Automatic optical-output drop circuit of optical amplifier

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Industrial application field]

The present invention relates to an optical output automatic reduction circuit of an optical amplifier, and opens the output end of the optical amplifier having a function of protecting the human eye, etc., with respect to the optical output output from the optical fiber amplifier constituting the optical communication system. It relates to an automatic optical output reduction circuit of an optical amplifier of time.

【0002】

[Conventional technology]

Generally, there are three types of optical amplifiers: semiconductor optical amplifiers, rare earth-added fiber optical amplifiers, and Raman optical amplifiers. Similar to a laser diode, a semiconductor optical amplifier utilizes a gain mechanism of a semiconductor active layer by injecting a current to operate a device below an oscillation threshold value to obtain an optical amplification action against an externally injected light. The rare earth-added fiber optical amplifier has Ed in the core of the fiber.^3-, Er³⁺An optical fiber to which earth elements such as these are added is used as an amplification medium, especially Ed.³⁺Since the added optical fiber has a laser transition frequency in the wavelength band of 1.55 μm and can perform optical amplification in that wavelength range, it can be expected to be applied to an optical communication system. Further, the Raman optical amplifier obtains an amplification effect by an optical power conversion process from excitation light to signal light by utilizing the induced Raman scattering phenomenon, which is a nonlinear optical effect. As an application form of these optical amplifiers to an optical communication system, they are applied to an optical amplification repeater, an optical preamplifier, an optical booster amplifier, and the like.

【0003】

By the way, when these optical amplifiers are used to amplify the output of the optical transmitter and output it, high-power light of several tens to several hundreds of mW is emitted to the output of the optical amplifier. There is a risk of injury, and it is necessary to protect the eyes etc. by some means. Therefore, conventionally, an optical output automatic reduction circuit for automatically reducing the optical output of an optical amplifier has been used.

【0004】

FIG. 2 is a block diagram showing an example of such a conventional optical output automatic reduction circuit. In this figure, an optical booster amplifier 102 is connected to the transmitting end of the optical transmitter 100, and an optical receiver (not shown) is connected to one output port of the optical booster amplifier 102. This optical booster amplifier 102 is a wavelength division multiplexing (WDM) coupler 121, Er.³⁺Additive fiber 122, this Er³⁺It is composed of an optical coupler 123 that amplifies and outputs the output of the additive fiber 122. One input port of the amplifier 160 is connected to one output end of the optical coupler 123 via an optical output monitor circuit 103 that monitors the optical output and a second reference voltage generation circuit 163 that generates a second reference voltage. .. The optical output monitor circuit 103 includes a light receiving element 131 and a signal conversion circuit 132. When the optical output monitor circuit 103 confirms that the optical output is at a certain level or higher, the light emitted from the optical coupler 123 is received by the light receiving element 131 and then converted into an electric signal by the signal conversion circuit 132. Further, the second reference voltage generation circuit 162 outputs a second reference voltage based on the output of the signal conversion circuit 132, and inputs the reference voltage to the amplifier 160.

【0005】

Further, the other input port of the amplifier 160 is connected to the other output end of the optical coupler 123 via a reflected light monitor circuit 104 that monitors the reflected light and a first reference voltage generating circuit 161 that generates a first reference voltage. To. This reflected light monitor circuit is composed of a light receiving element 141 and a signal conversion circuit 142. In this reflected light monitor circuit, when it is confirmed that the reflected light is above a certain level, the light emitted from the optical coupler 123 is received by the light receiving element 131, and then converted into an electric signal by the signal conversion circuit 142. Further, the first reference voltage generation circuit 161 outputs the first reference voltage based on the output of the signal conversion circuit 142, and inputs the reference voltage to the amplifier 160.

【0006】

The reference voltage from the reference voltage generating circuit 152 is input to one input port of the comparator 151, and the output voltage of the amplifier 160 is input to the other input port of the comparator 151. The WDM coupler 121 of the optical booster amplifier 102 is connected to the output port of the comparator 151 via the optical output control circuit 106, the drive circuit 107, and the excitation laser diode 108. In the optical output control circuit 106, the optical output is controlled based on the compared output voltage of the comparator 151.

