JP5255494B2 - Optical amplifier - Google Patents

Description

  The present invention relates to an optical amplifying device applied to the field of optical communication and the like.

  In the conventional optical amplifying device, the optical signal power before and after amplification in the optical amplifier is detected by the light receiving diode and the optical input power and the optical output power are detected, and the pump laser diode is controlled based on these detected values, and the gain of the optical amplifier is determined. Constant control (AGC control) is performed to control the gain of the optical amplifier to a desired value.

  By the way, in Patent Document 1, an output signal from a light receiving diode is supplied to a log amplifier (logarithmic conversion circuit), and AGC control is executed based on a conversion result by the log amplifier, thereby providing a wide dynamic range (allowable input). (Technology for realizing the scope) is disclosed.

JP-A-2004-266251

  By the way, it is known that the log amplifier has frequency dependence in its gain characteristic in a low frequency region. For this reason, at a low frequency, the gain characteristics of the log amplifier are disturbed, and there is a problem that the accuracy of optical amplification cannot be increased.

  Therefore, the problem to be solved by the present invention is to provide an optical amplifying device capable of increasing the accuracy of optical amplification.

In order to solve the above-described problems, the present invention provides a light receiving element that detects an optical power of the input optical signal and a log that amplifies the output signal of the light receiving element in an optical amplifying apparatus that amplifies and outputs the input optical signal A first detecting means having an amplifier; an amplifying means for amplifying the inputted optical signal; a light receiving element for detecting the optical power of the optical signal amplified by the amplifying means; and a log for amplifying the output signal of the light receiving element. A second detection means having an amplifier; an adjustment means for adjusting the power of the optical signal input to each light receiving element of the first detection means and the second detection means to be substantially the same; Control means for controlling the gain of the amplifying means to be a predetermined target value based on the detection result by the second detecting means and the adjustment amount of the adjusting means, and the adjusting means includes the second adjusting means. Inspection An attenuator provided in front of the light receiving element of the means, a first coupler for branching the inputted optical signal and leading it to the first detecting means and the amplifying means, and a light signal outputted from the amplifying means And a second coupler that leads to the second detection means via the attenuator and outputs it to the outside, and sets the attenuation amount of the attenuator based on the branching ratio of the first and second couplers. The power of the optical signal input to each light receiving element of the first detection means and the second detection means is adjusted to be substantially the same.

Further, another aspect of the present invention, the by branching ratio of the first and second coupler by setting the attenuation amount of the attenuator, light input to the first detecting means to the light receiving elements of said second detecting means The signal power is adjusted so as to be substantially the same.

According to another aspect of the present invention, in the above invention, the adjustment unit further includes an attenuator provided in front of the light receiving element of the first detection unit, and the light receiving element of the first and second detection unit By setting the attenuation amount of the attenuator provided in the preceding stage, the power of the optical signal input to each light receiving element of the first detection means and the second detection means is adjusted to be substantially the same. Features.

  Another invention is characterized in that, in the above invention, the optical power of the optical signal input to each light receiving element of the first and second detection means is set to be approximately −20 dBm or less. To do.

  According to another aspect of the present invention, in the above invention, the amplification means can change an amplification gain of the optical signal, and the adjustment means is an optical signal input to at least one light receiving element in accordance with the amplification gain. It is characterized by adjusting the power of.

  In another aspect of the invention, the optical signal is an uncompressed serial digital video signal (SD-SDI / HD-SDI signal).

  According to the optical amplification device of the present invention, optical amplification can be performed accurately.

It is a block diagram which shows the structural example of the optical amplifier of this invention. It is a figure which shows the relationship between input light and PD monitor value. It is a graph of the measured value which shows the relationship between the bit rate of PD monitor error, and the power of input light. It is a setting example of each parameter when this embodiment is used as a booster amplifier. It is a graph of the measured value in the conditions 1-4 shown in FIG. It is a graph of the measured value in the conditions 5-8 shown in FIG. It is a setting example of each parameter when this embodiment is used as an inline amplifier. It is a graph of the measured value in the conditions 9-12 shown in FIG. It is a graph of the measured value in the conditions 13-16 shown in FIG.

