JP2006267078A - Optical measuring instrument - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polarization monitor using a reduced number of inexpensive components, capable of attaining sufficient precision by a simple manufacturing process, and capable manufacturing easily the polarization monitor of high performance. <P>SOLUTION: In this polarization monitor, a parallel beam is divided into four beams by a prism, and the respective beams get incident into three or four polarizer areas having different axial azimuths formed on a sheet of substrate. The present invention uses the polarization monitor wherein a transmittance of the beam in any of the polarizer areas gets minimum or 1/2 of maximum, when the transmittance of the beam in different one of the polarizer areas gets maximum, and wherein relative angles of transmitted polarization directions in perpendicular incidence into the respective areas of a polarization array are shifted by a significant level from 0° or integer times of π/4. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical measuring instrument for measuring a polarization state among optical measuring instruments used in fields such as optical fiber communication, optical measurement, and optical control.

  Optical parameters include wavelength, optical power, and polarization state. In communication, the wavelength is determined by ITU, etc., and the signal is transmitted according to the power level. On the other hand, the polarization state is often monitored for control (compensation) of polarization mode dispersion that causes disturbance of the optical signal waveform. In general, a measuring instrument that measures the polarization state also serves as an optical power measuring instrument. Therefore, in an environment where the wavelength is fixed, the state of the optical signal can be specified using an optical measuring instrument called a polarization monitor. . This shows that polarization monitoring is important as an optical measuring instrument.

Although there are many structures known as a conventional polarization monitor, a configuration using reflected light is not suitable for accurate measurement because it involves a change in polarization state and polarization-dependent loss during reflection. Further, as a configuration not using reflected light, a configuration described in Patent Document 1 and a method described in Patent Document 2 are methods in which the same beam is incident on a polarizer array having different axial directions (a part of the beam also passes through the wave plate). The configuration can be raised. In addition, the beam is divided into four by a prism, and each of the four divided beams is received by a photodiode (hereinafter referred to as a PD) through a polarizer having a different axial orientation, a combination of a polarizer and a wave plate, or a blank path. In addition, a configuration described in Patent Document 3 that calculates the polarization state from the received light intensity of each PD is known.
United States Patent No. 4,158,506 International patent information WO2004008196 Japanese Patent No. 3103954 Japanese Patent No. 3325825 Naoki Hashimoto, Tsutomu Aoyama, Nao Sato, Osamu Ishikawa, Shojiro Kawakami, Photonic Crystal Polarization Monitor, The 65th JSAP Autumn Meeting, 2a-ZC-5, September 2, 2004. Toyohiko Yadagai “Introduction to Applied Optical Measurement”, pp42-45, Maruzen Co., Ltd., February 15, 2005

  In the configuration described in Patent Document 1, the light receiving unit is divided into six parts. However, as described in Patent Document 2 and Non-Patent Document 1, there are four pieces of data necessary for measuring Stokes parameters and DOP, which is excessive. is there.

  The configuration described in Patent Document 2 is excellent in that the individual axis adjustment of the polarizer is unnecessary, but it is necessary to use an expensive integrated light receiving element array as compared with a single light receiving element, and four There is a problem that the loss is large because the center of the beam is incident on the boundary of the light receiving unit.

  In the configuration described in Patent Document 3, four wedges are joined to form one prism, but such a prism is difficult to assemble and tends to be expensive. Further, in any of the polarization monitors described in Patent Document 1 to Patent Document 3, the angle between the polarizers is required to be an exact integral multiple of π / 4 (rad). In order to satisfy the degree of polarization (DOP) suitable for practical use, it is not practical considering that the required alignment accuracy is 0.05 ° or less.

  In view of the above, an object of the present invention is to realize a polarization monitor that is inexpensive and uses a small number of components, can obtain sufficient accuracy with a simple manufacturing process, and can easily produce a high-performance polarization monitor.

  According to the present invention, there is provided a polarization monitor including a parallel beam source, at least one prism and at least one quarter-wave plate, and a polarizer array formed on the same substrate, the one or two prisms. , The parallel beam is divided into four, the quarter wavelength plate and the first region of the polarizer array are arranged in the first branch optical path, and the second, third, and fourth optical paths are respectively in the polarizer array. The second, third, and fourth regions are arranged, and the incident directions of the beams with respect to the respective regions of the polarizer array are all different, or the incident directions of the beams incident on at least two regions are different from each other, and either When the transmission of the beam to the region of the region becomes maximum, the transmittance of the beam of any one of the different regions becomes about half of the minimum or maximum value, and the transmission polarization method at normal incidence of each region of the polarizer array Relative angular uses a polarization monitor are shifted a significant extent from an integral multiple of 0 degrees or [pi / 4.

