Optical signal selection device and optical signal selection method

Abstract

To digitally control a predetermined attenuation range.SOLUTION: An optical signal selection device comprises: a collimator array which has a plurality of ports arrayed along a predetermined direction, and inputs and outputs optical signals; an optical modulator which diffracts an optical signal input from a first port among the plurality of ports at a predetermined angle, and couples paths of the first port and a second port different from the first port; and a control unit which writes, into the optical modulator, a diffraction grating pattern for coupling the paths of the first port and second port, and an attenuation pattern for suppressing crosstalk between the first port and second port.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to an optical signal selection device and an optical signal selection method. [Background technology]

[0002] High-speed, large-capacity information communication technology using optical wavelength division multiplexing (WDM) is known. Patent Document 1 discloses a technology for controlling the amount of attenuation in the gain equalization operation of a wavelength selective switch using LCOS (Liquid Crystal On Silicon) and a diffraction grating. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-156647 Summary of the Invention [Problem to be solved by the invention]

[0004] The prior art does not describe a method for controlling a predetermined amount of attenuation by quantizing the attenuation range from 0 to -10 dB in logarithmic intervals in 0.1 dB increments, which is desired in a wavelength selective switch.

[0005] An object of the present disclosure is to provide an optical signal selection device and an optical signal selection method that can digitally control a predetermined attenuation range. [Means for solving the problem]

[0006] The optical signal selection device disclosed herein includes a collimator array in which a plurality of ports are arranged along a predetermined direction for inputting and outputting optical signals; an optical modulator that diffracts an optical signal input from a first port among the plurality of ports at a predetermined angle to couple a path between the first port and a second port different from the first port; and a control device that writes, into the optical modulator, a diffraction grating pattern for coupling the paths between the first port and the second port and an attenuation pattern for suppressing crosstalk between the first port and the second port.

[0007] The optical signal selection method disclosed herein includes the steps of diffracting an optical signal input from a first port among a plurality of ports at a predetermined angle to couple a path between the first port and a second port different from the first port, and writing a diffraction grating pattern for coupling the path between the first port and the second port and an attenuation pattern for suppressing crosstalk between the first port and the second port into an optical modulator. [Effects of the Invention]

[0008] According to the present disclosure, the predetermined attenuation range can be digitally controlled. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram illustrating the principle configuration of an optical signal selecting device according to the present disclosure. [Figure 2] FIG. 2 is a diagram for explaining the temperature change of the birefringence characteristics of the liquid crystal when a parallel-aligned liquid crystal cell using positive liquid crystal is used. [Figure 3A] FIG. 3A is a diagram showing a basic drawing pattern according to the embodiment. [Figure 3B] FIG. 3B is a diagram for explaining a writing pattern for performing parabolic (spherical) aberration correction according to the embodiment. [Figure 3C] FIG. 3C is a diagram for explaining correction for a combination of FIG. 3A and FIG. 3B. [Figure 4] FIG. 4 is a diagram illustrating an example of component arrangement in a light selecting device according to the present disclosure. [Figure 5] FIG. 5 is a diagram for explaining a method for controlling the amount of attenuation according to the first embodiment. [Figure 6] FIG. 6 is a diagram showing a first example of a binary mask according to the first embodiment. [Figure 7] FIG. 7 is a diagram showing a second example of a binary mask according to the first embodiment. [Figure 8] FIG. 8 is a diagram showing a third example of a binary mask according to the first embodiment. [Figure 9] FIG. 9 is a diagram for explaining the light intensity pattern of the irradiation beam according to the first embodiment. [Figure 10] FIG. 10 is a diagram for explaining the integral value of the Gaussian distribution according to the first embodiment. [Figure 11] FIG. 11 is a table showing control patterns of a binary mask according to the first embodiment. [Figure 12] FIG. 12 is a diagram showing a first example of a binary mask according to the second embodiment. [Figure 13] FIG. 13 is a diagram showing a second example of a binary mask according to the second embodiment. [Figure 14] FIG. 14 is a diagram showing a third example of a binary mask according to the second embodiment. [Figure 15] FIG. 15 is a diagram showing a fourth example of a binary mask according to the second embodiment. [Figure 16] FIG. 16 is a diagram illustrating an example of the amount of attenuation and the writing pattern according to the second embodiment. [Figure 17] FIG. 17 is a diagram for explaining the WATT method according to the third embodiment. [Figure 18] FIG. 18 is a diagram for explaining the relationship between the channel slot and the binary mask according to the third embodiment. [Figure 19] FIG. 19 is a flowchart showing the flow of the drawing pattern creation process according to the third embodiment. [Figure 20] FIG. 20 is a flowchart showing the flow of the LUT comparison process according to the third embodiment. [Figure 21] FIG. 21 is a diagram showing an example of a background pattern and a selection pattern when curved-image correction according to the fourth embodiment is not performed. [Figure 22] FIG. 22 is a diagram schematically showing the relationship between the selection pattern and the irradiation beam according to the fourth embodiment. [Figure 23] FIG. 23 is a diagram for explaining the shape of the irradiation beam according to the fourth embodiment. [Figure 24] FIG. 24 is a diagram for explaining a correction pattern according to the fourth embodiment. [Figure 25] FIG. 25 is a diagram showing an example of a shape obtained by a simulation of a correction pattern according to the fourth embodiment. [Figure 26] FIG. 26 is a diagram showing a simulation result according to the fourth embodiment. [Figure 27] FIG. 27 is a graph showing the simulation results according to the fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. Note that the present disclosure is not limited to these embodiments, and in the following embodiments, the same components are designated by the same reference numerals, and redundant description will be omitted.

[0011] [Embodiment] (Optical signal selection device) 1 is a diagram illustrating the principle configuration of an optical signal selecting device according to the present disclosure. The optical signal selecting device 1 according to the present disclosure is a free space optics (FSO) wavelength selective switch that uses LCOS (Liquid Crystal On Silicon) for the optical modulator.

[0012] 1, the optical signal selecting device 1 includes a collimator array 10, a beam expanding optical system 12, a spectroscopic optical system 14, a position angle converting optical system 16, an optical modulator 18, and a control device 20. The optical signal selecting device 1 is a type of WSS (Wavelength Selective Switch).

