JP4137938B2 - Optical power monitor and optical amplifier having the optical power monitor - Google Patents

Description

  The present invention relates to an optical amplifier and an optical power monitor applicable to the optical amplifier.

  In recent years, an erbium-doped fiber amplifier (EDFA) and other optical amplifiers applicable to an optical communication system or an optical network system have been put into practical use. The optical signal supplied to the optical amplifier or output from the optical amplifier has a signal spectrum superimposed on the noise spectrum.

  For example, when a plurality of repeaters each having an optical amplifier are provided in the middle of an optical fiber transmission line, the noise spectrum generated by each optical amplifier can be accumulated to accurately monitor the optical power related to the signal spectrum. There is a need to deal with this because it will not be possible.

  Conventionally, an optical amplifier including an optical amplification medium and means for pumping the optical amplification medium so that the optical amplification medium has a gain band is known.

  For example, in an optical pumping type optical amplifier having a doped fiber doped with a rare earth element as an optical amplification medium, pump light having an appropriately set wavelength is supplied to the doped fiber. When an optical signal is input to the doped fiber that is pumped by the pump light, the optical signal is amplified in the doped fiber according to the principle of stimulated emission.

  In a semiconductor laser type optical amplifier, a bias current is supplied to an optical amplifying medium provided as a semiconductor chip, thereby pumping the optical amplifying medium.

  In practical optical amplifiers, optical power is monitored for various purposes. For example, when the optical signal input to the optical amplifier is interrupted, the power of the optical signal supplied to the optical amplifying medium is monitored in order to stop the pumping of the optical amplifying medium.

  In addition, the power of the optical signal output from the optical amplification medium is monitored in order to perform control for keeping the output power of the optical amplifier constant.

  In order to monitor the power of the optical signal, for example, the optical signal is supplied to a photodiode. When an optical signal is supplied to a reverse-biased photodiode, a photocurrent corresponding to the power of the optical signal is generated in the photodiode, thereby monitoring the power of the optical signal.

  When monitoring the power of an optical signal output from an optical amplifying medium, the optical signal has a signal spectrum superimposed on a noise spectrum generated in the optical amplifying medium. The power of the optical signal related to the signal spectrum cannot be accurately monitored only by the conversion.

  A similar problem occurs when noise spectrum is accumulated due to the use of a plurality of cascaded optical amplifiers.

  Therefore, an object of the present invention is to provide an optical power monitor that can accurately monitor the power of an optical signal related to a signal spectrum without being affected by a noise spectrum.

  Another object of the present invention is to provide an optical amplifier having such an optical power monitor.

  Other objects of the present invention will become clear from the following description.

According to one aspect of the present invention, an optical amplifier for an optical signal having a signal spectrum superimposed on a noise spectrum, the signal spectrum being provided by a main signal, an optical amplification medium provided on the main optical path; A first means for pumping the optical amplifying medium so that the optical amplifying medium has a gain band including the wavelength of the optical signal; and the optical signal operatively connected to the main optical path from the main optical path. A second means for extracting and an optical power monitor for the extracted optical signal , wherein the optical power monitor converts the optical signal extracted by the second means to the first optical signal; A first optical coupler that branches into a second optical signal; and a spontaneous emission included in the first optical signal, the first optical coupler having a first passband including a wavelength of the optical signal given by the main signal as a passband. Given by light and the main signal A first optical bandpass filter for extracting a third optical signal including the optical signal to be transmitted; and a second optical bandpass filter including a wavelength of the optical signal given by the main signal as a passband, and being narrower than the first passband A second optical bandpass filter having a passband and extracting a fourth optical signal including a spontaneous emission light included in the second optical signal and an optical signal given by the main signal; A first photodetector that outputs a first electrical signal indicating the optical power of the optical signal; a second photodetector that outputs a second electrical signal indicating the optical power of the fourth optical signal; Operatively connected to a second photodetector, performing a predetermined operation based on the first and second electrical signals and the bandwidth of the first and second passbands, and provided by the main signal , Including spontaneous emission An optical amplifier and an operational amplifier for outputting an error signal indicating the optical power of no optical signal is provided.

  According to an aspect of the present invention, the power of the optical signal related to the signal spectrum can be accurately monitored without being affected by the noise spectrum, and various controls (for example, control of pump light) in the optical amplifier can be performed based on the monitoring. It can be performed.

  Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. Throughout the drawings, substantially the same parts are denoted by the same reference numerals.

  Referring to FIG. 1, a first basic configuration of an optical power monitor according to the present invention is shown. An optical signal OS having a signal spectrum SS1 superimposed on the noise spectrum NS1 is supplied to the optical coupler 2. The noise spectrum NS1 is, for example, due to ASE (amplified spontaneous emission light) generated in the optical amplification medium, and the signal spectrum SS1 is given by, for example, modulation by the main signal. The center wavelength of the signal spectrum SS1 is λ0.

  The optical coupler 2 branches the supplied optical signal OS into a first beam B1 and a second beam B2. The branching ratio in the optical coupler 2 is 1: 1 here, but the present invention is not limited to this.

  The first beam B1 passes through the first optical bandpass filter 4 and becomes a beam B3. The second beam B2 passes through the second optical bandpass filter 6 and becomes a beam B4.

  Filters 4 and 6 have passbands PB1 and PB2 including wavelength λ0, respectively. The pass band PB1 is wider than the pass band PB2.

  The beam B3 has a signal spectrum SS2 superimposed on the noise spectrum NS2. The noise spectrum NS2 is narrower than the noise spectrum NS1 according to the pass band PB1 of the filter 4.

  The beam B4 has a signal spectrum SS3 superimposed on the noise spectrum NS3. The noise spectrum NS3 is narrower than the noise spectrum NS2 because the passband PB2 of the filter 6 is narrower than the passband PB1 of the filter 4.

  The beam B3 is converted into a first electric signal S1 by a first photodetector (PD) 8. The signal S1 has a level (for example, a voltage level or a current level) corresponding to the average power of the beam B3.

  The beam B4 is converted into a second electrical signal S2 by the second photodetector 10. Signal S2 has a level (eg, voltage level or current level) corresponding to the average power of beam B4.

  Then, the arithmetic unit 12 performs a predetermined calculation based on the signals S1 and S2, thereby obtaining the power of the optical signal OS related to the signal spectrum SS1. A specific example of the calculation will be described later.

  The operation principle of the optical power monitor of FIG. 1 will be described with reference to (A), (B), and (C) of FIG.

FIG. 2A shows the spectrum of the optical signal OS supplied to the optical coupler 2. Now, power and 2P _sig of the signal spectrum SS1, the power of the noise spectrum NS1 is to 2P _ASE, by signal spectrum SS1 is sufficiently narrower than the noise spectrum NS1, the input power P _in of the optical signal OS is the following formula Given.

P _in = 2P _sig + 2P _ASE (1)
Referring to FIGS. 2B and 2C, the spectra of beams B3 and B4 are shown, respectively. Assuming that the transmittance of the filters 4 and 6 at the wavelength λ 0 is 100%, since the branching ratio of the optical coupler 2 is 1: 1, the powers of the signal spectra SS2 and SS3 are respectively P _sig . The power of the noise spectrum NS2 is expressed by P _ASE / K ₁ using a constant K ₁ (1 <K ₁ ) determined by the pass band PB1 of the filter 4, and the power of the noise spectrum NS3 is It is expressed by P _ASE / K ₂ using a constant K ₂ (K ₁ <K ₂ ) determined by the pass band PB2.

The voltage level V ₁ of the electrical signal S1 photodetector 8 outputs is proportional to the power of the beam B3, the voltage level V ₂ of the electrical signal S2 photodetector 10 outputs to the proportional to the power of the beam B4, the voltage level V ₁ and Each V ₂ is given by the following equation.

V ₁ ∝ P _sig + P _ASE / K ₁ (2)
V ₂ ∝ P _sig + P _ASE / K ₂ (3)
(2) to ₁ times K a (3) is _doubled K a and determine these differences is obtained (4).

K ₁ V ₁ −K ₂ V ₂ ∝ (K ₁ −K ₂ ) P _sig (4)
Thus, by performing a linear operation based on the equations (2) and (3), a value proportional to the power P _sig of the optical signal related to the signal spectrum SS1 can be obtained as shown in the equation (4). .

