Pulse spectrometer and irradiation unit for multi-fiber

Abstract

To provide a practical structure in a pulse spectrometer for transmitting pulse light separately by a plurality of fibers and extending the pulse, the structure irradiating the same region on an irradiation plane with superimposed beams of light.SOLUTION: The broadband pulse light from a pulse source 1 is divided by an array waveguide diffraction grating 3 as a dividing element according to a wavelength and then adjusted so that the time and wavelength of light in pulses correspond one to one when transmitted by a bundle fiber 21 before being emitted to a subject S via an irradiation unit 4. The light emitted from each core of the bundle fiber 21 is superimposed by a first lens 41 in substantially the same region R1 in a first plane P1 perpendicular to an optical axis A, with the image of the first region R1 projected by second lenses 421, 422, whereby emitted to the subject S.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The invention of this application relates to a technique for performing spectroscopic measurement by utilizing the correspondence between time and wavelength in pulsed light. [Background technology]

[0002] A typical pulse light source is a pulsed laser (pulse laser). In recent years, much research has been done into broadening the wavelength of pulse lasers, and a typical example of this is the generation of supercontinuum light (hereafter referred to as SC light) using nonlinear optical effects. SC light is light obtained by passing light from a pulse laser source through a nonlinear element such as a fiber, and broadening the wavelength by nonlinear optical effects such as self-phase modulation and optical soliton. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2013-205390 A Summary of the Invention [Problem to be solved by the invention]

[0004] Although the wavelength range of the above-mentioned broadband pulse light is significantly expanded, the pulse width (time width) remains close to that of the input pulse used to generate the SC light. However, the pulse width can also be expanded by utilizing the group delay in a transmission element such as a fiber. In this case, by selecting an element with appropriate chromatic dispersion characteristics, the pulse can be expanded with a one-to-one correspondence between the time (elapsed time) within the pulse and the wavelength.

[0005] The relationship between time and wavelength in broadband pulsed light whose pulse is stretched in this way (hereinafter referred to as broadband stretched pulsed light) can be effectively used in spectroscopic measurement. When broadband stretched pulsed light is received by a certain photoreceiver, the temporal change in light intensity detected by the photoreceiver corresponds to the light intensity of each wavelength, i.e., the spectrum. Therefore, the temporal change in the output data of the photoreceiver can be converted into a spectrum, and spectroscopic measurement becomes possible without using a special dispersive element such as a diffraction grating. In other words, by irradiating an object with broadband stretched pulsed light, receiving the light from the object with a photoreceiver, and measuring the temporal change, it becomes possible to know the spectral characteristics of the object (e.g., spectral transmittance).

[0006] Thus, broadband stretched pulsed light is considered to be particularly useful in fields such as spectrometry. However, it is known that when the output of a pulsed light source is increased to output stronger light, unintended nonlinear optical effects occur in the pulse stretcher element, causing the one-to-one correspondence between time and wavelength (hereinafter referred to as time-wavelength correspondence) to be lost. When the time-wavelength correspondence is lost, it leads to a significant decrease in measurement accuracy, especially when used in spectrometry.

[0007] To solve such a problem, it is effective to use multiple fibers as an extension element to reduce the energy of light transmitted by one fiber and prevent unintended nonlinear optical effects from occurring. However, when time-wavelength compatibility is realized by transmitting light through multiple fibers in this way, the pattern of the irradiated light is shifted on the irradiation surface. As a configuration for realizing time-wavelength compatibility using multiple fibers, it is possible to use a multicore fiber or a bundle fiber, but in either case, the light emitted from each core forms a pattern that is shifted from each other on the irradiation surface and does not completely overlap.

[0008] When light is irradiated in a shifted pattern like this, the peripheral areas that do not overlap have different irradiation conditions compared to the central area, and the irradiation characteristics become non-uniform within the area. In particular, in a configuration in which light is divided according to wavelength and transmitted through fibers, the wavelength of light emitted from each fiber (or each core) is different, so the wavelength components differ depending on the location within the irradiation area, and even for the same object, the measurement results differ due to the shift in the placement position, resulting in a malfunction (reduced accuracy).

[0009] This problem is not generally known because multiple-core fibers such as multicore fibers and bundle fibers were developed for communication purposes as known in the field of space division multiplexing, and are not used for the purpose of uniformly irradiating light onto an area for the purpose of spectroscopy, etc. Therefore, the technical problem of overlapping irradiation onto the same irradiation area is not known. The present invention has been made to solve this problem, and aims to provide a practical configuration in a pulse spectroscopy device that achieves time-wavelength correspondence by dividing and transmitting pulsed light through multiple fibers, in which light is irradiated in an overlapping manner onto the same area on the irradiation surface, thereby preventing a decrease in measurement accuracy due to a shift in the irradiation pattern. [Means for solving the problem]

