Light source apparatus and light measuring apparatus

Abstract

A light source apparatus 200 generates emitted light L1 to be radiated onto a sample. A pulsed light source 210 generates near-infrared wideband pulsed light L0. A pulse stretcher 220 stretches the wideband pulsed light L0 in the time axis direction to generate near-infrared wavelength swept light L1a, which is a pulse train including a plurality of pulses having different central wavelengths. A wavelength converting device 250 converts the wavelength of the near-infrared wavelength swept light L1a emitted from the pulse stretcher 220 to generate the emitted light L1.

Description

Light source device and light measurement device

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

[0002] Spectroscopic analysis is widely used for the component analysis and inspection of objects. In spectroscopic analysis, an object is irradiated with irradiating light and the spectrum of the resulting object light is measured. Then, based on the relationship between the spectrum of the object light and the spectrum of the irradiating light, optical characteristics such as reflectance characteristics (wavelength dependence) or transmittance characteristics can be obtained.

[0003] Wavelength-swept spectroscopy is known as one of the methods for measuring optical properties. A wavelength-swept spectrometer generates wavelength-swept light, whose wavelength changes over time, and irradiates the test object with it. The wavelength-swept light is a pulse or pulse train in which time and wavelength have a one-to-one relationship. The time waveform of the light obtained by irradiating the test object with the wavelength-swept light is then detected by a photodetector. The output waveform of the photodetector represents a spectrum in which the time axis corresponds to the wavelength.

[0004] Japanese Patent Application Laid-Open No. 2020-159973

[0005] Patent Document 1 discloses a light source device for a spectroscopic measurement device using wavelength sweeping spectroscopy. Conventional light source devices use SC light in the 900 nm to 1300 nm band, and due to the configuration of the optical waveguide, 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 the above-mentioned problems, and one exemplary purpose of an embodiment thereof 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.

[0007] 1. A light source device according to an aspect of the present disclosure generates output light to be irradiated onto a sample. The light source device includes a pulsed light source that generates near-infrared pulsed light, a pulse stretcher that stretches the near-infrared pulsed light in the time axis direction to generate near-infrared wavelength swept light, and a wavelength conversion device that converts the wavelength of the near-infrared wavelength swept light output from the pulse stretcher to generate output light.

[0008] 2. 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 pulsed light source that generates near-infrared pulsed light, a pulse stretcher that stretches the near-infrared pulsed 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 output from the pulse stretcher based on a nonlinear optical effect to generate wavelength-swept light other than near-infrared light.

[0009] Any combination of the above components, or mutual substitution of the components or expressions of the present disclosure between methods, devices, systems, etc., are also valid aspects of the present disclosure.

[0010] According to an aspect of the present disclosure, wavelength-swept light in a wavelength band other than the near-infrared can be generated with high efficiency.

[0011] 1. A block diagram showing a basic configuration of a light measurement device according to an embodiment. A diagram showing wavelength swept light. A diagram explaining spectroscopy by the light measurement device of FIG. 1. A diagram showing a light source device according to embodiment 1. A diagram explaining wavelength conversion in a wavelength conversion device. A diagram showing a light source device according to Example 1.1. A diagram showing an example configuration of a pulse stretcher that generates wavelength swept light of a pulse train. A diagram showing a light source device according to Example 1.2. A diagram explaining an operation example of the light source device of FIG. 8. A diagram explaining an operation example of the light source device of FIG. 8. A diagram explaining another operation example of the light source device of FIG. 8. A diagram showing a light source device according to embodiment 2. A diagram explaining wavelength conversion in the wavelength conversion device of FIG. 12. A diagram showing a light source device according to embodiment 3. A diagram showing an example configuration of a pulse stretcher that generates wavelength swept light of a pulse train. A diagram showing a light source device according to embodiment 4. A diagram explaining wavelength conversion in the wavelength conversion device of FIG. 16. A diagram showing a light source device according to embodiment 5. A diagram showing an example configuration of the pulse stretcher of FIG. 18.

[0012] (Summary of the Embodiments) A summary of some exemplary embodiments of the present disclosure will be provided. This summary is intended to provide a basic understanding of one or more embodiments as a prelude to the detailed description that follows, and is not intended to limit the scope of the invention or disclosure. Furthermore, this summary is not intended to be a comprehensive overview of all possible embodiments, nor does it limit essential elements of the embodiments. For convenience, the term "one embodiment" may refer to one embodiment (example or variant) or multiple embodiments (examples or variants) disclosed herein.

[0013] A light source apparatus according to an embodiment of the present disclosure generates output light to be irradiated onto a sample, and includes a pulse light source that generates near-infrared pulsed light, a pulse stretcher that stretches the near-infrared pulsed light in a time axis direction to generate near-infrared wavelength swept light, and a wavelength conversion device that converts the wavelength of the near-infrared wavelength swept light output from the pulse stretcher to generate output light.

[0014] The near-infrared region is used in optical communications, and many highly efficient and reliable devices are available. Therefore, by generating wavelength-swept light in the near-infrared region and then converting the wavelength, it is possible to generate highly efficient wavelength-swept light in bands other than the near-infrared region.

[0015] In one embodiment, the near-infrared wavelength swept light may be a pulse train including a plurality of pulses with different center wavelengths.

[0016] In one embodiment, the light source apparatus may further include a wavelength conversion laser, and the wavelength conversion device may generate the emitted light by a nonlinear optical effect between the laser light generated by the wavelength conversion laser and the near-infrared wavelength swept light.

