WO2009125635A1

WO2009125635A1 - Semiconductor laser and modulation method of semiconductor laser

Info

Publication number: WO2009125635A1
Application number: PCT/JP2009/053985
Authority: WO
Inventors: 尚文鈴木; 正芳辻; 隆由阿南; 健一郎屋敷; 大畠山; 公良深津; 武志赤川
Original assignee: 日本電気株式会社
Priority date: 2008-04-08
Filing date: 2009-03-03
Publication date: 2009-10-15

Abstract

Provided is a semiconductor laser which can reduce power consumption of a light source for optical interconnection sharply. Also provided is a modulation method of a semiconductor laser. A semiconductor laser (100) comprises a surface emission laser (106), and a modulator (113) formed on the surface emission laser (106) while being isolated electrically. The surface emission laser (106) has an n-type DBR layer (102), an active layer (103), a current constriction structure (104), and a p-type DBR layer (105) formed on an n-type semiconductor substrate (101). A modulation portion (113) having an n-type semiconductor layer (108), an absorption layer (109) consisting of a quantum well, and a p-type semiconductor layer (110) is formed on an undoped semiconductor layer (107). The modulator (113) has a set of a plurality of electrodes and the transverse mode of the surface emission laser (106) is modulated by inputting different signals to the set of electrodes.

Description

Semiconductor laser and semiconductor laser modulation method

The present invention relates to a semiconductor laser used in the field of optical communication and a method for modulating the semiconductor laser.

Since optical communication is capable of long-distance and large-capacity transmission, long-distance communication has been widely used practically from early on. On the other hand, electrical signal transmission has been mainly used for short-distance communication. However, with the increase in data transmission speed, signal distortion and crosstalk, which are problems of electrical signals even at short distances, cannot be ignored. ing. For this reason, optical transmission is being applied also to near field communication. In particular, in recent years, optical interconnection using optical communication at a shorter distance, such as between information processing devices in the same room or in a device, has attracted attention and has been actively studied.

The challenge for the practical application of this optical interconnection is the reduction of power consumption. Conventionally, direct modulation has been used for relatively short-distance optical communications. This increases or decreases (modulates) the amount of current input to the semiconductor laser as the light source, thereby modulating the intensity of light emitted from the laser. As an actual circuit configuration, as shown in FIG. 7, a signal output from an IC 501 such as a serializer or a switching element is input to a laser driving circuit (driver) 502 through a transmission path. Next, a current signal for modulating the laser is generated by the driver 502 and supplied to a laser (LD) 503. In such direct modulation, the power consumption of a laser driving circuit for modulating current is generally larger than that of a laser. Therefore, it is important to reduce the power consumption of the driver.

The main reason why the power consumption of the driver is large is that the signal from the IC 501 is attenuated while propagating through the transmission line, so that it is necessary to amplify it. Therefore, if a laser is directly connected to the IC 501 and the laser can be modulated by the output signal of the IC 501, the power consumption of the driver 502 can be reduced. Further, this configuration eliminates the need for the driver 502, and thus has an advantage that the chip cost and the mounting cost can be reduced.

However, for the following reasons, it is difficult to reduce power consumption with the above configuration as the modulation speed increases. In short-distance communication such as optical interconnection, since the attenuation in an optical transmission line such as a fiber is small, the light output from the light source can be kept small. However, since the modulation response speed of the direct modulation laser depends on the bias current, a bias current greater than that required from the point of light output is required during high-speed operation. For this reason, power consumption increases. This problem is alleviated by downsizing the laser and reducing the area of the active layer, which adversely affects electrostatic breakdown resistance and ease of fabrication. In addition, it is difficult to achieve both high speed and low power consumption in the above configuration due to restrictions on the IC side.

Generally, an IC is manufactured by a CMOS with low power consumption, but it is difficult to achieve both high speed and large current in a CMOS. On the other hand, when the laser is directly modulated as described above, it is necessary to increase the bias current in order to improve the modulation speed. In this case, in order to realize a sufficient extinction ratio, it is necessary to increase the modulation signal from the IC in accordance with the bias current. This is difficult with CMOS as described above. In addition, the supply voltage to the CMOS tends to decrease with miniaturization, but the operating voltage of the laser cannot be made smaller than the voltage corresponding to the energy of the oscillation wavelength.

