JP3535669B2 - Semiconductor laser array 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 array 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 is a semiconductor laser device disclosed in Japanese Patent No. 68111. 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 having a specific polarization state (TE or TM polarization), and the other mainly of another polarization state ( TM or TE polarized light)
Generate or amplify the wave. 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.

[0004]

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 of 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 using MOCVD or the like can be considered, but it is very difficult to optimize each semiconductor laser independently. (3) The manufacturing method for forming an array is difficult. Optical communication,
In particular, an array of semiconductor lasers is indispensable for optical interconnection and wavelength division multiplexing communication, but no consideration is given to arraying of semiconductor lasers.

Therefore, the object of the present invention is to solve the problems in the structure and manufacturing of the conventional polarization modulation semiconductor laser, and to optimize the TE mode semiconductor laser array structure and the TM semiconductor laser array structure. Using a semiconductor laser array structure, wavelength control is performed for at least one oscillation mode (securing wavelength stability) and a relatively low-cost semiconductor laser array having a wide polarization modulation operation range, a method for manufacturing the same, and the semiconductor laser array are provided. It is to provide an apparatus, a system and the like using the.

[0006]

FIG. 1 schematically shows the principle of a representative example of the present invention. In FIG. 1, 1 is a first semiconductor laser array structure in which a plurality of first semiconductor laser structures are formed in parallel, and 2 is a second semiconductor laser array structure in which a plurality of second semiconductor laser structures are formed in parallel. The semiconductor laser array structure 3 of 3 represents a void (gap) formed between the two and / or a filler filled therein. Each of the semiconductor laser array structures 1 and 2 alone has a TM mode (or TE mode) in the first resonator 7 and a T mode in the second resonator 8 in each semiconductor laser structure.
E mode (or TM mode) is excited. On the other hand, by optically combining the two, the first and second
Both the TE mode and the TM mode are excited by the composite resonator including the third resonator 9 in addition to the above resonator. Therefore, the TM mode of the first semiconductor laser structure of the first semiconductor laser array structure 1 is changed to the second semiconductor laser array structure 2 of the first semiconductor laser structure.
To the TM mode of the second semiconductor laser structure, and similarly the TE mode of the second semiconductor laser structure of the second semiconductor laser array structure 2 is the first semiconductor laser of the first semiconductor laser array structure 1. It is necessary to couple with the TE mode of the structure. This means that each first pair
Regarding the semiconductor laser structure and the second semiconductor laser structure, the propagation constants of TE modes and TM modes are
It means that they are almost equal. 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 second semiconductor laser array structure oscillating in a second polarization mode and a second semiconductor laser array structure oscillating in a second polarization mode are arranged in series in the waveguide direction. A first semiconductor laser array structure composed of a plurality of first semiconductor laser structures, wherein a plurality of the first semiconductor laser structures are arranged on the same substrate in parallel to the waveguiding direction. A distributed Bragg reflector or distributed feedback reflector is provided for each first semiconductor laser structure having a common first active region where the gain for the mode is superior to the gain for the second polarization mode. And a second semiconductor laser array structure having a plurality of second semiconductor laser structures having the same number as the first semiconductor laser structure, and the second semiconductor laser structure is the first semiconductor laser structure. alike A second active region having a common second active region in which the gain for the second polarization mode is superior to the gain for the first polarization mode, and a distributed Bragg filter is provided for each second semiconductor laser structure. A reflection type reflector, a distributed feedback type reflector or a Fabry-Perot type reflector is provided, and the first semiconductor laser structure and the second semiconductor laser structure forming a pair respectively have a first polarization mode. And the propagation constants of the second polarization modes are substantially equal to each other, and the Bragg wavelength of the distributed Bragg reflector or the distributed feedback reflector is the gain spectrum of the semiconductor laser array structure. Oscillation between the first polarization mode and the second polarization mode is performed by modulating the carrier that is set near the peak wavelength and is injected into at least one of the first and second semiconductor laser structures. Mo A polarization modulator capable semiconductor laser array, characterized in that for switching (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 at which both can oscillate simultaneously can be cast.

If one is TE Fabry-Perot mode and the other is TM DFB or DBR mode, it is possible to set a threshold gain at which both can oscillate simultaneously, which facilitates device fabrication and mounting, and also causes complex resonance. The operating range of polarization modulation by the device can be further widened. In this case, a stable TM
Only the mode needs to be used as the signal light. According to the first aspect of the invention, in order to realize a semiconductor laser array capable of polarization modulation as described above, a design guideline for improving controllability of semiconductor laser fabrication and improving an operation range capable of polarization modulation. Is given.

A second invention for achieving the above object is characterized in that the first semiconductor laser array structure and the second semiconductor laser array structure are arranged with a gap in the waveguide direction. (Corresponding to claim 2). As a result, the phase can be adjusted by filling the gap with a filling material (the gap may be left as it is), and the polarization modulation by the composite resonator can be made more reliable.

A third aspect of the present invention for attaining the above object is the first and second semiconductor laser array structures, each of which has a substrate and a laminated structure independently formed thereon. , Are arranged on a support base with a gap in the waveguide direction (corresponding to claim 3).

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

A fourth aspect of the invention for attaining the above object is the first and second semiconductor laser array structures, wherein at least an active layer and a waveguide layer are separately formed on the same substrate. The laminated structure on the same substrate is arranged with a gap in the waveguide direction (corresponding to claim 4).

A fifth invention for achieving the above object is characterized in that a gap is filled between the first and second semiconductor laser array structures with a filler to form a phase adjusting region. (Corresponding to claim 5). This adjusts the phase and further ensures polarization modulation by the composite resonator.

A sixth aspect of the invention for achieving the above object is a material in which the substance filled in the gap is capable of electrically controlling the refractive index, and an optical element for modulating the optical length of the phase adjusting region. A long modulation means is provided (corresponding to claim 6). 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 seventh invention for attaining the above object is characterized in that the second semiconductor laser array structure has a distributed feedback resonator or a distributed Bragg reflection resonator (claim 7). Correspondence).

An eighth aspect of the invention for attaining the above object is that the opposing end faces of the first and second semiconductor laser array structures are formed obliquely with respect to the waveguide direction with a gap therebetween. (Corresponding to claim 8). As a result, when both semiconductor laser array structures are DFB or DBR lasers, the influence of end facet reflection is suppressed, and polarization modulation by the compound resonator is ensured.

A ninth invention for achieving the above object is characterized in that the second semiconductor laser array structure has a Fabry-Perot type resonator (corresponding to claim 9).

With this structure, since the structure of the second semiconductor laser array structure of the Fabry-Perot resonator type can be simplified, arraying of the multi-wavelength semiconductor laser structure is facilitated. In addition, the second semiconductor laser array structure of the Fabry-Perot type can be flexibly designed in accordance with the first semiconductor laser array structure of the DFB or DBR type, and the oscillation of a mode dominant in the second semiconductor laser array structure can be obtained. Even if the quality of light is sacrificed, the oscillation light of the dominant mode in the first semiconductor laser array structure can be reliably used in the polarization modulation operation.

