Background
With the development of optical technology, optical lenses are also used in various aspects of life. The integration, miniaturization and portability are a great trend of optical devices nowadays, and the traditional large-size and heavy-weight optical lens is difficult to meet the requirement of the trend, so that the micro lens with small volume, light weight and convenient integration becomes a very important component in optical instruments.
Surface measurements for microlenses, especially free-form microlenses, become important. Conventional lens surface measurement methods can be classified into contact and non-contact. In the contact measurement aspect, for example, the surface of the transmission element is measured by using a three-coordinate measuring machine, a contourgraph and the like, and the measurement position is a point or a line, so that the surface shape cannot be integrally measured, and a plurality of surfaces cannot be synchronously measured. Non-contact measurement methods, such as an interference microscope and the like, have high measurement accuracy but have the problems of high requirements on measurement environment, small dynamic range of measurement, high measurement cost, incapability of on-line measurement and the like.
The invention discloses a method and a system for detecting multiple surface shapes of a transmission element, and relates to an invention patent application document with a Chinese patent application number CN109307480A, the application publication date of which is 30.9.2018 and named as a method for detecting multiple surface shapes of the transmission element. The system and method fit the surface shape of the transparent element through multiple iterations by adopting a transmission type inverse Hartmann structure. The method disclosed by the patent is only suitable for measuring the surface shape of the transmission element with a larger volume, but the measurement of the micro lens has insufficient spatial resolution and low measurement precision.
Therefore, it is one of the technical problems to be solved in the art to realize accurate measurement of multiple surfaces of a micro-transmission element.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to solve the technical problems that the traditional method has higher difficulty in measuring the multiple surfaces of the micro transmission element, lower spatial resolution, lower detection precision, smaller dynamic range and can not measure the multiple surfaces synchronously.
The invention is realized by the following technical scheme: a synchronous measurement method for the polyhedral large dynamic range of a micro-transmission element comprises the following steps:
establishing an inverse Hartmann optical detection system based on a microscopic phase deflection method, wherein the detection system comprises a projection screen, a beam splitter prism, a micro-transmission element to be detected, a standard plane mirror, a microscope objective, an imaging lens, a CCD detector and a computer;
obtaining a structural position parameter S of the detection system through system parameter calibration;
establishing a modeled detection system in a computer according to the structural position parameter S, and simulating and obtaining ideal light spot distribution of points projected on the surface of an ideal micro-transmission element to be measured in the CCD detector, which has no processing error, in the modeled detection system by a light ray tracing method;
generating four-step 90-degree phase shift sine straight stripes in the x direction and the y direction by using a computer, displaying the stripes on a projection screen, collecting stripe light rays penetrating through the micro-transmission element to be detected, a micro-objective lens and an imaging lens by using a CCD (charge coupled device) detector, solving phase distribution corresponding to the stripes collected by the CCD detector by using a four-step phase shift method through phase unwrapping and phase expansion, obtaining actual light spot distribution of points on the transmission surface of the micro-transmission element to be detected corresponding to the phases projected in the CCD detector, and calculating the difference between the ideal light spot distribution and the actual light spot distribution to obtain light aberration (delta epsilon)x,Δεy) According to the horizontal directionObtaining a slope error caused by a surface processing error of the micro-transmission element to be detected by a light aberration model, and calculating a transmission wave aberration delta F of the surface error by applying integralsurf;
According to the structural position parameter S of the detection system, in the modeled detection system, the surface shape error is added to the ideal micro-transmission element to obtain the reconstructed surface error transmitted wave aberration
The added surface shape error is used as an optimization variable, and an iterative reconstruction algorithm is used for realizing
The difference delta F between the transmitted wave and the surface error introduced by the surface error of the micro-transmission element to be measured
surfMinimum deviation, according to optimum
And completing transmission wavefront reconstruction of each surface error of the micro-transmission element to be measured by the corresponding surface error.
Preferably, the microscope objective adopts a microscope objective with long working distance.
