Light source apparatus and light measuring apparatus

Abstract

To provide a light source apparatus capable of generating wavelength sweeping light at a high performance in a wavelength band other than a near-infrared wavelength band.SOLUTION: A light source apparatus 200 produces outgoing light L1 to irradiate a specimen. A pulse light source 210 generates near-infrared broad-band pulse light L0. A pulse stretcher 220 stretches the broad-band pulse light L0 in a time axis direction and generates near-infrared wavelength sweeping light L1a. A wavelength conversion device 250 converts wavelengths of the near-infrared wavelength sweeping light L1a emitted from the pulse stretcher 220 and generates the outgoing light L1.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present disclosure relates to a light source device and an optical measurement device.

Background Art

[0002] Spectral analysis is widely used for component analysis and inspection of objects. In spectral analysis, irradiation light is irradiated onto an object, and the spectrum of the object light obtained as a result of the irradiation is measured. Then, based on the relationship between the spectrum of the object light and the spectrum of the irradiation light, optical characteristics such as reflection characteristics (wavelength dependence) or transmission characteristics can be obtained.

[0003] As one of the measurement methods for optical characteristics, wavelength-sweeping spectroscopy is known. A wavelength-sweeping spectroscope generates wavelength-sweeping light whose wavelength changes over time and irradiates the inspection target with it. The wavelength-sweeping light is a pulse or a pulse train in which time and wavelength have a one-to-one relationship. Then, the time waveform of the light obtained by irradiating the inspection target with the wavelength-sweeping light is detected by a light receiver. The output waveform of the light receiver represents a spectrum in which the time axis corresponds to the wavelength.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Patent Document 1 discloses a light source device for a spectroscopic measurement device using wavelength-sweeping spectroscopy. The conventional light source device uses SC light in the band of 900 nm to 1300 nm, and due to the configuration of an optical waveguide, an optical fiber, etc., the wavelength band that the light source device can generate is also limited to the near-infrared region of 900 nm to 1300 nm.

[0006] The present disclosure has been made in view of such problems, and an exemplary object of one of its aspects is to provide a light source device capable of generating wavelength-swept light with high efficiency in a wavelength band other than the near-infrared range. **Means for Solving the Problems**

[0007] A light source device according to an aspect of the present disclosure generates wavelength-swept light to be irradiated onto a sample. The light source device includes a pulse light source that generates near-infrared pulse light, a pulse stretcher that stretches the near-infrared pulse light in the time-axis direction to generate near-infrared wavelength-swept light, and a wavelength conversion device that wavelength-converts the near-infrared wavelength-swept light emitted from the pulse stretcher based on a nonlinear optical effect to generate wavelength-swept light in a wavelength band other than the near-infrared range.

[0008] In addition, any combination of the above components, and those obtained by mutually substituting the components and expressions of the present disclosure among methods, devices, systems, etc. are also valid as aspects of the present disclosure. **Advantages of the Invention**

[0009] According to an aspect of the present disclosure, wavelength-swept light in a wavelength band other than the near-infrared range can be generated with high efficiency. **Brief Description of the Drawings**

[0010]

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Embodiments for Carrying Out the Invention

[0011] (Overview of Embodiments) The overview of some exemplary embodiments of the present disclosure will be described. This overview is for the purpose of providing a basic understanding of the embodiments as a prelude to the detailed description to follow, and simplifies and describes some concepts of one or more embodiments. It does not limit the scope of the invention or the disclosure. Also, this overview is not an all-inclusive overview of all conceivable embodiments and does not limit essential components of the embodiments. For convenience, "one embodiment" may be used to refer to one embodiment (example or modification) or a plurality of embodiments (examples or modifications) disclosed in this specification.

[0012] A light source device according to one embodiment is a light source device that generates wavelength-swept light to be irradiated onto a sample, and generates near-infrared pulse light. The light source device includes a pulse light source, a pulse stretcher that stretches the near-infrared pulse light in the time axis direction to generate near-infrared wavelength-swept light, and a wavelength conversion device that wavelength-converts the near-infrared wavelength-swept light emitted from the pulse stretcher based on a non-linear optical effect to generate wavelength-swept light other than near-infrared.