【0007】

Further, in the drive circuit 107, the excitation laser diode 108 is driven based on the control signal of the optical output control circuit 106. Therefore, in the optical booster amplifier 102, when the drive circuit 107 is driven, an amplified output having an amplification factor of, for example, 20 dBm can be obtained, so that the output voltage supplied from the optical booster amplifier 106 to the optical receiver 110 is only the gain. Since it is lowered, the light output can be automatically lowered. When the drive circuit 107 is not driven, no optical signal is transmitted from the optical transmitter 100 to the optical receiver (not shown) via the optical booster amplifier 102.

【0008】

FIG. 3 is an example of a block diagram in which the block configuration is simplified from the optical output automatic reduction circuit of the optical fiber amplifier of FIG. The same configurations as those in FIG. 2 are designated by the same reference numerals, and detailed description thereof will be omitted here.

【0009】

In FIG. 3, the reflected light monitor circuit 104 is connected to the output end of the optical coupler 123, and the excitation light source monitor circuit 109 is not connected to the output end of the optical coupler 123. Laser light is incident on the input end of the excitation light source monitor circuit 109 from the output end of the excitation laser diode 108. The excitation light source monitor circuit 109 is composed of a light receiving element 191 and a signal conversion circuit 192. The light emitted from the laser diode 108 is received by the light receiving element 191 and then converted into an electric signal by the signal conversion circuit 192.

【0010】

Further, the reference voltage generation circuit 152 outputs a reference voltage based on the output of the signal conversion circuit 192, and inputs the reference voltage to the amplifier 151. The comparator 151 outputs a comparison voltage based on the outputs of the reference voltage generation circuit 152 and the signal conversion circuit 142. At this time, the drive circuit 107 is driven and the excitation laser diode 108 emits light, so that the excitation light source monitor circuit 109 can be operated and the optical booster amplifier 2 can have an amplification factor of, for example, 20 dBm. The output voltage can be lowered by the gain. Therefore, even in the optical output automatic reduction circuit of the optical fiber amplifier of FIG. 3, the optical output can be automatically reduced in the same manner as the optical output automatic reduction circuit of the optical fiber amplifier of FIG. It is possible to prevent the human eyes that handle the light from being adversely affected.

【0011】

As an example of the optical output automatic reduction circuit of the optical fiber amplifier as described above, there is Japanese Patent Application Laid-Open No. 4-324335. In the optical output automatic reduction circuit of the optical fiber amplifier described in Japanese Patent Application Laid-Open No. 4-324335, the output end side of the optical amplifier is similar to the optical output automatic reduction circuit of the optical fiber amplifier shown in FIGS. Since it is possible to automatically prevent the high light output from being emitted from the output end side when it is opened, it is possible to eliminate the risk of accidentally seeing the high light output in the eyes.

【0012】

[Problems to be Solved by the Invention]

In the optical output automatic reduction circuit of these optical fiber amplifiers, the level difference between the magnitude of the signal light detected by the optical output monitor circuit and the magnitude of the reflected return light detected by the reflected light monitor circuit is obtained by the differential amplifier. By comparing the difference between the level difference in the open state of the output end of the optical amplifier and the reference voltage set in the middle of the level difference in the connected state with a comparator, the output end of the optical amplifier is opened. It was judged whether it was there or was in a connected state. Therefore, in this type of automatic optical output reduction circuit, the difference between the logarithmic amplifier and the reference voltage set approximately in the middle of the level difference in the connected state in order to obtain the level difference in the open state of the output end of the optical amplifier is set. A reference voltage generation circuit is required for comparison with a comparator, and there is a problem that the circuit configuration becomes complicated.

【0013】

Further, in this kind of light output automatic reduction circuit, when the excitation light source monitor circuit for monitoring the state of the excitation light source and the reflected light monitor circuit for monitoring the reflected return light are used, a differential amplifier is not required, but the reflected light is reflected. From the magnitude of the reflected return light detected by the monitor circuit, a reference voltage for determining the open state and the connected state of the output end of the optical amplifier is required. In addition, since it is necessary to generate two types of reference voltages depending on the state of the excitation light source in this automatic optical output reduction circuit, it is necessary to provide two reference voltage generation circuits for that purpose, and the occupied area of these circuits is also taken into consideration. It had to be, and there was a problem when trying to miniaturize it.

【0014】

Therefore, an object of the present invention is to provide an optical output automatic reduction circuit of an optical fiber amplifier which has good operability and maintainability and can be made compact.

