JP2004177728A - Electro-absorption modulator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a modulator technology with which deterioration of modulator characteristics is suppressed by suppressing increase of carrier density in an active layer of an electro-absorption (EA) modulator and further efficiency of electric field application to the active layer in an impedance control type EA modulator is improved. <P>SOLUTION: The semiconductor EA modulator comprises an optical waveguide having the active layer to absorb light with the electric field application formed therein. By widening the width of the optical waveguide 106 of the EA modulator part at the light incident part where the light intensity is maximum and forming the optical waveguide into a tapered shape continuously getting narrower as going closer from here to the light emitting part, light absorption per unit area is averaged in the optical axis direction, dependence on input light intensity is reduced in extinction and chirping characteristics, etc. of the EA modulator and further deterioration of frequency response is suppressed. Furthermore, in the impedance control type EA modulator, an effective voltage applied to the active layer part is improved and the extinction characteristics of the EA modulator can be realized. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a technology related to a semiconductor electro-absorption modulator, which is one of the main components of a core optical transmission having a transmission speed of 2.5 Gbit / s or more. The present invention relates to a technology effective when applied to a mounted semiconductor laser module for optical communication, an optical transmission module, an optical transmission device, and an optical communication system.
[0002]
[Prior art]
According to the studies made by the present inventors, the following techniques can be considered for a semiconductor electroabsorption modulator.
[0003]
(Prior art 1)
Conventional technology 1 will be described using an example of a semiconductor electroabsorption modulator integrated light source having a transmission speed of 10 Gbit / s for optical transmission.
[0004]
A 10 Gbit / s semiconductor electroabsorption modulator integrated laser (hereinafter referred to as an EA (Electro-Absorption) modulator integrated laser) is a DFB laser (Distributed feedback laser) section driven by a constant current, and an EA modulator operated by a modulation voltage. Unit. The EA modulator turns on and off the light of the DFB laser by shifting the absorption edge of the active layer of the EA modulator by utilizing the quantum confinement Stark effect generated by applying a voltage to the EA modulator. It is an EA modulator (for example, see Non-Patent Document 1).
[0005]
A laser module is configured by mounting this EA modulator integrated laser, a Peltier, a lens, an isolator, an optical fiber, a monitor photodiode, and the like in the same package. Further, by mounting this laser module together with a laser drive current source, a modulator drive circuit, a bias amplitude control circuit, a temperature control circuit, and the like, an optical transmission module for 10 Gbit / s optical transmission is configured. These laser modules and optical transmission modules are called semiconductor laser devices.
[0006]
In order for the optical transmission module for 10 Gbit / s optical transmission to obtain desired characteristics, in the EA modulator integrated laser, characteristics such as a band, an optical output at the time of modulation, an extinction ratio, and an α parameter which is an index of fiber dispersion tolerance are used. , The desired properties must be satisfied.
[0007]
On the other hand, in the conventional EA modulator integrated laser, the laser current is usually 65 mA. However, if the current is further increased to obtain an optical output, the light incident on the EA modulator increases, and the modulator semiconductor active layer is increased. The carrier density in the inside increases. This phenomenon can be confirmed by a photocurrent current flowing through the modulator. When the carrier density increases extremely, the electric field applied to the EA modulator is cut off, and a voltage drop occurs in the EA modulator active layer. This voltage drop causes a difference between the voltage externally applied and the voltage effectively applied to the active layer.
[0008]
The extinction ratio, band, and chirp characteristics, which are important characteristics of the EA modulator integrated laser, depend on the voltage effectively applied to the EA modulator active layer. The characteristics will change. That is, if the current of the laser is changed to increase the light intensity input to the EA modulator, the characteristics of the modulator change.
[0009]
Further, it is known that the above-mentioned electric field interruption causes deterioration of frequency response. The same phenomenon occurs in a single EA modulator element that is not nomoly integrated with a laser when light is incident from the outside.
[0010]
(Prior art 2)
Conventional technique 2 will be described using an example of an electro-absorption modulator using a semiconductor impedance control type electrode structure with a transmission speed of 40 Gbit / s for optical transmission.
[0011]
A 40 Gbit / s semiconductor electroabsorption modulator (hereinafter, referred to as an EA modulator) has the same principle of turning on and off light as the EA modulator described in (Prior Art 1). The method of applying a high-frequency electric field to the modulator is different, and the EA modulator is an EA modulator using an impedance control type electrode structure (for example, see Non-Patent Document 2). The impedance control type electrode structure realizes higher-speed operation because the CR time constant of the entire modulator does not limit the operating frequency by matching the traveling direction of the microwave with the traveling direction of light. is there.
[0012]
By mounting the EA modulator, a Peltier, a lens, an optical fiber, and a driver IC for driving the modulator in the same package, an EA modulator optical element module is configured.
