CN112596139A

CN112596139A - Grating structure writing method of short-wave range reflection type volume grating

Info

Publication number: CN112596139A
Application number: CN202011502556.2A
Authority: CN
Inventors: 晋云霞; 孙静; 孔钒宇; 何冬兵; 邵建达
Original assignee: Shanghai Institute of Optics and Fine Mechanics of CAS
Current assignee: Shanghai Institute of Optics and Fine Mechanics of CAS
Priority date: 2020-12-18
Filing date: 2020-12-18
Publication date: 2021-04-02

Abstract

The invention provides a grating structure writing method of a short-wave range reflection type volume grating. The method comprises a prism coupling exposure method and a correlation exposure method. The central wavelength of the reflection type volume grating prepared by the grating structure writing method can reach 325nm to 650 nm. The method provided by the invention provides a new idea for the development of the short-wavelength reflective volume grating, and compared with the existing preparation technology, the method widens the technical field of short wavelength, and has great practical application value in the fields of semiconductor laser wave locking, laser beam combination and the like.

Description

Grating structure writing method of short-wave range reflection type volume grating

The technical field is as follows:

the invention relates to a method for preparing a diffraction optical element, in particular to a grating structure writing method of a short-wave reflection type volume grating based on photorefractive glass.

Background art:

the semiconductor laser has the advantages of high efficiency, small volume, long service life, low cost and the like, and is widely applied to the fields of measurement, communication and the like. However, the conventional semiconductor laser has the problems of wide line width, easy drift of wavelength along with the change of temperature and the like, and the narrow-bandwidth frequency stabilization semiconductor laser plays a critical role in the research and development of high-tech products and basic research, so the narrow-bandwidth frequency stabilization semiconductor laser is particularly important for the research and development of the line width voltage and the frequency stabilization technology of the semiconductor laser. In recent years, a reflective volume grating based on PTR glass has the characteristics of excellent reflection efficiency, strong Bragg wavelength selection and angle selection, and is widely applied to line width narrowing and wavelength locking in semiconductor laser as an external cavity technical means.

With the continuous development and breakthrough of semiconductor laser technology, semiconductor lasers are gradually developing towards short wavelengths and high powers. Short wavelength reflective bulk gratings are in great demand, and the current preparation systems: the Luoerio mirror interference system and the double-beam interference system have relatively mature preparation of the reflective gratings of visible and infrared wave bands. There are also difficulties in short wavelength fabrication due to limitations in the exposure wavelength and the absorption line of the PTR. Zhang Xiaofu, Chenyi et al propose "preparation method of multi-wavelength volume Bragg grating", but the shortest used wavelength can only reach 432nm [ patent No CN104133267A ], and preparation method of reflection type volume grating with shorter wavelength is not related in relevant documents and patents. The invention provides a grating writing method of a short-wave reflection type volume grating, which can realize the preparation of the reflection type volume grating with the wavelength of 325nm to 650 nm.

The invention content is as follows:

the invention provides a grating writing method of a short wave reflection type volume grating, namely a prism coupling exposure method and a correlation exposure method. The wavelength of the reflective volume grating prepared by adopting the prism coupling exposure method can be 375nm-650nm, and the preparation of the reflective volume grating with shorter wavelength of 325nm-378nm can be realized by adopting the correlation exposure method.

The technical solution of the invention is as follows:

1. a prism coupled exposure method, the method comprising the steps of:

setting the exposure wavelength lambda of the PTR glass to be exposed_{Exposure method}Refractive index of₁Using the wavelength λ at the grating_{Make it}Refractive index of_avThe exposure angle of two ultraviolet parallel lights in the PTR glass is theta₀Exposure to lightWavelength lambda_{Exposure method}The wavelength of two beams of ultraviolet parallel light for exposing the PTR glass to be exposed is determined;

polishing the upper surface and the lower surface of the PTR glass to be exposed respectively to form a light-transmitting incident surface and a light-transmitting emergent surface;

making a base angle theta₂Isosceles triangular prism of, and theta₂＝θ₀Two isosceles surfaces of the isosceles triangular prisms are respectively plated with an ultraviolet antireflection film, and the isosceles triangular prisms (1) are exposed at an exposure wavelength lambda_{Exposure method}Refractive index of₂And n is₂≈n₁The bottom surface of the isosceles prism is matched with the size of the upper surface of the PTR glass;

adhering the incident surface of the bottom surface PTR glass of the isosceles prism with matching liquid, and adhering the emergent surface of the PTR glass with the black light absorption sheet; the refractive index n of the matching fluid₃And n is₃＝n₁；

Two ultraviolet parallel lights vertically enter the two waists of the prism, and generate interference on the entrance surface or inside of the PTR glass.

The exposure angle theta₀In the range of 30 DEG to 60 DEG, the grating of said reflective volume grating using a wavelength lambda_{Make it}In the range of 375nm to 650 nm.

