JP2807651B2 - Semiconductor electro-absorption optical modulator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a semiconductor electroabsorption type optical modulator which modulates an optical signal from a light source such as a laser diode according to an input signal.

[0002]

2. Description of the Related Art In conventional optical communication systems, baseband transmission of digital signals is common, and optical modulators have also been developed for baseband signal transmission. In particular, external optical modulators have been used for modulating optical signals at high carrier frequencies. There are roughly two types of external optical modulators, one of which is a Mach-Zehnder optical modulator and the other is a semiconductor electroabsorption optical modulator.

[0003] A Mach-Zehnder optical modulator is formed by forming a waveguide on a substance whose refractive index to light changes according to the electric field strength, that is, a substance having an electro-optic effect. As a material having an electro-optical effect, LiNbO _{3 is} generally used.
Is used. The principle of operation is that an input optical signal is split into two, input to the first and second optical waveguides, and transmitted. An electric field is applied to the first optical waveguide, which is one of the optical paths, to cause a change in the refractive index. By changing the refractive index, the light transmission speed is changed. At the output of the modulator, the two divided optical signals are combined again. At this time, if no apparent optical path difference occurs between the two optical signals, the input optical signal is emitted as it is, but if the optical path difference is １ ／ of the wavelength, the optical signals cancel each other. Therefore, no optical signal is output. The intensity modulation is performed by this action. This Mach-Zehnder type optical modulator is disclosed in, for example, prior art document 1 “GE Betts”.
et al. , “High-Sensitivity”
Lumped-Element Bandpass M
odulators in LiNbO ₃ ", Jour
nal of Lightwave Technology
gy, Vol. 7, No. 12, pp. 2078-20
82, December 1989 ".

In the Mach-Zehnder type optical modulator, an electric field is applied to a first electrode formed on the first optical waveguide and a first electrode provided outside the first optical waveguide so as to face the first electrode. Between the two electrodes, but at a high frequency, because the length of each electrode is relatively long,
A high-frequency signal is input from one end of the first electrode using the electrode as a transmission line, and the terminal is terminated by connecting a 50Ω terminating resistor to the other end of the first electrode. According to this method, the traveling direction of the light and the traveling direction of the electric signal coincide with each other, and the intensity can be modulated to a higher frequency. This is called a traveling-wave Mach-Zehnder optical modulator.

On the other hand, a semiconductor electro-absorption type optical modulator utilizes the fact that the light absorptivity of a semiconductor changes according to an electric field applied to the semiconductor. The semiconductor electroabsorption type optical modulator has a feature that it is not necessary to use a traveling wave type as seen in a Mach-Zehnder type optical modulator because its size is as small as about 200 μm. In addition, since it looks like a single capacitor in terms of high frequency, generally, a semiconductor is sandwiched between the two.
A resistance of 50Ω is added between the two electrodes to keep the reflection coefficient small. The semiconductor electro-absorption type optical modulator is disclosed in, for example, prior art document 2 “K. Wakita et a.
l. , "High-Speed InGaAlAs / I
nAlAs Multiple Quantum We
II Optical Modulator ", Jou
rnalof Lightwave Technology
gy, Vol. 8, No. 7, pp. 1027-103
1, July 1990 ".

All of the optical modulators have a transmission band from DC to several tens GHz by adopting such a configuration.

[0007]

In recent years, communication using a millimeter wave or higher frequency, which is a frequency of 30 GHz or higher, has been actively studied. Among them, a millimeter wave signal is transmitted through an optical fiber cable. Transmission systems have been proposed. However, the current optical modulator has insufficient modulation efficiency indicating how much an optical signal is modulated by a high-frequency signal, so that the characteristics of the entire system are not improved. In addition, it is difficult to reduce the size of the entire device due to an amplifier introduced to compensate for low modulation efficiency. Further, there is a problem that it is difficult to reduce power consumption because a large number of amplifiers are required.

