optical signal 340 is in the intensity-modulated state, light can be received by the conventionally used intensity-modulation optical receiver. Further, if the semiconductor laser used in the present invention has a variable wavelength, it can be used as a transmitter for wavelength division multiplexing communication.

(Seventh Embodiment) FIG. 26 shows an example in which the fifth embodiment of the present invention is applied to an optical transmitter. The major difference from the sixth embodiment is that the wavelengths of the semiconductor lasers forming the semiconductor laser array are different, so that the wavelength division multiplexing is used for transmission. The other functions are the same as in the sixth embodiment. In FIG. 26, reference numeral 332 denotes a semiconductor laser array of the present invention (fifth embodiment), and the individual semiconductor lasers have different oscillation wavelengths. Polarizers do not need to be individually attached because the planes of polarization are aligned. Also, the optical coupling means 334
Can be easily constructed by using a waveguide type junction.

(Eighth Embodiment) Next, an example in which the device of the present invention is applied to an optical network will be described. 27 and 28 show an example of application to a bus type optical network and a ring type optical network, in which optical nodes 401 to 406 are equipped with an optical transmitter including the above embodiment and an appropriate receiver. By disposing a polarizer on the emission surface of the semiconductor laser described in the above embodiment, only specific polarized light (for example, TM light) can be taken out and sent to the transmission line 400. Further, if two light receivers are arranged, the signal light is branched and made incident on each, and one is received in the TE mode and the other is received in the TM mode, polarization diversity can be easily realized. 411-
Reference numeral 416 is a terminal device.

When the semiconductor laser of the above embodiment is used, lights of different polarizations can be sent out at the same time without using a polarizer, so that the network can be made multifunctional. For example, in a wavelength multiplexing system using a wavelength tunable laser and a wavelength tunable filter, the wavelength tunable filter can be used as a light source for polarization diversity with a very simple structure by providing polarization dependency.

The above description has been made in the 1.15 μm band,
The same holds true for other wavelength bands and material systems. In the present embodiment, the case where it is configured as an optical transmitter is shown, but of course it can also be used in the transmitting part in an optical transceiver. Furthermore,
The applicable optical communication system is not limited to simple two-point optical communication as long as it is a system that handles intensity-modulated signals.
It can also be applied to TVs, optical LANs, etc.

(Ninth Embodiment) An example in which this embodiment is used for the transmission part in an optical transceiver will be described with reference to FIG. An optical signal is taken into the node 701 using the optical fiber 700 connected to the outside as a medium, and a part of the optical signal is incident on the receiving device 703 including a wavelength tunable optical filter and the like by the branching unit 702. This receiver 703 extracts only an optical signal of a desired wavelength and performs signal detection. This is processed by a control circuit by an appropriate method and sent to the terminal. On the other hand, in the case of transmitting an optical signal from the node 701, the polarization modulation semiconductor laser 704 of the above-mentioned embodiment is driven by the control circuit according to the signal by an appropriate method as described above, polarization-modulated, and the polarization plate 707 ( As a result, the polarized light modulation signal is converted into an amplitude intensity modulation signal), and the output light (which may further include an isolator) is made incident on the optical transmission line 700 via the merging unit 706. Also,
It is possible to widen the wavelength variable range by providing two or more semiconductor lasers and a plurality of wavelength tunable optical filters.

[0118]

The present invention has the following effects. (1) Since the TE mode semiconductor laser structure and the TM mode semiconductor laser structure can be designed substantially independently of each other, the device can be easily optimized. (2) Since the burden on the process is reduced, the yield is improved. (3) Antireflection, coupling efficiency and phase can be easily adjusted by using the air gap formed between the TE mode semiconductor laser structure and the TM mode semiconductor laser structure. (4) When one semiconductor laser structure is actively operated and the other laser structure is aligned, the mounting operation can be performed by checking the optical coupling state of both semiconductor laser structures. Positioning of the two semiconductor laser structures can be stably performed for each operation with high accuracy.
At this time, if one semiconductor laser structure is a wide stripe electrode type Fabry-Perot semiconductor laser structure, the alignment becomes easier. (5) When positioning is performed using the structure of the member on which the two semiconductor laser structures are mounted, it is not necessary to drive the semiconductor laser structure, and the two semiconductor laser structures can be more easily aligned. Becomes (6) When the TE / TM mode boundary, that is, the refractive index of the material filled between the end faces of the two semiconductor laser structures can be electrically controlled, the coupling of both modes can be actively controlled. . Therefore, it is possible to switch the polarization mode by this electrical control.