The tenth invention for achieving the above object is as follows:
Of the end faces of the first and second semiconductor laser array structures which face each other with a gap, the end face of the first semiconductor laser array structure, which is a DFB or DBR laser, is formed obliquely to the waveguide direction. It is characterized in that (claim 1
Corresponding to 0). Thus, when one semiconductor laser array structure is a DFB or DBR laser and the other semiconductor laser array structure is a Fabry-Perot type, the influence of end facet reflection is suppressed and polarization modulation by the compound resonator is ensured.

The eleventh invention for achieving the above object is as follows:
An AR coat is applied to the facing end faces of the first and second semiconductor laser array structures so as to be non-reflecting (corresponding to claim 11). 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 array are suppressed, the characteristics of the semiconductor laser array are averaged, and the yield is improved.

A twelfth invention for achieving the above object is as follows:
At least one of the active layers of the first and second semiconductor laser array structures has a quantum well structure or a strained quantum well structure (corresponding to claim 12). 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 thirteenth invention for achieving the above object is as follows:
At least one of the first and second semiconductor laser array structures includes a common active region in which a gain peak for the first polarization mode can be changed by a carrier injection amount,
Each semiconductor laser structure is provided with a distributed feedback reflector or a distributed Bragg reflector having a Bragg wavelength set near the different gain peak (claim 13). This makes it possible to realize a multi-wavelength semiconductor laser array with a relatively simple structure.

A fourteenth invention for achieving the above object is to:
A method of making a semiconductor laser as described above, comprising:
The step of producing the semiconductor laser array structure, the step of producing the second semiconductor laser array structure independently of this step, and the waveguide direction so as to optically couple the first and second semiconductor laser array structures. And a step of arranging the semiconductor laser array in series on the same supporting base with a gap therebetween (claim 14).

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

A fifteenth invention for achieving the above object is to:
The step of arranging the first and second semiconductor laser array 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 array structures, comprises placing the first semiconductor laser array structure on the support. And fixing the second semiconductor laser array structure, the first semiconductor laser array structure is caused to function as a photodetector, and at least a part of the plurality of second semiconductor laser structures of the second semiconductor laser array structure is caused to emit light. The method further comprises the step of positioning and fixing the second semiconductor laser array structure by receiving the light of the semiconductor laser array structure (corresponding to claim 15). Thereby, both semiconductor laser array structures can be aligned more easily.

A sixteenth invention for achieving the above object is to:
The step of arranging the first and second semiconductor laser array structures in series in the waveguide direction with a gap on the same support so as to optically couple the markers and the semiconductor lasers. The method includes adjusting the markers formed in the array structure to a desired positional relationship and disposing and fixing the semiconductor laser array structure (corresponding to claim 16). This allows easy alignment and reliable optical axis adjustment.

A seventeenth invention for achieving the above object is as follows:
The step of arranging the first and second semiconductor laser array structures in series in the waveguide direction on the same support base with a gap therebetween so as to optically couple the semiconductor laser array structures with the semiconductor laser mounting surface formed on the support base. Includes arranging the semiconductor laser array structure by abutting the side surface of the semiconductor laser array structure on a vertically upright plane (corresponding to claim 17). This allows easy alignment.

The eighteenth 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 18). The phase can be adjusted even if there is a gap between the two semiconductor laser array structures, but the phase can be adjusted more flexibly by filling with a substance having a desired refractive index.

A nineteenth invention for achieving the above object is as follows:
A method of manufacturing the above-mentioned semiconductor laser array, which comprises a step of manufacturing a first semiconductor laser array structure on a semiconductor substrate, a step of manufacturing a second semiconductor laser array structure on the substrate, And a step of forming a gap at a boundary portion between the first and second semiconductor laser array structures, which is a method for manufacturing a polarization-modulatable semiconductor laser array (corresponding to claim 19).

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

A twentieth invention for achieving the above object is as follows:
The step of producing the first semiconductor laser array structure includes
Stacking a first active layer and a first optical waveguide layer only on a region of the first semiconductor laser array structure on the semiconductor substrate; and forming a first active layer on the first optical waveguide layer. At least partially forming a first grating having a pitch controlled to have a Bragg wavelength near a gain peak, and forming the second semiconductor laser array structure on the semiconductor substrate. Laminating the second active layer and the second optical waveguide layer only in the region of the second semiconductor laser array structure, and manufacturing the first semiconductor laser array structure and the second semiconductor laser array structure. The step of producing a semiconductor laser array structure includes a step of stacking a common clad layer and a contact layer together on the entire surface of the optical waveguide layer (corresponding to claim 20).

The twenty-first 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 array structures simultaneously forms a slit-shaped gap and a ridge waveguide at the boundary between the regions of the first and second semiconductor laser array structures. It includes a step of performing (corresponding to claim 21).

A twenty-second 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 22).

The twenty-third aspect of the invention for achieving the above object is to provide a polarization modulation semiconductor laser array and a polarizer for selecting and outputting only one polarization in the output section of the semiconductor laser array. And a control circuit for controlling and driving the semiconductor laser array for switching the polarization state of the output light of the semiconductor laser structure forming each pair of the semiconductor laser array according to the input signal. (Corresponding to claim 23). 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.

A twenty-fourth invention for achieving the above object is as follows:
The above-mentioned semiconductor laser array capable of polarization modulation, polarization selecting means for transmitting light of one polarization of the output light from the semiconductor laser array, and semiconductor laser structure forming each pair of the semiconductor laser array. Is an optical transceiver having a control circuit for controlling and driving the semiconductor laser for switching the polarization state of the output light according to the input signal, and a receiving means for receiving the input signal (claim 24). Correspondence). The same effect as that of the optical transmitter of the twenty-third invention is exhibited.

A twenty-fifth invention for achieving the above object is as follows:
A light source device having the polarization modulation semiconductor laser array described above and polarization selection means for extracting only one of two polarization modes, TE and TM, of the light emitted from the polarization modulation semiconductor laser array. (Corresponding to claim 25). The same effect as that of the optical transmitter of the twenty-third invention is exhibited.

The twenty-sixth invention for achieving the above object is an optical transmission system or an optical communication system including a transmitter or a transceiver using the semiconductor laser array of the present invention ( (Corresponding to claim 26). 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-seventh invention for achieving the above object is as follows:
The optical transmitter or the transmitter / receiver can send out optical signals of a plurality of different wavelengths to form a wavelength multiplexing type network (corresponding to claim 27).

