System including a laser module

Abstract

The system (1) includes a laser module (30) including a first laser source (36) configured to generate a narrowband first source laser light (33), and a plurality of paths (310) formed by optical fibers without using free space. The plurality of paths includes a first path (301) for splitting the first source light pulse to generate a Stokes light pulse (51) and a pump light pulse (52), a second path (302) for amplifying and broadening the wavelength range by a first train (81) including a first amplifier (81b), a first HCPCF (81a), and an HNLPCF (85) connected to provide the Stokes light pulse (51), and a third path (303) for amplifying by a second train (82) including a second amplifier (82b) and a second HCPCF (82a) connected to provide the pump light pulse (52).

Description

Technical Field

[0001] The present invention relates to a system including a laser module.

Background Art

[0002] WO2014 / 061147 discloses a microscope. This microscope includes a first optical splitter that splits a light beam from a light source into a first pump light beam and a second pump light beam, a Stokes light source that receives the second pump light beam as an input and outputs a Stokes light beam, a multiplexer that multiplexes the first pump light beam and the Stokes light beam to generate a multiplexed light beam, a first light collector that collects the multiplexed light beam in a sample, a first detector that detects CARS light generated from the sample (CARS light has a wavelength different from that of the multiplexed light beam), a second optical splitter that partially branches at least one of the second pump light beam and the Stokes light beam as a reference light beam, a second multiplexer that multiplexes the light beam from the sample and the reference light beam to generate an interference light, and a second detector that detects the interference light.

Summary of the Invention

[0003] In order to monitor or observe a non-linear optical process such as CARS (Coherent Anti-Stokes Raman Scattering), it is necessary to supply a broadband pulse (broadband optical pulse, pulse with a wide wavelength range) such as a Stokes light pulse and a narrowband pulse (narrowband optical pulse, pulse with a narrow wavelength range) such as a pump light pulse from a compact system, and acquire a signal generated by a process using them.

[0004] One aspect of the present invention is a system including a laser module, the laser module including a first laser light source configured to generate (produce) a narrow-band first source laser light, and a plurality of paths configured without using free space by an optical fiber and / or a photonic integrated circuit. These plurality of paths include (i) a first path (first route, first section, first stage) for splitting a first source optical pulse to generate a broadband first optical pulse and a narrow-band second optical pulse, (ii) a second path (second route, second section, second stage) for amplifying and broadening the wavelength range by a first train (first series) including a spliced (joined, connected) first amplifier, a first hollow-core photonic crystal fiber (HCPCF), and a highly nonlinear photonic crystal fiber (HNLPCF) to supply the broadband first optical pulse, and (iii) a third path (third route, third section, third stage) for amplifying by a second train (second series) including a spliced (joined, connected) second amplifier and a second HCPCF to supply the narrow-band second optical pulse. In the second path, by directly splicing (joining, connecting) two types of photonic crystal fibers (PCFs), namely HCPCF and HNLPCF, to the amplifier without free space, the compression function provided by HCPCF and the supercontinuum (SC) generation function provided by HNLPCF can be integrated (incorporated) together with the amplifier into one series (one system, one series) of a fiber or a photonic integrated circuit, and by omitting a compressor using one or more diffraction gratings in free space and other free-space optical elements, the system including the laser module can be made compact.Also, in the third path, by directly splicing (butting, connecting) the second HNLPCF (different from the first HNLPCF) for the narrow-band second optical pulse and the amplifier without a free space, the compression function provided by the HCPCF and the amplifier can be integrated into one series (one system, a single series) of fibers or photonic integrated circuits, and by omitting additional compressors using free-space diffraction gratings and free-space optical elements, the system including the laser module can be made more compact.

[0005] The plurality of paths may include a fourth path for multiplexing the broadband first optical pulse and the narrow-band second optical pulse and outputting them as one irradiation beam for irradiating a target with the temporally overlapping first optical pulse and second optical pulse. The fourth path may include a chirp rate adjuster that adjusts at least one of the chirp rate of the first optical pulse supplied from the second path and the chirp rate of the second optical pulse supplied from the third path to be substantially equal. The first optical pulse may include a first wavelength range, and the second optical pulse may include a second wavelength range shorter than the first wavelength range. In this system, the first optical pulse and the second optical pulse can be emitted as irradiation light through the fourth path from an integrated optical fiber or a photonic integrated circuit (optical integrated circuit) without using free-space optical elements, providing a compact system.

[0006] The plurality of paths may include a fifth path for generating a narrowband third optical pulse having a third wavelength range shorter than the second wavelength range from the second source laser light, the fifth path comprising a third train including a third amplifier spliced (joined, connected) to supply the third optical pulse, a third HCPCF, and second harmonic generation (SHG). The plurality of paths may further include a sixth path for multiplexing a broadband first optical pulse, a narrowband second optical pulse, and a narrowband third optical pulse, overlapping the first optical pulse, the second optical pulse, and the third optical pulse with a time delay, and outputting them as one irradiation beam to irradiate a target. This system may further include an optical module for supplying the first optical pulse, the second optical pulse, and the third optical pulse to the target as an irradiation beam. This laser module may include an oscillator configured to output a mode-locked base laser that is split for the generation of the first source laser light and the second source laser light. One of the typical ranges of the wavelength of the first source laser light is centered on 1030 nm, and one of the typical ranges of the wavelength of the second source laser light is centered on 1560 nm.

[0007] This system may include a detector configured to detect a signal beam generated by the target as a result of irradiating the target with the irradiation beam. This system may also include a scanner configured to scan the target with the irradiation beam to acquire a signal at each pixel for performing two-dimensional microscopic imaging (2D microscopic imaging). This system may also include a scanner configured to scan the target with the irradiation beam to acquire a signal at each voxel for performing three-dimensional microscopic imaging (3D microscopic imaging).

