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CN-122016723-A - Device and method for measuring tiny refractive index change with high precision

CN122016723ACN 122016723 ACN122016723 ACN 122016723ACN-122016723-A

Abstract

The invention belongs to the field of optical measurement, and particularly relates to a device and a method for measuring tiny refractive index change with high precision. It is intended to provide a device capable of measuring refractive index change with high efficiency. The device comprises a laser light source, a half wave plate, a beam splitting prism, a polarizer, a reflecting mirror, a sample to be detected, an elasto-optical modulator, a photoelectric detector, a signal acquisition and digital phase locking module and a computer. The laser beam is split to form reference light and measuring light, the measuring light and the sample act to generate phase change, the two light beams are combined and then are subjected to periodic phase modulation through an elasto-optical modulator, a photoelectric detector converts optical signals into electric signals, a signal acquisition and digital phase locking module synchronously acquires and processes the signals and transmits the signals to a computer, and the computer reversely pushes the refractive index variation. The invention improves the measurement precision and the anti-interference capability through the homologous design of polarization precise regulation, modulation and phase locking, has quick response and simple and easy integration structure, and is suitable for detecting the change of the tiny refractive index in multiple fields such as biosensing, material characterization and the like.

Inventors

  • LI KEWU
  • ZHANG PENGSHENG
  • WANG SHUANG

Assignees

  • 中北大学

Dates

Publication Date
20260512
Application Date
20260225

Claims (10)

