JPH10209973A - Optical wavelength multiplex transmission circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate the setting of optical transmission wavelength by measuring the output wavelength of each optical transmitter in an optical wavelength multiplex transmission circuit based on an electric reference value without utilizing the wavelength characteristics of optical element. SOLUTION: Optical transmission units 11-13 respectively generate the optical signal of single wavelength with respectively different wavelengths and the wavelengths of respective optical signals are respectively controlled by wavelength control circuits 21-23. The optical signals of optical transmission units 11-13 are multiplexed in wavelengths by an optical synthesizer 1. The wavelength arrangement of transmission optical signals is outputted as the change of peak power on time base from a wavelength variable filter 4 by a sawtooth wave impressed from a sweep control circuit 3. At a wavelength monitor circuit 7, the time from the start of sweep to the input of every peak power is measured, the quantity of deviation from reference time is supplied to the wavelength control circuits 21-23 as a control signal and when the quantity of deviation exceeds a prescribed value, an alarm is outputted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a means for monitoring the amount of deviation of each optical wavelength from a predetermined value in an optical wavelength multiplexing transmission circuit and controlling each optical wavelength to an appropriate value based on the monitoring result. .

[0002]

2. Description of the Related Art Conventionally, as this kind of optical wavelength division multiplexing transmission circuit with a wavelength monitoring function, for example, Proceedings of the Communication Society Conference of the Institute of Electronics, Information and Communication Engineers 1995, p.
699, Miyaji et al., "Wavelength Stabilization Method in Dense Wavelength Division Multiplexing Transmission".

FIGS. 4 and 5 are a block diagram and an operation explanatory diagram of the conventional optical wavelength division multiplexing transmission circuit, respectively.
5 for the optical wavelengths λ1, λ2, and λ3.
An optical multiplexer 101 having transmission characteristics as shown in FIG.
Optical splitter 102, optical / electrical conversion circuit 103, amplifier circuit 1
04, multipliers 151 to 153 and the control circuit 105.

[0004] Each of the optical transmission circuits 161 to 163 oscillates a bias circuit 111 to 113 for supplying a current for driving a semiconductor laser (hereinafter referred to as an LD) 141 to 143 and a unique frequency f1, f2, f3. Oscillator 1
21 to 123 and adders 131 to 133.

Next, the operation will be described. LD1
Since the outputs of the oscillators 121 to 123 are respectively added to the outputs of the bias circuits 111 to 113 for driving 41 to 143, the optical signals output from the LDs 141 to 143 are amplitude-modulated by the frequencies f1 to f3, respectively. It has become. The output wavelength-multiplexed by the optical multiplexer 101 is split by the splitter 102 and converted into an electric signal by the optical / electrical conversion circuit 103. After the output of the optical / electrical conversion circuit 103 is amplified by the amplifier circuit 104, the multipliers 151 to 153 output the frequency f synchronized with the modulation signal.
Synchronous detection is performed by multiplying the signals by 1 to f3.

Therefore, when the wavelength of the optical signal output from the optical transmission circuits 161 to 163 deviates from the inherent transmission wavelength of the optical multiplexer 101, the optical loss increases, and the modulated signals f1 to f
3 also decreases in proportion to the attenuation of the optical signal. Therefore, the magnitude of the synchronous detection output output from the multipliers 151 to 153 depends on the transmission wavelength characteristic of the optical multiplexer 101 and the optical wavelength output from the LDs 141 to 143, as shown in FIG. The transmission center wavelength of the optical multiplexer 101 and the LD 141 to
143 is the maximum when the optical output wavelengths match, and LD
The light output wavelengths of 141 to 143 become smaller as they deviate from the transmission center wavelength of the optical multiplexer 101.

The synchronous detection output is monitored by the control circuit 105 for each optical wavelength, and the output wavelengths of the LDs 141 to 143 are controlled so that the synchronous detection output is always maximized. 101 is adapted to the transmission wavelength characteristic.

[0008]

As described above, in the conventional optical wavelength multiplexing transmission circuit, the output light wavelengths of the LDs 141 to 143 are controlled so as to conform to the transmission wavelength characteristics of the optical multiplexer 101. The output light wavelength is the optical multiplexer 1
01 is unambiguously determined by the transmission wavelength characteristic. If the wavelength interval of the transmission characteristic is too narrow, there is a problem of interference between adjacent wavelengths, and if the wavelength interval is too wide, it is limited. There has been a problem that efficient wavelength arrangement within a band cannot be performed, and the wavelength is not always set to an optimum value for transmission characteristics.

In addition, since the control is performed in accordance with the specific wavelength of the optical multiplexer and the wavelength interval is not monitored, even if the wavelength changes due to the aging of the optical multiplexer or abnormality of the control system, the wavelength is not changed. The deviation amount of fluctuation cannot be monitored.

