Light source device for light measurement, spectroscopic measurement device, and spectroscopic measurement method

Abstract

To provide a light source device for light measurement in which the uniqueness of time wavelength is not lost even when high output is used, and to enable high-precision, high-speed spectroscopic measurement. SOLUTION: A broadband pulsed light having a continuous spectrum over a wavelength width of at least 50 nm in the range of 900 to 1300 nm is emitted from a pulse light source 1, and is split into wavelengths by a splitter 3, and the light of each wavelength is transmitted through extension fibers 41 to 4n and output from a coupler 5. Each extension fiber 41 to 4n has a different length so that the elapsed time within one pulse corresponds one-to-one to the wavelength at the output end.

Description

[Technical Field]

[0001] The invention of this application relates to a light source device for light measurement that emits broadband pulsed light, and also to a spectroscopic measurement technique that uses the light source device. [Background technology]

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

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-205390 [Patent Document 2] U.S. Patent No. 7,184,144 [Patent Document 3] US Patent Application Publication No. 2017 / 0122806 [Patent Document 4] Japanese Patent Application Publication No. 9-15661 [Patent Document 5] Japanese Patent Application Laid-Open No. 2003-279480 [Patent Document 6] Japanese Patent Application Publication No. 2019-45271 [Patent Document 7] Japanese Patent Application Laid-Open No. 2002-162345 [Patent Document 8] Japanese Patent Application Publication No. 8-122833 [Patent Document 9] Japanese Patent Application Laid-Open No. 2004-233341 [Patent Document 10] Japanese Patent Application Laid-Open No. 2001-91357 Summary of the Invention [Problem to be solved by the invention]

[0004] Although the wavelength range of the above-mentioned broadband pulse light is stretched, the pulse width (time width) remains narrow. However, by utilizing the group delay in a transmission medium such as fiber, the pulse width can also be stretched. In this case, by selecting an element with appropriate dispersion characteristics, the pulse can be stretched with a one-to-one correspondence between the elapsed time (time instant) within the pulse and the wavelength. Pulse light in this state where the elapsed time within the pulse and the wavelength correspond one-to-one is sometimes called chirped pulse light or linearly chirped pulse light.

[0005] The correspondence between elapsed time and wavelength in broadband pulsed light (hereinafter referred to as broadband stretched pulsed light) can be effectively utilized in spectroscopic measurements. That is, when broadband stretched pulsed light is received by a detector, the temporal change in light intensity detected by the detector corresponds to the light intensity of each wavelength, i.e., the spectrum. Therefore, the temporal change in the detector's output data can be converted into a spectrum, making spectroscopic measurements possible without using a special dispersive element such as a diffraction grating. That is, by irradiating a sample with broadband stretched pulsed light, receiving the light from the sample with a detector, and measuring the temporal change, the spectral characteristics of the sample (e.g., spectral transmittance) can be determined.

[0006] Thus, broadband stretched pulsed light is considered to be particularly useful in fields such as spectroscopy. However, research by the inventors has revealed 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, destroying the uniqueness (one-to-one correspondence) between elapsed time and wavelength. Loss of the uniqueness between elapsed time and wavelength leads to a significant decrease in measurement accuracy, particularly when used in spectroscopy. The invention of this application is based on this finding, and aims to provide a light source device for light measurement that does not lose the uniqueness of the elapsed time and wavelength even when high output is used, and to enable high-precision, high-speed spectroscopic measurements by using such a light source device. [Means for solving the problem]

[0007] In order to solve the above problems, the spectroscopic measurement device of this application includes a pulse light source equipped with a nonlinear fiber that emits pulse light having a continuous spectrum over a wavelength width of at least 100 nm due to the nonlinear optical effect of the nonlinear fiber, a splitter that spatially divides the pulse light emitted from the nonlinear fiber according to wavelength bands, and a plurality of single-mode fibers, the number of which corresponds to the number of wavelength bands divided by the splitter. The splitter is an arrayed-waveguide grating, and the nonlinear fiber is arranged so that the emitted light is incident on an input-side slab waveguide of the arrayed-waveguide grating, and each of the plurality of single-mode fibers is arranged so that light of each wavelength band from the output-side slab waveguide of the arrayed-waveguide grating is incident thereon. Each of the plurality of single-mode fibers has a different length according to the wavelength of the incident light so that the elapsed time within one pulse corresponds one-to-one to the wavelength. This spectroscopic measurement device includes a detector arranged at a position where light from an object (excluding the case where the object is light) illuminated with light emitted from each of the plurality of single-mode fibers is incident, and a calculation means for calculating the spectral characteristics of the object (excluding the case where the object is light) according to the output from the detector. In order to solve the above problem, the spectroscopic measurement device of this application includes a plurality of Single ModeThe fiber may be a multi-core fiber and element fibers constituting a plurality of fiber sets, each of which is composed of element fibers having the same pattern but different lengths, the core of each element fiber and each core of the multi-core fiber are connected, and the number and length of the multi-core fibers are selected so that the total lengths of the transmission paths formed by the cores of each element fiber and each core of the multi-core fiber are different from each other. In order to solve the above problem, the spectroscopic measurement device of this application may have a configuration in which the nonlinear fiber is a fiber that generates the nonlinear optical effect so that supercontinuum light is emitted. In order to solve the above problems, the spectroscopic measurement method of this application comprises: a broadband light emission step of generating a nonlinear optical effect in pulsed light by the nonlinear fiber in a pulsed light source equipped with a nonlinear fiber, thereby emitting pulsed light having a continuous spectrum over a wavelength width of at least 100 nm; a splitting step of spatially splitting the pulsed light outputted in the broadband light outputting step into light of each wavelength range by inputting the pulsed light into an input-side slab waveguide of the arrayed-waveguide diffraction grating and outputting light of each wavelength range from an output-side slab waveguide; a pulse elongation step in which a plurality of single-mode fibers are connected so that light in each wavelength range is incident from an output-side slab waveguide of the arrayed-waveguide diffraction grating, and pulsed light in each spatially divided wavelength range is incident on each single-mode fiber and transmitted, thereby achieving a one-to-one correspondence between the elapsed time within one pulse and the wavelength; an irradiation step of irradiating an object (excluding the case where the object is light) with the pulsed light whose pulse width has been extended by the pulse extension step; a detection step of detecting, with a detector, light from an object irradiated with the pulsed light whose pulse width has been extended by the pulse extension step (excluding the case where the object is light); a calculation step of calculating the spectral characteristics of the object according to the output from the detector; It is equipped with Each of the plurality of single mode fibers used in the pulse stretching step has a different length depending on the wavelength of the incident light so that the elapsed time within one pulse corresponds one-to-one to the wavelength. In order to solve the above problem, the spectroscopic measurement method of this application includes a plurality of Single Mode The fiber may be configured as element fibers constituting a plurality of fiber sets and a multi-core fiber, each fiber set being composed of a plurality of element fibers having the same pattern but different lengths, the core of each element fiber being connected to each core of the multi-core fiber, and the number and length of the multi-core fibers being selected so that the total lengths of each transmission path consisting of the core of each element fiber and each core of the multi-core fiber are different from each other. In order to solve the above problems, the spectroscopic measurement method of this application is area The pulsed light emitted in the light emitting step may be supercontinuum light. [Effects of the Invention]

