An angle measurement system and method based on microcavity optical frequency comb

Abstract

The present application relates to the field of optical angle measurement, in order to solve the problems of the existing optical measurement system, such as complex structure, great limitation, and unable to meet the large range, high precision absolute angle measurement, etc., and propose a kind of angle measurement system and measurement method based on microcavity optical frequency comb;Including microcavity optical frequency comb unit and the optical fiber collimating mirror, diffraction grating, focusing lens, optical fiber coupler, optical fiber and spectrometer arranged at its output;The optical fiber collimating mirror collimates and emits the high repetition rate optical frequency comb signal generated by the microcavity optical frequency comb unit to the diffraction grating;Then the first order diffraction beam diffracted by the diffraction grating is focused on its focal plane by the focusing lens, the optical fiber coupler is coaxially arranged with the focusing lens, and the incident end of the optical fiber coupler coincides with the focal point of the focusing lens, the output end of the optical fiber coupler is connected with the input end of the optical fiber, the output end of the optical fiber is connected with the spectrometer, the spectrometer distinguishes the transmitted optical comb spectral component, obtains the center frequency of the coupled beam spectrum, and then obtains the grating rotation angle.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical angle measurement, and in particular to an angle measurement system and method based on microcavity optical frequency comb. BACKGROUND

[0002] Angle is one of the basic quantities to describe the geometry or motion of an object; angle measurement plays an extremely important role in precision machining, micro-electro-mechanical systems, online detection, military, aviation and navigation, and communication.

[0003] As one of the commonly used angle measurement methods, optical angle measurement has the characteristics of non-contact, high accuracy and high sensitivity, and with the emergence of more high-quality and stable laser light sources, optical angle measurement is widely used in various fields.

[0004] The commonly used optical angle measurement methods include differential wavefront sensing method, laser interference method and optical autocollimation method. Among them, the laser autocollimator is widely used in optical autocollimation method for angle measurement. Although the laser autocollimator can provide high accuracy and measurement resolution, it uses single-wavelength laser as the light source, and is limited by the size of the light spot and the size of the sensitive area of the detector. The angle measurement range is only a few hundred angular seconds, which cannot meet the requirements of large-scale angle measurement.

[0005] In the prior art, femtosecond optical frequency comb is used to replace single-wavelength laser as the light source, and grating is used to replace plane mirror to improve the autocollimation angle measurement method. The method mainly uses a series of light patterns after diffraction of the femtosecond optical frequency comb to expand the measurement range. However, due to the small repetition frequency of the traditional femtosecond optical frequency comb, the focused light spots of the light patterns will overlap, and an additional F-P cavity is needed to filter the spectrum, which increases the complexity and instability of the overall structure of the system and also increases the system cost. At the same time, it can only be used for relative angle measurement and cannot realize absolute angle position measurement, which has certain limitations in practical application. SUMMARY

[0006] To solve the technical problems of the prior art, such as complex structure, poor stability, high cost and large use limitation of the optical autocollimation method, and the inability to meet the requirements of large-scale and high-precision absolute angle measurement, the present application provides an angle measurement system and method based on microcavity optical frequency comb.

[0007] The design idea of the present application is: based on the mechanism of self-collimation of the first-order diffraction beam; according to the diffraction theory, different longitudinal mode components in the microcavity optical frequency comb form a group of first-order diffraction beams with different diffraction angles after passing through the grating, and the size of the diffraction angle is related to the longitudinal mode frequency. Compared with the traditional laser autocollimator which can only detect a single reflected beam in a limited measurement range, the angle measurement method based on the microcavity optical frequency comb can measure the tilt angle of the grating in a larger measurement range by detecting the first-order diffraction beam group; the angle measurement range, i.e. the difference between the diffraction angles of the first and last order diffraction beams, is determined by the spectral range of the laser.

[0008] To achieve the above object, the technical solution of the present application is:

[0009] An angle measurement system based on a microcavity optical frequency comb, characterized in that it comprises a microcavity optical frequency comb unit, a fiber collimator arranged at the signal output end of the microcavity optical frequency comb unit, a diffraction grating, a focusing lens, a fiber coupler, a fiber connected to the output end of the fiber coupler, and a spectrometer connected to the output end of the fiber.

