JP2655479B2 - WDM optical transmission equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength division multiplexing optical transmission apparatus for multiplexing and transmitting optical signals of different wavelengths, and more particularly, to an optical bandpass filter used in a receiving apparatus for determining a pass center wavelength of an optical bandpass filter. The present invention relates to a wavelength division multiplexing optical transmission device that can follow the wavelength of a signal and stably match.

[0002]

2. Description of the Related Art In optical communication, a plurality of optical signals having different wavelengths are multiplexed and transmitted on one optical fiber in order to increase transmission efficiency. Such a communication system is called a wavelength division multiplexing optical transmission system.

FIG. 9 shows a schematic configuration of a conventional wavelength division multiplexing optical transmission device. This wavelength division multiplexing optical transmission device includes a transmitting device 11, a receiving device 12, and an optical fiber 13 connecting these devices.

The transmitting device 11 has data signal input terminals 14, 15, and 16 for three channels for inputting a data signal representing data to be transmitted. These data signal input terminals 14, 15, 16 are connected to semiconductor laser drive circuits 17, 18, 19, respectively. The semiconductor lasers 21, 22, and 23 are connected to the corresponding semiconductor laser drive circuits 17, 18, and 19, respectively, and emit light according to the drive current supplied from these. These semiconductor lasers 21, 22, and 23 are connected to an optical coupler 24. The optical coupler 24 multiplexes the light emitted by the three semiconductor lasers 21, 22, and 23 and sends the multiplexed light to the optical fiber 13.

[0005] The receiving device 12 includes an optical bandpass filter 25 connected to the receiving end of the optical fiber 13. A selection signal for switching the pass center wavelength from the channel selection circuit 26 is input to the optical bandpass filter 25. The channel selection circuit 26 is connected to a channel selection signal input terminal 27. Optical bandpass filter 2
The light that has passed through 5 is input to the photoelectric converter 28. The output side of the photoelectric converter 28 is connected to the reception data signal output terminal 29.

The transmitting device 11 transmits data signals to be transmitted for three channels to data signal input terminals 14, 15, 16.
Enter each from Semiconductor laser drive circuit 17, 1
Reference numerals 8 and 19 output driving currents obtained by superimposing these data signals on a DC current. The semiconductor lasers 21, 22, and 23
Light with an intensity corresponding to these driving currents is emitted. Therefore,
The intensity of light emitted from the semiconductor lasers 21, 22, and 23 is
It changes according to the data signal. Semiconductor laser 21, 2
The light emitted by 2, 23 has different wavelengths from each other. The three light beams emitted from the semiconductor lasers 21, 22, and 23 having different wavelengths are multiplexed by the optical coupler 24 and transmitted to one optical fiber 13.

The light that has passed through the optical fiber 13 is input to an optical bandpass filter 25 of the receiving device 12. The optical band-pass filter 25 is capable of passing light within a predetermined band centered on the center wavelength of the light, and extracts light of one wavelength from the multiplexed light.
The intensity of the extracted light is converted into an electric signal by the photoelectric converter 28 and output from the data signal output terminal 29. Selection of the wavelength to be extracted is performed by a selection signal input from the channel selection signal input terminal 27. In accordance with the selection signal, the channel selection circuit 26 supplies a control signal having a predetermined value corresponding to the wavelength of the light to be extracted to a wavelength control unit (not shown) of the optical bandpass filter 25. Thus, the pass center wavelength of the optical band-pass filter 25 is changed according to the selection signal, and 1 out of the multiplexed light is changed.
Light of two wavelengths can be extracted and received.

By the way, the intensity of an optical signal transmitted through an optical fiber is attenuated as the transmission distance becomes longer due to the transmission loss of the optical fiber. In order to compensate for the attenuation, a relay station is provided in the middle of the transmission line to amplify the optical signal or to amplify the optical signal received by the receiving station. The amplification of an optical signal is shifting from a method in which light is once converted into an electric signal to an optical direct amplification method in which the light is amplified as it is. The optical direct amplifier used in this optical direct amplification system has a narrow wavelength band of light that can be amplified, which is several tens of nanometers. Therefore, when a multiplexed optical signal is collectively amplified by an optical direct amplifier, it is necessary to keep the wavelength of the multiplexed optical signal within a narrow amplification band of the optical direct amplifier. Such a method of multiplexing and transmitting optical signals having different wavelengths in a narrow wavelength band is particularly called a narrow-band wavelength multiplexing optical transmission method.

[0009]

In the narrow-band wavelength division multiplexing optical transmission system, the wavelength difference between multiplexed optical signals is small. An optical bandpass filter with a narrow passband is used in the device. For this reason, good reception cannot be achieved unless the wavelength of the optical signal and the pass center wavelength of the optical bandpass filter are accurately matched. On the other hand, the wavelength of an optical signal fluctuates due to fluctuations in the ambient temperature of the transmission device and the transmission path and deterioration due to aging. Further, the center wavelength of light passing through the optical band-pass filter also changes due to deterioration due to ambient temperature and aging. Therefore, when feedback control is not performed on the difference between the wavelength of the optical signal and the center wavelength of the optical bandpass filter 25 as in the channel selection circuit 26 shown in FIG. A shift occurs between the wavelength and the center wavelength of the transmission. For this reason, there is a problem that the intensity of the optical signal extracted by the optical band-pass filter becomes weak. Also, when the wavelength shift becomes large, the difference in intensity between the optical signal of the channel originally desired to be received and the optical signal of the adjacent channel decreases, the S / N ratio (signal-to-noise ratio) deteriorates, and the data error rate increases. In some cases.

