CN109038204B

CN109038204B - Stimulated Raman scattering imaging light source based on photonic crystal fiber

Info

Publication number: CN109038204B
Application number: CN201810730228.4A
Authority: CN
Inventors: 杨康文; 吴昱兴; 沈悦; 郝强; 曾和平
Original assignee: University of Shanghai for Science and Technology
Current assignee: University of Shanghai for Science and Technology
Priority date: 2018-07-05
Filing date: 2018-07-05
Publication date: 2020-08-04
Anticipated expiration: 2038-07-05
Also published as: CN109038204A

Abstract

The invention relates to a stimulated Raman scattering imaging light source based on a photonic crystal fiber, wherein seed light output by a laser oscillator is amplified by a pre-amplification module and then output, and directly enters a parametric oscillation structure; the amplified pump light enters the parametric oscillation structure from the optical coupler, the photonic crystal fiber in the parametric conversion module generates Stokes light through the nonlinear effect of the photonic crystal fiber, the output of the parametric conversion module passes through the optical beam splitter to divide the light beam into two paths, one path is directly output, the other path is fed back to the repetition frequency tuning module and the time delay module to change the repetition frequency of the Stokes light participating in feedback oscillation, the Stokes light which is synchronous with the pump light but has different repetition frequencies is provided and is coupled into the parametric oscillation structure through the optical coupler again, and the requirements of the stimulated Raman scattering imaging light source are met. The synchronous but different repetition frequencies of the Stokes light and the pump light in one set of device are realized.

Description

Stimulated Raman scattering imaging light source based on photonic crystal fiber

Technical Field

The invention relates to an imaging light source, in particular to a stimulated Raman scattering imaging light source based on a photonic crystal fiber.

Background

Coherent Raman Scattering (CRS) imaging technology is widely used in biology and medicine because it has the characteristics of no-mark, non-invasive and chemical-specific, and utilizes chemical bond vibration as imaging contrast. CRS imaging is achieved in two ways, Coherent Anti-Stokes Raman Scattering (CARS) and Stimulated Raman Scattering (SRS). In the CARS imaging technology, due to the existence of non-resonant background noise, the peak value of the generated CARS scanning signal shifts in a frequency domain and cannot completely correspond to a Raman signal, so that the accuracy of substance component analysis is influenced, and the imaging sensitivity is reduced. The SRS technology has no non-resonance background noise, and the spectrum information of the SRS technology is completely consistent with the spontaneous Raman spectrum, so that the obtained imaging information is more accurate, the SRS signal and the molecular concentration are in a direct proportional relation, and the molecular concentration can be quantitatively analyzed according to the SRS signal.

The SRS technology requires measurement of relatively weak Stimulated Raman Gain (SRG) and Stimulated Raman loss (SR L) in strong background light, and thus requires radio frequency modulation of one of the pump light and the stokes light, SR L signal and SRG have antisymmetry, and when modulated light appears, the detected light is enhanced in the SRG and attenuated in SR L, a pulse envelope having the same wavelength as the pump light and the stokes light is output, and the SRG is extracted by a demodulation technology.

At present, two common methods for realizing the stimulated raman scattering imaging light source are available: one is that the stimulated Raman scattering imaging light source needs two lasers with different central wavelengths, the two signals are modulated to be synchronous through a complex electronic feedback circuit, and then one beam of light is added with repetition frequency modulation; the other method is to combine a solid laser and a parametric oscillation technology to modulate one of the pump light and the Stokes light to realize synchronization of the two beams of light but different repetition frequencies, and then to perform light path control on the two beams of light to realize spatial overlapping. The first method has a complex system structure, two lasers are expensive to manufacture, and the cost is increased to a great extent; the second method uses a solid laser, which is not only greatly affected by the environment and unstable in light beam, but also requires a high threshold for modulating the light beam and requires regular maintenance by a professional. Therefore, it is necessary to propose a new solution to solve the above problems.

Disclosure of Invention

The invention provides a stimulated Raman scattering imaging light source based on a photonic crystal fiber aiming at the problems of the stimulated Raman scattering imaging light source, wherein a repetition frequency tuning module is utilized to provide Stokes light with different repetition frequencies from pump light for the stimulated Raman scattering imaging light source, so that the generation condition of the stimulated Raman scattering is met; meanwhile, the optical parametric oscillation structure is applied to output pump light and Stokes light which are synchronous in time and space, so that the narrow-band stimulated Raman scattering imaging light source is realized.