Next, an embodiment of the present invention will be described.
FIG. 1 is a diagram illustrating a configuration example of an optical amplification device according to an embodiment of the present invention. As shown in this figure, the optical amplifying apparatus 1 amplifies an optical signal input from an optical transmission line 10 made of an optical fiber for transmitting an optical signal with a predetermined gain, and then amplifies it to an optical transmission line 14 also made of an optical fiber. Output.

  The optical amplifying apparatus 1 includes a front-stage coupler 11, an amplification optical fiber 12, a rear-stage coupler 13, an attenuator 15, a light receiving element 16, a log amplifier 17, an A / D (Analog to Digital) conversion circuit 18, a control circuit 19, and a D / A. A (Digital to Analog) conversion circuit 20, a drive circuit 21, a laser diode 22, an attenuator 23, a light receiving element 24, a log amplifier 25, and an A / D conversion circuit 26 are main components.

  Here, the front-stage coupler 11 is called, for example, a tap coupler, branches light input from the optical transmission line 10, guides one to the amplification optical fiber 12, and guides the other to the attenuator 15. Note that, for example, about 1 to 10% of input light is guided to the attenuator 15. The amplification optical fiber 12 is composed of, for example, an erbium-doped optical fiber (EDF), and amplifies the optical signal input from the front-stage coupler 11 with the excitation laser light supplied from the laser diode 22 and outputs the amplified optical signal. The post-stage coupler 13 branches the light output from the amplification optical fiber 12, outputs one to the optical transmission line 14, and guides the other to the attenuator 23. Note that, for example, about 1 to 10% of the input light is guided to the attenuator 23.

  The attenuator 15 attenuates the branched light from the previous-stage coupler 11 by the attenuation amount AT 1 and inputs the attenuated light to the light receiving element 16. The light receiving element 16 is configured by, for example, a photodiode, and converts the light input from the attenuator 15 into an electrical signal corresponding to the power and outputs the electrical signal. The log amplifier 17 is a circuit that calculates and outputs a logarithmic function of the signal supplied from the light receiving element 16. The A / D conversion circuit 18 converts the signal (analog signal) output from the log amplifier 17 into a digital signal and supplies it to the control circuit 19.

  On the other hand, the attenuator 23 attenuates the branched light from the post-stage coupler 13 by the attenuation amount AT 2 and inputs the attenuated light to the light receiving element 24. As in the case described above, the light receiving element 24 is configured by, for example, a photodiode and converts the light input from the attenuator 23 into an electrical signal corresponding to the power and outputs the electrical signal. The log amplifier 25 is a circuit that calculates and outputs a logarithmic function of the signal supplied from the light receiving element 24. The A / D conversion circuit 26 converts the signal (analog signal) output from the log amplifier 25 into a digital signal and supplies it to the control circuit 19.

  The control circuit 19 includes, for example, a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like, and the CPU operates the RAM according to a program stored in the ROM. For example, output from the optical amplifying apparatus 1 by executing arithmetic processing as an area and outputting control data to the D / A conversion circuit 20 based on data supplied from the A / D conversion circuits 18 and 26. AGC (Automatic Gain Control) is executed so that the optical signal to be transmitted becomes constant. Note that the control circuit 19 may be configured by, for example, a DSP (Digital Signal Processor). The D / A conversion circuit 20 converts the control data (digital signal) output from the control circuit 19 into a corresponding analog signal and supplies it to the drive circuit 21. The drive circuit 21 controls the laser diode 22 based on the control signal supplied from the D / A conversion circuit 20. The laser diode 22 oscillates excitation laser light based on the control of the drive circuit 21 and supplies the laser light to the amplification optical fiber 12.

  Next, the operation of the optical amplifying apparatus 1 configured as described above will be described. It is assumed that an optical signal having an optical power of Pin (dBm) and a bit rate of ν (bps) is input from the optical transmission line 10 to the optical amplifying apparatus 1. As the optical signal, for example, an uncompressed serial digital video signal (SD-SDI / HD-SDI signal, hereinafter referred to as “SDI signal”) can be assumed.