In order to solve such a problem, there has been proposed a receiving apparatus which detects the intensity of an optical signal passing through an optical band-pass filter and performs feedback control of the center wavelength of the optical signal so that the intensity is maximized. ing. In the control in this receiving apparatus, the direction in which the wavelength has shifted cannot be determined even if only the change in the light intensity is detected. Therefore, the pass center wavelength of the optical band-pass filter is swept over a predetermined band, and the wavelength at which the intensity of the optical signal becomes maximum during the sweep is detected. And, to the wavelength detected by the sweep,
The pass center wavelength of the optical band pass filter is set. Therefore, it is necessary to provide a means for sweeping the pass center wavelength of the optical band-pass filter and a means for temporarily storing the wavelength at which the light intensity is maximized. Therefore, there is a problem that the configuration of the control circuit becomes complicated.
Further, since the pass center wavelength is swept over a predetermined band, the optical signal may be out of the pass band, so that the optical signal cannot be normally received during the sweep.

Accordingly, a first object of the present invention is to provide a wavelength division multiplexing optical transmission apparatus having a simple structure capable of making the center wavelength of the optical bandpass filter coincide with the wavelength of an optical signal.

It is a second object of the present invention to stably match the center wavelength of the optical bandpass filter with the wavelength of the optical signal.

A third object of the present invention is to provide a wavelength division multiplexing optical transmission device capable of multiplexing optical signals of many wavelengths in a narrow bandwidth.

[0014]

According to the first aspect of the present invention, there is provided an optical signal emitting means for emitting light of a predetermined wavelength which is intensity-modulated by data to be transmitted, and a wavelength of light emitted by the optical signal emitting means. A first control light emitting unit that emits light having a wavelength shorter by a first length and intensity-modulated by a first control signal having a predetermined frequency, and an optical signal emitting unit that emits light A second control light emitting means for emitting light having a wavelength longer by a second length than the wavelength of the light and intensity-modulated by a second control signal having a frequency different from that of the first control signal; Optical coupling means for inputting and multiplexing the light emitted by the first and second control light emitting means and the light emitted by the optical signal emitting means, respectively, and multiplexing the light by the optical coupling means. A transmission path for transmitting light, The light passing through the transmission path is input, the passing loss increases before and after the passing center wavelength, and the bandwidth at the predetermined passing loss is smaller than the wavelength difference of the light emitted by the first and second control light emitting means. An optical band-pass filter, a photoelectric converter that converts the intensity of light passing through the optical band-pass filter into an electric signal, and first and second control signals based on the electric signal converted by the photoelectric converter. Extraction means for extracting frequency components, comparison means for comparing the amplitudes of the frequency components of the first and second control signals extracted by the extraction means, and the comparison result of the comparison means emits light by the optical signal emission means. The pass center wavelength of the optical band-pass filter is changed so as to have a predetermined value when the wavelength of the optical signal to be transmitted matches the pass center wavelength of the optical band-pass filter. It is and a heart wavelength changing means in the wavelength-multiplexed optical transmission system.

That is, according to the first aspect of the present invention, with respect to the wavelength of the optical signal whose intensity has been modulated by the data to be transmitted, the light of the wavelengths before and after the wavelength is intensity-modulated with control signals of different frequencies, and these are multiplexed. Send. The receiving side converts the intensity of light passing through the optical band-pass filter into an electric signal, and extracts frequency components of two control signals from the converted electric signal. Then, by comparing the amplitudes of the extracted frequency components, the pass center wavelength is changed so that the pass center wavelength of the optical band-pass filter matches the wavelength of the optical signal. For example, it is assumed that a deviation has occurred between the center wavelength of the optical bandpass filter and the wavelength of the optical signal due to the influence of temperature fluctuation. Since the pass loss characteristic of the optical band-pass filter increases before and after the pass center wavelength, the pass loss of one of the lights on which the control signal is superimposed increases, and the pass loss of the other light increases. Decrease. Therefore, by comparing the amplitude of the frequency component of the control signal, the direction in which the wavelength shifts can be determined, and the wavelength of the optical signal and the center wavelength of the optical bandpass filter can be matched by relatively simple control means.

According to the second aspect of the present invention, input means for inputting data signals representing data to be transmitted for n channels (n is an integer of 1 or more), and first to (n + 2) th frequency signals having mutually different frequencies are provided. First to (n + 2) th control signal generation means for generating a control signal; and the first to nth control signal generation means distributed to the data signal of each channel input from the input means.
First to n-th superimposing means for superimposing the control signal on the data signal of each channel, and intensity modulation by the data signal of each channel on which the control signal is superimposed by the first to n-th superimposing means. First to n-th optical signal light emitting means for emitting light in which the wavelengths of these lights are different from each other, and the wavelength difference between the adjacent wavelengths is a constant wavelength difference,
The wavelength is shorter than the light having the shortest wavelength among the lights emitted by the first to n-th optical signal light emitting means by a certain wavelength difference and is n-th light.
A first control light emitting unit that emits light whose intensity is modulated by a control signal of +1 and a wavelength difference that is more constant than the light of the longest wavelength among the light emitted by the first to nth optical signal light emitting units. A second control light emitting unit that emits light whose wavelength is long and whose intensity is modulated by the (n + 2) th control signal;
The light emitted by the optical signal emitting means and the first light, respectively.
Optical coupling means for inputting and multiplexing the light emitted by the second control light emitting means, and a transmission line for transmitting the light multiplexed by the optical coupling means,
An optical band-pass filter for inputting light passing through the transmission path, increasing a pass loss before and after the pass center wavelength, and having a bandwidth at a predetermined pass loss twice or more a predetermined wavelength difference; and A photoelectric conversion means for converting the intensity of light passing through the band-pass filter into an electric signal, and a selection signal for selecting light to be received from light emitted by the first to n-th light signal emission means are input. Selection signal input means, and a photoelectric conversion means for converting a frequency component of a control signal transmitted by light having a wavelength that is shorter than the wavelength of light selected by the selection signal input from the selection signal input means by a predetermined wavelength difference. First extracting means for extracting from the electric signal converted by the above, and a wavelength longer by a certain wavelength difference than the wavelength of the light selected by the selection signal inputted from the selection signal input means. Extracting means for extracting the frequency component of the control signal transmitted by the photoelectric conversion means from the electric signal converted by the photoelectric conversion means, and comparing the amplitudes of the frequency components extracted by the first and second extracting means. Means and a pass center of the optical band-pass filter so that the comparison result of the comparing means becomes a predetermined value when the wavelength of the light selected by the selection signal coincides with the pass center wavelength of the optical band-pass filter. The wavelength multiplexing optical transmission device is provided with a transmission center wavelength changing means for changing the wavelength.

