CN114324240A - Refractive index measuring device and measuring method - Google Patents
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Abstract
The application relates to a refractive index measuring device and a method, wherein a laser emitting device emits measuring light and detecting light, the measuring light enters a double-optical-path differential compensation device through an optical fiber circulator, and the compensated measuring light is formed under the actions of light splitting, differential frequency shift and an optical fiber grating. The compensated measuring light returns to the laser emitting device through the optical fiber circulator to be modulated to form modulated detection light, and the data processing device determines the refractive index change according to the modulated detection light. The application adopts the optical fiber circulator and the double-optical-path differential compensation device to enable the compensated measuring light to return to the laser generating device to generate the laser frequency shift feedback effect. The laser frequency shift feedback effect has high sensitivity, and can amplify light intensity signal change caused by the fiber grating, thereby improving the sensitivity of the refractive index measuring device.
Description
Technical Field
The present disclosure relates to refractive index measurement technologies, and in particular, to a refractive index measurement apparatus and a refractive index measurement method.
Background
The refractive index, like mass and density, is one of the most important basic parameters of a substance. The change of the property of the substance can be conveniently judged by measuring the refractive index. Therefore, the refractive index measurement technology is widely applied to the fields of biomedical research, disease diagnosis, food safety, environmental pollution detection and the like. Fiber gratings are one of the main methods of fiber-optic refractive index measurement. When the refractive index of the outside of the fiber changes, it causes the effective index of the core propagating mode to change, thereby changing the resonant wavelength of the fiber grating. The change of the refractive index of the medium outside the optical fiber can be measured by detecting the resonance wavelength drift of the optical fiber grating through the spectrometer. The fiber grating has the advantages of high response speed, no electromagnetic interference, small volume and the like.
However, most of the energy of light is limited in the fiber core of the optical fiber, and the evanescent wave outside the optical fiber is very weak, so that the resonance wavelength of the fiber grating is very little influenced by the change of the external refractive index, and the sensitivity of the fiber grating refractive index measurement method is very low.
Disclosure of Invention
In view of the above-mentioned problems in the background art, the present application provides a refractive index measurement apparatus and a measurement method with low cost, simple structure, fast response speed and high sensitivity.
A refractive index measurement device, comprising: a laser emission device including a first emission port and a second emission port from which measurement light is emitted; a fiber optic circulator including a first circulator port, a second circulator port, and a third circulator port, the measurement light being input from the second circulator port and output from the third circulator port; one end of the double-optical-path differential compensation device is connected with the port of the third circulator and used for receiving the measuring light, the other end of the double-optical-path differential compensation device is connected with the port of the first circulator and used for emitting the compensated measuring light to the optical fiber circulator, and the double-optical-path differential compensation device comprises a first light splitting frequency shift unit, a second light splitting frequency shift unit and an optical fiber grating; the laser emitting device is further configured to receive the compensated measurement light through the second emitting port, perform light intensity modulation based on the compensated measurement light, emit the modulated measurement light through the second emitting port, perform light intensity modulation based on the compensated measurement light, and emit the modulated probe light through the first emitting port; and the data processing device is connected with the first emergent port.
In one embodiment, the dual optical path differential compensation apparatus further comprises: a first fiber polarization beam splitter comprising a first polarization port, a second polarization port, and a third polarization port, the first fiber polarization beam splitter receiving the measurement light through the third polarization port; the first fiber polarization beam splitter is used for splitting the measuring light into a first laser beam and a second laser beam, the first laser beam is output from the first polarization port, and the second laser beam is output from the second polarization port; the first optical splitting frequency shift unit is connected with the first polarization port and is used for carrying out differential frequency shift on the first laser beam; one end of the second optical splitting frequency shift unit is connected with the second polarization port, the other end of the second optical splitting frequency shift unit is connected with the fiber bragg grating, and the second optical splitting frequency shift unit is used for carrying out differential frequency shift on the second laser beam; the fiber grating is used for causing the intensity of the second laser beam after differential frequency shift to change after a surrounding medium is changed.
In one embodiment, the dual optical path differential compensation apparatus further comprises: and the second optical fiber polarization controller is arranged between the second light splitting frequency shift unit and the fiber bragg grating and is used for changing the polarization state of the second laser beam subjected to differential frequency shift.
In one embodiment, the dual optical path differential compensation apparatus further comprises: the second optical fiber polarization beam splitter comprises a fourth polarization port, a fifth polarization port and a sixth polarization port, the fourth polarization port is connected with the first light splitting frequency shift unit, the fifth polarization port is connected with the fiber bragg grating, and the sixth polarization port is connected with the first annular port.
In one embodiment, the refractive index measuring apparatus further comprises: and one end of the first optical fiber polarization controller is connected with the third annular port, the other end of the first optical fiber polarization controller is connected with the dual-optical-path differential compensation device, and the first optical fiber polarization controller is used for changing the polarization state of the measuring light.