Furthermore, the polarization modulation operation range is wide, the phase matching is easy even if the phases are out of phase, the yield is high even if selective regrowth is used, and the multi-wavelength polarization modulation laser array is easy. The effect that it can be manufactured is also exhibited.

Also, by selecting one polarization mode of the polarization-modulated light output with a polarizer or the like, it is possible to easily obtain an intensity-modulated light output with a high extinction ratio. There is also an effect that the child can be used as a part of the isolator and the configuration can be facilitated. Further, in the optical transmission system or wavelength multiplexing system including a transmitter or a transmitter / receiver using the semiconductor laser of the present invention, an optical transmission system capable of high-speed large-capacity or ultra-high-density wavelength multiplexing is constructed at a relatively low price There is also an effect that you can.

[Brief description of drawings]

FIG. 1 is a diagram for explaining the principle of the present invention as a typical example.

FIG. 2 is a perspective view for explaining the first embodiment of the present invention.

FIG. 3 is a sectional view in the resonance direction of the semiconductor laser structure for explaining the first embodiment of the present invention.

FIG. 4 is a sectional view of a semiconductor laser structure in a direction perpendicular to a resonance direction for explaining a first embodiment of the present invention.

FIG. 5 is a diagram illustrating a bandgap structure of one active layer according to the first embodiment of the present invention.

FIG. 6 is a diagram illustrating a bandgap structure of the other active layer according to the first embodiment of the present invention.

FIG. 7 is a diagram showing a relationship between a current injection amount and a polarization mode into two semiconductor laser structures.

FIG. 8 is a perspective view for explaining a second embodiment of the present invention.

FIG. 9 is a cross-sectional view in the resonance direction of a Fabry-Perot type semiconductor laser structure for explaining a second embodiment of the present invention.

FIG. 10 is a sectional view of a Fabry-Perot type semiconductor laser structure for explaining a second embodiment of the present invention in a direction perpendicular to the resonance direction.

FIG. 11 is a diagram showing a relationship between a current injection amount and a polarization mode into two semiconductor laser structures.

FIG. 12 is a perspective view for explaining a third embodiment of the present invention.

FIG. 13 is a sectional view in the resonance direction of a polarization modulation semiconductor laser for explaining a third embodiment of the present invention.

FIG. 14 is a sectional view of a polarization modulation semiconductor laser in a direction perpendicular to a resonance direction for explaining a third embodiment of the present invention.

FIG. 15 is a diagram illustrating a manufacturing method according to the third embodiment of the present invention.

FIG. 16 is a diagram illustrating a bandgap structure of one active layer according to the third embodiment of the present invention.

FIG. 17 is a perspective view for explaining a fourth embodiment of the present invention.

FIG. 18 is a diagram illustrating a manufacturing method according to the fourth embodiment of the present invention.

FIG. 19 is a diagram illustrating a bandgap structure of a common active layer according to a fourth embodiment of the present invention.

FIG. 20 is a diagram for explaining the operation of the fourth embodiment of the present invention (shown in (a) when the current injection amount is small, and in (b) when the current injection amount is large). It is a figure which shows the mode of change of the gain profile of a polarization mode.

FIG. 21 is a plan view for explaining a semiconductor laser array according to a fifth embodiment of the present invention.

FIG. 22 is a sectional view in the resonance direction of a polarization modulation semiconductor laser for explaining a fifth embodiment of the present invention.

FIG. 23 is a diagram for explaining the bandgap structure of one active layer of the fifth embodiment of the present invention.

FIG. 24 is a diagram showing how the gain profile of one active layer changes to explain the operation of the fifth embodiment of the present invention.

FIG. 25 is a schematic diagram showing a configuration example of a transmitter in the system of FIGS. 27 and 28.

FIG. 26 is a schematic diagram showing a configuration example of a transmitter using the polarization modulation semiconductor laser array of the present invention in the system of FIGS. 27 and 28.

FIG. 27 is a schematic diagram showing a configuration example of a bus type optical LAN system using the semiconductor device of the present invention.

FIG. 28 is a schematic diagram showing a configuration example of a loop type optical LAN system using the semiconductor device of the present invention.

FIG. 29 is a schematic diagram showing a configuration example of a transceiver in the system of FIGS. 27 and 28.

FIG. 30 is a cross-sectional view in a resonance direction for explaining a conventional example.