[0010] In order to solve the above problems, the pulse spectroscopy device of the invention of this application includes a pulse light source, and a multicore fiber or a bundle fiber that transmits each divided pulse light obtained by dividing the pulse light from the pulse light source, and each divided pulse light output from the multicore fiber or the bundle fiber has a one-to-one correspondence in time and wavelength, and includes a photoreceiver that receives light from an object irradiated with each divided pulse light. In this pulsed spectroscopic device, On the output side of the multi-core fiber or bundle fiber, One or more lenses that allow the split pulse light beams emitted from each core of the multicore fiber or each core of the bundle fiber to overlap in substantially the same region in a plane perpendicular to the optical axis. (However, this does not include microlens arrays.)A first lens system comprising: one or more lenses that project an image of the substantially identical area onto an illumination surface; (However, this does not include microlens arrays.) A second lens system consisting of is provided. In addition, in this pulse spectroscopic device, each core of the multicore fiber or each core of the bundle fiber is located at a position where light having different wavelengths from one another is incident from the pulse light source. In order to solve the above problems, a pulse spectroscopy device according to another invention of this application includes a pulse light source, and a multicore fiber or a bundle fiber that transmits each divided pulse light obtained by dividing a pulse light from the pulse light source, and each divided pulse light output from the multicore fiber or the bundle fiber has a one-to-one correspondence in time and wavelength, and includes a photoreceiver that receives light from an object irradiated with each divided pulse light. In this pulsed spectroscopic device, On the output side of the multi-core fiber or bundle fiber, One or more lenses that allow the split pulse light beams emitted from each core of the multicore fiber or each core of the bundle fiber to overlap in substantially the same region in a plane perpendicular to the optical axis. (However, this does not include microlens arrays.) A first lens system comprising: one or more lenses that project an image of the substantially identical area onto an illumination surface; (However, this does not include microlens arrays.) A second lens system consisting of is provided. In this pulse spectrometer, the first lens system and the second lens system are systems that enlarge and project the image of the output end of each core onto the irradiation surface. In the pulse spectroscopic device according to each aspect of the present invention, the second lens system may be a lens system made up of a plurality of lenses capable of adjusting the projection magnification onto the irradiation surface. In addition, in the pulse spectroscopic device according to each invention, the first lens system may be a lens system that converts each divided pulse light emitted from each core of the multicore fiber or each core of the bundle fiber into parallel light so that the divided pulse light beams overlap in substantially the same area.

[0011] In order to solve the above problems, the multi-fiber irradiation unit of the present invention is a unit connected to the output side of a multi-fiber that is a multicore fiber or a bundle fiber. This unit includes one or more lenses that allow the light emitted from each core of the multicore fiber or each core of the bundle fiber to overlap in substantially the same area in a plane perpendicular to the optical axis. (However, this does not include microlens arrays.) and a first lens system for projecting an image of the substantially same area onto an illumination surface. Consists of one or more lenses (excluding microlens arrays) and a second lens system. The first lens system and the second lens system are systems that enlarge and project the image of the output end of each core onto the irradiation surface. In the multi-fiber irradiation unit, the second lens system may be a lens system made up of a plurality of lenses capable of adjusting the projection magnification onto the irradiation surface. In addition, in the multi-fiber irradiation unit, the first lens system may be a lens system that converts light emitted from each core of the multi-core fiber or each core of the bundle fiber into parallel light so that the light overlaps in substantially the same area. Effect of the Invention

[0012] As described below, according to the pulse spectroscopy device of this application, the pulsed light emitted from each core of the multicore fiber or each core of the bundle fiber overlaps in substantially the same area in a plane perpendicular to the optical axis, so that even if the position of the object is slightly shifted, the irradiation conditions do not change, and highly reproducible spectroscopy measurement is possible. In this case, since the irradiation distance can be made long, high accuracy is not required for the mechanism for placing the object, and there is also a high degree of freedom in the optical aspects, such as the placement of filters. This makes it a practical pulse spectroscopy device. In addition, the multi-fiber irradiation unit has the effect of increasing the degree of freedom in the placement position of the object and the optical or mechanical design in applications other than multi-fibers used to achieve time-wavelength correspondence in pulse spectroscopy devices. [Brief description of the drawings]

[0013] [Figure 1] 1 is a schematic diagram of a pulse spectroscopy device according to an embodiment. [Diagram 2] FIG. 1 is a schematic diagram showing how time-wavelength correspondence is achieved by group delay. [Diagram 3] FIG. 1 is a plan schematic diagram of an arrayed waveguide grating used as a dividing element. [Figure 4] 1 is a schematic diagram of an irradiation unit in a pulse spectroscopy device according to an embodiment. [Diagram 5] FIG. 2 is a schematic diagram showing a configuration of an irradiation unit of a reference example. [Figure 6] 2 is a diagram illustrating a main part of an example of a measurement program provided in the pulse spectrometer. FIG. [Figure 7] FIG. 11 is a schematic plan view showing the influence of a positional deviation of an object. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Next, a mode (embodiment) for carrying out the invention of this application will be described. Fig. 1 is a schematic diagram of a pulse spectroscopy device according to an embodiment. The pulse spectroscopy device shown in Fig. 1 includes a pulse light source 1 and a correspondence unit 2 that realizes time-wavelength correspondence for pulsed light from the pulse light source 1, and is a device that performs spectroscopic measurement by utilizing the time-wavelength correspondence.

