Delayed Mach-Zehnder Interferometer Using Wavelength-Insensitive Optical Power Divider

• Main Authors: Ci-Syu Chen, 陳麒旭
• Other Authors: Shih-Hsiang Hsu
• Format: Others
• Language: zh-TW
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/66159416902386319754

碩士 === 國立臺灣科技大學 === 光電工程研究所 === 103 === The delayed Mach-Zehnder interferometer (DMZI) can be applied to the chromatic dispersion (CD) monitoring, optical signal-to-noise ratio (OSNR), and differential phase shift keying (DPSK) modulator/demodulator. The optical isolation of a non-ideal DMZI is reduced in the phase modulation. Then less extinction ratio and worse bit error rate would be followed besides less sensitive system monitoring. The above is coming from the uneven interferometer splitting ratios and the DMZI frequency offset, which will cause a declined OSNR, which implies the importance of the group index, ng, in the delayed arm. The optical low coherence interferometer (OLCI) was utilized to characterize the group index of 4.62 in the TM polarization using silicon-on-insulator based microring resonator, which deviated from the theoretical value of 4.17 due to the process variation of the waveguide width. The OLCI, constructed by the SMF-28 fibers, could demonstrate 0.01 accuracy on group index and further improvement up to 0.00002 index accuracy could be achieved by the polarization maintained fiber based OLCI. In the interferometer splitting ratio, the first optical power divider should be 50:50 in order to demonstrate the output maximum optical isolation simultaneously on constructive and destructive output ports. The second optical divider ratio will depend on the additional optical loss on the delalyed arm of the decoupled region. For wavelength division multiplexing (WDM) system applications, two wavelength-insensitive optical power dividers were proposed, Mach-Zehnder directional coupler (MZDC) and hybrid plasmon waveguide (HPW). In this paper, the commercial software of Photo Design and RSoft were taken for numerical simulation on the design of the silicon-wire based MZDC. Compared with the traditional direction coupler (DC) and multimode interferometer (MMI), the optical power splitter from MZDC owns the wavelength independence and arbitrary splitting ratios. On the other hands, the HPW optical power splitter is take advantage of the metal on top of silicon-wire. The decoupled region in the above two types of power dividers was using delayed arm to couple two DC spectrum for insensitive wavelength response and flexible optical power splitter splitting ratios. Silicon-wire based optical power splitter is sub-micron size, the curved structure will significantly affect the spectral response and need to be takn into account in the coupling regions of MZDC. The simulation showed that the splitting ratio of 50:50 and 0.02 variation demonstrated on the silicon-wire based MZDC in the C-Band. The manufacture errors caused the waveguide width varied from 0.35 m to 0.4 m and the waveguide spacing from 0.35 m to 0.32 m. The spectral results experimentally showed the splitting ratio of 47:53 with the variation of 0.08, which is the same as the simulation results corrected form the processing variation. Under the same manufacture error, the 50:50 splitting from DC could be theoretically derived as 47:53 and the power divider variation is up to 0.16. It could be concluded that the processing tolerance in MZDC is better than DC. The splitting ratio and its variation of HPW based MZDC were 50:50 and 0.068 from the S to L bands, respectively. The technologies we were demonstrating will allow DMZI for better optical isolation.