[0017] In one embodiment, the wavelength conversion laser may be a pulsed laser that emits pulsed laser light.

[0018] In one embodiment, when the period of the pulse train is T1, the interval between multiple pulses is t1, the period of the pulsed laser light is T2, and m is a natural number, the relationship T2 = T1 + m × t1 may be satisfied. This makes it possible to generate a wavelength-swept light pulse train with an interval of T2, and to set the wavelength variation width for each pulse depending on the value of m.

[0019] In one embodiment, the wavelength conversion laser may be a CW (Continuous Wave) laser that emits continuous light.

[0020] In one embodiment, the pulse stretcher may include a splitter that spatially splits near-infrared pulsed light according to wavelength and outputs 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 outputs the combined beams as near-infrared wavelength swept light.

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

[0022] In one embodiment, the PPLN element may have a chirped period of period reversal.

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

[0024] In one embodiment, the wavelength conversion device may convert the wavelength of the near-infrared wavelength swept light output from the pulse stretcher based on a nonlinear optical effect to generate wavelength swept light other than the near-infrared wavelength.

[0025] 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 and a second near-infrared wavelength swept light including another part of the spectrum of the near-infrared pulsed light, which overlap on a time axis, and the wavelength conversion device may wavelength-convert the first near-infrared wavelength swept light and the second near-infrared wavelength swept light based on a nonlinear optical effect.

[0026] In one embodiment, the nonlinear optical effect may be difference frequency generation, which allows for the generation of wavelength-swept light at long wavelengths.

[0027] In one embodiment, the nonlinear optical effect may be sum frequency generation, which allows for the generation of wavelength-swept light at short wavelengths.

[0028] 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 having different center wavelengths.

[0029] In one embodiment, the pulse stretcher may include a splitter that spatially splits near-infrared pulsed light according to wavelength and outputs multiple split beams, multiple fibers that impart different delays to the multiple split beams, and a coupler that spatially combines the multiple beams output from the multiple fibers and outputs the near-infrared wavelength-swept light. The multiple fibers may include a pair of fibers having substantially the same optical path length. With this configuration, the wavelength of the output light can be designed based on two wavelengths that pass through the pair of fibers having the same optical path length.

[0030] In one embodiment, the wavelength conversion device may perform wavelength conversion by second harmonic generation or third harmonic generation.

[0031] In one embodiment, the near-infrared wavelength swept light may be a pulse train including a plurality of pulses with different center wavelengths.

[0032] In one embodiment, the wavelength conversion device may include a PPLN (Periodically Poled Lithium Niobate) element.

[0033] In one embodiment, the PPLN element may have a chirped period of period reversal.

[0034] A light measurement device according to one embodiment may include any of the light source devices described above and a light receiving device that measures object light obtained by irradiating an object with light emitted from the light source device.

[0035] (Embodiments) The present disclosure will be described below based on preferred embodiments with reference to the drawings. The same or equivalent components, parts, and processes shown in each drawing will be given the same reference numerals, and redundant explanations will be omitted as appropriate. Furthermore, the embodiments are examples rather than limitations on the disclosure, and all features and combinations thereof described in the embodiments are not necessarily essential to the disclosure.

[0036] 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 multiple members do not necessarily represent the relative size of each other. Even if a member A is depicted as being thicker than another member B in the drawings, member A may actually be thinner than member B.

[0037] 1 is a block diagram showing the basic configuration of a light measurement device 100 according to an embodiment. The light measurement device 100 is a wavelength sweep type spectroscope 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. are shown as simplified boxes, but this does not mean that the components that make up each of them are housed in a single housing.

[0038] The light source device 200 irradiates the object OBJ with wavelength-swept light L1, the wavelength of which changes over time. The wavelength-swept light L1 has a one-to-one correspondence between time and wavelength. This means that the wavelength-swept light L1 has a "unique wavelength."

[0039] 2 is a diagram showing the wavelength swept light L1. The upper part of FIG. 2 shows the intensity (time waveform) I of the wavelength swept light L1. ＷＳ The lower part shows the time variation of the wavelength λ of the wavelength swept light L1. In this example, the wavelength swept light L1 is a single pulse light, and its dominant wavelength is λ １ , the dominant wavelength at the trailing edge is λ ｎ and the wavelength within one pulse is λ １ From λ ｎIn this example, the wavelength swept light L1 is a positive chirp pulse (λ １ >λ ｎ ) The wavelength swept light L1 may be a negative chirp pulse whose wavelength increases with time (λ １ <λ ｎ As will be described later, the wavelength swept light L1 may be a pulse train.

[0040] Returning to FIG. 1 , the light receiving device 300 receives light (object light) L2 obtained by 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 optical sensors 302 and 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 optical sensor 302. A portion of the wavelength-swept light L1 generated by the light source device 200 is extracted as reference light L3 via a separate path using an optical element such as a beam splitter and is detected by the optical sensor 304.

[0041] The A / D converter 310 converts the output signals S2 and S3 of the optical sensors 302 and 304 into digital signals D2 and D3. The time waveform I of the object light L2 indicated by the digital signal D2 is ＯＢＪ (t) and the time waveform I of the reference light L3 indicated by the digital signal D3 ＲＥＦ (t) is taken into the processor 400 .

[0042] In wavelength-swept spectroscopy, there is a one-to-one correspondence between time and wavelength in the wavelength-swept light L1. This correspondence is naturally also held by the reference light L3, and is also inherited by the object light L2. By utilizing this correspondence between time and wavelength, the arithmetic processing device 400 calculates the time waveform I of the object light L2. ＯＢＪ (t) is the frequency domain spectrum I ＯＢＪ (λ). The arithmetic processing unit 400 converts the time waveform I of the reference light L3 into ＲＥＦ (t) is converted to a spectrum and scaled appropriately to obtain the reference spectrum I ＲＥＦ Calculate (λ).

