JP4077175B2 - Light source deterioration state detection circuit and optical fiber amplifier - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical fiber amplifier used in an optical communication system and the like, and a circuit for detecting the state of a pumping light source used in the optical fiber amplifier.
[0002]
[Prior art]
In an optical transmission system, an optical amplifier that can amplify an input optical signal without converting it into an electrical signal is a key device. In particular, the optical fiber amplifier has excellent features such as high gain, high output, wide band, low noise, and polarization independence, and has already been put into practical use. In the optical fiber amplifier, pumping light from a pumping light source is introduced together with input light into an optical fiber to which a rare earth element such as erbium (Er) is added, thereby amplifying the input light with energy.
[0003]
Some optical fiber amplifiers are designed to improve reliability by constantly monitoring the state of the excitation light source. In this type of optical fiber amplifier, the output light from the pumping light source is photoelectrically / electrically converted by a photodiode and the signal is monitored to check the normality of the pumping light source (whether it is faulty or not). ing. This technique applies a semiconductor laser driving circuit disclosed in, for example, Japanese Patent No. 2965597, and replaces the semiconductor laser referred to in this publication with an excitation light source for amplification.
[0004]
Incidentally, optical fiber amplifiers are often provided with an automatic level control (ALC) function in order to keep the output light level after amplification constant regardless of the input light level. However, if the ALC is functioning, an optical surge may occur when the input light is restored from a state where the input light level is significantly lowered, and there is a risk of damaging an optical receiver or the like connected in the subsequent stage.
[0005]
Therefore, in order to avoid such a situation, it is considered that when the input level of the input light to be amplified becomes very low or is cut off, the amplification gain of the optical amplifier is made almost zero. The amplification gain of the optical amplifier is reduced to almost zero not only when the input light level is significantly reduced but also when the optical transmission line on the output side is disconnected. By doing in this way, the safety | security of a recovery operator's human body can be ensured. In addition, for the purpose of system testing and maintenance, the amplification gain may be lowered by external control. Hereinafter, a state in which the amplification gain of the optical amplifier is almost zero is referred to as a standby state.
[0006]
For example, in the optical amplifier described in Japanese Patent Application Laid-Open No. 8-037497, the driving power of the pumping light source is made zero or very small in the standby state, thereby minimizing the amplification gain of the amplifier.
[0007]
However, in the invention described in this publication, the excitation light source does not emit light when the drive current to the excitation light source is stopped in the standby state. Therefore, there is a problem that the normality of the excitation light source cannot be monitored.
[0008]
[Problems to be solved by the invention]
As described above, in the conventional optical fiber amplifier, the driving current to the pumping light source is stopped in a state where the amplification gain of the optical fiber amplifier is lowered. There was a problem of being unable to monitor.
[0009]
The present invention has been made in view of the above circumstances. An object of the present invention is to provide a deterioration state detection circuit for a light source and an optical fiber amplifier capable of monitoring the deterioration state of a pumping light source in a state where the amplification gain of the optical fiber amplifier is lowered. It is to provide.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, a deterioration state detection circuit for a light source according to the present invention includes an optical fiber amplifier for amplifying the input light by combining the input light and the pump light output from the light source in a rare earth doped optical fiber. A circuit for detecting a deterioration state of the light source, a pulse generation circuit for generating a pulse signal in a standby state of the optical fiber amplifier, and a drive circuit for driving the light source according to the pulse signal; A photoelectric conversion element that receives a part of the light emitted from the light source and outputs an optical / electrical conversion signal; and a monitoring unit that monitors the optical / electrical conversion signal and detects a deterioration state of the light source, The pulse width of the pulse signal is set to a pulse width sufficiently faster than the response speed of the inversion distribution of the rare earth-doped optical fiber, and the duty ratio of the pulse signal is increased by the optical fiber amplifier. Wherein the gain has a small duty ratio to a degree that does not cause.
