Index and Gain Coupled DFB Laser Grating
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Solution Overview
Problem
Conventional DFB lasers either index-coupled or gain-coupled, but not both, limiting their ability to achieve narrow linewidth and robustness against environmental fluctuations for applications like spectroscopy and communication.
Innovation Solution
A DFB laser structure with an active region surrounded by waveguide layers and a three-dimensional refractive grating formed using selective area epitaxy, modulating both the real and imaginary parts of the refractive index through mask openings and grating features, respectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional DFB lasers use only index-coupling or gain-coupling, then the device structure is simpler, but the emission linewidth is wider and mode stability is reduced
Solution Approach 1:
The patent combines both index-coupling and gain-coupling mechanisms within a single DFB laser structure. The index-coupling is achieved through a refractive index grating in the waveguide layer, while gain-coupling is implemented through periodic modulation of the active region. This merging of two coupling mechanisms enables narrow emission linewidth and improved mode stability without requiring separate laser structures.
Solution Approach 2:
The patent introduces a three-dimensional grating structure with vertical sidewalls that extends through multiple layers (waveguide and active region). This 3D structure allows simultaneous index-modulation in the waveguide and gain-modulation in the active region, achieving both index-coupling and gain-coupling effects within a single grating element rather than requiring separate 2D structures.
2Reliability
If conventional DFB lasers use only index-coupling or gain-coupling, then the device is easier to manufacture, but robustness against environmental fluctuations is reduced
Solution Approach 1:
The patent merges index-coupling and gain-coupling into a unified grating structure that is formed through selective area epitaxy. This combined structure provides inherent compensation for environmental fluctuations (temperature, current variations) because the two coupling mechanisms respond differently to these changes, improving robustness while maintaining manufacturability through a single epitaxial growth process.
Solution Approach 2:
The patent utilizes changes in material composition and structural parameters during selective area epitaxy to create the dual-coupling grating. By controlling growth conditions, layer composition, and grating geometry, the laser achieves simultaneous index and gain modulation with improved environmental stability while remaining compatible with standard semiconductor fabrication processes.
3Manufacturing precision
If mask openings are formed to modulate current flow, then the imaginary part of refractive index is modulated, but the real part of refractive index requires additional grating structure
Solution Approach 1:
The patent merges the functions of current modulation and refractive index modulation into a single three-dimensional grating structure. The mask openings modulate current flow to achieve gain-coupling (imaginary part modulation), while the same grating structure's periodic variation in refractive index provides index-coupling (real part modulation). This eliminates the need for separate gratings for each function.
Solution Approach 2:
The three-dimensional grating structure serves multiple functions simultaneously: it acts as a current confinement pattern through mask openings, provides refractive index modulation for index-coupling, and creates gain modulation for gain-coupling. This multi-functionality reduces the number of separate components needed while achieving precise control over both real and imaginary parts of the refractive index.
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
Enables single-mode operation with narrow emission linewidth and improved mode stability, robustness against environmental fluctuations, and efficient device performance.
Implementation Method 1
The mask openings modulate a current flow into the active region, thus, modulating the imaginary part of the refractive index of the laser
Implementation Method 2
The refractive grating provides modulation of the real part of the effective refractive index of the laser
Implementation Method 3
index and gain coupled distributed feedback laser
Data Source
AI summary
A laser includes an active region surrounded by first and second waveguide layers. Two or more mask openings are formed within a dielectric layer on a surface parallel to the active region. A refractive grating is formed on the dielectric mask openings and includes three-dimensional grating features spaced apart in the light-propagation direction of the laser. The refractive grating provides modulation of a real part of the effective refractive index of the laser and modulation of the imaginary part is provided by modulation of the current flow through the mask openings.