[0013] Since the near-infrared region is used in optical communication and many highly efficient and reliable devices are provided, after generating wavelength-swept light in the near-infrared region, wavelength conversion can be performed to generate highly efficient wavelength-swept light in a band other than near-infrared.

[0014] In one embodiment, the pulse stretcher may generate a first near-infrared wavelength-swept light including a part of the spectrum of the near-infrared pulsed light that overlaps on the time axis, and a second near-infrared wavelength-swept light including another part of the spectrum of the near-infrared pulsed light. The wavelength conversion device may perform wavelength conversion on the first near-infrared wavelength-swept light and the second near-infrared wavelength-swept light based on a nonlinear optical effect.

[0015] In one embodiment, the nonlinear optical effect may be difference frequency generation. Thereby, wavelength-swept light with a longer wavelength can be generated.

[0016] In one embodiment, the nonlinear optical effect may be sum frequency generation. Thereby, wavelength-swept light with a shorter wavelength can be generated.

[0017] In one embodiment, the first near-infrared wavelength-swept light and the second near-infrared wavelength-swept light may each be a pulse train including a plurality of pulses with different center wavelengths.

[0018] In one embodiment, the pulse stretcher may include a splitter that spatially divides the near-infrared pulsed light according to wavelength and emits a plurality of split beams, a plurality of fibers that impart different delays to the plurality of split beams, and a coupler that spatially combines the plurality of beams output from the plurality of fibers and emits them as near-infrared wavelength-swept light. The plurality of fibers may include pairs of fibers having substantially equal optical path lengths. According to this configuration, the wavelength of the emitted light can be designed based on two wavelengths passing through a pair of fibers having equal optical path lengths.

[0019] In one embodiment, the wavelength conversion device may perform wavelength conversion by second harmonic generation or third harmonic generation.

[0020] In one embodiment, the near-infrared wavelength-swept light may be a pulse train including a plurality of pulses with different center wavelengths.

[0021] In one embodiment, the wavelength conversion device may include a PPLN (Periodically Poled Lithium Niobate) element.

[0022] In one embodiment, the period of the periodic inversion of the PPLN element may be chirped.

[0023] An optical measurement device according to one embodiment may include any of the above-described light source devices and a light receiving device that measures object light obtained by irradiating an object with the emitted light of the light source device.

[0024] (Embodiment) Hereinafter, the present disclosure will be described with reference to the drawings based on preferred embodiments. The same or equivalent components, members, and processes shown in each drawing are denoted by the same reference numerals, and repeated descriptions will be omitted as appropriate. Further, the embodiments are illustrative and not restrictive, and not all features and combinations thereof described in the embodiments are necessarily essential to the present disclosure.

[0025] The dimensions (thickness, length, width, etc.) of each member shown in the drawings may be enlarged or reduced as appropriate for ease of understanding. Furthermore, the dimensions of a plurality of members do not necessarily represent their size relationships, and on the drawing, even if a member A is drawn thicker than another member B, member A may be thinner than member B.

[0026] FIG. 1 is a block diagram showing the basic configuration of an optical measurement device 100 according to an embodiment. The optical measurement device 100 is a wavelength-sweeping spectrometer that measures the spectrum of an object OBJ, and mainly includes a light source device 200, a light receiving device 300, and an arithmetic processing device 400. In some figures, the light source device 200, the light receiving device 300, etc. may be shown simply as boxes for simplification, but this is not intended to mean that the members constituting each are housed in a single housing.

[0027] The light source device 200 irradiates the object OBJ with a wavelength-swept light L1 whose wavelength changes over time. The wavelength-swept light L1 has a one-to-one correspondence between time and wavelength. This is what is meant by the wavelength-swept light L1 having "wavelength uniqueness".

[0028] FIG. 2 is a diagram showing the wavelength-swept light L1. The upper part of FIG. 2 shows the intensity (time waveform) I WS (t) of the wavelength-swept light L1, and the lower part shows the time change of the wavelength λ of the wavelength-swept light L1. In this example, the wavelength-swept light L1 is a single pulse of light, and the main wavelength is λ1 at the leading edge and λ n at the trailing edge, and the wavelength changes from λ1 to λ n over time within one pulse. In this example, the wavelength-swept light L1 is a positive chirp pulse (λ1 > λ n ) whose frequency increases with time, in other words, whose wavelength becomes shorter with time. Note that the wavelength-swept light L1 may be a negative chirp pulse (λ1 < λ n ) whose wavelength becomes longer with time. As will be described later, the wavelength-swept light L1 may be a pulse train.