That is, according to the second aspect of the present invention, the control signal is transmitted to the light for transmitting the data signal.
Even if the number of lights to be multiplexed increases, the light dedicated to the control
And only the light emitted by the second control light emitting means is required.
Thereby, the wavelength band can be used effectively.
Further, since the wavelength difference of the multiplexed light is equal, even if the light to be received is switched, the light of the wavelength before and after the light is at a certain wavelength difference from the center wavelength of the optical band-pass filter. That is, it is possible to make the pass center wavelength coincide with the wavelength of each optical signal by using the same pass loss characteristic of the optical band pass filter. Therefore, even if the received light is switched, fluctuations in tuning accuracy and S / N ratio (signal-to-noise ratio) can be reduced.

According to the third aspect of the present invention, the first to (n + 2) th
The first to n-th control signal generating means have the same amplitude.
+2 control signal is generated, and the first to n-th optical signal light emitting means and the first and second control light emitting means emit light having the same maximum intensity and the same intensity. The optical bandpass filter emits light, and the pass loss increases symmetrically before and after the pass center wavelength around the pass center wavelength, and the pass center wavelength changing means extracts the comparison result of the comparing means by the first and second extracting means. The pass center wavelength of the optical band-pass filter is changed so that the amplitude of the frequency component of the control signal becomes equal.

That is, according to the third aspect of the present invention, the wavelength difference and the intensity of the multiplexed light are made equal, the modulation degree of the control signal is made the same, and the pass loss characteristic of the optical band-pass filter is changed to the pass center. It was made symmetric about the wavelength. Thus, when the wavelength of the optical signal to be received matches the center wavelength of the transmission, the amplitude of the control signal to be extracted becomes equal regardless of the optical signal of any channel received. Therefore, there is no need to prepare in advance the comparison results of the comparison means for the optical signals of each wavelength. Further, the detection that the amplitudes are equal can be realized by a simple circuit, and the configuration of the device is simplified.

According to the fourth aspect of the present invention, an optical amplifying means is provided between the optical coupling means and the optical bandpass filter to amplify the light multiplexed by the optical coupling means at once as light. Since the center wavelength of the light passing through the optical band-pass filter can be accurately matched with the wavelength of the optical signal, it is possible to multiplex light of many wavelengths within a narrow band. Thus, an optical direct amplifier having a narrow wavelength band can be used as the amplifier.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to embodiments.

FIG. 1 shows a system configuration of a wavelength division multiplexing optical transmission apparatus according to an embodiment of the present invention. This wavelength division multiplexing optical transmission device includes a transmission device 11 and a reception device 12 like the conventional wavelength division multiplexing optical transmission device shown in FIG.
And an optical fiber 13 connected between them.

FIG. 2 shows a schematic configuration of a transmission device in the wavelength division multiplex transmission device shown in FIG. The transmitting device 11 converts data signals for three channels into optical signals and transmits the signals, similarly to the conventional transmitting device 11 shown in FIG. First semiconductor laser drive circuit (LD drive circuit) 31 and first low frequency signal generation circuit 32
Are connected to the first low-frequency signal superimposing circuit 33.
The first low-frequency signal superimposing circuit 33 superimposes the first low-frequency sine wave signal 35 output from the first low-frequency signal generating circuit 33 on the driving current 34 supplied from the first semiconductor laser driving circuit 31. It is supposed to. The first low-frequency signal superimposing circuit 33 is connected to the first semiconductor laser 36. The first semiconductor laser 36 emits a first light 38 according to a first drive current 37 supplied from the first low-frequency signal superimposing circuit.

Similarly, the second semiconductor laser drive circuit 41 and the second low frequency signal generation circuit 42 are connected to a second low frequency signal superposition circuit 43. The second low-frequency signal superimposing circuit 43 adds the second low-frequency signal generating circuit 4 to the driving current 44 supplied from the second semiconductor laser driving circuit 41.
3 is superimposed on the second low-frequency sine wave signal 45. The second low-frequency signal superimposing circuit 43
Is connected to the semiconductor laser 46. The second semiconductor laser 46 emits a second light 48 according to a second drive current 47 supplied from the second low-frequency signal superimposing circuit 43.

Similarly, the third to fifth semiconductor laser driving circuits 51, 61, 71 and the third to fifth low frequency signal generating circuits 52, 62, 72 are connected to the third to fifth low frequency signal. They are connected to corresponding ones of the superimposing circuits 53, 63, 73, respectively. The third to fifth low-frequency signal superimposing circuits 53, 63, and 73 are the third to fifth semiconductor lasers 5.
6, 66 and 76 respectively. The second to fourth semiconductor laser driving circuits 41, 51,
Reference numeral 61 is connected to corresponding ones of the data signal input terminals 14, 15, and 16, respectively. The first to fifth semiconductor lasers 36, 46, 56, 66, 76 are connected to the optical coupler 24, respectively. The optical coupler 24 multiplexes the input first to fifth lights 38, 48, 58, 68, 78 so that the multiplexed light 81 is transmitted from the transmission signal output terminal 82 to the optical fiber 13. Has become.

