CN113029526B - A synthetic aperture common-phase error estimation method and device - Google Patents

Abstract

The invention belongs to the technical field of optical detection, and provides a method and a device for estimating a synthetic aperture common-phase error, wherein two paths of light rays needing to eliminate the common-phase error are introduced into a light beam interference module, and a light beam synthesizer capable of realizing a static ABCD method is used for separating the two paths of light rays to obtain four paths of coherent light beams; respectively introducing the obtained four paths of coherent light beams into a spectrometer to obtain light intensity signals of different spectral bands; and (3) utilizing a fringe sensor to track fringes and acquiring the common-phase error of the two paths of light rays and a large-range system aiming at the phase difference of different spectral bands.

Description

A comprehensive aperture common phase error estimation method and device

technical field

The invention belongs to the technical field of optical measurement, and in particular relates to a method and a device for realizing optical comprehensive aperture fringe tracking by using a diffraction system to obtain a common phase error.

Background technique

Optical synthesis aperture technology (OSA), also known as optical synthesis aperture technology, refers to arranging multiple sub-apertures in a certain way to form a large optical aperture. The target beam discretely collected by the sub-aperture array is converged to the beam combiner for interferometric combination, so as to obtain the spatial resolution equivalent to that of the equivalent single-aperture system. Its baseline length is not limited by the aperture size of a single telescope. It is expected to break through the limitations of traditional optical high-resolution imaging systems due to size, weight, cost and technical feasibility, and realize ultra-high-resolution imaging. Both astronomy and military fields have extensive application value. At present, countries such as the United States, the United Kingdom, France and Japan attach great importance to the development and application of optical synthetic aperture technology.

At present, optical synthetic aperture technology refers to two basic forms of passive (passive) Michelson type and Fizeau type. Optical synthetic aperture arrays are generally divided into dense aperture arrays (Fizeau type) and sparse aperture arrays (including Fizeau type and Michelson type). Among them, the dense aperture array refers to the (co-phase) spliced mirror telescope; the sparse aperture array (consisting of a relatively small number of sub-telescopes) with a very long baseline and cannot be imaged instantaneously is often called an optical synthesis aperture telescope (with stellar light interference As the basis); the baseline is short (relative to the diameter of the sub-aperture), and the array composed of a relatively small number of sub-apertures that can be imaged instantaneously is often called a sparse aperture array. No matter which of the above, it only partially fills the ideal mirror surface of the imaging system.

In the prior art, the common-phase error is analyzed by using the diffraction pattern of the circular hole in the sub-aperture, and the error is obtained by performing a correlation operation with the known template. Using this method, the requirements for the confocal error of the two sub-mirrors to be inspected are relatively high, and it is not intuitive To obtain the two-way optical path difference that needs to eliminate the common phase error,

Contents of the invention

In order to understand the technical defects in the above-mentioned technologies, the present invention proposes a comprehensive aperture common-phase error estimation method and device. The method of fringe tracking using a fringe sensor can quickly and intuitively obtain the common-phase error of the two sub-mirrors without first accurate Calibration of confocal error, high tolerance to confocal error of two beams. To achieve the above object, the present invention adopts the following specific technical solutions:

A comprehensive aperture common phase error estimation method, comprising:

S1. Using a beam combiner that can realize the static ABCD method to separate the two rays that need to eliminate the common phase error, and obtain four coherent beams;

S2. Introduce four coherent light beams into the spectrometer respectively to obtain light intensity signals of different spectral bands;

S3. Use the fringe sensor to track the fringe, and obtain the common-phase error of the two light rays according to the phase difference of different spectral bands.

Preferably, the common phase error is obtained by the following formula:

Among them, A, B, C, and D are the obtained four-way light intensity values respectively;

N is the total light intensity;

φ ₁₂ is the optical path difference introduced by the two rays;

为系统固有的光程差。

is the inherent optical path difference of the system.

Preferably, the following steps are also included before step S1:

S0. Align the synthetic aperture device that has completed preliminary adjustments to the North Star and receive starlight.

A method for estimating the common-phase error of a synthetic aperture uses the steps of the above-mentioned method to realize the common-phase error estimation of interference beams of different spectral bands in a spliced telescope.

A comprehensive aperture co-phase error estimation device, comprising: an energy collection module, a beam interference module and a data processing module;

The energy collection module is used to collect light energy information;

The beam interference module is used to split two paths of light into four paths of coherent light, and perform fringe tracking on each path of interfering light within a smaller bandwidth;

The data processing module is used to process the collected spectral phase information, and obtain the common-phase error of the two rays according to the phase difference of different spectral segments.

