Slanted Diffraction Grating Littrow Configuration
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Solution Overview
Problem
Dielectric transmission type gratings in Littrow configurations for external cavity diode lasers suffer from low reflectance in the R-1 diffraction order and high stray light in other orders, leading to inefficient power distribution and manufacturing complexities, particularly with additional coatings required for improved performance.
Innovation Solution
A slanted type diffraction grating geometry is used in a Littrow configuration to concentrate incident light power into the R-1 reflection and T0 transmission diffraction orders, achieving high diffraction efficiency without additional coatings and optimizing for unpolarized light, with adjustable operation wavelength by rotating or stretching the grating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a binary surface relief grating is formed in SiO2 for transmission type Littrow configuration, then the manufacturing process is simple, but the reflectance to the R-1 diffraction order is low (maximum about 5-10%)
Solution Approach 1:
The patent changes the geometric parameters of the grating structure by introducing a slanted profile with specific angles (alpha and beta) rather than using a conventional binary rectangular profile. This parameter change enables the grating to achieve high reflectance (>15%, up to >50% in some embodiments) to the R-1 diffraction order while maintaining transmission type configuration and avoiding complex additional coatings.
2Reliability
If a TiO2 coating is added to improve reflectance to R-1 diffraction order, then the reflectance increases (nearly 20% achieved), but the manufacturing process becomes more complex and difficult to control
Solution Approach 1:
The patent extracts and eliminates the need for additional TiO2 coating layers by incorporating the reflectance-enhancing functionality directly into the grating profile geometry itself. The slanted grating structure with optimized angles achieves high reflectance through its shape alone, removing the separate coating step and simplifying the manufacturing process while maintaining or improving performance.
Solution Approach 2:
The patent uses the substrate material (SiO2 or other dielectric materials) in a composite structural form with a slanted profile, where the geometric configuration works together with the material properties to achieve high reflectance without requiring additional coating materials like TiO2.
3Ease of manufacture
If conventional gratings are used in transmission type Littrow configuration, then the manufacturing is simpler, but the total efficiency is well below 100% due to high stray light in R0 and T-1 diffraction orders
Solution Approach 1:
The patent optimizes the slanted grating parameters (depth, period, and angles alpha and beta) to control the diffraction efficiency distribution. By carefully selecting these parameters, the grating directs most of the incident light power into the desired R-1 and T0 diffraction orders while minimizing stray light in unwanted orders, achieving total efficiency close to 100%.
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 achieves very high diffraction efficiency with minimal stray light, allowing for tunable and stable operation across a wide range of wavelengths, simplifying manufacturing and enabling efficient operation for both polarized and unpolarized light, significantly improving the performance of external cavity diode lasers.
Implementation Method 1
the incident angle of the light beam and the grating geometry being adjusted to concentrate the incident light power to the R-1 reflection diffraction order backwards to the direction of the incident light beam and to the T0 transmission diffraction order through the diffraction grating
Implementation Method 2
Said direction of the R-1 diffraction order backwards to the direction of incidence is achieved when the phase shift between light beams reflected to said direction from adjacent grating lines separated by a distance d equals to the multiple of the designed wavelength to achieve a constructive interference between said beams
Data Source
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AI summary
The light manipulation arrangement (1) of the present invention comprises a light source (2) and a transmission type diffraction grating (3), the light source being arranged to produce a light beam (i) directed to the diffraction grating, the incident angle (?) of the light beam and the grating geometry being adjusted to concentrate the incident light power to the R -1 reflection diffraction order backwards to the direction of the incident light beam and to the T 0 transmission diffraction order through the diffraction grating. According to the present invention, the diffraction grating (3) is of slanted type.