[0008] One typical use of this system is a system that includes detection and / or analysis of CARS signals from a target. This system may include an optical module that supplies a first optical pulse as a Stokes optical pulse and a second optical pulse as a pump optical pulse to generate a CARS signal. The optical module may include an optical module (optical path) that supplies a first optical pulse as a Stokes optical pulse, a second optical pulse as a pump optical pulse, and a third optical pulse as a probe optical pulse to generate a CARS (TD-CARS) signal.

Brief Description of the Drawings

[0009] Some embodiments will be better understood from the detailed description with reference to the following drawings.

Figure 1

Figure 2

Figure 3

Figure 4

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Figure 7

Modes for Carrying Out the Invention

[0010] Embodiments herein and their various features and advantageous details are illustrated in the accompanying drawings and will be more fully described with reference to the non-limiting embodiments illustrated in the drawings and detailed in the following description. Descriptions of well-known components and processing techniques are omitted so as not to unnecessarily obscure the embodiments herein. The examples used herein are merely intended to facilitate an understanding of how the embodiments herein may be implemented and to further enable those skilled in the art to implement the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.

[0011] In this specification, many terms used in fiber lasers and nonlinear optics are presented, and their abbreviations are used. The following list are the abbreviations used in this specification. FL Fiber Laser Fiber laser OSC Oscillator Oscillator LD Laser Diode Laser diode PD Photo Diode Photo diode EVOA Electronically Controlled Variable Optical Attenuator Electronically controlled variable optical attenuator SAM Saturable Absorber Mirror Saturable absorber mirror FC / APC Ferrule Connecter / Angled Physical Contact Ferrule connector / Angled physical contact (flat polished joint) Er Erbium Erbium EDFA Erbium Doped Fiber Amplifier Erbium-doped fiber amplifier Yb Ytterbium Ytterbium YDFA Ytterbium Doped Fiber Amplifier Ytterbium-doped fiber amplifier SMF Single Mode Fiber PM Polarization Maintaining HNLF Highly Nonlinear Fiber PCF Photonic Crystal Fiber Photonic Crystal Fiber HCPCF Hollow‐Core Photonic Crystal Fiber Hollow-core photonic crystal fiber HNLPCF Highly Non-Liner Photonic Crystal Fiber Highly nonlinear photonic crystal fiber SCPCF Supercontinuum Photonic Crystal Fiber Supercontinuum Photonic Crystal Fiber WDM Wavelength Division Multiplexing CIR Optical Circulator SC Super Continuum SHG Second Harmonic Generation FWHM Full Width Half Maximum CARS Coherent Anti-Stokes Raman Spectroscopy Coherent anti-Stokes Raman spectroscopy CPA Chirped Pulse Amplification CFBG Chirped Fiber Bragg Grating Chirped Fiber Bragg Grating IW Isolator / WDM Hybrid Isolator / WDM Hybrid TW Tap / WDM Hybrid Tap / WDM Hybrid TIW Tap / Isolator / WDM Hybrid Tap / Isolator / WDM Hybrid NPD Non-photon Power Dissipation Non-photon Power Dissipation

[0012] FIG. 1 shows a system 1 according to an embodiment of the present invention. The system 1 supplies a Stokes optical pulse 51 as a first optical pulse, a pump optical pulse 52 as a second optical pulse, and a probe optical pulse 53 as a third optical pulse, and generates (generates) CARS light (CARS signal, signal beam) 55 at a point 5a of a target (object, sample) 5 irradiated by a beam (light beam) including the Stokes optical pulse 51, the pump optical pulse 52, and the probe optical pulse 53. It has an optical module 10 for. The optical module 10 includes a laser module 30 for supplying a first beam 31 in which the Stokes optical pulse 51 and the pump optical pulse 52 temporally overlap, and the probe optical pulse 53, and the Stokes optical pulse 51, the pump optical pulse 52, and the probe optical pulse 53. And an optical plate 20 including a plurality of optical elements 29 for combining or coupling (unifying) the optical pulses as an irradiation beam 54. The system 1 is configured to scan (scan) the target 5 with the Stokes optical pulse 51, the pump optical pulse 52, and the probe optical pulse 53 via a lens 45 and other optical elements, and obtain CARS light 55 from the target 5. It may include a scanning module (scanner, scanning module) 40 and a detector 65 configured to detect CARS light 55 for analysis. The system 1 may include a controller (processor) 60 for controlling the entire system 1. The controller 60 may include other functions such as a laser control module (laser controller) 61 and an analyzer 62.

[0013] The scanning module (scanner) 40 may be a fingertip scanning interface module, a non-invasive sampler, an invasive sampler, a flow path (flow path), or a wearable scanning interface. Each type of scanning interface may be replaceable. The scanning module (scanning module, scanner) 40 scans the target 5 with the irradiation beam 54 and may be configured to acquire the CARS signal 55 at each pixel (pixel, point) 5a in order to perform two-dimensional CARS microscopy imaging (2D CARS microscopy imaging). The scanner 40 may be configured to scan the target 5 with the irradiation beam 54 and acquire the CARS signal 55 at each voxel 5a in order to perform three-dimensional CARS microscopy imaging (3D CARS microscopy imaging).

[0014] One embodiment of the laser module 30 is a fiber laser module (full fiber laser module). The fiber laser module 30 includes a 1μm laser generation stage (first laser light source) 36 configured to generate a narrow-band (narrow band, narrow bandwidth) first source laser light 33, a Stokes-pump pulse generation stage 37 for generating a Stokes light pulse 51 and a pump light pulse 52 from the first source laser light 33, a probe pulse generation stage 38 for generating a probe light pulse 53 from a second source laser light 34, and an oscillator (oscillator, OSC) 35 configured to output a mode-locked base laser 35a, and the base laser 35a is split for the generation of the first source laser light 33 and the second source laser light 34.