[0008] As will be explained below, with the optical measurement light source device of this application, broadband pulsed light is split into light of each wavelength by a splitter, and the pulse is extended by delays according to the propagation distance in each fiber transmitting the light of each wavelength, so that the problem of unintended nonlinear optical effects causing the loss of time-wavelength uniqueness does not occur. Therefore, optical measurement can be performed by irradiating an object with broadband pulsed light with ensured time-wavelength uniqueness at high illuminance. This enables high-speed, high-quality optical measurement. Furthermore, when the splitter is an arrayed waveguide grating, the low loss allows for even higher illuminance light irradiation, and the connection to each fiber is easy, making it easy to manufacture. Furthermore, if the plurality of fibers are arranged in a plurality of fiber sets with the same pattern but different lengths, costs can be reduced. Furthermore, according to the spectroscopic measurement device and spectroscopic measurement method of this application, light from a light source is divided in time and irradiated onto an object, eliminating the need for time-consuming operations such as scanning a diffraction grating, enabling high-speed spectroscopic measurement. Furthermore, when performing pulse stretching to ensure time-wavelength uniqueness, a configuration is adopted in which each wavelength is transmitted through separate fibers of different lengths, so that time-wavelength uniqueness is not lost even when irradiating the object with light at high illuminance. This allows for high-precision spectroscopic measurement that requires irradiation with high-power light, such as spectrometry of highly absorbing objects, resulting in a high-speed, highly reliable device and method. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic diagram of a light source device for light measurement according to a first embodiment; [Figure 2] FIG. 1 is a schematic diagram illustrating the principle of pulse stretching of broadband pulsed light. [Figure 3] 10A and 10B show the results of an experiment to confirm unintended nonlinear optical effects when high-intensity broadband pulsed light is pulse-stretched using a group delay fiber. [Figure 4] FIG. 1 is a plan view schematic diagram of an arrayed waveguide grating employed as a splitter. [Figure 5] FIG. 10 is a schematic diagram of another example divider. [Figure 6] FIG. 10 is a schematic diagram of another example divider. [Figure 7] FIG. 10 is a schematic diagram of a light source device for light measurement according to a second embodiment. [Figure 8] 1 is a schematic diagram of a spectroscopic measurement device according to a first embodiment. [Figure 9] FIG. 2 is a diagram illustrating a main part of an example of a measurement program included in the spectroscopic measurement device. [Figure 10] FIG. 10 is a schematic diagram of a spectroscopic measurement device according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Next, a mode (embodiment) for carrying out the invention of this application will be described. First, an embodiment of the light source device for light measurement according to the present invention will be described. Fig. 1 is a schematic diagram of a light source device for light measurement according to a first embodiment. The light source device for light measurement shown in Fig. 1 comprises a pulse light source 1 and a pulse stretching unit 2. The pulse stretching unit 2 is a unit that stretches the pulse of light from the pulse light source 1 so that the relationship between the elapsed time within one pulse and the wavelength is one to one.

[0011] The pulse light source 1 is a light source that emits pulsed 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. The term "a continuous spectrum over a wavelength width of at least 10 nm in the range of 900 nm to 1300 nm" refers to any continuous wavelength width of at least 10 nm within the range of 900 to 1300 nm. For example, the spectrum may be continuous over a wavelength width of 900 to 910 nm or over a wavelength width of 990 to 1000 nm. It is more preferable that the spectrum be continuous over a wavelength width of at least 50 nm, and even more preferable that the spectrum be continuous over a wavelength width of at least 100 nm. Furthermore, "a continuous spectrum" means that the spectrum includes a continuous spectrum over a certain wavelength width. This does not necessarily mean that the spectrum of the pulsed light is continuous over the entire spectrum, but may also be partially continuous. The reason for specifying the range from 900 nm to 1300 nm is that the light source device of this embodiment is intended for use in optical measurement in this wavelength range. Light with a continuous spectrum over a wavelength width of at least 10 nm is typically SC light. Therefore, in this embodiment, the pulsed light source 1 is an SC light source. However, other broadband pulsed light sources such as an SLD (Superluminescent Diode) light source may also be used.

[0012] 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. Furthermore, 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 single mode, even a multimode fiber can be used as the nonlinear element 12 as long as it exhibits sufficient nonlinearity.