The second to fourth semiconductor laser driving circuits 4 connected to the data signal input terminals 14, 15, 16
1, 51 and 61 output drive currents 44, 54 and 64 which are amplitude-modulated by the input data signal. First
The fifth semiconductor laser drive circuits 31 and 71 output DC drive currents 34 and 74, respectively. The first to fifth low frequency signal generation circuits 32, 42, 52, 62, 72 are provided with first to fifth low frequency sine wave signals 35, 45, 55, 65, having different frequencies and equal amplitudes. 75 is generated. The frequency of the first low frequency sine wave signal 35 is 922 Hertz, and the second to fifth low frequency sine wave signals 45, 55, 6
The frequencies of 5, 75 are sequentially increased by 1 kHz. First to fifth low frequency signal superimposing circuits 33, 43, 5
3, 63 and 73 are drive currents 34, 44, 54, 64 and 7
4 to the first to fifth low frequency sine wave signals 35, 45, 5
5, 65 and 75 are used to modulate at the same modulation degree. The modulated first to fifth drive currents 37,
The first to fifth semiconductor lasers 36, 46, 56, 66, and 76 to which 47, 57, 67, and 77 are input have first to fifth light whose intensity changes according to the input drive current. 38, 48, 58, 68 and 78 emit light.

The first to fifth semiconductor lasers 36, 46,
The maximum intensities of the light emitted from 56, 66 and 76 are the same. As for the wavelength of light, the wavelength of the first semiconductor laser 36 is the longest, and the second to fifth semiconductor lasers 46, 5
The wavelength decreases in the order of 6, 66, and 76 with the same wavelength difference. In the present embodiment, the wavelength of the first light 38 emitted by the first semiconductor laser 36 is 1540 nanometers, and the wavelength difference of each light is set to 5 nanometers.

FIG. 3 shows a spectrum of the intensity of the multiplexed light transmitted from the transmitting apparatus having such a configuration. These are the first to fifth in FIG.
Are the intensities of the first to fifth lights 38, 48, 58, 68, 78 emitted by the semiconductor lasers 36, 46, 56, 66, 76 of FIG. The light transmitted from the transmitting device 11 is
Light whose wavelength is shortened by 5 nm from 1540 nm is multiplexed and transmitted. The maximum intensities of these lights are the same. First light 38 and fifth light 78 carry first and fifth low frequency sinusoidal signals 35 and 75, respectively, and include second light 48, third light 58, and fourth light 68. Carry the data signal and the second through fourth low frequency sine wave signals 45, 55, 65, respectively.

FIG. 4 shows a schematic configuration of a receiving device of the wavelength division multiplexing optical transmission device shown in FIG. Transmission device 1
The light transmitted from 1 passes through the optical fiber 13 and is input from the reception signal input terminal 91 to the optical band-pass filter 25 of the receiver 12. The light that has passed through the optical bandpass filter 25 is guided to the optical splitter 92. One of the lights split by the optical splitter 92 is input to the photoelectric converter 28, and the photoelectric converter 28 converts the light intensity into an electric signal. The output of the photoelectric converter 28 is connected to the reception data output terminal 29. The other light split by the optical splitter 92 is input to the pin photodiode 93. The pin photodiode 93 converts the intensity of the input light into a current signal. The current signal converted by the pin photodiode 93 is input to a current / voltage conversion circuit 94, where it is converted into a voltage signal. The output of the current-voltage conversion circuit 94 is input to first and second bandpass filters 95 and 96.

The first and second bandpass filters 95,
The voltage signal passing through 96 is input to first and second peak detection circuits 97 and 98, respectively. The first peak detection circuit 97 is connected to a positive input terminal of the operational amplifier 99, and the second peak detection circuit 98 is connected to a negative input terminal. The operational amplifier 99 outputs a voltage signal corresponding to the difference between the output voltages of the peak detection circuits 97 and 98. The operational amplifier 99 is connected to the low-pass filter 101,
Are passed to the amplifier 102.
The amplifier 102 is connected to a wavelength controller (not shown) of the optical bandpass filter 25.

On the other hand, the channel selection signal input terminal 27 is connected to the channel selection circuit 26. The first frequency selection signal 103 output from the channel selection circuit 26 is input to the first band pass filter 95. Similarly, the second frequency selection signal 104 is supplied to the second bandpass filter 9.
6 has been entered.

FIG. 5 shows the transmission loss characteristics of the optical bandpass filter. A dashed line 111 in the figure represents a passing loss characteristic. Further, it indicates the intensity of the first to fifth lights 38, 48, 58, 68, 78 that have passed through the optical bandpass filter. In FIG. 5, the pass center wavelength of the optical bandpass filter 25 is 1550 nm, and the third light 5
8, which corresponds to the wavelength. The passage loss characteristics are symmetrical. At 1545 nanometers, which is the wavelength of the second light 48, and 1555 nanometers, which is the wavelength of the fourth light 68, the intensity of the light passing therethrough is lower by about 15 dB (decibel) than the central transmission wavelength. The optical bandpass filter 25 can change its center wavelength, and the one used in the present embodiment changes the center wavelength by changing the angle of light incident on the dielectric multilayer film. The angle of the dielectric multilayer film is controlled by changing the voltage applied to the piezoelectric element supporting the dielectric multilayer film.

