JPH0824281B2 - Frequency stabilization circuit for optical multiplexer / demultiplexer - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to frequency stabilizing circuits used in optical multiplexers and demultiplexers of optical add / drop transmission circuits.

[0002]

2. Description of the Related Art In the field of large-capacity optical communication, optical signals are generally multiplexed and transmitted. Since the wavelength interval of each optical signal becomes narrower as the multiplicity is increased, it is necessary to stabilize the frequency. Therefore, Japanese Patent Laid-Open No. 1-1
In Japanese Patent No. 66594, a reference laser that performs multimode oscillation in which the wavelength is controlled and whose wavelength is stable is used, and this output light is used after being separated into each wavelength.

On the other hand, FIG. 2 shows a stabilizing circuit conventionally used in an optical multiplexer and an optical demultiplexer of an optical add / drop transmission circuit. The frequency stabilization circuit of the optical multiplexer / demultiplexer includes an optical multiplexer 11, a first temperature adjustment circuit 12 for stabilizing the temperature of the optical multiplexer 11, and an optical demultiplexer 13.
And a second temperature adjusting circuit 14 for stabilizing the temperature of the optical demultiplexer 13. In such a frequency stabilizing circuit of the optical multiplexer / demultiplexer, the optical multiplexer 11 has a first,
Second, third, ... Optical input signals 16 ₁ , 16 ₂ , 1
6 ₃ , ... Is input and the optical frequency multiplex output signal 17 is output. In the first temperature adjustment circuit 12,
A first initial set value 18 for temperature adjustment is input.

The optical demultiplexer 13 has an optical frequency input signal 1
9 is input and the first, second, third, ... Optical output signals 2
0 ₁ , 20 ₂ , 20 ₃ , ... Are output. A second initial set value 21 for temperature adjustment is input to the second temperature adjustment circuit 14.

By the way, the transmission characteristics of the optical multiplexer 11 can be adjusted by the temperature. Therefore, in the frequency stabilizing circuit of the conventional optical multiplexer / demultiplexer, the transmission characteristic of the optical multiplexer 11 is adjusted by manually adjusting the first initial setting value 18 input to the first temperature adjusting circuit 12. It is designed to keep it optimal. Similarly, the transmission characteristics of the optical demultiplexer 13 can be adjusted by the temperature. Therefore, similarly, the second initial setting value 21 input to the second temperature adjusting circuit 14 is manually adjusted to keep the transmission characteristic of the optical demultiplexer 13 at an optimum level.

[0006]

In the frequency stabilizing circuit of such an optical multiplexer / demultiplexer used conventionally, the initial setting value 1
The temperatures of the optical multiplexer 11 and the optical demultiplexer 13 are separately adjusted by the temperature adjustments 8 and 21 to stabilize the respective frequencies. Therefore, these transmission characteristics may be different between the optical multiplexer 11 and the optical demultiplexer 13. Furthermore, since only the initial value was adjusted, it was not possible to cope with changes in the characteristics of the optical multiplexer / demultiplexer with time. Further, since the transmission characteristic is manually set to the optimum, there is a problem that the optimum adjustment is not always performed.

Therefore, an object of the present invention is to provide a frequency stabilizing circuit for an optical multiplexer / demultiplexer whose transmission characteristics are the same in the optical multiplexer and the optical demultiplexer.

[0008]

