We report a silicon nitride (Si3N4) Mach-Zehnder interferometer (MZI) waveguide for the evanescent-wave detection of carcinogenic volatile organic compound (VOC) pyridine vapor for environment safety. The Si3N4 MZI waveguide is coated with cross-linked dipolar dyes as sensitive cladding for specific pyridine sensing. Waveguide engineering in virtue of evanescent field, cladding thickness and group refractive index regulation is carried out. The sensor chip with width/height of 2μm/200 nm is fabricated by photolithography/developing and ICP etching. In pyridine sensing, the MZI sensor shows the high sensitivity of 19 pm/ppm and the lowest detection limit of 1.5 ppm and fast response of 60s.
Silicon nitride (Si3N4) waveguides have significant applications in silicon photonics because of their low transmission loss, large transparent band range, and compatibility with CMOS processes. However, there is no electro-optic (EO) effect in Si3N4 waveguide and consequently it lacks active EO-tuning capacity. To activate Si3N4 waveguide, we propose the hybrid integration of EO polymer as cladding on Si3N4 waveguide. The waveguide is rationally designed to optimize the overlap factor of optical and electric fields on EO cladding for efficient EO modulation. Mach-Zehnder interferometer (MZI) EO switches are fabricated by photolithography and ICP etching. To enable the EO effect of cladding, electric field poling is carried out by applying high-voltage electric field and high-temperature thermal field to generate the strong in-device EO effect. By the optimization of waveguide engineering and electric-field poling, the lowest switching voltage of 11.4 V is achieved, showing a half-wave voltage length (VπL) product of 5.7 Vcm. The extracted in-device Pockels coefficient (EO coefficient, γ33) is as high as 72 pm/V, much higher than that of lithium niobate. The measured rise time and fall time of high-speed EO switching are 48.75 ns and 57.78 ns. The extinction ratio for on and off state was higher than 10 dB. This Si3N4/EO polymer hybrid EO switch may find application in optical cross connect, optical add-drop multiplexing, high-speed filter for DWDM and optical phase array for high-speed beam steering.
CMOS-compatible Si3N4 waveguide offers the advantage of compact size, low cost, and integrate-ability in optical fiber sensing network. To develop a Si3N4 waveguide chip for the sensing of toxic and carcinogenic pyridine vapor, this work demonstrated the following two aspects in waveguide engineering. The first effort was waveguide material engineering: the functionalization of Si3N4 waveguide by simple spin-coating a sensitive and specific porous dipolar polymer for pyridine detection. The other effort was the waveguide device engineering in virtue of evanescent field and group refractive index regulation to realize the high sensitivity of waveguide. For the Mach-Zehnder interferometer (MZI) with width/height of 1.5 μm/300 nm and 5 mm length, the sensitivities at TE and TM modes were 31587 nm/RIU and 30293 nm/RIU, both of which are exceptionally high for refractive index sensing. Experimentally, the sensor chip was fabricated by standard CMOS process including photolithography and ICP etching. We conceptually demonstrated the sensing of hazardous pyridine vapor with packaged Si3N4 MZI pyridine sensor in optical fiber transmission system. The sensing performance showed that the limit of detection was 1.92 ppm (lower than the threshold limit of 5 ppm for adverse effects) and the sensitivity was as high as 15.6 pm/ppm with a large linear dynamic range of 2.5-400 ppm. And in the subsequent improvement, we obtained the sensitivity of 63 pm/ppm and the detection limit of 476 ppb by optimizing the thickness of sensitive cladding.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.