CN102192785B - Integrated optical waveguide Fourier transform spectrograph based on liquid refractive index modulation - Google Patents

Abstract

The invention discloses an integrated optical waveguide Fourier transform spectrograph based on liquid refractive index modulation, relating to a light MEMS (Micro-Electro-Mechanical Systems) processing technology, an integrated optical waveguide sensing technology and a digital signal processing technology. The integrated optical waveguide Fourier transform spectrograph comprises a light source, a chip of an integrated optical waveguide interferometer, an optical detector, a sample cell, a flow control sampling system and a digital signal processing system, wherein the sample cell of the integrated optical waveguide Fourier transform spectrograph is fixed on the surface of the chip of the optical waveguide interferometer, and the flow control sampling system is communicated with the sample cell; light emitted from the light source enters the chip of the integrated optical waveguide interferometer through prism coupling (or optical grating coupling or end face coupling) so as to become wave guiding light; and an interference optical signal output by the chip of the integrated optical waveguide interferometer in a coupling way is received by the optical detector, and an electrical signal generated by the optical detector is transmitted to the digital signal processing system which is connected with the optical detector so as to be processed to realize the inversion reconstruction of an input spectrum. The integrated optical waveguide Fourier transform spectrograph disclosed by the invention has the advantages of novel method, simple device structure, convenience for use, small size, light weight and easiness for manufacturing.

Description

Integrated Optical Waveguide Fourier Transform Spectrometer Based on Liquid Refractive Index Modulation

technical field

The invention relates to the technical field of integrated optical waveguide sensing, and is a Fourier transform spectrometer based on an integrated optical waveguide interferometer chip that is highly sensitive to the refractive index of liquid, especially a Fourier transform spectrometer based on the principle of integrated optical waveguide interference and the refractive index of surface liquid A novel portable Fourier transform spectrometer for the modulation method.

Background technique

Spectrometers are powerful tools for analyzing the composition and structure of matter. Spectrometers are widely used in environmental monitoring, chemical analysis, biomedicine, space exploration, military technology and functional materials, especially in miniaturization. Portable spectrometers have huge market demand in these fields. Different from the large-scale spectral analysis equipment in the laboratory, the miniaturized, portable spectrometer can meet the requirements of on-site real-time and rapid testing, so it has a broader application prospect and a good development trend.

There are many classification methods for spectrometers. According to the working principle, they can be divided into three categories: prism dispersion spectrometers, grating spectrometers, and modulation transform spectrometers. Prism dispersion and grating spectrometers are classic spectrometers based on the principle of geometric optics, while modulation transform spectrometers are spectral analysis instruments based on the principle of modulation calculation. The former is a spectroscopic instrument based on slits, using prisms or gratings as spatial dispersion elements, and the latter is an instrument based on optical modulation to complete spectral component detection, mainly based on interference modulation to complete dispersion. Different from the former, the results collected by the modulation transform spectrometer must be calculated and transformed to obtain the actual measurement spectrum. Common modulation-transform spectrometers include Fourier transform spectrometers, Hadamard transform spectrometers, and Fabry-Perot spectrometers. Classical dispersive spectrometer is simple in structure, mature in system, and widely used; while modulation transform spectrometer is more complex in system composition than classical dispersive spectrometer, usually including moving parts, but modulation transform spectrometer is not limited by the incident slit, and can pass diffuse incident Aperture or interferometric modulation can obtain spectral signals with higher signal-to-noise ratio and higher resolution, which are suitable for higher-end applications.

Most of the common Fourier transform spectrometers are based on the traditional moving mirror Michelson interferometer structure. Although the Fourier transform spectrometer with this structure has the advantages of high throughput, multi-channel, high spectral resolution and wide spectral range, the spectrometer The moving mirror used as a reflector in the middle requires a high-precision drive system and a good shock-absorbing environment. At the same time, the system also has the disadvantages of large volume, heavy mass, complex mechanical structure and difficulty in miniaturization. In addition, spectrometers employ spatially free beams, which are susceptible to environmental interference.

