JP2010243575A - Optical hybrid, optical demodulator, and optical receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a mounting density in an optical receiver and to eliminate the need of accurately positioning, in an optical hybrid. <P>SOLUTION: Local oscillation light and received signal light are made incident on fiber collimators 20 and 21, respectively. The received signal light is made incident on a beam splitter 27 and the local oscillation light is made incident on the beam splitter 27 through a λ/4 wavelength plate 26 and a right angle reflection prism 28, to branch spatially synthesized light into 50:50. The branched light is further branched by a polarized beam splitter 30, according to horizontal and vertical polarized components and reflected by a right angle reflection prism 29, to be guided to four fiber collimators for output 22 to 25. Thus, it is constituted so that the fiber collimators can be arranged in one and the same direction. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical hybrid used in a coherent optical transmission system, an optical demodulator, and an optical receiver using the optical hybrid.

  In optical communication, high-density multiplexing is performed by wavelength multiplexing, but the optical signal itself is transmitted on and off by transmitting and receiving the optical signal. In addition to this, a coherent optical communication system that transmits a signal also to a phase component of an optical signal has attracted attention as an economical system capable of high-density bit transmission. The optical receiver in this system uses an optical hybrid that separates received light according to phase components. For example, Patent Document 1 discloses an optical hybrid in which a polarization beam splitter and a polarization maintaining coupler are combined, and this method can be realized by an optical fiber or a planar optical waveguide structure. This system shows a case where the phase difference of light is 90 °, but quartz is used as the medium, and the phase difference changes sensitively to temperature changes due to the thermal characteristics of the material. It was necessary to have.

  Therefore, recently, a digital coherent transmission technique that digitally processes received signal light to prevent signal quality deterioration has attracted attention. Non-Patent Document 1 proposes a 90 ° optical hybrid as shown in FIG. This optical hybrid is a two-input four-output optical hybrid, and has fiber collimators 1 and 2 on the input side and fiber collimators 3, 4, 5, and 6 on the output side. The fiber collimator is obtained by adding a collimating lens to the tip of an optical fiber. Here, the received signal light is applied to the fiber collimator 1, and the local oscillation light is applied to the fiber collimator 2. The optical axis in the space of the received signal light and the local oscillation light is arranged at an angle of 90 °, and the beam splitter 7 is provided at the intersection point at an angle of 45 ° with respect to each optical axis. Here, the received signal light and the local oscillation light are in a linearly polarized state, and a λ / 4 wavelength plate 8 for converting linearly polarized light into circularly polarized light is provided on the output side of the fiber collimator 2 of the local oscillation light. In the beam splitter 7, the reception signal light and the local oscillation light are respectively split at 50:50, and the reception signal light and the local oscillation light are spatially combined. Thereafter, the transmission component and the reflection component are added to the polarization beam splitters 9 and 10. The polarization beam splitters 9 and 10 are three-dimensional beam splitters that split incident light into a horizontal polarization component and a vertical polarization component. The horizontal polarization component passes through the beam splitters 9 and 10 and is coupled to the fiber collimators 3 and 5, respectively. The vertically polarized component is reflected by the beam splitters 9 and 10 and coupled to the fiber collimators 6 and 4, respectively. At this time, the signal components coupled to the fiber collimators 3, 4, 5, and 6 are represented by S + L, S-L, S + jL, and S-jL, respectively, in a complex component display. S is signal light, L local oscillation light, and j is an imaginary number. Therefore, the coherent optical receiver performs differential detection of the S + L component, the S−L component, and the S + jL component, the S−jL component, and performs electric signal processing.

JP-A-8-28682

Kikuchi et al., "Phase-Diversity Homodyne Detection Multilevel Optical Modulation With Digital carrier Phase Estimation", IEEE, Journal of Selected Topics in Quantum Electronics, Vol.12, No.4, pp.563-570, 2006.

  In the conventional optical hybrid shown in FIG. 1, fiber collimators are arranged in four directions for input and output, and input / output optical fibers cannot be arranged in the same direction. Therefore, it is necessary to increase the area of the optical fiber, and there is a drawback that the mounting density inside the optical receiver is reduced. Further, since the three-dimensional polarization beam splitters 9 and 10 are used between the beam splitter 7 for combining the light and the fiber collimators 3, 4, 5 and 6 for coupling, the light beam does not pass through the central portion of the beam splitter. In this case, the distance to the fiber collimator is shifted between the four output units, and the optical transmission quality is deteriorated. Therefore, there is a drawback that the positioning must be performed accurately. Further, since two three-dimensional polarization beam splitters are used, there is a disadvantage that the cost becomes high.

  The present invention has been made paying attention to such conventional problems, and is configured so that the input and output optical fibers can be arranged in one direction, and the optical transmission quality is deteriorated without performing precise positioning. An object of the present invention is to provide an optical hybrid, an optical demodulator, and an optical receiver that are not allowed to occur.

