We report here the fabrication, charaterisation and refractive index sensing of two microchanneled chirped fiber Bragg
gratings (MCFBGs) with different channel sizes (~550μm and ~1000μm). The chirped grating structures were UV-inscribed
in optical fibre and the microchannels were created in the middle of the CFBGs by femtosecond (fs) laser
assisted chemical etching method. The creation of microchannels in the CFBG structures gives an access to the external
index liquid, thus inducing refractive index (RI) sensitivity to the structure. In comparison with previously reported FBG
based RI sensors, for which the cladding layers usually were removed, the MCFBGs represent a more ideal solution for
robust devices as the microchannel will not degrade the structure strength. The two MCFBGs were spectrally
charaterised for their RI and temperature responses and both gratings exhibited unique thermal and RI sensitivities,
which may be utilised for implementation of bio-chemical sensors with capability to eliminate temperature crosssensitivity.
KEYWORDS: Polarization, Fiber lasers, Fiber Bragg gratings, Laser systems engineering, Sensing systems, Structured optical fibers, Polarizers, Optical filters, Signal attenuation, Signal to noise ratio
Using three fibre gratings with excessively tilted structures in the cavity, we have experimentally demonstrated a
multiwavelength switchable erbium-doped fibre ring laser system. The three tilted gratings act as in-fibre polariser and
polarisation dependent loss filters to induce the polarisation hole burning effect in the cavity for the operation of the laser
at single, double, triple and quadruple wavelengths. The laser system has demonstrated good stability under room
temperature conditions and also achieved a high degree of polarization (~30dB), high optical signal to noise ratio (up to
63dB) and high side mode suppression (~50dB). The system has also been investigated for temperature and strain
sensing by subjecting the seeding fibre Bragg gratings (FBG) to temperature and strain variations. Since the loss band of
the polarisation dependent loss filter is broader than the bandwidth of the seeding FBG, the laser output shifts in
wavelength with the applied temperature and strain. The fibre ring laser has shown good responses to the temperature
and strain, providing sensitivities of approximately 11.7 pm/°C and 0.85pm/με respectively.
A novel tunable and reconfigurable microwave photonic filter based on two cascaded Mach-Zehnder modulators (MZMs)
and a dispersive medium is presented, theoretically discussed and experimentally demonstrated. A single-wavelength
laser diode (LD) and the first MZM are used to obtain a multi-wavelength optical source, and the second MZM is
modulated with the signal to be processed. The dispersive medium provides the time delay for different taps, since
different wavelength experiences different time delay, when it travels in the optical fiber. By adjusting the modulation
frequency and the bias voltage on the first MZM, the wavelength spacing and the relative amplitude of the optical tones
after the first MZM can be changed, thus making the filter tunable and reconfigurable. The presented microwave
photonic filter has been implemented in the experiment. The experimental results agree well with the simulation results,
and show that the present microwave photonic filter has good tunability and reconfigurability. The mainlobe-to-sidelobe
ratio (MSR) of around 25dB is achieved for the presented filter in the experiment.
In this paper, the authors present and experimentally demonstrate an all-optical frequency up-conversion and
demultiplexing method in a radio-over-fiber (RoF) system. A Mach-Zehnder modulator (MZM) and a microwave
photonic filter based on a fiber ring structure are used to simultaneously realize the frequency up-conversion and
demultiplexing functions. In this proposed system, only a fiber ring and a photodiode (PD) are needed in the base station
(BS) to fulfill the signal processing functions. This simple solution makes the base stations more cost-effective, and
shows good application potential in the future radio-over-fiber systems.
A novel all-optical frequency up-conversion method implementing microwave photonic filter in a radio-over-fiber (RoF)
link is proposed and demonstrated. The electrooptical phase modulator, electrooptic intensity modulator in combination
with 75-km single-mode fiber (SMF) is used to form the microwave photonic filter and fulfill the frequency upconversion
function at the same time. The technique requires large modulation index at the phase modulator, which
simultaneously increases the efficiency of the frequency conversion. The proposed approach has been demonstrated both
theoretically and experimentally.
KEYWORDS: Microwave photonic filters, Single mode fibers, Electronic filtering, Optical filters, Multiplexing, Linear filtering, Radio optics, Radio over Fiber, Telecommunications, Microwave radiation
A method for subcarrier demultiplexing in Radio-over-Fiber system has been proposed and verified experimentally. A
continuously tunable single resonance microwave photonic filter using the tunable fiber Mach-Zehnder interferometer
(MZI) as the slicing filter, is implemented to realize the demultiplexing. Two subcarriers, one is 2.4GHz representing the
wireless LAN signal , the other is 900MHz representing the Cellular signal, can be demultiplexed separately. The
proposed approach has been demonstrated both theoretically and experimentally.
KEYWORDS: Microwave radiation, Signal generators, Single mode fibers, Signal processing, Frequency conversion, Modulation, Radio optics, Heterodyning, Optical fibers, Scattering
Microwave signal generation and processing such as frequency conversion are proposed and experimentally
demonstrated based on stimulated Brillouin scattering (SBS) in single-mode fibers (SMFs). A simple scheme to generate
microwave/millimeter-wave sources is realized by utilizing the optical heterodyne technique between an optical carrier
and its Stokes light. Stable microwave sources with the frequencies of about 10.56 and 21.71 GHz are experimentally
realized using the first- and second-order SBS frequency shifts based on standard SMFs. A microwave frequency
up/down conversion method is presented without premodulation for bi-direction radio-over-fiber systems by using fiber
SBS. The microwave signal of 1.5 GHz is experimentally up-converted to 9.06 and 12.06 GHz, and the microwave
signal of 9 GHz is down-converted to 1.56 GHz, respectively.
After an analysis of the spectral characteristics of the long-period grating (LPG) with decreasing the fiber cladding diameter, we experimentally investigated the spectra of etched LPG pairs (LPGPs) with ~3 dB transmissivity (as in-fiber M-Z interferometers). The evolutions of the transmission spectra were characterized as the cladding diameters were decreased by HF etching process. A shift of the stop-band of LPG and interference pattern of LPGP to longer wavelength was observed with the reduction of cladding diameter, in which that of higher order cladding mode induced a larger shift. The responses of the LPGs and LPGPs with different etching degrees to the change of the surrounding refractive-index were measured, and an increased sensitivity is observed in the experiment.
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