Electro-Optic Frequency Comb with Harmonic RF Cascading
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Solution Overview
Problem
Current electro-optic frequency comb architectures face limitations in achieving high bandwidth and tunable repetition rates, particularly in exceeding 120 GHz bandwidth and megahertz repetition rates, with existing methods often restricted by RF power and frequency generator capabilities.
Innovation Solution
The proposed solution involves a cascaded electro-optic modulator architecture driven by sequential lower harmonics, utilizing three phase-locked loops (PLLs) to stabilize and control the phase and frequency of each modulator, allowing for modulation at any individual harmonic and repetition rate without component changes, and employing a narrow linewidth seed laser synchronized with a 10 MHz rubidium clock.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If conventional single-stage electro-optic modulation is used, then device complexity is low, but optical bandwidth is limited to below 120 GHz
Solution Approach 1:
The patent divides the frequency comb generation into multiple stages using three cascaded electro-optic modulators (EOMs). Each EOM operates at a different harmonic frequency (11-12.5 GHz, 1-2 GHz, and 75-150 MHz respectively), progressively expanding the optical bandwidth. This segmented approach enables achieving >120 GHz bandwidth that cannot be obtained with a single modulator stage.
2Adaptability or versatility
If fixed frequency generators are used, then device complexity is low, but adaptability to different repetition rates is poor
Solution Approach 1:
The patent implements dynamic frequency control by replacing fixed frequency generators with phase-locked loops (PLLs) that can be electronically tuned. The PLLs allow the system to adjust modulation frequencies and repetition rates dynamically without changing physical components, enabling adaptation to different application requirements while maintaining phase coherence across all modulator stages.
3Area of stationary object
If high RF power is provided to achieve high bandwidth, then optical bandwidth increases, but RF power availability becomes limited
Solution Approach 1:
The patent segments the RF power requirements across three modulator stages, each operating at different power levels. The first EOM handles the highest frequency and power requirements for initial comb generation, while subsequent EOMs operate at lower frequencies and power levels to expand bandwidth. This segmentation distributes the total RF power burden, making high bandwidth achievement feasible with available RF power.
4Area of stationary object
If cascaded modulators are used to increase bandwidth, then optical bandwidth exceeds 120 GHz, but phase stability becomes more difficult to maintain
Solution Approach 1:
The patent employs phase-locked loops (PLLs) to provide feedback control for each modulator stage. The PLLs continuously monitor and adjust the phase and frequency of the RF signals driving each EOM, ensuring phase coherence is maintained across all cascaded stages. This feedback mechanism compensates for phase drift and instability that would otherwise accumulate through the cascade, preserving comb line stability despite the increased bandwidth.
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 enables the generation of an electro-optic frequency comb with >120 GHz bandwidth and a tunable megahertz repetition rate, providing stability and versatility for applications requiring precise frequency control, such as spectroscopy and optical communications.
Implementation Method 1
These combs are generated by modulating non-linear electro-optic crystals with radio frequencies, which creates equally spaced sidebands centered around the continuous-wave (CW) seed laser
Implementation Method 2
utilizing three phase-locked loops (PLLs) to stabilize and control the phase and frequency of each modulator
Data Source
AI summary
The present disclosure is directed to an electro-optic frequency comb having a plurality of cascaded electro-optic modulators driven at sequential lower harmonics, wherein the last megahertz modulation dictating the repetition rate. This architecture can modulate at any individual harmonic and repetition rate without changes to the components. This comb can be used in any applications where a stable and tunable repetition rate is needed.