CN103869462A - Device for carrying out splicing mirror common-phase control by utilizing cavity ring-down technology - Google Patents

Abstract

The invention discloses a device for controlling the common phase of a splicing mirror by using a cavity ring-down technology. The laser comprises a laser, a mode matching optical device, at least one reflector, a converging lens, a photoelectric detector, a function generator, a collecting card and a computer. This device will turn into the detection to the detection of splicing mirror phase place to the optical resonator who has the splicing mirror to constitute and ring down the detection of time, improves optical resonator's ring down time through adjusting the slope of splicing sub mirror and translating, realizes the common phase place control to the splicing mirror.

Description

A device for co-phase control of splicing mirrors using optical cavity ring down technology

technical field

The invention belongs to the field of optics, and relates to a device for realizing co-phase control of splicing mirrors by using optical cavity ring-down technology.

Background technique

Optical cavity ring-down technology (Cavity Ring-Down, CRD) is an ultra-high-sensitivity detection technology. This technology does not directly measure the light intensity, but measures the ring-down time of the beam in the optical resonant cavity and the fluctuation noise of the output power of the light source. It does not affect the measurement results, and is an absolute measurement technique with simple devices. Compared with traditional measurement methods, optical cavity ring-down technology has incomparable advantages and wide application fields. Since it was proposed in the 1980s, it has attracted the attention of researchers from many countries in the world, and the scope of application fields is also expanding. Optical cavity ring-down technology has achieved spectral measurement of substances including gases, liquids, solids, plasmas, and atmospheric suspended particles. Optical cavity ring down technology is also widely used in trace gas detection, material composition in flame, solid film absorption, optical fiber bending loss, plasma free radical concentration, high reflectivity measurement, etc.

When the wavelength is constant, the resolution of the telescope increases with the aperture of the primary mirror. However, the large-aperture single primary mirror poses unprecedented challenges to mirror surface preparation, processing and inspection. The method of splicing mirrors can not only achieve the optical performance of large-aperture telescopes, but also reduce the processing cost and cycle of mirrors, opening up a new path for large telescopes. However, the imaging quality of a telescope of the same aperture can only be achieved when the spliced mirrors are strictly co-phased. Since the late 1990s, people have proposed a variety of co-phase detection methods, such as the use of edge displacement sensors between spliced sub-mirrors, the detection of far-field spots in telescopes, and the interferometer for optical component surface detection.

For an optical resonant cavity composed of splicing mirrors and reflectors, from the perspective of optical cavity ring down, the degree of inclination and translation of the splicing sub-mirror is related to the ring down time of the optical cavity. When the spliced sub-mirrors are strictly co-phased, the ring-down time of the optical resonator is the largest; when the spliced sub-mirrors do not satisfy the co-phase, diffraction loss will be introduced in the resonant cavity, reducing the ring-down time of the resonant cavity.

Contents of the invention

Based on the fact that when the spliced sub-mirrors are strictly co-phased, the ring-down time of the optical resonant cavity is the largest; when the spliced sub-mirrors do not meet the co-phase, diffraction loss will be introduced in the resonant cavity, reducing the ring-down time of the resonant cavity, the present invention proposes A new type of device for co-phase control of splicing mirrors is proposed by using optical cavity ring down technology.

A device for co-phase control of splicing mirrors using cavity ringdown technology, including lasers, mode matching optical devices, splicing mirrors, optical resonant cavity mirrors, focusing lenses, photodetectors, function generators, data acquisition cards and computers , characterized by:

The optical resonant cavity mirror at least includes a first optical resonant cavity mirror; it may also include a second optical resonant cavity mirror. The splicing mirror and the optical resonant cavity mirror form a stable optical resonant cavity;

The beam emitted by the laser is modulated by the mode-matching optical device and is incident into the optical resonant cavity;

A focusing lens, located behind the first optical resonant cavity mirror, focuses the light beam passing through the optical resonant cavity mirror onto the photodetector;

The photodetector is connected with the data acquisition card to convert the optical signal into an electrical signal;

The data acquisition card is connected with the computer and is used to collect the electrical signal output by the photodetector and send the data to the computer;

The computer controls the function generator to generate waveforms, receives the electrical signal input by the acquisition card, and connects with the splicing mirror;

Function generator, one end is connected to the computer, and the other end is connected to the laser;

When co-phase control is performed, the computer applies disturbance to the spliced sub-mirror to detect the change of the ringdown time of the resonant cavity. If the ringdown time increases, the next time the forward disturbance is applied, otherwise the reverse disturbance is applied.

