Supercontinuum Generation in a Silica Spiral Waveguide

Abstract

A low-loss silica spiral waveguide is used for demonstrating on-chip supercontinuum generation. The broadest measured spectrum spans an octave (936 -1888 nm) at -50 dB from peak when 2.17 nJ pulses are launched. [5], and wavelength division multiplexing [6]. In such context, on-chip waveguides for SCG would bring important functionalities of photonic integrated circuits. Although silica has a small Kerr coefficient of 2.6 × 10 -20 m 2 W -1 , it has a much lower linear loss compared to other materials, a crucial factor for the success of fiber based devices. Recently, a chip-based, silica waveguide functioning as a low-loss optical delay line was reported [7]. Here, the ability for SCG using the waveguide is tested. A silica waveguide with a total physical path length of 3.5 m consisting of four, cascaded, double-interleaved Archemidian spirals is used in the experiment (Fig. 1a). The outer radius of each spiral is 7.0 mm and the chip size is 2.5 cm × 6.9 cm. A pulse train with 80-MHz repetition rate and FWHM of 180fs is launched from an optical parametric oscillator (Spectra-Physics OPAL). The energy and the polarization of the pulse are controlled using a variable neutral density filter and a half-wave plate, as shown in Fig. 1b. An objective lens with 12-mm focal length is used to free-space couple the light into the waveguide. At the waveguide end, a cleaved multimode fiber is closely