Semiconductor Laser Diffractive Grating Phase Alignment
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Solution Overview
Problem
Semiconductor lasers face challenges in emitting desirable wavelengths due to phase differences between diffractive grating regions, leading to cancellation of laser emission at design wavelengths and failure to emit single wavelength lasers at offset wavelengths.
Innovation Solution
A semiconductor laser design incorporating a first and second diffractive grating region with segments having discrete peaks and space regions, where the pitch of the gratings is the same, but the wavelength interval of the second discrete peaks differs, and one segment has an optical length shorter or longer than others by an odd multiple of the grating pitch, allowing phase alignment and emission of desirable wavelengths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional semiconductor laser with SG-DFB and SG-DR regions is used, then the laser structure is simple and easy to manufacture, but a phase difference of 90 degrees is generated between incoming light and reflected light at the design wavelength, causing 180 degree phase difference between opposite-direction lights and cancellation of desirable wavelength emission
Solution Approach 1:
The diffractive grating is divided into multiple segments along the light propagation direction, with each segment having a specific optical length. By segmenting the grating and controlling the optical length of each segment to be an odd multiple of half the pitch, the patent achieves phase alignment of reflected lights while maintaining the overall grating structure for wavelength selection.
Solution Approach 2:
Different segments of the diffractive grating are assigned different optical lengths (odd multiples of half pitch), creating local variations in phase characteristics. This local quality differentiation allows specific segments to compensate for phase differences and enable constructive interference at desired wavelengths.
2Reliability
If the diffractive grating operates at offset wavelengths from the design wavelength, then the 90 degree phase difference is offset, but a single wavelength laser cannot be emitted due to lack of phase alignment
Solution Approach 1:
The patent changes the optical length parameter of diffractive grating segments to odd multiples of half the pitch. This parameter change transforms the phase relationship from 90 degrees (destructive interference) to 0 or 180 degrees (constructive interference), enabling single wavelength laser emission at desired wavelengths.
3Reliability
If segments have different optical lengths (odd multiple of half pitch), then phase alignment is achieved and desirable wavelength emission is enabled, but the manufacturing precision requirement increases
Solution Approach 1:
By defining the optical length as odd multiples of half pitch (a clear mathematical relationship), the patent transforms a complex phase alignment problem into a manufacturable parameter specification. This parameter definition enables systematic control of phase relationships through precise but achievable dimensional tolerances.
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 design ensures zero phase difference between lights traveling in opposite directions, enabling the semiconductor laser to emit a laser at a desirable wavelength by overlapping discrete peaks and controlling the reflection spectrum, thus overcoming previous emission limitations.
Implementation Method 1
a phase difference of 90 degrees is, however, generated between a light incoming to the SG-DR region and the SG-DFB region and a light reflected by a diffractive grating of the SG-DR region and the SG-DFB region
Implementation Method 2
a phase difference of 180 degrees is generated between lights transmitting in a resonator in directions opposite to each other, in the design wavelength range. Accordingly, a desirable wavelength light is canceled
Data Source
AI summary
A semiconductor laser has first and second diffractive grating regions. The first diffractive grating region has segments, has a gain, and has first discrete peaks of a reflection spectrum. The second diffractive grating region has segments combined to each other, and has second discrete peaks of a reflection spectrum. Each segment has a diffractive grating and a space region. Pitches of the diffractive grating are substantially equal to each other. A wavelength interval of the second discrete peaks is different from that of the first discrete peaks. A part of a given peak of the first discrete peaks is overlapped with that of the second discrete peaks when a relationship between the given peaks of the first discrete peaks and the second discrete peaks changes. A first segment located in the first diffractive grating region or the second diffractive grating region has an optical length shorter or longer than the other segments of the first diffractive grating region and the second diffractive grating region by odd multiple of half of the pitch of the diffractive grating of the first diffractive grating region.