CN116026244A - System for measuring lens group lens surface spacing and refractive index - Google Patents
System for measuring lens group lens surface spacing and refractive index Download PDFInfo
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Abstract
The present disclosure relates to a system for measuring lens group lens spacing and refractive index. The system comprises: the light source device is used for generating a first optical frequency comb signal and a second optical frequency comb signal, wherein the first optical frequency comb signal and the second optical frequency comb signal have a preset repetition frequency difference; the measuring device is used for enabling the first optical frequency comb signal to be incident into the reference light path and the measuring light path, generating a reflected optical signal and enabling the reflected optical signal to be reflected back to the coupler, wherein the reference light path comprises a second reflecting mirror, the measuring light path comprises a first reflecting mirror and a lens group to be measured, the lens group to be measured comprises N lenses to be measured, and N is greater than or equal to 1; the coupler is used for enabling the second optical frequency comb signal to interfere with the reflected optical signal and generating a measurement interference optical signal; and the signal acquisition processing device is used for determining the mirror surface distance and/or the refractive index of the lens group to be measured according to the interference light signal. By the method, the mirror surface distance and the refractive index of the lenses in the lens group can be measured in high precision and in real time.
Description
Technical Field
The disclosure relates to the technical field of optical precision metering, in particular to a lens group lens surface spacing and refractive index measuring system.
Background
With the technical development of various research fields, the requirements on the performance of an optical system are higher and higher, particularly for high-precision optical systems such as exposure objective lenses of lithography machines, the accurate and rapid measurement of the lens group lens surface distance is important for improving the performance of the optical system and ensuring the assembly quality. When the optical measurement method is used for measuring the lens group mirror surface distance, the optical path value is used for calculating the geometric thickness of the lens, the refractive index of the lens is required to be referred to, and the error between the nominal value and the true value of the refractive index of the lens can influence the measurement accuracy, so that the refractive index of the lens needs to be measured in real time.
Disclosure of Invention
In view of this, the present disclosure proposes a technical solution of a system for measuring a lens group plane spacing and a refractive index.
According to an aspect of the present disclosure, there is provided a system for measuring a lens group lens surface pitch and a refractive index, the system including a light source device, a measuring device, a coupler, and a signal acquisition processing device; the light source device is used for generating a first optical frequency comb signal and a second optical frequency comb signal, wherein the first optical frequency comb signal and the second optical frequency comb signal have a preset repetition frequency difference; the measuring device is used for enabling the first optical frequency comb signal to be incident into a reference light path and a measuring light path, generating a reflected light signal and enabling the reflected light signal to be reflected back to the coupler, wherein the reference light path comprises a second reflecting mirror, the measuring light path comprises a first reflecting mirror and a lens group to be measured, and the lens group to be measured comprises N lenses to be measured, and N is greater than or equal to 1; the coupler is used for enabling the second optical frequency comb signal to interfere with the reflected optical signal to generate a measurement interference optical signal; the signal acquisition processing device is used for determining the mirror surface distance and/or the refractive index of the lens group to be tested according to the interference light signal.
In one possible implementation, the measuring device includes a circulator, a collimator lens, and a spectroscopic device;
the circulator is used for enabling the first optical frequency comb signal to be incident to the collimating mirror; the collimating mirror is used for enabling the first optical frequency comb signal to be emitted from the optical fiber to a free space; the beam splitter is configured to split the outgoing first optical frequency comb signal into a measurement signal and a reference signal, so that the measurement signal is incident on the measurement light path, and the reference signal is incident on the reference light path.
In a possible implementation manner, the light splitting device is configured to combine the measurement signal reflected by the lens group to be measured and the first mirror and the reference signal reflected by the second mirror into the reflected light signal.
In one possible implementation, the collimator lens is used to couple the reflected light signal from free space into an optical fiber.
In one possible implementation, the circulator is configured to cause the reflected optical signal to be incident on the coupler.
In one possible implementation, the collimating mirror comprises a variable focus collimating mirror.
In one possible implementation manner, the signal acquisition and processing device comprises a detector, a filter device, a digital acquisition card and a computer processing unit; the detector is used for converting the measurement interference optical signal into a measurement electrical signal; the filter device is used for filtering the measurement electric signal; the digital acquisition card is used for storing the filtered measurement electric signals to the computer processing unit; and the computer processing unit is used for carrying out time-frequency analysis on the filtered measurement electric signals and determining the mirror surface distance and/or the refractive index of the lens group to be measured.
In a possible implementation manner, the performing time-frequency analysis on the filtered measurement electric signal to determine a mirror distance and/or a refractive index of the lens group to be measured includes: analyzing the filtered measurement electric signals and determining phase frequency information of the measurement electric signals; determining the optical path between adjacent mirror surfaces in the lens group to be detected according to the phase frequency information; and determining the mirror surface distance and/or the refractive index of the lens group to be tested according to the optical path between the adjacent mirror surfaces.
In one possible implementation manner, the determining the optical path between the adjacent mirrors in the lens group to be measured according to the phase frequency information includes: determining the time difference between two adjacent measurement electric signals according to the phase frequency information; determining a repetition frequency ratio between the measurement electric signal and the first optical frequency comb signal according to a repetition frequency difference preset by the first optical frequency comb signal and the second optical frequency comb signal; and determining the optical path between the adjacent mirror surfaces in the lens group to be tested according to the time difference and the repetition frequency ratio.
