JP2005159938A - Optical clock reproducing apparatus and optical clock reproducing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reproduce an optical clock in accordance with a high-speed optical signal. <P>SOLUTION: An input optical signal 19 is branched by an optical branch circuit 3, branched optical signals 21a, 21b are inputted/transmitted to traveling wave type EAMs 5a, 5b in a common mode state, and transmitted light is converted into electric signals by photo-detectors 10a, 10b. A sine wave signal is outputted from a VCO 22 in accordance with bipolar phase comparing signal 16 that is a difference between both the electric signals. An optical clock signal is outputted from a laser 23 in accordance with the sine wave signal, and branched into an optical clock signal 18a and an optical clock signal 18b for output. A high-speed photo-detector 6 outputs the electric signals 20a, 20b to the traveling wave type EAMs 5a, 5b synchronously with the optical clock signal 18a. At such a time, lengths of high-frequency electric lines 7a, 7b are made different from each other. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical clock recovery device and an optical clock recovery method that are generally used in optical communication technology.

  In a regenerative repeater or an optical terminal device in an optical fiber communication system, it is necessary to regenerate a clock signal synchronized with the transmitted optical signal. The demand for higher bit rates of optical signals has increased with the increase in communication capacity in recent years, and optical gate elements have been used for phase comparators to support higher speed optical signals. A clock recovery device has been proposed.

  A conventional clock recovery device using an electro-absorption optical modulator (EAM) as an optical gate element (Non-Patent Document 1 C. Boemer, C. Schubert, C. Schmidt, E. Hilliger, V. Marembert, J. Berger, S. Ferber, E. Dietrich. R. Ludwig, B. Schmauss and HG Weber, “160 Gbit / s clock recovery with electro-optical PLL using bidirectionally operated electroabsorption modulator as phase comparator”, Electronics Letters, vol. 39, no. 14, pp. 1071-1073, 2003) is shown in FIG.

  In FIG. 5, 41 is a 3 dB coupler, 42 is an optical delay device, 43a and 43b are optical circulators, 44 is EAM, 45a and 45b are photodiodes (PD), 46 is a differential amplifier, 47 is a low-pass filter, and 48 is Voltage controlled oscillator (VCO), 49 is a quadruplexer, 50 is an input optical signal, 51 is a reproduction frequency-divided clock, 52a and 52b are branched optical signals, 53 is a quadruple clock, 61a and 61b are the electric power of the PDs 45a and 45b, respectively. A signal 62 is a phase comparison signal.

  The input optical signal 50 is equally branched into the branched optical signals 52a and 52b by the 3 dB coupler 41. The branched optical signal 52a is guided to one input / output port of the EAM 44 by the optical circulator 43a, and the branched optical signal 52b is delayed by a certain time (Δt) by the optical delay device 42, and then branched optical signal 52a by the optical circulator 43b. Is guided to the input / output port of the EAM 44 opposite to the port of the EAM 44 from which the signal is guided, modulated by the applied quadruple clock 53 in the EAM 44, and output from the input / output port opposite to the input port. Then, the light passes through the optical circulators 43a and 43b again and is converted into electric signals 61a and 61b by the PDs 45a and 45b, respectively, the difference is amplified by the differential amplifier 46, the high frequency component is removed by the low-pass filter 47, and the bipolar The phase comparison signal 62 is applied to the VCO 48.

  Here, the VCO 48 oscillates a sine wave whose frequency is increased or decreased with respect to the reference frequency F in accordance with the polarity and magnitude of the phase comparison signal. One of the outputs branched from the VCO 48 becomes a quadruple clock 53 (frequency: 4F) by the quadruple multiplier 49 and is applied to the EAM 44. Here, when the bit rate of the input optical signal 50 is 4 nF, the phase difference between the branched optical signals 52 a and 52 b and the quadruple clock 53 determines the optical power transmitted through the two input / output ports of the EAM 44. . Therefore, since the electrical signals 61a and 61b output from the PDs 45a and 45b depend on the phase difference between the branched optical signals 52a and 52b and the quadruple clock 53, the voltage difference between the electrical signals 61a and 61b is reduced by a low-pass filter. By removing the high frequency component by 47, the phase comparison signal 62 can be used.

  Here, the relationship between the phase difference between the input optical signal 50 and the quadruple clock 53 and the phase comparison signal 62 will be described with reference to FIG. In FIG. 6, the horizontal axis represents the relative phase difference between the input optical signal 50 and the quadruple clock 53, and the vertical axis represents the electrical signal 61a of the PD 45a, the electrical signal 61b of the PD 45b, and the phase comparison signal 62. Are the respective voltages. The waveform of the electrical signal 61a is delayed from the waveform of the electrical signal 61b by the delay time (Δt) by the optical delay device. The phase comparison signal 62 corresponds to the difference between the waveforms of the electric signal 61a and the electric signal 61b, and the phase comparison signal 62 is a signal proportional to the phase difference within the lock range, that is, a phase comparison signal. In order to obtain a linear phase comparison signal 62 having the largest amplitude and a phase difference of 0, when the waveforms of the electric signal 61a and the electric signal 61b are sinusoidal, the delay time Δt is set to the bit period of the input optical signal 50. It is better to halve.

With such a configuration, a phase-locked loop of the input optical signal 50 (bit rate: 4 nF) and the quadruple clock 53 (frequency: 4F) is formed, and the other of the outputs of the VCO 48 is divided into the reproduction divided clock 51. For example, when n is 4, the bit rate of the input optical signal 50 is 160 Gbit / s (bit period: 6.25 ps), and the delay time (Δt) by the optical delay device 42 Is about 3 ps (about 1/2 of the bit period), the 10 GHz reproduction frequency division clock 51 can be taken out.
Also, with such a configuration, a clock signal synchronized with a high-speed optical signal can be reproduced.