In one embodiment, the laser emitting apparatus includes: a laser for emitting a laser beam; the optical fiber coupler is connected with the laser and is used for splitting the laser beam into the measuring light and the detecting light; the laser is also used for receiving the compensated measuring light fed back by the optical fiber coupler, and emitting a modulated laser beam after carrying out light intensity modulation based on the compensated measuring light.
In one embodiment, the data processing apparatus comprises: a photodetector for converting an optical signal of the modulated detection light into an electrical signal; the signal processing unit is connected with the photoelectric detector and used for demodulating the electric signal to obtain a voltage signal corresponding to the light intensity of the compensated measuring light; and the computer is connected with the signal processing unit and used for determining the refractive index change according to the voltage signal corresponding to the compensated light intensity of the measuring light.
A refractive index measuring method is applied to a refractive index measuring device, the refractive index measuring device comprises a laser emitting device, a fiber optic circulator, a double-optical-path differential compensation device and a data processing device, and the method comprises the following steps:
the laser emitting device emits measuring light through a second emitting port;
the optical fiber circulator receives the measuring light through a second circulator port and outputs the measuring light to the dual-optical-path differential compensation device through a third circulator port;
the double-optical-path differential compensation device carries out compensation processing on the received measuring light to obtain compensated measuring light, and the compensated measuring light is input into the optical fiber circulator through a first circulator port;
the laser emitting device receives the compensated measuring light from a first circulator port of the optical fiber circulator, and emits modulated detection light through a first emitting port after light intensity modulation is carried out on the basis of the compensated measuring light;
the data processing device receives the modulated probe light from the first exit port and determines a refractive index change according to the modulated probe light.
In one embodiment, the dual optical path differential compensation apparatus includes a first optical splitting frequency shift unit, a second optical splitting frequency shift unit, and a first fiber polarization beam splitter, and the outputting the measurement light to the dual optical path differential compensation apparatus through a third circulator port includes:
the first optical fiber polarization beam splitter receives the measuring light from the third circulator port and splits the measuring light to obtain a first laser beam and a second laser beam;
the first optical fiber polarization beam splitter inputs the first laser beam into the first optical splitting frequency shift unit through a first polarization port, and inputs the second laser beam into the second optical splitting frequency shift unit through a second polarization port.
In one embodiment, the determining a refractive index change from the modulated probe light comprises:
converting the modulated optical signal of the detection light into an electrical signal;
demodulating the electric signal and determining the voltage change corresponding to the light intensity of the compensated measuring light;
and determining the refractive index change according to the voltage signal corresponding to the light intensity of the compensated measuring light.
The application provides a refracting index measuring device and measuring method, laser emitting device outgoing survey light and probe light, survey light passes through the optic fibre circulator gets into the differential compensation arrangement of two light paths forms the survey light after the compensation through beam split, difference shift frequency and fiber grating's effect. The compensated measuring light returns to the laser emitting device through the optical fiber circulator to be modulated to form modulated detection light, and the data processing device determines the refractive index change according to the modulated detection light. The application adopts the optical fiber circulator and the double-optical-path differential compensation device to enable the compensated measuring light to return to the laser generating device to generate the laser frequency shift feedback effect. The laser frequency shift feedback effect has high sensitivity characteristic, and can amplify light intensity signal change brought by the fiber bragg grating, so that the sensitivity and the resolution of the refractive index measuring device are improved. The dual-optical-path differential compensation device can effectively reduce measurement errors caused by laser power thermal drift, environmental disturbance and the like. Simultaneously, laser generating device can the outgoing survey light in this application, can accept the survey light after the compensation again, has realized refractive index measuring device's receiving and dispatching integral type structure, greatly reduced refractive index measuring device's complexity, the cost is reduced.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments or the conventional technologies of the present application, the drawings used in the descriptions of the embodiments or the conventional technologies will be briefly introduced below, it is obvious that the drawings in the following descriptions are only some embodiments of the present application, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
Fig. 1 is a schematic view of a refractive index measurement apparatus according to an embodiment of the present application.
Fig. 2 is a schematic view of a refractive index measurement apparatus according to another embodiment of the present application.
Fig. 3 is a schematic diagram of a first optical splitter and frequency shift unit according to an embodiment of the present disclosure.
Fig. 4 is a schematic diagram of a second optical splitter/frequency shift unit according to an embodiment of the present disclosure.
The reference numbers illustrate:
the refractive index measuring device 10, the laser emitting device 100, the laser 101, the fiber coupler 102, the fiber circulator 110, the dual optical path differential compensation device 120, the first optical division frequency shift unit 121, the second optical division frequency shift unit 122, the fiber grating 123, the first fiber polarization beam splitter 124, the second fiber polarization controller 125, the second fiber polarization beam splitter 126, the first acousto-optic frequency shifter 1211, the second acousto-optic frequency shifter 1212, the third acousto-optic frequency shifter 1221, the fourth acousto-optic frequency shifter 1222, the data processing device 130, the photodetector 131, the signal processing unit 132, the computer 133, and the first fiber polarization controller 140.
