JP5015881B2 - Variable dispersion compensator - Google Patents

Description

  The present invention relates to a dispersion compensator used in optical fiber communication.

  With the explosive spread of the Internet, wavelength division multiplexing (WDM) communication is moving from a conventional point-to-point system to a ring-mesh system. This is because a ring mesh type system can flexibly cope with changes in communication demand between nodes by using a transparent wavelength selective switch or the like that processes an optical signal in an optical state. However, in a ring mesh type network, the dispersion value of the path dynamically changes as the optical path is switched. For this reason, adaptability is also required for dispersion compensation of optical communication paths. Conventional dispersion compensators are mainly of a type that collectively compensates for a plurality of channels. However, in a ring mesh type network using a wavelength selective switch, the distance of the path that passes is different for each wavelength. For this reason, there is a demand for setting a different dispersion value for each WDM wavelength.

  As an adaptive dispersion compensation technique that meets such a demand, for example, a technique using a spectroscope and a mirror array (Patent Document 1), a technique using a waveguide (Patent Document 1, Non-Patent Document 1), a three-dimensional mirror, The thing by a spectroscopic element (nonpatent literature 2) etc. was proposed.

  Furthermore, a variable dispersion compensator with a smaller size and lower cost has been proposed, which uses an LCOS (Liquid Crystal on Silicon) type spatial phase modulation element by combining an arrayed waveguide grating (hereinafter referred to as AWG) and a spatial optical system. ing. The tunable dispersion compensator using AWG has a feature that a large dispersion value can be set by using a high order diffraction order from several tens to several thousand based on the flexible optical design of AWG. . If the relationship between the bandwidth of the communication channel and the AWG FSR (Free Spectral Range) design value is appropriately set, dispersion compensation can be performed for a plurality of channels at once. By combining an AWG with an LCOS type spatial phase modulation element, it was possible to set a more flexible dispersion compensation value.

FIG. 11 is a diagram illustrating a configuration example of a tunable dispersion compensator according to the related art. FIG. 11A shows the configuration of a tunable dispersion compensator (TODC: Tunable Optical Dispersion Compensator) in which one WDM communication channel and the AWG FSR value are matched. The TODC is composed of an AWG, a condensing lens, a spatial phase modulation element, and the like. The AWG FSR is configured to correspond to one WDM communication channel. According to the configuration of FIG. 11A, dispersion compensation can be performed collectively for 40 WDM communication channels from λ ₁ to λ ₄₀ , for example.

  FIG. 11B is a diagram showing the light transmittance of the variable dispersion compensator having the configuration shown in FIG. It can be seen that on the optical frequency axis, signal processing is collectively performed for 40 communication channels that coincide with the cycle of the FSR. However, dispersion compensation cannot be performed independently for each channel.

  FIG. 12A is a diagram illustrating a configuration example of a dispersion compensator capable of performing dispersion compensation independently for each communication channel. This tunable dispersion compensator includes an AWG 34, a cylindrical lens 35, a condenser lens 36, an LCOS element 37, and the like. This configuration is a reflection-type variable dispersion compensator in which an optical signal is reflected by an LCOS element and a single AWG 34 serves as both demultiplexing and multiplexing of the optical signal. The optical signal group subjected to dispersion compensation is input to the input port 38 of the optical circulator 11. The dispersion-compensated optical signal group is output from the output port 39 of the optical circulator 11. A plurality of pixel groups arranged in the spectral axis direction (x-axis) of the AWG 34 on the LCOS element 37 are divided into six groups, and one WDM communication channel (ch1,... Ch6) is assigned to each group of pixel groups. (Non-patent Document 3). Dispersion compensation can be performed independently for each channel by giving a different phase distribution φ (x) to each group of pixels on the LCOS element. FIG. 12B shows group delay characteristics set independently for each channel.

  FIG. 13 is a diagram showing an example of setting the phase distribution for one WDM communication channel in the variable dispersion compensator having the configuration of FIG.

JP 2002-303805 (pages 5-7, FIG. 1 and FIG. 11) K. Takiguchi, K. Okamoto, and T. Goh, “Dispersion slope equalizer on planar Lightwave circuit for 40Gbit / s based WDM transmission,” Electron. Lett, 37 (24), p.1469-1470, 2001. National Institute of Information and Communications Technology, “Research and Development Report of FY 2004 Research and Development of Highly Functional Integrated Optical Switching Nodes to Realize Economical Optical Networks,” 2006 K. Seno, K. Suzuki, K. Watanabe et al., “Channel-by-channel tunable optical dispersion compensator comprising of arrayed-waveguide grating and liquid crystal on silicon” OWP4, Proceeding of OFC2008.

  However, the conventional variable dispersion compensator using the spatial phase modulation element has the following problems. As described above, according to the configuration of FIG. 11A, dispersion compensation could not be performed independently for each WDM communication channel. Further, according to the configuration of FIG. 12A, although dispersion compensation can be performed independently for a plurality of WDM communication channels, the required spatial phase modulation element becomes large. There was a problem. That is, in order to realize dispersion compensation for many channels, a spatial phase modulation element that is long in a direction corresponding to the spectral axis direction of the AWG is required.

  For example, in the configuration of FIG. 12A, dispersion compensation is performed for six communication channels having a bandwidth of 100 GHz. Here, when the number of communication channels increases, the size of the LCOS element in the spectral axis direction (x-axis direction) increases. More specifically, the number of LCOS elements corresponding to one WDM communication channel is 128, and the pixel arrangement pitch is 8 μm. At this time, the length of the LCOS element per channel in the spectral axis (x-axis) direction needs to be about 1000 μm. Therefore, the total length of the LCOS element exceeds 40 mm. If the size of the LCOS element in the direction of the spectral axis is to be shortened, there is a concern that characteristics such as a dispersion compensation amount and a channel transmission band are degraded. Therefore, depending on the required chromatic dispersion value and the number of channels, an LCOS element having a large number of pixels and a very long side is required.

  As is generally known, as the chip size increases, the mass productivity decreases and the cost increases. An increase in the size of the spatial phase modulation element is not preferable in terms of mass productivity and manufacturing cost. Therefore, in a multi-channel variable dispersion compensator using a spatial phase modulation element, it has been required to realize mass productivity and low cost.

  In addition, when a tunable dispersion compensator is configured using a spatial phase modulation element, there is a problem that light transmission characteristics are deteriorated at the optical frequency (wavelength) corresponding to the end of the AWG FSR. There is also a problem in using a pixel corresponding to the end of the FSR in the pixel group of the spatial phase modulation element.

  The present invention has been made in view of the above-described problems, and an object thereof is to realize a multi-channel variable dispersion compensator that realizes higher mass productivity and low cost. Furthermore, a multi-channel variable dispersion compensator with a more flat light transmission characteristic is realized by effectively using pixels of the spatial phase modulation element corresponding to the FSR. Maintenance of the tunable dispersion compensator is simplified and the cost is reduced.

In order to achieve the above object, the present invention provides a dispersion compensator for optical signal groups included in a plurality of continuous wavelength bands, wherein each wavelength band is one communication. One optical signal corresponding to each communication wavelength of the communication wavelength group, and the dispersion compensator is configured to demultiplex the optical signal group for each of the plurality of wavelength bands. And a first optical multiplexing / demultiplexing group of the number of the communication wavelength groups, further demultiplexing the optical signal group in each communication wavelength group demultiplexed by the optical group multiplexing / demultiplexing means, The first port to which the optical signal group of the odd-numbered wavelength band demultiplexed by the optical group multiplexing / demultiplexing means is input, and the light of the even-numbered wavelength band demultiplexed by the optical group multiplexing / demultiplexing means A second port to which a signal group is input, and is demultiplexed by the first port and the second port. The optical frequency of the optical signal group to be generated has an optical frequency difference corresponding to 1/2 of the FSR of each of the first optical multiplexing / demultiplexing means, and the FSR value is equal to twice the bandwidth of the wavelength band. And a plurality of element elements arranged in the direction of the demultiplexing axis of each of the first optical multiplexing / demultiplexing means, and the number of communication phase groups of spatial phase modulation element groups, The plurality of element elements of the spatial phase modulation element are divided into a plurality of sections in which the respective optical signals within one wavelength band are respectively collected, and the demultiplexing is independently performed in the respective sections corresponding to the respective optical signals. And a spatial phase modulation element group in which a phase defined by a function of second order or higher is set with the axis distance as a parameter .