[0010] The microcavity optical frequency comb unit is used to generate a high-repetition-rate optical frequency comb signal.

[0011] The fiber collimator is used to collimate and emit the high-repetition-rate optical frequency comb signal generated by the microcavity optical frequency comb unit onto the diffraction grating.

[0012] The diffraction grating is used to diffract the high-repetition-rate optical frequency comb signal to generate first-order diffraction beams with different diffraction angles.

[0013] The focusing lens is used to focus the first-order diffraction beams with different diffraction angles on its focal plane to generate focal spots of different longitudinal mode components.

[0014] The fiber coupler is coaxially arranged with the focusing lens, and the incident end of the fiber coupler coincides with the focal point of the focusing lens. The fiber coupler is used to couple the first-order diffraction beams with different diffraction angles into the fiber.

[0015] The spectrometer is used to resolve the spectral components of the first-order diffraction beams transmitted by the fiber, obtain the center frequency of the first-order diffraction beams, and further obtain the rotation angle of the diffraction grating.

[0016] The fiber coupler is used to receive the part of the longitudinal mode components whose focal spots are located at the incident end of the fiber coupler.

[0017] The fiber is used to transmit the part of the longitudinal mode components received by the fiber coupler.

[0018] The spectrometer is used for measuring the rotation angle of the grating by distinguishing the spectral components of the comb light transmitted by the optical fiber and obtaining the center frequency of the spectrum of the coupled light beam.

[0019] Further, the diffraction grating is a reflective grating.

[0020] Further, the microcavity optical frequency comb unit generates a high repetition frequency optical frequency comb signal with a spectral range of 100-150 nm and a center wavelength of 1550-1565 nm.

[0021] Further, the high repetition frequency optical frequency comb signal light beam emitted by the optical fiber collimator intersects the laser incident point on the diffraction grating with the optical axis of the focusing lens at an angle in the range of 40°-80°.

[0022] Further, the focusing lens is an achromatic lens with a focal length in the range of 15-30 mm.

[0023] Meanwhile, the present application also proposes an angle measurement method based on a microcavity optical frequency comb, which adopts the above-mentioned angle measurement system based on a microcavity optical frequency comb, and the special feature thereof lies in comprising the following steps:

[0024] Step one, generating a high repetition frequency optical frequency comb signal through a microcavity optical frequency comb unit;

[0025] Step two, collimating the high repetition frequency optical frequency comb signal generated in step one through an optical fiber collimator and then emitting it to the diffraction grating;

[0026] Step three, diffracting the high repetition frequency optical frequency comb signal through the diffraction grating to generate a group of first-order diffraction beams with different diffraction angles, wherein the different diffraction angles correspond to different longitudinal mode components of the high repetition frequency optical frequency comb signal light beam, and the different diffraction angles focus on the focal plane of the focusing lens to generate equidistant focal spots;

[0027] When the diffraction grating rotates, the angle between the high repetition frequency optical frequency comb signal light beam emitted by the optical fiber collimator and the normal line of the diffraction grating changes, thereby moving the focal spots of the different diffraction angles on the focal plane of the focusing lens.

[0028] Step four, receiving part of the focal spots of the different diffraction angles through the optical fiber coupler, coupling the different diffraction angles into the optical fiber, and then transmitting them to the spectrometer through the optical fiber.

[0029] Step five, the spectrum components of the received first-order diffraction beams of different diffraction angles are distinguished by a spectrometer, the center frequency of the first-order diffraction beam spectrum is obtained, and thus the angle between the high-repetition-rate optical frequency comb signal light beam emitted by the fiber collimator and the normal line of the diffraction grating is obtained, and the measurement of the rotation angle of the diffraction grating is completed.

[0030] Further, in step five, the angle α between the high-repetition-rate optical frequency comb signal light beam of the fiber collimator and the normal line of the diffraction grating satisfies the following formula:

[0031]

[0032] Wherein, Φ is the angle between the high-repetition-rate optical frequency comb signal light beam emitted by the fiber collimator and the optical axis of the focusing lens, c is the speed of light in vacuum, g is the grating period, v i is the optical frequency corresponding to the i-th first-order diffraction beam.

