Tunable Optical Filters Based on Different Configurations with Cholesteric Liquid Crystals

Optical filters with different configurations based on cholesteric liquid crystals （CLCs） are designed. The central wavelength from CLCs can be tuned by the electric field or temperature. For the electric field tuning, the ITO is designed with circular patterns, which can make the tunable range 18 nm. For the temperature tuning, two-layer- CLC configurations are used. The experimental results indicate that a deepened or broadened bandgap from the CLC can be achieved by different handedness or concentrations of chiral dopants. The spectrum study is carried out.

A high performance tunable optical filter based on cascaded polarization interference filter

A new kind of tunable optical filter is proposed for DWDM optical communication application. It is based on cascaded polarization interference filter (PIF). The period and bandpass width of each PIF are decided by its optical path difference between o-ray and e-ray (OPDOE). When their OPDOEs are proportionately designed, the tuning range and bandpass width depend on OPDOE in the first and the last PIF, respectively. The tuning range, bandpass width and crosstalk are independent each other. The crosstalk is related to the OPDOE ratios among PIFs and can be suppressed by designing the PIF's OPDOE. A set of OPDOE is suggested that are l1, 2 × l1, 22 ×l1, 23 ×l1, 24 ×l1, ..., 2N-4 × l1, 15 × 2N-7 ×l1, 10 × 2N-6 × l1 and 2N-2 ×l1 from the first to the last. This suggested OPDOEs can yield -50-dB crosstalk for any tuning range and bandpass width. The insert loss is less than 1 dB. As its loose alignment requirement, there is no limitation on cascaded PIF number. When 11 PIFs are cascaded, it can achieve 170-nm tuning range, -50-dB crosstalk, bandpass width applicable to 25-GHz channel spacing and 1 dB insert loss.

Wideband Tunable Frequency-Doubling Optoelectronic Oscillator Using a Polarization Modulator and an Optical Bandpass Filter

A wideband tunable frequency-doubling optoelectronic oscillator （FD-OEO） is proposed and experimentally demonstrated based on a polarization modulator and an optical bandpass filter （OBPF）. The central frequency of the correspondingly fundamental OEO could be adjusted by tuning the bandwidth and central frequency of the OBPF, which could also be regarded as a photonic-assisted tunable microwave filter. The frequency tuning range of the FD-OEO covers from 9.5 to 32.8？GHz, and the single sideband phase noise of the fundamental signal is lower than -100dBc/Hz at an offset of 10？kHz. Moreover, the frequency stability of the generated signal is investigated by measuring its Allan deviation. The Allan deviation of the generated fundamental signal at 10？GHz is 2.39×10^-9.

Tunable narrowband antireflection optical filter with a metasurface

A narrowband tunable antireflection optical filter is proposed and numerically studied. The structure is a metasurface based on plasmonic nanoparticles on an electro-optic film in a three-layer configuration of metaldielectric-metal(MDM) in the visible near-infrared range. By tuning the voltage and thus tuning the refractive index of the dielectric Li Nb O_3, one can shift the wavelength of minimum reflection as desired. The parameters of gold nanoparticles and other elements used for the filter design and refractive index of the dielectric are obtained by the finite-element method(FEM). An analytical theory is presented to explain the FEM simulation results, and they agree well with each other. It is found that the frequency of the plasmonic resonance wave on the metasurface should be equal to that of the Fabry–Perot resonator formed by the MDM to have a good filtering property. Theoretical spectra obtained by FEM simulation show that the structure has extensive potential for the design of tunable narrow-band filters for modulators, displayers, and color extraction for imaging.

La-doped PMN-PT transparent ceramics with ultra-high electro-optic effect and its application in optical devices

Transparent electro-optic(EO)ceramics of La-doped 0.75Pb(Mg_(1/3)Nb_(2/3))O_(3)-0.25PbTiO_(3)(0.75PMN-0.25PT)were prepared successfully.High transparency of 69%in the near-infrared(IR)wavelength(1550 nm)was achieved at 2 mo1%La doping,meanwhile it shows an extremely high quadratic EO coeficient of 45.4×10^(-16)m^(2)·V^(-2),which s indispensable for applications in EO devices.The distribution of a polar nanodomain structure of the samples experiences disorder-order-disorder evolution in a La doping range.It is found that a parallelly-stacked polar nanodomain structure with an easier and faster polarization switching in the 2 mol%La-doped sample suggests that an ordering distribution of polar nanoregions would be critical to inducing large EO effect,transparency,and piezoelectric response.A triple-cavity tunable optical filter(TOF)with a single transmission peak and a tuning voltage below 30 V in a tuning range of 190-197 THz was designed based on our ceramics.The work is believed to bridge the relationship among doping-engineering,EO properties,and polarization behavior,which would guide the further optimization of transparent EO ceramics.

Research at the University of Kent and Subsequent Research Activities

The author＇s research activities undertaken at the Applied Optics Group, the University of Kent at Canterbury are reviewed, during his time there from 1988-1992 and 1994-1996, followed by a summary of recent research. The areas of interest are high finesse ring resonators, tunable optical filters, novel optical fiber grating sensors in glass and polymer, femtosecond laser inscription and micromachining, environmental pollution monitoring, hydrogen activated Pd films on silicon and impurity measurement on silicon wafers.