Optical Phase Locking for Single-Sideband AM Signals
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Solution Overview
Problem
Existing optical carrier-suppressed coherent-AM links are sensitive to environmental changes, affecting the phase integrity of RF signals transmitted over optical fibers, necessitating a method to lock the optical phase and maintain amplitude and phase fidelity.
Innovation Solution
A method involving a radio-frequency locking signal and a photonic integrated circuit with a microresonator filter and finite impulse response filter, where the RF input signal and locking signal are impressed onto a suppressed optical carrier, filtered, and phase-dithering is used to stabilize the differential phase between signal and local-oscillator arms, ensuring phase stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If optical carrier-suppressed coherent-AM links are used for RF signal transmission, then bandwidth efficiency and transmission capacity are improved, but phase stability deteriorates due to environmental sensitivity
Solution Approach 1:
The patent implements a feedback mechanism where the optical phase is continuously monitored and adjusted using a phase-locking loop. The system detects phase deviations caused by environmental changes and applies corrective adjustments to maintain stable phase relationship between optical carrier and modulated signal, thereby resolving the contradiction between high transmission capacity and phase stability
Solution Approach 2:
The patent employs dynamic parameter adjustment by changing the operating point of the optical modulator and adjusting the local oscillator frequency to compensate for environmental variations. This allows the system to maintain optimal phase stability while preserving the high bandwidth efficiency of carrier-suppressed modulation
2Productivity
If single-sideband modulation is used to improve bandwidth efficiency, then bandwidth usage is optimized, but phase sensitivity to environmental changes increases
Solution Approach 1:
The patent introduces an intermediary phase-locking mechanism that mediates between the single-sideband modulated signal and the optical carrier. This intermediary system actively compensates for environmental perturbations, allowing the system to enjoy the bandwidth efficiency of SSB modulation while mitigating its inherent phase sensitivity to environmental changes
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 effectively locks the optical phase, enabling high-fidelity transmission of RF signals over optical fibers, preserving amplitude and phase integrity even in the presence of environmental perturbations.
Implementation Method 1
filtering out one sideband of the first optical signal with the microresonator filter
Implementation Method 2
impressing the radio-frequency input signal and the radio-frequency locking signal onto the optical field of the suppressed carrier using an electro-optic modulator
Implementation Method 3
phase-dithering is used to stabilize the differential phase between signal and local-oscillator arms, thereby locking the optical phase
Data Source
AI summary
This invention provides an approach to lock the optical phase of a single sideband, carrier-suppressed coherent-AM analog optical link, so that for example an RF signal can be transmitted with high fidelity over fibers. In some embodiments, a method comprises providing a RF locking signal; impressing an RF input signal and the RF locking signal onto the optical field of a suppressed carrier; introducing the optical spectrum to a photonic integrated circuit comprising a microresonator filter and a finite impulse response filter; selectively passing the double sideband, associated with the locking frequency, through the finite impulse response filter; and recovering a RF output signal, wherein a feedback loop provides dithering to stabilize the optical phase of the link and thus preserve amplitude/phase integrity for the RF-photonic signal. The disclosed method is especially suited to the filtering of RF-photonic signals via use of the resonance passbands derived from microdisks or micro-rings.