Ultra-Low Power Parametric Frequency Conversion of High Data Rates on a Photonic Chip

Traditionally nonlinear optical processes in solid state devices such as amplification, switching and wavelength conversion require relatively high powers for operation, which limits the prospect of their miniaturization and integration on-chip [1]. Here we utilize four-wave mixing (FWM), a nonlinear process used in high bandwidth optical communications, to demonstrate ultra-low-power parametric frequency conversion of 5 Gbit/s data in a silicon photonic structure. Our modeling predicts high conversion efficiency up to 0-dB is possible through GVD-engineering and free-carrier lifetime reduction. Summary of Research: FWM devices operating at low peak powers around 2030 mW have been demonstrated by using extremely long lengths (11.4 km) of optical fiber [2]. Also, parametric processes using even lower pump powers (a few 100 μW) have been observed in silica glass microspheres and microtoroids, however the extremely high quality factors limit their response times to approximately 100 ns [3,4]. In silicon, the nonlinear process of FWM has been demonstrated for parametric amplification, wavelength conversion, signal regeneration, and optical phase conjugation, and is implemented using centimeter-scale devices, which require peak powers on the order of 100 mW for operation [5]. Since FWM is a nonlinear process, it is by definition a function of the optical intensity. The platform we use in order to increase the optical intensity in the nonlinear medium consists of a micro-scale photonic structure that confines light both in the transverse and longitudinal direction. The structures are based on silicon nanowaveguides with high transverse confinement due to the strong index contrast between the silicon core and the SiO2 cladding. To further enhance the efficiency, microcavities are used for longitudinal confinement. The resonator is a 10 μm radius silicon ring with crosssectional height and width of 300 nm by 450 nm, respectively. The spacing between the bus waveguide and the ring is 400 nm. The transmission spectrum of the TM-like mode for the ring device is shown in Figure 1. The quality factor (Q) of the resonances of the ring are measured as 45,000. Using powers on the order of a few milliwatts we are able to perform wavelength conversion via FWM at 5-Gbit/s data rates through this ring resonator. We use input pump and input data signal powers of 4.4 mW and 100 μW, respectively. The conversion efficiency for this device at these powers is -25 dB. FWM Figure 1: Resonance spectrum of ring and FWM spectrum with pump, input data and converted data.