Further, since a modulation signal for control is superimposed on the optical transmission signal for the purpose of controlling the optical wavelength of the LD, the eye opening degree of the signal waveform deteriorates, and as a result, the SN ratio of the signal deteriorates. was there.

[0011]

According to the present invention, an output wavelength of a semiconductor laser is controlled based on the setting of an electrical reference value without using the wavelength characteristics of an optical element. In an optical wavelength multiplexing transmission circuit having at least two or more optical transmission units having different wavelengths, a wavelength sweeping unit for converting an optical wavelength output from each of the optical transmission units into a signal on a time axis, And means for monitoring the wavelength of the light output from each transmitting unit based on the output of the transmitting unit.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an example of a wavelength division multiplexing transmission circuit according to the present invention. Optical transmission unit 11
To 13 generate optical signals of a single wavelength having different wavelengths, and the wavelengths of the optical signals are respectively set to wavelength control circuits 21 to 23
Is controlled by The optical signals of the optical transmission units 11 to 13 are wavelength-multiplexed in the optical multiplexer 1,
, One of which becomes a transmission output, and the other output is used for wavelength monitoring. Although a wavelength-independent optical multiplexer is used as the optical multiplexer 1, an arrayed waveguide grating (AWG) may be used. The wavelength monitoring output of the optical demultiplexer 2 is input to a voltage control type tunable filter 4 to extract only a specific wavelength component, and is input to an optical / electrical conversion circuit 5. The voltage control type wavelength tunable filter 4 is configured such that the center wavelength of the transmitted light is changed by the control voltage from the sweep control circuit 3. For example, a filter using a commercially available dielectric multilayer interference filter is used. Can be The sweep control circuit 3 outputs, for example, a sawtooth control voltage in order to sweep the transmission center wavelength of the voltage control type tunable filter 4. The optical / electrical conversion circuit 5 converts the optical power level output from the voltage control type tunable filter 4 into a voltage. The peak detection circuit 6 outputs light /
The peak voltage is detected by detecting a change in the output voltage from the electric conversion circuit 5, and a pulse signal is output when the peak voltage is detected. Wavelength monitoring circuit 7
Detects the time interval between each pulse signal based on the sweep start signal from the sweep control circuit 3 and the pulse signal from the peak detection circuit 6. That is, the first, second,..., And n-th pulses output from the peak detection circuit 6 have preset reference values for the sweep time interval from the start of the sweep, respectively. Is compared with the reference value of the sweep time interval, and the difference information is output to the wavelength control circuits 21 to 23. The wavelength monitoring circuit 7 also monitors the difference between the pulse detection time and the reference value, and outputs an alarm signal when the time difference becomes equal to or greater than a predetermined value. The wavelength control circuits 21 to 23 each include a wavelength monitoring circuit 7
Control signal corresponding to the difference information from the optical transmission unit 11
To 13 to control the transmission light wavelength of each optical transmission unit.

FIG. 2 is a block diagram showing a more detailed configuration of the wavelength monitoring circuit 7 of FIG. The signal from the peak detection circuit 6 is input to the time interval detection circuit 8. Further, the timing circuit 9 receives the sweep timing signal from the sweep control circuit 3 and outputs sweep start time information to the time interval detection circuit 8. The time interval detecting circuit 8 detects the time difference between the sweep start time and the pulse input, and outputs the first pulse input time information to the time difference detecting circuit 31, the second pulse input time information to the time difference detecting circuit 32,. The second pulse input time information is output to the time difference detection circuit 33. Time difference detection circuit 3
Reference numerals 1 to 33 compare the input time interval information with their respective reference values (Ref. 1 to Ref.n), and use the difference signal as a time difference output to control the corresponding wavelength control circuit 2.
1 to 23. Further, the time difference detection circuits 31 to 33
Is output to the comparison circuit 41, and it is determined whether or not the time difference between the detection pulse input time and the reference value is within a predetermined time range. If the time difference is longer than the predetermined time, an alarm signal is output. Is output.

