JP2000059317A - Optical transmitter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To set a cross point of an optical output waveform from the optical transmitter to a middle level between a high level and a low level. SOLUTION: An identification device 1 provides an output of an identification recovery signal based on an input signal 7 to the identification device 1 and a clock 8, a duty factor conversion circuit 9 converts a duty factor of the identification recovery signal into a converted identification recovery signal, which is amplified by an amplifier 2 to be an amplitude enough to drive an electrooptic converter. Then the amplified identification recovery signal drives the electrooptic converter.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical transmitter for converting an electric signal into an optical signal. In particular, 2.5Gbi
The present invention relates to an optical transmitter using an electro-absorption optical modulator used as a light source in a system having a transmission speed of t / s or more.

[0002]

2. Description of the Related Art FIG. 6 is an explanatory diagram of a conventional optical transmitter disclosed in, for example, the 1997 IEICE General Conference B-10-206. FIG. () And (c) are explanatory diagrams of the operation.

In FIG. 6A, reference numeral 1 denotes a discriminator, reference numeral 2 denotes an amplifier, and reference numeral 3 denotes an electro-optical converter. Here, an electro-absorption optical modulator (hereinafter abbreviated as EA) is used. 4
Is an LD, and 5 is an EA (Electro-Absorption) modulator. Reference numeral 6 denotes an optical fiber, 7 denotes a signal input terminal, and 8 denotes a clock input terminal. S1 is the output of the amplifier 2, and s2 is the optical output of the electro-optical converter 3. In FIG. 6B, s1 is the output waveform of the amplifier 2, and s2 is the optical output waveform of the electro-optical converter 3. FIG. 6C shows the input / output characteristics of the electro-optical conversion circuit.

Next, the operation of the conventional optical transmitter will be described with reference to FIG. In FIG. 6, a signal input terminal 7 and a clock input terminal 8 are connected to inputs of the discriminator 1, and the discriminator 1 outputs reproduced data synchronized with a clock to the amplifier 2. The output of amplifier 2 is connected to the input of EA3.
The discriminator 1 outputs a discrimination reproduction signal from the input signal 7 and the clock 8 to the discriminator 1, and the amplifier 2 converts the discrimination reproduction signal output from the discriminator 1 to an amplitude sufficient to drive the EA3. Amplify. Then, EA3 is driven by the amplified identification reproduction signal.

In the output waveforms of the discriminator 1 and the amplifier 2, unless the cross point is adjusted, the cross point is at the center between the high level and the low level of the waveform as shown in s1 of FIG. On the other hand, in the optical output waveform output from EA3, the extinction characteristic of EA3 is not linear with respect to the input as shown in FIG. 6C, so that the cross point deviates from the center between the high level and the low level. 6B, that is, an optical waveform as shown in FIG. In general, standards such as ITU-T assume a waveform in which the cross point of the waveform is at the center between the high level and the low level. Therefore, the optical waveform shown in FIG. And transmission characteristics standards are not satisfied.

[0006]

The conventional optical transmitter shown in FIG. 6 has a problem that the cross point of the optical output waveform of the EA 3 is shifted from the center of the waveform, so that the transmission characteristics are deteriorated.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to use a duty conversion circuit to set the cross point at the center between the high level and the low level of the waveform.

[0008]

An optical transmitter according to a first aspect of the present invention includes a discriminator that inputs data and a clock and outputs reproduced data synchronized with the clock, and converts a duty of the reproduced data from the discriminator. And an amplifier for amplifying the reproduced data whose duty has been converted, and an electro-optical converter for converting the reproduced data amplified by the amplifier from electricity to light and outputting an optical signal. .

An optical transmitter according to a second aspect of the present invention includes a discriminator that inputs data and a clock and outputs reproduced data synchronized with the clock, a duty conversion circuit that converts a duty of the reproduced data from the discriminator, An amplifier for amplifying the reproduced data whose duty has been converted, an electro-optical converter for converting the reproduced data amplified by the amplifier from electricity to light and outputting an optical signal, and detecting the duty of the output of the duty conversion circuit And a comparator for determining a difference between an output of the duty detection circuit and a predetermined value and outputting the difference, and controlling the duty conversion circuit so that the output of the comparator is reduced. It is.

