We propose a hybrid plasmonic zeolitic imidazolate framework-8 (ZIF-8) nanostructure to achieve near-infrared dual-band sensing of trace amounts of volatile organic compound (VOC) gases via metal-organic framework patch array integrated on metal (Au) film. To achieve dual-band VOC gas sensing, two absorption peaks related to the surface lattice resonance (SLR) and surface plasmon polaritons (SPP) resonance are constructed in this plasmonic structure, to match the near-infrared absorption bands of methane and ethanol gas molecules respectively. For an 80 nm thick Au layer, the height and width of ZIF-8 patch and the gap between ZIF-8 patches are optimized to be 0.86, 0.925, and 0.43 μm. Then, this structure shows an SLR at 1392.64 and a SPP resonance at 1653.72 nm, which have peak intensities of 0.735 and 0.855, and the Q-values of 1435 and 253, respectively. Furthermore, the third resonance peak related to the Fano resonance is investigated and can be considered as a feasible alternative to calibrate the measurement without external references.
We report the fabrication of high performance inverted polymer solar cells with simply modified indium tin oxide (ITO) by an ultrathin aluminum (Al) and sodium chloride (NaCl) composite layer. The device efficiency and stability were both improved. The optimized device with poly(3-hexylthiophene) as the donor and [6,6]-phenyl-C61-butyric acid methylester as the acceptor under AM 1.5 (100 mw cm−2) radiation achieved a high power conversion efficiency of 3.88% with an open-circuit voltage of 0.60 V and a fill factor of 0.61, which is significantly higher than those of the inverted devices with only Al or NaCl as modification interlayer, respectively. Moreover, the stability is enhanced by about 70% more than that of the conventional device. The significant enhancement is attributed to the reduced work function of ITO electrode from 4.75 to 3.90 eV by modification as well as the improvement of the electrode interface.
We demonstrate an ultra-narrow-band mode-selection method based on a hybrid-microsphere-cavity which consists of a coated silica microsphere. Optical field distribution and narrow-band transmission spectrum of the whispering gallery modes (WGM) are investigated by finite-difference time-domain method. WGM transmission spectra are measured for microsphere and tapered fibers with different diameters. A high refractive index layer coated on the microsphere-cavity make the Q factor increased, the transmission spectrum bandwidth compressed and the side-mode suppression ratio increased. Parameters of the hybrid-microsphere-cavity, namely, the coated shell thickness and its refractive index are optimized under different excitation light source as to investigate the whispering-gallery-modes’ transmission spectrum. The 3dB bandwidth of the proposed filter can be less than MHz which will have great potential for applications in all-optical sensing and communication systems.
A fiber-wireless sensor system based on a power-over-fiber technique is developed to offer a flexible, distributed sensing ability over a middle distance, especially under environments that are sensitive to electromagnetic interference. In this system, the optical energy of a high-power laser in the base station is transmitted via a fiber and then converted into electrical energy by a photovoltaic power converter (PPC) in the remote unit. This optically power-supplied remote unit operates as the coordinator in the wireless sensor network (WSN) and exchanges the sensing information with the base station via another fiber. In our demonstration system, the sensing information can be collected by a WSN 2 km away and be transmitted back. In order to improve the power supply ability of PPC, a maximum power point tracking technique is applied. More than 80% of PPC’s maximum output power can be obtained. Moreover, to reduce the power consumption of the remote unit and the sensor nodes, a simple and stable low-power communication protocol is designed.
We report on the construction of a pulse-pumped fiber laser using highly doped gain fiber within a ring-shaped all-fiber
resonator. The pump laser is pulse modulated and coupled into a segment of highly doped Erbium doped fiber. The ring
cavity is close-looped in an all-fiber manner. The pulsed-lasing in kHz repetition rate down to single-shot operation are
tunable by pulsed-modulation of the pump laser and tuning of an intracavity variable optical coupler. The lasing power
increases for a higher pump pulse energy and repetition rate which sets the limit of the output pulse energy. We measure
the time-domain characteristics of the lasing pulses and analyze the dynamical property of the pulsed-pumping process
theoretically based on time-dependent rate equation.
