Omni-directional band edge lasing emission from a dye-doped cholesteric liquid crystal infiltrated photonic crystal fiber
This work demonstrates an omni-directional lasing emission in a photonic crystal fiber (PCF) which is selectively injected with dye-doped cholesteric liquid crystal (DDCLC) and azo-CLC into the hollow core and the cladding holes, respectively. Experimental results indicate that the helical axis of the DDCLC will align perpendicularly to the fiber wall and thus the band edge lasing emission of the DDCLC within the PCF can be pumped by a pulse laser and measured in radial direction. This work also demonstrates that the direction of the lasing emission of the PCF can be controlled optically.
Introduction Results & Discussion
Sample preparation
Experimental setup
Fig. 2. (a) Schematic of the process for selectively injecting materials in the PCF. DDCLC and azo-CLC are injected into the core and the cladding of the PCF as the lasing source and the light valve, respectively. (b) Cross section of the PCF and the prescriptions of the injected materials in the core and cladding, respectively. (c) The POM images of the selectively injected DDCLC PCF. The top and bottom images are the sample before and after the exposure of UV light, respectively.
Fig. 3. The experimental setup. The 532 nm laser is for pumping lasing emission while the 355 nm laser and 442 nm laser are for controlling the light valve.
Fig. 1. Broadband fluorescence can be produced in the cell via spontaneous emission, at the short- and long-wavelength edges (SWE & LWE) of cholesteric liquid crystal reflection band (CLCRB), fluorescence can propagate via multi-reflection, which results in a very small group velocity and a very large density of photon state (DOS) for the fluorescence.
Due to the distributed feedback of the active multilayer in the multi-reflection process, a high gain can be achieved for a low-threshold lasing emission. .
Experiments
Wavelength
LWE
SWE
Pumped pulse (source)
CLCRB (cavity)
Fluorescence of laser dye (Active medium)
Fluorescence/Reflectance
Lasing output Lasing output
Fig. 6. Schematic of the mechanism for the optically controllable lasing emission. The azo-CLC in the cladding of the PCF can transform between scattering focal conic state and transparent isotropic state isothermally via the photo induced isomerization of the azo LC.
Fig. 5. The lasing spectra of the DDCLC injected PCF measured at 0° and 180°, (a) before UV irradiation or after 442 nm laser irradiation, (b) after UV irradiation, and (c) after UV irradiation on 0° only. The corresponding pictures of lasing pattern for (a), (b), and (c) are shown in (d), (e), and (f), respectively.
Fig. 4. (a) Reflection spectrum and lasing spectrum of the DDCLC infiltrated PCF. (b) Polarization investigation of the lasing emission. Variations in (c) the lasing emission spectrum of the DDCLC injected PCF and (d) its peak intensity and corresponding full-width at the half maximum (FWHM) with various pumped energy.
(a) (b)
(c) (d)
Lasing in PCF
Optically controllable lasing direction
Mechanism
ACKNOWLEDGEMENT
The authors would like to acknowledge the financial support provided by the National Science Council of Taiwan (contract NSC 100-2112-M-006-012-MY3) and the Advanced Optoelectronic Technology Center in National Cheng Kung University under the projects of the Ministry of Education.
Chung-Yueh Chiu
1, Jia-De Lin
1, Ting-Shan Mo
2, and Chia-Rong Lee
1*
1Department of Photonics and Advanced Optoelectronics Technology Center, National Cheng Kung University, Tainan, Taiwan 701, Republic of China
2Department of Electronic Engineering, Kun Shan University of Technology, Tainan, Taiwan 710, Republic of China
Cleaving
3
1 2 4
Fiber to spectrometer Mirror
Mirror
Mirror
10X
60X
XYZ manipulator
XYZ manipulator Mirror
Polarizer
λ/2 plate
Fiber to spectrometer
Sample fiber
60X
10X 532 nm
355nm 442 nm
100 μm
Azo dye doped CLC (focal conic)
Laser dye doped CLC (planar)
NLC (HTW 114200-100)
Chiral (S811)
Laser dye (P597) 76.43 wt % 23.11 wt % 0.46 wt %
NLC (E7)
Chiral (S811)
Azo
(azo LC 1205) 70.3 wt% 10.76 wt % 18.94 wt %
540 560 580 600 620 640 660 680 700 0
10000 20000 30000 40000 50000 60000
Wavelength (nm)
Lasing intensity (a.u)
0.0 0.2 0.4 0.6 0.8 1.0
Reflectance
5400 560 580 600 620 640
10000 20000 30000 40000
Lasing intensity (a.u)
Wavelength (nm)
LCP
RCP
540 560 580 600 620 640
0 10000 20000 30000 40000 50000 60000
2.7 1.9 1.5 1.1 0.9 0.7 0.5
Wavelength (nm)
Pump en ergy
(J/pulse )
Lasing intensity (a.u)
0.0 0.5 1.0 1.5 2.0 2.5 3.0
0 10000 20000 30000 40000 50000 60000
Pump energy (J/pulse)
Lasing intensity (a.u)
0 10 20 30 40 50
FWHM (nm)
540 560 580 600 620 640 660 680 700
0 2000 4000 6000 8000 10000
Lasing intensity (a.u)
Wavelength (nm)
540 560 580 600 620 640 660 680 700 0
1000 2000 3000 4000 5000
Wavelength (nm)
Lasing intensity (a.u)
0.0 0.2 0.4 0.6 0.8 1.0
Reflectance
5400 560 580 600 620 640 660 680 700 1000
2000 3000 4000 5000 6000 7000 8000
Wavelength (nm)
Lasing intensity (a.u)
0.0 0.2 0.4 0.6 0.8 1.0
Reflectance
532nm
0°
180°
λ=355nm-beam irradiation
trans→cis
Isothermal CLC → I
phase transition of LCs
Isothermal I → CLC
phase transition of LCs
λ=442nm-beam irradiation
cis→trans CLC phase
Focal conic state
Isotropic phase unwinding
LC molecule
trans - azo LC 1205 cis - azo LC 1205
100µm
100μm
A P
100μm
A P
(a)
(b)
(c)
(a) (b) (c)
(d) (e) (f)