Preferably, the beam interference module includes: a spectrometer and a beam combiner for implementing the static ABCD method.

Preferably, the beam combiner can be a structure that uses a prism to realize light splitting, or a structure that uses a photonic chip to realize light splitting.

Preferably, a synthetic aperture system with two sub-mirrors in one sub-aperture, or a synthetic aperture system with three sub-mirrors in one sub-aperture, is suitable for spliced telescopes.

Preferably, the device and the actual optical path are coupled by a common optical path or a vertical optical path, which can reduce the influence of atmospheric turbulence on the spliced telescope and realize sky observation.

The present invention can obtain following technical effect:

1. The common-phase error measurement of the large-aperture synthetic aperture system can be realized without moving parts.

2. Use the method of dividing the spectrum and cooperate with the spectrometer to realize the estimation of the common phase error of the spliced telescope.

3. It can not only realize star observation, but also reduce the impact of turbulence on the system to realize sky observation.

4. The device has a large tolerance to the confocal error of the system, and can correct the confocal error and common phase error at the same time.

Description of drawings

Fig. 1 is the flow chart of a kind of comprehensive aperture common phase error estimation method of an embodiment of the present invention;

Fig. 2 is a schematic diagram of a comprehensive aperture common-phase error estimation device according to an embodiment of the present invention;

Fig. 3 is the schematic diagram that the system of an embodiment of the present invention contains three mirrors;

Fig. 4 is the schematic diagram that the system of an embodiment of the present invention contains two mirrors;

Fig. 5 is a schematic diagram of utilizing a spectroscope to realize the static ABCD method according to an embodiment of the present invention;

Fig. 6 is a schematic diagram of implementing the static ABCD method by using a photonic chip according to an embodiment of the present invention.

Reference signs:

The first beam 1 , the second beam 2 , the energy collection module 3 , the beam interference module 4 , and the data processing module 5 .

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, but not to limit the present invention.

The purpose of the present invention is to provide a method and device for adjusting the common phase error of spliced telescopes by using the spectral segment method and cooperating with the spectrometer in the scene of adjusting the common phase of the telescope. A synthetic aperture common-phase error estimation method and device provided by the present invention will be described in detail below through specific embodiments.

As shown in Fig. 1 and Fig. 2, first align the synthetic aperture system that has completed the preliminary adjustment with Polaris, so that the energy receiving module 3 receives starlight; then introduce the two paths of light that need to eliminate the common phase error into the beam interference module 4, and obtain four coherent light with a phase difference of π/2; the obtained four paths of light are respectively introduced into the spectrometer to obtain light intensity signals of different spectral bands, and the method of fringe tracking is carried out by using a fringe sensor. The processing module 5 obtains the common-phase error between the two rays and the large-scale system:

Among them, A, B, C, and D are the obtained four-way light intensity values respectively;

N is the total light intensity;

φ ₁₂ is the optical path difference introduced by the two rays;

为系统固有的光程差。

is the inherent optical path difference of the system.

In a preferred embodiment of the present invention, the beam interference module 4 includes a beam combiner for implementing the static ABCD method and a spectrometer for dispersing the four-way light obtained by the beam combiner to observe the beam fringe information after dispersion.

The beam combiner can implement the static ABCD method through two paths, as shown in Figure 5, using a beamsplitter prism built with volume optics to generate four-way coherent light, or as shown in Figure 6, using an integrated photonic chip to implement the static ABCD method.

As an existing technology, the static ABCD method uses static optical elements to realize the spatial phase modulation method, which can measure four phase states simultaneously. As shown in Figure 5, the achromatic phase shifter introduced in one interference arm of the beam combiner makes p The polarized light moves π/2 relative to the s-polarized light, and the polarization beam splitter separates the p-polarized light and the s-polarized light, so that the four output arm beams are out of phase by π/2, that is, 0, π/2, π, 3π /2 four phase states.

In a preferred embodiment of the present invention, when the optical path difference of the fringe sensor is large enough that the interference fringes of white light cannot be observed, but the interference fringes can still be observed in each spectrum of the interference light, so the incident light is dispersed by the spectrometer, The coherence length of the detected fringes is enlarged. The fringes observed in the dispersed light carry the spectral information of the fringes of each channel for fringe tracking.

