Study Of The Time-domain Scanning Low- Coherence Measurement Svstem For Measuring Optical Waveguide Devices

The applications of various multiplexing techniques in on-chip optical interconnects significantly improve the capacity of a single optical link, such as polarization-division multiplexing (PDM), coarse wavelength-division multiplexing (CWDM), and mode-division multiplexing (MDM). From the point of the propagation of light, the channels and devices supporting the multiplexing techniques are both multipath type. Currently, the measurement of these multipath-type channels and devices is performed as the measurement of their spectral response, while the measurement of their actual structure parameters is still a problem. Actually, the measurement of the structure parameters is important no matter to the knowledge of the fabrication errors of the channels and devices, or to the improvement of the transmission performance of the channels and devices.Low-coherence interferometry (LCI) is a practical measurement technique which utilizes the temporal coherence of a broadband light source for the characterization of the multipath components with high accuracy and the optical imaging with high resolution. We build the time-domain LCI system and make some improvement in the measurement accuracy when it is used for the characterization of optical devices. In addition, combining with the development of the multiplexing techniques in optical interconnects and on account of the measurement problems of the channels and devices used in multiplexing techniques, we utilize the measurement system to analyze the optical components used in multiplexing techniques. The main contents and contributions of our work are listed as bellow:1. The building of the time-domain scanning LCI system and the improvement of the phase measurement accuracy. The theory of LCI is studied, and the time-domain scanning LCI measurement system is built, including experimental setup and data processing program. In addition, the factors affecting the phase measurement accuracy of the time-domain scanning LCI system are discussed. After classifying the factors and summarizing the previous works, this thesis shows that the phase measurement accuracy accumulates with the increase in the path number when the system is used to characterize a multipath device. The accumulative effect is caused by the fluctuation of the environment temperature. It is analyzed in theory and experiment. The experiments on an arrayed-waveguide gratings (AWG) show that when the scanning speed increases to 4.8 mm/s, the accumulative effect can be ignored, and the phase measurement accuracy of all paths can reach 5×10-3 rad.2. The polarization measurement of single-mode waveguide and the characterization of the single-mode-type device using time-domain scanning LCI system. Since the channel of PDM and the waveguide of the CWDM devices are both single-mode waveguide, this thesis proposes an effect method for the experimental analysis of the single-mode waveguides and devices using the time-domain scanning LCI measurement system on account of the problem of the measurement of channel parameters and structure parameters. The experimental results of a single-mode waveguide suggest that LCI can be used for the qualitative and quantitative analysis of the polarization. The experimental results of the CWDM device consisting of MZIs (Mach-Zehnder Interferometer) suggest that the phase errors of the MZIs and the coupling coefficient errors of the directional couplers are the main reasons for the performance deterioration of the device.3. The channel analysis of the on-chip MDM technique using the time-domain scanning LCI system. The channel parameter of the multimode waveguide used as the channel in MDM is hard to be measured, as well as the intermodal crosstalk of the multimode waveguide with nonideal transmission structure, like bends. Therefore, we propose that the time-domain scanning LCI can be utilized to do the channel analysis. The experimental results of the straight multimode waveguide agree well with the simulation results, which suggests that the time-domain scanning LCI can be used for the mode identification and the quantitative analysis of multimode waveguides. On this basis, the experimental analysis on the bend multimode waveguide indicates that the change of the curvature in the multimode waveguide is the main source of the modal crosstalk, and the time-domain scanning LCI can be used to not only quantitatively analyze the crosstalk but also locate the position where crosstalk occurs.