C. Boemer, C. Schubert, C. Schmidt, E. Hilliger, V. Marembert, J. Berger, S. Ferber, E. Dietrich. R. Ludwig, B. Schmauss and HG Weber, “160 Gbit / s clock recovery with electro-optical PLL using bidirectionally operated electroabsorption modulator as phase comparator ”, Electronics Letters, vol. 39, no. 14, pp. 1071-1073, 2003

  However, the conventional clock recovery apparatus of FIG. 5 requires the optical circulators 43a and 43b, so it is difficult to make monolithic, and there is a problem in miniaturization of the apparatus. Further, if the optical circulators 43a and 43b in the conventional example are replaced with 3 dB couplers, monolithic can be realized, but the input optical signal 50 must pass through the two replaced 3 dB couplers before reaching the PD 45a or PD 45b. However, there is a problem that the sensitivity is deteriorated because the loss increases in principle by 6 dB. Further, the optical signal output in both directions from the EAM 44 is distributed not only to the PDs 45a and 45b but also to the input side 3 dB coupler 41 by the replaced 3 dB coupler, and a part of the optical signal is returned to the input side of the apparatus. In order to prevent this return light, it is necessary to provide an optical isolator before the input signal light 50 is incident on the 3 dB coupler 41, which increases the number of parts, complicates the configuration, and is disadvantageous to downsizing. It was.

  Further, in the configuration of the conventional example, other optical gate elements can be applied to the EAM 44. However, since light enters the optical gate element from both directions, an optical gate element that does not depend on the light traveling direction is used. There must be. Therefore, in place of the conventional EAM 44, an optical gate element such as a high-speed traveling wave type EAM, which depends on the traveling direction of light, cannot be used, and it is difficult to further increase the speed.

  An object of the present invention is to provide an optical clock recovery device and an optical clock recovery method that are small in size, high in sensitivity, and capable of handling higher-speed optical signals.

An optical clock recovery device of the present invention that solves the above problems is
In an optical clock recovery device that outputs an optical clock signal synchronized with an encoded input optical signal,
A first optical branch circuit for branching an input optical signal;
The first optical branch signal is optically connected to one output side of the first optical branch circuit, and an electric clock signal is applied, and transmitted according to the electric field of the applied electric clock signal. A first optical modulator that changes a transmitted light power of an optical signal to be transmitted;
A first optical receiver optically connected to an output side of the first optical modulator and converting an optical signal transmitted through the first optical modulator into an electrical signal;
A second branch optical signal that is optically connected to the other output side of the first optical branch circuit and is in phase with the first branch optical signal is input, and an electrical clock signal is applied and applied. A second optical modulator that changes a transmitted light power of an optical signal that is transmitted according to an electric field of the electrical clock signal;
A second optical receiver optically connected to an output side of the second optical modulator and converting an optical signal transmitted through the second optical modulator into an electrical signal;
A voltage signal corresponding to the current difference between the electrical signal output from the first light receiver and the electrical signal output from the second light receiver is input, and is generated according to a voltage change of the voltage signal. A voltage controlled oscillator in which the frequency of the sine wave signal changes;
A laser that is connected to an output side of the voltage controlled oscillator and generates an optical clock signal synchronized with a sine wave signal that is an output of the voltage controlled oscillator;
A second optical branch circuit connected to the laser and branching the optical clock signal;
A third optical receiver optically connected to one output side of the second optical branch circuit and converting the optical clock signal into the electrical clock signal;
While the electrical clock signal is input to the first optical modulator, the electrical clock signal input to the first optical modulator is smaller than the length corresponding to the bit period of the input optical signal, and less than zero. An electrical clock signal having a large electrical length difference is input to the second optical modulator,
An optical clock signal synchronized with the input optical signal is output from the other output side of the second optical branch circuit.

The optical clock recovery device of the present invention is
In an optical clock recovery device that outputs an optical clock signal synchronized with an encoded input optical signal,
A first optical branch circuit for branching an input optical signal;
The first optical branch signal is optically connected to one output side of the first optical branch circuit, and an electric clock signal is applied, and transmitted according to the electric field of the applied electric clock signal. A first optical modulator that changes a transmitted light power of an optical signal to be transmitted;
A first optical receiver optically connected to an output side of the first optical modulator and converting an optical signal transmitted through the first optical modulator into an electrical signal;
A phase difference which is optically connected to the other output side of the first optical branch circuit and is smaller than a length corresponding to the bit period of the input optical signal and larger than zero with respect to the first branched optical signal And a second optical modulation that changes the transmitted optical power of the optical signal transmitted according to the electric field of the applied electric clock signal. And
A second optical receiver optically connected to an output side of the second optical modulator and converting an optical signal transmitted through the second optical modulator into an electrical signal;
A voltage signal corresponding to the current difference between the electrical signal output from the first light receiver and the electrical signal output from the second light receiver is input, and is generated according to a voltage change of the voltage signal. A voltage controlled oscillator in which the frequency of the sine wave signal changes;
A laser that is connected to an output side of the voltage controlled oscillator and generates an optical clock signal synchronized with a sine wave signal that is an output of the voltage controlled oscillator;
A second optical branch circuit connected to the laser and branching the optical clock signal;
A third optical receiver optically connected to one output side of the second optical branch circuit and converting the optical clock signal into the electrical clock signal;
The electrical clock signal is input to the first optical modulator and the second optical modulator in an in-phase state,
An optical clock signal synchronized with the input optical signal is output from the other output side of the second optical branch circuit.

