KR100307885B1 - Optical phase locked loop circuit - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical phase locked loop circuit that can be utilized in optical time division type optical communication, and aims to reproduce a pulse train having the same phase and frequency as an incident optical pulse signal. The optical phase locked loop circuit includes a high frequency generator for generating a first high frequency signal, a light source driven by the high frequency generator to emit a clock optical pulse, and a voltage-controlled oscillator for generating a second high frequency signal. And mixing the first and second high frequency signals generated from the first controller, the high frequency generator, and the voltage controlled oscillator to filter, amplify, and convert only the light waves generated by mixing the incident light pulse signal and the clock light pulse. A down-converter mixer for downconverting to a low frequency signal, a pulse converter for converting a first signal and a low frequency signal into an electrical pulse signal, and measuring a phase difference of each electrical pulse signal output from the pulse converter And a second controller for outputting a control voltage proportional to the phase difference, and A control oscillator is controlled to synchronize the incident optical pulse signal with the second high frequency signal and to drive the optical clock stably.

Description

Optical phase locked loop circuit {OPTICAL PHASE LOCKED LOOP CIRCUIT}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical phase locked loop circuit that can be utilized for optical time division type optical communication, and more particularly, to an optical phase locked loop circuit for synchronizing a phase using a high frequency local oscillator and a down-converter mixer. It is about.

The optical phase synchronous loop circuit used in 100Gb / s optical time division type optical communication system is a core technology used for high speed optical communication system.It generates a control signal that accurately distinguishes the optical signal sequence transmitted from the receiver by channel according to time. Giving has a function. For these circuits, the methods proposed in the United States, Japan, and Europe have proceeded simultaneously to the optical signal and the clock optical signal in a medium in which a nonlinear optical phenomenon occurs, and using the optical signal generated therefrom to signal from a high frequency band to a low frequency band. Although conversion has been attempted to synchronize the optical phase, it has still been based on optical clock generation using a low-frequency local oscillator and up-converter mixer. A typical example of this method is the method proposed by NTT in Japan, and the conventional optical phase locked loop circuit using this method is implemented by using an up-converter mixer to obtain a four-wave mixed signal. This up-converter mixer is an expensive device than the down-converter mixer to be used in the present invention, and has a disadvantage in that its size is also large. In addition, the conventional method has a disadvantage in that an optical clock becomes unstable as the frequency of the up-converter mixer is continuously changed in the phase synchronization process.

Accordingly, an object of the present invention is to provide an optical phase locked loop circuit capable of stably driving an optical clock.

Another object of the present invention is to provide an optical phase locked loop circuit which can reduce manufacturing cost and size.

It is still another object of the present invention to provide an optical phase locked loop circuit capable of synchronizing phase using a down-converter mixer.

An optical phase locked loop circuit for achieving the above objects includes a high frequency generator for generating a first predetermined high frequency signal; A light source driven by the high frequency generator to emit a clock light pulse; A voltage controlled oscillator for generating a second high frequency signal; A first control unit which filters, amplifies, and converts only the light waves generated by mixing the incident light pulse signal and the clock light pulse into a first signal; A down-converter mixer for mixing down the first and second high frequency signals generated from the high frequency generator and the voltage controlled oscillator and down converting them into low frequency signals; A pulse converter for converting the first signal and the low frequency signal into electrical pulse signals, respectively; And a second controller for measuring a phase difference of each electrical pulse signal output from the pulse converter and outputting a control voltage proportional to the phase difference; The voltage controlled oscillator is controlled by the control voltage to synchronize the incident optical signal with the second high frequency signal.

1 is a block diagram showing an optical phase locked loop circuit according to a first embodiment of the present invention;

2 is a block diagram showing an optical phase locked loop circuit according to a second embodiment of the present invention;

3 is a view showing a wavelength spectrum of light waves generated when an optical pulse signal having the same pulse repetition rate and a clock optical pulse proceed simultaneously to a semiconductor optical amplifier.

4 shows radio frequency (rf) spectra for electrical signals from photodetectors generated when the pulse repetition rate of an optical pulse signal becomes an integer multiple of a clock optical pulse.

<Explanation of symbols for main parts of the drawings>

103: light source

104: high frequency generator

106: semiconductor optical amplifier

107: light filter

108: optical amplifier

109: light detector

110: pulse converter

111: phase comparator

112 loop filter

113: amplifier

114: voltage controlled oscillator

115: down-converter mixer

201: frequency filter

202: frequency converter

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Unlike the conventional method, the optical phase synchronization is implemented using a high frequency (RF) signal generator and a low frequency conversion mixer. 1 is a block diagram of an optical phase locked loop circuit according to a first embodiment of the present invention, which may be used when the pulse repetition rate of the incident optical pulse signal 101 and the high frequency signal of the voltage controlled oscillator 114 are the same. A circuit block diagram is shown.

