Measuring device, measurement compensation device, and measurement method

Abstract

This measurement device comprises: an interference waveform generation unit that generates an interference waveform signal in accordance with interference light of first light and second light received on an imaging plane; a distribution measurement unit that measures a first optical field distribution of the intensity and phase of the first light on the imaging plane on the basis of the interference waveform signal; a distribution simulation unit that simulates, on the basis of the measured first optical field distribution, a second optical field distribution of the intensity and phase of the first light on a plurality of planes at different distances from the imaging plane with respect to a direction opposite to the direction of propagation of the first light propagated from an end face of an optical waveguide; a selection unit that selects a plane on which the area of a region of the simulated second optical field distribution is the smallest from among the plurality of planes; and an output unit that outputs, to a predetermined device, information on the simulated second optical field distribution on the selected plane.

Description

Technical Field

[0001] The present invention relates to a measuring device, a measurement compensation device, and a measurement method.

Background Art

[0002] An optical transmission system using an optical fiber as an optical waveguide is widely used as a system that realizes a fixed-line with a large transmission capacity due to the broadband characteristics and low loss characteristics of the optical fiber. In order to further increase this transmission capacity, space division multiplexing (SDM) is being studied. In space division multiplexing in an optical transmission system, instead of a single single-mode fiber (SMF), a plurality of single-mode fibers (parallelized single-mode fibers), multi-core fibers (MCF), coupled-core multi-core fibers (CC-MCF), multi-mode fibers (MMF), or multi-core multi-mode fibers (MCMMF) may be used as the optical waveguide.

[0003] The plurality of spatial degrees of freedom possessed by these optical waveguides are utilized as independent channels. As a result, it is possible to increase the transmission capacity per fiber. Multi-mode fibers and multi-mode multi-core fibers (hereinafter referred to as "multi-mode fibers, etc.") can increase the number of modes per unit cross-sectional area of the optical waveguide as compared with a plurality of single-mode fibers and multi-core fibers. Therefore, use in a spatial multiplexing method with high space utilization efficiency is expected for multi-mode fibers, etc. (see Non-Patent Document 1).

[0004] The construction of optical transmission systems using multimode fibers requires optical fibers with appropriate performance and devices with performance corresponding to the input and output of the multimode core. Here, in order to properly evaluate the performance of multimode fibers, the optical electric field distribution of the intensity and phase of the optical signal at the end face of the multimode fiber must be measured. Furthermore, in order to properly design the device, the optical electric field distribution of the intensity and phase of the optical signal at the end face of the optical waveguide of the device must be measured.

[0005] One reason why information on the optical electric field distribution (profile) is necessary is that it is needed to evaluate the amount of nonlinear noise generated in the optical waveguide due to nonlinear optical effects within the optical fiber. Since nonlinear effects within the optical fiber increase with optical power, they become the ultimate limiting factor for transmission capacity. Therefore, from the perspective of evaluating the performance of the transmission system, information on the optical electric field distribution is important.

[0006] In order to evaluate nonlinear effects in multimode fibers and the like, it is necessary to know the area of ​​the optical electric field distribution region at the end face of the optical waveguide for each mode of the optical signal. This optical electric field distribution includes information on the intensity and phase of the optical signal propagated from the end face of the optical waveguide. In order to calculate the area of ​​the optical electric field distribution region, it is necessary to measure the optical electric field distribution at the end face of the optical waveguide (see Non-Patent Literature 2).

[0007] Furthermore, one reason why information on the optical electric field distribution at the end face of the optical fiber and the end face of the optical waveguide of the device is necessary for device design is that this information is needed to design input / output sections with lower coupling losses. In input / output sections where optical signals are coupled by bringing the optical fiber into contact with the device, the coupling efficiency between the optical waveguide in the device and the optical fiber is determined by the overlap between the region of the optical electric field distribution at the end face of the optical waveguide of the device and the region of the optical electric field distribution at the end face of the optical fiber.

