Tunable Semiconductor Laser Using Half-Wave Coupled Partial Reflectors
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Solution Overview
Problem
Traditional wavelength tunable lasers have limited tuning range and high fabrication complexity, which restricts their application in optical communication systems due to the limitations of refractive index change in semiconductor materials and complex fabrication processes.
Innovation Solution
A tunable semiconductor laser design utilizing two resonant cavities with different optical path lengths and a half-wave bow-tie coupler, where the coupling elements are back-to-back connected through a short coupling waveguide, allowing for high single-mode selectivity and wide tuning range through the Vernier effect, with refractive index modulation of one waveguide to switch output wavelengths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If traditional grating-based lasers (DFB, DBR) are used to achieve single-mode output, then wavelength tuning is possible, but the tuning range is limited to 10 nm due to refractive index limitations
Solution Approach 1:
The laser is divided into two separate resonant cavities with different optical path lengths, each capable of supporting multiple modes. The coupling between these segmented cavities creates a Vernier effect that enables wide wavelength tuning while maintaining single-mode output, resolving the contradiction between tuning range and mode selectivity
Solution Approach 2:
The patent introduces dynamic control of the coupling coefficient between the two cavities through a tunable coupler mechanism. By dynamically adjusting the coupling strength, the system can switch between different operating modes and achieve wide wavelength tuning range without sacrificing fabrication simplicity
2Adaptability or versatility
If digital super-mode DFB or sampled grating DBR lasers are used to achieve wider tuning range, then wavelength adaptability improves, but fabrication complexity and cost increase due to grating etching and epitaxial regrowth
Solution Approach 1:
The patent extracts and removes the complex grating structures from the laser design, replacing them with simple straight waveguides and basic reflectors. This extraction of the grating element eliminates the need for complex epitaxial regrowth and grating etching processes, significantly simplifying fabrication while maintaining wide tuning capability through the coupled-cavity Vernier mechanism
Solution Approach 2:
Instead of changing the physical structure through complex gratings, the patent achieves wavelength tuning by changing the refractive index parameter of the waveguide materials through electro-optic or thermo-optic effects. This parameter-based tuning approach maintains fabrication simplicity while achieving wide tuning range
3Adaptability or versatility
If coupled-cavity lasers with etched grooves or micro machining are used to achieve wavelength switching, then tuning range increases through Vernier effect, but fabrication difficulty and mode selectivity performance deteriorate
Solution Approach 1:
Instead of using complex etched grooves or micro-machined structures to couple the cavities, the patent inverts the approach by using simple straight waveguides with carefully controlled coupling regions. The coupling is achieved through evanescent field interaction between adjacent straight waveguides, which is inherently more precise and easier to manufacture than etched groove couplers, while maintaining the Vernier effect for wide tuning 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
The design achieves a wide tuning range with improved mode selectivity and simplified fabrication, reducing costs and power consumption, making it suitable for large-scale photonic integration and practical application in optical communication systems.
Implementation Method 1
One partial reflector is used as an output port and the other is used as a coupling element. Said coupling element could reflect part of the light back to the original resonant cavity and transmit remaining light to the other one.
Implementation Method 2
In one embodiment, such coupling element could be achieved through an optical beam expander and a central transmissive total internal reflection (TIR) corner mirror group.
Implementation Method 3
The two optical resonant cavities have different optical path lengths thus only one resonant frequency of the two resonant cavities coincides within the gain spectrum.
Implementation Method 4
At least a portion of one optical waveguide can be pumped to provide optical gain.
Implementation Method 5
Changing the current applied into at least a portion of one optical waveguide can change its refractive index and consequently switch the output wavelength between several channels.
Data Source
AI summary
The present invention discloses a tunable semiconductor laser based on half-wave coupled partial reflectors. The laser comprises two resonant cavities; one resonant cavity is mainly composed of an optical waveguide, a first partial reflector and a second partial reflector, and the other resonant cavity is mainly composed of an optical waveguide, a first partial reflector and a second partial reflector. The resonant cavities are arranged along the same straight line and coupled to each other, and the two second partial reflectors in the two resonant cavities are connected by a common coupling waveguide. The present invention has the best single-mode selection, and an emitted wavelength can be switched between a series of channels; an optical grating needs not to be manufactured, and the structure is simple; and the laser has a high degree of freedom in coupler design and a great manufacturing tolerance and can realize large-scale digital tuning.