Detailed Description
In order to make the objects, technical solutions and advantages of the present application more clear, the present application is further described in detail below by using an implementation example and with reference to the accompanying drawings. It should be emphasized that the following description is merely exemplary in nature and is intended to illustrate the application and not limit the scope and application of the invention.
The numbering of the components as such, e.g., "first", "second", etc., is used herein only to distinguish the objects as described, and does not have any sequential or technical meaning. In the description of the present application, it is to be understood that the terms "on", "surface", and the like, indicate orientations or positional relationships based on those shown in the drawings, are merely for convenience in describing the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed in a specific orientation, and be operated, and thus, should not be construed as limiting the present application.
Referring to fig. 1, the present embodiment provides a refractive index measurement apparatus 10. The refractive index measuring apparatus 10 includes a laser emitting device 100, a fiber circulator 110, a dual optical path differential compensation device 120, and a data processing device 130. The laser emission device 100 includes a first emission port and a second emission port, and the measurement light is emitted from the second emission port and the probe light is emitted from the first emission port. The first exit port is the port a in fig. 1, and the second exit port is the port b in fig. 1. The laser emitting device 100 emits a laser beam and splits the laser beam into measurement light and probe light.
The fiber optic circulator 110 includes a first circulator port, a second circulator port, and a third circulator port, with measurement light being input from the second circulator port and output from the third circulator port. The first circulator port is the port of fig. 1, the second circulator port is the port of fig. 1, and the third circulator port is the port of fig. 1. The dual optical path differential compensation device 120 includes a first optical division frequency shift unit 121, a second optical division frequency shift unit 122, and a fiber grating 123. One end of the dual optical path differential compensation device 120 is connected to the third circulator port for receiving the measurement light. The other end of the dual optical path differential compensation device 120 is connected to the first circulator port, and is configured to emit the compensated measurement light to the optical fiber circulator 110. The compensated measuring light enters the laser emitting device 100 through the second emitting port, and generates a self-mixing interference effect (also called laser frequency shift feedback effect) with a laser beam (i.e. an original optical field) emitted by the laser emitting device 100, so that after the light intensity of the original laser is modulated, the laser emitting device 100 emits the modulated laser, and performs beam splitting processing through the modulated laser to obtain the modulated measuring light and the modulated probe light, wherein the laser emitting device 100 emits the modulated probe light through the first emitting port and emits the modulated measuring light through the second emitting port. The data processing device 130 is connected to the first exit port, and obtains a change in refractive index by the modulated probe light. Specifically, the above connection relationship of the present application can be realized by an optical fiber, and is not specifically described below.
According to the refractive index measuring device 10 provided by the embodiment of the present application, the laser emitting device 100 emits the measuring light through the second emitting port, the measuring light enters the dual optical path differential compensation device 120 through the optical fiber circulator 110, and the compensated measuring light is formed under the actions of light splitting, differential frequency shift and fiber bragg grating. The compensated measuring light returns to the laser emitting device 100 through the optical fiber circulator 110 to be subjected to light intensity modulation to form modulated detection light, the laser emitting device 100 emits the modulated detection light through the first emitting port, and the data processing device calculates the refractive index change according to the modulated detection light. The refractive index measuring device 10 employs the optical fiber circulator 110 and the dual optical path differential compensation device 120 to return the compensated measuring light to the laser generating device 100 for generating the laser frequency shift feedback effect. The laser frequency shift feedback effect has a high sensitivity characteristic, and can amplify the light intensity signal change brought by the fiber grating 123, thereby improving the sensitivity and resolution of the refractive index measuring device 10. The dual optical path differential compensation device 120 can also effectively reduce measurement errors caused by thermal drift of laser power, environmental disturbance and the like. Meanwhile, the laser emitting device 100 can emit the measurement light and receive the compensated measurement light, so that the receiving and transmitting integrated structure of the refractive index measurement device 10 is realized, the complexity of the refractive index measurement device 10 is greatly reduced, and the cost is reduced.
In one embodiment, the dual optical path differential compensation device 120 further comprises a first fiber polarization beam splitter 124. The first fiber polarization splitter 124 includes a first polarization port, a second polarization port, and a third polarization port. The first polarization port is the port c in fig. 2, the second polarization port is the port e in fig. 2, and the third polarization port is the port d in fig. 2. The first fiber polarization splitter 124 receives the measurement light through a third polarization port. The first fiber polarization beam splitter 124 is connected to the fiber circulator 110 through an optical fiber.