Visible light communication (VLC) has been regarded as a promising solution in short-range intelligent communication
system. Nowadays, the research is focused on integrating the multi-input multi-output (MIMO) technique in the VLC
system, to achieve a larger transmission capacity and stronger transmission reliability. However, one important issue
should be addressed due to the use of MIMO technology: the multipath inter-symbol interference. The multipath intersymbol
interference comes from the reflection of the signal in the room and channel crosstalk between different
channels. In this paper, we propose a novel optical system used in the MIMO VLC system to reduce multipath
interference dramatically. Signals from different LEDs can be separated by using parabolic lens plated with reflecting
film. This structure can reduce the reflection effect effectively as well. We present the simulation results to observe the
distribution of optical power on the imaging plane for various receiving positions and low correlation between all
channels. We can find that the optical power density becomes stronger than non-imaging system and the interference is
sharply decreased, thus the SNR and BER are also optimized. Analysis about the optical system is given in this paper.
The fine manipulations of cylindrical vector beams (CVBs) based on metallic microstructures, such as sub-wavelength
focusing, have entered many interdisciplinary areas, and the important applications have been found in many fields
including optical micromanipulation, super-resolution imaging, micro-machining and so on. But so far, the
sub-wavelength focusing of azimuthally polarized beams is encountered, since the manipulation mechanisms rely
heavily on the excitation of surface plasmon polaritons, which brings the polarization limitation. We theoretically
investigated the focusing behavior of CVBs in 1D metallic photonic crystals (MPCs). The simulation results show that a
1D MPC plano-concave lens can focus cylindrical vector beams into scale of sub-wavelength. The negative refraction at
the interface between the air and the 1D MPC is analyzed at the frequencies corresponding to the second photonic band,
which makes the 1D MPC has the ability to focus higher Fourier components of light beams. The cylindrical
plano-concave structure is constructed to focus the radially and azimuthally polarized beams simultaneously. The
behavior is demonstrated by Finite Element Method (FEM). The shape of focusing field can be tailored, by changing the
polarization ratio of the incident beams. In addition, the effective sub-wavelength focusing phenomenon can also be
realized in variety of wave ranges, by choosing the proper materials and adjusting the parameters. We believe that it’s the
first time to realize the simultaneous sub-wavelength focusing of radially and azimuthally polarized beams, the
application of which is quite promising in broad prospects.
KEYWORDS: Sensing systems, Power supplies, Solar cells, Sensors, Active remote sensing, Internet, Active optics, Solar energy, Phase only filters, Resistance
Internet Of Things (IOT) drives a significant increase in the extent and type of sensing technology and equipment.
Sensors, instrumentation, control electronics, data logging and transmission units comprising such sensing systems will
all require to be powered. Conventionally, electrical powering is supplied by batteries or/and electric power cables. The
power supply by batteries usually has a limited lifetime, while the electric power cables are susceptible to
electromagnetic interference. In fact, the electromagnetic interference is the key issue limiting the power supply in the
strong electromagnetic radiation area and other extreme environments. The novel alternative method of power supply is
power over fiber (PoF) technique. As fibers are used as power supply lines instead, the delivery of the power is
inherently immune to electromagnetic radiation, and avoids cumbersome shielding of power lines. Such a safer power
supply mode would be a promising candidate for applications in IOT. In this work, we built up optically powered active
sensing system, supplying uninterrupted power for the remote active sensors and communication modules. Also, we
proposed a novel maximum power point tracking technique for photovoltaic power convertors. In our system, the actual
output efficiency greater than 40% within 1W laser power. After 1km fiber transmission and opto-electric power
conversion, a stable electric power of 210mW was obtained, which is sufficient for operating an active sensing system.
While monolithic integration especially based on InP appears to be quite an expensive solution for optical devices,
hybrid integration solutions using cheaper material platforms are considered powerful competitors because of the high
freedom of design, yield optimization and relative cost-efficiency. Among them, the polymer planar-lightwave circuit
(PLC) technology is regarded attractive as polymer offers the potential of fairly simple and low-cost fabrication, and of
low-cost packaging. In our work, polymer PLC was fabricated by using the standard reactive ion etching (RIE)
technique, while other active and passive devices can be integrated on the polymer PLC platform. Exemplary polymer
waveguide devices was a 13-channel arrayed waveguide grating (AWG) chip, where the central channel cross-talk was
below -30dB and the polarization dependent frequency shift was mitigated by inserting a half wave plate. An optical 900
hybrid was also realized with one 2×4 multi-mode interferometer (MMI). The excess insertion losses are below 4dB for
the C-band, while the transmission imbalance is below 1.2dB. When such an optical hybrid was integrated vertically
with mesa-type photodiodes, the responsivity of the individual PD was around 0.06 A/W, while the 3 dB bandwidth
reaches 24 ~ 27 GHz, which is sufficient for 100Gbit/s receivers. Another example of the hybrid integration was to
couple the polymer waveguides to fiber by applying fiber grooves, whose typical loss value was 0.2 dB per-facet over a
broad spectral range from 1200-1600 nm.
