CN104613882A - Lens center thickness measuring device based on optical phase demodulation and measuring method using same - Google Patents

Abstract

The invention discloses a lens center thickness measurement device and measurement method based on optical phase demodulation, which is characterized in that it includes a laser focusing light source, a beam splitter I, a reflector I, a reflector II, a beam splitter II, a power detector and computer, the laser focus light source, beam splitter I and reflector I are on the same horizontal line, the beam splitter I is located between the laser focus light source and reflector I, and the reflector II is located directly below the beam splitter I, The beam splitter II is located directly below the reflector I, the reflector II, the beam splitter II and the power detector are on the same horizontal line, and the computer receives data from the power detector. The invention has the advantages that the device has simple structure, low cost and reliable performance, realizes non-contact detection, and improves detection speed and precision.

Description

A lens center thickness measurement device based on optical phase demodulation and its measurement method

technical field

The invention relates to a lens center thickness measurement device and a measurement method, belonging to the field of optical lens detection.

Background technique

In the field of optics, the lens is one of the most important parts of optical instruments. The three basic parameters of the lens are central thickness, refractive index and radius of curvature. The error of the lens central thickness processing is an important factor affecting the imaging of the optical system. For example, in high-precision optical system products such as aviation and aerospace, there are strict requirements on the tolerance of the lens. The optical axis deflection angle, radial offset and axial clearance of the lens need to be precisely adjusted according to the center thickness of the lens in the lens. .

The existing methods for measuring the thickness of the lens center include contact measurement and non-contact measurement.

In contact measurement, calipers, micrometers and other measuring tools are generally used to measure the center thickness of the lens and the air gap of the lens group. This type of method is slow and inaccurate in measurement speed, and it is easy to scratch the polished or coated surface of the measured lens, resulting in an additional increase in stray light of the system after the instrument is assembled.

Non-contact measurement is a measurement technology that has developed rapidly in recent years. It has the advantages of fast, accurate, and non-damaging. Although this technology has not yet been fully popularized in the field of lens center thickness measurement, it is still developing. For example, patent CN102435146 and patent CN203100685 each proposed a device for measuring the thickness of the lens center based on the confocal method. The above two detection devices are relatively complicated, have high production costs, cumbersome measurement methods, and the accuracy cannot reach the ideal effect. Therefore, a new technical solution is needed to solve the above technical problems.

Contents of the invention

The object of the present invention is to provide a lens center thickness measuring device with simple structure, low manufacturing cost and simple measuring operation; the present invention also provides a measuring method using the device.

The technical scheme adopted in the present invention is:

A lens center thickness measurement device based on optical phase demodulation, which includes laser focused light source, beam splitter I, mirror I, mirror II, beam splitter II, power detector and computer, said laser focused light source, beam splitter I and mirror I are on the same horizontal line, the beam splitter I is located between the laser focusing light source and the mirror I, the mirror II is located directly below the beam splitter I, and the beam splitter II is located on the side of the mirror I Directly below, the reflector II, the beam splitter II and the power detector are on the same horizontal straight line, and the computer receives the data from the power detector.

The measurement method is: first measure the interference light power before adding the lens, that is, turn on the laser focusing light source to emit the beam, and the beam is divided into two optical paths through the beam splitter I, namely the measurement optical path and the reference optical path; the beam of the measurement optical path directly reaches Reflector Ⅰ is refracted by reflector Ⅰ to beam splitter Ⅱ; the light beam of the reference optical path is refracted from reflector Ⅱ to beam splitter Ⅱ; the light of the two optical paths finally converges and interferes at the beam splitter Ⅱ, and the power detector detects that there is no The size of the interference light power before adding the lens; then measure the size of the interference light power after adding the lens, that is, place the lens to be measured between the beam splitter I and the reflector I, and ensure that the center point of the lens and the laser focus light source emit The light beams are on the same straight line, the laser focusing light source is connected to emit the light beam, and the light beam is divided into two light paths through the beam splitter I, namely the measurement light path and the reference light path; the light beam of the measurement light path is inserted into the lens and reaches the reflector I, and is refracted by the reflector I to the beam splitter II; the light beam of the reference optical path is refracted by the reflector II to the beam splitter II; the light of the two optical paths finally converges at the beam splitter II and interferes, and the power detector measures the power of the interference light after adding the lens; Since there is a certain functional relationship between the lens center thickness and the ratio of the two interference light powers, the size of the lens center thickness can be calculated by a computer.

Since the phase difference is zero before the lens is added, there will be a phase difference after the lens is added, so the phase difference is obtained from the ratio of the two interfering light powers before and after. According to the proportional relationship between light intensity and power, the ratio of phase to power can be obtained functional relationship, that is

(I _{with lens} is the interference light intensity after adding lens, I _{without lens} is the interference light intensity before adding lens, P _{with lens} is the interference light power value after adding lens, P _{without lens} is the value before adding lens Interfering optical power value), through subsequent demodulation of the phase difference by the power ratio, the central thickness of the lens, the central thickness of the lens ( , n is the refractive index of air, is the refractive index of the measured lens).

The invention has the advantages that the device has simple structure, low cost and reliable performance, realizes non-contact detection, and improves detection speed and precision.

Description of drawings

Fig. 1 is a schematic structural view of the measuring device of the present invention.

Fig. 2 is a process flow chart of the measurement steps of the present invention.

