CN110456519B

CN110456519B - Polarization beam splitter, preparation method thereof and polarization beam splitting method

Info

Publication number: CN110456519B
Application number: CN201910658560.9A
Authority: CN
Inventors: 崔金明; 张昊清; 黄运锋; 李传锋
Original assignee: University of Science and Technology of China USTC
Current assignee: University of Science and Technology of China USTC
Priority date: 2019-07-19
Filing date: 2019-07-19
Publication date: 2021-07-09
Anticipated expiration: 2039-07-19
Also published as: CN110456519A

Abstract

A polarization beam splitter, a manufacturing method thereof and a polarization beam splitting method are provided, wherein the polarization beam splitter comprises: the two identical dove prisms are opposite in bottom surface and are symmetrically arranged; the multilayer optical film is plated between the two dove prisms and is formed by stacking the dove prisms in a high-refractive-index and low-refractive-index staggered mode; the incident light which is incident to one dove prism in the direction parallel to the optical axis of the dove prism can generate restrained internal total reflection and film interference at the interface of the multilayer optical film after being transmitted by the dove prism so as to realize polarization beam splitting, and s-component emergent light and p-component emergent light are respectively output from the two dove prisms in parallel. The invention realizes high polarization extinction ratio of the whole wave band from ultraviolet to near infrared, has the advantage of symmetrical input and output, and can be applied to polarization optical fiber devices.

Description

Polarization beam splitter, preparation method thereof and polarization beam splitting method

Technical Field

The invention belongs to the technical field of basic optical elements, and particularly relates to a polarization beam splitter, a preparation method thereof and a polarization beam splitting method, wherein the polarization beam splitter is feasible for a wide band from ultraviolet to near-infrared bands and has a high polarization extinction ratio.

Background

Polarizers and polarizing beam splitters are optical elements that are widely used in optical instruments, lasers, electro-optic displays, optical recorders, and the like. Only reflected light is transmitted and used in the polarizer, while transmitted and reflected light are equally important in a Polarizing Beam Splitter (PBS). In principle, any physically and chemically different effect on the orthogonal components of unpolarized light may be used as the PBS construction. Various forms of polarizing beam splitters have been constructed using Brewster's angle effect, birefringence, thin film interference, light absorption, and the like, alone or in combination. The following are mainly used at home and abroad, and the characteristics and the defects are respectively listed: 1. the double refraction (Birefringent) polarization beam splitter has good performance based on double refraction and total reflection, the bandwidth is from ultraviolet to near infrared, the extinction ratio of reflected light and transmitted light is high, and the defects are that the price is expensive and the size is limited; 2. the Wire grid polarization beam splitter has the biggest defect that the Wire grid polarization beam splitter can only work in an infrared region, the bandwidth is from infrared to far infrared based on diffraction, and the extinction ratio of transmitted light and reflected light is not high; 3. thin film polarizing beam splitters (Thin film plate-cube) are based on Thin film interference, which have the disadvantage of a narrow bandwidth. Therefore, for an ideal PBS with a wide bandwidth and a large viewing angle, and having a high extinction ratio for both reflected light and refracted light, only a polarization beam splitter based on birefringence is better, which may be expensive and limited by size. There is therefore still a need for a high performance PBS.

Disclosure of Invention

Accordingly, the present invention is directed to a polarization beam splitter, a method for manufacturing the same, and a polarization beam splitting method, so as to solve at least one of the above problems.

As an aspect of the present invention, there is provided a polarization beam splitter including:

the two identical dove prisms are opposite in bottom surface and are symmetrically arranged; and

the multilayer optical film is plated between the two dove prisms and is formed by stacking the dove prisms in a high refractive index and low refractive index staggered mode;

the incident light which is incident to one dove prism in the direction parallel to the optical axis of the dove prism can generate restrained internal total reflection and film interference at the interface of the multilayer optical film after being transmitted by the dove prism so as to realize polarization beam splitting, and s-component emergent light and p-component emergent light are respectively output from the two dove prisms in parallel.