【0015】

[Means for solving problems]

In order to achieve such an object, the invention according to claim 1 comprises an optical fiber amplifier that amplifies an optical signal supplied from an optical transmitter, an optical output monitor circuit that monitors the optical signal, and an output of the optical fiber amplifier. It is an optical output automatic reduction circuit of an optical amplifier including a reflected light monitor circuit that monitors the reflected light from the optical output connector at the end, and a part of the optical output of the optical fiber amplifier is monitored by the optical output monitor circuit. Based on the comparison output of a comparison device that constantly compares the signal-converted optical output monitor signal and the reflected light monitor signal that has been signal-converted by monitoring a part of the reflected light from the optical output connector with the reflected light monitor circuit. A switch for selecting whether to output one of the reference voltages and the amplification degree of the optical fiber amplifier according to the first or second reference voltage are controlled based on the operation of this switch.

【0016】

In the invention according to claim 2, the bias circuit includes an excitation laser diode and a drive circuit for reducing the bias current of the diode.

【0017】

In the invention according to claim 3, the optical output connector is configured so that the bias current of the excitation laser diode and the optical output transmitted from the optical transmitter are automatically restored when the disconnection of the connector is recovered.

【0018】

In the invention according to claim 4, the optical fiber amplifier includes an input port and a plurality of input ports whose output branch ratio is determined based on the output of the optical amplifier and the optical-electric conversion efficiency of the reflected light monitor circuit and the optical output monitor circuit. An optical coupler having an output port was provided.

【0019】

[Action]

According to claim 1, in the reflected light monitor circuit shown in FIG. 1, a voltage fluctuation of about 30 dBm can be expected depending on whether the reflected light monitor voltage is in the open state or the connected state of the optical output connector. In the optical output monitor circuit, the optical output monitor voltage and the reflected light monitor are selected depending on whether the optical connector is in the open state or the connected state by selecting the setting level of the optical output monitor voltage. The relationship between voltage output levels is reversed. In the comparator, a comparative output is obtained by constantly comparing two voltage levels, the reflected light monitor voltage which is the output of the reflected light monitor circuit and the optical output monitor voltage which is the output of the light output monitor circuit. In the optical output control circuit, based on the comparative output of the comparator, when the optical output connector is connected, the normal reference voltage is used as the reference voltage, and when the optical output connector is open, it affects the eyes and the like. The switch is switched so that the optical output level does not exist and the optical output power reaches the reference voltage at a level that can be automatically restored. The optical output is automatically controlled based on the reference voltage and the optical output monitor voltage selected in this way.

【0020】

According to claim 2, the optical output can be set to a constant level by providing the bias circuit with an excitation laser diode and a drive circuit for reducing the bias current of the diode.

【0021】

In the invention according to claim 3, the optical output connector can automatically restore the bias current of the excitation laser diode and the optical output transmitted from the optical transmitter when the disconnection of the connector is recovered. Maintenance work can be done smoothly.

【0022】

In the invention of claim 4, the optical fiber amplifier is provided with an input port and a plurality of output ports in which the output branch ratio is determined based on the output of the optical amplifier, the reflected light monitor circuit, and the optical-electric conversion efficiency of the optical output monitor circuit. By providing the optical coupler to have, the optical output can be easily branched.

【0023】

[Example]

Next, the optical output automatic reduction circuit of the optical fiber amplifier of the present invention will be described with reference to FIG. FIG. 1 is a block diagram showing an embodiment of an optical output automatic reduction circuit of the optical fiber amplifier of the present invention. In this embodiment, the optical amplifier is an optical fiber amplifier, and Er as its optical fiber amplifier.³⁺An example of using an additive fiber and applying it to an optical booster amplifier will be described.

【0024】

In FIG. 1, an optical booster amplifier 2 is connected to the transmitting end of the optical transmitter 1, and a receiving end of the optical receiver 10 is connected to one output port of the optical booster amplifier 2. This optical booster amplifier 2 is a wavelength division multiplexing (WDM) coupler 21, Er.³⁺Additive fiber 22, this Er³⁺It is composed of an optical coupler 23 that amplifies and outputs the output of the additive fiber 22.

【0025】

The optical coupler 23 is provided with four ports, the input port is the port 23a, and the other ports 23b to 23d are the output ports. The optical output from the optical fiber amplifier is input to the port 23a of the optical coupler 23, and the optical signals are converted into electrical signals at the ports 23b and 23c of the optical coupler 23 so that each signal reaches a certain level or higher. An optical output monitor circuit 3 and a reflected light monitor circuit 4 for monitoring this are connected. Further, the output port of the optical coupler 23 is provided with an optical connector at the output end of the optical fiber amplifier.