[0013]
Even in the EA modulator of 40 Gbit / s, there are major problems such as the dependency of the EA modulator characteristic on the optical input intensity and the deterioration of the frequency response when the optical input intensity increases, as described in (Prior Art 1). In addition, in the 40 Gbit / s EA modulator, it is very difficult to realize sufficient extinction characteristics for the following reasons.
[0014]
At present, an EA modulator driving driver capable of realizing a high-speed operation of 40 Gbit / s has difficulty in increasing the output, and has only realized a voltage of about 3 V. At an amplitude voltage of 3 V or less, the extinction characteristic is insufficient in combination with the current EA modulator. Further, in an EA modulator having an impedance control type electrode structure, it is known that the intensity of the microwave output from the EA modulator drive driver is attenuated as it passes through the impedance control type electrode.
[0015]
In the case of a conventional EA modulator having a constant optical waveguide width, the confinement coefficient is constant in the optical axis direction of the waveguide, but the voltage applied by the microwave is in the optical axis direction of the waveguide in the light emission direction. Decay towards. For this reason, on the waveguide incident side where the microwave electric field intensity is strong, the amount of light absorption during modulation is large, and the amount of absorption is almost close to the saturation level.
[0016]
On the other hand, the amount of light absorption is smaller on the exit side of the waveguide where the microwave electric field strength is weaker than on the incidence side. If the saturation level of light absorption is high on the waveguide incident side, it can be said that light can be more absorbed when the microwave electric field intensity is high. That is, the relationship between the light absorption level and the microwave intensity in the waveguide hinders efficient application of an electric field to the modulator active layer.
[0017]
(Conventional technology 3)
As a third conventional technique, in an EA modulator, a signal light is absorbed to generate a light absorption current inside. Therefore, if the intensity of the signal light is large, the light absorption current becomes large and the high-speed operation is restricted. Therefore, it is important to efficiently extract the light absorption current in order to improve the high frequency characteristics.
[0018]
Therefore, in such an EA modulator, there is a technique characterized in that the total thickness of the light confinement layer and the light absorption layer is larger at one end than at the other end. According to this technique, it is possible to provide an EA modulator that can efficiently extract a light absorption current by making the generation region of the light absorption current uniform (for example, see Patent Documents 1 and 2).
[0019]
[Non-patent document 1]
Aoki, et al. [M. Aoki, et. al. ], "High Speed (10 Gigabit Persec) and Low Drive Voltage (1 Volt Peak-to-Peak) Indium Gallium Arsenide / Indium Gallium Arsenide Phosphorus Emq. High-speed (10 Gbit / s) and low-drive-voltage (1 V peak-to-peak) InGaAs / InGaAsP MQW electroabsorption mechanism-integrated relay integrators lectron. Lett. ], 28 volumes [vol. 28]; 1157-1158, 1992
[0020]
[Non-patent document 2]
Shirai, et al. [M. shirai, et. al. ], The 28th European Conference on Optical Communications (ECOC 2002) Proceedings 9.5.4 [Proc. 28 ^th European Conference on Optical Communications (ECOC2002), 9.5.4], “Impedance Controlled Electrodes (ICIE) Semiconductor Modulators for 1.3 μm 40 Gigabyte Persec Transceivers [IMPEDANCE-CONTROLLED-CONTROLLED-CONTROL SEMICONDUCTOR MODUATORS FOR 1.3-μm-40-Gbit / s TRANSCEIVERS] "
[0021]
[Patent Document 1]
JP 2001-142036 A (Abstract on the first page, etc.)
[0022]
[Patent Document 2]
JP 2001-24289 A (Abstract on page 1 etc.)
[0023]
[Problems to be solved by the invention]
By the way, as a result of the inventor's study on the EA modulator technology as described above, two problems that can be solved by the present invention are considered.
[0024]
One is to suppress an increase in carrier density in the EA modulator active layer. Due to this increase in the carrier density, the electric field applied to the EA modulator is cut off. That is, if the output of the laser is increased to increase the light intensity input to the EA modulator, the characteristics of the modulator change. In addition, this increase in carrier density causes deterioration of frequency response.
[0025]
A second problem is to improve the efficiency of applying an electric field intensity to the modulator active layer in an EA modulator having an impedance control type electrode structure. In a high-speed modulation operation, it is difficult to obtain a sufficient extinction characteristic due to limitations of the EA modulator and a driver for driving the EA modulator. In particular, in the EA modulator having the impedance control type electrode structure, the microwave intensity is large on the input side of the impedance control type electrode, that is, on the optical waveguide input side of the modulator, and is attenuated on the output side, that is, on the optical input side of the modulator waveguide. It is known to
[0026]
In the case of a conventional EA modulator having a constant optical waveguide width, the confinement coefficient is constant in the optical axis direction of the waveguide, but the voltage applied by the microwave is in the optical axis direction of the waveguide in the light emission direction. Decay towards. For this reason, on the waveguide incident side where the microwave electric field intensity is strong, the light absorption amount at the time of modulation approaches the saturation level, and on the waveguide exit side where the microwave electric field intensity is weak, the light absorption amount is smaller than that on the incident side. The relationship between the light absorption level and microwave intensity in this waveguide hinders efficient application of an electric field to the modulator active layer.