The optical clock recovery device of the present invention is
The optical clock signal output from one side of the second optical branch circuit is input to the first optical branch circuit,
The input optical signal is input to the third light receiver.

The optical clock recovery device of the present invention is
In an optical clock recovery device that outputs an optical clock signal synchronized with an encoded input optical signal,
A first optical branch circuit for branching an input optical signal;
A first traveling-wave optical modulator optically connected to one output side of the first optical branch circuit;
A first optical receiver optically connected to an output side of the first traveling wave optical modulator and converting an optical signal transmitted through the first traveling wave optical modulator into an electrical signal;
A second traveling wave optical modulator optically connected to the other output side of the first optical branch circuit;
A second optical receiver optically connected to the output side of the second traveling wave optical modulator and converting an optical signal transmitted through the second traveling wave optical modulator into an electrical signal;
A sine wave signal generated in response to a voltage change is electrically connected to a conductive electrode of the opposite polarity to the conductive electrode of the first light receiver and the first light receiver of the second light receiver. A voltage controlled oscillator whose frequency changes;
An active mode-locked laser that is connected to the output side of the voltage controlled oscillator and generates an optical clock signal synchronized with a sine wave signal that is the output of the voltage controlled oscillator;
A second optical branch circuit connected to the active mode-locked laser and branching the optical clock signal;
A third optical receiver optically connected to one output side of the second optical branch circuit for converting the optical clock signal into an electrical clock signal;
An electrical length difference smaller than a length corresponding to the bit period of the input optical signal and larger than zero is connected to the third light receiver and the first and second traveling wave optical modulators, respectively. Two high frequency electrical lines that each propagate the electrical clock signal;
Two termination resistors electrically connected to the first and second traveling wave optical modulators, respectively;
An optical clock signal synchronized with the input optical signal is output from the other output side of the second optical branch circuit.

The optical clock recovery device of the present invention is
The first optical waveguide connected to the input side of the first optical branch circuit, the one output side of the first optical branch circuit, and the input side of the first traveling wave optical modulator are connected. A second optical waveguide, an output side of the first traveling wave optical modulator, a third optical waveguide connecting the first optical receiver, and the other output side of the first optical branch circuit; A fourth optical waveguide connecting the input side of the second traveling wave type optical modulator, and a fifth optical waveguide connecting the output side of the second traveling wave type optical modulator and the second light receiver. Having a waveguide,
The first, second, third, fourth and fifth optical waveguides, the first optical branch circuit, the first and second traveling wave optical modulators, and the first and second optical waveguides The third light receiver, the two high-frequency electric lines, and the two termination resistors are monolithically formed on the same semiconductor substrate.

The optical clock recovery device of the present invention is
The first, second, third, fourth and fifth optical waveguides, the first optical branch circuit, the first and second traveling wave optical modulators, and the first and second The light receiver is formed using the same epitaxial layer.

The optical clock recovery method of the present invention is
In an optical clock recovery method for outputting an optical clock signal synchronized with an encoded input optical signal,
A first optical modulator and a first optical receiver that change the power of the optical signal transmitted through the first optical signal branched from the input optical signal in accordance with the electric field of the applied electric clock signal. Converted into a first electrical signal,
A second optical modulator and a second optical receiver that change the power of the optical signal transmitted through the second optical signal branched from the input optical signal according to the electric field of the applied electric clock signal, Converted into a second electrical signal,
Find the voltage signal corresponding to the current difference between the first electrical signal and the second electrical signal,
Obtain a sine wave signal whose frequency changes according to the voltage change of the voltage signal, generate an optical clock signal synchronized with this sine wave signal,
The optical clock signal is branched, one of the branched light is converted into an electric clock signal and input to the first and second optical modulators, and the other of the branched light clock signals is synchronized with the input optical signal. Output as
Moreover, the input phase of the first branched optical signal input to the first optical modulator and the input phase of the second branched optical signal input to the second optical modulator are matched, and the first An electrical clock signal having an electrical length difference smaller than a length corresponding to the bit period of the input optical signal and greater than zero with respect to the electrical clock signal input to one optical modulator is the second optical signal. It inputs to a modulator, It is characterized by the above-mentioned.

The optical clock recovery method of the present invention is
In an optical clock recovery method for outputting an optical clock signal synchronized with an encoded input optical signal,
A first optical modulator and a first optical receiver that change the power of the optical signal transmitted through the first optical signal branched from the input optical signal in accordance with the electric field of the applied electric clock signal. Converted into a first electrical signal,
A second optical modulator and a second optical receiver that change the power of the optical signal transmitted through the second optical signal branched from the input optical signal according to the electric field of the applied electric clock signal, Converted into a second electrical signal,
Find the voltage signal corresponding to the current difference between the first electrical signal and the second electrical signal,
Obtain a sine wave signal whose frequency changes according to the voltage change of the voltage signal, generate an optical clock signal synchronized with this sine wave signal,
The optical clock signal is branched, one of the branched light is converted into an electric clock signal and input to the first and second optical modulators, and the other of the branched light clock signals is synchronized with the input optical signal. Output as
In addition, the input optical signal has the input phase of the second branched optical signal input to the second optical modulator with respect to the input phase of the first branched optical signal input to the first optical modulator. Having a phase difference smaller than a length corresponding to a bit period of time and larger than zero, and inputting an electric clock signal to the first optical modulator and the second optical modulator in an in-phase state. Features.