[0033] The beneficial effects of the present application are as follows:

[0034] [1] The angle measurement system based on the microcavity optical frequency comb of the present application has a simple structure, is easy to install and adjust, greatly saves production cost, realizes the miniaturization of the angle measurement system, has high system integration, and can realize the requirements of large-range and high-precision absolute angle measurement.

[0035] [2] The microcavity optical frequency comb unit is used as an incident light source in the present application, which can effectively improve the miniaturization and system integration of the measurement system, and the wide spectrum characteristics of the microcavity optical frequency comb are also used to effectively guarantee the requirements of large-range and high-precision angle measurement.

[0036] [3] The achromatic lens is used as the focusing lens in the present application, which can effectively reduce the influence of chromatic aberration on the measurement results.

[0037] [4] The angle measurement method based on the microcavity optical frequency comb of the present application combines the manipulation of the diffraction beam spectrum by the diffraction grating with the frequency domain characteristics of the microcavity optical frequency comb, ingeniously uses the principle of laser collimation to convert the angle change into the spectral component change of the microcavity optical frequency comb, and completes the angle measurement through the discrimination of the spectral amplitude-frequency characteristics, thereby realizing the large-range absolute angle measurement. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 Fig. 1 is a structural schematic diagram of an angle measurement system based on a microcavity optical frequency comb according to the present application;

[0039] Figure 2 Fig. 3 is a spectral diagram of a microcavity optical frequency comb unit in an embodiment of the present application;

[0040] Figure 3A schematic diagram of a microcavity optical frequency comb-based angle measurement method of the present application;

[0041] Figure 4 A spectral component fitting distribution diagram of a spectrometer in an embodiment of the present application;

[0042] Figure 5 A schematic diagram of the relationship between the included angle a and the laser frequency in an embodiment of the present application;

[0043] Reference signs:

[0044] 1-microcavity optical frequency comb unit, 2-fiber collimator, 3-diffraction grating, 4-focusing lens, 5-fiber coupler, 6-optical fiber, 7-spectrometer. DETAILED DESCRIPTION

[0045] As shown in Figure 1 , a microcavity optical frequency comb-based angle measurement system, comprising a microcavity optical frequency comb unit 1 and a fiber collimator 2, a diffraction grating 3, a focusing lens 4, a fiber coupler 5, an optical fiber 6 and a spectrometer 7 arranged at the signal output end of the microcavity optical frequency comb unit 1;

[0046] As shown in Figure 2 , the microcavity optical frequency comb unit 1 is used to generate a high-repetition-rate optical frequency comb signal, the generated optical frequency comb signal has a repetition rate of 45-55GHz, a spectral range of 100-150nm and a center wavelength of 1550-1565nm, in this embodiment, the optical frequency comb signal has a repetition rate of 50GHz, a spectral range of 130nm and a center wavelength of 1560.2nm; the fiber collimator 2 is used to collimate and emit the high-repetition-rate optical frequency comb signal generated by the microcavity optical frequency comb unit 1 onto the diffraction grating 3;

[0047] The diffraction grating 3 is used to diffract the high-repetition-rate optical frequency comb signal emitted by the fiber collimator 2 to generate a first-order diffracted beam with different diffraction angles; in this embodiment, the diffraction grating 3 is a reflective grating with a grating period of 1.67μm;

[0048] The optical axis of the focusing lens 4 intersects the high-repetition-rate optical frequency comb signal beam emitted by the fiber collimator 2 at a laser incidence point on the diffraction grating 3, and the included angle is fixed at 67.61°; the focusing lens 4 is an achromatic lens with a focal length range of 30mm, and the focusing lens 4 is used to focus the first-order diffracted beams with different diffraction angles on the focal plane to generate focal spots of different longitudinal mode components.