[0008] Therefore, with the aim of optimizing the coupling efficiency between the optical waveguide within the device and the optical fiber, information on the optical electric field distribution at the end face of the optical waveguide in the device and the optical electric field distribution at the end face of the optical fiber are measured in advance, and the optical waveguide is designed so that the information on each measured optical electric field distribution matches as closely as possible.

[0009] Digital holography is sometimes used to measure the intensity and phase distribution of the optical electric field at the end face of an optical waveguide (see Non-Patent Document 3). In a digital holography optical system, object light propagates from the end face of the optical waveguide, and the imaging surface (image sensor) receives the interference light of the object light and the reference light (plane wave). The interference waveform signal corresponding to the received interference light is analyzed by digital signal processing to measure the intensity and phase distribution of the optical electric field at the end face of the optical waveguide.

[0010] However, if the distances between each component of the optical system are not precisely controlled, existing methods cannot improve the accuracy of measuring the electric field distribution at the end face. For example, in the optical system of digital holography, the distance between the end face of the optical waveguide and the imaging optical system, the distance between each lens in the imaging optical system, and the distance between the imaging optical system and the imaging surface must be precisely controlled. If the distances between each component of the optical system differ from the ideal distance, the measured image of the electric field distribution will be a defocused image in the region of the electric field distribution at the end face of the optical waveguide. Therefore, it is not possible to improve the accuracy of measuring the electric field distribution at the end face of the optical waveguide. To address this problem, the image of the electric field distribution may be defocused to maximize its clarity (contour sparsity), similar to how defocus compensation is performed to maximize the clarity of images in biological microscopes (see Non-Patent Literature 4). [Prior art documents] [Non-patent literature]

[0011] [Non-Patent Document 1] Mizuno, Takayuki, et al. "Dense space-division multiplexed transmission systems using multi-core and multi-mode fiber." Journal of lightwave technology 34.2 (2016): pp.582-592. [Non-Patent Document 2] Rademacher, Georg, and Klaus Petermann. "Nonlinear Gaussian noise model for multimode fibers with space-division multiplexing." Journal of Lightwave Technology 34.9 (2016): pp.2280-2287. [Non-Patent Document 3] Shimizu, Shimpei, et al. "Volume holographic spatial mode demultiplexer with a dual-wavelength method." Applied optics 57.2 (2018): pp.146-153. [Non-Patent Document 4] Zhang, Yibo, et al. "Edge sparsity criterion for robust holographic autofocusing." Optics letters 42.19 (2017): pp.3824-3827. [Overview of the project] [Problems that the invention aims to solve]

[0012] However, in images of the electric field distribution of multimode light at the end face of an optical waveguide, the edges become blurred in both the real and imaginary parts, such as the edges in the image of the electric field distribution of the LP11 mode. Therefore, it is difficult to sharpen the edges of the electric field distribution image (compensate for defocus) using methods similar to those used for correcting images from a biological microscope or natural images.

[0013] Thus, if the distances between each component of the optical system are not precisely controlled, there is a problem in that the measurement accuracy of the optical electric field distribution at the end face of the optical waveguide cannot be improved.

[0014] In view of the above circumstances, the present invention aims to provide a measuring device, a measuring compensation device, and a measuring method that can improve the measurement accuracy of the optical electric field distribution at the end face of an optical waveguide, even when the distances between each component of the optical system are not precisely controlled. [Means for solving the problem]

[0015] One aspect of the present invention is a measuring device comprising: an interference waveform generation unit that generates an interference waveform signal in response to the interference light of a first light and a second light received on an imaging surface; a distribution measurement unit that measures the first optical electric field distribution of the intensity and phase of the first light on the imaging surface based on the interference waveform signal; a distribution simulation unit that simulates the second optical electric field distribution of the intensity and phase of the first light in a plurality of planes at different distances from the imaging surface in the opposite direction to the propagation direction of the first light propagated from the end face of an optical waveguide, based on the measured first optical electric field distribution; a selection unit that selects from the plurality of planes the plane in which the area of ​​the simulated second optical electric field distribution region is minimized; and an output unit that outputs information of the simulated second optical electric field distribution in the selected plane to a predetermined device.