[0043] The processing of the arithmetic processing device 400 is not particularly limited. For example, the arithmetic processing device 400 may ＲＥＦ (λ) and the spectrum I of the object light L2 ＯＢＪ Based on (λ), the transmittance T(λ) of the object OBJ can be calculated. The same applies to the reflectance R(λ). T(λ) = I ＯＢＪ (λ) / I ＲＥＦ (λ) R(λ) = I ＯＢＪ (λ) / I ＲＥＦ (λ)

[0044] In addition, when the stability of the wavelength swept light L1 is high, the spectrum of the wavelength swept light L1 is measured in advance, and a reference spectrum I ＲＥＦ (λ) may also be used.

[0045] 3 is a diagram illustrating the spectroscopy by the optical measurement device 100 of FIG. 1. As described above, the wavelength swept light L1 has a one-to-one correspondence between time t and wavelength λ, and therefore its time waveform I ＲＥＦ (t) is the frequency domain spectrum I ＲＥＦ (λ).

[0046] Time waveform I of object light L2 ＯＢＪ In the case of (t), the time t and the wavelength λ correspond one-to-one. ＯＢＪ (t) is the spectrum I of the object light L2 ＯＢＪ (λ).

[0047] The processor 400 calculates the two spectra I ＯＢＪ (λ) and I ＲＥＦ (λ) ratio I ＯＢＪ (λ) / I ＲＥＦ Based on (λ), the transmission spectrum T(λ) of the object OBJ can be calculated.

[0048] The relationship between the wavelength λ of the wavelength swept light L1 and time t is expressed as a function λ=f(t). In the simplest terms, the wavelength λ changes linearly with respect to time t according to a linear function. ＯＢＪ (t) is the time t ｘWhen the transmission spectrum T(λ) decreases at wavelength λ ｘ = f (t ｘ ) means that it has an absorption spectrum.

[0049] The processing in the arithmetic processing unit 400 is not limited to this. ＯＢＪ (t) and I ＲＥＦ (t) ratio T(t) = I ＯＢＪ (t) / I ＲＥＦ After calculating (t), the variable t of the time waveform T(t) may be converted to λ to calculate the transmission spectrum T(λ).

[0050] The above is the basic configuration and operation of the light measurement device 100. Next, the configuration of the light source device 200 will be described based on several embodiments.

[0051] 4 is a diagram showing a light source device 200 according to the first embodiment. In this embodiment, the light source device 200 is configured to be able to generate wavelength-swept light L1 in a wavelength band other than the near-infrared. The light source device 200 includes a pulse light source 210, a pulse stretcher 220, a wavelength conversion device 250, and a wavelength conversion laser 260.

[0052] The pulsed light source 210 emits broadband pulsed light L0 having a broad, continuous spectrum in the near-infrared region. The broadband pulsed light L0 is SC (Super Continuum) light, and the spectrum of the broadband pulsed light L0 is continuous over a wavelength range of at least 10 nm, preferably 100 nm, and more preferably 400 nm, for example, in the range of 900 nm to 1300 nm.

[0053] For example, the pulsed 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.

[0054] The nonlinear element further broadens the spectral width of the ultrashort pulses generated by the ultrashort pulse laser through nonlinear phenomena. A fiber is suitable as the nonlinear element, and for example, a photonic crystal fiber or other nonlinear fiber can be used. A single-mode fiber is suitable, but multi-mode fibers can also be used as long as they exhibit sufficient nonlinearity. The broadband pulsed light L0 output from the nonlinear element has a pulse width on the order of femtoseconds to nanoseconds.

[0055] Other broadband pulsed light sources such as a superluminescent diode (SLD) light source may be used as the pulsed light source 210. Alternatively, it is preferable to use a light source with high spatial coherence for coupling to a fiber.

[0056] The pulse stretcher 220 stretches the broadband pulsed light L0 in the time axis direction to generate near-infrared wavelength swept light L1a. The wavelength of the wavelength swept light L1a is λa. １ From λa ｎ changes over time towards

[0057] The wavelength conversion device 250 converts the wavelength of the near-infrared wavelength swept light L1a emitted from the pulse stretcher 220, and generates output light that is wavelength swept light L1 other than near-infrared. The wavelength of the wavelength swept light L1 is λ １ ~λ ｎ changes over time towards

[0058] In this embodiment, a wavelength conversion laser 260 is provided for wavelength conversion. The wavelength conversion laser 260 is a pulsed laser or a CW laser, and generates laser light L1b with a wavelength λb. The wavelength conversion laser 260 can be a solid-state laser, a fiber laser, or a semiconductor laser.

[0059] The wavelength conversion device 250 generates the output light L1 by the nonlinear optical effect between the laser light L1b generated by the wavelength conversion laser 260 and the near-infrared wavelength swept light L1a.

[0060] The nonlinear optical effects that can be used in the wavelength conversion device 250 include sum frequency generation (SFG), difference frequency generation (DFG), optical parametric generation (OPG), and four wave mixing (FWM).

[0061] λ ｉ is λa ｉ The frequency corresponding to each wavelength λ is ω. When using SFG, ω ｉ =ωa ｉ When using DFG, the relationship of ω ｉ =ωa ｉ The relationship of −ωb holds.