[0049] The fiber coupler 5 is coaxially arranged with the focusing lens 4, and the incident end of the fiber coupler 5 coincides with the focal point of the focusing lens 4, and the fiber coupler 5 is used to receive the part of the longitudinal mode components of the focal spot located at the incident end of the fiber coupler 5; the output end of the fiber coupler 5 is connected with the input end of the optical fiber 6, and is used to transmit the part of the longitudinal mode components received by the fiber coupler 5; the output end of the optical fiber 6 is connected with the input end of the optical spectrum analyzer 7, and the optical spectrum analyzer 7 is used to obtain the center frequency of the spectrum of the coupled light beam by distinguishing the spectrum components of the optical comb transmitted by the optical fiber 6, so as to realize the measurement of the rotation angle of the grating.

[0050] Meanwhile, the embodiment also proposes a kind of angle measurement method based on microcavity optical frequency comb, comprising the following steps:

[0051] Step one, generate high-repetition optical frequency comb signal meeting system requirements through microcavity optical frequency comb unit 1;

[0052] Step two, collimate the high-repetition optical frequency comb signal generated in step one by fiber collimator 2, and emit to the diffraction grating 3;

[0053] Step three, diffract the high-repetition optical frequency comb signal by the diffraction grating 3, generate a group of first-order diffracted beams with different diffraction angles, and different diffraction angles of the first-order diffracted beams correspond to different longitudinal mode components of the high-repetition optical frequency comb signal beam;Different diffraction angles of the first-order diffracted beams are focused on the focal plane of the focusing lens 4, and generate equidistant focal spots;

[0054] When the diffraction grating 3 rotates, the angle between the high-repetition optical frequency comb signal beam emitted by the fiber collimator 2 and the normal line of the diffraction grating 3 also changes, so that the focal spot of the first-order diffracted beam with different diffraction angles moves on the focal plane of the focusing lens 4;

[0055] Step four, receive part of the first-order rotating diffracted beams with different frequencies by the fiber coupler 5, then couple into the optical fiber 6, and then transmit to the optical spectrum analyzer 7 through the optical fiber 6;

[0056] Step five, distinguish the spectrum components of the received part of the first-order diffracted beams by the optical spectrum analyzer 7, obtain the center frequency of the spectrum of the part of the first-order diffracted beams, so as to obtain the angle α between the high-repetition optical frequency comb signal beam emitted by the fiber collimator 2 and the normal line of the diffraction grating 3, and complete the measurement of the rotation angle of the diffraction grating 3. Figure 4 As shown in the figure, it is a spectrum component fitting distribution diagram of the optical spectrum analyzer, Figure 5 It is a diagram of the relationship between the angle α and the laser frequency.

[0057] As Figure 3As shown, the first-order diffraction beams with different diffraction angles can be obtained by the diffraction grating 3, i is a certain one of the first-order diffraction beams in the plurality of first-order diffraction beams received by the fiber coupler 5 and transmitted to the spectrometer 7, and a is the included angle between the high-repetition-rate optical frequency comb signal light beam emitted by the fiber collimator and the normal line of the diffraction grating.

[0058] β i represents the diffraction angle of the i-th first-order diffraction beam relative to the normal line of the grating.

[0059] When the fiber collimator 2 and the focusing lens 4 are fixed, the included angle between the emission direction of the fiber collimator 2 and the optical axis of the focusing lens 4 is fixed and represented as Φ, and when the i-th first-order diffraction beam is aligned with the optical axis of the focusing lens 4, it can be obtained from the angle relationship that Φ = a + β. i i Therefore, according to the grating equation:

[0060]

[0061] It can be deduced that the included angle a between the high-repetition-rate optical frequency comb signal light beam emitted by the fiber collimator 2 and the normal line of the diffraction grating 3 satisfies the following formula:

[0062]

[0063] Wherein: Φ is the included angle between the high-repetition-rate optical frequency comb signal light beam emitted by the fiber collimator 2 and the optical axis of the focusing lens 4, c is the speed of light in vacuum, g is the grating period, v i is the optical frequency corresponding to the i-th first-order diffraction beam.​