The first fiber polarization beam splitter 124 is used to split the measurement light into a first laser beam and a second laser beam. The first laser beam is output from the first polarization port and the second laser beam is output from the second polarization port. The first optical splitting and frequency shifting unit 121 is connected to the first polarization port, and is configured to perform differential frequency shifting on the first laser beam. Specifically, the first optical splitting frequency shift unit 121 and the first fiber polarization beam splitter 124 are connected by an optical fiber. Referring to fig. 3, the first optical frequency division and shift unit 121 includes a first acousto-optic frequency shifter 1211 and a second acousto-optic frequency shifter 1212. The first laser beam passes through the first acousto-optic frequency shifter 1211 to generate 0-level light and +1(-1) -level light, the +1(-1) -level light enters the second acousto-optic frequency shifter 1212 and then outputs-1 (+1) -level light, and the-1 (+1) -level light is the first laser beam after differential frequency shifting.
One end of the second optical splitting and frequency shifting unit 122 is connected to the second polarization port, and the other end is connected to the fiber grating 123. The second optical splitting and frequency shifting unit 122 is configured to perform differential frequency shifting on the second laser beam. Specifically, the second optical splitting frequency shift unit 122 is connected to the first fiber polarization beam splitter 124 through an optical fiber. Referring to fig. 4, the second optical frequency division shifting unit 122 includes a third acousto-optic frequency shifter 1221, a fourth acousto-optic frequency shifter 1222. The second laser beam passes through the third acousto-optic frequency shifter 1221 to generate 0-level light and +1(-1) -level light, the +1(-1) -level light enters the fourth acousto-optic frequency shifter 1222 to output-1 (+1) -level light, and the-1 (+1) -level light is the second laser beam after differential frequency shift.
The fiber grating 123 is used to induce a change in the intensity of the differentially shifted second laser beam after changing the surrounding medium. The fiber grating 123 is a sensitive unit of the refractive index measuring apparatus 10, and can cause the intensity of the second laser beam after the differential frequency shift to change by changing a medium around the fiber grating. The second laser beam output from the fiber grating 123 and the differentially shifted first laser beam output from the first optical splitting frequency shift unit 121 are combined and output, that is, the compensated measurement light. The fiber grating 123 may be a large-angle tilt grating, a small-angle tilt grating, a long-period grating, a D-type grating, a cladding corrosion-type fiber grating, etc., and the measurement sensitivity of different types of fiber gratings 123 is different. The sensitivity can be further improved by plating a metal film layer around the fiber grating 123. The embodiment of the present application does not specifically limit the type of the fiber grating 123. In one embodiment, the dual optical path differential compensation device 120 further comprises a second fiber polarization controller 125. The second fiber polarization controller 125 is disposed between the second optical splitter 122 and the fiber grating 123. The second fiber polarization controller 125 is connected to the fiber grating 123 through an optical fiber. The second optical fiber polarization controller 125 is connected to the second optical splitting frequency shift unit 122 through an optical fiber. The second fiber polarization controller 125 is used to change the polarization state of the second laser beam after performing the differential frequency shift.
The second laser beam emitted from the first fiber polarization beam splitter 124 is linearly polarized laser, the polarization direction is determined relative to the transmission fiber, but there may be an included angle between the polarization direction and the polarization direction of the fiber grating 123, and the second fiber polarization controller 125 may implement alignment of the two, so that the polarization state of the differentially frequency-shifted second laser beam incident to the fiber grating 123 is p-polarization state laser relative to the fiber grating 123. When the fiber grating 123 is a polarization sensitive device (e.g., a large-angle tilt grating, a small-angle tilt grating, a long-period grating, etc.), the fiber grating 123 may be more sensitive when the polarization state of the second laser beam after the differential frequency shift incident on the fiber grating 123 is adjusted to the p-polarization state.
In one embodiment, the dual optical path differential compensation device 120 further comprises a second fiber polarization beam splitter 126. The second fiber polarization splitter 126 includes a fourth polarization port, a fifth polarization port, and a sixth polarization port. The fourth polarization port is the port f in fig. 2, the fifth polarization port is the port g in fig. 2, and the sixth polarization port is the port g in fig. 2. The fourth polarization port is connected to the first optical division frequency shift unit 121. The fifth polarization port is connected to the fiber grating 123. The sixth polarization port is connected with the first circulator port. The first laser beam emitted from the first optical frequency-splitting shift unit 121 is input through the fourth polarization port, the second laser beam emitted from the fiber grating 123 is input through the fifth polarization port, and the two beams are combined and then output to the compensated measurement light through the sixth polarization port. The compensated measurement light returns to the optical fiber circulator 110 through the first circulator port, and returns to the laser emitting device 100 through the second circulator port, and generates a self-mixing interference effect (also called laser frequency shift feedback effect) with the original optical field of the laser emitting device 10 to modulate the output light intensity of the laser emitting device 10. The laser emitting device 10 emits the modulated measuring light through the second emitting port, and emits the modulated probe light through the first emitting port.
