Abstract-The high index contrast silicon-on-insulator platform is the dominant CMOS 1 compatible platform for photonic integration. The successful use of silicon photonic chips in optical communication applications has now paved the way for new areas where photonic chips can be applied. It is already emerging as a competing technology for sensing and spectroscopic applications. This increasing range of applications for silicon photonics instigates an interest in exploring new materials, as silicon-oninsulator has some drawbacks for these emerging applications, e.g. silicon is not transparent in the visible wavelength range. Silicon nitride is an alternate material platform. It has moderately high index contrast, and like silicon-on-insulator, it uses CMOS processes to manufacture photonic integrated circuits. In this paper, the advantages and challenges associated with these two material platforms are discussed. The case of dispersive spectrometers, which are widely used in various silicon photonic applications, is presented for these two material platforms.

PECVD silicon nitride photonic wire waveguides have been fabricated in a CMOS pilot line. Both clad and unclad single mode wire waveguides were measured at ¼ 532, 780, and 900 nm, respectively. The dependence of loss on wire width, wavelength, and cladding is discussed in detail. Cladded multimode and singlemode waveguides show a loss well below 1 dB/cm in the 532-900 nm wavelength range. For singlemode unclad waveguides, losses G 1 dB/cm were achieved at ¼ 900 nm, whereas losses were measured in the range of 1-3 dB/cm for ¼ 780 and 532 nm, respectively.

Silicon photonics typically builds on a silicon-on-insulator based high-index-contrast waveguide system. Silicon nitride provides an alternative moderate-index-contrast system that is manufacturable in the same CMOS environment. This paper discusses the relative benefits of both platforms.

The generation of an octave spanning supercontinuum covering 488 nm to 978 nm (at -30 dB) is demonstrated for the first time on-chip. This result is achieved by dispersion engineering a 1 cm long Si 3 N 4 waveguide and pumping it with an 100 fs Ti:Sapphire laser emitting at 795 nm. This work offers a bright broadband source for biophotonic applications and frequency metrology. OCIS codes:(320.6629) Supercontinuum Generation; (190.4390) Nonlinear optics, integrated optics. http://dx.doi.org/10.1364/XX.99.099999Over the last decade, the progress of supercontinuum (SC) generation in photonic crystal fibers [1][2][3] has led to a series of advancements in spectroscopy [4], optical coherence tomography [5] and precise frequency metrology [6]. Recently SC generation on integrated CMOS compatible waveguide platforms has been attracting significant attention. Previous efforts mostly aimed at the telecom wavelength window [7] for WDM communication and at the mid-infrared range [8] for spectroscopic sensing. However, a SC covering the red to near-infrared spectral window where tissue and cells possess low absorption and scattering coefficients could offer particular advantages for biological applications such as bioimaging [9] and Raman spectroscopy [10,11].To produce a SC below 1 μm on a CMOS-compatible integrated platform, there are two main hurdles to overcome: transparency of the waveguide and phase matching. The first one can be addressed by using silicon nitride as the waveguide material rather than silicon [12]. Recently a SC down to 665 nm has been obtained using a silicon nitride waveguide pumped at 1335 nm [13]. The second hurdle is to obtain anomalous dispersion required for efficient SC generation in Si 3 N 4 waveguides. * Corresponding author: haolan.zhao@ugent.be At visible wavelengths, this is not trivial because Si 3 N 4 possesses a strong normal material dispersion due the proximity to the material bandgap. The strong normal material dispersion thus needs to be compensated by the waveguide dispersion. A frequency comb using a silicon nitride microcavity has been demonstrated with comb lines down to 765 nm circumventing this requirement by using a combination of χ(2) and χ(3) nonlinear processes [14] yet it requires careful dispersion management. In this letter, inspired by the work on silicon platform [15,16], we implement a similar method to achieve anomalous dispersion in a silicon nitride waveguide by partially underetching the silicon oxide underneath the Si 3 N 4 waveguide core. We demonstrate an SC ranging from 488 nm to 978 nm when pumping the waveguide at 795 nm. To the best of our knowledge, this is the first demonstration of an octave spanning supercontinuum extending in the sub-500 nm wavelength range on an integrated platform. It constitutes a first step to a fully integrated broadband source for e.g. biophotonic applications.The waveguide used in the experiment is fabricated in a CMOS pilot line at imec [17]. A 300 nm-thick silicon nitride film is grown via low-pressure chemical vapor deposit...

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