  In order to solve this problem, the optical hybrid of the present invention is an optical hybrid that separates received signal light into four optical signals having different phases, and receives the received signal light as a light beam. An input unit; a local oscillation light input unit that inputs linearly polarized local oscillation light as a light beam; and a λ / 4 wavelength plate that circularly polarizes the linearly polarized light beam obtained from the local oscillation light input unit; The four output units that emit output light separated into different phases and the light beams of the local oscillation light that have passed through the reception signal light and the λ / 4 wavelength plate are incident on the same position while maintaining a perpendicular relationship to each other. A non-polarizing beam splitter that branches incident light, and reflects one of the received signal light and local oscillation light to enter the non-polarizing beam splitter, and is branched by the non-polarizing beam splitter. The first reflecting means for reflecting light and the light branched by the non-polarizing beam splitter are incident directly and through the first reflecting means, respectively, and are separated into horizontal polarization and vertical polarization depending on the polarization state. In addition, a polarization beam splitter that guides each reflected light to two output units of the output unit, and reflects each light that has passed through the polarization beam splitter and guides it to two other output units of the output unit. A second reflection means, wherein the reception signal light input section, the local oscillation light input section and the output section are arranged in the same direction.

    In order to solve this problem, the optical hybrid of the present invention separates received signal light (Sx, Sy) polarization-multiplexed with two orthogonally polarized signal lights in a polarization state and has four different phases. An optical hybrid that separates the optical signal into eight different optical signals by inputting the received signal light into a received signal light input unit that forms a light beam, and linearly polarized local oscillation light A local oscillation light input section that is a beam, eight output sections that emit output light separated into different phases, and a first section that separates the local oscillation light parallel to each other while maintaining different heights relative to the base surface. One orthogonal polarization component block and two orthogonal polarization components that maintain the same height as the light beam separated by the first polarization separation block with respect to the plane on which the received signal light is based Two parallel light beams ( a second polarization separation block that separates x) and (Sy), and a λ / 4 wavelength plate that circularly polarizes two linearly polarized light beams obtained from the first polarization separation block; The received signal light having the same height with respect to the base surface and the local oscillation light beams that have passed through the λ / 4 wavelength plate are incident on the same position while maintaining a perpendicular relationship with each other. A non-polarizing beam splitter that branches the reflected light, and reflects either the received signal light or the local oscillation light to enter the non-polarizing beam splitter, and reflects the light branched by the non-polarizing beam splitter The light branched by the first reflecting means and the non-polarizing beam splitter is incident directly and through the first reflecting means, and is separated into horizontal polarization and vertical polarization depending on the polarization state, and the respective reflections. A polarization beam splitter that guides light to four output units of the output unit, and a second reflection unit that reflects each light that has passed through the polarization beam splitter and guides it to the other four output units of the output unit; The reception signal light input unit, the local oscillation light input unit, and the output unit are arranged in the same direction.

  Here, the non-polarizing beam splitter and the polarizing beam splitter may be arranged in a positional relationship of 90 °.

  Here, the non-polarizing beam splitter and the polarizing beam splitter may be of a flat plate type.

  Here, the reception signal light input unit, the local oscillation light input unit, and the output unit are fiber collimators in which a collimator lens is added to the tip of an optical fiber, and may be arranged in parallel to each other.

    In order to solve this problem, the optical receiver of the present invention is an optical receiver that separates received signal light into four different phase optical signals and converts them into electrical signals, and receives the received signal light. A receiving signal light input unit for generating a light beam, a local oscillation light input unit for inputting a linearly polarized local oscillation light to generate a light beam, and a linearly polarized light connected to the local oscillation light input unit for converting the linearly polarized light into a circularly polarized light / 4 wavelength plate, four light receiving elements that receive output light separated into different phases and generate electric signals, and the received signal light and the light beam of the local oscillation light that has passed through the λ / 4 wavelength plate are mutually connected. A non-polarized beam splitter that is incident on the same position while maintaining a vertical relationship, splits the incident light, and reflects one of the received signal light and the local oscillation light and enters the non-polarized beam splitter, By the non-polarizing beam splitter The first reflecting means for reflecting the branched light and the light branched by the non-polarizing beam splitter are incident directly and via the first reflecting means, and are converted into horizontal polarization and vertical polarization depending on the polarization state. A polarizing beam splitter that separates and reflects each reflected light to two light receiving elements of the light receiving elements; and the other two light receiving elements of the light receiving elements that reflect the respective lights that have passed through the polarizing beam splitter. And a second reflection means for guiding the light beam to the light receiving element, and the light beam from the reception signal light input section and the local oscillation light input section and the light beam to the light receiving element are arranged in parallel to each other It is.

  In order to solve this problem, the optical receiver of the present invention separates received signal light (Sx, Sy) polarization-multiplexed by two orthogonally polarized signal lights in a polarization state and uses four different signals. An optical receiver that separates into eight optical signals different from each other by phase separation and converts them into electrical signals, a received signal light input unit that receives the received signal light as a light beam, and a linearly polarized light A local oscillation light input unit that inputs local oscillation light to form a light beam, eight light receiving elements that emit output light separated into different phases, and different heights from the surface on which the local oscillation light is based A first polarization separation block that separates in parallel and maintains the same height, and a light beam separated by the first polarization separation block with respect to the base surface of the received signal light, respectively. Keep two parallel lights with two orthogonal polarization components A second polarization separation block that separates the beams (Sx) and (Sy), and a λ / 4 wavelength that converts the two linearly polarized light beams obtained from the first polarization separation block into circular polarization, respectively. The received signal light having the same height relative to the plate and the base surface and the local oscillation light beams that have passed through the λ / 4 wavelength plate are incident on the same position while maintaining a perpendicular relationship with each other. A non-polarizing beam splitter that branches the incident light, and a light that is reflected by one of the received signal light and the local oscillation light and enters the non-polarizing beam splitter, and is branched by the non-polarizing beam splitter. And the light branched by the non-polarizing beam splitter is incident directly and via the first reflecting means, and is separated into horizontal polarization and vertical polarization depending on the polarization state, husband A polarization beam splitter that guides the reflected light to four output units of the output unit, and a second beam that reflects each light that has passed through the polarization beam splitter and guides it to the other four output units of the output unit And a light beam from the reception signal light input unit, the local oscillation light input unit, and a light beam to the light receiving element are arranged in parallel.