In one embodiment, refractive index measurement apparatus 10 further comprises a first fiber polarization controller 140. One end of the first optical fiber polarization controller 140 is connected to the third ring port, and the other end is connected to the dual optical path differential compensation device 120. The first optical fiber polarization controller 140 is connected with the optical fiber circulator 110 through an optical fiber. The first fiber polarization controller 140 is connected to the first fiber polarization splitter 124 through an optical fiber. The first fiber polarization controller 140 is used to change the polarization state of the measurement light. The measurement light output from the third circulator port of the fiber circulator 110 is elliptically polarized light. The first fiber polarization controller 140 may change the elliptically polarized light into linearly polarized light, so that the polarization direction of the measurement light may be adjusted by rotating the first fiber polarization controller 140. By rotating the first fiber polarization controller 140 to change the polarization direction of the measurement light, the first fiber polarization beam splitter 124 can split the measurement light into the first laser beam and the second laser beam with equal light intensity, thereby improving the accuracy of the refractive index measurement apparatus 10.
In one embodiment, the laser emitting device 100 includes a laser 101 and a fiber coupler 102. The laser 101 is used to emit a laser beam. The laser beam pattern emitted by the laser 101 may be a single longitudinal mode. The fiber coupler 102 is connected to the laser 10, and is configured to split the laser beam into measuring light and probe light. The laser 101 is further configured to receive the compensated measurement light fed back by the fiber coupler 102, perform light intensity modulation on the compensated measurement light, and emit a modulated laser beam.
Illustratively, the compensated measurement light is output from the sixth polarization port of the second fiber polarization beam splitter 126, and then returned to the fiber circulator 110 through the first circulator port and then returned to the fiber coupler 102 through the second circulator port. The laser 101 receives the compensated measurement light fed back by the fiber coupler 102, and the compensated measurement light and the original optical field of the laser 101 generate a self-mixing interference effect (also called laser frequency shift feedback effect) to modulate the output light intensity of the laser 101. The laser 101 outputs a modulated laser beam, the fiber coupler 102 receives and splits the modulated laser beam, and emits modulated measuring light through the second exit port and emits modulated probe light through the first exit port. The second exit port is the port b of the optical fiber coupler 102 in fig. 2, and the first exit port is the port a of the optical fiber coupler 102 in fig. 2.
In one embodiment, the data processing device 130 includes a photodetector 131, a signal processing unit 132, and a computer 133. The photodetector 131 is used to convert the modulated optical signal of the detection light into an electrical signal. The signal processing unit 132 is connected to the photodetector 131, and is configured to demodulate the electrical signal to obtain a voltage signal corresponding to the light intensity of the compensated measuring light. After the compensated measurement light returns to the laser 101, a self-mixing interference effect occurs between the compensated measurement light and the original optical field in the laser 101, and the laser 101 emits a modulated laser beam. The first laser beam emitted from the first optical splitter/frequency shifter 121 and the second laser beam emitted from the fiber grating 123 are combined to form compensated measurement light.
The first laser beam causes the output intensity of the laser 101 to be modulated according to the formula:
the second laser beam causes the output intensity modulation formula of the laser 101 to be:
where I is the stable output intensity of the laser 101 without modulation, and Δ I is the change in the output intensity of the laser 101 after modulation. G is the gain coefficient of the laser 101 to the compensated measuring light, and G is related to the relative magnitude of the relaxation oscillation frequency and the beam frequency shift quantity of the laser 101 and can reach a value of 106。G(Ω1) Is the gain factor, G (omega), of the laser 101 for the first laser beam2) Is the gain factor of the laser 101 for the second laser beam. t is time, κ is the feedback coefficient of the compensated measurement light, which is the ratio of the amplitudes of the returned and output light fields. Kappa1Is the feedback coefficient, κ, of the laser 101 to the first laser beam2Is the feedback coefficient of the laser 101 to the second laser beam. Phi is ar、φmIs a fixed phase offset of the signal; phi is a1Feeding back a phase for an external cavity corresponding to the first laser beam; phi is a2Feeding back the phase of the external cavity corresponding to the second laser beam; omega1Is the differential frequency shift quantity, omega, of the first acousto-optic frequency shifter and the second acousto-optic frequency shifter2Is the difference frequency shift quantity of the third acousto-optic frequency shifter and the fourth acousto-optic frequency shifter.