The technical scheme of the invention is as follows: a stimulated Raman scattering imaging light source based on a photonic crystal fiber comprises a laser oscillator, a pre-amplification module, an optical coupler, a main amplification module, a parametric conversion module, a beam splitter, a repetition frequency tuning module and a time delay module; seed light output by the laser oscillator is output after the average power is improved through the pre-amplification module, and directly enters a parametric oscillation structure with an active amplification module or enters a parametric oscillation structure without the active amplification module through the active amplification module; the parametric oscillation structure with the active amplification module comprises an optical coupler, a main amplification module, a parametric conversion module, a beam splitter, a repetition frequency tuning module and a time delay module which are connected in sequence in a closed mode; the parametric oscillation structure without the active amplification module comprises an optical coupler, a parametric conversion module, a beam splitter, a repetition frequency tuning module and a time delay module which are connected in sequence in a closed mode; the amplified pump light enters the parametric oscillation structure from the optical coupler, the photonic crystal fiber in the parametric conversion module generates Stokes light through the nonlinear effect of the photonic crystal fiber, the output of the parametric conversion module passes through the optical beam splitter to divide the light beam into two paths, one path is directly output, the other path is fed back to the repetition frequency tuning module and the time delay module to change the repetition frequency of the Stokes light participating in feedback oscillation, the Stokes light which is synchronous with the pump light but has different repetition frequencies is provided and is coupled into the parametric oscillation structure through the optical coupler again, and the requirements of the stimulated Raman scattering imaging light source are met.

The optical coupler adopts an optical fiber wavelength division multiplexer or a dichroic mirror to couple the feedback signal and the pump light into the same parametric oscillation cavity to complete parametric oscillation feedback.

The parameter conversion module formed by the photonic crystal fiber enables the pump light to generate nonlinear parameter conversion in the photonic crystal fiber, generates Stokes light required by stimulated Raman scattering, also provides a gain medium for parametric oscillation, improves the power of the Stokes light and compresses the spectrum width of the Stokes light.

The repetition frequency tuning module selects an acousto-optic modulator or an electro-optic modulator to realize the tunability of the Stokes light repetition frequency participating in parametric oscillation, so that the light source outputs double pulses of synchronous Stokes light and pump light but different repetition frequencies.

The time delay module enables Stokes light and pump light to be superposed in time and space by adjusting time delay, and amplification of Stokes light power and compression of spectrum width of the Stokes light power are achieved.

The invention has the beneficial effects that: the stimulated Raman scattering imaging light source based on the photonic crystal fiber and the application of the repetition frequency tuning module realize the synchronization of Stokes light and pump light but different repetition frequencies in one set of device, solve the problem of synchronization and modulation of two lasers in the traditional technology, and ensure that the device has simple structure and convenient operation; the synchronous stimulated Raman scattering imaging light source solves the cost problem that laser output with different central wavelengths can be realized only by two lasers in the traditional method, and the requirement of the light source can be realized only by one set of parametric oscillator; the structure of the feedback cavity enables the output Stokes light to realize the output of narrow-band spectrum under the effect of dispersion filtering, and the feedback cavity is used for stimulated Raman scattering imaging, so that the spectral resolution of light source imaging is high, and the reliability of a detection result is good; the optical parametric oscillation structure is applied to the stimulated Raman scattering imaging light source, so that the Stokes light power amplification is realized, the signal-to-noise ratio and the output power of the Stokes light are improved, and the detection sensitivity of material analysis is improved; compared with a solid laser, the laser source has the advantages of easy integration, good beam quality, stable laser signal, easy maintenance and high cost performance by the application of the optical fiber technology.

Drawings

FIG. 1 is a frame diagram of a structure of a stimulated Raman scattering imaging light source module based on a photonic crystal fiber according to the present invention;

FIG. 2 is a structural diagram of an embodiment of a stimulated Raman scattering imaging light source based on photonic crystal fiber according to the present invention;

FIG. 3 is a diagram of a second structure of an embodiment of a stimulated Raman scattering imaging light source based on photonic crystal fiber according to the present invention;

FIG. 4 is a three-junction diagram of an embodiment of a stimulated Raman scattering imaging light source based on photonic crystal fibers according to the present invention.