2. A correlation exposure method, the method comprising the steps of:

let us assume that the grating of the PTR glass to be exposed uses a wavelength lambda_{Make it}Refractive index n of_avTwo ultraviolet parallel lights at incident angle theta₁Obliquely incident on the PTR glass and generating interference in the PTR glass, and the exposure angle is theta₀；

Polishing two incidence surfaces of the PTR glass to be exposed and plating an ultraviolet anti-reflection film to form a light-passing surface;

the exposure angle theta₀In the range of 60 DEG to 90 DEG, the grating of said reflective volume grating using a wavelength lambda_{Make it}In the range of 325nm to 378 nm.

The invention has the advantages that:

1. compared with the known reflective bulk grating preparation technology, the method provided by the invention can be used for preparing the reflective bulk grating with shorter wavelength.

2. The method provided by the invention has the advantages of simple structure, easiness in operation and capability of realizing batch production. The prism is easy to process, low in cost, stable in structure and easy to fix, and can ensure the stability of grating writing in the exposure process.

Drawings

FIG. 1 is a schematic view of prism coupling exposure

FIG. 2 is a schematic diagram of a correlation exposure, in which a is a schematic diagram of an exposure method and b is a schematic diagram of an exposure principle

Detailed Description

The following detailed description of the embodiments of the present invention is provided with reference to specific examples and drawings, but the present invention is not limited to the description of the embodiments and the scope of the present invention.

1. A prism coupled exposure method, the method comprising the steps of:

(1) two beams of ultraviolet

parallel light

2,3 are provided for exposing the grating write medium PTR glass 9 at an exposure wavelength λ_{Exposure method}；

(2) Polishing the upper surface and the lower surface of PTR glass 9 to be exposed respectively to form a light-transmitting incident surface 8 and a light-transmitting emergent surface 10, wherein the PTR glass 9 is exposed at an exposure wavelength lambda_{Exposure method}Refractive index of₁Using the wavelength λ at the grating_{Make it}Refractive index of_av；

(3) Selecting a base angle of theta₂The isosceles prism 1, two

equal waist surfaces

4,5 of the isosceles prism 1 are respectively plated with a layer of ultraviolet antireflection film, and the ultraviolet antireflection film is coated at the exposure wavelength lambda_{Exposure method}The refractive index of the lower triangular prism is n₂Requiring exposure at an exposure wavelength λ_{Exposure method}Refractive index n of lower triangular prism 1₂Refractive index n of PTR glass 9₁Close to, i.e. n₂≈n₁The base 6 of the prism 1 is matched in size to the upper surface 8 of the PTR glass 9;

(4) the bottom face 6 of the prism 1 is bonded to the incident face 8 of the PTR glass 9 using a matching fluid 7, the refractive index of the matching fluid 7 being n, the refractive index of the PTR glass 9₁The same is true. The exit surface 10 of the PTR glass 9 was coated with a black ink using a matching fluid 7A light sheet 11;

(5) two ultraviolet

parallel lights

2,3 are emitted at an incident angle theta₁The light perpendicularly enters the two

waists

4,5 of the prism 1 at 90 DEG, and interferes with the incident surface 8 or the inside of the PTR glass 9 at an exposure angle theta₀. According to a geometric relationship, the exposure angle theta₀Base angle theta with triangular prism₂Equal, i.e. theta₀＝θ₂. According to the fringe period generated by the interference of the two

parallel lights

2 and 3 and the relationship between the used wavelength and the period of the volume grating, the following results are obtained:

the method is implemented by changing the exposure angle theta₀I.e. base angle theta of the prism₂And the reflective type volume grating with different wavelengths can be prepared. Taking into account the exposure angle theta₀Within a reasonable range, the exposure angle can be between 30 and 60 degrees, and the wavelength of the reflective bulk grating prepared by the method can reach 375 to 650 nm.

2. A correlation exposure method, the method comprising the steps of:

(1) two incident surfaces 8 of the PTR glass 9 are respectively polished and plated with a layer of ultraviolet antireflection film to form a light transmitting surface, and the PTR glass uses the wavelength lambda of the grating_{Make it}Refractive index n of_av；

(2) Two ultraviolet

parallel lights

2,3 are set at an incident angle theta₁To the light-passing surface 8 of the PTR glass 9 and to generate interference inside the PTR glass with an exposure angle theta₀From the refractive index formula, θ₀＝90°-arcsin(sinθ₁/n_av)；

(3) According to the fringe period generated by the interference of the two

parallel lights

the wavelength of the reflective volume grating that can be produced by this method can be 325nm to 378nm, taking into account that the exposure angle is within a reasonable range.

Example 1: the prism coupling exposure method for preparing the reflection type volume grating with the wavelength of 450 +/-0.5 nm comprises the following specific steps:

(1) providing parallel

ultraviolet light

2,3 with an exposure wavelength lambda_{Exposure method}＝325nm。

(2) Polishing the incident surface 8 and the exit surface 10 of the PTR glass 9 to be exposed, the refractive index of the PTR glass 9 at an exposure wavelength of 325nm being n₁1.528, refractive index n at a grating use wavelength of 450nm_av＝1.512

(3) Calculating an exposure angle θ₀Is 45.6 degrees. Selecting base angle theta₂An isosceles prism 1 of 45.6 DEG and having a refractive index n₂1.528, two

equal waist surfaces

4 and 5 of the triangular prism 1 are plated with a 325nm ultraviolet antireflection film, and the 325nm transmittance is increased.

