CN114705136B - Auto-collimation absolute angle measurement method and system based on spectrum resolution technology - Google Patents
Auto-collimation absolute angle measurement method and system based on spectrum resolution technology Download PDFInfo
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Abstract
The invention relates to an auto-collimation absolute angle measurement method and system based on a spectrum resolution technology, wherein the method comprises the following steps: the optical frequency comb transmits optical pulses containing a plurality of longitudinal modes to the optical fiber circulator; the light pulse guided in by the optical fiber circulator is transmitted to the grating by the optical fiber collimating mirror, and a group of first-order diffracted light beams with different diffraction angles are generated after being diffracted by the grating; when the included angle between the grating normal and the incident beam is changed, the incident beam with a certain spectral width can be recoupled into the fiber collimating mirror and emitted to the fiber circulator after diffraction of the grating and partial longitudinal mode component; the measurement of the included angle between the grating normal and the incident beam is realized by the resolution of the optical comb spectral components derived by the optical fiber circulator. The invention organically combines the control of the grating on the spectrum of the diffracted light beam with the frequency domain characteristic of the optical frequency comb, converts the angle change into the spectral component change of the optical frequency comb, and completes the absolute measurement of the included angle between the incident light beam and the normal line of the grating by distinguishing and analyzing the spectral amplitude and frequency characteristics.
Description
Technical Field
The invention relates to an auto-collimation absolute angle measurement method and system based on a spectrum resolution technology, and relates to the field of optical precision measurement.
Background
The angle measurement has wide application in the fields of precision manufacturing and processing, satellite antenna measurement, synthetic aperture optical system assembly and the like. In order to meet the requirement of high-performance angle measurement, optical non-contact angle measurement methods such as auto-collimation angle measurement, differential wavefront sensing, multi-target laser interference and the like have been developed.
The autocollimation goniometry method is usually used as a commercial standard method to measure the accuracy of other goniometry methods due to its high accuracy and measurement resolution, but due to the limitation of the aperture of the objective lens, the angular measurement range can only reach hundreds of angular seconds. The differential wavefront sensing method can only detect effective interference signals within a small rotation range. The multi-target laser interferometry requires a plurality of target mirrors to be installed on the measured object, and the complexity of the system is increased. In addition, the conventional optical interference measurement method is also affected by phase ambiguity, and only incremental measurement can be realized, and optical continuity cannot be cut off, which is very inconvenient for many applications.
In the prior art, an autocollimator causes alignment errors of a laser source and an autocollimation unit in the assembling process, so absolute measurement in a complete sense cannot be realized, namely, an included angle between a normal line of a measured mirror and an incident beam is measured, but only angle variation in a certain range can be measured, so that the method is excluded from the applications of measuring the surface direction of a spliced lens, measuring the absolute attitude of a moving object, resetting measurement after restarting a system in the precision manufacturing and processing processes, and the like.
Disclosure of Invention
In view of the above problems, the present invention provides a method and a system for auto-collimation absolute angle measurement based on spectrum analysis technology, which can realize large-scale, dynamic and high-precision.
In a first aspect, the present invention provides an auto-collimation absolute angle measurement method based on a spectrum resolution technology, the method comprising:
the optical frequency comb transmits light pulses containing a plurality of longitudinal modes to the optical fiber circulator;
the light pulse introduced by the optical fiber circulator is transmitted to the grating by the optical fiber collimating mirror, and a group of first-order diffracted light beams with different diffraction angles are generated after the light pulse is diffracted by the grating;
when the included angle between the grating normal and the incident beam is changed, the incident beam with a certain spectral width can be recoupled into the fiber collimating mirror through the partial longitudinal mode component after the grating diffraction and is transmitted to the fiber circulator;
the center frequency of the coupled light beam spectrum is obtained through the resolution of the optical comb spectral components derived by the optical fiber circulator, and further the measurement of the included angle between the grating normal and the incident light beam is realized.
Furthermore, the grating normal and the light-emitting direction of the fiber collimator, i.e. the incident beam direction, have an initial angle.
Further, the spectral distribution of the coupled beam is at the center frequency f c Approximately symmetrically distributed, positive first-order diffraction angle beta corresponding to longitudinal mode of optical frequency comb spectrum range i And the diffraction light beam corresponding to the longitudinal mode is approximately parallel to the incident light beam direction and returns when the incidence angle is exactly equal to the incidence angle alpha.
