CN107064100A - Fiber Raman spectrometer based on dispersion time-varying - Google Patents

Abstract

The invention discloses a kind of fiber Raman spectrometer based on dispersion time-varying, including laser detection system and Raman spectroscopic detection system, it is a kind of using the different phenomenon of speed that different frequency is propagated in dispersive optical fiber, so as to tell the spectrometer of the spectral signature of Raman signal in time domain.Spectrometer does not need traditional light-splitting device, while avoiding complex optical path design, can improve mechanical stability, and device size and weight can be reduced again, saves cost again portable.

Description

Optical fiber Raman spectrometer based on time-varying dispersion

technical field

The invention relates to the field of Raman spectrometers, in particular to an optical fiber Raman spectrometer based on time-varying dispersion.

Background technique

The Raman spectral line was first discovered by the Indian physicist Raman in 1928 when he was studying the scattering of liquid benzene. It is a kind of scattering spectrum. When light is irradiated on an object, part of the light will be inelastically scattered. In addition to the same elastic component as the incident light (Rayleigh scattering), the scattered light also has components that increase and decrease in frequency compared to the incident light. The frequency The reduced component is called the Stokes line, and the frequency-increased component is called the anti-Stokes line, and the frequencies of the two components are symmetrically distributed on both sides of the excitation light frequency.

The Raman effect is mainly the result of molecular vibration, the interaction of optical phonons in the lattice with the excitation light source. When a photon interacts with a molecule, the molecule absorbs a photon and enters an unstable virtual energy state, and then emits a photon very quickly. At this time, if the vibration or rotation energy level of the molecule is higher than the initial energy level , then the frequency of emitted photons will be lower than that of the original photons, which is called Stokes light. On the contrary, the vibration or rotation energy level of molecules is lower than the initial one, and the energy of photons will increase, and the frequency will increase, which is called anti-Stokes light The regular change of photon frequency recorded by Raman spectrometer is called Raman spectrum.

Each substance has a specific vibration or rotational energy level, corresponding to a specific Raman spectral line, and generally does not change with the incident wavelength, so the Raman spectral line is also called a fingerprint spectral line, which is widely used in objects Component calibration.

At present, Raman spectrometers have been developed into the following forms: confocal microscope Raman spectroscopy, resonance Raman spectroscopy, surface-enhanced Raman scattering and needle-tip surface-enhanced Raman scattering. These spectrometers are obtained by spatial spectroscopy. Spectral information requires gratings and aberration-eliminating lenses. The design of the optical path is complicated, the calibration is cumbersome, and the mechanical stability is not high. At the same time, when the size of the CCD is fixed, it cannot meet the requirements of large spectral measurement range and high spectral resolution at the same time. Require.

Contents of the invention

The invention provides an optical fiber Raman spectrometer based on time-varying dispersion, aiming at reducing the weight of the spectrometer and expanding the spectrum measurement range while ensuring the resolution.

The technical solution of the present invention is: a fiber Raman spectrometer based on time-varying dispersion includes a laser detection system and a Raman spectrum detection system.

The laser detection system includes a pulse laser, a first collimator and an acousto-optic modulator.

The Raman spectrum detection system includes a second collimator, a coupler, a first photodetector and a second second detector, an oscilloscope, an ordinary optical fiber and a dispersion optical fiber.

The pulsed laser is connected to the first collimator through an optical fiber, and the acousto-optic modulator is relatively parallel to the first collimator.

The second collimator is connected to the coupler through an optical fiber, and the coupler is connected to the first photodetector through an ordinary optical fiber; the coupler is connected to the second photodetector through a dispersion fiber; the first photodetector The detector and the second photodetector are respectively connected to the oscilloscope through the serial bus.

Preferably, the length of the ordinary fiber is shorter than the length of the dispersion fiber.

Preferably, the coupler is a 3dB optical coupler.

Preferably, the laser is a fiber mode-locked soliton laser, and the laser adopts nonlinear polarization rotation mode locking, graphene mode locking, dye passive mode locking or active mode locking.

Preferably, the dispersion fiber is a distributed linear chirped grating or a photonic crystal fiber.

Preferably, the spectrometer further includes a prism group and a lens system.

Preferably, the prism group includes a reflective prism and a dichroic prism, and the reflective prism and the dichroic prism are placed relatively horizontally in the longitudinal direction; the lens group includes a front-end objective lens and a rear-end objective lens, and the lens group Placed between the sample and the second collimator.