[0013] The collimator array 10 has a plurality of ports for inputting and outputting optical signals. The plurality of ports are arranged along a predetermined direction. Among the plurality of ports, the input port outputs the optical signal S1 toward the beam expanding optical system 12.

[0014] The beam expanding optical system 12 expands and shapes the optical signal S1 to a predetermined aspect ratio, and outputs the expanded optical signal S1 to the spectroscopic optical system 14.

[0015] The spectroscopic optical system 14 disperses the optical signal S1 received from the beam expanding optical system 12, separates the optical signal S1 by wavelength, and outputs the separated optical signals S1. The optical signals S1 of each wavelength are arranged in the direction of the paper. The spectroscopic optical system 14 outputs the multiple optical signals S1 separated by wavelength to the position angle conversion optical system 16.

[0016] The position angle conversion optical system 16 converts the multiple optical signals S1 received from the beam expansion optical system 12 into parallel optical signals at respective predetermined heights, and outputs them to the same height position of the optical modulator 18. The position angle conversion optical system 16 is realized by a single lens or a spherical mirror, etc.

[0017] The optical modulator 18 angle-modulates the optical signal S1 received from the position angle conversion optical system 16 so that the optical signal S1 is coupled to a predetermined output port. The optical modulator 18 is realized by, for example, LCOS. The optical modulator 18 angle-modulates the optical signal S1 and outputs an optical signal S2 to the position angle conversion optical system 16.

[0018] The position angle conversion optical system 16 converts the optical signal S2 into a parallel beam of a predetermined height. The optical signal S2 travels in the opposite direction to the optical signal S1, through the spectroscopic optical system 14, the beam expansion optical system 12, and the collimator array 10. The optical signal S2 is converted back into parallel light having the same beam waist as when it was incident, and is coupled to a predetermined output port of the collimator array 10.

[0019] The control device 20 controls each part of the optical signal selecting device 1. The control device 20 has, for example, an information processing device such as a CPU (Central Processing Unit) or an MPU (Micro Processing Unit), and a storage device such as a RAM or a ROM. The control device 20 executes a program that controls the operation of the optical signal selecting device 1 according to the present invention. The control device 20 may be realized by an integrated circuit such as an ASIC (Application Specific Integrated Circuit) or an FPGA (Field Programmable Gate Array). The control device 20 may be realized by a combination of hardware and software.

[0020] The control device 20 controls the optical modulator 18. The control device 20 draws an astigmatism-correcting phase modulation pattern on the optical modulator 18, which acts as a one-dimensional concave lens or convex mirror to eliminate astigmatic differences caused by the phase angle conversion optical system of the optical modulator 18. The control device 20 draws a diffraction grating pattern on the optical modulator 18 to couple the paths of a first port and a second port among the multiple ports of the optical modulator 18. The control device 20 draws a blazed diffraction grating pattern on the optical modulator 18 as the diffraction grating pattern, which controls the output beam to a predetermined angle. The control device 20 writes an attenuation pattern on the optical modulator to suppress crosstalk between the first port and the second port. The control device 20 draws a phase modulation pattern, in which the astigmatism-correcting phase modulation pattern and the blazed diffraction grating pattern are superimposed, on the optical modulator 18, and uses the optical modulator 18 as an angle modulator for port switching.

[0021] Therefore, the optical signal S1 incident from the input port maintains its energy minus the loss of the optical system and is irradiated onto the optical modulation section of the optical modulator 18. For this reason, the optical modulator 18 is provided with two types of areas: an angle modulation section (selection region) where the optical signal S1 is coupled to the output port, and an angle modulation section (non-selection region) where the optical signal S1 is not coupled to the output port. The control device 20 can control the amount of attenuation by controlling the area ratio between the selection region and the non-selection region. Note that when applied to an optical system that does not require astigmatism correction, the angle modulation section (selection region) and the angle modulation section (non-selection region) can be blazed diffraction grating patterns that do not superimpose an astigmatism-corrected phase modulation pattern; however, the following description will be given assuming that a phase modulation pattern with astigmatism correction is used.

[0022] FIG. 2 is a diagram illustrating the temperature change in the birefringence characteristics of a liquid crystal when a parallel-aligned liquid crystal cell using positive-type liquid crystal is used. The horizontal axis of FIG. 2 represents applied voltage, and the vertical axis represents retardation (Δnd). FIG. 2 shows a graph when the liquid crystal is nematic. As shown in FIG. 2, dotted line 101 represents the amount of retardation change over the same voltage change range at low temperatures (e.g., 20°C). Solid line 102 represents the amount of retardation change over the same voltage change range at high temperatures (e.g., 80°C). As shown by dotted line 101 and solid line 102, the amount of retardation change decreases as the temperature increases. Note that FIG. 2 shows an example of a parallel-aligned cell, but in the case of a vertically aligned cell using negative-type liquid crystal, retardation is small when low voltage is applied and large when high voltage is applied. In this way, the change in retardation with voltage in the case of a vertically aligned cell is opposite to that in the case of a parallel aligned cell, but the range of change in retardation narrows at higher temperatures, just like in a positive liquid crystal. The phase modulation amount (phase delay) described below will be explained on the assumption that the temperature change of retardation has been corrected.

[0023] Next, an overview of a drawing pattern to be written to the optical modulator 18 according to the present disclosure will be described. Fig. 3A is a diagram showing a basic drawing pattern according to the embodiment. In Fig. 3A, the horizontal axis x represents the number of pixels [pix (pixels)], and the vertical axis y represents the phase delay [rad (radians)]. In this case, assuming that the phase tilt (Tilt in aberration theory) is b, the DC component (Piston in aberration theory) is c, and the intersection position with the x-axis is Pm as drawing parameters to be written to the optical modulator 18, the phase curve 103 for correcting the aberration of the original Tilt and Piston can be expressed by the following equation (1).

[0024]

number

[0025] The maximum phase modulation amount of light reflected and returned from the optical modulator 18 according to the embodiment is 2π (the phase amount when the wavelength λ used is 1λ is 2π). Therefore, when writing the original beam deflection phase curve into the optical modulator 18, the control device 20 divides the phase curve 103 by 2π as a remainder term, as shown by the sawtooth curve 104 in FIG. 3A, and performs folding in the main region of 2π.