Referring to FIG. 1, the optical phase-locked loop circuit includes a high frequency generator 104 for generating a first high frequency signal, a light source 103 driven by the high frequency generator 104, and outputting a clock light pulse, according to a control voltage. A voltage controlled oscillator 114 for generating a second high frequency signal to be changed, a first control unit 116 for filtering and amplifying only the light waves generated by mixing the incident light pulse signal and the clock light pulse, and converting them into a first signal; A down-converter mixer 115 for mixing down the first and second high frequency signals generated from the high frequency generator 104 and the voltage controlled oscillator 114 and down converting them into a low frequency signal, and electrically converting the first and low frequency signals to electrical pulses. A second control unit 11 for measuring a phase difference between the pulse converter 110 for converting the signal and an electrical pulse signal output from the pulse converter 110 and outputting a control voltage proportional to the phase difference 7) consists of. As described above, this control voltage is input to the voltage controlled oscillator 114.

The above-described first control unit 116 is a semiconductor optical amplifier 106 that mixes an optical pulse signal and a clock optical pulse to output a four-wave mixed signal, and is connected to the semiconductor optical amplifier 106 and filters only the four-wave mixed signal. An optical filter 107, an optical amplifier 108 connected to the optical filter 107 and amplifying a four-wave mixed signal, and the four-wave mixed signal amplified and connected to the optical amplifier 108 as an electrical signal. It consists of the photodetector 109 which converts into one signal.

On the other hand, the second control unit 117 measures the phase difference of each electrical pulse signal output from the pulse converter 110 and outputs a first voltage proportional to the phase difference 111, the phase comparator 111 And a loop filter 112 connected to and filtering the first voltage, and an amplifier 113 connected to the loop filter 112 and amplifying the amplified first voltage to output the amplified control voltage.

In order to explain the operation of the optical phase locked loop circuit according to the above-described configuration, it is assumed that the pulse repetition rate of the incident optical pulse signal 101 is 10 GHz and the pulse width is 10 psec. In this case, it is assumed that the RF frequency of the voltage controlled oscillator 114 is also 10 GHz which is the same as the pulse repetition rate of the optical pulse signal 101.

Referring to FIG. 1, when the high frequency signal generated from the high frequency generator 104 is set to 10G + 100KHz, the pulse repetition rate is 10G + 100KHz from the light source 103 driven by the high frequency generator 104. A clock optical pulse 102 having a pulse width of 10 psec is emitted. The clock optical pulse 102 and the optical pulse signal 101 travel together as a single optical fiber by the 3-dB optical fiber combiner 105 and enter the semiconductor optical amplifier 106. Four wave mixing effects occur, and the wavelength spectrum of the light waves emitted from the semiconductor optical amplifier 106 becomes as shown in FIG. 3. In FIG. 3, reference numeral 301 denotes a clock light pulse, 302 denotes an incident light pulse signal, and 303 corresponds to a light wave newly generated by a four-wave mixing phenomenon. Of these three light waves, only the light wave 303, which is a four-wave mixed signal, is transmitted through the optical filter 107. Since the intensity of the light wave 303 is very weak, the optical wave is further amplified by the optical fiber optical amplifier 108, and thus the photodetector ( 109). The photodetector 109 generates an electrical signal of 100 KHz (named signal A), which includes a phase change of the optical pulse signal 101.

On the other hand, the high frequency signals respectively generated from the high frequency generator 104 and the voltage controlled oscillator 114 are input to the down-converter mixer 115 so that a low frequency signal of 100 KHz (named signal B) from the mixer 115 is generated. This signal includes the phase change of the voltage controlled oscillator 114. The two electrical signals A and B are simultaneously converted into electrical pulse signals by the pulse converter 110, and the phase difference between the two signals A and B is measured by the digital phase comparator 111, and a voltage proportional to the phase difference is a loop filter. It is generated by the 112 and the amplifier 113. This voltage is immediately applied to the voltage controlled oscillator 114 to perform a phase synchronization process. When the phase synchronization is performed, the phases of the signal A and the signal B coincide with each other, and the high frequency signal generated from the voltage controlled oscillator 114 in this phase synchronization state exactly matches the phase of the transmitted optical pulse signal 101. .

In this method, even if the high frequency signal of the high frequency generator 104 changes slightly with time, since the frequencies of the signals A and B are always the same, there is no need for a high frequency high frequency generator.

Fig. 2 is a block diagram of an optical phase locked loop circuit according to a second embodiment of the present invention, which can be used when the pulse repetition rate of the incident optical pulse signal 101 becomes an integer multiple of the high frequency signal of the voltage controlled oscillator. A diagram illustrating a phase locked loop circuit.