(3) The bottom edge 6 of the triangular prism is bonded with the PTR glass incidence surface 8 by using matching fluid 7, so that light reflection at the interface is prevented, and meanwhile, the PTR glass emergence surface 10 is pasted with a black light absorbing sheet 11, so that Fresnel diffraction is prevented.

(4) Two beams of 325nm

parallel ultraviolet light

2,3 are respectively emitted at an incidence angle theta₁When the light enters the two equi-

waisted surfaces

4,5 of the prism perpendicularly at 90 °, interference occurs between the incident surface 8 of the PTR glass 9 and the inside of the body, and the PTR glass is exposed to a certain dose of ultraviolet light and then the exposure is stopped.

(5) And (3) preparing a reflective type body grating initial sample through subsequent heat treatment and cutting, testing the central wavelength of the reflective type body grating initial sample, and continuously performing operation adjustment on the steps (3) to (5) to test the exposure angle and the central wavelength so as to enable the central wavelength to fall in a required range.

Example 2: and preparing the reflective volume grating with the central wavelength of 376 +/-0.5 nm by using a correlation exposure mode.

(1) Both incident faces 8 of the PTR glass 9 to be exposed are polished.

(2) Refractive index n of PTR glass 9 at a use wavelength of 376nm_avCalculate exposure angle θ as 1.52₀Is 59.8 degrees, and the incident angle theta is obtained according to the refraction fixed rate₁＝49.85°。

(3) Make itUsing two beams of ultraviolet

parallel light

2,3 in theta₁This was made incident on the PTR glass 9 at an angle of 49.85 °, and after exposure to a dose of uv light, the exposure was stopped.

(4) And (3) preparing a reflective type body grating initial sample through subsequent heat treatment and cutting, testing the central wavelength of the reflective type body grating initial sample, and continuously performing operation adjustment on the steps (2) to (4) to test the exposure angle and the central wavelength so as to enable the central wavelength to fall in a required range.

The method of the invention changes the exposure angle theta₀The method provided by the invention can relate to the preparation of 325nm short-wave reflective body gratings, widens the technical field of short-wave reflective body gratings, has the advantages of simple structure, easy operation, contribution to mass production and good practical prospect in the fields of laser beam combination, spatial filtering, laser wave locking and the like.

Claims

1. a grating structure writing method of short-wave range reflective volume grating, is characterized in that, this method comprises the steps as follows:

① Let the refractive index of the PTR glass (9) to be exposed at the _exposure wavelength λ be n ₁ , and the refractive index at the wavelength λ _of the grating be n _av , and the two beams of ultraviolet parallel light (2, 3) are exposed to the PTR glass. The exposure angle in (9) is θ ₀ , and the exposure wavelength λ is the wavelength of the ultraviolet parallel light (2, 3) for _exposing the PTR glass (9) to be exposed;

② The upper surface and the lower surface of the PTR glass (9) to be exposed are polished respectively to form a light-transmitting incident surface (8) and an exit surface (10);

③ Make an isosceles prism (1) with a base angle of θ ₂ , and θ ₂ =θ ₀ , the two isosceles surfaces (4, 5) of the isosceles prism (1) are respectively coated with an ultraviolet antireflection coating, the The refractive index of the isosceles prism (1) under the _exposure wavelength λ is n ₂ , and n ₂ ≈ n ₁ , the bottom surface (6) of the isosceles prism (1) and the upper surface (8) of the PTR glass (9) ) size matching;

④ Use the matching liquid (7) to bond the bottom surface (6) of the isosceles prism (1) with the incident surface (8) of the PTR glass (9), and the exit surface (10) of the PTR glass (9) with black The light-absorbing sheet (11) is bonded; the refractive index of the matching liquid (7) is n ₃ , and n ₃ =n ₁ ;

⑤ The two beams of ultraviolet parallel light (2, 3) are vertically incident on the two isosceles surfaces (4, 5) of the triangular prism (1), and interference occurs on the incident surface (8) or the interior of the PTR glass (9).

2. The grating structure writing method of the short-wave range reflective volume grating according to claim 1, wherein the range of the exposure angle θ ₀ is 30°-60°, and the The grating uses wavelength λ in _the range of 375nm-650nm.

3. A method for writing a grating structure of a short-wave range reflective volume grating, characterized in that the method comprises the following steps:

① Assume that the grating of the PTR glass (9) to be exposed uses the refractive index n _av at _the wavelength λ, and the two beams of ultraviolet parallel light (2, 3) are obliquely incident on the PTR glass (9) at the incident angle θ ₁ , and interference occurs inside the PTR glass, and the exposure angle is θ ₀ ;

② Polishing and coating the two incident surfaces (8) of the PTR glass (9) to be exposed with an ultraviolet anti-reflection film to form a light-transmitting surface.

4. The grating structure writing method of the short-wave range reflective volume grating according to claim 3, wherein the range of the exposure angle θ ₀ is 60°-90°, and the reflective volume grating has a The grating uses wavelength λ in _the range of 325nm-378nm.