[0015] Figure 2 shows one of the wavelength plans of the CARS optical system 1. The Stokes light pulse (first light pulse) 51 has a wavelength of 1085 - 1230 nm (400 cm -1 ~1500 cm -1) has a first range R1, the pump light pulse (second light pulse) 52 has a second range R2 with a wavelength of 1040 nm, the probe light pulse (third light pulse) 53 has a third range R3 with a wavelength of 780 nm, and the TD-CARS light pulse (CARS light, time-dependent CARS, time-delayed CARS) 55 has a range R5 with a wavelength of 680 - 760 nm. The Stokes light pulse 51 and the pump light pulse 52 may include pulse widths on the order of 1 - several hundred femtoseconds at several tens to several hundred mW. The probe light pulse 53 may include pulse widths on the order of 1 - several picoseconds at several tens to several hundred mW. Time-resolved coherent anti-Stokes Raman scattering or time-delayed coherent anti-Stokes Raman scattering (TD-CARS) microscopy is also known as a technique for suppressing non-resonant background by utilizing the difference (variation) in the time responses of virtual electronic transitions and Raman transitions. There is a need for a system that can easily apply such a measurement method to various applications.

[0016] On the optical plate 20, a plurality of optical elements (free-space optical elements) 29 such as mirrors, prisms, dichroic mirrors, etc. for constructing several optical paths in the free space of the optical plate 20 are mounted. One of these optical paths is the optical path 23 for supplying the probe light pulse 53, which includes a delay module (delay, modulation module) 23a for controlling the time delay between the pump light 52 and the probe light 53. Other free-space optical elements may be provided to combine the beams of the Stokes light 51, the pump light 52, and the probe light 53 and separate the CARS beam 55.

[0017] FIG. 3 shows one example of an optical module 90 including a fiber laser module (fiber laser assembly) 93 and an optical plate 92. This fiber laser module 93 provides two basic light sources 95 and 96 for supplying a Stokes light pulse 51, a pump light pulse 52, and a probe light pulse 53. One includes a wavelength centered at 1032 nm, and the other includes a wavelength centered at 1560 nm. These two outputs 95 and 96 serve as inputs to the optical plate 92 and match the input requirements of the optical plate 92. The output 95 at 1032 nm supplies an optical pulse with a pulse time FWHM of about 66 ps at 12 MHz. The FWHM bandwidth (bandwidth) of the spectrum is about 14 nm, and the average output power directly output from the FC / APC connector connected to the collimator is in the range of 450 mW to 520 mW. This output is sent to a free space diffraction grating compressor 71 for pulse compression. After the compressor 71, the beam is split into two arms 21 and 22 for generating CARS Stokes and CARS pump, respectively. The power in the output 96 of the 1032 nm fiber laser is for compensating for the loss due to propagation in free space, and the power level needs to meet the input requirements at a further stage on the optical plate.

[0018] The output 96 at 1560 nm is provided at 12 MHz, which is exactly the same pulse repetition rate as the output 95 at 1032 nm. The FWHM pulse width is approximately 35 ps, and the FWHM spectral bandwidth is approximately 7 nm. The average output ranges from 130 mW to 180 mW. This output 96 is sent to the free-space diffraction grating compressor 72 for pulse compression. After the compressor 72, the beam 96 is used in SHG23s via a non-linear crystal to provide the CARS probe beam 53 at a wavelength of 780 nm. SHG23s may include PPLN (periodically poled lithium niobate) 23s having a probe pulse shape control function. The probe pulse supplied as the probe light 53 has two opposing requirements. That is, a narrow-band probe pulse is necessary for high spectral resolution in the system, and a probe pulse having a sharp edge is necessary for the time resolution of the system when using a time delay to suppress the resonant CARS signal 55. By using PPLN23s, higher conversion efficiency and a wider bandwidth can be obtained compared to simply bonding crystals together. At the same time, by using the periodic structure of PPLN, a positive interference result is obtained that generates a much steeper probe edge than an equivalent Gaussian pulse with the same bandwidth. Details of this module 93 are disclosed in the applicant's PCT / JP2021 / 033384, and the entire content of this PCT application is incorporated herein by reference.

[0019] The fiber laser module 93 includes: (1) an oscillator (oscillator, OSC) 35 configured to output a mode-locked base laser 35a that is split for the generation of a first light source (light source) 95 and a second light source (light source) 96; (2) a generator (generating device, generation stage, generation stage) 320 configured to generate a first source laser beam 33 by stretching the wavelength range of the base laser 35a; (3) a first amplifier 330 including a first preamplifier 340 and a first chirped pulse amplification (CPA) unit 350 for the first light source 95; (4) a second amplifier 360 including a second preamplifier 370 and a second chirped pulse amplification (CPA) unit 380 for the second light source 96; and (5) an LD power distributor 390 configured to distribute the laser power from a first laser diode (LD0) 395 as the oscillation source of the oscillator 35, as the pump power (※1) of the generator 320, as the pump power (※2) of the first preamplifier 340, and as the pump power (※3) of the second preamplifier 370.

[0020] The LD power distributor includes a first EVOA (electrically controlled variable optical attenuator) 391 for stabilizing the laser power supplied to the oscillator 35 and a second EVOA 392 for stabilizing the laser power supplied to the generator 320. In this fiber laser module 93, preamplifiers 340 and 370 are respectively provided in each of the amplifiers 330 and 360 for the source lights 95 and 96, and the LD power distributor 390 distributes the laser power from the common laser diode LD0 395 to each of the preamplifiers 340 and 370 in addition to the oscillator 35 and the generator 320. With this configuration, not only can the number of LDs be reduced, but the operable laser diode (common LD) 395 can be operated at 90% to 100% of the designed output level of the LD.

[0021] The entire laser module 93 includes four sub-assemblies (stages), which are the oscillator stage (OSC) 35, the 1μm generation stage (generator) 320, the 1032nm CPA stage 350, and the 1560nm CPA stage 360. Each stage will be described below.

