CN105137513A - Broadband photon screen based on phase coding - Google Patents

Abstract

The invention discloses a kind of broadband photon of phase coding sieves, diameter is D, including transparent flat substrate and the opaque metallic film being plated in the transparent flat substrate, does is the opaque metallic film equipped with the light passing aperture of ring-band shape distribution, and the position distribution of the light passing aperture meets equation , in formula, f is the focal length of broadband photon sieve, and n is the annulus serial number of light passing annulus, and λ is the operation wavelength of photon screen, R is the radius of broadband photon sieve, and α is that code coefficient, k are wave number three times, and xm and ym are the center of m-th of aperture on n-th of light passing annulus, m=1,2,3.., num, wherein , , aperture radius . The present invention devises width photon screen that is a kind of while having phase coding plate encoding function and conventional photonic sieve focusing function, photon screen is greatly reduced to the sensibility of wavelength, and in the case where not influencing photon screen resolution ratio, the bandwidth of photon screen has been widened, while having improved energy efficiency.

Description

A phase-encoded broadband photon sieve

technical field

The invention relates to an optical element, in particular to a photon sieve, in particular to a phase-coded broadband photon sieve.

Background technique

In the prior art, a photon sieve is a diffractive optical element proposed by Kipp in 2001, which is similar to a Fresnel zone plate, which allows odd or even Fresnel zone plates to transmit light while allowing adjacent wave zones to pass through. With opaque. The photon sieve designs the light-transmitting wave bands into light-transmitting microholes, and the microholes are located on the wave bands. The difference between the distance of light waves passing through the center of each microhole to the focus and the distance from the optical axis to the focus is an integer multiple of the wavelength, which can be Achieve focusing and imaging for high-resolution microscopy, spectral imaging, X-ray imaging, UV lithography, etc.

As diffractive optical elements, photon sieves have large chromatic aberrations. Generally speaking, for a photon sieve with a focal length f, only the design wavelength λ is clearly imaged. Therefore, when the incident light wavelength is λ+Δλ, it will be focused to f+Δf position, and background noise will be generated at the original focal plane position.

In order to solve the above problems, Gimenez et al. proposed a fractal photon sieve in the literature "F.Giménez, J.A.Monsoriu, W.D.Furlan, and A.Pons, "Fractalphotonsieve," Opt.Express14(25), 11958-11963(2006)" To extend the depth of focus and reduce chromatic aberration. However, this photonic sieve comes at the expense of reducing the resolution of the design wavelength at the in-focus position. Andersen et al. proposed a telescopic system using a photon sieve as the primary mirror in the literature "G.Andersen, and D.Tullson, "Broadbandantiholephotonsievetelescope," Appl.Opt.46(18), 3706-3708(2007)". In the system, another diffractive optical element is designed to compensate the chromatic aberration characteristics of the photon sieve, achieving a certain wide-spectrum imaging effect. However, it has two mirrors larger than the primary mirror of the photon sieve to collimate and focus the light path, and the structure of this method is relatively complicated. Design by Zhou et al. in the literature "C.X.Zhou, X.C.Dong, L.F.Shi, C.T.Wang, and C.L.Du, "Experimental study of multiwave length photos sieve designed by random-area-divided approach," Appl. Opt. 48(8), 1619–1623 (2009)" And processed a three-wavelength photon sieve. The photon sieve is designed with three sets of non-overlapping holes for three different wavelengths, for imaging the three wavelengths. However, it has low diffraction efficiency and only images the designed three wavelengths. The Chinese patent application publication number CN104865627A discloses a broadband photon sieve based on wavefront encoding technology. The broadband photon sieve has a phase encoding plate. There is a photon sieve attached. The phase encoding plate is set before the photon sieve, and the structure is slightly complicated.

Therefore, for the above-mentioned shortcomings in the prior art, it is obviously of positive practical significance to develop a broadband photon sieve, which not only has the focusing function of the traditional photon sieve, but also has the encoding function of the phase encoding plate, and has a simple structure. .