[0026] 3B is a diagram illustrating a drawing pattern for performing parabolic (spherical) aberration correction according to an embodiment. In FIG. 3B, the horizontal axis x represents the number of pixels [pix], and the vertical axis y represents the phase delay [rad]. A phase curve 105 for parabolic aberration correction (which is equivalent in shape to a cylindrical lens because it mainly corrects in one direction, as described below) can be expressed by the following equation (2), where a is the curvature of the parabola vertex and Pc is the vertex coordinate of the parabola. (Note that FIG. 3B illustrates a convex lens shape, so the curvature is a negative value.)

[0027]

number

[0028] When writing a drawing pattern to the optical modulator 18, if there is a constraint of a maximum phase modulation amount of 2π, the control device 20 divides the phase curve 105 by 2π and performs folding in the main region of 2π as shown in curve 106.

[0029] FIG. 3C is a diagram for explaining the correction of a combination of FIG. 3A and FIG. 3B. In FIG. 3C, the horizontal axis x represents the number of pixels [pix.], and the vertical axis y represents the phase modulation amount [rad]. The phase curve 107 in FIG. 3C is a phase curve showing a correction that combines the DC component (Piston), the first-order phase tilt (Tilt), and the parabolic aberration correction. When writing the phase curve 107 on the optical modulator 18, the control device 20 calculates the phase curve 107 using the following equation (3), which is the sum of equations (1) and (2), and writes a curve 108 that is the remainder term obtained by dividing the phase curve 107 by 2π and folding it in the main region of 2π.

[0030]

number

[0031] In this embodiment, a, b, c, Pc, and Pm are selected as drawing parameters for drawing a drawing pattern on the optical modulator 18 used by the control device 20. Here, it is important to note that the following three independent phase modulation parameters of the optical modulator 18 are physically controllable:

[0032] 1. DC component (variable range 0 to 2π) δ: Parameter for fine-tuning the focus position 2. Tilt coefficient β: Parameter for controlling the deflection direction of the reflected beam 3. Curvature α of the paraboloid apex: Lens power or spherical aberration correction term

[0033] Therefore, the relationship between the drawing parameters of equation (3) and the physical phase modulation parameters 1 to 3 above is compared. By using δ, β, and α, the following equation (4) can be obtained.

[0034]

number

[0035] The phase modulation parameters can be uniquely described in a three-dimensional basis function space spanned by three basis functions x0, x1, and x2 (parameters δ, β, and α). On the other hand, by expanding equation (3), the following equation (5) is obtained.

[0036]

number

[0037] By comparing equations (4) and (5), equations (6), (7), and (8) are obtained.

[0038]

number

[0039]

number

[0040]

number

[0041] Note that δ may be set to 0 because it has almost no effect on beam manipulation (manipulation of the optical signal) within the range of the principal value of 2π that can be controlled by the optical modulator 18. Therefore, from equations (6) to (8), it can be seen that, for example, changing the vertex coordinate Pc of the paraboloid vertex is equivalent to the control device 20 manipulating the phase modulation parameter β (tilt coefficient) that affects the beam deflection. Therefore, the operation of shifting the vertex coordinate Pc of the paraboloid and the operation of changing the tilt coefficient b can be said to be equivalent tilt correction operations from the perspective of the phase modulation parameter β, which is a physical wavefront manipulation.

[0042] In Figures 3B and 3C, an example of an upwardly convex convex lens shape (or an equivalent concave mirror) is used as the refractive index paraboloid (the sign of the paraboloid curvature α is negative). However, in the case of a downwardly convex concave lens shape (or an equivalent convex mirror), both can be treated using the same expression by inverting the sign of the paraboloid curvature α (the sign of the paraboloid curvature becomes positive).

[0043] FIG. 4 is a diagram illustrating an example of the arrangement of components in an optical selecting device according to the present disclosure. The example illustrated in FIG. 4 illustrates an example of the arrangement of components when the optical signal selecting device 1 is viewed from above. As illustrated in FIG. 4, this embodiment has a folded arrangement structure to reduce the size of the optical signal selecting device 1. The spherical mirror 22 and the polarization separation element 24 constitute an optical element 30 that affects the coupling efficiency between ports in the present disclosure. In the example illustrated in FIG. 4, the folding of the optical signal L is described as being performed by the spectroscopic optical system 14 and the spherical mirror 22, but the present disclosure is not limited to this. For example, in the present disclosure, the folding optical system may be configured by adding a folding mirror that folds the optical signal L and a transmissive spherical lens or the like.

[0044] In an optical system in which light is obliquely incident on spherical mirror 22 as shown in Figure 4, the shape of the beam irradiated onto optical modulator 18 generates astigmatism, which changes the effective focal position of the spherical mirror, when observed on a plane (tangential plane) parallel to the plane of incidence of spherical mirror 22 as shown in Figure 4, and when observed on a plane (sagittal plane) perpendicular to the plane of incidence as shown in Figure 1. If the focal length of spherical mirror 22 when light is perpendicularly incident on spherical mirror 22 is f, the focal position ft as seen on the tangential plane when light is obliquely incident is expressed by the following equation (9), where θ is the angle of incidence.

[0045]

number

[0046] The plane perpendicular to the plane of incidence shown in Figure 1 is the sagittal plane (YZ plane), and Figure 4 shows the state as viewed from the side. In this case, the incident light and outgoing light on spherical mirror 22 are perpendicular to spherical mirror 22 when viewed from the sagittal plane, and the focal length when viewed from the side is f, but when considering the actual optical path, the focal length is longer by the amount of oblique incidence. Therefore, if the focal length is represented as fs, it can be expressed by the following equation (10).

[0047]

number

[0048] When the spherical mirror 22 is arranged for oblique incidence, the optical modulator 18 must be placed at the focal position ft of the tangential plane to improve the wavelength resolution on the optical modulator 18 surface. On the other hand, the focal position of the sagittal plane is farther away from the tangential plane, as seen in a comparison of equations (9) and (10), resulting in a mismatch in focal positions (astigmatic difference). Therefore, when the optical modulator 18 surface is placed on the tangential plane, a phase modulation pattern is applied so that the optical modulator 18 functions as a convex mirror (or a concave lens plus a flat mirror) on the sagittal plane, eliminating the effects of astigmatic difference on the reflected light. This allows the reflected light on the tangential and sagittal planes of the optical modulator 18 to be adjusted so that the end of the single-mode fiber connected to the collimator array in Figure 1 is a conjugate plane for the incident and exit light, improving the recombination efficiency of the light returning from the return path.