FIG. 6 shows a circuit configuration of the band-pass filter. The band-pass filters 95 and 96 are called T-notch active filters. An input terminal 121 for inputting a signal is connected to a positive input terminal 123 of the first operational amplifier 122. First operational amplifier 1
A resistor 126 is connected between the output terminal 124 and the negative input terminal 125. A resistor 127 whose other end is grounded is connected to the negative input terminal 125.
Further, the second operational amplifier 12 is connected to the negative input terminal 125.
8 output terminals are connected. Second operational amplifier 12
The output terminal 8 is connected to the negative input terminal of the second operational amplifier 128 to form a buffer for converting impedance. Further, a variable resistor 129 whose other end is grounded is connected to the negative input terminal 125 of the first operational amplifier 122. Intermediate output terminal 131 of variable resistor 129
Is connected to the positive input terminal of the third operational amplifier 132. The negative input terminal of the third operational amplifier 132 and the output terminal of the third operational amplifier 132 are connected, and constitute a buffer for converting impedance.

Output terminal 124 of first operational amplifier 122
Between the positive input terminal of the second operational amplifier 128 and the positive input terminal of the second operational amplifier 128, capacitors 133 and 134 connected in series and resistors 135 and 136 connected in series are connected in parallel.
A resistor 1 is connected to the connection point between the capacitors 133 and 134.
37 and one end of the resistor 138 are connected, respectively.
The other ends of the resistors 137 and 138 are connected to the output terminals of the third operational amplifier 132, respectively. In addition, resistor 1
One end of each of the capacitors 141 and 142 is connected to a connection point between 35 and 136. The other ends of the capacitors 141 and 142 are the third
Are connected to the output terminal of the operational amplifier 132. First
The output terminal 124 of the operational amplifier is connected to the signal output terminal 143.

This band-pass filter increases the negative feedback of the first operational amplifier 122 at frequencies other than the pass center frequency, and lowers the gain at the other frequencies as compared with the gain at the pass center frequency, thereby reducing the band pass. Get the characteristics. Assuming that the resistance values of the resistors 135, 136, 137, and 138 are R and the capacitances of the capacitors 133, 134, 141, and 142 are C, the pass center frequency can be obtained by 1 / 2πRC.

FIG. 7 shows the pass band characteristics of the T-notch active filter shown in FIG. The pass center frequency is 922 Hertz and the sharpness (Q) is 66. The change of the pass center frequency of the bandpass filters 95, 96 is achieved by changing the resistors 135, 136,
137, 138 and capacitors 133, 134, 141,
This is done by switching 142.

Then, the receiving apparatus 12 having such a configuration will be described.
Will be described. First, a channel selection signal for selecting a channel to be received is input from a channel selection signal input terminal 27. In response to the channel selection signal, the channel selection circuit 26 initially sets the pass center wavelength of the optical band-pass filter 25 to the wavelength of light stored in advance.
This is performed by applying a predetermined voltage to a wavelength controller (not shown) of the optical bandpass filter 25. At the same time, the first and second frequency selection signals 103, 10
4 is supplied to first and second bandpass filters 95 and 96. The pass center frequency of the band-pass filters 95 and 96 is set to the frequency of the low-frequency sine wave signal that is superimposed on the light of the adjacent wavelength before and after the wavelength of the optical signal of the channel to be received. The correspondence between the wavelength of each light and the frequency of the control signal is predetermined between the transmitting device 11 and the receiving device 12.

Here, the optical signal to be received is the third light 5
8 will be described. In this case, the second light 4
8, the frequency of the second low-frequency sine wave signal 45 superimposed on the center frequency of the first band-pass filter 95,
The frequency of the fourth low-frequency sine wave signal 65 superimposed on the fourth light 68 is set to the pass center frequency of the second band-pass filter 96. The second and fourth extracted by the first and second bandpass filters 95 and 96, respectively.
The peak values of the amplitudes of the frequency components of the low-frequency sine wave signals 45 and 65 of the first and second peak detection circuits 97 and 98
Is detected by Then, a voltage signal corresponding to the difference between the detected peak values is output from the operational amplifier 99.

First, it is assumed that the wavelength of the third light 58 matches the wavelength of the optical bandpass filter 25. The pass loss characteristic (dotted line 111 in FIG. 5) of the optical band-pass filter 25 is symmetric about the pass center wavelength, so that the third light 5
The transmission loss of the second and fourth light beams 48 and 68 adjacent to each other at the same wavelength difference before and after the wavelength of 8 becomes equal. On the other hand, since the light of each wavelength is transmitted from the transmitting device 11 at the same intensity, the second light passing through the optical bandpass filter 25
The light 48 and the fourth light 68 also have the same light intensity. Since the modulation degrees of the second and fourth low-frequency sine wave signals 45 and 65 superimposed on these optical signals are equal, the low-frequency sine wave signals extracted by the first and second band-pass filters 95 and 96 are low. The peak value of the amplitude of the sine wave signal component is the same. Therefore, no output voltage appears from the operational amplifier 99, and the pass center wavelength of the optical bandpass filter 25 is maintained at the current wavelength.

Next, the operation when the wavelength of the third light 58 and the center wavelength of the light passing through the optical band-pass filter 25 deviate from each other will be described.

FIG. 8 shows a pass loss characteristic when the wavelength of the third light and the pass center wavelength of the optical band pass filter are shifted. The same reference numerals are given to the light corresponding to FIG. 5, and the description is omitted. If the wavelength shifts, the second light 48
And the wavelength of the fourth light 68 are not symmetrical with respect to the center wavelength of the light passing through the optical band-pass filter 25, and the intensity of the light passing therethrough is different. FIG. 8 shows a case where a difference of about 8 dB occurs for the sake of explanation. In practice, such a large difference does not occur since the control is always performed.

