All-optical control of polarization splitting with a dielectric-clad azobenzene liquid crystal.

We report the design, fabrication, and characterization of an optically switchable polarizing beam splitter with a prism/azobenzene liquid crystal/prism hybrid structure. The beam splitter can operate in the polarization-splitting mode and the non-splitting mode. The switching between the modes is realized by the photoisomerization-induced phase transitions in the azobenzene liquid crystal, featuring all-optical control, bistability, and fast response. Such an active polarization-handling element is highly desirable as it not only simplifies and compacts sophisticated optical systems but also increases the degree of freedom in optical circuit design.

Meta-q-plate for complex beam shaping.

Optical beam shaping plays a key role in optics and photonics. In this work, meta-q-plate featured by arbitrarily space-variant optical axes is proposed and demonstrated via liquid crystal photoalignment based on a polarization-sensitive alignment agent and a dynamic micro-lithography system. Meta-q-plates with multiple-, azimuthally/radially variant topological charges and initial azimuthal angles are fabricated. Accordingly, complex beams with elliptical, asymmetrical, multi-ringed and hurricane transverse profiles are generated, making the manipulation of optical vortex up to an unprecedented flexibility. The evolution, handedness and Michelson interferogram of the hurricane one are theoretically analysed and experimentally verified. The design facilitates the manipulation of polarization and spatial degrees of freedom of light in a point-to-point manner. The realization of meta-q-plate drastically enhances the capability of beam shaping and may pave a bright way towards optical manipulations, OAM based informatics, quantum optics and other fields.

Multi-stable variable optical attenuator based on a liquid crystal gel-filled photonic crystal fiber.

This work demonstrates a multi-stable variable optical attenuator (VOA) that is fabricated by infiltrating a photonic crystal fiber (PCF) with a liquid crystal (LC) gel. Varying the cooling rate or biasing the electric field during gelation yields various degrees of scattering. Therefore, LC gel-filled PCFs with various transmittances can be realized. At a wavelength of 1550 nm, an attenuation rate of -33.4 dB/cm is obtained at a cooling rate of 30°C/min and a biasing voltage of 400 V during gelation. The proposed all-in-fiber VOA exhibits tunable attenuation and multiple stable states at room temperature.

Bistable light-driven π phase switching using a twisted nematic liquid crystal film.

A light-activated optical phase switch was developed, exploiting the conversion between left-handed and right-handed twisted nematic liquid crystals. Theoretical and experimental analyses revealed that the handedness inversion of the twisted nematic film altered the optical phase of the output waves by π. Herein, the competition between the helical twisting powers of the two reverse-handed chiral dopants determines the handedness of the twisted nematic film. The photo-responsibility and the bistability are attributed to the azobenzene chromophores in one of the chiral additives.

Polarization-independent bistable light valve in blue phase liquid crystal filled photonic crystal fiber.

This article demonstrates a bistable optical valve in a photonic liquid crystal fiber using the thermal hysteresis effect of the phase transition between the cholesteric phase and the blue phase (BP). The attenuation is due to various scattering losses in different phases. Both cholesteric and BPs can exist stably at room temperature (RT) and can also be switched to each other using temperature-control processes. The transmission spectrum and the intensity of the guided light can be controlled with various extents of scattering loss. For optical communications, this device can be manipulated over a loss difference of 10 dB at RT and insensitive to the polarization of light.

Optical bistability in a silicon nitride microring resonator with azo dye-doped liquid crystal as cladding material.

This investigation reports observations of optical bistability in a silicon nitride (SiN) micro-ring resonator with azo dye-doped liquid crystal cladding. The refractive index of the cladding can be changed by switching the liquid crystal between nematic (NLC) and photo-induced isotropic (PHI) states by. Both the NLC and the PHI states can be maintained for many hours, and can be rapidly switched from one state to the other by photo-induced isomerization using 532 nm and 408 nm addressing light, respectively. The proposed device exhibits optical bistable switching of the resonance wavelength without sustained use of a power source. It has a 1.9 nm maximum spectral shift with a Q-factor of over 10000. The hybrid SiN- LC micro-ring resonator possesses easy switching, long memory, and low power consumption. It therefore has the potential to be used in signal processing elements and switching elements in optically integrated circuits.

Metastasis over implantable venous access ports.