In one possible implementation manner, the determining the mirror surface distance and/or the refractive index of the lens group to be tested according to the optical path between the adjacent mirror surfaces includes: determining the optical path change between the first reflecting mirror and the second reflecting mirror before and after the lens group to be measured is placed in the system; and determining the mirror surface distance and/or the refractive index of the lens group to be tested according to the optical path change and the optical path between the adjacent mirror surfaces.
According to the measuring system for the mirror surface spacing and the refractive index of the lens group, a first optical frequency comb signal generated by a light source device is incident to a reference light path and a measuring light path through a measuring device, a reflected light signal is determined, and the reflected light signal and a second optical frequency comb signal are interfered by a coupler to generate a measuring interference light signal; the signal acquisition processing device is used for carrying out time-frequency analysis on the interference light signal, so that the mirror surface distance and the refractive index of the lens group to be measured can be rapidly and accurately measured simultaneously in real time.
Other features and aspects of the present disclosure will become apparent from the following detailed description of exemplary embodiments, which proceeds with reference to the accompanying drawings.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate exemplary embodiments, features and aspects of the present disclosure and together with the description, serve to explain the principles of the disclosure.
FIG. 1 shows a schematic diagram of a system for measuring lens group pitch and refractive index in accordance with an embodiment of the present disclosure;
FIG. 2 illustrates a schematic diagram of a positional relationship of a different reflective surface corresponding to an interference signal in the time domain, in accordance with an embodiment of the present disclosure;
FIG. 3 illustrates a schematic diagram of time-frequency analysis of measured electrical signals in accordance with an embodiment of the present disclosure;
FIG. 4 is a schematic diagram showing a phase frequency curve and a phase difference correspondence curve of two RF interference signals according to the disclosed embodiments;
fig. 5 shows a schematic diagram of a dual optical comb multiple heterodyne interference principle and an interference signal amplitude-frequency plot in accordance with an embodiment of the present disclosure.
Detailed Description
Various exemplary embodiments, features and aspects of the disclosure will be described in detail below with reference to the drawings. In the drawings, like reference numbers indicate identical or functionally similar elements. Although various aspects of the embodiments are illustrated in the accompanying drawings, the drawings are not necessarily drawn to scale unless specifically indicated.
The word "exemplary" is used herein to mean "serving as an example, embodiment, or illustration. Any embodiment described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments.
The term "and/or" is herein merely an association relationship describing an associated object, meaning that there may be three relationships, e.g., a and/or B, may represent: a exists alone, A and B exist together, and B exists alone. In addition, the term "at least one" herein means any one of a plurality or any combination of at least two of a plurality, for example, including at least one of A, B, C, and may mean including any one or more elements selected from the group consisting of A, B and C.
In addition, numerous specific details are set forth in the following detailed description in order to provide a better understanding of the present disclosure. It will be understood by those skilled in the art that the present disclosure may be practiced without some of these specific details. In some instances, methods, means, elements, and circuits well known to those skilled in the art have not been described in detail in order not to obscure the present disclosure.
A common optical system consists of a plurality of lenses, each lens having a geometric thickness that determines its position along the optical axis in the optical system; the geometric distance of the surfaces between adjacent lenses is used to compensate for errors in the manufacturing process and to perform tolerance testing. The geometric thickness of a lens and the geometric distance of the surface between adjacent lenses can be expressed by the mirror pitch of the lens group. Therefore, the lens spacing of the lens group is accurately and rapidly measured, which is important to improving the performance of the optical system and ensuring the assembly quality of the optical system, especially for high-precision optical systems such as exposure objective lenses of lithography machines.
In the prior art, a non-contact and nondestructive optical measurement method is generally adopted for measuring the mirror surface spacing of the lens group. However, since the direct measurement result of the optical measurement method is the optical path length, the optical measurement method in the prior art generally needs to solve the geometric thickness of the lens according to the refractive index nominal value of each lens in the lens group in combination with the measurement of the optical path length. Calculating the geometric thickness of the lens from the index nominal value will inevitably produce errors, since the index nominal value of the lens is not the true index of refraction at the current ambient conditions. Therefore, in order to accurately measure the mirror pitch of the lens group, it is necessary to measure the refractive index of the lens in real time.
In the prior art, methods such as confocal and low coherence interferometry are commonly used to measure the mirror spacing of a lens group. However, the mechanical scanning process exists in the measuring process of the methods, and the measuring process is sensitive to vibration of the measuring environment. In addition, when the number of lenses in the lens group to be measured increases, the time of mechanical scanning also increases, resulting in a limitation in the measurement speed.
The present disclosure provides a system for measuring lens group pitch and refractive index that may be used to measure lens group pitch and refractive index. The measurement system provided by the present disclosure is described in detail below.
FIG. 1 shows a schematic diagram of a system for measuring lens group pitch and refractive index in accordance with an embodiment of the present disclosure; as shown in fig. 1, the measuring system may include a light source device 101, a measuring device 102, a coupler 104, and a signal acquisition processing device 105 along the light propagation direction.