The gain coefficient G special for laser frequency shift feedback can amplify weak feedback signals, and can be generally 106The amplification of weak signals can be realized, so that the laser frequency shift feedback principle has high sensitivity. The modulated probe light is generated by the laser frequency shift feedback effect of the first laser beam, the second laser beam and the original optical field in the laser 101. The photodetector 131 converts the optical signal of the modulated detection light into an electrical signal. The signal processing unit 132 demodulates the electrical signal, and can accurately detect voltage signals corresponding to the light intensities of the first laser beam and the second laser beam from the modulated probe light. When the first medium is put around the fiber grating 123 in the refractive index measuring device 10, the signal processing unit 132 can obtain the sumAnd the light intensity of the first laser beam and the light intensity of the second laser beam corresponding to the first medium respectively correspond to the voltage signals. When a second medium is placed around the fiber grating 123 in the refractive index measuring apparatus 10, the signal processing unit 132 may obtain voltage signals corresponding to the light intensity of the first laser beam and the light intensity of the second laser beam corresponding to the second medium, respectively. In the embodiment of the present application, the wavelength of the measuring light is fixed when the medium around the fiber grating 123 is changed, that is, the refractive index measuring apparatus 10 measures the change of the refractive index when the medium is changed by measuring the light intensity change of the first laser beam and the light intensity change of the second laser beam at the same wavelength.
The computer 133 is connected to the signal processing unit 132 for determining the refractive index change according to the compensated voltage signal corresponding to the light intensity of the measuring light. The computer 133 may obtain the refractive index change based on the voltage signals corresponding to the light intensity of the first laser beam and the light intensity of the second laser beam respectively corresponding to the first medium, and the voltage signals corresponding to the light intensity of the first laser beam and the light intensity of the second laser beam respectively corresponding to the second medium. The voltage variation corresponding to the light intensity of the first laser beam can reflect the error signal variation of the refractive index measuring device 10 caused by the thermal drift of the power of the laser 101, the environmental disturbance and the like. The voltage change corresponding to the light intensity of the second laser beam can reflect the error signal change of the refractive index measuring device 10 caused by the power thermal drift of the optical device 101, the environmental disturbance and the like, and can also reflect the refractive index changes of the first medium and the second medium at the same time. Finally, the refractive index changes caused by different media are reflected through the difference of the voltage changes corresponding to the light intensities of the first laser beam and the second laser beam, and the measurement error of the refractive index measurement device 10 is compensated to a certain extent, so that the sensitivity and the resolution of the refractive index change measurement of the refractive index measurement device 10 can be improved.
The computer 133 may further calculate the sensitivity and the resolution of the refractive index measuring device 10 based on a voltage signal corresponding to the light intensity of the first laser beam and a voltage signal corresponding to the light intensity of the second laser beam corresponding to the first medium, a voltage signal corresponding to the light intensity of the first laser beam and a voltage signal corresponding to the light intensity of the second laser beam corresponding to the second medium, and a difference between the refractive index of the first medium and the refractive index of the second medium. The sensitivity of the refractive index measurement device 10 is:
where S is the sensitivity of the refractive index measurement device 10. And deltan is the difference between the refractive indexes of the first medium and the second medium. Delta U1The difference value between the voltage value corresponding to the light intensity of the first laser beam when the first medium is placed around the fiber grating 123 and the voltage value corresponding to the light intensity of the first laser beam when the second medium is placed around the fiber grating 123. Delta I2The difference value between the voltage value corresponding to the light intensity of the second laser beam when the first medium is placed around the fiber grating 123 and the voltage value corresponding to the light intensity of the second laser beam when the second medium is placed around the fiber grating 123.
Further, the resolution of the refractive index measurement apparatus 10:
wherein, VnS is the sensitivity of the refractive index measuring device 10 and R is the resolution of the refractive index measuring device 10 for the voltage jitter corresponding to the static intensity jitter of the laser 101. The refractive index measuring device 10 provided by the embodiment of the application can qualitatively measure the change of the refractive index of the medium to be measured, namely, the change trend of the medium to be measured can be measured, and has higher sensitivity.
The embodiment of the application also provides a refractive index measuring method which is applied to the refractive index measuring device 10. The refractive index measuring apparatus 10 includes a laser emitting device 100, a fiber circulator 110, a dual optical path differential compensation device 120, and a data processing device 130. The refractive index measurement method comprises the following steps:
the laser emitting device 100 emits the probe light through the first emitting port and emits the measurement light through the second emitting port;
the fiber optic circulator 110 receives the measurement light through the second circulator port and outputs the measurement light to the dual optical path differential compensation device 120 through the third circulator port;
the dual optical path differential compensation device 120 performs compensation processing on the received measurement light to obtain compensated measurement light, and inputs the compensated measurement light into the optical fiber circulator 110 through the first circulator port;
the laser emitting device 100 receives the compensated measuring light from the first circulator port of the optical fiber circulator 110, performs light intensity modulation based on the compensated measuring light, emits the modulated measuring light through the second exit port, and emits the modulated probe light through the first exit port;
the data processing device 130 receives the probe light from the first exit port and obtains a refractive index change according to the modulated probe light.