  In order to solve this problem, the optical demodulator of the present invention separates the received signal light into four optical signals having different phases and demodulates the received signal light based on the difference between the received signal light and the signal light one bit before. A received signal light input unit that receives received signal light as a light beam, a first non-polarized beam splitter that branches the light beam of the received signal light input unit, A λ / 4 wavelength plate that circularly polarizes a linearly polarized light beam branched by one non-polarizing beam splitter, four output units that emit output light obtained by separating received signal light into four different phases, A light beam that is branched by the first non-polarizing beam splitter and that does not pass through the λ / 4 wavelength plate and a light beam that passes through the λ / 4 wavelength plate are incident while maintaining a perpendicular relationship with each other. The second non-polarized bifurcation that branches by photosynthesis A first splitter that reflects one of the received signal light and the local oscillation light to be incident on the non-polarized beam splitter and reflects the light branched by the non-polarized beam splitter; The light separated by the non-polarizing beam splitter is incident directly and through the first reflecting means, and is separated into horizontal polarization and vertical polarization according to the polarization state, and the respective reflected light is separated from the output unit. A polarization beam splitter that leads to two of the output units, and a second reflecting means that reflects each light that has passed through the polarization beam splitter and guides it to two other output units of the output unit, The reception signal light input unit and the output unit are arranged in the same direction, and two light beams of the reception signal light branched by the first non-polarization beam splitter are provided in the second non-polarization beam splitter. It is characterized in that the time difference between each other to reach a light beam splitter to form a branch passage so as to correspond to the reciprocal of the symbol rate of the received signal light.

  In order to solve this problem, the optical demodulator of the present invention separates received signal light (Sx, Sy) polarization-multiplexed with two orthogonally polarized signal lights in a polarization state and separates the received signal. A differential optical demodulator that separates and demodulates received signal light into eight different phase optical signals based on the difference between the light and the signal light one bit before, and receives the received signal light A reception signal light input section that is a beam, eight output sections that emit output light separated into different phases, and two orthogonal polarizations that maintain different heights relative to the base surface of the reception signal light. A polarization separation block that separates two parallel light beams (Sx) and (Sy) having a wave component, and two linearly polarized light beams branched from the polarization separation block are circularly polarized. λ / 4 wave plate and the same height with respect to the base surface The received signal light and the delayed received signal light beams that have passed through the λ / 4 wavelength plate are incident on the same position while maintaining a perpendicular relationship with each other, A first reflecting means for reflecting one of the received signal light and the delayed received signal light to be incident on the non-polarized beam splitter and reflecting the light branched by the non-polarized beam splitter; The light branched by the splitter is incident directly and through the first reflecting means, and is separated into horizontal polarization and vertical polarization according to the polarization state, and each reflected light is output from four output sections of the output section. A polarization beam splitter that guides the light to each of the four output units of the output unit by reflecting each light that has passed through the polarization beam splitter. The reception signal light input unit and the output unit are arranged in the same direction, and the two reception signal light beams branched by the first non-polarization beam splitter reach the second non-polarization beam splitter. The branch path is formed so that the mutual time difference corresponds to the reciprocal of the symbol rate of the received signal light.

  According to the present invention having such characteristics, since the first and second reflecting means are used, the input / output portions can be arranged in the same direction, and the optical fiber can be easily routed. As a result, the mounting area can be reduced. Further, since both the transmitted light and the reflected light of the beam splitter are added to one polarizing beam splitter, only one polarizing beam splitter is required, and the number of parts can be reduced. If the relative position of the output unit is not changed, accurate positioning can be eliminated, and the adjustment work can be simplified.

FIG. 1 is a diagram showing an example of a conventional optical hybrid. FIG. 2 is a diagram showing the configuration of the optical hybrid according to the first embodiment of the present invention. FIG. 3 is a diagram showing a configuration of an optical hybrid according to the second embodiment of the present invention. FIG. 4A is an AA arrow view according to the second embodiment. FIG. 4B is a BB line view according to the second embodiment. FIG. 4C is a CC arrow view according to the second embodiment. FIG. 5A is an AA line arrow view according to a modification of the second embodiment. FIG. 5B is a BB line arrow view according to a modification of the second embodiment. FIG. 6 is a diagram showing a configuration of a DQPSK optical demodulator according to the third embodiment of the present invention. FIG. 7 is a diagram showing a configuration of a DQPSK optical demodulator according to the fourth embodiment of the present invention. FIG. 8 is an AA arrow view according to the fourth embodiment.