A kind of optical fiber Raman spectrometer testing method based on dispersion time-varying, described method comprises the steps:

1) The pulsed laser emits pulsed laser light, which forms space light after passing through the first collimator or reflector;

2) Using an acousto-optic modulator to select a part of the light, so that the light output frequency is tens to hundreds of hertz;

3) After the pulsed laser reaches the surface of the object to be measured, it is reflected and scattered, and part of the light is collected by the optical fiber through the second collimator;

4) The collected reflected and scattered light enters the coupler through the optical fiber and is equally divided into two paths of light;

5) One of the paths of light propagates in the ordinary optical fiber, enters the photodetector first, and displays the pulse on the oscilloscope as the time starting point 0;

6) Another path of light propagates in the dispersion fiber. Since the light propagation constant of each frequency component in the dispersion fiber is different, after the other part of the reflected light and Raman scattered light pass through the dispersion fiber, the time for the light of different frequency components to reach the detector is different. same, let the response function of the detector be f(t);

7) In the case of fixed parameters, calibrate the delay function of light with different wavelengths propagating in the two optical fibers, that is, λ=g(t);

8) According to the time-response function measured by the fixed relationship, the spectrum of reflected light and Raman light is obtained: Raman(λ)=f(g ^-1 (λ)), and the time curve of the response is displayed on the oscilloscope.

The beneficial effects of the present invention are: a fiber optic Raman spectrometer based on time-varying dispersion eliminates the original spatial spectroscopic components and CCD array detectors, and replaces them with dispersion optical fibers and high-speed detectors, which can not only reduce the weight of the spectrometer, but also It can measure a wider range of spectra while ensuring resolution; the spectrometer does not require traditional spectroscopic devices, and at the same time avoids complex optical path design, which can not only improve mechanical stability, but also reduce device size and weight, saving cost and easy to carry. This spectrometer is a spectrometer that resolves in the time domain, and its accuracy is determined by the response rate of the detector, but its measurement range is not limited, while the traditional spectrometer splits light in the spatial domain, and its resolution is determined by the length of the grating. While the accuracy is high, it cannot meet the measurement of a wide range of spectra.

Description of drawings

With reference to the accompanying drawings, more objects, functions and advantages of the present invention will be clarified through the following description of the embodiments of the present invention, wherein:

Fig. 1 shows the structural representation of a kind of optical fiber Raman spectrometer based on dispersion time-varying of the present invention;

FIG. 2 shows a schematic structural diagram of Embodiment 2 of a fiber Raman spectrometer based on time-varying dispersion of the present invention.

detailed description

The objects and functions of the present invention and methods for achieving the objects and functions will be clarified by referring to the exemplary embodiments. However, the present invention is not limited to the exemplary embodiments disclosed below; it can be implemented in various forms. The essence of the description is only to help those skilled in the relevant art comprehensively understand the specific details of the present invention.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the drawings, the same reference numerals represent the same or similar components, or the same or similar steps.

Example 1

FIG. 1 is a schematic structural diagram of a fiber Raman spectrometer based on time-varying dispersion of the present invention. As shown in Figure 1, a fiber Raman spectrometer based on time-varying dispersion includes a laser detection system and a Raman spectrum detection system.

The laser detection system includes a pulsed laser 101, a first collimator 102, and an acousto-optic modulator 103; the pulsed laser 101 is connected to the first collimator 102 through an optical fiber, and the acousto-optic modulator 103 is placed relatively parallel to the first collimator 102 , the pulsed light emitted by the acousto-optic modulator 103 just reaches the sample 104 to be tested.

The pulsed laser 101 is a fiber mode-locked soliton laser. The pulsed laser 101 can be mode-locked by nonlinear polarization rotation, passively mode-locked by graphene or dye, or actively mode-locked. The mode-locked mode is determined according to the actual situation.

The Raman spectroscopy detection system includes a second collimator 110 , a coupler 105 , a first photodetector 108 and a second photodetector 111 , an oscilloscope 109 , an ordinary optical fiber 106 and a dispersion optical fiber 107 .

The second collimator 110 is connected with the coupler 105 by an optical fiber, and the coupler 105 is connected with the first photodetector 108 by an ordinary optical fiber 106; the coupler 105 is connected with the second photodetector 111 by a dispersion fiber 107; the first photodetector The detector 108 and the second photodetector 111 are respectively connected to the oscilloscope 109 through a serial bus.

The length of the ordinary optical fiber 106 is shorter than that of the dispersion optical fiber 107 . Ordinary optical fiber 106 has small dispersion, short pulses, and forms sharp pulses; dispersion optical fiber 107 is relatively long and has a large dispersion coefficient, so that the optical delay of two frequencies at each nanometer interval wavelength can reach about 500ps; the coupler 105 is a 3dB optical coupler ; The dispersion fiber 107 can be a distributed linear chirped grating or a photonic crystal fiber.

The cross-section of the photonic crystal fiber has a relatively complex refractive index distribution, usually containing air holes arranged in different forms. Fiber core propagation.