The twenty-eighth invention for achieving the above object is as follows:
A light source device including the polarization modulation semiconductor laser array described above and polarization selection means for extracting only one of two polarization modes, TE and TM, of the light emitted from the polarization modulation semiconductor laser array. By using a polarization bias semiconductor laser array by superimposing a current modulated according to a transmission signal on a predetermined bias current and supplying the polarization-modulated semiconductor laser array with the intensity-modulated signal light according to the transmission signal. Is taken out and the signal light is transmitted toward the optical receiving side (corresponding to claim 28).

[0042]

DETAILED DESCRIPTION OF THE INVENTION

(First Embodiment) First, an embodiment will be described in which polarization-modulated lasers having the same characteristics are arrayed. FIG. 2 is a schematic view of the first embodiment, where 1 is a first semiconductor laser array and 2 is a semiconductor laser array.
Is a second semiconductor laser array, 3 is a void and / or filler, 4 is a heat sink, and 5 is a marker. Although not shown here, the semiconductor laser array 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 array will be described. 3 is a sectional view in a direction including the oscillation axis of the first semiconductor laser, and FIG. 4 is a sectional view in a vertical direction thereof. For example, on an n-type (100) InP substrate 101, a MOCVD method (Metal Organic Che) is used.
(Malical Vapor Deposition) and C
BE method (Chemical Beam Epitax)
y) is used to form the n-InP cladding layer 102, the undoped active layer 103, and the p-InGaAsP optical guide layer 104.
Are stacked. 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 −0.9%, thickness is 9 nm), and 122 is unstrained InGa.
AsP barrier layer (band gap 0.99 eV, thickness 1 n
m) and the number of wells was three.

After that, the grating 108 having a desired pitch is formed on the entire surface of the wafer. In this example, the phase shift grating 108 having a pitch of 325 nm and a depth of 50 nm was formed. Then, the p-InP clad layer 10
5, the p-InGaAs contact 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.

Further, as shown in FIG. 4, 2.5 μm wide ridge structures are formed at 100 μm intervals for transverse mode control. In FIG. 4, 111a and 111b are ridge type optical waveguides (actually, similar structures are further continued on both sides),
Numeral 112 is SiO ₂ for preventing current from flowing except the ridge portion.
An insulating film such as a film. Further, 109 is a positive electrode formed on the substrate surface side (the positive electrode 109 is, as shown in FIG. 3, two electrodes 109a and 109 in the resonance direction of each semiconductor laser).
110, which is a negative electrode on the substrate side. In the present embodiment, an example in which the positive electrodes 109a and 109b are divided into two parts (this makes it possible to adjust the injection carrier distribution and widen the polarization modulation operation range for each semiconductor laser), but a single electrode may be used. Absent. In FIG. 4, the protruding laminated structure between the plurality of ridge-type optical waveguides 111 is not required functionally, and is the result of the etching process for forming the ridge-type optical waveguides 111a, 111b. It is nothing more than what is formed.

As a result of applying the tensile strain multiple quantum structure to the active layer 103 and setting the Bragg wavelength of each semiconductor laser structure of the array 1 in the vicinity of its gain peak wavelength (by setting the pitch of the grating 108 and the like), the TM gain is obtained. Always exceeds the TE gain, so the TM-polarized DFB is always
It oscillates in the mode. In the present embodiment, the grating 108 is formed after growing the active layer 103. This is because it is considered that the manufacturing accuracy of the grating is higher than the wavelength controllability of crystal growth in the present technology. (That is, it is better to grow the active layer and determine the gain peak wavelength, and then determine the pitch of the grating etc. accordingly), and if both can be manufactured with high accuracy, form the grating directly on the substrate. Then, the active layer or the like may be grown. This also applies to the following examples.

Next, a method of manufacturing the second semiconductor laser array 2 will be described. In the present embodiment, the second semiconductor laser array 2 has its layer thickness and composition controlled in order to make the propagation constant almost equal to the TE mode of the first semiconductor laser array 1. The other structure may be substantially the same as that of the first semiconductor array 1. The lateral mode control of the second semiconductor laser array 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 array 1. When the width of the ridge structure is different, the other structure parameters are also changed accordingly to change both laser arrays 1,
The propagation constants of 2 should be equal. However, the pitch of the ridge was set to 100 μm accurately so as to match the pitch of the first semiconductor laser array 1. In this way, each semiconductor laser structure of the first semiconductor laser array 1 and each semiconductor laser structure of the second semiconductor laser array 2 form a pair to form a plurality of semiconductor lasers.

A band diagram of the active layer of the second semiconductor laser array 2 is shown in FIG. 6 (SCH layers are formed on the upper and lower sides of the active layer). 123 is unstrained InG
aAs well layer (thickness: 7.5 nm), 124 is strain-free In
It was a GaAsP barrier layer (band gap 0.99 eV, thickness 10 nm), and the number of wells was 5. As a result, since the transition between heavy holes and electrons becomes dominant, the TE gain always exceeds the TM gain, and the Bragg wavelength of each semiconductor laser structure of the second semiconductor laser array 2 is close to the peak wavelength of the TE gain. Is set, so DF of TE polarization is always
It oscillates in B mode.

In order to form a composite resonator with the first semiconductor laser and the second semiconductor laser of each of the laser arrays 1 and 2, it is desirable that the reflectance of the end faces, particularly the facing end faces, be as low as possible. In this example, antireflection coating (AR coat) was applied to all the end faces. Since it is expected that the operating range of polarization modulation will differ depending on the resonator length, we decided to select the desired array from several arrays with different resonator lengths. In this way, the structures of the first and second semiconductor laser arrays 1 and 2 can be easily controlled independently. Alternatively, it is a great feature of the present invention that it is possible to select from a plurality of arrays formed.

Next, a method of mounting the two semiconductor laser arrays 1 and 2 on the heat sink 4 will be described with reference to FIG. For example, the first semiconductor laser array 1 is die-bonded to a desired position indicated by the marker 5 by shrimp side-down or epi-side up (FIG. 2 shows an example of epi-side up). The second semiconductor laser array 2 causes the semiconductor laser structure of the first semiconductor laser array 1 to function as a waveguide-type photodetector while causing some or all of the semiconductor laser structures to emit light by pulse current driving. , Adjust the position. Since the alignment is performed at a plurality of points of the semiconductor laser array, the position can be adjusted more easily and accurately than in the case of a single semiconductor laser. After the position adjustment of the second semiconductor laser array 2 is completed, the semiconductor laser structure of the first semiconductor laser array 2 is pulse-driven to reversely drive the semiconductor laser structure of the second semiconductor laser array 2 before die bonding. Die bonding is performed after it is operated as a photo detector and it is confirmed that it can receive light. As a result, the semiconductor laser structure forming the pair of the two semiconductor laser arrays 1 and 2 is fixed on the heat sink 4 in an optimal optical coupling state. Even if the optical power coupling efficiency is high, it is difficult to control the size of the air gap 3 generated between the two semiconductor laser arrays 1 and 2, so that the phase shifts, and thus polarization modulation is less likely to occur (in TE mode or TM mode). It only works on either side). At this time, the phase (optical length) of competing light waves is adjusted by filling the voids generated between the two semiconductor laser arrays 1 and 2 with a substance 3 having a desired refractive index such as gel, polymer or compound semiconductor. However, polarization modulation can be applied with good yield. When the phase matching conditions are different in each pair of semiconductor laser structures, the refractive index of the liquid crystal is changed by filling the gap 3 with liquid crystal, forming an electrode on it, and applying a voltage instead of gel or polymer. Or transmittance (transmittance is an absorptance if the expression is changed, the refractive index and the transmittance are equal from the viewpoint of complex refractive index, and it is possible to apply polarization modulation with good yield even by adjusting the transmittance. Can be controlled. Alternatively, the phase can be finely adjusted by providing a phase matching region in each semiconductor laser structure and adjusting the carrier injection amount.