[0062] The type of nonlinear optical effect, the wavelength λb of the laser light L1b, is the wavelength band λ of the required wavelength swept light L1. １ ~λ ｎ The wavelength λb of the laser light L1b is preferably, for example, 1064 nm, 1300 nm, or 1550 nm.

[0063] The wavelength conversion device 250 can be a periodically poled module, such as a bulk or waveguide PPLN (periodically poled lithium niobate) element or a PPMgO (periodically poled MgO-doped lithium niobate) element. Periodically poled modules typically only convert wavelengths over a few nanometers to several tens of nanometers. Therefore, to achieve broadband wavelength conversion, the periodically poled module should have a chirped periodically poled structure. Alternatively, multiple gratings, in which a single PPLN element contains multiple PPLN periods, and fan-out gratings, in which a single PPLN element contains fan-shaped polarizations, can also be used to achieve broadband wavelength conversion.

[0064] FIG. 5 is a diagram illustrating wavelength conversion in the wavelength conversion device 250. As shown in FIG.

[0065] Mid-infrared to far-infrared wavelength band: A difference frequency generation DFG between the laser light L1b and the wavelength swept light L1a can be used, and an Er fiber laser with λb=1550 nm can be used as the wavelength conversion laser 260. In this case, it is possible to cover the mid-infrared band with a wavelength of 2 μm to 4 μm and the far-infrared band with a wavelength of 4 μm to 8 μm.

[0066] The wavelength swept light L1 in the mid-infrared to far-infrared range can also be generated by using an OPG or FWM.

[0067] Visible range: Sum frequency generation SFG of the laser light L1b and the wavelength swept light L1a can be used, and the wavelength conversion laser 260 is a solid-state laser (Nd:YAG, Nd:YVO) with λb=1064 nm. ４ ), or a Yb fiber laser with λb=1030 nm can be used, which can cover wavelengths from 450 nm to 800 nm.

[0068] Ultraviolet Range After wavelength swept light in the visible range is generated using SFG, wavelength swept light L1 in the ultraviolet range may be generated using second harmonic generation (SHG).

[0069] The above is the configuration of the light source device 200. Next, we will explain the advantages of the light source device 200. The advantages of the light source device 200 become clear when compared with the comparative technology.

[0070] In the comparative technology, the configuration of the light source device described in Patent Document 1 is directly replaced with a wavelength band other than the near-infrared. That is, the light source device includes an SC light source for a target wavelength band other than the near-infrared, an AWG that functions in this wavelength band, and an optical fiber.

[0071] For example, consider adapting the comparative technology described in Patent Document 1 to the visible wavelength range, which has wavelengths shorter than the near-infrared range. In this case, SC light can be generated relatively easily using wavelength conversion or short-pulse lasers. However, fabricating optical waveguides at short wavelengths is known to significantly increase the effects of light scattering due to shape anomalies in the waveguide itself (the negative fourth power of the wavelength), resulting in significant scattering losses. Research is also being conducted on compact microscope devices using optical waveguides, but the high optical loss of optical waveguides in the visible wavelength range is known to be a major technical challenge, necessitating the development of new optical waveguide manufacturing processes. Furthermore, since the core diameter of a single-mode optical fiber is roughly proportional to the wavelength, compared with a core diameter of φ9.5 μm for optical fibers used in the 1.5 μm wavelength band, an optical fiber for the 400 nm wavelength band has a core diameter of approximately φ3 μm. This places extremely strict demands on the bonding and mechanical precision of each component, assembly tolerances, and stability. Furthermore, it is known that deterioration over time is severe in the ultraviolet wavelength band of 400 nm or less, and development of the materials themselves for optical fibers and optical waveguides is necessary.

[0072] We are considering applying the comparative technology described in Patent Document 1 to the mid-infrared wavelength band, which has a longer wavelength than the near-infrared region. SC light can be generated relatively easily using wavelength conversion technology, but absorption of molecular vibrations is strong at mid-infrared wavelengths, and it is difficult to use SiO2, which is used in optical fibers and waveguides. ２ The absorption by impurities contained in the optical fiber is very large. Furthermore, the development of materials that can obtain the optimum dispersion for waveguiding has not progressed, making it difficult to fabricate optical waveguide devices in the mid-infrared. In other words, it is necessary to start by developing the materials for the optical waveguide and optical fiber themselves.

[0073] In this embodiment, near-infrared wavelength-swept light L1a is generated by a pulsed light source 210 and a pulse stretcher 220, which are enclosed by a dashed line 201 in Fig. 4. The portion enclosed by the dashed line 201 can be realized by using a known technology that has already proven its effectiveness, and thus there is no need to develop a new device. After generating the near-infrared wavelength-swept light L1a, the wavelength of the wavelength-swept light L1a is converted by utilizing a nonlinear optical effect, thereby generating wavelength-swept light L1 in a desired wavelength band.

[0074] The present disclosure extends to various devices and methods that can be understood as the block diagram of Fig. 4 or derived from the above description, and is not limited to a specific configuration. Specific configuration examples and examples of the light source device 200 according to embodiment 1 will be described below, not to narrow the scope of the present disclosure, but to aid in understanding and clarify the essence and operation of the present disclosure and the present invention.

[0075] 6 is a diagram showing a light source device 200A according to Example 1.1. In this example, the wavelength-swept light L1a generated by the pulse stretcher 220A is a pulse train including n pulses with different center wavelengths. The wavelength conversion laser 260A is a CW laser.