大学微技术研究所(IMT)的Omar Manzardo等人研制的一种基于MOEMS技术的微型傅里叶变换光谱仪[O.Manzardo，H.P.Herzig，C.R.Marxer，and N.F.de Rooij，Opt.Lett.24(1999)1705-1707.]，该光谱仪使用硅微镜作为Michelson干涉计的扫描反射镜，使用范围在-10V～+10V的斜坡电压静电驱动器驱动硅微镜的移动，可以实现对微镜系统的精确扫描，最大位移可达39μm，重复误差±13nm，可以在可见光波段获得10nm的分辨力，同时该光谱仪结构紧凑，尺寸仅为5mm×4mm。但是这种光谱仪在使用过程中同样是采用了空间自由光束进行干涉，容易受到外界环境干扰的缺点仍然存在。The continuous development of micro-opto-electromechanical systems (MOEMS) technology, photoelectric detection technology and advanced processing technology provides more and more possibilities for the miniaturization and miniaturization of modulated Fourier transform spectrometers. One of the more prominent is the 1999 Swiss

A kind of miniature Fourier transform spectrometer based on MOEMS technology [O.Manzardo, HP Herzig, CR Marxer, and NFde Rooij, Opt.Lett.24 (1999) 1705- developed by Omar Manzardo et al. 1707.], the spectrometer uses a silicon micromirror as the scanning mirror of the Michelson interferometer, and uses an electrostatic driver with a slope voltage ranging from -10V to +10V to drive the movement of the silicon micromirror, which can realize precise scanning of the micromirror system, with a maximum The displacement can reach 39μm, the repeat error is ±13nm, and the resolution of 10nm can be obtained in the visible light band. At the same time, the spectrometer has a compact structure, and the size is only 5mm×4mm. However, this kind of spectrometer also uses space free light beams for interference during use, and the disadvantage of being easily interfered by the external environment still exists.

Contents of the invention

The purpose of the present invention is to disclose a kind of integrated optical waveguide Fourier transform spectrometer based on liquid refractive index modulation, to overcome the above-mentioned deficiency of the existing Fourier transform spectrometer based on the Michelson interferometer structure of traditional moving mirror, realize a kind of A high-speed, high-sensitivity spectrometer with simple structure, anti-environmental interference, and no need for moving parts.

For achieving the above object, technical solution of the present invention is:

An integrated optical waveguide Fourier transform spectrometer based on liquid refractive index modulation, including a light source, an integrated optical waveguide interferometer chip, a photodetector, a sample pool, a flow control sampling system, and a digital signal processing system; the sample pool is fixed on On the surface of the optical waveguide interferometer chip, the flow control sampling system is connected to the sample cell; the light emitted by the light source is coupled into the integrated optical waveguide interferometer chip through the prism to become waveguide light, and the interference optical signal coupled out from the integrated optical waveguide interferometer chip is The photodetector receives, and the electrical signal generated by the photodetector is transmitted to the digital signal processing system connected with the photodetector for processing, so as to realize the inversion and reconstruction of the input spectrum.

In the integrated optical waveguide Fourier transform spectrometer based on liquid refractive index modulation, the integrated optical waveguide interferometer chip is an optical waveguide Mach-Zehnder interferometer chip, an optical waveguide Young's interferometer chip, an optical waveguide polarization One of a polarization interferometer chip, an optical waveguide Michelson interferometer chip, an optical waveguide Fabry-Perot interferometer chip, a dual-mode interference optical waveguide chip, or a deformed structure of the above-mentioned interferometer chip.

In the integrated optical waveguide Fourier transform spectrometer based on liquid refractive index modulation, the light emitted by the light source is either coupled through a grating or coupled through an end surface.

In the integrated optical waveguide Fourier transform spectrometer based on liquid refractive index modulation, when the spectrometer is used or tested, a fluidic sampling system is used to change the liquid refractive index in the sample cell, so that the refractive index changes uniformly with time.

In the integrated optical waveguide Fourier transform spectrometer based on liquid refractive index modulation, the sample pool and fluidic sampling system are manufactured by micro-machining technology.

The integrated optical waveguide Fourier transform spectrometer based on liquid refractive index modulation improves the resolution of the spectrometer by adjusting the sensitive window length of the integrated optical waveguide interferometer chip. When the sensitive window changes between 0-20mm, the window length The longer the spectrometer, the higher the resolution.