[0015] The pulse light source 1 is a light source that emits pulse light with a continuous spectrum. In this embodiment, for example, the light source emits light with a continuous spectrum over a wavelength width of at least 10 nm in the range of 900 nm to 1300 nm. "A spectrum that is continuous over a wavelength width of at least 10 nm in the range of 900 nm to 1300 nm" means any continuous wavelength width of 10 nm or more in the range of 900 to 1300 nm. For example, it may be continuous over 900 to 910 nm, or it may be continuous over 990 to 1000 nm. It is more preferable that it is continuous over a wavelength width of 50 nm or more, and more preferable that it is continuous over a wavelength width of 100 nm or more. In addition, "the spectrum is continuous" means that it contains a spectrum that is continuous over a certain wavelength width. This is not limited to the case where it is continuous over the entire spectrum of the pulse light, and it may be partially continuous.

[0016] The reason for the range of 900 nm to 1300 nm is that the pulse spectroscopy device of the embodiment is mainly used for spectroscopic analysis in the near infrared region. Light having a continuous spectrum over a wavelength width of at least 10 nm is typically SC light. Therefore, in this embodiment, the pulse light source 1 is an SC light source. However, a broadband pulse light source other than an SC light source may also be used.

[0017] The pulse light source 1, which is an SC light source, includes an ultrashort pulse laser 11 and a nonlinear element 12. A gain-switched laser, a microchip laser, a fiber laser, or the like can be used as the ultrashort pulse laser 11. A fiber is often used as the nonlinear element 12. For example, a photonic crystal fiber or other nonlinear fiber can be used as the nonlinear element 12. Although the fiber mode is often a single mode, a multimode fiber can also be used as the nonlinear element 12 as long as it shows sufficient nonlinearity.

[0018] As described above, the correspondence unit 2 is a unit that makes the relationship between time and the wavelength of light one-to-one. This point will be explained using Fig. 2. Fig. 2 is a schematic diagram showing how group delay is used to realize one-to-one correspondence between time and wavelength. When the SC light L1, which has a continuous spectrum in a certain wavelength range, is passed through a group delay fiber 9 having a positive dispersion characteristic in the wavelength range, the pulse width is effectively expanded. As shown in FIG. 2(1), the SC light L1 has an ultrashort pulse, but has the longest wavelength λ at the beginning of the pulse. 1 As time passes, shorter and shorter wavelengths of light appear, and at the end of the pulse, the shortest wavelength λ n When this light is passed through a normal dispersion group delay fiber 9, the shorter the wavelength of light, the later it propagates through the normal dispersion group delay fiber 9, so the time difference within one pulse is increased as shown in Figure 2 (2), and when it is output from the fiber 9, the light with the shorter wavelength is delayed further than the light with the longer wavelength. As a result, as shown in Figure 2 (3), the output SC light L2 becomes light whose pulse width is extended while the uniqueness of time versus wavelength is ensured. That is, at time t 1 ~t n is the wavelength λ 1 ~λ n The pulse is stretched in a one-to-one correspondence with each of the

[0019] It is also possible to use an anomalous dispersion fiber as the group delay fiber 9 for pulse stretching. In this case, the SC light is dispersed in such a way that the long wavelength light present at the beginning of the pulse is delayed and the short wavelength light present at the later time advances, so that the temporal relationship within one pulse is reversed, and the pulse is stretched in such a way that the short wavelength light is present at the beginning of the pulse and the longer wavelength light is present as time passes. However, compared to the case of normal dispersion, it is often necessary to make the propagation distance longer for pulse stretching, and loss is likely to be large. Therefore, in this respect, normal dispersion is preferable.

[0020] In order to realize time-wavelength compatibility, the pulse spectrometer of the embodiment does not use the group delay in a single fiber as described above, but rather splits and transmits light through multiple fibers and optimizes the length of each fiber, in order to suppress unintended nonlinear optical effects in the fibers. The realization of time-wavelength correspondence by splitting and transmitting through multiple fibers is based on the inventor's research. According to the inventor's research, for example, when measuring an absorption spectrum by irradiating a highly absorbing object S with light and dispersing the transmitted light, it becomes necessary to irradiate the object S with strong light, which requires high-intensity light with time-wavelength correspondence. Also, from the viewpoint of increasing the signal-to-noise ratio of the measurement or performing the measurement at high speed, it may become necessary to irradiate the object S with strong light.

[0021] In order to irradiate the object S with light that has achieved time-wavelength compatibility at high illuminance, it is necessary to input broadband pulsed light with high intensity to a group delay fiber and extend the pulse while maintaining the high intensity. However, it has been found that when high-intensity broadband pulsed light is input to a group delay fiber, unintended nonlinear optical effects occur, causing a problem of losing the time-wavelength uniqueness. Based on this knowledge, in this embodiment, a configuration is adopted in which the time-wavelength compatibility is achieved by dividing and transmitting the light through multiple fibers.