To perform such a linear operation, the arithmetic unit 1 12 includes an amplifier 14 for multiplying the constants K ₁ into an electric signal S1 photodetector 8 has output, constant electrical signal S2 photodetector 10 is output K ₂ , And a subtracter (comparator) 18 for obtaining a difference between the output signals of the amplifiers 14 and 16.

  Thereby, according to the principle mentioned above, the power of the optical signal OS related to the signal spectrum SS1 can be accurately monitored without being influenced by the noise spectrum NS1.

It is also possible to monitor the power of the noise spectrum NS1 without being affected by the signal spectrum SS1. For example, since the following equation is obtained by obtaining the difference between the equations (2) and (3), a value proportional to the power P _{ASE of the} noise spectrum can be obtained based on the following equation.

V ₁ −V ₂ ∝ (1 / K ₁ −1 / K ₂ ) P _ASE (5)
Referring to FIG. 3, the embodiment of the optical power monitor of FIG. 1 is shown. The optical signal OS is supplied from the port 20 to the optical coupler 2. The optical coupler 2 outputs beams B1 and B2, and the beams B1 and B2 pass through the optical bandpass filters 4 and 6, respectively, to become beams B3 and B4.

  Beams B3 and B4 are incident on photodiodes 22 and 24, respectively. The cathode of the photodiode 22 is connected to a positive power supply line, and the anode is grounded via a resistor R1, whereby a reverse bias is applied to the photodiode 22.

  When the beam B3 enters the photodiode 22, the potential of the anode of the photodiode 22 changes according to the power of the beam B3, and this change can be extracted as a voltage signal.

  The cathode of the photodiode 24 is connected to the + power supply line, and the anode is grounded via the resistor R2, whereby a reverse bias is applied to the diode 24. When the beam B4 is incident on the photodiode 24, the anode potential of the photodiode 24 changes according to the power of the beam B4. Therefore, this change can be extracted as a voltage signal.

  The anode of the photodiode 22 is connected to the + input port of the operational amplifier 26 via a resistor R3. The operational amplifier 26 is used as a voltage follower.

  The negative input port of the operational amplifier 26 is grounded, and a resistor R4 is connected between the positive input port and the output port.

  The output port of the operational amplifier 26 is connected to the + input port of the operational amplifier 28 via the resistor R5. The operational amplifier 28 is for multiplying the output level of the operational amplifier 26 by a constant.

  The negative input port of the operational amplifier 28 is grounded, and the positive input port is connected to the output port via the variable resistor VR1. The gain of the operational amplifier 28 can be adjusted by adjusting the value of the variable resistor VR1.

  The output port of the operational amplifier 28 is connected to the + input port of the operational amplifier 30 via a resistor R6. The operational amplifier 30 is used as a subtracter (comparator) for obtaining an error signal.

  For the photodiode 24, operational amplifiers 32 and 34 corresponding to the operational amplifiers 26 and 28, respectively, are provided. Further, resistors R7, R8, R9 and R10 are provided corresponding to the resistors R3, R4, R5 and R6, respectively, and a variable resistor VR2 is provided corresponding to the variable resistor VR1.

  The resistor R10 is for connecting the output port of the operational amplifier 34 and the negative input port of the operational amplifier 30. The + input port and output port of the operational amplifier 30 are connected by a resistor R11. The output signal of the operational amplifier 30 is output through the port 36.

  Therefore, the ports 20 and 36 are an input port and an output port of this optical power monitor, respectively.

  According to this embodiment, the optical power monitor of FIG. 1 can be obtained using a simple analog circuit. Therefore, the power of the optical signal OS at the input port 20 is accurately monitored, and the monitoring data is output to the output port 36. Can be output from. Although not described, the arithmetic unit 12 in FIG. 1 may be configured by a digital circuit.

  Referring to FIGS. 4A and 4B, examples of characteristics of the optical bandpass filters 4 and 6 are shown, respectively. In each, the vertical axis represents attenuation (dB) and the horizontal axis represents wavelength (nm).

  If a wavelength range in which attenuation is smaller than 20 dB is defined as a pass band, in the example of FIG. 4A, the pass band of the filter 4 is about 25 nm, and in the example of FIG. The passband is about 4 nm.

  When the filter 4 has a relatively wide pass band as shown in FIG. 4A, both the noise spectrum and the signal spectrum are reflected in the output level of the operational amplifier 28 in FIG. Therefore, by connecting the output port of the operational amplifier 28 to the port 38 separately from the port 36 as indicated by a broken line, the optical power reflecting both the noise spectrum and the signal spectrum can be monitored.

