Novel schemes for optical frequency comb generation
Optical frequency comb (OFC) laser sources are extremely interesting for their wide range of potential applications in the fields of metrology, molecular spectroscopy and telecommunications. The main characteristic of OFCs is the equally-spaced discretization of the optical spectrum, which corresponds to a periodic train of pulses in the time domain: a classic example of such optical source being a mode-locked laser. Over the past 20 years, nonlinear optical interactions of continuous wave (CW) laser beams coupled into optical cavities have been exploited to generate OFCs. Nowadays, compact structures for OFC generation are integrated on-chip: some examples of such resonators are disks, waveguides rings or photonic crystal cavities.
Behind the specific structures used to produce such micro-combs, the classical generation scheme involves the coupling of a CW narrowband laser into a nonlinear micro-resonator. The Lugiato-Lefever equation (LLE) is a model which is generally used for describing the evolution of the optical field in the cavity. Recently, slightly different schemes have been set up, which have permitted to reveal interesting dynamical situations. In this frame, we recently considered the use of gaussian pulsed chirped light as pump beam. We discovered that strong chirps are useful in order to broaden the locking range of the single soliton state, which is the most interesting comb state for metrology applications.
During the last year, we collaborated with the Leibniz Institute for Astrophysics in Potsdam (AIP), for describing novel interesting microcomb generation schemes. In these experiments, the repetition rate of the output frequency combs is no longer necessarily fixed by the free-spectral-range of the resonator, but it can also be locked to the pump modulation frequency. Phase and amplitude modulated pumps can thus be considered, leading to novel degrees of freedom for stable optical frequency comb generation.
Fig: The two figures on the left represent simulated cavity swepts while varying the detuning parameter with a super-gaussian pump of order 4. Multi- and single soliton stedy states emerge clearly from a chaotic background, depending on the value of the chirp parameter. On the right a typical single soliton frequency comb observed by means of this scheme.
F. R. Talenti, T. Hansson, and S. Wabnitz, “Control of Kerr Cavity Soliton Combs by Chirped Pumping,” in OSA Advanced Photonics Congress (AP) 2020 (IPR, NP, NOMA, Networks, PVLED, PSC, SPPCom (Optical Society of America, 2020), paper JTu2D.4.
M. Chavez-Boggio, Daniel Bodenmüller, Adnan Baig, Syed Ahmed, Tobias Hansson, Francesco Rinaldo Talenti, Stefan Wabnitz, and Daniele Modotto,” Frequency comb generation in silicon nitride ring resonators with amplitude modulated pump,” J. Conference 11672, Laser Resonators, Microresonators, and Beam Control XXIII, SPIE PHOTONICS WEST (2021)
MOCCA – Multiscale Optical Frequency Combs: Advanced Technologies and Applications