Therefore, as shown in FIG. 8, the laser (LD) 603 and the IC 601 are AC-coupled via the capacitor 602, and the DC component must be supplied from another line. In this case, since the capacitor 602 needs to have a certain capacity or more in order to pass the low frequency component, it is not easy to integrate this capacity in the IC 601 or the laser 603. Therefore, a chip capacitor is used. Since the chip capacitor is larger than the semiconductor laser, the distance between the IC 601 and the laser 603 is increased. Further, considering the mounting tolerance, it is necessary to provide a certain distance between the IC 601 and the capacitor 602 and between the capacitor 602 and the laser 603. For this reason, attenuation and waveform deterioration occur until the signal from the IC 601 reaches the laser 603. In addition, when a large number of outputs from the switching element are converted into light and output, it is necessary to mount a large number of lasers 603, but in this case, the area occupied by the capacitor 602 is relatively large. High-density mounting required for this becomes difficult.

On the other hand, if the supply voltage to the IC 601 is made higher than the driving voltage of the laser 603, the IC 601 and the laser 603 can be directly coupled without using the capacitor 602, that is, DC coupling is possible. Is avoided. However, in this case, there arises a problem that the power consumption of the IC 601 increases.

In the case of using a light source in which a modulator is integrated in a light emitting unit instead of direct modulation, the above problem can be solved if the modulator can operate at a low voltage and a low current. In long-distance communication, a light source combining a semiconductor laser and an MZ type modulator is widely used, and a light source in which an EA modulator is integrated in a semiconductor laser is also put into practical use. However, since these modulators require an operating voltage of several volts, it is difficult to drive with the output signal of the IC as described above. Moreover, since these are comparatively large, they are not suitable for high-density mounting as described above. Further, the modulator is premised on a combination with an edge emitter type laser, but it is desirable to use a surface emitting laser (VCSEL) excellent in power consumption, cost and high density as a light source for optical interconnection. However, a complex optical waveguide structure is required for coupling the modulator and the VCSEL, and it is difficult to integrate and increase the density, and it is not practical from the viewpoint of cost.

Therefore, it is desirable to have a modulation mechanism that can be driven with low voltage and low current by the output of the IC, and that can be integrated into a VCSEL that is small in size. What can be considered. In this way, the light whose transverse mode is modulated in accordance with the input signal is converted into light intensity modulation by inputting the light whose optical coupling efficiency varies greatly depending on the transverse mode, for example, a single mode fiber (SMF).

Although the purpose is greatly different, as a structure for modulating the transverse mode as described above, a surface emitting laser (see FIG. 1) that includes a light-absorbing layer around a non-absorbing region that is transparent to light ( VCSEL) is disclosed.
JP 2006-253484 A

However, in the technique described in Patent Document 1, since a change in the in-plane distribution of reflectance is realized only by the presence or absence of absorption in the peripheral portion, a relatively large voltage is required for mode switching. In addition, unintended mode changes are likely to occur due to noise on the modulator. Furthermore, in this structure, it is assumed that a higher-order mode is excited when an electric field is not applied, but actually, in this case as well, not only the higher-order mode ("0") but also the fundamental mode ( The component “1”) exists to some extent. Therefore, the off level of the signal becomes high and it is difficult to realize a high extinction ratio.

The present invention has been made in order to solve such problems, and an object of the present invention is to provide a semiconductor laser and a method for modulating the semiconductor laser capable of significantly reducing power consumption of a light source for optical interconnection. .

In order to solve the above-described problems, a semiconductor laser modulation method according to the present invention is characterized by modulating a transverse mode by inputting different signals from one or a plurality of electrode sets. .

The semiconductor laser according to the present invention includes a semiconductor laser and a set of one or a plurality of electrodes provided in the semiconductor laser, and modulates a transverse mode by inputting different signals to the set of electrodes. It is.

In the present invention, it is possible to provide a semiconductor laser and a semiconductor laser modulation method capable of significantly reducing power consumption of a light source for optical interconnection.

