Variable-frequency optical combs, heterodyne sensor, and process for performing spectroscopy
Inventors
Plusquellic, David F. • Long, David A. • Douglass, Kevin O. • Hodges, Joseph T. • FLEISHER, ADAM J.
Assignees
United States Department of Commerce
Publication Number
US-9903808-B2
Publication Date
2018-02-27
Expiration Date
2035-01-06
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Abstract
A comb source includes a continuous wave frequency source to provide a continuous wave radiation; a first modulator in optical communication with the continuous wave frequency source; a second modulator in optical communication with continuous wave frequency source; and a waveform driver in electrical communication with the first modulator and the second modulator. A process for producing an analyte spectrum includes producing a first comb from a continuous wave frequency and a first waveform; producing a reference comb and a probe comb from the first comb; subjecting a sample to the probe comb; producing a sample comb in response to subjecting the sample to the probe comb; producing a composite comb from the reference comb and the sample comb; producing a second comb from the continuous wave frequency and a second waveform; and combining the second comb and the composite comb to produce the analyte spectrum.
Core Innovation
The invention relates to a comb source that generates phase coherent optical frequency combs from a continuous wave frequency source using a first and second modulator driven by a waveform driver providing first and second waveforms with variable amplitude and frequency. This comb source produces first and second optical frequency combs with independently selectable frequency spacings, allowing the frequency spacing among teeth in each comb to be varied from 1 kHz to 50 GHz. The modulators, such as electro-optic phase modulators or dual-drive Mach-Zehnder modulators, produce power-leveled combs with high-fidelity individual frequency components.
A heterodyne sensor incorporating the comb source includes a splitter dividing the first comb into a probe and reference comb, a probe arm that subjects a sample to the probe comb producing a sample comb, and combiners to produce a composite comb from the reference and sample combs and then combine this with the second comb as a local oscillator to produce an analyte spectrum. The analyte spectrum includes heterodyned frequencies in a radiofrequency domain allowing multiplexed spectroscopic detection of a sample across a broad spectral region. The comb source and heterodyne sensor enable tailoring of tooth spacing, bandwidth, and amplitude distribution of optical frequency combs, providing precise and high-speed measurements with phase coherence and without mechanical motion.
The background problem addressed by the invention is that femtosecond optical frequency combs generated from mode-locked pulsed lasers have wide bandwidths but low power per frequency component and fixed comb spacing limited by laser cavity dimensions. This limitation hampers sensitivity and restricts the ability to vary comb spacing. The invention overcomes these deficiencies by using continuous wave radiation and modulators driven by tunable waveforms to produce optical frequency combs with variable and independently adjustable comb spacings and amplitudes, enabling enhanced sensitivity, flexible spectral coverage, and high-speed heterodyne detection for spectroscopic applications.
Claims Coverage
The claims include two independent claims directed to a comb source and a heterodyne sensor, outlining their main inventive features.
Comb source with independently variable dual modulators
A comb source comprising a continuous wave frequency source, a first and a second modulator in optical communication with the source, and a waveform driver electrically connected to both modulators to provide independent first and second waveforms. Each waveform has variable amplitude and variable frequency or harmonic frequencies, enabling production of first and second optical frequency combs with independently variable frequency spacings.
Heterodyne sensor with comb splitting and recombination for analyte spectrum
A heterodyne sensor including the comb source of variable dual modulator combs, a splitter that divides the first comb into probe and reference combs, a probe arm for applying the probe comb to a sample to produce a sample comb, a reference arm to receive the reference comb, a first combiner to combine the sample and reference combs into a composite comb, a local oscillator arm receiving the second comb, and a second combiner to combine the second comb and the composite comb to produce an analyte spectrum comprising heterodyned frequencies.
The independent claims cover a comb source with dual modulators driven by independently variable waveforms producing optical frequency combs with tunable frequency spacing and a heterodyne sensor that utilizes such combs split and combined to generate an analyte spectrum with heterodyned frequencies, facilitating flexible, sensitive spectroscopic measurements.
Stated Advantages
Simultaneous recording of an entire absorption spectrum without dead time due to wavelength scanning.
Operation does not depend on mode-locked femtosecond lasers, enabling use of continuous wave lasers like diode lasers.
Higher optical power per comb tooth due to fewer teeth, enhancing sensitivity.
High-speed multiplexed measurement with phase coherence at the heterodyne receiver without mechanical motion.
Precisely controllable and variable frequency spacing and amplitude distribution of comb teeth for spectral optimization.
Capability for chirped waveforms maintaining phase coherence for enhanced spectral coverage and speed measurements.
Rugged and potentially fully fiber-coupled implementation.
Supports high acquisition rates and ultra-sensitive measurements of short-lived species.
Documented Applications
Absorption spectroscopy.
Emission spectroscopy.
Cavity enhanced spectroscopy and cavity ring-down spectroscopy.
Chemical dynamics studies.
Point source monitoring.
Remote sensing and multi-pass cell or open atmosphere analysis.
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