  By using the configuration of the present invention, there is an effect that it is possible to realize an optical clock recovery device and an optical clock recovery method that are small in size, high in sensitivity, and capable of handling higher-speed optical signals.

  Hereinafter, the details of the embodiment will be described with reference to the drawings.

  FIG. 1 is a diagram showing the configuration of an optical clock recovery apparatus according to an embodiment of the present invention, in which 19 is an input optical signal (bit rate: nF bit / s, where n is a natural number), 1 is an InP substrate, 2 Is an InP / InGaAsP optical waveguide, 3 is an optical branch circuit, and is an InP / InGaAsP multimode interference type (MMI) coupler. Reference numerals 4a and 4b denote InP / InGaAsP optical waveguides having the same length. Reference numerals 21a and 21b denote branched optical signals. 5a and 5b are traveling wave type optical modulators, which are traveling wave type EAMs comprising InAlGaAs / InAlAs multiple quantum well absorption layers. Reference numerals 9a and 9b denote InP / InGaAsP optical waveguides. Reference numerals 10a and 10b denote light receivers (PD), which are pin type photodiodes (PD) manufactured using the same epitaxial layer as the traveling wave type EAMs 5a and 5b. Here, the low pass filter in the conventional example can be made unnecessary by designing the bands 10a and 10b to be low. Reference numeral 11 denotes electrical wiring, which connects the p-type electrode of the PD 10a, the n-type electrode of the PD 10b, and the electrode pad 12. With this connection, the output current polarities of the PD 10a and PD 10b are opposite to each other. Reference numeral 11b denotes a termination resistor. The termination resistor 11b converts a current signal into a voltage signal.

  16 is a phase comparison signal, 17 is an electrical wiring, 22 is a voltage controlled oscillator (VCO), 23 is an active mode-locked laser, 24 is an optical branch circuit, 18a and 18b are optical clock signals (frequency: F Hz), 25a and 25b Is an optical fiber. Reference numeral 6 denotes a high-speed photoreceiver, which is an InP / InGaAs UTC-PD (Japanese Patent Laid-Open No. 9-275224) excellent in high speed and high output performance. Reference numerals 7a and 7b denote high-frequency electric lines. The length of the high-frequency electric line 7a is shorter than that of the high-frequency electric line 7b, and the difference in electric length is 1/2 of the bit period (T = 1 / nF) of the input optical signal 19. Is set to a length corresponding to the time (T / 2). Reference numerals 20a and 20b denote electric clock signals. Reference numerals 8a and 8b denote termination resistors having the same resistance values as the characteristic impedances of the traveling wave type EAMs 5a and 5b and the high frequency electric lines 7a and 7b.

  FIG. 2 is a diagram showing a cross section of the optical waveguide 2, the MMI coupler 3, the optical waveguide 4a, the traveling wave EAM 5a, the optical waveguide 9a, and the PD 10a of FIG.

  In FIG. 2, on an InP substrate 1, an n-InP cladding layer 31, an i-InGaAsP core layer 32, an i-InAlGaAs / AnAlAs multiple quantum well absorption layer 33, an i-InGaAsP core layer 34, a p-InP cladding layer 35, and A p-InGaAs cap layer 36 is sequentially stacked by epitaxial growth. A metal electrode 37 is formed on the p-InGaAs cap layer 36. The n-InP cladding layer 31, the i-InGaAsP core layer 32, the i-InAlGaAs / AnAlAs multiple quantum well absorption layer 33, the i-InGaAsP core layer 34, the p-InP cladding layer 35, and the p-InGaAs cap layer 36 are used as an optical waveguide. 2, 4a, 4b, 9a, 9b and the MMI coupler 3 are connected to an n-InP cladding layer 31, an i-InGaAsP core layer 32, an i-InAlGaAs / AnAlAs multiple quantum well absorption layer 33, a p-InP cladding layer 33, i The traveling wave type EAMs 5a and 5b and the PDs 10a and 10b can be configured by the InGaAsP core layer 34, the p-InP cladding layer 35, the p-InGaAs cap layer 36, and the metal electrode 37, respectively.

  Next, the operation of the optical clock recovery apparatus of the present embodiment will be described with reference to FIGS.

  In FIG. 1, an input optical signal 19 incident on the optical waveguide 2 from the side surface of the InP substrate 1 is branched into branched optical signals 21a and 21b by the MMI coupler 3 and guided through the optical waveguides 4a and 4b, respectively, at the same timing. It is guided to traveling wave type EAM 5a, 5b. On the other hand, the optical clock signal 18a propagates through the optical fiber 25a, enters from the back surface of the InP substrate 1, is converted into the electrical clock signals 20a and 20b by the UTC-PD 6, and propagates through the high-frequency electrical lines 7a and 7b, respectively. The traveling wave type EAMs 5a and 5b are controlled and terminated by terminating resistors 8a and 8b, respectively. Here, the high-frequency electrical line 7a is set to an electrical length shorter than that of the high-frequency electrical line 7b by an amount corresponding to half the time (T / 2) of the bit period (T) of the input optical signal 19. The timing at which the electric clock signal 20a is input to the traveling wave type EAM 5a is earlier by T / 2 than the timing at which the electric clock signal 20b is input to the traveling wave type EAM 5b.