It is sectional drawing which shows the semiconductor laser concerning the 1st Embodiment of this invention. It is a top view which shows arrangement | positioning of the electrode in a semiconductor laser. It is a figure which shows the relationship between the applied voltage and absorption coefficient in the absorption layer of a modulator. It is sectional drawing which shows the semiconductor laser concerning the 2nd Embodiment of this invention. It is a top view which shows arrangement | positioning of the electrode in a semiconductor laser. 1 is a cross-sectional view showing a semiconductor laser according to a first embodiment of the present invention. It is a top view of FIG. 3A. It is a figure which shows a part of process of the manufacturing method of the semiconductor laser concerning the 1st Example of this invention. It is a figure which shows a part of process of the manufacturing method of the semiconductor laser concerning the 1st Example of this invention. It is a figure which shows a part of process of the manufacturing method of the semiconductor laser concerning the 1st Example of this invention. It is a figure which shows a part of process of the manufacturing method of the semiconductor laser concerning the 1st Example of this invention. It is a figure which shows a part of process of the manufacturing method of the semiconductor laser concerning the 1st Example of this invention. It is a top view of a denial part. It is sectional drawing which shows the semiconductor laser concerning the 2nd Example of this invention. It is a figure which shows the structure of DFB-LD402 in FIG. 5A. It is a top view of Drawing 5A. It is a figure which shows a part of process of the manufacturing method of the semiconductor laser concerning the 2nd Example of this invention. It is a figure which shows a part of process of the manufacturing method of the semiconductor laser concerning the 2nd Example of this invention. It is a figure which shows a part of process of the manufacturing method of the semiconductor laser concerning the 2nd Example of this invention. It is a figure which shows a part of process of the manufacturing method of the semiconductor laser concerning the 2nd Example of this invention. It is a figure which shows a part of process of the manufacturing method of the semiconductor laser concerning the 2nd Example of this invention. It is a figure which shows the circuit structure in the conventional laser direct modulation. It is a figure which shows the structure of AC coupling | bonding of IC and a laser.

Explanation of symbols

110-112, 205, 206, 316, 317, 319, 320, 321, 413-415 Electrode 432-434 Pad electrode 100 Semiconductor laser 101 n-type semiconductor substrate 102 n-

type DBR layer

103, 203 Active layer 104 Current confinement structure 105 p-type DBR layer 106 surface-emitting

laser

107, 304 undoped semiconductor layer 108 n-type semiconductor layer 109 absorption layer 110 p-type semiconductor layer 113

modulator

202, 203, 403 modulator 204 optical waveguide 301 substrate 305

first DBR layer

306, 308, 404, 406, 426

Cladding layer

307, 405 Active layer 309 p-AlAs layer 310 p-Al0.9Ga0.1As layer 312 p + -GaAs layer 313 n-GaAs layer 314 Light absorption layer 315 p-GaAs layer 330 Mesa structure 331 Polyimide 332 Pro Implanted region 333 Undoped InGaP layer 401 substrate 407 p-

type InP layer

408, 429 contact layer 409 Fe-doped semi-insulating InP layer 410, 423 n-type InP layer 411

gratings

412, 425

light absorbing layers

421, 427, 428 p-type InP Layer 422 Mask 430 Groove 309 p-AlAs layer

[First embodiment]
Next, embodiments of the present invention will be described in detail with reference to the drawings. Here, a case where the present invention is applied to a surface emitting laser will be described. 1A is a cross-sectional view showing a semiconductor laser according to a first embodiment of the present invention, FIG. 1B is a plan view showing the arrangement of electrodes in the semiconductor laser, and FIG. 1C is an applied voltage and absorption in an absorption layer of the modulator. It is a figure which shows the relationship of a coefficient.

As shown in FIG. 1A, a semiconductor laser 100 includes a semiconductor laser composed of a surface emitting laser 106 on an n-type semiconductor substrate 101, and a modulator 113 formed on the surface emitting laser 106 by being electrically separated. Have. The modulator 113 includes a plurality of electrode sets 111 and 112, and modulates the transverse mode by inputting different signals to the electrode sets. In the present embodiment, the semiconductor laser is described as a surface emitting laser, but can also be applied to an edge emitting laser as will be described later.

The surface emitting laser 106 has an n-type DBR layer 102 as a first reflecting mirror, an active layer 103, a current confinement structure 104, and a p-type DBR layer 105 as a second reflecting mirror on an n-type semiconductor substrate 101. . On the undoped semiconductor layer 107 thereabove, a modulation section 113 having an n-type semiconductor layer 108, an absorption layer 109 made of a quantum well, and a p-type semiconductor layer 110 is formed.

Electrodes are formed on the n-type semiconductor substrate 101 and the p-type DBR layer 105, respectively, through which current is supplied to the surface emitting laser 106 to emit light. On the p-type semiconductor layer 110,

electrodes

111 and 112 as shown in FIG. 1B are formed. An opening portion of the current confinement structure 104, that is, a portion where current can pass is circular, and laser light is generated in the vicinity of the active layer 103 in the lower portion of the circular shape. The electrode 111 is formed above the center of the circle, and the electrode 112 is formed above the periphery of the circle. This structure is a back-emitting surface emitting laser that emits laser light from the substrate side.