A light source device 101 for generating a first optical frequency comb signal and a second optical frequency comb signal, wherein the first optical frequency comb signal and the second optical frequency comb signal have a preset repetition frequency difference;
the measuring device 102 is configured to make the first optical frequency comb signal incident on a reference optical path and a measuring optical path, generate a reflected optical signal, and make the reflected optical signal retroreflected to the coupler 104, where the reference optical path includes a second reflector 1032, the measuring optical path includes a first reflector 1031 and a lens group to be measured, and the lens group to be measured includes N lenses to be measured, where N is greater than or equal to 1;
a coupler 104 for interfering the second optical frequency comb signal with the reflected optical signal to generate a measurement interference optical signal;
the signal acquisition and processing device 105 is used for determining the mirror surface distance and/or the refractive index of the lens group to be tested according to the interference light signal.
Wherein, the light source device 101 may include at least two optical frequency comb generating devices for generating a first optical frequency comb signal and a second optical frequency comb signal, respectively; the first optical frequency comb signal and the second optical frequency comb signal may also be generated by other means, which is not particularly limited by the present disclosure.
The repetition frequency of the first optical frequency comb signal can be determined as f r1 The repetition frequency of the second optical frequency comb signal can be determined as f r2 The first optical frequency comb signal and the second optical frequency comb signal are used for realizing double optical comb multi-heterodyne interference. The first optical frequency comb signal and the second optical frequency comb signal have a tiny preset repetition frequency difference delta f r The frequency difference may be set according to actual usage requirements, which is not specifically limited in this disclosure.
The lens group to be measured may be placed in the outgoing light direction of the measuring device 102, where the upper limit of the number of lenses to be measured in the lens group to be measured is limited by the intensity of the first optical frequency comb signal. The number of lenses to be measured can be increased infinitely as long as the intensity of the first optical frequency comb signal can satisfy that the reflected light generated at each reflecting surface is collected.
The lens to be measured may be any type of optical lens, for example, a concave lens or a convex lens, which is not particularly limited in the present disclosure.
The materials and specifications of each lens to be tested in the lens group to be tested may be the same or different, and the disclosure is not limited in detail.
The measuring device 102 will be described in detail in connection with possible implementations of the present disclosure, which will not be described herein.
The coupler 104 may overlap the second optical frequency comb signal with the reflected optical signal, so that the second optical frequency comb signal interferes with the reflected optical signal, and the conversion from the optical frequency domain to the radio frequency domain is implemented, thereby generating a measurement interference optical signal in the radio frequency domain. Coupler 104 may be any type of coupler, such as a fiber optic coupler or a space coupler, as not specifically limited by the present disclosure.
The signal acquisition processing device 105 will be described in detail in connection with possible implementations of the present disclosure, and will not be described here.
The mirror surface distance of the lens group to be measured, which represents the distance between two adjacent mirror surfaces in the lens group to be measured, may include the geometric thickness of each lens to be measured in the lens group to be measured and the surface geometric distance between two adjacent lenses to be measured. The refractive index of the lens group to be measured comprises the refractive index of each lens to be measured in the lens group to be measured.
According to the measuring system for the mirror surface spacing and the refractive index of the lens group, a first optical frequency comb signal generated by a light source device is incident to a reference light path and a measuring light path through a measuring device, a reflected light signal is determined, and the reflected light signal and a second optical frequency comb signal are interfered by a coupler to generate a measuring interference light signal; the signal acquisition processing device is used for carrying out time-frequency analysis on the interference light signal, so that the mirror surface distance and the refractive index of the lens group to be measured can be rapidly and accurately measured simultaneously in real time.
In one possible implementation, the measurement device 102 includes a circulator 1021, a collimator 1022 and a beam splitting device 1023; a circulator 1021 for making the first optical frequency comb signal incident to the collimator 1022; a collimator 1022 for emitting the first optical frequency comb signal from the optical fiber to the free space; the beam splitter 1023 is configured to split the outgoing first optical frequency comb signal into a measurement signal and a reference signal, so that the measurement signal is incident on the measurement light path, and the reference signal is incident on the reference light path.
Taking fig. 1 as an example, as shown in fig. 1, the measuring device 102 may include a circulator 1021, a collimator 1022, and a beam splitter 1023 along the light propagation direction.
A circulator 1021 may be used to make the first optical frequency comb signal incident on the collimator 1022. The circulator 1021 may be any type of circulator according to the system optical path setting in practical use, for example, a three-port circulator, which is not specifically limited in this disclosure.
The collimator 1022 may be used to make the first optical frequency comb signal exit from the optical fiber to the free space, and adjust the focusing state of the output first optical frequency comb signal. The first optical frequency comb signal emitted from the optical fiber to the free space may be in a parallel state or in a slightly converging state or a diverging state. The collimating mirror 1022 may be any type of collimating mirror, such as a transmissive collimating mirror, as not specifically limited in this disclosure. In one possible implementation, the collimating mirror 1022 includes a variable focus collimating mirror. When the collimating mirror 1022 is a variable-focus collimating mirror, the focal point of the outgoing beam can be changed by the collimating mirror 1022, so as to change the intensity of the reflected light signal on each surface, and improve the signal-to-noise ratio of the reflected light signal, thereby improving the measurement accuracy and increasing the number of measurable lenses.