Further, the included angle between the grating normal and the incident beam is further obtained by coupling the center frequency of the light beam spectrum:
where alpha is the angle between the normal of the grating and the incident beam, c is the speed of light, g is the period of the grating, f c A central optical frequency.
Further, the grating adopts a reflective grating.
In a second aspect, the present invention also provides an auto-collimating absolute goniometry system, the system comprising:
a single optical comb for emitting an optical pulse having a plurality of longitudinal modes;
the optical fiber circulator is used for leading in or leading out an optical signal;
the optical fiber collimating mirror is used for collimating and transmitting the optical signal guided by the optical fiber circulator;
the grating is used for enabling part of longitudinal mode components in first-order diffraction beams with different diffraction angles generated after the optical signals emitted by the fiber collimator mirror are diffracted to return to the fiber circulator through the fiber collimator mirror;
and the spectrum analyzer is used for measuring an included angle between the grating normal and an incident beam through distinguishing and analyzing optical comb spectral components led out by the optical fiber circulator.
In a third aspect, the present invention further provides an auto-collimation absolute goniometry system, comprising:
a dual optical comb for transmitting an optical pulse having a plurality of longitudinal modes;
the optical fiber circulator is used for leading in or leading out an optical signal;
the optical fiber collimating mirror is used for collimating and transmitting the optical signal guided by the optical fiber circulator;
the grating is used for diffracting the optical signal emitted by the fiber collimating mirror to generate partial longitudinal mode components in first-order diffraction beams with different diffraction angles, and returning the partial longitudinal mode components to the fiber circulator through the fiber collimating mirror;
and the signal processing device is used for distinguishing and analyzing the optical comb spectral components led out by the optical fiber circulator through a double optical comb spectrum distinguishing and analyzing technology, so that the measurement of the included angle between the grating normal and the incident beam is realized.
Further, the double-optical-frequency comb comprises two optical-frequency combs with a small repetition frequency difference, and the first optical-frequency comb and the second optical-frequency comb are combined by an optical fiber coupler and then sent to the optical fiber circulator.
Further, the optical fiber grating noise suppression device further comprises a double optical comb noise suppression unit, wherein the double optical comb noise suppression unit adopts tight locking or non-tight locking.
Further, the grating adopts a reflective grating.
Due to the adoption of the technical scheme, the invention has the following advantages:
1. the invention organically combines the control of the grating on the spectrum of the diffracted light beam with the frequency domain characteristic of the optical frequency comb, skillfully utilizes the principle of the self-collimation of the first-order diffracted light beam of the grating to convert the angle change into the spectral component change of the optical frequency comb, completes the absolute measurement of the included angle between the incident light beam and the normal line of the grating by distinguishing and analyzing the spectral amplitude frequency characteristic, and ensures the realization of the wide-range angle measurement by the wide-spectrum characteristic of the optical frequency comb.
2. The invention takes the double-optical comb spectrum precise resolution technology as the method for measuring the spectrum amplitude-frequency characteristic, can realize the dynamic high-precision reconstruction of the diffraction spectrum, and provides a key technical support for the dynamic high-precision measurement of the angle value.
In conclusion, the invention can be widely applied to absolute angle measurement.
Drawings
Various additional advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the invention. Like reference numerals refer to like parts throughout the drawings. In the drawings:
fig. 1 is a schematic diagram of a single optical comb absolute type precise angle measurement method according to an embodiment of the present invention.
Fig. 2 shows the spectral distribution of the coupled light beam according to the incident angle α of the embodiment of the present invention.
Fig. 3 is a schematic diagram of an absolute precision angle measurement method by a double optical comb method according to an embodiment of the present invention.
FIG. 4 is a schematic diagram of a dual optical comb measurement according to an embodiment of the present invention, wherein (a) is a schematic diagram of time domain linear sampling; and (b) is a frequency domain multi-heterodyne interference schematic diagram.
Detailed Description
It is to be understood that the terminology used herein is for the purpose of describing particular example embodiments only, and is not intended to be limiting. As used herein, the singular forms "a", "an" and "the" may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms "comprises," "comprising," "including," and "having" are inclusive and therefore specify the presence of stated features, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and/or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order described or illustrated, unless specifically identified as an order of performance. It should also be understood that additional or alternative steps may be used.
