Cemented Prism Grating Dispersion Element Wedge Angle
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Solution Overview
Problem
Conventional immersion gratings experience intensity modulation due to optical path differences between signal and noise light, caused by imperfect cementing and high refractive index mediums, leading to interference and undesirable wavelength-dependent intensity changes in spectral devices and wavelength selective switches.
Innovation Solution
A dispersion element with a prism and optical element integrated by cementing non-parallel surfaces, where the diffraction optical surface is reflective and the angle between the transmission and diffraction surfaces is carefully controlled to prevent overlap of ordinary and noise light, ensuring no intensity modulation occurs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional cementing methods are used to join the chip and prism, then the manufacturing process is simple, but intensity modulation occurs due to optical path differences between signal and noise light
Solution Approach 1:
The patent introduces asymmetry by making the diffraction optical surface non-parallel to the transmission surface, creating a wedge angle. This asymmetric geometry causes noise light reflected at the cementing surface to travel a different optical path than signal light, preventing their overlap and eliminating intensity modulation while maintaining manufacturing simplicity
Solution Approach 2:
The patent adds a dimensional parameter (wedge angle) to the previously parallel surface configuration. By introducing this angular dimension between the diffraction optical surface and transmission surface, the patent creates spatial separation between signal and noise light paths, resolving the intensity modulation problem without complicating the cementing process
2Manufacturing precision
If the diffraction optical surface is made parallel to the transmission surface, then the manufacturing precision is easier to maintain, but noise light overlaps with signal light causing intensity modulation
Solution Approach 1:
The patent deliberately introduces asymmetry by specifying that the diffraction optical surface be non-parallel to the transmission surface. This asymmetric wedge configuration ensures that even with standard manufacturing tolerances, noise light reflected at the cementing surface will follow a different path than signal light, eliminating overlap and interference
Solution Approach 2:
The patent extracts the noise light component from the optical system by redirecting it through the wedge angle into a separate path. By removing the parallelism constraint, the patent separates noise light from signal light spatially, preventing their interaction and eliminating intensity modulation
3Measurement precision
If a high refractive index medium like silicon is used, then the dispersion performance is improved, but intensity modulation occurs due to reflection at the cementing surface
Solution Approach 1:
The patent uses the wedge angle (asymmetric configuration) to redirect reflected noise light away from the signal light path. This allows the use of high refractive index materials like silicon for improved dispersion performance while preventing the harmful reflection effect through geometric separation of light paths
Solution Approach 2:
The patent converts the harmful reflection at the cementing surface into a useful separation mechanism. By introducing the wedge angle, the reflected noise light is directed into a different path, and this previously harmful reflection becomes the mechanism that separates noise from signal, eliminating intensity modulation while maintaining high dispersion performance
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
The solution effectively prevents overlap of ordinary and noise light, eliminating intensity modulation and ensuring accurate wavelength separation without interference, even when using high refractive index mediums.
Implementation Method 1
a diffraction grating is formed on a surface of the optical element
Implementation Method 2
the diffraction optical surface is reflective
Data Source
AI summary
A dispersion element includes a prism having a first transmission surface and an oppositely disposed second transmission surface, and an optical element having a third transmission surface and an oppositely disposed diffraction optical surface on which a diffraction grating is arranged. The prism and the optical element are integrated into one body by cementing the first transmission surface to the third transmission surface. The third transmission surface and the diffraction optical surface are non-parallel to each other in a plane perpendicular to grooves of the diffraction grating.