The beam splitter 1023 may be configured to split the outgoing first optical frequency comb signal into two beams of a measurement signal and a reference signal, and make the measurement signal incident on the measurement optical path and the reference signal incident on the reference optical path. The beam splitter 1023 may be any type of beam splitter, for example, a beam splitter, which is not particularly limited in this disclosure.
The directions of the measurement signal and the reference signal generated by the light-splitting device 1023 are, for example, as shown in fig. 1, perpendicular to each other, so long as the reflected light can be reflected back to the light-splitting device along the measurement light path and the reference light path, and the directions of the measurement signal and the reference signal depend on the light-splitting device 1023, which is not specifically limited in the present disclosure.
The lens group to be measured may be placed between the first mirror 1031 and the spectroscopic device 1023. For a specific manner of placing the lens group to be tested, reference may be made to a manner of placing lenses in the related art, for example, placing the lens group on a bracket, which is not specifically limited in the present disclosure.
After the measurement signal is incident on the lens group to be measured, reflected light may be generated at the front and rear two mirrors of each lens in the lens group to be measured and the first mirror 1031. After the reference signal is incident on the second mirror 1032, reflected light may also be generated. All of the reflected light may be re-retroreflected along the measurement and reference light paths to the beam-splitting device 1023.
In one possible implementation, the beam splitter 1023 is configured to combine the measurement signal reflected by the lens group under test and the first mirror 1031, and the reference signal reflected by the second mirror 1032 into a reflected optical signal.
The measurement signal reflected by the lens group to be measured and the first mirror 1031 and the reference signal reflected by the second mirror 1032 are reflected back to the spectroscopic device 1023 in the free space primary path, and are combined into a reflected light signal by the spectroscopic device 1023.
In one possible implementation, a collimating mirror 1022 is used to couple the reflected optical signal from free space into the optical fiber.
The reflected light signals combined by the spectroscopic device 1021 are incident on the collimator 1022, and the reflected light can be coupled into the optical fiber from the free space by the collimator 1022. The reflected optical signal may be re-incident to the circulator 1021 along the optical path. The repetition frequency of the reflected optical signal is the same as that of the first optical frequency comb signal.
In one possible implementation, circulator 1021 is used to make the reflected optical signal incident to coupler 104.
The reflected optical signal may be incident to the coupler 104 through the circulator and interfere with the second optical frequency comb signal, which is the local oscillation light, at the coupler 104, to generate a measurement interference optical signal.
Taking fig. 1 as an example, as shown in fig. 1, the circulator 1021 may be a three-port circulator. The first optical frequency comb signal is incident to the port 1 of the circulator 1021 and is emitted to the collimating mirror 1022 from the port 2 of the circulator 1021; the reflected optical signal is incident on port 2 of the circulator 1021 and exits from port 3 of the circulator 1021 to the coupler 104.
In one possible implementation, the signal acquisition processing device 105 includes a detector 1051, a filter device 1052, a digital acquisition card (not shown), and a computer processing unit 1053; a detector 1051 for converting the measurement interference optical signal into a measurement electrical signal; a filter device 1052 for filtering the measurement electrical signal; the digital acquisition card is used for storing the filtered measurement electric signals to the computer processing unit; the computer processing unit 1053 is configured to perform time-frequency analysis on the filtered measurement electrical signal to determine a mirror pitch and/or a refractive index of the lens group to be measured.
Taking fig. 1 as an example, as shown in fig. 1, the signal acquisition processing device 105 includes a detector 1051, a filter device 1052, a digital acquisition card and a computer processing unit 1053 along the transmission direction of the measurement interference light signal.
The detector 1051 may be configured to collect the measurement interference optical signal output by the coupler 104, and convert the measurement interference optical signal from an optical signal in an rf domain to a measurement electrical signal. The detector 1051 may be any type of detector for acquiring optical interference signals, as this disclosure is not limited in detail.
The type of electrical signal measured depends on the detector 1051, typically a radio frequency electrical signal, but may be other types of electrical signals, as this disclosure is not limited in detail.
A filter device 1052 may be used to filter the measured electrical signal, such as high pass filtering and low pass filtering. The filter device 1052 may be any type of electrical filter device, such as a radio frequency electrical filter, which is not specifically limited by the present disclosure. The filter is used for filtering high-frequency noise, low-frequency direct current signals and the like, so that the signal-to-noise ratio of the collected signals is better, and the measurement accuracy is higher.
In order to prevent spectral aliasing of the dual optical comb system to achieve accurate measurement of spectral phase and thereby ensure accuracy and authenticity of the measured electrical signal for time-frequency analysis by the computer processing unit 1053, the bandwidth of the filter device 1052 is less than 1/2 of the repetition frequency of the first optical frequency comb signal and/or the second optical frequency comb signal.
The digital acquisition card can be used for storing the measured electrical signals after the filtering processing to the computer processing unit 1053, and the parameters of the digital acquisition card should meet the nyquist sampling theorem, that is, the sampling frequency of the digital acquisition card should be greater than 2 times of the frequency of the measured electrical signals.
