Wide-Band Spectral Analysis With Dual Frequency-Shifting Optical Cavities
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Solution Overview
Problem
Existing spectral analysis techniques for optical and radiofrequency signals face limitations in spectral resolution, bandwidth, and probability of interception, particularly in devices like grating spectrometers, Michelson interferometers, and real-time spectrum analyzers, which struggle with high-frequency signals and dynamic spectra.
Innovation Solution
A device utilizing two frequency-shifted optical cavities to spatially separate and shift optical signals, generating a photocurrent that is filtered and processed to provide a temporal representation of frequency information, enabling real-time analysis of broadband signals with high spectral resolution and 100% probability of interception.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a grating spectrometer is used for spectral analysis, then the device is simple and low cost, but the frequency resolution is no better than tens of GHz
Solution Approach 1:
The invention divides the optical signal into multiple frequency-shifted copies using two separate optical cavities with different round-trip frequencies. Each cavity generates a comb of frequency-shifted replicas, and the interference between these replicas at the detector enables high-resolution spectral analysis. This segmentation of the spectrum into multiple shifted copies allows resolution beyond the limitations of single-grating approaches.
2Measurement precision
If a Michelson interferometer is used for spectral analysis, then the spectral resolution can be a few GHz, but the time required to measure a spectrum is of the order of a second
Solution Approach 1:
The invention uses two optical cavities operating continuously with different round-trip frequencies, generating overlapping combs of frequency-shifted replicas. The continuous interference pattern at the detector provides real-time spectral information without requiring mechanical scanning or time-consuming Fourier transforms. This continuous operation enables measurement speeds in the microsecond range while maintaining high spectral resolution.
3Adaptability or versatility
If a scanning analyzer is used for spectral analysis, then the spectral width can be greater than 20 GHz, but the probability of interception is typically 1%
Solution Approach 1:
The invention employs two optical cavities with different round-trip frequencies that generate periodic combs of frequency-shifted replicas. The interference between these periodic combs creates a time-varying signal at the detector that contains spectral information across a wide bandwidth. This periodic frequency shifting mechanism enables simultaneous coverage of broad spectral widths while maintaining high probability of interception through continuous real-time analysis.
4Productivity
If real-time spectrum analyzers with analog-to-digital conversion are used, then the spectral analysis is performed in real time, but the sampling rate is limited to a few GS/s resulting in spectral widths greater than 1 GHz
Solution Approach 1:
The invention replaces the electronic sampling and digital Fourier transform process with an optical interference-based frequency-to-time mapping mechanism. Two optical cavities generate frequency-shifted replicas that interfere at the detector, directly converting spectral information into temporal signal variations. This optical domain processing bypasses the Nyquist sampling limit, enabling real-time analysis of signals with spectral widths exceeding 20 GHz without requiring ultra-fast analog-to-digital converters.
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 device achieves real-time spectral analysis with bandwidths exceeding 20 GHz, providing a temporal representation of frequency information with high resolution and 100% probability of interception, overcoming limitations of existing methods.
Implementation Method 1
a first frequency shifter adapted to shift the optical frequency of the first signal by a first frequency f1 by round trip in said first cavity
Implementation Method 2
a detector adapted to coherently detect the first signal transmitted by the first cavity and the second signal transmitted by the second cavity and generate a photocurrent proportional to a light intensity detected by said detector
Data Source
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AI summary
Device (D) for wide-band spectral analysis of a signal of interest, comprising: - a source (S) for generating the signal of interest (Si); - an optical splitter element (ES) for spatially separating the signal of interest into a first signal (V1) and a second signal (V2); - a first frequency-shifting optical cavity (DBDF, BDF1) comprising a first frequency-shifter (AOM1) for shifting the optical frequency of the first signal from a first frequency f1 by forcing the signal to make a return journey in the first cavity, the first cavity having a first travel time τ1; - a second frequency-shifting optical cavity (DBDF, BDF2) comprising a second frequency-shifter (AOM2) for shifting the optical frequency of the second signal from a second frequency f2 by forcing the signal to make a return journey in the second cavity, the second cavity having a second travel time τ2; the first and second optical cavities being designed so that a maximum number of return journeys made by the signal in the first and second cavities is equal to predetermined N; - a detector (PD) for coherently detecting the first signal (W1) transmitted by the first cavity and the second signal (W2) transmitted by the second cavity and generating a photocurrent (Tr) proportional to a light intensity detected by the detector, - an analogue low pass filter (LP) for filtering photocurrent frequencies below min (formula (I)), - a processor (UT) configured to calculate a squared modulus of the photocurrent filtered by the low pass filter, from which a temporal representation of frequency information about the signal of interest is determined.