An object of the present invention is to solve the above-mentioned problems and to provide a semiconductor electro-absorption type optical modulator having improved modulation efficiency as compared with the conventional example and capable of performing optical modulation with lower power consumption. To provide.

[0009]

According to a first aspect of the present invention, there is provided a semiconductor electro-absorption type optical modulator comprising a semiconductor electro-absorption type optical modulator for modulating an optical signal from a light source in accordance with an input high frequency signal. In the semiconductor electro-absorption type optical modulator, the input high-frequency signal is impedance-converted from the characteristic impedance of the transmission line transmitting the high-frequency signal to a predetermined terminal impedance higher than the characteristic impedance. And a terminating resistor connected to the input terminal of the semiconductor electro-absorption type optical modulator and having a terminating impedance.

According to a second aspect of the present invention, there is provided a semiconductor electroabsorption type optical modulator according to the first aspect, wherein the impedance conversion circuit includes an input terminal and an output terminal of the impedance conversion circuit. And a transmission line having a predetermined electrical length and a shunt capacitance connected between an input terminal of the impedance conversion circuit and ground.

Further, the semiconductor electro-absorption type optical modulator according to claim 3 is a semiconductor electro-absorption type optical modulator according to claim 1 or 2, wherein the semiconductor electro-absorption type optical modulator is monolithic by a semiconductor manufacturing process. Characterized in that the semiconductor device is an integrated semiconductor device.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. <Characteristics of this Embodiment> FIG. 1 is a block diagram of a semiconductor electro-absorption type optical modulator according to an embodiment of the present invention. This semiconductor electro-absorption type optical modulator is provided in a semiconductor electro-absorption type optical modulator having a semiconductor electro-absorption type optical modulator 20 for modulating an optical signal from a light source such as a laser diode in accordance with an input high-frequency signal. From the characteristic impedance Z ₀ = Z _{in of} the transmission line for transmitting the high frequency signal to a predetermined termination impedance Z _out = _RL , and outputs the converted signal to the input terminal of the semiconductor electro-absorption optical modulator 20. And a terminating resistor _RL having a terminating impedance _RL connected to an input terminal of the semiconductor electroabsorption optical modulator 20.

<Background of the Invention> Since conventional optical modulators have been developed mainly for baseband transmission, designs have been made with emphasis on the band from direct current. Therefore, the first
As shown in FIG. 3 of the prior art, a terminating resistor R _{L of} 50Ω is generally connected in parallel with the
Is driven by the high-frequency amplifier 3 having the output impedance of However, in the case of a subcarrier communication system for transmitting a millimeter wave using an optical fiber cable, it is sufficient that a high characteristic can be obtained in a band of several GHz at a specific millimeter wave frequency. Basically, since the optical modulator is driven by a voltage, most of the high-frequency power from the high-frequency amplifier 3 is consumed by the termination resistor _RL of 50Ω in the current connection method. To increase the driving impedance. That is, the modulation efficiency can be improved by increasing the voltage amplitude.
This can be realized by using subcarrier transmission, and such a method has hardly been considered in the past.

A prior art document 1 using such a concept of impedance conversion using the Mach-Zehnder type optical modulator 17 of the second conventional example shown in FIG. 9 at a low frequency of about 100 MHz exists. When a zender type optical modulator is used, it is necessary to use a traveling wave type at several GHz or more. In FIG. 9, a transmission line 18 is a transmission line inside the Mach-Zehnder type optical modulator 17. In that case, the following two improvement methods can be considered.

One is to increase the characteristic impedance Z ₀ and the terminating resistance _RL of the internal transmission line 18 so that the optical modulator 1
That is, impedance conversion is performed so as to match the input impedance of No. 7. However, in practice, the characteristic impedance Z ₀ is limited to about 200Ω from the viewpoint of the loss of the transmission line 18, and the improvement of the input / output power ratio of the signal to be transmitted in that case is about 6 dB. The second method is to increase the driving impedance of the terminating resistor _RL and the high-frequency amplifier 3 while keeping the characteristic impedance Z ₀ of the transmission line 18 at 50Ω. However, even with this method, it is difficult to obtain a significant improvement at a frequency of several GHz or more due to the resistance loss of the electrodes. Even when an experiment is performed at about 5 GHz, only an improvement of about 2 dB can be obtained.