(First embodiment)
FIG. 2 is a configuration diagram of the optical hybrid according to the first embodiment of the present invention. The optical hybrid of the present embodiment is a two-input, four-output single polarization optical hybrid, and fiber collimators are arranged in parallel from the side in the figure. Here, the fiber collimator 20 is an input unit of local oscillation light in which a collimating lens is added to a polarization-maintaining optical fiber (PMF) that guides local oscillation light, and the fiber collimator 21 is collimated to the optical fiber that guides received signal light A reception signal light input unit to which a lens is added, which are arranged in parallel. In parallel with this, fiber collimators 22, 23, 24, and 25 serving as output portions are arranged at equal intervals, and a collimator is provided at the tip of each optical fiber. A λ / 4 wavelength plate 26 that converts linearly polarized light into circularly polarized light is provided on the emission side of the local oscillation light. On the optical axis of the reception signal light fiber collimator 21, a flat plate-type non-polarizing beam splitter 27 is provided at an angle of 45 ° with respect to the optical axis of the reception signal light. In the right side portion of FIG. 2, triangular prism-shaped right-angle reflecting prisms 28 and 29 are provided. The right-angle reflecting prism 28 is a first reflecting means having a reflecting surface arranged at an angle of 45 ° with respect to the optical axes of the local oscillation light and received signal light which are two incident lights. The polarizing beam splitter 30 is disposed at an angle of 45 ° with respect to the reflected light reflected here and at an angle of 90 ° with respect to the non-polarizing beam splitter 27. The polarization beam splitter 30 is a splitter that reflects a vertical polarization component and transmits a horizontal polarization component, and is configured by a parallel plate type beam splitter. The right angle reflection prism 29 is disposed at a position where the light transmitted through the polarizing beam splitter 30 is reflected so that the reflection surface thereof forms an angle of 90 ° with the reflection surface of the right angle reflection prism 28, and the reflected light is output to the fiber collimator 24 on the output side. This is a second reflecting means for guiding to the 25th side. Here, AR (Anti-reflection) blocks 31 and 32 for adjusting the optical path length are arranged on the optical axes before incidence of the fiber collimator 23 and the fiber collimator 25. The AR blocks 31 and 32 are glass blocks having antireflection coatings on the front and back surfaces, and the thickness and refractive index are selected according to the optical path length to be adjusted. The AR block 31 matches the optical path length of the light incident on the fiber collimators 22 and 23, and the AR block 32 matches the optical path length of the light incident on the fiber collimators 24 and 25.

  Next, the operation of the present embodiment will be described. Locally oscillated light and light-receiving signal light in a linearly polarized state are incident on the optical hybrid from the respective optical fibers of the fiber collimators 20 and 21. These incident lights become parallel light beams directed to the right-angle reflecting prism side 28 through the collimator. The received signal light enters the non-polarized beam splitter 27 and passes through the inside. On the other hand, the local oscillation light is converted into circularly polarized light by the λ / 4 wavelength plate 26 and enters the right-angle reflecting prism 28. Then, as shown in FIG. 2, the light is reflected in the downward direction and is incident on the same position as the output portion of the reception signal light of the non-polarizing beam splitter 27. Then, the received light signal light and the local oscillation light are spatially combined and branched at 50:50 on the reflecting surface. A part of the light incident on the beam splitter 27 is reflected and a part of the light is transmitted. The transmission component of the received light signal and the reflection component of the local oscillation light are reflected by the right-angle reflection prism 28 and enter the polarization beam splitter 30. The polarization beam splitter 30 branches the incident light into a vertical polarization component and a horizontal polarization component. The component reflected again by the polarization beam splitter 30 enters the fiber collimator 22. The light transmitted through the polarization beam splitter 30 is reflected by the right angle reflection prism 29 and is transmitted to the fiber collimator 24. The reflection component of the received light signal and the transmission component of the local oscillation light enter the polarization beam splitter 30 from the non-polarization beam splitter 27. The polarization beam splitter 30 reflects the vertically polarized component and enters the fiber collimator 23 via the AR block 31. The horizontal polarization component passes through the polarization beam splitter 30, is reflected by the right-angle reflecting prism 29, and is transmitted to the fiber collimator 25 via the AR block 32. Here, the signal components coupled to the optical fibers 24, 25, 22, and 23 are represented by S + L, SL, S + jL, and S-jL, respectively, in a complex component display.

  According to the present embodiment, six optical fibers for input / output can be arranged in the same direction of the optical fiber, in the case of FIG. It can be a hybrid. In the case of FIG. 1, two three-dimensional polarization beam splitters are required, but in the present embodiment, one flat beam splitter 30 is sufficient. When a flat type polarization beam splitter is used, the polishing of the front and back surfaces is sufficient, so that the price can be lower than that of a three-dimensional type. Even if the position of the beam splitter 30 is slightly displaced in the X-axis direction or the Y-axis direction in the figure, the relative distance between the fiber collimators 22 and 23 and the fiber collimators 24 and 25 does not change. No degradation occurs. For example, when the beam splitter 30 is displaced in the Y direction, it is only necessary to shift the fiber collimators 22 and 23 in the Y direction while maintaining the relative distance between the fiber collimators 22 and 23, and it is not necessary to change the positions of the fiber collimators 24 and 25. The same applies when the beam splitter 30 is displaced in the X direction. Therefore, if the relative position is maintained, precise positioning can be eliminated, and the manufacturing process can be simplified.

  In this embodiment, a light receiving element such as a photodiode is provided at the tip of each fiber collimator. The AR blocks 31 and 32 are arranged to adjust the optical path length to the light receiving element, but the AR block is not always necessary. That is, by adjusting the length of the optical fiber itself, the optical path lengths of S + L and S−L may be matched at the position of the light receiving element, and the optical path lengths of S + jL and S−jL may be matched. The non-polarizing beam splitter and the polarizing beam splitter may be a three-dimensional non-polarizing beam splitter or a three-dimensional polarizing beam splitter.