[0010] An optical transmitter according to a third aspect of the present invention is a discriminator that inputs data and a clock and outputs reproduced data synchronized with the clock, a duty conversion circuit that converts a duty of the reproduced data from the discriminator, An amplifier for amplifying the reproduced data whose duty has been converted, an electro-optical converter for converting the reproduced data amplified by the amplifier from electricity to light and outputting an optical signal, and a duty detection for detecting the duty of the output of the amplifier A comparator for calculating a difference between an output of the duty detection circuit and a predetermined value and outputting the difference, and controlling the duty conversion circuit so that the output of the comparator is reduced.

An optical transmitter according to a fourth aspect of the present invention includes an identifier for inputting data and a clock and outputting reproduced data synchronized with the clock, a duty conversion circuit for converting the duty of the reproduced data from the identifier, An amplifier for amplifying the reproduced data whose duty has been converted, an electro-optical converter for converting the reproduced data amplified by the amplifier from electricity to light and outputting an optical signal, and an output light of the electro-optical converter. An opto-electric converter that partially converts the electricity into electricity, a duty detection circuit that detects the duty of the output of the opto-electric converter, and a difference between the output of the duty detection circuit and a predetermined value is determined. And a comparator for controlling the duty conversion circuit so that the output of the comparator is reduced.

According to a fifth aspect of the present invention, in the optical transmitter, the duty conversion circuit controls the duty conversion circuit by using a duty conversion circuit having a differential output, detecting a duty of an inverted phase output of the differential output. It is.

An optical transmitter according to a sixth aspect of the present invention is such that the amplifier uses a differential amplifier, detects a duty of an inverted phase output of the differential output, and controls a duty conversion circuit.

According to a seventh aspect of the present invention, in the optical transmitter, the duty detection circuit detects the duty of the output of the duty conversion circuit using a power sensor.

According to an eighth aspect of the present invention, in the optical transmitter, the duty detecting circuit detects the duty of the output of the duty converting circuit by using an integrating circuit.

In an optical transmitter according to a ninth aspect of the present invention, the electro-optical converter converts the output of the amplifier from electricity to light using an electro-absorption type optical modulator.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 FIG. 1 is a configuration diagram of an optical transmitter according to the present embodiment. FIG. 1A is a block diagram illustrating the configuration, and FIG. 1B is an operation explanatory diagram. FIG.
In (a), 1 is a discriminator, 2 is an amplifier, and 3 is an electro-optical converter. Here, an electro-absorption optical modulator (Electro-Absor) is used.
ption; abbreviated as EA). 4 is LD, 5 is EA (Elect
ro-absorption) modulator. Reference numeral 6 denotes an optical fiber, 7 denotes a signal input terminal, 8 denotes a clock input terminal, 9 denotes a duty conversion circuit, and 10 denotes a control terminal of the duty conversion circuit. s1 is the output of the discriminator 1, s2 is the output of the duty conversion circuit 9, s3 is the output of the amplifier 2, and s4 is the optical output of the electro-optical converter 3. In FIG. 1B, s1 is the output waveform of the discriminator 1, s2 is the output waveform of the duty conversion circuit 9, s3 is the output waveform of the amplifier 2, and s4 is the electro-optical converter 3.
FIG.

Next, the operation of the optical transmitter shown in FIG. 1 will be described. In FIG. 1A, the signal input terminal 7 and the clock input terminal 8 are connected to the input of the discriminator 1 and
Outputs reproduced data synchronized with the clock to the duty conversion circuit 9. The duty conversion circuit 9 outputs the converted data of the duty to the amplifier 2. Amplifier 2
Is connected to the input of EA3. In the discriminator 1, the discrimination reproduction signal is output from the input signal 7 and the clock 8 to the discrimination unit 1, and the duty conversion circuit 9 converts the duty of the discrimination reproduction signal output from the discrimination unit 1, and the amplifier 2 The identification reproduction signal output from the duty conversion circuit 9 is amplified to an amplitude enough to drive the EA3. Then, EA is applied to the amplified identification reproduction signal.
Drive 3

The output waveform of the discriminator 1 has a cross point at the center between the high level and the low level as shown in s1 of FIG. 1 (b). As in the case of the device, the cross point is not at the center between the high level and the low level in the optical output waveform due to the extinction characteristic of the EA. On the other hand, the duty conversion circuit 9 sets the cross point of the output waveform as shown in FIG.
As shown in s2, by taking the extinction characteristic of the EA into consideration and setting it at a state deviated from the center between the high level and the low level, the cross point of the optical output waveform output from the EA3 can be changed to s4 As shown in the figure, it can be the center between the high level and the low level.