According to the present invention, it is possible to make a very high improvement by adding such an impedance matching circuit 10 to the semiconductor electroabsorption type optical modulator 20 which has been actively studied in recent years. It turns out from simulation.

<Semiconductor Electroabsorption Optical Modulator> The configuration and operation of a semiconductor electroabsorption optical modulator according to an embodiment of the present invention will be described with reference to FIG.

In FIG. 1, a high-frequency signal modulated according to a digital data signal has a characteristic impedance Z _0.
Is input to the high-frequency amplifier 3 via a transmission line having The high-frequency amplifier 3 has an input impedance Z ₀ and an output impedance Z ₀ that are equal to each other and equal to the characteristic impedance of the connected transmission line, and after amplifying an input high-frequency signal, an impedance matching circuit is input via an input terminal T1. Output to 10 Impedance conversion circuit 10 has an input impedance Z _in the output impedance Z _out, is connected between the input terminal and the output terminal of the impedance conversion circuit 10 and preferably characteristic impedance Z ₀ = 21.3Ω and predetermined The transmission line 15 has an electrical length and a shunt capacitance (also referred to as a shunt capacitance) Cs connected between the input terminal of the impedance conversion circuit 10 and the ground. Impedance conversion from a characteristic impedance Z ₀ = Z _in (preferably 50Ω) of a transmission line for transmitting a signal to a predetermined terminal impedance Z _out = _RL (preferably 5000Ω) higher than Z _in and semiconductor electric absorption. To the input end of the optical modulator 20.

Compared to the characteristic impedance Z ₀ = Z _in (preferably 50Ω), the termination impedance Z _out =
By increasing R _L (preferably 5000Ω), the voltage amplitude increases, and the modulation efficiency of the optical modulator 20 driven by an electric field can be increased. Due to this effect, the output power of the photoelectric converter 6 through the optical fiber cable 5 of the optical fiber link system, which will be described in detail later, becomes (Z ₀ / Z _out ) ² .

Here, the input terminal of the semiconductor electro-absorption optical modulator 20 is connected to a DC bias application terminal T2 via a terminating resistor _RL, and the terminal T2 is grounded via a high-frequency bypass capacitance Cb. You. Here, the terminating resistor _RL is connected between the input terminal of the optical modulator 20 and the ground in terms of high frequency. Further, as shown in FIG. 1, the equivalent circuit of the semiconductor electro-absorption type optical modulator 20 is configured by a series circuit of an equivalent inductance Lw of a bonding wire and a junction capacitance Cj.

In the optical modulation device configured as described above, the high-frequency amplifier 3
Output impedance Z ₀ and impedance matching circuit 1
The input impedance Z _{in of} 0 is set equal, and the output impedance Z _out of the impedance matching circuit 10 and the input impedance Z _ina of the input terminal of the optical modulator 20 are set equal. Therefore, a high-frequency signal can be transmitted from the high-frequency amplifier 3 to the optical modulator 20 with the maximum efficiency, and the wasted power can be minimized.

[0022] In the above embodiment, the impedance matching circuit 10 is constituted by a transmission line 15 and the shunt capacitance C _s, the present invention is not limited to this, although not shown, as shown below Various impedance matching circuits may be used. (A) a circuit in which a series circuit of a capacitance and a transmission line is connected between a first input terminal and a first output terminal;
(B) a circuit in which a series circuit of an inductance and a transmission line is connected between a first input terminal and a first output terminal;
(C) a circuit using an inductance in place of the shunt capacitance Cs in FIG. 1, (d) a first input terminal and a first
, For example, the characteristic inductance Z ₀ =
Circuit connecting only 200Ω transmission lines.