  The polarizer axis angle αn ′ is a polarizer array that satisfies the relationship of Equation 1 with respect to the incident angle θn of the beam.

  Further, the incident angle θ with respect to each region of the polarizer array is the same, and the angle between the axial orientations of each region of the polarizer array satisfies the combinations of Equations 2, 3, 4, and 5. It is also effective to use a polarizer array.

  Furthermore, it is effective to use a polarizer array in which the angle between the axial orientations of the respective regions of the polarizer array satisfies Equations 6, 7, and 8.

  Further, in the present invention, the parallel beam is divided into four by a quadrangular pyramid prism having five surfaces that are not parallel to each other as an optical path, and the beam is incident at a position symmetrical to the boundary line of the polarizer array. Alternatively, a parallel beam is divided into four using a pentagonal prism having two non-parallel three surfaces as an optical path, and the beam is incident on a position symmetrical to the boundary line of the polarizer array.

Example 1

  A first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a perspective view showing the configuration of the first embodiment of the present invention. Optical fiber 101, collimating lens 102, pentagonal prism 103, pentagonal prism 104, quarter-wave plate 105, photonic crystal polarizer array 106, PD107 with lens, PD108 with lens, PD109 with lens, PD110 with lens Consists of.

  FIG. 2 is a diagram in which the progress of the light beam is added to FIG. The light emitted from the optical fiber 101 is converted into a parallel beam by the collimator lens 102, is incident so that the center of the beam overlaps the apex of the pentagonal prism 103, and the beam is divided into two and emitted in an oblique direction. Next, the two beams are incident so that the centers of the two beams overlap with the apex of the pentagonal prism 104, and the individual beams are divided into two, emitted in an oblique direction, and divided into four. Thereafter, only the beam 201 is transmitted through the quarter-wave plate 105, and the four beams 201 to 204 are incident on the photonic crystal polarizer array 106. Next, although the transmittance varies depending on the incident polarization state, the light enters the PDs 107 to 110 respectively. The incident polarization state can be known by analyzing the received light intensity of the four PDs 107 to 110. Regarding the incident polarization state parameter (Stokes parameter), non-patent document 1 describes general matters, and in particular, non-patent document 2 describes matters relating to the polarization monitor.

  Next, the axial direction and transmission polarization direction of the photonic crystal polarizer array 106 will be described. FIG. 3 is a schematic diagram of the photonic crystal polarizer array used. Region 301 has an axial orientation of 0.21 °, region 302 has an axial orientation of −89.79 °, region 303 has an axial orientation of 45 °, and region 304 has The axial direction is −45 °. Each incident angle θ is 7 °. Although the relative angle of the axial direction of each region is significantly different from an integer multiple of π / 4, the polarization state of the output light from the optical fiber 101 is a deviation that maximizes the transmittance with respect to the region 303. When in a wave state, the transmittance of the region 304 is minimum, the transmittance of the region 302 is 1/2 of the maximum value, and the transmittance of the region 301 is 1/2 of the maximum value. (The relative angle of the transmitted polarization direction perceived by each beam is an integral multiple of π / 4)

  Next, a more general explanation is given. In the present embodiment, the four beams are incident on the respective regions of the polarizer array in different directions at the same incident angle (four branches in four directions), but the incident direction of the beam and the axial direction of the polarizer, Since the transmission polarization direction number 9 is related to the polar angle θn, the azimuth angle φn, and the polarizer axis direction αn ′ among the polarization directions that are actually transmitted, Expression 1 is satisfied.

  Therefore, when the angle between the transmission polarization directions αn ′ of each optical path needs to satisfy any of 0, π / 4, and π / 2, and the polar angle is common as in this embodiment, If the azimuth angle is determined every 90 degrees, the axial azimuth angle of each region of the polarizer array needs to satisfy the combinations of Equation 2, Equation 3, Equation 4, and Equation 5. It can be said that the example areas 301 to 304 are filled with sufficient accuracy. In this configuration, the numbering of each region of the polarizer array is for convenience, and it will be appreciated by those skilled in the art that there is no problem even if the regions of the polarizer array, for example, the regions 302 and 304 are replaced. It will be easy to understand.