[0016] One aspect of the present invention is a measurement and compensation device comprising: a distribution measurement unit that measures a first optical electric field distribution of the intensity and phase of the first light on the imaging surface based on an interference waveform signal corresponding to the interference light of the first and second light received on the imaging surface; a distribution simulation unit that simulates a second optical electric field distribution of the intensity and phase of the first light on a plurality of planes at different distances from the imaging surface in the opposite direction to the propagation direction of the first light propagated from the end face of an optical waveguide, based on the measured first optical electric field distribution; a selection unit that selects from the plurality of planes the plane in which the area of ​​the simulated second optical electric field distribution region is minimized; and an output unit that outputs information of the simulated second optical electric field distribution on the selected plane to a predetermined device.

[0017] One aspect of the present invention is a measurement method performed by a measuring device, comprising the steps of: generating an interference waveform signal in response to interference light of a first light and a second light received on an imaging surface; measuring a first optical electric field distribution of the intensity and phase of the first light on the imaging surface based on the interference waveform signal; simulating a second optical electric field distribution of the intensity and phase of the first light in a plurality of planes at different distances from the imaging surface in the opposite direction to the propagation direction of the first light propagated from the end face of an optical waveguide, based on the measured first optical electric field distribution; selecting a plane from the plurality of planes that minimizes the area of ​​the region of the simulated second optical electric field distribution; and outputting information of the simulated second optical electric field distribution in the selected plane to a predetermined device. [Effects of the Invention]

[0018] The present invention makes it possible to improve the measurement accuracy of the optical electric field distribution at the end face of an optical waveguide, even when the distances between each component of the optical system are not precisely controlled. [Brief explanation of the drawing]

[0019] [Figure 1] This figure shows an example of the configuration of the measuring device in the first embodiment. [Figure 2]It is a diagram showing an example of the optical electric field distribution of the intensity and phase of object light in the first embodiment. [Figure 3] It is a flowchart showing an example of the operation of the measurement compensation device in the first embodiment. [Figure 4] It is a diagram showing an example of the configuration of the measurement device in the second embodiment. [Figure 5] It is a diagram showing an example of the hardware configuration of the measurement device in each embodiment.

Modes for Carrying Out the Invention

[0020] Embodiments of the present invention will be described in detail with reference to the drawings. (First Embodiment) FIG. 1 is a diagram showing an example of the configuration of a measurement device 1a in an embodiment. The measurement device 1a is a device for measuring the optical electric field distribution at the end face of an optical waveguide. The measurement device 1a includes an interference waveform generation device 2a and a measurement compensation device 3.

[0021] First, the interference waveform generation device 2a will be described. The interference waveform generation device 2a is a device that generates a signal (interference waveform signal) corresponding to interference light. The interference waveform generation device 2a includes, for example, an off-axis or in-line digital holography optical system. In FIG. 1, the interference waveform generation device 2a includes an optical waveguide 20, a collimator lens 21, a mirror 22, an optical waveguide 23, an imaging optical system 24, a beam splitter 25, and an interference waveform generation unit 26 as components in an off-axis digital holography optical system.

[0022] The imaging optical system 24 includes a lens 240 and a lens 241 as a set of lens pairs. Instead of including a set of lens pairs, the imaging optical system 24 may include a plurality of lenses considering aberration and magnification. The interference waveform generation unit 26 includes an imaging surface 260 (image sensor).

[0023] The optical waveguide 20 is, for example, an optical fiber such as a single-mode fiber. The optical waveguide 20 may contain a material such as silicon or indium phosphide. Reference light 100-1 is input to the optical waveguide 20. The optical waveguide 20 transmits the reference light 100-1. The optical waveguide 20 outputs the reference light 100-2 to the collimator lens 21.

