Monolithic Narrow-Linewidth Semiconductor Laser With Integrated Grating
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Solution Overview
Problem
Existing narrow linewidth semiconductor laser devices have large form factors, are difficult to assemble, and lack compatibility with integrated photonic platforms, while also suffering from thermal and acoustic noise.
Innovation Solution
A compact semiconductor laser device with a monolithic integration of an active gain section and a waveguide section, featuring anti-reflection and high-reflectivity coatings, a grating for narrow bandwidth, and adjustable operating wavelength through thermal, electrical, or thermo-electrical means, with optional phase and heater sections for enhanced flexibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a very long laser cavity is used to achieve narrow linewidth, then the linewidth is reduced, but the form factor increases and thermal and acoustic noise increase
Solution Approach 1:
The patent embeds a long effective cavity length within a compact physical footprint by nesting the grating structure within the semiconductor laser chip itself. The grating is formed directly in the waveguide layer, creating a nested configuration where the optical path is extended through multiple reflections within the compact chip structure, achieving long cavity equivalent performance in a small form factor device.
Solution Approach 2:
The patent transitions from a linear extended cavity to a compact structure by utilizing the vertical dimension and optical feedback mechanisms. The grating is formed at a specific depth within the waveguide, and the optical field interacts with the grating through evanescent coupling, effectively using the vertical dimension to achieve long optical path length within a compact horizontal footprint.
2Measurement precision
If a hybrid architecture with external grating is used to achieve narrow linewidth, then the linewidth is reduced, but the device becomes difficult to assemble and cannot easily be combined with other integrated photonic platforms
Solution Approach 1:
The patent merges the grating structure with the semiconductor laser chip by forming the grating directly within the waveguide layer of the same chip. This monolithic integration eliminates the need for separate external gratings and their associated alignment and assembly steps, making the device easy to manufacture and compatible with standard integrated photonic platforms.
Solution Approach 2:
The patent uses the waveguide layer as an intermediary medium that serves dual functions: guiding the optical field and containing the grating structure. This intermediary approach allows the grating to be formed directly in the waveguide using standard semiconductor fabrication techniques, eliminating the need for separate grating components and simplifying integration with other photonic devices.
3Measurement precision
If a grating with high reflectivity is used to achieve narrow linewidth, then the linewidth is reduced, but the device becomes more sensitive to manufacturing precision
Solution Approach 1:
The patent optimizes the grating parameters (period, depth, duty cycle) to achieve high reflectivity while maintaining robustness against manufacturing variations. By carefully selecting the grating period to match the wavelength and adjusting the etch depth to reach the high-index contrast layer, the design achieves high Q-factor with relaxed tolerances compared to other compact cavity designs.
Solution Approach 2:
The patent utilizes the composite structure of the semiconductor laser chip, combining layers of different refractive indices (GaAs, AlGaAs, InGaAsP) to create the grating. This composite material approach provides high index contrast that enhances grating reflectivity while the layered structure naturally accommodates manufacturing variations through the inherent properties of the semiconductor materials.
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 achieves ultra-narrow linewidth, excellent environmental stability, and compatibility with integrated photonic platforms, reducing noise and form factor while maintaining performance.
Implementation Method 1
a grating formed on, above or below to the waveguide section... the grating is designed and manufactured to have high reflectivity, narrow bandwidth
Implementation Method 2
anti-reflection coating (ARC) on an end facet of the waveguide section
Implementation Method 3
high-reflectivity coating (HRC) on an end facet of the gain section
Implementation Method 4
The operating wavelength of the device is tuned thermally, electrically, or thermo-electrically... The device of this invention can be positioned on top of one or more thermoelectric coolers (TECs) to control the temperature of the device
Implementation Method 5
a heater is disposed on a portion of the device surface to provide additional flexibility in adjusting the operating wavelength of the device
Data Source
AI summary
A novel narrow linewidth laser device is disclosed that is formed monolithically on a semiconductor substrate, such as an indium phosphide substrate, that includes a continuous waveguide with a gain section and a grating section wherein a grating is constructed so that its power reflectivity profile has a ratio of reflectivity slope over reflectivity at the 3 dB point below the reflectivity peak on the red side (longer wavelength side) of the grating larger than a value of 2/nm. The operating wavelength of the device may be tuned thermally, electrically, or thermo-electrically to be on the red side of the fiber Bragg grating reflectivity profile, preferably at the 3 dB point below the reflectivity peak or lower. In another embodiment, a second grating is formed on a second grating section of the waveguide on the opposite side of the gain section than the first grating section and wherein the reflectivity profile of the second grating overlaps at least a portion of the reflectivity profile of the first grating.