The input light input to the front-stage coupler 11 is branched according to the branching ratio (TP1) of the front-stage coupler 11, most of the input light is input to the amplification optical fiber 12, and the rest is input to the attenuator 15. As a specific example, for example, when the front-stage coupler 11 is a 20 dB coupler (when the branching ratio is 1/100), 1/100 of the input light is input to the attenuator 15, and the others are the amplification optical fiber 12. Is input. The attenuator 15 attenuates the branched light from the front-stage coupler 11 by an attenuation amount AT1 (dB) and inputs the attenuated light to the light receiving element 16. As a specific example, for example, when the attenuation AT1 of the attenuator 15 is 3 dB, the branched light from the preceding coupler 11 is attenuated by 3 dB and is input to the light receiving element 16 as the input light PDIN1. The light receiving element 16 converts the input light PDIN1 from the attenuator 15 into a corresponding electric signal and outputs it to the log amplifier 17. The log amplifier 17 calculates a logarithmic function of the electric signal output from the light receiving element 16 and outputs the logarithmic function to the A / D conversion circuit 18. The A / D conversion circuit 18 converts the signal (analog signal) supplied from the log amplifier 17 into a digital signal and outputs it to the control circuit 19. The control circuit 19 considers the branching ratio TP1 of the preceding-stage coupler 11 and the attenuation amount AT1 of the attenuator 15 from the digital signal supplied from the A / D conversion circuit 18, and PDM1 as a monitor value of the optical power Pin of the input light Is calculated by the following equation (1). Note that PDIN1 = Pin−TP1−AT1.
PDM1 = PDIN1 + Δ1 + TP1 + AT1 = Pin + Δ1 (1)

  Here, Δ1 is an error having bit rate dependency (usually Δ1 ≦ 0). More specifically, in the circuit shown in FIG. 2, CW (Continuous Wave) light of 1550 nm is input to the light receiving element 16 so that the actually measured input light value PDIN is equal to the PD monitor value calculated by the control circuit 19. After adjusting the parameters of the control circuit 19, modulated 1550 nm light was input, and the value obtained by subtracting the input light actual measured value PDIN from the PD monitor value was measured as Δ. FIG. 3 is a graph showing actual measurement results. In this graph, the bit rate is changed between 622 Mbps and 1 Mbps, the input light power is changed between about -37 dBm and about -4 dBm, the value of Δ is measured, and a graph is created based on the measured result. doing. From the graph of the actual measurement results, the value of Δ tends to increase as the bit rate decreases and as the input light power increases. That is, in these cases, the power of the monitored light is smaller than the actual power of the input light.

On the other hand, the light amplified by the amplification optical fiber 12 is input to the post-stage coupler 13. As in the case described above, most of the input light input to the post-stage coupler 13 is output to the optical transmission line 14 according to the branching ratio (TP2) of the post-stage coupler 13, and the rest is attenuator. 23. As a specific example, for example, when the post-stage coupler 13 is a 20 dB coupler, 1/100 of the input light is input to the attenuator 23, and the rest is output to the optical transmission line 14. The attenuator 23 attenuates the branched light from the post-stage coupler 13 by an attenuation amount AT2 (dB) and inputs the attenuated light to the light receiving element 24. As a specific example, for example, when the attenuation AT2 of the attenuator 15 is 12 dB, the branched light from the post-stage coupler 13 is attenuated by 12 dB and is input to the light receiving element 24 as the input light PDIN2. As will be described later, the branching ratios of the front-stage coupler 11 and the rear-stage coupler 13 and the attenuation amounts of the attenuators 15 and 23 are set based on the relationship with the gain of the optical amplifying apparatus 1. The light receiving element 24 converts the power of the input light PDIN2 from the attenuator 23 into a corresponding electric signal and outputs it to the log amplifier 25. The log amplifier 25 calculates a logarithmic function of the electrical signal output from the light receiving element 24 and outputs the logarithmic function to the A / D conversion circuit 26. The A / D conversion circuit 26 converts the signal supplied from the log amplifier 25 into a digital signal and outputs the digital signal to the control circuit 19. The control circuit 19 considers the branching ratio TP2 of the post-stage coupler 13 and the attenuation AT2 at the attenuator 23 from the digital signal supplied from the A / D conversion circuit 26 as a monitor value of the optical power Pout of the output light. PDM2 is calculated by the following formula (2). Note that PDIN2 = Pout−TP2−AT2.
PDM2 = PDIN2 + Δ2 + TP2 + AT2 = Pout + Δ2 (2)