Preferably, the structural position parameter S includes one or more of x, y, z coordinate values of each component in the detection system in a rectangular coordinate system, an inclination angle, an offset in the direction of the inclination angle, and an angle of a beam splitter prism and a refractive index of a medium between each part in an optical path.
Preferably, the light ray aberration (Δ ∈)x,Δεy) The method for calculating (a) comprises the steps of,
obtaining an ideal light spot distribution, wherein the ideal light spot distribution comprises the transmitted wave aberration F introduced by the ideal micro-transmission elementsystInformation;
obtaining the surface error transmitted wave aberration delta F introduced by the surface processing error of the micro-projection element to be measuredsurf;
By said F
syst、ΔF
surfObtaining actual light spot distribution, wherein the actual light spot distribution comprises the transmitted wave aberration F of the micro-transmission element to be measured
measInformation, and
obtaining light aberration (delta epsilon) by making difference between actual light spot distribution and ideal light spot distributionx,Δεy)。
Preferably, based on light ray aberration (Δ ε)
x,Δε
y) Obtaining the slope error of transmitted wave aberration caused by the surface processing error of the micro-transmission element to be measured according to the transverse light aberration model, and calculating the transmitted wave aberration delta F introduced by the surface error of the transmission element to be measured by using an integration method
surfWherein the method comprises introducing transmitted wave aberration caused by surface processing errors of the micro-transmission element to be detected
That is, there is a relationship:
wherein M represents the number of transmission surfaces of the micro-transmission element to be measured,
representing the i-th transmitted surface error transmitted wave aberration.
Transmitted wave aberration of each surface of the micro-transmission element
And reconstructing surface error transmitted wave aberration
Both conform to the Zernike polynomial, i.e., both conform to the following equation
Wherein N is the number of terms taken by the Zernike polynomial,
a j-th term of the zernike polynomial representing an i-th reconstructed transmitted surface error transmitted wave aberration.
Preferably, the transmitted wave aberration of each surface error of the micro-transmission element is adjusted by an iterative reconstruction algorithm
Corresponding Zernike polynomial coefficients are gradually optimized to obtain a set of Zernike polynomial coefficients
So that
And Δ F
surfWith minimum deviation, i.e.
Satisfy the equation
Where σ is an additional constraint, to
Transmitted wave aberration of each surface of the corresponding reconstructed micro-transmission element
Transmitted wave aberration of surface errors of micro-transmission element to be measured
Compared with the prior art, the invention has the beneficial effects that: the spatial resolution is improved by the long working distance microscope objective, so that the CCD detector can acquire a high spatial resolution deformation transmission fringe image. The method can synchronously reconstruct the surface of the micro-transmission element by an iterative reconstruction algorithm, has the characteristics of high precision, good universality and large dynamic range, does not need an additional compensation optical element compared with other micro-measurement methods, and reduces the measurement cost and the complexity.
Detailed Description
The present invention will be described in detail with reference to the specific embodiments shown in the drawings, which are not intended to limit the present invention, and structural, methodological, or functional changes made by those skilled in the art according to the specific embodiments are included in the scope of the present invention.
Example (b):
as shown in fig. 1, a method for detecting the surface shape of multiple surfaces of a transmission element includes step 1, constructing an inverse hartmann optical detection system based on a microphase deflection method, wherein the detection system includes a projection screen 1, a beam splitter prism 2, a micro transmission element 3 to be detected, a standard plane mirror 4, a microscope objective 5, an imaging lens 6, a CCD detector 7 and a computer. The beam splitter prism 2 is a broadband cubic beam splitter prism. The micro-transmission element 3 to be measured is a micro aspheric lens through which light can transmit. The microscope objective 5 is a long working distance microscope objective, the working distance is 34mm, and the magnification is 10 times. The micro-transmission element 3 to be measured is arranged between the beam splitter prism 2 and the standard plane mirror 4. The adjustment makes the optical axis of the imaging lens 6 and the lens of the CCD detector 7 coincide with the optical axis of the long-working-distance micro-objective 5, and the optical axis of the micro-objective 5 is adjusted to be vertical to the light emergent surface of the beam splitter prism 2. The projection screen 1 displays a group of sinusoidal stripe images with modulated light intensity in the horizontal and vertical directions, and the sinusoidal stripes pass through the beam splitter prism 2, the micro-transmission element 3 to be detected, the standard plane mirror 4, the microscope objective 5 and the imaging lens 6, and then the CDD detector 7 can acquire deformed stripe images containing surface shape information of the front and back surfaces of the micro-transmission element 3 to be detected. In the device, a CCD detector 1 and a projection screen 3 are respectively connected with a computer.