The computer processing unit 1053 may be configured to perform time-frequency analysis on the filtered measurement electrical signal to determine a mirror pitch and/or a refractive index of the lens group under test. The computer processing unit 1053 may be any electronic device or system capable of performing a corresponding process of determining the mirror pitch and/or refractive index of the lens group under test, which is not specifically limited in this disclosure.
The computer processing unit 1053 may be, for example, a User Equipment (UE), a mobile device, a User terminal, a handheld device, a computing device, or an in-vehicle device, and some examples of the terminal are: a display, a Smart Phone or portable device, a Mobile Phone (Mobile Phone), a tablet, a notebook, a palm top, a Mobile internet device (Mobile Internetdevice, MID), a wearable device, a Virtual Reality (VR) device, an Augmented Reality (AR) device, a wireless terminal in industrial control (Industrial Control), a wireless terminal in unmanned (self driving), a wireless terminal in teleoperation (Remote medical Surgery), a wireless terminal in Smart Grid (Smart Grid), a wireless terminal in transportation security (Transportation Safety), a wireless terminal in Smart City (Smart City), a wireless terminal in Smart Home (Smart Home), a wireless terminal in the internet of vehicles, and the like. For example, the server may be a local server or a cloud server.
The process of determining the mirror pitch and/or refractive index of the lens group to be measured by performing time-frequency analysis on the filtered measurement electrical signal by the computer processing unit 1053 will be described in detail below in connection with possible implementation manners of the present disclosure, and will not be described in detail here.
In one possible implementation, performing time-frequency analysis on the filtered measurement electric signal to determine a mirror pitch and/or a refractive index of the lens group to be measured includes: analyzing the filtered measurement electric signals to determine phase frequency information of the measurement electric signals; determining the optical path between adjacent mirror surfaces in the lens group to be measured according to the phase frequency information; and determining the mirror surface distance and/or the refractive index of the lens group to be tested according to the optical path between the adjacent mirror surfaces.
After the reflected optical signal enters the coupler 104, the second optical frequency comb signal performs asynchronous optical sampling, so that 2n+2 measurement interference optical signals can be generated, and the signals are converted from the optical frequency domain to the radio frequency domain. The measurement interference light signal corresponds to the reflection surface of each lens mirror surface (2 lenses each), the reflection surfaces of the first mirror 1031 and the second mirror 1032, respectively. The position relation of each measurement interference optical signal in the time domain can reflect the physical position relation of the corresponding reflecting surface in space.
Fig. 2 shows a schematic diagram of a positional relationship of different reflective surfaces corresponding to interference signals in the time domain according to an embodiment of the present disclosure. As shown in fig. 2, an example is given in which a lens group to be measured including 3 lenses to be measured is placed in the system. The measurement interference light signals S1 to S8 may represent 8 measurement interference light signals collected after the lens group to be measured is placed in the system, and S1 to S8 are arranged at time domain positions according to the time sequence generated by the corresponding reflected light. Wherein, the measurement interference light signal S1 corresponds to the reflecting surface of the second mirror 1032, the measurement interference light signal S2 corresponds to the reflecting surface of the 1 st mirror of the lens 201 to be measured, the measurement interference light signal S3 corresponds to the reflecting surface of the 2 nd mirror of the lens 201 to be measured, the measurement interference light signal S4 corresponds to the reflecting surface of the 1 st mirror of the lens 202 to be measured, the measurement interference light signal S5 corresponds to the reflecting surface of the 2 nd mirror of the lens 202 to be measured, the measurement interference light signal S6 corresponds to the reflecting surface of the 1 st mirror of the lens 203 to be measured, the measurement interference light signal S7 corresponds to the reflecting surface of the 2 nd mirror of the lens 203 to be measured, and the measurement interference light signal S8 corresponds to the reflecting surface of the first mirror 1031. By measuring the positional relationship of the interference light signals S1 to S8 in the time domain, the spatial physical relationship of the reflecting surface of each mirror surface in the lens group to be measured can be reflected.
When the lens group to be measured is not placed in the system, measuring interference signals S1 and S8' corresponding to the second reflecting mirror and the first reflecting mirror can be determined; then placing the lens group to be measured into a system, and determining measurement interference signals S1 to S8 corresponding to the second reflecting mirror, the first reflecting mirror and two reflecting surfaces of each lens to be measured in the lens group to be measured; the mirror surface distance and the refractive index of the lens group to be measured can be determined by combining the position relation of the interference signals in the time domain in the two processes.
The electrical measurement signal converted and determined by the probe 1051 also has the above characteristics. By analyzing the filtered measurement electrical signal, phase frequency information of the measurement electrical signal can be determined.
Fig. 3 shows a schematic diagram of time-frequency analysis of measured electrical signals according to an embodiment of the disclosure. As shown in fig. 3, by fourier transforming the measurement electric signal of fig. 3 (a), the phase frequency information of fig. 3 (c) and the amplitude frequency information (i.e., phase frequency curve and amplitude frequency curve) of fig. 3 (b) corresponding to the measurement electric signal can be obtained. According to the phase frequency information corresponding to each measured electric signal, the optical path between the adjacent mirror surfaces in the lens group to be measured can be determined. The optical path may represent the path that light actually propagates, while the optical path that light passes between adjacent mirrors may be determined by the mirror spacing and refractive index of the lens group to be measured. Therefore, by determining the optical path between adjacent mirrors in the lens group to be measured, the mirror pitch and/or refractive index of the lens group to be measured can be determined.