[0011]
By taking such means, the light source generates pulsed light in the standby state, and this pulsed excitation light is introduced into the rare earth-doped optical fiber. The pulse width of the pulsed light is sufficiently faster than the response speed of the inversion distribution of the rare earth-doped optical fiber, and the duty ratio depends on the set gain of the optical fiber amplifier in the standby state. Preferably, the duty ratio is set such that the amplification gain in the standby state is substantially zero.
[0012]
Therefore, in the standby state, although the amplification gain of the optical fiber amplifier is almost zero, the pump light having the same power as that of normal light is incident on the photoelectric conversion element. This makes it possible to detect the state of the light source even when the amplification gain of the optical fiber amplifier is lowered.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
(First embodiment)
FIG. 1 is a block diagram showing a configuration of a light source deterioration state detection circuit according to a first embodiment of the present invention. This circuit is provided in an optical fiber amplifier having a rare earth doped optical fiber (not shown).
[0014]
In FIG. 1, a semiconductor laser 101 as a light source is driven by a drive current 205 supplied from a semiconductor laser drive circuit 102. The pumping light output from the semiconductor laser 101 enters the rare earth-doped optical fiber and is used for amplification of the optical signal.
[0015]
Part of the excitation light from the semiconductor laser 101 is photoelectrically / electrically converted by the photodiode 104, and a monitor signal reflecting the intensity is output from the monitor circuit 105. This monitor signal is given to the deterioration detection circuit 106, and when the output level of the semiconductor laser 101 becomes lower than a specified value, a deterioration signal is output. Thereby, it is detected that the semiconductor laser 101 has deteriorated due to a change with time, for example.
[0016]
Incidentally, the degradation state detection circuit of the light source shown in FIG. The pulse generation circuit 103 gives a pulse signal to the semiconductor laser driving circuit 102 when the semiconductor laser 101 enters a standby state. Therefore, in the standby state, the semiconductor laser drive circuit 102 is pulse-driven by the pulse signal supplied from the pulse generation circuit 103, and the semiconductor laser 101 emits light intermittently.
[0017]
In the above configuration, the pulse generation circuit 103 generates a pulse having a pulse width that is short enough that the optical fiber amplifier cannot respond and that has a small duty ratio such that the amplification gain of the optical fiber amplifier does not occur.
[0018]
Generally, the frequency characteristic of amplification gain with respect to pumping light of an optical fiber amplifier has a cutoff frequency of about 2 kHz (step response time of about 0.5 msec). Therefore, when the amplification fiber is pumped with pulsed pumping light having a pulse width of, for example, several μs, the time response of the inversion distribution of the rare-earth doped optical fiber is slow, so the gain of the optical fiber amplifier follows the change of the pumping light. Can not.
[0019]
When the excitation light pulse width of the semiconductor laser 101 is sufficiently short with respect to the response time of the optical fiber amplifier and is driven by a pulse with a small duty ratio, the instantaneous amplification gain of the optical fiber amplifier becomes equal to the time average gain. For this reason, the time average gain of the optical fiber amplifier is suppressed to the duty ratio in the case of continuous oscillation driving with the same current. Therefore, by driving the semiconductor laser 101 with a short pulse width and a small duty ratio, the gain of the optical fiber amplifier can be made substantially zero while the semiconductor laser 101 emits light with normal power. That is, even when the semiconductor laser 101 is in a standby state, the semiconductor laser 101 emits light with a normal power although it is intermittent. Therefore, it is possible to detect the deterioration state of the semiconductor laser 101 by monitoring the intensity.
[0020]
As described above, in this embodiment, the pulse generation circuit 103 is provided, and a pulse signal is given to the semiconductor laser driving circuit 102 that drives the semiconductor laser 101. Thereby, in the standby state, the semiconductor laser 101 emits pulses. Thus, the pulse generation circuit 103 generates a pulse having a pulse width that is short enough that the optical fiber amplifier that operates by the pumping light from the semiconductor laser 101 cannot respond and that has a small duty ratio such that the amplification gain of the optical fiber amplifier does not occur. Generate in In this way, the semiconductor laser 101 emits light at a normal level while suppressing the amplification gain to substantially zero, and the degradation state of the semiconductor laser 101 can be detected by monitoring the intensity. . From the above, it is possible to monitor the deterioration state of the semiconductor laser 101 even in the standby state.
