阅读说明：本技术 光学元件的界面测量方法和设备 (Method and apparatus for measuring interface of optical element ) 是由 吉莱斯·弗莱斯阔特 西尔万·珀蒂格朗德 于 2020-03-02 设计创作，主要内容包括：一种用于测量形成包括称为“参考”光学元件的至少一个光学元件的多个类似光学元件的一部分的待测量光学元件(5)的界面的设备和方法(100),该方法(100)包括以下步骤：所述参考光学元件和测量光束(11)的相对定位(102)；获取(104)“参考”图像；相对于视场定位(106)待测量光学元件(5),以允许获取“测量”图像；确定(107)所述待测量光学元件(5)相对于参考光学元件的位置差别；调整(110)所述待测量光学元件(5)的位置,以消除所述位置差别；以及,借助于所述测量光束(11)来测量(112)待测量光学元件(5)的界面。(An apparatus and a method (100) for measuring an interface of an optical element (5) to be measured forming part of a plurality of similar optical elements including at least one optical element, called "reference" optical element, the method (100) comprising the steps of: -the relative positioning (102) of the reference optical element and the measuring beam (11); -acquiring (104) a "reference" image; positioning (106) the optical element (5) to be measured with respect to the field of view, to allow the acquisition of a "measurement" image; determining (107) a difference in position of the optical element (5) to be measured relative to a reference optical element; -adjusting (110) the position of the optical element (5) to be measured to eliminate the position difference; and measuring (112) the interface of the optical element (5) to be measured by means of the measuring beam (11).)

1. A method (100) for measuring the interface of an optical element (5) to be measured forming part of a plurality of similar optical elements comprising at least one optical element, called "reference optical element", said method (100) being carried out by a measuring apparatus (1) comprising:

-an imaging channel (VI) configured to generate an illumination beam (9) and comprising an imaging device (3, 6, 13) configured to acquire, in a field of view of the imaging device (3, 6, 13), an image of an optical element illuminated by the illumination beam (9); and

-a measurement channel (VM) configured to generate a measurement beam (11) at a determined position with respect to the field of view and comprising an optical distance sensor (2) configured to generate distance and/or thickness measurements;

characterized in that the method (100) comprises the following steps:

-a relative positioning (102) of the at least one reference optical element and the measuring beam (11) to allow measuring an interface of the at least one reference optical element;

-acquiring (104) an image, called "reference image", of the at least one reference optical element thus positioned;

-positioning (106) an optical element to be measured (5) with respect to the field of view to allow the acquisition of an image, called "measurement image", of the optical element to be measured;

-determining (107), based on the reference and measurement images, a difference in position of the optical element to be measured (5) in the field of view relative to the at least one reference optical element;

-adjusting (110) the position of the optical element (5) to be measured in the field of view to eliminate the position difference; and

-measuring (112) the interface of the optical element (5) to be measured by means of the measuring beam (11).

2. The method (100) according to claim 1, wherein the step (102) of relative positioning of the at least one reference optical element and the measuring beam (11) comprises aligning the measuring beam (11) to be perpendicular to at least a portion of an interface of the at least one reference optical element.

3. The method (100) according to claim 1 or 2, comprising acquiring a plurality of reference images by using a plurality of reference optical elements of the plurality of optical elements.

4. The method (100) according to any one of the preceding claims, wherein the step of determining a difference in position (107) comprises the step of comparing the reference and measurement images.

5. The method (100) according to the preceding claim, wherein said comparing step comprises the steps of:

-identifying (108) and locating at least one corresponding feature shape in the reference and measurement images, respectively;

-determining (109) a difference in position between the corresponding feature shapes in the reference and measurement images.

6. The method (100) according to claim 4 or 5, wherein the comparing step comprises an image correlation step.

7. The method (100) according to any one of the preceding claims, wherein the position adjustment step (110) comprises:

-displacement of the optical element to be measured relative to the field of view; and/or

-displacement of the measuring beam relative to the field of view.