  In this specification, the term “communication wavelength” corresponds to a communication channel. More specifically, for example, it corresponds to a WDM communication channel. Therefore, one optical signal corresponds to one communication channel, and a plurality of communication channels are included in one communication wavelength group. The optical group multiplexing / demultiplexing means corresponds to a group demultiplexing filter.

  Here, FSR means Free Spectral Range.

The invention according to claim 2 is a dispersion compensator for optical signal groups included in a plurality of continuous wavelength bands, wherein each wavelength band corresponds to one communication wavelength group, and each communication of the communication wavelength group One optical signal corresponds to the wavelength, and the dispersion compensator includes optical group demultiplexing means for group-dividing the optical signal group into an odd-numbered wavelength band and an even-numbered wavelength band, and the optical group combining. A first optical multiplexing / demultiplexing unit that further demultiplexes the optical signal group in each wavelength band demultiplexed by the demultiplexing unit, the odd-numbered wavelength band demultiplexed by the optical group multiplexing / demultiplexing unit And a second port to which the even-numbered optical signal group of the wavelength band demultiplexed by the optical group multiplexing / demultiplexing means is input, The optical frequency of the optical signal group demultiplexed by the first port and the second port is the first optical multiplexing / demultiplexing. Has a difference in optical frequency corresponding to 1/2 of the stages of FSR, the FSR value is a first optical demultiplexing means equal to twice the bandwidth of the wavelength band, by said first optical demultiplexing means A second optical multiplexing / demultiplexing unit that further demultiplexes the demultiplexed optical signal group in a second demultiplexing axis direction orthogonal to the demultiplexing axis direction of the first optical multiplexing / demultiplexing unit; A spatial phase modulation element including a plurality of element elements two-dimensionally arranged in a first arrangement direction corresponding to the demultiplexing axis direction of the optical multiplexing / demultiplexing means and a second arrangement direction corresponding to the second demultiplexing axis direction In the first arrangement direction, the plurality of element elements are divided into a plurality of sections in which the respective optical signals within one wavelength band are condensed, and the respective sections corresponding to the respective optical signals. Independently, using the distance of the demultiplexing axis of the first optical multiplexing / demultiplexing means group as a parameter, the second order or higher A phase defined by a function is set, and one of the wavelength bands corresponds to a continuous element element row in the first arrangement direction. In the second arrangement direction, the element element row is provided for each wavelength band. And a spatial phase modulation element arranged repeatedly adjacently. Here, the optical group demultiplexing means for performing the group demultiplexing into the odd-numbered wavelength band and the even-numbered wavelength band corresponds to the interleave type group demultiplexing filter.

The invention according to claim 3 is the tunable dispersion compensator according to claim 2 , wherein the element element row of the spatial phase control element includes at least two element elements in the second arrangement direction. And a predetermined phase distribution is given in the second arrangement direction.

The invention according to claim 4 is the variable dispersion compensator according to claim 1 or 2 , wherein the first optical multiplexing / demultiplexing means is connected to the first port and the second port, respectively. In addition, two input / output waveguides, a slab waveguide, and an arrayed waveguide are sequentially connected to each other, and the two input / output waveguides are 1 / of the AWG at the boundary with the slab waveguide. It is characterized by being connected to a position distant by 2FSR.

A fifth aspect of the present invention is the variable dispersion compensator according to any one of the first to fourth aspects, wherein the spatial phase modulation element is an LCOS element or a MEMS mirror array.

A sixth aspect of the present invention is the variable dispersion compensator according to any one of the first to fifth aspects, wherein the spatial phase modulation element reflects an incident optical signal corresponding to the communication wavelength, and the optical group compensator. The demultiplexing unit, the first optical multiplexing / demultiplexing unit, and the second optical multiplexing / demultiplexing unit have a reflection type configuration that multiplexes the optical signals subjected to dispersion compensation.

  As described above, according to the present invention, a plurality of variable dispersion compensator blocks (hereinafter referred to as TODC blocks) using spatial phase modulation elements in which the size in the direction corresponding to the spectral axis of the AWG is kept short are combined, and more A multi-channel variable dispersion compensator that realizes good mass productivity and low cost can be realized. Maintenance and operation of the tunable dispersion compensator can also be simplified and reduced in cost. Furthermore, the type of TODC block can be reduced by setting the AWG FSR used in the TODC block to be equal to the entire bandwidth of the WDM communication channel group covered by the TODC block. Furthermore, by setting the FSR so as to have a predetermined relationship with the total bandwidth of the WDM communication channel group covered by the TODC block, the light transmission characteristics can be flattened.

  In the present invention, a multi-channel variable dispersion compensator is configured by combining a plurality of variable dispersion compensator blocks (TODC blocks) using spatial phase modulation elements whose size in the direction corresponding to the spectral axis of the AWG is kept short. Has characteristics. Further, the AWG FSR used in the TODC block is set to be equal to the entire bandwidth of the WDM communication channel group covered by the TODC block. Furthermore, by setting the FSR so as to have a predetermined relationship with the total bandwidth of the WDM communication channel group covered by the TODC block, the light transmission characteristics can be flattened.

Embodiment 1 FIG. 1 is a block diagram showing the overall configuration of a tunable dispersion compensator according to Embodiment 1 of the present invention. The tunable dispersion compensator 100 is composed of a plurality of TODC blocks and a group demultiplexing filter. For example, an optical signal in which an optical signal group having 40 wavelengths from λ ₁ to λ ₄₀ is multiplexed is input to the input port In of the first group demultiplexing filter 101. The multiplexed optical signal is divided into four wavelength groups (G1, G2,...) From λ ₁ to λ ₁₀ , λ ₁₁ to λ ₂₀ , λ ₂₁ to λ ₃₀ and λ ₃₁ to λ ₄₀ by the first group demultiplexing filter 101. G3, G4) are group-demultiplexed. The optical signal group of each wavelength group output from the port 1, port 2, port 3, and port 4 of the wavelength group demultiplexing filter 101 is input to the TODC blocks 103a, 103b, 103c, and 103d through optical fibers or the like, respectively. . The optical signal groups of the wavelength groups G1 to G4 are compensated for dispersion by the TODC blocks 103a, 103b, 103c, and 103d, respectively, and are connected to the ports 1 to 4 of the second wavelength group demultiplexing filter 102. Optical signal group of the four wavelength groups after dispersion compensation (G1, G2, G3, G4 ) are multiplexed by the second wavelength group branching filter 102, 40 again having a central wavelength of from lambda ₁ to lambda ₄₀ Are multiplexed on the optical signal of the communication channel and output from the output port out.

  In the block diagram shown in FIG. 1, it is described that there are two wavelength group demultiplexing filters 101 and 102. However, when a reflection type configuration is used as the TODC block, a reflection plate is provided. An equivalent function can be realized by one wavelength group demultiplexing filter capable of generating waves and demultiplexing. The wavelength group demultiplexing filters 101 and 102 can be composed of, for example, a dielectric multilayer film.