Contents of the invention

The object of the present invention is to provide a phase-coded broadband photon sieve, which can widen the bandwidth of the photon sieve without affecting the resolution of the photon sieve.

In order to achieve the purpose of the above invention, the technical solution adopted by the present invention is: a phase-coded broadband photon sieve with a diameter of D, comprising a transparent plane substrate and an opaque metal film plated on the transparent plane substrate, the opaque The light metal thin film is provided with ring-like distribution of light-through holes, and the position distribution of the light-through holes satisfies the equation , where f is the focal length of the broadband photon sieve, n is the ring number of the light-passing ring, λ is the working wavelength of the photon sieve, R is the radius of the broadband photon sieve, α is the cubic encoding coefficient, k is the wave number, x _m and y _m is the center position of the mth small hole on the nth light-passing ring, m=1, 2, 3, ..., num, where , , hole radius .

In the above technical solution, the three-time encoding coefficient α>20.

In a further technical solution, the three-time encoding coefficient α=20π.

In the above technical solution, the transparent flat substrate is glass with a thickness of 2 mm.

In the above technical solution, the opaque metal thin film is an opaque chromium film with a thickness of 100 nm.

Due to the use of the above-mentioned technical solutions, the present invention has the following advantages compared with the prior art:

1. The invention creatively introduces the phase encoding phase into the traditional photon sieve focusing formula, and designs a width photon sieve with both the phase encoding plate encoding function and the traditional photon sieve focusing function, which greatly reduces the photon sieve Sensitivity to wavelength, and without affecting the resolution of the photon sieve, it broadens the bandwidth of the photon sieve and improves the energy efficiency at the same time;

2. The structure of the present invention is simple, portable and easy to process.

Description of drawings

Fig. 1 is the structural representation of broadband photon sieve in embodiment one;

Fig. 2 is a schematic diagram of the small hole distribution of the broadband photonic sieve of Fig. 1;

Fig. 3 is a schematic diagram of the small hole distribution of a traditional photonic sieve;

Fig. 4 is a schematic diagram of a device for testing the imaging performance of a traditional photonic sieve;

Figure 5 is the experimental test results of the traditional photonic sieve at the design wavelength of 632.8nm;

Fig. 6 is a schematic diagram of a device for testing the imaging performance of a broadband photon sieve;

Figure 7 is the transmittance curve of the bandpass filter in Figure 6

Figure 8 is the imaging result of a traditional photon sieve under a broadband light source;

Figure 9 is the imaging result of a broadband photon sieve under a broadband light source;

Fig. 10 is a PSF comparison diagram of a traditional photon sieve and a broadband photon sieve at (α=20Π);

Fig. 11 is the MTF curve diagram of traditional photon sieve and broadband photon sieve at different wavelengths;

Figure 12 is the imaging results of traditional photonic sieves at different wavelengths λ=625.8-639.8nm;

Figure 13 is the intermediate blurred image of the broadband photonic sieve at different wavelengths λ=625.8-639.8nm;

Fig. 14 is the final restored image of the broadband photonic sieve at different wavelengths λ=625.8-639.8nm.

Among them: 1. Transparent flat substrate; 2. Opaque metal film; 3. Laser with a wavelength of 632.8nm; 4. Beam expander; 5. Filter; 6. Scattering turntable; 7. Collimator; 8. Traditional Photon sieve; 9. CCD; 10. Display; 11. Broadband light source; 12. Bandpass filter; 13. Broadband photon sieve.

Detailed ways

The present invention will be further described below in conjunction with accompanying drawing and embodiment:

Embodiment 1: Referring to Fig. 1, a broadband photon sieve of phase encoding, with a diameter of D, includes a transparent plane substrate and an opaque metal film plated on the transparent plane substrate, and the opaque metal film is provided with The light-through holes are distributed in a ring shape, and the position distribution of the light-through holes satisfies the equation , where f is the focal length of the broadband photon sieve, n is the ring number of the light-passing ring, λ is the working wavelength of the photon sieve, R is the radius of the broadband photon sieve, α is the cubic encoding coefficient, k is the wave number, x _m and y _m is the center position of the mth small hole on the nth light-passing ring, m=1,2,3 _... num, where , , hole radius .