By moving the mode to match the distance of the components in the optical device or the focal length of the lens, the laser light emitted by the laser is an eigenmode of the optical cavity. There are two methods to achieve the mode matching of the optical resonator. The first method is to measure the q parameter of the laser output beam. According to the matrix optics method, the parameters of the mode matching optical system are calculated when the mode matching conditions are met; the second method is to fix the optical The state of the resonant cavity remains unchanged, aiming at the longest ring-down time of the optical resonator, and adjusting the parameters of the matching optical system. When the ring-down time of the optical cavity is the longest, the mode coupling in the optical resonator is the smallest, and the ring-down time of the optical cavity maximum.

The optical resonant cavity formed by the splicing mirror and at least one optical resonant cavity mirror is a stable cavity; the optical resonant cavity includes at least one reflecting mirror, and when only one reflecting mirror is used, the reflecting mirror is coaxially parallel to the splicing mirror to form a straight cavity; using When multiple mirrors are used, the mirrors and spliced mirrors form a folding cavity.

The output beam of the laser is a Gaussian beam, which can be a Hermite-Gaussian beam or a Laguerre-Gaussian beam. The output beam in a special mode can reduce the loss of the spliced sub-mirror gap.

The converging lens is located in front of the photodetector and plays the role of converging the light beam into the photosensitive area of the photodetector. The computer needs to calculate the ring-down time of the optical resonant cavity, and the ring-down time τ of the ring-down cavity is defined as the time required for the outgoing light intensity I(t) to decay to 1/e of the initial transmitted light intensity I ₁ .

The tilt and translation of the splicing sub-mirror can change the loss of the optical resonant cavity, but the relationship between the tilt and translation of the splicing sub-mirror and the loss of the resonant cavity is complicated. When performing common phase control, the computer applies disturbance to the splicing sub-mirror to detect the ringing of the resonant cavity Time changes, if the ringing time increases, the next time a positive disturbance is applied, otherwise a reverse disturbance is applied.

Principle of the present invention is as follows:

For an optical resonator composed of spliced mirrors, the common phase error of the spliced mirrors will introduce diffraction loss in the resonant cavity, resulting in a reduction in the ringdown time of the optical resonant cavity. Only when the spliced mirrors strictly meet the common phase condition, the optical resonance The cavity has the longest ring down time. Therefore, in order to realize the co-phase control of the splicing mirror, the present invention first forms the splicing mirror and at least one reflecting mirror into an optical resonant cavity, and aims at the longest ring-down time of the optical resonant cavity, and adjusts the splicing sub-mirror by random optimization. The tilt and translation can realize the common phase control of the splicing mirror.

Description of drawings

Fig. 1 is a schematic diagram of the optical path of an embodiment of the device of the present invention;

The simulation result of the relationship between the size of the translation error and the ring-down time between the splicing mirrors of Fig. 2;

Fig. 3 Simulation results of co-phase control based on stochastic parallel gradient descent algorithm.

Detailed ways

The present invention will be described in detail below in conjunction with the embodiments and accompanying drawings, but the present invention is not limited thereto.

As shown in Figure 1, a co-phase control device for splicing mirrors using cavity ring down technology, including lasers (1), mode matching optical devices (2), splicing mirrors (3), optical resonant cavity mirrors ((4- 1) and (4-2)), focusing lens (5), photodetector (6), function generator (7), data acquisition card (8), computer (9).

The method of co-phase control of splicing mirrors using the device shown in Figure 1 is as follows:

1) The splicing mirror (3) is composed of two splicing sub-mirrors. In order to reduce the loss introduced by the gap between the splicing sub-mirrors, the output mode of the laser (1) is TEM ₁₀ -mode beam;

2) Referring to Figure 1, the optical resonant cavity includes a first optical resonant cavity mirror (4-1), and the first optical resonant cavity mirror (4-1) is a plane mirror; it also includes a second optical resonant cavity mirror ( 4-2), its radius of curvature R=6 meters; the splicing mirror (3) is a plane mirror, the first optical resonant cavity mirror (4-1), the second optical resonant cavity mirror (4-2) and the splicing mirror ( 3) Form a semi-confocal cavity, that is, the cavity length L=R/2;