[0024] The collimator lens 21 outputs a reference light 100-2 (a plane wave with a predetermined inclination) to the mirror 22. The mirror 22 reflects the reference light 100-2 to the beam splitter 25. Alternatively, the collimator lens 21 may be omitted, and the reference light 100-2 propagated from the end face of the optical waveguide 20 (single-mode fiber) may be used as an approximate plane wave. Alternatively, the optical waveguide 20 may be omitted, and the reference light 100-2 propagated from a pinhole may be used as an approximate plane wave.

[0025] The optical waveguide 23 is, for example, a multimode fiber (such as a spatial multiplexing fiber). The optical waveguide 23 may contain materials such as silicon or indium phosphide. Object light 110-1 is input to the optical waveguide 23. The optical waveguide 23 transmits the object light 110-1. The optical waveguide 23 outputs object light 110-2 to the imaging optical system 24.

[0026] The imaging optical system 24 receives object light 110-2 from the optical waveguide 23. The imaging optical system 24 uses lenses 240 and 241 to form an image of the optical electric field distribution of the object light 110-2 on the imaging plane 260 (focal plane).

[0027] The beam splitter 25 transmits the object light 110-2 output from the imaging optical system 24. The beam splitter 25 receives the reference light 100-2 reflected by the mirror 22. The beam splitter 25 reflects the reference light 100-2 to the imaging surface 260.

[0028] The interference waveform generation unit 26 is, for example, a near-infrared camera. Object light 110-2 is input to the imaging surface 260 from the beam splitter 25. Reference light 100-2 is input to the imaging surface 260 from the beam splitter 25. As a result, the imaging surface 260 receives the interference light of the object light 110-2 and the reference light 100-2. The imaging surface 260 captures the interference light of the object light 110-2 and the reference light 100-2. The interference waveform generation unit 26 generates an interference waveform signal according to the interference light received by the imaging surface 260. The interference waveform generation unit 26 outputs the interference waveform signal to the measurement compensation device 3.

[0029] Next, we will explain the measurement compensation device 3. The measurement compensation device 3 is a device that measures the optical electric field distribution. Here, the measurement compensation device 3 compensates for the measurement results. The object light 110-2 propagating from the end face of the optical waveguide 23 spreads spatially in the direction of propagation and perpendicular to it. The measurement compensation device 3 utilizes this to compensate for the information (measurement result) of the defocused optical electric field distribution on the imaging surface 260 by digital signal processing. In this digital signal processing, prior information such as the deviation from the focal length and defocus distance of the optical system is not required.

[0030] The measurement compensation device 3 comprises a memory 30, a distribution measurement unit 31, a distribution simulation unit 32, a selection unit 33, and an output unit 34. The memory 30 stores the interference waveform signal output from the interference waveform generation unit 26. The memory 30 may also store a computer program in advance.

[0031] The distribution measurement unit 31 (complex distribution demodulation unit) acquires an interference waveform signal corresponding to the interfering light from the memory 30 or the interference waveform generation unit 26. The distribution measurement unit 31 performs a two-dimensional Fourier transform on the acquired interference waveform signal. The distribution measurement unit 31 performs a low-pass filter on the result of the two-dimensional Fourier transform. For example, the distribution measurement unit 31 extracts a bandwidth appropriate as the spatial frequency of the object light 110-2 from the result of the two-dimensional Fourier transform.

[0032] The distribution measurement unit 31 frequency-shifts the bandwidth extracted by the low-pass filter processing to a frequency near "0". The distribution measurement unit 31 then performs a two-dimensional inverse Fourier transform (demodulation) on the two-dimensional Fourier transform result of the bandwidth that has been frequency-shifted to a frequency near "0". This derives information on the optical electric field distribution (complex distribution) at the imaging surface 260.

[0033] The distribution simulation unit 32 virtually changes the propagation distance of object light 110 in the digital domain through calculations based on information about the optical electric field distribution on the imaging surface 260. That is, the distribution simulation unit 32 simulates the optical electric field distribution in each of the virtual planes, which are virtually defined at multiple positions in the propagation direction of object light 110.