For convenience of description, spatially relative terms, such as "inner", "outer", "lower", "upper", and the like, may be used herein to describe one element or feature's relationship to another element or feature as illustrated in the figures. Such spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures.
The invention provides an auto-collimation absolute angle measurement method and system based on a spectrum resolution technology, wherein the method comprises the following steps: the optical frequency comb transmits optical pulses containing a plurality of longitudinal modes to the optical fiber circulator; the light pulse introduced by the optical fiber circulator is transmitted to the grating by the optical fiber collimating mirror, and a group of first-order diffracted light beams with different diffraction angles are generated after the light pulse is diffracted by the grating; when the included angle between the grating normal and the incident beam is changed, the incident beam with a certain spectral width can be recoupled into the fiber collimating mirror through the partial longitudinal mode component after the grating diffraction and is transmitted to the fiber circulator; the center frequency of the coupled light beam spectrum is obtained through the resolution of the optical comb spectral components derived by the optical fiber circulator, and further the measurement of the included angle between the grating normal and the incident light beam is realized. Therefore, the invention organically combines the control of the grating on the spectrum of the diffracted light beam with the frequency domain characteristic of the optical frequency comb, skillfully utilizes the principle of the self-collimation of the grating first-order diffracted light beam, converts the angle change into the spectral component change of the optical frequency comb, and completes the absolute measurement of the included angle between the incident light beam and the normal line of the grating by the resolution of the amplitude-frequency characteristic of the spectrum.
Exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. While exemplary embodiments of the invention are shown in the drawings, it should be understood that the invention can be embodied in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.
The optical frequency comb is used as a precision optical ruler of a frequency domain and has a series of stable frequency components in a wide spectral range. The emergence of the optical frequency comb promotes the development of the field of geometric quantity measurement, provides a new development direction for the geometric quantity measurement, and also initially shows the prospect in the aspect of absolute measurement of the angle quantity.
The auto-collimation absolute angle measurement method provided by the embodiment is based on a mechanism of auto-collimation and diffraction of first-order diffracted light beams, different longitudinal mode components in the optical frequency comb form a group of first-order diffracted light beams with different diffraction angles in space after passing through the grating, and the diffraction angle of the first-order diffracted light beams depends on the longitudinal mode frequency of the first-order diffracted light beams. Assuming that the frequency of the optical frequency comb is f in the spectrum range in the initial state i Positive first-order diffraction angle beta corresponding to the longitudinal mode of (1) i And when the diffraction beam corresponding to the longitudinal mode is exactly equal to the incident angle alpha, the diffraction beam corresponding to the longitudinal mode returns in the original path parallel to the incident beam direction, is coupled by the fiber collimator again, and is finally collected through the fiber circulator. Because of the core diameter size of the fiber, there is a certain spectral width of the light beam re-coupled into the fiber. As shown in fig. 1, when the diffraction angle is beta i The coupling efficiency corresponding to this longitudinal mode is highest just as much as the incident angle α. The larger the included angle between the diffracted beam and the incident beam is, the larger the deviation between the diffracted beam and the fiber core of the optical fiber after being focused by the optical fiber collimating lensLarge, the lower the corresponding coupling efficiency. Ignoring the original spectral distribution of the coupled beam (the coupled spectral range is small, and the intensity of the coupled beam can be approximated to be constant over the spectral range of the coupled beam), the spectral distribution of the coupled beam is theoretically at the frequency f i Approximately symmetrically distributed about a center frequency. When the grating rotates, because the incident angle changes, the spectral component of the coupled light beam correspondingly changes, the absolute angle measurement method provided by the embodiment realizes the accurate measurement of the included angle α between the grating normal and the incident light beam by the precise resolution of the spectral component of the optical comb, and the absolute angle measurement principle of the embodiment is as follows:
diffraction angle beta of ith longitudinal mode in optical frequency comb according to grating equation i With longitudinal mode frequency f i Satisfies the following relation:
wherein c is the speed of light, g is the grating period, and α is the angle between the grating normal and the incident beam.