[0022] The fiber laser module 93 includes an FL module that functions as a pump LD and power distribution 390. There are three LDs 395 - 397, and LD0 (395), LD1 (396), and LD2 (397) can obtain maximum outputs of 600mW, 850mW, and 850mW at 980nm respectively. LD0 (395) supplies pump power to the oscillator 35, the amplifier of the 1μm generator 320, and the pre-amplifier stages 340 and 370 before the CPA stages 350 and 380. First, the output (laser power) from LD0 (395) is directly connected (spliced) to a 20 / 80 coupler (FL14). Then, the 20% arm is connected to EVOA1 (391) and is electronically controlled. The software loop can accurately control the output power from the oscillator 35 in conjunction with this component. The 80% arm from FL14 is then split at a 50 / 50 ratio by a coupler (FL15). One arm from FL15 is sent to EVOA2 (392) and is used for amplifier output control to generate a stable 1μm at the generator 320. The other 50% arm from FL15 is split again at 50 / 50, and each arm is connected (spliced) to the pre-amplifier pump inputs of the CPA stages 330 and 360.

[0023] The fiber laser OSC35 is constructed with an Er-doped active fiber, provides an output wavelength in the C-band range (1530 nm to 1565 nm), and the laser diode LD0(395) of the distributor 390 operates at 976 nm. The fiber used in this oscillator 35 includes PM-SMF having anomalous dispersion and normal dispersion at the C-band wavelength. This is to manage the resonator dispersion so as to minimize unnecessary non-linear effects in the resonator. The fiber length is accurately adjusted according to the repetition frequency (12 MHz) of the output specification. The laser output 35a is mode-locked by SAM, the FWHM spectral bandwidth is 6 to 8 nm, and the average output is 1 to 1.5 mW, depending on the characteristics of SAM and the Er fiber. 10% of the output 35a is split by the fiber coupler and sent to the photodiode PD0 for the oscillator power monitor. This OSC power monitor is fed back to the electronic substrate that controls the applied voltage to EVOA1(391) to control the output power of OSC35 constantly. The remaining 90% is split 50 / 50 and sent to the 1-μm generator stage 320 and the 1560-nm CPA stage (second amplifier) 360, respectively.

[0024] The function of stage 320 is to generate, from the 1560 nm base laser 35a, the first source laser beam 33 with a narrow band of 1 μm wavelength as the first laser light source. The purpose is to obtain exactly the same repetition rate in both the 1 μm arm and the 1.5 μm arm. In this stage 360, power amplification is performed by an EDFA (Er02) incorporated in this stage 360, and the average output from the amplifier is about 18 mW. 1% of the power is coupled and sent to the PD1 for power monitoring immediately after the amplifier output. The signal from PD1 serves as feedback to the board that controls EVOA2 (392), so that the output power from this EDFA can be kept constant. The output pulse of the EDFA is directly compressed by a part of the fiber with negative dispersion. At the splice spot to HNLF325, the duration of the FWHM pulse is compressed to about 60 fs, which corresponds to a peak power of about 25 kW. When the optical pulse with this peak power is sent to the short HNLF, the wavelength is extended from 1560 nm and finally covers the range from 1 μm to 1.7 μm. This is the so-called SC (supercontinuum) generation process. That is, with this peak power, the pulse propagates through HNLF325 with strong non-linear effects, and the spectrum spreads to both the short wavelength side and the long wavelength side from 1560 nm, and finally a supercontinuum spectrum ranging from 1 μm to 1.7 - 1.8 μm can be formed. This 1 μm part is the target taken for the next amplification stage 330.

[0025] The 1032 nm CPA stage 330 includes processes of preamplification (pre - amplification), pulse stretching, and final amplification. The 50% pump branches that are not connected to any EVOA in the distributor 390 are here branched again into 50 / 50 by another fiber coupler (FL16). One arm is connected to the pre - amplifier 340 of this 1032 nm CPA stage 330, and the other arm is connected to the pre - amplifier 370 of the 1560 nm CPA stage 360 which will be described later. The generated 1 μm laser is sent to port #1 of the 1 μm CIR333. From port #1 to port #2 of this CIR333, only the 1 μm part is selected from the SC spectrum due to the characteristics of the components. At port #2, a Yb fiber (Yb01), CFBG335, and 1030 / 980 WDM / Tap hybrid component 336 are connected (joined, spliced) in sequence. The selected 1 μm seed first meets the Yb fiber and is amplified. Then, the CFBG335 reflects 40% of the power within the wavelength range of 1018 nm to 1053 nm. Wavelengths outside this range directly pass through the CFBG335 and are output from the WDM336. The output of the WDM336 is used as a monitor for the spectrum (to tap2) and power (to PD2) after this pre - amplifier 340. The reflected part passes through the Yb fiber (Yb01) again and is amplified a second time before returning to port #2. The pre - amplified 1 μm pulse entering port #2 is output from port #3 of the CIR333. At this point, the 1 μm pulse is stretched and is ready to be amplified by the final amplifier 350.

[0026] LD1(396) is an individual laser diode that supplies up to 850 mW of pump power to the 1032 nm final amplifier 350. First, the seed (input) from CIR port #3 is spliced to the isolator / WDM hybrid component 337. This component protects the previous stage from damage by reflected light and residual pump. Then, the Yb fiber (Yb02) and WDM338 are connected (spliced) in sequence, completing the configuration of the 1032 nm CPA stage 330. As the final output (the first light source), it supplies an optical pulse of 12 MHz with an FWHM pulse duration of approximately 66 ps. The spectral FWHM bandwidth is approximately 14 nm, and the average output directly output from the FC / APC connector connected to the collimator ranges from 450 mW to 520 mW. A 1% Tap is coupled to PD3 and tap3 respectively to monitor power and spectrum. PD3 also provides feedback to form a control loop for the constant output from the 1032 nm CPA stage 330.