3) Match the distance of the components in the optical device (2) by moving the mode, so that the beam waist injected into the optical resonant cavity is located on the mirror surface of the spliced sub-mirror. This implementation example simulates the impact of the translation error between the spliced sub-mirrors on the resonant cavity The impact of ring down time, as shown in Figure 2;

4) The computer (9) modulates the output power of the laser (1) through the function generator (7) to generate a square wave output signal. On the falling edge of the laser power, the photodetector (6) is collected by the acquisition card (8) For the measured laser intensity signal, the computer (9) calculates the ring-down time of the optical resonator by means of curve fitting, and defines the ring-down time τ as the decay of the outgoing light intensity I(t) to 1/e of the initial transmitted light intensity I ₁ time required;

5) In this embodiment, the stochastic parallel gradient descent algorithm is used as the stochastic optimization control method. Taking the maximum ringdown time τ as the control target of the stochastic parallel gradient descent algorithm, the random parallel gradient descent algorithm is used to calculate the translation error of the spliced sub-mirror in real time. This embodiment simulates the control effect on the translation error of the spliced sub-mirror, as shown in Figure 3 Show.

Claims (5)

1. A device for co-phase control of spliced mirrors using cavity ring down technology, including lasers (1), mode-matching optical devices (2), spliced mirrors (3), optical resonant cavity mirrors (4), and focusing lenses (5), photodetector (6), function generator (7), data acquisition card (8) and computer (9), it is characterized in that: The splicing mirror (3) and the optical resonator mirror (4) form a stable optical resonator; the optical resonator mirror includes at least one first optical resonator mirror (4-1); The beam emitted by the laser (1) is modulated by the mode-matching optical device (2) and is incident into the optical resonant cavity; The focusing lens (5), located behind the first optical resonant cavity mirror (4-1), focuses the light beam passing through the first optical resonant cavity mirror (4-1) onto the photodetector (6); The photodetector (6), connected with the data acquisition card (8), converts the optical signal into an electrical signal; The data acquisition card (8), connected to the computer (9), is used to collect the electrical signal output by the photoelectric detector (6), and send the data to the computer (9); The computer (9) controls the function generator (7) to generate waveforms, receives the electrical signal input by the acquisition card (8), and connects with the splicing mirror (3); A function generator (7), one end is connected to the computer (9), and the other end is connected to the laser (1); When co-phase control is performed, the computer (9) applies disturbance to the spliced sub-mirrors to detect the change of the ringdown time of the resonant cavity. If the ringdown time increases, a forward disturbance is applied next time, otherwise a reverse disturbance is applied. 2. The device for co-phase control of splicing mirrors using cavity ring down technology according to claim 1, characterized in that the mode matching optical device (2) is a positive lens, a negative lens, or a positive lens and a negative lens At least one element in the mode-matching optical device (2) can change the focal length or move along the laser beam transmission direction. 3. As claimed in claim 1, the device for co-phase control of splicing mirrors using cavity ring down technology is characterized in that, said splicing mirror (3) is composed of at least two splicing sub-mirrors, and the splicing sub-mirrors have A device that can be adjusted for tilt or pan. 4. The device for co-phase control of splicing mirrors using cavity ring-down technology according to claim 1, characterized in that the optical resonant cavity includes a splicing mirror (3) and at least one optical resonant cavity mirror (4) ; The optical resonant cavity is a stable cavity: When only one optical resonant cavity mirror is used, the optical resonant cavity mirror is a first optical resonant cavity mirror (4-1), and the first optical resonant cavity mirror (4-1) and the splicing mirror ( 3) Coaxial parallel to form a straight cavity; When multiple optical resonator mirrors are used, the optical resonator mirror includes a first optical resonator mirror (4-1), and a second optical resonator mirror (4-2), the first The optical resonant cavity mirror (4-1), the second optical resonant cavity cavity mirror (4-2) and the splicing mirror (3) form a folding cavity. 5. The device for co-phase control of splicing mirrors using cavity ring down technology as claimed in claim 1, characterized in that, the waveform generated by the function generator (7) is a square wave, and the high level and low level of the square wave The level lasts for a minimum time of 5 microseconds.

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