[0027]
Accordingly, the present invention solves the first problem described above, and suppresses an increase in the carrier density in the active layer of the electroabsorption modulator, thereby suppressing deterioration in the characteristics of the modulator. It is an object to provide a modulator.
[0028]
Furthermore, the present invention solves the second problem described above, and provides a semiconductor electroabsorption modulator capable of improving the efficiency of applying an electric field to an active layer in an impedance control electroabsorption modulator. It is the purpose.
[0029]
Note that the above-described conventional techniques (Patent Documents 1 and 2) are similar as techniques for solving the same problems as the present invention, but differ in the structure of the optical waveguide. That is, in Patent Documents 1 and 2, the thickness direction of the optical waveguide is specified, but in the present invention, the width direction on the plane of the optical waveguide is specified.
[0030]
[Means for Solving the Problems]
The present invention relates to the first problem, that is, the suppression of the increase in the carrier density in the EA modulator active layer, by reducing the concentration of the light absorption and making the light absorption uniform. It is possible to suppress an increase in density.
[0031]
Specifically, it is conceivable to increase the optical waveguide width in the direction parallel to the InP substrate at the input portion of the EA modulator where the light intensity is high, and reduce the light density in the active layer where light absorption occurs. The light intensity inside the EA modulator is absorbed by the active layer in the axial direction of the waveguide, so that the light intensity at the optical waveguide length x from the optical waveguide entrance is P (x) = P (0 ) Exp (−Γαx). Here, Γ is the light confinement coefficient of the optical waveguide, α is the absorption coefficient of the active layer, x is the length of the optical waveguide from the optical waveguide entrance, and P (0) is the incident light intensity. That is, the incident light gradually decreases from the optical waveguide entrance end toward the exit direction.
[0032]
Therefore, by increasing the width of the EA modulator optical waveguide at the entrance where the light intensity is the largest, and by continuously making the taper shape narrower from the entrance to the exit, the light density at the entrance side where the light intensity is large is increased. It becomes possible to reduce. This makes it possible to make the amount of light absorbed per unit area closer to the direction of averaging in the optical axis direction, thereby suppressing an excessive increase in carrier density. Therefore, by adopting the above structure, it is possible to reduce the input light intensity dependency in the extinction characteristic, the chirp characteristic, and the like of the EA modulator, and to suppress the deterioration of the frequency response.
[0033]
Furthermore, the present invention can solve the second problem, that is, the improvement of the efficiency of applying the electric field intensity to the modulator active layer in the EA modulator having the impedance control type electrode structure by the same means. It is.
[0034]
In the electroabsorption modulator using the 40 Gbit / s semiconductor impedance control type electrode structure described in (Prior art 2), the width of the optical waveguide in the direction parallel to the InP substrate is increased on the EA modulator input side. The width of the waveguide is continuously reduced to a tapered shape toward the modulator output side. By adopting this structure, the effective applied voltage of the active layer portion can be improved for the following two reasons.
[0035]
The first reason is that, as described above, the carrier density can be averaged in the optical axis direction, and the effect of blocking the electric field applied to the waveguide active layer portion is reduced.
[0036]
Next, the second reason will be described. In an EA modulator having an impedance control type electrode structure, it is known that the intensity of the microwave output from the EA modulator drive driver attenuates as it passes through the impedance control type electrode.
[0037]
In the case of a conventional EA modulator having a constant optical waveguide width, the confinement coefficient is constant in the optical axis direction of the waveguide, but the voltage applied by the microwave is in the optical axis direction of the waveguide in the light emission direction. Decay towards. For this reason, on the waveguide incident side where the microwave electric field intensity is strong, the amount of light absorption at the time of modulation increases, and the light absorption approaches the saturation level. Here, the saturation level of light absorption refers to a state in which no light absorption occurs even when an electric field is applied. It is known that light absorption hardly occurs as the saturation level is approached.
[0038]
On the other hand, the amount of light absorption is smaller on the exit side of the waveguide where the microwave electric field strength is weaker than on the incidence side. For example, if the saturation level of light absorption is high on the waveguide incident side, it can be said that light can be further absorbed even in a strong electric field without reducing the light absorption amount due to saturation. The saturation level of light absorption can be achieved by increasing the optical waveguide width.
[0039]
Therefore, by adopting the optical waveguide structure of the present invention, an electric field is applied to the optical waveguide active layer with a sufficiently strong microwave with a small intensity attenuation on the incident side of the optical waveguide having a light absorption saturation level higher than the emission side. Therefore, light can be efficiently extinguished.
[0040]
For the above two reasons, the effective applied voltage of the active layer can be improved, and the extinction characteristics of the EA modulator can be improved. It is needless to say that the reduction of the input light intensity dependency in the EA modulator characteristics and the suppression of the deterioration of the frequency response are simultaneously realized.