In the present invention, (a) an absolute frequency stabilized light source for outputting a reference optical signal, and (b) an optical signal output from the absolute frequency stabilized light source is input. And an optical multiplexer for inputting one output of the optical switch and a plurality of optical signals and multiplexing the input optical signals. (D) An optical coupler for multiplexing the other output of the optical switch and the output of the optical multiplexer and branching into two, and (e) a first optical receiver for receiving one branch output of this optical coupler. When,
(F) an oscillator for optical frequency modulating the absolute frequency stabilizing light source, (g) a first multiplier for multiplying the oscillation output of this oscillator by the output of the first optical receiver, and (h) this first A first low-pass filter that removes high-frequency components from the output of the multiplier and outputs a frequency error signal indicating an error between the frequencies of the two.
(I) When an optical demultiplexer that inputs an optical frequency-multiplexed signal and performs optical demultiplexing and (u) the other output of the optical switching device is sent to the transmission line via the optical coupler, it is routed through the ring. A second optical receiver for receiving the optical signal of the absolute frequency stabilized light source inputted as the optical frequency multiplexed signal, and (l) a second optical receiver for multiplying the output of the second optical receiver by the oscillation output of the oscillator. 2) a second low-pass filter for removing a high-frequency component from the output signal of the second multiplier and outputting a frequency error component; and (w) a first low-pass filter. The first temperature adjusting circuit for adjusting the temperature of the optical multiplexer so that the error signal supplied to the wave filter is minimized, and (f) the error signal supplied to the second low-pass filter is minimized. A second temperature adjustment circuit for adjusting the temperature of the optical demultiplexer is provided in the frequency stabilization circuit of the optical multiplexer / demultiplexer.

In this circuit, the first temperature adjusting circuit is adjusted in a state where no optical signal is input to the optical multiplexer from other than the optical switch, and then the optical switch is switched. The frequency stabilizing operation is performed by controlling the second temperature adjusting circuit.

That is, in the present invention, in the temperature adjusting circuit for adjusting the temperature of the optical multiplexer, the optical signal obtained from the optical multiplexer is received by the first optical receiver, and this and the absolute frequency stabilizing light source are connected. The output of the optical frequency-modulated oscillator is multiplied by the first multiplier, and the result of this multiplication is passed through the first low-pass filter to obtain a frequency error signal indicating the error between the two frequencies. The temperature is adjusted so that the error is minimized, and the optimum transmission characteristics of the optical multiplexer are matched with the optical frequency of the absolute frequency stabilized light source. Also, regarding the temperature adjustment circuit that adjusts the temperature of the optical demultiplexer, the optical signal of the absolute frequency stabilized light source is sent to the transmission line by the optical switch.
This optical signal returned via the ring is input to the optical demultiplexer and received by the second optical receiver. Then, the output of the oscillator is the optical frequency modulation of the absolute frequency stabilizing light source and the second
By multiplying the result of multiplication by a second low-pass filter to obtain a frequency error signal indicating an error between the frequencies of the both, and temperature adjustment is performed so that this frequency error is minimized. The optimum transmission characteristics of the optical demultiplexer are adapted to the optical frequency of the absolute frequency stabilizing light source. As a result, the transmission characteristics of the optical multiplexer and the optical demultiplexer are the same.

[0011]

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

FIG. 1 shows the configuration of a frequency stabilizing circuit of an optical multiplexer / demultiplexer according to an embodiment of the present invention. The frequency stabilizing circuit of this optical multiplexer / demultiplexer includes an optical multiplexer / demultiplexer 31 and a first temperature adjusting circuit 32 for adjusting the temperature thereof, and an optical demultiplexer 33 and a second temperature adjusting circuit for adjusting the temperature thereof. In addition to the adjusting circuit 34, the absolute frequency stabilizing light source 35 and other circuit elements are provided. Here, the absolute frequency stabilizing light source 35 is supplied with a predetermined oscillation output 37 from the oscillator 36 and inputs the frequency-modulated optical signal 38 to the input side of the optical switch 39. The optical switch 39 is
The optical signal 38 is input to the optical multiplexer 31 or the optical coupler 41 as an optical input signal 42 _N.

The optical multiplexer 31 receives the first to Nth optical input signals 42 _{1 to} 42 _{N and} multiplexes them. The multiplexed optical signal 43 is input to the optical coupler 41. The optical coupler 41 outputs this as an optical frequency multiplex output signal 44, and also supplies a part of it to the first optical receiver 46 for the optical multiplexer 31. The first optical receiver 46 is composed of a photodiode, converts the input optical frequency multiplex output signal 44 into an electrical signal, and uses this as an optical frequency multiplex output detection signal 47 for the first optical multiplexer 31. To the multiplier 48 of the. The oscillation output 37 from the oscillator 36 is also input to the first multiplier 48, and the multiplication result signal 49 passes through the first low-pass filter 51 for the optical multiplexer 31. Then, the signal is input to the first temperature adjusting circuit 32 as the first temperature adjusting signal 52.