[0022] In this embodiment, the multiple fibers are a bundle fiber 21. A splitting element that splits light so that the light is incident on each fiber (hereinafter referred to as an element fiber) that constitutes the bundle fiber 21 is provided on the incident side of the bundle fiber 21. As for the splitting element, an element that splits light according to wavelength is used, and in this embodiment, an array waveguide grating (AWG) 3 is used.

[0023] When using the bundle fiber 2 as a group delay element, it is possible to simply split the light from the pulse light source 1 into multiple light beams and input them to each fiber to generate group delay. Although this configuration is fine, in order to realize a group delay amount according to the wavelength, a splitting element that splits the light for each wavelength is provided in this embodiment. As such a splitting element, an arrayed waveguide grating 3 is used in this embodiment.

[0024] FIG. 3 is a schematic plan view of an arrayed waveguide grating used as a splitting element. The arrayed waveguide grating is an element developed for optical communication, and its use for spectroscopic measurement is not known. As shown in FIG. 3, the arrayed waveguide grating 3 is configured by forming functional waveguides 32 to 36 on a substrate 31. Each functional waveguide is made up of a number of grating waveguides 32 with slightly different optical path lengths, slab waveguides 33 and 34 connected to both ends (incident side and exit side) of the grating waveguide 32, an incident side waveguide 35 that inputs light to the incident side slab waveguide 33, and each exit side waveguide 36 that extracts light of each wavelength from the exit side slab waveguide 34.

[0025] The slab waveguides 33 and 34 are free spaces, and the light incident through the incident-side waveguide 35 spreads in the incident-side slab waveguide 33 and enters each grating waveguide 32 in the same phase. Since each grating waveguide 32 has a slightly different length, the light that reaches the end of each grating waveguide 32 is shifted in phase by this difference. Light is diffracted and emitted from each grating waveguide 32, and the diffracted lights pass through the exit-side slab waveguide 34 while interfering with each other, and reach the entrance end of the exit-side waveguide 36. At this time, due to the phase shift, the interference light has the highest intensity at a position according to the wavelength. In other words, light with different wavelengths is incident on each exit-end waveguide 36 in sequence, and the light is spatially separated. Strictly speaking, each exit-side waveguide 36 is formed so that each entrance end is located at a position where the light is separated in this way.

[0026] Each element fiber in the bundle fiber 21 is connected to each output side waveguide 36 by a relay fiber 22. Each relay fiber 22 and each element fiber are connected by a connector element 23 such as a fan-in fan-out device. For this reason, the pulse light divided for each wavelength is transmitted to each element fiber via the relay fiber 22, and a delay according to the wavelength occurs at this time. That is, the relay fiber 22 has a different length according to the wavelength, and a time difference is provided in the transmission between the wavelengths. When the light emitted from each element fiber is superimposed (combined) at the target S, a state is created in which light with a one-to-one correspondence between time and wavelength is irradiated, similar to the case of pulse stretching.

[0027] In order to irradiate the object S with light in which time-wavelength correspondence is realized as described above, the pulse spectrometer includes an irradiation unit 4 as shown in Fig. 1. The irradiation unit 4 is a unit provided on the exit side of the bundle fiber 2. Fig. 4 is a schematic diagram of an irradiation unit in a pulse spectroscopy device according to an embodiment. The irradiation unit 4 is a unit that causes the light beams emitted from the respective element fibers to overlap and irradiate substantially the same area on an irradiation surface. As shown in Fig. 4, the irradiation unit 4 is composed of first and second lenses 41, 421, and 422, and a housing (not shown) that houses these lenses 41, 421, and 422.

[0028] The first lens 41 is a lens that makes the light emitted from the core of each element fiber overlap in substantially the same first region in a plane perpendicular to the optical axis (indicated by A in FIG. 4). The optical axis A here is the optical axis at the emission end face of the bundle fiber 21. More precisely, the optical axis A is a line extending perpendicularly from the center of the entire bundle fiber 21 to the end face. In the bundle fiber 21, a plurality of element fibers are usually bundled in a centrosymmetric manner, so that the center is the entire center of the bundle fiber 21. If it is not centrosymmetric, it is the center of the region surrounded by the envelope of the end faces of the fibers that make up the bundle (the center of gravity when the region is assumed to be a homogeneous plate).

[0029] In FIG. 4, the first region is indicated by R1. R1 The plane to which belongs is indicated as P1. As shown in Fig. 4, the first region R1 is a small region located near the output end surface of the bundle fiber 21. In this embodiment, as shown in Fig. 4, the first lens 41 is a lens that collimates the light that spreads and is output from the core of each element fiber and irradiates the first region R1.

[0030] The second lenses 421 and 422 are lenses that project an image of the first region R1 onto a second region. The second region is indicated by R2 in FIG. 4. The plane to which the second region R2 belongs (the plane perpendicular to the optical axis A) is indicated by P2. The second lenses 421 and 422 are two lenses. Of the two second lenses, the lens 421 closer to the output end face of the bundle fiber 21 is called the front lens, and the lens 422 farther from the output face is called the rear lens.

[0031] The front lens 421 is a lens for adjusting the magnification of the image in the first region R1. Therefore, like a zoom lens, a mechanism is provided for holding the front lens 421 movably along the optical axis. The rear lens 422 is a lens for focusing light on the second region R2. The magnification can be appropriately selected, but is in the range of, for example, about 0.5 to 3 times.

