Low loss, high contrast optical waveguides based on CMOS compatible LPCVD processing

A new class of integrated optical waveguide structures is presented, based on low cost CMOS compatible LPCVD processing. This technology allows for medium and high index contrast waveguides with very low channel attenuation. The geometry is basically formed by a rectangular crosssection silicon nitride (Si3N4) filled with and encapsulated by silicon dioxide (SiO2). The birefringence and minimal bend radius of the waveguide is completely controlled by the geometry of the waveguide layer structures. Experiments on typical geometries will be presented, showing excellent characteristics (channel attenuation 0.06 dB/cm, IL 0.6 dB, PDL 0.2 dB, Bg «1×10, bend radius 500 m). Introduction As demand for telecommunication bandwidth increases and the optical fiber networks move steadily towards the customer premises, demand for optical switching and routing components is rising. As a consequence, optical components are replacing electronics for signal processing [1-3]. The adoption rate for optical components is being hampered, however, by their high costs stemming from two major sources: large optical footprint (i.e. high chip realestate) and high packaging costs. By integrating multiple functions at a higher density on a single optical chip much of these costs can be amortized across several devices. In order to achieve a high density photonic platform, the index contrast and channel attenuation of the waveguide must be sufficiently large and small enough, respectively, to allow for tight curvature and cascading of multiple structures. This opens the pathway to use micro ring resonators as the universal building block in systems capable of providing switching and routing functionality [1,2,46]. A new waveguiding technology, designed, developed and patented by by LioniX BV is capable of meeting these demands outlined above. It comprises of alternating CMOS-compatible LPCVD layers which are fully transparent for wavelengths from < 500 nm up to 2 μm and beyond. The technology allows for medium and high index contrast waveguides. In this paper we describe the fabrication and performance of three typical waveguide geometries and give examples of (realized) applications. Both designs exhibit very low waveguide attenuation values but otherwise have totally different characteristics and applications.. Waveguide concept Stoichiometric silicon nitride (Si3N4) fabricated using LPCVD processing is widely used in integrated optics, primarily because of its large refractive index (2.0) enabling very compact devices [2,6,10]. The major drawback of Si3N4 is its large internal tensile stress (~1GPa) which limits its layer thickness to 350 nm. As a consequence devices fabricated with Si3N4 show a very large polarization dependency, thereby severely limiting their use in telecom applications. By combining it with a second layer that has a very large compressive stress, such as LPCVD SiO2 (TEOS), however, the total stress of the composite layer stack is strongly reduced. As a result the thickness of the total stack can be considerably larger than the critical layer thickness of Si3N4 alone [7,8]. 400 106