  Referring to FIG. 5, there is shown a second basic configuration of the optical power monitor according to the present invention. An optical signal OS having a signal spectrum SS superimposed on the noise spectrum NS is supplied to the photodetector 40.

  The photodetector 40 outputs an electrical signal S11 having a level (for example, a voltage level or a current level) that changes in accordance with the instantaneous power of the optical signal OS.

  The electric signal S11 is supplied to the low-pass filter 42 and the operational amplifier 44. The filter 42 passes the DC component of the supplied signal S11 as the output signal S12.

  The operational amplifier 44 outputs an error signal ES corresponding to the difference between the supplied signals S11 and S12.

  Referring to FIGS. 6A to 6D, waveforms of the optical signal OS, the signals S11 and S12, and the error signal ES are shown, respectively.

  The signal spectrum SS of the optical signal OS is given by the main signal. Therefore, in the optical signal OS and the electric signal S11, a waveform in which the main signal component is superimposed on the DC noise component is obtained. Then, when the signal S11 passes through the low-pass filter 42, the main signal component is blocked, and the signal S12 has a DC waveform as shown in FIG. 6C.

  The error signal ES given as the difference between the signals S11 and S12 has a waveform corresponding to the main signal component.

  Therefore, when the operation speed of the operational amplifier 44 does not follow the modulation speed of the main signal, the power or level of the error signal ES directly represents the power of the signal spectrum SS.

  When the operational amplifier 44 can operate at high speed, the main signal component appears in the error signal ES as shown in FIG. 6D, and thus the power of the optical signal OS related to the signal spectrum SS is calculated based on the error signal ES. It is preferable to provide an arithmetic unit 46 that performs this.

  The arithmetic unit 46 may include a peak detector 48 that acts on the error signal ES, for example.

  As described above, according to the second basic configuration of the optical power monitor of the present invention, the noise component is electrically canceled using the low-pass filter 42 and the operational amplifier 44, so that it is affected by the noise spectrum. Therefore, the power of the optical signal related to the signal spectrum can be accurately monitored.

  Referring to FIG. 7, the embodiment of the optical power monitor of FIG. 5 is shown. The optical signal OS is supplied from the input port 50 to the photodiode 54 through the optical bandpass filter 52. The filter 52 is for determining the noise spectrum NS, and has a relatively wide pass band, for example, as shown in FIG.

  The cathode of the photodiode 54 is connected to a positive power supply line, and the anode is grounded via a resistor R12. The photodiode 54 has an operation characteristic that can sufficiently follow the modulation speed of the main signal.

  The anode of the photodiode 54 is connected to the + input port of the operational amplifier 56 through the resistor R13. The operational amplifier 56 is used as a voltage follower having high speed characteristics.

  The negative input port of the operational amplifier 56 is grounded, and the positive input port is connected to the output port via a resistor R14.

  The output port of the operational amplifier 56 is connected to the input port of the low-pass filter 58 and the + input port of the operational amplifier 60. The operational amplifier 60 corresponds to the operational amplifier 44 of FIG.

  The output port of the band pass filter 58 is connected to the negative input port of the operational amplifier 60 through a resistor R15. The negative input port and the output port of the operational amplifier 60 are connected by a resistor R16.

  Here, the operational amplifier 60 has an operation characteristic that cannot follow the modulation speed of the main signal. Accordingly, the power of the signal spectrum SS is reflected in the output signal of the operational amplifier 60, so that the output signal can be taken out by the output port 62.

  As described above, according to this embodiment, the power of the optical signal related to the signal spectrum can be accurately monitored without being affected by the noise spectrum. Since the power of the noise spectrum NS is reflected in the output signal of the low-pass filter 58, by connecting the output port of the filter 58 to the port 64 as indicated by the broken line, the light is transmitted through the port 64. The noise power of the signal OS can be monitored.

  Referring to FIG. 8, the basic configuration of an optical amplifier according to the present invention is shown. A main optical path 70 is set between the input port 66 and the output port 68. An optical amplifying medium 72 is provided on the main optical path 70.