[0034] The distribution simulation unit 32 simulates the optical electric field distribution in each virtual plane, for example, using the angular spectrum method (Reference 1: Matsushima, Kyoji, and Tomoyoshi Shimobaba. "Band-limited angular spectrum method for numerical simulation of free-space propagation in far and near fields." Optics express 17.22 (2009): pp.19662-19673). This derives information about the optical electric field distribution (complex distribution) in each virtual plane.

[0035] Figure 2 shows an example of the intensity and phase of the optical electric field distribution of object light 110-2 in the first embodiment. The core 230 is the core of the optical waveguide 23. The plane 120 is the focal plane of the lens 241. Each plane 200 is a plane (each plane in the digital domain) that is virtually defined at multiple positions in the propagation direction from the optical waveguide 23 toward the imaging plane 260.

[0036] In Figure 2, the information (profile) of the defocused optical electric field distribution obtained as an interference waveform signal represents the information of the optical electric field distribution in regions 201-0 and 202-0 in a plane 120 (imaging plane 260) away from the end face of the optical waveguide 23.

[0037] The distribution simulation unit 32 simulates the propagation of object light 110 in real space in the digital domain by digital signal processing. The distribution simulation unit 32 derives regions 201 and 202 of the optical electric field distribution in each plane 200 by propagating object light 110 in the forward or reverse direction of propagation in the digital domain.

[0038] For example, the distribution simulation unit 32 virtually moves regions 201-0 and 202-0 of the measured optical electric field distribution by digital signal processing in the opposite direction to the propagation direction of object light 110, by a distance corresponding to the focal length and defocus distance of the imaging optical system 24. If an appropriate distance (accurate propagation distance) is known for the movement of regions 201-0 and 202-0, the measurement compensation device 3 can compensate for the defocus of the optical electric field distribution image by propagating object light 110 in the digital domain.

[0039] Object light 110 propagating from the end face of core 230 spreads spatially in the direction of propagation and perpendicular to it. In other words, the areas of regions 201-2 and 202-2 of the optical electric field distribution in plane 200-2 (the end face of core 230) are the smallest of regions 201 and 202 of the optical electric field distribution in each plane 200. Therefore, the appropriate distance (accurate propagation distance) for the travel distance of regions 201-0 and 202-0 is the propagation distance between plane 200-2 and plane 120.

[0040] The distribution simulation unit 32 quantifies the beam diameter of the object light 110 by fitting the regions of the two-dimensional distribution, such as a Gaussian distribution, to the regions 201 and 202 of the measured photoelectric field distribution of the object light 110, respectively, using the regions of the two-dimensional distribution, such as a Gaussian distribution, as parameters.

[0041] The distribution simulation unit 32 may, for example, derive the variance of the intensity and phase measurements in the region of the optical electric field distribution of the object light 110 along each of the two-dimensional axes representing the plane 120. Based on the variance of the derived measurements, the distribution simulation unit 32 may quantify the beam diameter of the object light 110.

[0042] The selection unit 33 compares the areas of regions 201 and 202 of the simulated optical electric field distribution across multiple planes 200. The selection unit 33 selects the plane 200 from among the multiple planes 200 that minimizes the area of ​​regions 201 and 202 of the optical electric field distribution. In Figure 2, the selection unit 33 selects plane 200-2. The position of plane 200-2 coincides with the position of the end face of the optical waveguide 23 (core 230). The optical electric field distribution information for regions 201-2 and 202-2 is accurate information regarding the optical electric field distribution at the end face of the core 230. In this way, the selection unit 33 detects the accurate optical electric field distribution regions 201-2 and 202-2 at the end face of the core 230.