Next, the operation method of the first embodiment will be described. FIG. 7 shows the first and second semiconductor laser arrays 1, 2.
Region of the semiconductor laser structure forming a pair (first
Of the semiconductor laser array 1) and the TE region (in the second semiconductor laser array 2) independently of the current (I
₁ and I ₂ ) and the distribution of polarization modes is shown. The boundary line A-B indicates that the threshold gains of the TE mode and the TM mode are substantially equal to each other. If the modulation signal is superposed on this line as a bias point (for example, the point M or the point N), the oscillation polarization mode is obtained. This realizes so-called polarization modulation, which switches. For example, in the case of the bias point M, an example in which the modulation signal is placed only on I ₁ is the bias point N.
In the case of, the example in which the modulation currents are put in reverse phase on I ₁ and I ₂ is shown. At this time, the modulation current is at most 1 mA, so that not only chirping is suppressed, but also the delay of the oscillation start time (so-called skew) for each semiconductor laser composed of the semiconductor laser structure forming each pair is extremely small. Become. When at least one positive electrode of the semiconductor laser structures of the semiconductor laser arrays 1 and 2 is divided into two,
By injecting carriers non-uniformly into the respective electrodes 109a and 109b, fine adjustment of the phase becomes possible, and the polarization modulation possible region can be further expanded.

The advantages of the first embodiment are summarized as follows. (1) The semiconductor laser array for TE and the semiconductor laser array for TM can be optimized independently. (2) In constructing this structure, an appropriate semiconductor laser array can be selected from a plurality of semiconductor laser arrays of the same type. (3) Both modes are good in terms of line width, etc.
Both TE mode light and TM mode light can be used for optical communication. (4) Even if there is a case where the phases do not match, it is easy to adjust the phase by adjusting the voids or the filler. (5) Since the modulation current is small, the delay (skew) of the oscillation start time is extremely small, so that the modulation speed and the transmission distance can be improved.

In this embodiment, the lateral mode control of the two semiconductor laser arrays 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, a multi-wavelength polarization modulation semiconductor laser array which is easier to manufacture and has different oscillation wavelengths for each semiconductor laser will be described. FIG. 8 is a schematic diagram thereof, and FIG. 12 is a plan view. In FIG. 12, 23 is a TM mode semiconductor laser array, 24 is a TE mode semiconductor laser array, 22 is a DBR region of each laser structure of the TM mode semiconductor laser array 23, and 21 is each of the TM mode semiconductor laser array 23. The TM gain region 3 of the laser structure is a void and / or a filler.

This embodiment differs from the first embodiment in the following points. (1) As the first semiconductor array laser 1, an array having a distributed Bragg reflector (DBR) and a semiconductor laser structure having different oscillation wavelengths is used. (2) A Fabry-Perot resonator semiconductor laser array is used as the second semiconductor laser array 2. (3) Heat sink (or support base for sub carrier, etc.)
A heat sink (or a support such as a subcarrier) having a surface 10 perpendicular to the laser fixing surface is used as a shape.

First, a method of manufacturing the first semiconductor laser array 1 will be described. FIG. 9 is a sectional view in the direction including the oscillation axis of the first semiconductor laser array 1. The vertical sectional view is the same as that of the first embodiment (see FIG. 4). The manufacturing method is, for example, a pitch of 325 nm to 0..100 nm in the DBR region on the n-type (100) InP substrate 131.
10 gratings in 4nm increments (50nm depth)
After forming the regions 138 at intervals of 10 nm, MOCVD is performed.
The n-InGaAsP optical guide layer 134 and the undoped active layer 133 are stacked by using the CBE method or the CBE method. afterwards,
The active layer 133 which becomes the DBR region is removed, and the p-InP clad layer 135 and p-InGaAs are formed on the active layer 133.
A contact layer (cap layer) 136 is laminated.

A band diagram of the active layer 133 is shown in FIG.
It was shown at 0. 151 is a tensile strained InGaAsP first well layer (strain rate −0.9%, thickness 9 nm), and 152 is a strain-free InGaAsP barrier layer (bandgap 0.99).
eV, thickness 1 nm), 153 is tensile strain InGaA
The sP second well layer (strain rate −0.7%, band gap 0.75 eV, thickness 10 nm).

Similar to the first embodiment, a plurality of ridge structures each having a width of 2.5 μm were formed at intervals of 100 μm for controlling the transverse mode (see FIG. 4). 139a and 139b are positive electrodes, 14
Reference numeral 0 is a negative electrode, and 142 is an AR coat formed on both end surfaces.

As a result of using the asymmetric strained quantum well structure as shown in FIG. 10 for the active layer 133, the gain spectrum thereof is significantly different from that of the usual strain-free heavy well active layer. First
In addition, by introducing tensile strain in the well layers 151 and 152, transition of electrons and light holes becomes dominant, and the TM mode gain always exceeds the TE mode gain at the peak wavelength. Secondly, since the well layer thickness and composition are asymmetrical, the ground level differs from well layer to well layer, and the gain spectrum greatly changes depending on the carrier injection amount. FIG. 11 shows
Typical TM of the first semiconductor laser array 1 of this embodiment
The gain spectrum of the mode is schematically represented by using the injected carrier density as a parameter. As the carrier injection amount increases, the peak size increases and the peak position shifts to the long wavelength side. Therefore, FIG.
By setting the Bragg wavelength of each semiconductor laser structure of the first semiconductor laser array 1 at the position of the arrow 1 (by setting the period of the grating 138, etc.) and controlling the magnitude of the loss, the wavelengths differ, It is possible to obtain the TM semiconductor laser array 23 having high stability and constantly oscillating in the TM mode. As the method of controlling the loss, in the present embodiment, a method of making the gain region 21 smaller as the threshold gain is larger was used (see FIG. 12). In the present embodiment, a DBR laser having a DBR region 22 having no ordinary gain is used, but a structure of a DBR laser including an active layer in the DBR region may be adopted for ease of fabrication. Gain area 21
By controlling the amount of current in the DBR region 22 and the DBR region 22, both the wavelength and the threshold gain can be controlled.