Among them, 1. Laser focusing light source, 2. Spectroscope Ⅰ, 3, Reflector Ⅰ, 4, Reflector Ⅱ, 5, Spectroscope Ⅱ, 6. Power detector, 7. Computer.

Detailed ways

As shown in Figure 1, a lens center thickness measurement device based on optical phase demodulation, which includes a laser focusing light source 1, a beam splitter I2, a mirror I3, a mirror II4, a beam splitter II5, a power detector 6 and a computer 7 , the laser focusing light source 1, the beam splitter I2 and the reflector I3 are on the same horizontal line, the beam splitter I2 is located between the laser focusing light source 1 and the reflector I3, the reflector II4 is located directly below the beam splitter I2, and the beam splitter II2 is located in the reflector Directly below the mirror I3, the mirror II4, the beam splitter II5 and the power detector 6 are on the same horizontal straight line, and the computer 7 receives the data from the power detector 6.

The method of using the above-mentioned device for measurement: as shown in Figure 2, first measure the interference light power before adding the lens, that is, turn on the laser focusing light source to emit the beam, and the beam is divided into two optical paths by the beam splitter I, that is, the measurement optical path and the reference optical path; the beam of the measuring optical path directly reaches the reflector Ⅰ, and is refracted by the reflector Ⅰ to the beam splitter II; the light beam of the reference optical path is refracted by the reflector II to the beam splitter II; Convergence interference occurs, and the power detector measures the magnitude of the interference light power before the lens is added; then measures the magnitude of the interference light power after adding the lens, that is, the lens to be measured is placed between the beam splitter I and the reflector I, and Make sure that the center point of the lens is on the same straight line as the beam emitted by the laser focusing light source. Turn on the laser focusing light source to emit the beam. Reach mirror Ⅰ, refracted by mirror Ⅰ to beam splitter Ⅱ; the light beam of the reference optical path is refracted by mirror Ⅱ to beam splitter Ⅱ; the light of the two optical paths finally converges at the beam splitter Ⅱ and interferes, and the power detector detects The size of the interference light power after adding the lens; since the center thickness of the lens and the ratio of the two interference light powers have a certain functional relationship, the size of the center thickness of the lens can be calculated by a computer.

suppose , are the light intensities of the reference light and the detection light before reaching the spectroscope Ⅱ5, then the interference light power can be obtained by the formula of the interference light power

phase difference , are the phases corresponding to the reference light and the detection light, respectively;

After the beam splitter I has , is half of the incident laser power value;

so there is

According to phase

The thickness of the lens center can be calculated ( , n is the refractive index of air, is the refractive index of the measured lens).

The phase difference is zero before adding the lens, and there will be a phase difference after adding the lens, so we can get the phase difference from the ratio of the two light intensities before and after. According to the proportional relationship between light intensity and power, we can get the ratio of phase to power functional relationship, that is

, and then we can demodulate the phase difference from the power ratio to obtain the central thickness of the lens.

The above descriptions of the principles and applications of the present invention have been made with reference to specific features, so that those skilled in the art can better understand the present invention, and other implementation forms can be designed to be applicable to the present invention without departing from the scope of the appended claims. specific purpose.

Claims (3)

1. the lens center thickness measurement mechanism based on optical phase demodulation, it is characterized in that, comprise Laser Focusing light source, spectroscope I, catoptron I, catoptron II, spectroscope II, power detecting instrument and computing machine, described Laser Focusing light source, spectroscope I and catoptron I are on same level straight line, described spectroscope I is between Laser Focusing light source and catoptron I, described catoptron II is positioned at immediately below spectroscope I, described spectroscope II is positioned at immediately below catoptron I, described catoptron II, spectroscope II and power detecting instrument are on same level straight line, the data of described computing machine received power detector.

2. a kind of lens center thickness measurement mechanism based on optical phase demodulation according to claim 1, it is characterized in that, measuring method is: the size first measuring the interference light power before not adding lens, namely Laser Focusing source emissioning light bundle is connected, light beam is divided into two light paths by spectroscope I, i.e. optical path and reference path; The light beam of optical path directly arrives catoptron I, refracts to spectroscope II by catoptron I; The light beam of reference path refracts to spectroscope II by catoptron II; Article two, the light of light path finally carries out convergence at spectroscope II place and interferes, power detecting instrument measure and do not add lens before the size of interference light power; Then the size of the interference light power after adding lens is measured, be placed between spectroscope I and catoptron I by lens to be measured, and the light beam that the central point of guarantee lens and Laser Focusing light source are launched is on same straight line, connect Laser Focusing source emissioning light bundle, light beam is divided into two light paths by spectroscope I, i.e. optical path and reference path; Arrive catoptron I after the light beam insertion lens of optical path, refract to spectroscope II by catoptron I; The light beam of reference path refracts to spectroscope II by catoptron II; Article two, the light of light path finally carries out convergence at spectroscope II place and interferes, power detecting instrument measure and add lens after the size of interference light power; Because the ratio of lens center thickness and two interference light power has certain funtcional relationship, so the size of lens center thickness can be calculated by Computer.

3. a kind of lens center thickness measuring method based on optical phase demodulation according to claim 2, it is characterized in that, the computing formula of described funtcional relationship is:

, I _{there are lens}for adding the interference light intensity after lens, I _{do not add lens}for not adding the interference light intensity before lens, P _{there are lens}for adding interference light performance number, P after lens _{do not add lens}for not adding the interference light performance number before lens.