[0021]
(Second Embodiment)
FIG. 2 is a block diagram showing the configuration of the second embodiment of the light source deterioration state detection circuit according to the present invention. 2 that are the same as those in FIG. 1 are denoted by the same reference numerals, and only different parts will be described here.
[0022]
In FIG. 2, the monitor signal 206 output from the monitor circuit 105 is supplied to the comparator 209 and compared with the deterioration reference voltage 208. The comparator output 210 corresponding to the result is input to the pulse detection circuit 211, and the deterioration signal 211 is output according to the state of the monitor signal 206.
[0023]
With reference to FIG. 3, it demonstrates per effect | action in the said structure. As shown in FIG. 3, the laser drive current 205 is pulsed by the pulse signal generated by the pulse generation circuit 103. Therefore, the monitor signal 206 also has a pulse shape corresponding to the laser drive waveform.
[0024]
Before the semiconductor laser 101 deteriorates, the level of the monitor signal 206 is higher than the deterioration reference voltage 208, so that the pulse-like output 210 is continuously output from the comparator 209. When the semiconductor laser 101 deteriorates from this state, the monitor signal 206 falls below the deterioration reference voltage 208. Then, the pulse from the comparator 209 is interrupted.
[0025]
The comparator output 210 is input to the pulse detection circuit 211. While the pulse of the comparator output 210 continues, the output of the pulse detection circuit 211 becomes low level (Low), and when the pulse stops, it becomes high level (High). That is, since the output 210 of the comparator 209 is in a pulse state while the semiconductor laser 101 is not deteriorated, the output 212 of the pulse detection circuit 211 is continuously low. When the semiconductor laser 101 deteriorates, the pulse is interrupted from the output of the comparator 209, so that the output of the pulse detection circuit 211 continuously becomes High and is output as the deterioration signal 212.
Even with the configuration as described above, the state of the semiconductor laser 101 in the standby state can be detected.
[0026]
(Third embodiment)
FIG. 4 is a block diagram showing a configuration of the third embodiment of the light source deterioration state detection circuit according to the present invention. In FIG. 4, parts common to those in FIGS. 1 and 2 are given the same reference numerals, and only different parts will be described here.
[0027]
In FIG. 4, a pulsed monitor signal 206 output from the monitor circuit 105 is input to the peak detection circuit 306. The peak detection circuit 306 detects the peak value of the monitor signal 206 and outputs the peak value. A peak signal 307 output from the peak detection circuit 306 is input to the comparator 309 and compared with the deterioration reference voltage 208.
[0028]
While the peak signal 307 exceeds the deterioration reference voltage 208, the output from the comparator 309 is low. On the other hand, when the semiconductor laser 101 deteriorates and the peak signal falls below the deterioration reference voltage 208, the output of the comparator 309 becomes High and is output as the deterioration signal 212.
Even with the configuration as described above, the state of the semiconductor laser 101 in the standby state can be detected.
[0029]
(Fourth embodiment)
FIG. 5 is a block diagram showing an embodiment of an optical fiber amplifier using a light source deterioration state detection circuit according to the present invention. In FIG. 5, parts common to those in FIGS. This optical fiber amplifier inputs pumping light from the semiconductor laser 101 to the rare earth doped optical fiber 425, amplifies the input light (Opt. In) by a pump action, and outputs it. The semiconductor laser 101 is driven by the output drive circuit 403 in the steady state, and is driven by the pulse drive circuit 404 in the standby state.
[0030]
The control unit 406 operates the output drive circuit 403 or the pulse drive circuit 404 based on the input disconnection detection signal, the output open detection signal, and the external control signal.
[0031]
The output drive circuit 403 operates when the optical fiber amplifier is in a steady state, and the pulse drive circuit 404 operates when the optical fiber amplifier is in a standby state. The steady state of the optical fiber amplifier indicates a normal operation mode in which the optical amplification gain is a normal value.