  Here, a light receiving element can be arranged at the tip of the fiber collimators 22 to 25 of the output unit to form an optical receiver. Further, instead of the fiber collimator, four light receiving elements are arranged directly at the position and the emitted light is directly converted into an electric signal, whereby an optical receiver can be obtained. In this case, since it can be integrated with the receiving module, the mounting density in the optical receiver can be improved.

(Second Embodiment)
Next, an optical hybrid according to a second embodiment of the present invention will be described with reference to FIGS. 3 and 4A to 4C. 4A, FIG. 4B, and FIG. 4C are the arrow views seen from the AA line, BB line, and CC line of FIG. 3, respectively. This embodiment is an optical hybrid for polarization multiplexing having two inputs and eight outputs, and a combined signal component of received light signal light (Sx, Sy) that has been polarization multiplexed is incident on an optical hybrid from a fiber collimator 41. In addition, linearly polarized local oscillation light (E _L0 ) is incident on the fiber collimator 40 in an oblique polarization state of 45 °. In parallel with this, eight fiber collimators are provided as output units. In FIG. 3, two fiber collimators overlap each other in the fiber collimators 42 to 45. For example, the fiber collimator 45 actually includes fiber collimators 45a and 45b as shown in FIG. 4C, and the fiber collimator 45b is provided directly above the fiber collimator 45a. The same applies to the other fiber collimators 42, 43, and 44. In addition, the λ / 4 wavelength plate 52 shown in FIG. 3 actually includes two λ / 4 wavelength plates, and as shown in FIG. 4A, the λ / 4 wavelength plate 52a is directly above the λ / 4 wavelength plate 52b. Is provided. Similarly, the λ / 2 plate 53 is composed of two λ / 2 wavelength plates as shown in FIG. 4B, and a λ / 2 wavelength plate 53a is provided immediately above the λ / 2 wavelength plate 53b. Further, the flat-type non-polarizing beam splitter 46, the flat-type polarizing beam splitter 47, the right-angle reflecting prisms 48 and 49, and the AR blocks 54 and 55 are the non-polarizing beam splitter 27 and the polarizing beam of the first embodiment described above. Since the splitter 30, the right-angle reflecting prisms 28 and 29, and the AR blocks 31 and 32 are arranged in the same manner and achieve the same function, detailed description thereof is omitted.

  In this embodiment, the first polarization separation block 50 is provided on the optical axis of the local oscillation light emitted from the fiber collimator 40. As shown in FIG. 4A, the polarization separation block 50 is constituted by a three-dimensional polarization beam splitter 57 provided on the base and a right-angle reflection prism 58 provided on the top thereof, and the local oscillation light is hatched according to the polarization state. Are maintained in different heights with respect to the base surface shown in FIG. On the upper and lower optical axes, λ / 4 wavelength plates 52a and 52b are arranged as shown in FIG. 4A.

  Further, as shown in FIG. 3, a second polarization separation block 51 is provided on the optical axis of the received signal light. The polarization separation block 51 includes a three-dimensional polarization beam splitter 60 and a right angle reflection prism 61 as shown in FIG. 4B. The polarization separation block 51 separates incident light into two parallel light beams of Sx component and Sy component according to the polarization state. These light beams are parallel to the surface of the base and have the same height as the local oscillation light having different heights with respect to the base surface, and are parallel light beams. The separated signal light is incident on the λ / 2 plates 53a and 53b. If it carries out like this, in the state isolate | separated up and down, it will be converted into the linearly polarized state of 45 degrees each. Similarly to the first embodiment described above, the received signal light and the local oscillation light are spatially combined by the non-polarizing beam splitter 46 and branched to 50:50. Thereafter, the transmission component and the reflection component are branched into a horizontal polarization component and a vertical polarization component by the polarization beam splitter 47. The horizontal polarization component passes through the polarization beam splitter 47 and is reflected by the right-angle reflection prism 49, and is coupled to the fiber collimator 45 and the fiber collimator 44. The vertically polarized component is reflected by the polarization beam splitter 47 and coupled to the fiber collimators 42 and 43. These operations occur in the same way up and down, and each is coupled to each of the four upper and lower fiber collimators.

  As a result, similarly to the first embodiment, the input and output optical fibers can be arranged in one direction, and the mounting floor area is the single polarization light shown in the first embodiment. Same as hybrid. Similarly to the first embodiment, the optical transmission quality is not deteriorated by the positional deviation of the beam splitter 47.

  In this embodiment, the polarization separation block 50 uses a combination of the polarization beam splitter 57 and the right-angle reflection prism 58. Instead, the three-dimensional polarization beam splitters 57 and 62 are moved up and down as shown in FIG. 5A. You may laminate | stack in two steps. In this case, since only the component reflected by the polarizing beam splitter 57 is incident on the upper polarizing beam splitter 62, all the components are reflected and added to the λ / 4 wavelength plate 52a. Accordingly, the extinction ratio in the upper stage is twice that in the case of FIG. 4A, so that this configuration can be used when high polarization separation characteristics are required.

