50 dB parametric on-chip gain in silicon photonic wires

Abstract

Received Month X, XXXX; revised Month X, XXXX; accepted Month X, XXXX; posted Month X, XXXX (Doc. ID XXXXX); published Month X, XXXX A pulsed mid-infrared pump at λ = 2173 nm is used to demonstrate wideband optical parametric gain in a low-loss 2-cm long silicon photonic wire. Using dispersion engineering to obtain negative second-order (β 2 ) and positive fourth-order (β 4 ) dispersion, we generate broadband modulation instability and parametric fluorescence extending from 1911 nm -2486 nm. Using a cw probe signal to interrogate the modulation instability spectrum, we demonstrate parametric amplification > 40 dB with an on-chip gain bandwidth wider than 580 nm, as well as narrowband Raman-assisted peak gain > 50 dB. © 2011 Optical Society of America OCIS Codes: 130.4310, 190.4380, 190.4970 Two-photon absorption (TPA) in Si vanishes at wavelengths approaching λ = 2200 nm, while its nonlinear Kerr refractive index n2 stays comparatively constant [1,2]. Hence, the nonlinear figure of merit (FOM) (n2/βλ) increases dramatically near silicon's TPA threshold. The large intrinsic nonlinearity of Si, when patterned into high-index-contrast dispersion-engineered silicon photonic wires, produces an ideal platform for the exploration of highly efficient, broadband, coherent nonlinear optical processes [3,4]. This platform can serve as an ideal host for chip-scale mid-IR applications [5-8] including molecular spectroscopy, free-space communication, and environmental monitoring.Previously we reported a mid-IR optical parametric amplifier (OPA) with on-chip gain over a bandwidth of 220 nm in a 4-mm long silicon wire [5]. Using an improved Si wire design, we demonstrate here broadband mid-IR modulation instability (MI), having a bandwidth greater than 580 nm centered at a 2173 nm pump wavelength. The intense MI spectrum correlates with unprecedented values of on-chip parametric gain, exceeding 40 dB. Moreover, we demonstrate that on-chip gain can exceed 50 dB in narrow Raman-scatteringassisted bands.Our silicon wire is fabricated on a 200 mm silicon-oninsulator (SOI) wafer in a CMOS pilot line and is 2 cm long, with cross-sectional dimensions of 900 nm x 220 nm (inset Fig. 1(a)). The top and bottom cladding consist of air and a 2 µm buried oxide (BOX), respectively. The waveguide operates in the fundamental quasi-TE mode, and has propagation losses of < 2.8 dB/cm for λ = 2000 -2500 nm. These engineered waveguide dimensions produce a waveguide effective nonlinear parameter γ ~ 130 W -1 m -1 and anomalous dispersion conditions (β2 < 0) at wavelengths from 1800 -2400 nm, as plotted in Fig. 1(a). Furthermore, 4 th -order dispersion is small and positive (β4 > 0) within the same wavelength range, which is needed for achieving broadband phase matching.To achieve an efficient degenerate four-wave-mixing (FWM) process, i.e. two pump photons converted into one signal and one idler photon, 2ωp = ωs + ωi, the phase = (ks + ki) − 2kp, P is the input pump peak power and L is the waveguide length. Graphically, when the −∆kl curve falls...

Mid-infrared integrated photonics on silicon: a perspective

“…For semi-standard SOI with 220-nm Si layer thickness, the optimal width for a Si waveguide operating near 2.1-μm wavelength was identified to be 900 nm, where, fortuitously, the second-order and fourth-order dispersion coefficients have opposite signs to facilitate broadband phase matching [101]. Using such waveguides, Kuyken et al [102] measured optical parametric amplification (OPA) with 550-nm net gain bandwidth (centered at 2.17-μm pump wavelength) and an impressive 30-dB Raman-assisted peak off-chip gain (with FWM contribution exceeding 20 dB). Both metrics represent major improvements over the initial on-chip mid-IR OPA demonstration by the same group where a non-optimized waveguide design was used [103].…”

Generation of 36 μm radiation and telecom-band amplification by four-wave mixing in a silicon waveguide with normal group velocity dispersion

“…Depending on the signs of β 2 and β 4 , a variety of phase matching conditions near to and far away from the pump can be obtained. In our previous work [6][7][8]13], anomalously dispersive waveguides (β 2 < 0) with a positive β 4 were used, such that phase matching both close to the pump (broadband phase matching) and …”

“…Efficient nonlinear optical effects on the silicon photonic platform, making use of the instantaneous thirdorder χ(3) nonlinear effect, can provide a solution to many of these challenges. Recent work has shown that fourwave mixing-based nonlinear optical functions including supercontinuum generation [6], optical parametric amplification [7,8] and wavelength conversion [7][8][9][10] can be integrated for mid-infrared light generation within compact silicon photonic integrated circuits. Moreover, silicon waveguides accomplishing bi-directional broadband spectral translation of optical signals between 1620 nm and 2440 nm in the mid-infrared [11], and between 1312 nm and 1884 nm in the short-wave infrared [12] have been demonstrated using four-wave mixing phase matched by anomalous dispersion.…”

“…Depending on the signs of β 2 and β 4 , a variety of phase matching conditions near to and far away from the pump can be obtained. In our previous work [6][7][8]13], anomalously dispersive waveguides (β 2 < 0) with a positive β 4 were used, such that phase matching both close to the pump (broadband phase matching) and far away from the pump (discrete band phase matching) could be observed simultaneously. In this paper air-clad silicon waveguides with a 400 nm thick silicon guiding layer and are designed to have normal dispersion and negative β4 around a wavelength of ~2200nm as illustrated in Figure 1(a) for the 1650 nm wide waveguide shown in the inset (assuming TE-polarized light).…”

“…The discrete MI band is the only band where phase matching occurs; the peak near 1800 nm is a known stray-light artifact within the spectrum analyzer. For waveguides designed with normal dispersion, there is no amplification of background noise near the pump, as is typically observed in silicon waveguides having anomalous dispersion [8]. This enormous reduction of amplified quantum noise (AQN) is significant, because the AQN deteriorates the performance of a spectral translator [11][12][13].…”