[0049] Therefore, in the case of an optical system such as the optical system of Figure 4 where light is obliquely incident on spherical mirror 22, the sign of the parabolic curvature shown by a in equation (3) or α in equation (4) is positive, and in addition to blazed diffraction grating-type phase modulation that controls the port coupling angle so that optical modulator 18 functions as a convex mirror (or a concave lens + flat reflecting mirror) with respect to the sagittal plane, parabolic phase modulation is also performed to correct astigmatism.

[0050] [First embodiment] A first embodiment of the present disclosure will be described.

[0051] FIG. 5 is a diagram illustrating a method for controlling the amount of attenuation according to the first embodiment. FIG. 5 shows patterns 201, 202, and 203 drawn on the optical modulator 18. Patterns 201 to 203 each represent a coupling pattern for a different port. As shown in FIG. 5, the pattern drawn on the optical modulator 18 is changed depending on the wavelength (selected channel) and the selected port. Pattern 201 is irradiated with an irradiation beam 301. Pattern 202 is irradiated with an irradiation beam 302. Pattern P3 is irradiated with an irradiation beam 303. In a given channel portion (pattern 202 shown in FIG. 5 is 1552.52 nm, and patterns 201 and 202 are examples of modulation patterns at adjacent wavelengths), the light intensity pattern distributions of irradiation beams 301 to 303 irradiated after dispersion are the same. Therefore, the pattern of the binary mask (non-selected region) that controls the amount of attenuation is defined relative to the center position of the light intensity of each irradiation beam. The irradiation pattern has a Gaussian distribution in both the vertical and horizontal directions, but the effective area A1 is determined in advance and a binary mask is defined for the effective area A1. The binary mask is also called a hybrid pattern.

[0052] Fig. 6 is a diagram showing a first example of a binary mask according to the first embodiment. Fig. 7 is a diagram showing a second example of a binary mask according to the first embodiment. Fig. 8 is a diagram showing a third example of a binary mask according to the first embodiment.

[0053] For example, as shown in Fig. 6, the control device 20 may determine effective areas A2 and A3, and provide binary masks 401 symmetrically with respect to the center positions of the vertical directions of the irradiation beams. Attenuation per unit area increases in the vertical center portions, as will be described later.

[0054] 7, the control device 20 may determine an effective area A4 in the center and provide binary masks 402 and 403 formed from the periphery. In this case, the amount of attenuation per unit area is smaller than in a binary mask formed from the center.

[0055] That is, the control device 20 switches the positions at which each binary mask is provided depending on the amount of attenuation.

[0056] 8, the control device 20 may combine binary mask 401, binary mask 402, and binary mask 403. In this case, the control device 20 controls binary mask 401, binary mask 402, and binary mask 403 so that they do not overlap with each other.

[0057] For example, as shown in FIGS. 6 to 8, by using two binary mask patterns, the attenuation amount can be set to 0 dB (no binary mask), −AdB (FIG. 6), −BdB (FIG. 7), and −CdB (FIG. 8), which is the square of the binary mask patterns (in this embodiment, 2 2 This allows for attenuation control in four ways (A = 4 ways). A, B, and C are different natural numbers. The attenuation changes depending on the area of ​​the binary mask. Here, we will explain how to determine the area of ​​the binary mask that is prepared in advance.

[0058] 9 is a diagram for explaining the light intensity pattern of the irradiation beam according to the first embodiment. Normally, the light intensity pattern of the irradiation beam irradiated onto the optical modulator 18 is a vertically elongated beam having a Gaussian light intensity distribution in both the vertical and horizontal directions. For simplicity, the following description will be given assuming that the beam has a Gaussian distribution only in the vertical direction and is constant in the horizontal direction, as shown in the left diagram of FIG.

[0059] In the right diagram of Figure 9, the horizontal axis represents the vertical position (mm) and the vertical axis represents the light intensity. In Figure 9, the vertical beam radius W(1 / e 2 If the radius at which the strength is achieved is 1.8 mm, then S = W / 2(S 2represents a parameter that represents the variance when considered as a normal distribution. ) is close to S=1 (mm), resulting in a slightly sharper Gaussian intensity distribution. In Figure 9, light intensity distribution 111 represents the light intensity distribution when S=1. Light intensity distribution 112 represents the light intensity distribution when S=2. Light intensity distribution 113 represents the light intensity distribution when S=3. In other words, if the area (integral value of light intensity) is the same overall, as the beam radius increases, the peak intensity decreases accordingly, resulting in a beam distribution that is wider overall.

[0060] FIG. 10 is a diagram illustrating the integral value of a Gaussian distribution according to the first embodiment. As shown in FIG. 10, the integral value of a Gaussian distribution can be expressed by an error function. In the upper diagram of FIG. 10, the horizontal axis is the x-axis and the vertical axis is the y-axis. In the upper diagram of FIG. 10, curve 114 represents a Gaussian distribution. In the lower diagram of FIG. 10, curve 114 represents the integral value (beam light intensity) 115 of half the entire curve 114 in the positive direction from x=0. As shown in the lower diagram of FIG. 10, integral value 115 increases rapidly from near 0 in FIG. 10 (the center of the beam) and changes less toward the periphery. Therefore, it can be seen that the attenuation of the binary mask per unit area is greater in the center and decreases toward the periphery.

[0061] FIG. 11 is a table showing binary mask control patterns according to the first embodiment. Table TB1 includes the following fields: "bit" (binary mask assignment for 5-bit control), "Ratio" (weighting for 5-bit control), "Norm." (weighting when all pixels are normalized to 1), "Calc." (calculated value when actual pixels are controlled), "a" (start pixel position of the binary mask), and "b" (end pixel position of the binary mask). Table TB1 shows an example of a 5-bit control pattern for a linear correction weighting mask when the pixel position at the center of the beam in FIG. 6 is set to 0, and the bit mask position is defined with the number of pixels as a parameter, with the inner side being a and the outer side being b. The minimum light intensity control width is 0.03 linearly, allowing for 32 levels of linear control. In this case, the number of pixels is 600, and the bit mask pattern is vertically symmetrical, with the central 300 pixels set to 0.