  The branched optical signals 21a and 21b controlled by the traveling wave type EAMs 5a and 5b are respectively guided through the optical waveguides 9a and 9b and converted into electric signals by the PDs 10a and 10b, respectively. Here, since the responses of the PDs 10a and 10b are slow, the outputs of the PDs 10a and 10b become currents proportional to the respective average received light power. The outputs of the PD 10a and PD 10b are combined, pass through the electric line 11, and become a voltage signal by the termination resistor 11b, and are taken out from the electrode pad 12 as the phase comparison signal 16. Here, since the output current polarities of the PD 10a and PD 10b are set oppositely, the phase comparison signal 16 is proportional to the difference between the average received light powers of the PD 10a and PD 10b and becomes a bipolar voltage. The phase comparison signal 16 flows through the electrical wiring 17 and is given to the VCO 22. Here, the VCO 22 oscillates a sine wave signal having a frequency shifted according to the voltage of the applied phase comparison signal 16. The active mode-locked laser 23 generates an optical clock signal synchronized with a sine wave signal that is an output of the VCO 22, and the optical clock signal is branched into two by an optical branch circuit 24 and output as optical clock signals 18a and 18b. . The optical clock signal 18a propagates again through the optical fiber 25a and is input to the UTC-PD 6 to form a phase locked loop. The optical clock signal 18b propagates through the optical fiber 25b and is extracted to the outside as an optical clock signal synchronized with the input optical signal 19.

  In FIG. 3, the time difference τ corresponding to the phase difference between the input optical signal 19 (bit period: T) and the optical clock signal 18a (period: nT, n = 4) is relatively changed by T / 4. The waveforms of the branched optical signals 21a and 21b (bit period: T) input to the traveling wave type EAMs 5a and 5b are indicated by dotted lines, and the waveforms of the electric clock signals 20a and 20b (period: nT, n = 4) are indicated by solid lines. Show. Here, for simplicity, the branched optical signals 21a and 21b are sinusoidal curves, and the electric clock signals 20a and 20b are Gaussian curves having a sufficiently narrow time width. The electric clock signal 20a input to the traveling wave type EAM 5a is always advanced by T / 2 from the electric clock signal 20b input to the traveling wave type EAM 5b. In FIG. 3B, the timing of the electric clock signal 20a input to the traveling wave type EAM 5a is advanced by T / 4 with respect to the branched optical signal 21a, and the timing of the electric clock signal 20b input to the traveling wave type EAM 5b is branched. This represents a state where the optical signal 21b is delayed by T / 4. The state of FIG. 3B is defined as a time difference τ = 0 (no phase difference) between the input optical signal 19 and the optical clock signal 18a. Such a state of τ = 0 can be realized by adjusting the length of the optical fiber 25a.

  The traveling wave type EAMs 5a and 5b change the transmitted light power of the branched optical signals 21a and 21b in accordance with the electric field applied by the electric clock signals 20a and 20b. Here, assuming that the average transmitted light power of the branched optical signal 21a in the state of τ = 0 is Po, the average transmitted light power of the branched optical signal 21b in the state of τ = 0 is also Po. Further, FIGS. 3A and 3C show the branched optical signals 21a and 21b, the electrical clock signals 20a and 20b, and the transmitted optical power when τ = −T / 4 and τ = + T / 4. is there. As shown in FIGS. 3A, 3B, and 3C, the transmitted light power of the traveling wave EAM 5a is 0 at τ = −T / 4, Po at τ = 0, and 2Po at τ = + T / 4. On the other hand, the transmitted light power of the traveling wave type EAM 5b is 2Po when τ = −T / 4, Po when τ = 0, and 0 when τ = + T / 4.

  FIG. 4 shows changes in the output current values of the PD 10a, PD 10b, and the phase comparison signal 16 when the time difference τ between the input optical signal 19 and the optical clock signal 18a is continuously changed (the phase comparison signal). 16 is converted into a voltage signal by the terminating resistor 11b, but for the sake of easy understanding, FIG. 4 shows the value of the phase comparison signal 16 by the current value before conversion). However, the output current polarity is positive in the PD 10a and negative in the PD 10b. FIGS. 4A and 4B show the output currents of the PDs 10a and 10b when the output currents when the transmitted light power Po is received by the PDs 10a and 10b are + Io and −Io, respectively. Since the phase comparison signal 16 is the sum of the output currents of the PD 10a and PD 10b, the phase comparison signal 16 is as shown in FIG. That is, when the time difference τ between the input optical signal 19 and the optical clock signal 18a is −T / 2 <τ <0 and the phase of the input optical signal 19 is delayed from the phase of the optical clock signal 18a, the current value of the phase comparison signal 16 Becomes negative, and when the time difference τ between the input optical signal 19 and the optical clock signal 18a is 0 <τ <+ T / 2 and the phase of the input optical signal is ahead of the phase of the optical clock signal 18a, the current of the phase comparison signal 16 The value becomes positive, and when τ = 0 and there is no phase difference, the current value of the phase comparison signal 16 becomes zero. In this way, the phase comparison signal 16 can be obtained.

  The VCO 22 generates a sine wave signal having a frequency of F Hz when the voltage value of the phase comparison signal 16 is 0, a frequency higher than F when positive, and a frequency lower than F when negative. When the voltage value of the phase comparison signal 16 is 0 (the time difference τ = 0 between the input optical signal 19 and the optical clock signal 18a), the optical clock signal 18a is generated at the frequency F Hz.