In the embodiment of the present application, the structure of the refractive index measurement apparatus 10 and the specific measurement process of the refractive index change may refer to the related descriptions of the foregoing embodiments, and the details of the embodiment of the present application are not repeated herein.
In the refractive index measurement method provided in the embodiment of the application, the laser emitting device 100 emits the measurement light through the second emitting port, the measurement light enters the dual optical path differential compensation device 120 through the optical fiber circulator 110, and the compensated measurement light is formed through the light splitting, the differential frequency shift and the optical fiber grating. The compensated measuring light returns to the laser emitting device 100 through the optical fiber circulator 110 to be subjected to light intensity modulation to form modulated detection light, the laser emitting device 100 emits the modulated detection light through the first emitting port, and the data processing device calculates the refractive index change according to the modulated detection light. The refractive index measuring method adopts the optical fiber circulator 110 and the dual optical path differential compensation device 120 to make the compensated measuring light return to the laser generating device 100 to generate the laser frequency shift feedback effect. The laser frequency shift feedback effect has a high sensitivity characteristic, and can amplify the light intensity signal change brought by the fiber grating 123, thereby improving the sensitivity and resolution of the refractive index measuring device 10. The dual optical path differential compensation device 120 can also effectively reduce measurement errors caused by thermal drift of laser power, environmental disturbance and the like. Meanwhile, the laser emitting device 100 can emit the measurement light and receive the compensated measurement light, so that the receiving and transmitting integrated structure of the refractive index measurement device 10 is realized, the complexity of the refractive index measurement device 10 is greatly reduced, and the cost is reduced.
In one embodiment, the dual optical path differential compensation device 120 includes a first optical splitter and frequency shift unit 121, a second optical splitter and frequency shift unit 122, and a first fiber polarization beam splitter 124, and the outputting the measurement light to the dual optical path differential compensation device 120 through a third circulator port includes:
the first fiber polarization beam splitter 124 receives the measurement light from the third circulator port, and splits the measurement light to obtain a first laser beam and a second laser beam;
the first fiber polarization beam splitter 124 inputs the first laser beam to the first optical division frequency shift unit 121 through the first polarization port, and inputs the second laser beam to the second optical division frequency shift unit 122 through the second polarization port. The first optical division frequency shift unit 121 performs differential frequency shift on the first laser beam, and the second optical division frequency shift unit 122 performs differential frequency shift on the second laser beam.
The dual optical path differential compensation device 120 further includes a fiber grating 123. The second laser beam after the differential frequency shift enters the fiber grating 123, and the light intensity is changed under the influence of the refractive index of the medium around the fiber grating 123. The first laser beam emitted from the first optical splitter/frequency shifter 121 and the second laser beam emitted from the fiber grating 123 are combined to form compensated measurement light. The compensated measurement light returns to the fiber optic circulator 110 through the first circulator port.
In one embodiment, calculating the refractive index change from the modulated probe light comprises:
converting the modulated optical signal of the detection light into an electrical signal;
demodulating the electric signal, and determining a voltage signal corresponding to the light intensity of the compensated measuring light;
and determining the refractive index change according to the voltage signal corresponding to the compensated light intensity of the measuring light.
It is to be understood that the modules mentioned in the above embodiments may also take other forms, not limited to the forms mentioned in the above embodiments, as long as they can achieve the corresponding functions.
In the description herein, references to the description of "some embodiments," "other embodiments," "desired embodiments," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the application. In this specification, a schematic description of the above terminology may not necessarily refer to the same embodiment or example.
The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.
The above-mentioned embodiments only express several embodiments of the present application, and the description thereof is more specific and detailed, but not construed as limiting the claims. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the concept of the present application, which falls within the scope of protection of the present application. Therefore, the protection scope of the present patent shall be subject to the appended claims.
Claims (10)
1. A refractive index measurement apparatus, comprising:
a laser emitting device (100) including a first emitting port and a second emitting port from which measurement light is emitted;
a fiber optic circulator (110) including a first circulator port, a second circulator port, and a third circulator port, the measurement light being input from the second circulator port and output from the third circulator port;
a dual optical path differential compensation device (120), one end of which is connected to the third circulator port and is used for receiving the measurement light, and the other end of which is connected to the first circulator port and is used for emitting the compensated measurement light to the optical fiber circulator (110), wherein the dual optical path differential compensation device (120) comprises a first optical division frequency shift unit (121), a second optical division frequency shift unit (122) and an optical fiber grating (123);
the laser emitting device (100) is further configured to receive the compensated measurement light through the second emitting port, perform light intensity modulation on the basis of the compensated measurement light, and emit the modulated probe light through the first emitting port;
a data processing device (130) connected to the first exit port.