The integrated optical waveguide Fourier transform spectrometer based on liquid refractive index modulation improves the resolution of the spectrometer by extending the variation range of the liquid refractive index in the sample cell.

In the integrated optical waveguide Fourier transform spectrometer based on liquid refractive index modulation, the surface of the integrated optical waveguide interferometer chip is provided with a layer of high refractive index film with a gradient structure to enhance the evanescent field of the integrated optical waveguide interferometer chip intensity, increasing the resolution of the spectrometer.

In the integrated optical waveguide Fourier transform spectrometer based on liquid refractive index modulation, the high refractive index film is titanium dioxide or tantalum pentoxide film.

The integrated optical waveguide Fourier transform spectrometer based on liquid refractive index modulation determines the relevant parameters of the optical waveguide by using a monochromatic light source with a known wavelength in combination with a spectral inversion calculation method; when the light source is a monochromatic light source with a fixed wavelength When using light, Fourier transform is performed on the measured interference pattern, and the relevant parameters of the optical waveguide are determined by comparing the Fourier transform spectrum with the emission spectrum of a monochromatic light source with a known wavelength, combined with the theory of guided wave optics.

In the integrated optical waveguide Fourier transform spectrometer based on liquid refractive index modulation, the relevant parameters of the optical waveguide are the thickness of the waveguide layer and the thickness of the high refractive index film on the upper surface of the waveguide layer.

In the integrated optical waveguide Fourier transform spectrometer based on liquid refractive index modulation, the fluidic sampling system includes two containers, two miniature peristaltic pumps, a stirring bar and pipelines; wherein, the inlet of a miniature peristaltic pump passes through The pipeline is connected with a container, and there is NaCl aqueous solution in the container, and the outlet is connected with another container through the pipeline, and there is deionized water in the other container; the two ends of the other container are respectively connected with the sample cell through the pipeline, and the Another miniature peristaltic pump is connected, so that the solution in the other container and the solution in the sample pool form a loop through another miniature peristaltic pump and pipeline;

Another container is provided with a stirring bar.

In the integrated optical waveguide Fourier transform spectrometer based on liquid refractive index modulation, the NaCl aqueous solution is 1 mL of 6% NaCl aqueous solution; 4 mL of deionized water.

Different from existing spectrometers, the integrated optical waveguide Fourier transform spectrometer based on liquid refractive index modulation involved in the present invention is characterized by changing the liquid refractive index on the surface of the integrated optical waveguide interferometer chip to realize the optical path difference of interfering light the linear modulation. The above-mentioned Fourier transform spectrometer based on the moving mirror Michelson interferometer structure realizes the linear modulation of the optical path difference of the interfering light by changing the relative position of the moving mirror and the fixed mirror. At the same time, during use, the guided light confined in the waveguide layer replaces the space free light beam in the traditional spectrometer. Therefore, the integrated optical waveguide Fourier transform spectrometer based on liquid refractive index modulation involved in the present invention, in addition to having In addition to the same advantages as the traditional Fourier transform spectrometer based on the Michelson interferometer structure, it also has the characteristics of simple structure, easy integration, miniaturization, and small environmental interference factors.

Description of drawings

Fig. 1 is the structure schematic diagram of the integrated optical waveguide Fourier transform spectrometer based on liquid refractive index modulation of the present invention;

Fig. 2 is the structural representation of the device used in a specific embodiment that the present invention provides;

Fig. 3 is a kind of structure of the integrated optical waveguide interferometer chip used in a specific embodiment that the present invention provides—planar composite optical waveguide polarization polarization interferometer chip;

Fig. 4 is a graph showing the relationship between the refractive index of the liquid on the surface of the integrated optical waveguide interferometer chip and time in a specific embodiment provided by the present invention;

Fig. 5 is a schematic diagram of the interference pattern monitored by the photodetector when the liquid in the sample cell changes from deionized water to a 1.2% NaCl aqueous solution by weight in a specific embodiment of the present invention;

Fig. 6 is the spectrogram that discrete Fourier transform is carried out to the interference pattern shown in Fig. 5 and obtains, and it is the spectrogram about sampling point and optical power;