【0026】

At the input port 23a of the optical coupler 23, the output signal of the optical fiber amplifier is a branch output at the ratio of "10" to the output port 23d and "1" to the output port 23c at the output port 23d and the output port 23c. can get. Further, at the input port 23a of the optical coupler 23, the reflected return light from the optical connector is branched at a ratio of "10" to the output port 23b with respect to the input port "1". Since the branch ratio of the optical coupler 23 is determined by the output of the optical fiber amplifier and the optical-electric conversion efficiency of the optical monitor circuit, a branch ratio other than these can be used.

【0027】

Further, one input port of the comparator 5 is connected to one output end of the optical coupler 23 via an optical output monitor circuit 3 that monitors the optical output. The optical output monitor circuit 3 includes a light receiving element 31 and a signal conversion circuit 32. In this optical output monitor circuit 3, the magnitude of the signal from the optical fiber amplifier is monitored. In this optical output monitor circuit 3, when it is confirmed that the optical output is above a certain level, the light emitted from the optical coupler 23 is received by the light receiving element 31, and then converted from current to voltage by the signal conversion amplifier circuit 32. Amplified output can be obtained.

【0028】

The other input port of the comparator 5 is connected to the other output end of the optical coupler 23 via a reflected light monitor circuit 4 that monitors the reflected light. The reflected light monitor circuit 4 includes a light receiving element 41 and a signal conversion circuit 42. In this reflected light monitor circuit 4, the magnitude of the reflected return light from the optical connector at the output end of the optical fiber amplifier is monitored. When it was confirmed that the reflected light was above a certain level, the light emitted from the optical coupler 23 was received by the light receiving element 31 and converted into an electric signal, and then converted from current to voltage by the signal conversion amplifier circuit 42. Amplified output is obtained.

【0029】

Further, the monitor output of the reflected light monitor circuit 4 is input to one input port of the comparator 5, and the monitor output of the optical output monitor circuit 3 is input to the other input port. In this comparison cormorant 5, the comparison output based on the output from the reflected light monitor circuit 4 and the output from the optical output monitor circuit 3 is output to the optical output control circuit 6.

【0030】

The optical output control circuit 6 includes a first reference voltage generating circuit 61 that generates a first reference voltage based on the comparison output of the comparator 5, a second reference voltage generating circuit 62 that generates a second reference voltage, and the like. The switch 63 that switches between the first reference voltage generation circuit 61 and the second reference voltage generation circuit 62, and the first or second reference voltage generated by the switching operation of this switch 63 are input to one input port and the other. It is composed of an amplifier 64 that supplies the output of the optical output monitor circuit 3 to the input port.

【0031】

Further, in the drive circuit 7, the excitation laser diode 8 is driven based on the control signal of the optical output control circuit 6. Therefore, in the optical booster amplifier 2, when the drive circuit 7 is driven, an amplified output having an amplification factor of, for example, 20 dBm can be obtained, so that the output voltage supplied from the optical booster amplifier 6 to the optical receiver 10 is only the gain. Since it is lowered, the light output can be automatically lowered. When the drive circuit 7 is not driven, no optical signal is transmitted from the optical transmitter 10 to the optical receiver 10 via the optical booster amplifier 2.

【0032】

Therefore, in the optical output automatic reduction circuit of the optical fiber amplifier shown in FIG. 1, the optical output can be automatically reduced, so that it is possible to prevent adverse effects on the human eye handling the optical fiber amplifier. Instead, the circuit configuration can be made compact.

【0033】

Next, the operation of the present invention will be described with reference to FIG. The signal input from the optical transmitter 1 is assumed to output +15 dBm at the output end by the optical fiber amplifier. When the optical connector, which is the output end of the optical fiber amplifier, is connected to the transmission line, the reflected return light from the output end is -14 dB (about 0.1% return light), which is open. Is explained assuming that the return light is -14 dB (about 4% return light), and the connection loss of the optical fiber 22 and the insertion loss of the optical coupler 23 are ignored for the sake of simplicity. Further, it is assumed that the optical-electric conversion efficiencies of the light receiving elements 31 and 41 in the optical monitor circuits 3 and 4 are both 1 A / W, and the outputs of the two optical monitor circuits 3 and 4 are the outputs of the optical connector circuits. The impedance gain of the two current-voltage conversion amplifiers is set to 1.27 kΩ for the optical output monitor and 4.39 kΩ for the reflected light monitor so that the magnitude relationship is reversed depending on the open state or the connected state of the optical connector.