[0043] The output unit 34 outputs information on the optical electric field distribution of regions 201-2 and 202-2 in the selected plane 200-2 to a predetermined device (not shown). The output unit 34 also outputs information representing the distance (propagation distance) from the selected plane 200-2 to plane 120 (focal plane) to a predetermined device (not shown). This allows for defocus correction based on the propagation distance information in subsequent corrections, similar to the current correction. Furthermore, since it becomes unnecessary to simulate optical electric field distributions for multiple positions, the amount of computation can be reduced.

[0044] Next, we will explain an example of the operation of the measuring device 1a (measurement compensation device 3). Figure 3 is a flowchart showing an example of the operation of the measurement compensation device 3 in the first embodiment. The distributed measurement unit 31 acquires an interference waveform signal corresponding to the interference light of the object light 110 and the reference light 100 received on the imaging surface 260 from the interference waveform generation unit 26 or the memory 30 (step S101).

[0045] The distribution measurement unit 31 measures the first optical electric field distribution of the intensity and phase of the object light 110 on the imaging surface 260 based on the acquired interference waveform signal (step S102). For the direction opposite to the propagation direction of the object light 110 propagated from the end face of the optical waveguide 23, the second optical electric field distribution of the intensity and phase of the object light 110 on multiple planes 200 at different distances from the imaging surface 260 is simulated based on the first optical electric field distribution measured on the imaging surface 260 (step S103).

[0046] The selection unit 33 selects from among multiple planes 200 the plane 200 that minimizes the area of ​​the region 201 of the simulated second electric field distribution. The selection unit 33 may also select from among multiple planes 200 the plane 200 that minimizes the area of ​​the region 202 of the simulated second electric field distribution (step S104).

[0047] The output unit 34 outputs information of the simulated second optical electric field distribution in the selected plane 200 to a predetermined device (not shown) or memory 30. The output unit 34 may also output information of the distance from the selected plane 200 to the plane 120 (focal plane) (propagation distance from the selected plane 200 to the imaging plane 260) to a predetermined device (not shown) or memory 30 (step S105).

[0048] As described above, the interference waveform generation unit 26 generates an interference waveform signal according to the interference light of the object light 110 (first light) and the reference light 100 (second light) received on the imaging surface 260. The distribution measurement unit 31 measures the first optical electric field distribution of the intensity and phase of the object light 110 on the imaging surface 260 based on the interference waveform signal. The distribution simulation unit 32 simulates the second optical electric field distribution of the intensity and phase of the object light 110 in multiple planes 200 at different distances from the imaging surface 260, in the opposite direction to the propagation direction of the object light 110 propagated from the end face of the optical waveguide 23, based on the measured first optical electric field distribution. The selection unit 33 selects the plane 200 from among the multiple planes 200 that minimizes the area of ​​regions 201 and 202 of the simulated second optical electric field distribution. The output unit 34 outputs information on the simulated second optical electric field distribution in the selected plane 200 to a predetermined device (not shown).

[0049] This makes it possible to improve the measurement accuracy of the optical electric field distribution at the end face of an optical waveguide, even when the distance between each component of the optical system (the arrangement of each component) is not precisely controlled. For example, it is possible to improve the measurement accuracy of the optical electric field distribution at the end face of an optical waveguide even when the lens defocus distance is unknown. For example, it is possible to improve the measurement accuracy of the optical electric field distribution at the end face of an optical waveguide even when indicators such as image clarity (contour sparsity) are unknown.

[0050] (Second Embodiment) In the second embodiment, the difference from the first embodiment is that the interference waveform generation device does not include an imaging optical system (lens). The second embodiment will be explained focusing on the differences from the first embodiment.

[0051] Figure 4 shows an example of the configuration of the measuring device 1b in the second embodiment. The measuring device 1b is a device for measuring the optical electric field distribution at the end face of an optical waveguide. The measuring device 1b comprises an interference waveform generator 2b and a measurement compensation device 3.