The angle between the propagation direction of the diffracted beam corresponding to the ith longitudinal mode and the incident beam can be expressed as:
θ i ＝β i -α (2)
the diffracted beam of each longitudinal mode is a gaussian beam with a certain radius, and each gaussian beam can be regarded as the superposition of a plurality of plane waves propagating in different directions. For a plane wave with an included angle theta between the propagation direction and the emergent light, the plane wave is focused by the optical fiber collimating lens with the focal length f, and the distance of the focusing position deviating from the center of the optical fiber core can be expressed as follows:
y＝fθ (3)
to calculate the coupling efficiency, the coupling parameter γ of the ith longitudinal mode is defined according to equation (4) i :
Wherein, ω is L Is a diffraction gaussianRadius of spot, omega, of light beam propagating to front surface of collimator 0 Is the mode field radius of the fiber.
The coupling efficiency etai (y) corresponding to the plane wave with the focal position deviated from the center of the fiber core by the distance y for the ith longitudinal mode can be calculated according to the optical fiber coupling efficiency formula, as shown in the formula (5):
where ρ is an integral variable, J 0 Is a zero order Bessel function and d is the sign of the integral.
A certain longitudinal mode is set to be f i The Gaussian beam is decomposed into a series of superposition of plane waves, wherein the distance from a convergent point to the center of the fiber core of the optical fiber after the plane waves with the same propagation direction as the original Gaussian beam pass through the lens is shown in a formula (6):
y i ＝fθ i (6)
longitudinal mode frequency of f i Overall coupling efficiency of gaussian beam<η i >Can be expressed as a weighted integral of the coupling efficiency of these plane waves, as shown in equation (7):
wherein A is i (y i And y) is the weight of the plane wave in each direction.
According to the angular spectrum principle, it can be expressed as formula (8):
substituting the formulas (5) and (8) into (7) to obtain the longitudinal mode frequency f i Overall coupling efficiency of gaussian beam<η i >。
Simulating the total coupling efficiency of each longitudinal mode of the optical frequency comb under different incidence angles alpha, wherein the simulation parameters are as follows: grating period 1 μm, lightThe distance from the grid to the front surface of the optical fiber collimating mirror is 0.2m, the focal length of the optical fiber collimating mirror is 37.13mm, the diameter of a waist spot of a Gaussian beam emitted by the optical fiber collimating mirror is 7mm, and the distance from the waist spot to the front surface of the optical fiber collimating mirror is 37.2mm; the core diameter of the single-mode fiber is 8.5 μm, and the mode field diameter in the fiber is 10.1 μm. As shown in fig. 2, when α is 51.78 °, 51.79 °, 51.80 °, and 51.81 °, the normalized spectral distribution of the coupled light beam, i.e., the coupling efficiency distribution of each longitudinal mode of the optical comb at different angles, is obtained. The spectral ranges of the corresponding coupling entering fibers at different angles are different, and the coupling efficiency at different frequencies is also different. It can be verified by the formula (7) that within the measurement range, the longitudinal mode frequency with the highest coupling efficiency in the spectrum coupled into the optical fiber is the longitudinal mode with the diffraction direction retroreflected parallel to the incident light beam direction. In the actual measurement process, the longitudinal mode frequency corresponding to the highest spectral coupling efficiency point, namely the central optical frequency f can be determined through a centroid algorithm c ：
Wherein i is the serial number of the longitudinal mode of the coupling spectrum, and N is the number of the longitudinal mode.
The method for calculating the center optical frequency is not limited in this embodiment, and the centroid method of formula (9) may be used, or the highest point may be directly calculated or other methods such as gaussian fitting may be used. The obtained central optical frequency f c The angle α between the normal of the grating and the incident beam can be calculated as shown in equation (10) by substituting the longitudinal mode frequency of the parallel retroreflection into the grating diffraction equation:
example 1: based on the above principle, the implementation process of the auto-collimation absolute angle measurement method provided by this embodiment includes:
s1, transmitting an optical pulse containing a plurality of longitudinal modes to an optical fiber circulator by an optical frequency comb;
s2, light pulses guided in by the optical fiber circulator are transmitted to a grating through an optical fiber collimating mirror, and a group of first-order diffracted light beams with different diffraction angles are generated after diffraction of the grating;
s3, when the included angle between the normal of the grating and the incident beam is changed, the incident beam with a certain spectral width can be recoupled into the optical fiber collimating mirror through partial longitudinal mode components after diffraction of the grating and is emitted to the optical fiber circulator;
and S4, acquiring the central frequency of the coupled light beam through resolution of the optical comb spectral component derived by the optical fiber circulator, and further realizing measurement of an included angle between the grating normal and the incident light beam.