Detailed Description

The frame diagram of the construction of the stimulated Raman scattering imaging light source module based on the photonic crystal fiber is shown in FIG. 1,

the laser oscillator realizes the output of pulse seed light in an active mode locking mode or a passive mode locking mode, the output seed light passes through the pre-amplification module, and the average power is improved. The output end of the pre-amplification module has two connection modes: the other one is that the pre-amplification module is connected with the optical coupler firstly and then connected with the main amplification module to amplify the seed optical power again, namely the seed optical power is mainly placed in the parametric oscillation structure; the other type is that the pre-amplification module is connected with the main amplification module firstly and then sequentially connected with the optical coupler, namely the pre-amplification module is mainly arranged outside the parametric oscillation structure. The output end of the module is sequentially connected with a parametric conversion module formed by photonic crystal fibers, and in the module, pump light generates nonlinear effect through the photonic crystal fibers to generate Stokes light. The output of the parametric conversion module is connected to the optical beam splitter, and the optical beam is divided into two paths: one path is taken as the output end of the light source and is used for stimulated Raman scattering imaging or real-time detection; the other path is sequentially connected with a repetition frequency tuning module, the module changes the repetition frequency of the Stokes light participating in feedback oscillation through an acousto-optic modulator or an electro-optic modulator, the Stokes light which is synchronous with the pump light but has different repetition frequencies is provided, and the requirement of the stimulated Raman scattering imaging light source is met. The output of the repetition frequency tuning module is connected with a time delay module, and the Stokes light and the pump light meet the phase matching condition by adjusting time delay. The output end of the time delay module is connected to the optical coupler to complete parameter feedback. In the invention, the application of the parametric oscillation structure not only amplifies the Stokes light power, but also compresses the spectrum width, thereby realizing a synchronous narrow-band stimulated Raman scattering imaging light source. One output end of the parameter conversion module is the output end of the light source.

Fig. 2 is a first embodiment of a stimulated raman scattering imaging light source based on a photonic crystal fiber, which is implemented as follows:

the oscillator of the Stimulated Raman Scattering (SRS) imaging light source adopts a semiconductor saturable absorption mirror (SESAM) passive mode locking mode, and cavity elements of the oscillator sequentially comprise: SESAM, wavelength division multiplexer WDM, Gain medium Gain, fiber Bragg grating FBG. The output end of the oscillator is connected with a pre-amplification module (WDM + Gain) for amplifying the optical power of the seeds, and the oscillator is separated from the pre-amplification module by an isolator ISO so as to prevent the cavity element from being damaged by return light; the output end of the pre-amplification module is connected with an optical coupler formed by WDM (wavelength division multiplexing) and used for coupling pump light and feedback Stokes light; WDM is connected with a main amplification module formed by Non-polarization-maintaining gain optical fibers Non-PMGain in sequence, so that the secondary amplification of the seed optical power is realized, and the requirements of parametric conversion and parametric oscillation are met; the output end of the main amplifier is connected with the photonic crystal fiber PCF, and because the main amplifier gain adopts a non-polarization-maintaining fiber, a polarization controller PC is added at the tail end of the main amplifier, namely the position which does not enter the PCF, and the polarization state of pump light is adjusted, so that pump light in a certain polarization state can enter the PCF to generate four-wave frequency mixing, and stokes light required by stimulated Raman scattering imaging is generated; the PCF output end is connected to a beam splitter module consisting of a two-part plectrum and a polarizing beam splitter PBS, the PBS divides the light beam into two parts, one part is used as the output end of a light source, and the other part is connected with a repetition frequency tuning module consisting of an acousto-optic modulator AOM, so that the tunability of the Stokes light repetition frequency participating in parametric oscillation is realized; the AOM output light passes through a Delay fiber and then enters a Delay motor Delay stage, the Delay fiber and the Delay motor jointly form a time Delay module, and the phase matching of Stokes light and pump light can be realized by changing the length of the Delay fiber or adjusting the distance of the Delay motor; and finally outputting the Stokes light to WDM to complete parameter feedback. The embodiment adopts a parametric oscillation system with an all-fiber structure, and realizes a synchronous narrowband stimulated Raman scattering imaging light source based on the photonic crystal fiber.

Fig. 3 is a structural diagram of a second embodiment of a stimulated raman scattering imaging light source based on a photonic crystal fiber, and the specific implementation process is as follows:

