JP2008193512A - Channel filter, and optical branching and inserting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a channel filter and an optical branching and inserting device which have high reliability and can be made compact and inexpensive. <P>SOLUTION: In the channel filter (100) in one embodiment of this invention, a wavelength demultiplexing means (102) demultiplexes wavelength multiplexed signal light into signal light of a plurality of channels with different wavelengths. An excitation light supplying means (106) supplies excitation light to each of the plurality of channels. An optical power adjusting means (118) adjusts optical power of each excitation light, and a light amplifying means (108) amplifies or attenuates each of optical light of the plurality of channels by the excitation light. A light detecting means (114) detects respective optical power of the amplified or attenuated signal light, and a control means (116) adjusts each of the optical power of the excitation light through the optical power adjusting means in accordance with the detected optical power. The signal light amplified or attenuated by the light amplifying means is multiplexed by a wavelength multiplexing means (104). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a channel filter and an optical add / drop multiplexer in a photonic network.

  In a photonic network, network functions such as routing and restoration are realized using an optical cross-connect device and an optical add / drop device. As shown in FIG. 10, the optical add / drop device 10 includes an optical splitter 12 that splits signal light, a splitter 14 that splits signal light from one port of the optical splitter, and an optical splitter. It comprises a channel filter 16 that transmits the signal light from the other port, a multiplexer 18 that combines the signal lights, and an optical coupler 20 that combines the signal lights from the channel filter and the multiplexer. .

  The channel filter 16 is inserted between the optical splitter 12 and the optical coupler 20 so as not to transmit the signal light of the channel branched by the optical splitter 12. That is, the channel filter 16 prevents the signal light of the channel branched by the optical splitter 12 from interfering with the signal light of the channel inserted by the optical coupler 20. As this channel filter, a micro electro mechanical system (MEMS) mirror is mainly used (see Non-Patent Document 1).

  In the optical add / drop device, the power of the signal light is reduced due to the insertion loss of the optical adder / channel filter and the loss of the demultiplexer / multiplexer. Therefore, in a normal node system configuration, as shown in FIG. 11, an optical amplifier (preamplifier) 22 is disposed on the input side of the optical add / drop multiplexer 10 and an optical amplifier (booster amplifier) 24 is disposed on the output side. Yes. That is, the preamplifier 22 amplifies the signal light whose power is reduced during propagation through the transmission fiber and inputs the amplified signal light to the optical add / drop multiplexer 10, and the booster amplifier 24 reduces the power while passing through the optical add / drop multiplexer 10. The amplified signal light is amplified and sent to the transmission fiber.

D. Neilson, et al., “Channel Equalization and Blocking Filter Utilizing Microelectromechanical Mirrors,” IEEE Journal of Selected Topics in Quantum Electronics, vol. 10, no. 3, May / June 2004, pp. 563-569

  However, since the MEMS mirror has a mechanical drive unit, a channel filter using the MEMS mirror is vulnerable to mechanical disturbances such as vibration, and the mirror drive reproducibility is poor when it is operated for a long time. There were problems with reliability. In addition, the preamplifier and the booster amplifier collectively amplify the multiplexed signal light having a plurality of wavelengths (channels), which not only increases the size of the apparatus but also causes cost.

  The present invention has been made in view of such a problem, and an object of the present invention is to provide a channel filter and an optical add / drop multiplexer that are highly reliable and can be reduced in size and price. .

  In order to achieve such an object, the present invention provides a channel filter according to claim 1, which is a channel filter and demultiplexes wavelength-multiplexed signal light into signal light of a plurality of channels having different wavelengths. Demultiplexing means; excitation light supply means for supplying excitation light to each of the plurality of channels; and optical power adjustment means capable of adjusting the optical power of the excitation light of the plurality of channels from the excitation light supply means; , Optical amplifying means for amplifying or attenuating each of the signal light of the plurality of channels with the pumping light whose optical power is adjusted by the optical power adjusting means, and each of the signal light amplified or attenuated by the optical amplifying means A light detecting means for detecting the light power; and the light power adjusting means is controlled according to the light power of the signal light detected by the light detecting means to And control means for adjusting the optical power of les, characterized in that a wavelength multiplexing means for multiplexing the amplified or attenuated signal light by the optical amplification unit.