According to the optical principle, the interference fringe intensity can be expressed as formula (3):

in,

为两干涉臂光程s₁与s₂之差引入的相位。λ is the wavelength of coherent light, I ₁ and I ₂ are the incident light intensity of each interference arm in the fringe sensor, γ ₁₂ is the complex coherence degree, the modulus is |γ ₁₂ |, and the phase is

is the phase introduced by the difference between the optical path s ₁ and s ₂ of the two interference arms.

The contrast or visibility of interference fringes can be expressed as the ratio of the fringe amplitude to the total background illumination, as shown in equation (4):

If we introduce the spectral number variable κ=1/λ of wavelength λ, let:

x＝(s ₂ -s ₁ )

Then the interference fringe intensity of each wavelength:

I(κ,x)＝I _s [1+|γ ₁₂ |cos(2πκx-φ ₁₂ )]+I _b (5)

In this case, x=s ₂ -s ₁ only represents the phase offset of the piston and does not contain a tilt component. When the light intensity of the two arms I ₁ =I ₂ , the visibility of the interference fringes is the modulus of the complex coherence:

V＝|γ ₁₂ | (6)

If the bandwidth of the fringe sensor is small enough, the observation of non-quasi-monochromatic light source interference can be expressed as formula (6). When the optical path difference x is an integer multiple of 2π for most wavelengths, bright interference fringes will appear. For a wide spectral range, bright fringes can only be observed when the two arms of the interferometer have the same dispersion and the optical path difference x is 0 for all wavelengths. According to the coherent envelope, as the optical path difference increases, the fringe visibility gradually decreases. Therefore, the spectral segment method is used to track the fringe and realize the detection of the common phase error.

The optical path difference between the synthetic wavefronts of the fringe sensor is expressed as: the product of the refractive index _ni of the beam passing through different media in each interference arm and the difference between the propagation path lengths x _1i and x _2i , as shown in equation (7):

Let the variable x _i =x _1i -x _2i , and assume that the beam travels through a pinhole delay line of length x ₀ and K dispersive media, then the phase delay of the introduced interference fringes is:

Since light propagates from different interference arms of the stripe sensor to the beam combiner through different lengths of vacuum channels and dispersion channels such as air and glass, the phase delay varies (depends) with different wavelengths: at shorter wavelengths, if The higher the refractive index of the medium, the slower the light travels in it, and the greater the optical path difference introduced. If we only consider the fringe sensor with limited bandwidth, there will be different specific wavelengths of light in this spectral band first and last to reach the beam combiner, the transmission of the entire light wave can be regarded as a group or include, and the group delay is proportional to The phase change rate of the wavenumber function at the center of the spectrum:

If only the path length difference of light transmission in vacuum is considered, that is, x(κ)=x ₀ , then the group delay is independent of the wave number and has nothing to do with the wavelength group delay(κ ₀ )=x ₀ , and the fringe phase delay is a linear function of the wave number The function 2πκx(κ)=2πκx ₀ .

Therefore, the phase tracking algorithm is mainly used to find the constant phase position where the fringe visibility is the highest, that is, the common phase, and is used to precisely track the common phase error of the stitching telescope; the group delay tracking algorithm is mainly used to search for interference fringes in this spectral band The constant group delay position, ie the coherence, where the number remains constant, is used to roughly track the common-phase error of the stitched telescopes.

Therefore, assuming that the light intensity of the four-way coherent light obtained by the spectrometer in the narrow band is A, B, C, and D, the amplitude and phase of the fringes finally obtained, that is, the common phase error, are as follows:

According to the principle of multi-center wavelength measurement, the phase delays obtained in different wavelength bands can greatly expand the measurement range and realize the fine tracking of common phase errors.

The device of the present invention is suitable for a synthetic aperture system with two sub-mirrors in one sub-aperture of spliced telescopes, as shown in Figure 4, or a synthetic aperture system with three sub-mirrors in one sub-aperture, as shown in Figure 3.

In a preferred embodiment of the present invention, for the interference of atmospheric turbulence when observing the sky, this experimental device is coupled with the actual optical path (can be placed in a common path or a vertical optical path), which can correct the instantaneous local seeing On the basis of keeping in sync with the sampling of the camera, short-exposure images with little influence on seeing can be selected, and in the subsequent calculation process, follow-up processing such as averaging is performed on the screened images, which can be obtained from the detection mechanism Improve the ability to trace the source of active optical system precision. In this case, the advantage of a single exposure of the case-displaced curvature sensor is more prominent.