  1. 1. The device for measuring the micro refractive index change with high precision is characterized by comprising a laser light source (1), a half wave plate (2), an unpolarized beam splitter prism (3), a first polarizer (4), a second polarizer (5), a first reflecting mirror (6), a second reflecting mirror (7), a sample to be detected (8), a polarized beam splitter prism (9), an elastometer (10), an analyzer (11), a photodetector (12), a signal acquisition and digital phase locking module (13) and a computer (14), wherein the elastometer (10) comprises an elastometer crystal and an LC resonant high-voltage driving circuit, the LC resonant high-voltage driving circuit is used for converting an external driving electric signal into periodic mechanical stress, the elastometer crystal is a crystal with the refractive index periodically changed after being subjected to the periodic mechanical stress, the signal acquisition and digital phase locking module (13) comprises a field programmable gate array and an acquisition unit, the acquisition unit is electrically connected with the field programmable gate array, the acquisition unit is in signal connection with the photodetector (12), the detector (12) is used for converting the electric signal into the resonant electric signal, the LC resonant high-voltage driving circuit is further connected with the field programmable gate array (LC high-voltage driving circuit, the field programmable gate array is used for transmitting data to a computer (14), the computer (14) is used for transmitting instructions to the field programmable gate array, the laser light source (1), the half wave plate (2) and the non-polarized light splitting prism (3) are sequentially distributed along a light path, two light output ends of the non-polarized light splitting prism (3) are respectively connected with a light input end of the first polarizer (4) and a light input end of the second polarizer (5) in a light path, the light output end of the first polarizer (4) is connected with the light incident end of the first reflector (6), the light output end of the second polarizer (5), the light incident end of the second reflector (7), the light incident end of the sample (8) to be detected and the light emergent end of the sample (8) to be detected are sequentially distributed along the light path, the light emergent end of the first reflector (6) and the light emergent end of the sample (8) to be detected are respectively connected with the light input end of the polarized light splitting prism (9), and the light output end of the first polarizer (6) is connected with the light input end of the light splitting prism (10) and the light input end of the light detector (11) are sequentially distributed along the light path.
  2. 2. A device for measuring small refractive index variations with high accuracy according to claim 1, characterized in that the laser light source (1) is a linearly polarized light output light source with monochromaticity larger than a first preset threshold value, the laser light source (1) being adapted to provide the incident light required for the measurement.
  3. 3. The device for measuring the micro refractive index change with high precision according to claim 1, wherein the half wave plate (2) is a phase modulation adjusting element with light intensity transmittance larger than a second preset threshold value, the unpolarized beam splitting prism (3) is used for realizing light intensity beam splitting according to a fixed beam splitting ratio, the beam splitting process is irrelevant to the polarization angle of incident light, and the polarization states of the two split beams are consistent with the incident light.
  4. 4. The device for measuring the micro refractive index change with high precision according to claim 1, wherein the first polarizer (4), the second polarizer (5) and the analyzer (11) are all high extinction ratio polarizers, the first polarizer (4) is used for regulating and controlling the polarization direction of reference light, the second polarizer (5) is used for regulating and controlling the polarization direction of the measured light, and the analyzer (11) is used for regulating and controlling the polarization direction of the interference light after beam combination, wherein the reference light is a light beam transmitted to the first polarizer (4) after beam splitting of the incident light is completed through the non-polarized beam splitting prism (3).
  5. 5. The device for measuring the micro refractive index change with high precision according to claim 1, wherein the elasto-optical modulator (10) is a long rod-shaped structure driven by single-piezoelectric quartz, the elasto-optical crystal is made of isotropic materials, the LC resonance high-voltage driving circuit receives an electric signal output by a field programmable gate array, and the electric signal output by the field programmable gate array is used as a modulation driving signal of the elasto-optical modulator and is used as a reference signal for digital phase locking processing by the signal acquisition and digital phase locking module (13).
  6. 6. The device for measuring micro refractive index variation with high precision according to claim 1, wherein the acquisition unit is configured to synchronously acquire a direct current component and an alternating current component in an electrical signal, the field programmable gate array is configured to perform digital phase locking processing on the acquired signal, and the field programmable gate array is further configured to register direct current component data and cooperatively transmit the registered direct current component data and the phase-locked processed data to the computer (14).
  7. 7. A method for measuring tiny refractive index change with high precision based on the device for measuring tiny refractive index change with high precision according to any one of claims 1-6 is characterized by comprising the following steps that S1, a laser light source (1) emits linearly polarized light, the linearly polarized light is incident to a non-polarized light splitting prism (3) after being regulated by a half wave plate (2), and the non-polarized light splitting prism (3) splits the linearly polarized light into reference light and measuring light; S2, the reference light is emitted to a first reflecting mirror (6) after the polarization direction of the reference light is regulated by a first polarizer (4), the reference light is emitted to a polarization beam splitting prism (9) after being reflected by the first reflecting mirror (6), the measurement light is emitted to a second reflecting mirror (7) after the polarization direction of the measurement light is regulated by a second polarizer (5), the reference light is emitted to a sample (8) to be detected after being reflected by the second reflecting mirror (7), the reference light and the measurement light are emitted to the polarization beam splitting prism (9) after the phase change is generated by the action of the sample (8) to be detected, the reference light and the measurement light are combined at the polarization beam splitting prism (9) to form interference light, S3, the interference light is emitted to a photoelectric detector (12) after the polarization direction of the interference light is regulated by an analyzer (11), the interference light is converted into an electric signal by the photoelectric detector (12), the electric signal is transmitted to an acquisition unit of a signal acquisition and digital phase locking module (13), and the data are converted by the acquisition unit and then transmitted to the field programmable gate array for digital phase locking processing, and the computer (14) calculates the refractive index variation of the sample (8) to be detected based on the processed data.
  8. 8. The method according to claim 7, wherein in step S2, the polarization direction of the reference light regulated by the first polarizer (4) is perpendicular to the polarization direction of the measurement light regulated by the second polarizer (5), and the phase change of the measurement light is determined by the refractive index distribution of the sample to be detected.
  9. 9. A method of measuring small refractive index variations with high accuracy according to claim 7, characterized in that in step S3, the periodic phase modulation of the interference light by the elasto-optical modulator (10) is implemented based on bessel function characteristics, which periodic phase modulation is used to establish a quantitative correlation of the interference light phase variation with the refractive index variation of the sample (8) to be detected.
  10. 10. The method for measuring small refractive index variation with high precision according to claim 7, wherein in step S4, the digital phase locking process is used for extracting the magnitude of the multiple harmonics in the ac component, and the computer (14) is used for back-pushing the refractive index variation of the sample (8) to be detected based on the correlation between the magnitude of the multiple harmonics and the phase variation.