[0062] [Second embodiment] A second embodiment of the present disclosure will be described below. In the second embodiment, control is performed by switching binary masks at predetermined pixel positions defined in advance.

[0063] Fig. 12 is a diagram showing a first example of a binary mask according to the second embodiment. Fig. 13 is a diagram showing a second example of a binary mask according to the second embodiment. Fig. 14 is a diagram showing a third example of a binary mask according to the second embodiment. Fig. 15 is a diagram showing a fourth example of a binary mask according to the second embodiment.

[0064] In the second embodiment, as shown in Fig. 12, the control device 20 performs fine adjustments of the attenuation, such as 0.1 dB, by adjusting the areas of binary masks 404 and 405 provided in the peripheral areas relative to the central effective area A5. Also, as shown in Fig. 13, the control device 20 performs coarse adjustments, i.e., by adjusting the areas of binary masks 406 in the central areas relative to the peripheral effective areas A6 and A7. This is because, as shown in Fig. 10, the attenuation is greater in the central area than in the peripheral areas for binary masks of the same area.

[0065] The second embodiment is effective when finely controlling the attenuation amount in dB units. For example, when the attenuation amount is set from 0 to -0.5 dB, the linear attenuation amount is 0% to 10.9%. However, when the attenuation amount is set from -3 dB to -3.5 dB, even with the same 0.5 dB range, the linear attenuation amount is 50% to 55.3%. Therefore, since the attenuation amount needs to be increased by a ratio of -0.5 dB (approximately 10.9%) relative to the initially set attenuation amount (starting attenuation amount), the larger the starting attenuation amount, the more precise the attenuation control even at -0.5 dB is required. Therefore, in the second embodiment, when large attenuation control is required, the central binary mask is used, and when small attenuation control is required, the peripheral binary mask is used to control the attenuation amount.

[0066] Fig. 14 shows a pattern for controlling the amount of attenuation by combining a coarse adjustment region and a fine adjustment region. In the example shown in Fig. 14, the control device 20 fixes a binary mask 406 for coarse adjustment in the center and provides effective areas A8 and A9. The control device 20 then controls the widths of the binary masks 404 and 405 for fine adjustment relative to the effective areas A8 and A9, thereby controlling the amount of attenuation in minute steps.

[0067] However, during high attenuation control in which the area of ​​binary mask 406 is set large, as in the attenuation pattern shown in Fig. 15, it may be difficult to control the amount of attenuation in small steps simply by adjusting the area of ​​binary mask 404 and binary mask 405, depending on the number of pixels and pixel pitch of the remaining surrounding effective areas A10 and A11. In this case, control device 20 may also control the deflection pattern of irradiation beam 301 to irradiation beam 303 in the selected area. This is because, in the case of dB setting, during high attenuation control, the area of ​​the remaining selected area is smaller than the area of ​​the masked non-selected area, and therefore the number of pixels available for attenuation steps is reduced.

[0068] For example, as described above, when the attenuation amount is changed from 0 to -0.5 dB, the linear attenuation amount is 0% to 10.9%. However, when the attenuation amount is changed from -3 dB to -3.5 dB, even with the same 0.5 dB step, the linear attenuation amount is 50% to 55.3%. For the initial 0 dB step, a pixel width that is 10.9% of the pixel area of ​​the optical modulator 18 can be masked by the surrounding fine adjustment region. However, when starting from -3 dB and attenuating to -0.5 dB, the area that already has 50% light intensity is masked by the central coarse adjustment region, and 5.3% must be controlled by the peripheral fine adjustment region. Thus, when the starting attenuation amount is large and a large area of ​​the coarse adjustment region is already masked, the rate of change relative to the number of surrounding pixels to achieve the same fine adjustment range (here, -0.5 dB) must be reduced. However, because the pixel size and number of pixels of the optical modulator 18 are finite, it becomes difficult to perform fine proportional control of the high attenuation region using area modulation alone.

[0069] FIG. 16 is a diagram illustrating an example of attenuation and drawing patterns according to the second embodiment. FIG. 16 shows an example of a drawing pattern in which the attenuation is controlled in steps of −0.1 dB. FIG. 16 shows a drawing pattern 210, a drawing pattern 211, a drawing pattern 212, a drawing pattern 213, a drawing pattern 214, a drawing pattern 215, a drawing pattern 216, a drawing pattern 217, a drawing pattern 218, and a drawing pattern 219. The attenuation of the drawing pattern 210 is 0 dB. The attenuation of the drawing pattern 211 is −0.5 dB. The attenuation of the drawing pattern 212 is −1 dB. The attenuation of the drawing pattern 213 is −1.7 dB. The attenuation of the drawing pattern 214 is −1.8 dB. The attenuation of the drawing pattern 214 is −1.8 dB. The attenuation of the drawing pattern 215 is −2.5 dB. The attenuation of the drawing pattern 216 is −2.6 dB. The attenuation of the drawing pattern 217 is −3.5 dB, the attenuation of the drawing pattern 218 is −3.8 dB, and the attenuation of the drawing pattern 219 is −4.2 dB.

[0070] In Fig. 16, the areas shown in black are non-selected areas. In reality, the control device 20 writes a pattern that suppresses inter-port coupling in the non-selected areas, but this is omitted here for simplicity of explanation. In Fig. 16, the areas where the aberration correction patterns are written are selected areas. The control device 20 writes a pattern that contributes to inter-port coupling in the selected areas.

[0071] The control device 20 does not form a mask region in the writing pattern 210. The control device 20 expands the patterns in the surrounding fine adjustment regions from writing pattern 210 to writing pattern 213, and controls the attenuation to -0.7 dB. The control device 20 sets the width of the binary mask in the surrounding fine adjustment regions to 0 in writing pattern 214, writes a pattern in the central coarse adjustment region, and controls the attenuation to -1.8 dB.

[0072] Furthermore, in the drawing pattern 215, the control device 20 makes the area of ​​the central coarse adjustment region the same as that of the drawing pattern 214, and increases the area of ​​the peripheral fine adjustment region, thereby finely adjusting the amount of attenuation.

[0073] Next, in the drawing pattern 216, the area of ​​the peripheral fine adjustment region is set to 0, and a pattern is written in the central coarse adjustment region to control the attenuation to −2.6 dB.