  Next, a method for manufacturing the photonic crystal polarizer array 106 will be described. Based on Patent Document 2 and Patent Document 4, the photonic crystal array 106 is formed by alternately forming amorphous silicon hydride and silicon dioxide (hereinafter referred to as SiO2) on a quartz substrate on which irregularities are formed by a process combining EB drawing and etching. It is a self-cloning type two-dimensional photonic crystal deposited in 14 cycles, and its operating wavelength is 1.55 μm for the communication wavelength. The in-plane 0.5 μm is common to each region, the stacking cycle is 0.63 μm, and the film thickness ratio between hydrogenated amorphous silicon and SiO 2 is 4: 6. In addition to the periodic multilayer film made of hydrogenated amorphous silicon and SiO2, antireflection films made of Nb2O5 and SiO2 are laminated on the uppermost layer and the lowermost layer. The extinction ratio is 50 dB or more, and the insertion loss is 0.5 dB or less.

  Next, the design of light beams and other optical components will be described.

  First, the apex angle of the pentagonal prisms 103 and 104 is 150 °, and the separation angle when the beam is incident on the center is about 14 °. In this embodiment, two pentagonal prisms are used, but they are easier to manufacture and cheaper as a result than a pyramid prism having the same function. However, it also has a demerit that increases the overall size, but there is no practical problem as long as two pentagonal prisms are used as in this embodiment. The beam diameter was set to 780 μm in consideration of the loss due to scattering at the ridge line of the prism and the overall dimensions. In addition, one PD is used for each beam for each beam. However, as described above, the tolerance for alignment is larger than that in which four PDs are integrated. Each beam is obliquely incident on the PD, which is effective for eliminating reflected return light.

  The work accuracy required for the pentagonal prism is further explained. When the tolerance of the apex angles of the pentagonal prisms 103 and 104 is within ± 0.2 °, the incident angle with respect to each region of the photonic crystal polarizer array 106 varies within a range of ± 0.1 °. This variation in incident angle does not affect DOP accuracy.

  In this embodiment, an inexpensive pentagonal prism is used to divide the beam into four diagonal directions, align the axis direction of the polarizer array with the incident direction of the beam, and deviate from the normal angular relationship, sacrificing accuracy. An inexpensive polarization monitor can be realized without doing so. Further, since the alignment of the polarizer is unnecessary, the manufacturing cost is low. Regarding the alignment of the wave plate, since it can be compensated by calibration if the deviation is about the mechanical accuracy, there is no need for this alignment. Further, the alignment of each pentagonal prism and lens-equipped PD is easy because compensation by calibration is effective and sufficient tolerance is ensured. In this embodiment, a DOP accuracy of 1% or less can be realized.

  Although not shown in the figure, a holder and a case for supporting the parts constituting this embodiment are naturally necessary, and the parts, the holder, and the case are joined by adhesive, solder, YAG welding, and the like.

(Example 2)

  A second embodiment of the present invention will be described with reference to FIGS. FIG. 4 is a perspective view showing the configuration of the second embodiment of the present invention. The optical fiber 401, the collimating lens 402, the pentagonal prism 403, the pentagonal prism 404, the pentagonal prism 405, the quarter wavelength plate 406, the photonic crystal polarizer array 407, and PDs 408 to 411 are included. The optical fiber 401, the collimating lens 402, the pentagonal prism 403, and the pentagonal prism 404 are the same as those described in the first embodiment, and the pentagonal prism 404 and the pentagonal prism 405 are the same.

  In this configuration, since the beam transmitted through the pentagonal prism 405 has a constant distance in the y direction, the distance between the PD 408 and the PD 411 can be made smaller than in the first embodiment. This embodiment is suitable for applications in which there are few size restrictions on the width (x-axis direction) and severe size restrictions on the height (y-direction).

  Next, the axial direction and transmission polarization direction of the photonic crystal polarizer array 407 will be described. FIG. 5 is a schematic diagram of the photonic crystal polarizer array used. The region 501 has an axial orientation of 0 °, the region 502 has an axial orientation of 0 °, the region 503 has an axial orientation of 45.21 °, and the region 504 has an axial orientation. -44.79 °. Each incident angle θ is 7 °. Although the relative angle of the axial direction of each region deviates from an integer multiple of π / 4, the transmitted polarization direction perceived by each beam is characterized by an integer multiple of π / 4. .

