Coherent Comb Laser Linewidth Narrowing via Polarization Maintaining Feedback
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Solution Overview
Problem
Current semiconductor lasers have broad optical linewidths, limiting their use in high-data-rate coherent communications and other applications due to high phase noise, and existing techniques for narrowing linewidths are complex, costly, or unstable.
Innovation Solution
A method using a polarization maintaining fiber-based secondary cavity to simultaneously narrow the linewidths of multiple mode-locked comb lines in coherent comb lasers, without relying on narrow linewidth local oscillators or Mach-Zender Modulators, by tapping and reinserting a fraction of the laser power through an attenuator, maintaining stability and reducing linewidth from several MHz to below 200 kHz.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional semiconductor lasers are used, then the device is simple and compact, but the optical linewidth is broad (several to tens of MHz) resulting in high phase noise
Solution Approach 1:
The patent implements an external cavity feedback system where a portion of the laser output is reflected back to the laser diode through optical feedback. This feedback mechanism stabilizes the optical frequency and reduces phase noise, achieving linewidth narrowing from several MHz to below 200 kHz while maintaining a relatively simple device structure
Solution Approach 2:
The patent embeds multiple functional components within a compact integrated structure. The external cavity, attenuator, and optical feedback path are nested around the core laser diode, creating a hierarchical structure where the laser diode is at the center, surrounded by the feedback mechanism, all contained within a unified housing
2Manufacturing precision
If existing linewidth narrowing techniques are applied, then the optical linewidth is reduced, but the system becomes complex and costly requiring narrow linewidth local oscillators and Mach-Zender Modulators
Solution Approach 1:
The patent extracts and eliminates the need for complex components such as narrow linewidth local oscillators and Mach-Zender modulators. By using a simple external cavity feedback approach with basic optical components (mirror, attenuator, coupler), the system achieves linewidth narrowing without requiring these sophisticated and expensive elements
Solution Approach 2:
The patent employs inexpensive, readily available optical components such as standard optical mirrors, fixed attenuators, and optical couplers instead of expensive specialized components. These simple components can be easily replaced or adjusted, providing a cost-effective solution for linewidth narrowing
3Manufacturing precision
If existing linewidth narrowing techniques are used, then the linewidth is reduced, but the system becomes unstable over time
Solution Approach 1:
The patent incorporates a fixed attenuator in the external cavity feedback path that is pre-configured to provide optimal attenuation levels. This preliminary setting of the feedback strength ensures stable operation and prevents drift in the linewidth over time, as the attenuation level is fixed and does not require active adjustment
Solution Approach 2:
The patent carefully controls and maintains specific parameters of the feedback system, including the feedback attenuation level and external cavity length, to optimize linewidth stability. By setting these parameters to optimal fixed values, the system achieves both narrow linewidth and long-term stability without drift
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 approach achieves stable and efficient narrowing of multiple linewidths, enhancing the performance of coherent comb lasers for high-data-rate communications and other applications by reducing phase noise and maintaining stability over time.
Implementation Method 1
tapping a fraction of a power from the CCL from the laser cavity to form a tapped beam; propagating the tapped beam to an attenuator to produce an attenuated beam and propagating the attenuated beam back to the laser cavity
Implementation Method 2
reinserting the attenuated beam into the laser cavity
Implementation Method 3
propagating the tapped beam to an attenuator to produce an attenuated beam
Data Source
AI summary
A technique for narrowing a linewidth of a plurality of lines of a coherent comb laser (CCL) concurrently comprises providing a mode-locked semiconductor coherent comb laser (CCL) adapted to output of at least 4 mode-locked lines; tapping a fraction of a power from the CCL from the laser cavity to form a tapped beam; propagating the tapped beam to an attenuator to produce an attenuated beam; and reinserting the attenuated beam into the laser cavity, where the reinserted beam has a power less than 10% of a power of the tapped beam. The reinsertion allows the CCL to be operated to output the mode-locked lines, each with a linewidth of less than 80% of the original linewidth. By propagating the tapped and attenuated beams on a solid waveguide, and ensuring that the secondary cavity is polarization maintaining, improved stability of the linewidth narrowing is ensured.