[0076] 7 shows an example of the configuration of a pulse stretcher 220A that generates the wavelength-swept light L1a of a pulse train. The pulse stretcher 220A includes a splitter 222, a delay line 228, and a coupler 232.

[0077] The pulse stretcher 220A receives the broadband pulsed light L0 and converts it into a pulse train of wavelength-swept light L1a.

[0078] The splitter 222 includes an arrayed waveguide grating (AWG) 224 and a lens 226. The lens 226 focuses the wideband pulsed light L0 emitted by the pulsed light source 210 onto the input end of the AWG 224.

[0079] The AWG 224 spatially divides the broadband pulsed light L0 into a plurality of n beams (referred to as split beams) L0 according to the wavelength. １ ~L0 ｎ The number of divisions (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 ith (1≦i≦n) divided beam is defined as λ ｉ The split beam L0 １ ~L0 ｎ Each of these is not a single spectrum but has a certain wavelength width, so λ ｉ is not a single wavelength, L0 ｉFor convenience, the wavelength band of the split beam L0 output from the AWG 224 is used to represent the wavelength band, and in some cases, the central wavelength of the split beam L0 output from the AWG 224 is used to represent the central wavelength of the split beam L0. １ ~L0 ｎ is directed to a delay line 228.

[0080] The delay line 228 divides the beams L0 １ ~L0 ｎ The delay line 228 may include multiple fibers 230_1 to 230_n of different lengths. ｉ are coupled to the input ends of the corresponding fibers 230_i.

[0081] It is assumed that the broadband pulse light L0 before splitting is a positive chirp pulse (up-chirp pulse) whose frequency increases (wavelength shortens) with time. That is, the longest wavelength λ is formed at the leading edge of the pulse. １ The pulse has a shortest wavelength λ at its trailing edge. ｎ Contains the ingredients:

[0082] The plurality of fibers 230_1 to 230_n have different lengths l １ ~l ｎ λ １ is the longest wavelength, λ ｎ is the shortest wavelength, in order to make the wavelength swept light L1 a positive chirped pulse like the broadband pulse light L0, １ <l ２ <…<l ｎ As an example, when n=20, the length l of the fiber 230 is １ ~l ｎ may be increased in 1 m increments from 1 m to 20 m.

[0083] The fibers 230_1 to 230_n do not need to have different group delay characteristics for each wavelength, and the same fiber (fibers with the same core / clad material) can be used.

[0084] The coupler 232 spatially superimposes and outputs the multiple split beams to which different delays have been imparted by the delay line 228. The coupler 232, like the splitter 222, includes an AWG 234 and a lens 236.

[0085] Returning to Fig. 6, the pulses included in the wavelength swept light L1a of the pulse train and the CW laser light L1b interact with the wavelength conversion device 250 to generate the wavelength swept light L1 of the pulse train. The center wavelength of each pulse included in the wavelength swept light L1 of the pulse train is λ １ , λ ２ , …λ ｎ 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. In this way, the light source device 200A in FIG. 6 can generate a pulse train of the wavelength swept light L1.

[0086] 8 is a diagram showing a light source device 200B according to Example 1.2. In this example, the wavelength-swept light L1a generated by the pulse stretcher 220A is a pulse train including a plurality of pulses, n, each having a different center wavelength.

[0087] The wavelength conversion laser 260B is a pulsed laser. The timing of the pulse of the laser light L1b generated by the wavelength conversion laser 260B is controlled so that it enters the wavelength conversion device 250 simultaneously with one of the multiple pulses included in the wavelength swept light L1a. The relationship between the pulse width of the laser light L1b and the pulse width of each pulse of the wavelength swept light L1a is not particularly limited. The wavelength conversion laser 260B may include multiple pulsed lasers operating at different phases. Furthermore, the seed laser of the pulsed light source 210 may also be used as the wavelength conversion laser 260B.

[0088] Fig. 9 is a diagram illustrating an example of the operation of the light source device 200B of Fig. 8. The wavelength conversion laser 260B generates laser light L1b at intervals equal to t1, which are the intervals between pulses generated by the pulse stretcher 220A.

[0089] At this time, the wavelength swept light L1 emitted from the wavelength conversion device 250 becomes a pulse train with a period t1, and the wavelength of each pulse is λ １ , λ２ , λ ３ ...and so on.

[0090] 10 is a diagram illustrating an example of the operation of the light source device 200B of FIG. 8. The wavelength conversion laser 260B emits pulses at a constant period T2. The period of the pulse train of the wavelength swept light L1a generated by the pulse stretcher 220A is T1, and the interval between the plurality of n pulses contained therein is t1. The period T2 of the pulse laser light L1b generated by the wavelength conversion laser 260B is determined to satisfy the following relational expression: T2=T1+t1

[0091] At this time, the wavelength swept light L1 emitted from the wavelength conversion device 250 becomes a pulse train with a period T2, and the wavelength of each pulse is λ １ , λ ２ , λ ３ ...and so on.

[0092] In general, the period T2 of the pulsed laser light L1b generated by the wavelength conversion laser 260B can be determined to satisfy the following relational expression: T2 = T1 + m × t1, where m is a natural number. The wavelength change width for each pulse of the wavelength swept light L1 can be set according to m.

