Fiber and Integrated Optics, 29:10–20, 2010 Copyright © Taylor & Francis Group, LLC ISSN: 0146-8030 print/1096-4681 online DOI: 10.1080/01468030903427045 Polarization-Insensitive Thermo-Optic Mach Zehnder Device Based on Silicon Oxinitride Waveguide with Fast Response Time P. P. SAHU 1 and A. K. DAS 2 1 Department of Electronics and Communication Engineering, Tezpur University, Assam, India 2 Department of Electronics and Telecommunication Engineering, Jadavpur University, Kolkata, India Abstract In this article, a thermo-optic structure with a silicon trench below the heater and stress-releasing grooves in both sides of the core is proposed for a thermo- optic Mach Zehnder switch using silicon oxinitride as a core and SiO 2 as a cladding. It is seen from thermal analysis by using the implicit finite difference method that the absolute value of the temperature gradient of the proposed structure, which mainly causes the release of stress anisotropy, is approximately nine times more than that of a conventional structure. The response time of the thermo-optic Mach Zehnder device, based on the proposed structure with a switching power of 177 mW is estimated as 180 s, which is about 100 times faster than that of the existing structure. Keywords response time, thermo-optic, Mach Zehnder device 1. Introduction Space division optical switches are indispensable devices for constructing optical network nodes such as wavelength division multiplexing (WDM) optical path cross-connect (OXC) systems [1–3], reconfigurable optical add-drop multiplexing (ROADM) nodes [4] with an Er CC -doped fiber amplifier (EDFA) gain equalizer [5], and packet switched optical network nodes based on multi-element semiconductor optical amplifier Mach Zehnder interferometer (SOA-MZI) switch arrays [6]. These nodes provide flexible operation, such as routing, protection, restoration, and reconfiguration, in WDM optical networks. Large-scale integrated optical switches, such as matrix switches and 1  N switches are essential devices in the OXC nodes, which connect multichannel optical fiber networks. In this regard, the design and fabrication of compact thermo-optic waveguide switches have gained much interest to achieve such high density photonic integration [6]. The fabrications of compact and ultra-compact devices of n at 2%–16% are also possible using SiO 2 /silicon oxinitride (SiON) [7] and InP/GaAsInP material [8]. Out of these materials, SiO 2 /SiON provides chemical inertness, a thermo-optic property, low material cost, and compatibility with conventional integrated circuit (IC) processing technology in comparison to InP/GaAsInP material. Integrated thermo-optic switches with a switching time of less than 1 ms are suitable for optical networks due to their high performance levels. On the other hand, in large-scale Received 18 June 2009; accepted 19 October 2009. Address correspondence to P. P. Sahu, Department of Electronics and Communication Engineering, Tezpur University, Assam 784 028, India. E-mail: pps@tezu.ernet.in 10