Tunable Lasers Using Multiple RSOAs for High Power Output
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Solution Overview
Problem
Conventional external cavity tunable lasers face challenges in achieving high power output due to coupling losses, limited gain from reflective semiconductor optical amplifiers (RSOAs) in silicon photonics, and gain saturation at high injection currents, which reduce wall plug efficiency.
Innovation Solution
The use of multiple RSOAs within a single laser cavity, coupled with a sophisticated optical coupler system that splits light into multiple output beams, reduces maximum optical power in any one place while maintaining aggregate input for multiple components, thereby increasing available gain and output power.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If injection current to the RSOA is increased to increase optical gain, then optical gain is improved, but gain saturation occurs due to limited available carrier concentration and over-heating, causing wall plug efficiency to drop
Solution Approach 1:
The patent divides a single high-power RSOA into multiple lower-power RSOAs (first RSOA and second RSOA) operating in parallel within the laser cavity. Each RSOA operates below its gain saturation threshold, collectively providing the required total optical gain without experiencing individual gain saturation or excessive heating, thereby maintaining higher wall plug efficiency.
2Power
If optical power in the PIC is increased to achieve higher output power, then output power is improved, but nonlinear losses in the PIC increase, quickly limiting optical power output and wall plug efficiency
Solution Approach 1:
The patent segments the optical power into multiple separate beams from multiple RSOAs rather than concentrating high power in a single beam. This distribution reduces the optical power density in any one location within the PIC, minimizing nonlinear optical losses while maintaining the required aggregate output power.
3Ease of manufacture
If hybrid integration of the laser onto the PIC is performed, then integration is achieved, but coupling losses from the RSOA to the external cavity and losses on the PIC become too high
Solution Approach 1:
The patent merges multiple RSOAs and their respective optical paths into a unified laser cavity system with a shared external cavity. This configuration allows the system to overcome individual coupling losses by providing multiple parallel optical paths, where the aggregate signal compensates for losses in each individual path, while maintaining the benefits of hybrid integration.
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
This configuration enhances the gain inside the laser cavity, leading to higher output powers and improved wall plug efficiency by distributing optical power across multiple output ports, effectively addressing the limitations of single RSOA gain and coupling losses.
Implementation Method 1
a first reflector at one end of the first gain medium for reflecting light back through the first gain medium; a second reflector at one end of the second gain medium for reflecting light back through the second gain medium
Implementation Method 2
a first coupler including a first input/output port optically coupled to the first gain medium, a second input/output port optically coupled to the second gain medium, and first and second output ports for outputting laser light
Data Source
AI summary
Higher power tunable lasers are feasible using photonics integrated circuit based external cavity laser configurations by using multiple RSOAs inside a single cavity to provide multiple on-chip coherent optical output at the same wavelength. The total collective output power in various output branches potentially adds up being higher than what commercial lasers can provide. Using multiple RSOA increases and distributes the number of gain materials, which keeps them in a linear regime and avoids available gain saturation, which thereby removes gain saturation limitation in optical amplifications.