[0052] The interference waveform generator 2b is a device that generates interference waveforms. The interference waveform generator 2b includes, for example, an off-axis or in-line digital holography optical system. In Figure 4, the interference waveform generator 2b includes an optical waveguide 20, a collimator lens 21, a mirror 22, an optical waveguide 23, a beam splitter 25, and an interference waveform generation unit 26 as components of the off-axis digital holography optical system.

[0053] Object light 110-1 is input to optical waveguide 23. Optical waveguide 23 transmits object light 110-1. Optical waveguide 23 outputs object light 110-2 to beam splitter 25.

[0054] In the second embodiment, since the interference waveform generator 2b does not have an imaging optical system (lens), the object light 110 is not imaged onto the imaging surface 260 by the imaging optical system. The object light 110 propagating from the optical waveguide 23 is received by the imaging surface 260 (image sensor) via the beam splitter 25. The position of plane 120 and the position of imaging surface 260 are the same. Here, the propagation distance from plane 200-2 to plane 120 in Figure 2 is equal to the distance from plane 200-2 to imaging surface 260.

[0055] The beam splitter 25 transmits the object light 110-2 output from the optical waveguide 23. The beam splitter 25 receives the reference light 100-2 reflected by the mirror 22. The beam splitter 25 reflects the reference light 100-2 to the imaging surface 260.

[0056] The interference waveform generation unit 26 generates an interference waveform signal in response to the interference light received on the imaging surface 260. The interference waveform generation unit 26 outputs the interference waveform signal to the measurement compensation device 3. The distribution measurement unit 31 acquires the interference waveform signal from the interference waveform generation unit 26 or the memory 30.

[0057] As described above, the imaging surface 260 receives object light 110-2 propagated from the end face of the optical waveguide 23 without going through the imaging optical system 24 (lenses 240 and 241). In other words, the imaging surface 260 receives object light 110-2 propagated from the end face of the optical waveguide 23 via a lensless optical system.

[0058] This makes it possible to improve the measurement accuracy of the optical electric field distribution at the end face of an optical waveguide, even when the distances between each component of the optical system are not precisely controlled. In a lensless holography measurement system, it is possible to simulate the spatial propagation of object light, so a lens for imaging object light at the end face is unnecessary. Therefore, it is possible to miniaturize the measurement device, achieve a broad bandwidth that does not depend on lenses, and eliminate aberrations.

[0059] (modified version) Instead of using digital holography to measure the electric field distribution, the measuring device may use a Shack-Hartmann wavefront sensor. Alternatively, the measuring device may use a predetermined optimization algorithm to measure the electric field distribution. A predetermined optimization algorithm is, for example, an iterative Fourier transform. An iterative Fourier transform is, for example, the Gercberg-Saxton algorithm.

[0060] (Example hardware configuration) Figure 5 shows an example of the hardware configuration of the measuring device 1 (measuring system) in each embodiment. The measuring device 1 corresponds to part or all of the measuring device 1a and the measuring device 1b.

[0061] The measuring device 1 is implemented as software by a processor 10, such as a CPU (Central Processing Unit), executing a program stored in a storage device 12 having a non-volatile recording medium (non-temporary recording medium) and a memory 11. The program may be recorded on a computer-readable non-temporary recording medium. Computer-readable non-temporary recording media include, for example, portable media such as flexible disks, magneto-optical disks, ROMs (Read Only Memory), CD-ROMs (Compact Disc Read Only Memory), and storage devices such as hard disks built into computer systems. The communication unit 13 performs predetermined communication processing.

[0062] Some or all of the functional parts of the measuring device 1 are analog or digital circuits, and may be implemented using hardware including electronic circuits (electronic circuits or circuits) such as LSI (Large Scale Integrated Circuit), ASIC (Application Specific Integrated Circuit), PLD (Programmable Logic Device), or FPGA (Field Programmable Gate Array).