FIG. 2 is a perspective view of the semiconductor electro-absorption type optical modulator of FIG. 1, FIG. 3 is a plan view thereof, and FIG.
5 is a longitudinal sectional view taken along line AA 'of FIG. 3, and FIG. 5 is a longitudinal sectional view taken along line BB' of FIG. Hereinafter, an actual configuration and a manufacturing method will be described with reference to FIGS. 2 to 5, the high-frequency amplifier 3 is not shown.

2 to 5, an impedance conversion circuit 10, a terminating resistor _RL, and a semiconductor electroabsorption optical modulator 20 are provided on an InP semi-insulating semiconductor substrate 30 having a ground conductor 31 formed on the entire back surface. It is formed. In the impedance conversion circuit 10, the transmission line 15 is formed by a microstrip conductor electrode 72 having a predetermined width and length, and the shunt capacitance Cs is determined by the electrodes 71 and 72 sandwiching an insulating film 81 made of, for example, SiO ₂ . And a MIM capacitor composed of Here, the electrode 71 is
Through hole 91 penetrating semiconductor substrate 30 in the thickness direction
Is connected to the grounding conductor 31 via a through-hole conductor 91a formed on the inner peripheral surface of the base and grounded.

The high frequency bypass capacitance Cb is
Electrode 73 sandwiching insulating film 82 made of, for example, SiO ₂
The electrode 74 is connected to the ground conductor 31 via a through-hole conductor 91a.
And grounded. Further, on the semiconductor substrate 30,
A terminating resistor _RL connected between the terminal T2 and the electrode 72 is formed.

In the semiconductor electro-absorption optical modulator 20, Si is used as an impurity on the semiconductor substrate 30.
After × ^{10 18} to 5 × 10 ¹⁸ / cm ³ in the implanted n + -type becomes at InAlAs thickness 100 to 500 Å n-type semiconductor layer 32 is formed by molecular beam epitaxy,
86 ° thick i-type InGaAlAs layer and 50 ° thick i
A superlattice layer 33 formed by alternately repeating the type InAlAs layers for 30 periods is formed by a molecular beam epitaxy method. Next, Be is used as an impurity, for example, 2 × 10 ^18.
P + type InAlA implanted at a concentration of about 5 × 10 ¹⁸ / cm ³
n-type semiconductor layer 34 having a thickness of 100 to 500 °
Is formed by molecular beam epitaxy, and further, Au /
After the ohmic electrode 35 made of the AuMn alloy is formed, the electrode 75 is formed. On the other hand, on the electrode 72 side, n
After the ohmic electrode 37 made of an Au / Ni / AuGe alloy is formed on the mold semiconductor layer 32, the electrode 72 is formed. On the electrode 73 side, A is formed on the n-type semiconductor layer 32.
After the ohmic electrode 36 made of the u / Ni / AuGe alloy is formed, the electrode 73 is formed. Further, the electrode 7
5 is connected to the ground conductor 31 via a through-hole conductor 92a formed on the inner peripheral surface of a through-hole 92 penetrating the semiconductor substrate 30 in the thickness direction, and is grounded.

An optical signal from a light source such as a laser diode enters the superlattice layer 33 on one side, exits from the opposing superlattice layer 33 and enters the optical fiber cable. On the other hand, the high-frequency signal is input via the input terminal T1 and is transmitted to the transmission line 15 of the inductance conversion circuit 10.
Is applied between the n-type semiconductor layer 32 and the electrode 75 via the electrode 72 and the ohmic electrode 37 of the semiconductor electro-absorption optical modulator 20.

In the semiconductor electro-absorption type optical modulator having the above-described configuration, an incident optical signal is intensity-modulated according to an input high-frequency signal and output. In this example, an MIM capacitor is used as the capacitance, and the transmission line is formed as a transmission line by forming a ground plane on the back surface of the substrate. Through-hole (also called via-hole) for connection to ground
91 and 92 are used. The terminating resistor _RL is formed by a mesa of the n-type semiconductor layer 32.