[0027] The 1560nm CPA stage 360 includes the processes of preamplification, pulse stretching, and final amplification. The concept is the same as that of the 1032nm CPA stage 330, but since it operates in a different wavelength range, the components are slightly different. The pump light source of the preamplifier 370 is the remaining half of the split pump from the distributor 390. The seed (input) of the 1560nm beam (the second source pulse) 34 is the remaining half further split from 80% of the OSC output 35a. The same concept as the 1032nm CPA stage 330 is also applied to the 1560nm CPA stage 360. However, the 1560nm CPA stage 360 uses the 1560nm CIR 361 port #1 to input the seed into the preamplification and pulse stretching processes by using the CFBG 363 and WDM 364 components operating at 1560nm. LD2 (397) is another independent laser diode that supplies up to 850mW of pump power to the 1560nm final amplifier 380. From port #3 of the CIR 361, the preamplified seed is sent to the Er fiber (Er04) and the tap / isolator / WDM hybrid component 365, completing the configuration of the 1560nm CPA stage 360.

[0028] The final output provides optical pulses at 12MHz as the 1560nm output 96. The FWHM pulse duration is approximately 35ps, and the FWHM spectral bandwidth is approximately 7nm. The average output ranges from 130mW to 180mW. A 1% Tap is coupled to PD4 and tap4 respectively to monitor the power and spectrum. PD4 also provides feedback to form a control loop for the constant output from the 1560nm CPA stage 360.

[0029] FIG. 4 shows one embodiment of the laser module 30 of the present invention. This laser module 30 is a full-fiber laser module (a laser module composed entirely of fibers), and includes an oscillator 35 for supplying a mode-locked base laser 35a that is branched into a first source laser beam (source laser beam) 33 and a second source laser beam (source laser beam) 34, a 1-μm laser generation stage (first laser light source) 36 for generating a narrow-band (narrow bandwidth, narrow wavelength range, narrow-band) first source laser beam 33 from the base laser 35a, and a plurality of paths (routes, optical fiber routes, optical fiber sections) 310.The plurality of paths 310 includes: (i) a first path 301 for branching a first source optical pulse 33 to generate a broadband (wide-bandwidth, wide-wavelength range, broad-band) first optical pulse (Stokes optical pulse) 51 and a narrow-band second optical pulse (pump optical pulse) 52; (ii) a first train 81 including a first amplifier 81b, a first hollow-core photonic crystal fiber (HCPCF) 81a, and a highly nonlinear photonic crystal fiber (HNLPCF) 85 that are directly connected (spliced without free space) to amplify and broaden (increase the wavelength range) the broadband first optical pulse (Stokes optical pulse) 51 for a second path 302; (iii) a third path 303 for amplifying a narrow-band second optical pulse (pump optical pulse) 52 by a second train 82 including a second amplifier 82b and a second HCPCF 82a that are directly connected (spliced); (iv) a fourth path 304 for multiplexing the Stokes optical pulse 51 and the pump optical pulse 52 and outputting the temporally overlapping Stokes optical pulse 51 and pump optical pulse 52 as one irradiation beam 31 for irradiating a target 5; and (v) a fifth path 305 for generating a narrow-band third optical pulse (probe optical pulse) 53 by a third train 83 including a third amplifier 83b, a third HCPCF 83a, and SHG23s that are directly connected (spliced) and supplying the probe optical pulse 53. The first path 301, the second path 302, the third path 303, and the fourth path 304 constitute a Stokes-pump pulse generation stage 37 for generating the Stokes optical pulse 51 and the pump optical pulse 52 from the first source laser light 33. The fifth path 305 constitutes a probe pulse generation stage 38 for generating the probe optical pulse 53 from the second source laser light 34.

[0030] The oscillator 35 may have the same or a common configuration as that described with reference to FIG. 3. The 1-μm laser generation stage 36 may include the generator 320, or the generator 320 and the 1-μm laser pre-amplification (pre-amplifier) 340 as described above. The first path 301 may include a 50 / 50 coupler 309 for separating (splitting) the first source laser light 33 into a second path 302 and a third path 303, and a narrow-band filter 301a for adjusting the input of the narrow-band pump light pulse 52. The wavelength range of the first source laser light 33 is centered around 1030 nm.

[0031] The first train (first arm, first line, first series of optical fibers) 81 of the second path 302 may include a fiber 81d for stretching, a pre-amplifier 81c, an amplifier 81b, an HCPCF 81a, and an HNLPCF 85 connected without free space. The pre-amplifier 81c and the amplifier 81b may each have the same or a common configuration as the pre-amplifier 340 and the amplifier 350 described above. Also, for stretching, instead of the stretching fiber 82d, a configuration using the CFBG described in the 1032-nm CPA stage 330 can be applied.

[0032] HCPCF81a replaces the free - space compressor (free - space squeezer) applied in the above - mentioned optical module 90, and sends out a compressed high - peak - output pulse from the end of HCPCF81a. HCPCF81a can be directly spliced (directly connected, directly joined, butted) to HNLPCF85 and can be used as a super - continuum PCF (SCPCF) for generating a broadband Stokes optical pulse 51. Some literature suggests that HCPCF81a can be used as an excellent fiber beam transmitter or a very efficient non - linear squeezer (for example, "Scalable hollow fiber pulse compressor for NIR and UV lasers." by Martin Maurel, Matthieu Chafer, Benoit Debord, Foued Amrani, Benoit Beaudou et al., SPIE Photonic West 2019, February 2019, San Francisco, USA. Paper 10899.hal - 02329692).

[0033] By using the first train 81 including the directly connected first amplifier 81b, the first HCPCF 81a, and the HNLPCF 85, Stokes light can be generated entirely by fiber from the first source laser light 33 having a wavelength range centered at 1030 nm, and an alignment-free (capable of free alignment (arrangement)) Stokes light pulse 51 can be supplied before the final collimation. In the second path 302, by splicing (joining, connecting) two different types of photonic crystal fibers (PCFs), namely, the HCPCF 81a and the HNLPCF 85, directly (without free space) to the amplifier 81b, the compression function provided by the HCPCF 81a and the supercontinuum (SC) generation function provided by the HNLPCF 85 can be integrated together with the amplifier 81b into a single series (continuous) of fibers (the first train, the first series) 81. Therefore, in the optical module 10 and the system 1 including the laser module 30, one or more free-space diffraction grating compressors and other free-space optical elements can be omitted, and the size can be made compact.