  As each TODC block 103 of the tunable dispersion compensator of the present invention, for example, the same configuration as that of the tunable dispersion compensator shown in FIG. Therefore, the input and output of each TODC block in FIG. 1 correspond to the input port 38 and the output port 39 of the optical circulator 11 in FIG. In FIG. 12A, a variable chromatic dispersion compensator having a reflection type is shown, but it should be noted that it can also be realized by a transmission type configuration in which two AWGs are arranged.

  For the individual TODC blocks 103a, 103b, 103c, 103d, the configuration parameters of the AWG are set so that the center wavelength of the spectroscopic operation corresponds to the center wavelength of each band of G1-G4, and the predetermined number of communication channels in each band Each is set so that the linear dispersion value conforms to. The basic configuration of each TODC block can be exactly the same. As shown in FIG. 12A, the phase can be set independently for each channel by a plurality of pixels arranged in the AWG spectral axis direction on the LCOS element included in each TODC block. . In the case of the configuration of FIG. 1, dispersion compensation can be performed independently for 10 WDM communication channels in one wavelength group band.

  Therefore, with the configuration shown in FIG. 1, the size corresponding to the spectral axis of each LCOS element can be shortened by suppressing the number of communication channels for performing dispersion compensation in each TODC block. That is, it is possible to realize a multi-channel variable dispersion compensator excellent in mass productivity and cost while suppressing an increase in size of the LCOS element. In particular, when the number of channels requiring dispersion compensation is very large, a smaller LCOS element is used compared to the case where one TODC block using only one LCOS element having a large side is used. It is cheaper to configure with a plurality of TODC blocks.

  More preferably, in each TODC block of the present embodiment, the AWG FSR can be set to be equal to the entire bandwidth of the communication channel included in one wavelength group. Specifically, the AWG FSR can be set to an optical frequency width corresponding to 10 channels of the WDM communication channel. For example, if one WDM communication channel width is 100 GHz, the FSR is set to 1000 GHz.

  By setting the AWG FSR and the total bandwidth of a plurality of communication channels included in one wavelength group to the same value, the configurations of the TODC blocks 103a, 103b, 103c, and 103d may be exactly the same. it can. That is, the tunable dispersion compensator 100 shown in FIG. 1 can be configured with only one type of TODC block having the same design specifications. Since the types of components of the tunable dispersion compensator 100 can be reduced, the manufacturing cost of the tunable dispersion compensator can be reduced. Furthermore, from the viewpoint of maintenance and operation of the tunable dispersion compensator, maintenance work can be simplified and cost can be reduced. In order to cope with the failure of the tunable dispersion compensator, it is not necessary to provide a plurality of types (for example, four types) of TODC blocks, and only one type of TODC block may be provided for maintenance. Note that maintenance and replacement can be simplified.

  FIG. 2 is a diagram showing an example of the light transmittance characteristic of the variable dispersion compensator of the present invention. In this example, the AWG FSR is set to the same value as the total bandwidth of the communication channels included in one wavelength group. The horizontal axis indicates the optical frequency, and the vertical axis indicates the light transmission characteristics as a dispersion compensator. The dispersion compensation characteristic is repeated for each FSR due to the circulatory property of the AWG. As for the light transmittance, band characteristics are repeated for each FSR. One FSR corresponds to the wavelengths of ten communication channels in one wavelength group (G1, G2, G3, G4).

  Although the variable dispersion compensator having the configuration shown in FIG. 1 has been described as an example in which 10 WDM communication channels are included in one wavelength group, the present invention is not limited to this. Similarly, the total number of channels of the system subject to dispersion compensation is 40, the number of wavelength groups is 4, and the number of corresponding TODC blocks is 4. However, these numbers are not limited at all.

  According to the variable chromatic dispersion compensator of the first embodiment described above, the multiplexed WDM optical signal is separated into a plurality of wavelength groups, and a TODC block corresponding to each wavelength group is provided, so that the spectral axis direction can be provided. LCOS elements with a short size can be used. A multi-channel variable dispersion compensator excellent in mass productivity and cost can be realized without requiring a large LCOS element. In addition, by setting the AWG FSR and the total bandwidth of the communication channels included in one wavelength group to the same value, it is possible to reduce the cost of the variable dispersion compensator, simplify the maintenance, and reduce the cost. it can.

  Embodiment 2 In this embodiment, a variable dispersion compensator is shown in which a TODC block having the same specifications can be used and the light transmission characteristics are flattened. In the first embodiment, the basic configuration of each TODC block can be the same. However, unless the AWG FSR and the total bandwidth of the communication channels included in one wavelength group are set to the same value, it is necessary to prepare a dedicated TODC block corresponding to each wavelength group. That is, for each wavelength group, it is necessary to set the configuration parameters of the AWG included in the TODC block so that the center wavelength of the spectral operation of the AWG corresponds to the center wavelength of each band of G1 to G4. The AWG chip constituting the TODC block must be different for each TODC block.

When the AWG FSR and the total bandwidth of the communication channels included in one wavelength group are set to the same value, one type of TODC block can be used. However, as shown in FIG. 2, it is inevitable that the light transmittance decreases in the communication channel corresponding to both ends of the FSR. When the AWG FSR and the entire bandwidth of the communication channel included in one wavelength group are set to the same value, the transmittance of the dispersion compensator also shows a characteristic that repeats for each FSR. As shown in FIG. 2, in general, the transmittance decreases in the communication channels at both ends of one wavelength group. For example, in the communication channels corresponding to λ ₁ and λ ₁₀ , the light transmittance is lower than that of the communication channel in the center of one wavelength group. In this embodiment, this problem is further improved.

  FIG. 3 is a diagram illustrating a configuration of a TODC block used in the variable dispersion compensator according to the second embodiment. The TODC block 103 is used as a component of a tunable dispersion compensator according to a second embodiment which will be described later with reference to FIG. The basic configuration of the TODC block 103 shown in FIG. 3 is the same as that of the variable dispersion compensator in the prior art shown in FIG. Further, as in the phase distribution shown in FIG. 13, it is defined by a function of second order or higher with the distance of the demultiplexing axis as a parameter. The AWG is different from the configuration of the prior art in that the AWG has two input / output waveguides connected to positions separated by 0.5 FSR on the boundary surface of the slab waveguide.

  Referring to FIG. 3, the TODC block includes a spatial phase modulation element 8 including an AWG 1, a cylindrical lens 6, a condenser lens 7, and an LCOS element. The AWG 1 includes a slab waveguide 3 and an arrayed waveguide 4. The multiplexed optical signal group is demultiplexed from one end of the arrayed waveguide 4 at an emission angle corresponding to the wavelength of the optical signal, and emitted from the end face A of the AWG substrate. On the LCOS element 8, a plurality of pixels are arranged along the spectral axis (x-axis direction) of AWG 1 corresponding to a plurality of WDM communication channels (for example, 10 channels). The TODC block 103 has a reflective configuration, and each optical signal emitted from the AWG 1 is reflected after being given a predetermined phase in the LCOS element 8 and returns to the AWG 1 again.

  The AWG 1 of the present TODC block has two input / output waveguides 16 and 17 that can input and output optical signal groups of a plurality of different wavelength groups. The first input / output waveguide 16 is connected to the slab waveguide 3 at a point on the boundary surface B opposite to the connection surface of the slab waveguide 3 to the arrayed waveguide 4. The first input / output waveguide 16 is connected to the first optical circulator 11 via an optical fiber or the like. The first optical circulator 11 functions as a port A, and an optical signal of a predetermined wavelength group is input (Ain) and output (Aout). Similarly, the second input / output waveguide 17 is connected to the slab waveguide 3 at a point b on the boundary surface B of the slab waveguide 3. The second input / output waveguide 17 is connected to the second optical circulator 14 via an optical fiber or the like. The second optical circulator 14 functions as a port B, and an optical signal having a wavelength group different from that of the port A is input (Bin) and output (Bout).