Determining the optical path between adjacent mirror surfaces in the lens group to be measured according to the phase frequency information in a possible mode combining the disclosure; and determining the mirror surface distance and/or the refractive index of the lens group to be measured according to the optical path between the adjacent mirror surfaces, which are not described in detail herein.
In one possible implementation manner, determining an optical path length between adjacent mirrors in a lens group to be measured according to phase frequency information includes: determining the time difference between two adjacent measurement electric signals according to the phase frequency information; determining a repetition frequency ratio between the measurement electric signal and the first optical frequency comb signal according to a preset repetition frequency difference between the first optical frequency comb signal and the second optical frequency comb signal; and determining the optical path between the adjacent mirror surfaces in the lens group to be measured according to the time difference and the repetition frequency ratio.
The phase frequency information determined by Fourier transform analysis, wherein the phase is a wrapping phase, namely the phase is truncated in the range of [ -pi, pi ] or [0,2 pi ], and phase unwrapping (also called phase unwrapping) is needed to obtain continuous phase frequency information.
Taking fig. 3 as an example, the continuous phase frequency information of fig. 3 (d) can be determined by phase unwrapping the phase frequency information of fig. 3 (c).
Fig. 4 is a schematic diagram showing a phase frequency curve and a phase difference correspondence curve of two radio frequency interference signals according to the disclosed embodiment. As shown in fig. 4, the phase difference correspondence curve can be determined by making a difference between the phase values corresponding to each frequency in the phase frequency curves after the phase expansion of any two radio frequency interference signals. By determining the slope value of the phase difference corresponding curve, the time difference between the corresponding two radio frequency interference signals can be determined. The time difference between any two radio frequency interference signals can be expressed as the following equation (1):
wherein, the liquid crystal display device comprises a liquid crystal display device,
a phase value curve representing a radio frequency interference signal, ">
A phase value curve representing another radio frequency interference signal, ">
Curve representing phase difference correspondence ++>
The slope value of the curve corresponding to the phase difference is represented, and Δt represents the time difference between any two radio frequency interference signals.
Correspondingly, the time difference between any two measured electrical signals can also be represented by the above formula (1).
Fig. 5 shows a schematic diagram of a dual optical comb multiple heterodyne interference principle and an interference signal amplitude-frequency plot in accordance with an embodiment of the present disclosure. As shown in fig. 5, since the reflected optical signal and the second optical frequency comb signal have a small preset repetition frequency difference Δf r Thus, every time a period of time passes, two optical comb signals will produce a certain time slip. According to the double optical comb multi-heterodyne interference principle, the information of the optical frequency domain is mapped to the radio frequency domain, and the interval between the radio frequency interference signals relative to the first optical frequency comb signals is reduced by delta f r /f r1 While the corresponding time domain information period, i.e. the period of the radio frequency interference signal, is amplified by f r1 /Δf r . Thus, a scaling factor from the optical frequency domain to the radio frequency domain can be determined, representing the repetition frequency ratio Δf between the radio frequency interference signal and the first optical frequency comb signal r /f r1 。
Correspondingly, the repetition frequency ratio between the measured electric signal and the first optical frequency comb signal is delta f r /f r1 。
According to the time difference between two adjacent measured electric signals on the time domain position and the repetition frequency ratio between the measured electric signals and the first optical frequency comb signals, the optical path between two corresponding adjacent mirror surfaces in the lens group to be measured can be determined. In combination with the above, the optical path length between the adjacent mirrors can also be determined by the mirror pitch and the refractive index of the lens group to be measured. Thus, the optical path between two adjacent mirrors can be expressed as the following formula (2):
L i ＝2·n(d i )·d i ＝c·Δt·Δf r /f r1 (2)
where n (di) is the refractive index of the corresponding medium, di is the mirror spacing between two adjacent mirrors, and c is the speed of light in vacuum.
Taking fig. 2 as an example, as shown in fig. 2, the lens group to be tested includes a lens 201 to be tested, a lens 202 to be tested, and a lens 203 to be tested.
When the materials of the 3 lenses to be tested are the same, the refractive index n phase of the 3 lenses to be tested can be determinedEtc., the refractive index of air can be determined to be a known fixed value n according to the measuring environment 0 . At this time, the optical path through which light enters from the lens 201 to be measured until exiting from the lens 203 to be measured can be expressed as the following formula (3):
wherein L is 1 、L 2 、L 3 、L 4 、L 5 Respectively represents the optical path difference delta t between two reflected lights generated by each light passing through the adjacent mirror surface 3-2 、Δt 4-3 、Δt 5-4 、Δt 6-5 、Δt 7-6 Respectively represent the time difference between every two adjacent measured electrical signals at the time domain position, d 1 、d 2 、d 3 、d 4 、d 5 Representing the mirror pitch of the lens group, i.e. d 1 Is the thickness of the 1 st lens, d 2 Is the distance between the adjacent surfaces of the 1 st and 2 nd lenses, d 3 Is the thickness of the 2 nd lens, d 4 Is the distance between the adjacent surfaces of the 2 nd and 3 rd lenses, d 5 Is the thickness of the 3 rd lens.
