Abstract
Kerr frequency comb generation relies on dedicated waveguide platforms that are optimized towards ultralow loss while offering comparatively limited functionality restricted to passive building blocks. In contrast to that, the silicon-photonic platform offers a highly developed portfolio of high-performance devices, but is deemed to be inherently unsuited for Kerr comb generation at near-infrared (NIR) telecommunication wavelengths due to strong two-photon absorption (TPA) and subsequent free-carrier absorption (FCA). Here we present a theoretical investigation that quantifies the impact of TPA and FCA on Kerr comb formation and that is based on a modified version of the Lugiato-Lefever equation (LLE). We find that silicon microresonators may be used for Kerr comb generation in the NIR, provided that the dwell time of the TPA-generated free-carriers in the waveguide core is reduced by a reverse-biased p-i-njunction and that the pump parameters are chosen appropriately. We validate our analytical predictions with time integrations of the LLE, and we present a specific design of a silicon microresonator that may even support formation of dissipative Kerr soliton combs.
Highlights
Generation of optical frequency combs in high-Q Kerrnonlinear microresonators [1,2] has the potential to unlock a wide range of applications such as timekeeping [3], frequency synthesis [4], optical communications [5], spectroscopy [6], and optical ranging [7,8]
We find that silicon microresonators may be suitable for Kerr comb generation in the NIR, provided that the dwell time of the two-photon absorption (TPA)-generated free carriers in the waveguide core is reduced by a reverse-biased p-i-n-junction and that the pump parameters are chosen appropriately
The simulation results indicate that modulation instability in silicon-photonic microresonators at telecommunication wavelengths is most likely to be observed if the waveguide is designed for anomalous group-velocity dispersion, if free-carrier absorption (FCA) is mitigated by a reverse-biased p-i-n-junction which leads to a sufficiently small carrier dwell time, and if the pump power and detuning are chosen properly
Summary
Generation of optical frequency combs in high-Q Kerrnonlinear microresonators [1,2] has the potential to unlock a wide range of applications such as timekeeping [3], frequency synthesis [4], optical communications [5], spectroscopy [6], and optical ranging [7,8]. To investigate the circumstances under which modulation instability can occur when pumping the resonator, we need to know whether any pair of resonator modes experiences a sufficiently high parametric gain to overcome the total loss in the resonator This loss includes linear propagation loss and coupling loss, which are equal for critical coupling, αiL = κ, and which are expressed by −1 in Eq (5), two-photon absorption, expressed by −r|a(t , τ )|2 in Eq (5), and free-carrier absorption, expressed by −σ Nc(t , τ − t v ) in Eq (5), where the normalized density of accumulated carriers strongly depends on the carrier dwell time teff and its normalized counterpart teff , see Eq (6).
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