CN1725042B - Scanning Grating Writing Method Based on Talbot Interferometer and Scanning Talbot Interferometer - Google Patents

Abstract

The invention relates to a scanning grating writing method based on a Talbot interferometer and a scanning Talbot interferometer, belonging to the field of optical technology. Using a Talbot interferometer, the incident beam is reflected, diffracted, and reflected in sequence to form interference fringes on the optical fiber, and at the same time, the formed interference fringes are moved horizontally along the optical fiber to scan and write the grating on the optical fiber. The scanning Talbot interferometer consists of a plane mirror, a horizontal translation stage, a phase mask, a zero-order blocking mask, a vertical translation stage and an optical fiber fixed on it. It has the advantages of conveniently tuning the Bragg wavelength for writing, low requirements on the pulse energy and coherence of the writing light source, and the small length of the plane mirror of the Talbot interferometer.

Description

Scanning Grating Writing Method Based on Talbot Interferometer and Scanning Talbot Interferometer

Technical field: The present invention relates to a scanning grating writing method based on a Talbot interferometer and a scanning Talbot interferometer, belonging to the field of optical technology.

Technical background: Since 1993, KOHill et al. verified for the first time that the optical fiber was directly placed in the ultraviolet near-field interference region generated by phase mask diffraction, and this writing method has been widely used in the production of fiber gratings. However, in the contact writing method of the phase mask, the writing Bragg wavelength of the fiber grating corresponds to the grating period of the phase mask, and the Bragg wavelength cannot be changed as required. In order to change the written Bragg wavelength and be greater than 2nm, there is a Talbot interferometer, which can change the writing wavelength of the fiber grating by adjusting the angle of the plane mirror; but the length of the grating written by this Talbot interferometer is limited by the length of the plane mirror With the coherence of the writing light source, making a narrow-bandwidth grating often requires a longer plane mirror (it is difficult to make a >60mm plane mirror that satisfies ultraviolet interference), and writing a grating has high requirements for the pulse energy density of the ultraviolet beam (such as writing I type grating, the energy density must be >100mJ/cm ² /pulse, and the cumulative energy density must be >500J/cm ² ); in addition, the coherence of the light source also has a great influence on writing the grating.

Summary of the invention: The object of the present invention is to overcome the deficiencies of the prior art, to provide a scanning grating writing system based on a Talbot interferometer that can easily tune the written Bragg wavelength and have low requirements on the pulse energy and coherence of the writing light source. input method, and a scanning Talbot interferometer for this method.

The technical solution of the present invention is: the scanning grating writing method based on the Talbot interferometer is to use the Talbot interferometer to make the incident light beam undergo reflection, diffraction and reflection in sequence to form interference fringes on the optical fiber, and at the same time make the formed interference fringes The fringe is moved horizontally along the fiber, thereby scanning and writing the grating across the fiber.

Using a Talbot interferometer with a horizontal translation stage and a vertical translation stage structure, the incident light beam passes through the plane mirror 1 on the horizontal translation stage 2, the phase mask 3 on the bracket, and the diffraction mirrors 5 and 6 on the horizontal translation stage 2 in sequence. And the light-shielding plate 4 blocks the zero-order diffracted light generated by the phase mask 3, performs reflection, diffraction, and reflection, and forms interference fringes on the optical fiber 7 on the vertical translation stage 8, and simultaneously moves the horizontal translation stage 2 horizontally to make the interference fringes along the The optical fiber moves, scans and writes the grating on the optical fiber; the incident light beam can also pass through the plane mirror 1 on the support, the phase mask 3 on the horizontal translation stage 2, the diffraction mirrors 5 and 6 on the support, and the shading plate (4 ) block the zero-order diffracted light generated by the phase mask (3), perform reflection, diffraction, and reflection, and form interference fringes on the optical fiber 7 on the vertical translation platform 8 fixed on the horizontal translation platform 2, and simultaneously move the horizontal translation Stage 2 moves the interference fringes along the optical fiber 7, so as to scan and write the grating on the optical fiber.