Referring to the configuration of FIG. 2, the phase locked loop circuit is similar to the diagram shown in FIG. 1, and is connected to the first control unit 116 described above when the pulse repetition rate of the optical pulse signal is an integer multiple of the second high frequency signal. A frequency filter 201 for passing only signals in a selected frequency range and a second signal passing through the frequency filter 201 are subjected to frequency conversion by the product of the reciprocal of the integer multiple, thereby converting the converted signal into the pulse converter ( It further includes a frequency converter 202 provided to 110.

Referring to FIG. 2, first, the RF frequency of the voltage controlled oscillator 114 is assumed to be 10 GHz, and the pulse repetition rate of the incident optical pulse signal 101 is an integer multiple of the RF frequency of the voltage controlled oscillator 114 described above. Is assumed to be 40 GHz, and the pulse width is assumed to be 10 psec. At this time, when the high frequency signal of the high frequency generator 104 is set to 10G + 100KHz, the light source 103 driven by the high frequency generator 104 has a clock repetition rate of 10G + 100KHz and a pulse width of 10psec. 102 is emitted. The clock optical pulse 102 and the optical pulse signal 101 travel together into a single optical fiber by the 3-dB optical fiber combiner 105 and are incident to the semiconductor optical amplifier 106. In the semiconductor optical amplifier 106, The four-wave mixing phenomenon occurs and the wavelength spectrum of the light waves emitted from the semiconductor optical amplifier 106 is also shown in FIG. 3. In this case, as shown in FIG. 4, since the electric signal including several frequency components is generated from the photodetector 109 as well as 400 KHz, a frequency filter 201 for passing only 400 KHz is used. By 202, its frequency is converted into 1/4 and converted into an electrical signal of 100 KHz, which includes a phase change of the optical pulse signal 101 (named signal A).

On the other hand, the high frequency signal generated from the high frequency generator 104 and the voltage controlled oscillator 114 is input to the down-converter mixer 115 to generate a 100 KHz low frequency signal (named signal B) from the mixer 115. This signal contains the phase change of the voltage controlled oscillator 114. The two electrical signals A and B are simultaneously converted into electrical pulse signals by the pulse converter 110, and the phase difference between the two signals A and B is measured by the digital phase comparator 111, and a voltage proportional to the phase difference is a loop filter. It is generated by the 112 and the amplifier 113. This voltage is immediately applied to the voltage controlled oscillator 114 to perform a phase synchronization process. When the phase synchronization is achieved, the phases of the signal A and the signal B coincide with each other, and the high frequency signal generated from the voltage controlled oscillator 114 in this phase synchronization state exactly matches the phase of the transmitted optical pulse signal 101. .

As described above, the present invention has the advantage of providing an optical phase locked loop circuit capable of stably driving an optical clock and reducing manufacturing cost and size. In addition, the present invention has the advantage that the phase can be synchronized using a down-converter mixer.

Claims (4)

In an optical phase locked loop circuit: A high frequency generator for generating a first preset high frequency signal; A light source driven by the high frequency generator to emit a clock light pulse; A voltage controlled oscillator for generating a second high frequency signal; A first control unit for filtering and amplifying only an optical wave generated by mixing an incident optical pulse signal and the clock optical pulse and converting the optical wave signal into a first signal; A down-converter mixer for mixing down the first and second high frequency signals generated from the high frequency generator and the voltage controlled oscillator and converting them down to a low frequency signal; A pulse converter for converting the first signal and the low frequency signal into electrical pulse signals, respectively; And A second control unit measuring a phase difference of each electrical pulse signal output from the pulse converter and outputting a control voltage proportional to the phase difference Including; The voltage controlled oscillator is controlled by the control voltage to synchronize an incident optical pulse signal with the second high frequency signal. Optical phase locked loop circuit, characterized in that. The semiconductor optical amplifier of claim 1, wherein the first controller is a semiconductor optical amplifier configured to output a four-wave mixed signal by mixing the optical pulse signal and the clock optical pulse, and an optical fiber connected to the semiconductor optical amplifier and filtering only the four-wave mixed signal. A filter, an optical amplifier connected to said optical filter and amplifying said four-wave mixed signal, and an optical detector connected to said optical amplifier and converting said amplified four-wave mixed signal into said first signal which is an electrical signal. An optical phase locked loop circuit. The phase comparator of claim 1, wherein the second control unit is connected to the phase comparator, the phase comparator which measures a phase difference of each electrical pulse signal output from the pulse converter and outputs a first voltage proportional to the phase difference. A loop filter for filtering a voltage, and an amplifier connected to the loop filter and amplifying the filtered first voltage to output the amplified control voltage. The frequency filter according to claim 1, wherein when the pulse repetition rate of the optical pulse signal is an integer multiple of the second high frequency signal, the frequency filter is connected to the first control unit and passes only a signal having a predetermined frequency range. And a frequency converter performing frequency conversion by a second signal multiplied by the reciprocal of the integer multiple to provide the converted signal to the pulse converter.