Optical frequency combs have been used extensively, and with remarkable success, to measure the absolute frequency of cw lasers. The use of frequency combs has also expanded to include applications such as precision ranging, component metrology, and spectroscopy, where the high coherence and wide optical bandwidth of combs is exploited to achieve high accuracy over a broad spectrum. We have been pursuing one particular approach that uses two, mutually coherent frequency combs with different repetition rates to make broadband coherent measurements through a down-sampling approach. This coherent dual-comb setup can be used in several different ways for precision measurements in ranging, spectroscopy, or cw optical waveform characterization. For precision ranging, the output of one comb is transmitted to a surface and its time-of-flight accurately measured by sampling the returning pulse with a second, offset frequency comb. Similarly, in spectroscopy or component metrology, one comb is transmitted through the sample and then mixed with the second comb. The resulting heterodyne signal contains the broadband optical phase and amplitude response of the sample. Finally, a similar setup can be used to characterize the instantaneous frequency of a rapidly modulated cw laser. With this system, the absolute frequency of a step-scanned cw laser can be determined over a 5 THz bandwidth at 300 microsecond time resolution and kHz-level accuracy. This technique should support future generation of arbitrary cw optical waveforms.
Proceedings Title: 4th International Workshop on OPS and OCDMA
Conference Dates: November 4-5, 2010
Conference Location: Tokyo, -1
Pub Type: Conferences
frequency comb, optical frequency metrology, ranging