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MULTI-HETERODYNE DETECTION WITH DUAL OPTICAL FREQUENCY COMBS GENERATED FROM CONTINOUS-WAVE LASERS

This technology offers a new frequency continuous-wave method to overcome limitations from traditional methods used in spectroscopy.  Currently, femtosecond optical frequency combs (FOFCs) generated from mode-locked pulsed lasers (MLL) offer a wide spectral bandwidth and ultra-narrow frequency component linewidths while serving as absolute frequency references when phase stabilized. However, there are limitations to this process including:

  • Due to the wide bandwidth of FOFCs, in some cases each frequency component has nanowatts or less of optical power that might limit ultimate sensitivity and use in spectroscopy.
  • Comb spacing that is given by a repetition rate for a pulsed laser is largely fixed for a given MLL by the physical dimension of the laser cavity and physical reconstruction of the system is required to change the comb spacing. 
  • Mode-locked femtosecond lasers are vastly more expensive and less robust than the present approach.

A new measurement method which utilizes electro-optic phase modulators, arbitrary waveform generators (AWG) and frequency multipliers to generate phase components from a continuous-wave laser has been created. The multi-heterodyne technique has significant advantages in comparison to traditional frequency scanning continuous-wave methods: 

  • The entire absorption spectra of a wide variety of species can be simultaneously recorded with no dead time due to wavelength scanning.
  • The comb spacing as well as the frequency component’s or teeth’s relative amplitudes are readily and precisely controlled and optimized at high speeds. 
  • The components are fiber-coupled and therefore, can be readily ruggedized.

Figure 1 illustrates the comb source (refer to patent for illustration of the heterodyne sensor):

Comb source 2 includes continuous wave frequency source 4 in optical communication with first modulator 6 and second modulator 8. First modulator 6 and second modulator 8 respectively include first comb output 16 and second comb output 18. Continuous wave frequency source 4 is configured to provide a continuous wave radiation that is communicated through optical path 14 to splitter 12. Splitter 12 splits the continuous wave radiation survey portion of the continuous wave radiation and then communicated through optical path 14 to first modulator 6 and second modulator 8. Optical path 14, e.g., can be in optical medium such as a fiber optic, free space, or combination thereof. Accordingly, splitter 12 can be coupled to a fiber optic or admit the continuous wave radiation via free space propagation of the continuous wave radiation. Waveform driver 10 is in electrical communication with first modulator 6 and second modulator 8 and is configured to produce a first waveform and the second waveform. The first waveform is communicated from waveform driver 10 to first modulator 6 through first waveform path 20. Similarly, the second waveform is communicated from waveform driver 10 to second modulator 8 through second waveform path 22. In response to receipt of the first waveform and the continuous wave radiation, first modulator 6 is configured to produce a first comb that is available for communication from first modulator 6 at first comb output 16. In response to receipt of the second waveform of the continuous wave radiation, second modulator 8 is configured to produce a second comb that is available for communication from second modulator 8 at second comb output 18. In this manner, comb source 2 is configured to produce a plurality of combs (e.g., the first comb, second comb, and the like) from the continuous wave radiation and a plurality of waveforms (e.g., the first waveform, second waveform, and the like).

 

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; 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.

Benefits: 

The entire absorption spectra of a wide variety of species can be simultaneously recorded with no dead time due to wavelength scanning. Arbitrary waveform generator controlled method allows the comb spacing as well as the teeth's relative amplitudes to be readily and precisely controlled and optimized at high speeds. The instrument is entirely fiber-coupled and therefore, can be readily ruggedized.

Inventors: 
Stephen Maxwell, David plusquellic, David Long, Kevin Douglass, Joseph Hodges, Adam Fleisher
Patent Number: 
9903808
Technology Type(s): 
Laser and Optics, Laser Application, Atomic Spectroscopy, Time and Frequency Services
Internal Laboratory Ref #: 
14-011
Patent Issue Date: 
February 27, 2018
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