[0093] 11 is a diagram illustrating another example of the operation of the light source device 200B of FIG. 8. The period T2 of the wavelength conversion laser 260B is equal to the period T1 of the wavelength swept light L1a. T2=T1

[0094] The timing Δt of the pulsed laser light L1b generated by the wavelength conversion laser 260B is variable relative to the pulse train of the wavelength swept light L1a. When Δt=0, the wavelength swept light L1 has a wavelength λ １ When Δt=t1, the wavelength swept light L1 has a wavelength λ ２ In general, when Δt=t1×i, the wavelength swept light L1 has a wavelength λ （ｉ＋１） Therefore, by increasing Δt for every m pulses (m is a natural number) of the laser light L1b, a pulse train of m wavelengths λ １ pulses, m wavelengths λ ２ pulses, m wavelengths λ ３Alternatively, if Δt is kept fixed, pulses of any wavelength can be continuously generated.

[0095] 12 is a diagram showing a light source device 200 according to embodiment 2. In this embodiment, the light source device 200 is configured to be able to generate wavelength-swept light L1 in a wavelength band other than the near-infrared. The light source device 200 includes a pulse light source 210, a pulse stretcher 220, and a wavelength conversion device 250.

[0096] The pulsed light source 210 emits broadband pulsed light L0 having a broad, continuous spectrum in the near-infrared region. The broadband pulsed light L0 is SC (Super Continuum) light, and the spectrum of the broadband pulsed light L0 is continuous over a wavelength range of at least 10 nm, preferably 100 nm, and more preferably 400 nm, for example, in the range of 900 nm to 1300 nm.

[0097] For example, the pulsed 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.

[0098] The nonlinear element further broadens the spectral width of the ultrashort pulses generated by the ultrashort pulse laser through nonlinear phenomena. A fiber is suitable as the nonlinear element, and for example, a photonic crystal fiber or other nonlinear fiber can be used. A single-mode fiber is suitable, but multi-mode fibers can also be used as long as they exhibit sufficient nonlinearity. The broadband pulsed light L0 output from the nonlinear element has a pulse width on the order of femtoseconds to nanoseconds.

[0099] Other broadband pulsed light sources such as a superluminescent diode (SLD) light source may be used as the pulsed light source 210. Alternatively, it is preferable to use a light source with high spatial coherence for coupling to a fiber.

[0100] The pulse stretcher 220 stretches the broadband pulsed light L0 in the time axis direction to generate near-infrared wavelength swept light L1a. The wavelength of the wavelength swept light L1a is λa. １ From λa ｎ changes over time towards

[0101] The wavelength conversion device 250 converts the wavelength of the near-infrared wavelength swept light L1a emitted from the pulse stretcher 220, and generates output light that is wavelength swept light L1 other than near-infrared. The wavelength of the wavelength swept light L1 is λ １ ~λ ｎ changes over time towards

[0102] The wavelength conversion device 250 can utilize second harmonic generation (SHG) and third harmonic generation (THG) as nonlinear optical effects.

[0103] λ ｉ is λa ｉ When SHG is used, λ ｉ = λa ｉ When THG is used, λ ｉ = λa ｉ The relationship between .times. ...

[0104] The wavelength conversion device 250 can be a periodically poled module, such as a bulk or waveguide PPLN (periodically poled lithium niobate) element or a PPMgO (periodically poled MgO-doped lithium niobate) element. Periodically poled modules typically only convert wavelengths over a few nanometers to several tens of nanometers. Therefore, to achieve broadband wavelength conversion, the periodically poled module should have a chirped periodically poled structure. Alternatively, multiple gratings, in which a single PPLN element contains multiple PPLN periods, and fan-out gratings, in which a single PPLN element contains fan-shaped polarizations, can also be used to achieve broadband wavelength conversion.

[0105] FIG. 13 is a diagram illustrating wavelength conversion in the wavelength conversion device 250 of FIG.

[0106] Visible Range: SHG can convert near-infrared wavelength swept light of 900 to 1300 nm into wavelength swept light in the visible range of 450 to 650 nm.

[0107] Ultraviolet region: THG can convert near-infrared wavelength swept light of 900 to 1300 nm into wavelength swept light in the ultraviolet region of 300 to 433 nm.

[0108] Alternatively, it is possible to convert the light into wavelength-swept light with a wavelength of 450 to 650 nm by SHG, and then generate wavelength-swept light in the ultraviolet region with a wavelength of 225 to 325 nm by further SHG.

[0109] The above is the configuration of the light source device 200. Next, we will explain the advantages of the light source device 200. The advantages of the light source device 200 become clear when compared with the comparative technology.

[0110] In the comparative technology, the configuration of the light source device described in Patent Document 1 is directly replaced with a wavelength band other than the near-infrared. That is, the light source device includes an SC light source for a target wavelength band other than the near-infrared, an AWG that functions in this wavelength band, and an optical fiber.

[0111] For example, consider adapting the comparative technology described in Patent Document 1 to the visible wavelength range, which has wavelengths shorter than the near-infrared range. In this case, SC light can be generated relatively easily using wavelength conversion or short-pulse lasers. However, fabricating optical waveguides at short wavelengths is known to significantly increase the effects of light scattering due to shape anomalies in the waveguide itself (the negative fourth power of the wavelength), resulting in significant scattering losses. Research is also being conducted on compact microscope devices using optical waveguides, but the high optical loss of optical waveguides in the visible wavelength range is known to be a major technical challenge, necessitating the development of new optical waveguide manufacturing processes. Furthermore, since the core diameter of a single-mode optical fiber is roughly proportional to the wavelength, compared with a core diameter of φ9.5 μm for optical fibers used in the 1.5 μm wavelength band, an optical fiber for the 400 nm wavelength band has a core diameter of approximately φ3 μm. This places extremely strict demands on the bonding and mechanical precision of each component, assembly tolerances, and stability. Furthermore, it is known that deterioration over time is severe in the ultraviolet wavelength band of 400 nm or less, and development of the materials themselves for optical fibers and optical waveguides is necessary.