  Note that the points a and b to which the two input / output waveguides 16 and 17 are connected are shifted by a distance corresponding to 1/2 of the FSR set in the AWG 1. Therefore, the transmission band of the optical signal input / output from the port A and the transmission band of the optical signal input / output from the port B are shifted by 0.5 FSR on the optical frequency axis.

  FIG. 4 is a diagram illustrating the light transmittance of the TODC block according to the second embodiment. The light transmittance of the optical signal input / output using the port A is indicated by a solid transmittance line 21, and the light transmittance of the optical signal input / output using the port B is the dotted line transmittance. This is indicated by the line 22. Since all the transmittance lines have the same AWG transmittance, the transmittance characteristics with the FSR as a repetition period are shown. Note, however, that the center of the transmission band is shifted by 0.5 FSR between the two ports.

  In the transmittance characteristic by the port A, a flat portion at the center of the transmission band can be allocated for use of the optical signal of the wavelength group G1. In order to use the optical signal of the wavelength group G2 adjacent to the wavelength group G1, a flat portion at the center of the transmission band in the transmittance characteristic by the port B can be used. Further, for the wavelength group G3 adjacent to the wavelength group G2, in the transmittance characteristics by the port A, a flat portion at the center of the next transmission band that is FSR away from the transmission band used for the wavelength group G1 can be used. Similarly, for the wavelength group G4 adjacent to the wavelength group G3, the flat portion at the center of the next transmission band that is FSR away from the transmission band used for the wavelength group G2 can be used again in the transmittance characteristics by the port B.

  As described above, the ports used in the TODC block shown in FIG. 3 are alternately selected for each wavelength group, so that the light transmission characteristics are flat for a continuous communication band including a number of WDM communication channels. Dispersion compensation can be realized. At this time, the FSR set in the AWG 1 in the TODC block is twice the total bandwidth of the channels in one wavelength group. In the first embodiment, as shown in FIG. 2, the AWG FSR and the total bandwidth of the channels in one wavelength group are set to be the same. That is, in the first embodiment, the AWG FSR value of the TODC block is set to match the wavelength separation interval of the group demultiplexing filters 101 and 102. On the other hand, in Example 2, it should be noted that the AWG FSR value of the TODC block is set to twice the separation interval of the group demultiplexing filter. Next, the overall configuration of the tunable dispersion compensator using the TODC block shown in FIG. 3 will be further described.

FIG. 5 is a block diagram showing the overall configuration of the tunable dispersion compensator according to the second embodiment of the present invention. Similar to the first embodiment, an optical signal obtained by multiplexing optical signals having 40 wavelengths from λ ₁ to λ ₄₀ is divided into four wavelength groups (G1, G2, G3, G4). Dispersion compensation is performed using four TODC blocks. The second embodiment is different from the first embodiment in that the ports connected to the two group demultiplexing filters in the TODC block are alternately selected for each wavelength group between the A port and the B port. .

An optical signal in which an optical signal group having 40 wavelengths from λ ₁ to λ ₄₀ is multiplexed is input to the input port in of the first group demultiplexing filter 201. The multiplexed optical signal is converted into four wavelength groups (G1, G2) from λ ₁ to λ ₁₀ , λ ₁₁ to λ ₂₀ , λ ₂₁ to λ ₃₀ and λ ₃₁ to λ ₄₀ by the first group demultiplexing filter 201. , G3, G4). The optical signal group of each wavelength group output from the port 1, port 2, port 3, and port 4 of the wavelength group demultiplexing filter 201 is input to the TODC blocks 203a, 203b, 203c, and 203d through optical fibers or the like, respectively. . The optical signals of each wavelength group are dispersion-compensated by the TODC blocks 203a, 203b, 203c, and 203d, respectively, and connected to each port of the second wavelength group demultiplexing filter 202. Optical signal group of the dispersion compensated four wavelength groups (G1, G2, G3, G4 ) are multiplexed by the second wavelength group branching filter 202, 40 again having a central wavelength of from lambda ₁ to lambda ₄₀ Are multiplexed into an optical signal including the optical signal group of the other communication channels.

  The port A is used in the TODC 203a that performs dispersion compensation on the optical signal group of the wavelength group G1. The port B is used in the TODC 203b that performs dispersion compensation for the optical signal group of the wavelength group G2 adjacent to the wavelength group G1. Further, the port A is used again in the TODC 203c that performs dispersion compensation for the optical signal group of the wavelength group G3 adjacent to the wavelength group G2. In the TODC 203d that performs dispersion compensation for the optical signal group of the wavelength group G4 adjacent to the wavelength group G3, the port B is used again. As described above, the A port and the B port are used alternately for each wavelength group from G1 to G4. As a result, as shown in FIG. 4, it is understood that the transmission bands corresponding to the port A and the port B are alternately used for the adjacent wavelength groups. Here, as the chromatic dispersion compensator, only the central region having a flat light transmittance is used in one transmission band corresponding to the FSR on the optical frequency axis. For this reason, only the flat central region is used without using the region corresponding to both ends of the FSR and at the both ends of the transmission band where the light transmittance decreases.

  According to the configuration of the second embodiment, the multiplexed WDM optical signal is separated into a plurality of wavelength groups, and the LCOS element having a short size in the direction of the spectral axis is used by including a plurality of one type of TODC blocks. be able to. A multi-channel variable dispersion compensator excellent in mass productivity and cost can be realized without requiring a large LCOS element. By setting the AWG FSR value of the TODC block to be twice the separation interval of the group demultiplexing filter, a variable dispersion compensator with a flat light transmission band can be realized. It is possible to reduce the cost of the tunable dispersion compensator, simplify the maintenance, and reduce the cost.

  In Example 2 described above, the connection point between the two input / output waveguides and the slab waveguide was shifted by a distance corresponding to 1/2 of the FSR set in the AWG 1. However, if the same technical idea is applied, a configuration including three input / output waveguides connected to the slab waveguide at a position shifted by a distance corresponding to 1/3 of the FSR can be provided. In this case, the TODC block includes three ports, port A, port B, and port C. It can be easily understood that a flat portion of light transmittance can be used in one wavelength group by dividing a plurality of consecutive wavelength groups into three groups that are alternately repeated. At this time, the AWG FSR value of the TODC block is set to three times the separation interval of the group demultiplexing filter. Furthermore, it is possible to expand the number of input / output waveguides and the number of ports to 3 or more based on the same concept.

  Example 3 In the above-described Example 1 and Example 2, an LCOS element having a one-dimensional configuration in which pixels are arranged only in the direction of the spectral axis of the AWG is used as the LCOS element. However, by arranging the pixels two-dimensionally on the LCOS element and introducing the second spectroscopic element into the TODC block, the configuration of the tunable dispersion compensator can be further simplified and the LCOS element can be reduced in size. First, a TODC block including an LCOS element in which pixels are two-dimensionally configured will be described.

  FIG. 6 is a diagram illustrating the configuration of the TODC block according to the third embodiment of the present invention. Similar to the first and second embodiments, the configuration is a reflection type, but is different in that it further includes a bulk diffraction grating 15 and demultiplexes the optical signal also by the bulk diffraction grating. Furthermore, the present embodiment has a great feature in that when viewed through the optical path, the demultiplexing surfaces of the AWG and the bulk type diffraction grating are orthogonal to each other. Hereinafter, a detailed description will be given focusing on the difference from the TODC block of the first and second embodiments.

  Similar to the TODC block of the first and second embodiments, the optical signal input from the input fiber 10 enters the input waveguide 2 of the AWG 1 via the circulator 11 and the connecting fiber 13. The optical signal incident on the input waveguide 2 propagates to the arrayed waveguide 4 through the slab waveguide 3. In the arrayed waveguide 4, optical signal groups having different wavelengths are demultiplexed. That is, the optical signal emitted from the emission end 5 propagates toward the bulk diffraction grating 15 in the z-axis direction at different emission angles according to the wavelength in the xz plane (demultiplexing plane).