  The optical signal supplied to the input port 66 is amplified by the optical amplification medium 72, and the amplified optical signal is output from the output port 68. The optical amplifying medium 72 is pumped by the pumping unit 74 so as to have a gain band including the wavelength of the optical signal.

  When the optical amplifying medium 72 is a doped fiber such as EDF (erbium doped fiber) or a nonlinear optical medium, the pumping unit 74 includes means for supplying pump light to the optical amplifying medium 72. When the optical amplifying medium 72 is provided by a semiconductor chip, the pumping unit 74 includes means for injecting a bias current into the semiconductor chip.

  An extraction unit 76 is operatively connected to the main optical path 70 in order to extract the optical signal whose optical power is to be monitored from the main optical path 70.

  In this application, one element and another element are operatively connected, including the case where these elements are directly connected, and further, the passing of electrical or optical signals between these elements This includes cases where these elements are provided with as much relevance as possible.

  For the extracted optical signal, an optical power monitor 78 according to the present invention is operatively connected to the extraction unit 76. The optical power monitor 78 generally has the first basic configuration shown in FIG. 1 or the second basic configuration shown in FIG.

  As described above, the optical power monitor 78 can accurately monitor the power of the optical signal related to the signal spectrum without being affected by the noise spectrum, and accordingly, various controls in the optical amplifier are favorably performed based on the monitoring result. be able to.

  For example, when the optical signal supplied to the input port 66 is extracted, it is possible to accurately control the pumping shutdown of the optical amplifying medium 72 based on the result of monitoring the power of the extracted optical signal. .

  Further, when the optical signal amplified in the optical amplification medium 72 is extracted, APC (automatic power control) can be accurately performed based on the monitoring result of the power of the extracted optical signal.

  Referring to FIG. 9, a first embodiment of an optical amplifier according to the present invention is shown. Corresponding to the optical amplifying medium 72 of FIG. 8, an erbium-doped fiber (EDF) 80 containing Er (erbium) or a compound thereof as a dopant is used. The EDF 80 has a first end 80A located on the input port 66 side and a second end 80B located on the output port 62 side.

  The pumping unit 74 in FIG. 8 includes a laser diode (LD) 82, a drive circuit 84 that supplies a bias current to the LD 82 so that the LD 82 outputs pump light having a predetermined wavelength, and pump light output from the LD 82. Is provided to the EDF 80 from at least one of the first end 80A and the second end 80B of the EDF 80.

  Specifically, the optical circuit includes a wavelength division multiplexing (WDM) coupler 86 connected to the first end 80A of the EDF 80 and the LD 82.

  In this embodiment, the extraction unit 76 of FIG. 8 includes an optical coupler 88 provided between the input port 66 and the WDM coupler 86 in order to monitor the input optical signal power at the input port 66. The optical signal extracted by the optical coupler 88 is supplied to the port 20 (50) of the optical power monitor 78 according to the present invention.

  Between the input port 66 and the optical coupler 88, there is a sufficiently small loss in the forward direction (the direction from the input port 66 to the output port 68), and the reverse direction (the direction from the output port 68 to the input port 66). Is provided with an optical isolator 90 having a sufficiently large loss. An optical isolator 92 having a sufficiently small loss in the forward direction and a sufficiently large loss in the reverse direction is provided between the second end 80B of the EDF 80 and the output port 68.

  The optical isolators 90 and 92 provided on both sides of the EDF 80 prevent the operation of the optical amplifier from becoming unstable due to the construction of the optical resonator structure including the EDF 80 when the optical amplifier is put into practical use. Because.

  The output signal of the optical power monitor 78 reflecting the input optical signal power at the input port 66 is supplied from the port 36 (62) to the control circuit 94. The control circuit 94 compares the input optical signal power at the input port 66 with a predetermined value, and blocks the pump light output by the LD 82 when the input optical signal power is smaller than the predetermined value.

  Specifically, when a control signal from the control circuit 94 is supplied to the drive circuit 84 and the pump light blocking condition is satisfied, the bias current supplied to the LD 82 by the drive circuit 84 is reduced or cut off. .

  When the wavelength of the optical signal supplied to the input port 66 is in the 1.55 μm band, the wavelength of the pump light output from the LD 82 is set to, for example, the 0.98 μm band or the 1.48 μm band.