Next, the actual effects of the present invention will be described. FIG. 7 shows a conventional optical transmitter and an optical transmitter according to the present invention, in which a single mode fiber (SMF) is 50 km long.
This is the power penalty for transmission. In the conventional optical transmitter, the cross point of the output optical waveform is deviated from the center between the high level and the low level to the low level side, so that the noise immunity on the mark side deteriorates and the bias voltage to the EA3 is -0.5 V Occasionally, a power penalty of about 5 dB occurs after transmission of the SMF 50 km. In contrast,
In the optical transmitter according to the present invention, since the cross point of the output light waveform is at the center between the high level and the low level by the duty conversion circuit, the noise immunity on the mark side is improved, the transmission penalty is improved by 4 dB, and the transmission is improved. The penalty can be 2 dB or less.

Embodiment 2 In this embodiment, the cross point of the optical waveform is always at the center between the high level and the low level by controlling the output of the duty detection circuit to be constant. . FIG. 2 is a configuration diagram of the optical transmitter according to the present embodiment. In the figure, 1
1 is a duty detection circuit, 12 is a comparator, and 13 is a reference voltage terminal to the comparator. Others are the same as those in FIG.

Next, the operation of the optical transmitter shown in FIG. 2 will be described. The discriminator 1 inputs data and a clock and outputs reproduced data synchronized with the clock. When the duty conversion circuit 9 converts the duty of the reproduced data from the discriminator 1, the amplifier 2 converts the reproduced data whose duty has been converted. Amplify. Then, the electro-optical converter 3 converts the output of the amplifier 2 from electricity to light, and outputs an optical signal. The duty detection circuit 11 detects the duty of the output of the duty conversion circuit 9. Then, the comparator obtains the difference between the output of the duty detection circuit 11 and the reference voltage, and controls the duty conversion circuit 9 so that the difference becomes small, so that the cross point of the optical waveform is always at the high level and the low level. , And the deterioration of transmission characteristics can be prevented. That is, even if the signal applied to the control terminal of the duty conversion circuit 11 changes due to the ambient temperature of the optical transmitter or the power supply fluctuation, the deterioration of the transmission characteristics can be suppressed even if the cross point of the optical waveform changes.

In the optical transmitter according to the present invention,
The same effect can be obtained by using the input to the duty detection circuit 11 as the output of the amplifier 2 instead of the output of the duty conversion circuit 9.

Embodiment 3 This embodiment shows an example in which an integrator is used as a duty detection circuit, and a duty conversion circuit having a differential output is used as a duty conversion circuit. FIG. 3A is a configuration diagram of an optical transmitter according to the present embodiment. Numeral 18 denotes an integrating circuit in which the duty detecting circuit 11 of FIG. S1 is the output of the amplifier 2, and s2 is the optical output of the electro-optical converter 3. The other parts are the same as those in FIG. FIG.
In (b), s1 is the positive phase output waveform of the duty conversion circuit 9, and s2 is the negative phase output waveform. Next, the operation according to the present embodiment is the same as the operation according to the second embodiment, and a description thereof will be omitted. Here, a case where an integrator 18 is used instead of the duty detection circuit 11 will be described. The integrator 18 in which a resistor and a capacitor are connected in parallel detects the average value of the input signal power, but when the duty of the data signal changes, the average value of the signal power changes. 18 can be used as the duty detection circuit 11. As an input to the duty detection circuit 11, an inverted phase output of the duty conversion circuit 9 is used as an input to the duty detection circuit 11, and the duty conversion circuit is controlled so that the output of the duty detection circuit becomes a constant value. The cross point of the light waveform can always be at the center between the high level and the low level. In addition, since it is not necessary to branch the signal for driving the EA3 and use it as an input to the duty conversion circuit by using an inverted-phase output of the duty conversion circuit as an input to the duty detection circuit, characteristics due to branching and the like are eliminated. Deterioration can be prevented.

In the optical transmitter according to the present invention,
The same effect can be obtained by using a power sensor instead of the duty detection circuit. The power sensor detects the average value of the input signal power, but when the duty of the data signal changes, the average value of the signal power changes. Therefore, the power sensor can be used as a duty detection circuit.

