Dual Etalon Transceiver for Atmospheric Species Detection

Technology #14130

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1A is a schematic illustration of a prior art DIAL measurement. 1B and 1C are graphs of intensity as a function of lateral position at the receiver in the DIAL measurement illustrated in FIG. 1A, FIGS. 2A and 2B are graphs of % transmission as a function of wavelength spanning 100 nm (FIG. 2A) and frequency offset spanning 100 GHz (FIG. 2B) for atmospheric transmission around the CO overtone at 2.38 microns (μm). The shown transmission spectra are for 17 km of propagation through a middle latitude summer atmosphere, produced using the MODTRAN atmospheric simulation package (Spectral Sciences, Inc., Burlington, Mass.).FIG. 3 is a schematic illustration of the optical setup for a single-etalon geometry for the gas detector.FIG. 4 is a schematic illustration of the optical setup for a dual-etalon geometry for the gas detector.IG. 5A is a schematic illustration of the optical setup for a dual-etalon geometry for the gas detector employing a single optical element in place of the first and second etalon, where two effective etalons are produced by utilizing the optical element at two different angles. The beamsplitter/waveplate combination separates incident light into two angularly offset beams, each of which interacts with the optical element to produce two effective etalons. The reflected and transmitted beams for each angle are measured using photo-detectors.FIG. 5B is an illustration of an optical design according to this invention that takes advantage of a relay-image design to minimize walk-off between the two incident beams, and to enable the beams reflected from the etalon to be separated from the incident beams at an intermediate focus, while maintaining near-normal incidence on the etalon.
Alan DeCew
Lincoln Laboratory, MIT
Eric Statz
Lincoln Laboratory, MIT
Jonathan Ashcom
Lincoln Laboratory, MIT
Managed By
Jack Turner
MIT Technology Licensing Officer
Patent Protection

Gas detector for atmospheric species detection

US Patent 8,599,381

The invention is a gas detector that is designed to be a self-referencing receiver.


Major application of this technology is in the field of spectroscopy.

Problem Addressed

The technical requirements for transmitters used in measuring the concentration of a target gas in the atmosphere over long ranges include high power, maximum sensitivity and high repetition rates. These requirements are quite difficult to meet practically. Therefore, there is a need for a gas detector that reduces or eliminates the transmitter technical requirements.


The  dual etalon receiver (DUET) is a gas detector that relaxes some of the transmitter requirements by having a self-referencing receiver. The receiver is configured to receive light from a light source through gas, the light source having an optical bandwidth on the order of an absorption line width of the gas. The gas detector also includes two detectors and a processor. The first detector detects light transmitted through the first etalon and the second detector detects light reflected from the first etalon. The processor determines the quantity of gas based on the detected transmitted and reflected light.


  • High sensitivity for remote detection of gases over long ranges.
  • It is more accurate than conventional spectrometers.