  The invention according to claim 2 is the channel filter according to claim 1, wherein the wavelength demultiplexing means, the optical power adjustment means, the optical amplification means, the light detection means, and the wavelength multiplexing. At least a part of the means is produced as a planar lightwave circuit.

  The invention according to claim 3 is a channel filter, wherein the optical circulator means for outputting the wavelength-multiplexed signal light input from the first port from the second port, and the optical circulator means Wavelength multiplexing and demultiplexing means for demultiplexing the wavelength-multiplexed signal light from the two ports into signal light of a plurality of channels having different wavelengths, and excitation light supply means for supplying excitation light to each of the plurality of channels , Optical power adjusting means capable of adjusting the optical power of each of the pump light of the plurality of channels from the pump light supply means, and signals of the plurality of channels by the pump light whose optical power is adjusted by the optical power adjusting means. A light amplifying means for amplifying or attenuating each of the light; a light reflecting means for reflecting each of the signal light amplified or attenuated by the light amplifying means; and the light reflecting hand Detecting light power of each of the signal light reflected by the light detection means, and controlling the light power adjusting means according to each light power of the signal light detected by the light detection means, the excitation light And control means for adjusting the respective optical powers, and the signal light reflected by the light reflecting means is multiplexed by the wavelength multiplexing / demultiplexing means, and the second port to the third port of the optical circulator It is output to.

  The invention according to claim 4 is the channel filter according to claim 3, wherein the wavelength multiplexing / demultiplexing means, the optical power adjusting means, the light amplifying means, the light reflecting means, and the light detection At least a part of the means is produced as a planar lightwave circuit.

  The invention according to claim 5 is the channel filter according to any one of claims 1 to 4, wherein the optical amplification medium is an Er-doped optical waveguide.

  A sixth aspect of the present invention is an optical add / drop device, comprising the channel filter according to any one of the first to fifth aspects.

  Since the channel filter and the optical add / drop device according to the present invention do not have a mechanical driving portion and are configured only by optical components, they are robust against mechanical disturbances. Further, since an optical amplifying medium such as an Er-doped optical waveguide or an Er-doped optical fiber is used for attenuation and amplification of the signal light of each channel, the signal light of the passing channel is amplified, and the booster amplifier that has been conventionally required is omitted. be able to. As described above, according to the present invention, it is possible to provide a channel filter and an optical add / drop multiplexer that are highly reliable and can be reduced in size and price.

  Hereinafter, some embodiments of the present invention will be described in detail with reference to the drawings.

(First embodiment)
FIG. 1 is a block diagram of a channel filter according to the first embodiment of the present invention. The channel filter 100 demultiplexes the wavelength-multiplexed signal light into signal light of a plurality of channels having different wavelengths, and combines the signal light of a plurality of channels having different wavelengths with the wavelength-multiplexed signal light. And a multiplexer 104. The channel filter 100 further includes multiplexers 106-1 to 106-N for combining the signal light from the duplexer 102 with the excitation light, optical amplification media 108-1 to N for amplifying the signal light with the excitation light, and amplification. Optical isolators 110-1 to 110 -N that transmit the transmitted signal light only in the forward direction, and optical branching devices 112-1 to 112 -N that branch the power of the transmitted signal light. The signal light from one port of the optical branching units 112-1 to 112 -N is wavelength-multiplexed by the multiplexer 104 and transmitted from the channel filter 100 as wavelength-multiplexed signal light.

  The channel filter 100 further detects the power of the signal light from the other port of the optical branching units 112-1 to 112 -N, and detects the power of the optical signals 114-1 to 114 -N for converting it into an electrical signal. Accordingly, control circuits 116-1 to 116 -N that adjust the attenuation amount of the pumping light and optical variable attenuators 118-1 to 118 -N that attenuate the pumping light according to the attenuation amount from the control circuit are provided. Further, the channel filter 100 includes a pumping light source 120 that generates pumping light and an optical branching device 120 that splits the generated pumping light into power and supplies it to the optical variable attenuators 118-1 to 118 -N. Here, N assumes the number of channels of the channel filter or a smaller number.