As another aspect of the present invention, there is provided a method of manufacturing the polarizing beam splitter described above, including the steps of:

dividing the multilayer optical film into two parts, and respectively plating the two parts on the bottom surfaces of the two dove prisms;

and (3) enabling the bottom surfaces of the two coated dove prisms to be opposite, and assembling the two coated dove prisms into the polarization beam splitter through a gluing or bonding process.

As still another aspect of the present invention, there is provided a polarization beam splitting method using the polarization beam splitter as described above, including the steps of:

the method comprises the steps of enabling a light beam to be parallel to the direction of an optical axis of one dove prism, enabling the light beam to enter from an incident surface of the dove prism, enabling the light beam to be transmitted to a multilayer optical film through the dove prism, generating restrained internal total reflection and film interference at an interface of the multilayer optical film, enabling a p component to be reflected and to be emitted from an emitting surface of the dove prism, enabling an s component to be transmitted and to be emitted from an emitting surface of the other dove prism, and respectively obtaining p component and s component emitting light parallel to the direction of the optical axis.

As still another aspect of the present invention, there is provided a polarizing fiber device including:

a polarizing beam splitter as described above;

a plurality of fiber collimators coupled to the input and output of the polarization beam splitter, respectively.

Based on the technical scheme, the invention has the beneficial effects that:

(1) the invention provides a high-performance Polarization Beam Splitter (PBS), which adopts a dove prism structure to ensure that the incidence angle at an optical film is larger than the total reflection angle, and realizes polarization beam splitting based on restrained internal total reflection and film interference.

(2) The present invention provides a polarizing beam splitter that is non-absorbing, broadband, wide-angle, and has a high polarization extinction ratio in reflected and transmitted light: the polarization extinction ratio of the whole wave band from ultraviolet to near infrared is always maintained above 1000:1, and the polarization extinction ratio of the whole wave band from visible wave band to infrared wave band can reach 10000:1 or more.

(3) The polarization beam splitter provided by the invention has the advantages of flexible size, symmetrical input and output, is convenient to couple with the optical fiber, and can be applied to polarization optical fiber devices.

Drawings

FIG. 1 is a schematic diagram of the construction of a polarizing beam splitter according to the present invention;

FIG. 2 is a simplified diagram of the thin film structure of the polarizing beam splitter of the present invention;

FIG. 3 is a partial component part of a polarizing beam splitter of the present invention;

FIG. 4 is a graph of refractive index versus wavelength for a transparent substrate according to example 1 of the present invention;

FIG. 5 is a graph showing the refractive index as a function of wavelength for the high refractive index thin film of example 1 in accordance with the present invention;

FIG. 6 is a graph of refractive index versus wavelength for a low refractive index film of example 1 in accordance with the present invention;

FIG. 7 is a graph showing the variation of the s component (Rs) with wavelength in reflected light according to example 1 of the present invention;

FIG. 8 is a graph showing the variation of the p-component (Tp) with wavelength in transmitted light according to example 1 of the present invention;

FIG. 9 is a graph showing the variation of Rs with wavelength after a slight change in the film thickness of the optical film in example 1 of the present invention;

FIG. 10 is a Tp curve showing the change of the film thickness of the optical thin film with the wavelength after a slight change in the film thickness in example 1 of the present invention;

FIG. 11 is a refractive index profile of a high refractive index film of example 2 of the present invention;

FIG. 12 is a graph of Rs as a function of wavelength for example 2 of the present invention;

FIG. 13 is a graph of Tp versus wavelength for example 2 of the present invention;

FIG. 14 is a plot of Rs as a function of wavelength for example 3 of the present invention;

FIG. 15 is a graph showing the variation of Tp with wavelength in example 3 of the present invention.

In the above drawings, the reference numerals have the following meanings:

a-a multilayer optical film; b. A C-Dove prism; d. E, F-film layer;

s1 — an incident surface; s2, S3 — exit face.

Detailed Description

In order that the objects, technical solutions and advantages of the present invention will become more apparent, the present invention will be further described in detail with reference to the accompanying drawings in conjunction with the following specific embodiments.