Fig. 7 is a theoretical simulation diagram of the relationship between the effective refractive index of the planar composite optical waveguide polarization polarization interferometer chip TE, TM guided mode and the refractive index of the surface liquid;

Fig. 8 is the light source spectrogram after wavelength calibration is carried out to the horizontal axis of Fig. 6, and it is the spectrogram about wavelength and optical power;

Fig. 9 is a schematic diagram of the interference pattern monitored by the photodetector when the liquid in the sample cell changes from deionized water to a 9% NaCl aqueous solution by weight in a specific embodiment of the present invention;

Fig. 10 is a light source spectrum diagram after performing discrete Fourier transform inversion on the interference pattern shown in Fig. 9 .

Detailed ways

The integrated optical waveguide Fourier transform spectrometer based on liquid refractive index modulation of the present invention has the same structure as the integrated optical waveguide biochemical sensor. As shown in Figure 1, it is a structural schematic diagram of an integrated optical waveguide Fourier transform spectrometer based on liquid refractive index modulation in the present invention, which includes a light source 1, an integrated optical waveguide interferometer chip 2, an optical detector 3, and a digital signal processing system 4 , sample pool 5, flow control sampling system 6. The integrated optical waveguide interferometer chip 2 is the core component of the spectrometer. The sample pool 5 is fixed on the surface of the integrated optical waveguide interferometer chip 2 , and the fluidic sampling system 6 communicates with the sample pool 5 . The light emitted by the light source 1 enters the integrated optical waveguide interferometer chip 2 through prism coupling (or grating coupling or end face coupling) to become guided wave light, and the fluidic sampling system 6 pumps the sample solution into the sample pool 5 to change the refraction of the liquid in the sample pool 5 rate, resulting in a phase difference of the guided light. The interference optical signal coupled out from the integrated optical waveguide interferometer chip 2 is received by the optical detector 3, and the electrical signal generated by the optical detector 3 is transmitted to the digital signal processing system 4 connected to the optical detector 3 to analyze the interference pattern and Do a Fourier transform to reconstruct the input light spectrum.

The integrated optical waveguide Fourier transform spectrometer based on liquid refractive index modulation of the present invention has a spectrum inversion and reconstruction principle similar to the Fourier transform spectrometer based on Michelson interferometer structure. When the input light is monochromatic light, the output interference light intensity after passing through the integrated optical waveguide interferometer chip 2 is

I _out ＝I _in [1+cos(Δφ)]＝I _in [1+cos(2πνl)] (1)

为波数，l＝LΔN为光程差，L为光波导干涉计芯片的敏感窗口长度，ΔN为导模有效折射率的变化。当样品池5内液体折射率发生变化时，导波有效折射率跟随发生变化，致使干涉光光程差产生变化，即实现光波导表面液体折射率对干涉光光程差的调制。Among them, I _in is the input light intensity, Δφ is the phase difference of the guided mode that interferes,

is the wave number, l=LΔN is the optical path difference, L is the sensitive window length of the optical waveguide interferometer chip, and ΔN is the change of the effective refractive index of the guided mode. When the refractive index of the liquid in the sample cell 5 changes, the effective refractive index of the guided wave changes accordingly, resulting in a change in the optical path difference of the interference light, that is, the modulation of the optical path difference of the interference light by the liquid refractive index on the surface of the optical waveguide is realized.

Similarly, when the input light is polychromatic light, after passing through the integrated optical waveguide interferometer chip 2, its interference light intensity distribution is

${\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span><span\; class="notranslate">\; \&Integral;</span>\mathrm{<span\; class="notranslate">\; iGO</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; \&nu;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{<span\; class="notranslate">\; \&infin;</span>}{<span\; class="notranslate">\; \&Integral;</span>}}{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; in</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&nu;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;\&nu;l</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span>\mathrm{<span\; class="notranslate">\; d\&nu;</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

The above formula contains two parts: the first part has nothing to do with the optical path difference l, and represents the DC component of the interference signal; the second part is related to the optical path difference, and represents the AC component of the interference optical signal. In practical applications, the AC part can be extracted separately for analysis, so there is

${\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{<span\; class="notranslate">\; \&infin;</span>}{<span\; class="notranslate">\; \&Integral;</span>}}{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; in</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&nu;</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;\&nu;l</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; d\&nu;</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

According to the definition of Fourier transform, the above formula can be written as

corresponding

From formula (5) and formula (6), it can be seen that the interference light intensity distribution of polychromatic light and its wave number power spectrum are Fourier transforms of each other. The optical power spectral distribution of the light source can be obtained only by performing one-dimensional Fourier transform on the intensity distribution of the interference pattern monitored by the optical detector 3 .