  When the phase of the input optical signal 19 is delayed, the voltage value of the phase comparison signal 16 becomes negative as described above, and the frequency of the output signal of the VCO 22 becomes lower than F, so that the frequency of the optical clock signal 18a becomes lower than F. At this time, since the phase of the optical clock signal 18a is gradually delayed, the phase difference between the branched optical signals 21a and 21b and the electrical clock signals 20a and 20b is gradually reduced, and the voltage value of the phase comparison signal 16 approaches 0, and finally. The phase difference becomes 0, the voltage value of the phase comparison signal 16 also becomes 0, the frequency of the output signal of the VCO 22 returns to F, and the frequency of the optical clock signal 18a also returns to F.

  Conversely, when the phase of the input optical signal 19 advances, the voltage value of the phase comparison signal 16 becomes positive as described above, and the frequency of the output signal of the VCO 22 becomes higher than F, so that the frequency of the optical clock signal 18a is higher than F. Become. At this time, since the phase of the optical clock signal 18a gradually advances, the phase difference between the branched optical signals 21a and 21b and the electric clock signals 20a and 20b gradually decreases, and the voltage value of the phase comparison signal 16 approaches 0, and finally. The phase difference becomes 0, the voltage value of the phase comparison signal 16 also becomes 0, the frequency of the output signal of the VCO 22 returns to F, and the frequency of the optical clock signal 18a also returns to F. In this way, the phase of the optical clock signal 18 a follows the phase change of the input optical signal 19 to realize a phase locked loop, and the optical clock signal 18 b has branched the output of the active mode locked laser 23. Since it is on one side, the optical clock signal 18b synchronized with the input optical signal 19 can be extracted to the outside.

  In the present embodiment, all the components 2, 3, 4a, 4b, 5a, 5b, 6, 7a, 7b, 8a, 8b, 9a, 9b, 10a, 10b, 11, 12 for obtaining the phase comparison signal 16 are provided. Since components that can be monolithically integrated on the InP substrate 1 are used, it is possible to reduce the size of the optical clock recovery device. Further, since there is no increase in attenuation of the input optical signal due to the monolithic structure as in the conventional example, the sensitivity is high. Further, since the flow of the optical signal is unidirectional, the input optical signal 19 does not return to the input side, and the traveling wave type EAMs 5a and 5b can be used. It can also work against.

  In the above-described embodiment, the MMI coupler using the same epitaxial layer as the traveling wave type EAM is described as the optical branching circuit 3, but other known light such as a Y-branching coupler and a directional coupler is described. A branch circuit may be used, or an optical branch circuit having another epitaxial structure may be used. Moreover, although UTC-PD was described as the high-speed light receiver 6, other well-known light receivers, such as an avalanche photodiode and a pin photodiode, may be used.

  Further, although traveling wave type EAM has been described as traveling wave type optical modulators 7a and 7b, other known optical modulators such as Mach-Zehnder type optical switches may be used. The traveling wave type optical modulators 7a and 7b are traveling wave type EAMs composed of InAIGaAs / InAlAs multiple quantum well absorption layers, but multiple quantum well absorption layers such as InGaAs / InAlAs, InGaAs / InGaAsP, and InGaAsP / InGaAsP are used. It may be a traveling wave type EAM having a semiconductor, or a semiconductor traveling wave type EAM having an InGaAsP / InP bulk absorption layer.

  Moreover, although pin photodiodes using the same epitaxial layer as the traveling wave type EAM have been described as the light receivers 10a and 10b, other known devices that can be fabricated on the substrate 1 such as UTC-PD or other epitaxial configuration pin-PDs. It may be a light receiver. Further, an external electric amplifier may be used to supplement the electric outputs of the two light receivers 10a and 10b.

  In addition, the p-type electrode of the light receiver 10a and the n-type electrode of the light receiver 10b are connected by the electric wiring 11, but the n-type electrode of the light receiver 10a and the p-type electrode of the light receiver 10b are connected by the electric wiring 11. May be. In this case, an inverting amplifier is used before the VCO 22, or a VCO whose frequency change is dependent on the applied voltage is used.

  Further, although the output current polarities of the two light receivers 10a and 10b are electrically connected so as to be opposite to each other, they may be electrically connected so that the polarities are the same. In this case, a method of taking the difference with an external differential amplifier is used.

  In addition, the optical clock signal 18a is incident on the UTC-PD 6 and the input optical signal 19 is incident on the optical waveguide 2, but the optical clock signal 18a is incident on the optical waveguide 2 and the input optical signal 19 is incident on the UTC-PD 6. It may be.

  The difference in electrical length between the high-frequency electrical lines 7a and 7b is a length corresponding to a time (T / 2) that is 1/2 of the bit period (T) of the input optical signal 19, but it is longer than 0 and shorter than T. The corresponding length may be sufficient.

Further, the electrical lengths of the high-frequency electrical lines 7a and 7b are different lengths and the optical waveguides 4a and 4b have the same optical path length. However, the high-frequency electrical lines 7a and 7b have the same electrical length and the optical paths of the optical waveguides 4a and 4b. The length may be a different length.
That is, the high frequency electric lines 7a and 7b have the same electrical length, and the input phase of the branched optical signal 21b input to the traveling wave type EAM 5b is set to the input phase of the branched optical signal 21a input to the traveling wave type EAM 5a. The optical waveguide lengths of the optical waveguides 4a and 4b may be different from each other so that the phase difference is smaller than the length corresponding to the bit period (T) of the input optical signal 19 and larger than zero.

  In the prior art and the embodiment, the description of the electrical connection such as a DC bias circuit is omitted in order to avoid complicated drawings.