[0013] The pulse stretcher unit 2 is a major feature of the light source device of this embodiment. Although the wavelength band of the light emitted from the pulse light source 1 is broadened, the pulse width remains a short pulse on the order of femtoseconds to nanoseconds. Since this makes it difficult to use for optical measurement, the pulse is stretched by the pulse stretcher unit 2. What is important here is that a configuration is adopted in which the pulse is stretched so that the relationship between the elapsed time and wavelength in one pulse is one to one. In this case, the light source device of this embodiment employs a configuration that takes into consideration the occurrence of unintended nonlinear optical effects.

[0014] The inventors have identified a problem in the course of their research that occurs when broadband pulsed light is stretched, resulting in the occurrence of unintended nonlinear optical effects that disrupt the uniqueness of the time-wavelength. This problem will be explained below with reference to Fig. 2. Fig. 2 is a schematic diagram illustrating the principle of pulse stretching of broadband pulsed light.

[0015] As a means for extending the pulse width of broadband pulsed light such as SC light, a configuration using a fiber with specific group delay characteristics, such as a dispersion compensating fiber (DCF), is preferably adopted. For example, when SC light L1, which has a continuous spectrum in a certain wavelength range, is passed through a group delay fiber 9 that has positive dispersion characteristics in that wavelength range, the pulse width is effectively extended. That is, as shown in Figure 2, although the SC light L1 is an ultrashort pulse, the longest wavelength λ1 exists at the beginning of one pulse, and as time passes, light with gradually shorter wavelengths appears, and at the end of the pulse, the shortest wavelength λn When this light is passed through a normal dispersion group delay fiber 9, the shorter the wavelength of light, the more delayed it propagates through the normal dispersion group delay fiber 9, so the time difference within one pulse is increased, and when it is output from the fiber 9, the shorter wavelength light is delayed further than the longer wavelength light. As a result, the output SC light L2 is light whose pulse width is extended while the uniqueness of time versus wavelength is ensured. That is, as shown in the lower part of Figure 2, n is the wavelength λ1 to λ n The pulses are stretched in a one-to-one correspondence with each other.

[0016] 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 a later time is advanced. This reverses the temporal relationship within a pulse, and the pulse is stretched in such a way that the short-wavelength light is present at the beginning of the pulse and the long-wavelength light is present as time passes. However, compared to normal dispersion, this often requires a longer propagation distance for pulse stretching, which tends to result in larger losses. Therefore, in this respect, normal dispersion is preferable.

[0017] In pulse stretching using such a group delay fiber, in the field of optical measurement, it is sometimes necessary to increase the intensity of the broadband pulsed light input to the fiber. For example, when measuring the absorption spectrum by irradiating a highly absorbing object with light and dispersing the transmitted light, it is necessary to irradiate the object with strong light, which in turn requires stretching strong light during pulse stretching. In addition, it may be necessary to irradiate the object with strong light from the perspective of increasing the signal-to-noise ratio of the measurement or performing the measurement at high speed.

[0018] To irradiate an object with pulse-stretched light at high illuminance, it is necessary to input high-intensity broadband pulsed light into a group delay fiber and stretch the pulse while maintaining high intensity. However, when high-intensity broadband pulsed light is input into a group delay fiber, unintended nonlinear optical effects may occur, destroying the time-wavelength uniqueness. Figure 3 shows the results of an experiment that confirmed this point.

[0019] Figure 3 shows the results of an experiment to confirm unintended nonlinear optical effects when high-intensity broadband pulsed light is stretched using a group delay fiber. The vertical axis in Figure 3 is a logarithmic scale. In the experiment shown in Figure 3, microchip laser light with a central wavelength of 1064 nm and a pulse width of 2 nanoseconds was input into a photonic crystal fiber as a nonlinear element to generate SC light, and the pulse was stretched using a 5 km long single-mode fiber as a group delay fiber. The single-mode fiber is a fiber with normal dispersion in the 1100 to 1200 nm range. In this experiment, the energy of the SC light input into the single-mode fiber was changed to 0.009 μJ, 0.038 μJ, 0.19 μJ, and 0.79 μJ.

[0020] As shown in Figure 3, when the SC light energy is up to 0.19 μJ, there is no significant variation in the output light intensity in the wavelength range of 1100 to 1200 nm. However, when the energy is 0.79 μJ, the output light intensity fluctuates significantly depending on the wavelength. This variation indicates that an unintended additional nonlinear optical effect occurs in the SC light as it enters and propagates through the single-mode fiber (group delay fiber). When this nonlinear optical effect occurs, a new wavelength is generated at a different time, destroying the time-wavelength uniqueness. Note that in the experiment whose results are shown in Figure 3, the pulse width of the incident SC light remains unchanged, which means that the peak value has changed.

[0021] Based on this knowledge, the inventors have optimized the configuration of the pulse stretcher. Specifically, as shown in Fig. 1, the light source device for light measurement of the embodiment includes a pulse stretcher unit 2 that stretches the pulse width of wideband pulsed light from a pulse light source 1, and the pulse stretcher unit 2 includes a splitter 3 and a plurality of fibers (hereinafter referred to as stretcher fibers) 41 to 4n.

[0022] The splitter 3 is an element that spatially splits the pulsed light emitted from the pulse light source 1 according to wavelength. As shown in FIG. 1, the extension fibers 41 to 4n are connected in parallel to the splitter 3. The incident end of each extension fiber 4 is arranged at a position where light of each wavelength that has been spatially split by the splitter 3 is incident. That is, the splitter 3 splits the broadband pulsed light into wavelengths λ1 to λ n When splitting the light into wavelengths λ1 and λ2, the input end of the elongated fiber 41 is placed at the output position of the light of wavelength λ1, the input end of the elongated fiber 42 is placed at the output position of the light of wavelength λ2, and so on. n The light is placed at the light emission position.