2. The refractive index measurement apparatus of claim 1, wherein the dual optical path differential compensation apparatus (120) further comprises:
a first fiber optic polarization beam splitter (124) comprising a first polarization port, a second polarization port, and a third polarization port, the first fiber optic polarization beam splitter (124) receiving the measurement light through the third polarization port;
the first fiber polarization beam splitter (124) is configured to split the measurement light into a first laser beam and a second laser beam, the first laser beam being output from the first polarization port, the second laser beam being output from the second polarization port;
the first optical splitting frequency shift unit (121) is connected to the first polarization port, and is configured to perform differential frequency shift on the first laser beam; one end of the second optical splitting frequency shift unit (122) is connected with the second polarization port, the other end of the second optical splitting frequency shift unit is connected with the fiber bragg grating (123), and the second optical splitting frequency shift unit (122) is used for performing differential frequency shift on the second laser beam;
the fiber grating (123) is used for causing the intensity of the second laser beam after differential frequency shift to change after changing the surrounding medium.
3. The refractive index measurement apparatus of claim 2, wherein the dual optical path differential compensation apparatus (120) further comprises:
and the second optical fiber polarization controller (125) is arranged between the second optical splitting frequency shift unit (122) and the fiber grating (123) and is used for changing the polarization state of the second laser beam after differential frequency shift.
4. The refractive index measurement apparatus of claim 3, wherein the dual optical path differential compensation apparatus (120) further comprises:
the second optical fiber polarization beam splitter (126) comprises a fourth polarization port, a fifth polarization port and a sixth polarization port, the fourth polarization port is connected with the first optical splitting frequency shift unit (121), the fifth polarization port is connected with the fiber bragg grating (123), and the sixth polarization port is connected with the first circulator port.
5. The refractive index measurement apparatus of claim 1, further comprising:
and a first optical fiber polarization controller (140), one end of which is connected with the third annular port, and the other end of which is connected with the dual optical path differential compensation device (120), wherein the first optical fiber polarization controller (140) is used for changing the polarization state of the measuring light.
6. The refractive index measuring apparatus according to claim 1, wherein the laser emitting apparatus (100) comprises:
a laser (101) for emitting a laser beam;
a fiber coupler (102) connected to the laser (101) for splitting the laser beam into the measurement light and the probe light;
the laser (101) is further configured to receive the compensated measurement light fed back by the optical fiber coupler (102), perform light intensity modulation on the compensated measurement light, and emit a modulated laser beam.
7. The refractive index measurement device according to claim 1, wherein the data processing device (130) comprises:
a photodetector (131) for converting an optical signal of the modulated probe light into an electrical signal;
the signal processing unit (132) is connected with the photoelectric detector (131) and is used for demodulating the electric signal to obtain a voltage signal corresponding to the light intensity of the compensated measuring light;
and the computer (133) is connected with the signal processing unit (132) and is used for determining the refractive index change according to the voltage signal corresponding to the light intensity of the compensated measuring light.
8. A refractive index measurement method applied to a refractive index measurement apparatus (10), the refractive index measurement apparatus (10) including a laser emission device (100), a fiber circulator (110), a two-optical-path differential compensation device (120), and a data processing device (130), the method comprising: the laser emitting device (100) emits measuring light through a second emitting port;
the fiber optic circulator (110) receives the measurement light through a second circulator port and outputs the measurement light to the dual optical path differential compensation device (120) through a third circulator port;
the double-optical-path differential compensation device (120) performs compensation processing on the received measuring light to obtain compensated measuring light, and inputs the compensated measuring light into the optical fiber circulator (110) through a first circulator port;
the laser emitting device (100) receives the compensated measuring light from a first circulator port of the optical fiber circulator (110), and emits modulated detection light through a first emitting port after light intensity modulation is carried out on the basis of the compensated measuring light;
the data processing device (130) receives the modulated probe light from the first exit port and determines a refractive index change from the modulated probe light.
9. The refractive index measurement method according to claim 8, wherein the dual optical path differential compensation device (120) includes a first split frequency shift unit (121), a second split frequency shift unit (122), and a first fiber polarization beam splitter (124),
the outputting the measurement light to the dual optical path differential compensation device (120) through a third circulator port, comprising:
the first optical fiber polarization beam splitter (124) receives the measuring light from the third circulator port and splits the measuring light to obtain a first laser beam and a second laser beam;
the first fiber polarization beam splitter (124) inputs the first laser beam to the first optical division frequency shift unit (121) through a first polarization port, and inputs the second laser beam to the second optical division frequency shift unit (122) through a second polarization port.
10. The refractive index measurement method of claim 9, wherein said determining a refractive index change from said modulated probe light comprises:
converting the modulated optical signal of the detection light into an electrical signal;
demodulating the electric signal and determining a voltage signal corresponding to the light intensity of the compensated measuring light;
and determining the refractive index change according to the voltage signal corresponding to the light intensity of the compensated measuring light.
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