It is a block diagram which shows the optical clock reproducing | regenerating apparatus concerning embodiment of this invention. It is sectional drawing which shows the cross section which follows the optical waveguide 2, the MMI coupler 3, the optical waveguide 4a, the traveling wave type EAM 5a, the optical waveguide 9a, and PD10a in the optical clock reproduction | regeneration apparatus concerning embodiment of this invention. It is a characteristic view which shows the timing of the branch optical signal and electrical clock signal in embodiment. It is a characteristic view which shows the phase relationship of the output current in embodiment. It is a block diagram which shows the clock reproduction apparatus by a prior art example. It is a characteristic view which shows the phase relationship in the clock reproduction apparatus by a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 InP board | substrate 2 Optical waveguide 3 Multimode interference type | mold (MMI) coupler 4a, 4b Optical waveguide 5a, 5b Traveling wave type electroabsorption optical modulator (traveling wave type EAM)
6 Single running carrier photodiode (UTC-PD)
7a, 7b High-frequency electrical lines 8a, 8b Termination resistors 9a, 9b Optical waveguides 10a, 10b Photodiodes (PD)
DESCRIPTION OF SYMBOLS 11 Electrical wiring 11a Termination resistor 12 Electrode pad 16 Phase comparison signal 17 Electrical wiring 18a, 18b Optical clock signal 19 Input optical signal 20a, 20b Electrical clock signal 21a, 21b Branching optical signal 22 Voltage controlled oscillator (VCO)
23 Active mode-locked laser 24 Optical branch circuit 25a, 25b Optical fiber 31 n-InP cladding layer 32 i-InGaAsP core layer 33 i-InAlGaAs / AnAlAs multiple quantum well absorption layer 34 i-InGaAsP core layer 35 p-InP cladding layer 36 p-InGaAs cap layer 37 metal electrode 41 3 dB coupler 42 optical delay elements 43a, 43b optical circulator 44 electroabsorption optical modulator (EAM)
45a, 45b Photodiode (PD)
46 Differential amplifier 47 Low pass filter 48 Voltage controlled oscillator (VCO)
49 Quadruple 50 Input optical signal 51 Divided clocks 52a and 52b Branched optical signal 53 Quadruple clock 61a Electrical signal 61b of photodiode 45a Electrical signal 62 of photodiode 45b Phase comparison signal

Claims (8)