As shown in FIG. 1C, when no voltage is applied to the

electrodes

111 and 112, the oscillation wavelength of the surface emitting laser and the absorption wavelength of the absorption layer 109 are set so that the absorption layer 109 has some absorption. . In this structure, the transverse mode can be changed by inputting a differential voltage signal to the

electrodes

111 and 112. In this embodiment, the transverse mode is modulated to express “0” in the higher order mode and “1” in the basic mode.

When a reverse bias is applied to the electrode 111 and a forward bias is applied to the electrode 112, the absorption coefficient of the absorber below the electrode 111 increases, and the absorption coefficient of the absorber below the electrode 112 decreases. That is, the absorption at the center is large and the absorption at the periphery is small. Therefore, a fundamental mode having a strong electric field distribution near the center is strongly suppressed, and a higher-order mode having a strong electric field distribution is excited in the peripheral part. If the sign of the voltage applied to the

electrodes

111 and 112 is reversed, the absorption distribution is reversed, so that the higher-order mode is suppressed and the fundamental mode is excited. By applying a differential voltage signal to both electrodes in this way, mode modulation with high mode selectivity and noise resistance becomes possible.

Here, the electrode 111 is formed at the center of the position corresponding to the current confinement structure of the surface emitting laser, and the electrode 112 is formed around the current confinement structure so as to surround the electrode 111. The shape is not limited to this. For example, the electrode 111 may be formed in a donut shape. In this case, the donut-shaped

currents

111 and 112 may be divided into a plurality of parts.

In the present embodiment, since both changes in the absorption coefficient at two locations affect the mode, it is possible to switch the mode with a relatively small voltage. In many cases, noise is applied to the signal lines to the two electrodes at the same level, but the difference between the two voltages in this case is constant, so the magnitude relationship between the amounts of absorption does not change. For this reason, unintended mode changes are unlikely to occur. Furthermore, since the fundamental mode can be sufficiently suppressed in the off state, an extremely high extinction ratio can be realized as compared with the structure of the aforementioned Patent Document 1 and the conventional direct modulation.

[Second Embodiment]
In the present embodiment, an edge emitting laser is used as the semiconductor laser. FIG. 2A is a sectional view showing a semiconductor laser according to a second embodiment of the present invention, and FIG. 2B is a plan view showing the arrangement of electrodes in the semiconductor laser. A structure in which DFB (Distributed Feedback) -LD 201 and modulator 202 are integrated as shown in FIG. 2A will be described. The active layer 203 of the DFB-LD and the optical waveguide 204 of the modulator are connected, and laser light generated by the DFB-LD is emitted through the modulator.

The band gap of the optical waveguide of the modulator is set slightly larger than the energy of the laser beam so as to have a small absorption coefficient for the laser beam. When a reverse bias is applied to the modulator, the band gap is reduced by the confined Stark effect or the Franz-Keldish effect, and the absorption coefficient is increased. In addition, when a forward bias is applied, the built-in potential is canceled and the absorption edge is shortened and the absorption coefficient is reduced. Here, the waveguide is set to have a width capable of generating a higher-order mode, and the electrodes are arranged near the center and both ends of the waveguide as shown in FIG. 2B. Here, a plurality of electrodes 205 near the center and electrodes 206 near both ends thereof may be provided.

When a forward bias is applied to the electrode 205 near the center and a reverse bias is applied to the end electrode 206, the absorption coefficient near the center decreases and the absorption coefficient near the end increases. Therefore, a fundamental mode having a strong electric field strength near the center is excited. On the other hand, when reverse bias is applied to the electrode 205 and forward bias is applied to the electrode 206, the absorption coefficient near the center increases and the absorption coefficient near the edge decreases, so that a higher-order mode having a strong electric field strength toward the edge is excited. The Thus, by applying a differential voltage signal to both electrodes, mode modulation is possible even in an edge-emitting laser.

In the conventionally used modulator integrated laser, an absorption modulator is integrated in a semiconductor laser. The operating principle of this modulator is to change the absorption coefficient by changing the voltage applied to the modulator as in the above example. However, in this absorption type modulator, a voltage is uniformly applied to the waveguide. In this configuration, in order to turn off the signal, it is necessary to absorb the laser beam almost completely by the modulation section, so that a high applied voltage and a relatively long modulator length are required. On the other hand, in the present embodiment, the modulator only needs to give an in-plane distribution to the absorption coefficient, and a required amount of light absorption is small. Therefore, modulation can be performed with a low applied voltage, and the length of the modulator can be significantly shortened.

First embodiment.
Next, the structure and manufacturing method of the first embodiment will be described using specific examples. In the first embodiment, an example in which the present invention is applied to an oxidized confined surface emitting laser having an oscillation wavelength of 1.3 μm formed on a GaAs substrate will be described. FIG. 3A is a sectional view showing a semiconductor laser according to the first embodiment of the present invention, and FIG. 3B is a plan view thereof.