[0032] As can be seen from FIG. 4, the distance to the first region R1 is short. This distance is about 4 to 10 mm. In other words, if the distance is this short, the light irradiation patterns from each element fiber can be overlapped on substantially the same region with one lens. However, if it is desired to increase the irradiation distance for some reason, it is not possible to overlap on substantially the same region because there is no lens with a suitable focal length. If it is desired to overlap by concentrating light instead of collimating it, this can be achieved with a lens with a long focal length, but it will not overlap on substantially the same region.

[0033] FIG. 5 illustrates this point, and is a schematic diagram showing the configuration of an irradiation unit of a reference example. In this reference example, the light emitted from a multi-core fiber 81 having three cores is focused and projected by a focusing lens 40 having a focal length of about 50 mm. The output ends of the three cores are In They are lined up vertically. A pattern E of light emitted from three cores is depicted on the right side of Fig. 5. As shown here, the light emitted from each core does not overlap with substantially the same region R on plane P, but is emitted in a shifted manner.

[0034] On the other hand, in the embodiment, the first lens 41 is configured to overlap the irradiation patterns in the first region R1, and the image of this region R1 is projected onto the second region R2 by the second lens, so that it is possible to obtain an irradiation pattern that overlaps with substantially the same region R2 as shown in Fig. 4 while taking a long irradiation region. As an example of dimensions, the first region R1 has a diameter of about 1 to 3 mm, and the second region R2 has a diameter of about 2 to 4 mm. In addition, "substantially" in "substantially the same area" means that the deviation of the irradiation pattern is within a range that does not cause a practical problem. For example, if the irradiation pattern is circular, it can be considered "substantially the same" if the deviation is 10% or less of the diameter. If it is not circular, it can be considered "substantially the same" if the deviation is 10% or less of the width as viewed in the longest direction and position.

[0035] The fact that the first lens 41 is a lens that collimates light (converts it into parallel light) and superimposes it on the first region R1 is significant in that it makes it easy to adjust the projection magnification by the front lens 421. The light superimposed in the first region R1 then separates again and travels in different directions, but if the first lens 41 is a collimating lens, the beam diameter reaches the front lens 421 with substantially the same diameter. The front lens 421 is moved along the optical axis to adjust the magnification, but even in this case, the beam diameter reaching the front lens 421 does not change, so the design of the front lens 421 and the rear lens 422 is easy.

[0036] In such an irradiation unit 4, a filter is appropriately provided in a housing (not shown) or at an exit side opening of the housing. The filter may be a neutral density filter or a wavelength selection filter such as a band pass filter or a cut filter. When the filter is provided in the housing, it may be provided anywhere, for example, between the front lens 421 and the rear lens 422, on the exit side of the rear lens 422, etc.

[0037] The device of the embodiment includes a holding member that holds the object S at a position (position of the second region R2) where the pulsed light is irradiated by the irradiation unit 4. In this embodiment, since the pulsed light is irradiated from above, the holding member is a receiving plate 5. Since the device of this embodiment is a device for measuring the spectral transmittance characteristics of the object S, the receiving plate 5 is translucent, and a light receiver 6 is provided at a position for receiving the transmitted light.

[0038] The device includes a calculation means 7 as a means for processing the output of the photoreceiver 6 to obtain a spectroscopic measurement result. In this embodiment, a general-purpose PC is used as the calculation means 7. An AD converter 70 is provided between the photoreceiver 6 and the calculation means 7, and the output of the photoreceiver 6 is input to the calculation means 7 via the AD converter 70. The calculation means 7 includes a processor 71 and a storage unit (hard disk, memory, etc.) 72. A measurement program 73 for processing output data from the photodetector 6 to calculate a spectrum and other necessary programs are installed in the storage unit 72. Fig. 6 is a diagram showing a schematic diagram of the main parts of an example of a measurement program included in the pulse spectrometer.

[0039] The example in FIG. 6 is an example of a program in which the measurement program 73 measures the absorption spectrum (spectral absorptance). Reference spectral data is used to calculate the absorption spectrum. The reference spectral data is a value for each wavelength that serves as a reference for calculating the absorption spectrum. The reference spectral data is acquired by making the light from the irradiation unit 4 incident on the light receiver 6 without passing through the object S. That is, the light is made incident directly on the light receiver 6 without passing through the object S, and the output of the light receiver 6 is input to the calculation means 7 via the AD converter 70, and a value for each time resolution Δt is acquired. Each value is calculated at each time (t 1 ,t 2 ,t 3 , ) is stored as the reference intensity (V 1 ,V 2 ,V 3 ,...). The time resolution Δt is an amount determined by the response speed (signal output period) of the photoreceiver 6, and means the time interval at which a signal is output.