【0034】

First, when the optical connector output is + 15dBmn, if the output end of the optical amplifier is connected to the transmission line, the optical output monitor voltage is -4V, the reflected light monitor voltage is -0.1 V, and the optical output. The reflected light monitor voltage has a larger voltage than the monitor voltage. At this time, the optical output control circuit 6 selects the first reference voltage from the output control signal of the comparator 5, and controls the drive current of the excitation laser diode 8 so that +15 dBm is output as the optical connector output.

【0035】

Next, at the moment when the optical connector is opened, the reflected return light increases and the reflected light monota voltage becomes -5.0 V, and the magnitude relationship between the optical output monitor voltage and the reflected light monitor voltage is reversed. As a result, the output control signal of the comparator 5 changes, the optical output control circuit 6 assumes that the second reference voltage is specialized, and the drive circuit 7 is set so as to lower the output level output from the optical fiber amplifier. It is driven to control the drive current of the excitation laser diode 8. Here, it is assumed that the output is constantly controlled to +5 dBm. The light output level at this time is controlled to a level that does not affect the human body, and is not limited to +5 dBm, and may be a level that does not affect the human body.

【0036】

Next, the moment the optical connector is connected to the transmission line again, the reflected return light decreases, so the reflected light monitor voltage becomes -0.01 V, the optical output monitor voltage becomes -0.4 V, and the optical output monitor voltage and reflected light monitor. The magnitude relationship of the voltage is reversed again. As a result, the optical output control circuit 6 drives the drive circuit 7 so that a constant output of +15 dBm can be obtained again as the optical connector output, and controls the drive current of the excitation laser diode 8.

【0037】

As described above, in this embodiment, the magnitude relationship between the optical output monitor voltage and the reflected light monitor voltage is always compared by the comparator 5, and the magnitude relationship is reversed to reverse the optical output of the optical output control circuit 6. The control signal changes. In this optical output control circuit 6, the optical output control signal selects and outputs either a normal level or a low output level.

【0038】

In the optical output control circuit 6 of this embodiment, since the optical fiber amplifier is controlled so that the optical output is constant, one reference voltage is used, but the present invention is not limited to this, and for example, optical transmission is used. When compensating for the mark rate, which is the ratio of the data signal "1" and the data signal "0" of the device 1, the compensation output of the mark rate becomes constant by using the voltage with the mark rate information as the reference voltage. It can also be applied to controllable optical fiber amplifiers.

【0039】

[Effect of the invention]

As described above, in the optical output automatic reduction circuit of the optical fiber amplifier according to claims 1 to 4, the optical output level is automatically reduced when the optical connector at the output end of the optical fiber amplifier is in the open state. Therefore, it is possible to avoid the risk of accidentally looking directly at the high-level laser due to work such as attaching and detaching the optical connector, and it automatically returns to the normal level by connecting to the transmission line again. Since it is not necessary to turn on / off the power of the device, operability can be improved, and a log amplifier and a reference voltage generation circuit are not required to determine the open state or the connection state of the optical connector. The circuit configuration can be simplified.

【0040】

In particular, in the invention according to claim 1, since the optical output can be automatically controlled, the operability can be improved and the circuit configuration can be simplified.

【0041】

Further, according to the invention of claim 2, the optical output can be set to a constant level by providing the bias circuit with an excitation laser diode and a drive circuit for reducing the bias current of the diode.

【0042】

Further, according to the invention of claim 3, when the disconnection of the connector is recovered, the bias current of the excitation laser diode and the optical output transmitted from the optical transmitter can be automatically restored. Maintenance work can be done smoothly. Further, according to the invention of claim 4, the light output can be easily branched.

[Simple explanation of drawings]

[Figure 1]

It is a block diagram of an Example of the optical output automatic reduction circuit of the optical fiber amplifier of this invention.

[Figure 2]

It is a block diagram which shows an example of the optical output automatic reduction circuit of the conventional optical fiber amplifier.

[Fig. 3]

It is a block diagram which shows an example of the optical output automatic reduction circuit of the conventional optical fiber amplifier.

[Explanation of symbols]

1 Optical transmitter 2 Optical booster amplifier 3 Optical output monitor circuit 4 Reflected light monitor circuit 5 Comparator 6 Optical output control circuit 7 Drive circuit 8 Excited laser diode 10 Optical receiver