Volume Bragg Grating Recording via Prism Total Internal Reflection
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Solution Overview
Problem
Existing methods for manufacturing reflective volume Bragg grating filters have limitations such as a limited usable wavelength range, complexity in sample preparation, and a restricted clear aperture due to material absorption, making it difficult to achieve wide wavelength tuning and efficient fabrication.
Innovation Solution
The method involves injecting recording light into a medium through the same surface as the input or output of the filter, using a prism to achieve total internal reflection, allowing for continuous tuning of the Bragg grating by adjusting the incident angle, which eliminates the need for polishing orthogonal faces and increases the clear aperture.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If side-writing method is used to record VBG filter, then the filter can be manufactured, but the clear aperture is limited to approximately 4-6 mm due to material absorption
Solution Approach 1:
Instead of injecting recording light through the side surface of the crystal (conventional method), the invention inverts the approach by injecting light through the end face (operating surface) of the crystal. This allows the recording beams to propagate along the optical axis and intersect inside the medium, enabling clear apertures much larger than 4-6 mm without being limited by material absorption at the side surfaces.
2Adaptability or versatility
If side-writing method is used, then VBG filter can be recorded, but the wavelength tuning range is limited to approximately 40 nm
Solution Approach 1:
The invention introduces a rotating stage that allows dynamic adjustment of the crystal orientation during recording. By rotating the crystal around the optical axis, the diffraction angle can be continuously varied, enabling wide wavelength tuning ranges (greater than 40 nm) while maintaining a simplified fixed-wavelength recording setup. This dynamic adjustment capability resolves the contradiction between tuning range and setup complexity.
3Ease of manufacture
If side-writing method is used, then VBG filter can be manufactured, but complex sample preparation including polishing orthogonal faces is required
Solution Approach 1:
The invention extracts and eliminates the requirement for polishing orthogonal side faces by changing the recording geometry. Instead of requiring two polished orthogonal faces for side-writing, the method only requires one polished end face through which recording light is injected. This removes the complex sample preparation step while simplifying the overall manufacturing process.
4Manufacturing precision
If recording wavelength is substantially shorter than operating wavelength, then VBG filter can be recorded, but total internal reflection prevents direct injection through operating surface
Solution Approach 1:
The invention uses the crystal's end face as an intermediary medium that allows short-wavelength recording light to enter the crystal without suffering from total internal reflection. By injecting light through the end face rather than the side face, and by rotating the crystal to achieve proper beam intersection geometry, the method enables precise grating recording while maintaining ease of light injection.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables continuous tuning of the Bragg wavelength over a wide range, increases the clear aperture, simplifies the fabrication process, and enhances the efficiency and stability of the recording process, allowing for filters with arbitrarily large apertures and simplified setup.
Implementation Method 1
using a prism to achieve total internal reflection
Data Source
AI summary
Methods for recording volume Bragg grating structures having a target wavelength are disclosed. Such a method may include providing a photosensitive recording medium, bringing a first face of the recording medium into contact with a face of a prism, the prism being made of a material that is transparent at a recording wavelength, and recording a Bragg grating onto the recording medium by exposing the prism to an incident light wave at the recording wavelength.