[Explanation of symbols]

1 1st semiconductor laser structure 2 2nd semiconductor laser structure 3, 168, 208, 306, 318 void | gap (gap) and / or filler 4 heat sink (support) 5 marker 6 pattern electrode 7 1st resonator 8 Second resonator 9 Third resonator 10 Support base vertical surfaces 101, 131, 161, 201, 311 Substrate 102, 105, 132, 135, 162, 165, 2
02, 205, 312, 315 Cladding layers 103, 133, 163a, 163b, 203, 313
a, 313b active layers 104, 134, 164a, 164b, 204, 314
a, 314b Optical guide layer (waveguide layer) 106, 136, 166, 206, 316 Cap layer 108, 167a, 167b, 207, 317
Diffraction gratings 109, 110, 139, 140, 169, 170, 2
19, 220, 319, 320 Metal electrodes 111, 172 Ridge waveguides 112, 173 Insulating films 115, 142, 171, 321 AR coats 121, 124, 181, 221, 223, 371, 3
73 well layers 122, 123, 182, 222, 372 barrier layers 174a, 174b, 214 selection mask 301 TM semiconductor laser array 302 TE laser array 303 DBR region 304 TM gain region 305 TE gain region 331 control circuit 332 polarization of the present invention Modulation semiconductor lasers 333 and 707 Polarizer (polarization selecting means) 334 Optical coupling means 335 and 400 Optical fiber (optical transmission line) 341 Optical transmitters 401 to 406 and 701 Nodes 411 to 416 Terminal device 702 Optical branching unit 703 Receiver 706 Junction

─────────────────────────────────────────────────── --- Continuation of the front page (56) Reference JP-A-6-265958 (JP, A) JP-A-7-45860 (JP, A) JP-A-7-231133 (JP, A) JP-A-8- 172245 (JP, A) JP 7-264138 (JP, A) JP 7-307530 (JP, A) JP 8-186315 (JP, A) JP 63-299291 (JP, A) JP-A-6-61571 (JP, A) JP-A-58-196088 (JP, A) JP-A-8-107249 (JP, A) JP-A-7-202342 (JP, A) JP-A-7-235718 (JP, A) Journal of Apply d Physics, 1988, 63 [2], p. 291-294 (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01S 5/00-5/50 H04B 10/02 H04B 10/28

Claims (30)