8. The method (100) according to any one of the preceding claims, wherein the step with respect to the optical element to be measured is performed for a plurality of optical elements to be measured from the same production group.

9. Method (100) according to any of the preceding claims, wherein the method is performed to measure the position and/or the gap of an interface of an optical element to be measured in the form of an optical component with a lens, such as an objective lens of a smartphone, the interface comprising a surface of the lens.

10. An apparatus (1) for measuring an interface of an optical element (5) to be measured forming part of a plurality of similar optical elements including at least one reference optical element, the apparatus comprising:

-an imaging channel (VI) configured to generate an illumination beam (9) and comprising an imaging device (3, 6, 13) configured to acquire, in a field of view of the imaging device (3, 6, 13), an image of an optical element illuminated by the illumination beam (9);

-a measurement channel (VM) configured to generate a measurement beam (11) at a determined position with respect to the field of view and comprising an optical distance sensor (2) configured to generate distance and/or thickness measurements; and

-a processing module (50) configured to process the distance and/or thickness measurements and images;

arranged to carry out all the steps of the method (100) according to any one of the preceding claims.

11. Device (1) according to the preceding claim, characterized in that said optical sensor (2) comprises a low coherence interferometer.

12. The device (1) according to any one of claims 10 or 11, characterized in that it comprises an optical element (7) for inserting a measuring beam (11) into an imaging channel (VI) so that it propagates in the field of view.

13. An apparatus (1) according to any one of claims 10 to 12, characterized in that the measurement channel (VM) is further configured to generate a second measurement beam incident on the opposite face of the optical element (5) to be measured.

14. The apparatus (1) according to any one of claims 10 to 13, further comprising a support (30) for accommodating the plurality of optical elements.

15. Apparatus (1) according to claim 14, characterized in that it further comprises displacement means (14) adapted to displace said support (30) in a plane perpendicular to the optical axis of the imaging means (3, 6, 13).

Technical Field

The invention relates to a method for measuring an interface of an optical element forming part of a plurality of substantially identical optical elements. The invention also relates to a measuring device for carrying out such a method.

The field of the invention is, without limitation, that of optical measurements of optical elements.

Background

During the manufacture of an optical element, such as a lens or an objective lens comprising a plurality of lenses, it may be necessary to control or measure the thickness or position of the constituent elements, or the gap between the constituent elements, along a measurement axis, such as the optical axis of the optical element.

For this purpose, it is known in particular to use low-coherence interferometry techniques. The measuring beam from the broad spectrum light source propagates through the surface of the optical element. Reflections of the beams on these surfaces are collected and analyzed by causing them to interfere with each other and/or with the reference beam to determine optical path differences between the coherent beams and thereby deduce the position and/or distance between the corresponding surfaces or interfaces. The thickness of the lenses, the distance between the lenses and/or the position of the lenses in the optical assembly may thus be determined, for example.

Such measurement techniques generally work by retro-reflection. It is necessary to have the measuring beam incident on all surfaces to be measured at an orthogonal or perpendicular angle of incidence so as to generate a reflected wave that can be captured by the measurement system. For measurement optical components, this condition generally means that it is necessary to have the measurement beam overlap or align with the optical axis of the component (and in particular the lens making up the component). There is therefore a need to implement an efficient method of aligning the measuring beams. In practice, it is desirable to be able to position the measuring beam accurately (e.g. on the order of microns for objects having dimensions of a few millimetres) relative to the optical axis of the assembly. It is desirable to have a method that enables such performance.

A system for measuring the position of a lens in an optical assembly using a low coherence interferometer is described in US 8,760,666B 2. The alignment of the measuring beam is carried out by causing the alignment beam to propagate through the optical elements of the assembly and detecting its deviation from the theoretical position by using a position-sensitive sensor of the CCD or PSD type. Since the theoretical position is not known in practice and, moreover, the alignment beam is attenuated by the lens through which it passes, this deviation is detected by rotating the optical assembly to deduce therefrom the path travelled by the alignment beam on the detector. The position of the component and its angular orientation are corrected to minimize the extension of the path.