[0112] We are considering applying the comparative technology described in Patent Document 1 to the mid-infrared wavelength band, which has a longer wavelength than the near-infrared region. SC light can be generated relatively easily using wavelength conversion technology, but absorption of molecular vibrations is strong at mid-infrared wavelengths, and it is difficult to use SiO2, which is used in optical fibers and waveguides. ２ The absorption by impurities contained in the optical fiber is very large. Also, the development of materials that can obtain the optimum dispersion for waveguiding has not progressed, so it is difficult to fabricate optical waveguide devices in the mid-infrared region. In other words, it is necessary to start by developing the materials for the optical waveguide and optical fiber themselves.

[0113] In this embodiment, near-infrared wavelength swept light L1a is generated by a pulsed light source 210 and a pulse stretcher 220, which are enclosed by a dashed line 201 in Fig. 12. For the portion enclosed by the dashed line 201, a well-known technology with a proven track record can be used, eliminating the need to develop a new device. After generating the near-infrared wavelength swept light L1a, the wavelength of the wavelength swept light L1a is converted using a nonlinear optical effect, thereby generating wavelength swept light L1 in a desired wavelength band.

[0114] 14 is a diagram showing a light source device 200A according to embodiment 3. In embodiment 3, wavelength swept light L1a generated by a pulse stretcher 220A is a pulse train including a plurality of pulses, n, having different center wavelengths.

[0115] 15 is a diagram showing an example of the configuration of a pulse stretcher 220A that generates a pulse train of wavelength swept light L1a. The pulse stretcher 220A includes a splitter 222, a delay line 228, and a coupler 232.

[0116] The pulse stretcher 220A receives the broadband pulsed light L0 and converts it into a pulse train of wavelength-swept light L1a.

[0117] The splitter 222 includes an arrayed waveguide grating (AWG) 224 and a lens 226. The lens 226 focuses the wideband pulsed light L0 emitted by the pulsed light source 210 onto the input end of the AWG 224.

[0118] The AWG 224 spatially divides the broadband pulsed light L0 into a plurality of n beams (referred to as split beams) L0 according to the wavelength. １ ~L0 ｎ The number of divisions (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 ith (1≦i≦n) divided beam is defined as λ ｉ The split beam L0 １ ~L0 ｎ Each of these is not a single spectrum but has a certain wavelength width, so λ ｉ is not a single wavelength, L0 ｉ For convenience, the wavelength band of the split beam L0 output from the AWG 224 is used to represent the wavelength band, and in some cases, the central wavelength of the split beam L0 output from the AWG 224 is used to represent the central wavelength of the split beam L0. １ ~L0 ｎ is directed to a delay line 228.

[0119] The delay line 228 divides the beams L0 １ ~L0 ｎThe delay line 228 may include multiple fibers 230_1 to 230_n of different lengths. ｉ are coupled to the input ends of the corresponding fibers 230_i.

[0120] It is assumed that the broadband pulse light L0 before splitting is a positive chirp pulse (up-chirp pulse) whose frequency increases (wavelength shortens) with time. That is, the longest wavelength λ is formed at the leading edge of the pulse. １ The pulse has a shortest wavelength λ at its trailing edge. ｎ Contains the ingredients:

[0121] The plurality of fibers 230_1 to 230_n have different lengths L １ ~L ｎ λ １ is the longest wavelength, λ ｎ is the shortest wavelength, in order to make the wavelength swept light L1 a positive chirped pulse like the broadband pulse light L0, L １ <L ２ <...<L ｎ As an example, when n=20, the length L of the fiber 230 is １ ~L ｎ may be increased in 1 m increments from 1 m to 20 m.

[0122] The fibers 230_1 to 230_n do not need to have different group delay characteristics for each wavelength, and the same fiber (fibers with the same core / clad material) can be used.

[0123] The coupler 232 spatially superimposes and outputs the multiple split beams to which different delays have been imparted by the delay line 228. The coupler 232, like the splitter 222, includes an AWG 234 and a lens 236.

[0124] Returning to Fig. 14, each pulse included in the wavelength swept light L1a of the pulse train interacts with the wavelength conversion device 250 to generate a second harmonic or a third harmonic.

[0125] The central wavelength of each pulse included in the wavelength swept light L1 of the pulse train is λ １ , λ ２, …λ ｎ 14, 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.

[0126] 16 is a diagram illustrating a light source device 200B according to embodiment 4. In embodiment 4, 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.

[0127] The first near-infrared wavelength swept light L1a_1 is a part of the spectrum of the broadband pulsed light L0 (λa １ ~λa ｎ ), and the second near-infrared wavelength swept light L1a_2 includes another part of the spectrum of the wideband pulsed light L0 (λa ｎ＋１ ~λa ２ｎ ) is included. ｘ The subscript x in is merely a convenient identifier for distinguishing between different wavelengths, and the value of x has no relation to the magnitude of the wavelength.

[0128] The wavelength conversion device 250B converts the wavelengths of the first near-infrared wavelength swept light L1a_1 and the second near-infrared wavelength swept light L1a_2 based on the nonlinear optical effect.

[0129] 17 is a diagram illustrating wavelength conversion in the wavelength conversion device 250B of FIG. 16. The nonlinear optical effect may be DFG (difference frequency generation). ｉ (i=1 to n) is the wavelength λa of the wavelength swept light L1a_1 ｉ and the wavelength λa of the wavelength swept light L1a_2 ｍ＋ｉ If the frequency corresponding to each wavelength λ is ω, then ω ｉ =ωa ｉ -ωa ｍ＋１ The DFG can generate wavelength swept light L1 with a long wavelength.