[0029] Returning to FIG. 1. The light receiving device 300 receives the light (object light) L2 obtained as a result of irradiating the object OBJ with the wavelength-swept light L1. The object light L2 may be reflected light or transmitted light. The light receiving device 300 includes light sensors 302, 304 such as photodiodes, an A / D converter 310, an optical system (not shown), and the like. The object light L2 is detected by the light sensor 302. A part of the wavelength-swept light L1 generated by the light source device 200 is taken out as reference light L3 through a different path using an optical element such as a beam splitter and detected by the light sensor 304.

[0030] The A / D converter 310 converts the output signals S2, S3 of the light sensors 302, 304 into digital signals D2, D3. The time waveform I OBJ (t) of the object light L2 indicated by the digital signal D2 and the time waveform I REF (t) of the reference light L3 indicated by the digital signal D3 are taken into the arithmetic processing device 400.

[0031] In the wavelength-sweeping spectroscopy, the time and wavelength in the wavelength-sweeping light L1 have a one-to-one correspondence. Naturally, this correspondence is also possessed by the reference light L3 and is also passed on to the object light L2. Utilizing this correspondence between time and wavelength, the arithmetic processing unit 400 converts the time waveform I OBJ (t) of the object light L2 into the spectrum I OBJ (λ) in the frequency domain. Also, the arithmetic processing unit 400 converts the time waveform I REF (t) of the reference light L3 into a spectrum and appropriately scales it to calculate the reference spectrum I REF (λ).

[0032] The processing of the arithmetic processing unit 400 is not particularly limited. As an example, the arithmetic processing unit 400 can calculate the transmittance T(λ) of the object OBJ based on the reference spectrum I REF (λ) and the spectrum I OBJ (λ) of the object light L2. The same applies to the reflectance R(λ). T(λ) = I OBJ (λ) / I REF (λ) R(λ) = I OBJ (λ) / I REF (λ)

[0033] Note that when the stability of the wavelength-sweeping light L1 is high, the spectrum of the wavelength-sweeping light L1 may be measured in advance and used as the reference spectrum I REF (λ).

[0034] FIG. 3 is a diagram for explaining the spectroscopy by the optical measurement apparatus 100 of FIG. 1. As described above, since the time t and the wavelength λ of the wavelength-sweeping light L1 correspond one-to-one, the time waveform I REF (t) can be converted into the spectrum I REF (λ) in the frequency domain.

[0035] The time waveform I OBJ(t) also becomes such that time t and wavelength λ correspond one-to-one. Therefore, the arithmetic processing unit 400 can convert the waveform I OBJ (t) of the object light L2 indicated by the output of the light receiving device 300 into the spectrum I OBJ (λ) of the object light L2.

[0036] The arithmetic processing unit 400 can calculate the transmission spectrum T(λ) of the object OBJ based on the ratio I OBJ (λ) / I REF (λ) of the two spectra I OBJ (λ) and I REF (λ).

[0037] Assume that the relationship between the wavelength λ and the time t in the wavelength-swept light L1 is represented by a function λ = f(t). Most simply, the wavelength λ changes linearly with respect to time t according to a linear function. When the time waveform I OBJ (t) of the object light L2 decreases at a certain time t x , it means that the transmission spectrum T(λ) has an absorption spectrum at the wavelength λ x = f(t x ).

[0038] Note that the processing in the arithmetic processing unit 400 is not limited to this. After calculating the ratio T(t) = I OBJ (t) / I REF (t) of the two time waveforms I OBJ (t) and I REF (t), the transmission spectrum T(λ) may be calculated by converting the variable t of this time waveform T(t) to λ.

[0039] The above is the basic configuration and operation of the optical measurement device 100. Subsequently, the configuration of the light source device 200 will be described based on several embodiments.