However, in the case of mass-produced optical components, for example for manufacturing objective lenses for smartphones, the measurement time must be minimized. In particular, the use of optical alignment techniques based on angular rotation of the sample as described above is not suitable.

Disclosure of Invention

It is an object of the present invention to overcome these drawbacks.

It is a further object of the invention to propose a method and a device for interfacial measurements (e.g. position measurements and measurement of the gap between surfaces) of an object (e.g. an optical element or component) which allow a fast and accurate positioning of the measuring beam with respect to the optical axis of the object.

It is also an object of the present invention to propose an interface or surface measuring method and device suitable for measuring on assemblies of lenses or microlenses, in particular with dimensions in the order of hundreds of micrometers to several millimeters.

It is also an object of the present invention to propose an interface measurement method and apparatus suitable for measuring on lenses of the free form (freeform) type or aspherical type having a radius of curvature in millimeters.

It is also an object of the present invention to propose an interface measurement method and apparatus suitable for performing measurements at high rates on a plurality of similar optical objects or elements.

At least one of these objects is achieved with a method for measuring the interface of an optical element to be measured forming part of a plurality of similar optical elements including at least one optical element called "reference optical element", the method being implemented by a measuring apparatus comprising:

-an imaging channel configured to generate an illumination beam and comprising an imaging device configured to acquire, in a field of view of the imaging device, an image of an optical element illuminated by the illumination beam; and

-a measurement channel configured to generate a measurement beam at a determined position relative to the field of view and comprising an optical distance sensor configured to generate distance and/or thickness measurements;

the method comprises the following steps:

-relative positioning of at least one reference optical element and a measuring beam to allow measurement of the interface of the reference optical element;

-acquiring an image, called "reference image", of the at least one reference optical element thus positioned;

-positioning the optical element to be measured with respect to the field of view to allow the acquisition of an image, called "measurement image", of the optical element to be measured;

-determining a difference in position of the optical element to be measured in the field of view relative to the at least one reference optical element based on the reference and measurement images;

-adjusting the position of the optical element to be measured in the field of view to eliminate said position difference; and

-measuring the interface of the optical element to be measured by means of the measuring beam.

In the scope of the present invention, an "optical element" can refer to any type of optical object intended, for example, to be inserted into a light beam, to be shaped, and/or to produce an image. It may refer to, for example:

a single optical component, such as a lens or a beam splitter;

an assembly of lenses and/or other optical components (e.g. an imaging or camera objective), or a beam shaping device;

optical waveguides, optical fibers, etc.

The optical element can in particular comprise or consist of a refractive or diffractive element, for example a lens. It can then comprise an optical axis corresponding to the propagation axis of the light beam passing through it. In particular for optical elements with refractive lenses, the optical axis can also be an axis perpendicular to all surfaces or interfaces of the optical element or the only axis.

By "plurality of similar optical elements" is meant a group of optical elements of the same type, of the same model, from the same batch or (especially in mass production) following the same manufacturing steps.

The method according to the invention makes it possible to carry out measurements of the interfaces of the optical element, to derive therefrom, for example, measurements of the distance or position of these interfaces and/or measurements of the thickness of the optical component or of the gap separating them. These interfaces can, for example, comprise lens surfaces.

These measurements can be made using the measuring beam of a retro-reflective operating distance sensor. For this purpose, the measuring beam needs to be incident perpendicularly (within the limits of the angular tolerance depending on the optical device used) on the interface to be measured. Typically, this condition requires that the measuring beam is aligned in an optimal or at least sufficient way with the optical axis of the optical element to be measured. In practice, this positioning is a delicate and time-consuming operation.

According to the invention, the positioning is determined for one or more optical elements, called reference optical elements, for example from the same batch, the same production sequence or a plurality of similar optical elements that have undergone the same manufacturing step. The measurement points thus determined correspond to reference points in the field of view of the imaging device.