  In the present embodiment, the wavelength-multiplexed signal light is input to the demultiplexer 102 and is demultiplexed into N channel signal lights having different wavelengths. The demultiplexed signal lights are combined with the excitation light of the optical variable attenuators 118-1 to 118-N by the multiplexers 106-1 to 106-N, and are amplified in the optical amplification media 108-1 to 108-N by the excitation light. Is done. Each amplified signal light is transmitted between the optical isolators 110-1 to 110-N to be isolated between its input and output, and then is branched by the optical branching units 112-1 to 112-N. The signal lights branched by the optical splitters 112-1 to 112-N are converted into electrical signals corresponding to the power by the photodetectors 114-1 to N, and converted into the electrical signals by the control circuits 116-1 to N. Accordingly, the attenuation amount of the excitation light is determined. The optical variable attenuators 118-1 to 118 -N attenuate the pumping light from the optical branching unit 122 based on the attenuation amount, and provide it to the multiplexers 106-1 to 106 -N.

  As shown in FIG. 10, this channel filter 100 is inserted between an optical splitter 12 that branches the signal light of the channel to be dropped and an optical coupler 20 that couples the signal light of the channel to be added. An add / drop device is configured. Therefore, among the optical amplification media 108-1 to 108-N of the channel filter 100, the one corresponding to the channel to be dropped (or the channel to be added) is not excited in order to sufficiently attenuate the signal light of the channel. Alternatively, the attenuation amount of the optical variable attenuator 118- * is adjusted by the control circuit 116- * (* corresponds to a channel to be dropped (or a channel to be added)) so as to be in a low excitation state.

  On the other hand, among the optical amplification media 108-1 to 108-N of the channel filter 100, the one corresponding to the channel through which the signal light passes is controlled so as to be in an excited state in order to sufficiently amplify the signal light of the channel. The attenuation amount of the optical variable attenuator 118- # is adjusted by the circuit 116- # (# corresponds to the channel to be passed). At this time, the control circuit 116- # uses the value detected by the photodetector 114- # to attenuate the optical variable attenuator 118- # so that the output from the optical splitter 112- # becomes a specified level. Control the amount. The signal light amplified by the optical amplifying medium 108-# is multiplexed by the multiplexer 104 via the optical splitter 112-# and transmitted as the output of the channel filter 100.

  In the present embodiment, the multiplexer 102 and the demultiplexer 104 are an arrayed waveguide grating (AWG), and the optical amplification medium 108 is an Er-doped tellurite glass waveguide doped with 1 wt% Er ions. 106, a fiber-type WEM optical coupler, an optical branching unit 112, a fiber-type optical branching unit, an optical detector 114, an InGaAs photodiode, an excitation light source 120, a 980 nm band laser diode, and an optical branching unit 122. For the optical splitter and optical variable attenuator 118, an attenuator using a Faraday rotator can be used. However, it is not limited to these optical components.

  The optical amplifying medium 108 is not limited to an Er-doped tellurite glass waveguide, but may be an Er-doped fluorinated glass waveguide, Er-doped phosphate glass waveguide, or Er-doped bismuth glass waveguide doped with 1 wt% or more of Er ions. For example, there is an advantage that the size of the channel filter can be reduced. Further, although there is some difficulty in miniaturization, an Er-added quartz glass fiber to which Er ions are added at 100 wtppm to 1 wt% may be used as an optical amplification medium.

  Each of the Er-doped optical waveguides (optical amplification medium 108) has an Er ion concentration, a waveguide length, and a confinement factor (the power of the light in the waveguide cross section so that the loss becomes 40 dB or more in the non-excited state or the low-excited state. The overlap between the mode distribution and the Er ion addition region is adjusted in advance. Specifically, an Er-doped optical waveguide for a channel with a wavelength of 1530 nm has an Er ion of 2 wt%, a waveguide length of 7 cm, and a confinement factor of 0.5, and an Er-doped optical waveguide for a channel with a wavelength of 1550 nm has an Er ion of 2 wt%. An Er-doped optical waveguide for a channel having a wavelength of 1580 nm and a wavelength of 1580 nm can have Er ions of 3 wt%, a waveguide length of 21.5 cm, and a confinement factor of 0.85. By doing so, it is possible to prevent the dropped channel signal light from passing through the channel filter 100 at an excessive level, and to prevent interference with the added channel signal light.

  Since the channel filter according to the present embodiment does not use a component having a mechanical drive unit, it is very robust against mechanical disturbances such as vibration. Further, since this channel filter has an optical amplification function with respect to the channel of the signal light passing therethrough, a booster amplifier can be omitted as shown in FIG. Therefore, compared with the conventional system configuration of the node shown in FIG. 11, the optical amplifier can be reduced, and the system can be reduced in size and price.