  In this embodiment, four beams are incident on each region of the polarizer array in two different directions symmetrical with respect to the yz plane at the same incident angle (four branches in two directions). Between the incident direction of the beam and the axial direction of the polarizer and the polarization direction of the actual transmission, the transmission polarization direction αn is expressed by the following equation (9) with respect to the polar angle θn, the azimuth angle φn, and the axial direction αn ′ of the polarizer. And the angle between the transmission polarization directions αn ′ of each optical path needs to satisfy one of 0, π / 4, and π / 2. It is necessary that the angle satisfies the expressions 6, 7, and 8. It can be said that the regions 501 to 504 of this embodiment are filled with sufficient accuracy.

  The advantages and characteristics of the present embodiment over the conventional example are almost the same as those of the first embodiment, but the required size is reduced instead of increasing the cost by the number of parts.

Example 3

  A third embodiment of the present invention will be described with reference to FIGS. FIG. 6 is a perspective view showing the configuration of the third embodiment of the present invention. An optical fiber 601, a collimating lens 602, a quadrangular pyramid prism 603, a quarter wavelength plate 604, a photonic crystal polarizer array 605, a quadrangular pyramid prism 606, and PDs 607 to 610.

  FIG. 7 is a perspective view in which an optical path is added to FIG. The light emitted from the optical fiber 601 is converted into parallel light by the collimator lens 602, is incident so that the center of the beam overlaps the apex of the quadrangular pyramid prism 603, and the beam is divided into four and emitted in an oblique direction. Next, the beam divided into the quadrangular pyramid prism 603 is incident on the photonic crystal polarizer array 605 after transmitting only the beam 601 in FIG.

  Next, the light beams are incident on the quadrangular pyramid prism 606, and the traveling directions of the four beams are the same, and the transmittance varies depending on the incident polarization state, but the light beams are incident on the PDs 607 to 610. The incident polarization state can be known by analyzing the received light intensity of the four PDs 607 to 610 described above.

  FIG. 7 is a schematic front view of the photonic crystal polarizer array 605 used in FIG. 5. The first region 801 has an axial orientation of 90 °, the second region 802 has an axial orientation of −44.79 °, and the third region 803. The fourth region 704 has an axial orientation of 90 ° and is the same as the first region 801. The fourth region 704 has an axial orientation of 44.21 ° and is divided into four regions. The axial orientation of each region in the photonic crystal polarizer array 605 is determined in the same manner as in the first embodiment. It is in the first region 801 that the beam transmitted through the wave plate enters. This photonic crystal polarizer array 605 is composed of a self-cloning type two-dimensional photonic crystal in which hydrogenated amorphous silicon and SiO 2 are alternately formed on a quartz substrate having irregularities formed by a process combining EB drawing and etching.

  Next, the design of the light beam will be described. First, the apex angles of the quadrangular pyramid prisms 603 and 606 are 150 °, and the separation angle when the beam is incident on the center is about 14 ° in both the vertical and horizontal directions (7 ° symmetrically with respect to the z axis). The beam diameter was set to 780 μm in consideration of the loss due to the ridgeline of the prism and the overall dimensions. In this case, the loss due to vignetting is suppressed to 0.3 dB or less. In addition, although one PD is used for each beam, the PD is arranged with an inclination of about 2 ° with respect to the incident beam, and multiple reflections between the PD and the photonic crystal polarizer array and the PD reflected light are arranged. It is also effective to prevent the light from entering other PDs. It is also effective to add a cylinder that blocks the reflected light to the periphery of the PD.

  The advantages and characteristics of the present embodiment over the conventional example are almost the same as those of the first embodiment, but the required size is reduced instead of increasing the component cost. The present embodiment has an advantage that the dimensions in the x direction (width) and the y direction (height) are smaller than those in the first embodiment.

  As described above, according to the present invention, a high-performance polarization monitor can be easily manufactured. Furthermore, it is inexpensive because it uses inexpensive parts, has a small number of parts, and does not require polarizer alignment. Although the present invention has been described with reference to several embodiments, it will be apparent to those skilled in the art that the present invention can be variously modified within the scope of the claims.