[0130] The nonlinear optical effect may be SFG (sum frequency generation). In this case, ω ｉ =ωa ｉ +ωaｍ＋１ The following relationship holds: SFG can generate wavelength swept light L1 with a short wavelength.

[0131] 18 is a diagram illustrating a light source device 200C according to a fifth embodiment. In the fifth embodiment, 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 having different center wavelengths.

[0132] FIG. 19 is a diagram showing an example of the configuration of the pulse stretcher 220C shown in FIG.

[0133] The AWG 224 spatially divides the broadband pulsed light L0 into a plurality of 2n beams (referred to as split beams) L0 according to the wavelength. １ ~L0 ２ｎ The delay line 228 includes 2n fibers 230_1 to 230_2n, the number of which is equal to the number of divisions.

[0134] The first fiber group 230_1 to 230_n generates the first wavelength swept light L1a_1, and the second fiber group 230_n+1 to 230_2n generates the second wavelength swept light L1a_2. The fibers in the first fiber group 230_1 to 230_2n correspond to the fibers in the second fiber group 230_n+1 to 230_2n, and the optical path lengths of the corresponding fiber pairs 230_i and 230_i+n are substantially equal. This configuration enables the generation of the first wavelength swept light L1a_1 and the second wavelength swept light L1a_2, which are pulse trains.

[0135] Although the embodiments of the present disclosure have been described using specific terms, this description is merely an example to facilitate understanding and does not limit the scope of the present disclosure or the claims. The scope of the present invention is defined by the claims, and therefore, embodiments, examples, and modifications not described herein are also included in the scope of the present invention.

[0136] The present disclosure relates to a light source device and a light measurement device.

[0137] REFERENCE SIGNS LIST 100 Light measurement device 300 Light receiving device 400 Processing device 200 Light source device 210 Pulse light source 220 Pulse stretcher 250 Wavelength conversion device 260 Wavelength conversion laser 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 emitted light to be irradiated on a sample, comprising: a pulse light source that generates near-infrared pulsed light; a pulse stretcher that stretches the near-infrared pulsed 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 to generate the emitted light.

2. The light source device according to claim 1, wherein the near-infrared wavelength-swept light is a pulse train including a plurality of pulses having different center wavelengths.

3. The light source device according to claim 2, further comprising a wavelength conversion laser, wherein the wavelength conversion device generates the emitted light by the interaction between the laser light generated by the wavelength conversion laser and the near-infrared wavelength-swept light.

4. The light source device according to claim 3, wherein the wavelength conversion laser is a pulse laser that emits pulsed laser light.

5. The light source device according to any one of claims 1 to 4, wherein when the period of the pulse train is T1, the interval between the plurality of pulses is t1, the period of the pulsed laser light is T2, and m is a natural number, the relationship T2 = T1 + m × t1 is satisfied.

6. The light source device according to claim 3, wherein the wavelength conversion laser is a CW (Continuous Wave) laser that emits continuous light.

7. The light source device according to any one of claims 1 to 4, wherein the pulse stretcher includes: a divider that spatially divides the near-infrared pulsed light according to wavelength and emits a plurality of divided beams; a plurality of fibers that give different delays to the plurality of divided beams; and a coupler that spatially multiplexes the plurality of beams output from the plurality of fibers and emits the multiplexed beams as the near-infrared wavelength-swept light.

8. The light source device according to any one of claims 1 to 4, wherein the wavelength conversion device includes a PPLN (Periodically Poled Lithium Niobate) element.

9. The light source device according to claim 8, wherein the period of the periodic inversion of the PPLN element is chirped.

10. An optical measurement device comprising: the light source device according to any one of claims 1 to 4; and a light receiving device that measures object light obtained by irradiating an object with the emitted light of the light source device.

11. The light source device according to claim 1, wherein the wavelength conversion device 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 having a wavelength other than near-infrared.

12. 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 11, characterized in that.

13. The light source device according to claim 12, wherein the non-linear optical effect is difference frequency generation.

14. The light source device according to claim 12, wherein the non-linear optical effect is sum frequency generation.

15. The light source device according to claim 12, wherein 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 having different central wavelengths.

16. The pulse stretcher includes a splitter that spatially splits the near-infrared pulsed light according to wavelength and emits a plurality of split beams, a plurality of fibers that give different delays to the plurality of split beams, and a coupler that spatially multiplexes the plurality of beams output from the plurality of fibers and emits them as the near-infrared wavelength-swept light. The plurality of fibers include pairs of fibers having substantially equal optical path lengths. The light source device according to any one of claims 12 to 14, characterized in that.

17. The light source device according to claim 11, wherein the wavelength conversion device performs wavelength conversion by second harmonic generation or third harmonic generation.

18. The light source device according to claim 11, wherein the near-infrared wavelength-swept light is a pulse train including a plurality of pulses having different central wavelengths.

19. The light source device according to any one of claims 11 to 15, 17, and 18, wherein the wavelength conversion device includes a PPLN (Periodically Poled Lithium Niobate) element.

20. The light source device according to claim 19, wherein the period of the periodic inversion of the PPLN element is chirped.

21. A light measurement device comprising: the light source device according to any one of claims 11 to 15, 17, and 18; and a light receiving device that measures object light obtained by irradiating an object with the emitted light of the light source device.

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