Different from other types of Fourier transform spectrometers, especially moving mirror Michelson interferometer Fourier transform spectrometers, the integrated optical waveguide Fourier transform spectrometer based on liquid refractive index modulation mentioned in the present invention does not contain moving parts , by changing the liquid refractive index on the surface of the optical waveguide to change the optical path difference of the interference light, the optical path difference can be written as

l=LΔN=LC ₁ Δn _c (6)

where _C is a constant and Δn _c is the change in the refractive index of the liquid. Within a certain range of liquid refractive index variation, the change ΔN of the effective refractive index of the guided mode has a good linear relationship with the change Δn _c of the liquid refractive index. If a suitable flow control sampling system 6 is adopted, the refractive index of the liquid in the sample cell 5 can increase or decrease linearly with time, that is:

l=LΔN=LC ₁ C ₂ t (7)

Among them, _C2 is a constant, and t is time.

It should be pointed out that the integrated optical waveguide Fourier transform spectrometer based on liquid refractive index modulation proposed by the present invention, its core component integrated optical waveguide interferometer chip 2 can have various structural forms: optical waveguide Mach-Zehnder interferometer Chip [RG. Heideman, P.V. Lambeck, Sensors and Actuators B 61 (1999) 100-127.], Optical Waveguide Young's Interferometer Chip [K. Schmitt, B. Schirmer, C. Hoffmann, A. Brandenburg, and P. Meyrueis , Biosens. Bioelectron. 22 (2007) 2591-2597; Graham H. Cross, Andrew Reeves, Stuart Brand, Marcus J. Swann, Louise L. Peel, Neville J. Freeman, and Jian R. Lu, J. Phys.D : Appl.Phys.37(2004)74-80.], optical waveguide polarization polarization interferometer chip [Zhi-mei Qi, Kiminori Itoh, Masayuki Murabayashi, and Hiroyuki Yanagi, J.Ligthwave Techn.18(8)(2000) 1106-1110.], optical waveguide Michelson interferometer chip [Shyh-Lin Tsao, and Shin-Ge Lee, Opt. and Quantum Electron.36(2004) 309-320.], optical waveguide Fabry-Perot interference Meter chip [Kinrot Noam, Nathan Menachem, J.Ligthwave Techn.24(5) (2006) 2139-2145.], dual-mode interference optical waveguide chip [Sergey S. Sarkisov, Darnell E. Diggs, Grigory Adamovsky, and Michael J. Curley, Appl. Opt. 40 (3) (2001) 349-359.] and other interferometer structures.

No method and device similar to the integrated optical waveguide Fourier transform spectrometer based on liquid refractive index modulation of the present invention has been found in the published literature.

In actual operation, the spectrometer can adopt the structure shown in Figure 2, and Figure 2 is a schematic structural view of the device used in a specific embodiment provided by the present invention, among which 1 is a light source, 2 is an integrated optical waveguide interferometer chip, and 3 is a light detector, 4 is a digital signal processing system, 5 is a sample cell, 61 is a container 1, 62 is a container 2, 63 is a micro peristaltic pump 1, 64 is a micro peristaltic pump 2, 65 is a stirring bar, and 61-65 are composed The flow control sampling system 6 in Fig. 1, 7 is a 45° analyzer, 8 is an input coupling prism, and 9 is an output coupling prism.