When the materials of the 3 lenses to be tested are different, it can be determined that the refractive indexes of the 3 lenses to be tested are n 1 、n 2 And n 3 . At this time, the optical path through which light enters from the lens 201 to be measured until exiting from the lens 203 to be measured can be expressed as the following formula (4):
in one possible implementation, determining the mirror pitch and/or the refractive index of the lens group to be measured according to the optical path between adjacent mirrors includes: determining the optical path change between the first reflector 1031 and the second reflector 1032 before and after the lens group to be measured is placed in the system; and determining the mirror surface distance and/or the refractive index of the lens group to be tested according to the optical path change and the optical path between the adjacent mirror surfaces.
When the lens group to be measured is placed in the system, a medium between equivalent common light paths of the first reflector 1031 and the second reflector 1032 changes, and the refractive index of the corresponding position is different from that of the lens group to be measured when the system is not placed due to the medium change, so that the optical path between the first reflector 1031 and the second reflector 1032 changes. The mirror surface distance and/or the refractive index of the lens group to be measured can be determined according to the optical path change and the optical path between the adjacent mirror surfaces.
Taking fig. 2 as an example, as shown in fig. 2, after the lens group to be measured is placed in the system, the position of the measurement electrical signal S8 'corresponding to the first mirror 1031 in the time domain changes relative to the position of the measurement electrical signal S8' corresponding to the first mirror 1031 before the lens group to be measured is placed in the system. The change in the optical path length between the first mirror 1031 and the second mirror 1032 can be reflected by the change in the position of the measurement electric signal in the time domain corresponding to the first mirror 1031.
When the materials of the 3 lenses to be tested are the same, the 3 lenses to be tested can be simultaneously put into the system. After the lens group to be measured is placed, the medium change between the first reflector 1031 and the second reflector 1032, including the medium at the positions of the lens 20l to be measured, the lens 202 to be measured and the lens 203 to be measured, is changed from air to a material corresponding to the lens to be measured, and the medium change can be expressed as a refractive index change (n-n 0 ). Therefore, the optical path length change Δl can be expressed as the following formula (5):
ΔL＝c·(Δt 8-1 -Δt 8′-1 )·Δf r /f r1 ＝2(n-n 0 )(d 1 +d 3 +d 5 ) (5)
wherein Δt is 8-1 Indicating the time difference, Δt, between the measured electrical signals corresponding to the first mirror 1031 and the second mirror 1032 after the lens group to be measured is placed in the system 8’-1 Representing the time difference between the measured electrical signals corresponding to the first mirror 1031 and the second mirror 1032 before the lens group to be measured is placed in the system.
According to the above formula (3) and formula (5), the refractive index of the lens to be measured can be determined by the mathematical relationship between the optical path length and the reflecting surface. The refractive index n of the lens to be measured can be expressed as the following formula (6):
further, according to the above formulas (3), (5) and (6), the mirror pitch d of the lens group to be measured can be determined by the mathematical relationship between the optical path length and the reflecting surface 1 、d 2 、d 3 、d 4 、d 5 。
When the materials of the 3 lenses to be tested are different, the three lenses to be tested can be sequentially added into the system, and after the lens 201 to be tested is placed in the system, the lenses 201 and 202 to be tested are placed in the system, and the optical path length changes of the lenses 201, 202 and 203 to be tested are placed in the system are respectively determined.
The lens 201 to be measured is put into the system, and the optical path length change delta L can be changed 1 Expressed as the following formula (7):
ΔL 1 ＝2(n 1 -n 0 )d 1 (7)
continuing to place the lens 202 under test into the system, the optical path length change ΔL may be varied 2 Expressed as the following formula (8):
ΔL 2 ＝2(n 2 -n 0 )d 3 (8)
continuing to place the lens 203 under test into the system, the optical path length change ΔL can be changed 3 Expressed as the following formula (9):
ΔL 3 ＝2(n 3 -n 0 )d 5 (9)
according to the above formula (4) and formulas (7) to (9), the refractive index of the 3 lenses to be measured can be determined to be n respectively by the mathematical relationship between the optical path length and the reflecting surface 1 、n 2 And n 3 . Refractive index n of lens 201 to be measured 1 Can be expressed as the following formula (10):
refractive index n of lens 202 under test 2 Can be expressed as the following formula (11):
refractive index n of lens 203 to be measured 3 Can be expressed as the following formula (12):
further, according to the above formula (4), and the formulas (7) to (12), the mirror pitch d of the lens group to be measured can be determined by the mathematical relationship between the optical path length and the reflecting surface 1 、d 2 、d 3 、d 4 、d 5 。
In the embodiment of the disclosure, a first optical frequency comb signal generated by a light source device is incident to a reference light path and a measuring light path through a measuring device, a reflected light signal is determined, and the reflected light signal and a second optical frequency comb signal are interfered by a coupler to generate a measuring interference light signal; the time-frequency analysis is carried out on the measurement interference optical signals through the signal acquisition processing device, and the mirror surface distance and the refractive index of the lens group to be measured can be measured rapidly, accurately and simultaneously in real time without prior knowledge of lenses. In addition, the measuring process is not affected by mechanical vibration of the system, and increasing the number of lenses to be measured does not increase the measuring time.