Example 2: as shown in fig. 1, the auto-collimation absolute angle measurement system proposed in this embodiment includes a single optical comb 1, a fiber circulator 2, a fiber collimator 3, and a reflective grating 4.
The normal of the reflective grating 4 and the light emitting direction of the fiber collimator 3, i.e. the incident light beam direction, form a certain initial angle. In the process of angle measurement, after an incident beam with a certain spectral width is diffracted by the reflective grating 4, part of longitudinal mode components can be recoupled into the optical fiber collimating mirror 3 approximately parallel to the incident direction all the time, and the effectiveness of measurement is ensured.
The single optical comb 1 emits light pulse containing a plurality of longitudinal modes to the optical fiber circulator 2;
the light pulse guided in by the optical fiber circulator 2 is transmitted to the reflective grating 4 through the optical fiber collimating mirror 3, and a group of first-order diffracted light beams with different diffraction angles are generated after being diffracted by the reflective grating 4;
when the included angle between the normal of the reflective grating 4 and the incident beam is changed, a part of longitudinal mode components of the incident beam with a certain spectral width after being diffracted by the reflective grating 4 can be recoupled into the optical fiber collimating mirror 3 and transmitted to the optical fiber circulator 2, and an optical signal led out by the optical fiber circulator 2 is transmitted to the optical spectrum analyzer 5 for performing resolution and calculation on optical comb spectral components.
Because the single optical comb 1 comprises a plurality of equally spaced longitudinal modes, a group of spatially separated first-order diffracted light beams can be generated after diffraction by the reflective optical grating 4. When the included angle between the normal of the reflective grating 4 and the incident beam is changed, the diffraction angles corresponding to all the longitudinal modes are changed, and the spectral components coupled into the optical fiber are also changed. Based on the fiber coupling characteristic, the longitudinal mode coupling efficiency of the original path returning completely parallel to the incident beam direction is the highest. Based on a grating diffraction formula, an included angle alpha between a grating normal line and an incident beam can be accurately obtained by calculating the central frequency of a coupled beam, and the wide spectral range of the optical frequency comb ensures the realization of wide-range angle measurement.
Example 3: the difference between this embodiment and embodiment 2 is that, as shown in fig. 3, this embodiment adopts a dual optical comb, which includes a first optical frequency comb 5 and a second optical frequency comb 6, the first optical frequency comb 5 and the second optical frequency comb 6 are combined by an optical fiber coupler 7 and then sent to an optical fiber circulator 2 to be led out, and are collimated by an optical fiber collimator 3 and then sent to a reflective optical grating 4, an optical signal led out by the optical fiber circulator 2 is sent to a signal processing device 8 for performing resolution and calculation on optical comb spectral components, the signal processing device 8 includes a detector 81, a filter 82 and a processor 83, and the specific process of performing resolution and calculation on optical comb spectral components is not described in detail.
Preferably, the dual optical comb system of the present embodiment may use two optical combs with slightly different repetition frequencies as the light source, wherein the first optical comb 5 is a signal optical comb with repetition frequency f r1 The second optical frequency comb 6 is a local oscillator optical comb, and the repetition frequency is f r2 ＝f r1 +Δf r . From the time domain perspective, since the two optical frequencies have different comb frequencies, as shown in the upper part of fig. 4 (a), the signal pulse and the local oscillator pulse will be periodically overlapped and dislocated in the time domain, and each measurement period (T) is provided update ＝1/Δf r ) A cross-correlation interference signal as shown in fig. 4 (a) will be generated. Considering from the frequency domain, it can be understood that the process of vertical mode heterodyne of the first optical-frequency comb 5 and the nearest second optical-frequency comb 6 as shown in the upper part of fig. 4 (b) transfers the information of the optical frequency domain to the radio frequency domain. In actual measurement, the time domain interference signal shown in fig. 4 (a) is subjected to fourier transform, the radio frequency domain spectrum shown below fig. 4 (b) is directly obtained, and then the radio frequency domain spectrum is subjected to a scale factor f 1 /Δf r Amplifying to obtain corresponding optical spectrum signals, mainly focusing on the information of the intensity spectrum in the embodiment, and accurately calculating the center frequency f of the spectrum by using a dual-optical comb intensity spectrum discrimination technology c And then, the angle value is calculated according to the formula (10), and in order to realize accurate measurement and tracing of the optical frequency, the embodiment requires that both the repetition frequency and the offset frequency of the two optical frequency combs be locked.