The integrated optical waveguide interferometer chip 2 of the present invention has adopted the polarization polarization interferometer chip [Zhi-mei Qi, Kiminori Itoh, Masayuki Murabayashi, and Hiroyuki Yanagi, J.Ligthwave Techn.18 (8) (2000] based on the planar composite optical waveguide ) 1106-1110.]. The structure of the chip is as shown in Figure 3, which is a structure of the integrated optical waveguide interferometer chip 2 used in a specific embodiment provided by the present invention—planar composite optical waveguide polarization polarization interferometer chip, 21 in the figure 22 is a waveguide layer made by ion exchange technology on the upper surface of the glass substrate, and 23 is a high refractive index gradient film with wedge-shaped structures at both ends. Exchange a waveguide layer 22 with a slightly higher refractive index than the glass substrate on the surface of the glass substrate by ion exchange technology, and then sputter a layer of high refractive index gradient film 23 with a length L and wedge-shaped structures at both ends on the waveguide layer (such as titanium dioxide, tantalum pentoxide, etc.), the thickness of the film is precisely controlled so that it only supports the transmission of the transverse electric (TE) guided mode but not the transverse magnetic (TM) guided mode.

的相位差，同时经过45°的检偏器7后两者发生干涉，使用光探测器3探测干涉光位相随时间的变化，再通过数字信号处理系统4对干涉图样进行分析处理。First, red light with a wavelength of 633nm is used as the monochromatic light source 1. The light emitted by the light source 1 is coupled by the input coupling prism 8 and propagates along the optical waveguide. The mode will be coupled into the thin film 23 to propagate, and interact with the liquid in the sample cell 5 on the upper part of the thin film 23 as the surface covering layer, and then be coupled into the optical waveguide through the wedge-shaped region on the other side of the gradient thin film 23 . When the TE guided mode interacts with the surface liquid, the equivalent refractive index changes by ΔN _TE . However, the TM guided mode in the guided wave is cut off in the high refractive index gradient film 23 and can only propagate along the optical waveguide. The degree of interaction between it and the surface liquid is much weaker than that of the TE guided mode. After the interaction, etc. The effective refractive index changes ΔN _TM , which can be used as a reference quantity. The TE guided mode and the TM guided mode are output from the optical waveguide together after being coupled by the output coupling prism 9, and there is a

At the same time, the two interfere after passing through the 45° analyzer 7, and use the optical detector 3 to detect the change of the interfering light phase with time, and then analyze and process the interference pattern through the digital signal processing system 4.

During operation, the refractive index of the solution in the sample cell 5 is required to change uniformly with time. The specific operation is as follows: the container 61 is filled with 1 mL of NaCl aqueous solution with a mass fraction of 6%, and the container 62 is filled with 4 mL of deionized water. First turn on the peristaltic pump 64 to circulate the deionized water from the container 62 into the sample pool 5 at a constant speed, then use the peristaltic pump 63 to pump the 6% NaCl aqueous solution from the container 61 into the container 62 at a constant speed, and use the stirring bar 65 to stir the solution at the same time. Mix the solution evenly. Then the peristaltic pump 64 circulates and pumps the diluted NaCl solution into and out of the sample pool 5 . Adjust the pump speed of two peristaltic pumps 63,64 to make the solution in the sample pool 5 change from deionized water to mass fraction after 9 seconds NaCl aqueous solution, the liquid refractive index changes during this process Δn _c =n _1.2% -n _water =0.0021297. The relationship between the change of liquid refractive index Δn _c and time t is shown in Fig. 4 . The constant C ₂ in formula (8) can be obtained = 0.0002366.

When the liquid on the surface of the planar composite optical waveguide high refractive index gradient film 23 changes from deionized water to 1.2% NaCl solution, the interference pattern monitored by the photodetector 3 is as shown in Figure 5, and it can be known from Figure 5 that in this The phase of the output light changes by about 8π in the process. Discrete Fourier transform is performed on the obtained interference pattern, and the result is shown in Figure 6. This is a spectrogram about the number of sampling points of the interference pattern and the power of the light source, not the final wavelength-optical power spectrogram, so it is necessary to correspond the horizontal axis of the spectrogram to the wavelength. This requires knowing the length L of the sensitive window of the optical waveguide in formula (8), and the constants C ₁ and C ₂ . Where L=10mm, C ₂ =0.0002366, and C ₁ is to be requested.

