The Research And Development Of Optical Passive Devices Based On Liquid Crystal Technology

This thesis introduces the research and development of several optical passive devices. Through theoretical simulation, we design and fabricate a single-channel variable optical attenuator, a bidirectional multi-channel tunable DWDM optical isolator and a40channel/100-GHz channel-spacing wavelength blocker based on liquid crystal technology.1. We discuss the electrically controlled birefringence effect of liquid crystal and the principle of LC based light intensity modulator. By utilizing the birefringence tunability of liquid crystal, a variable optical attenuator is proposed. We also analyze the LC cell’s residual phase and total-internal-reflection induced birefringence, which affect the VOA’s performance. A well-placed true zero-order QWP is applied to eliminate the residual phase. The LC based variable optical attenuator with an over50dB dynamic range is demonstrated. With the adjustment of the QWP’s orientation angle, the LC cell’s driving voltage can decrease dramatically.2. We introduce the principle of a magneto-optical effect based isolator. By utilizing LC cell and phase modulator, a bidirectional multi-channel tunable DWDM optical isolator for C-band is designed and demonstrated.100-GHz channel spacing and over30dB contrast ratio is achieved. The spectral response at ITU grids are further flattened by using a wave plate stacking technique.3. A dynamic dense-wavelength-division multiplexing (DWDM) channel blocker and equalizer is developed based on liquid crystal (LC) and dispersion control technology. A multi-pixel LC array is adopted to regulate the power level of each DWDM channel while a reflective grating diffracts the input signals spatially to corresponding LC pixels. A dispersion control unit is proposed and employed to enhance the dispersion and compensate the intrinsic nonlinear dispersion of the grating. Therefore all LC pixels could handle corresponding lights centered at the ITU Grids. A40-channel,100-GHz channel-spacing dynamic wavelength blocker/equalizer is thus demonstrated with-5dB insertion loss (IL) and over40dB extinction ratio. The maximum center frequency shift of all40channels is-±2GHz, which means our dispersion control technology works very well for grating based DWDM devices. The Polarization dependent loss(PDL), Return Loss(RL) and channel bandwidth are satisfied with the commercial requirement.4. We measured the surface plasmon polariton (SPP) enhanced Goos-Hanchen (GH) shift based on LC and grating technologies. An optical setup is used to convert the spatial displacement to incidence angle variation to a Littrow mounted diffraction grating. As a consequence, the GH shift information could be obtained from the back-reflected center wavelength that fulfills the Littrow condition. A LC cell is used to adjust the polarization state of the incident light without mechanical movement. About10μm GH shift difference between TE (Transverse Electric) and TM (Transverse Magnetic) mode lights were measured associated with the SPP excitation. The corresponding center wavelength shift of the returned beam is404pm. The relationship between energy conversion and GH shift is also investigated.