[0074] By repeating the above-described operation, the control device 20 can digitally control the amount of attenuation at predetermined intervals, for example, from −0.1 dB to −9.6 dB.

[0075] In the second embodiment, an example was described in which the area was divided into three areas, one coarse adjustment area symmetrical to the center and two equivalent fine adjustment areas, but the present disclosure is not limited to this. The area does not have to be symmetrical as long as it is divided into multiple coarse adjustment areas and multiple fine adjustment areas, and the number of divisions may be more than three.

[0076] The second embodiment is particularly suited to area gradation in the Fourier plane of a pixel-type spatial light modulator (SLM) such as an LCOS as the light modulator 18. In devices such as LCOS, where the minimum area resolution is determined by the pixel pitch, weighting using a Gaussian distribution of the irradiated beam is used to minimize the quantization error limited by the pixel pitch, even when the pixel pitch is the same in the peripheral and central areas. This has the advantage of enabling a large attenuation range with small dB resolution. This method is called the weighted dithering ATTenuation method, hereinafter referred to as the WATT method.

[0077] [Third embodiment] A third embodiment of the present disclosure will be described below. In the third embodiment, a specific algorithm of the WATT method is set.

[0078] FIG. 17 is a diagram for explaining the WATT method according to the third embodiment. An example in which the WATT method is suitable for an LCOS as the optical modulator 18 will be described below. FIG. 17(a) is a schematic diagram of the drawing area of ​​the LCOS placed on the Fourier plane formed by the optical signal selecting device 1. Here, the number of vertical pixels of the LCOS is m, and the number of horizontal pixels is n. It is assumed that 1st to Lth channel slots are drawn in the effective area of ​​the LCOS to select a port corresponding to a predetermined wavelength (frequency). FIG. 17(a) shows patterns of channel Ch1, channel ChK, and channel ChL.

[0079] FIG. 17(b) shows the pattern of channel ChK. Channel ChK is divided into two regions, WSS region R1 and WSS region R2. WSS region R1 and WSS region R2 are also called optical modulation sections. A vertically elongated irradiation beam 311 is irradiated onto WSS region R1. A vertically elongated irradiation beam 312 is irradiated onto WSS region R2. That is, an irradiation beam is irradiated onto WSS region R1 and WSS region R2, respectively.

[0080] Fig. 18 is a diagram for explaining the relationship between a channel slot and a binary mask according to the third embodiment, Fig. 18 shows an example of a channel ChK.

[0081] 18(a) shows the relationship between the irradiation beams and their center positions. Center position O1 indicates the center position of the irradiation beam 311. Center position O2 indicates the center position of the irradiation beam 312.

[0082] 18(b) shows a drawing pattern for coupling from an input port to an output port. The control device 20 writes a selection pattern 501, for example, that couples a predetermined input port A to a predetermined output port B, into the channel ChK.

[0083] 18(c) shows a drawing pattern for not coupling an input port to an output port. When the output of a predetermined input port A is not to be coupled to any port, the control device 20 writes a non-selection pattern 502 to the channel ChK.

[0084] Fig. 18(d) shows a drawing pattern for performing coarse adjustment of the attenuation amount. When performing the coarse adjustment shown in Fig. 13, the control device 20 writes a non-selection pattern 502 between row numbers a and b near the center position O1 of channel ChK and between row numbers c and d near the center position O2, as shown in Fig. 18(d). The control device 20 writes a selection pattern 501 in the effective area of ​​the other channel ChK.

[0085] Fig. 18(e) shows a drawing pattern for fine-tuning the amount of attenuation. When performing the fine adjustment shown in Fig. 12, the control device 20 writes a non-selection pattern 502 between row numbers e and f near the end of the irradiation beam 311 of channel ChK, and between row numbers g and h near the end of the irradiation beam 312, as shown in Fig. 18(e). The control device 20 writes a selection pattern 501 in the other effective areas of channel ChK.

[0086] In the method of switching between selected and non-selected patterns using a binary mask according to the third embodiment, even when non-selected regions are distributed at intervals, the horizontal pattern of the channel slots remains the same, and a predetermined attenuation pattern can be formed by switching only the vertical row pixel positions. For example, in the case of combining the switching points shown in Figures 18(d) and 18(e), the control device 20 writes a selected pattern 501 in the region from row number 1 to row number e-1 and a non-selected pattern 502 in the region from row number e to row number f. The control device 20 writes the selected pattern 501 in the region from row number f+1 to row number a-1 and a non-selected pattern 502 in the region from row number a to row number b. The control device 20 writes the selected pattern 501 in the region from row number b+1 to row number c-1 and a non-selected pattern 502 in the region from row number c to row number d. The control device 20 writes a selection pattern 501 in the area from row number d+1 to row number g-1, and writes a non-selection pattern 502 in the area from row number g to row number h. The control device 20 writes the selection pattern 501 in the area from row number h+1 to row number m.

[0087] (Drawing pattern creation process) Next, a description will be given of a drawing pattern creation process according to the third embodiment. Fig. 19 is a flowchart showing the flow of the drawing pattern creation process according to the third embodiment.

[0088] Before starting the process, the pair of switching ports and the amount of attenuation are determined, and then the process is started. The pair of switching ports and the amount of attenuation can be specified by the user using a command, for example.

[0089] When the combination of switching ports and the attenuation amount are determined, the control device 20 selects a port switching combination pattern (step S10). At this time, even if the port switching combination pattern is different, the attenuation amount pattern is common depending on the attenuation amount. Then, the process proceeds to step S12.

[0090] The control device 20 checks the amount of attenuation (ATT amount) (step S12), and then proceeds to step S14.

[0091] The control device 20 determines whether the attenuation is 0 dB (step S14). If it is determined that the attenuation is 0 dB (step S14; Yes), the process proceeds to step S16. If it is not determined that the attenuation is 0 dB (step S14; No), the process proceeds to step S18.

[0092] If the determination in step S14 is Yes, the control device 20 does not need to control the amount of attenuation, so it reads a predetermined port selection pattern (step S16). Then, the control device 20 writes the port selection pattern to memory. Then, the processing in FIG. 19 ends.

[0093] If the determination in step S14 is No, the control device 20 executes a lookup table (LUT) comparison process (step S18). Specifically, the control device 20 executes the LUT comparison process to acquire pattern switching coordinates for ATT to provide a predetermined amount of attenuation between ports. The LUT is assumed to be prepared in advance.