[0040] (Embodiment 1) FIG. 4 is a diagram showing the light source device 200 according to Embodiment 1. In the present embodiment, the light source device 200 is configured to be able to generate wavelength-swept light L1 in a wavelength band other than near-infrared. The light source device 200 includes a pulse light source 210, a pulse stretcher 220, and a wavelength conversion device 250.

[0041] The pulse light source 210 emits broadband pulse light L0 having a broadband continuous spectrum in the near-infrared range. The broadband pulse light L0 is SC (Super Continuum) light, and the spectrum of the broadband pulse light L0 is continuous over a wavelength range of at least 10 nm, preferably 100 nm, more preferably 400 nm, for example, in the range of 900 nm to 1300 nm.

[0042] For example, the pulse light source 210 may include an ultrashort pulse laser and a nonlinear element. Examples of the ultrashort pulse laser include a gain-switched laser, a microchip laser, and a fiber laser.

[0043] The nonlinear element further broadens the spectral width of the ultrashort pulses generated by the ultrashort pulse laser by a nonlinear phenomenon. A fiber is suitable as the nonlinear element, and for example, a photonic crystal fiber or other nonlinear fibers can be used. The single-mode case is preferable as the mode of the fiber, but a multimode fiber can also be used as long as it exhibits sufficient nonlinearity. The broadband pulse light L0 output from the nonlinear element has a pulse width on the order of femtoseconds to nanoseconds.

[0044] As the pulse light source 210, other broadband pulse light sources such as an SLD (Superluminescent Diode) light source may be used. Alternatively, it is preferable to use a light source with high spatial coherence for coupling to the fiber.

[0045] The pulse stretcher 220 stretches the broadband pulse light L0 in the time axis direction to generate near-infrared wavelength-swept light L1a. The wavelength of the wavelength-swept light L1a is such that the wavelength ranges from λa1 to λa nChanges with time towards

[0046] The wavelength conversion device 250 wavelength-converts the near-infrared wavelength-swept light L1a emitted from the pulse stretcher 220 and generates the emitted light L1 which is the wavelength-swept light with a wavelength other than near-infrared. The wavelength of the wavelength-swept light L1 changes with time towards λ1~λ n Changes over time towards

[0047] As the non-linear optical effect in the wavelength conversion device 250, second harmonic generation (SHG) and third harmonic generation (THG) can be utilized.

[0048] λ i is determined by λa i and the non-linear optical effect used. When using SHG, the relationship of λ i =λa i / 2 holds. When using THG, the relationship of λ i =λa i / 3 holds.

[0049] As the wavelength conversion device 250, a periodic poling module such as a bulk or waveguide PPLN (Periodically Poled Lithium Niobate) element or a PPMgO (Periodically poled MgO doped lithium niobate) element can be used. Since the periodic poling module can usually only convert a wavelength range of several nm to several tens of nm, in order to realize broadband wavelength conversion, the periodic poling module is preferably adopted with a structure in which the period of the periodic poling gradually changes (chirps). Alternatively, a multiple grating in which a single PPLN element contains multiple periods of PPLN, or a fan-out grating in which a single PPLN element contains sectorial inversion polarization, can also be used as an element for realizing broadband wavelength conversion.

[0050] FIG. 5 is a diagram for explaining wavelength conversion in the wavelength conversion device 250 of FIG. 4.

[0051] · Visible region By SHG, the wavelength-swept light in the near-infrared range of 900 to 1300 nm can be converted into the wavelength-swept light in the visible region of 450 to 650 nm.

[0052] · Ultraviolet region By THG, the wavelength-swept light in the near-infrared range of 900 to 1300 nm can be converted into the wavelength-swept light in the ultraviolet region of 300 to 433 nm.

[0053] Alternatively, after converting to the wavelength-swept light of 450 to 650 nm by SHG, it is also possible to generate the wavelength-swept light in the ultraviolet region of 225 to 325 nm by further SHG.

[0054] The above is the configuration of the light source device 200. Subsequently, the advantages of the light source device 200 will be described. The advantages of the light source device 200 will become clear by comparison with the comparative technology.

[0055] In the comparative technology, the configuration of the light source device described in Patent Document 1 is directly replaced in the wavelength range other than the near-infrared. That is, the light source device includes an SC light source in the target wavelength band other than the near-infrared, and an AWG and an optical fiber that function in this wavelength band.

