Non-Reciprocal Fiber-Ring Brillouin Laser Source
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Solution Overview
Problem
Current stabilized laser sources face challenges in achieving low phase noise and stable frequency references, particularly in generating microwave signals, due to limitations in Brillouin laser oscillation and frequency locking mechanisms.
Innovation Solution
A non-reciprocal fiber-ring Brillouin laser source is developed, incorporating an optical circulator and coupler, with a frequency-locking mechanism that controls the pump optical frequency to maintain resonant propagation in the backward direction, producing Brillouin laser signals with reduced Schawlow-Townes noise and phase noise, and employing dual pump laser sources to generate optical difference frequencies for further noise reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional Brillouin laser source is used, then laser oscillation is achieved, but high phase noise and frequency instability occur
Solution Approach 1:
The system segments the optical signal into two distinct paths using a circulator: a forward path that experiences only single-pass Brillouin scattering (generating the laser signal) and a backward path that enables resonant oscillation (providing frequency reference). This segmentation allows the harmful Schawlow-Townes noise from resonant oscillation to be isolated from the forward Brillouin signal, while still utilizing the resonant path for frequency stabilization through the locking mechanism.
Solution Approach 2:
The patent introduces an intermediary frequency-locking mechanism that mediates between the backward resonant oscillation and the forward Brillouin signal. The locking mechanism uses the stable resonant frequency as a reference to stabilize the pump laser frequency, which in turn stabilizes the forward Brillouin signal. This intermediary system transfers frequency stability without transferring phase noise.
2Reliability
If resonant oscillation is enabled in the fiber-ring, then frequency reference stability is improved, but Schawlow-Townes noise is generated
Solution Approach 1:
The system applies local quality by giving different functional characteristics to different sections of the fiber-ring resonator. The backward-propagating signal experiences high-Q resonant oscillation conditions optimized for frequency reference stability, while the forward-propagating signal experiences controlled single-pass Brillouin scattering conditions that minimize noise. The circulator creates this local quality differentiation by directing different signals through different paths within the same physical structure.
3Reliability
If dual pump laser sources are used, then optical difference frequency generation is achieved, but device complexity increases
Solution Approach 1:
The patent merges the functions of two pump laser sources by using a single pump laser that simultaneously generates both forward and backward propagating signals through the circulator. This single source configuration achieves the same effect as dual sources (generating two different optical difference frequencies) while reducing device complexity. The circulator enables one laser to serve dual purposes: generating the Brillouin signal in the forward direction and providing the frequency reference in the backward direction.
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 significantly reduced phase noise in the output electrical signal, enabling stable microwave signals with improved frequency stability and reduced noise characteristics, suitable for radio-frequency and microwave-frequency applications.
Implementation Method 1
The optical circulator is arranged so as to (i) limit to a single round trip propagation of an optical signal around the fiber-ring optical resonator in a forward direction, and (ii) permit resonant propagation of an optical signal around the fiber-ring optical resonator in a backward direction
Implementation Method 2
The fiber-ring optical resonator is arranged so as to produce from the first input portion of the pump optical signal a Brillouin laser optical signal, at a Brillouin laser frequency ν1S=ν1−νB
Implementation Method 3
The frequency-locking mechanism couples the pump laser source and the fiber-ring optical resonator by controlling the pump optical frequency ν1 to maintain resonant propagation of the second input portion of the pump optical signal around the fiber-ring optical resonator in the backward direction
Implementation Method 4
The optical coupler directs out of the fiber-ring optical resonator (i) an output portion of the second input portion of the pump optical signal, at the pump optical frequency ν1, to act as an optical feedback signal to the frequency-locking mechanism, and (ii) an output portion of the Brillouin laser optical signal, at the Brillouin laser frequency ν1S, to act as optical output of the laser source
Data Source
AI summary
A stabilized laser source includes a fiber-ring Brillouin laser that incorporates a circulator for non-reciprocal operation and for launching of a pump optical signal. Most of the pump optical signal is launched in a forward direction and drives Brillouin laser oscillation in the backward direction, a portion of which exits via an optical coupler as the optical output of the laser source. A small fraction of the pump optical signal is launched in the backward direction via the optical coupler, and a fraction of that backward-propagating pump optical signal exits via the optical coupler as an optical feedback signal. A frequency-locking mechanism receives the optical feedback signal and controls the pump optical frequency to maintain resonant propagation of the backward-propagating pump optical signal. A second pump optical signal can be launched in the forward direction to generate a second Brillouin laser oscillation.