[0041]
Further, the present invention provides an EA modulator as described above, or an EA modulator integrated light source (laser) in which an EA modulator having an impedance control type electrode structure and a laser (for example, a single mode laser or the like) are integrated. The present invention can be applied to a mounted semiconductor element module, an optical transmission module, an optical transmission device, and the like, so that the optical output stability and reliability can be improved.
[0042]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In all the drawings for describing the embodiments, the same members are denoted by the same reference numerals, and a repeated description thereof will be omitted.
[0043]
(Embodiment 1)
Referring to FIG. 1, a description will be given of a semiconductor EA modulator of a 1.5 μm wavelength band which is used for optical transmission of 20 km with a transmission speed of 10 Gbit / s as a first embodiment of the present invention. In addition, FIG. 2 illustrates a semiconductor element module on which the semiconductor EA modulator of FIG. 1 is mounted, and FIG. 3 illustrates a modified example of the semiconductor EA modulator. 1A and 1B show a semiconductor EA modulator according to the first embodiment, in which FIG. 1A is a plan view, and FIG. 1B is a cross-sectional view taken along the line aa ′ of FIG. FIG. 2 is a plan view of a semiconductor device module on which a semiconductor EA modulator is mounted. 3A and 3B show a modified example of the semiconductor EA modulator, wherein FIG. 3A is a plan view, and FIG. 3B is a cross-sectional view taken along the line aa ′ of FIG.
[0044]
The element of the semiconductor EA modulator in the 1.5-μm wavelength band, which is used for optical transmission at a transmission speed of 10 Gbit / s and 20 km in this embodiment, is formed on an n-type InP semiconductor substrate 100 by the first crystal growth. By a known selective growth method using a metal vapor phase method, an InGaAsP lower optical guide layer 101, a strained multiple quantum well layer (hereinafter referred to as "quantum well layer") 102 composed of eight periods of InGaAsP well layers and barrier layers, and an InGaAsP upper optical guide layer. 103, an InP cladding layer 104, and an InGaAs contact layer 105 are formed.
[0045]
Next, in order to form the EA modulator section optical waveguide 106 having an active layer that absorbs light by applying an electric field, the EA modulator section is formed by ordinary photolithography and wet etching using a Br-based etchant. An optical waveguide 106 is formed. In this optical waveguide formation, the width of the optical waveguide in the direction parallel to the InP substrate of the EA modulator section is, for example, 2 μm on the input side of the EA modulator and continuously increases toward the output side of the EA modulator. To form a shape that is thinner to 1.4 μm. Specifically, this can be realized by designing the pattern of the photomask to have a tapered shape.
[0046]
Here, the EA modulator section optical waveguide 106 formed in the tapered shape includes the lower light guide layer 101, the quantum well layer 102, and the upper light guide layer 103, which absorb light when the EA modulator operates. In. Further, both sides of the optical waveguide are buried by the Fe-InP layer for the purpose of reducing the capacity, and regrowth is performed.
[0047]
Subsequently, after a passivation film 107 is formed on the entire surface of the semiconductor, through holes are formed so that an electric field is applied to the tapered EA modulator active layer, and then a p-side electrode 108 and an n-side electrode 109 are formed. After the formation, the element shown in FIG. 1 is manufactured. The length of the modulator, which is the length for injecting current into the EA modulator optical waveguide 106, is 160 μm in consideration of the capacity of the modulator that determines the band of the element and the extinction ratio, and there is no reflection on the end face of the EA modulator. Coated.
[0048]
Subsequently, the EA modulator 201 for optical transmission of the above-described element is mounted on a chip carrier 202 having a high-frequency design with a terminating resistor, and a Peltier substrate 203, a lens 204, an optical fiber 205, and the like are mounted in the same package. A semiconductor element module as shown in FIG.
[0049]
When the EA modulator is mounted, the EA modulator section is arranged such that the wide side of the optical waveguide is the light input and the narrow side is the light output side. Therefore, since it is formed in a tapered shape from the light incident side to the light emitting direction, an increase in carrier density can be suppressed.
[0050]
This makes it possible to reduce the input light intensity dependency in the EA modulator characteristics and to suppress the deterioration of the frequency response.
[0051]
In the present embodiment, the size of the tapered shape is 2 μm on the light input side of the EA modulator and 1.4 μm on the output side. However, the optimum value differs depending on the layer structure including the strained multiple quantum well.
[0052]
Further, a structure in which a passive optical waveguide 301 to which a current is not applied before and after the EA modulator optical waveguide 106 in the shape of the waveguide by a design such as a reduction in capacitance can be considered as shown in FIG. In this case, the same effect as in the case of FIG. 1 can be obtained.