the oscillator of the SRS imaging light source adopts a Nonlinear Polarization Rotation (NPR) passive mode locking mode, and oscillator cavity elements comprise: WDM, Gain, PC, isolator ISO, PC, output coupler OC. The output end of the oscillator is connected with a pre-amplification module used for amplifying the optical power of the seeds, and the oscillator and the pre-amplification module are separated by ISO to prevent the cavity elements from being damaged by return light; the output end of the pre-amplification module is connected with an optical coupler formed by WDM (wavelength division multiplexing) and used for coupling pump light and feedback Stokes light; the output of the optical coupler is connected with a main amplification module formed by a polarization maintaining Gain fiber PM Gain, so that the secondary amplification of the seed optical power is realized, and the requirements of parametric conversion and parametric oscillation are met; the main amplifier output end is sequentially connected with the PCF, and the pump light generates four-wave mixing in the PCF to generate Stokes light required by stimulated Raman scattering imaging; the output end of the PCF is connected to a beam splitter module consisting of a half-plectrum and a PBS (polarization beam splitter), the PBS divides a light beam into two parts, one part is used as the output end of a light source, and the other part is connected with a repetition frequency tuning module consisting of an electro-optical modulator (EOM), so that the tunability of Stokes light repetition frequency is realized; EOM output light passes through a Delay fiber and then enters a Delay motor Delay stage, the Delay fiber and the Delay motor jointly form a time Delay module, the length of the Delay fiber or the distance of the Delay motor is changed, and phase matching of Stokes light and pump light is realized; and finally outputting the Stokes light to WDM to complete parameter feedback. The embodiment adopts a parametric oscillation system with an all-fiber structure, and realizes a synchronous narrowband stimulated Raman scattering imaging light source based on the photonic crystal fiber.

Fig. 4 is a three-junction diagram of an embodiment of a stimulated raman scattering imaging light source based on a photonic crystal fiber, and the specific implementation process is as follows:

the oscillator of the stimulated Raman scattering imaging light source adopts a nonlinear amplification ring mirror (NA L M) passive mode locking mode with an 8-shaped cavity structure, an oscillator cavity element comprises two closed cavities connected by an output coupler OC, the first closed cavity comprises a WDM, a band-pass filter BP, OC, ISO and Gain which are sequentially connected in a closed loop mode, the second closed cavity comprises a WDM, Gain, WDM and a dispersion compensation optical fiber (DCF) which are sequentially connected in a closed loop mode, the output coupler OC of the first closed cavity of the oscillator outputs seed light, the output end of the oscillator is connected with a pre-amplification module for amplifying the power of the seed light, the two modules are separated by the ISO to prevent the return light from being reflected into a damaged cavity element, the output end of the pre-amplification module couples the seed light into a main amplification module with a space structure consisting of polarization maintaining Gain optical fibers through a focusing lens, a Dichroic Mirror (DM) of 980nm high-transmission high-reflection pump light is arranged behind the main amplification module, the continuous light is input from the backward to realize the secondary amplification of the power of the seed light, the requirements of parametric conversion and amplification are met, the amplification of the excitation Raman scattering imaging light, the amplification of the imaging light, the imaging light is realized by the optical fiber, the optical fiber is realized by the optical fiber, the.

Claims

1. A stimulated Raman scattering imaging light source based on a photonic crystal fiber is characterized by comprising a laser oscillator, a pre-amplification module, an optical coupler, a main amplification module, a parametric conversion module, a beam splitter, a repetition frequency tuning module and a time delay module; seed light output by the laser oscillator is output after the average power is improved through the pre-amplification module, and directly enters an all-fiber structure parameter oscillation structure with an active amplification module or enters the all-fiber structure parameter oscillation structure without the active amplification module through the active amplification module; the all-fiber structure parametric oscillation structure with the active amplification module comprises an optical coupler, a main amplification module, a parametric conversion module, a beam splitter, a repetition frequency tuning module and a time delay module which are connected in sequence in a closed manner; the all-fiber structure parametric oscillation structure without the active amplification module comprises an optical coupler, a parametric conversion module, a beam splitter, a repetition frequency tuning module and a time delay module which are connected in sequence in a closed manner; the amplified pump light enters the all-fiber structure parametric oscillation structure from the optical coupler, the photonic crystal fiber in the parametric conversion module is generated by nonlinear effect of the photonic crystal fiber to generate Stokes light, the output of the parametric conversion module passes through the optical beam splitter to divide the light beam into two paths, one path is directly output, the other path is fed back to the repetition frequency tuning module and the time delay module to change the repetition frequency of the Stokes light participating in feedback oscillation, the Stokes light which is synchronous with the pump light but has different repetition frequencies is provided, and the Stokes light enters the all-fiber structure parametric oscillation structure through the optical coupler again in a coupling mode, so that the requirement of the stimulated Raman scattering imaging light source is met.

2. The stimulated raman scattering imaging light source of claim 1, wherein the parametric conversion module formed by the photonic crystal fiber causes the pump light to generate nonlinear parametric conversion in the photonic crystal fiber to generate stokes light required for stimulated raman scattering, and also provides a gain medium for parametric oscillation, thereby increasing the power of the stokes light and simultaneously compressing the spectral width of the stokes light.

3. The stimulated raman scattering imaging light source based on photonic crystal fiber of claim 2, wherein the time delay module combines stokes light and pump light in time and space by adjusting the time delay, so as to realize amplification of stokes light power and compression of spectrum width thereof.