Thin-Film Filter for Tunable Laser Side-Mode Suppression
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Solution Overview
Problem
Current silicon photonics platforms face challenges in creating compact, polarization-independent wavelength-tunable lasers with a sufficient free-spectral-range and side-mode suppression ratio for wide-band DWDM communication and LIDAR applications, particularly in designing small ring resonators and achieving high reflectivity while suppressing side-mode lasing.
Innovation Solution
A thin-film filter is applied to the high-reflectivity facet of a tunable laser gain chip, comprising multiple pairs of layers with specific optical thicknesses and refractive indices, configured to provide high reflectivity (>90%) within a tunable range and a reflectivity dip (<50%) around the side mode wavelength, enhancing the Vernier reflection tuner's performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a small ring resonator is used to reduce device size, then the device complexity is reduced, but the free-spectral-range becomes insufficient and side-mode suppression ratio deteriorates
Solution Approach 1:
The patent divides the single resonator system into two coupled ring resonators with different radii. This segmentation allows each resonator to contribute differently to the overall spectral response, enabling sufficient free-spectral-range and side-mode suppression while keeping individual resonator sizes compact. The Vernier effect arises from the interaction between these segmented resonators with different modal patterns.
Solution Approach 2:
The patent employs a composite structure consisting of two ring resonators with different radius ratios (first resonator radius/second resonator radius between 0.95-1.05). This composite resonator system combines the optical paths of both resonators to create a Vernier pattern, achieving enhanced spectral selectivity and side-mode suppression without requiring individually large resonator dimensions.
2Power
If a high-reflectivity facet is used to enhance laser output, then the laser power is improved, but side-mode lasing is not suppressed
Solution Approach 1:
The patent applies local quality modification by introducing a thin-film filter with non-uniform reflectivity characteristics across the spectral range. The filter provides high reflectivity (>90%) at the desired laser wavelength while creating a reflectivity dip (<50%) at side-mode wavelengths. This localized spectral selectivity suppresses side-mode lasing without compromising the overall laser output power.
Solution Approach 2:
The thin-film filter acts as an intermediary element between the high-reflectivity facet and the optical field. It mediates the interaction by selectively reflecting desired wavelengths while transmitting or absorbing side-mode wavelengths, thereby enabling both high laser power and effective side-mode suppression simultaneously.
3Reliability
If a thin-film filter with high reflectivity is applied to suppress side-modes, then the selectivity is improved, but the device complexity increases
Solution Approach 1:
The patent utilizes a thin-film filter structure that can be deposited directly on the high-reflectivity facet of the laser cavity. This thin-film approach achieves the required spectral selectivity and side-mode suppression without requiring bulky mechanical filters or complex optical assemblies. The filter's flexible design allows it to conform to the laser chip geometry, reducing overall device complexity.
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 improved wavelength tunability, selectivity, and stability by maintaining high reflectivity across the desired range while effectively suppressing side-mode lasing, thereby enhancing the performance of wavelength-tunable lasers in silicon photonics platforms for DWDM and LIDAR applications.
Implementation Method 1
a film including multiple pairs of layers each containing a first layer and a second layer sequentially stacking to an outer side of the high-reflectivity facet. Each of the first layer and the second layer in each pair has one unit of respective optical thickness except one first or second layer in one pair having a larger optical thickness.
Implementation Method 2
The film is configured to produce inner reflectivity of the laser light from the high-reflectivity facet at least greater than 90% for wavelengths in the tunable range starting from the first wavelength but at least smaller than 50% for wavelengths in a 25 nm range around the second wavelength.
Implementation Method 3
a cavity between a high-reflectivity facet and an anti-reflection facet designed to emit a laser light of a wavelength in a tunable range determined by at least two Vernier-ring resonators with a joint-free-spectral-range between a first wavelength and a second wavelength
Data Source
AI summary
A thin-film device for a wavelength-tunable semiconductor laser. The device includes a cavity between a high-reflectivity facet and an anti-reflection facet designed to emit a laser light of a wavelength in a tunable range determined by two Vernier-ring resonators with a joint-free-spectral-range between a first wavelength and a second wavelength. The device further includes a film including multiple pairs of a first layer and a second layer sequentially stacking to an outer side of the high-reflectivity facet. Each layer in each pair has one unit of respective optical thickness except one first or second layer in one pair having a larger optical thickness. The film is configured to produce inner reflectivity of the laser light from the high-reflectivity facet at least >90% for wavelengths in the tunable range starting from the first wavelength but at least <50% for wavelengths in a 25 nm range around the second wavelength.