[0040] Each time t 1 ,t 2 ,t 3 Reference strength V at , 1 ,V 2 ,V 3 ,... are the corresponding wavelengths λ 1 ,λ 2 ,λ 3 ,..., the intensity (spectrum) of the pulse at time t 1 ,t 2 ,t 3 The relationship between , and wavelength has been investigated in advance, and the value V 1 ,V 2 ,V 3 ,... for each λ 1 ,λ 2 ,λ 3 ,..., are treated as values. When the light that has passed through the object S is incident on the photoreceiver 6, the output from the photoreceiver 6 is converted to the analog signal at each time t 1 ,t 2 ,t 3 ,..., are stored in memory as the measured values ​​(v 1 ,v 2 ,v3 Each measurement is compared with a reference spectrum data (v 1 / V 1 ,v 2 / V 2 ,v 3 / V 3 ,...), and the result is an absorption spectrum (taking the logarithm of the reciprocal as necessary). The measurement program 73 is programmed to carry out the above-mentioned calculation processing.

[0041] Next, the operation of the above-mentioned pulse spectrometer will be described. When performing spectrometry using the pulse spectroscopy device of the embodiment, first, the pulse light source 1 is operated in a state where the target object S is not placed. The broadband pulse light from the pulse light source 1 is split by the arrayed waveguide grating 3 as a splitting element and transmitted to each element fiber of the bundle fiber 21 via each relay fiber 22. The transmitted light is emitted from the irradiation unit 4 in a state where time-wavelength correspondence is realized, and reaches the photoreceiver 6. Then, the output data from the photoreceiver 6 is processed to obtain reference spectrum data in advance.

[0042] Next, the object S is placed on the receiving plate 5, and the pulsed light source 1 is operated again. The pulsed light is similarly divided to achieve the same time-wavelength correspondence, and is irradiated onto the object S via the irradiation unit 4. The light transmitted through the object S reaches the photoreceiver 6, and the output data from the photoreceiver 6 is input to the calculation means 7 via the AD converter 70. Then, the absorption spectrum is calculated by the measurement program 73. In this operation, the patterns of emitted light from each element fiber are overlapped and irradiated without shifting in the second region R2 where the object S is located. Therefore, even if the position of the object S shifts slightly, the irradiation conditions do not change, and highly reproducible spectroscopic measurement is possible.

[0043] The above points will be further explained with reference to Fig. 7. Fig. 7 is a schematic plan view showing the influence of a positional deviation of an object. Fig. 7(1-1) and Fig. 7(2-1) show a case where the irradiation pattern E1 and the irradiation pattern E2 are deviated as in the reference example of Fig. 5, while Fig. 7(1-2) and Fig. 7(2-2) show a case where the irradiation pattern E1 and the irradiation pattern E2 overlap in the same region as in the embodiment. Regarding the relationship between the irradiation area and the size of the object S, there are two cases: the irradiation area is smaller than the object S and light is irradiated only to a certain area of ​​the object S, and the irradiation area is larger than the object S and light is irradiated to the entire area of ​​the object S (the entire area of ​​the incident surface). Figures 7(1-1) and 7(1-2) show the former case, and Figures 7(2-1) and 7(2-2) show the latter case.

[0044] Here, let us assume that, among the components contained in the target object S, component X is detected with the wavelength of light of irradiation pattern E1, and component Y is detected with the wavelength of irradiation pattern E2. Let us assume that irradiation pattern E1 is light of wavelength λ1, and the amount of component X can be known from the absorptance of light of wavelength λ1. Let us also assume that irradiation pattern E2 is light of wavelength λ2, and the amount of component Y can be known from the absorptance of light of wavelength λ2. Also, as shown in FIG. 7(1-1), assume that the object S has projections and projections, and the irradiation pattern E1 is irradiated onto the projections and the irradiation pattern E2 is irradiated onto the recesses. Both irradiation patterns E1 and E2 are smaller than the object S. In this case, even if the object S contains the same amount of component X and component Y, the amount of the components contained in the cross section of the projections along the light propagation direction is large for both X and Y, and the amount of the components contained in the cross section of the recesses is small for both X and Y. Therefore, the amount of component X detected by the light of the irradiation pattern E1 passing through the projections is large, and conversely, the amount of component Y detected by the light of the irradiation pattern E2 passing through the recesses is small. That is, a relative difference occurs in the detection amount of the components X and Y. In this way, when the irradiation patterns E1 and E2 are misaligned, it is impossible to determine whether the difference in relative component amounts is due to a difference in the position (thickness) of the object S or due to the object not containing the same amounts. On the other hand, when the irradiation patterns E1 and E2 overlap, as shown in Fig. 7(1-2), even if the target S has unevenness, the measurement can be performed at the same position, so there is no difference in the measurement results of the component amount due to the difference in thickness. Therefore, accurate measurement is possible.

[0045] Also, as shown in Fig. 7(2-1), if the irradiation pattern is larger than the object S, for example, if the irradiation pattern E2 is not irradiated onto the object S, the component Y cannot be detected even if it is contained in the object S. On the other hand, as shown in Fig. 7(2-2), if the irradiation pattern E1 and the irradiation pattern E2 overlap, both the component X and the component Y can be detected.