Note that Δ2 is an error having bit rate dependency as in the case described above (usually Δ2 ≦ 0). The control circuit 19 calculates the gain monitor value Gm (dB) of the optical amplifying apparatus 1 by the following equation (3) based on the PDM1 and PDM2 obtained by the equations (1) and (2).
Gm = PDM2−PDM1 = (Pout−Pin) + (Δ2−Δ1) (3)

Here, in the constant gain control, control is performed so that Gm becomes equal to the target gain value Gs (dB), and therefore Gm is expressed by the following equation (4).
Gm = Gs = (Pout−Pin) + (Δ2−Δ1) (4)

  At this time, since true gain G = Pout−Pin = Gs + (Δ1−Δ2), an error of (Δ1−Δ2) is generated with respect to the target gain value Gs. Here, since Δ1 and Δ2 depend on the magnitude of the input power of the light input to the light receiving element as described above, in the present embodiment, the light input to the light receiving element 16 and the light receiving element 24. By setting the front-stage coupler 11, the rear-stage coupler 13, and the attenuators 15 and 23 so that the power is substantially the same, the occurrence of errors is reduced.

  More specifically, since PDIN2 = Pout−TP2−AT2 and Pout = Pin + Gs, PDIN2 = Pin + Gs−TP2−AT2 is obtained. Also, since PDIN1 = Pin−TP1−AT1, in order to satisfy PDIN1≈PDIN2, Pin−TP1−AT1≈Pin + Gs−TP2−AT2 must be satisfied. When this equation is simplified, Gs + TP1 + AT1 ≈TP2 + AT2 is obtained. That is, TP1, TP2, AT1, AT2 may be set according to the gain target value Gs. As a specific example, for example, if Gs = 9 (dB), TP1 = 20 (dB), TP2 = 20 (dB), AT1 = 13 (dB), AT2 = 22 (dB), 9 + 20 + 13 = 20 + 22 Therefore, the condition is satisfied.

  Next, an example in which the optical amplifying apparatus 1 of the present embodiment is applied to a booster amplifier (an amplifier that is mainly disposed on the output side of the transmitter, and an amplifier that is disposed on the input side of the receiver is referred to as a preamplifier). Will be described. As an example of the booster amplifier parameter setting, as shown in FIG. 4, the gain target value Gs is 9 (dB), the optical input range is −10 to +11 (dBm), and the total attenuation amount of TP1 and AT1. L1 (= TP1 + AT1) is 33 (dB). In such a case, as shown in Conditions 1 to 8, L2 (= TP2 + AT2) as a total value of the attenuation amounts of TP2 and AT2, and the PD monitor error when the bit rate condition was changed were measured. These are FIGS. 5 and 6. FIG. 5 shows a graph of measurement results of the actual gain when the input light power Pin is changed in the range of −10 to +11 (dBm) under the conditions 1 to 4 in FIG. As shown in this figure, for condition 2 that satisfies L2 = L1 + Gs, which is the optimum condition, the actual gain G is 9 (dB), which is the same as the target gain value Gs, regardless of the input power of light. FIG. 6 shows a graph of measurement results of the actual gain when the input light power Pin is changed in the range of −10 to +11 (dBm) under the conditions 5 to 8. As shown in this figure, for condition 6 that satisfies L2 = L1 + Gs, which is the optimum condition, the actual gain G is 9.0 (dB), which is the same as the target gain value Gs, regardless of the input power of light. . Further, even in the case of conditions 3, 4, 7, and 8 having a deviation of plus or minus 4 (dB) from the optimum value, both 155 Mbps and 40 Mbps are within the gain error range of 1 (dB). . At this time, as shown in FIGS. 5 and 6, the error tends to increase as the input increases.