[0053]
In the present embodiment, a quaternary mixed crystal of InGaAsP, which is a P-based material, is used for the multiple quantum well of the EA modulator. On the other hand, when an Al-based material is used for a multiple quantum well, a modulator having a low chirp and a large extinction ratio can be designed due to the characteristics of the band offset (see Shimizu et al. [J. Shimizu, et al.], 7th Optoelectronics and Communications Conference (Owcy Sea 2002) Technical Digest [Tech. Dig. ^th Optoelectronics and Communications Conference (OECC2002)], pp506-507, 2002). Also in this case, by adopting the waveguide structure of the present invention, similar effects such as reduction in input light intensity dependency can be obtained.
[0054]
(Embodiment 2)
Referring to FIG. 4, a description will be given of a semiconductor EA modulator integrated DFB laser with a wavelength of 1.5 μm for a transmission speed of 10 Gbit / s and 20 km, as a second embodiment of the present invention. In addition, a modified example of the semiconductor EA modulator integrated DFB laser will be described with reference to FIG. 4A and 4B show a semiconductor EA modulator integrated DFB laser according to a second embodiment, in which FIG. 4A is a plan view, and FIG. 4B is a cross-sectional view taken along the line aa ′ of FIG. 5A and 5B show a modified example of the semiconductor EA modulator integrated DFB laser, in which FIG. 5A is a plan view, and FIG. 5B is a sectional view taken along the line aa ′ of FIG.
[0055]
In the present embodiment, the element of the semiconductor EA modulator integrated DFB laser having a wavelength of 1.5 μm band, which is used for optical transmission of 10 Gbit / s and 20 km, has an oxide mask for selective growth on an n-type InP semiconductor substrate 100. After the formation, as a first crystal growth, an InGaAsP lower light guide layer 101, a quantum well layer 102 consisting of eight periods of an InGaAsP well layer and a barrier layer, and an InGaAsP An upper light guide layer 103 is formed. By using the selective growth, the total thickness of the quantum well layer 102 in the EA modulator section is formed smaller than the total thickness in the laser section. Therefore, the absorption wavelength of the quantum well layer 102 in the EA modulator section is smaller than that in the laser section.
[0056]
Further, a diffraction grating is formed, a cladding layer 104, and an InGaAs contact layer 105 are formed. Next, in order to form an optical waveguide, the EA modulator section optical waveguide 106 and the laser section optical waveguide 401 are collectively formed by ordinary photolithography and wet etching using a Br-based etchant. In this optical waveguide formation, the width of the optical waveguide in the direction parallel to the InP substrate of the EA modulator section is, for example, 2 μm on the input side of the EA modulator and continuously increases toward the output side of the EA modulator. To form a shape that is thinner to 1.4 μm. Specifically, this can be realized by designing the pattern of the photomask to have a tapered shape.
[0057]
Here, the EA modulator section optical waveguide 106 formed in the tapered shape includes the lower light guide layer 101, the quantum well layer 102, and the upper light guide layer 103, which absorb light when the EA modulator operates. In. Thereafter, both sides of the optical waveguide of the Fe-InP layer are buried and regrown, and at the same time, a window structure without the optical waveguide is formed on the emission side of the EA modulator.
[0058]
Subsequently, after forming a through-hole so that an electric field is applied to the tapered EA modulator active layer, the element shown in FIG. 4 is manufactured through the formation of the p-side electrode 108 and the n-side electrode 109. You. The length of the modulator, which is a length for injecting current into the EA modulator optical waveguide 106, is 160 μm in consideration of the extinction ratio and the capacity of the modulator that determines the band of the element, and the front end face on the EA modulator side is used. Has a non-reflective coating, and a rear end face has a reflective coating.
[0059]
Subsequently, as in the first embodiment, the above-described element is mounted on a chip carrier in which a terminating resistor or the like is incorporated, and a Peltier substrate, a lens, an optical fiber, a monitor photodiode, and the like are mounted in the same package. A module is configured.
[0060]
The EA modulator integrated laser mounted on this semiconductor element module has an optical waveguide width tapered from the light incident side to the emission direction of the EA modulator, so that an increase in carrier density can be suppressed. .
[0061]
This makes it possible to reduce the input light intensity dependency in the EA modulator characteristics and to suppress the deterioration of the frequency response.
[0062]
In the present embodiment, the size of the tapered shape is 2 μm on the light input side and 1.4 μm on the output side of the EA modulator, but this optimum value differs depending on the layer structure including the strained multiple quantum well. .
[0063]
Further, in the waveguide shape, as shown in FIG. 5, the transition region from the laser part optical waveguide 401 to the EA modulator part optical waveguide 106 has an inverse tapered shape, and the tapered shape from the light input side to the emission side of the EA modulator. A structure for forming a shape is also conceivable. In this case, the degree of freedom in designing the waveguide width of the laser is increased, which is effective in, for example, controlling the transverse mode.
[0064]
In the present embodiment, as a means for integrating the EA modulator and the laser, a crystal selective growth method in which the EA modulator section quantum well layer and the laser section quantum well layer are simultaneously grown is used. Similar effects can be obtained in the case where the EA modulator section optical waveguide is formed in a tapered shape even when integration is performed by the butt joint method for growth.