When the wavelength shifts, the optical bandpass filter 25
There is a difference in the intensity of light passing through the first and second
The second extracted by the band-pass filters 95 and 96 of FIG.
There is also a difference between the peak values of the amplitudes of the frequency components of the fourth low-frequency sine wave signals 45 and 65, and the operational amplifier 99 outputs a voltage signal corresponding to the difference. Further, the magnitude relation of the light intensity of the second light 48 and the fourth light 68 passing through the optical bandpass filter 25 is reversed depending on the direction in which the wavelength shift occurs. Accordingly, the polarity of the voltage signal appearing at the operational amplifier 99 also changes. Based on this, it is known in which direction the pass center wavelength of the optical bandpass filter 25 should be changed, and the pass center wavelength is changed in a direction in which no voltage signal appears. When the wavelength of the optical signal coincides with the passing center wavelength again, no voltage appears in the operational amplifier 99, and the passing center wavelength is maintained in this state.

The change of the pass center wavelength as described above utilizes the fact that the pass loss of the optical bandpass filter used in the receiving device increases as the wavelength becomes farther from the pass center wavelength. . In other words, the wavelength of the light to be received is at the center of the wavelengths of the two light beams on both sides of the light. Will match.
Then, the coincidence of the passing losses of the two adjacent lights is detected by extracting the low-frequency sine wave signal component superimposed on these lights and comparing the amplitudes thereof.

In the wavelength division multiplexing optical transmission apparatus of this embodiment, the center wavelength of the optical band pass filter can be kept within an error of about 1 nanometer from the wavelength of the optical signal. The stability of the control of the pass center wavelength largely depends on the stability of the pass center frequency of the band-pass filter that extracts the low-frequency sine wave signal component from the photoelectrically converted electric signal. However, if the difference between the frequencies of the low-frequency sine wave signals is increased, the sharpness (Q) of the band-pass filter can be reduced.
As a result, the frequency characteristics near the pass center frequency become smooth. Therefore, even if the center frequency of the pass is slightly shifted due to a change in temperature or aging, the peak value of the amplitude of the low-frequency signal component extracted by the band-pass filter can be made to hardly change. Therefore, the pass center wavelength of the optical band pass filter can be stably matched with the wavelength of the received optical signal without being largely influenced by the stability of the pass center frequency of the band pass filter.

Here, the first light 38 and the fifth light 78
The function of will be described. In order to make the wavelength of the light to be received coincide with the center wavelength of the light to pass, light having a low-frequency sine wave signal superimposed on both sides of the wavelength of the received light is required. Therefore, when it is desired to receive the second light 48, which is the light having the longest wavelength among the light for transmitting the data signal, the light on which the low-frequency sine wave signal having the longer wavelength is superimposed is required. . This is the first light 38. Similarly,
When it is desired to receive the fourth light 68, the third light 58 and the fifth light 78 are used to control the pass center wavelength, so that the fifth light 78 is required.

In this embodiment, the frequency difference between the low-frequency sine wave signals is set equal. However, if the low-frequency sine wave signal can be separated for each frequency by the band-pass filter on the receiving side, even if the frequency difference is not the same. Good. The frequency of the low-frequency sine wave signal is preferably several kilohertz to several hundred kilohertz. Further, in this embodiment, the optical band pass filter has a pass loss characteristic symmetrical with respect to the pass center wavelength, but the characteristic may be asymmetrical. Furthermore, even if the wavelength difference of each light, the light intensity, and the degree of modulation of the low-frequency sine wave signal are various, the wavelength of the optical signal can be matched with the center wavelength of the optical band-pass filter. For example, the output voltage of the operational amplifier 99 when each optical signal to be received coincides with the pass center wavelength of the optical band-pass filter is checked, and this is stored in a ROM (read only memory) in advance. This value is read out according to the received light, and the pass center wavelength of the optical band-pass filter may be changed so that the output voltage value of the operational amplifier becomes the same as the read value.

Further, if an optical band-pass filter having a pass loss characteristic in which a change in the pass loss is large with respect to a change in the wavelength is used, the tuning accuracy can be further improved. Further, among these characteristics, the tuning accuracy can be further improved by setting the wavelength difference of the multiplexed optical signal to the wavelength difference from the pass center wavelength at the place where the rate of change of the transmission loss is the largest. . That is, even a slight wavelength shift greatly changes the pass loss, and accordingly, the amplitude of the low-frequency sine wave signal extracted by the band-pass filter also changes greatly. Therefore, the wavelength of the optical signal and the center wavelength of transmission can be accurately matched.

The light that has passed through the optical band-pass filter 25 includes not only the optical signal of the channel desired to be received but also the optical signals of the adjacent wavelengths. However, if the intensity of these lights differs from the intensity of the optical signal of the channel to be received by 15 dB or more, the optical signal data of the channel to be received is transmitted at the same error rate as when there is no optical signal of the adjacent wavelengths. Can be demodulated. Therefore, even if the light that has passed through the optical band-pass filter includes the optical signals on both sides, an S / N ratio that does not adversely affect the reception can be obtained.

Further, since the wavelength difference of the multiplexed light is the same, and the pass loss characteristic of the optical band-pass filter is symmetrical before and after the pass center wavelength, the best S / N ratio can be obtained. An optical signal can be received. That is, when the wavelength difference is different, the wavelength of one of the lights for extracting the low-frequency sine wave signal becomes close to the passing center wavelength, the intensity difference from the received optical signal is small, and the S / N ratio is deteriorated.
On the other hand, if the wavelength difference is equal, the difference in intensity between the received optical signal and the light adjacent thereto is also equal, and the best S / N ratio can be obtained.