  Next, actual measurement values when the optical amplifying apparatus 1 according to the present embodiment is applied as an in-line amplifier (mainly an amplifier arranged in the middle of a transmission line) will be described. As an example of setting parameters for the in-line amplifier, as shown in FIG. 7, the gain target value Gs is 30 (dB), the optical input range is −31 to −11 (dBm), and L1 (= TP1 + AT1) is 13 ( dB). In such a case, as shown in Conditions 9 to 16, FIGS. 8 and 9 show the PD monitor error measured when the bit rate is changed with L2 (= TP2 + AT2). FIG. 8 shows a graph of the measurement result of the actual gain when the input light power Pin is changed in the range of −31 to −11 (dBm) under the conditions 9 to 12. As shown in this figure, for condition 10 that satisfies L2 = L1 + Gs, which is the optimum condition, the actual gain G is 30 (dB), which is the same as the target gain value Gs, regardless of the input power of light, and remains constant. Yes. FIG. 9 shows a graph of measurement results of actual gain when the input light power Pin is changed in the range of −31 to −11 (dBm) under the conditions 13 to 16. As shown in this figure, for the condition 14 that satisfies L2 = L1 + Gs, which is the optimum condition, the actual gain G is 30.0 (dB), which is the same as the target gain value Gs, regardless of the input power of light, and is constant. I keep it. Even in the case of the conditions 11, 12, 15, and 16 having a deviation of plus or minus 4 (dB) from the optimum value, both 155 Mbps and 40 Mbps are within the gain error range of 1 (dB). . Note that even if it is 155 Mbps, as shown in the condition 9, when it deviates from the optimum value (−20 dB in this example), the gain error may increase.

  Thus, in the optical amplifying apparatus 1 of the present embodiment, the front-stage coupler 11, the rear-stage coupler 13, the attenuators 15 and 23, and the gain target value are set so that Gs + TP1 + AT1≈TP2 + AT2 is established. Since the power of the light input to the elements 16 and 24 can be made substantially the same, the value of (Δ2−Δ1) in the equation (4) can be brought close to “0”. For this reason, for example, even in the case of a check field signal (pathological signal) including many low frequency components in which “0” or “1” is continued, such as an SDI signal, it does not depend on the power of the input light. , The gain can be kept constant. In the case of an SDI pathological signal, it is known that the minimum signal speed is about several tens of Mbps. In other words, in a pathological signal of HD (1.485 Gbps) and SD (270 Mbps), there is a time that a bit pattern of “1” (or “0”) × 19 + “0” (or “1”) × 1 continues. In this high (low) mark rate region, the bit rate temporarily becomes 1/20, and a signal equivalent to 74.25 / 13.5 Mbps appears in HD / SD. As shown in FIG. 3, at a signal speed of several tens of Mbps (for example, a signal of 40 Mbps), the error does not increase by setting the input to the light receiving element (PD input) to be −20 (dBm) or less. Therefore, for example, if various parameters are set such that the optical power input to the light receiving elements 16 and 24 is −20 (dBm) or less, the error in gain can be further reduced.

In addition, in said form example, it is an example, Comprising: Various deformation | transformation embodiments exist besides this. For example, in the above embodiment, the two attenuators 15 and 23 are used, but the attenuator 15 may be excluded and only the attenuator 23 may be used. In that case, various parameters may be set so that Gs + TP1≈TP2 + AT2. Further, when the branching ratios of the front-stage coupler 11 and the rear-stage coupler 13 can be arbitrarily selected (set), the attenuators 15 and 23 are not provided and the branch ratios of the front-stage coupler 11 and the rear-stage coupler 13 are adjusted. Also good. In that case, various parameters may be set so that Gs + TP1≈TP2. Further, the attenuator includes all optical components that can be misaligned fusion parts, couplers, and other loss media. For example, a 17 dB coupler as an attenuator may be connected to the tip of a 13 dB tap coupler to reduce the overall loss to 30 dB. In this embodiment, “substantially equal” means to include a certain amount of deviation. Note that the allowable deviation X can be roughly determined from FIG. 3 by the allowable gain error ΔG _MAX , the maximum PD input P _MAX to be used, and the minimum bit rate ν _MIN of the input signal. For example, when ΔG _MAX = ± 1 dB, P _MAX = −12 dB, and ν _MIN = 100 Mbps, the slope at PDIN = −12 dBm is 0.2 dB / dB from the curve of 100 Mbps in FIG. 3, and therefore ΔG _MAX = To achieve ± 1 dB, X = ± 1 dB / (0.2 dB / dB) = ± 5 dB. As P _MAX is larger and ν _MIN is smaller, it becomes more severe. For example, when ΔG _MAX = ± 1 dB, P _MAX = −6 dB, and v _MIN = 40 Mbps, from the curve of 40 Mbps in FIG. Since the inclination is 1 dB / dB, in order to set ΔG _MAX = ± 1 dB, X is about ± 1 dB.