A distributed linear chirped grating is a grating whose grating period changes along the longitudinal direction of the fiber.

The pulsed laser 101 used in this embodiment is a fiber mode-locked soliton laser.

A specific method for obtaining spectra based on a time-varying dispersion optical fiber Raman spectrometer comprises the following steps:

1) The fiber mode-locked soliton laser 101 emits pulsed laser light with a wavelength of about 1 micron, with a pulse width of tens to hundreds of femtoseconds, which becomes spatial light after passing through the first collimator 102;

2) Since the repetition frequency of the mode-locked laser is very high, the acousto-optic modulator 103 is used to select a part of the light, so that the light output frequency is tens to hundreds of Hz;

3) The pulsed laser light is reflected and scattered after reaching the surface of the sample 104 to be tested, and part of the light will be collected by the optical fiber through the second collimator 110;

4) The collected reflected and scattered light enters the 3dB optical coupler 105 through the optical fiber, and is equally divided into two paths of light;

5) One of the paths of light propagates in the ordinary optical fiber 106 and enters the photodetector 108 earlier. Due to the small dispersion, the pulse is very short, and it will be a very sharp pulse in the oscilloscope 109, which is used as the time starting point 0 moment;

6) The other path of light propagates in the dispersion fiber 107. Since the light propagation constants of each frequency component in the dispersion fiber 107 are different, after another part of the reflected light and Raman scattered light pass through the dispersion fiber 107, the light of different frequency components reaches the detector. The time is different, let the response function of the detector be f(t), and the time t is relative to the aforementioned time 0;

7) In the case of fixed parameters, the delay function of light with different wavelengths propagating in the two optical fibers can be calibrated, that is, λ=g(t);

8) According to the above fixed relationship and the measured time response function, the pulsed laser light reaches the high-speed second photodetector 111 after being broadened by the dispersion fiber 107, and the time curve of its response is displayed on the oscilloscope 109 to obtain reflected light and Raman light The spectrum of : Raman(λ)=f(g ⁻¹ (λ)).

Using the relationship between time delay and dispersion, the corresponding Raman spectrum can be obtained. The pulse energy required by the short-distance measurement method is very small, so there is no need to amplify the laser pulse, and it does not damage the sample surface. It is a real non-destructive testing.

Example 2

FIG. 2 is a schematic structural diagram of Embodiment 2 of a fiber Raman spectrometer based on time-varying dispersion of the present invention. The difference between this embodiment and Embodiment 1 is that a reflective prism 211, a dichroic mirror 212, and a lens system 213 are added to the structural diagram of Embodiment 1 to realize long-distance Raman measurement technology to suppress background light and avoid The effect of fluorescence.

The reflective prism 211 and the sample to be tested 204 are placed in the reflection direction of the dichroic mirror 212 along the optical path, and the lens system 213 is placed in the transmission direction of the dichroic mirror 212 .

Wherein, the shapes of the reflective prism 211 and the dichroic mirror 212 are not limited to be isosceles right angles, as long as they can realize the reflection and transmission of the laser beam.

The pulse laser 210 used in this embodiment is a solid-state laser Nd:YAG laser.

A specific method of long-distance measurement technology based on dispersion time-varying optical fiber Raman spectrometer comprises the following steps:

1) Solid-state laser Nd:YAG laser 210 emits pulsed laser light with a wavelength of about 1.064 microns, and the pulse width is 150 femtoseconds;

2) Since the repetition frequency of the laser is very high, it is necessary to use an acousto-optic modulator 203 to select a part of the light, so that the light output frequency is tens to hundreds of Hz;

3) The pulsed light reaches the sample 204 to be tested after being reflected by the reflective prism 211 and the dichroic mirror 212. The dichroic mirror 212 reflects in the short-wave direction and transmits in the long-wave direction;

4) The sample 204 to be tested reflects the pulsed light and transmits it through the dichroic mirror 212. The reflected light and scattered light pass through the optical lens system 213 and become parallel light and enter the collimator 202. The front lens diameter of the optical lens system is 2 inches to 4 inches, test distance from 1 to 20m;

5) The reflected light and the scattered light enter the 3dB optical coupler 205 and are equally divided into two paths of light;

6) One of the paths of light propagates in the ordinary optical fiber 206 and enters the photodetector 208 earlier. Due to the small dispersion, the pulse is very short, and it will be a very sharp pulse in the oscilloscope 209, which is used as the time starting point 0 moment;

7) Another path of light propagates in the dispersive optical fiber 207. Since the optical fiber is relatively long and the dispersion coefficient is large, the light delay of the two frequencies at each nanometer interval wavelength can reach about 500 ps, which is higher than the minimum response time of the photodetector. In this way, for the spectral range of 200nm, the pulse width is extended to 100ns;