As shown in FIG. 3A, the structure of this embodiment has a surface emitting laser (VCSEL) 302 on an n-type GaAs substrate 301 and a modulator 303 including an absorption layer thereon. The VCSEL 502 and the modulator 303 are electrically separated by an undoped semiconductor layer 304. The VCSEL 302 includes a first DBR layer (n-type semiconductor mirror layer) 305 in which a pair of an n-type GaAs layer and an n-type Al0.9Ga0.1As phase is used as a basic unit, and an n-type Al0.3Ga0.7As cladding layer. 306, an active layer 307 composed of an undoped GaInNAs quantum well and a GaAs barrier layer, a p-Al0.3Ga0.7As cladding layer 308, a p-AlAs layer 309, a p-Al0.9Ga0.1As layer 310, a p-type GaAs layer and a p-type A basic unit is a pair of Al0.9Ga0.1As layers, and a second DBR layer (p-type semiconductor mirror layer) 311 and a p + -GaAs layer 312 are stacked.

The modulator is composed of an n-GaAs layer 313, an undoped GaInNAs quantum well, a light absorption layer 314 comprising a GaAs barrier layer, and a p-GaAs layer 315, and two sets of

electrodes

316, 317 as shown in FIG. Is formed. Protons are injected into a portion 318 located between the

electrodes

316 and 317 in the p-GaAs layer 315, and the lower portions of both electrodes are electrically separated. Furthermore,

electrodes

319 and 320 for supplying current to the VCSEL 302 and an n-side electrode 321 for the modulator are provided. Further, the wavelengths of the absorption edges of the active layer 307 of the VCSEL 302 and the light absorption layer 314 of the modulator 303 are set so that the latter is shorter by about 70 nm than the former.

Next, a method for manufacturing the above structure will be described. 4A to 4E are views showing the method of manufacturing the semiconductor laser according to the first embodiment of the present invention in the order of steps, and FIG. 4F is a plan view of the electrode portion. First, on the n-type GaAs substrate 301, a first DBR layer (n-type semiconductor mirror layer) 305, an n-type Al0.3Ga0.7As cladding layer 306, an active layer 307 composed of an undoped GaInNAs quantum well and a GaAs barrier layer, p-Al0 .3Ga0.7As cladding layer 308, p-AlAs layer 309, p-Al0.9Ga0.1As layer 310, a pair of p-type GaAs layer and p-type Al0.9Ga0.1As layer as a basic unit, 2 DBR layers (p-type semiconductor mirror layers) 311, p + -GaAs layers 312, undoped InGaP layers 333, undoped GaAs layers 304, n-GaAs layers 313, light-absorbing layers 314 comprising undoped GaInNAs quantum wells and GaAs barrier layers, P-GaAs layer 305 is sequentially deposited by metal organic chemical vapor deposition (MOCVD) method Layer (FIG. 4A: Step 1).

In the above layer structure, the layer thicknesses of the undoped InGaP layer 333 to the p-GaAs layer 315 are adjusted so that the sum of the optical path lengths is an integral multiple of λ / 2. Here, λ is the oscillation wavelength. The light absorption layer 314 is disposed near the antinode of the standing wave, that is, near the maximum value.

Next, a SiO ₂ film is formed by thermal CVD, a circular resist pattern is formed thereon by photolithography, and the SiO ₂ film is etched using this resist pattern as a mask (step 2). Thereby, a circular SiO ₂ film pattern is formed.

Next, etching is performed from the surface to the surface of the first DBR layer (n-type semiconductor mirror layer) 305 using this SiO ₂ film pattern as a mask to form a mesa structure 330 (FIG. 4B: step 3).

Next, heating is performed at a temperature of about 400 ° C. for about 10 minutes in a furnace in a steam atmosphere. As a result, only the p-AlAs layer 309 whose side surface is exposed in step 3 is selectively oxidized simultaneously (step 4). Further, a resist pattern is formed on the mesa structure 330 formed in Step 3 by photolithography so that the outer periphery is exposed, and then the outer periphery is etched to the p + -GaAs layer 312 by etching (Step 5). Note that the undoped InGaP layer 333 is inserted as an etching stop layer in this step, and is not essential in terms of operation principle.

Next, by repeating the same step as the step 5, another cylindrical step is provided in the mesa structure 330 as shown in FIG. 4C (step 6). As a result, a part of the n-GaAs layer 313 is exposed. Next, an n-side electrode is formed on the first DBR layer 305 exposed in step 3 and the n-GaAs layer 313 exposed in step 6, as follows.