[0023] The lengths of the extension fibers 41 to 4n differ depending on the wavelength of the incident light (the connection position relative to the splitter 3). The length of each extension fiber 41 to 4n is determined so that there is a one-to-one relationship between the wavelength and the time elapsed within one pulse at the output end of each extension fiber 41 to 4n. In this embodiment, as in the above, pulse extension is performed while maintaining the relationship in which light on the longer wavelength side is present at the beginning of one pulse and light on the shorter wavelength side gradually appears as time passes, so that the extension fibers transmitting light with shorter wavelengths are longer in length. That is, assuming that λ1 is the longest wavelength and λn is the shortest wavelength, the lengths of the extension fibers 41, 42, ..., 4n are defined as m1, m2, ...m n Then, m1 <m2<···<m n It is as follows. As a more specific example, 20 single mode fibers having lengths varying in 1 meter increments from 1 to 20 meters can be used as the extension fibers 41 to 4n.

[0024] Since the difference in length is optimized in this way, each of the elongated fibers 41 to 4n does not necessarily have to be a specific group delay fiber. In other words, it is not essential to adopt a fiber having an appropriate group delay characteristic according to the wavelength. If the same fiber (fiber with the same core / clad material) is used and the length is differentiated according to the wavelength, time-wavelength uniqueness at each output end can be achieved. In this sense, each of the elongated fibers 41 to 4n may be a multimode fiber. From the viewpoint of preventing unintended nonlinear optical effects, a multimode fiber may be preferable to a single-mode fiber in some cases.

[0025] In any case, since the difference in length of each extension fiber 41-4n is optimized, when the broadband pulse light is split into light of each wavelength and propagates through each extension fiber 41-4n, time-wavelength uniqueness is achieved at each output end. That is, the split light is delayed according to the wavelength, the length of each extension fiber 41-4n, and the refractive index of the core. Therefore, by appropriately selecting the length of each extension fiber 41-4n according to the wavelength and the refractive index of the core, time-wavelength uniqueness is achieved at each output end. Note that if the difference in wavelengths split by the splitter 3 is Δλ and the difference in length of each extension fiber 41-4n is Δm, Δm may not be constant even if Δλ is constant (the wavelength interval is constant). This is because, even if each extension fiber 41-4n is not a group delay fiber, the group delay is wavelength-dependent, and Δm may be differentiated to take this into account. Although the same fibers (with the same characteristics) are used for the extension fibers 41 to 4n, fibers with different characteristics may also be used. When fibers with different characteristics are used, the difference in length is appropriately selected according to the difference in characteristics.

[0026] After the pulse is stretched, at each time t1 to t n and each wavelength λ1 to λ n Although there is a one-to-one correspondence between t1 and t nmay be discrete times. In other words, there may be a situation where light of wavelength λ1 is observed at time t1, then after a period of time (there is a time period when no light is present) light of wavelength λ2 is observed at time t2, and so on. Even in this situation, if the time is specified, the wavelength can be specified, so it can be said that time-wavelength uniqueness is ensured. Of course, there may also be cases where the wavelength changes continuously as time changes continuously.

[0027] 1, in this embodiment, a coupler 5 is provided at the output end of each of the elongated fibers 41 to 4n. The coupler 5 is an element that overlaps the beams output from the output ends of the elongated fibers 41 to 4n so that the beams are irradiated onto the same irradiation area. As the coupler 5, in addition to a fused fiber coupler, a mechanism that holds the output ends of the elongated fibers 41 to 4n so that the same irradiation area is irradiated, or an optical system such as a lens, may be used. Also, a fan-in / fan-out device may be used as the coupler 5. Furthermore, an optical coupler using a planar optical circuit or an arrayed waveguide grating may also be used.

[0028] Next, the splitter 3 will be described in more detail. In this embodiment, an arrayed waveguide grating is used as the splitter 3. Fig. 4 is a schematic plan view of the arrayed waveguide grating used as the splitter 3. 4, the arrayed waveguide diffraction grating is constructed by forming functional waveguides 32 to 36 on a substrate 31. Each functional waveguide comprises a large number of arrayed waveguides 32 with slightly different optical path lengths, slab waveguides 33 and 34 connected to both ends (incident side and exit side) of the arrayed 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.

[0029] The slab waveguides 33 and 34 are free space, and light incident through the input waveguide 35 spreads in the input slab waveguide 33 and enters each arrayed waveguide 32. Because each arrayed waveguide 32 has a slightly different length, the light reaching the end of each arrayed waveguide 32 is shifted in phase by this difference. Light is diffracted and emitted from each arrayed waveguide 32, and the diffracted light interferes with each other while passing through the output slab waveguide 34 and reaching the input end of the output waveguide 36. Due to the phase shift, the interference light has its highest intensity at a position corresponding to its wavelength. In other words, light of successively different wavelengths enters each output waveguide 36, and the light is spatially separated. Strictly speaking, each output waveguide 36 is formed so that its input end is positioned at the position where the light is separated in this way.

[0030] The arrayed waveguide grating shown in FIG. 4 was developed for wavelength division multiplexing (WDM) in the field of optical communications. However, the inventors have found that it can be used as the splitter 3 for pulse stretching in the light source device of the embodiment, although the application and wavelength range are significantly different. Such an arrayed waveguide grating can be fabricated, for example, by surface treatment of a silicon substrate 31. Specifically, a cladding layer (SiO2 layer) is formed on the surface of the silicon substrate 31 by flame deposition, an SiO2-GeO2 layer for the core is also formed by flame deposition, and then the SiO2-GeO2 layer is patterned by photolithography to form each of the waveguides 32 to 36. The line width of each of the arrayed waveguides 32 may be, for example, about 5 to 6 μm.

[0031] For example, when used for light with a continuous spectrum over a wavelength range of about 900 to 1300 nm, the number of output waveguides 36 is about 128, and the light is split into wavelengths that differ by 3 to 50 nm and output. The elongated fibers 41 to 4n are connected to the output-side waveguides 36 of the arrayed-waveguide diffraction grating, respectively. Therefore, light spatially divided according to wavelength as described above is incident on the elongated fibers 41 to 4n, and the light of each wavelength is transmitted through the separate elongated fibers 41 to 4n, giving each a different delay time.