[0063] Although embodiments of this invention have been described in detail above with reference to the drawings, the specific configuration is not limited to these embodiments and includes designs and the like that do not depart from the spirit of this invention. [Industrial applicability]

[0064] The present invention is applicable to devices for measuring the distribution of optical electric fields (optical measuring devices). [Explanation of Symbols]

[0065] 1, 1a, 1b... Measuring device, 2a, 2b... Interference waveform generator, 3... Measurement compensation device, 20... Optical waveguide, 21... Collimator lens, 22... Mirror, 23... Optical waveguide, 24... Imaging optical system, 25... Beam splitter, 26... Interference waveform generator, 30... Memory, 31... Distribution measurement unit, 32... Distribution simulation unit, 33... Selection unit, 34... Output unit, 100... Reference light, 110... Object light, 120... Plane, 200... Plane, 201... Region, 202... Region, 230... Core, 240... Lens, 241... Lens, 260... Imaging plane

Claims

1. An interference waveform generation unit generates an interference waveform signal in response to the interference light of the object light and the reference light received on the imaging surface, A distribution measurement unit measures the object light electric field distribution of the intensity and phase of the object light on the imaging surface based on the interference waveform signal, A distribution simulation unit simulates the reference optical electric field distribution of the intensity and phase of the object light in multiple planes at different distances from the imaging surface, in the opposite direction to the propagation direction of the object light propagating from the end face of the optical waveguide, based on the measured object optical electric field distribution. A selection unit that selects from among the plurality of planes the plane that minimizes the area of ​​the region of the simulated reference optical electric field distribution, An output unit that outputs information of the simulated reference optical electric field distribution in the selected plane to a predetermined device. Equipped with, The distribution simulation unit quantifies the beam diameter of the object light based on the variance of the measured intensity and phase values ​​in the region of the object light electric field distribution, and simulates the reference light electric field distribution based on the quantified beam diameter. Measuring device.

2. The measuring device according to claim 1, wherein the output unit outputs information of the propagation distance from the selected plane to the imaging surface to the predetermined device.

3. The measurement device according to claim 1 or 2, wherein the distribution measurement unit measures the object's optical electric field distribution based on the interference waveform signal of the digital holography.

4. The measuring device according to claim 1 or 2, wherein the imaging surface receives the object light propagated from the end face of the optical waveguide without passing through an imaging optical system.

5. A distribution measurement unit measures the electric field distribution of the object light on the imaging surface based on an interference waveform signal corresponding to the interference light of the object light and the reference light received on the imaging surface, and the intensity and phase of the object light. A distribution simulation unit simulates the reference optical electric field distribution of the intensity and phase of the object light in multiple planes at different distances from the imaging surface, in the opposite direction to the propagation direction of the object light propagating from the end face of the optical waveguide, based on the measured object optical electric field distribution. A selection unit that selects from among the plurality of planes the plane that minimizes the area of ​​the region of the simulated reference optical electric field distribution, An output unit that outputs information of the simulated reference optical electric field distribution in the selected plane to a predetermined device. Equipped with, The distribution simulation unit quantifies the beam diameter of the object light based on the variance of the measured intensity and phase values ​​in the region of the object light electric field distribution, and simulates the reference light electric field distribution based on the quantified beam diameter. Measurement compensation device.

6. A measurement method performed by a measuring device, The steps include generating an interference waveform signal in response to the interference light of the object light and the reference light received on the imaging surface, The steps include measuring the object light electric field distribution of the intensity and phase of the object light on the imaging surface based on the interference waveform signal, A step of simulating the reference optical electric field distribution of the intensity and phase of the object light in multiple planes at different distances from the imaging surface, in the direction opposite to the propagation direction of the object light propagated from the end face of the optical waveguide, based on the measured object optical electric field distribution, The steps include selecting from the plurality of planes the plane that minimizes the area of ​​the region of the simulated reference optical electric field distribution, The steps include outputting information about the simulated reference optical electric field distribution in the selected plane to a predetermined device, and Includes, The simulation step includes quantifying the beam diameter of the object light based on the variance of measured intensity and phase values ​​in the region of the object light electric field distribution, and simulating the reference light electric field distribution based on the quantified beam diameter. Measurement method.

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