On the other hand, the optical demultiplexer 33 uses the optical frequency input signal 5
4 is input and the first to Mth optical output signals 55 _{1 to} 55 _M are output. Here, the Mth optical output signal 55
_{The M} is input to the second optical receiver 57 for the optical demultiplexer 33, and is supplied as the optical output detection signal 58 to the second multiplier 59 for the optical demultiplexer 33. The oscillation output 37 from the oscillator 36 is also input to the second multiplier 59, and the multiplication result signal 61 passes through the second low-pass filter 62 for the optical demultiplexer 33. Then, it is input to the second temperature adjusting circuit 34 as the second temperature adjusting signal 63.

First, the case where the absolute frequency stabilization of the optical multiplexer 31 and the optical demultiplexer 33 is performed by the frequency stabilizing circuit of such an optical multiplexer / demultiplexer will be described. First, when stabilizing the absolute frequency of the optical multiplexer 31, the first to (N-1) th optical input signals 42 _{1 to} 42 _N-1 are not input to the optical multiplexer 31. The same applies to the case where the optical demultiplexer 33 is subjected to absolute frequency stabilization. Then, the optical switch 39 is set in a state in which the optical signal 38 output from the absolute frequency stabilizing light source 35 is input to the optical multiplexer 31 side as the optical input signal 42 _N.

In this state, the multiplexed optical signal 43 output from the optical multiplexer 31 is received by the first optical receiver 46 via the optical coupler 41. That is, only the optical signal of the absolute frequency stabilizing light source 35 subjected to frequency modulation is received by the first optical receiver 46. The optical frequency multiplex output detection signal 47 obtained from the first optical receiver 46 and the oscillation output 37 obtained from the oscillator 36 are multiplied by the first multiplier 48, and the multiplication result signal 49 obtained as a result is 1 is input to the low-pass filter 51. By passing the multiplication result signal 49 through the first low-pass filter 51, the first frequency as an error signal of the optical frequency of the optical signal of the absolute frequency stabilizing light source 35 and the optimum transmission frequency of the optical multiplexer 31 is obtained. Signal 52 for temperature adjustment
Is obtained. This is fed back to the first temperature adjusting circuit 32 so as to minimize the error represented by the first temperature adjusting signal No. 52. As a result, the optical multiplexer 31
It is possible to match the optimum transmission characteristics of the above with the optical frequency of the absolute frequency stabilizing light source 35.

Next, in order to stabilize the absolute frequency of the optical demultiplexer 33,
explain about. Frequency stabilization for optical demultiplexer 33
At the time of operation, the optical switch 39 switches the output destination, and the optical input
Signal 42_NEnters the optical coupler 41 instead of the optical multiplexer 31
Shoot. This optical input signal 42 _NAre transmitted to the transmission line.
The optical signal 38 output from the absolute frequency stabilizing light source 35
Use by not dropping at a lower node or branching
By doing so, this optical signal is transmitted to this upper node at the optical frequency.
It returns as input signal 54. The optical demultiplexer 33
To receive.

The received optical frequency input signal 54 remains modulated by the oscillator 36. Therefore, the received optical frequency input signal 54 and this oscillator 36
The oscillation output 37 output from the above is multiplied by the second multiplier 59, and the multiplication result signal 61 obtained as a result is passed through the second low-pass filter 62. As a result, an error signal between the optical frequency of the optical signal 38 output from the absolute frequency stabilizing light source 35 and the optimum transmission frequency of the optical demultiplexer 33 is obtained. The second temperature adjusting circuit 3 for temperature adjustment uses this as a second temperature adjusting signal 63 so as to minimize this error signal.
Return to 4. As a result, the optimum transmission characteristic of the optical demultiplexer 33 is changed to the optical signal 3 output from the absolute frequency stabilizing light source 35.
8 optical frequencies can be tuned. In this way, the transmission characteristic of the optical demultiplexer 33 matches the transmission characteristic of the optical multiplexer 31.