The invention provides a polarization beam splitter, a preparation method thereof and a polarization beam splitting method, based on restrained internal total reflection, by means of dove prism and thin film interference, the traditional limit is broken through, a broadband from ultraviolet to near-infrared wave bands is realized, and the polarization beam splitter is high in extinction ratio. And the optical fiber coupler has the characteristics of symmetrical input and output and convenience for optical fiber coupling.

FIG. 1 is a schematic diagram of the basic components of a polarizing beam splitter of the present invention. It can be seen that the present invention employs a "sandwich" structure. The polarizing beam splitter of the present invention includes identical transparent substrate Dove (Dove) prisms B, C and multilayer optical film a. The bottom surfaces of the Dove prisms B, C are opposite and symmetrical; multilayer optical film A is plated between Dove prisms B, C and stacked in a high and low index alternating fashion, where "high" and "low" represent the relative magnitudes between the indices of refraction of two adjacent optical films. The light beam is incident in parallel to the optical axis of the Dove prism, after being refracted by the Dove mirror incident surface S1, the light beam is deflected to the direction of the multilayer optical film A to be transmitted, and restrained internal total reflection and film interference are generated at the interface of the multilayer optical film A, so that the P component of the light beam on the multilayer optical film A is reflected, the S component is transmitted, and finally, the P component and the S component emergent light in parallel to the optical axis of the Dove prism are obtained through the refraction of the Dove prism emergent surfaces S2 and S3 respectively.

The selected Dove prism appearance image is an isosceles right-angle prism with a vertex angle cut off. The refractive index of the Dove prism B, C is between the highest and lowest refractive indices of the multilayer optical film A, and preferably, the Dove prism is selected as much as possible

Wherein n is₀Is a Dove prism material refractive index, n₁、n₂Respectively the highest refractive index and the lowest refractive index of the multilayer dielectric film. For this reason, the Dove prism needs to select a material with high refractive index, and the refractive index n0 is generally larger than 1.7, such as high refractive index glass, Al₂O₃Silicon or germanium, and the like.

The multilayer optical film structure of the invention is composed of a plurality of dielectric films with different refractive indexes, fig. 2 is a simplified film structure of the polarization beam splitter of the invention, 2 kinds of dielectric films with different refractive indexes are stacked in a staggered mode according to the refractive indexes, only three layers of the dielectric films are marked in the drawing and are respectively marked as film layers D, E, F, wherein the refractive index of the film layer D is n1, the refractive index of the film layer E is n2, the refractive index of the film layer F is n1, and the relation n1> n2 is met, and the whole film is of a structure with high refractive indexes and low refractive indexes alternated, and the number of layers is generally tens of layers. The refractive indexes of the optical film material and the Dove prism material need to meet the conditions of n1, n0 and n2, so that the restrained internal total reflection condition is met. Of course, in other embodiments, for example, dielectric films of 3 different refractive indexes may also be used, as long as a high-low refractive index staggered stack structure can be formed.

The film thickness of the optical film can be optimized by determining the material of the optical film, the material of the Dove prism (namely, determining the refractive indexes n0, n1 and n2) and the number of the coating layers. Specifically, firstly, a set of film thickness parameters can be arbitrarily assumed as initial conditions (generally, the film thickness of each layer can be selected to be λ/4 as an initial parameter), and the transmittance and the reflectance of S, P components with different wavelengths of the thin film structure under the set of initial parameters can be calculated by using a fresnel formula and a computer program numerical calculation method. Then, the polarization extinction ratios are respectively calculated through the transmission coefficients and the reflection coefficients of the S component and the P component of each wavelength, the polarization extinction ratios of each wavelength are sequentially used as optimization targets, the film thickness parameters are numerically optimized, and the film thickness of each layer meeting the requirements can be finally obtained.