The scanning Talbot interferometer used in the scanning grating writing method consists of a plane mirror 1, a horizontal translation stage 2, a phase mask 3, a light shield 4 for zero-order blocking, a diffraction mirror 5, and a diffraction mirror 6. And the vertical translation stage 8 and the optical fiber 7 fixed on it, the phase mask 3 is located between the plane mirror 1 and the diffraction mirrors 5, 6, and the zero-order blocking light shield 4 is located between the diffraction mirrors 5, 6. According to the needs of the scanning and writing method, the plane mirror 1, the zero-order blocking light shield 4, the diffraction mirror (plane mirror) 5, and the diffraction mirror (plane mirror) 6 can be fixed on the horizontal translation stage 2, and the phase mask 3 is formed by Supported by the bracket, the vertical translation stage 8 is separated from the horizontal translation stage 2, and scanning writing is realized through interference fringe movement. It is also possible to fix the phase mask 3 and the vertical translation stage 8 on the horizontal translation stage 2, and the plane mirror 1, the diffraction mirror (plane mirror) 5, the diffraction mirror (plane mirror) 6, and the zero-order blocking shading plate 4 are supported by the bracket , the structure in which the vertical translation platform 8 is placed on the horizontal translation platform 2; when the horizontal translation platform 2 performs horizontal translation, it will drive the vertical translation platform 8, so that the optical fiber on the vertical translation platform 8 can move horizontally and realize scanning writing .

In the scanning Talbot interferometer, the rotation of the two plane mirrors (diffraction mirrors) 5 and 6 plays a decisive role in changing the Bragg wavelength written in the fiber grating. According to the principle of reflection, when the angle of the reflective plane mirror changes δ, the direction of the reflected beam changes Δ equal to 2δ. Therefore, when the two plane mirrors rotate δ towards each other, under the given Bragg condition, the Bragg response wavelength is:

${\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; B</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; eff</span>}}\mathrm{<span\; class="notranslate">\; \&Lambda;</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; eff</span>}}{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; uv</span>}}}{\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&delta;</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

At the same time, if the rotation axes of the two plane mirrors (diffraction mirrors) of 5 and 6 coincide with the incident ±1st-order diffracted beams, the ridges of the interference area of the two writing interference beams will move to:

ΔL=(W _s /2)[cot(θ/2+2δ)-cot(θ/2)] (2)

Therefore, when the scanning Talbot interferometer is used to tune the Bragg wavelength of the writing grating, as long as the translation stage 8 on which the optical fiber is placed should be translated accordingly, the optical fiber to be written can be located in the writing interference area, that is, the grating is written in the optical fiber.

Since the present invention adopts a conveniently adjustable movement structure and a scanning writing method, it has the following advantages:

1. The wavelength of the written grating Bragg can be easily adjusted according to the needs, and the length range of the written grating is wide;

2. The length of the plane mirror in the Talbot interferometer is greatly reduced, and the size of the plane mirror only needs to be larger than the size of the laser spot (> 1mm);

3. The requirements for the coherence length of the light source are significantly reduced, and the requirements for the coherence of the written light source are reduced;

4. Significantly reduces the requirement for laser pulse energy.

BRIEF DESCRIPTION OF THE DRAWINGS: The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

Fig. 1 is a schematic diagram of the structure of the interference fringe movement of the present invention,

Fig. 2 is a schematic diagram of the optical fiber movement structure of the present invention,

Fig. 3 is the graph that Bragg wavelength of the present invention changes with the angle of plane mirror rotation,

FIG. 4 is a graph showing the movement of the ridges in the interference region of the two writing interference beams as a function of the rotation angle of the plane mirror according to the present invention.