After the absolute frequency stabilization of the optical multiplexer 31 and the optical demultiplexer 33 is performed as described above, the first to (N-th)
The optical input signals 42 _{1 to} 42 _N-1 of 1) are input to the optical multiplexer 31, and transmission / reception is performed via the optical demultiplexer 33.

[0020]

As described above, according to the present invention, the optical signal output from the absolute frequency stabilizing light source is passed through the ring, and the transmission characteristics of the optical multiplexer and the optical demultiplexer are matched to the absolute frequency. I was allowed to. Therefore, not only the transmission characteristics of the optical multiplexer and the optical demultiplexer become the same, but also the both can be kept in the optimum transmission characteristics. In addition, it is possible to cope with fluctuations in transmission characteristics of the optical multiplexer / demultiplexer over time, keep the loss of the optical multiplexer / demultiplexer to a minimum, stabilize the receiving sensitivity, and keep the receiving sensitivity good. it can.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a frequency stabilizing circuit of an optical multiplexer / demultiplexer according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a frequency stabilizing circuit of a conventionally used optical multiplexer / demultiplexer.

[Explanation of symbols]

 31 Optical Multiplexer 32 First Temperature Adjustment Circuit 33 Optical Demultiplexer 34 Second Temperature Adjustment Circuit 35 Absolute Frequency Stabilizing Light Source 36 Oscillator 37 Oscillation Output 41 Optical Coupler 44 Optical Frequency Multiplexed Output Signal 46 First Optical Receiver 48 First Multiplier 51 First Low-pass Filter 52 First Temperature Adjustment Signal 54 Optical Frequency Input Signal 57 Second Optical Receiver 59 Second Multiplier 62 Second Low-pass Filter 63 Second temperature adjustment signal

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location H04B 10/06 10/14

Claims (2)

[Claims] 1. An absolute frequency stabilizing light source for outputting a reference optical signal, and an optical switch for inputting an optical signal output from the absolute frequency stabilizing light source and switching the output to one of two. And an optical multiplexer for inputting one output and a plurality of optical signals of the optical switch, and for multiplexing the input optical signals, and the other output of the optical switch and the output of the optical multiplexer. An optical coupler that multiplexes and branches into two, a first optical receiver that receives one branched output of this optical coupler, an oscillator that performs optical frequency modulation on the absolute frequency stabilizing light source, and an oscillation output of this oscillator And a first multiplier for multiplying the output of the first optical receiver by a first multiplier for removing a high frequency component from the output of the first multiplier and outputting a frequency error signal indicating an error between the two frequencies. 1 low-pass filter and optical frequency multiplexed signal input An optical demultiplexer that performs optical demultiplexing by means of an optical demultiplexer, and when the other output of the optical switching device is sent to the transmission line via the optical coupler, the optical frequency multiplexed signal is input via a ring. A second optical receiver for receiving the optical signal of the absolute frequency stabilized light source; a second multiplier for multiplying the output of the second optical receiver by the oscillation output of the oscillator; and the second multiplication A second low-pass filter that removes a high-frequency component from the output signal of the filter and outputs a frequency error component; and the optical filter that minimizes the error signal supplied to the first low-pass filter. A first temperature adjusting circuit for adjusting the temperature of the optical demultiplexer, and a second temperature adjusting circuit for adjusting the temperature of the optical demultiplexer so that an error signal supplied to the second low-pass filter is minimized. A frequency stabilizing circuit for an optical multiplexer / demultiplexer, comprising: an adjusting circuit. 2. During the frequency stabilizing operation, the first temperature adjusting circuit is adjusted in a state in which an optical signal other than the optical switching device is not input to the optical multiplexer, and then the optical signal is adjusted. 2. The frequency stabilizing circuit for an optical multiplexer / demultiplexer according to claim 1, wherein the switching device is switched and the second temperature adjusting circuit is adjusted.