According to the theory of guided wave optics, when the refractive index of the liquid changes, the effective refractive index of the guided mode also changes. For the planar composite optical waveguide polarization polarization interferometer chip, the effective refractive index of the TE guided mode and the effective refractive index of the TM guided mode both change with the refractive index of the surface liquid. The substrate 21, waveguide layer 22, high refractive index gradient film 23, and surface liquid of the planar composite optical waveguide polarization polarization interferometer chip constitute a four-layer plate structure. The theoretical value shown in Figure 7 is obtained by simulating this structure. It can be seen from FIG. 7 that when the refractive index n _c of the liquid on the surface of the high refractive index gradient film 23 changes in the range of 1.33 to 1.37, the changes of the effective refractive index of the TE and TM guided modes are close to linear. And C ₁ =0.1149530-0.0031479=0.118051.

Put the values of L, C ₁ , and C ₂ into formula (7) and perform wavelength correspondence on the spectrum shown in Figure 6 to obtain the spectrum shown in Figure 8. It can be seen from Figure 8 that the spectral peak appears at At 639.2 nanometers, although there is a slight deviation from the wavelength of the known light source, the spectrum can still well illustrate that the power spectrum of the light source can be retrieved from the interference pattern, but the spectral peak in Figure 8 is wider, which is different from the interference The number of periods of the pattern is related. If the concentration range of the solution in the sample cell 5 is increased, the interference period can be increased, the width of the spectral peak can be reduced, and the resolution of the spectrometer can be improved. FIG. 9 shows the interference pattern when the concentration in the sample cell 5 is 9% NaCl aqueous solution, and FIG. 10 shows the spectrum after inversion. Comparing Figure 8 and Figure 10, it is found that the position of the spectral peak in Figure 10 is closer to the wavelength of the light source than that in Figure 8, and the width of the spectral peak in Figure 10 is narrower than that in Figure 8, and the resolution of the spectrometer is improved . This method based on liquid refractive index modulation remains applicable when extending the light source from red to polychromatic.

In addition, the integrated optical waveguide Fourier spectrometer based on liquid refractive index modulation of the present invention also has the function of determining optical waveguide parameters. When the light source 1 is monochromatic light with a fixed wavelength, Fourier transform is performed on the measured interference pattern. By comparing the Fourier transform spectrogram with the emission spectrogram of a monochromatic light source of known wavelength, and in conjunction with the theory of guided wave optics, the relevant parameters of the optical waveguide (such as the thickness of the waveguiding layer 22, the high refraction of the upper surface of the waveguiding layer 22) can be determined. Rate film 23 thickness, etc.). For example, using red light with a wavelength of 633nm as the light source 1, while the liquid in the sample cell 5 changes from deionized water to a NaCl aqueous solution with a weight ratio of 1.2%, the refractive index of the liquid changes uniformly with time during this process, and the formula ( C ₂ in 7) = 0.0002366. The change of solution concentration in the sample cell 5 causes photodetector 3 to monitor the interference pattern as shown in Figure 5, and discrete Fourier transform is done to this interference pattern to obtain the spectrogram as shown in Figure 6, which is about the sampling point and Spectrum of light source power, which shows a spectral peak at the corresponding sampling point. This spectral peak should appear at the wavelength of 633nm, so formula (7) should be used to correspond the sampling point to 633nm. In formula (7), L=10mm, C ₂ =0.0002366, combined with λ=633nm, it can be deduced that C ₁ =0.118051. When C ₁ , the refractive index of the substrate 21 (n _S ), the refractive index of the waveguide layer 22 (n _f ), the thickness of the waveguide layer 22 (h), and the refractive index of the gradient film 23 (n _TiO2 ) are known, according to The thickness (h _TiO2 ) of the high refractive index gradient film 23 can be determined by the waveguide equation of the four-layer plate structure of the optical waveguide. Similarly, if h _TiO2 is known, but the thickness h of the wave guiding layer 22 is unknown, the thickness h of the wave guiding layer 22 can also be determined according to this method.