[0056] For example, consider applying the comparative technique described in Patent Document 1 to the visible wavelength band with a wavelength shorter than the near-infrared region. In this case, SC light can be generated relatively easily using wavelength conversion, short pulse lasers, etc. On the other hand, it is known that when fabricating an optical waveguide at a short wavelength, the influence of light scattering due to the abnormal shape of the waveguide itself becomes large (the -4th power of the wavelength), and the loss due to scattering becomes extremely large. Although research has been conducted on small microscope devices using optical waveguides, it is known that the large optical loss in the visible wavelength range of the optical waveguide is one of the main technical issues, and it is necessary to develop a new manufacturing process for the optical waveguide. Also, since the core diameter of a single-mode optical fiber is approximately proportional to the wavelength, for an optical fiber with a core diameter of φ9.5μm used in the 1.5μm wavelength band, the core diameter of an optical fiber for the 400nm wavelength band is about φ3μm. Therefore, the requirements for the adhesion of each component, mechanical accuracy, assembly tolerance, and stability become extremely strict. Furthermore, it is known that in the ultraviolet wavelength band below 400nm, aging deterioration is severe, and development is required from the material itself of the optical fiber and optical waveguide.

[0057] Consider applying the comparative technique described in Patent Document 1 to the mid-infrared wavelength band with a wavelength longer than the near-infrared region. SC light can be emitted relatively easily using wavelength conversion technology, etc. However, at mid-infrared wavelengths, the absorption of molecular vibrations is strong, and the absorption due to impurities contained in SiO2 used in optical fibers and waveguides is extremely large. Also, since the development of materials that can obtain the optimal dispersion for guiding waves has not progressed, it is difficult to fabricate an optical waveguide device at mid-infrared wavelengths. That is, it is necessary to start from the development of the material itself of the optical waveguide and optical fiber.

[0058] In this embodiment, near-infrared wavelength-swept light L1a is generated by the pulse light source 210 and the pulse stretcher 220 surrounded by the broken line 201 in FIG. 4. For the part of this broken line 201, since a known technique with proven results can be used, the development of a new device is not necessary. And after generating the near-infrared wavelength-swept light L1a, the wavelength of the wavelength-swept light L1a can be wavelength-converted using the nonlinear optical effect to generate the wavelength-swept light L1 in the target wavelength band.

[0059] (Embodiment 2) FIG. 6 is a diagram showing a light source device 200A according to Embodiment 2. In Embodiment 2, the wavelength-swept light L1a generated by the pulse stretcher 220A is a pulse train including a plurality of n pulses having different center wavelengths.

[0060] FIG. 7 is a diagram showing a configuration example of a pulse stretcher 220A that generates the wavelength-swept light L1a of the pulse train. The pulse stretcher 220A includes a splitter 222, a delay line 228, and a coupler 232.

[0061] The pulse stretcher 220A receives the broadband pulse light L0 and converts it into the wavelength-swept light L1a of the pulse train.

[0062] The splitter 222 includes an arrayed waveguide grating (AWG) 224 and a lens 226. The lens 226 condenses the broadband pulse light L0 emitted from the pulse light source 210 onto the incident end of the AWG 224.

[0063] The AWG 224 spatially splits the broadband pulse light L0 into a plurality of n beams (referred to as split beams) L01 to L0 n according to the wavelength and outputs them. The number of splits (number of channels) n is equal to the number of fibers 230. The number of channels n can be, for example, 4, 8, 16, 32, 64, 128, etc. The wavelength of the i-th (1 ≦ i ≦ n) split beam is denoted as λ i Note that since the split beams L01 to L0 n each have a certain wavelength width rather than a single spectrum, λ i is not a single wavelength but is used to conveniently represent the wavelength band that L0 i has, and in some cases, is used to represent the center wavelength of the wavelength band. The split beams L01 to L0 n output from the AWG 224 are guided to the delay line 228.

[0064] The delay line 228 has a plurality of split beams L01 to L0 nDifferent delays are applied to. The delay line 228 may include a plurality of fibers 230_1 to 230_n with different lengths. The i-th split beam L0 i is coupled to the incident end of the corresponding fiber 230_i.

