A multi-channel surface-enhanced Raman scattering (SERS) probe based on a multi-core photonic crystal fiber (PCF) is
investigated. The multi-core fiber contains seven hollow core PCFs arranging in a compact hexagon pattern that one PCF
is in the center with six other surrounded, and the total diameter including the protective jacket is less than 200μm. The
seven PCFs can guide light respectively, providing seven channels for sensing. The excitation light is coupled into each
core from one end (measuring-tip) of the fiber while the sample entrance is at the other end (probing-tip). Analyte
solution mixed with the silver nanoparticles enters each core via the capillary effect, and the silver nanoparticles serve as
the SERS substrate. The excitation light transmitting in each hollow core can interact directly with the analyte and the
silver nanoparticles in the air cores along the fiber axis. The SERS signal scattered by the sample propagates through the
fiber back to the measuring-tip; then couples out of the fiber into the Raman spectrometer. Comparing to a single core
PCF SERS probe, the multi-core probe not only takes the advantages of high efficiency of light usage and large
interaction space for SERS in each channel, but also is more robust and could provide multi-data. Basing on the seven
data of the analyte from the seven channels, an accurate average result could be achieved with less instability. Different
concentration Rhodamine 6G solutions have been used as test samples, and the multi-channel sensing idea has been
demonstrated by the proof-of-concept experiments.
Fiber SERS (surface enhanced Raman scattering) sensors have attracted significant interest in molecule sensing. In this
paper, we briefly review our previous work on various configurations for fiber SERS probes, including side-polished
fibers and various photonic crystal fibers (PCFs). In addition, we will report our recent experiments on a double
substrate "sandwich" structure for fiber SERS probe. The approach is to coat one SERS substrate on the tip of a
multimode fiber and mix the second substrate in solution with the target analyte molecules. Upon dipping the coated
fiber probe into the solution, randomly formed structures of the two substrates will sandwich the analyte molecules in
between. Our results show that the "sandwich" configuration exhibits significantly higher sensitivity than direct SERS detection.
Detection of biological samples in low concentration is of great significance to the basic research in science, the
development of medical technology and many other fields related to our lives. Surface-Enhanced Raman Scattering
(SERS), well-known as a powerful analytical tool with high sensitivity, is especially suitable for biomolecule detection
as it enables near infrared (NIR) excitation and label-free detection. SERS probe made of conventional optical fiber
provides better flexibility in detection; however, it requires a complicated fabrication process and doesn't serve as a
well-set detecting platform. In this talk we propose and demonstrate a photonic crystal fiber (PCF) based SERS probe,
which has the new advantages of simplicity in fabrication, better light confinement and increased light-analyte
interaction volume. The PCF-based SERS probes are prepared in three different ways: mixed solution of sample and
gold nanoparticles filled in air holes of PCF, sample solution dried in gold coated air holes and sample solution filled in
gold coated air holes, respectively. Sample solution of adenine is in concentration of about 10-6M. Almost every
characteristic peak of adenine can be observed in the spectra detected by each of the three probes.
We demonstrate, for the first time to our knowledge, a hollow core photonic crystal fiber
(HCPCF) surface-enhanced Raman probe. The probe consists of a HCPCF (also known as a
holey fiber) with a layer of Au nanoparticles coated on the inner surface of the air holes serving
as the substrate of surface enhanced Raman scattering (SERS). The sample being tested enters
the air holes by the capillary effect. The excitation light is coupled into the fiber core from one
end (measuring-tip) while the sample entrance is at the other end (probing-tip) of the fiber. The
SERS signal scattered by the sample propagates through the fiber core back to the measuring-tip;
then is coupled out of the fiber into the Raman spectrometer. The advantages of such probes
include, the confinement of light inside the HCPCF provides a higher light efficiency; and the
nanoparticles coated inside the air holes offers a larger interaction area for SERS. Both
experimental results and theoretical analysis are presented and discussed.
We demonstrate that all the inter- and intra-channel nonlinear impairments can be eliminated simultaneously by optical phase conjugation (OPC) in a power-symmetry system. However, for practical systems without power-symmetry, it is found that the effects of OPC on various nonlinearities are different in the same link. Even some nonlinearities are suppressed and some are enhanced. Therefore, optimizing the transmission link with OPC to suppress the dominant
nonlinearity is demanded. By using 1-km-long highly nonlinear fiber (HNLF) and tuning the pump wavelength near the zero dispersion wavelength of the HNLF, we experimentally generate the phase conjugation of the dispersed ~300 fs pulses. OPC with conversion efficiency of about -16 dB and conversion bandwidth of about 38 nm is obtained.
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