As described above, by manufacturing the device in a monolithic manner, the optical modulator 20 and the impedance matching circuit 10 can be connected in the shortest distance, so that the loss due to the resistance of the transmission line 15 can be reduced, and the impedance matching circuit can be reduced. Since the ten shapes are formed by a semiconductor process, they can be formed with very high accuracy, and the yield and the like can be greatly improved. Further, the impedance matching circuit 10 and the semiconductor electroabsorption optical modulator 2 are formed on the semiconductor substrate 30 by a monolithic semiconductor manufacturing process.
Since the semiconductor electro-absorption type optical modulation device having the value of 0 can be manufactured, the device is small and lightweight. By using such an optical modulator, a millimeter-wave optical fiber link system as described below can be formed at low cost.

The device can be manufactured as a monolithic semiconductor device by a known semiconductor manufacturing process, and has the following specific advantages. (A) Since the bonding wire is not used by making it monolithic, the influence of the bonding wire is eliminated, and the pattern size accuracy can be improved and mass production can be performed. (B) The size of the impedance matching circuit 10 can be reduced by using a highly accurate semiconductor manufacturing process. The downsizing of the impedance matching circuit 10 leads to a reduction in the loss of the impedance matching circuit, and high conversion efficiency characteristics can be obtained. (C) By the semiconductor manufacturing process, it is possible to easily form a very small capacitance required particularly for a millimeter wave or the like. (D) When the optical modulator 20 and the impedance matching circuit 10 are connected by a connector, for example, due to the monolithic structure, the impedance of the connector is 50Ω.
No special connectors are used.

<Optical Fiber Link System> FIG. 7 is a block diagram showing the configuration of an optical fiber link system using the semiconductor electro-absorption type optical modulator of FIG.
The transmitting part is shown, and (b) shows the receiving part.

In the transmission section shown in FIG. 7A, a digital data signal is inputted to a modulator 1, and the modulator 1 converts an intermediate frequency signal having a predetermined intermediate frequency into a digital signal such as a PSK modulation method according to the digital data signal. The signal is modulated by the modulation method, and an intermediate frequency modulation signal is output to the frequency converter 2. The frequency converter 2 converts the input intermediate frequency modulation signal into a higher radio frequency such as a millimeter wave, and converts the converted high frequency signal to the optical modulator 20 via the high frequency amplifier 3 and the impedance matching circuit 10. Output.
On the other hand, an unmodulated optical signal having a predetermined wavelength from the laser diode 4 that is a light source enters the optical modulator 20.
The optical modulator 20 modulates the intensity of the incident optical signal in accordance with the input high-frequency signal, and transmits the modulated optical signal to a wireless base station remote from the optical modulator 20 via the optical fiber cable 5. The light enters the photoelectric converter 6 provided. The photoelectric converter 6 photoelectrically converts the input optical signal into a millimeter-wave wireless signal, and the wireless signal is radiated from the antenna 8 via the high-frequency power amplifier 7.

In the receiving section shown in FIG. 7B, the radio signal radiated from the antenna 8 of the transmitting section is received by the antenna 11, and thereafter, the receiving high-frequency amplifier 12 and the input signal are converted into a lower intermediate frequency signal. The signal is output to the demodulator 14 via the frequency converter 13 for conversion. The demodulator 14 demodulates the input signal into an original digital data signal and outputs it.

[0034]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the simulation by the present inventor, a thick and long transmission line was used for the impedance matching circuit 10 in consideration of a hybrid production,
Actually, it can be formed with a length of 1 mm or less and a width of about several tens of μm. By manufacturing as described above, it is possible to form the impedance matching circuit 10 on the semiconductor substrate 30 of the semiconductor electro-absorption type optical modulator device. It is possible to form a small and high-performance optical modulator 20.