[0065] Assume that the broadband pulsed light L0 before splitting is a positive chirp pulse (up-chirp pulse) whose frequency increases (wavelength decreases) with time. That is, the component of the longest wavelength λ1 is included in the leading edge of the pulse, and the shortest wavelength λ n is included in the trailing edge of the pulse.

[0066] The plurality of fibers 230_1 to 230_n have different lengths L1 to L n If λ1 is the longest wavelength and λ n is the shortest wavelength, in order to make the wavelength-swept light L1 the same positive chirp pulse as the broadband pulsed light L0, it is only necessary to satisfy the relationship of L1 < L2 < … < L n For example, when n = 20, the lengths L1 to L n of the fibers 230 may increase in steps of 1 m from 1 m to 20 m.

[0067] The fibers 230_1 to 230_n do not necessarily have different group delay characteristics for each wavelength, and the same fiber (fiber of the same core / clad material) can be used.

[0068] The coupler 232 spatially overlaps and emits a plurality of split beams with different delays imparted by the delay line 228. The coupler 232 includes an AWG 234 and a lens 236, similar to the splitter 222.

[0069] Returning to FIG. 6. Each pulse included in the wavelength-swept light L1a of the pulse train generates a second harmonic or a third harmonic by interacting with the wavelength conversion device 250.

[0070] The central wavelength of each pulse included in the wavelength-swept light L1 of the pulse train is λ1, λ2, … λ nAs a result, the time interval between each pulse of the wavelength-swept light L1 is substantially equal to the time interval between each pulse of the wavelength-swept light L1a. Thus, according to the light source device 200A in FIG. 6, the wavelength-swept light L1 of the pulse train can be generated.

[0071] (Embodiment 3) FIG. 8 is a diagram showing a light source device 200B according to Embodiment 3. In Embodiment 3, the wavelength-swept light L1a generated by the pulse stretcher 220B includes a first near-infrared wavelength-swept light L1a_1 and a second near-infrared wavelength-swept light L1a_2 that overlap on the time axis.

[0072] The first near-infrared wavelength-swept light L1a_1 includes a part of the spectrum of the broadband pulsed light L0 (λa1 to λa n ), and the second near-infrared wavelength-swept light L1a_2 includes another part of the spectrum of the broadband pulsed light L0 (λa n+1 to λa 2n ). Note that the subscript x of the wavelength λa x is merely a convenient identifier for distinguishing different wavelengths, and the value of x is independent of the magnitude of the wavelength.

[0073] The wavelength conversion device 250B wavelength-converts the first near-infrared wavelength-swept light L1a_1 and the second near-infrared wavelength-swept light L1a_2 based on a non-linear optical effect.

[0074] FIG. 9 is a diagram for explaining wavelength conversion in the wavelength conversion device 250B of FIG. 8. The non-linear optical effect may be DFG (difference frequency generation). The wavelength λ i (i = 1 to n) included in the wavelength-swept light L1 is determined based on the wavelength λa i of the wavelength-swept light L1a_1 and the wavelength λa m+i of the wavelength-swept light L1a_2. Let the frequency corresponding to each wavelength λ be ω. Then, the relationship ω i = ωa i - ωa m+1 holds. In DFG, the wavelength-swept light L1 with a long wavelength can be generated.

[0075] The non-linear optical effect may be SFG (sum frequency generation). In this case, ω i = ωa i + ωa m+1 holds. In SFG, a wavelength-swept light L1 with a short wavelength can be generated.

[0076] (Embodiment 4) FIG. 10 is a diagram showing a light source device 200C according to Embodiment 4. In Embodiment 4, the wavelength-swept light L1a generated by the pulse stretcher 220C includes a first near-infrared wavelength-swept light L1a_1 and a second near-infrared wavelength-swept light L1a_2 that overlap on the time axis. The first near-infrared wavelength-swept light L1a_1 and the second near-infrared wavelength-swept light L1a_2 are each a pulse train including a plurality of pulses with different central wavelengths.

[0077] FIG. 11 is a diagram showing a configuration example of the pulse stretcher 220C in FIG. 10.