[0065]
(Embodiment 3)
With reference to FIG. 6, as a third embodiment of the present invention, a 1.3 μm wavelength impedance controlled EA modulator for optical transmission at a transmission speed of 40 Gbit / s will be described. In addition, a semiconductor element module equipped with the impedance control type EA modulator of FIG. 6 will be described with reference to FIG. 6A and 6B show an impedance-controlled EA modulator according to the third embodiment. FIG. 6A is a plan view, and FIG. 6B is a cross-sectional view taken along the line aa ′ of FIG. FIG. 7 is a plan view of a semiconductor device module equipped with an impedance control EA modulator.
[0066]
In the present embodiment, the element of the 1.3 μm wavelength impedance controlled EA modulator for light transmission at a transmission speed of 40 Gbit / s is formed on a Fe-doped InP semiconductor substrate 601 by using a metalorganic vapor phase method. An InP buffer layer 602 is formed, and an active layer 603 including an InGaAsP lower light guide layer, a strained multiple quantum well layer, and an InGaAsP upper light guide layer is grown.
[0067]
Subsequently, a mask is formed in a region to be the EA modulator optical waveguide 604 having an active layer that absorbs light by applying an electric field, and the active layer in other regions is removed by dry etching. Thereafter, in order to form a passive optical waveguide 605 before and after the EA modulator waveguide by performing a cleaning process or the like, a passive optical waveguide layer 606 including an InGaAsP layer is formed by a metalorganic vapor phase method, and the EA modulator section is activated. A butt joint connection is made so as to be optically continuous with the layer 603.
[0068]
Next, the p-InP cladding layer 607 and the contact layer 600 are formed in a crystal growth step, the n-InP buffer layer 602 in the high impedance line portion 608 is completely removed by etching, and the Fe-InP substrate is exposed. Let it.
[0069]
Subsequently, an optical waveguide composed of the EA modulator optical waveguide 604 and the passive optical waveguide 605 is formed by dry etching. As shown in FIG. 6, the width of the optical waveguide in the direction parallel to the InP substrate is, for example, 2 μm in the passive optical waveguide 605 on the light input side of the EA modulator, as shown in FIG. Is formed in a tapered shape so as to continuously become thinner to 1.4 μm from the input to the output, and the passive optical waveguide 605 on the output side is formed with a width of 1.4 μm.
[0070]
Here, the EA modulator section optical waveguide 604 formed in a tapered shape includes a lower optical guide layer, a quantum well layer, and an upper optical guide layer in which light is absorbed when the EA modulator operates. Thereafter, both sides of the optical waveguide by the Fe-InP layer 105 are buried and regrown.
[0071]
Further, in this device, the anode and the cathode have an impedance control type electrode formed in a coplanar structure on the element surface, and both the p-type and the n-type electrodes are taken from the element surface. The Fe-InP buried layer in the formation region 609 is removed by dry etching to expose the n-InP buffer layer 602. Thereafter, through formation of a passivation film 610, formation of a through hole, and formation of a p-type electrode and an n-type electrode 609 composed of a high impedance line portion 608 and an upper portion 611 immediately above the active layer, an impedance control type as shown in FIG. An EA modulator is obtained.
[0072]
Here, in the high impedance line section 609, the waveguide width and the distance to the n-type electrode 609 serving as the ground are optimized in consideration of impedance matching with the driver IC.
[0073]
The EA modulator 701 for optical transmission of the above element is mounted on a chip carrier 702 designed for high frequency, and the high frequency substrate 703 including the terminating resistor, the Peltier substrate 203, the lens 204, and the input / output optical fiber 205 are mounted in the same package. Thus, a semiconductor element module as shown in FIG. 7 is configured.
[0074]
This module also has a built-in driver IC 704 for driving the EA modulator. This is because the output amplitude of the driver IC is transmitted to the EA modulator without attenuating as much as possible by shortening the distance from the driver IC to the EA modulator. However, if the output amplitude of the driver IC is sufficient, there is no need to incorporate the driver IC, and the same effect can be expected.
[0075]
The EA modulator mounted on the EA modulator module has a tapered optical waveguide width from the light incident side to the emission direction of the EA modulator, so that an increase in carrier density can be suppressed. Furthermore, on the incident side of the waveguide where the saturation level of light absorption is large, since an electric field is applied to the optical waveguide active layer with a sufficient microwave with little attenuation of intensity, it can be said that light can be further absorbed. Therefore, light can be efficiently extinguished, and the extinction characteristics are improved.
[0076]
In the present embodiment, the EA modulator alone has been described. However, a similar effect can be obtained in an impedance-controlled EA modulator integrated laser integrated with a DFB laser.
[0077]
(Embodiment 4)
Referring to FIG. 8, an example in which the present invention is applied to a semiconductor optical element module as a fourth embodiment of the present invention will be described. FIG. 8 is a plan view of the semiconductor optical device module according to the fourth embodiment.