In an optical clock recovery device that outputs an optical clock signal synchronized with an encoded input optical signal,
A first optical branch circuit for branching an input optical signal;
The first optical branch signal is optically connected to one output side of the first optical branch circuit, and an electric clock signal is applied, and transmitted according to the electric field of the applied electric clock signal. A first optical modulator that changes a transmitted light power of an optical signal to be transmitted;
A first optical receiver optically connected to an output side of the first optical modulator and converting an optical signal transmitted through the first optical modulator into an electrical signal;
A second branch optical signal that is optically connected to the other output side of the first optical branch circuit and is in phase with the first branch optical signal is input, and an electric clock signal is applied and applied. A second optical modulator that changes a transmitted light power of an optical signal that is transmitted according to an electric field of the electrical clock signal;
A second optical receiver optically connected to an output side of the second optical modulator and converting an optical signal transmitted through the second optical modulator into an electrical signal;
A voltage signal corresponding to the current difference between the electrical signal output from the first light receiver and the electrical signal output from the second light receiver is input, and is generated according to a voltage change of the voltage signal. A voltage controlled oscillator in which the frequency of the sine wave signal changes;
A laser that is connected to an output side of the voltage controlled oscillator and generates an optical clock signal synchronized with a sine wave signal that is an output of the voltage controlled oscillator;
A second optical branch circuit connected to the laser and branching the optical clock signal;
A third optical receiver optically connected to one output side of the second optical branch circuit and converting the optical clock signal into the electrical clock signal;
While the electrical clock signal is input to the first optical modulator, the electrical clock signal input to the first optical modulator is smaller than a length corresponding to the bit period of the input optical signal, and less than zero. An electrical clock signal having a large electrical length difference is input to the second optical modulator,
An optical clock regenerator that outputs an optical clock signal synchronized with the input optical signal from the other output side of the second optical branching circuit. In an optical clock recovery device that outputs an optical clock signal synchronized with an encoded input optical signal,
A first optical branch circuit for branching an input optical signal;
The first optical branch signal is optically connected to one output side of the first optical branch circuit, and an electric clock signal is applied, and transmitted according to the electric field of the applied electric clock signal. A first optical modulator that changes a transmitted light power of an optical signal to be transmitted;
A first optical receiver optically connected to an output side of the first optical modulator and converting an optical signal transmitted through the first optical modulator into an electrical signal;
A phase difference which is optically connected to the other output side of the first optical branch circuit and is smaller than a length corresponding to the bit period of the input optical signal and larger than zero with respect to the first branched optical signal And a second optical modulation that changes the transmitted optical power of the optical signal transmitted according to the electric field of the applied electric clock signal. And
A second optical receiver optically connected to an output side of the second optical modulator and converting an optical signal transmitted through the second optical modulator into an electrical signal;
A voltage signal corresponding to the current difference between the electrical signal output from the first light receiver and the electrical signal output from the second light receiver is input, and is generated according to a voltage change of the voltage signal. A voltage controlled oscillator in which the frequency of the sine wave signal changes;
A laser that is connected to an output side of the voltage controlled oscillator and generates an optical clock signal synchronized with a sine wave signal that is an output of the voltage controlled oscillator;
A second optical branch circuit connected to the laser and branching the optical clock signal;
A third optical receiver optically connected to one output side of the second optical branch circuit and converting the optical clock signal into the electrical clock signal;
The electrical clock signal is input to the first optical modulator and the second optical modulator in an in-phase state,
An optical clock regenerator that outputs an optical clock signal synchronized with the input optical signal from the other output side of the second optical branching circuit. The optical clock regeneration apparatus according to claim 1 or 2,
The optical clock signal output from one side of the second optical branch circuit is input to the first optical branch circuit,
An optical clock regenerator that inputs the input optical signal to the third light receiver. In an optical clock recovery device that outputs an optical clock signal synchronized with an encoded input optical signal,
A first optical branch circuit for branching an input optical signal;
A first traveling-wave optical modulator optically connected to one output side of the first optical branch circuit;
A first optical receiver optically connected to an output side of the first traveling wave optical modulator and converting an optical signal transmitted through the first traveling wave optical modulator into an electrical signal;
A second traveling wave optical modulator optically connected to the other output side of the first optical branch circuit;
A second optical receiver optically connected to the output side of the second traveling wave optical modulator and converting an optical signal transmitted through the second traveling wave optical modulator into an electrical signal;
A sine wave signal generated in response to a voltage change is electrically connected to a conductive electrode of the opposite polarity to the conductive electrode of the first light receiver and the first light receiver of the second light receiver. A voltage controlled oscillator whose frequency changes;
An active mode-locked laser that is connected to the output side of the voltage controlled oscillator and generates an optical clock signal synchronized with a sine wave signal that is the output of the voltage controlled oscillator;
A second optical branch circuit connected to the active mode-locked laser and branching the optical clock signal;
A third optical receiver optically connected to one output side of the second optical branch circuit for converting the optical clock signal into an electrical clock signal;
An electrical length difference smaller than a length corresponding to the bit period of the input optical signal and larger than zero is connected to the third light receiver and the first and second traveling wave optical modulators, respectively. Two high frequency electrical lines that each propagate the electrical clock signal;
Two termination resistors electrically connected to the first and second traveling wave optical modulators, respectively;
An optical clock regenerator that outputs an optical clock signal synchronized with the input optical signal from the other output side of the second optical branching circuit. The optical clock regeneration apparatus according to claim 4, wherein
The first optical waveguide connected to the input side of the first optical branch circuit, the one output side of the first optical branch circuit, and the input side of the first traveling wave optical modulator are connected. A second optical waveguide, an output side of the first traveling wave optical modulator, a third optical waveguide connecting the first optical receiver, and the other output side of the first optical branch circuit; A fourth optical waveguide connecting the input side of the second traveling wave type optical modulator, and a fifth optical waveguide connecting the output side of the second traveling wave type optical modulator and the second light receiver. Having a waveguide,
The first, second, third, fourth and fifth optical waveguides, the first optical branch circuit, the first and second traveling wave optical modulators, and the first and second optical waveguides And an optical clock recovery device, wherein the third light receiver, the two high-frequency electric lines, and the two termination resistors are monolithically formed on the same semiconductor substrate. The optical clock regeneration apparatus according to claim 5, wherein
The first, second, third, fourth and fifth optical waveguides, the first optical branch circuit, the first and second traveling wave optical modulators, and the first and second The optical clock recovery device is formed using the same epitaxial layer. In an optical clock recovery method for outputting an optical clock signal synchronized with an encoded input optical signal,
A first optical modulator and a first optical receiver that change the power of the optical signal transmitted through the first optical signal branched from the input optical signal in accordance with the electric field of the applied electric clock signal. Converted into a first electrical signal,
A second optical modulator and a second optical receiver that change the power of the optical signal transmitted through the second optical signal branched from the input optical signal according to the electric field of the applied electric clock signal, Converted into a second electrical signal,
Find the voltage signal corresponding to the current difference between the first electrical signal and the second electrical signal,
Obtain a sine wave signal whose frequency changes according to the voltage change of the voltage signal, generate an optical clock signal synchronized with this sine wave signal,
The optical clock signal is branched, one of the branched light is converted into an electric clock signal and input to the first and second optical modulators, and the other of the branched light clock signals is synchronized with the input optical signal. Output as
Moreover, the input phase of the first branched optical signal input to the first optical modulator and the input phase of the second branched optical signal input to the second optical modulator are matched, and the first An electrical clock signal having an electrical length difference smaller than a length corresponding to the bit period of the input optical signal and greater than zero with respect to the electrical clock signal input to one optical modulator is the second optical signal. An optical clock recovery method comprising inputting to a modulator. In an optical clock recovery method for outputting an optical clock signal synchronized with an encoded input optical signal,
A first optical modulator and a first optical receiver that change the power of the optical signal transmitted through the first optical signal branched from the input optical signal in accordance with the electric field of the applied electric clock signal. Converted into a first electrical signal,
A second optical modulator and a first optical receiver that change the power of the optical signal transmitted through the second optical signal branched from the input optical signal according to the electric field of the applied electric clock signal, Converted into a second electrical signal,
Find the voltage signal corresponding to the current difference between the first electrical signal and the second electrical signal,
Obtain a sine wave signal whose frequency changes according to the voltage change of the voltage signal, generate an optical clock signal synchronized with this sine wave signal,
The optical clock signal is branched, one of the branched light is converted into an electric clock signal and input to the first and second optical modulators, and the other of the branched light clock signals is synchronized with the input optical signal. Output as
In addition, the input optical signal has the input phase of the second branched optical signal input to the second optical modulator with respect to the input phase of the first branched optical signal input to the first optical modulator. Having a phase difference smaller than a length corresponding to a bit period of time and larger than zero, and inputting an electric clock signal to the first optical modulator and the second optical modulator in an in-phase state. A characteristic optical clock recovery method.

Images