[0032]
The input light to be amplified is partly branched by the optical branching unit 407 and optical / electrically converted by the photodiode 408, and an input optical power signal corresponding to the intensity of the input light is output from the input optical monitor circuit 409. The input optical power signal is input to the input break detection circuit 410 and compared with the input break reference voltage. When the input optical power signal falls below the input cutoff reference voltage, the input cutoff detection circuit 410 outputs an input cutoff detection signal to the control unit 406. As a result, the control unit 406 detects that the input light has been cut off, and places the optical fiber amplifier in a standby state.
[0033]
The input light that has passed through the optical splitter 407 is combined with the pumping light in the optical multiplexer 424 and amplified in the rare earth doped optical fiber 425. This amplified light is output via the optical branching device 427 and the output reflected light branching device 415.
[0034]
Among these, the output light of the output reflected light splitter 415 is optical / electrically converted by the photodiode 416 and then given to the monitor circuit 417, and an output reflected light power signal corresponding to the reflected light intensity is output. This output reflected light power signal is input to the output open detection circuit 418 and compared with the output open reference signal.
[0035]
When the output reflected light power signal exceeds the output open reference signal, the output open detection circuit 418 outputs the output open detection signal to the control unit 406. As a result, the control unit 406 detects that the optical transmission line on the output side has been disconnected, and puts the optical fiber amplifier in a standby state.
[0036]
If the optical fiber amplifier is in a steady state, the semiconductor laser 101 is driven by the output drive circuit 403. The amplified light that has passed through the rare earth-doped optical fiber 425 is branched by the optical branching device 427, and a photocurrent corresponding to the output power is output from the output photodiode 428. This photocurrent is input to the monitor circuit 429, and the output voltage is applied to the output drive circuit 403. Thus, the drive current to the semiconductor laser 101 is controlled based on the output setting voltage.
[0037]
The semiconductor laser drive current is supplied to the semiconductor drive current monitor 432, and the output voltage and the deterioration reference voltage 434 are compared by the semiconductor laser current deterioration detector 435 to detect the deterioration of the semiconductor laser 101. That is, when the semiconductor laser 101 deteriorates, the semiconductor laser current deterioration detection unit 435 uses the function of the control loop so that the drive current increases due to the decrease in the light emission amount. When the value exceeds 434, the semiconductor laser 101 determines that the failure has deteriorated and outputs a deterioration signal.
[0038]
On the other hand, if the optical fiber amplifier is in a standby state, the pulse driving circuit 404 is pulse-driven based on the output signal of the pulse generating circuit 103. At this time, the pulse driving circuit 404 pulses the semiconductor laser 101 with a pulse width that is so short that the optical fiber amplifier cannot respond, and with a duty ratio that is so small that the gain of the optical fiber amplifier does not occur.
[0039]
At this time, while the amplification gain of the optical amplifier is suppressed to the minimum, the semiconductor laser 101 outputs pulsed light having an intensity corresponding to the deterioration state. This pulsed light is photo / electrically converted by the photodiode 104 and supplied to the monitor circuit 105. When the level of the optical / electrical conversion signal becomes lower than the specified value, the deterioration detection circuit 106 determines that the semiconductor laser 101 has deteriorated and outputs a deterioration signal.
[0040]
With the above configuration, it is possible to provide an optical fiber amplifier that can monitor the deterioration state of the pumping light source even when the amplification gain of the optical fiber amplifier is lowered.
[0041]
【The invention's effect】
As described in detail above, in the present invention, in the standby state, the semiconductor laser is pulse-driven with a pulse width that is short enough that the optical amplifier does not respond and has a duty ratio that is so small that no gain is generated. The pumping light output sufficient to detect the deterioration of the semiconductor laser can be obtained while the gain is substantially zero. As a result, it is possible to provide a light source deterioration state detection circuit and an optical fiber amplifier that can monitor the deterioration state of the pumping light source even when the amplification gain of the optical fiber amplifier is lowered.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a light source deterioration state detection circuit according to a first embodiment of the present invention.