Detailed ways:

Example 1: The scanning grating writing method based on the Talbot interferometer is to use the Talbot interferometer to make the incident beam undergo reflection, diffraction and reflection in sequence to form interference fringes on the optical fiber, and at the same time make the formed interference fringes along the horizontal direction of the optical fiber Move to scan and write the grating on the fiber. Using a Talbot interferometer with a horizontal translation stage and a vertical translation stage structure, the incident light beam passes through the plane mirror on the horizontal translation stage, the phase mask on the bracket, the diffraction mirror on the horizontal translation stage, and 4 pairs of phases inserted into the light shield The zero-order diffracted light generated by the mask 3 is blocked, reflected, diffracted, and reflected to form interference fringes on the optical fiber on the vertical translation stage, and at the same time move the horizontal translation stage horizontally to make the interference fringes move along the optical fiber and scan on the optical fiber Write raster.

As shown in Figure 1, the scanning Talbot interferometer used in the scanning grating writing method consists of a plane mirror 1, a horizontal translation stage 2, a phase mask 3, a zero-order blocking light shield 4, and diffraction mirrors 5 and 6 , and a vertical translation stage 8 and an optical fiber 7 fixed thereon. The plane mirror 1, the zero-order blocking shading plate 4, the diffraction mirrors (plane mirrors) 5 and 6 are fixed on the horizontal translation stage 2, the phase mask 3 is supported by a bracket, and the phase mask 3 is located between the plane mirror 1 and the diffraction mirrors 5 and 6 Between them, the zero-order blocking shading plate 4 is located between the diffractive mirrors 5 and 6, and the vertical translation stage 8 is separated from the horizontal translation stage 2.

When working, the plane mirror 1 which reflects the incident beam and the two plane mirrors 5 and 6 which reflect the ±1st-order diffracted light are simultaneously driven by the horizontal translation platform 2 to move in the horizontal direction, so that the interference fringes move along the optical fiber 7 , thus scanning and writing the raster.

Example 2: The scanning grating writing method based on the Talbot interferometer is to use the Talbot interferometer to make the incident light beam undergo reflection, diffraction and reflection in sequence to form interference fringes on the optical fiber, and at the same time make the formed interference fringes along the horizontal direction of the optical fiber Move to scan and write the grating on the fiber. A Talbot interferometer with a horizontal translation stage and a vertical translation stage structure is used to make the incident beam pass through the plane mirror on the support, the phase mask on the horizontal translation stage, the diffraction mirror on the support, and insert the light shield to generate the phase mask. The zero-order diffracted light is blocked, reflected, diffracted, and reflected, and interference fringes are formed on the optical fiber fixed on the vertical translation stage on the horizontal translation stage. At the same time, the horizontal translation stage is moved horizontally to make the interference fringes move along the optical fiber. Scanning write gratings on fiber optics.

As shown in Figure 2, the scanning Talbot interferometer used in the scanning grating writing method consists of a plane mirror 1, a horizontal translation stage 2, a phase mask 3, a zero-order blocking light shield 4, and diffraction mirrors 5 and 6 , and a vertical translation stage 8 and an optical fiber 7 fixed thereon. The phase mask 3 and the vertical translation stage 8 are fixed on the horizontal translation stage 2, the plane mirror 1, the diffraction mirrors (plane mirrors) 5 and 6, and the zero-order blocking light shield 4 are supported by the bracket, and the phase mask 3 is located between the plane mirror 1 and the diffraction Between the mirrors 5 and 6 , the zero-order blocking shading plate 4 is located between the diffractive mirrors 5 and 6 , and the vertical translation stage 8 is placed on the horizontal translation stage 2 .

When working, the horizontal translation stage 2 simultaneously drives the phase mask 3 on which the diffraction function is performed, and the optical fiber 7 to be written in the grating is translated in the horizontal direction, so that the optical fiber moves along the interference fringes, thereby scanning and writing the grating.