(57) [Claims] 1. A compound resonator type semiconductor laser in which two different semiconductor laser structures having both the first and second polarization modes and at least an active layer and a waveguide layer are arranged in series in the waveguide direction. The first semiconductor laser structure has an active region in which the gain for the first polarization mode is superior to the gain for the second polarization mode and the distributed feedback resonator or the distributed Bragg reflection resonator. An active region in which the gain of the second semiconductor laser structure for the second polarization mode is superior to that of the first polarization mode, and the distributed feedback resonator, distributed Bragg reflection resonator, or Fabry-Perot resonator The first semiconductor laser structure and the second semiconductor laser structure are configured such that the propagation constants of the first polarization modes and the propagation constants of the second polarization modes are substantially equal to each other. First The semiconductor laser structure and the second semiconductor laser structure are arranged with a gap in the waveguide direction, and the Bragg wavelength of the distributed feedback resonator or distributed Bragg reflection resonator is the peak of the gain spectrum of the semiconductor laser structure. The oscillation mode is set between the first polarization mode and the second polarization mode by modulating the carrier injected into at least one of the first and second semiconductor laser structures, which is set near the wavelength. A semiconductor laser capable of polarization modulation, which is characterized in that the laser is switched. 2. The first and second semiconductor laser structures,
2. The polarized wave according to claim 1, wherein the substrate and the laminated structure on the substrate are independently formed, and are arranged on the support base with a gap in the waveguide direction. Modulatable semiconductor laser. 3. The first and second semiconductor laser structures,
A structure in which at least an active layer and a waveguide layer are formed separately on the same substrate, and the laminated structure on the same substrate is arranged with a gap in the waveguide direction. Item 2. A semiconductor laser capable of polarization modulation according to Item 1. 4. The polarized wave according to claim 1, 2 or 3, wherein a filler is filled in a gap between the first and second semiconductor laser structures to form a phase adjustment region. Modulatable semiconductor laser. 5. The substance filled in the gap is a material capable of electrically controlling the refractive index, and an optical length modulation means for modulating the optical length of the phase adjusting region is provided. A semiconductor laser capable of polarization modulation according to claim 4. 6. The polarization-modulatable semiconductor according to claim 1, wherein the second semiconductor laser structure has a distributed feedback resonator or a distributed Bragg reflection resonator. laser. 7. The polarization modulation according to claim 6, wherein end faces of the first and second semiconductor laser structures, which face each other with a gap, are formed obliquely with respect to the waveguide direction. Possible semiconductor laser. 8. The second semiconductor laser structure includes a Fabry-Perot type resonator.
A semiconductor laser capable of polarization modulation according to any one of 1. 9. The end face of the first semiconductor laser structure among the end faces facing each other with a gap between the first and second semiconductor laser structures is formed obliquely to the waveguide direction. The polarization-modulatable semiconductor laser according to claim 8. 10. The AR coating is applied to the end faces of the first and second semiconductor laser structures, which face each other so as to be non-reflecting, as claimed in any one of claims 1 to 9. A semiconductor laser capable of polarization modulation. 11. The active layer of at least one of the first and second semiconductor laser structures has a quantum well structure or a strained quantum well structure, according to any one of claims 1 to 10. A semiconductor laser capable of polarization modulation according to the description. 12. A composite resonator type semiconductor laser array in which two different semiconductor laser arrays having both the first and second polarization modes are arranged in series in the waveguide direction, and a plurality of first semiconductors are provided. A first semiconductor laser array having a laser structure is formed by arranging a plurality of the first semiconductor laser structures on the same substrate in parallel with a waveguide direction, and a gain peak for a first polarization mode is a carrier injection amount. Each of the first semiconductor laser structures including a common active region that can be tuned by means of a distributed feedback reflector or distributed Bragg reflector with a Bragg wavelength set near the different gain peak is provided. And the second semiconductor laser array including the same number of second semiconductor laser structures as the first semiconductor laser structure includes the second semiconductor laser array.
A semiconductor laser structure is arranged in the same manner as the first semiconductor laser structure, and includes a common active region in which the gain for the second polarization mode is superior to the gain for the first polarization mode. A Fabry-Perot resonator is provided to the second semiconductor laser structure, and the first semiconductor laser structure and the second semiconductor laser structure forming a pair respectively have first polarization modes and second polarization modes. Of the polarization modes are substantially equal to each other, and the first semiconductor laser array and the second semiconductor laser array are arranged with a gap in the waveguide direction. Polarization characterized by switching the oscillation mode between the first polarization mode and the second polarization mode by modulating a carrier injected into at least one of the second semiconductor laser structures. Tone can be a semiconductor laser array. 13. The polarization-modulatable semiconductor laser according to claim 12, wherein a filler is filled in a gap between the first and second semiconductor laser arrays to form a phase adjustment region. array. 14. The substance filled in the gap is a material capable of electrically controlling the refractive index, and an optical length modulating means for modulating the optical length of the phase adjusting region is provided. 14. A semiconductor laser array capable of polarization modulation according to claim 13. 15. A method for producing a semiconductor laser according to claim 1, wherein a step of producing a first semiconductor laser structure and a step of producing a second semiconductor laser structure are performed independently of this step. And a step of arranging the first and second semiconductor laser structures in series in the waveguide direction with a gap on the same support so as to optically couple them, and the polarization modulation method. Manufacturing method of possible semiconductor laser. 16. The step of arranging the first and second semiconductor laser structures in series in the waveguide direction with a gap on the same support so as to optically couple the first and second semiconductor laser structures with each other. After the second semiconductor laser structure is placed on the support and fixed, the second semiconductor laser structure emits light and the first
The second semiconductor laser structure is made to function as a photodetector to receive the light of the second semiconductor laser structure.