Claims (11)

1. An integrated optical waveguide Fourier transform spectrometer based on liquid refractive index modulation, comprising a light source, an integrated optical waveguide interferometer chip, a photodetector, a sample pool, a flow control sampling system, and a digital signal processing system; it is characterized in that , the sample cell is fixed on the surface of the integrated optical waveguide interferometer chip, and the flow control sampling system is connected to the sample cell; The output interference optical signal is received by the optical detector, and the electrical signal generated by the optical detector is transmitted to the digital signal processing system connected to the optical detector for processing, so as to realize the inversion and reconstruction of the input spectrum; Among them, the relevant parameters of the optical waveguide are determined by using a monochromatic light source with a known wavelength combined with a spectral inversion calculation method; when the light source is a monochromatic light with a fixed wavelength, the measured interference pattern is Fourier transformed, and by comparing The Fourier transform spectrum and the emission spectrum of a monochromatic light source with known wavelengths, combined with the theory of guided wave optics, determine the relevant parameters of the optical waveguide; When the spectrometer is used or tested, the fluidic sampling system is used to change the refractive index of the liquid in the sample cell, so that the refractive index changes uniformly with time. 2. The integrated optical waveguide Fourier transform spectrometer based on liquid refractive index modulation according to claim 1, wherein the integrated optical waveguide interferometer chip is an optical waveguide Mach-Zehnder interferometer chip, an optical waveguide Young's interferometer chip, optical waveguide polarization polarization interferometer chip, optical waveguide Michelson interferometer chip, optical waveguide Fabry-Perot interferometer chip, dual-mode interference optical waveguide chip, or one of the above The deformation structure of the interferometer chip. 3 . The integrated optical waveguide Fourier transform spectrometer based on liquid refractive index modulation according to claim 1 , wherein the light emitted by the light source is coupled through a grating or through an end face. 4 . 4. The integrated optical waveguide Fourier transform spectrometer based on liquid refractive index modulation according to claim 1, characterized in that, the sample pool and fluidic sampling system are made by micro-machining technology. 5. the integrated optical waveguide Fourier transform spectrometer based on liquid refractive index modulation according to claim 1 or 2, is characterized in that, improves spectrometer resolution by adjusting the sensitive window length of integrated optical waveguide interferometer chip, when sensitive window When changing between 0-20mm, the longer the window length, the higher the resolution of the spectrometer. 6. The integrated optical waveguide Fourier transform spectrometer based on liquid refractive index modulation according to claim 1, characterized in that the resolution of the spectrometer is improved by expanding the range of variation of the liquid refractive index in the sample cell. 7. The integrated optical waveguide Fourier transform spectrometer based on liquid refractive index modulation according to claim 1 or 2, wherein the surface of the integrated optical waveguide interferometer chip is provided with a high refractive index film with a gradient structure, To enhance the evanescent field intensity of the integrated optical waveguide interferometer chip and improve the resolution of the spectrometer. 8 . The integrated optical waveguide Fourier transform spectrometer based on liquid refractive index modulation according to claim 7 , wherein the high refractive index film is titanium dioxide or tantalum pentoxide film. 9. The integrated optical waveguide Fourier transform spectrometer based on liquid refractive index modulation according to claim 1, wherein the relevant parameters of the optical waveguide are the thickness of the waveguide layer and the high refraction of the upper surface of the waveguide layer rate film thickness. 10. The integrated optical waveguide Fourier transform spectrometer based on liquid refractive index modulation according to claim 1, wherein the fluidic sampling system includes two containers, two miniature peristaltic pumps, a stirring bar and pipelines ; Wherein, a miniature peristaltic pump inlet communicates with a container through a pipeline, and there is NaCl aqueous solution in the container, and the outlet communicates with another container through a pipeline, and deionized water is arranged in the other container; the two ends of the other container respectively pass through the pipeline Connected with the sample pool, another micro peristaltic pump is connected to one pipeline, so that the solution in the other container and the solution in the sample pool form a loop through another micro peristaltic pump and pipeline; Another container is provided with a stirring bar. 11. The integrated optical waveguide Fourier transform spectrometer based on liquid refractive index modulation according to claim 10, wherein the NaCl aqueous solution is 1 mL of NaCl aqueous solution with a mass fraction of 6%; deionized water is 4 mL.

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