(Second Embodiment)
FIG. 3 is a block diagram of a channel filter according to the second embodiment of the present invention. Compared with the channel filter 100 according to the first embodiment, the channel filter 200 includes a photodetector 214 instead of the photodetectors 114-1 to N and a control circuit instead of the control circuits 116-1 to N. 216 is provided with an optical variable attenuator 218 instead of the optical variable attenuators 118-1 to 118 -N. Other components are the same as those in the first embodiment.

  In the present embodiment, the photodetector 214 detects the power of each signal light from the optical splitters 112-1 to 112 -N, converts it into an electrical signal, and provides it to the control circuit 216. The control circuit 216 controls the optical variable attenuator 218 to adjust the attenuation amount of the pumping light according to the power of the signal light of each channel detected. The variable optical attenuator 218 attenuates the pumping light of each channel according to the attenuation amount from the control circuit 216. In this way, it is possible to reduce the size by combining functions common to each channel into one functional block. The function of the channel filter as a whole is the same as in the first embodiment.

  Furthermore, as shown in FIG. 4, the multiplexers 106-1 to 106 -N and the optical variable attenuators 118-1 to 118 -N can be configured as one planar lightwave circuit 220. It is also possible to configure the duplexer 102 as a planar lightwave circuit. In the planar lightwave circuit 220, the multiplexers 106-1 to 106-N and the variable optical attenuators 118-1 to 118-N can be made of quartz waveguides. The optical variable attenuators 118-1 to 118-N are thermo-optic switches that change the transmittance of light waves by attaching a heater (not shown) to one arm of a Mach-Zehnder (MZ) interferometer and controlling the temperature of the heater. Can be configured. Also, as shown in FIG. 5, the planar lightwave circuit 220 of FIG. 4 can be used in combination with an optical branching device 122 that is also fabricated as a planar lightwave circuit.

  4 and 5, the multiplexers 106-1 to 106-N and the optical branching devices 112-1 to 112-N are illustrated as being manufactured by MZ interferometers. Depending on the conditions, a directional coupler may be used. Note that the optical circuits shown in FIGS. 4 and 5 are merely examples, and can be manufactured as planar lightwave circuits having other configurations, and the invention is not limited to these.

(Third embodiment)
FIG. 6 is a block diagram of a channel filter according to the third embodiment of the present invention. The channel filter 300 is different from the channel filter 200 according to the second embodiment in that an optical circulator 302, an optical multiplexer / demultiplexer are used instead of the optical multiplexer 102, the optical multiplexer 104, and the optical isolators 110-1 to 110-N. 304 and a reflection mirror 306 are provided. Other components are the same as those in the first embodiment.

  In this embodiment, the wavelength-division multiplexed signal light is transmitted through the optical circulator 302 and then demultiplexed by the multiplexer / demultiplexer 304 into signal light of a plurality of channels having different wavelengths. The demultiplexed signal lights are combined with the excitation light from the optical variable attenuator 218 by the multiplexers 106-1 to 106-N, and are amplified in the optical amplification media 108-1 to 108-N by the excitation light. The amplified signal lights are reflected by the reflection mirror 306, are further amplified in the optical amplification media 108-1 to 108-N, and are split in power by the optical branching units 112-1 to 112-N. Each signal light branched by the optical splitters 112-1 to 112 -N is converted into an electric signal corresponding to the power by the photodetector 214, and the attenuation amount of the pumping light is determined by the control circuit 216 according to the electric signal. It is determined. The variable optical attenuator 218 attenuates the excitation light from the optical branching device 122 based on the attenuation amount, and provides it to the multiplexers 106-1 to 106 -N.

  Here, also in the channel filter 300 according to the present embodiment, as in the first and second embodiments, the signal light is transmitted by the optical amplification medium 108- * corresponding to the channel to be dropped (or the channel to be added). In order to sufficiently attenuate, the control circuit 216 adjusts the attenuation amount of the corresponding channel of the optical variable attenuator 218 so as to be in the non-excitation state or the low excitation state. Further, in order to sufficiently amplify the signal light with the optical amplifying medium 108- # corresponding to the channel through which the signal light passes, the control circuit 216 attenuates the corresponding channel of the optical variable attenuator so as to be in the pumped state. Is adjusted. The signal light amplified by the optical amplifying medium 108-# is multiplexed by the multiplexer / demultiplexer 304 via the optical branching device 112-#, and is transmitted as the output of the channel filter 300.