Next, a method of manufacturing the second semiconductor laser array 2 will be described. FIG. 14 is a sectional view including the oscillation axis of the second semiconductor laser array 2, and FIG. 1 is a vertical sectional view thereof.
5 shows. The manufacturing method is, for example, n-type (100)
On the InP substrate 161, an n-InP clad layer 162,
Undoped active layer 163, n-InGaAsP optical guide layer 164, p-InP cladding layer 165 and p-In
The P contact layer 166 is laminated. The structure of the active layer 163 is the same as that of the second semiconductor laser array of the first embodiment here (see FIG. 6). However, the transverse mode control is not dared. For example, the electrode stripe 16 having a width of 50 μm
9 is only formed with a pitch of 100 μm. As a result, it always oscillates in the TE mode, but unlike the case of the first embodiment, it always oscillates in the TE multi-fabric-Perot mode because there is no grating and there is no transverse mode control mechanism. 170 is a substrate side electrode, 172 is AR
It's a coat.

Next, the optical coupling of the two semiconductor laser arrays 1 and 2 will be described. First, it is desirable that the facing end faces of the first and second semiconductor laser arrays 1 and 2 have a reflectance as low as possible. Therefore, as shown in FIGS. 9 and 14, AR coats 142 and 172 are formed on both end surfaces of the laser. Further, since the widths of the first and second semiconductor laser arrays are set to be substantially equal to each other and the side surfaces thereof are brought into contact with the vertical surface 10 of the heat sink 4, it is desirable to provide a surface close to the cleavage. .

In FIG. 8, a surface 10 perpendicular to the semiconductor laser fixing surface is formed on the heat sink 4, and the semiconductor laser arrays 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 dare to perform active alignment (alignment using the method of detecting by oscillating) as in the first embodiment. A marker (not shown) is installed in advance on the heat sink 4 and the laser chips 1 and 2, and alignment is performed (passive alignment) to obtain sufficient structure.
That is, in the case of the present embodiment, the alignment of the optical waveguides of the two semiconductor laser arrays 1 and 2 is performed only with the positional accuracy in the direction perpendicular to the cleavage plane. This is because the use of a semiconductor laser structure having a wide electrode stripe structure for the second semiconductor laser array 2 increases the degree of freedom in aligning the optical axis in the lateral direction. If necessary, the same active alignment as in the first embodiment may be partially performed.

As described above, the use of the TE Fabry-Perot semiconductor laser array 24 makes it very easy to adjust the optical axis, which is a major feature of this embodiment.

Next, the driving method will be described. The TM semiconductor laser array 23 oscillates in the TM mode and the TE semiconductor laser array 24 oscillates in the TE mode as in the first embodiment, but in this embodiment, the TE mode is the Fabry-Perot mode and the multimode. Because it oscillates at
The condition that the mode and the TE mode have the same threshold gain is more lenient than in the case of the first embodiment. This means that the operation area in which the polarization modulation can be performed is widened (see also the description of the third embodiment for this).

FIG. 13 shows the distribution of polarization modes when currents are independently applied to the laser structures forming the pair of the first and second semiconductor laser arrays 1 and 2. The boundary line A-
B indicates that the threshold gains of the TE mode and the TM mode are almost equal to each other. A bias point (for example, a point M or a point N) on this line is used to superpose the modulation signal, so that the polarization mode is switched. Wave modulation is realized. First
Since the Fabry-Perot semiconductor laser array 24 is used on one side as compared with the embodiment, the large feature is that the bias region capable of polarization modulation is wide. This means that the control range of light output and oscillation wavelength is wide.

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) A semiconductor laser array capable of multi-wavelength polarization modulation can be easily realized. (3) Since the Fabry-Perot semiconductor laser array is used for one side, the optical axis alignment becomes easy. (4) Even if the phases do not match, the phase can be easily controlled 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) Next, a multi-wavelength polarization modulation semiconductor laser array according to a third embodiment will be described in which both semiconductor laser arrays are formed on a common substrate and the oscillation wavelengths are different. The overall appearance is the same as in FIGS.

The design guidelines for this example are as follows. (1) The first semiconductor laser array 1 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 2 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 1 is set to the active region 21 and the DBR region 2.
Adjust by changing the size of 2. (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 1 will be described. FIG. 16 is a sectional view in the direction including the oscillation axes of the first and second semiconductor laser arrays 1 and 2. The vertical sectional view is almost the same as that of the first embodiment (see FIG. 4).

This manufacturing method is, for example, an n-type (10
0) n-InP clad layer 202 on InP substrate 201
Of the undoped active layers 203a and p-I only on the first semiconductor laser array region using a selective mask.
The nGaAsP light guide layer 204a is laminated. At this time, the MOCVD method, the CBE method, or the like is suitable as the growth method. At this time, abnormal growth easily occurs in the vicinity of the mask edge portion, but this may be left as it is. A band diagram of the active layer 203a is shown in FIG. 271 is tensile strain InGaAs
First well layer (strain rate −0.9%, thickness 9 nm), 273
Is a strain-free InGaAsP barrier layer (bandgap 0.9
9 eV, thickness 10 nm), 272 is tensile strain InGa
It is an AsP second well layer (strain rate −0.7%, band gap 0.8 eV, thickness 10 nm).

Ten grating regions (depth: 50 nm) 207 were formed laterally at intervals of 100 μm at pitches of 325 nm to 0.4 nm only in the DBR regions on the optical guide layer 204a. TM in this embodiment
No grating is formed in the gain region. The lengths of the DBR region and the TM gain region in the resonance direction gradually differ on the array as shown in FIG. this is,
This is because the semiconductor lasers have different threshold gains.

Next, after removing the selection mask and forming a new selection mask so as to cover the first semiconductor laser array region, n-I slightly formed as a buffer layer is formed.
A second active layer 203b and a second light guide layer 204b are selectively grown on the nP clad layer 202. In this case as well, abnormal growth easily occurs near the edges, but this may be maintained. The structure of the second active layer 203b preferably 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, p is applied to the entire wafer.
The -InP clad layer 205 and the p-InGaAs contact layer 206 are laminated.

After that, the boundary between the two semiconductor laser array regions is removed in a slit shape. At this time, the depth is n-
Until reaching the InP clad layer 202, the gap pattern is inclined so that the end face side of the first semiconductor laser array 1 is oblique to the waveguide direction, and the end face side of the second semiconductor laser array 2 is in the waveguide direction. Make a right angle to it. This is for the first semiconductor laser array 1 to avoid reflection at the void portion 208 as much as possible, and for the Fabry-Perot resonator to be formed in the second semiconductor laser array region. This process is a normal MO
Although it may be performed by the CVD method and dry etching, CBE
The reliability is further enhanced by continuously performing the apparatus and the RIBE apparatus in a high vacuum-bonded composite process apparatus without exposing to the atmosphere.