And 2, calibrating the established structural position parameter S of the detection system by using a three-coordinate measuring machine with the measurement precision reaching the micron order. The detection system structure position parameter S comprises: the device comprises a projection screen (1), a beam splitter prism (2), a micro-transmission element (3) to be measured, a standard plane mirror (4), a micro-objective (5), an imaging lens (6), a CCD detector (7) and other elements, wherein one or more of the x, y and z coordinate values, the inclination angle and the offset in the direction of the inclination angle in a rectangular coordinate system, the angle of the beam splitter prism (2) and the refractive index of a medium between each part in an optical path are combined.
And 3, establishing a modeled detection system in the computer according to the structural position parameter S of the detection system, and simulating and obtaining the ideal light spot distribution of the point on the surface of the ideal micro-transmission element to be detected, which has no processing error and is projected in the CCD detector 7, in the modeled detection system by a ray tracing method.
And 4, generating four-step 90-degree phase-shift sine stripes in the x direction and the y direction by using a computer, and displaying the sine stripes on a projection screen. The CCD detector collects the stripe light which penetrates through the micro-transmission element 3 to be detected and the micro-objective 5. And solving the phase distribution corresponding to the stripes acquired by the CCD detector 7 by adopting a four-step phase shifting method and a phase unwrapping method, and obtaining the actual light spot distribution of the point on the transmission surface of the micro-transmission element to be detected, which corresponds to the phase, projected in the CCD detector 7. The actual light spot distribution comprises the transmitted wave aberration F of the micro-transmission element 3 to be measured
measAnd (4) information. F
measIncluding the introduction of transmitted wave aberration F by an ideal micro-transmission element
systSurface error transmitted wave aberration delta F introduced by surface errors
surfI.e. by
Obtaining light aberration (delta epsilon) by making difference between actual light spot distribution and ideal light spot distribution
x,Δε
y) Obtaining the transmitted wave aberration slope error caused by the surface processing error of the micro-transmission element 3 to be detected according to the transverse light aberration model, and then carrying out integral operation on the slope distribution to obtain the surface error transmitted wave aberration delta F
surf。ΔF
surfComprises a micro-transmission element 3,Transmitted wave aberration introduced by machining errors of the latter two surfaces
Namely the existence of the relationship with
Transmitted wave aberration of both front and rear surfaces of the micro-transmission element 3
And reconstructing surface error transmitted wave aberration
All conform to a Zernike polynomial, i.e.
Where the two front and back surfaces of the i surface are (i ═ 1, 2), and j is the number of terms of the zernike polynomial, in this example, j takes 22 terms.
And 5, adding a surface shape error to the ideal micro-transmission element in the modeled detection system according to the structural position parameter S of the detection system, taking the added surface shape error as an optimization variable, and adjusting the transmission wave aberration of each surface error of the micro-transmission element 3 to be detected
Corresponding Zernike polynomial coefficient to obtain the transmitted wave aberration of the reconstructed surface error
Solving a set of optimal solution polynomial coefficients
So that
And Δ F
surfWith minimum deviation, i.e.
Satisfy the equation
Where σ is an additional constraint.
To be provided with
Corresponding transmission wave aberration of each surface of the reconstruction micro-transmission element 3
And
and the measured front and back surface error transmitted wave aberrations of the micro-transmission element are respectively used for completing the front and back surface error transmitted wave front reconstruction of the micro-transmission element 3.
Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.