  Each of the Er-doped optical waveguides (optical amplification medium 108) has an Er ion concentration, a waveguide length, and a confinement factor (the power of the light in the waveguide cross section so that the loss becomes 40 dB or more in the non-excited state or the low-excited state. The overlap between the mode distribution and the Er ion addition region is adjusted in advance. Specifically, an Er-doped optical waveguide for a channel with a wavelength of 1530 nm has Er ions of 2.5 wt%, a waveguide length of 12 cm, a confinement factor of 0.30, and an Er-doped optical waveguide for a channel with a wavelength of 1550 nm has Er ions. An Er-doped optical waveguide for a channel having a wavelength of 1565 nm should have an Er ion of 2.5 wt%, a waveguide length of 12 cm, and a confinement factor of 0.82. it can. By doing so, it is possible to prevent the dropped channel signal light from passing through the channel filter 300 at an excessive level, and to prevent interference with the added channel signal light.

  Since the channel filter according to the present embodiment does not use a component having a mechanical drive unit, it is very robust against mechanical disturbances such as vibration. Furthermore, unlike the channel filters according to the first and second embodiments, the channel filter 300 according to the present embodiment combines and demultiplexes signal light with one multiplexer / demultiplexer, which is advantageous for downsizing. It is. In addition, when separate multiplexers and demultiplexers are used, there is a problem that the band is limited due to a difference in transmission spectrum caused by a manufacturing error or the like, but when using one multiplexer / demultiplexer Such a problem does not occur.

  Furthermore, as shown in FIG. 7, the multiplexers 106-1 to 106 -N, the optical branching devices 112-1 to 112 -N, and the optical variable attenuators 118-1 to 118 -N can be configured as one planar lightwave circuit 320. It is also possible to configure the multiplexer / demultiplexer 304 as a planar lightwave circuit. In the planar lightwave circuit 320, the multiplexers 106-1 to 106-N, the optical branching devices 112-1 to 112-N, and the optical variable attenuators 118-1 to 118-N can be made of quartz waveguides. The optical variable attenuators 118-1 to 118-N are thermo-optic switches that change the transmittance of light waves by attaching a heater (not shown) to one arm of a Mach-Zehnder (MZ) interferometer and controlling the temperature of the heater. Can be configured. Further, as shown in FIG. 8, the planar lightwave circuit 320 of FIG. 7 can be used in combination with the optical branching device 122 and the photodetector 214 that are also produced as planar lightwave circuits. The photodetector 214 can be configured as a photodiode array 322, for example. 7 and 8, the multiplexers 106-1 to 106-N and the optical branching devices 112-1 to 112-N are illustrated as being manufactured by MZ interferometers. A directional coupler may be used depending on the conditions of the excitation light.

  Furthermore, as shown in FIG. 9, the planar lightwave circuit 320 of FIG. 7 can be used in combination with an Er-doped optical waveguide array 324 that is also fabricated as a planar lightwave circuit. The Er-doped optical waveguide array 324 includes Er-doped optical waveguides 108-1 to 108-N, and a reflection mirror 306 is formed on the end face. Thus, by using the Er-doped waveguide array and the reflection mirror 306 as one planar lightwave circuit, the size of the channel filter can be reduced by 20% compared to the conventional case.

  The Er-doped waveguides 108-1 to 108-N are Er-added tellurite glass waveguides, Er-doped fluorinated glass waveguides, Er-doped phosphate glass waveguides, and Er-doped bismuth glass waveguides added with 1 wt% or more of Er ions. be able to. Furthermore, by making the lengths of the Er-doped optical waveguides 108-1 to 108-N that prevent signal light transmission or optical amplification of each channel uniform, the Er-doped optical waveguide array 324 can be easily manufactured. The optical circuits shown in FIGS. 7 to 9 are merely examples, and can be manufactured as planar lightwave circuits having other configurations, but are not limited thereto.

  While the present invention has been described with respect to several specific embodiments, the embodiments described herein are merely illustrative in view of the many possible embodiments to which the principles of the present invention can be applied. It is not intended to limit the scope of the invention. The configuration and details of the embodiment exemplified here can be changed without departing from the spirit of the present invention. Further, the components for explanation may be changed, supplemented, or changed in order without departing from the spirit of the present invention.