[0094] The LUT comparison process according to the third embodiment will be described with reference to Fig. 20. Fig. 20 is a flowchart showing the flow of the LUT comparison process according to the third embodiment.

[0095] The control device 20 refers to the LUT and acquires the switching coordinates of the attenuation mask (binary mask) (step S30). At this time, the control device 20 usually acquires the LCOS coordinate values ​​with the smallest row number on the 1 side first. Then, the process proceeds to step S32.

[0096] The control device 20 determines whether the switching coordinates are within the selection pattern (step S32). If it is determined that the switching coordinates are within the selection pattern (step S32; Yes), the process proceeds to step S34. If it is not determined that the switching coordinates are within the selection pattern (step S32; No), the process proceeds to step S36.

[0097] If the determination in step S32 is Yes, the control device 20 acquires the drawing values ​​of the predetermined coordinates of the selected pattern (step S34), and then proceeds to step S38.

[0098] If the determination in step S32 is No, the control device 20 acquires the drawing values ​​of the predetermined coordinates of the non-selected pattern (step S36), and then proceeds to step S38.

[0099] The control device 20 determines whether drawing values ​​have been acquired for all rows (step S38). Specifically, the control device 20 determines whether the processes from step S30 to step S36 have been executed for row numbers 1 to m. If it is determined that drawing values ​​have been acquired for all rows (step S38; Yes), the process proceeds to step S40. If it is not determined that drawing values ​​have been acquired for all rows (step S38; No), the process proceeds to step S30, and the processes from step S30 to step S38 are repeated.

[0100] If the determination in step S38 is Yes, the control device 20 creates an attenuation pattern switching pattern (step S40). Then, the process returns to the process shown in Fig. 19, and the control device 20 writes the created attenuation pattern switching pattern into memory.

[0101] Here, for the selected and non-selected patterns, the blazed diffraction grating and quadratic surface pattern for (astigmatism) correction must be calculated prior to calculating the attenuation pattern, or the calculation results must be recorded in the LUT beforehand. However, for the attenuation amount, the attenuation amount and the switching coordinates for the binary mask pattern can be determined in advance, so it is only necessary to record the correspondence between the attenuation amount and the switching coordinates, making it possible to record attenuation patterns over a wide attenuation range with an LUT with a very small capacity.

[0102] In the WATT method according to the third embodiment, the control device 20 determines the pattern to be written to control the attenuation amount according to the pattern of the beam irradiated onto the LCOS. Therefore, if the similarity of the irradiation patterns between different channel slots is sufficiently high, the control device 20 can control all channel slots with the same attenuation pattern.

[0103] To share the attenuation control pattern across all channel slots, it is important to align the optical system and keep the coordinates of the center position O1 of the irradiation beam 311 and the center position O2 of the irradiation beam 312 close to a constant value across the entire drawing area. Similarly, it is desirable that the switching coordinates for the WSS regions R1 and R2 also remain close to a constant value across the entire drawing area. If the coordinates of the center position O1 of the irradiation beam 311 and the center position O2 of the irradiation beam 312, or the switching coordinates for the WSS regions R1 and R2, differ depending on the channel, the relative positions of the attenuation patterns between channels must be corrected to match the shifts in the coordinates of the center position O1 of the irradiation beam 311 and the center position O2 of the irradiation beam 312, or the switching coordinates for the WSS regions R1 and R2.

[0104] [Fourth embodiment] A fourth embodiment of the present disclosure will be described below. In the fourth embodiment, the binary mask of the present disclosure is applied to a curvature correction pattern.

[0105] FIG. 21 is a diagram showing an example of a background pattern and a selection pattern when no curvature image correction is performed according to the fourth embodiment. FIG. 21 shows a drawing pattern for the optical modulation unit of the optical modulator 18. FIG. 21 shows a selection pattern 220 that suppresses inter-port coupling and a background pattern 221. The selection pattern 220 is an example of a drawing pattern for coupling between predetermined ports. The background pattern 221 is an example of a drawing pattern for suppressing coupling between predetermined ports. The selection pattern 220 is a pattern with a 50 GHz bandwidth centered on a wavelength of 1552.52 nm. In FIG. 21, the left side is the short wavelength side and the right side is the long wavelength side. As shown in FIG. 21, the selection pattern 220 is an identical vertical modulation pattern written in a selection width corresponding to 50 GHz within the channel width, and is formed linearly in a slit shape.

[0106] 22A and 22B are diagrams schematically showing the relationship between a selection pattern and an irradiation beam according to the fourth embodiment. FIG. 22A shows a selection pattern 230 and a background pattern 231. FIG. 22B shows a schematic diagram of the shape of an irradiation beam 321 irradiated onto the optical modulator 18. As shown in FIG. 22B, the irradiation beam 321 is ideally irradiated onto the optical modulator 18 so as to fit within the selection pattern 230.

[0107] FIG. 23 is a diagram illustrating the shape of an irradiation beam according to the fourth embodiment. An irradiation beam 331 shown in FIG. 23(a) shows the shape of an irradiation beam irradiated onto the optical modulator 18, obtained by capturing the image. An irradiation beam 332 shown in FIG. 23(b) shows a schematic shape of the irradiation beam irradiated onto the optical modulator 18. As shown in FIGS. 23(a) and 23(b), the irradiation beam irradiated onto the optical modulator 18 has a curved shape. Therefore, there is a possibility that the irradiation beam irradiated onto the selection pattern 230 may deviate from the selection pattern 230, resulting in loss. Therefore, in the fourth embodiment, the selection pattern is corrected to prevent loss in the optical system due to the irradiation beam deviating from the selection pattern 230 at its periphery.

[0108] 24A and 24B are diagrams for explaining a correction pattern according to the fourth embodiment. Fig. 24A shows the shape of an irradiation beam. Fig. 24B shows the shape of a correction pattern. As shown in Fig. 24A, an irradiation beam 332 has a curved shape.