When setting the wavelength difference, it is necessary to pay attention to the following points. After passing through the optical band-pass filter, the intensity difference between the optical signal to be received and the light on both sides of the optical signal is more than a certain level so that a sufficient S / N ratio can be obtained. After passing through the optical band-pass filter, the intensities of the light on both sides of the wavelength are obtained so that a low-frequency sinusoidal signal can be extracted therefrom.

In the present embodiment, five light beams are multiplexed. However, the present invention is not limited to this. Further, in this embodiment, only one channel is selected from the multiplexed light in the receiving device 12 and received. However, optical fiber 1
After splitting the optical signal passing through 3 by the optical splitter, if the receiving device 12 is provided for each split light, it is natural that the optical signals of a plurality of channels can be received simultaneously.

[0052]

As described above, according to the first aspect of the present invention, with respect to the wavelength of the optical signal whose intensity is modulated by the data to be transmitted, the light of the wavelengths before and after the wavelength is controlled by the control signals of different frequencies. The signals are modulated, multiplexed and transmitted. The receiving side converts the intensity of the light passing through the optical band-pass filter into an electric signal,
The frequency components of the two control signals are extracted. Then, by comparing the amplitudes of these extracted frequency components,
The pass center wavelength was changed so that the pass center wavelength of the optical band-pass filter coincides with the wavelength of the optical signal. If the center wavelength of the optical band-pass filter and the wavelength of the optical signal deviate from each other, the magnitude relation of the amplitude of the frequency component extracted according to the deviated direction is reversed, so that the direction in which the wavelength is deviated can be easily detected. . Therefore, the wavelength of the optical signal and the center wavelength of the optical band-pass filter can be matched by relatively simple control means. In addition, since the frequency component of the control signal can be relatively stably extracted from the electric signal, the wavelength of the optical signal can be stably matched with the center wavelength of the optical band-pass filter.

According to the second aspect of the present invention, the control signal is also superimposed on the light transmitting the data to be transmitted. For this reason, even if the number of lights to be multiplexed increases, the light dedicated to the control signal is only the light emitted by the first and second control light emitting means. Thereby, the wavelength band can be used effectively. In addition, since the wavelength difference of the multiplexed light is equal, even if the light to be received is switched, the light of the wavelengths before and after the light is located at a certain wavelength difference from the center wavelength of the optical band-pass filter. Using the same loss characteristics, it is possible to match the center wavelength of the light passing with the wavelength of each optical signal. Therefore, even if the light to be received is switched, fluctuations in tuning accuracy and S / N ratio can be reduced. Further, even when light of many wavelengths is multiplexed in a narrow band, since the wavelength differences are equal, interference between these lights can be suppressed uniformly.

Further, according to the third aspect of the present invention, the wavelength difference and the intensity of the multiplexed light are made equal, the modulation degree of the control signal is made the same, and the pass loss characteristic of the optical bandpass filter is made equal. Symmetry was made about the center wavelength of the light passing through. Thus, when the wavelength of the optical signal desired to be received matches the center wavelength of the transmission, the amplitude of the control signal to be extracted becomes equal no matter which channel light is received. Therefore, it is not necessary to prepare comparison results when the wavelengths match each other in advance. Further, since the detection that the amplitudes are equal can be realized by a relatively simple circuit configuration, the apparatus can be simplified. Also, a good S / N ratio can be obtained on average irrespective of the channel of the optical signal to be received.

According to the fourth aspect of the present invention, there is provided an optical amplifier between the optical coupler and the optical band-pass filter for collectively amplifying the light multiplexed by the optical coupler as it is. Provided. Since the pass center wavelength of the optical bandpass filter can be accurately matched with the wavelength of the optical signal,
Multiple wavelengths of light can be multiplexed within a narrow band,
The light can be amplified collectively by using an optical direct amplifier having a narrow wavelength band. Therefore, even if the light intensity is attenuated due to long-distance transmission, only the receiving station can separate the multiplexed light into the respective wavelengths, and the configuration of the optical communication system can be simplified.

[Brief description of the drawings]

FIG. 1 is a system configuration diagram showing a system configuration of a wavelength division multiplexing optical transmission device according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a schematic configuration of a transmission device of the wavelength division multiplexing optical transmission device shown in FIG.

FIG. 3 is a characteristic diagram showing the intensity of multiplexed light transmitted by a transmission device.

FIG. 4 is a block diagram illustrating a schematic configuration of a receiving device of the wavelength division multiplexing optical transmission device illustrated in FIG.

FIG. 5 is a characteristic diagram showing the intensity of light that has passed through an optical bandpass filter when the center wavelength of the light passes and the wavelength of the optical signal match.

FIG. 6 is a circuit diagram illustrating a circuit configuration of a band-pass filter.

FIG. 7 is a characteristic diagram showing pass band characteristics of the band pass filter of FIG.

FIG. 8 is a characteristic diagram showing the intensity of light that has passed through the optical bandpass filter when the center wavelength of the optical signal and the wavelength of the optical signal are shifted.

FIG. 9 is a block diagram illustrating a schematic configuration of a conventionally used wavelength division multiplexing optical transmission device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 11 Transmitting device 12 Receiving device 13 Optical fiber 14-16 Data signal input terminal 24 Optical coupler 25 Optical bandpass filter 26 Channel selection circuit 27 Channel selection signal input terminal 28 Photoelectric converter 29 Received data signal output terminal 31, 41, 51 , 61, 71 Semiconductor laser drive circuit (LD drive circuit) 32, 42, 52, 62, 72 Low frequency signal generation circuit 33, 43, 53, 63, 73 Low frequency signal superposition circuit 34, 37, 44, 47, 54 , 57, 64, 67, 7
4 77 Drive current 35, 45, 55, 65, 75 Low frequency sine wave signal 36, 46, 57, 66, 76 Semiconductor laser 38, 48, 58, 68, 78 Light 81 Multiplexed light 82 Transmission signal output terminal Reference Signs List 91 reception signal input terminal 92 optical splitter 93 pin photodiode 94 current-voltage conversion circuit 95, 96 band-pass filter 97, 98 peak detection circuit 99, 122, 128, 132 operational amplifier (op-amp) 101 low-pass filter 102 amplifier 103, 104 Frequency selection signal 111 Pass loss characteristic 121 Input terminal 123 Positive input terminal 124 Output terminal 125 Negative input terminal 126, 127, 135, 136, 137, 138 Resistor 129 Variable resistor 131 Intermediate output terminal 133, 134, 141 , 142 capacitor 143 signal output terminal