The method according to the invention uses the following facts: optical elements that have been manufactured according to the same or similar manufacturing steps exhibit similar specific patterns or features of reflected and/or transmitted light intensity when they are similarly illuminated. Images produced by illumination beams reflected, transmitted and/or scattered by the optical elements and containing such specific patterns or features can thus be utilized to determine the relative displacement or deviation of these optical elements in the field of view of the imaging device.

It is noted that when the optical elements comprise or consist of transparent members, the images obtained are generally not images of these elements or of their surfaces, but of optical signatures due to the interaction of the illumination with these members.

The displacement information thus obtained can then be used to position the optical element much more quickly and efficiently with respect to a reference point in the field of view. The measuring beam positioned at the reference or measuring point is then automatically aligned with the optical axis of the optical element to be measured. The position of the measuring beam corresponds to an optimum position at which the most accurate possible measurement of the interface of the optical element can be obtained. By positioning the measuring beam with reference to the pattern or shape of the features, the optimum position of the measuring beam can be reliably positioned for all similar optical elements, thereby making it possible to obtain reliable, repeatable and reproducible measurements. Knowledge of the positioning of the measuring beam relative to the feature shape is thus used to automatically position the optical element to be measured relative to one or more reference optical elements and, after positioning at least one of the feature patterns, to derive therefrom the position of the measuring beam directly and without additional effort for subsequent optical element measurements.

The step of determining the measurement point on the one or more reference optical elements and thus the relative positioning of the one or more reference optical elements and the measurement beam can be performed by known methods. This step need not be repeated for other optical elements to be measured.

The method according to the invention can be implemented in particular for controlling optical elements or optical components during their production, for example objectives formed by lenses or microlenses, such as (in particular in mass production) smartphones or objectives for the motor vehicle industry. In fact, in this case, it is very important to minimize the measurement time in order to be able to maintain a high production speed. The method according to the invention makes it possible to determine the average optical axis in the optical element or component to be measured corresponding to an optimized alignment of the measuring beam as quickly and as reliably as possible, without the measuring beam being used to scan the element until a satisfactory measuring signal is obtained, and without the optimization having to be carried out for every optical element of the same, mass-produced batch. In particular, by using information about the measurement of the individual optical elements of the batch, the positioning of the measuring beam can be carried out quickly.

The step of relative positioning of the reference optical element and the measuring beam may comprise aligning the measuring beam perpendicular to at least a portion of an interface of the at least one reference optical element.

According to a non-limiting embodiment, a method according to the present disclosure may include acquiring a plurality of reference images by using a plurality of reference optical elements of the plurality of optical elements.

In this case, the reference image can be generated based on a combination of a plurality of reference images. The combination may be generated, for example, by using the intensities of the different reference images.

According to a non-limiting embodiment of the method according to the invention, the step of determining the difference in position may comprise the step of comparing the reference image and the measurement image.

During this comparison step, the similarity of shapes, particularly image light intensity versus shape, can be used to determine the relative position of the optical element with respect to the field of view.

The comparing step may thus comprise the steps of:

-identifying and locating at least one corresponding feature shape in the reference image and the measurement image, respectively;

-determining a difference in position or relative displacement between the corresponding feature shapes in the reference image and the measurement image.

Alternatively or additionally, the comparing step may comprise an image correlation step.

Image correlation techniques are in fact particularly suitable for measuring the difference in position or the relative displacement between two images. This is a technique for measuring the displacement field of a part or all of an image relative to another image or a reference image.

In general, the step of determining the positional difference between the images can be performed by implementing any known image registration method.

The difference in position or relative displacement may be expressed in the form of a geometric transformation, for example a rigid geometric transformation with translation and rotation.

According to a non-limiting embodiment, the position adjustment step may comprise:

-displacement of the optical element to be measured relative to the field of view; and/or

-measuring the displacement of the light beam relative to the field of view.

Position adjustments are made to compensate for the position differences identified in the previous step. It is performed at least in translation, which may be sufficient for positioning the measuring beam. Alternatively, it can also be done rotationally for higher accuracy.