  In this embodiment, the polarization separation block 51 uses a combination of the polarization beam splitter 60 and the right-angle reflection prism 61. Instead, the three-dimensional polarization beam splitters 60 and 63 are moved up and down as shown in FIG. 5B. You may laminate | stack in two steps. In this case, since only the component reflected by the polarizing beam splitter 60 is incident on the upper polarizing beam splitter 63, all the components are reflected and added to the λ / 2 wavelength plate 53a. In this case, the extinction ratio in the upper stage is twice that in the case of FIG. 4B, so this configuration can be used when high polarization separation characteristics are required.

  Further, although not used in the present embodiment, polarizers can be provided before and after the right-angle reflecting prisms 48, 49, 58, 61 to increase the extinction ratio.

  Here, a light receiving element can be arranged at the tip of the fiber collimators 42 to 45 of the output unit to form an optical receiver. Further, instead of the fiber collimator, eight light receiving elements are directly arranged at the position, and the emitted light is directly converted into an electric signal, whereby an optical receiver can be obtained. In this case, since it can be integrated with the receiving module, the mounting density in the optical receiver can be improved.

(Third embodiment)
FIG. 6 is a block diagram of a differential DQPSK optical demodulator according to the third embodiment of the present invention. The DQPSK optical demodulator of the present embodiment is a 1-input, 4-output, single-polarization DQPSK optical demodulator, and five fiber collimators 70 to 74 are arranged in parallel from the side in the figure. In this embodiment, the received signal light (Es) in the linearly polarized state is incident through the fiber collimator 70. The received signal light is split 50:50 by a flat plate-type non-polarizing beam splitter 75. The reflected optical signal is reflected by the mirror 76, converted to circularly polarized light by the λ / 4 wavelength plate 77, and reflected by the right-angle reflecting prism 80. The branched transmitted light and reflected light are respectively added to a flat plate-type non-polarizing beam splitter 78, spatially synthesized at the same position, and further split 50:50. Of the received signal light, the light beam reflected by the beam splitter 75 and reflected by the λ / 4 wavelength plate 77 and the right-angle reflecting prism 80 and incident on the non-polarized beam splitter 78 is referred to as delayed received signal light. Between the non-polarizing beam splitter 75 and the non-polarizing beam splitter 78, a Mach Cender interferometer is formed. Therefore, if the vertical mode interval (Free spectral range) corresponding to the optical path length difference of the delayed received signal light with respect to the received signal light is set equal to the symbol rate of the transmission signal, the condition of interfering with the received signal light one bit before is satisfied. Therefore, it functions as an optical demodulator for DQPSK. Other configurations are the same as those of the optical hybrid according to the first embodiment. That is, both the transmission component and the reflection component of the non-polarization beam splitter 78 are incident on the polarization beam splitter 79 and branched into a horizontal polarization component and a vertical polarization component. The horizontally polarized light component passes through the polarization beam splitter 79, is reflected by the right-angle reflecting prism 81, and is coupled to the fiber collimators 73 and 74. The vertically polarized component is reflected by the polarization beam splitter 79 and coupled to the fiber collimators 71 and 72. Also in this embodiment, in order to compensate for the deviation of the optical path length, AR blocks 82 and 83 may be inserted as shown in FIG. Here, the output signals coupled to the fiber collimators 73, 74, 71, 72 have phases of π / 4, 3π / 4, 5π / 4, and 7π / 4. Also in this case, the same effects as those of the above-described embodiments can be obtained.

  Here, a light receiving element can be arranged at the tip of the fiber collimators 71 to 74 of the output unit to form an optical receiver. Further, instead of the fiber collimator, four light receiving elements are arranged directly at the position and the emitted light is directly converted into an electric signal, whereby an optical receiver can be obtained. In this case, since it can be integrated with the receiving module, the mounting density in the optical receiver can be improved.

(Fourth embodiment)
In the third embodiment described above, a single-polarization type DQPSK optical demodulator has been described. However, as shown in the second embodiment, a DQPSK optical demodulator for polarization multiplexing is used. be able to. In this embodiment, as shown in FIGS. 7 and 8, a polarization separation block 90 is provided on the optical axis serving as the output of the fiber collimator 70. As shown in FIG. 8, the polarization separation block 90 includes a three-dimensional polarization beam splitter 92 and a right-angle reflection prism 93, and makes incident light into two upper and lower light beams parallel to the surface of the base. A non-polarizing beam splitter 75 is disposed on the two optical axes. In this embodiment, λ / 4 wavelength plates 77a and 77b are provided on the upper and lower optical axes, and the fiber collimators 71 to 74 are also provided in two stages. The subsequent configuration is the same as that of the third embodiment, and the same effect can be obtained.

  In each of the embodiments described above, the right-angle reflecting prisms 28, 48, and 80 are used as the first and second reflecting means in order to match the directions of the two input portions, and the directions of the output portions are matched. In order to achieve this, the right-angle reflecting prisms 29, 49, 81 are used. However, these need only have a function of reflecting incident light and outgoing light, and use a mirror disposed at a position of 45 ° with respect to the optical axis. Can do.

  In the first embodiment, the positions of the fiber collimator 20 and the λ / 4 wavelength plate 26 that receive the local oscillation light and the position of the fiber collimator 21 may be reversed. The local oscillation light may be directly incident on the beam splitter 27 as circularly polarized light, and the received signal light may be incident on the beam splitter 27 via the right angle reflection prism 28. The same applies to the second embodiment.

