Temporal soliton generation in an ultra-high-effective-Q Kerr resonator enabled by Raman gain

Abstract

We demonstrate temporal pattern formation in a coherently driven fiber ring cavity whose effective finesse is continuously reconfigured using distributed Raman amplification. We achieve an effective finesse of up to $\mathcal{F}_{\mathrm{eff}}\approx800$, corresponding to a linewidth of approximately 725 Hz ($Q\approx2.7\times10^{11}$) at 1555 nm. By exploiting the resulting increase in effective photon lifetime, we excite stable temporal cavity solitons and generate a low-repetition-rate frequency comb with a spacing of 580~kHz. Finally, we analyze the impact of the Raman loss-compensation mechanism, particularly its associated noise and show that a trade-off exists between soliton excitation threshold and stability.

Figures (4)

• Figure 1: (a). Experimental setup. CW laser: 1555 nm laser, EDFA: Erbium doped fiber amplifier, BPF: Optical bandpass filter, PC: polarization controller, ISO: polarization independent dual stage isolator, WDM: wavelength division multiplexer, Photodetectors PD1, PD3: 200 kHz , PD2: 1 GHz, PID: servo controller, OSA: optical spectrum analyzer 20 pm resolution, OSC: 1 GHz oscilloscope, ESA: electronic spectrum analyzer 43.5 GHz. (b) Linear cavity characterization: drop-port normalized transmission vs Raman pump power, showing the progressive increase of the effective finesse. The solid curve is a guide to the eye. The inset illustrates a single cavity ringdown measurement, corresponding to a single data point on the effective finesse curve.
• Figure 2: Laser detuning scans at the (a) drop and (b) through ports show that increasing Raman pump power (at fixed driving power 56 mW) widens soliton steps, reflecting increased effective finesse. Inset in (a): Dashed lines represent co-propagating resonances and solid lines counter propagating resonances at a pump power of 34.37 dBm.
• Figure 3: Evolution of the temporal cavity soliton optical spectrum as a function of the effective finesse at different detunings: $\delta = 0.54$ rad, $\delta = 1.1$ rad and $\delta = 2.3$ rad. (a-c) Experimental spectra measured at increasing Raman pump powers, corresponding to an effective finesse sweep. Stable soliton operation is observed over effective finesse ranges of 64–374 for $\delta = 0.54$ rad, 82–534 for $\delta = 1.1$ rad, and 131–790 for $\delta = 2.3$ rad. (d-f) Corresponding numerical simulations based on the Ikeda-map model.
• Figure 4: (a) Electrical spectrum of the soliton repetition rate within a bandwidth of 100 MHz at $\delta = 1.1$ rad and $\mathcal{F}_{\rm eff} = 300$. (b) Single-sideband (SSB) phase noise of the soliton repetition rate, measured at 622 MHz (1073rd harmonic) and rescaled to the fundamental frequency, for two different effective finesse values at a fixed detuning $\delta = 1.1$ rad.