In the description of this specification, descriptions with reference to the terms "one embodiment", "some embodiments", "example", "specific examples", or "some examples" mean that specific features described in connection with the embodiment or example , structure, material or characteristic is included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms are not necessarily directed to the same embodiment or example. Furthermore, the described specific features, structures, materials or characteristics may be combined in any suitable manner in any one or more embodiments or examples. In addition, those skilled in the art can combine and combine different embodiments or examples and features of different embodiments or examples described in this specification without conflicting with each other.

Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention, those skilled in the art can make the above-mentioned The embodiments are subject to changes, modifications, substitutions and variations.

The above specific implementation manners of the present invention do not constitute a limitation to the protection scope of the present invention. Any other corresponding changes and modifications made according to the technical concept of the present invention shall be included in the protection scope of the claims of the present invention.

Claims (7)

1. A synthetic aperture co-phasing error estimation method is characterized by comprising the following steps:

s1, separating two paths of light rays needing to eliminate common phase errors by using a light beam synthesizer capable of realizing a static ABCD method to obtain four paths of coherent light beams;

s2, respectively introducing the four paths of coherent light beams into a spectrometer to obtain light intensity signals of different spectral bands;

and S3, tracking the stripes by using a stripe sensor, and acquiring the common phase error of the two paths of light rays aiming at the phase difference of different spectral bands.

The fringe sensor synthetic wavefront optical path difference is obtained by the following formula:

x _1i and x _2i As a propagation pathRadial length, n _i Let variable x be refractive index _i ＝x _1i -x _2i And assuming that the beam travels a length x during its propagation ₀ The phase delay of the introduced interference fringes is as follows:

considering only fringe sensors with limited bandwidth, the transmission of the entire light wave can be viewed as a group, with the group delay being proportional to the rate of change of phase as a function of the center wavenumber in the spectral region:

considering only the path length difference of light transmitted in vacuum, i.e. x (κ) = x ₀ The group delay is independent of the wavenumber and independent of the wavelength by group delay (κ) ₀ )＝x ₀ Fringe phase retardation is a linear function of wavenumber 2 π κ x (κ) =2 π κ x ₀ 。

2. The synthetic aperture co-phasing error estimation method of claim 1, wherein the co-phasing error is obtained by:

a, B, C, D is the obtained light intensity values of the four coherent light beams respectively;

n is the total light intensity;

φ ₁₂ the optical path difference introduced for the two paths of light rays;

is the inherent optical path difference of the system,

γ ₁₂ is complex phase dryness;

i, [ gamma ] ₁₂ I is gamma ₁₂ The mold of (4);

is the co-phase error.

3. The synthetic aperture co-phasing error estimation method according to claim 2, further comprising, before the step S1, the steps of:

and S0, aligning the synthetic aperture device which is subjected to preliminary adjustment to the polaris to receive starlight.

4. A synthetic aperture co-phasing error estimation method, characterized in that the co-phasing error estimation of different spectral bands of interference beams in a spliced telescope is realized by using the steps of the method according to any one of claims 1 to 3.

5. A synthetic aperture co-phasing error estimation device implemented with the synthetic aperture co-phasing error estimation method according to any one of claims 1-3, comprising: the device comprises an energy collection module, a light beam interference module and a data processing module;

the energy collection module is used for collecting light energy information;

the beam interference module includes: the device comprises a spectrometer and a beam combiner for realizing a static ABCD method, wherein a beam interference module is used for splitting two paths of light into four paths of coherent light, performing fringe tracking on each path of interference light in a smaller bandwidth relative to the original two paths of light, and dispersing incident light through the spectrometer to enlarge the detected fringe coherence length;

and the data processing module is used for processing the acquired spectral phase information and obtaining the common phase error of the two paths of light rays aiming at the phase difference of different spectral bands.

The synthetic aperture common-phase error estimation device is suitable for a synthetic aperture system with two sub-mirrors arranged in one sub-aperture of a splicing telescope or a synthetic aperture system with three sub-mirrors arranged in one sub-aperture.

6. The synthetic aperture co-phasing error estimation device of claim 5, wherein the beam combiner is configured to split light by using a prism or a photonic chip.

7. The synthetic aperture co-phasing error estimation device of claim 5, wherein the device is coupled with a light path to be measured in a co-optical path or vertical optical path mode, so that the influence of atmospheric turbulence on a spliced telescope can be reduced, and the sky observation can be realized.

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