Since it is necessary to achieve a high polarization extinction ratio over a very wide wavelength range, the more the number of layers of the film, the more parameters can be optimized, and the easier it is to achieve the optimization goal. Generally, the number of the film layers can be between 10 and 200, and between 50 and 60, so that the high polarization extinction ratio of the ultraviolet to infrared full-wave band can be realized.

Based on the above, the invention further provides a preparation method of the polarization beam splitter, which determines the number of layers and the thickness of the optical thin film material, the Dove prism material and the coating film, and comprises the following steps:

dividing the multilayer optical film A into two parts, and respectively plating the two parts on the bottom surfaces of the Dove prisms B, C to form the structure shown in FIG. 3;

then two coated Dove prisms are assembled into the polarization beam splitter shown in FIG. 1 by gluing or bonding process with their bottom surfaces facing each other.

Due to the requirement of a bonding process, the optical surface type of the bottom surface of the Dove mirror has certain requirements, and generally needs to reach the order of lambda/10, wherein lambda is the typical wavelength of the working of the polarizing device.

Wherein the multilayer optical filmThe film is symmetrically distributed between the two Dove prisms, so that the two Dove prisms can be coated simultaneously; for example, in example 1, 27 films were applied to each Dove mirror, using a commonly used optical coating material, ZrO, to form a coating₂、MgF₂As a film material, the number of films of the entire device corresponds to 53.

The polarization beam splitter can ensure that the input and the output of the whole device are symmetrical, and the device becomes a device with two inlets and two outlets in the horizontal direction, and is convenient to apply. For example, the polarization beam splitter can be applied to a polarization fiber device by adding a fiber collimator to couple the input end and the output end of the polarization beam splitter.

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Example 1

High-performance PBS from ultraviolet band to near-infrared band (350 nm-1800 nm). The Dove prisms with the two bottom surfaces coated with the films are assembled into a component by using optical cement or a gluing process. The two bottom surfaces need optical cement in the subsequent process, so that the precision of the processed surface type needs to be higher and reaches lambda/10, and other light-transmitting surfaces such as an incident surface, an emergent surface and a top surface reach lambda/4. The two trapezoidal faces are opaque, so that no face shape requirement exists. The base material of Dove prism is Al₂O₃. The Dove prism of the embodiment adopts typical sizes, the length of the bottom surface is 44.94mm, the width of the bottom surface is 12.7mm, the length of the top surface is 19.54mm, the width of the top surface is 12.7mm, and the height between the bottom surface and the top surface is 12.7mm, so that the Dove prism can be scaled according to the requirements in practical application. The dimension is for Al₂O₃The substrate can refract and reflect parallel light incident from the middle point of the inclined edge of the trapezoid to approximately the middle point of the bottom surface.

Dove prism Al₂O₃The variation curve of refractive index n0 with wavelength is shown in FIG. 4, the high refractive index of the optical filmFilm n1 uses ZrO₂MgF is used for the low refractive index film n2₂The refractive index curves of both are shown in fig. 5 and 6. The three materials are selected because their refractive indices can cover the ultraviolet to infrared bands and satisfy n1>n0>n 2. The film thickness parameters after numerical calculation and optimization are listed in table 1. A structure with high and low refractive index interleaving with each other can be seen. Note that in the Table, for each Al block, the values are shown₂O₃The Dove prism is coated with 27 layers of film parameters. ZrO is used at the outermost layer after the two coated Dove prisms are connected₂There are actually 53 films. By utilizing a Fresnel formula, the refractive index of the Dove prism, the refractive index of each optical film and the film thickness are substituted into the formula, and a transmission matrix is calculated by adopting a computer program numerical value calculation method, so that the variation of the leakage component along with the wavelength can be finally obtained, namely, the S component (Rs) in reflected light and the P component (Tp) in refracted light along with the wavelength variation curve can be obtained in the figures 7 and 8. From the leakage component curve, it can be seen that the polarization extinction ratio can reach more than 1000:1 in the range of 350nm to 1800 nm. Considering the possible error in the actual coating process, FIGS. 9 and 10 show the thickness of each layer plus-0.5, 0.5]As a result of the Rs and Tp after the nm error, it can be seen that even if the coating process has defects, the extinction ratio can still be kept high in the whole wave band.