[0032] Next, the overall operation of the light source device for light measurement according to this embodiment will be described. The coupler 5 is placed at a predetermined position depending on the purpose of the optical measurement. Ultrashort pulse light emitted from the ultrashort pulse laser 11 is broadened by the nonlinear element 12 to become broadband pulse light, which then enters the splitter 3. The splitter 3 then spatially splits the light according to wavelength, and the light of each wavelength enters each of the elongated fibers 41 to 4 n. The light of each wavelength is delayed in each of the elongated fibers 41 to 4 n, and is emitted from each of the elongated fibers 41 to 4 n with time-wavelength uniqueness achieved. The emitted light is then irradiated onto an irradiation area directed by the coupler 5.

[0033] According to the optical measurement light source device of this embodiment, the broadband pulsed light is split into light of each wavelength by the splitter 3, and the pulse is stretched by delays according to the propagation distance in each elongated fiber 41-4n transmitting the light of each wavelength. This prevents the problem of unintended nonlinear optical effects causing the loss of time-wavelength uniqueness. That is, the power of the broadband pulsed light is dispersed and propagated through each elongated fiber 41-4n, so even when high-power broadband pulsed light is emitted from the pulse light source 1, the power of the light propagating through each elongated fiber 41-4n is kept low. This prevents the loss of time-wavelength uniqueness. Furthermore, the light from each elongated fiber 41-4n is superimposed by the coupler 5, allowing the target to be irradiated with stretched, high-power broadband pulsed light. This enables optical measurement with a high signal-to-noise ratio, even for targets with high absorption.

[0034] Furthermore, the arrayed waveguide grating used as the splitter 3 has low loss, enabling even higher illuminance light irradiation. Furthermore, the arrayed waveguide grating has high compatibility with fibers, making it easy to connect to each extended fiber. This has the effect of making it easy to manufacture.

[0035] Next, another example of the splitter 3 will be described. Fig. 5 is a schematic diagram of another example of the splitter 3. In the above embodiment, an arrayed waveguide grating was used as the splitter 3, but the example in Fig. 5 uses a diffraction grating 371 as the splitter 3. In this example, by combining the diffraction grating 371 with a non-parallel mirror pair 38, light is focused at different positions depending on the wavelength.

[0036] Specifically, the splitter 3 includes an angular dispersion module 37 that sets different angles relative to the optical axis depending on the wavelength, a non-parallel mirror pair 38 connected to the angular dispersion module 37, a beam splitter 372 that extracts light of each wavelength reflected by the non-parallel mirror pair 38, and an incident optical system 39 that inputs the light of each wavelength extracted by the beam splitter 372 into each of the extended fibers 41 to 4n.

[0037] 5, the angular dispersion module 37 includes a diffraction grating 371 onto which the broadband pulsed light is incident, a collimator lens 373 that converts the light wavelength-dispersed by the diffraction grating 371 into parallel light, and a condenser lens 374 that focuses the parallel light converted by the collimator lens 373 onto an incident point P of the non-parallel mirror pair 38. The extraction beam splitter 372 is disposed between the collimator lens 373 and the condenser lens 374.

[0038] The light of each wavelength dispersed by the diffraction grating 371 is focused by the focusing lens 374 and directed to the incident point P of the non-parallel mirror pair 38. The angle at which the light reaches the incident point P varies depending on the wavelength and is a continuously varying angle. The non-parallel mirror pair 38 is composed of a pair of flat mirrors 381 tilted by a slight angle α. Therefore, as shown in FIG. 5, the incident light of each wavelength is reflected alternately by the flat mirror 381 and returns. At this time, due to the focusing angle θ, the tilt angle α, and the distance D between the non-parallel mirror pair 38 viewed from the incident point P when focusing the light at the incident point P, the light of wavelengths λ1 to λn returns exactly to the position of the incident point P, albeit at intervals. Therefore, this light is reflected at the incident point P and reaches the beam splitter 372, where a portion of the light is reflected and extracted. The extracted light is incident on each of the elongated fibers 41 to 4n by the input optical system 39.

[0039] In this way, the broadband pulsed light is spatially divided according to wavelength and transmitted through each of the elongated fibers 41 to 4n. Also in this embodiment, the length of each of the elongated fibers 41 to 4n is set to be different according to the wavelength of the incident light, so that time-wavelength uniqueness is achieved at the output end. As can be seen from FIG. 5, the light of a wavelength that returns exactly to the position of the incident point P has a slightly different optical path length according to the wavelength, which causes time dispersion. Therefore, it is desirable to take this dispersion into consideration when selecting the length of the elongated fibers 41 to 4n.

[0040] In addition to the above, various other types of divider 3 can be used. Examples of these are shown in Figure 6. Figure 6 is a schematic diagram showing yet another example of a divider 3. As the splitter 3, one using a pair of diffraction gratings 301 can be used, as shown in Fig. 6(1). A configuration can be adopted in which the pair of diffraction gratings 301 disperse light into wavelengths, and the light of each wavelength is made incident on each of the elongated fibers 41 to 4n via a microlens array 302. The microlens array 302 is an element in which microlenses are arranged to collect the light of each wavelength and make it incident on the core of each of the elongated fibers 41 to 4n.

[0041] 6(2), it is also possible to use a splitter 3 that employs a prism pair. In this example, the light is dispersed by a pair of prisms 303, and similarly, the light is collected by a microlens array 302 and made to enter the cores of the elongated fibers 41 to 4n. In any case, if the light is divided into wavelengths by the splitter 3 and transmitted through each extended fiber 41 to 4n for each wavelength, and time-wavelength uniqueness is achieved by adjusting the fiber length, unintended nonlinear optical effects are prevented and time-wavelength uniqueness is not lost even when high-intensity broadband pulse light is emitted from the pulse source 1.