[0034] Also, by using the all-fiber (full-fiber) Stokes generation system (generation system, the second path) 302, the loss in propagating through free space can be reduced, so that the power level of the Stokes light pulse 51 can be easily improved or the energy consumption in the laser module 30 can be reduced. When the HCPCF 81a is used as a compressor, in the case of generating (producing) a broadband Stokes light pulse, it is considered that a HCPCF 81a with a length of 5 to 12 m, more preferably 7 to 9 m, is required.

[0035] The second train (second arm, second line, second series of optical fibers) 82 in the third path (route) 303 may include a stretching fiber (elongated fiber) 82d connected without free space, a preamplifier (preamplifier prefire) 82c, an amplifier 82b, and an HCPCF 82a. The preamplifier 82c and the amplifier 82b may each have the same or common configuration as the preamplifier 340 and the amplifier 350 described above. Also, for stretching, instead of the stretching fiber 82d, a configuration using a CFBG described in the 1032 nm CPA stage 330 may be applied.

[0036] By using the second train 82 in which the second amplifier 82b and the second HCPCF 82a are directly connected, it is possible to generate all pump light by fibers from the first source laser light 33 having a wavelength range centered on 1030 nm, and an alignment-free pump light pulse 52 can be supplied before the final collimation. In the third path 303, by directly joining (connecting) the HCPCF 82a to the amplifier 82b without free space, an integrated single and series (continuous) fiber series (second train) 82 is provided. Therefore, in the optical module 10 and the system 1 including the laser module 30, one or more free space diffraction grating compressors and other free space optical elements can be omitted, and the size can be made compact.

[0037] Also, by using a pump generation system (generation system, third path) 303 consisting entirely of fibers (full fiber), the loss in propagating through free space can be reduced, so the power level of the pump light pulse 52 can be easily increased or the energy consumption in the laser module 30 can be reduced. When the HCPCF 82a is used as a compressor, in applications for generating narrow-band pump light pulses, it is considered that an HCPCF 82a with a length of 10 to 20 m, more preferably 12 to 15 m, is required.

[0038] The fourth path 304 may include a chirp rate adjuster 308 for changing at least one of the chirp rate (chirp ratio) of the Stokes optical pulse (first optical pulse) 51 supplied by the first path 302 and the chirp rate (chirp ratio) of the pump optical pulse (second optical pulse) 52 supplied by the third path 303 so that they are substantially equal. This fourth path 304 includes a chirp rate adjuster (conditioner) 308 for controlling the chirp rate of the Stokes optical pulse 51. The chirp rate adjuster 308 may include a CIR 308a and a CFBG 308b connected to the CIR 308a. The output from the second path 302 is input to the CFBG 308a via the CIR 308a, the reflected light from the CFBG 308a is input to the CIR 308a, the corrected Stokes optical pulse 51 is output from the CIR 308a, and is overlapped with the pump pulse 52 by the WDM 307. The chirp rates (multiple chirp rates, CR) of the Stokes optical pulse 51 and the pump optical pulse 52 may be processed in the same manner as the spectral condensing technique. In this system 1, by using the fourth path 304 integrated (integrated, integrated) with the second path 302 and the third path 303, the Stokes optical pulse 51 and the pump optical pulse 52 can be emitted as an irradiation beam 31 to which they are combined without using a free space optical element for collecting the Stokes optical pulse 51 and the pump optical pulse 52. Therefore, a more compact system 1 can be provided, and the power loss in propagating through the free space can be reduced.

[0039] The third train (third arm, third line, third series of optical fibers) 82 in the fifth path 305 may include a stretching fiber (elongated fiber) 83d connected without free space, a preamplifier (preamplifier, pre - amplifier) 83c, an amplifier (amplifier, amplifier) 83b, an HCPCF 83a, and an SHG 23s. The preamplifier 83c and the amplifier 83b may each have the same or common configuration as the preamplifier 370 and the amplifier 380 of the 1560 nm CPA stage 360 described above. Also, for stretching, instead of the stretching fiber 83d, a configuration using the CFBG described in the 1560 nm CPA stage 360 may be applied.

[0040] By using the third train 83 including the directly connected (joined) second amplifier 83b, the second HCPCF 83a, and the SHG 23s, all from the second source laser light 34 having a wavelength range centered on 1560 nm can generate (produce) probe light by the fiber, and before the final collimation, an alignment - free probe light pulse 52 having a third range R3 of wavelengths shorter than the second range R2 of wavelengths can be provided, unlike the second range R2 of wavelengths. Therefore, in the optical module 10 and the system 1 including the laser module 30, one or more free - space diffraction grating compressors and other free - space optical elements for generating the 780 nm probe light pulse 53 from the 1560 nm base light pulse can be omitted, and the system 1 and the optical module 10 can be made compact. Also, the loss in propagating through free space can be reduced. When using the HCPCF 83a as a compressor, an HCPCF 83a with a length of 5 - 12 m, more preferably 7 - 9 m, is considered necessary. The SHG 23s may include PPLN as described above.

[0041] In this system 1, the laser module 30 emits a composite beam 31 including a Stokes optical pulse 51 compressed in a wavelength range R1, a pump optical pulse 52 compressed in a wavelength range R2, and a probe optical pulse 53 compressed in a wavelength range R3. Therefore, the optical module 10 including the laser module 30 only needs to have an optical path 23 for controlling the delay and modulation of the probe pulse 53 by a lens or a lens system 45 using a free-space optical element 29, and an optical path for combining the beam 31 and the probe pulse 53 for irradiating the target 5. For this reason, the space for arranging the free-space optical element 29 on the optical plate 20 can be minimized, and the loss in propagating through the free space can be reduced. Thereby, it becomes possible to provide a compact CARS signal generation and detection system 1. Also, by minimizing the area and the number of elements to be mounted on the free space (free air, free air space), the influence of vibration, temperature, and other environmental changes can be suppressed, and it becomes possible to provide a highly reliable system 1. If the delay module 23a and the modulation module 23d are not necessary, it is possible to provide a laser module 30 that supplies laser light including not only the Stokes optical pulse 51 and the pump optical pulse 52 but also the probe 53 (overlapped) including a path similar to the fourth path 304, and a system 1 that does not require a free-space optical element may be provided.