  The optical signal supplied to the input port 66 passes through the optical isolator 90, the optical coupler 88, and the WDM coupler 86 in this order, and is supplied to the EDF 80 from its first end 80A. When an optical signal is supplied to the EDF 80 that is pumped by the pump light from the LD 82, the optical signal is amplified and output from the second end of the EDF 80. The amplified optical signal passes through the optical isolator 92 and the output port 68 in this order, and is output from the optical amplifier.

  In this embodiment, since the optical power monitor 78 and the control circuit 94 according to the present invention are used, the power related to the signal spectrum can be accurately monitored without being affected by the noise spectrum of the input optical signal, and the presence or absence of the signal spectrum. It is possible to accurately perform the shutdown control of the pump light. For example, in an optical network to which a plurality of optical amplifiers are applied, a malfunction of control due to noise light such as ASE can be prevented.

  Referring to FIG. 10, a second embodiment of the optical amplifier according to the present invention is shown. This embodiment is characterized in that the optical power monitor 78 is monitoring the output optical signal power at the output port 68. For this purpose, an extraction optical coupler 88 ′ is provided between the second end 80 </ b> B of the EDF 80 and the optical isolator 92.

  A part of the optical signal amplified in the EDF 80 is extracted by the optical coupler 88 ′ and supplied to the port 20 (50) of the optical power monitor 78. The output signal of the optical power monitor 78 reflecting the power related to the signal spectrum of the extracted optical signal is supplied to the control circuit 96 from the port 36 (62).

  Here, the control circuit 96 controls the bias current that the drive circuit 84 supplies to the LD 82 so that the level of the output signal of the optical power monitor 78 becomes constant.

  By providing such a feedback loop, APC (automatic power control) in which the output power of the optical amplifier is kept constant becomes possible. In this APC, the power relating to the signal spectrum is kept constant based on the fact that the optical power monitor 78 cancels the noise spectrum of the amplified optical signal.

  Thus, according to the present embodiment, APC that is not affected by the noise spectrum becomes possible.

  Referring to FIG. 11, a third embodiment of the optical amplifier according to the present invention is shown. Here, an optical circulator 98 is used in place of the optical isolator 90 of FIG. The optical circulator 98 passes light in the forward direction from the first port 98A to the second port 98B, but does not pass light in the reverse direction from the second port 98B to the first port 98A. The light supplied to the port 98B is output from the third port 98C.

  Therefore, the optical signal supplied to the input port 66 is supplied to the EDF 80 through the optical circulator 98, the optical coupler 88, and the WDM coupler 86 in this order.

  When an optical signal is amplified in the EDF 80, a forward ASE from the first end 80A to the second end 80B and a backward ASE from the second end 80B to the first end 80A are generated in the EDF 80. It is known that the gain in the EDF 80 is reflected in the forward ASE and the backward ASE.

  The backward ASE output from the first end 80A of the EDF 80 is supplied to the second port 98B of the optical circulator 98 through the WDM coupler 86 and the optical coupler 88 in this order. The backward ASE is supplied to the optical bandpass filter 100 for determining the noise band through the third port 98C.

  The backward ASE that has passed through the filter 100 is converted into an electrical signal corresponding to the power by the photodetector 102, and this electrical signal is supplied to the ASE power monitor 104.

  The ASE power monitor 104 includes operational amplifiers 106 and 108. The output signal of the photodetector 102 is input to the + input port of the operational amplifier 106 via the resistors R17 and R18. The connection point of the resistors R17 and R18 is grounded by the resistor R19.

  The negative input port of the operational amplifier 106 is grounded, and the positive input port is connected to its output port via a resistor R20.

  The output port of the operational amplifier 106 is connected to the + input port of the operational amplifier 108 via a resistor R21.

  The negative input port of the operational amplifier 108 is grounded, and the positive input port is connected to its output port via a variable resistor VR3.

  According to such an ASE power monitor 104, the power of the backward ASE generated in the EDF 80 can be monitored by the output signal of the operational amplifier 108.

  In this embodiment, the output signals of the optical power monitor 78 and the ASE power monitor 104 are supplied to the control circuit 110. Based on the output signal of the optical power monitor 78, the control circuit 110 performs shutdown control of pump light similar to that in the first embodiment of FIG. In addition, the control circuit 110 controls the bias current that the drive circuit 84 supplies to the LD 82 so that the output signal of the ASE power monitor 104 is kept constant only when the pump light is not shut down. .