FIG. 2 is a block diagram showing the configuration of a second embodiment of a light source deterioration state detection circuit according to the present invention.
FIG. 3 is a diagram for explaining the operation of the light source deterioration state detection circuit shown in FIG. 2;
FIG. 4 is a block diagram showing a configuration of a third embodiment of a light source deterioration state detection circuit according to the present invention;
FIG. 5 is a block diagram showing an embodiment of an optical fiber amplifier using a degradation state detection circuit for a light source according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 101 ... Semiconductor laser 102 ... Semiconductor laser drive circuit 103 ... Pulse generation circuit 104 ... Photo diode 105 ... Monitor circuit 106 ... Degradation detection circuit 205 ... Laser drive current 206 ... Monitor signal 208 ... Degradation reference voltage 209 ... Comparator 210 ... Comparator output 211 ... Pulse detection circuit 212 ... Degradation signal 306 ... Peak detection circuit 307 ... Peak signal 309 ... Comparator 403 ... Output drive circuit 404 ... Pulse drive circuit 405 ... Pulse generation circuit 406 ... Control unit 407 ... Optical splitter 408 ... Input optical photodiode 409 ... Input light monitor circuit 410 ... Input disconnection detection circuit 415 ... Output reflected light splitter 416 ... Photodiode 417 ... Monitor circuit 418 ... Output open detector circuit 424 ... Optical multiplexer 425 ... Rare earth doped optical fiber 427 ... Optical splitter 428 Output photodiode 429 ... monitor circuit 432 ... semiconductor driving current monitor 434 ... degradation reference voltage 435 ... semiconductor laser current degradation detecting unit

Claims (4)

A circuit for detecting a deterioration state of the light source, used in an optical fiber amplifier for amplifying the input light by combining input light and pumping light output from the light source in a rare earth-doped optical fiber,
A pulse generation circuit for generating a pulse signal in a standby state of the optical fiber amplifier;
A drive circuit for driving the light source in accordance with the pulse signal;
A photoelectric conversion element that receives a part of the light emitted from the light source and outputs a photoelectric conversion signal;
Monitoring means for monitoring the light / electricity conversion signal and detecting the deterioration state of the light source,
The pulse generation circuit generates the pulse signal having a pulse width sufficiently faster than the response speed of the inversion distribution of the rare earth-doped optical fiber and a small duty ratio so that the amplification gain of the optical fiber amplifier does not occur. A circuit for detecting a deterioration state of a light source. The monitoring means includes
A comparator that compares the photoelectric conversion signal with a predetermined reference voltage and outputs the result;
The deterioration state detection circuit for a light source according to claim 1, further comprising a deterioration detection circuit for detecting a deterioration state of the light source in accordance with an output level of the comparator. The monitoring means includes
A peak detection circuit for detecting and outputting a peak of the photoelectric conversion signal;
2. The light source deterioration state detection circuit according to claim 1, further comprising: a comparator that compares the peak detection circuit with a predetermined reference voltage and detects a deterioration state of the light source according to a result of the comparison. In an optical fiber amplifier having two operating states, a steady state and a standby state in which the amplification gain is lower than the steady state,
A rare earth doped optical fiber;
A light source that generates and outputs excitation light;
An optical multiplexer for combining the input light to be amplified and the pumping light in the rare earth-doped optical fiber;
A pulse generation circuit for generating a pulse signal in the standby state;
A drive circuit for driving the light source in accordance with the pulse signal;
A photoelectric conversion element that receives light emitted from the light source and outputs a photoelectric conversion signal;
Monitoring means for monitoring the light / electricity conversion signal and detecting the deterioration state of the light source,
The pulse generation circuit generates the pulse signal having a pulse width sufficiently faster than a response speed of the inversion distribution of the rare earth-doped optical fiber and a small duty ratio so that an amplification gain of the optical fiber amplifier does not occur. An optical fiber amplifier.

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