16. The method for manufacturing a polarization-modulatable semiconductor laser according to claim 15, further comprising the step of positioning and fixing the semiconductor laser structure. 17. A step of arranging the first and second semiconductor laser structures in series in the waveguide direction on the same support base with a gap therebetween so as to optically couple the first and second semiconductor laser structures is formed on the support base. 17. The polarization-modulatable semiconductor according to claim 15, further comprising the step of adjusting the marker and the marker formed on the semiconductor laser structure to a desired positional relationship and disposing and fixing the semiconductor laser structure. Laser manufacturing method. 18. The step of arranging the first and second semiconductor laser structures in series in the waveguide direction with a gap on the same support so as to optically couple the semiconductor laser structures, and the semiconductor formed on the support. The polarization-modulatable semiconductor laser according to claim 15 or 16, further comprising a step of arranging the semiconductor laser structure by abutting a side surface of the semiconductor laser structure on a plane that is upright to be perpendicular to the laser mounting surface. Production method. 19. The method according to claim 15, further comprising the step of filling the gap with a substance having a desired refractive index.
19. A method for manufacturing a semiconductor laser capable of polarization modulation according to any one of 18 to 18. 20. A method of manufacturing a semiconductor laser according to claim 1 or 3, wherein a step of forming a first semiconductor laser structure on a semiconductor substrate, and a second semiconductor laser structure on the substrate. A method of manufacturing a polarization-modulatable semiconductor laser, comprising: a step of manufacturing the semiconductor laser structure; and a step of forming a gap at a boundary portion between the first and second semiconductor laser structures. 21. A step of fabricating the first semiconductor laser structure includes a step of laminating a first active layer and a first optical waveguide layer only on a region of the first semiconductor laser structure on the semiconductor substrate. Forming a first grating in the first optical waveguide layer, the pitch of which is controlled so as to have a Bragg wavelength near the gain peak of the first active layer, and the second semiconductor A step of producing a laser structure, a step of laminating a second active layer and a second optical waveguide layer only on a region of the second semiconductor laser structure on the semiconductor substrate; and a step of laminating the second optical waveguide layer on the second optical waveguide layer. Forming a second grating whose pitch is controlled so as to have a Bragg wavelength near the gain peak of the second active layer, and further producing the first semiconductor laser structure and the second semiconductor laser structure. For manufacturing the semiconductor laser structure of A step of collectively laminating a common clad layer and a contact layer on the first optical waveguide layer on which the first grating is formed and the second optical waveguide layer on which the second grating is formed. 21. The method of manufacturing a semiconductor laser capable of polarization modulation according to claim 20, further comprising: 22. In both the step of forming the first semiconductor laser structure and the step of forming the second semiconductor laser structure, a first cladding layer, an active layer, and an optical waveguide layer are formed on the entire surface of the semiconductor substrate. The step of laminating, and the Bragg wavelength in the vicinity of the gain peak of the active layer is provided only on the optical waveguide layer in the region of the first semiconductor laser structure while leaving the optical waveguide layer in the region of the second semiconductor laser structure as it is. 21. The method according to claim 20, further comprising: a step of forming a grating having a controlled pitch, and a step of collectively laminating a common second cladding layer and a contact layer over the entire surface of the optical waveguide layer. Of manufacturing a semiconductor laser capable of polarization modulation of. 23. The step of forming a gap at the boundary between the first and second semiconductor laser structures comprises forming a slit-like gap and a ridge waveguide at the boundary between the regions of the first and second semiconductor laser structures. 23. The method for manufacturing a polarization-modulatable semiconductor laser according to claim 20, 21 or 22, further comprising the step of forming simultaneously. 24. The method according to claim 20, further comprising the step of filling the gap with a substance having a desired refractive index.
24. A method for manufacturing a semiconductor laser capable of polarization modulation according to any one of 23 to 23. 25. A polarization modulation semiconductor laser or array according to any one of claims 1 to 14, polarization selection means for transmitting light of one polarization of output light from said semiconductor laser or array, and said semiconductor. An optical transmitter having a control circuit for controlling and driving the semiconductor laser for switching the polarization state of output light of a laser or an array according to an input signal. 26. A polarization modulation semiconductor laser or array according to any one of claims 1 to 14, and polarization selection means for transmitting light of one polarization of the output light from the semiconductor laser or array. An optical transceiver comprising a control circuit for controlling and driving the semiconductor laser or array for switching the polarization state of the output light of the semiconductor laser or array according to an input signal, and a receiving means for receiving the input signal. . 27. A polarization-modulating semiconductor laser or array according to any one of claims 1 to 14, and 2 of TE and TM of light emitted from the polarization-modulating semiconductor laser or array.
2. A light source device, comprising: a polarization selecting means for extracting only one light of one polarization mode. 28. The polarization modulation semiconductor laser or array according to any one of claims 1 to 14, and 2 of TE and TM among the light emitted from the polarization modulation semiconductor laser or array.
An optical transmitter or a transceiver provided with a light source device comprising a polarization selecting means for extracting only one light of one polarization mode, a transmitting means for transmitting the light extracted by the polarization selecting means, and the transmitting means. An optical communication system comprising an optical receiver or a transceiver for receiving transmitted light. 29. An optical communication system according to claim 28, wherein said optical transmitter or transceiver is capable of transmitting optical signals of a plurality of different wavelengths to form a wavelength division multiplexing network. 30. A polarization-modulating semiconductor laser or array according to claim 1, and two of TE and TM among the light emitted from the polarization-modulating semiconductor laser or array.
Using a light source device composed of a polarization selecting means for extracting only one light of one polarization mode, a current biased according to a transmission signal is superimposed on a predetermined bias current and supplied to the polarization modulation semiconductor laser or array. By doing so, the signal light whose intensity is modulated according to the transmission signal is taken out from the polarization selecting means, and the signal light is transmitted toward the light receiving side.