Claims

1. A method for angle measurement based on microcavity optical frequency comb, characterized in that, The method comprises the following steps: Step one, build the angle measurement system of microcavity optical frequency comb, the angle measurement system of microcavity optical frequency comb includes microcavity optical frequency comb unit (1) and the fiber collimator (2) arranged in the signal output end of microcavity optical frequency comb unit (1), the diffraction grating (3), the focusing lens (4), the fiber coupler (5), the optical fiber (6) connected in the output end of fiber coupler (5) and the optical spectrum instrument (7) connected with the output end of optical fiber (6) are sequentially arranged on the emergent light path of fiber collimator (2); High repetition rate optical frequency comb signal is generated by microcavity optical frequency comb unit (1); Step two, the high repetition rate optical frequency comb signal generated in step one is collimated and emitted to the diffraction grating (3) after collimating by the fiber collimator (2); The high repetition rate optical frequency comb signal beam emitted by the fiber collimator (2) and the optical axis of the focusing lens (4) intersect at the laser incident point on the diffraction grating (3), and the included angle Φ between them is any fixed value in the range of 40°-80°; Step three, the high repetition rate optical frequency comb signal is diffracted by the diffraction grating (3) to generate a group of first-order diffraction beams with different diffraction angles, and different diffraction angles correspond to different longitudinal mode components of the high repetition rate optical frequency comb signal beam; different diffraction angles of the first-order diffraction beam are focused on the focal plane of the focusing lens (4) to generate equidistant focal spots; Step four, the focal spot of the first-order diffraction beam with different diffraction angles is received by the fiber coupler (5), and the first-order diffraction beam with different diffraction angles is coupled into the optical fiber (6), and then transmitted to the optical spectrum instrument (7) through the optical fiber (6); Step five, the optical spectrum component of the received first-order diffraction beam with different diffraction angles is distinguished by the optical spectrum instrument (7), the center frequency of the first-order diffraction beam spectrum is obtained, and the included angle between the high repetition rate optical frequency comb signal beam emitted by the fiber collimator (2) and the normal line of the diffraction grating (3) is obtained, so that the measurement of the rotation angle of the diffraction grating (3) is completed; The included angle α between the high repetition rate optical frequency comb signal beam emitted by the fiber collimator (2) and the normal line of the diffraction grating (3) satisfies the following formula: Wherein: Φ is the angle between the high repetition rate optical comb signal light beam emitted by the optical fiber collimator (2) and the optical axis of the focusing lens (4), c is the speed of light in vacuum, g is the grating period, v i is the optical frequency corresponding to the i-th first-order diffracted light beam.

2. The angle measurement method based on microcavity optical frequency comb according to claim 1, characterized in that: The microcavity optical frequency comb unit (1) is used to generate high repetition rate optical frequency comb signal; The fiber collimator (2) is used to collimate and emit the high repetition rate optical frequency comb signal generated by the microcavity optical frequency comb unit (1) to the diffraction grating (3); the diffraction grating (3) is used to diffract the high repetition rate optical frequency comb signal to generate first-order diffraction beams with different diffraction angles; The focusing lens (4) is used to focus the first-order diffraction beams with different diffraction angles on its focal plane to generate focal spots of different longitudinal mode components; the fiber coupler (5) is coaxially arranged with the focusing lens (4), and the incident end of the fiber coupler (5) coincides with the focal point of the focusing lens (4); the fiber coupler (5) is used to couple the first-order diffraction beams with different diffraction angles into the optical fiber (6). The spectrometer (7) is used for resolving the spectral components of the first-order diffracted light beam transmitted by the optical fiber (6), obtaining the center frequency of the first-order diffracted light beam, and further obtaining the rotation angle of the diffraction grating (3).

3. The angle measurement method based on the microcavity optical frequency comb according to claim 2, characterized in that: The diffraction grating (3) is a reflective grating.

4. The angle measurement method based on the microcavity optical frequency comb according to claim 3, characterized in that: The optical frequency comb signal generated by the microcavity optical frequency comb unit (1) has a repetition frequency of 45-55 GHz, a spectral range of 100-150 nm, and a center wavelength of 1550-1565 nm.

5. The angle measurement method based on the microcavity optical frequency comb according to claim 4, characterized in that: The focusing lens (4) is an achromatic lens, and the focal length range satisfies 15-30 mm.

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