[0046] As can be seen from FIG. 7, when the irradiation patterns are overlapped in substantially the same region, even if the object S is shifted slightly, the reproducibility does not decrease. In other words, it is not necessary to place the object S in the exactly same position, and there is an advantage that high accuracy is not required for the placement position of the object S. This point is particularly prominent in the case of an application in which a pulsed light is irradiated to a product flowing (conveyed) on a production line, and a spectroscopic analysis is performed in real time to determine whether it is good or bad. That is, in such an application, the object S is moved while irradiating the irradiation region with a pulsed light, and data is obtained from the light receiver 6 at the timing when the object S passes through the irradiation region without stopping the object S, and spectroscopic analysis is performed. In such a case, the timing shift corresponds to the above-mentioned shift in the placement position, but the configuration of the embodiment in which high accuracy is not required for the placement position provides the advantage that the reproducibility does not decrease even if the timing is shifted slightly.

[0047] The fact that the irradiation distance can be long is also of great significance in various spectroscopic measurement applications. For example, as described above, when irradiating the transported object S with pulsed light, if the irradiation distance is short, it is easily affected by the accuracy of the transport mechanism. In other words, if the accuracy of the transport mechanism is low and the object S is transported with a deviation in the optical axis direction, the object S is likely to collide with the irradiation unit 4. For this reason, a highly accurate transport mechanism is required. If the irradiation distance is long, such a problem does not occur and a highly accurate transport mechanism is not required. This is also true when stopping the object S in the irradiation area.

[0048] In addition to mechanical aspects, being able to extend the irradiation distance also has optical advantages. When the irradiation distance is short, it becomes difficult to place a filter as described above, but this is easy with the embodiment. Also, there may be cases where it is necessary to change the direction of light midway for some reason, making it necessary to place a mirror or the like. Even in such cases, this is easy with the configuration of the embodiment.

[0049] In addition, in Fig. 4, the first lens 41 and the second lenses 421, 422 are depicted as being composed of one lens, but may be composed of multiple lenses for the purpose of removing chromatic aberration, etc. Also, the second lens may be composed of one lens, instead of the two lenses of the front lens 421 and the rear lens 422. In this case, a configuration in which the magnification is changed by replacing the lens using a revolver mechanism, etc. may be adopted. Furthermore, the rear lens 422 defines the distance to the final projection surface, and the irradiation distance can also be changed by replacing the rear lens 422.

[0050] In the above embodiment, each relay fiber 22 and each element fiber in the bundle fiber 21 may be the same fiber, or may be fibers different in terms of material and length. Even if the material is the same, if the length is changed, the overall group delay amount changes, so element fibers of different lengths may be used depending on the wavelength. The same applies to the material. By selecting the fiber length and material so that the group delay amount is optimal depending on the wavelength, the value of Δλ / Δt can be made more uniform, and spectroscopic measurement with uniform resolution (small difference in resolution depending on the wavelength band) can be realized. Since it is often complicated to mutually change the material and length of each element fiber in the bundle fiber 21, it is practical to change the length and material of the relay fiber 22 depending on the wavelength.

[0051] Also, a multi-core fiber may be used as the group delay element. In the case of a multi-core fiber, the irradiation unit 4 is configured to include a first lens 41 that superimposes the light emitted from each core onto a substantially identical first region, and second lenses 421, 422 that project an image of the first region R1 onto a second region R2. As a specific example of a multi-core fiber, for example, one having a core diameter of about 100 to 150 μ and a core number of about 7 can be suitably used. The size of the first region R1 and the size of the second region R2 are approximately the same as those of the bundle fiber.

[0052] In addition, the number of cores of the multi-core fiber is practically several to 10, but the number of element fibers of the bundle fiber 21 can be more than this, and a bundle fiber in which several tens of element fibers are bundled can also be used. For this reason, when the number of divisions in the division element is increased, the bundle fiber is preferable. The reason for increasing the number of divisions is to increase the number of cores to reduce the transmission power per core and further suppress the occurrence of unintended nonlinear optical effects, to divide more finely when dividing according to wavelength to finely adjust the amount of group delay, or both. For example, when the above-mentioned arrayed waveguide diffraction grating is used as the division element, a bundle fiber in which the element fibers are divided into about 50 to 70 pieces and the same number of element fibers are bundled can be used.

[0053] As for the dividing element, although the number of divisions will be smaller, a configuration in which multiple stages of fiber couplers are used for division or multiple stages of dichroic mirrors for division is also possible. Although the above-mentioned example of the operation of the device is to measure the absorption spectrum, there are also cases where the device measures spectral characteristics such as the reflection spectrum (spectral reflectance) and internally scattered light. In addition, a configuration may be possible in which a plurality of ordinary fibers are used in parallel without bundling them, without using a multi-core fiber or a bundle fiber. In this case, the irradiation unit 4 may be connected to the plurality of fibers via a connector element such as a fine fan-out device.

[0054] The pulse spectrometer may be configured to acquire reference spectrum data in real time. In this case, a beam splitter is used to split the light emitted from the bundle fiber or multi-core fiber into two, one of which is irradiated onto the object S, and the other is incident on a reference receiver. Light that has not passed through the object S is incident on the reference receiver, and the data obtained by similarly AD-converting the output from the light splitter becomes the reference spectrum data. The beam splitter in this configuration may be provided in the irradiation unit 4, or may be provided separately on the exit side of the irradiation unit 4.