  The optical signal emitted from the emission end 5 is converted into a parallel beam by the cylindrical lens 6 in the thickness direction of the AWG substrate, that is, the y direction. The optical signal emitted from the cylindrical lens 6 can be regarded as parallel light in the yz plane. On the other hand, the x direction in the plane of the AWG substrate is converted into a sufficiently wide parallel beam by the lens action of the slab waveguide 3. That is, when the light is emitted from the emission end 5, the optical signal emitted from the AWG 1 can be regarded as parallel light in the xz plane. By passing through the cylindrical lens 6, the optical signal can be regarded as parallel light in both the x direction and the y direction.

  The configuration of the TODC block according to the third embodiment is characterized in that it includes a bulk diffraction grating that further demultiplexes the optical signal demultiplexed by the AWG 1. The optical signal emitted from the cylindrical lens 6 is further demultiplexed by the bulk diffraction grating 15 whose normal is inclined by θi with respect to the z-axis and the grating vector is set in the yz plane. The optical signal demultiplexed by the bulk diffraction grating 15 is condensed on the spatial phase control element 8 by the condenser lens 7. Here, the dispersion direction of the AWG 1 and the dispersion direction of the bulk diffraction grating 15 are in a relationship in which the two demultiplexing surfaces are orthogonal to each other when the demultiplexing surfaces are viewed along the optical path.

  According to FIG. 6A, the AWG 1 and the spatial phase control element 8 are described so as to be arranged in parallel with each other, but strictly speaking, they need not be parallel. FIG. 6 exemplarily shows a case where a specific bulk diffraction grating described later is used and the incident angle θi is 46.76 °. At this time, the optical path is refracted at about 90 ° in the bulk diffraction grating. For this reason, in the drawing, the AWG and the spatial phase control element are expressed as if they were arranged in a parallel positional relationship. Therefore, in this embodiment, there is no limitation on the refraction angle θi of the bulk type diffraction grating. The TODC block of the present embodiment has a spatial phase control element pixel as a result of the relationship between the demultiplexing surface of AWG1 and the demultiplexing surface of bulk diffraction grating 15 being relatively orthogonal when viewed along the optical path. It is characterized in that it can be configured in two dimensions with anisotropy.

  To explain the relationship between the wavelength (optical frequency) and the position of the focused beam of the optical signal, consider the locus that the focused beam draws on the spatial phase control element when the wavelength is virtually continuously changed. Try. In this embodiment, the angular dispersion of the AWG 1 is set to be sufficiently larger than the angular dispersion of the bulk diffraction grating 15, so that the condensed beam on the spatial phase control element 8 is scanned in a raster shape according to the wavelength of the optical signal. The

  For example, the diffraction order of the bulk diffraction grating 15 may be set to 1, and the FSR of the AWG 1 may be set to be equal to the entire bandwidth of the WDM communication channel of one wavelength group in the communication system to be subjected to dispersion compensation. Such a raster scan of the beam can be performed by using an AWG that has a high degree of freedom in design parameters and can easily realize a desired FSR as the first spectroscopic element. Even if a bulk diffraction grating is used as the first spectroscopic element, a desired angular dispersion cannot be set easily. Note that dispersion compensation operation peculiar to this embodiment is realized by allocating and combining appropriate angular dispersions to the demultiplexing characteristics of the first and second spectroscopic elements. I want to be. Similar to the TODC blocks of the first and second embodiments, the optical signal reflected by the spatial phase control element 8 reverses its optical path and propagates in the direction opposite to the forward path, and passes through the circulator 11 to the output fiber 12. It is emitted from.

  FIG. 7A is a diagram illustrating a configuration of a spatial phase control (LCOS) element suitable for the TODC block according to the third embodiment. The coordinate system on the spatial phase control element 8 is defined as u axis-v axis. As described above, the FSR of AWG 1 is set equal to the entire bandwidth of the WDM communication channel in one wavelength group in the communication system that is the object of dispersion compensation. At this time, an optical signal in the entire band of one wavelength group corresponds to interference light of a certain diffraction order of AWG1. Assuming that the wavelength of the virtually unmodulated optical signal is continuously changed, the position of the focused beam draws a locus on the line segment Lm for the optical signal of diffraction order m by the demultiplexing action of AWG1. .

  This optical signal of diffraction order m corresponds to, for example, an optical signal group in the mth specific wavelength group. Similarly, for an optical signal of diffraction order m + 1, a locus on adjacent Lm + 1 is drawn. This optical signal of diffraction order m + 1 corresponds to an optical signal group in the (m + 1) th wavelength group adjacent to the mth wavelength group. Therefore, the optical signal component within the entire band of one wavelength group corresponds to a pixel column localized on one locus line Lm that is scanned and drawn on the spatial phase control element 8. In other words, each optical signal within the entire band of one wavelength group is independently phased by a plurality of pixel rows arranged in the u-axis direction localized on one locus Lm, and dispersion compensation is performed. Is realized.

  Dispersion characteristics (group delay characteristics) can be set for different wavelength groups for each pixel array arranged in the u-axis direction. That is, the TODC block according to the third embodiment has a characteristic that different dispersion characteristics (group delay characteristics) can be set for each wavelength group by setting different phase distributions independently for each pixel column. In FIG. 6, the direction of the line of intersection between the spectral plane (ie, yz plane) of the bulk type diffraction grating 15 and the pixel formation surface of the spatial phase control element 8 is the dispersion direction by the bulk type diffraction grating 15 on the spatial phase control element 8. It becomes. The dispersion axis defined by this intersection line is taken as the z ′ axis. In FIGS. 7A and 7B, the z′-axis is a direction connecting the end points of the locus lines such as Lm and Lm + 1 or a direction connecting the start points.

With reference to FIG. 7A, the relationship between the focused beam diameter and the pixel structure formed on the u-axis and v-axis planes will be further examined. In FIG. 7A, the shape of each pixel is displayed as a square for simplicity. In the following, it should be noted that the method of setting the phase for each pixel will be described by focusing on the relative relationship between the focused spot beam radius and the pixel pitch in each of the u axis and the v axis. In addition, the shape of the condensed beam corresponding to an optical signal having a certain optical frequency (wavelength) that is not modulated is generally an ellipse according to the characteristics of the condensing lens and the cylindrical lens. Here, the ellipse radius in the v-axis direction is wv. The ellipse radius refers to a radius at which the light intensity of the focused spot is 1 / e ^{2 of the} peak value, that is, a radius at which the light intensity of the focused spot is 13.5% of the peak light intensity.

In the v-axis direction, the condensing spot raster that describes the locus Lm moves dv for each optical frequency corresponding to the FSR of the arrayed waveguide grating based on the angular dispersion of the bulk diffraction grating 15. Therefore, overlapping of beams of adjacent wavelength groups can be eliminated by satisfying the following equation for the elliptical radius of the focused spot in the v-axis direction.
wv ≦ dv / 2 Formula (1)
The ellipse radius wv in the v-axis direction is a radius at which the light intensity of the focused spot is 1 / e ^{2 of the} peak value. Crosstalk performance can be realized.

  In the configuration of FIG. 7A, the direction of the locus Lm determined by the linear dispersion values of the AWG 1 and the bulk diffraction grating 15 is made to coincide with the u-axis direction of the spatial phase modulation element 8. Furthermore, the pixel pitch in the v-axis direction is set to pSLMv, and pSLMv and dv are matched. With the above-described pixel configuration, each optical signal in the entire band of one wavelength group can correspond to one pixel column aligned in the u-axis direction. As a result, dispersion can be imparted to the optical signals in all wavelength groups using the LCOS having the minimum number of pixels. By reducing the number of pixels, the cost of LCOS can be kept low.