Since the light propagation constants of each frequency component of the dispersive fiber 207 are different, after the other part of the reflected light and Raman scattered light pass through the dispersive fiber 207, the time for the light of different frequency components to reach the detector is not the same, so the response function of the detector is f (t), the moment t is relative to the aforementioned moment 0;

8) In the case of fixed parameters, the delay function of light with different wavelengths propagating in the two optical fibers can be calibrated, that is, λ=g(t);

9) According to the above fixed relationship and the measured time response function, the pulsed laser light reaches the high-speed second photodetector 214 after being broadened by the dispersion fiber 207, and the time curve of its response is displayed on the oscilloscope 209 to obtain reflected light and Raman Spectrum of light: Raman(λ)=f(g ⁻¹ (λ)).

Other embodiments of the invention will be apparent to and understood by those skilled in the art from consideration of the specification and practice of the invention disclosed herein. The description and examples are considered exemplary only, with the true scope and spirit of the invention defined by the claims.

Claims (8)

1. A fiber optic Raman spectrometer based on time-varying dispersion, said fiber optic Raman spectrometer comprising a laser detection system and a Raman spectrum detection system; The laser detection system includes a pulsed laser, a first collimator and an acousto-optic modulator; The Raman spectrum detection system includes a second collimator, a coupler, a first photodetector, a second detector, an oscilloscope, an ordinary optical fiber and a dispersion optical fiber; The pulsed laser is connected to the first collimator through an optical fiber, and the acousto-optic modulator is placed relatively parallel to the first collimator; The second collimator is connected to the coupler through an optical fiber, and the coupler is connected to the first photodetector through an ordinary optical fiber; the coupler is connected to the second photodetector through a dispersion fiber; the first photodetector The detector and the second photodetector are respectively connected to the oscilloscope through the serial bus. 2. A kind of optical fiber Raman spectrometer based on time-varying dispersion according to claim 1, characterized in that, the length of the common optical fiber is shorter than the length of the dispersion optical fiber. 3. A kind of optical fiber Raman spectrometer based on time-varying dispersion according to claim 1, characterized in that, the coupler is a 3dB optical coupler. 4. A kind of optical fiber Raman spectrometer based on dispersion time-varying according to claim 1, is characterized in that, described laser is fiber mode-locked soliton laser, and described laser adopts nonlinear polarization rotation mode-locked, graphene-locked Mode, dye passively mode-locked or actively mode-locked. 5 . A fiber Raman spectrometer based on time-varying dispersion according to claim 1 , wherein the dispersion fiber is a distributed linear chirped grating or a photonic crystal fiber. 6. A kind of optical fiber Raman spectrometer based on time-varying dispersion according to claim 1, characterized in that the spectrometer also includes a prism group and a lens system. 7. a kind of optical fiber Raman spectrometer based on dispersion time-varying according to claim 6, is characterized in that, described prism group comprises reflective prism and dichroic prism, and described reflective prism is placed in dichroic prism The reflection direction; the lens system includes a front-end objective lens and a rear-end objective lens, and the lens group is placed in the transmission direction of the dichroic prism. 8. a method of testing utilizing the time-varying optical fiber Raman spectrometer based on dispersion according to claim 1, said method comprising the steps: 1) The pulsed laser emits pulsed laser light, which forms spatial light after passing through the first collimator or mirror group; 2) The acousto-optic modulator selects a part of the light, so that the frequency of the light is tens of hertz to hundreds of hertz; 3) After the pulsed laser reaches the surface of the object to be measured, it is reflected and scattered, and a part of the light is directly collected by the optical fiber through the second collimator or transmitted by the dichroic mirror and collected by the lens system and becomes parallel light through the second collimator. fiber optic collection; 4) The collected reflected and scattered light enters the coupler through the optical fiber and is equally divided into two paths of light; 5) One of the paths of light propagates in the ordinary optical fiber, enters the photodetector first, and displays the pulse on the oscilloscope as the time starting point 0; 6) Another path of light propagates in the dispersion fiber. Since the light propagation constant of each frequency component in the dispersion fiber is different, after the other part of the reflected light and Raman scattered light pass through the dispersion fiber, the time for the light of different frequency components to reach the detector is different. same, let the response function of the detector be f(t); 7) In the case of fixed parameters, calibrate the delay function of light with different wavelengths propagating in the two optical fibers, that is, λ=g(t); 8) According to the time response function measured by the fixed relationship, the spectra of reflected light and Raman light are obtained: Raman(λ)=f(g ⁻¹ (λ)), and the time curve of the response is displayed on the oscilloscope.