As shown in FIG. 4, the transverse mode waveguide is 100
A plurality of ridge waveguides each having a width of 10 μm were formed in the TM semiconductor laser array region in the TM semiconductor laser array region. The second semiconductor laser arrays 2 all have an electrode stripe structure with a width of 10 μm in order to have the same threshold gain. Finally, the DBR region, TM gain region, phase adjustment region and T
Electrode 2 is used so that carriers can be independently injected into the E gain region.
09a to 209d and 210 are provided. 2111 is DB
It is an AR film provided on the end face of the R laser.

As a result of using the asymmetric strained quantum well structure for the active layer 203a, its gain spectrum is significantly different from that of the usual strain-free multi-well active layer. First, by introducing tensile strain in the two well layers 271 and 272, the transition between electrons and a light hole (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. 18 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, the Bragg wavelength of each semiconductor laser structure of the first semiconductor laser array 1 is set at the positions of arrows (λ ₁ , λ ₂ , λ ₃ ...) In FIG. 18 (by setting the period of the grating 207, etc.). By controlling the magnitude of the loss, it is possible to obtain the semiconductor laser array 1 having different wavelengths, high wavelength stability, and constantly oscillating in the TM mode. In the present embodiment, the method of controlling the loss is such that the larger the threshold gain, the smaller the gain region (see FIG. 12). This embodiment is DB
Since the active layer 203a is included in the R region, it is a pure frame DBR.
Although not a laser, 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 it is easy to manufacture.
Of course, a DBR laser having a normal DBR region without gain may be used.

On the other hand, the TE mode semiconductor laser array 2
Uses a Fabry-Perot resonator and a bulk active layer 203b 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, it is possible to always oscillate in the Fabry-Perot mode of TE polarization which is equal to the TM mode threshold gain of each TM mode DBR laser. 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. T
When the wavelength range of the M-mode DBR laser array 1 is wide, the TE-mode Fabry-Perot semiconductor laser array 2
This can be dealt with by applying an asymmetric compressive strain quantum well structure or the like to the active layer.

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 the competing light waves is obtained by filling the void 208 formed between the two semiconductor laser arrays with a filler 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. 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, In
It is also possible to adjust the phase by epitaxially growing a semiconductor such as P and then forming an electrode and varying 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 array can be a very simple electrode stripe laser array, so that the cost is low. (3) Phase control is easy even if the phases may not match. (4) The operating range in which polarization modulation is possible is wide.

(Fourth Embodiment) FIG. 19 shows an embodiment in which the semiconductor laser array of the present invention is applied to an optical transmitter for optical communication. In FIG. 19, 331 is a control circuit, 332 is the semiconductor laser array of the present invention shown in the first embodiment, 33
3 is a polarizer, 334 is an optical coupling means for coupling the light propagating in space to the optical fiber array, 335 is an optical fiber array, 336 is an electric signal sent from the terminal, 337.
Is a drive signal sent from the control circuit 331 to drive the semiconductor laser 332, and 338 is a drive signal 337.
The optical signal 339 output by driving the semiconductor laser array 332 in accordance with the above-described method passes through the polarizer 333 adjusted so as to extract only one of the two orthogonal polarization states of the optical signal 338. , 340 is an optical signal transmitted through the optical fiber array 335, and 341 is an optical transmitter using the semiconductor laser array 332 of the present invention. In this embodiment, the optical transmitter 341 includes the control circuit 33.
1, a semiconductor laser array 332, a polarizer 333, an optical coupling unit 334, an optical fiber array 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 drive signal 337 is sent to the semiconductor laser array 332 of the present invention. Drive signal 337
Is inputted to the semiconductor laser array 332, the driving signal 3
An optical signal 338 whose polarization state changes according to 37 is output. (In this case, the lasers of the semiconductor laser array 332 usually have different drive signals 337a, 337b, 33, respectively.
7c ... Optical signals 338 of the same wavelength but different
, 338b, 338c, ... Are output, but in the description here, in the case where it is clear, they are simply described as the optical signal 338. ) The optical signal 338 is converted into an optical signal 339 of one polarization by the polarizer 333, and is further coupled to the optical fiber array 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.

(Fifth Embodiment) FIG. 20 shows an example in which an optical transmitter is applied to the second or third embodiment of the present invention. The difference from the fourth embodiment is that the wavelengths of the semiconductor lasers that form the semiconductor laser array are different, so that wavelength multiplexing is possible, and as a result, there is one fiber 335. The other functions are the same as those in the fourth embodiment. still,
The polarizers 333 do not need to be individually attached because the planes of polarization are aligned (this is the same in the fourth embodiment). Further, the optical coupling means 334 can be easily achieved by using a waveguide type junction.

(Sixth Embodiment) Next, an example in which the device of the present invention is applied to an optical network will be described. 22 and 23 show an example of application to a bus type optical network and a ring type optical network.
Is equipped with an optical transmitter including the above embodiment and a suitable receiver. By disposing a polarizer on the emission surface of the semiconductor laser array described in the above embodiment, only specific polarized light (for example, TM light) can be extracted 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 to 416 are terminal devices.

Further, when the semiconductor laser array 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 array and a wavelength tunable filter,
By making the wavelength tunable filter polarization dependent, it can be used with a very simple configuration as a light source for polarization diversity.

Although 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.

(Seventh Embodiment) An example in which the present embodiment is used for a transmitting portion 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, when an optical signal is transmitted from the node 701, the polarization modulation semiconductor laser array 704 of the above embodiment is driven in accordance with the signal by the control circuit as described above by an appropriate method to perform polarization modulation, and the polarization plate 707. (This converts the polarization modulation signal into an amplitude intensity modulation signal)
The output light (through which an isolator may be further inserted) is made incident on the optical transmission path 700 through the merging portion 706.
In addition, it is possible to extend the wavelength variable range by providing two or more wavelength variable optical filters.

[0087]

The present invention has the following effects. (1) Since the TE mode semiconductor laser array and the TM mode semiconductor laser array can be independently designed, 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 array structure and the TM mode semiconductor laser array structure. (4) When one semiconductor laser array structure is actively operated and the other laser array structure is aligned, the mounting work can be performed by checking the optical coupling state of both semiconductor laser array structures. Further, the two semiconductor laser array structures can be stably aligned with each other with high accuracy. At this time, by aligning one semiconductor laser array structure with a wide-striped electrode type Fabry-Perot semiconductor laser array structure, alignment becomes easier. (5) When positioning is performed using the structure of a member on which two semiconductor laser array structures are mounted, it is not necessary to drive the semiconductor laser array structure, and the two semiconductor laser array structures can be more easily aligned. Is possible. (6) When the TE mode / TM mode boundary, that is, the refractive index of the material filled between the end faces of the two semiconductor laser array structures can be electrically controlled, the coupling of both modes can be actively controlled. . Therefore, it is possible to switch the polarization wave mode by this electrical control.

