Sagnac Loop Mirror Laser Cavity on Silicon Photonics
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Solution Overview
Problem
Silicon-based lasers face challenges due to silicon's indirect bandgap, making it difficult to achieve lasing, and existing external cavities for lasers are not efficient for telecommunication wavelengths, requiring improved designs for semiconductor optical amplifiers and resonator configurations.
Innovation Solution
A novel optical cavity configuration using a Sagnac loop mirror and micro-ring resonator with a tunable filter, allowing for broadband reflection and wavelength selection, integrated with a gain medium for efficient lasing at telecommunication wavelengths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If silicon is used as the gain medium material, then the die size is small and electrical pumping efficiency is high, but lasing is difficult to achieve due to indirect bandgap
Solution Approach 1:
The patent uses a hybrid composite structure combining silicon waveguides with III-V semiconductor gain media (InGaAsP quantum wells). The silicon substrate provides low-loss waveguiding and electrical pumping, while the bonded III-V layer provides direct bandgap lasing. This composite approach resolves the contradiction by integrating materials with complementary properties.
2Manufacturing precision
If Distributed Bragg Reflectors (DBRs) are used to build laser cavities, then the cavity structure is well-defined, but high lithography resolution is required and the structure is sensitive to fabrication variations
Solution Approach 1:
The patent extracts the wavelength selection function from the complex DBR structure and implements it using a Sagnac loop mirror with integrated ring resonators. This simpler mirror design based on interference effects achieves wavelength selectivity without requiring high-resolution lithography for DBR gratings, thus reducing fabrication complexity while maintaining cavity definition.
Solution Approach 2:
The patent changes the cavity mirror design parameters from DBR gratings to Sagnac loop mirrors with ring resonators. This parameter change allows the cavity to achieve wavelength selection through resonant coupling conditions rather than Bragg reflection, reducing sensitivity to fabrication variations and lithography resolution requirements.
3Reliability
If external cavities are designed for laser operation, then lasing can be achieved, but the existing cavity designs are not efficient for telecommunication wavelengths
Solution Approach 1:
The patent applies local quality optimization by designing the Sagnac loop mirror with ring resonators specifically tuned for telecommunication wavelengths (1550 nm). The cavity length, ring radius, and coupling parameters are locally optimized for this wavelength range, achieving high efficiency at telecommunication wavelengths while maintaining reliable lasing operation.
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 configuration achieves high side mode suppression ratio, narrow linewidth, and high on-chip output power, enabling reliable operation for data communication systems without the need for cooling or hermetic sealing.
Implementation Method 1
at least one of the first mirror element and the second mirror element is a Sagnac loop mirror
Implementation Method 2
A novel optical cavity configuration using a Sagnac loop mirror and micro-ring resonator with a tunable filter
Implementation Method 3
Lasing is a radiative recombination process in semiconductors, where an electron in the conduction recombines with a hole in the valance band and a photon is emitted
Data Source
Figure 1A~1B
Figure 2
Figure 3A~3B
AI summary
We have demonstrated a novel Sagnac loop and micro-ring based laser cavity which is simple and reliable, with accurately controlled reflectivity and negligible excess loss. The resonant wavelength of a 2 μm radius micro-ring is shown to be lithographically controlled to a standard deviation of 3.6 nm. Both C- and O-Band lasers based on Sagnac loop mirror and micro-ring cavity have been demonstrated. The lasers are shown to be able to be modulated at 40 Gb/s.