[0078]
In this embodiment, the EA modulator 201 for optical transmission of 10 Gbit / s shown in FIG. 1 or FIG. 3 described in the first embodiment is mounted on the chip carrier 202 having a terminating resistor and designed for high frequency. . Subsequently, the Peltier substrate 203, the lenses 204 and 803, the optical fiber 205, the DFB laser 801 mounted on the chip carrier 802, and the like are mounted in the same package.
[0079]
At this time, hybrid integration is performed so that the light of the DFB laser 801 is coupled by the lens 803 to the input side of the EA modulator where the optical waveguide width is widened. Also in such an optical element module, since the light of the DFB laser 801 is input to the side having the wider EA modulator section optical waveguide, the increase in the carrier density can be suppressed. This makes it possible to reduce the input light intensity dependency in the EA modulator characteristics and to suppress the deterioration of the frequency response.
[0080]
Similarly, also in the 40 Gbit / s optical transmission impedance control EA modulator as shown in FIG. 6 described in the third embodiment, hybrid integration with the DFB laser described above is possible. Also in this case, since the optical waveguide width is formed in a tapered shape from the light incident side to the emission direction of the EA modulator, an increase in carrier density can be suppressed.
[0081]
Furthermore, since an electric field is applied to the optical waveguide active layer with a sufficient microwave having a small attenuation in intensity on the incident side of the waveguide having a high light absorption saturation level, light can be further absorbed. Therefore, light can be efficiently extinguished, and the extinction characteristics are improved.
[0082]
(Embodiment 5)
Referring to FIG. 9, an example in which the present invention is applied to an optical transmission module as a fifth embodiment of the present invention will be described. FIG. 9 shows a configuration diagram of an optical transmission module according to the fifth embodiment.
[0083]
In this embodiment, the semiconductor optical element module 901 equipped with the 10 Gbit / s optical transmission EA modulator shown in FIG. 2 described in the first embodiment is replaced with a DFB laser module 902, a laser driving current source 903, and a laser drive current source 903. The optical transmission module is configured by mounting the temperature control circuit 904, the modulator drive circuit 905, the modulator bias amplitude control circuit 906, the modulator temperature control circuit 907, and the like in the same package.
[0084]
At this time, it is arranged such that the optical output from the DFB laser module 902 becomes the input of the semiconductor optical element module 901 according to the present invention. The input of the semiconductor optical element module 901 means that the optical input having the wider EA modulator section optical waveguide width is used as the optical input, so that an increase in carrier density can be suppressed. This makes it possible to reduce the input light intensity dependency in the EA modulator characteristics and to suppress the deterioration of the frequency response. Therefore, by using the present invention, it is possible to realize an optical transmission module having a stable optical waveform and transmission characteristics.
[0085]
Also in the optical element module (FIG. 7) equipped with the 40 Gbit / s optical transmission impedance control type EA modulator described in the third embodiment, the optical waveform and transmission An optical transmission module with stable characteristics can be realized.
[0086]
Further, in the present embodiment, the example of the optical transmission module has been described. However, if the arrangement of the optical element module and the DFB laser module is the same, the above-described effects can be obtained.
[0087]
(Embodiment 6)
Referring to FIG. 10, an example in which the present invention is applied to an optical transmission device as a sixth embodiment of the present invention will be described. FIG. 10 shows a configuration diagram of an optical transmission device according to the sixth embodiment.
[0088]
The optical transmission device according to the present embodiment includes a framer 1001 for adding a SONET pattern such as an overhead, a signal control device 1002 for managing information such as control signals, a multiplexer 1003 for bundling low-speed signals, a power supply 1004, and the above-described embodiment. 5 basically includes the optical transmission module 1005 described above. Electrical signals of various interfaces are input and output as optical signals.
[0089]
By incorporating the optical transmission module 1005 to which the present invention is applied into the optical transmission device, an optical transmission device with stable characteristics and high reliability can be realized.
[0090]
【The invention's effect】
According to the present invention, a semiconductor laser module and an optical transmission module using the semiconductor electro-absorption modulator integrated laser, which is one of the important components of the trunk line optical transmission, and has a problem of linearity of the front-rear ratio, Therefore, the output stability and reliability of the semiconductor laser module and the optical transmission module can be improved. Further, by using these optical transmission modules, it is possible to realize a highly reliable optical transmission device and a trunk optical transmission system.
[Brief description of the drawings]
FIGS. 1A and 1B are a plan view showing a semiconductor EA modulator according to a first embodiment of the present invention and a cross-sectional view showing an aa ′ cross section of FIG.
FIG. 2 is a plan view showing a semiconductor element module on which the semiconductor EA modulator according to the first embodiment of the present invention is mounted.
FIGS. 3A and 3B are a plan view showing a modified example of the semiconductor EA modulator according to the first embodiment of the present invention, and a cross-sectional view taken along the line aa ′ of FIG.
FIGS. 4A and 4B are a plan view showing a semiconductor EA modulator integrated DFB laser according to a second embodiment of the present invention, and a cross-sectional view taken along the line aa ′ of FIG. 4A.