Furthermore, the polarization modulation operation range is wide, the phase matching is easy even when the phases may not match, 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 a transmitter or a wavelength multiplexing system comprising transmitters and receivers using the semiconductor laser array of the present invention, an optical transmission system capable of high-speed, large-capacity or ultra-high-density wavelength-multiplexing is relatively inexpensive. There is also the effect that it can be configured.

[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 array structure for explaining the first embodiment of the present invention.

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

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 the relationship between the amount of current injection into the two semiconductor laser structures of the first embodiment and the polarization mode.

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

FIG. 9 is a sectional view in the resonance direction of a DBR type semiconductor laser array structure for explaining a second embodiment of the present invention.

FIG. 10 is a diagram illustrating a bandgap structure of one active layer according to the second embodiment of the present invention.

FIG. 11 is a diagram showing how the gain profile of one active layer changes for explaining the operation of the second embodiment of the present invention.

FIG. 12 is a plan view for explaining a semiconductor laser array according to a second embodiment of the present invention.

FIG. 13 is a diagram showing the relationship between the amount of current injection into the two semiconductor laser structures of the second embodiment and the polarization mode.

FIG. 14 is a cross-sectional view in the resonance direction of a Fabry-Perot type semiconductor laser array structure for explaining a second embodiment of the present invention.

FIG. 15 is a cross-sectional view of a Fabry-Perot type semiconductor laser array structure in a direction perpendicular to the resonance direction for explaining the second embodiment of the present invention.

FIG. 16 is a cross-sectional view in the resonance direction of a polarization modulation semiconductor laser array for explaining a third embodiment of the present invention.

FIG. 17 is a diagram illustrating a bandgap structure of one active layer according to the third embodiment of the present invention.

FIG. 18 is a diagram showing how the gain profile of one active layer changes to explain the operation of the third embodiment of the present invention.

FIG. 19 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. 21 and 22.

FIG. 20 is a schematic diagram showing a configuration example of a transmitter using the multi-wavelength polarization modulation semiconductor laser array of the present invention in the system of FIGS. 21 and 22.

FIG. 21 is a schematic diagram showing a configuration example of a bus type optical LAN system using the polarization modulation semiconductor laser array of the present invention.

FIG. 22 is a schematic diagram showing a configuration example of a loop type optical LAN system using the polarization modulation semiconductor laser array of the present invention.

FIG. 23 is a schematic diagram showing a configuration example of a transceiver in the system of FIGS. 21 and 22.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 1st semiconductor laser array structure 2 2nd semiconductor laser array structure 3, 208 Air gap (gap) and / or filling material 4 Heat sink (support) 5 Marker 7 1st resonator 8 2nd resonator 9th Resonator 10 of 3 Vertical surface of support 21 Gain region 22 DBR region 23 TM semiconductor laser array 24 TE laser array 101, 131, 161, 201 Substrate 102, 105, 135, 162, 165, 202, 2
05 clad layers 103, 133, 163, 203a, 203b
Active layers 104, 134, 164, 204a, 204b
Optical guide layer (waveguide layer) 106, 136, 166, 206 Contact layer (cap layer) 108, 138, 207 Diffraction gratings 109, 110, 139, 140, 169, 170, 2
09, 210 metal electrode 111 ridge waveguide 112 insulating film 115, 142, 172, 211 AR coat 121, 123, 151, 153, 271, 272
Well layers 122, 124, 152, 273 Barrier layer 331 Control circuit 332, 704 Polarization modulation semiconductor laser arrays 333, 707 Polarizers (polarization selecting means) 334 Optical coupling means 335, 400 Optical fibers (optical fiber arrays) 341 Optical transmitters 401 to 406, 701 Nodes 411 to 416 Terminal device 702 Optical branching unit 703 Receiver 706 Merging unit

─────────────────────────────────────────────────── ─── Continuation of front page (56) Reference JP-A-7-264138 (JP, A) JP-A-7-307530 (JP, A) JP-A-7-235718 (JP, A) JP-A-7- 231133 (JP, A) JP-A 7-162088 (JP, A) JP-A 2-117190 (JP, A) JP-A 8-172237 (JP, A) JP-A 6-140720 (JP, A) Journal of Apply d Physics, USA, 1988, Vol. 63, No. 2, p. 291-294 (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01S 5/00-5/50 H04B 10/02-10/28

Claims (28)