It should be noted that, although the lens group lens surface pitch and refractive index measurement system is described above by taking fig. 1 as an example, those skilled in the art will understand that the present disclosure should not be limited thereto. In fact, the user can flexibly set the specific structure of the lens group mirror surface spacing and refractive index measurement system according to personal preference and/or practical application scene, so long as the process can be used for measuring the lens group mirror surface spacing and/or refractive index.
The foregoing description of the embodiments of the present disclosure has been presented for purposes of illustration and description, and is not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the various embodiments described. The terminology used herein was chosen in order to best explain the principles of the embodiments, the practical application, or the technical improvements in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.
Claims (10)
1. The system is characterized by comprising a light source device, a measuring device, a coupler and a signal acquisition and processing device;
the light source device is used for generating a first optical frequency comb signal and a second optical frequency comb signal, wherein the first optical frequency comb signal and the second optical frequency comb signal have a preset repetition frequency difference;
the measuring device is used for enabling the first optical frequency comb signal to be incident into a reference light path and a measuring light path, generating a reflected light signal and enabling the reflected light signal to be reflected back to the coupler, wherein the reference light path comprises a second reflecting mirror, the measuring light path comprises a first reflecting mirror and a lens group to be measured, and the lens group to be measured comprises N lenses to be measured, and N is greater than or equal to 1;
the coupler is used for enabling the second optical frequency comb signal to interfere with the reflected optical signal to generate a measurement interference optical signal;
the signal acquisition processing device is used for determining the mirror surface distance and/or the refractive index of the lens group to be tested according to the interference light signal.
2. The system of claim 1 or 2, wherein the measuring device comprises a circulator, a collimator mirror and a spectroscopic device;
the circulator is used for enabling the first optical frequency comb signal to be incident to the collimating mirror;
the collimating mirror is used for enabling the first optical frequency comb signal to be emitted from the optical fiber to a free space;
the beam splitter is configured to split the outgoing first optical frequency comb signal into a measurement signal and a reference signal, so that the measurement signal is incident on the measurement light path, and the reference signal is incident on the reference light path.
3. The system of claim 2, wherein the light splitting device is configured to combine the measurement signal reflected by the lens group under test and the first mirror and the reference signal reflected by the second mirror into the reflected light signal.
4. The system of claim 2, wherein the collimating mirror is configured to couple the reflected light signal from free space into an optical fiber.
5. The system of claim 2, wherein the circulator is configured to cause the reflected optical signal to be incident on the coupler.
6. The system of claim 2, wherein the collimating mirror comprises a variable focus collimating mirror.
7. The system of claim 1 or 2, wherein the signal acquisition processing device comprises a detector, a filter device, a digital acquisition card, and a computer processing unit;
the detector is used for converting the measurement interference optical signal into a measurement electrical signal;
the filter device is used for filtering the measurement electric signal;
the digital acquisition card is used for storing the filtered measurement electric signals to the computer processing unit;
and the computer processing unit is used for carrying out time-frequency analysis on the filtered measurement electric signals and determining the mirror surface distance and/or the refractive index of the lens group to be measured.
8. The system of claim 7, wherein the time-frequency analysis of the filtered measurement electrical signal to determine the mirror pitch and/or refractive index of the lens group under test comprises:
analyzing the filtered measurement electric signals and determining phase frequency information of the measurement electric signals;
determining the optical path between adjacent mirror surfaces in the lens group to be detected according to the phase frequency information;
and determining the mirror surface distance and/or the refractive index of the lens group to be tested according to the optical path between the adjacent mirror surfaces.
9. The system of claim 8, wherein determining the optical path between adjacent mirrors in the lens group under test based on the phase frequency information comprises:
determining the time difference between two adjacent measurement electric signals according to the phase frequency information;
determining a repetition frequency ratio between the measurement electric signal and the first optical frequency comb signal according to a repetition frequency difference preset by the first optical frequency comb signal and the second optical frequency comb signal;
and determining the optical path between the adjacent mirror surfaces in the lens group to be tested according to the time difference and the repetition frequency ratio.
10. The system of claim 8, wherein determining the mirror pitch and/or refractive index of the lens group under test based on the optical path between the adjacent mirrors comprises:
determining the optical path change between the first reflecting mirror and the second reflecting mirror before and after the lens group to be measured is placed in the system;
and determining the mirror surface distance and/or the refractive index of the lens group to be tested according to the optical path change and the optical path between the adjacent mirror surfaces.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN117130006A (en) * | 2023-08-24 | 2023-11-28 | 光维(广东)科技有限公司 | Automatic aliasing elimination double-optical comb ranging device and method |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN117130006A (en) * | 2023-08-24 | 2023-11-28 | 光维(广东)科技有限公司 | Automatic aliasing elimination double-optical comb ranging device and method |
| CN117130006B (en) * | 2023-08-24 | 2024-05-03 | 光维(广东)科技有限公司 | Automatic aliasing elimination double-optical comb ranging device and method |
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