FIGS. 5A and 5B are a plan view showing a modified example of the semiconductor EA modulator integrated DFB laser according to the second embodiment of the present invention, and a cross-sectional view showing an aa ′ section of FIG. It is.
FIGS. 6A and 6B are a plan view showing an impedance-controlled EA modulator according to a third embodiment of the present invention and a cross-sectional view taken along the line aa ′ of FIG. 6A.
FIG. 7 is a plan view showing a semiconductor element module on which an impedance control type EA modulator according to a third embodiment of the present invention is mounted.
FIG. 8 is a plan view showing a semiconductor optical device module according to a fourth embodiment of the present invention.
FIG. 9 is a configuration diagram illustrating an optical transmission module according to a fifth embodiment of the present invention.
FIG. 10 is a configuration diagram illustrating an optical transmission device according to a sixth embodiment of the present invention.
[Explanation of symbols]
100 n-type InP substrate 101 101 InGaAsP lower light guide layer 102 102 quantum well layer 103 InGaAsP upper light guide layer 104 104 InP clad layer 105 105 InGaAs contact layer 106 EA modulator section optical waveguide Reference numerals 107, passivation film, 108, p-side electrode, 109, n-side electrode, 201, 10 Gbit / s EA modulator for optical transmission, 202, chip carrier, 203, Peltier substrate, 204, aspheric lens, 205, optical fiber , 301: passive optical waveguide, 401: laser optical waveguide, 601: Fe-doped InP semiconductor substrate, 602: n-InP buffer layer, 603: active layer, 604: EA modulator optical waveguide, 605: passive optical waveguide, , 606... A passive optical waveguide layer; 607, a p-InP cladding layer; Impedance line section, 609 n-type electrode, 610 passivation film, 611 immediately above active layer, 701 EA modulator for 40 Gbit / s optical transmission, 702 chip carrier, 703 high-frequency substrate including terminal resistor, 704 driver IC, 801: DFB laser, 802: Chip carrier, 803: Lens, 901: Semiconductor optical element module, 902: DFB laser module, 903: Laser drive current source, 904: Laser temperature control circuit, 905: Modulator drive circuit, Reference numeral 906 denotes a modulator bias amplitude control circuit, 907 denotes a modulator temperature control circuit, 1001 denotes a framer, 1002 denotes a signal control device, 1003 denotes a multiplexer, 1004 denotes a power source, and 1005 denotes an optical transmission module.

Claims (10)

A semiconductor electroabsorption modulator in which an optical waveguide having an active layer that absorbs light by applying an electric field is formed,
A semiconductor electroabsorption modulator, wherein the optical waveguide is formed to have a structure in which a width on a plane is smaller on an emission side than on a light incidence side. A semiconductor electroabsorption modulator in which an anode and a cathode electrode have an impedance control type electrode formed in a coplanar structure on the element surface, and an optical waveguide having an active layer for applying an electric field and absorbing light is formed. So,
A semiconductor electroabsorption modulator, wherein the optical waveguide is formed to have a structure in which a width on a plane is smaller on an emission side than on a light incidence side. The semiconductor electroabsorption modulator according to claim 1 or 2,
A width of the optical waveguide is narrowed from a light incident side to a light emitting side in a traveling direction of the light. The semiconductor electroabsorption modulator according to claim 1 or 2,
A semiconductor electroabsorption modulator, wherein a passive optical waveguide to which a current is not applied is coupled to an entrance side and / or an exit side of the optical waveguide. A semiconductor electro-absorption modulator integrated light source using the semiconductor electro-absorption modulator according to claim 1, 2, 3, or 4,
The semiconductor electroabsorption modulator and the laser are integrated on the same substrate,
A semiconductor electroabsorption modulator integrated light source, wherein the laser is formed in a structure integrated on a wide side of the optical waveguide. A semiconductor element module using the semiconductor electro-absorption modulator according to claim 1, 2, 3, or 4,
A semiconductor device, wherein the semiconductor electroabsorption modulator is mounted on a chip carrier, and has a structure in which light modulated by the semiconductor electroabsorption modulator is incident from the wide side of the optical waveguide. module. A semiconductor element module using the semiconductor electro-absorption modulator according to claim 1, 2, 3, or 4,
A semiconductor device module having a structure in which the semiconductor electroabsorption modulator and a laser are mounted on a chip carrier, and light of the laser is incident from a wide side of the optical waveguide. A semiconductor device module using the semiconductor electroabsorption modulator integrated light source according to claim 5,
A semiconductor device module having a structure in which the semiconductor electroabsorption modulator integrated light source is mounted on a chip carrier. An optical transmission module using the semiconductor element module according to claim 6, 7, or 8,
An optical transmission module having a structure in which the semiconductor element module is mounted on a substrate. An optical transmission device using the optical transmission module according to claim 9,
An optical transmission device, wherein the optical transmission module has a structure incorporated in the device.

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