First, after applying a photoresist on the entire surface of the wafer, only the photoresist is removed by lithography. After depositing AuGe / AuNi / Ti / Pt / Au, the photoresist is removed and the metal on the photoresist is lifted off to lift off the electrode 320 on the first DBR layer 305 and the electrode on the n-GaAs layer 313. 321 is formed (FIG. 6D: Step 7).

Next, after the mesa structure is embedded with the polyimide 331, the polyimide on the mesa structure 330 and the electrode 320 formed in step 7 is removed by lithography (step 8). Next, electrodes are formed on the p + -GaAs layer 312 at the outer periphery of the mesa structure 330 exposed at step 5 and the p-GaAs layer 315 at the top of the mesa as follows.

First, after applying a photoresist on the wafer and patterning by mask exposure, Ti / Pt / Au is deposited, the photoresist is removed, and Ti / Pt / Au on the photoresist is lifted off to p-

side Electrodes

319, 316, and 317 are formed (FIG. 6E: Step 9). At this time, as shown in FIG. 6F, the

electrodes

316 and 317 on the p-GaAs layer 315 are formed at the central portion and the peripheral portion, respectively. Further, at this time, five pad electrodes (not shown) and wirings connecting them to the

electrodes

320, 321, 319, 316, and 317 are simultaneously formed on the polyimide.

Next, a portion other than between the

electrodes

316 and 317 is covered with a photoresist by a photolithography technique, and then proton implantation is performed (FIG. 6F: step 10). At this time, the acceleration voltage at the time of injection is adjusted so that protons reach the front of the light absorption layer 314. Thereafter, the resist is removed. Since the proton injection region 332 produced by this step has a high resistance, the p-GaAs under the electrode 316 and the p-GaAs under the electrode 317 can be electrically separated.

Finally, after the back surface of the n-type GaAs substrate 301 is polished to a thickness of 150 μm, a back electrode made of AuGe / AuNi / Ti / Au is formed by vapor deposition (step 11). This metal can be used to fuse the element to a heat sink or the like with solder. Thus, the device is completed.

In the present embodiment, a surface emitting laser is used as the semiconductor laser. By applying a differential voltage signal to both electrodes, mode selectivity is high and noise-resistant mode modulation is possible. Since the mode is selected by two sets of electrodes, the mode selection system is strong. In addition, since a single mode component can be removed, a high extinction ratio can be realized. Furthermore, unintended mode changes are unlikely to occur as long as the same noise is applied to both electrodes.

Second embodiment.
Next, the structure and manufacturing method of the second embodiment will be specifically described as a second example. Here, an example in which the present invention is applied to an edge emitting laser having an oscillation wavelength of 1.3 μm formed on an InP substrate will be described. 5A is a cross-sectional view showing a semiconductor laser according to a second embodiment of the present invention, FIG. 5B is a view showing the structure of the DFB-LD 402, and FIG. 5C is a plan view of FIG. 5A.

As shown in FIG. 5A, the structure of this embodiment has a DFB-LD 402 on a n-type InP substrate 401 and a modulator 403 including an absorption layer on the side thereof. As shown in FIG. 5B, the DFB-LD 402 includes an n-type InGaAsP cladding layer 404, an active layer 405 composed of an undoped InGaAsP quantum well and an InGaAsP barrier layer, a p-type InGaAsP cladding layer 406, a p-type InP layer 407, and a p + -InGaAs contact layer 408. Are stacked, a Fe-doped semi-insulating InP layer 409, and an n-type InP layer 410. A grating 411 is formed between the n-type InP substrate 401 and the n-type InGaAsP clad layer 404.

On the other hand, the modulator 403 also has a structure similar to that of the DFB-LD 402, but has a light absorption layer 412 including an undoped InGaAsP quantum well and an InGaAsP barrier layer instead of the active layer 405. The wavelengths of the absorption edges of the active layer 405 of the DFB-LD and the light absorption layer 412 of the modulator are set so that the latter is about 70 nm shorter than the former. The DFB-LD 402 has a p-side electrode 413, and the modulator 403 has two p-

side electrodes

414 and 415. The two p-

side electrodes

414 and 415 are formed on the light absorption layer 412, but as shown in FIG. 5C, the electrode 414 is near the center of the light absorption layer, and the electrode 415 is at the end of the light absorption layer. Placed in the part. Protons are injected into the p-type semiconductor layer located between the electrode 414 and the electrode 415, and the lower part of both electrodes is electrically separated. Further, a common n electrode of the DFB-LD 402 and the modulator 403 is formed on the back of the n-type InP substrate 401.