[0055] In the above explanation, the spectroscopic measurement of the transmitted light from the object S is taken as an example, but the light receiver 6 may be provided at a position to receive the reflected light from the object S, and the spectroscopic measurement of the reflected light from the object S may be performed. Furthermore, the spectroscopic measurement may be performed by capturing the scattered light or fluorescence from the object S irradiated with light by the irradiation unit 4. In other words, the light from the object S may be the transmitted light, reflected light, fluorescence, scattered light, etc. from the object S irradiated with light.

[0056] As the pulse light source 1, in addition to one that emits SC light, an ASE (Amplified Spontaneous Emission) light source, an SLD (Superluminescent diode) light source, or the like may also be used. Furthermore, the above-mentioned irradiation unit 4 is a unit provided on the output side of a multi-core fiber or a bundle fiber, and is a multi-fiber irradiation unit. "Multi-fiber" is a general term for multi-core fibers and bundle fibers. The multi-fiber irradiation unit is not limited to cases where the multi-fiber is used to realize time-wavelength compatibility of broadband pulsed light. It is preferably used in applications where light needs to be divided and transmitted for some reason and overlapped on the irradiation surface. Note that there may be cases where only the output end of the bundle fiber is bundled and the input end is not bundled. [Explanation of symbols]

[0057] 1 Pulsed light source 2. Correspondence Unit 21 Fiber bundle 211 element fiber 22 Relay fiber 3. Arrayed Waveguide Grating 4 Irradiation unit 41 First Lens 421 Second Lens 422 Second Lens 5 Receiving plate 6 Receiver 7 Calculation means 70 AD converter S Object

Claims

1. A pulsed light source; a multi-core fiber or a bundle fiber for transmitting each divided pulse light obtained by dividing a pulse light from a pulse light source, A pulse spectroscopic device, comprising: a photoreceiver that receives light from an object irradiated with each divided pulse light, the divided pulse light being in one-to-one correspondence with a time and a wavelength of the divided pulse light emitted from a multicore fiber or a bundle fiber; On the output side of the multi-core fiber or bundle fiber, a first lens system including one or more lenses (excluding a microlens array) that allow each divided pulse light outputted from each core of the multicore fiber or each core of the bundle fiber to overlap in substantially the same region in a plane perpendicular to the optical axis; a second lens system consisting of one or more lenses (excluding a microlens array) that projects an image of the substantially same area onto an illumination surface; There is a system in place, A pulse spectroscopic device, characterized in that each core of a multicore fiber or each core of a bundle fiber is located at a position where light having different wavelengths from one another is incident from a pulse light source.

2. A pulsed light source; a multi-core fiber or a bundle fiber for transmitting each divided pulse light obtained by dividing a pulse light from a pulse light source, A pulse spectroscopic device, comprising: a photoreceiver that receives light from an object irradiated with each divided pulse light, the divided pulse light being in one-to-one correspondence with a time and a wavelength of the divided pulse light emitted from a multicore fiber or a bundle fiber; On the output side of the multi-core fiber or bundle fiber, a first lens system including one or more lenses (excluding a microlens array) that allow each divided pulse light outputted from each core of the multicore fiber or each core of the bundle fiber to overlap in substantially the same region in a plane perpendicular to the optical axis; a second lens system consisting of one or more lenses (excluding a microlens array) that projects an image of the substantially same area onto an illumination surface; There is a system in place, A pulse spectroscopic device, wherein the first lens system and the second lens system are systems for enlarging and projecting an image of the output end of each core onto an irradiation surface.

3. 2. The pulse spectrometer according to claim 1, wherein the second lens system is made up of a plurality of lenses capable of adjusting a projection magnification onto the irradiation surface.

4. 4. The pulse spectroscopic device according to claim 1, 2 or 3, wherein the first lens system is a lens system that converts each divided pulse light emitted from each core of the multicore fiber or each core of the bundle fiber into parallel light so that the divided pulse light overlaps in the substantially same region.

5. A multi-fiber irradiation unit connected to an output side of a multi-fiber that is a multi-core fiber or a bundle fiber, a first lens system including one or more lenses (excluding a microlens array) that allow light emitted from each core of the multicore fiber or each core of the bundle fiber to overlap in substantially the same area in a plane perpendicular to the optical axis; a second lens system consisting of one or more lenses (excluding a microlens array) that projects an image of the substantially same area onto an illumination surface; Equipped with The first lens system and the second lens system are a multi-fiber irradiation unit that is a system for enlarging and projecting an image of the output end of each core onto an irradiation surface.

6. 6. The multi-fiber irradiation unit according to claim 5, wherein the second lens system is made up of a plurality of lenses capable of adjusting the projection magnification onto the irradiation surface.

7. The multi-fiber irradiation unit according to claim 6, characterized in that the first lens system is a lens system that converts light emitted from each core of the multi-core fiber or each core of the bundle fiber into parallel light so that the parallel light overlaps in the substantially same area.

Images