  The present invention can reduce the number of parts of the polarization beam splitter, and can eliminate the need for accurate positioning unless the relative position of the output unit is changed. Therefore, an optical hybrid used in a coherent optical transmission system, It is suitable for an optical demodulator and an optical receiver using the same.

1, 2, 3, 4, 20, 21, 22, 23, 24, 25, 40, 41, 42, 43, 44, 45, 70, 71, 72, 73, 74 Fiber collimator 45a Lower fiber collimator 45b Upper Fiber collimator 7 Non-polarizing beam splitter 8, 26, 52, 52a, 52b, 77, 77a, 77b λ / 4 wave plate 9, 10, 57, 60, 62, 63, 92 Three-dimensional polarizing beam splitter 27, 46, 75, 78 Flat type non-polarizing beam splitter 30, 47, 79 Flat type polarizing beam splitter 53, 53a, 53b λ / 2 plate 28, 29, 48, 49, 58, 61, 80, 81, 93 Right angle reflecting prism 31, 32, 54, 55, 81, 82 AR block 50, 51, 90 Polarization separation block 76 Mirror

Claims (9)

An optical hybrid that separates received signal light into four different-phase optical signals,
A received signal light input unit that receives the received signal light to form a light beam;
A local oscillation light input unit that inputs linearly polarized local oscillation light into a light beam;
A λ / 4 wavelength plate that circularly polarizes a linearly polarized light beam obtained from the local oscillation light input unit;
Four output units for emitting output light separated into different phases;
A non-polarizing beam splitter that splits the incident light, and the received signal light and the local oscillation light beam that has passed through the λ / 4 wavelength plate are incident on the same position while maintaining a perpendicular relationship;
A first reflecting means for reflecting either the received signal light or the local oscillation light to be incident on the non-polarizing beam splitter and reflecting the light branched by the non-polarizing beam splitter;
The light branched by the non-polarizing beam splitter is incident directly and via the first reflecting means, and is separated into horizontal polarization and vertical polarization according to the polarization state, and the respective reflected light is separated from the output section. A polarizing beam splitter leading to two of the outputs,
Second reflecting means for reflecting each light that has passed through the polarizing beam splitter and guiding the light to two other output units among the output units,
An optical hybrid, wherein the received signal light input unit, the local oscillation light input unit, and the output unit are arranged in the same direction. Light that is separated into eight different optical signals by separating the received signal light (Sx, Sy) polarization-multiplexed with two orthogonally polarized signal lights in the polarization state and separating them into four different phases. Hybrid,
A reception signal light input unit configured to input the reception signal light into a light beam;
A local oscillation light input unit that inputs linearly polarized local oscillation light into a light beam;
8 output units for emitting output light separated into different phases;
A first polarization separation block that separates the local oscillation light parallel to each other while maintaining a different height from the base surface;
Two parallel lights having the same height as the light beams separated by the first polarization separation block with respect to the base surface of the received signal light, respectively, and having two orthogonal polarization components A second polarization separation block that separates the beams (Sx) and (Sy);
A λ / 4 wavelength plate that circularly polarizes two linearly polarized light beams obtained from the first polarization separation block;
The received signal light having the same height with respect to the base surface and the local oscillation light beams that have passed through the λ / 4 wavelength plate are incident on the same position while maintaining a perpendicular relationship with each other. A non-polarizing beam splitter that splits the emitted light,
A first reflecting means for reflecting either the received signal light or the local oscillation light to be incident on the non-polarizing beam splitter and reflecting the light branched by the non-polarizing beam splitter;
The light branched by the non-polarization beam splitter is incident directly and through the first reflecting means, and is separated into horizontal polarization and vertical polarization according to the polarization state, and each reflected light is output from the output unit. A polarizing beam splitter leading to four outputs,
Second reflecting means for reflecting each light that has passed through the polarizing beam splitter and guiding it to the other four output units of the output unit,
An optical hybrid, wherein the received signal light input unit, the local oscillation light input unit, and the output unit are arranged in the same direction.   The optical hybrid according to claim 1, wherein the non-polarizing beam splitter and the polarizing beam splitter are arranged in a positional relationship of 90 ° with each other.   The optical hybrid according to claim 3, wherein the non-polarizing beam splitter and the polarizing beam splitter are of a flat plate type.   The received signal light input unit, the local oscillation light input unit, and the output unit are fiber collimators in which a collimator lens is added to the tip of an optical fiber, and are arranged in parallel to each other. Optical hybrid according to item. An optical receiver for separating received signal light into four different phase optical signals and converting them into electrical signals,
A received signal light input unit that receives the received signal light to form a light beam;
A local oscillation light input unit that inputs linearly polarized local oscillation light into a light beam;
A λ / 4 wavelength plate that is connected to the local oscillation light input unit and converts linearly polarized light into circularly polarized light;
Four light receiving elements that receive output light separated into different phases and convert it into electrical signals;
A non-polarizing beam splitter that splits the incident light, and the received signal light and the local oscillation light beam that has passed through the λ / 4 wavelength plate are incident on the same position while maintaining a perpendicular relationship;
A first reflecting means for reflecting either the received signal light or the local oscillation light to be incident on the non-polarizing beam splitter and reflecting the light branched by the non-polarizing beam splitter;
The light branched by the non-polarizing beam splitter is incident directly and through the first reflecting means, and is separated into horizontal polarization and vertical polarization according to the polarization state, and each reflected light is separated from the light receiving element. A polarization beam splitter leading to two light receiving elements;
Second reflecting means for reflecting each light that has passed through the polarizing beam splitter and guiding it to the other two light receiving elements among the light receiving elements,