  As described above, since the gain in the EDF 80 is reflected in the backward ASE, the optical signal at the input port 66 has a signal spectrum by performing feedback control based on the output signal of the ASE power monitor 104 in this way. In addition, the gain of the optical amplifier can be controlled to be constant.

  Referring to FIG. 12, a fourth embodiment of the optical amplifier according to the present invention is shown. In the first embodiment of FIG. 9, the optical amplifying medium 72 (see FIG. 8) has a one-stage configuration, whereas in the fourth embodiment of FIG. 12, the optical amplifying medium 72 has a two-stage structure. ing. Here, the EDF 80 (# 1), LD 82 (# 1), drive circuit 84 (# 1), and WDM coupler 86 (# 1) correspond to the EDF 80, LD 82, drive circuit 84, and WDM coupler 86 in FIG. It is used.

  In addition, an EDF 80 (# 2) is provided between the optical isolator 90 and the optical coupler 88. In order to pump the EDF 80 (# 2), an LD 82 (# 2) and a drive circuit 84 (# 2) for applying a bias current to the LD 82 (# 2) so that the LD 82 (# 2) outputs pump light; A WDM coupler 86 (# 2) for supplying pump light to the EDF 80 (# 2) is used. The WDM coupler (# 2) is provided between the optical isolator 90 and the EDF 80 (# 2).

  The optical signal supplied to the input port 66 passes through the optical isolator 90 and the WDM coupler 86 (# 2) in this order, and is supplied to the first stage EDF 80 (# 2), where it is amplified.

  The optical signal amplified in the EDF 80 (# 2) passes through the optical coupler 88 and the WDM coupler 86 (# 1) in this order and is supplied to the second-stage EDF 80 (# 1), where it is further amplified. The optical signal amplified in the EDF 80 (# 1) is output from the optical amplifier through the optical isolator 92 and the output port 68 in this order.

  In this embodiment, the optical power monitor 78 performs power monitoring on the signal spectrum of the optical signal amplified in the EDF 80 (# 2). Based on the monitoring result, the control circuit 112 performs shutdown control of the pump light on the drive circuit 84 (# 1 and # 2).

  In this embodiment, since the power is monitored after the optical signal is amplified by the first stage EDF 80 (# 2), an optical amplifier having a good noise factor can be provided. That is, once the optical signal is once amplified with sufficient gain by the first stage EDF 80 (# 2), even if branching for optical power monitoring (by the optical coupler 88) is performed thereafter, the noise factor is increased. Is difficult to deteriorate.

  An APC loop for the second stage EDF 80 (# 1) may be provided. In this case, the control target of the APC loop is a bias current supplied from the drive circuit 84 (# 1) to the LD 82 (# 1).

  Referring to FIG. 13, a fifth embodiment of the optical amplifier according to the present invention is shown. Here, in addition to the fourth embodiment of FIG. 12, the optical circulator 98, the optical bandpass filter 100, the photodetector 102, and the ASE power monitor 104 in the third embodiment of FIG. 11 are added and improved accordingly. The control circuit 114 is used.

  The control circuit 114 performs shutdown control on the drive circuits 84 (# 1 and # 2) based on the output signal of the optical power monitor 78, and only when the pump light is not shut down, the ASE power monitor 104. The bias current supplied from the drive circuit 84 (# 1) to the LD 82 (# 1) is controlled so that the output signal of the current is kept constant. This enables accurate gain control based on the signal spectrum for EDF 80 (# 1).

It is a block diagram which shows the 1st basic composition of the optical power monitor by this invention. It is a figure which shows the spectrum in each part of FIG. It is a figure which shows embodiment of the optical power monitor of FIG. It is a figure which shows the example of the characteristic of an optical bandpass filter. It is a block diagram which shows the 2nd basic composition of the optical power monitor by this invention. It is a wave form diagram in each part of FIG. It is a figure which shows embodiment of the optical power monitor of FIG. It is a block diagram which shows the basic composition of the optical amplifier by this invention. 1 is a block diagram showing a first embodiment of an optical amplifier according to the present invention. FIG. It is a block diagram which shows 2nd Embodiment of the optical amplifier by this invention. It is a block diagram which shows 3rd Embodiment of the optical amplifier by this invention. It is a block diagram which shows 4th Embodiment of the optical amplifier by this invention. It is a block diagram which shows 5th Embodiment of the optical amplifier by this invention.