  In the above embodiment, only the branching ratio of the front-stage coupler 11 and the rear-stage coupler 13 is considered, but the insertion loss may be considered together with the branching ratio. In that case, for example, an insertion loss may be included for TP1 and TP2.

  In the above embodiment, the gain of the optical amplifying apparatus 1 is fixed, but the gain may be changed. In such a case, for example, the attenuator 23 (or attenuator 15) is a variable optical attenuator (VOA), and the control circuit 19 controls the attenuator 23 (or attenuator 15 according to the value of the gain target value Gs). ) Is adjusted so that the conditional expression Gs + TP1 + AT1≈TP2 + AT2 is satisfied. In this case, it goes without saying that the attenuator which is not the variable optical attenuator of the attenuator 23 or the attenuator 15 may be excluded.

DESCRIPTION OF SYMBOLS 1 Optical amplifying device 10, 14 Optical transmission line 11 Pre-stage coupler (1st coupler)
12 Amplifying optical fiber (amplifying means)
13 Second-stage coupler (second coupler)
15, 23 Attenuator (Adjustment means)
16 Light receiving element (part of the first detecting means)
17 Log amplifier (part of the first detection means)
18, 26 A / D conversion circuit 19 Control circuit (control means)
20 D / A conversion circuit 21 Drive circuit 22 Laser diode 24 Light receiving element (part of second detection means)
25 Log amplifier (part of the second detection means)

Claims (6)

In an optical amplifying apparatus that amplifies and outputs an input optical signal,
A first detector having a light receiving element for detecting the optical power of the input optical signal and a log amplifier for amplifying an output signal of the light receiving element;
Amplifying means for amplifying the input optical signal;
A second detection means having a light receiving element for detecting the optical power of the optical signal amplified by the amplification means, and a log amplifier for amplifying the output signal of the light receiving element;
Adjusting means for adjusting the power of optical signals input to the respective light receiving elements of the first detecting means and the second detecting means to be substantially the same;
Control means for controlling the gain of the amplifying means to be a predetermined target value based on the detection results by the first and second detecting means and the adjustment amount of the adjusting means;
Have
The adjustment means includes an attenuator provided in front of the light receiving element of the second detection means, a first coupler that branches the input optical signal and guides the light to the first detection means and the amplification means, and the amplification And a second coupler for branching the optical signal output from the means and guiding it to the second detection means via the attenuator and outputting it to the outside, based on the branching ratio of the first and second couplers. An optical amplifying apparatus comprising: adjusting an attenuation amount of an attenuator so that powers of optical signals input to the light receiving elements of the first detection unit and the second detection unit are substantially the same. .   The adjusting means sets the branching ratio of the first and second couplers and the attenuation amount of the attenuator to thereby adjust the optical signals input to the light receiving elements of the first detecting means and the second detecting means. 2. The optical amplifying apparatus according to claim 1, wherein the power is adjusted to be substantially the same. The adjusting means further includes an attenuator provided at the front stage of the light receiving element of the first detecting means, and the attenuation amount of the attenuator provided at the front stage of the light receiving element of the first and second detecting means , respectively. 3. The optical amplification according to claim 1, wherein the power is adjusted so that the powers of the optical signals inputted to the respective light receiving elements of the first detection means and the second detection means are substantially the same. apparatus.   4. The light according to claim 1, wherein the optical power of the optical signal input to each light receiving element of the first and second detection means is set to be approximately −20 dBm or less. Amplification equipment.   The amplification means can change an amplification gain of the optical signal, and the adjustment means adjusts the power of the optical signal input to at least one of the light receiving elements according to the amplification gain. Item 5. The optical amplification device according to any one of Items 1 to 4.   6. The optical amplifying apparatus according to claim 1, wherein the optical signal is an uncompressed serial digital video signal (SD-SDI / HD-SDI signal).

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