[0078] The AWG 224 spatially divides the broadband pulsed light L0 into a plurality of 2n beams (referred to as divided beams) L01 to L0 2n according to the wavelength and outputs them. The delay line 228 includes 2n fibers 230_1 to 230_2n equal to the number of divisions.

[0079] The first wavelength-swept light L1a_1 is generated by the first fiber group 230_1 to 230_n, and the second wavelength-swept light L1a_2 is generated by the second fiber group 230_n + 1 to 230_2n. The fibers of the first fiber group 230_1 to 230_2n and the fibers of the second fiber group 230_n + 1 to 230_2n are associated with each other, and the optical path lengths of the corresponding fiber pairs 230_i and 230_i + n are substantially equal. With this configuration, the first wavelength-swept light L1a_1 and the second wavelength-swept light L1a_2, which are pulse trains, can be generated.

[0080] Although embodiments according to the present disclosure have been described using specific terms, this description is merely illustrative for facilitating understanding and does not limit the present disclosure or the scope of the claims. The scope of the present invention is defined by the scope of the claims, and thus, embodiments, examples, and modifications not described herein are also included in the scope of the present invention.

Description of Reference Numerals

[0081] 100 Optical measurement device 300 Light receiving device 400 Arithmetic processing unit 200 Light source device 210 Pulse light source 220 Pulse stretcher 250 Wavelength conversion device 222 Splitter 224 AWG 226 Lens 228 Delay line 230 Fiber 232 Coupler 234 AWG 236 Lens L0 Broadband pulsed light L1a Wavelength-swept light L1b Laser light L1 Wavelength-swept light L2 Object light L3 Reference light

Claims

1. A light source device for generating wavelength-swept light to be irradiated on a sample, comprising: a pulse light source for generating near-infrared pulsed light; a pulse stretcher for stretching the near-infrared pulsed light in the time axis direction to generate near-infrared wavelength-swept light; a wavelength conversion device for wavelength-converting the near-infrared wavelength-swept light emitted from the pulse stretcher based on a non-linear optical effect to generate wavelength-swept light other than near-infrared; The light source device is characterized by comprising the above components.

2. The pulse stretcher generates a first near-infrared wavelength-swept light including a part of the spectrum of the near-infrared pulsed light and a second near-infrared wavelength-swept light including another part of the spectrum of the near-infrared pulsed light, which overlap on the time axis; The wavelength conversion device wavelength-converts the first near-infrared wavelength-swept light and the second near-infrared wavelength-swept light based on a non-linear optical effect. The light source device according to Claim 1 is characterized by this.

3. The light source device according to Claim 2 is characterized in that the non-linear optical effect is difference frequency generation.

4. The light source device according to Claim 2 is characterized in that the non-linear optical effect is sum frequency generation.

5. The light source device according to Claim 2 is characterized in that each of the first near-infrared wavelength-swept light and the second near-infrared wavelength-swept light is a pulse train including a plurality of pulses with different central wavelengths.

6. The pulse stretcher includes: a splitter for spatially splitting the near-infrared pulsed light according to wavelength and emitting a plurality of split beams; a plurality of fibers for giving different delays to the plurality of split beams; a coupler for spatially multiplexing the plurality of beams output from the plurality of fibers and emitting them as the near-infrared wavelength-swept light; The light source device according to any one of Claims 2 to 4 is characterized in that the plurality of fibers include pairs of fibers having substantially equal optical path lengths.

7. The light source device according to Claim 1 is characterized in that the wavelength conversion device performs wavelength conversion by second harmonic generation or third harmonic generation.

8. The light source device according to Claim 1 is characterized in that the near-infrared wavelength-swept light is a pulse train including a plurality of pulses with different central wavelengths.

9. The light source device according to any one of Claims 1 to 5, 7, and 8 is characterized in that the wavelength conversion device includes a PPLN (Periodically Poled Lithium Niobate) element.

10. ​ The light source device according to claim 9, wherein the period of the periodic inversion of the PPLN element is chirped.

11. A light source device according to any one of claims 1 to 5, 7, and 8, a light receiving device that measures object light obtained by irradiating an object with the emitted light of the light source device, and a light measurement device characterized by comprising the same.

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