The organic acetone vapor sensing characteristics of side-polished fiber coating with cholesteric liquid crystal film were investigated. The cholesteric liquid crystal used in our experiments is a mixture compound, which contains 30% cholesteryl oleyl carbonate, 60% cholesteryl pelargonat, and 25% cholesteryl chloride. When cholesteric liquid crystal film was coated on the surface of side-polished fiber, an interference transmission spectrum of fiber could be observed. When the fiber is exposing in acetone vapor, a blue shift of the interference spectrum was found. The higher concentration of acetone vapor is, the larger blue shift of spectrum is found. The shift of transmission spectrum is linear to the concentration of acetone vapor. The sensitivity is 1.356nm/vol% when the concentration of acetone vapor ranges from 3vol% to 16vol%. This study demonstrates a new all-fiber low-cost and portable acetone vapor sensor. It can be also used to investigate the helical structure and molecular orientation of cholesteric liquid crystal.
A novel light power sensor is demonstrated by using side polished fiber (SPF) overlaid with a photoresponsive
liquid crystal hybrid film. The mixture of 15%Azo, 20% ZLI811, and 65% nematic liquid crystal is overlaid on the flat
area of SPF to form a mixture film of ~30m thickness. The film is irradiated by light of wavelength of 405nm through a
phase mask with a period of ~528nm. An absorption peak in the transmission spectrum of 1520-1620nm of optical fiber
is observed. Experiment shows that the wavelength of absorption peak will shift toward shorter wavelength as the
irradiation power increases. The change of wavelength of absorption peak is approximately linear to the irradiation
power while the irradiation powers are between 30-80mw in our initial experiments. The measured sensitivity of light
power is about 1.154pm/uW for the demonstrated sensor.
An optically switchable photoluminence (PL) photonic material using azobenzene-doped cholesteric liquid crystal (CLC)
-dispersed quantum dots (QDs) is demonstrated in the film and capillary tube, respectively. In the film, upon the light
irradiation the trans-to-cis photoisomerization of azobenzene makes the QD-dispersed CLC cell highly transparent thus
allowing most excitation photon to pass through the CLC cell and decreases the intensity of PL. In the capillary tube,
there are two situations upon the light irradiation: the intensity of PL decreases when the irradiation applied on the PL
excitation position; the intensity of PL increases when the irradiation applied ahead the PL excitation position. In view of
the considerable interests in PL of QDs for photonic applications, our study on optically switchable PL from azobenzene
doped CLC-dispersed QDs introduces a new approach of controlling emission of QDs by means of light. This may open
the door to new exploitation for applications of QD such as light switchable, emission based liquid-crystal display (LCD)
or optical communication device.
We have achieved an all-optical tuning in photonic crystal fiber (PCF) by filling the photoresponsive liquid crystal (LC)
into the air-hole cladding. The photo-induced phase transformation of the photoresponsive LC modulates the effective
refractive index of the photoresponsive LC-filled air-hole cladding, thereby creating an optically tunable environment.
Under the laser irradiation the output intensity of guided light can be modulated by the photoresponsive LC-filled
photonic bandgap structure. The tuning behavior of the guided light is independent on the polarization direction by using
the linear-polarized He-Ne laser as probe. We also demonstrate the potential use of photoresponsive LC-filled PCF in
all-optical communication device using an optical spectrum of wide bandwidth amplified from an erbium-doped fiber
amplifier (EDFA) system.
We report an all-optical switching transmission grating fabricated by holographic polymer dispersed liquid crystal (HPDLC)
technique. The all-optical switching ability is achieved by doping the nematic LC with azobenzene. The trans-cis
deformation of doped azobenzene under the irradiation of pumping light induces the phase transformation of the phaseseparated
LC microdomains and further creates an index modulation environment to switch the grating efficiency. We
also observe the grating formation by monitoring the diffracted intensity at different writing laser power. An optimum of
writing power (150 mW/cm2) is required to get maximum diffraction efficiency.
The development of porous nanostructured materials, such as polymer Bragg gratings, offer an attractive and unique platform for chemical and biological recognition elements. Much of the efforts in polymeric gratings have been focused on holographic polymer dispersed liquid crystal (H-PDLC) gratings with demonstrated applications in switching, lasing, and display devices. Here, we present the application of porous polymer photonic bandgap structures produced using a modified holographic method that includes a solvent as a phase separation fluid. The resulting gratings are simple to fabricate, stable, tunable, and highly versatile. Moreover, these acrylate porous polymer photonic bandgap structures were generated using a simple one-beam setup. In this paper, we describe the application of these nanoporous polymer gratings as a general template for biochemical recognition elements. As a prototype, we developed an oxygen (O2) sensor by encapsulating the fluorophore (tris(4,7-diphenyl-1,10-phenathroline)ruthenium(II) within these nanostructured materials. Thus, the obtained O2 sensors performed through the full-scale range (0%-100%) with a response time of less than 1 second. Most importantly, the use of the inherent property of these gratings to transmit or reflect a particular wavelength spectrum, based on the grating spacing, enables us to selectively enhance the detection efficiency for the wavelengths of interest.
Significant research efforts have been focused on the development of effective means for the optical detection of organic molecules using porous one-dimensional photonic bandgap (PBG) structures. To date, efforts have been focused on porous silicon microstructures, which are typically created using a controlled electrochemical etching process in a hydrofluoric acid solution. Generally, these sensors rely on changes in the optical resonance that occurs when the porous structure is filled by the analyte of interest and allows for simple and effective optical detection schemes. Here, we present a simple method for the production of polymer Bragg reflection gratings containing periodic porous layers, and we demonstrate optical detection of organic solvent vapors using these structures. To create the structures, a pre-polymer syrup containing a monomer, a photoinitiator, a co-initiator, liquid crystals (LC), and a non-reactive solvent (acetone or toluene) is sandwiched between two pieces of glass, and the periodic structure is then formed by applying an optical interference pattern generated using a simple one-beam laser setup. More importantly, we demonstrate that acetone vapor penetrates the porous structure and induces a change in the effective refractive index of these gratings that result in a shift in the reflection wavelength. This shift is pronounced, and can easily be observed by eye, or detected by optical means. We also demonstrate that this shift depends on the particular type of chemical vapor and vapor concentration, and the detection is reversible and repeatable. Finally, the addition of aminosilane to the pre-polymer syrup is shown to improve the stability of the resulting gratings, suggesting that this photopolymer fabrication technique could be used to create structures suitable for biological applications in aqueous environments.