CN206601536U - It is a kind of to excite BSW to realize the optical chips of Beams coupling based on grating - Google Patents

Abstract

The utility model discloses an optical chip based on a grating pair coupled to excite BSW to realize a non-diffraction beam, comprising a glass base layer, a Bragg reflection unit composed of high and low refractive index media alternately, and a grating pair etched on the surface of the Bragg reflection unit; On the grating pair on the surface of the Bragg reflection unit, the two beams of surface waves interfere after excitation, so as to realize the generation of non-diffracting Bloch surface wave (BSW) beams. The optical chip has the characteristics of compact structure, high integration and miniaturization, and has important applications in beam shaping and nano-optical operations.

Description

An optical chip based on a grating-coupled excitation BSW to realize a diffraction-free beam

technical field

The utility model relates to the technical field of generation of all-medium non-diffraction light, in particular to an optical chip that realizes non-diffraction light beams based on grating pair coupling excitation BSW.

Background technique

The Bloch wave (BSW) exists on the surface of the photonic crystal defect layer and the surrounding dielectric layer, and can be regarded as an analogue of low loss and high localized surface plasmon (SPP). Similar to SPP, BSW is used in nanoscale optical circuits, chemical and biological sensing, gas sensing, fluorescence radiation enhancement, and surface-enhanced Raman scattering (SERS), etc. BSWs and SPP have the following differences: (1) BSWs have no metal absorption loss, so the Bloch wave has a high quality factor and a long propagation length; (2) There are many choices of dielectric materials that can be used to make photonic crystals, so it can be BSWs in the deep ultraviolet to near-infrared bands have been produced, but the transmission loss of SPPs in the ultraviolet and visible bands is very high; (3) the fluorescence is severely quenched on the metal surface, but this problem does not exist on the surface of the medium.

Both SPPs and BSWs have diffraction problems when propagating at the interface, which leads to coupling losses between substrate elements due to the lateral expansion of wave packets during light transmission. In the past few years, with the development of plasmonic technology, researchers have proposed many methods to generate non-diffraction light, such as engraving periodic gratings on metal films, and using spatial light modulators to generate plasmonic Airy light; A pair of gratings is written on the metal film, which can generate a cosine Gaussian plasma beam; the plasma Airy light can be changed into a linear light by using a wedge-shaped metal-dielectric metal structure. Optical chips with these structures all have certain limitations, and the main problems are: (1) large loss. The imaginary part of the metal dielectric constant is very large, and the optical chip that uses a metal structure to realize a non-diffraction beam has a large loss, which reduces the transmission length of the non-diffraction beam. (2) The practicability is poor. The self-bending effect of non-diffraction light and the short transmission distance have greatly reduced its use effect in the practical process.

Utility model content

The purpose of the utility model is to overcome the absorption loss of the metal, and realize the non-diffraction light of the whole medium by using the coupling of the dielectric grating pair and the Bragg reflection unit. It is an optical chip with a simple structure and low processing cost.

The technical scheme that the utility model realizes above-mentioned purpose is as follows:

An optical chip based on a grating pair coupling excitation BSW to realize a non-diffraction beam, the optical chip includes a glass substrate, a Bragg reflection unit, a grating pair and deionized water; wherein, the Bragg reflection unit and the deionized water are sequentially discharged on the glass On the substrate; the grating is placed in the top layer of the Bragg reflection unit; the BSW beam will be generated between the Bragg reflection unit and the grating pair and the deionized water, and the two beams of BSW produced by the grating will interfere to produce a non-diffraction BSW beam .

Wherein, the Bragg reflection unit is composed of high refractive index medium Si ₃ N ₄ layers and low refractive index medium SiO ₂ layers alternately, and the top layer is a SiO ₂ defect layer, totally 14 layers.

Wherein, the alternate Si3N4, SiO2 and defect layer thicknesses in the Bragg reflection unit can be adjusted to control the reflection curve of the Bragg reflection unit and adjust the position of the BSW coupling output resonant peak.

Wherein, the period of the grating pair is 460nm, the line width is 200nm, the depth is 100nm, the length is 30μm, the number of periods is 20, and the angle between the grating pair is 170 degrees, which can be adjusted by changing the length and angle of the grating pair Changing the length of the non-diffracting beam changes the coupling efficiency by changing the depth and linewidth of the grating pair.

The principle of the technical solution of the utility model is: an optical chip based on a grating pair coupling excitation BSW to realize a non-diffraction beam, the optical chip includes a glass substrate, a Bragg reflection unit, a grating pair engraved on the top layer of the Bragg reflection unit and deionized water; Wherein, the Bragg reflection unit, the grating pair and the deionized water will generate two beams of BSW after being excited by the laser, and the interference of the two beams of BSW will generate non-diffracting light waves; The angle between the two groups of gratings is variable, the period is variable, the line width is variable, the depth is variable, the position is variable, and the length of the single slit is variable; the period of the grating pair matches the wavelength of the BSW of the Bragg reflection unit, and the maximum coupling can be achieved Efficiency; changing the depth and line width of the grating pair can improve the coupling efficiency of BSW; writing small hole obstacles on the non-diffraction BSW path, non-diffraction BSW will produce self-repairing phenomenon; changing the size of the small hole can change the self-repairing distance .

The Bragg reflection unit composed of a multilayer dielectric film will generate BSW, and the laser beam hitting the grating pair will couple and excite the BSW. The two gratings have a certain angle, so the two Bloch waves will overlap, and the overlapping parts will interfere. Formation of non-diffracting light waves.