In the scanning Talbot interferometer that changes the writing Bragg wavelength, the grating period _Δpm of the phase mask is 1084nm, when the _wavelength λuv of the ultraviolet writing beam is 248nm, the diffraction angle θ of the ±1st order diffracted light /2=13.225°; the distance W _s between the two plane mirrors is 10mm, as a result of formula (2), the distance L from the phase template to the writing interference area is 42.6mm; in the core of the optical fiber, the effective reflectivity n _eff is 1.46.

Substituting the above data into formula (1), we can get Figure 3, which shows the relationship between the Bragg wavelength and the angle change of the 5 and 6 plane mirrors. At the same time, the translation stage 8 on which the optical fiber is placed should be translated according to the rule of formula (2) so that the optical fiber to be written is located in the writing interference area, and the movement of the rhombic ridges in the interference area of the two writing interference beams varies with the angle of rotation of the plane mirror The curve is shown in Figure 4.

Claims (4)

1. a scanning type grating writing method based on Talbot interferometer, it is characterized in that adopting the Talbot interferometer with horizontal translation platform (2) and vertical translation platform (8) structure, incident light beam is passed through on the horizontal translation platform successively The plane mirror (1), the phase mask (3) on the bracket, the two diffraction mirrors (5, 6) on the horizontal translation stage, and the light shield (4) block the zero-order diffracted light generated by the phase mask (3) , perform reflection, diffraction, and reflection, and form interference fringes on the optical fiber (7) on the vertical translation stage (8), and move the horizontal translation stage (2) horizontally at the same time, so that the interference fringes move along the optical fiber, thereby scanning and writing on the optical fiber raster. 2. a scanning type grating writing method based on Talbot interferometer, it is characterized in that adopting the Talbot interferometer with horizontal translation platform (2) and vertical translation platform (8) structure, incident light beam is passed through the plane mirror on the support successively ( 1), the phase mask (3) on the horizontal translation stage, the two diffraction mirrors (5, 6) supported by the bracket, and the light shield (4) block the zero-order diffracted light generated by the phase mask (3), and carry out Reflection, diffraction, reflection, form interference fringes on the optical fiber (7) in the vertical translation stage (8) fixed on the horizontal translation stage, and move the horizontal translation stage (2) horizontally at the same time, so that the interference fringes move along the optical fiber, thus in Scanning write gratings on fiber optics. 3. a scanning type Talbot interferometer for the scanning type grating writing method described in claim 1 is characterized in that it is made of plane mirror (1), horizontal translation stage (2), phase mask (3), zero order blocking The shading plate (4), two diffraction mirrors (5, 6), and the vertical translation stage (8) and the optical fiber (7) fixed on it and the bracket are composed of a plane mirror (1), a zero-order blocking shading plate (4 ), two diffraction mirrors (5, 6) are fixed on the horizontal translation platform (2), the phase mask (3) is supported by a bracket, and the phase mask (3) is located between the plane mirror (1) and the two diffraction mirrors (5, 6), the zero-order blocking shading plate (4) is located between the two diffractive mirrors (5, 6), the vertical translation stage (8) is separated from the horizontal translation stage (2), and the horizontal translation stage (2) can complete Left and right can move freely horizontally, and the vertical translation platform (8) can complete free movement up and down. 4. the scanning type grating writing method according to claim 2 uses scanning type Talbot interferometer, it is characterized in that it is made of plane mirror (1), horizontal translation stage (2), phase mask (3), zero-order blocking The light shielding plate (4), two diffractive mirrors (5, 6), and the vertical translation stage (8) and the optical fiber (7) fixed on it and the bracket are composed, and the phase mask (3) and the vertical translation stage (8 ) is fixed on the horizontal translation platform (2), the plane mirror (1), two diffractive mirrors (5, 6), and the zero-order blocking light shield (4) are supported by the bracket, and the phase mask (3) is located on the plane mirror (1) Between the two diffractive mirrors (5, 6), the zero-order blocking shading plate (4) is located between the two diffractive mirrors (5, 6), and the vertical translation stage (8) is placed on the horizontal translation stage (2) .

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