[0042] Next, a light source device for light measurement according to a second embodiment will be described below with reference to Fig. 7, which is a schematic diagram of the light source device for light measurement according to the second embodiment. The light source device for optical measurement according to the second embodiment differs from that according to the first embodiment in the configuration of the pulse stretching unit 2. As shown in Fig. 7, the pulse stretching unit 2 according to the second embodiment also includes a plurality of stretching fibers. These stretching fibers include fibers 41 to 4n (hereinafter referred to as element fibers) that constitute a plurality of fiber sets 4G1 to 4Gn.

[0043] Each fiber set 4G1 to 4Gn is composed of a plurality of element fibers 41 to 4n that have the same pattern but different lengths. This is intended to reduce costs by sharing the elongated fibers. However, if left as is, there will be elongated fibers of the same length, and different delays cannot be achieved in those parts. For this reason, multi-core fibers 61 to 6n are combined. In this configuration, the core of one element fiber 41 to 4n and each core of the multi-core fibers 61 to 6n connected to it form one transmission path, so the number and lengths of the multi-core fibers 61 to 6n are selected so that the transmission paths have different lengths.

[0044] As an example, to achieve something equivalent to the 20 elongated fibers 41 to 4n (20 different transmission paths) exemplified in the first embodiment, each fiber set 4G1 to 4Gn is made up of five element fibers 41 to 45 whose lengths vary in 1-meter increments from 1 to 5 meters. Four such sets are prepared. Three multi-core fibers with the number of cores each are prepared. The three multi-core fibers 61 to 63 have lengths of 5 meters, 10 meters, and 15 meters. No multi-core fiber is connected to the first fiber set 4G1, and a 5-meter multi-core fiber 61 is connected to the next fiber set 4G2. That is, each core of the 5-meter multi-core fiber 61 is connected to the core of each of the element fibers 41 to 45. A 10-meter multi-core fiber 62 is connected to the next fiber set 4G3. A 15-meter multi-core fiber 63 is connected to the last fiber set 4G4. In this way, 20 transmission paths with different lengths in 1-meter increments from 1 to 20 meters were formed.

[0045] The above is just one example, and any combination is possible as long as the total lengths of the transmission lines are different from each other. There may be cases where the number of cores in the multi-core fibers 61 to 6n is greater than the number of component fibers 41 to 4n in the fiber sets 4G1 to 4Gn, but in that case, it is sufficient to leave them empty (unconnected). Note that when there are two fiber sets, one multi-core fiber is sufficient. It is also possible to use a bundle fiber instead of the multi-core fibers 61 to 6n. In the above example, a bundle fiber consisting of five fibers is prepared. The bundle fibers have lengths of 5 meters, 10 meters, and 15 meters, and are similarly connected to the fiber sets 4G2, 4G3, and 4G4, respectively.

[0046] As in the first embodiment, ideally the number of wavelengths split by the splitter 3 would match the number of transmission paths formed by multiple elongated fibers, but they do not have to match. If the number of transmission paths is greater, that number will be left empty. Also, depending on the purpose of the optical measurement, there may be wavelengths that are not used for measurement, and therefore no elongated fibers may be connected to the splitter 3 for those wavelengths (the number of elongated fibers may be less).

[0047] In the second embodiment, too, the light is divided into wavelengths by the splitter 3 and transmitted through each of the extended fibers 41 to 4n, 61 to 6n for each wavelength, so that even when high-intensity broadband pulsed light is emitted from the pulse source 1, unintended nonlinear optical effects are prevented and the uniqueness of the time wavelength is not lost. Furthermore, since the pulse stretching unit 2 includes a plurality of fiber sets 4G1 to 4Gn each made up of a plurality of different element fibers 41 to 4n in the same pattern, the cost is low. 7, the fiber sets 4G1 to 4Gn are connected to the splitter 3, and the multi-core fibers 61 to 6n are connected to the rear stages thereof, but this relationship may be reversed. That is, the multi-core fibers 61 to 6n may be connected to the splitter 3, and the fiber sets 4G1 to 4Gn may be connected to the rear stages thereof.

[0048] Next, the spectroscopic measurement device and the spectroscopic measurement method of the present invention will be described. Fig. 8 is a schematic diagram of a spectroscopic measurement device of the first embodiment. The spectroscopic measurement device shown in Fig. 8 includes a light measurement light source device 10, an irradiation optical system 71 that irradiates an object S with light emitted from the light measurement light source device 10, a detector 72 arranged at a position where the light from the irradiated object S is incident, and a calculation means 73 that calculates the optical spectrum of the object S according to the output from the detector 72.

[0049] The light source device for light measurement (hereinafter simply referred to as light source device) 10 is that of the first embodiment. Of course, the second embodiment may also be used. In this embodiment, the irradiation optical system 71 includes a beam expander 711. This is in consideration of the fact that the light from the light source device 10 is time-stretched broadband pulsed light, but is light from the ultrashort pulse laser 11 and has a small beam diameter. Alternatively, a scanning mechanism such as a galvanometer mirror may be provided to cover a wide irradiation area by beam scanning.

[0050] In this embodiment, it is assumed that the absorption spectrum of the object S is to be measured, and therefore the detector 72 is provided at a position where transmitted light from the object S is incident. A transparent receiving plate 74 is provided on which the object S is placed. The illumination optical system 71 is configured to irradiate light from above, and the detector 72 is provided below the receiving plate 74.

[0051] In this embodiment, a general-purpose PC is used as the calculation means 73. An AD converter 75 is provided between the detector 72 and the calculation means 73, and the output of the detector 72 is input to the calculation means 73 via the AD converter 75. The calculation means 73 includes a processor 731 and a storage unit (hard disk, memory, etc.) 732. The storage unit 732 is installed with a measurement program 733 that processes output data from the detector 72 to calculate an absorption spectrum, and other necessary programs.