Further, in a typical optical fiber dual-optical comb system with full locking of the repetition frequency and the offset frequency, the line width of the comb teeth of the optical frequency comb is in the order of 10 to 100kHz, the line width of the comb teeth transmitted to the sub-frequency comb after the multi-longitudinal mode heterodyne interference of the dual-optical comb is also in the order of 10 to 100kHz, and the interval between the comb teeth of the sub-frequency comb is only in the order of kHz, so that the longitudinal modes of the sub-frequency comb cannot be independently distinguished, and the corresponding frequency spectrum measurement accuracy is low. To solve this problem, the technique of dual optical comb noise suppression can be used to realize the high mutual coherence of the two optical frequency combs, thereby providing technical support for the high-precision spectral measurement of this embodiment. Further, the embodiment further includes a dual optical comb noise suppression unit, the dual optical comb noise suppression unit adopts tight locking or non-tight locking, and the non-tight locking method includes three methods, namely a synchronous locking method, a digital compensation method and a self-compensation method. The embodiment does not restrict the type of noise suppression technology, and noise suppression is not necessary, but the measurement precision is higher after suppression, and the method can be selected according to actual needs.
The dynamic angle measuring range depends on the spectral width of the optical frequency comb and the period value of the grating, the measuring accuracy depends on the measuring precision of the spectral center frequency of the coupled light beam and the period value of the grating, and the maximum measuring speed is equal to the difference of the repetition frequencies of the two optical frequency combs. Taking the optical frequency comb spectral bandwidth range from 1550nm to 1590nm as an example, assuming that the grating period is 1 μm, the corresponding angle measurement range can be calculated according to the formula (10) to be about 1.85 °, i.e., 6600 ". Taking the repetition frequency of 50MHz as an example, the system angle measurement accuracy can reach 0.07' from the perspective of single longitudinal mode traceability. The maximum speed measurement of the system can be set by controlling the repetition frequency difference, and the repetition frequency difference value corresponding to the repetition frequency of 50MHz is set to be about 1-5 kHz, namely, the maximum speed measurement is 1-5 kHz. It should be noted that, under the condition that other parameters are not changed, the grating period is increased, the measurement accuracy can be synchronously improved, but the corresponding dynamic angle measurement range is reduced. In the actual design of the system, the selection of each parameter should be determined according to the requirement of the measurement index, which is not limited in this embodiment.
The angle value is measured by the precise resolution of the radio frequency spectrum of the double-optical comb interference signal. The essence of the dual optical comb spectrum discrimination is that the information of the optical frequency domain is transmitted to the radio frequency domain through multi-longitudinal mode heterodyne interference between two optical frequency combs with a tiny difference of repetition frequencies (difference of repetition frequencies), and the acquisition of the optical frequency information is realized through a low-frequency detection mode. The method for measuring the spectrum amplitude-frequency characteristic by using the double-optical comb spectrum precise resolution can realize the dynamic high-precision reconstruction of the diffraction spectrum and provide key technical support for the dynamic high-precision angle measurement of the angle value.
It should be noted that in this embodiment, two optical frequency combs are used as light sources, light is combined first and then emitted through the fiber collimator 3, and the center frequency of the coupling spectrum can be calculated dynamically and accurately based on the double optical comb spectral component analysis technique. However, if there is no high requirement for precision and speed measurement, the single optical comb of embodiment 2 is used as a light source, and directly emitted through the fiber collimator 3, and then the central frequency value of the coupled beam spectrum is calculated based on the high-precision spectrum analyzer 5, so that the angle α between the grating normal and the incident beam can be measured. In this form, both the repetition frequency and the offset frequency of the optical frequency comb do not need to be locked, and the measurement accuracy and the measurement speed mainly depend on the spectral measurement accuracy and speed of the spectral analyzer 5 on the premise that other parameters are not changed. The functions performed by the systems of example 2 and example 3 are identical, and there is only a difference in the method of measuring the center frequency of the coupled spectrum.