Next, a method for manufacturing the above structure will be described. 6A to 6E are views showing a semiconductor laser manufacturing method according to the second embodiment of the present invention in the order of the steps. First, the grating 411 is formed on the n-type InP substrate 407 by interference exposure (step 1). Next, an active layer 405 including an n-type In0.83Ga0.27As0.36P0.64 cladding layer 404, an undoped In0.8Ga0.2As0.64P0.36 quantum well and an In0.83Ga0.27As0.36P0.64 barrier layer, and a p-type In0. .83Ga0.27As0.36P0.64 cladding layer 406 and p-type InP layer 421 are sequentially deposited by metal organic chemical vapor deposition (MOCVD) (step 1). Next, a SiO ₂ film is deposited on the wafer by thermal CVD, and a SiO ₂ stripe mask 422 having a width of 300 μm and a pitch of 400 μm is formed by photolithography and etching (step 2). Next, the portion without the mask is etched up to the n-type InP substrate 401 by wet etching (FIG. 6A: step 3). The grating formed in step 1 is also deleted by this etching. Of course, the grating of the portion covered with the SiO ₂ mask 422 remains, and the upper portion becomes the DFB-LD.

On the other hand, a modulator is formed on the portion etched in this step. Subsequently, the n-type InP layer 423, the n-type In0.83Ga0.27As0.36P0.64 cladding layer 424, the undoped In0.86Ga0.14As0.51P0.49 quantum well, and the In0.83Ga0.27As0.36P0.64 are again formed by MOCVD. A light absorption layer 425 made of a barrier layer, a p-type In0.83Ga0.27As0.36P0.64 cladding layer 426, and a p-type InP layer 427 are sequentially stacked by metal organic chemical vapor deposition (MOCVD) (step 4 in FIG. 6B). . These layers are selectively grown on the portion without the mask formed in step 3. Next, the SiO ₂ mask 422 is removed, a new SiO ₂ film is deposited by thermal CVD, and a striped SiO ₂ mask is formed by photolithography and etching (step 5). The stripe direction of the mask produced in this step is formed in a direction orthogonal to that produced in step 2. The stripe width is, for example, 1.5 μm in the portion on the DFB-LD and 2 μm in the portion on the modulator, for example, and the width is linearly changed near the junction. The stripe pitch can be set to 300 μm, for example.

Using this stripe mask, etching reaching the n-type InP substrate 401 is performed (step 6). Next, an Fe-doped semi-insulating InP layer 409 and an n-type InP layer 410 are formed by MOCVD (FIG. 6C: Step 7). These layers are selectively grown on the portion without the mask formed in step 5, and function as a current blocking layer. Next, after removing the SiO ₂ mask, a p-type InP layer 428 and a p + -InGaAs contact layer 429 are stacked by MOCVD (step 8). Next, two grooves 430 with a pitch of, for example, 30 μm are formed to reach the n-type InP substrate 401 so as to sandwich the active layer (and light absorption layer) stripe formed in step 6 by photolithography and mesa etching (step 9).

Then, after forming a SiO ₂ film on the wafer by photolithography and etching, the active layer (and the light-absorbing layer) to remove the SiO ₂ film on the stripe (Figure 6D: Step 10). Next, an electrode is formed in the part where SiO ₂ is removed by the following procedure. First, after applying a resist, the resist on the part where SiO ₂ is removed in step 8 is removed by photolithography. Next, after depositing Ti / Pt / Au, the metal on the resist is removed by lift-off (step 11). Thereby, a p-side electrode is formed. At this time, as shown in FIG. 6E, only one electrode 413 is formed on the DFB-LD, but two

electrodes

414 and 415 are formed on the modulator. At this time, for example, three pad electrodes 432 to 434 are formed in portions outside a groove having a pitch of 30 μm formed in step 7 and connected to the electrodes 413 to 415, respectively. Wirings connecting them are also formed simultaneously in this step.

Next, a resist is applied to the entire surface of the wafer, and the resist is removed between the

electrodes

414 and 415 by photolithography. Subsequently, protons are injected up to the top of the light absorption layer 425, that is, the p-type InP layer 427 and the p-type In0.83Ga0.27As0.36P0.64 cladding layer 426 (step 10). Thereby, the lower part of both electrodes is electrically separated. Next, after the back surface of the n-type InP substrate 401 is polished to a thickness of 150 μm, AuGe / AuNi / Ti / Au is vapor-deposited to form a back surface n-electrode (not shown) (step 11). The wafer thus formed is cleaved at 400 μm intervals so as to include the DFB-LD and the modulator, and coating is applied to both end faces to complete the device.

