High-resolution broadband transmission spectrometer and method based on ASE light and tuned FPI

Abstract

The invention provides a high-resolution broadband transmission spectrometer and method based on ASE light and tuned FPI, and relates to the field of transmission spectrum detection and analysis, and the spectrometer comprises a light source, a tunable FPI filter and an optical switch which are connected in sequence. The other end of the optical switch is also provided with a to-be-tested sample pool and an optical fiber beam splitter; the optical fiber beam splitter is also connected with the to-be-tested sample pool; and the other end of the optical fiber beam splitter is sequentially connected with a scrambler, a collimating convex lens, a cylindrical lens, a VIPA element, a blazed grating, a focusing lens and a low-noise two-dimensional detector. According to the high-resolution broadband transmission spectrometer and method based on the ASE light and the tuned FPI, high-resolution and high-scanning-rate transmission spectrum detection is achieved on the basis of the flat wide-spectrum ASE light source by means of the high-speed frequency scanning function of the optical fiber FP and in combination with VIPA device detection.

Description

Technical Field

[0001] The invention relates to the field of transmission spectrum detection and analysis, and in particular to a high-resolution broadband transmission spectrometer and method based on ASE light and tuned FPI. Background Art

[0002] The detection of transmission spectrum has great value both in science and practicality. There are many existing detection methods, but they generally have problems such as high cost, small measurement bandwidth or low measurement rate, which limits the widespread use of transmission spectrum detection in environmental testing, industrial production and other fields. For example, monitoring the concentration of greenhouse gas CO2 in the atmosphere through absorption transmission spectrum requires the transmission spectrometer to have high-speed measurement capability and high spectral resolution. Summary of the invention

[0003] The purpose of the present invention is to provide a high-resolution broadband transmission spectrometer and method based on ASE light and tuned FPI, which realizes transmission spectrum detection with high resolution and high scanning rate based on a flat broadband ASE light source and a tunable FPI filter high-speed frequency scanning function, combined with VIPA element detection.

[0004] To achieve the above object, the present invention provides a high-resolution broadband transmission spectrometer based on ASE light and tunable FPI, comprising an ASE light source, a tunable FPI filter, and an optical switch connected in sequence; The other end of the optical switch is also provided with a sample pool to be tested and an optical fiber beam splitter, and the optical fiber beam splitter is also connected to the sample pool to be tested; The other end of the optical fiber beam splitter is connected in sequence with a polarization scrambler, a collimating convex lens, a cylindrical lens, a VIPA element, a blazed grating, a focusing lens, and a low-noise two-dimensional detection device.

[0005] Preferably, the ASE light source, the tunable FPI filter, the optical switch, the sample pool to be tested, the optical fiber beam splitter, the polarization scrambler, and the collimating convex lens are connected by optical fibers.

[0006] Preferably, the window of the VIPA element disperses the incident light beam longitudinally, and then the light beam passes through the blazed grating for transverse dispersion to improve the resolution.

[0007] The method based on high-resolution broadband transmission spectroscopy with ASE light and tuned FPI includes The light beam emitted by the light source is transmitted through a single-mode optical fiber, and after passing through a tunable FPI filter, it is divided into two paths through an optical switch. One path is used as a reference light to monitor the input power of the signal light source, and the other path passes through the sample pool to be tested. The two paths of light are converged by a fiber beam splitter and then passed through a polarization scrambler to homogenize the polarization mode; the converged light is collimated by a convex lens and then converged into a strip-shaped light spot by a cylindrical lens and enters the window of the VIPA element to disperse the light longitudinally, and then dispersed transversely by a blazed grating. The parallel light after dispersion separation is converged by a convex lens and received by a low-noise two-dimensional detection device for imaging.

[0008] Therefore, the present invention adopts the above-mentioned high-resolution broadband transmission spectrometer and method based on ASE light and tuned FPI, and the technical effects are as follows: Compared with traditional spectrometers, the present invention can quickly measure the transmission spectrum, and the measurement speed is determined by the signal strength and the tuning speed of the optical fiber FPI. The present invention has the ability to quickly scan the transmission spectrum, and can have a more precise response time in monitoring the concentration change of the substance. The ability to measure the short-term change of the substance is a significant advantage of the present invention.

[0009] The transmission spectrometer of the present invention is based on an amplified spontaneous radiation light source and has the characteristics of a wide spectrum. It covers a larger spectral range and can more accurately invert the transmission characteristics and concentration characteristics of various objects under test.

[0010] The present invention also has the positive effect of reducing the cost of measuring the transmission spectrum of a material. No expensive tuned laser or spectrometer is required. A low-cost ASE light source and optical fiber FPI combined with a mature spectroscopic detection system can construct the transmission spectrum measurement device proposed in the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 It is the system structure diagram; Figure 2 This is an example of the optical fiber FP transmission characteristic curve; Figure 3 This is an example of the shape and range of the spectrum of a spontaneously emitted amplification source (ASE); Figure 4 Schematic diagram of the method for measuring the free spectral range of FPI by electro-optical modulation; Figure 4 (a) is a schematic diagram of the frequency domain; Figure 4 (b) Figure 4 (a) Corresponding time domain diagram on an oscilloscope.