In the simulation, it is assumed that the semiconductor electroabsorption optical modulator 20 has an equivalent circuit in which the junction capacitance Cj and the inductance Lw of the bonding wire are connected in series. The junction capacitance Cj is set to 400 fF according to the literature of the related art, and the inductance Lw is set to 0.
5 nH. The terminating resistor _RL is introduced to reduce the reflection coefficient at the input end of the optical modulator 20, and is set to 5000Ω in the simulation. By increasing the resistance value, the conversion efficiency can be increased, but since the band becomes smaller, it is determined by the trade-off. The impedance matching circuit 10 has a shunt capacitance Cs
And the transmission line 15. In this simulation, the target frequency was 40 GHz and the band was 200
MHz. At this time, the capacitance value of the shunt capacitance Cs is 3.38 pF, and the transmission line 15 has a thickness of 2
3 μm thick and 1 m wide on 50 μm GaAs semiconductor substrate
m and length 3.38 mm. The length, width, and the like of the transmission line 15 can be further reduced. Although a GaAs semiconductor substrate is used in the simulation, a similar result can be obtained with a material constant of an InP semiconductor substrate.

FIG. 6 is a graph showing the frequency characteristics of the input / output power ratio, which are the simulation results of the semiconductor electroabsorption optical modulator of FIG. 1 and the conventional example. In this simulation, the signal modulated by the optical modulator 20 is guided to the light receiver as the photoelectric converter 6 through the optical fiber cable and becomes a high-frequency signal again. Since the high-frequency signal output from the photodetector is proportional to the square of the voltage amplitude in the optical modulator 20, the square of the voltage amplitude is expressed as a relative value using decibels in the characteristic comparison in the simulation. For reference, the modulation efficiency in the 50Ω system used in the first conventional example is shown.

For example, in subcarrier transmission for transmitting a digital data signal using a modulated signal obtained by modulating a carrier signal having a high frequency such as a quasi-millimeter wave or a millimeter wave in accordance with an input digital data signal, a higher frequency is used. In FIG. 6, since it is only necessary to be able to transmit a narrow-band modulated signal, in FIG.
Alternatively, transmission can be performed using a carrier signal having a frequency near the peak of 40 GHz. Therefore, from the viewpoint of subcarrier transmission, for example, from FIG.
It can be seen that the modulation efficiency at z is improved by about 30 dB. As a result, an amplifier for 30 dB is not required, the size can be reduced, and the power consumption can be reduced.

[0038]

As described above in detail, according to the present invention, there is provided a semiconductor electro-absorption type optical modulator including a semiconductor electro-absorption type optical modulator for modulating an optical signal from a light source in accordance with an input high-frequency signal. The input high-frequency signal is impedance-converted from the characteristic impedance of the transmission line transmitting the high-frequency signal to a predetermined terminal impedance higher than the characteristic impedance and output to the input terminal of the semiconductor electro-absorption optical modulator. An impedance conversion circuit, and a terminating resistor connected to the input terminal of the semiconductor electroabsorption optical modulator and having the terminating impedance are provided. Therefore, since the impedance conversion circuit is provided and impedance matching can be performed, the modulation efficiency is improved as compared with the conventional example, and light modulation can be performed with lower power consumption. In addition, since a semiconductor electroabsorption optical modulator including an impedance matching circuit and a semiconductor electroabsorption optical modulator can be manufactured on a semiconductor substrate by a monolithic semiconductor manufacturing process, the device is small and lightweight. It has the advantage that.

According to a second aspect of the present invention, there is provided a semiconductor electroabsorption type optical modulator, wherein the impedance conversion circuit comprises an input terminal and an output terminal of the impedance conversion circuit. And a shunt capacitance connected between the input terminal of the impedance conversion circuit and the ground. Therefore, the impedance conversion circuit can be configured using a simpler circuit, and the manufacturing cost can be reduced.