[0052] In this embodiment, the light source device 10 that irradiates stretched pulsed light with time-wavelength uniqueness is used, and therefore the measurement program 733 is optimized accordingly. Fig. 9 is a diagram schematically showing the main parts of an example of the measurement program 733 provided in the spectroscopic measurement device.

[0053] The example in FIG. 9 is an example of a program in which the measurement program 733 measures an 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 directing light from the light source device 10 to the detector 72 without passing through the object S. That is, light is directly directed to the detector 72 without passing through the object S, and the output of the detector 72 is input to the calculation means 73 via the AD converter 75 to acquire values for each time resolution Δt. Each value is stored as a reference intensity (V1, V2, V3, . . .) for each time Δt (t1, t2, t3, . . .). The time resolution Δt is a quantity determined by the response speed (signal output period) of the detector 72 and refers to the time interval at which a signal is output.

[0054] The reference intensities V1, V2, V3, at each time t1, t2, t3, are the intensities (spectrum) of the corresponding wavelengths λ1, λ2, λ3,. The relationship between the times t1, t2, t3, and wavelengths within one pulse is examined in advance, and the values V1, V2, V3, at each time are treated as the values of λ1, λ2, λ3,. When light that has passed through the object S is incident on the detector 72, the output from the detector 72 passes through the AD converter 75 and is similarly stored in memory as values (measured values) at each time t1, t2, t3, ... (v1, v2, v3, ...). Each measured value is compared with the reference spectrum data (v1 / V1, v2 / V2, v3 / V3, ...), and the result is the absorption spectrum (taking the logarithm of each reciprocal as necessary). The measurement program 733 is programmed to perform the above-mentioned calculations.

[0055] Next, the operation of the spectroscopic measurement device will be described. The following description also describes an embodiment of a spectroscopic measurement method. When performing spectroscopic measurement using the spectroscopic measurement device of the embodiment, the light source device 10 is operated without placing the object S, and the output data from the detector 72 is processed to obtain reference spectral data in advance. Then, the object S is placed on the receiving plate 74, and the light source device 10 is operated again. The output data from the detector 72 is then input to the calculation means 73 via the AD converter 75, and the optical spectrum is calculated using the measurement program 733.

[0056] In the above example, the absorption spectrum is measured using transmitted light from the object S, but there are also cases where reflected light from the object S is incident on the detector 72 to measure the reflection spectrum (spectral reflectance), or where fluorescence emitted by excitation with light irradiated on the object S is incident on the detector 72 to measure the fluorescence spectrum. Furthermore, there are also cases where the spectral characteristics of the scattering spectrum of the object S, such as Rayleigh scattering or Raman scattering, are measured. Therefore, the light from the object S can be transmitted light, reflected light, fluorescence, scattered light, etc. from the object S irradiated with light. Furthermore, if the measurement of the light source device 10 or the sensitivity characteristics of the detector 72 change over time, a measurement is performed to obtain a reference spectrum (measurement without placing the object S), and a calibration operation is performed periodically to update the reference spectrum.

[0057] According to the spectroscopic measurement device and spectroscopic measurement method of this embodiment, light from the pulse light source 1 is divided in time and irradiated onto the object S, eliminating the need for time-consuming operations such as sweeping a diffraction grating, allowing for high-speed spectroscopic measurement. Furthermore, when performing pulse stretching to ensure time-wavelength uniqueness, a configuration is adopted in which each wavelength is transmitted through separate elongated fibers 41 to 4n of different lengths, so that time-wavelength uniqueness is not lost even when light is irradiated onto the object S with high illuminance. Therefore, spectroscopic measurement that requires irradiation with high-power light, such as spectroscopic measurement of a highly absorbing object S, can be performed with high precision, resulting in a high-speed and highly reliable spectroscopic measurement device and spectroscopic measurement method.

[0058] Next, a spectroscopic measurement device and a spectroscopic measurement method according to a second embodiment will be described. Fig. 10 is a schematic diagram of the spectroscopic measurement device according to the second embodiment. 10, the spectroscopic measurement device of the second embodiment is provided with a branching element 76 that branches the light emitted from the light source device 10. In this embodiment, a beam splitter is used as the branching element 76. The branching element 76 splits the optical path from the light source device 10 into a measurement optical path and a reference optical path. As in the first embodiment, a receiving plate 74 is disposed in the measurement optical path, and a measurement detector 72 is disposed at a position where it receives light that has passed through the object S on the receiving plate 74.

[0059] A reference detector 702 is disposed on the reference optical path. The light that is branched by the branching element 76 and travels along the reference optical path is directly incident on the reference detector 702. This light (reference light) is incident on the detector 702 without passing through the object S, and is used to obtain reference spectrum data in real time.

[0060] The measurement detector 72 and the reference detector 702 are connected to the calculation means 73 via AD converters 75 and 705, respectively. The measurement program 733 in the calculation means 73 is programmed to perform real-time reference intensity spectrum reference. Specifically, the measurement detector 72 inputs measurement values v1, v2, v3,... at each time t1, t2, t3,..., and the reference detector 72 inputs reference intensities V1, V2, V3,... (reference spectrum data) at the same times t1, t2, t3,..., from the reference detector 72. The measurement program 733 calculates v1 / V1, v2 / V2, v3 / V3,... based on the relationship between the times t1, t2, t3,... and the wavelengths λ1, λ2, λ3,... within one pulse, which has been previously determined, and uses this as the absorption spectrum. Reflection and scattering spectra can also be measured using the reference spectrum data acquired in real time. In the spectroscopic measurement method of the second embodiment using the spectroscopic measurement device of the second embodiment, the reference spectral data is acquired in real time, and therefore the reference spectral data is not acquired periodically, which is the same as in the first embodiment.

