Supercontinuum-based 10-GHz flat-topped optical frequency comb generation

Abstract

The generation of high-repetition-rate optical frequency combs with an ultra-broad, coherent and smooth spectrum is important for many applications in optical communications, radio-frequency photonics and optical arbitrary waveform generation. Usually, nonlinear broadening techniques of comb-based sources do not provide the required flatness over the whole available bandwidth. Here we present a 10-GHz ultra-broadband flat-topped optical frequency comb (> 3.64-THz or 28 nm bandwidth with ~365 spectral lines within 3.5-dB power variation) covering the entire C-band. The key enabling point is the development of a pre-shaping-free directly generated Gaussian comb-based 10-GHz pulse train to seed a highly nonlinear fiber with normal dispersion profile. The combination of the temporal characteristics of the seed pulses with the nonlinear device allows the pulses to enter into the optical wave-breaking regime, thus achieving a smooth flat-topped comb spectral envelope. To further illustrate the high spectral coherence of the comb, we demonstrate high-quality pedestal-free short pulse compression to the transform-limited duration.

Expansion of VCSEL-Based Optical Frequency Combs in the Sub-THz Span: Comparison of Non-Linear Techniques

“…This scheme mainly exploits the enhanced Self Phase Modulation Effect (SPM) [23] exhibited by HNLF fibers and has been commonly used for comb expansion and broadband signal generation [6], [24], [25]. The expansion scheme is formed by two sub-stages.…”

“…They are based on the concatenation of numerous nonlinear optical stages to optimize the generation of new frequencies from an initial dual optical source. Finally, the use of EO modulators in cascade configuration is one of the most commonly used technique for comb generation and/or expansion [21], [6], especially for high repetition rates above the modulation bandwidth of the laser source under use. Optical combs that cover above 3THz have been reported with EO modulators.…”

Experimental Study of VCSEL-Based Optical Frequency Comb Generators

“…The maturity of commercially available LD would benefit the resulting OFCG taking it from the laboratory to the application field in a reliable and cost efficient way. Several techniques have already demonstrated promising results [7], [8]. They can be grouped in direct or indirect techniques.…”

“…The most extended approach is the use of external Electro Optical modulators (EO-OFCG) [6], [8]. The resulting comb is tunable and can offer a span in the THz range using a cascade of modulators that requires a careful management of the RF power and the phase of the electrical and the optical signals all along the set-up.…”

“…In this letter this stage consists of two standard phase modulators (3dB bandwidth up to 10GHz) in cascade configuration. This scheme is the core of larger architectures that have successfully produced enhanced optical frequency combs [6], [8]. As the bias conditions of the VCSEL do not affect the EO stage, we also use I bias = 11.4mA to facilitate the comparison.…”