Embodiment 4 In this embodiment, by using the differential amplifier as the amplifier 2, the output of the opposite phase is input to the duty detection circuit, and the output of the duty detection circuit is made constant. FIG. 4 is a configuration diagram of the optical transmitter according to the present embodiment. In FIG. 4A, reference numeral 14 denotes a normal-phase output terminal of the amplifier, and 15 denotes a negative-phase output terminal. Further, s1 indicates the normal phase output of the amplifier 2, and s2 indicates the negative phase output.
The other parts are the same as those in FIG. In FIG. 4B, s1
Represents a positive-phase output waveform of the amplifier 2, and s2 represents a negative-phase output waveform. Next, the operation will be described. In FIG. 4, a discriminator 1 receives data and a clock and outputs reproduced data synchronized with the clock. When the duty conversion circuit 9 converts the duty of the reproduced data from the discriminator 1, the amplifier 2 amplifies the data whose duty has been converted, and the electro-optical converter 3 converts the output of the amplifier 2 into an electric signal. Is converted into a light, and an optical signal is output, the duty detection circuit 11 detects the duty of the output of the amplifier 2. Then, the comparator 12 obtains a difference between the output of the duty detection circuit 11 and the reference voltage 13, and controls the duty conversion circuit 9 so as to reduce the difference. Therefore,
A differential amplifier is used as the amplifier 2, the positive-phase output of the differential amplifier is output to the optical converter, the negative-phase output is output to the duty detection circuit, and the output of the duty detection circuit is set to the reference voltage. By controlling the duty conversion circuit, the cross point of the optical waveform can always be at the center between the high level and the low level. By making the amplifier 2 a differential amplifier, the signal for driving the EA 3 does not need to be branched and input to the duty conversion circuit, so that the characteristic deterioration due to the branch can be prevented.

In the optical transmitter according to the present invention,
The same effect can be obtained by using a power sensor instead of the duty detection circuit 11. The power sensor detects the average value of the input signal power, but when the duty of the data signal changes, the average value of the signal power changes. Therefore, the power sensor can be used as the duty detection circuit 11. .

The same effect can be obtained by using an integration circuit instead of the duty conversion circuit. An integrator with a resistor and a capacitor connected in parallel detects the average value of the input signal power, but when the duty of the data signal changes, the average value of the signal power changes. It can be used as a duty detection circuit.

Embodiment 5 In this embodiment, the duty is detected based on a part of the output light of the optical signal. FIG. 5 is a configuration diagram of the optical transmitter according to the present embodiment. In the figure, 2 is an amplifier, 16 is an optical coupler, 17
Is an optical-electrical conversion circuit. Others are the same as those in FIG. Next, the operation will be described. In FIG. 5, the discriminator 1 inputs data and a clock, outputs reproduced data synchronized with the clock, and a duty conversion circuit 9 converts the duty of the reproduced data. The amplifier 2 amplifies the reproduced data whose duty has been converted, and the electro-optical converter 3 converts the output of the amplifier 2 from electricity to light, and outputs an optical signal.
Then, the duty detection circuit 11 converts a part of the output light of the electro-optical converter 3 into electricity. The duty detection circuit 11 detects the duty of the output of the photoelectric converter 17. Then, the comparator obtains the difference between the output of the duty detection circuit 11 and the reference voltage 13, and controls the duty conversion circuit 9 so as to reduce the difference, whereby the cross point of the output light waveform is always set to the high level. It can be a low level center.

In the optical transmitter according to the present invention,
The same effect can be obtained by using a power sensor instead of the duty detection circuit 11. The power sensor detects the average value of the input signal power, but when the duty of the data signal changes, the average value of the signal power changes. Therefore, the power sensor can be used as the duty detection circuit 11. .

The same effect can be obtained by using an integrating circuit 18 instead of the duty detecting circuit 11. An integrator with a resistor and a capacitor connected in parallel detects the average value of the input signal power, but when the duty of the data signal changes, the average value of the signal power changes. It can be used as a duty detection circuit.

[0032]

According to the optical transmitters of the first to ninth aspects, the cross point of the optical output waveform is set at the center between the high level and the low level, so that the transmission characteristics can be improved.

According to the optical transmitters according to the second to ninth aspects, the cross point of the optical output waveform is set at the center between the high level and the low level. Point fluctuation can be suppressed.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an optical transmitter according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram of an optical transmitter according to a second embodiment of the present invention.

