Cost-Saving Electro-Optic Comb Generator Uses Its Own Internal Radio Frequency Source to Produce Tunable Broadband, Widely-Spaced Frequency Combs

Abstract

Researchers at the University of Central Florida have developed a unique architecture for an electro-optic modulation (EOM) tunable comb generator that combines a photonically filtered optoelectronic oscillator (OEO) with a series of external phase modulators. Using the ultra-narrow resonances of a 100,000-finesse Fabry-Perot etalon (FPE), the new design enables oscillation frequency and comb tooth spacing for spectrally flat, broadband, widely spaced frequency combs. For example, the new architecture has produced spectra as broad as approximately 5 nanometers (nm), while other OEO-driven comb generators have only produced optical combs spanning less than 2 nm.

Most optical frequency comb sources require an external radio frequency (RF) reference such as a high-frequency RF synthesizer, which can be costly. However, with the new architecture, the comb generator creates its own RF source to drive the modulators, eliminating the need for an external reference signal. Also, the FPE enables extremely selective filtering, enhanced OEO frequency stability, and narrower optical linewidths. Incorporating the phase modulators outside the OEO cavity allows for independent tuning and optimization of the comb spectral phase for ultrashort pulse generation without affecting oscillation.

Technical Details

The UCF invention consists of an OEO-EOM comb architecture that generates tunable electro-optic combs using an optoelectronic oscillator. In an example configuration, the architecture comprises three subsystems:

1. A standard Pound-Drever-Hall (PDH) locking scheme to stabilize the frequency of a narrow linewidth CW fiber laser to a 15 kHz FWHM passband of a 100,000 finesse FPE.
2. A photonically filtered OEO responsible for simultaneously generating a strong RF drive signal and carving the initial pulses for EOM comb generation.
3. Two cascaded LiNbO₃ phase modulators (PMs), to generate the EOM comb.

Experimental results demonstrate regeneratively-created electro-optic combs whose comb teeth spacing is tunable to 7.5 GHz, 9 GHz, 10.5 GHz and 12 GHz?with the center comb tooth linewidths running hundreds of hertz. When using linear pulse compression, the system demonstrates ultrashort pulses with picosecond-level autocorrelation pulse widths at a repetition rate of 10.5 GHz.

Partnering Opportunity

The research team is looking for partners to develop the technology further for commercialization.

Stage of Development

Prototype available.

Benefit

Market Application