[0109] FIG. 25 is a diagram showing an example of a shape obtained by simulation of a correction pattern according to the fourth embodiment. FIG. 25 shows an example of a correction pattern obtained by simulation. FIG. 25 shows a simulation model of an optical modulation unit. The simulation model 600 has an opening 601, a mask portion 602, and a mask portion 603. An irradiation beam pattern 610 is shown in the opening 601. The irradiation beam pattern 610 has a shape that is convex to the right. This is because the simulation model 600 shows the result of viewing the optical modulation unit from above, with the right side being the short wavelength side and the left side being the long wavelength side. Note that FIGS. 21 to 24 show the optical modulation unit as viewed from the back, with the right side being the long wavelength side and the left side being the short wavelength side. The mask portions 602 and 603 represent binary masks. The mask portions 602 and 603 are shown using the coordinates of the opening edges 605 and 606, with the opening 601 being centered at 0 (0 mm) on the X axis. 25, opening edge 605 is formed at a position of -2.68 mm on the X coordinate. Opening edge 606 is formed at a position of +2.68 mm on the X coordinate. Opening 601 is formed in the range from -2.68 mm to +2.68 mm on the X axis.

[0110] 26 is a diagram showing simulation results according to the fourth embodiment. Table TB2 includes items such as "edge coordinate [mm]," "coupling efficiency [%]," "coupling efficiency [dB]," "normalized coupling efficiency [%]," and "normalized coupling efficiency [dB]."

[0111] "Edge coordinate [mm]" represents the edge coordinate of the opening 601. "Coupling efficiency [%]" represents the linear value of the coupling efficiency between the input port and the output port. "Coupling efficiency [dB]" represents the coupling efficiency between the input port and the output port. "Normalized coupling efficiency [%]" represents the linear value of the normalized coupling efficiency between the input port and the output port. "Normalized coupling efficiency [dB]" represents the normalized coupling efficiency between the input port and the output port.

[0112] Table TB2 shows the calculation results for the coupling efficiency when the aperture size is varied from 0 mm to 10 mm (±5 mm) and 0.8 mm (±0.4 mm) at the center of the X axis. The "coupling efficiency [%]" and "coupling efficiency [dB]" do not take into account losses other than vignetting in the optical system, so the absolute values ​​are smaller than the insertion loss of a real optical system, which is −5 dB to −8 dB. To consider the attenuation resulting from control by the optical modulator 18, the "normalized coupling efficiency [%]" and "normalized coupling efficiency [dB]" are normalized by the light intensity when the aperture 601 is 10 mm (±5 mm). As the "normalized coupling efficiency [dB]" shows, when the aperture 601 is 0.8 mm (±0.4 mm), the attenuation is −9.45 dB.

[0113] Fig. 27 is a graph showing the simulation results for the fourth embodiment. In Fig. 27, the horizontal axis represents the edge coordinates of the opening. The vertical axis on the left represents the linear value of the normalized coupling efficiency. The vertical axis on the right represents the normalized coupling efficiency.

[0114] Waveform 121 shows the change in the normalized coupling efficiency. Waveform 122 shows the change in the linear value of the normalized coupling efficiency. Line 123 shows the change in the linear value of the normalized coupling efficiency when the beam radius in the vertical direction is 1 / e 2 27, by controlling the aperture 601, the amount of attenuation can be precisely controlled.

[0115] As described above, in this embodiment, by providing the optical modulator with a selection area and a non-selection area, the attenuation amount can be digitally controlled at predetermined intervals. Furthermore, even when the vertical beam irradiated on the optical modulator 18 is curved, the attenuation amount can be controlled using the same algorithm as when the beam is not curved.

[0116] The components of each device shown in the figure are conceptual functional components and do not necessarily have to be physically configured as shown. In other words, the specific form of distribution and integration of each device is not limited to that shown in the figure, and all or part of them can be functionally or physically distributed and integrated in any unit depending on various loads and usage conditions. This distribution and integration configuration may also be performed dynamically.

[0117] Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the contents of these embodiments. Furthermore, the above-described components include those that can be easily imagined by a person skilled in the art, those that are substantially the same, and those that are within the so-called equivalent range. Furthermore, the above-described components can be combined as appropriate. Furthermore, various omissions, substitutions, or modifications of the components can be made without departing from the spirit of the above-described embodiments. [Explanation of symbols]

[0118] 1 Optical signal selection device 10 Collimator Array 12 Beam expansion optics 14 Spectroscopic optical system 16 Position angle conversion optical system 18 Optical Modulator 20 Control device 22 spherical mirror 24 Polarization separation element 30 Optical system elements

Claims

1. a collimator array in which a plurality of ports are arranged in a predetermined direction and which inputs and outputs optical signals; an optical modulator that diffracts an optical signal input from a first port among the plurality of ports at a predetermined angle to couple a path between the first port and a second port different from the first port; a control device that writes, into the optical modulator, a diffraction grating pattern for coupling paths between the first port and the second port and an attenuation pattern for suppressing crosstalk between the first port and the second port; An optical signal selection device comprising:

2. the control device writes a blazed diffraction grating pattern onto the optical modulator as the diffraction grating pattern; 2. The optical signal selection device according to claim 1.

3. the control device writes, as the diffraction grating pattern, a pattern for inter-port coupling formed by adding a phase correction pattern for correcting aberrations of an optical system to the blazed diffraction grating pattern and folding back at a main value into the optical modulator; 3. The optical signal selection device according to claim 2.

4. the control device writes the attenuation pattern in an area of ​​the inter-port coupling pattern corresponding to a predetermined attenuation amount in the optical modulator to form a hybrid pattern; 4. The optical signal selection device according to claim 3.

5. the hybrid pattern is a binary mask; 5. The optical signal selection device according to claim 4.

6. the control device controls the binary mask by dividing the non-selection region into a non-selection region where the attenuation amount is controlled to be large and a non-selection region where the attenuation amount is controlled to be small.

6. The optical signal selection device according to claim 5.

7. A plurality of the binary masks are provided, the control device controls the plurality of binary masks so that they do not overlap; 6. The optical signal selection device according to claim 5.

8. the control device switches the position where the binary mask is provided depending on the amount of attenuation.

8. The optical signal selection device according to claim 7.

9. a step of diffracting an optical signal input from a first port among a plurality of ports at a predetermined angle and coupling a path between the first port and a second port different from the first port; writing, into an optical modulator, a diffraction grating pattern for coupling paths between the first port and the second port and an attenuation pattern for suppressing crosstalk between the first port and the second port; An optical signal selection method, comprising:

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