Broad-bandwidth Near-IR Parametric Amplification in Amorphous Silicon Waveguides

Abstract

We report broad-bandwidth optical parametric amplification using a 6-mm-long hydrogenated amorphous silicon (a-Si:H) waveguide. Amplification is obtained over more than 55 THz (~440 nm) centered at telecommunication wavelengths.OCIS codes: (190.4380) Nonlinear optics, four-wave mixing; (190.4390) Nonlinear optics, integrated optics CMOS-compatible on-chip optical amplification is a crucial building block for realizing on-chip optical networks. The use of crystalline silicon (c-Si), which exhibits a high linear and nonlinear refractive index and is compatible with current micro-fabrication technology, has resulted in a variety of exciting demonstrations including broadbandwidth amplification using parametric processes [1] and oscillation utilizing the Raman effect [2]. However, in c-Si the net parametric amplification is limited by two photon absorption (TPA) and TPA-induced free carrier absorption (FCA) to be 5.2 dB at telecommunication wavelengths in pulsed experiments. Strong (50 dB) and broadband (37.5 THz) parametric amplification were obtained in the mid-infrared regime where TPA is avoided [3], however, operating within this long-wavelength regime limits the applications for telecommunications. Exploiting the Raman effect has resulted in 13 dB amplification, but the crystalline nature of the material inherently limits the gain to a very narrow bandwidth (~2 nm) [2].Recently, hydrogenated amorphous silicon (a-Si:H) has been shown to possess an extremely high optical nonlinearity with reduced impact of TPA [4][5], and parametric amplification as high as 26.5 dB has been achieved in pulsed experiments [6]. However, due to the relatively high group velocity dispersion (GVD) of ~1600 ps/(nm•km), the net amplification bandwidth was limited to ~110 nm [6]. Here, by carefully controlling the geometry of a hydrogenated amorphous silicon waveguide for near-zero GVD at the pump wavelength, we demonstrate optical amplification over more than 440 nm (55 THz). This represents the largest parametric gain bandwidth yet demonstrated in either c-Si or a-Si:H nanowaveguides.The a-Si:H waveguide is fabricated using standard CMOS manufacturing techniques as detailed in [7]. The cross-section of the fabricated waveguide is 198 nm x 500 nm and the waveguide length is 6 mm. The propagation loss of the waveguide is measured to be ~3.5 dB/cm in TE-mode. The TE-mode profile and the cross section are plotted in Fig. 1(a). Fig. 1(b) shows the SEM picture of the fabricated a-Si:H waveguide. We numerically calculate the GVD of the designed waveguide and the curve is plotted in Fig 1(c). The GVD of the waveguide is near zero and anomalous (~5 ps/(nm•km)), in order to obtain broad-bandwidth operation. Fig. 1 (a) Cross-section and TE-mode profile of the designed waveguide. (b) SEM picture of the fabricated aSi:H waveguide. (c) Calculated GVD of the waveguide. (bottom) Experimental setup for the broad band parametric amplification measurement. (OBPF: optical bandpass filter. EDFA: erbium-doped fiber amplifier. HNLF: highly nonlinear fiber. P...

GHz Near-IR Optical Parametric Amplifier using a Hydrogenated Amorphous Silicon Waveguide

“…Previously, we reported -13 dB conversion efficiency at 10 GHz and +16 dB conversion efficiency at 90 MHz [7]. In this paper, we show that on-chip amplification at 1 GHz can be achieved using our a-Si:H waveguide.…”

“…2 b). The OPA gain becomes stronger when the wavelength detuning is larger and the gain is expected to peak at 1462 nm [5]. We are not able to measure the gain/conversion with wavelength detuning >70nm due to our CW laser tuning range.…”

“…Recently, hydrogenated amorphous silicon (a-Si:H) has been found to posses stronger nonlinearity and higher nonlinear FOM (figure of merit) than c-Si. In the near-IR regime, gain as high as 26.5 dB [4] and gain bandwidth as broad as 55 THz [5] has been shown in a-Si:H. However, these optical amplification demonstrations were operated at a low repetition rate (∼MHz) to mitigate the two-photon absorption induced free carrier effect. In order for optical amplifiers to be useful in telecommunication applications, GHz operation is critical.…”

“…In this paper, we show that on-chip amplification at 1 GHz can be achieved using our a-Si:H waveguide. This represents the first silicon OPA at telecommunications data rates.The a-Si:H waveguide is fabricated using standard CMOS manufacturing techniques as detailed in [5]. The crosssection of the fabricated waveguide is 215 nm × 500 nm and the waveguide length is 6 mm.…”

“…The a-Si:H waveguide is fabricated using standard CMOS manufacturing techniques as detailed in [5]. The crosssection of the fabricated waveguide is 215 nm × 500 nm and the waveguide length is 6 mm.…”