Currently available technologies that generate a low noise 10 GHz pulse train with RF phase noise utilize optical frequency division, but as a result, suffer from stabilization and calibration difficulties. The conventional optical frequency divider is comprised of four main components: a mode-locked laser, a separate continuous wave (CW) laser, a nonlinear f-2f interferometer, and an optical pulse train interleaver.
An ultralow noise portable frequency comb created by UCF researchers improves on a prior invention (US 7,697,579) by utilizing a high finesse etalon as an integral part of the mode-locked laser that simultaneously stabilizes the carrier offset, produces sub-Hertz level axial mode components, and provides important error signals that enable octave spanning optical frequency division—all within a single laser. This streamlined system fits in a standard rack-mountable chassis with a demonstrated lowest phase noise at 10 GHz, and 1550 nm from this type of source. Within this system, there is no need for an f-2f interferometer, no second harmonic generation stages for stabilization, or a separate CW laser locked to an etalon. Because of the higher efficiency of this invention, it is more easily deployable in the field and with a less strenuous system calibration.
This invention includes an ultralow noise, portable frequency comb device based on a fiber cavity mode-locked laser using semiconductor optical amplifiers as the gain elements, combined with an environmentally stable macroscopic Fabry-Pérot etalon as a secondary optical reference. This device uses regenerative mode-locking, thus the laser is not slaved to an electronic reference. The ultrahigh finesse etalon, located inside the laser, serves as the stable optical reference to which all error signals and stabilization are referenced. In comparison to current technologies that create optical linewidths at the sub Hz level, this device creates ultra-narrow, optical comb lines with Hz level linewidths. This design decouples and independently stabilizes the carrier envelope offset frequency and repetition rate fluctuations by using a linear optical frequency division that reduces RF noise by a factor of 10log(N2), where N is the optical bandwidth of the mode-locked laser divided by the pulse repetition rate.
- Greatly reduces the overall system size and power consumption
- Reduces phase noise
- Increases the overall cavity Q
- Enables measurement of extremely low phase noise
- High-precision radar
- Next generation optical clocks
- Fiber optic communications
- Communication broadcasting and receiving
- Signal intelligence
- Signal processing
- Clock recovery