The perspective view which shows the structure of 1st Embodiment. 1 is a perspective view in which a light beam is added to FIG. Front view of photonic crystal polarizer array 106 The perspective view which shows the structure of 2nd Embodiment. Front view of photonic crystal polarizer array 407 The perspective view which shows the structure of embodiment of FIG. FIG. 5 is a perspective view in which a light beam is added. Front view of photonic crystal array 605

Explanation of symbols

101 optical fiber 102 collimating lens 103 prismatic prism 104 pentagonal prism 104
105 1/4 wavelength plate 106 Photonic crystal polarizer array 107-110 PD with lens
201 to 204 Beams 301 to 304 Photonic crystal polarizer array region 401 Optical fiber 402 Collimate lens 403 Pentagram prism 404 Penta prism 405 Penta prism 406 1/4 wavelength plate 407 Photonic crystal polarizer array 408 411 PD with lens
501 to 504 Photonic crystal polarizer array region 601 Optical fiber 602 Collimator lens 603 Square pyramidal prism 604 1/4 wavelength plate 605 Photonic crystal polarizer array 606 Quadrangular pyramid prism 607 to 610 PD with lens
701-704 Beam 801-804 Region of photonic crystal polarizer array

Claims (7)

  A parallel beam source, at least one light branching means and at least one quarter-wave plate, a polarizer array formed on the same substrate having at least three regions having different transmission polarization directions, and four photodiodes A parallel beam is divided into four by the one or two optical branching means, a quarter wavelength plate and a first region of a polarizer array are arranged in the first branching optical path, The second, third, and fourth optical paths are respectively provided with the second, third, and fourth regions of the polarizer array, and the incident direction of the beam with respect to each region of the polarizer array is all or at least two regions. When the incident directions of the beams incident on the beam are different from each other and the transmittance of the beam to any region is maximized, the transmittance of the beam in any region is about 1 which is the minimum or maximum value. The relative angle of the transmitted polarization direction at normal incidence in at least two regions of the polarizer array is arranged at an angle different from 0 degrees or an integral multiple of π / 4. Optical measuring instrument.   In an orthogonal coordinate system in which the traveling direction of the original parallel beam is the z direction, the incident angle of the branched light flux with respect to each region of the polarizer array is φ and θ in polar coordinate display, and the polarizer array projected onto the xy plane Transmission polarization directions α1 to α4 include a transmission polarization direction serving as a reference out of (0, π / 4, 3π / 4, π / 2) with any transmission polarization direction as a reference. The transmission polarization direction αn ′ (where n is the number of the polarizer region) at normal incidence of the polarizer array region is αn ′ = arctan [{cos (αn) cos (θn ) Sin (φn) + sin (αn) cos (φn)} / {cos (αn) cos (θn) cos (φn) −sin (αn) sin (φn)}] Optical measurement according to 1 Vessel.   The incident angle with respect to each region of the polarizer array is the same, and the angle between the axial orientations of each region of the polarizer array is α1 ′ = arctan [{cos (θ) sin (φ1) + cos ( φ1)} / {cos (θ) cos (φ1) −sin (φ1)}], α2 ′ = arctan [{cos (θ) sin (φ1) −cos (φ1)} / {cos (θ) cos (φ1 ) + Sin (φ1)}], α3 ′ = − arctan [1 / cos (θ)], α4 ′ = arctan [cos (θ)].   The angle between the axial orientations of the respective regions of the polarizer array is | αn′−αn + 1 ′ | = arctan [cos (θ)], | αn′−αn + 2 ′ | = arctan [1 / cos (θ)], The optical measuring instrument according to claim 2, wherein | αn′−αn + 3 ′ | = 0, π / 2 is satisfied.   The polarizer array is a polarizer made of a two-dimensional photonic crystal, the periodic direction of each region is orthogonal or parallel to the axial direction, and an angle formed between the periodic directions of each region is defined in claims 1 to 4. Any of the above is satisfied in a range of ± 0.05 ° with respect to a predetermined angle   6. An optical measurement comprising a data correction mechanism including a data input / output mechanism, a recording medium on which calibration data is recorded, and an arithmetic unit in addition to the optical measuring instrument according to claim 1. vessel   A parallel beam is divided into four by one or two prisms, and the prism has an optical path with three surfaces that are not parallel to each other, or a prism with an optical path that has five surfaces that are not parallel to each other. The optical measuring instrument according to any one of claims 1 to 6, wherein:

Images