In this embodiment, the three-time encoding coefficient α is 20π.

In this embodiment, the transparent planar substrate is glass with a thickness of 2mm.

In this embodiment, the opaque metal thin film is an opaque chromium film with a thickness of 100 nm.

On the basis of the above disclosure, a specific photonic sieve is designed, as shown in FIG. 2 , which is a schematic diagram of the small hole distribution of the broadband photonic sieve of this embodiment.

As shown in Figure 3, it is a schematic diagram of the small hole distribution of the traditional photon sieve. It can be seen that the structure of the traditional photon sieve is concentric rings, but the broadband photon sieve of this embodiment is no longer concentric rings as can be seen from Figure 1, but It is a structural form that is symmetrical about y=x. Since the coding items introduced in this embodiment are relatively small in value, it is not obvious that the image is symmetrical about y=x.

A broadband photon sieve with a focal length of 500nm, a diameter of 50mm, a working center wavelength of 632.8nm, and a coding coefficient of 20π is designed by using UV lithography technology.

A performance test was performed on the broadband photonic sieve obtained above and a traditional photonic sieve. The design wavelength of the traditional photonic sieve is 632.8nm.

As a comparison, Figure 4 is a schematic diagram of a device for testing the imaging performance of a traditional photonic sieve. The incident laser beam emitted by a laser 3 with a wavelength of 632.8nm is focused by a beam expander 4 to a small hole in a filter 5 for filtering. The laser beam passes through the scattering turntable 6 to remove blocks. A collimator 7 with a focal length of 550 mm and an aperture of 55 mm and a CCD 9 with a pixel size of 4.54 μm (AVT Prosilica GX2750C) were used for imaging testing and displayed on a monitor 10 .

Figure 5 shows the experimental test results of the traditional photonic sieve at the design wavelength of 632.8nm. In the figure, (a) is the PSF characteristic, (b) is the resolution rake test result, and (c) is the central area of the test result (b) zoom in. Upon careful inspection, the resolution limit of photonic sieves is about 50lp/mm.

As shown in Figure 6, it is a schematic diagram of the device for testing the imaging performance of the broadband photonic sieve. The beam emitted by the broadband light source 11 passes through the band-pass filter 12 (THORLABScompanyFL632.8-10) with a center wavelength of 632.8nm and FWHM10nm, using the same parallel The light pipe 7 irradiates the broadband photon sieve 13 , and the imaging test is performed by the CCD 9 and displayed on the display 10 . FIG. 7 is a transmittance curve of the bandpass filter in FIG. 6 .

Replace the broadband photon sieve in Figure 6 with the traditional photon sieve, and the imaging results are shown in Figure 8, where (a) is the PSF characteristic, (b) is the resolution rake test result, (c) is the resolution rake (b) The enlarged picture of the central area shows that the traditional photon sieve has a large chromatic aberration. When the central wavelength is 632.8nm and the bandwidth of FWHM10nm is incident, the traditional photon sieve produces strong background noise on the imaging plane.

Figure 9 shows the test results of the broadband photonic sieve under the central wavelength of 632.8nm and the incident bandwidth of FWHM10nm. Experimental results Figure 9(a) shows that the PSF images measured in the laboratory have the same "L"-shaped features, Figure 9(b) shows the intermediate blurred image of the broadband photon sieve, and Figure 9(c) is the final restored image , Figure 9(d) is an enlargement of the central area of the restored image Figure 9(c). The blurred image in the middle is restored to a clear image through an appropriate filter function, and the resolution is basically the same as that of the traditional photon sieve at the design wavelength of 632.8nm. Under the central wavelength of 632.8nm and FWHM10nm illumination, the resolution of the broadband photonic sieve is 501p/nm.