[0012] Reference numerals 1. Light source; 2. Tunable FPI filter; 3. Optical switch; 4. Sample pool to be tested; 5. Fiber beam splitter; 6. Polarization scrambler; 7. Collimating convex lens; 8. Cylindrical lens; 9. VIPA element; 10. Blazed grating; 11. Focusing lens; 12. Low-noise two-dimensional detection device. DETAILED DESCRIPTION

[0013] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0014] Unless otherwise defined, technical or scientific terms used in the present invention shall have the common meanings understood by one having ordinary skills in the field to which the present invention belongs.

[0015] Embodiment 1 like Figure 1 As shown, a high-resolution broadband transmission spectrometer based on ASE light and tunable FPI includes a light source 1, a tunable FPI filter 2, and an optical switch 3 connected in sequence; The other end of the optical switch 3 is also provided with a sample pool 4 to be tested and an optical fiber beam splitter 5, and the optical fiber beam splitter 5 is also connected to the sample pool 4 to be tested; The other end of the optical fiber beam splitter 5 is connected in sequence to a polarization scrambler 6 , a collimating convex lens 7 , a cylindrical lens 8 , a VIPA element 9 , a blazed grating 10 , a focusing lens 11 , and a low-noise two-dimensional detection device 12 .

[0016] The method based on high-resolution broadband transmission spectroscopy with ASE light and tuned FPI includes like Figure 3 As shown in the figure, the most basic light source of the system is the 1.5um band amplified spontaneous emission light source (ASE light source). Under the condition of achieving a 30nm spectral range, this light source has a great cost advantage over the wide-range tunable laser. The wide-spectrum light source generated by ASE is transmitted by polarization-maintaining fiber (single-mode fiber transmission). After passing through the tunable FPI filter 2, the spectrum is interfered and filtered by the tunable FPI filter 2 into a comb spectrum with FSR=300GHz (free spectral range) as the interval, as shown in the figure. Figure 2 As shown, the transmittance peak structure has a full width at half maximum of 30 MHz for each transmittance peak.

[0017] The optical switch 3 is divided into two paths, one of which is used as a reference light to monitor the input power of the signal light source (without passing through the sample pool 4 to be tested), and the other passes through the sample pool 4 to be tested. The above two paths of light are converged by the optical fiber beam splitter 5 and then passed through the polarization scrambler 6 to homogenize the polarization mode, so as to avoid the polarization factor causing the difference between the reference light and the signal light in the subsequent splitting and dispersion elements. The converged light is collimated by the convex lens 7 and then converged into a strip light spot by the cylindrical lens 8 to enter the window of the VIPA element 9 to disperse the light longitudinally, and then dispersed transversely by the blazed grating 10. The dispersed light is distributed in a two-dimensional point shape in space, and after being converged by the convex lens 11, it is received by the low-noise two-dimensional detection device 12. Here, a low-noise near-infrared CCD is used as the low-noise two-dimensional detection device 12, and light of different wavelengths is displayed on different pixels. The splitting capability of the entire dispersion system is 60GHz, and the fineness is 87, which is enough to clearly separate each transmittance peak on the CCD imaging array.

[0018] After passing through the tunable FPI filter 2, the ASE light source 1 forms a comb light with equal wavelength intervals. The piezoelectric device in the tunable FPI filter 2 is controlled by voltage to control the comb teeth position of the comb spectrum. The optical switch 3 is controlled by a square wave signal to change the path. One path can measure the reference light power (without passing through the sample pool 4 to be tested), and the other path can measure the light power after passing through the sample (passing through the sample pool 4 to be tested). The two paths of light are converged by the optical fiber beam splitter 5 and then scrambled by the polarization scrambler 6 to prevent the polarization of the light from affecting the interference and dispersion of the subsequent VIPA element 9 and the blazed grating 10.

[0019] Finally, the light intensity data obtained from the low-noise two-dimensional detection device 12 is used to calculate the transmittance spectra of different wavelengths, and then the transmission characteristics of the measured sample or the concentrations of different components of the sample can be inverted through inversion.

[0020] The structure using VIPA element 9 for spectroscopy and low-noise two-dimensional detection device 12 for detection has a wide spectral detection range. At this time, the transmission spectrum width depends on the spectral width of the provided signal light source. The spectrum of ASE light source 1 can reach 30nm. The wide spectrum is conducive to the simultaneous measurement of different components of the sample and improving the accuracy of measurement data such as sample concentration.

[0021] The spectrum of the ASE light source is wide and continuous. It is directly matched with the VIPA element 9 and the blazed grating 10 for splitting. Light of different frequencies will be aliased on the low-noise two-dimensional detection device 12. Therefore, a tunable FPI filter 2 is used to filter the continuous spectrum of the ASE light source 1 into a comb spectrum separated by equally spaced wavelengths. Light of different wavelengths can be clearly imaged on the two-dimensional detection device. By scanning the tunable FPI filter 2 to change the transmission wavelength, a transmission spectrum covering the entire ASE spectral range can be obtained.