1 is a block diagram of a channel filter according to a first embodiment of the present invention. It is a figure which shows the system configuration example using the optical add / drop device by this invention. It is a block diagram of the channel filter which concerns on the 2nd Embodiment of this invention. It is a figure which shows an example which comprised the multiplexer and optical variable attenuator of the channel filter which concerns on this invention as a planar lightwave circuit. It is a figure which shows an example which produced the optical branching device as a planar lightwave circuit, and was comprised in combination with the planar lightwave circuit of FIG. It is a block diagram of the channel filter which concerns on the 3rd Embodiment of this invention. It is a figure which shows an example which comprised the multiplexer, the optical branching device, and the optical variable attenuator of the channel filter which concerns on this invention as a planar lightwave circuit. It is a figure which shows an example which each produced the optical branching device and the photodetector as a planar lightwave circuit, and combined with the planar lightwave circuit of FIG. FIG. 8 is a diagram illustrating an example in which an Er-doped optical waveguide array is manufactured as a planar lightwave circuit and configured in combination with the planar lightwave circuit of FIG. 7. It is a general block diagram of an optical add / drop device. It is a figure which shows the general system configuration example using an optical add / drop device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 12 Optical branching device 20 Optical coupler 22 Preamplifier 24 Booster amplifier 100 Channel filter according to the first embodiment 106 Multiplexer 108 Optical amplifying medium 110 Optical isolator 112 Optical branching device 118 Optical variable attenuator 200 In the second embodiment Channel filter 220 Planar light wave circuit 300 Channel filter according to the third embodiment 302 Optical circulator 320 Planar light wave circuit 322 Photodiode array 324 Er-doped optical waveguide array

Claims (6)

Wavelength demultiplexing means for demultiplexing wavelength-multiplexed signal light into signal light of a plurality of channels having different wavelengths;
Excitation light supply means for supplying excitation light to each of the plurality of channels;
Optical power adjustment means capable of adjusting the optical power of each of the excitation light of a plurality of channels from the excitation light supply means,
An optical amplifying means for amplifying or attenuating each of the signal lights of the plurality of channels by the pumping light whose optical power is adjusted by the optical power adjusting means;
A light detection means for detecting the optical power of each of the signal light amplified or attenuated by the light amplification means;
Control means for controlling the optical power adjusting means to adjust the optical power of the excitation light according to the optical power of the signal light detected by the optical detection means;
A channel filter comprising: wavelength multiplexing means for multiplexing the signal light amplified or attenuated by the optical amplification means. The channel filter according to claim 1, wherein
A channel filter characterized in that at least a part of the wavelength demultiplexing means, the optical power adjusting means, the optical amplifying means, the light detecting means, and the wavelength multiplexing means is fabricated as a planar lightwave circuit. Optical circulator means for outputting wavelength multiplexed signal light input from the first port from the second port;
Wavelength multiplexing / demultiplexing means for demultiplexing the wavelength-multiplexed signal light from the second port of the optical circulator means into signal light of a plurality of channels having different wavelengths;
Excitation light supply means for supplying excitation light to each of the plurality of channels;
Optical power adjustment means capable of adjusting the optical power of each of the excitation light of a plurality of channels from the excitation light supply means,
An optical amplifying means for amplifying or attenuating each of the signal lights of the plurality of channels by the pumping light whose optical power is adjusted by the optical power adjusting means;
A light reflecting means for reflecting each of the signal light amplified or attenuated by the light amplifying means;
A light detecting means for detecting the optical power of each of the signal lights reflected by the light reflecting means;
Control means for controlling the optical power adjusting means to adjust the optical power of the excitation light according to the optical power of the signal light detected by the optical detection means, and
The channel filter, wherein the signal light reflected by the light reflecting means is multiplexed by the wavelength multiplexing / demultiplexing means and output from the second port of the optical circulator to the third port. The channel filter according to claim 3, wherein
A channel filter, wherein at least a part of the wavelength multiplexing / demultiplexing means, the optical power adjusting means, the optical amplifying means, the light reflecting means, and the light detecting means is fabricated as a planar lightwave circuit. The channel filter according to any one of claims 1 to 4,
The channel filter, wherein the optical amplification medium is an Er-doped optical waveguide.   An optical add / drop device comprising the channel filter according to claim 1.

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