An experimental investigation on a novel electrically controlled optical chopper based on holographic polymer dispersed
liquid crystal (H-PDLC) gratings is presented in this paper. In order to realize the chopping function, a corresponding
electrical driving source and controlling circuit are developed for the phase type H-PDLC grating, so that the H-PDLC
chopper can not only modulate a light beam with variable frequencies at different duty ratios but also generate other
types of waveform modulation such as the sinusoidal modulation to replace the traditional rectangular modulation.
Experimental results on one-channel, two-channel and four-channel
H-PDLC optical choppers showed that, in
comparison with the mechanical chopper counterpart, this device had the advantages of (1) lower noise without
mechanical moving part, (2) higher conveniences in terms of changing its operational frequencies, duty ratios and
modulation curves, and (3) multi-channel modulation capability. Therefore, it will have a great potential for applications
that requires frequency modulations such as frequency modulated confocal microscopy system.
The optical chopper array based on Holographic Polymer Dispersed Liquid Crystal (H-PDLC) working at high
frequencies, for example 1KHz, 2KHz, and its application in an improved Frequency Division Multiplexed Fluorescence
Confocal Microscope (FDMFCM) system are reported in this article. The system is a combination of the confocal
microscopy and the frequency division multiplexing technique. Taking advantages of the optical chopper array based on
H-PDLC that avoids mechanical movements, the FDMFCM system is able to obtain better Signal-Noise Ratio (SNR),
smaller volume, more independent channels and more efficient scanning. What's more, the FDMCFM maintained the
high special resolution ability and realized faster temporal resolution than pervious system. Using the proposed device,
the FDMFCM system conducts successful parallel detection of rat neural cells. Fluorescence intensity signals from two
different points on the specimen, which represent concentration of certain kind of proteins in the sample cells, are
achieved. The experimental results show that the proposed H-PDLC optical chopper array has feasibility in FDMFCM
system, which owes to its unique characteristics such as fast response, simple fabrication and lower consumption etc.
With the development of H-PDLC based devices, there will be prospective in upgrading FDMFCM system's
performance in the biomedical area.
Tunable photonic crystals (PCs), which are infiltrated with nematic liquid crystals (LCs), tune photonic band gap
(PBG) by rotating directors of LCs when applied with the external electrical field. Using the plane wave expansion
method, we simulated the PBG structure of two-dimensional tunable PCs with a triangular lattice of circular column,
square column and hexagon column, respectively. When PCs are composed of LCs and different substrate materials
such as germanium (Ge) and silicon (Si), the influence of structural parameters including column shape and packing
ration on PBG is discussed separately. Numerical simulations show that absolute PBG can't be found at any
conditions, however large tuning range of polarized wave can be achieved by rotating directors of LCs. The
simulation results provide theoretical guidance for the fabrication of field-sensitive polarizer with big tunable band
range.
A novel two channel multi-frequencies division multiplexed confocal fluorescence microscopy (FDMCF) system based
on the holographic polymer dispersed liquid crystal (H-PDLC) optical chopper modulation is reported. The characteristic
of unique FDMCF system is that within the FDMCF system, the
multi-channel exciter laser beams are modulated with
different carrying frequencies, after the fluorescence signals are collected, and through data analyzing process, the
FDMCF system can realize the multiply points parallel detection synchronously with high temporal and spatial
resolution. Besides, combined with the electrically controlled H-PDLC grating array working as the optical chopper to
replace the mechanical chopper, it can improve and develop the FDMCF system from two channels to unlimited system.
The paper has done the experiments to demonstrate the two-channel FDMCF system based on H-PDLC modulation and
analysis the benefits from the electrically-controlled integrated electro-optical H-PDLC devices.
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