Compared with the traditional technology, the utility model has the following characteristics:

(1) The surface structure is simple: only two groups of gratings with a certain angle and small holes at specific positions need to be written on the top layer of the Bragg reflection unit;

(2) Ease of processing: There are no strict requirements for the position of the grating pair, slit length, depth, line width, etc., which greatly reduces the difficulty of processing;

(3) Strong practicability: obstacles are placed on the transmission path of the diffracted light wave, and the non-diffraction light wave can quickly self-repair, which increases the practicability of the non-diffraction beam.

Description of drawings

Fig. 1 is a schematic diagram of the three-dimensional structure of an optical chip based on a grating pair coupled excitation BSW to realize non-diffraction beam generation according to the present invention;

Fig. 2 is a schematic cross-sectional view of the structure of an optical chip based on a grating-coupled excitation BSW to realize non-diffraction beam generation according to the present invention;

Figure 3 shows the experimental front focal plane image, back focal plane image, theoretical front focal plane image, theoretical and experimental intensity profiles of the non-diffracting cosine Gaussian Bloch wave beam beam obtained by using the chip, and a single grating excites the surface Bloch wave The image of the front focal plane, where Fig. 3(a) is the image plane diagram generated by the non-diffraction BSW, and Fig. 3(b) and Fig. 3(d) are the fitting schematic diagrams of the cross-section of the non-diffracting beam obtained by experiment and theory, respectively. Figure 3(c) is a schematic diagram of the simulation results using FDTD, Figure 3(e) is a schematic diagram of a single grating excitation, Figure 3(f) and Figure 3(g) are Figure 3(a) and Figure 3(e) ) corresponding to the back focal plane map.

Reference numerals mean: 1 is a glass substrate, 2 is a Bragg reflection unit, 3 is a grating pair, 4 is deionized water, 5 is a Si3N4 layer, 6 is a SiO2 layer, and 7 is a _SiO2 defect layer.

detailed description

Below in conjunction with accompanying drawing and specific embodiment the utility model is described in further detail.

Example 1:

Referring to FIG. 1-2 , an optical chip based on grating pair coupled excitation BSW to realize non-diffraction beam includes glass substrate 1 , Bragg reflection unit 2 , grating pair 3 , and deionized water 4 . The Bragg reflection unit is composed of 66nm Si ₃ N ₄ layers 5 and 110nm SiO ₂ layers 6 alternately, and the top SiO ₂ defect layer 7 has a thickness of 450nm. The grating pairs are engraved with a period of 460nm, an angle of 170°, a depth of 100nm, and a linewidth of 200nm. The wavevector 460nm of the BSW on the surface of the Bragg reflector unit matches the period of the grating pair. The 633nm excitation light is incident from the top of the optical chip, and is coupled with the Bragg reflection unit and the grating pair to generate a non-diffraction BSW. The non-diffraction BSW and the excitation light are radiated at different angles, and the BSW angle is 64 degrees. We can use Fig. 3(f) and Fig. 3(g) Radiation angles are derived from the back focal plane map. Figure 3(a) is the image plane generated by the non-diffracting BSW, Figure 3(c) is the result of the non-diffracting beam simulated by FDTD, and Figure 3(e) is the case of a single grating excitation. Figure 3(b) and Figure 3(d) are the fitting of the experimental and theoretical results of the non-diffracting beam cross-section respectively. It can be seen that the FWHM at different propagation positions is unchanged, and the experimental and theoretical FWHM are consistent, The cross-sectional curve fitting diagram can intuitively see the non-diffraction characteristics of the non-diffraction BSW light.

The parts not elaborated in this utility model belong to the known technology in the art.

Claims (4)

1. an optical chip based on a grating coupled excitation BSW to realize a diffraction-free beam, is characterized in that: the optical chip includes a glass substrate (1), a Bragg reflection unit (2), a grating pair (3) and deionized water (4 ); wherein, the Bragg reflection unit (2), deionized water (4) are discharged sequentially on the glass substrate (1); the grating pair (3) is placed in the Bragg reflection unit (2) top layer; the A BSW beam is generated between the Bragg reflection unit (2) and the grating pair (3) and the deionized water, and the two BSW beams generated by the grating pair (3) interfere to generate a non-diffraction BSW beam. 2. A kind of optical chip based on grating pair coupling exciting BSW to realize non-diffraction light beam according to claim 1, it is characterized in that: described Bragg reflection unit (2) is made of high refractive index medium Si ₃ N ₄ layers (5 ) and low refractive index medium SiO ₂ layers (6) alternately, the top layer is a SiO ₂ defect layer (7), a total of 14 layers. 3. A kind of optical chip based on grating pair coupling exciting BSW to realize non-diffraction light beam according to claim 1, it is characterized in that: in described Bragg reflection unit (2) alternate Si3N4, SiO2 and defect layer thickness all can be Tuning to control the reflection curve of the Bragg reflection unit and adjust the position of the BSW coupling output resonant peak. 4. A kind of optical chip based on grating pair coupling excitation BSW to realize non-diffracting light beam according to claim 1, it is characterized in that: described grating pair (3) period is 460nm, line width is 200nm, and depth is 100nm, The length is 30 μm, the number of periods is 20, and the angle between the grating pair is 170 degrees. The length of the non-diffracting beam can be changed by changing the length and angle of the grating pair, and the coupling efficiency can be changed by changing the depth and line width of the grating pair. .