  Below, the example of the TODC block of a present Example is shown with a specific numerical example. The arrayed waveguide grating was fabricated using a silica-based optical waveguide having a relative refractive index difference of 1.5%. The path length difference ΔL of the arrayed waveguide was 202 μm, and the arrayed waveguide pitch at the exit end 5 of the arrayed waveguide was 12 μm. According to this configuration, the free spectral range of the arrayed waveguide grating is approximately 1000 GHz.

  The bulk type diffraction grating 15 uses, for example, a volume phase holographic diffraction grating (VPHG) having a grating period of 940 lines / mm. The bulk type diffraction grating 15 is not limited to the VPHG type, and a function similar to that of the VPHG can be realized by using a transmission type blaze diffraction grating, a reflection type holographic diffraction grating, or a reflection type blaze diffraction grating. When the incident angle θi is 46.76 °, the angular dispersion value of VPHG with a grating period of 940 lines / mm is 1.37 mrad / nm. The focal length of the cylindrical lens 6 was 1 mm, and the focal length of the condenser lens 7 was 80 mm.

  In the LCOS type spatial phase control element 8, the number of pixels and the pitch in the u-axis direction are 1280 and 8 μm, respectively, and the number of pixels and the pitch in the v-axis direction are 4 and 920 μm, respectively. Therefore, the size of the region where the LCOS pixels are formed is about 10.2 mm × 3.7 mm. This configuration is merely an example, and the pixel pitch in the u-axis direction may be in the range of 5 μm to 10 μm.

  According to the configuration of the optical system described above, the beam radius wv in the v-axis direction is about 300 μm, and it has been confirmed that the relationship of Expression (1) is satisfied. The linear dispersion value in the v-axis direction on LCOS is found to be 0.11 mm / nm as the product of the above-mentioned angular dispersion value of VPHG and the focal length of the condenser lens 7. Therefore, the position of the focused spot moves dv = 920 μm per 1000 GHz (about 8.4 nm) which is the FSR of the AWG. It was confirmed that both the spot movement amount dv corresponding to the FSR of the arrayed waveguide grating and the pixel pitch pSLMv in the v-axis direction were 920 μm.

  The linear dispersion value in the u-axis direction of the LCOS element is 1.22 mm / nm, and 128 pixels contribute to the phase modulation of an optical signal having a frequency range of 100 GHz. Therefore, the TODC block having the configuration of the present embodiment makes it possible to perform dispersion compensation independently for each optical signal of 10 WDM communication channels arranged at 100 GHz intervals in one wavelength group. Furthermore, dispersion compensation can be performed independently for a plurality of optical signal groups of different wavelength groups for each pixel array arranged in the v-axis direction.

  In the configuration example of the LCOS shown in FIG. 7A, the case where the pSLMv and dv are substantially matched and one pixel row arranged in the u-axis direction corresponds to one wavelength group is exemplified. explained. As another configuration example, a configuration example will be described in which dv is set larger than pSLMv and a plurality of pixels are assigned to one wavelength group in the v-axis direction, as shown in FIG. Also in this case, the crosstalk between adjacent wavelength groups can be kept low by satisfying the relationship of the expression (1). In the pixel configuration of FIG. 7A, it is necessary to make the direction of the locus Lm coincide with the direction of the u axis. On the other hand, in the pixel configuration of FIG. 7B, by using a plurality of pixels included in the width of dv centering on the locus Lm in the v-axis direction for controlling one wavelength group m, The locus Lm and the u axis need not be parallel.

  The advantage of the pixel configuration of FIG. 7B is that an arbitrary optical coupling loss can be added to the optical signal. A plurality of pixels in the v-axis direction can set a phase tilted with respect to the v-axis direction independently of the phase setting with respect to the u-axis direction. Referring to FIG. 6 again, the optical signal reflected by the LCOS and passed through the bulk diffraction grating 15 is tilted with respect to the AWG waveguide eigenmode in the y-axis direction at the output end 5 of the arrayed waveguide grating. The light enters the AWG 1 with a distribution. Therefore, it is possible to add a wavelength-dependent loss to the transmission characteristics of the TODC block and compensate the wavelength dependence of the optical signal intensity.

  As an LCOS for realizing the configuration of FIG. 7B, an LCOS in which pixels are arranged on a general square lattice was used. The pixel pitch is 8 μm in both the u-axis direction and the v-axis direction. The configuration of the optical system other than LCOS was the same as that described with reference to FIG. Since dv = 920 μm, 115 pixels are assigned to one wavelength group in the v-axis direction around the locus Lm. At any wavelength, that is, at any wavelength group number m and any position on the u-axis, the phase value given to 115 pixels assigned in the v-axis direction is a phase change with a maximum inclination angle of 0.3 degrees. Was linearly changed in the v-axis direction corresponding to. With this linearly tilted phase, the optical signal intensity at that wavelength could be controlled in the range of 0 dB to -40 dB.

  The variable dispersion compensator according to the first embodiment shown in FIG. 1 is obtained by using a TODC block including LCOS elements in which pixels shown in FIG. 7A or 7B are two-dimensionally arranged. It can be modified to a simpler configuration.

  In the above description related to LCOS, the pixel width and the space between the pixels are not touched by paying attention only to the pixel pitch, but the space between the pixels is narrow to increase the light control efficiency regardless of the usage. It is preferable to do. In general, 1 μm or less is preferable.

  FIG. 8 is a block diagram illustrating the overall configuration of the dispersion compensator according to the third embodiment. FIG. 8 represents the dispersion compensator divided into blocks focusing on the function as the dispersion compensator. Hereinafter, the comparison relationship between the TODC block shown in FIG. 6 and a specific configuration will be described. The LCOS element 8 in the TODC block of FIG. 6 has a configuration in which pixels are arranged in two dimensions (2-Dimension) as shown in FIGS. 7A and 7B. Called an element.

In the tunable dispersion compensator 300 of FIG. 8, for example, an optical signal in which an optical signal group having a wavelength of 40 from λ ₁ to λ ₄₀ is multiplexed is input to the input port In of the spectrometer 301 and is demultiplexed. And input to the first group demultiplexing filter 302. The multiplexed optical signal is divided into four wavelength groups (G1, G2,..., Λ ₁ to λ ₁₀ , λ ₁₁ to λ ₂₀ , λ ₂₁ to λ ₃₀ and λ ₃₁ to λ ₄₀ by the first group demultiplexing filter 302. G3, G4) are group-demultiplexed. The optical signal group of each wavelength group from the first wavelength group demultiplexing filter 302 is a pixel group 306a in each column (first column, second column, third column, fourth column) on the 2D-LCOS element 305. , 306b, 306c, and 306d. The optical signal groups of the four wavelength groups (G1, G2, G3, G4) after the dispersion compensation are multiplexed by the second wavelength group demultiplexing filter 303 and the spectroscope 304, and again from λ ₁ to λ _40. The signals are multiplexed into the optical signals of 40 communication channels having wavelengths and output from the output port out.

  The two spectrometers 301 and 304 in FIG. 8 correspond to AWG1 in the TODC block in FIG. Here, since the TODC block shown in FIG. 6 has a reflection type configuration, it should be noted that the functions of the spectrometer 301 and the spectrometer 304 can be realized by one AWG. The two group demultiplexing filters 302 and 303 in FIG. 8 correspond to the bulk diffraction grating 15 (second spectroscopic means) in the TODC block shown in FIG. Similar to the AWG 1, the functions of the two group demultiplexing filters 302 and 303 can be realized by one bulk diffraction grating 15.