The finite-difference time-domain (FDTD) method, which solves time-dependent Maxwell’s curl equations numerically,
has been proved to be a highly efficient technique for numerous applications in electromagnetic. Despite the simplicity
of the FDTD method, this technique suffers from serious limitations in case that substantial computer resource is
required to solve electromagnetic problems with medium or large computational dimensions, for example in high-index
optical devices. In our work, an efficient wavelet-based FDTD model has been implemented and extended in a parallel
computation environment, to analyze high-index optical devices. This model is based on Daubechies compactly
supported orthogonal wavelets and Deslauriers-Dubuc interpolating functions as biorthogonal wavelet bases, and thus is
a very efficient algorithm to solve differential equations numerically. This wavelet-based FDTD model is a
high-spatial-order FDTD indeed. Because of the highly linear numerical dispersion properties of this high-spatial-order
FDTD, the required discretization can be coarser than that required in the standard FDTD method. In our work, this
wavelet-based FDTD model achieved significant reduction in the number of cells, i.e. used memory. Also, as different
segments of the optical device can be computed simultaneously, there was a significant gain in computation time.
Substantially, we achieved speed-up factors higher than 30 in comparisons to using a single processor. Furthermore, the
efficiency of the parallelized computation such as the influence of the discretization and the load sharing between
different processors were analyzed. As a conclusion, this parallel-computing model is promising to analyze more
complicated optical devices with large dimensions.
Applying coherent detection technique to advanced modulation formats makes it possible to electronically compensate
the signal impairments. A key issue for a successful deployment of coherent detection technique is the availability of
cost-efficient and compact integrated receivers, which are composed of an optical 90° hybrid mixer and four photodiodes
(PDs). In this work, three different types of optical hybrids are fabricated with polymer planar lightwave circuit (PLC),
and hybridly integrated with four vertical backside illuminated III-V PDs. Their performances, such as the insertion loss,
the transmission imbalance, the polarization dependence and the phase deviation of 90° hybrid will be discussed.
In this work, a direct DQPSK receiver was fabricated, which comprises a polymer waveguide based delay-line
interferometer (DLI); a polymer based optical hybrid, and two monolithic pairs of > 25 GHz bandwidth photodiodes that
are vertically coupled to the polymer planar lightwave circuit (PLC) via integrated 45° mirrors. The common mode
rejection ratio (CMRR) is used to characterize the performance of coherent receivers, by indicating the electrical power
balance between the balanced detectors. However, the standard CMRR can only be measured when the PDs can be
illuminated separately. Also, the standard CMRR does not take into account the errors in the relative phases of the
receiver outputs. We introduce an adapted CMRR to characterize the direct receiver, which takes into account the
unequal responsivities of the PDs, the uneven split of the input power by the DLI and hybrid, the phase error and the
extinction ratio of the DLI and hybrid.
All-optical wavelength converters (AOWCs) based on nonlinear processes of semiconductor optical amplifiers (SOAs) have attracted interest to overcome the wavelength blocking issues in future transparent networks. While many schemes work well, pattern effect impairments that are due to the finite lifetime of charge carriers are an issue most of the time. Recently, wavelength conversion and pattern effect mitigation techniques that work by properly shaping the passband of filters following the converter have been introduced. However, due to the necessity of selecting filter slope and position precisely, one would expect that the schemes are extremely sensitive to any drift of the center wavelength. In this work, we demonstrate a 40 Gbit/s SOA-based wavelength converter with more than 15 dB dynamic input power range. In addition, the center wavelength of the converted signal has a tolerance of ~0.2 nm towards the red spectral region and of ~0.1nm towards blue spectral region, respectively. This success is due to combining advantageously pattern effect mitigation techniques connected to the pulse reformatting optical filter, the red-shift and the blue-shift optical filter.
Wavelength converters for phase sensitive modulation formats based on semiconductor optical amplifiers
are discussed. Advantages and limits are discussed based on an actual implementation.
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