BACKGROUND: The totally implantable venous access port (TIVAP) is an important device for patients receiving chemotherapy. We have reported, to our knowledge, the first case of a metastatic tumor over a TIVAP implanted via the Seldinger technique with a subclavian vein puncture. METHODS: Our patient, a 48-year-old man with hard palate cancer, had metastasis over the TIVAP. CT studies showed that the tumor had spread along the catheter from the neck to the chest wall. RESULTS: The cause of death was multiple lung metastases and intractable tumor bleeding over the TIVAP. CONCLUSIONS: We present a novel case of metastasis over the TIVAP implanted by use of the Seldinger technique. This technique is used for patients receiving prolonged cytotoxic therapy for malignancy. Although the Seldinger technique is quick and more effective, we prefer the cephalic vein cut-down technique when an aggressive, advanced cancer of head and neck is involved.

Random lasing in blue phase liquid crystals.

Random lasing actions have been observed in optically isotropic pure blue-phase and polymer-stabilized blue-phase liquid crystals containing laser dyes. Scattering, interferences and recurrent multiple scatterings arising from disordered platelet texture as well as index mismatch between polymer and mesogen in these materials provide the optical feedbacks for lasing action. In polymer stabilized blue-phase liquid crystals, coherent random lasing could occur in the ordered blue phase with an extended temperature interval as well as in the isotropic liquid state. The dependence of lasing wavelength range, mode characteristics, excitation threshold and other pertinent properties on temperature and detailed make-up of the crystals platelets were obtained. Specifically, lasing wavelengths and mode-stability were found to be determined by platelet size, which can be set by controlling the cooling rate; lasing thresholds and emission spectrum are highly dependent on, and therefore can be tuned by temperature.

Loss-reduced photonic liquid-crystal fiber by using photoalignment method.

We present a loss-reduced photonic liquid-crystal fiber (PLCF) using the noncontact photoalignment method. The photoexcited and adsorbed azo dye on the capillary surface of a PLCF induces uniform and highly ordered orientation of the liquid crystal (LC). The anchoring force of the photoalignment effect is combined with that generated by surface boundary conditions of the photonic crystal fiber (PCF). Transmission loss resulting from LC scattering can be reduced from -2.8 to -1.3 db/cm within 10 min. This photoinduced alignment yields a permanent boundary for the LC in the PCF that reduces scattering loss and can be further modulated by electrical fields. The electrical tunable effect and fast dynamic response of the photoaligned PLCF are also presented. This low-loss PLCF can be applied conveniently in various PLCF devices.

Photo and electrical tunable effects in photonic liquid crystal fiber.

This work demonstrates photo alignment and electrical tuning effects in photonic liquid crystal fiber (PLCF). Applying voltages of 0 approximately 130V and 250 approximately 400V shifts the short and long wavelength edges of the transmission bands by about 45 nm and 74 nm toward longer wavelengths, respectively. An electro-tunable notch filter is formed in the PLCF without the use of gratings. The range of tunability of the notch filter is around 180 nm with an applied voltage of 140 approximately 240 V. This photo-induced alignment yields a permanently tilted LC structure in PCF, which reduces the threshold voltage, and can be further modulated by electric fields. The polarization dependent loss and fast response time of photo-aligned PLCF is also demonstrated. The finite-difference frequency-domain method is adopted to analyze the shift of the transmission bandgap, and the simulation results are found to correlate well with experimental data.

Microcapillary electrophoresis chips utilizing controllable micro-lens structures and buried optical fibers for on-line optical detection.

In this study, a new design of a controllable micro-lens structure capable of the enhancement of LIF detection system has been demonstrated, which can be further integrated with buried optical fibers on a micro-CE chip for sample separation and detection. Two pneumatic side-chambers were placed between a micro-CE channel and an optical fiber channel. The intervals between the side-chamber and the microchannel were used to form two surfaces of the controllable micro-lens structure. Deformations of the two surfaces can be generated after pressurized index-matching fluid was injected into the pneumatic side-chambers. The side-chambers can be deflected as a double convex lens to focus both the excitation light source and the fluorescent emission signal. The profile and the focal length of the micro-lens structure can be actively adjusted by applying different liquid pressures so that biosamples with a low concentration can be detected. Using low-cost polymeric materials such as polydimethylsiloxane, rapid and reliable fabrication techniques involving standard lithography and replication process was employed for the formation of the proposed chip device. Experimental results revealed the controllable micro-lens structure can be successfully deformed as a convex lens to focus the laser light source and the collected fluorescence signal can be enhanced accordingly. The power amplitude of excitation laser light can be enhanced by 5.4-fold. FITC dye and DNA markers were then utilized for micro-CE testing. The results indicated that the signal amplitude could be enhanced 2.5-fold when compared to the case without the activation of the micro-lens. According to the experimental results, the developed device has a great potential to be integrated with other microfluidic devices for further biomedical applications.