Further, according to a third aspect of the present invention, there is provided a semiconductor electroabsorption type optical modulator according to the first or second aspect, wherein the semiconductor electroabsorption type optical modulator is manufactured by a semiconductor manufacturing process. It is a monolithic semiconductor device. Therefore, the device has the following specific effects. (A) Since the bonding wire is not used by making it monolithic, the influence of the bonding wire is eliminated, and the pattern size accuracy can be improved and mass production can be performed. (B) By using a highly accurate semiconductor manufacturing process, the impedance matching circuit can be downsized. A reduction in the size of the impedance matching circuit leads to a reduction in loss of the impedance matching circuit, and high conversion efficiency characteristics can be obtained. (C) By the semiconductor manufacturing process, it is possible to easily form a very small capacitance required particularly for a millimeter wave or the like. (D) When the optical modulator and the impedance matching circuit are connected by a connector, for example, due to the monolithic structure, a special connector is not used because the impedance of the connector portion is 50Ω.

[Brief description of the drawings]

FIG. 1 is a block diagram of a semiconductor electro-absorption type optical modulator including an impedance matching circuit 10, a terminating resistor _RL, and a semiconductor electro-absorption type optical modulator 20 according to an embodiment of the present invention.

FIG. 2 is a perspective view of the semiconductor electro-absorption light modulator of FIG.

FIG. 3 is a plan view of the semiconductor electro-absorption type optical modulator of FIG.

FIG. 4 is a longitudinal sectional view taken along line AA ′ in the semiconductor electro-absorption optical modulator of FIG. 3;

FIG. 5 is a longitudinal sectional view taken along line BB ′ in the semiconductor electro-absorption optical modulator of FIG. 3;

6 is a graph showing frequency characteristics of an input / output power ratio, which are simulation results of the semiconductor electroabsorption optical modulator of FIG. 1 and a conventional example.

7 is a block diagram showing a configuration of an optical fiber link system using the semiconductor electro-absorption type optical modulator of FIG. 1, wherein (a) shows a transmission unit and (b) shows a reception unit.

FIG. 8 is a block diagram showing a first conventional light modulator.

FIG. 9 is a block diagram illustrating a second conventional light modulator.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Modulator, 2 ... Frequency converter, 3 ... High frequency amplifier, 4 ... Laser diode, 5 ... Optical fiber cable, 6 ... Photoelectric converter, 7 ... High frequency power amplifier, 8 ... Antenna, 10 ... Impedance matching circuit, 11 ... Antenna, 12 ... High frequency amplifier, 13 ... Frequency converter, 14 ... Demodulator, 15 ... Transmission line, 20 ... Electro-absorption type optical modulator, T1 ... Input terminal, T2 ... DC bias application terminal, Cs ... Shunt capacitance _RL : Terminating resistance, Cb: High-frequency bypass capacitance.

────────────────────────────────────────────────── ─── Continuing from the front page (72) Eiichi Ogawa Inventor Eiichi Oka, Soraku-cho, Kyoto Prefecture, 5th, Sanraya, Koiya, 5th ATR Optical Co., Ltd. . ^6, DB name) G02F 1/00 - 1/015 502 H04B 10/00 - 10/158 H01S 3/10 H01S 3/103

Claims (3)

(57) [Claims] 1. A semiconductor electro-absorption type optical modulator comprising a semiconductor electro-absorption type optical modulator for modulating an optical signal from a light source according to an input high-frequency signal. An impedance conversion circuit that converts the characteristic impedance of the transmission line to be transmitted from a characteristic impedance to a predetermined terminal impedance higher than the characteristic impedance and outputs the result to an input terminal of the semiconductor electro-absorption optical modulator; And a terminating resistor connected to the input end of the device and having the terminating impedance. 2. The impedance conversion circuit according to claim 1, wherein the impedance conversion circuit is connected between an input terminal and an output terminal of the impedance conversion circuit and has a predetermined electrical length. 2. A semiconductor electro-absorption type optical modulator according to claim 1, further comprising a shunt capacitance connected to the shunt capacitance. 3. The semiconductor electro-absorption type optical modulation device according to claim 1, wherein the semiconductor electro-absorption type optical modulation device is a semiconductor device that is made monolithic by a semiconductor manufacturing process.