(57) [Claims] 1. A composite resonator in which a first semiconductor laser array structure that oscillates in a first polarization mode and a second semiconductor laser array structure that oscillates in a second polarization mode are arranged in series in the waveguide direction. A first semiconductor laser array structure comprising a plurality of first semiconductor laser structures, wherein a plurality of the first semiconductor laser structures are arranged on the same substrate in parallel to the waveguide direction. And having a common first active region in which the gain for the first polarization mode is superior to the gain for the second polarization mode,
Second semiconductor laser structure having the same number of second semiconductor laser structures as the first semiconductor laser structure and a distributed Bragg reflection type reflector or a distributed feedback type reflector. An array structure is formed by arranging the second semiconductor laser structure in the same manner as the first semiconductor laser structure, and the gain for the second polarization mode is superior to the gain for the first polarization mode. A second Bragg reflector type reflector, a distributed Bragg reflector type reflector, or a Fabry-Perot type reflector for each second semiconductor laser structure having a second active region. 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. Reflector or The Bragg wavelength of the distributed feedback reflector is set near the peak wavelength of the gain spectrum of the semiconductor laser array structure, and the carrier injected into at least one of the first and second semiconductor laser structures is modulated to obtain the Bragg wavelength. A semiconductor laser array capable of polarization modulation, wherein an oscillation mode is switched between a first polarization mode and a second polarization mode. 2. The first semiconductor laser array structure and the second semiconductor laser array structure.
2. The semiconductor laser array structure according to claim 1, wherein said semiconductor laser array structure is arranged with a gap in the waveguide direction. 3. The first and second semiconductor laser array structures each have a structure in which a substrate and a laminated structure on the substrate are independently formed, and a support base is provided with a gap in the waveguide direction. The semiconductor laser array according to claim 1, wherein the semiconductor laser array is arranged above. 4. The first and second semiconductor laser array structures have a structure in which at least an active layer and a waveguide layer are separately formed on the same substrate, and a laminated structure on the same substrate is The semiconductor laser array according to claim 1, wherein the semiconductor laser array is arranged with a gap in the waveguide direction. 5. The phase adjusting region according to claim 1, wherein a gap is filled between the first and second semiconductor laser array structures with a filling material. Semiconductor laser array capable of polarization modulation. 6. 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. 6. A semiconductor laser array capable of polarization modulation according to claim 5. 7. The polarization modulator according to claim 1, wherein the second semiconductor laser array structure has a distributed feedback type resonator or a distributed Bragg reflection type resonator. Semiconductor laser. 8. The polarized wave according to claim 7, wherein end faces of the first and second semiconductor laser array structures, which face each other with a gap, are formed obliquely with respect to the waveguide direction. Modulatable semiconductor laser array. 9. The second semiconductor laser array structure has a Fabry-Perot resonator.
7. A semiconductor laser array capable of polarization modulation according to any one of 1 to 6. 10. An end face of the first semiconductor laser array structure, of the end faces of the first and second semiconductor laser array structures facing each other with a gap, is formed obliquely with respect to the waveguide direction. 10. A semiconductor laser array capable of polarization modulation according to claim 9. 11. The end faces of the first and second semiconductor laser array structures, which face each other so as to be non-reflective,
11. A semiconductor laser array capable of polarization modulation according to claim 1, wherein an R coat is applied. 12. The active layer of at least one of the first and second semiconductor laser array structures has a quantum well structure or a strained quantum well structure. 5. A semiconductor laser array capable of polarization modulation according to. 13. At least one of the first and second semiconductor laser array structures includes a common active region in which a gain peak for the first polarization mode can be changed by a carrier injection amount, and each semiconductor laser structure has a common active region. On the other hand, the semiconductor laser array according to claim 12, further comprising a distributed feedback reflector or a distributed Bragg reflector having a Bragg wavelength set near the different gain peaks. 14. A method of manufacturing a semiconductor laser array according to claim 1, 2 or 3, wherein a step of manufacturing a first semiconductor laser array structure and a second semiconductor laser independent of this step. A step of producing an array structure, and a step of arranging the first and second semiconductor laser array structures in series in the waveguide direction with a gap on the same support so as to optically couple them. A method for manufacturing a semiconductor laser array capable of polarization modulation. 15. A step of arranging the first and second semiconductor laser array 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 array structures. After arranging and fixing the structure on the support base, a plurality of second semiconductor laser array structures having a plurality of second structures are formed.
Positioning the second semiconductor laser array structure by causing at least a part of the semiconductor laser structure to emit light and at the same time to cause the first semiconductor laser array structure to function as a photodetector to receive the light of the second semiconductor laser array structure. 15. The method for manufacturing a polarization-modulatable semiconductor laser array according to claim 14, further comprising: and fixing. 16. A step of arranging the first and second semiconductor laser array structures in series in the waveguide direction with a gap therebetween so as to optically couple the semiconductor laser array structures is formed on the support table. 16. The polarization modulation according to claim 14, further comprising the step of adjusting the marker and the marker formed on the semiconductor laser array structure to a desired positional relationship to arrange and fix the semiconductor laser array structure. Method for manufacturing a possible semiconductor laser array. 17. A step of arranging the first and second semiconductor laser array structures in series in the waveguide direction on the same support table with a gap therebetween so as to optically couple the semiconductor laser array structures is formed on the support table. 16. The polarization modulation according to claim 14, further comprising a step of arranging the semiconductor laser array structure by abutting a side surface of the semiconductor laser array structure on a plane that is upright perpendicular to the semiconductor laser mounting surface. Of manufacturing various semiconductor laser arrays. 18. The method according to claim 14, further comprising the step of filling the gap with a substance having a desired refractive index.
18. A method of manufacturing a semiconductor laser array capable of polarization modulation according to any one of 1 to 17. 19. A method for producing a semiconductor laser array according to claim 1, 2 or 4, wherein a step of producing a first semiconductor laser array structure on a semiconductor substrate, and a step of producing a second semiconductor laser array structure on the substrate. A method of manufacturing a polarization-modulatable semiconductor laser array, comprising: a step of producing a semiconductor laser array structure; and a step of forming a gap at a boundary portion of the first and second semiconductor laser array structures. . 20. A step of fabricating the first semiconductor laser array structure comprises laminating a first active layer and a first optical waveguide layer only on a region of the first semiconductor laser array structure on the semiconductor substrate. And a step of at least partially forming in the first optical waveguide layer a first grating having a pitch controlled so as to have a Bragg wavelength near the gain peak of the first active layer. The step of producing the second semiconductor laser array structure includes a step of laminating a second active layer and a second optical waveguide layer only on a region of the second semiconductor laser array structure on the semiconductor substrate. And a step of manufacturing the first semiconductor laser array structure and a step of manufacturing the second semiconductor laser array structure, in which a common clad layer and a contact layer are collectively laminated on the entire surface of the optical waveguide layer. Method of manufacturing a polarization-modulatable semiconductor laser array according to claim 19, wherein it contains. 21. A step of forming a gap at a boundary portion between the first and second semiconductor laser array structures, wherein a slit-like gap and a ridge are formed at a boundary portion between regions of the first and second semiconductor laser array structures. 21. The method of manufacturing a semiconductor laser array capable of polarization modulation according to claim 19, further comprising the step of simultaneously forming a waveguide. 22. The method according to claim 19, further comprising the step of filling the gap with a substance having a desired refractive index.
22. A method of manufacturing a semiconductor laser array capable of polarization modulation according to any one of 21 to 21. 23. A polarization modulation semiconductor laser array according to any one of claims 1 to 13, a polarization selecting means for transmitting light of one polarization of the output light from the semiconductor laser array, and the semiconductor laser array. An optical transmitter having a control circuit for controlling and driving the semiconductor laser array for switching the polarization state of the output light of each pair of the semiconductor laser structures according to the input signal. 24. A polarization modulation semiconductor laser array according to any one of claims 1 to 13, polarization selection means for transmitting light of one polarization of output light from the semiconductor laser array, and the semiconductor. A semiconductor laser structure which forms a pair of laser arrays, and has a control circuit for controlling and driving the polarization state of the output light of the semiconductor laser structure according to an input signal, and a receiving means for receiving the input signal. Optical transceiver that does. 25. The polarization-modulated semiconductor laser array according to claim 1, and one of two polarization modes TE and TM of the light emitted from the polarization-modulated semiconductor laser array. A light source device, comprising: a polarization selecting means for extracting only light. 26. One of two polarization modes, TE and TM, of the polarization modulation semiconductor laser array according to claim 1 and light emitted from the polarization modulation semiconductor laser array. An optical transmitter or a transceiver provided with a light source device comprising a polarization selecting means for extracting only light, a transmitting means for transmitting the light extracted by the polarization selecting means, and a light transmitted by the transmitting means. An optical communication system having an optical receiver or a transceiver. 27. The optical communication system according to claim 26, wherein the optical transmitter or the transmitter / receiver is capable of transmitting a plurality of optical signals of different wavelengths to form a wavelength multiplexing type network. 28. The polarization-modulated semiconductor laser array according to claim 1, and one of two polarization modes TE and TM of the light emitted from the polarization-modulated semiconductor laser array. A light source device composed of a polarization selecting means for extracting only light is used to superimpose a current modulated according to a transmission signal on a predetermined bias current and supply it to each pair of semiconductor laser structures of the polarization modulation semiconductor laser 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.