TABLE 1

Example 2

If with Ta₂O₅Substituted ZrO₂As the high refractive index substance, the corresponding coating parameters are given in this example. Ta₂O₅The refractive index profile is shown in FIG. 11, and FIGS. 12 and 13 for Ta₂O₅Rs and Tp, which are high refractive index films, vary with wavelength. Wherein initial refers to the film thickness still according to previous example 1Optimized is according to Ta₂O₅The refractive index of (2) is optimized for the film thickness. The film thickness after optimization is shown in table 2.

TABLE 2

Example 3

High performance PBS in near infrared band (780 nm-3000 nm), still Al using Dove prism₂O₃The high refractive index film of the optical thin film is ZrO₂The low refractive index film is MgF₂. Still containing 53 layers of film. The optimized Rs and Tp curves along with the wavelength are shown in the figures 14 and 15, and the film thickness is shown in the table 3. As can be seen from FIGS. 14 and 15, the PBS of the present invention has a good effect in the near infrared, and the extinction ratio can be maintained at 10000:1 in the whole wavelength band.

TABLE 3

The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are only exemplary embodiments of the present invention and are not intended to limit the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A polarizing beam splitter, comprising:

the multilayer optical film is plated between the two dove prisms and is formed by stacking the dove prisms in a high-refractive index and low-refractive index staggered mode, and the multilayer optical film is symmetrically distributed between the two dove prisms;

the polarization beam splitter comprises a dove prism, a multi-layer optical film, a polarization beam splitter and a polarization beam splitter, wherein incident light which is incident to the dove prism in a direction parallel to the optical axis of the dove prism can generate restrained internal total reflection and film interference at an interface of the multi-layer optical film after being transmitted by the dove prism so as to realize polarization beam splitting, s-component emergent light and p-component emergent light are respectively output in parallel from the two dove prisms, and the polarization extinction ratio of the polarization beam splitter in a wave band range of 350nm-1800nm is;

the polarization beam splitter is prepared by the following steps:

dividing the multilayer optical film into two same parts, and plating the parts on the bottom surfaces of the two dove prisms simultaneously;

the bottom surfaces of the two coated dove prisms are opposite, and the two coated dove prisms are assembled into the polarization beam splitter through a gluing or bonding process;

the film thickness of the multilayer optical thin film is optimized through the following steps:

respectively calculating the transmission and reflection coefficients of the s and p components by a Fresnel formula according to the refractive index of the optical thin film material, the refractive index of the dove prism material and the film number of the optical thin film;

and calculating the polarization extinction ratio according to the transmission and reflection coefficients of the s and p components, and optimizing the film thickness of the multilayer optical film by taking the polarization extinction ratio as an optimization target.

2. The polarizing beam splitter of claim 1, wherein the refractive index of the dove prism is between the highest and lowest refractive indices of the multilayer optical film.

3. The polarizing beam splitter according to claim 2,

wherein n is₀Refractive index of dove prism material, n₁、n₂Respectively the highest refractive index and the lowest refractive index of the multilayer dielectric film.

4. The polarizing beam splitter of claim 1, wherein the bottom surface of the dove prism is optically planar up to the order of λ/10, where λ is a typical wavelength at which the polarizing device operates.

5. The polarizing beam splitter of claim 1, wherein the multilayer optical film comprises 2 to 3 different refractive index film materials and the number of film layers is between 10 and 200.

6. The polarizing beam splitter of claim 1, wherein:

the dove prism is made of glass and Al₂O₃Silicon or germanium;

the material selected for the multilayer optical film is ZrO₂/MgF₂、Ta₂O₅/MgF₂、ZrO₂/SiO₂Or Ta₂O₅/SiO₂。

7. A polarization beam splitting method using the polarization beam splitter according to any one of claims 1 to 6, comprising the steps of:

8. A polarizing fiber device comprising:

the polarizing beam splitter according to any one of claims 1 to 6;