An optical receiver characterized in that a light beam from the reception signal light input section and the local oscillation light input section and a light beam to the light receiving element are arranged in parallel. The received signal light (Sx, Sy) that is polarization-multiplexed with two orthogonally polarized signal lights is separated in the polarization state and separated into four different phases to separate them into eight different optical signals. An optical receiver for converting into an electrical signal,
A reception signal light input unit configured to input the reception signal light into a light beam;
A local oscillation light input unit that inputs linearly polarized local oscillation light into a light beam;
8 light receiving elements that emit output light separated into different phases;
A first polarization separation block that separates the local oscillation light parallel to each other while maintaining a different height from the base surface;
Two parallel lights having the same height as the light beams separated by the first polarization separation block with respect to the base surface of the received signal light, respectively, and having two orthogonal polarization components A second polarization separation block that separates the beams (Sx) and (Sy);
A λ / 4 wavelength plate that circularly polarizes two linearly polarized light beams obtained from the first polarization separation block;
The received signal light having the same height with respect to the base surface and the local oscillation light beams that have passed through the λ / 4 wavelength plate are incident on the same position while maintaining a perpendicular relationship with each other. A non-polarizing beam splitter that splits the emitted light,
A first reflecting means for reflecting either the received signal light or the local oscillation light to be incident on the non-polarizing beam splitter and reflecting the light branched by the non-polarizing beam splitter;
The light branched by the non-polarization beam splitter is incident directly and through the first reflecting means, and is separated into horizontal polarization and vertical polarization according to the polarization state, and each reflected light is output from the output unit. A polarizing beam splitter leading to four outputs,
Second reflecting means for reflecting each light that has passed through the polarizing beam splitter and guiding it to the other four output units of the output unit,
An optical receiver characterized in that a light beam from the reception signal light input unit and the local oscillation light input unit and a light beam to the light receiving element are arranged in parallel. A differential optical demodulator that separates and demodulates the received signal light into four different phase optical signals based on the difference between the received signal light and the signal light one bit before,
A received signal light input unit that receives the received signal light to form a light beam;
A first non-polarizing beam splitter for branching the light beam of the received signal light input unit;
A λ / 4 wavelength plate for circularly polarizing a linearly polarized light beam branched by the first non-polarizing beam splitter;
Four output units for emitting output light obtained by separating received signal light into four different phases;
The light beam branched by the first non-polarizing beam splitter and incident on the light beam that does not pass through the λ / 4 wavelength plate and the light beam that has passed through the λ / 4 wavelength plate while maintaining a perpendicular relationship with each other. A second non-polarizing beam splitter that branches by photosynthesis,
First reflection means for reflecting either the received signal light or the local oscillation light to be incident on the non-polarized beam splitter and reflecting the light branched by the non-polarized beam splitter;
The light separated by the non-polarization beam splitter is incident directly and through the first reflecting means, and is separated into horizontal polarization and vertical polarization according to the polarization state, and the respective reflected light is separated from the output unit. A polarizing beam splitter leading to two of the outputs,
Second reflecting means for reflecting each light that has passed through the polarizing beam splitter and guiding the light to two other output units of the output unit,
The reception signal light input unit and the output unit are arranged in the same direction, and the two reception signal light beams branched by the first non-polarization beam splitter reach the second non-polarization beam splitter. The optical demodulator is characterized in that the branch path is formed so that the time difference between them corresponds to the reciprocal of the symbol rate of the received signal light. The received signal light (Sx, Sy) that is polarization-multiplexed by two orthogonally polarized signal lights is separated in the polarization state, and the received signal light is determined by the difference between the separated received signal light and the signal light one bit before. Is a differential optical demodulator that separates and demodulates the optical signal into eight different-phase optical signals,
A reception signal light input unit configured to input the reception signal light into a light beam;
8 output units for emitting output light separated into different phases;
A polarization separation block that separates the received signal light into two parallel light beams (Sx) and (Sy) that maintain different heights with respect to the base surface and have two orthogonal polarization components;
A λ / 4 wavelength plate that circularly polarizes two linearly polarized light beams branched from the polarization separation block;
The received signal light having the same height with respect to the base surface and the delayed received signal light beams that have passed through the λ / 4 wavelength plate are incident on the same position while maintaining a perpendicular relationship with each other, A non-polarizing beam splitter that splits the incident light;
First reflection means for reflecting either the received signal light or the delayed received signal light to be incident on the non-polarized beam splitter and reflecting the light branched by the non-polarized beam splitter;
The light branched by the non-polarization beam splitter is incident directly and through the first reflecting means, and is separated into horizontal polarization and vertical polarization according to the polarization state, and each reflected light is output from the output unit. A polarizing beam splitter leading to four outputs,
Second reflecting means for reflecting each light that has passed through the polarizing beam splitter and guiding it to the other four output units of the output unit,
The reception signal light input unit and the output unit are arranged in the same direction, and the two reception signal light beams branched by the first non-polarization beam splitter reach the second non-polarization beam splitter. An optical demodulator in which a branch path is formed such that the time difference between the two corresponds to the reciprocal of the symbol rate of the received signal light.

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