The method according to the invention may further comprise optimizing the positioning of the measuring beam relative to the optical element to be measured.

This optimization can be done by locally displacing the measuring beam relative to the element to optimize a measurement parameter, such as the detected intensity or a difference from the desired measurement. The local displacement can be performed, for example, according to a grid or path of points, or implemented such that the error gradient is minimized.

Of course, the optimization is similar to that carried out for the relative positioning of the reference optical element and the measuring beam. However, they are still much faster because the most time-consuming step for positioning the measuring beam to allow even non-optimal interface measurements is performed quickly by adjusting the position of the measuring beam by comparing the reference image and the measuring image.

According to a non-limiting embodiment, the steps of the method with respect to the optical element to be measured can be performed for a plurality of optical elements to be measured coming from the same production line.

Advantageously, the method according to the invention can be implemented to measure the position and/or the clearance of an interface of an optical element in the form of an optical component with a lens (e.g. an objective lens of a smartphone), said interface comprising a surface of the lens.

According to another aspect of the present invention, there is provided an apparatus for measuring the interface of an optical element to be measured forming part of a plurality of similar optical elements including at least one reference optical element, the apparatus comprising:

-an imaging channel configured to generate an illumination beam and comprising an imaging device configured to acquire, in a field of view of the imaging device, an image of an optical element illuminated by the illumination beam;

-a measurement channel configured to generate a measurement beam at a determined position relative to the field of view and comprising an optical distance sensor configured to generate a measurement of distance and/or thickness; and

-a processing module configured to process the measurements of distance and/or thickness and the images;

which are arranged to carry out all the steps of the method according to the invention.

The device implementing the method according to the invention represents a measurement system, which means that when the measuring beam (for example with the optical axis of the optical element to be measured) is correctly aligned, available measurement signals are obtained, which make it possible to identify the interfaces, their positions and the gaps.

The apparatus thus allows, for example, production control of optical elements to verify that they meet specifications. It is furthermore noted that if there is no measurement signal available after adjusting the position, this may mean that the measurement beam may not be aligned with the optical axis of, for example, the optical element to be measured, or that the element does not have an optical axis common to all its components, which indicates that the optical element is defective and must be rejected. This assumption may occur, for example, if the optical components are misaligned, decentered, or tilted.

According to one non-limiting embodiment, the optical sensor may comprise a low coherence interferometer.

Such interferometers are particularly suitable for making distance and/or gap measurements.

Any type of known and suitable low coherence interferometer can be used. Such an interferometer can in particular implement:

time-domain low coherence interferometry techniques with delay lines for generating optical delays between interfering waves;

-a spectral domain low coherence interferometry technique with a spectrometer for analyzing the interference signal; or

Low coherence interferometry technique by means of wavelength scanning, with a tunable laser source.

The device according to the invention may further comprise an optical element for inserting the measuring beam into the imaging channel such that it propagates in the field of view.

These optical elements can include, for example, beam splitters or beam splitting cubes.

According to a particular, by no means limiting embodiment of the device, the measuring channel may also be configured to generate a second measuring beam incident on the opposite face of the optical element to be measured.

In this case, the optical element to be measured can be measured on both faces thereof.

Advantageously, the device according to the invention may also comprise a support for accommodating a plurality of optical elements.

The support can consist of, for example, a support for a sample intended to receive a plurality of optical elements to be measured in receptacles or openings, which can be aligned, for example, in the form of a grid.

Preferably, the optical elements to be measured are aligned on the support such that their respective optical axes are parallel to the optical axes of the imaging device and the measuring beam. In practice, for optical elements with precise tolerances (e.g. lens barrels), the parallelism can be made sufficiently accurate by tolerances and mechanical adjustments.

In this case, the apparatus according to the present invention may include a displacement device capable of displacing the support in a plane perpendicular to the optical axis of the imaging device.

These displacement means can for example comprise a translation and/or rotation stage.

The alignment of the optical element to be measured is then only performed in a plane perpendicular to the optical axis of the imaging device, which can be easily obtained at high speed.