  The 2D-LCOS element 305 includes a first column of pixel groups 306a corresponding to the wavelength group G1, a second column of pixel groups 306b corresponding to the wavelength group G2, a third column of pixel groups 306c corresponding to the wavelength group G3, and a wavelength. Dispersion compensation is performed by the pixel group 306d in the fourth column corresponding to the group G4. Here, in the 2D-LCOS element, pixel groups in each column (first column, second column, third column, and fourth column) arranged in the u-axis direction within one element plane are two-dimensionally integrated. Note that the pixels are arranged and arranged. Therefore, the optical signal processing from when the optical signal is emitted from the spectroscope 301 (AWG1) to the space, subjected to the optical signal processing by the bulk diffraction grating and the 2D-LCOS element, and again incident on the spectroscope 304 (AWG1) is performed. This is realized by a set of TODC blocks. That is, the same function as the tunable dispersion compensator that requires the four TODC blocks shown in FIG. 1 can be realized by one TODC block shown in FIG.

  Note that although it has been described that each pixel column of the 2D-LCOS element 305 is from the first column to the fourth column, phase setting is performed using a plurality of pixels in the v-axis direction for one wavelength group. Note that you can also. In this case, a plurality of pixel columns arranged in the u-axis direction are arranged for one wavelength group.

  According to the tunable dispersion compensator according to the first embodiment shown in FIG. 1, separate wavelength group demultiplexing filters 101 and 102 are required in addition to the four TODC blocks. On the other hand, since the tunable dispersion compensator 300 according to the third embodiment can be configured with only one TODC block shown in FIG. 6, the configuration of the tunable dispersion compensator can be greatly simplified.

  Example 4 Similar to the tunable dispersion compensator of Example 1, the tunable dispersion compensator of Example 2 shown in FIG. 5 has a simpler configuration by using the 2D-LCOS element shown in FIG. Can be transformed into That is, in the TODC block using the LCOS element in which the pixels are two-dimensionally shown in FIG. 6, the two input / output waveguides 16 and 17 connected to the AWG as in FIG. It is possible to realize variable dispersion compensation having a flat light transmission characteristic for a continuous communication band (wavelength group) including a WDM communication channel.

  FIG. 9 is a configuration diagram of a TODC block used in the variable dispersion compensator of the fourth embodiment. The configuration shown in FIG. 9 is that the second demultiplexing means (bulk type diffraction grating) 15 is added to the TODC block (FIG. 3) used in the variable dispersion compensator of the second embodiment. This is different from the configuration of the TODC block shown in FIG. Further, in terms of having two input / output waveguides 16 and 17 connected to a position equivalent to 0.5 FSR on the boundary surface of the slab waveguide 3, it is common to the configuration of the TODC block of FIG. The difference is that the interleave type group demultiplexing filter 19 is provided. Hereinafter, the description will be given focusing on these differences. In FIG. 9, for simplicity, the optical path bending by the second demultiplexing means 15 is omitted and is shown in a simplified manner.

The TODC block shown in FIG. 9 has a reflective configuration. An optical signal in which an optical signal group having 40 wavelengths from λ ₁ to λ ₄₀ is multiplexed is input to the TODC block via the optical circulator 11. After being compensated for dispersion in the TODC block, it is output from the optical circulator 11 again. The multiplexed input optical signal to the optical circulator 11 is input to the interleave type group demultiplexing filter 19. The interleave type group demultiplexing filter 19 demultiplexes the multiplexed optical signal group including a plurality of wavelength groups into an odd-numbered wavelength group and an even-numbered wavelength group. That is, two wavelength groups (G 1 and G 3) from λ ₁ to λ ₁₀ and λ ₂₁ to λ ₃₀ are group-demultiplexed at the output on the port A side of the interleave type group demultiplexing filter 19. Two wavelengths (G2, G4) from λ ₁₁ to λ ₂₀ and λ ₃₁ to λ ₄₀ are group-demultiplexed at the output on the port B side of the interleaved group demultiplexing filter 19. The optical signal groups from the A port and the B port are input to the two input / output waveguides 16 and 17 connected to the positions separated by 0.5 FSR on the boundary surface of the slab waveguide 3, respectively. Similar to the TODC of the second embodiment, the FSR value of the AWG 1 is set to twice the wavelength group separation interval of the interleave type group demultiplexing filter 19.

  The LCOS element 8 in the TODC block of FIG. 9 is a 2D-LCOS element in which pixels are arranged in a two-dimensional manner as shown in FIG. 7 as in the third embodiment.

  FIG. 10 is a block diagram illustrating an overall configuration of a dispersion compensator according to the fourth embodiment. FIG. 10 represents the dispersion compensator divided into blocks focusing on the function as the dispersion compensator. Hereinafter, description will be made in comparison with a specific configuration of the TODC block shown in FIG.

In the tunable dispersion compensator 400 of FIG. 10, for example, an optical signal obtained by multiplexing optical signal groups having 40 wavelengths from λ ₁ to λ ₄₀ is converted into an odd-numbered wavelength by an interleaved group demultiplexing filter 401. The interleaved group is demultiplexed into a group and an even-numbered wavelength group. The A wavelength group (G1, G3) and the B wavelength group (G2, G4), which are demultiplexed by the interleave group, are input to the A port and the B port of the spectrometer 402, respectively. Here, the spectroscope 402 corresponds to AWG1 in FIG. Further, as in the third embodiment, the first wavelength group demultiplexing filter 403 corresponds to the second demultiplexing means 15 in FIG. The optical signal group of each wavelength group from the first wavelength group demultiplexing filter 403 is a pixel group in each column (first column, second column, third column, fourth column) on the 2D-LCOS element 407. Dispersion compensation is performed by 408a, 408b, 408c, and 408d. The optical signal groups of the four wavelength groups (G 1, G 2, G 3, G 4) after dispersion compensation are combined by the second wavelength group demultiplexing filter 404 and the spectroscope 405. Further, the interleaved group demultiplexing filter 406 interleaves the odd-numbered wavelength group and the even-numbered wavelength group and multiplexes them again into the optical signals of 40 communication channels having the center wavelengths from λ ₁ to λ _40. And output from the output port Out.

  Similarly to the third embodiment, the spectroscopes 402 and 405 and the group demultiplexing filters 403 and 404 are realized by one AWG 1 and one second demultiplexing unit 15 by the TODC block having the reflection type configuration of FIG. Needless to say, you can.

  The 2D-LCOS element 407 includes a first column of pixel groups 408a corresponding to the wavelength group G1, a second column of pixel groups 408b corresponding to the wavelength group G2, a third column of pixel groups 408c corresponding to the wavelength group G3, and a wavelength. Dispersion compensation is performed by the pixel group 408d in the fourth column corresponding to the group G4. Here, it should be noted that in the 2D-LCOS element 407, pixels are arranged in a two-dimensional manner in which pixel groups of each column are integrated in one element plane. Therefore, an optical signal is processed until an optical signal is emitted from the spectroscope 402 (AWG1) to the space, subjected to optical signal processing by the bulk diffraction grating 15 and the 2D-LCOS element, and again incident on the spectroscope 405 (AWG1). Is realized by a set of TODC blocks. That is, it should be noted that one TODC block shown by FIG. 9 can realize the same function as the tunable dispersion compensator shown in FIG.

  In the tunable dispersion compensator according to the second embodiment illustrated in FIG. 5, separate wavelength group demultiplexing filters 201 and 202 are required in addition to the four TODC blocks. On the other hand, since the variable dispersion compensator 400 of the fourth embodiment can be configured with only one TODC block shown in FIG. 9, the configuration of the variable dispersion compensator can be greatly simplified.