In this embodiment, an edge emitting laser is used as the semiconductor laser. By applying a differential voltage signal to both electrodes, mode modulation is possible even in an edge-emitting laser. Since the modulator requires a small amount of light absorption, it can be modulated with a low applied voltage, and the length of the modulator can be significantly shortened.

As mentioned above, although the Example of this invention was described, the implementation method of this invention is not limited to the above-mentioned various forms, A various deformation | transformation is possible in the range which does not deviate from the summary. Regarding the wavelength and material of the semiconductor light emitting device, those other than those listed in the examples can be selected.

This application claims priority based on Japanese Patent Application No. 2008-100019 filed on Apr. 8, 2008, the entire disclosure of which is incorporated herein.

The present invention contributes to low power consumption, high speed, and miniaturization of a semiconductor laser and an integrated circuit including the semiconductor laser, and has various applicability in optical communication and related technical fields. is there.

Claims

A modulation method of a semiconductor laser, wherein a transverse mode is modulated by inputting different signals from one or a plurality of electrode sets.
2. The semiconductor laser according to claim 1, wherein the transverse mode is modulated by inputting different signals from a set of one or a plurality of electrodes formed at a position corresponding to the current confinement structure of the surface emitting laser. Modulation method.
2. The method of modulating a semiconductor laser according to claim 1, wherein the transverse mode is modulated by inputting different signals from a set of one or a plurality of electrodes formed on the optical waveguide of the edge-emitting laser. 3.
4. The modulation of a semiconductor laser according to claim 2, wherein a differential signal is input to a pair of electrodes of a modulator formed on the surface-emitting laser or the edge-emitting laser. 5. Method.
5. The method of modulating a semiconductor laser according to claim 1, wherein the transverse mode is modulated by changing a refractive index or an absorption coefficient of a part of the layers according to a voltage applied to the electrode. .
The light emitted from the semiconductor laser is incident on an optical fiber or an optical element having different optical coupling efficiency or transmittance depending on the transverse mode, thereby converting the modulation of the transverse mode into the light intensity modulation. The method for modulating a semiconductor laser according to any one of claims 1 to 5.
The method of modulating a semiconductor laser according to claim 2, wherein the transverse mode is modulated by inputting a differential signal to a pair of electrodes respectively provided at a central portion and an outer peripheral portion of the current confinement structure.
By inputting a differential signal to the first electrode formed at the center position on the optical waveguide along the light emitting direction and the second electrode provided on the right side, the left side or the left and right sides with respect to the center position. 4. The method for modulating a semiconductor laser according to claim 3, wherein the transverse mode is modulated.
A semiconductor laser;
A set of one or more electrodes provided in the semiconductor laser;
A semiconductor laser that modulates the transverse mode by inputting different signals to the set of electrodes.
A surface emitting laser;
A modulator formed on the surface-emitting laser and electrically separated from the surface-emitting laser;
The modulator has a set of one or a plurality of electrodes at a position corresponding to the current confinement structure of the surface emitting laser, and modulates a transverse mode by inputting different signals to the set of electrodes. The semiconductor laser according to claim 9.
An edge emitting laser;
A modulator formed on the edge-emitting laser and electrically separated from the surface-emitting laser;
The modulator has a set of one or a plurality of electrodes formed on the optical waveguide of the edge-emitting laser, and modulates a transverse mode by inputting different signals to the set of electrodes. The semiconductor laser according to claim 9.
The semiconductor laser according to any one of claims 9 to 11, wherein the modulation section includes a pair of electrodes, and a differential signal is input to the pair of electrodes to modulate a transverse mode.
The semiconductor laser according to any one of claims 9 to 12, wherein the modulation section includes a layer whose refractive index or absorption coefficient changes according to voltage.
The semiconductor laser according to claim 9, wherein the set of electrodes is arranged at a position where the intensity of the laser beam is different from that of the excited transverse mode.
The semiconductor laser according to claim 9, wherein one electrode is disposed in the vicinity of the peak of the light intensity of the fundamental mode.
The semiconductor laser includes a first reflecting mirror, an active layer formed on the first reflecting mirror, the current confinement structure, and a second reflecting mirror formed on the current confinement structure. The semiconductor laser according to claim 10, wherein the semiconductor laser is a light emitting laser.
The semiconductor laser according to claim 16, wherein the semiconductor substrate side is an emission surface.