[0061] According to the spectroscopic measurement device and spectroscopic measurement method of the second embodiment, it is not necessary to separately acquire reference spectral data, thereby improving the efficiency of the overall measurement process. Furthermore, in the first embodiment, frequent calibration is required when the characteristics of the light source device 10 and the detector 72 are prone to change, but this is not necessary in the second embodiment. Even if the characteristics of the light source device 10 and the detector 72 do not change, calibration may be required when the measurement environment changes (for example, when temperature conditions or background light conditions are different). In the second embodiment, calibration is not required even in such cases, thereby improving measurement efficiency. However, in the second embodiment, the light beam from the light source device 10 is split into two, so the light beam that can be irradiated onto the object S is correspondingly reduced. Therefore, the first embodiment is more advantageous when it is necessary to irradiate the object S with light at a higher intensity for measurement.

[0062] In addition to the above-mentioned spectroscopic measurement, various other optical measurements can also be used for the light source device for optical measurement. For example, an application in which an object is irradiated with light to be observed, as in a microscope, can be considered a type of optical measurement, as can measuring distance by irradiating light. The light source device for optical measurement of the present invention can be used for such various optical measurements. The fact that the spectrum is continuous over a certain wavelength range included in the wavelength range of 900 to 1300 nm is significant in that it is suitable for optical measurement in the near-infrared region, which is particularly effective for material analysis, etc. However, there are various types of spectroscopic measurement outside this wavelength range, and the spectroscopic measurement device and spectroscopic measurement method are not limited to this wavelength range.

[0063] Furthermore, although the wavelength width of the continuous spectrum is set to at least 10 nm, this is also an example, and continuous pulsed light with a narrower wavelength width may also be used. For example, when the target is a gas, such as in the analysis of atmospheric components, and it is only necessary to measure a specific component (specific absorption spectrum), continuous pulsed light with a narrow wavelength width may also be used. [Explanation of symbols]

[0064] 1. Pulsed light source 10 Light source device 11 Ultrashort pulse laser 12 Nonlinear elements 2 Pulse stretcher units 3 divider 41~4n elongated fiber 4G1~4Gn fiber optic 5 Coupler 61~6n multi-core fiber 71 Irradiation optical system 72 detectors 73 Calculation means 75 AD converter S Object

Claims

1. a pulse light source including a nonlinear fiber, the pulse light source emitting pulse light from the nonlinear fiber, the spectrum of which is continuous over a wavelength width of at least 100 nm due to a nonlinear optical effect in the nonlinear fiber; a splitter that spatially splits the pulsed light emitted from the nonlinear fiber according to wavelength ranges; A plurality of single-mode fibers, the number of which corresponds to the number of wavelength bands to be split by the splitter, It is equipped with the splitter is an arrayed-waveguide grating, the nonlinear fiber is arranged so that output light is incident on an input-side slab waveguide of the arrayed-waveguide grating, and the plurality of single-mode fibers are arranged so that light of each wavelength range from the output-side slab waveguide of the arrayed-waveguide grating is incident on each of the plurality of single-mode fibers, each of the plurality of single mode fibers has a length that varies according to the wavelength of the incident light so that the elapsed time within one pulse corresponds one-to-one to the wavelength; a detector disposed at a position where light from an object (excluding a case where the object is light) illuminated with light emitted from each of the plurality of single mode fibers is incident; a calculation means for calculating the spectral characteristics of the object (excluding the case where the object is light) according to the output from the detector; A spectroscopic measurement device comprising:

2. the plurality of single-mode fibers are element fibers constituting a plurality of fiber sets and a multi-core fiber; Each fiber set is composed of multiple element fibers with the same pattern but different lengths.

2. The spectroscopic measurement device according to claim 1, wherein a core of each element fiber and each core of the multicore fiber are connected, and the number and length of the multicore fibers are selected so that the total lengths of the transmission paths consisting of the core of each element fiber and each core of the multicore fiber are different from each other.

3. 3. The spectroscopic measurement device according to claim 1, wherein the nonlinear fiber is a fiber that generates the nonlinear optical effect so as to emit supercontinuum light.

4. a broadband light emission step of, in a pulse light source equipped with a nonlinear fiber, inputting pulsed light into the nonlinear fiber to cause a nonlinear optical effect in the pulsed light, thereby emitting pulsed light having a continuous spectrum over a wavelength width of at least 100 nm; a splitting step of spatially splitting the pulsed light emitted in the broadband light emitting step into light of each wavelength range by making the pulsed light emitted in the broadband light emitting step enter an incident-side slab waveguide of the arrayed-waveguide diffraction grating and emitting light of each wavelength range from an output-side slab waveguide; a pulse elongation step in which a plurality of single-mode fibers are connected so that light in each wavelength range is incident from an output-side slab waveguide of the arrayed-waveguide diffraction grating, and pulsed light in each spatially divided wavelength range is incident on each single-mode fiber and transmitted, thereby achieving a one-to-one correspondence between the elapsed time within one pulse and the wavelength; an irradiation step of irradiating an object (excluding the case where the object is light) with the pulsed light whose pulse width has been extended by the pulse extension step; a detection step of detecting, with a detector, light from an object irradiated with the pulsed light whose pulse width has been extended by the pulse extension step (excluding the case where the object is light); a calculation step of calculating the spectral characteristics of the object according to the output from the detector; It is equipped with a spectroscopic measurement method, characterized in that each of the plurality of single-mode fibers used in the pulse stretching step has a different length depending on the wavelength of the incident light so that the elapsed time within one pulse corresponds one-to-one to the wavelength.

5. the plurality of single-mode fibers are element fibers constituting a plurality of fiber sets and a multi-core fiber; Each fiber set is composed of multiple element fibers with the same pattern but different lengths.

5. The spectroscopic measurement method according to claim 4, wherein a core of each element fiber and each core of the multi-core fiber are connected, and the number and length of the multi-core fibers are selected so that total lengths of the transmission paths consisting of the core of each element fiber and each core of the multi-core fiber are different from each other.

6. 6. The spectroscopic measurement method according to claim 4, wherein the pulsed light emitted in the broadband light emitting step is supercontinuum light.

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