[0042] FIG. 5 shows another embodiment of the system 1. This system 1 is based on a method of acquiring CARS by two beams including a Stokes optical pulse 51 and a pump optical pulse 52, and the pump optical pulse 52 also functions as a probe optical pulse. An example of a wavelength plan for two-beam CARS is shown in FIG. 6. The Stokes optical pulse 51 has a wavelength of 1085 to 1230 nm (400 cm -1 ~1500 cm -1) has a first range R1, and the pump light pulse 52 has a second range R2 with a wavelength of 1040 nm, which is shorter than the first range R1. A CARS signal 55 with a wavelength range of approximately 900 to 1000 nm is generated. In this system 1, the optical module 10 including the laser module 30 only needs to have an optical path for separating the CARS signal 55 from the return light through the lens 45 as a path using the free-space optical element 29. Note that when the system 1 is a system for detecting a forward CARS signal rather than a system for detecting an epi (backward) CARS signal, a configuration that does not use a free-space optical element may be adopted.

[0043] The laser module 30 of the present system 1 is a laser module (laser light supply unit by all-fiber solution, full-fiber laser module) by an all-fiber solution (entirely composed of fibers), and includes a laser light source 100 configured to generate narrow-band source laser light 33, and a plurality of paths 310 composed of optical fibers without using free space. The laser module 30 including the plurality of paths 310 may be composed of a photonic integrated circuit without using free space. The plurality of paths 310 include: (i) a first path 301 for splitting the source laser light 33 to generate broadband first laser light (Stokes light) 51 and narrow-band second laser light (pump light) 52; (ii) a second path 302 for broadening and amplifying the wavelength range of the broadband first laser light 51; (iii) a third path 303 for amplifying the narrow-band second laser light 52; and (iv) a fourth path 304 for multiplexing (overlapping) the broadband first laser light 51 and the narrow-band second laser light 52, and outputting them as an irradiation beam by overlapping at least partially spatially (temporally in terms of the path) the broadband first laser light 51 and the narrow-band second laser light 52 to irradiate the target 5. The second path 302 may include the first train 81 described above, and the third path 303 may include the second train 82 described above. The third path 303 may include a delay stage (delay line) 82e for compensating the time required to pass through the PCF 85 in the second path 302, and the pump light pulse 52 can be overlapped with the Stokes light pulse 51 for scanning. The delay stage 82e may include, for example, an optical fiber of a certain length.

[0044] The laser light source 100 may include an oscillator 35 and a 1-μm laser generation stage 36. A pulse picker (PP) 101 and a preamplifier 102 can be provided between the first path 301 and the laser light source 100. The PP 101 can be provided at any position before or after the preamplifier 102. The PP 101 may be provided to reduce the average power.

[0045] As described above, the present invention generally relates to a spectroscopic or microscopic system 1 using laser light (laser beam) pulses generated by a laser module 30. In the above description, the laser module 30 has been described as a full-fiber module, but it can also be realized using a photonic integrated circuit (optical integrated circuit) that does not use free space for connecting elements.

[0046] We initially focused only on directly generating a fiber-based SC without going to a free-space compressor and then returning to the PCF. In this process, currently, about 60% on the optical plate is occupied for using many free-space optical elements such as mirrors, prisms, and filters. Such a configuration is very complex and costly. In the system 1 of this example, a full-fiber type or photonic integrated circuit type laser module 30 can be provided, which can solve this problem.

[0047] As one of the embodiments of the present invention, the laser module 30 described above is a laser beam supply device for emitting an irradiation beam for generating the CARS signal 55 on the target 5. The system 1 of the present invention may further include a detector 65 configured to detect a signal beam generated by the target as a result of irradiating the target with the irradiation beam. The signal beam 55 may include the results (resonance components, resonant components) of a non-linear optical process generated by the laser pulses 51 and 52 (and 53). One of the non-linear optical processes is the CARS process described above. The present system 1 is also applicable to other non-linear optical processes, for example, second harmonic generation (SHG); sum frequency generation (SFG); difference frequency generation (DM); third harmonic generation (THG); third sum frequency generation (TSFG); coherent anti-Stokes Raman spectroscopy (CARS); stimulated Raman scattering (SRS) (stimulated Raman gain (SRG), stimulated Raman loss (SRL)); optical Kerr effect (OKE); Raman-induced Kerr effect (RIKE); stimulated Rayleigh scattering; stimulated Brillouin scattering (SBS); stimulated Kerr scattering; stimulated Rayleigh-Bragg scattering; stimulated Mie scattering; self-phase modulation (SPM); cross-phase modulation (XPM); two-photon absorption; and two-photon excited fluorescence (TPEF) and other processes.

