Spatial Filter Coating for Single Lateral Mode Laser Control
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Solution Overview
Problem
Existing semiconductor laser devices face challenges in controlling the lateral beam propagation to maintain a single lateral mode over a wide range of currents and temperatures without the need for semiconductor material regrowth, and in achieving spatial lateral control beyond the limitations of etch depth and width of the ridge.
Innovation Solution
The process involves fabricating a ridge-type semiconductor laser with a spatial filter coating on one facet, using a multilayer coating as a spatial filter to control the lateral mode behavior, allowing for precise control of the beam shape by determining the position, size, and shape of the filter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a ridge laser structure is used to eliminate material regrowth, then manufacturing complexity is reduced, but spatial lateral control of the laser output is limited by etch depth and ridge width
Solution Approach 1:
The patent transitions from controlling lateral mode through geometric constraints (ridge width and depth in two dimensions) to optical property control through multilayer coating reflectivity modulation. By adding the dimensional control parameter of coating reflectivity, the system achieves spatial lateral control without modifying the physical ridge geometry, thus maintaining manufacturing simplicity while enhancing control capability.
Solution Approach 2:
The patent changes the control parameter from physical dimensions (ridge width and etch depth) to optical properties (coating reflectivity). By varying the reflectivity of the multilayer coating in different spatial regions, the system can control lateral mode behavior and beam shape without altering the ridge geometry, thereby maintaining ease of manufacture while improving spatial control.
2Ease of manufacture
If conventional lithographical techniques are used on the wafer, then fabrication is simplified, but further processing of lasers after cleaving is not possible
Solution Approach 1:
The patent applies the multilayer spatial filter coating to the facet surface after cleaving but before final device assembly and testing. This preliminary action allows for precise control of lateral mode behavior to be established early in the fabrication process, enabling further processing steps such as device mounting and packaging to proceed without additional complex lithography operations.
Solution Approach 2:
The patent replaces conventional lithographical techniques (which require flat wafer surfaces and precise alignment) with a coating-based approach that can be applied to the cleaved facet surface. This substitution uses optical deposition processes instead of mechanical lithography, enabling processing after cleaving while maintaining fabrication simplicity.
3Reliability
If the ridge width and etch depth are increased to control lateral mode, then single lateral mode behavior is achieved, but the control range is restricted
Solution Approach 1:
The patent changes the control mechanism from fixed geometric parameters (ridge width and etch depth) to variable optical parameters (coating reflectivity). By adjusting the reflectivity of the multilayer coating, the system can maintain single lateral mode operation across a broader range of operating conditions including different currents and temperatures, thereby expanding the operating range while ensuring mode stability.
Solution Approach 2:
The patent introduces dynamic control capability through the multilayer coating structure, which can be designed with graded or patterned reflectivity profiles. This allows the lateral mode control to adapt to varying operating conditions such as current changes and temperature variations, maintaining single mode operation dynamically across an extended operating range rather than being restricted to a narrow fixed parameter range.
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 the fabrication of a single lateral mode laser that operates effectively across a broader range of currents and temperatures, maintaining stable performance up to higher power levels, as demonstrated by improved Light vs. Current characteristics.
Implementation Method 1
a reflectivity modification coating is applied in a spatially controlled manner so as to allow a single lateral mode laser to be fabricated. The reflectivity modification coating, in a preferred aspect of the invention, is a multilayer coating that serves as a spatial filter to allow a specific region of the facet to control the spatial behavior of the lateral mode of the laser.
Implementation Method 2
one of the device facets is first anti-reflection (AR) coated
Data Source
Figure 1
Figure 2a~6b
Figure 7a~8b
AI summary
An etched-facet single lateral mode semiconductor photonic device is fabricated by depositing an anti reflective coating on the etched facet, and depositing a reflectivity modifying coating in a spatially controlled manner to modify the spatial performance of the emitted beam.