Ville Ulvila

Frequency comb generation by a continuous-wave-pumped optical parametric oscillator based on cascading quadratic nonlinearities

We report optical frequency comb generation by a continuous-wave pumped optical parametric oscillator (OPO) without any active modulation. The OPO is configured as singly resonant with an additional nonlinear crystal (periodically poled MgO:LiNbO3) placed inside the OPO for phase mismatched second harmonic generation (SHG) of the resonating signal beam. The phase mismatched SHG causes cascading χ(2) nonlinearities, which can substantially increase the effective χ(3) nonlinearity in MgO:LiNbO3, leading to spectral broadening of the OPO signal beam via self-phase modulation. The OPO generates a stable 4 THz wide (-30 dB) frequency comb centered at 1.56 μm.

High-power mid-infrared frequency comb from a continuous-wave-pumped bulk optical parametric oscillator

We demonstrate that it is possible to obtain a mid-infrared optical frequency comb (OFC) experimentally by using a continuous-wave-pumped optical parametric oscillator (OPO). The comb is generated without any active modulation. It is based on cascading quadratic nonlinearities that arise from intra-cavity phase mismatched second harmonic generation of the signal wave that resonates in the OPO. The generated OFC is transferred from the signal wavelength (near-infrared) to the idler wavelength (mid-infrared) by intracavity difference frequency generation between the OPO pump wave and the signal comb. We have produced a mid-infrared frequency comb which is tunable from 3.0 to 3.4 µm with an average output power of up to 3.1 W.

Tuning and stability of a singly resonant continuous-wave optical parametric oscillator close to degeneracy

Wavelength tuning and stability characteristics of a singly resonant continuous-wave optical parametric oscillator (cw OPO) in the proximity of signal-idler degeneracy have been studied. The OPO is made singly resonant by using a Bragg grating as a spectral filter in the OPO cavity. The signal-idler frequency difference can be tuned from 0.5 to 7 THz, which makes the OPO suitable for cw THz generation by optical heterodyning. The operation of the OPO within this singly-resonant regime is characterized by a strong self-stabilization effect. A gradual transition to an unstable, doubly-resonant regime is observed for a signal-idler detuning smaller than ~0.5 THz.

Spectral characterization of a frequency comb based on cascaded quadratic nonlinearities inside an optical parametric oscillator

We present an experimental study of optical frequency comb generation based on cascaded quadratic nonlinearities inside a continuous-wave-pumped optical parametric oscillator. We demonstrate comb states which produce narrow-linewidth intermode beat note signals, and we verify the mode spacing uniformity of the comb at the Hz level. We also show that spectral quality of the comb can be improved by modulating the parametric gain at a frequency that corresponds to the comb mode spacing. We have reached a high average output power of over 4 W in the near-infrared region, at ~2 {\mu}m.

Infrared Laser Frequency Combs for Multispecies Gas Detection

We discuss two methods for mid-infrared frequency comb generation in quadratic nonlinear materials. The first one of these methods is based on half-harmonic generation in a degenerate femtosecond optical parametric oscillator, which is synchronously pumped with a near-infrared laser frequency comb. The second method uses a continuous-wave-pumped optical parametric oscillator. In this approach, the quadratic nonlinearity is used not only for frequency down conversion, but also for the actual frequency comb generation from a continuous-wave pump laser field. Both methods can be used to produce coherent broadband mid-infrared light that is ideal for real-time spectroscopic detection of small traces of biomarkers, toxics, and other interesting molecular compounds. In particular, these methods provide access to the 3–5 μm molecular fingerprint region, which contains strong fundamental vibrational stretching bands of hydrocarbons.

Dynamics and Design Trade-Offs in CW-Pumped Singly-Resonant Optical Parametric Oscillator Based Combs

We analyze frequency comb generation in CW-pumped singly-resonant optical parametric oscillators using cascaded second-order nonlinearities. We explain experimental results, trade-offs and current limits on performance, and examine scaling towards broader bandwidths in the future.

Mid-infrared frequency comb generation using a continuous-wave pumped optical parametric oscillator

We report a mid-infrared frequency comb generator, which produces up to 3 W of output power. The comb mode spacing is 208 MHz, the spectral bandwidth is ~300 GHz, and the center wavelength is tunable between 3 and 3.4 μm. The comb generation is based on intracavity difference frequency mixing between near-infrared pump and signal beams of a continuous-wave-pumped optical parametric oscillator. The signal beam, which is resonant in the cavity, acquires a comb structure through cascading quadratic nonlinearities in a periodically poled lithium niobate crystal. This comb structure is transferred to the spectrum of the mid-infrared idler beam via the difference frequency mixing process.

Optical Frequency Comb Generation by Continuous-Wave Pumped Optical Parametric Oscillator Based on Cascading χ(2) Nonlinearities

We present a continuous-wave pumped optical parametric oscillator capable of producing an optical frequency comb without any active modulation. The use of the technique for mid-infrared frequency comb generation is discussed.