[0048] FIG. 7 shows different embodiments of the system 1 with different types of laser modules 30. A plurality of paths 310 of this laser module 30, in addition to the first path 301, the second path 302, the third path 303, the fourth path 304, and the fifth path 305 described above, multiplex the Stokes optical pulse (broadband second optical pulse) 51, the pump optical pulse (narrowband second optical pulse) 52, and the probe optical pulse (narrowband third optical pulse) 53, and output, as an irradiation beam 54, the superposition of the Stokes optical pulse 51, the pump optical pulse 52, and the probe optical pulse 53 with a time delay, and irradiate the target 5. The third train 83 of the fifth path 305 may further include a programmable optical path delay module (PDL, programmable optical path delay module: POPDM) 86 for controlling the delay and modulation (using the delay) of the probe optical pulse 52 with respect to the Stokes optical pulse 51 and the pump optical pulse 52. The sixth path 306 may include a chirp plate conditioner 308 having the same or corresponding configuration as the chirp plate conditioner (chirp plate control device) 308 of the fourth path 304 in order to control the chirp plate of the probe optical pulse 53. In this laser module 30, the Stokes optical pulse 51 and the pump optical pulse 52 are multiplexed or combined (wavelength-division multiplexed) by the first WDM 307a of the fourth path 304, and after the probe optical pulse 53 with a time delay is multiplexed or combined (wavelength-division multiplexed) with the Stokes optical pulse 51 and the pump optical pulse 52 by the second WDM 307b of the sixth path 306, it is supplied as the irradiation beam 54. Therefore, in the system 1 including this laser module 30, substantially, there is no need for a space for arranging the free-space optical element 29 including the optical path 23 for controlling the delay and modulation of the probe pulse 53, and there is also no need for the free-space optical element arranged therein. Therefore, it is possible to suppress the influence of environmental variations such as vibration and temperature, and provide a highly reliable and compact system 1.

[0049] The PDL86, which can precisely control the optical path delay in a short time (once without substantial delay), may include an on-chip multi-channel selector that selects a path suitable for a desired delay from among multiple paths having multiple delays due to length, structure, and / or medium (optical material), and gradually increases or decreases the delay through electrical or optoelectronic programming or commands. The PDL86 may include an optical device (optoelectronic device) or fiber that can change the optical path delay using an integrated heater or pressure (applied force). The laser module 30 may include a pulse picker (PP) 301b for controlling the pulse width of the pump optical pulse 52 generated by the third path 303. By relatively broadening the pulse width of the pump optical pulse 52 within the range where it acts as the pump light, the input energy for generating the base CARS signal probed by the probe optical pulse 53 can be increased, and the level of the CARS signal (TD-CARS) 55 generated by the probe optical pulse 53 can be increased.

[0050] The foregoing description of specific embodiments is for the purpose of fully disclosing the general nature of the embodiments herein. Others can, by applying current knowledge, easily modify and / or adapt such specific embodiments for various uses without departing from the general concept. Therefore, such adaptations and modifications should be understood to be within the meaning and scope of the disclosed embodiments and equivalents, and it is intended that they be understood. It should be understood that the language or terms employed herein are for the purpose of description and not of limitation. Therefore, although the embodiments herein are described from the perspective of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be implemented with modifications within the spirit and scope of the appended claims.

Claims

1. A system having a laser module, The laser module includes a first laser light source configured to generate a narrow-band first source laser light, And a plurality of paths configured without using free space by an optical fiber and / or a photonic integrated circuit, the plurality of paths including: A first path for splitting the first source laser light to generate a broadband first optical pulse and a narrow-band second optical pulse, A second path for amplifying and broadening the wavelength range by a first train including a connected first amplifier, a first hollow-core photonic crystal fiber (HCPCF), and a highly nonlinear photonic crystal fiber (HNLPCF) for supplying the broadband first optical pulse, A third path for amplifying by a second train including a connected second amplifier and a second HCPCF for supplying the narrow-band second optical pulse. A system.

2. In the system according to claim 1, The plurality of paths further includes a fourth path for multiplexing the broadband first optical pulse and the narrow-band second optical pulse and outputting the first optical pulse and the second optical pulse that temporally overlap as one irradiation beam to irradiate a target. A system.

3. In the system according to claim 2, The fourth path includes a chirp plate adjuster for changing at least one of the chirp plate of the first optical pulse supplied from the second path and the chirp plate of the second optical pulse supplied from the third path to make them substantially equal. A system.

4. In the system according to any one of claims 1 to 3, A system in which the first optical pulse includes a first wavelength range and the second optical pulse includes a second wavelength range shorter than the first wavelength range. **Claim 5** In the system according to claim 4, The plurality of paths includes a fifth path for generating a narrowband third optical pulse including a third wavelength range shorter than the second wavelength range from the second source laser light, and for supplying the third optical pulse, a fifth path further including a third train including a connected third amplifier, a third HCPCF, and second harmonic generation (SHG). **Claim 6** In the system according to claim 5, The plurality of paths further includes a sixth path for multiplexing the broadband first optical pulse, the narrowband second optical pulse, and the narrowband third optical pulse, and outputting the first optical pulse, the second optical pulse, and the third optical pulse so as to overlap with a time delay as one irradiation beam to irradiate a target. **Claim 7** In the system according to claim 6, The system further includes an optical module for supplying the first optical pulse, the second optical pulse, and the third optical pulse to the target as the irradiation beam. **Claim 8** In the system according to claim 5, The laser module further includes an oscillator configured to output a mode-locked base laser that is split for generation of the first source laser light and the second source laser light. **Claim 9** In the system according to any one of claims 1 to 3, The wavelength range of the first source laser light is centered at 1030 nm. **Claim 10** In the system according to claim 5, A system in which the wavelength range of the first source laser light is centered around 1030 nm and the wavelength range of the second source laser light is centered around 1560 nm.

11. In the system according to claim 2 or 3, A system further comprising a detector configured to detect a signal beam generated by the target as a result of irradiation of the target with the irradiation beam.

12. In the system according to claim 11, A system further comprising a scanner configured to scan the target with the irradiation beam to acquire signals at each pixel.

13. In the system according to claim 11, A system further comprising a scanner configured to scan the target with the irradiation beam to acquire signals at each voxel.

14. In the system according to claim 1, A system further comprising an optical module configured to supply the first optical pulse as a Stokes optical pulse and the second optical pulse as a pump optical pulse to generate a CARS signal.

15. In the system according to claim 7, The optical module further includes an optical path configured to supply the first optical pulse as a Stokes optical pulse, the second optical pulse as a pump optical pulse, and the third optical pulse as a probe optical pulse to generate a CARS signal.

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