[0022] The high measurement rate of the spectrometer depends on the scanning rate of the tunable FPI filter 2, the wide spectral range depends on the coverage of the ASE light source, and the subsequent splitting and detector affect the measurement resolution of the transmission spectrometer.

[0023] The comb teeth spacing and wavelength of the multiple light combs filtered out by the ASE light source through the tunable FPI filter 2 will also change with the voltage loaded on the FPI. In order to accurately measure the transmission spectrum, these changes must be calibrated in the following way.

[0024] First, an initial operating voltage is connected to the tunable FPI filter 2. At this operating voltage, a transmittance peak of the tunable FPI filter 2 Stable at wavelength At the tunable FPI filter 2, a KHz narrow linewidth single-frequency light is introduced to find the bright spot pixel on the CCD (low-noise two-dimensional detection device 12) at the detection end. , then the voltage can be ,wavelength and pixels Then keep changing the voltage and scan another single frequency light Follow the transmittance peak , until the voltage Down The transmission intensity of the single-frequency light is tuned to the maximum. With the initial The heterodyne interference beat frequency is in the RF range, and the wavelength position change of the transmittance peak is measured And the applied voltage changes , multiple measurements to obtain a transmittance peak The relationship curve between the position and the applied voltage.

[0025] Since the FSR of the tunable FPI filter 2 changes under different applied voltages, in order to obtain a high-precision transmission spectrum, the FSR change of the tunable FPI filter 2 must be measured simultaneously. Figure 4 , the single-frequency light is subjected to 30G electro-optical modulation to generate two sidebands, the single-frequency light is swept through the tunable FPI filter 2 into the low-noise two-dimensional detection device 12, the timing signal is received on the oscilloscope, and the free spectral range of the tunable FPI filter 2 is calculated ; ; in, are the modulation frequency and the single-frequency optical sweep rate, It refers to the time interval between two groups of transmitted signals on the oscilloscope. , are the time when two adjacent timing signals appear on the oscilloscope.

[0026] In the example description of the present invention, when the external scanning voltage has high stability, the voltage change step is small and the scanning speed is fast, the resolution of the transmission spectrometer depends on the transmittance peak half-width of 30Mhz of the tunable FPI filter 2, and the measurement rate depends on the sampling interval of the spectroscopic detection system CCD. The FPI filters the wide-spectrum ASE light source into comb-shaped light with an interval of about 2.4nm, and the light of each wavelength can be easily detected separately by the spectroscopic system. Based on the data and reference measured in the above manner, the corresponding comb wavelength under each voltage can be calculated, and the corresponding imaging point on the CCD can also be derived through the dispersion relationship. By changing the external voltage or scanning the FPI in other ways, the transmission wavelength changes, and the collected voltage data and CCD light intensity distribution data can be inverted within seconds to obtain a transmission spectrum covering a 30nm spectral range with a resolution of 30Mhz.

[0027] Therefore, the present invention adopts the above-mentioned high-resolution broadband transmission spectrometer and method based on ASE light and tunable FPI filter, utilizes the high-speed frequency scanning function of optical fiber FP based on flat broadband ASE light source, and combines with VIPA element detection to realize transmission spectrum detection with high resolution and high scanning rate.

[0028] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A high-resolution broadband transmission spectrometer based on ASE light and tuned FPI, characterized by: It includes an ASE light source, a tunable FPI filter, and an optical switch connected in sequence; The other end of the optical switch is also provided with a sample pool to be tested and an optical fiber beam splitter, and the optical fiber beam splitter is also connected to the sample pool to be tested; The other end of the optical fiber beam splitter is connected in sequence with a polarization scrambler, a collimating convex lens, a cylindrical lens, a VIPA element, a blazed grating, a focusing lens, and a low-noise two-dimensional detection device.

2. The high-resolution broadband transmission spectrometer based on ASE light and tuned FPI according to claim 1, characterized in that: The ASE light source, the tunable FPI filter, the optical switch, the sample pool to be tested, the optical fiber beam splitter, the polarization scrambler, and the collimating convex lens are connected by optical fibers.

3. The high-resolution broadband transmission spectrometer based on ASE light and tuned FPI according to claim 1, characterized in that: The window of the VIPA element disperses the incident light beam longitudinally, and then the light beam passes through the blazed grating for transverse dispersion, thereby improving the resolution.

4. A method based on high-resolution broadband transmission spectrometer using ASE light and tuned FPI, characterized in that: include The light beam emitted by the light source is transmitted through a single-mode optical fiber, and after passing through a tunable FPI filter, it is divided into two paths through an optical switch. One path is used as a reference light to monitor the input power of the signal light source, and the other path passes through the sample pool to be tested. The two paths of light are converged by a fiber beam splitter and then passed through a polarization scrambler to homogenize the polarization mode; the converged light is collimated by a convex lens and then converged into a strip-shaped light spot by a cylindrical lens and enters the window of the VIPA element to disperse the light longitudinally, and then dispersed transversely by a blazed grating. The parallel light after dispersion separation is converged by a convex lens and received by a low-noise two-dimensional detection device for imaging.

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