Ultrahigh Temperature-Sensitive Silicon MZI with Titania Cladding

There have been many efforts to adjust temperature-dependent wavelength shift (TDWS) of a photonic waveguide device using a cladding material with a negative thermo-optic coefficient (TOC) differently from a core material with a positive TOC (Kokubun et al., 1998; Lee et al., 2007, 2008; Alipour et al., 2010; Guha et al., 2013; Bovington et al., 2014; Lee, 2014). Polymers have been popularly used as the cladding material with a negative TOC (Kokubun et al., 1998; Lee et al., 2007, 2008), and titania (TiO2) is recently attracting attention with a highly negative TOC (Alipour et al., 2010; Guha et al., 2013; Bovington et al., 2014; Lee, 2014) and its merit of complementary-metal-oxide-semiconductor (CMOS) compatibility in fabrication when it is used for a silicon photonic waveguide device. Silicon has a very high TOC of 1.8× 10−4/°C and there have been many efforts to reduce the high TDWS of silicon photonic devices such as a ring resonator by using polymer (Kokubun et al., 1998; Lee et al., 2007, 2008) or titania cladding (Alipour et al., 2010; Guha et al., 2013; Lee, 2014) with a highly negative TOC. In case of silicon photonic Mach-Zehnder interferometer (MZI), there were reports showing the way to reduce the TDWS of MZI without using a cladding with a negative TOC (Uenuma and Moooka, 2009; Guha et al., 2010; Dwivedi et al., 2013). TDWS of silicon MZI was shown to be reduced by using different widths of waveguide (Uenuma and Moooka, 2009; Guha et al., 2010) or by using different polarization (Dwivedi et al., 2013) in each of the MZI arm, respectively. The difference in each of the MZI arm can induce a different temperature-dependent phase change for the each arm, resulting reduction in TDWS of MZI. The previous efforts of silicon photonic devices using a negative thermo-optic cladding have been focused on reducing the TDWS, but there have been demands also on high TDWS in such applications of low power temperature tuning (Masood et al., 2013) and integrated-photonic temperature sensors (Irace and Breglio, 2003; Kim et al., 2010; Deng et al., 2014). So, it would also be attractive if there is amethod to intensify the TDWSof the silicon device by using a claddingmaterial such as titania with a very high TOC. There have been MZIs using titania for chemical sensing (Qi et al., 2002; Celo et al., 2009), but no reports on temperature sensors using titania cladding to the best of our knowledge. In this regard, here, we combine the method used to in reducing TDWS of silicon MZI with different dimension for each arm and the method of adding titania cladding on the silicon MZI to show the possibility of ultrahigh temperature-sensitive silicon MZI.