Next, the operation of the circuit of FIG. 1 will be described with reference to the waveform diagram of FIG. Optical transmission units 11 to 13
The optical signals output from are output by the optical multiplexer 1, and the optical spectrum of the output is as shown in FIG. Here, λ1 is the optical transmission wavelength of the optical transmission circuit 11, λ2 is the optical transmission wavelength of the optical transmission circuit 12, and λn is the optical transmission wavelength of the optical transmission circuit 13. The optical signal multiplexed by the optical multiplexer 1 is branched by the optical demultiplexer 2 and a part is guided to the voltage control type tunable filter 4 for wavelength monitoring. Voltage control type tunable filter 4
Is controlled by the sweep control circuit 3. The output waveform of the sweep control circuit 3 has a sawtooth waveform as shown in FIG. 3B, and the change in voltage with respect to time is controlled with high accuracy. Note that the sweep waveform may be a triangular wave. Since the transmission center wavelength of the voltage control type tunable filter 4 changes in proportion to the control voltage of the sweep control circuit 3, the transmission center wavelength changes in proportion to time as shown in FIG. The change range of the transmission center wavelength is set to cover the range from the lower limit to the upper limit of the light wavelength to be controlled. As a result of this sweep, as shown in FIG. 3 (D), the time t1, when the transmission center wavelength of the voltage control type tunable filter 4 and the wavelengths λ1, λ2,.
Peak power is output at t2,... tn. That is,
The wavelength array of the optical transmission signal is converted into a change in peak power on the time axis. The light transmitted through the voltage control type tunable filter 4 is converted into a voltage by an optical / electrical conversion circuit 5 and applied to a peak detection circuit 6. When the peak power is detected by the peak detection circuit 6, a peak pulse signal as shown in FIG. The wavelength monitoring circuit 7 measures the time from the start of the sweep to the input of each peak pulse signal, and compares the set wavelength with the actual reference wavelength by comparing with the preset reference time. The difference is detected as time difference information, and the information is transmitted to the wavelength control circuits 21 to 23. Wavelength control circuit 2
1 to 23 control the optical signal wavelengths of the optical transmission units 11 to 13 so as to be the set wavelengths, respectively, according to the time difference information transmitted from the wavelength monitoring circuit 7. Further, as shown in FIG. 3F, the wavelength monitoring circuit 7 compares the time difference information output from each of the time difference detection circuits 31 to 33 with a predetermined time ± Δt. If it exceeds, an alarm signal is output.

[0015]

As described above, according to the present invention,
Since it is not necessary to use an optical multiplexer having an optical wavelength characteristic, the optical transmission wavelength can be set arbitrarily, and the wavelength distribution of the optical transmission signal is converted into a time interval between electric pulses. Therefore, it is possible to easily monitor the optical transmission wavelength. Furthermore, since there is no need to superimpose a special signal for control on the optical transmission signal as the main signal, the optical transmission signal does not deteriorate.

[0016]

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a wavelength division multiplexing transmission circuit according to the present invention.

FIG. 2 is a block diagram illustrating an example of a wavelength monitoring circuit in the wavelength division multiplexing transmission circuit according to the present invention.

FIG. 3 is a waveform chart showing the operation of each unit in FIG.

FIG. 4 is a block diagram of a conventional wavelength multiplex transmission circuit.

FIG. 5 is an operation explanatory diagram of FIG. 4;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical multiplexer 2 Optical demultiplexer 3 Sweep control circuit 4 Voltage control type wavelength variable filter 5 Optical / electrical conversion circuit 6 Peak detection circuit 7 Wavelength monitoring circuit 8 Time interval detection circuit 9 Timing control circuit 11-13 Optical transmission unit 21 -23 wavelength control circuit 31-33 time difference detection circuit 41 comparison circuit 101 optical multiplexer 102 optical demultiplexer 103 optical / electrical conversion circuit 104 amplifier circuit 105 CPU (optical wavelength control circuit) 111-113 LD bias control circuit 121-123 Oscillator 131-133 Addition circuit 141-143 Semiconductor laser (LD) 151-153 Multiplier 162-163 Optical transmission unit

Claims (4)

[Claims] 1. An optical wavelength division multiplexing transmission circuit having at least two optical transmission units having different optical wavelengths, a wavelength sweeping means for converting an optical wavelength output from each of the optical transmission units into a signal on a time axis. Means for monitoring the wavelength of light output from each transmission unit based on the output from the wavelength sweeping means. 2. The optical wavelength division multiplexing transmission circuit according to claim 1, further comprising a voltage control type wavelength tunable filter and a wavelength sweep control circuit as wavelength sweep means. 3. A light level detecting means for detecting a peak level of a signal outputted from said wavelength sweeping means, and each peak level position of the signal converted on said time axis is compared with a corresponding reference time position. Means for detecting the amount of deviation of each optical wavelength output from each transmission unit from the reference value, and means for controlling the optical wavelength output from each transmission unit based on the amount of deviation. 2. The optical wavelength division multiplexing transmission circuit according to claim 1, wherein: 4. A light level detecting means for detecting a peak level of a signal output from said wavelength sweeping means, and each peak level position of the signal converted on said time axis is compared with a corresponding reference time position. 2. The apparatus according to claim 1, further comprising means for detecting an amount of deviation of each optical wavelength output from each transmission unit from a reference value, and means for detecting that the amount of deviation exceeds a predetermined value. WDM transmission circuit.