  Similar to the second embodiment, by separating the multiplexed WDM optical signal into a plurality of wavelength groups and including only one TODC block, an LCOS element having a short size in the spectral axis direction can be used. A multi-channel variable dispersion compensator excellent in mass productivity and cost can be realized without requiring a large LCOS element. By setting the AWG FSR value of the TODC block to be twice the wavelength group separation interval of the interleave type group demultiplexing filter, a variable dispersion compensator with a flat light transmission band can be realized. It is possible to reduce the cost of the tunable dispersion compensator, simplify the maintenance, and reduce the cost.

  As described in detail in Example 3 and Example 4, by using a 2D-LCOS element to form a two-dimensional pixel, an LCOS element in which the size in the direction corresponding to the spectral axis of the AWG is shortened can be obtained. Note that you get the same effect as using it. A multi-channel variable dispersion compensator can be configured by further reducing the number of TODC blocks compared to the variable dispersion compensator having the configuration of the first or second embodiment. Further, the AWG FSR used in the TODC block is set to be equal to the entire bandwidth of the WDM communication channel group covered by the TODC block. Further, by setting the FSR so as to have a predetermined relationship with the total bandwidth of the WDM communication channel group covered by the TODC block, it is possible to realize flattening of the light transmission characteristics.

  The present invention can be used for a chromatic dispersion compensator in an optical communication system.

1 is a block diagram illustrating an overall configuration of a tunable dispersion compensator according to Embodiment 1. FIG. FIG. 3 is a diagram illustrating light transmittance characteristics of the tunable dispersion compensator according to the first embodiment. 6 is a configuration diagram of a TODC block used in the variable dispersion compensator of Embodiment 2. FIG. It is a figure which shows the light transmittance of the TODC block which concerns on Example 2. FIG. FIG. 6 is a block diagram illustrating an overall configuration of a tunable dispersion compensator according to a second embodiment. 6 is a configuration diagram of a TODC block used in the variable dispersion compensator of Example 3. FIG. 6 is a configuration diagram of an LCOS element used in a TODC block used in a tunable dispersion compensator of Example 3. FIG. FIG. 9 is a block diagram illustrating an overall configuration of a tunable dispersion compensator according to a third embodiment. FIG. 10 is a configuration diagram of a TODC block used in the variable dispersion compensator of Example 4. FIG. 10 is a block diagram illustrating an overall configuration of a tunable dispersion compensator according to a fourth embodiment. It is a figure which shows the structure of the variable dispersion compensator of the prior art using a spatial phase modulation element. It is a figure which shows the other structure of the variable dispersion compensator of the prior art using a spatial phase modulation element. It is a figure which shows the example of the phase setting in the variable dispersion compensator of the prior art using a spatial phase modulation element.

Explanation of symbols

1, 34 AWG
3 Slab waveguide 4 Array waveguide 7, 36 Condensing lens 8, 37 Spatial phase modulator 11, 14, 30 Optical circulator 15 Bulk diffraction grating 16, 17 Input / output waveguide 19, 401, 406 Interleaved group demultiplexing Filter 100, 200, 300 Variable dispersion compensator 101, 102, 201, 202, 302, 303 Group demultiplexing filter 103, 103a, 103b, 103c, 103d, 203a, 203b, 203c, 203d, 400 TODC block 301, 304 minutes 305,407 2D-LCOS element

Claims (6)

A dispersion compensator for optical signal groups included in a plurality of continuous wavelength bands, wherein each wavelength band corresponds to one communication wavelength group, and one optical signal corresponds to each communication wavelength of the communication wavelength group The dispersion compensator is
Optical group multiplexing / demultiplexing means for demultiplexing the optical signal group for each of the plurality of wavelength bands;
A first optical multiplexing / demultiplexing unit group of the number of communication wavelength groups, which further demultiplexes optical signal groups in each communication wavelength group demultiplexed by the optical group multiplexing / demultiplexing unit, The first port to which the odd-numbered optical signal group of the wavelength band demultiplexed by the demultiplexing means is input and the even-numbered optical signal group of the wavelength band demultiplexed by the optical group multiplexing / demultiplexing means. The optical frequency of the optical signal group that is demultiplexed by the first port and the second port is 1 / of the FSR of the first optical multiplexing / demultiplexing means. A first optical multiplexing / demultiplexing means group having an optical frequency difference corresponding to 2 and the FSR value being equal to twice the bandwidth of the wavelength band;
A plurality of element elements arranged in the direction of a demultiplexing axis of each of the first optical multiplexing / demultiplexing means, the number of communication phase groups of spatial phase modulation element groups, wherein the plurality of spatial phase modulation elements The element element is divided into a plurality of sections in which each of the optical signals within one wavelength band is collected, and each element corresponding to each of the optical signals is independently set as a secondary using the distance of the demultiplexing axis as a parameter. A variable dispersion compensator comprising: a spatial phase modulation element group in which a phase defined by the above function is set. A dispersion compensator for optical signal groups included in a plurality of continuous wavelength bands, wherein each wavelength band corresponds to one communication wavelength group, and one optical signal corresponds to each communication wavelength of the communication wavelength group The dispersion compensator is
Optical group demultiplexing means for demultiplexing the optical signal group into an odd-numbered wavelength band and an even-numbered wavelength band;
A first optical multiplexing / demultiplexing unit for further demultiplexing the optical signal group in each wavelength band demultiplexed by the optical group multiplexing / demultiplexing unit, wherein the odd-numbered demultiplexed by the optical group multiplexing / demultiplexing unit A first port to which an optical signal group in the wavelength band is input and a second port to which an even-numbered optical signal group in the wavelength band demultiplexed by the optical group multiplexing / demultiplexing means is input. The optical frequency of the optical signal group demultiplexed by the first port and the second port has a difference in optical frequency corresponding to 1/2 of the FSR of the first optical multiplexing / demultiplexing means, A first optical multiplexing / demultiplexing unit having the FSR value equal to twice the bandwidth of the wavelength band;
A second optical multiplexing unit that further demultiplexes the optical signal group demultiplexed by the first optical multiplexing / demultiplexing unit in a second demultiplexing axis direction orthogonal to the demultiplexing axis direction of the first optical multiplexing / demultiplexing unit. Demultiplexing means;
A plurality of element elements two-dimensionally arranged in a first arrangement direction corresponding to a demultiplexing axis direction of the first optical multiplexing / demultiplexing means and a second arrangement direction corresponding to the second demultiplexing axis direction; Spatial phase modulation element, wherein the plurality of element elements in the first arrangement direction are divided into a plurality of sections in which the respective optical signals within one wavelength band are respectively collected and correspond to the respective optical signals In each of the sections, a phase defined by a function of a second order or higher is set using the distance of the demultiplexing axis of the first optical multiplexing / demultiplexing means group as a parameter, and one of the wavelength bands is continuous. A spatial phase modulation element in which, in the second arrangement direction, the element element rows are repeatedly arranged adjacent to each other in the second arrangement direction. Variable dispersion compensator. The element element row of the spatial phase control element is divided into at least two or more element elements in the second arrangement direction, and a predetermined phase distribution is given in the second arrangement direction. The tunable dispersion compensator according to claim 2 . The first optical multiplexing / demultiplexing means is an AWG in which two input / output waveguides connected to the first port and the second port, a slab waveguide, and an arrayed waveguide are sequentially connected. There, the two input and output waveguides, wherein at the boundary between the slab waveguide, according to the each claim 1 or 2, characterized in that it is connected to the 1 / 2FSR corresponds away of the AWG Variable dispersion compensator. The tunable dispersion compensator according to any one of claims 1 to 4 , wherein the spatial phase modulation element is an LCOS element or a MEMS mirror array. The spatial phase modulation element reflects an incident optical signal corresponding to the communication wavelength, and the optical group multiplexing / demultiplexing unit, the first optical multiplexing / demultiplexing unit, and the second optical multiplexing / demultiplexing unit are dispersion-compensated. variable dispersion compensator according to claim 1, wherein it is a reflection-type structure for multiplexing the optical signals.

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