In order to further verify the broadband performance of the photonic sieve obtained by the present invention, the traditional photonic sieve of the present embodiment and the broadband photonic sieve were compared under different wavelength photo illuminations, and the comparison was carried out by computer simulation, and the results were as follows:

Figure 10 shows the PSF of traditional photonic sieves and broadband photonic sieves (α=20Π) under illumination of different wavelengths (λ=625.8~639.8nm). It can be seen from Figure 10(a) that the traditional photonic sieve has a strong focusing ability at the design wavelength λ=632.8nm, but as the wavelength deviates, the focusing ability is greatly weakened and cannot be clearly imaged. However, the PSF of the broadband photonic sieve in Fig. 10(b) maintains a good consistency in the range of wavelength λ = 625.8nm ~ 639.8nm. When λ<627.8nm and λ>637.8nm, the PSF consistency deviates slightly.

Figure 11 shows the MTF (Fourier transform of PSF) curves of traditional photon sieves and broadband photon sieves at different wavelengths. As the wavelength deviates from the design wavelength, the MTF curve of traditional photonic sieves drops rapidly, and a zero point appears, resulting in the loss of spatial frequency. On the contrary, the broadband photonic sieve maintains good consistency in the range of wavelength λ=625.8～639.8nm, and slightly decreases when λ<627.8nm and λ>637.8nm. Since the MTF has good consistency at different wavelengths, and there is no zero point from high frequency to low frequency, the intermediate blurred image can be restored by designing an appropriate filter. Therefore, the introduction of the phase encoding term in the focusing formula of the photon sieve can greatly reduce the sensitivity of the photon sieve to wavelength and achieve the purpose of expanding the bandwidth.

Figure 12 shows the imaging results of traditional photonic sieves at different wavelengths λ=625.8-639.8nm. As the wavelength deviates from the design wavelength of 632.8nm, the imaging blur increases. The bandwidth of traditional photon sieve is .

Figure 13 shows the intermediate blurred images of broadband photonic sieves at different wavelengths (λ=625.8-639.8nm), and all images have almost the same blurring characteristics at different wavelengths.

Figure 14 shows the final restoration images of broadband photonic sieves at different wavelengths (λ=625.8-639.8nm). The intermediate blurred images at all wavelengths can be well restored, and have basically the same resolution as the traditional photon sieve at the design wavelength. When the wavelength deviates greatly from the design wavelength (λ<627.8nm and λ>637.8nm), the MTF decreases slightly, resulting in a slight deviation of the final restored image. For the broadband photon sieve of this embodiment prepared with a diameter of 50 mm, a focal length of 500 mm, and an encoding coefficient α=20Π, the bandwidth of the broadband photon sieve is about 14 nm after testing, and the bandwidth of the broadband photon sieve is about 88 times that of the traditional photon sieve.

Claims (5)

1. the broadband photon sieve of a phase coding, diameter is D, comprise transparent flat substrate and be plated in the suprabasil light tight metallic film of this transparent flat, it is characterized in that: described light tight metallic film is provided with the logical light aperture of ring-band shape distribution, and the position distribution of described logical light aperture meets equation , in formula, f is the focal length of broadband photon sieve, and n is the endless belt sequence number of logical ring of light band, and λ is the operation wavelength of photon screen, and R is the radius of broadband photon sieve, and α is three code coefficients, and k is wave number, x _mand y _mthe center of m aperture on the n-th logical ring of light band, m=1,2,3 ..., num, wherein , , aperture radius .

2. the broadband photon sieve of phase coding according to claim 1, is characterized in that: described three code coefficient α > 20.

3. the broadband photon sieve of phase coding according to claim 2, is characterized in that: described α=20 π.

4. the broadband photon sieve of phase coding according to claim 1, it is characterized in that: described transparent flat substrate is glass, its thickness is 2mm.

5. the broadband photon sieve of phase coding according to claim 1, is characterized in that: described light tight metallic film is light tight chromium film, and its thickness is 100nm.