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical indication H04J 14/02

Claims (4)

(57) [Claims] 1. An optical signal emitting means for emitting light of a predetermined wavelength which is intensity-modulated by data to be transmitted, and an optical signal emitting means having a wavelength shorter than the wavelength of light emitted by the optical signal emitting means by a first length. A first control light emitting unit that emits light that is intensity-modulated by a first control signal of a predetermined frequency, and a second length with respect to a wavelength of light emitted by the optical signal emitting unit A second control light emitting unit that emits light having a wavelength longer than that of the first control signal and intensity-modulated by a second control signal having a different frequency from the first control signal; and the first and second control lights. Light coupling means for inputting and multiplexing the light emitted by the light emitting means and the light emitted by the optical signal light emitting means, a transmission line for transmitting the light multiplexed by the optical coupling means, Light that has passed through the transmission path An optical band-pass filter in which a pass loss increases before and after the pass center wavelength and a bandwidth at a predetermined pass loss is wider than a wavelength difference of light emitted by the first and second control light emitting means; Photoelectric conversion means for converting the intensity of light passing through the optical band-pass filter into an electric signal; and extracting frequency components of the first and second control signals from the electric signal converted by the photoelectric conversion means. Extracting means; comparing means for comparing the amplitudes of frequency components of the first and second control signals extracted by the extracting means; and comparing the comparison result of the comparing means with the optical signal emitted by the optical signal emitting means. During the pass, the pass center wavelength of the optical band pass filter is changed so as to have a predetermined value when the wavelength matches the pass center wavelength of the optical band pass filter. Wavelength division multiplexing optical transmission apparatus characterized by comprising a wavelength changing means. 2. An input means for inputting n channels (n is an integer of 1 or more) of data signals representing data to be transmitted, and a first signal generator for generating first to (n + 2) th control signals having mutually different frequencies. First to (n + 2) th control signal generating means; and first to superimpose the first to n-th control signals distributed to the data signals of the respective channels input from the input means on the data signals of the respective channels. To the n-th superimposing means, and the intensity of each light is modulated by the data signal of each channel on which the control signal is superimposed by the first to n-th superimposing means, and the wavelengths of these lights are different from each other. The first to emit light whose wavelength difference is a certain wavelength difference
An n-th optical signal emitting unit, wherein the first to n-th optical signal emitting units emit light having a wavelength shorter than the light having the shortest wavelength by the predetermined wavelength difference and the (n + 1) th control signal. A first control light emitting unit that emits intensity-modulated light; and a wavelength that is equal to the predetermined wavelength difference than the light having the longest wavelength among the light emitted by the first to n-th optical signal light emitting units. A second control light emitting unit that emits light whose intensity is modulated by the (n + 2) th control signal for a long time; light emitted by the first to nth optical signal emitting units; Optical coupling means for inputting and multiplexing the light emitted by the control light emitting means, a transmission path for transmitting the light multiplexed by the optical coupling means, and inputting the light passing through the transmission path Before the pass center wavelength An optical band-pass filter in which the transmission loss increases and the bandwidth at the predetermined transmission loss is at least twice the predetermined wavelength difference; and a photoelectric conversion for converting the intensity of light passing through the optical band-pass filter into an electric signal. Means, a selection signal input means for inputting a selection signal for selecting light to be received from the light emitted by the first to n-th light signal emission means, and input from the selection signal input means. First extracting means for extracting a frequency component of a control signal transmitted by light having a wavelength shorter than the wavelength of light selected by the selection signal by the predetermined wavelength difference from the electric signal converted by the photoelectric conversion means; A frequency of a control signal transmitted by light having a wavelength longer by the predetermined wavelength difference with respect to a wavelength of light selected by the selection signal input from the selection signal input means. A second extraction unit for extracting a component from the electric signal converted by the photoelectric conversion unit; a comparison unit for comparing the amplitudes of the frequency components extracted by the first and second extraction units; The pass changing the pass center wavelength of the optical band pass filter so that the comparison result becomes a predetermined value when the wavelength of the light selected by the selection signal matches the pass center wavelength of the optical band pass filter. A wavelength division multiplexing optical transmission device comprising: a center wavelength changing unit. 3. The first to (n + 2) th control signal generating means generates first to (n + 2) th control signals having the same amplitude, and the first to nth optical signal light emitting means and the first and nth control signal generating means. The second control light emitting means emits light whose maximum intensity is equal to each other and which is intensity-modulated with the same modulation factor, and the optical band-pass filter passes symmetrically before and after the center wavelength around the center wavelength. The loss increases, and the passing center wavelength changing means determines that the comparison result of the comparing means is equal to the first and second wavelengths.
3. The wavelength division multiplexing optical transmission device according to claim 2, wherein the pass center wavelength of the optical band-pass filter is changed so that the amplitude of the frequency component of the control signal extracted by the extraction means becomes equal. . 4. An optical amplifying means is provided between the optical coupling means and the optical band-pass filter for amplifying the light multiplexed by the optical coupling means at once as light. The wavelength division multiplexing optical transmission device according to claim 1, 2 or 3.