The embodiments in the present specification are described in a progressive manner, and the same and similar parts among the embodiments are referred to each other, and each embodiment focuses on the differences from the other embodiments. In the description of the present specification, reference to the description of the terms "preferably," "further," or the like, means 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 embodiments or examples of the specification. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.
Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it should be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.
Claims (8)
1. An auto-collimation absolute angle measurement method based on a spectrum resolution technology is characterized by comprising the following steps:
the optical frequency comb transmits light pulses containing a plurality of longitudinal modes to the optical fiber circulator;
the light pulse introduced by the optical fiber circulator is transmitted to the grating by the optical fiber collimating mirror, and a group of first-order diffracted light beams with different diffraction angles are generated after the light pulse is diffracted by the grating;
when the included angle between the grating normal and the incident beam is changed, the incident beam with a certain spectral width can be recoupled into the fiber collimating mirror through the partial longitudinal mode component after the grating diffraction and is transmitted to the fiber circulator;
obtaining the center frequency of the spectrum of the coupling beam by analyzing the spectral components of the optical comb derived by the optical fiber circulator, and further realizing the measurement of the included angle between the normal of the grating and the incident beam, wherein the spectral distribution of the coupling beam is the center frequency f c Approximately symmetrically distributed, and the light frequency comb is a positive stage corresponding to the longitudinal mode of the spectral rangeAngle of diffraction beta i And when the diffraction beam corresponding to the longitudinal mode is equal to the incident angle alpha, the diffraction beam corresponding to the longitudinal mode returns approximately in parallel to the original path of the incident beam direction, and the included angle between the grating normal and the incident beam is further obtained through the central frequency of the spectrum of the coupled beam:
where alpha is the angle between the normal of the grating and the incident beam, c is the speed of light, g is the period of the grating, f c A central optical frequency.
2. The method of claim 1, wherein the grating normal and the exit direction of the fiber collimator, i.e. the incident beam direction, have an initial angle.
3. The method according to claim 1, wherein the grating is a reflective grating.
4. An auto-collimating absolute goniometric system for carrying out the method of any one of claims 1 to 3, characterized in that it comprises:
a single optical comb for emitting an optical pulse having a plurality of longitudinal modes;
the optical fiber circulator is used for leading in or leading out an optical signal;
the optical fiber collimating mirror is used for collimating and transmitting the optical signal guided by the optical fiber circulator;
the grating is used for enabling part of longitudinal mode components in first-order diffraction beams with different diffraction angles generated after the optical signals emitted by the fiber collimator mirror are diffracted to return to the fiber circulator through the fiber collimator mirror;
and the spectrum analyzer is used for measuring an included angle between the grating normal and an incident beam through distinguishing and analyzing optical comb spectrum components led out by the optical fiber circulator.
5. An auto-collimating absolute goniometric system for carrying out the method of any one of claims 1 to 3, characterized in that it comprises:
a dual optical comb for transmitting an optical pulse having a plurality of longitudinal modes;
the optical fiber circulator is used for leading in or leading out an optical signal;
the optical fiber collimating mirror is used for collimating and transmitting the optical signal guided by the optical fiber circulator;
the grating is used for enabling part of longitudinal mode components in first-order diffraction beams with different diffraction angles generated after the optical signals emitted by the fiber collimator mirror are diffracted to return to the fiber circulator through the fiber collimator mirror;
and the signal processing device is used for distinguishing and analyzing the optical comb spectral components led out by the optical fiber circulator through a double optical comb spectrum distinguishing and analyzing technology, so that the measurement of the included angle between the grating normal and the incident beam is realized.
6. The auto-collimation absolute angle measuring system of claim 5, wherein the dual-optical-frequency comb comprises two optical-frequency combs with a small repetition frequency difference, and the first optical-frequency comb and the second optical-frequency comb are combined by an optical fiber coupler and then sent to the optical fiber circulator.
7. The auto-collimating absolute goniometry system of claim 5 or 6, further comprising a dual optical comb noise suppression unit that employs tight locking or non-tight locking.
8. The auto-collimating absolute angle measuring system of claim 5 or 6, wherein the grating is a reflective grating.
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| CN107192355B (en) * | 2017-06-30 | 2019-08-09 | 清华大学 | A kind of double light comb precision angle methods and angle measuring system |
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