FIG. 3 is a configuration diagram of an optical transmitter according to a third embodiment of the present invention.

FIG. 4 is a configuration diagram of an optical transmitter according to a fourth embodiment of the present invention.

FIG. 5 is a configuration diagram of an optical transmitter according to a fifth embodiment of the present invention.

FIG. 6 is a configuration diagram of a conventional optical transmitter.

FIG. 7 is a diagram showing transmission characteristics according to the present invention and conventional transmission characteristics.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 discriminator 2 amplifier 3 electro-optical converter 4 LD 5 EA (Electro-absoption) modulator 6 optical fiber 7 signal input terminal 8 clock input terminal 9 duty conversion circuit 10 duty conversion circuit control terminal 11 duty detection circuit 12 comparator 13 Reference voltage terminal 14 In-phase output of amplifier 15 Reverse transmission output of amplifier 16 Optical coupler 17 Optical-electrical conversion circuit 18 Integrator

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01L 33/00 H04B 10/152 10/142 (72) Inventor Kenichi Uto 2-2-2 Marunouchi, Chiyoda-ku, Tokyo No. 3 Mitsubishi Electric Corporation F-term (reference) 5F041 EE25 FF14 5K002 AA01 CA10 CA14 FA01

Claims (9)

[Claims] 1. A discriminator that inputs data and a clock and outputs reproduced data synchronized with the clock, a duty conversion circuit that converts a duty of the reproduced data from the discriminator, and outputs the reproduced data whose duty has been converted. An optical transmitter, comprising: an amplifier for amplifying; and an electro-optical converter for converting reproduced data amplified by the amplifier from electricity to light and outputting an optical signal. 2. A discriminator that inputs data and a clock and outputs reproduced data synchronized with the clock, a duty conversion circuit that converts a duty of the reproduced data from the discriminator, and outputs the reproduced data whose duty has been converted. An amplifier that amplifies, an electro-optical converter that converts reproduced data amplified by the amplifier from electricity to light, and outputs an optical signal; a duty detection circuit that detects a duty of an output of the duty conversion circuit; Find the difference between the output of the circuit and the predetermined value,
An optical transmitter, comprising: a comparator for outputting the difference; and controlling the duty conversion circuit so that the output of the comparator is reduced. 3. A discriminator that inputs data and a clock and outputs reproduced data synchronized with the clock, a duty conversion circuit that converts a duty of the reproduced data from the discriminator, and outputs the reproduced data whose duty has been converted. An amplifier for amplifying, an electro-optical converter for converting reproduced data amplified by the amplifier from electricity to light and outputting an optical signal, a duty detection circuit for detecting a duty of an output of the amplifier, and an output of the duty detection circuit And a comparator for obtaining a difference between the duty conversion circuit and a predetermined value, and outputting the difference, wherein the duty conversion circuit is controlled so that the output of the comparator is reduced. 4. A discriminator that inputs data and a clock and outputs reproduced data synchronized with the clock, a duty conversion circuit that converts a duty of the reproduced data from the discriminator, and outputs the reproduced data whose duty has been converted. An amplifier for amplifying, an electro-optical converter for converting reproduced data amplified by the amplifier from electricity to light and outputting an optical signal, and an optical-optical converter for converting a part of output light of the electro-optical converter to electricity. An electrical converter, a duty detection circuit for detecting the duty of the output of the optical-electrical converter, and a comparator for determining a difference between the output of the duty detection circuit and a predetermined value, and outputting the difference, An optical transmitter, wherein the duty conversion circuit is controlled so that an output of a comparator is reduced. 5. The duty conversion circuit according to claim 2, wherein the duty conversion circuit uses a duty conversion circuit having a differential output, detects a duty of a negative-phase output of the differential output, and controls the duty conversion circuit. 5. The optical transmitter according to any one of 4. 6. The amplifier according to claim 2, wherein the amplifier uses a differential amplifier, detects a duty of a reverse-phase output of the differential output, and controls a duty conversion circuit. Optical transmitter. 7. The optical transmitter according to claim 2, wherein the duty detection circuit detects a duty of an output of the duty conversion circuit using a power sensor. 8. The optical transmitter according to claim 2, wherein the duty detection circuit detects the duty of the output of the duty conversion circuit using an integration circuit. 9. The optical device according to claim 1, wherein the electro-optical converter converts the output of the amplifier from electricity to light using an electro-absorption optical modulator. Transmitter.