Description

Device and method for measuring tiny refractive index change with high precision Technical Field The invention relates to the field of optical measurement, in particular to a device and a method for measuring tiny refractive index change with high precision. Background The accurate measurement of the tiny refractive index change is one of core technologies in the fields of biosensing, optical material characterization, environment trace detection and the like. For example, in the detection of biomolecular interactions, the combination of target molecules and sensing interfaces can cause small changes (typically as low as 10 -6 orders of magnitude) in the refractive index of the medium, and the accurate detection of the changes directly determines the measurement accuracy of molecular interaction kinetic parameters, and in the preparation process of optical functional materials, the small refractive index unevenness corresponding to the internal stress distribution of the materials also needs to be measured with high accuracy to realize early identification of defects. Therefore, high sensitivity, high stability measurement of small refractive index changes has become a key need for technical development in the relevant field. The existing micro refractive index change measuring method mainly comprises a Michelson interference method, an optical fiber Bragg grating method, an electro-optical modulation interference method and the like. The Michelson interferometry is easy to be interfered by environment vibration, temperature drift and other external factors, the measurement precision is difficult to break through and is of the order of 10 -5, the fiber Bragg grating method relies on wavelength offset detection of a grating, the resolution is limited by the precision of a spectrometer, the response speed is low, even if an elastic light modulation related measuring device is adopted, the existing scheme also has the problems that the design of a light path polarization regulation link is simple, the polarization state matching degree of reference light and measured light is low, the signal-to-noise ratio of an interference signal is insufficient, meanwhile, a driving signal of the elastic light modulation is different from a reference signal processed by phase locking, and extra phase noise is introduced, so that the improvement of the measurement precision is further restricted. Disclosure of Invention The invention aims to provide a device and a method for measuring tiny refractive index change with high precision, and aims to provide a device capable of measuring refractive index change with high efficiency. In order to achieve the above purpose, the invention adopts the following technical scheme: The invention provides a device for measuring tiny refractive index change with high precision, which comprises a laser light source, a half wave plate, a non-polarized beam splitter prism, a first polarizer, a second polarizer, a first reflecting mirror, a second reflecting mirror, a sample to be detected, a polarized beam splitter prism, an elastic light modulator, a polarization analyzer, a photoelectric detector, a signal acquisition and digital phase locking module and a computer, wherein the first reflecting mirror is used for reflecting the sample to be detected; the elastic light modulator comprises an elastic light crystal and an LC resonance high-voltage driving circuit, wherein the LC resonance high-voltage driving circuit is used for converting an external driving electric signal into periodic mechanical stress, the elastic light crystal is a crystal with a refractive index periodically changed after being subjected to the periodic mechanical stress, the signal acquisition and digital phase locking module comprises a field programmable gate array and an acquisition unit, the field programmable gate array is electrically connected with the acquisition unit, the acquisition unit is in signal connection with a photoelectric detector, the acquisition unit is used for converting an optical signal output by the photoelectric detector into an electric signal, the field programmable gate array is electrically connected with the LC resonance high-voltage driving circuit, the field programmable gate array is used for outputting a control signal to the LC resonance high-voltage driving circuit, the field programmable gate array is electrically connected with a computer, the computer is used for transmitting data to the computer, the field programmable gate array is used for transmitting instructions, a laser light source, a half wave plate and a non-polarization splitting prism are sequentially arranged along an optical path, two optical output ends of the non-polarization splitting prism are respectively connected with an optical input end of a first polarizer and an optical input optical path of a second polarizer, an optical output end of the first polarizer is electrically connected with an optical input e