Explanation of symbols

2 Optical couplers 4 and 6 Optical bandpass filters 8 and 10 Photo detector 12 Arithmetic unit

Claims (9)

An optical amplifier for an optical signal having a signal spectrum superimposed on a noise spectrum, the signal spectrum being provided by a main signal,
An optical amplification medium provided on the main optical path;
First means for pumping the optical amplification medium such that the optical amplification medium has a gain band including the wavelength of the optical signal;
A second means operatively connected to the main optical path for extracting the optical signal from the main optical path;
An optical power monitor for the extracted optical signal ,
The optical power monitor
A first optical coupler for branching the optical signal extracted by the second means into a first optical signal and a second optical signal;
A first passband including the wavelength of the optical signal provided by the main signal as a passband; a third light containing spontaneous emission light included in the first optical signal and an optical signal provided by the main signal; A first optical bandpass filter for extracting an optical signal;
Spontaneously emitted light including the wavelength of the optical signal given by the main signal as a pass band, having a second pass band narrower than the first pass band, and included in the second optical signal, and the main signal A second optical bandpass filter for extracting a fourth optical signal including the optical signal given by
A first photodetector for outputting a first electrical signal indicating the optical power of the third optical signal;
A second photodetector for outputting a second electrical signal indicating the optical power of the fourth optical signal;
Operatively connected to the first and second photodetectors, performing predetermined calculations based on the first and second electrical signals, and the bandwidth of the first and second passbands, and And an operational amplifier that outputs an error signal that is given by the main signal and that indicates the optical power of the optical signal that does not include spontaneously emitted light . The optical amplifier according to claim 1, comprising:
The main optical path is set between the input port and the output port,
The optical amplifying medium includes a first doped fiber doped with a rare earth element having a first end and a second end, and a second doped fiber doped with a rare earth element having a third end and a fourth end. And the first end, the second end and the fourth end are operatively connected to the input port, the third end and the output port, respectively.
The first means includes: a first pump light source that outputs a first pump light; and the first doped fiber that emits the first pump light from at least one of the first end and the second end. A first optical circuit for supplying the second pump light, a second pump light source for outputting the second pump light, and the second pump light from at least one of the third end and the fourth end. A second optical circuit for supplying to the second doped fiber,
The second means comprises a second optical coupler operatively connected between the second end and the third end;
The optical power monitor monitors the input optical signal power at the third end,
Means for comparing the input optical signal power with a predetermined value;
Means for blocking the first and second pump lights when the input optical signal power is smaller than the predetermined value . The optical amplifier according to claim 1,
The main optical path is set between the input port and the output port,
The optical amplification medium comprises a doped fiber doped with a rare earth element having a first end and a second end operatively connected to the input port and the output port, respectively.
The first means includes a pump light source that outputs pump light, and an optical circuit for supplying the pump light from at least one of the first end and the second end to the doped fiber. Optical amplifier. The optical amplifier according to claim 3 , wherein
The second means comprises a second optical coupler operatively connected between the input port and the first end;
The optical power monitor is an optical amplifier that monitors the input optical signal power at the input port. The optical amplifier according to claim 4 , wherein
Means for comparing the input optical signal power with a predetermined value;
Means for blocking the pump light when the input optical signal power is smaller than the predetermined value. The optical amplifier according to claim 3 , wherein
The second means comprises a second optical coupler operatively connected between the second end and the output port;
The optical power monitor is an optical amplifier that monitors the output optical signal power at the output port. The optical amplifier according to claim 6 , comprising:
An optical amplifier further comprising a feedback loop for controlling the power of the pump light so that the output optical signal power becomes substantially constant. The optical amplifier according to claim 3 , wherein
An optical circulator for extracting amplified spontaneous emission light operatively connected between the input port and the first end and output from the first end;
Means for monitoring the power of the amplified spontaneous emission light. The optical amplifier according to claim 2 , wherein
An optical circulator for extracting spontaneously emitted light amplified in the second doped fiber that is operatively connected between the second end and the third end and output from the third end;
Means for monitoring the power of the amplified spontaneous emission light.

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