An optical sensor for temperature measurement with much higher reflected light power based on Fresnel reflection and a collimator is presented. The sensor includes only a light source, three couplers, two photodetectors and two sensing ends. One of the sensing ends is designed with a collimator which is covered by solidified epoxy resin with an oil-paper cover, and another is a fiber end with protective cladding. The measurement principle is based on relative Fresnel reflective intensity. Various ambient temperatures are measured in the experiment. The measured data is fitted to linear equation very well. Experiment is implemented by comparing the performances of the fiber-sensor and the collimator-sensor, and the latter shows a much higher reflected light power which means a high signal to noise ratio (SNR) and longer measurement distance may be gained. This is very important and useful for long distance measurement and the situation of many sensors working in parallel mode, which is sensitive to the reflected light power.
Photonic waveguides are fundamental components for photonic integrated circuits (PICs). Although a wide spectrum of nanophotonic structures, i.e., silicon waveguides and plasmonic waveguides, have been exploited for optical interconnects, these structures either can only support one polarization or they are not able to be integrated within a 1-μm scale due to strong crosstalk. The hurdle for high-density information transmission and waveguide integration is mainly the lack of a compact waveguide structure that can support different polarization states with low crosstalk. We propose and numerically demonstrate an ultralong-range waveguide that supports both transverse electric- and transverse magnetic-like polarizations. The propagation length of this waveguide is several decimeters with working bandwidths as great as 160 nm for both polarizations. In addition, this design is very compact with a small center-to-center distance of 1 μm between two adjacent waveguides while the isolation is as high as more than 69.3 dB. This waveguide is also able to guide light efficiently through a 90 deg bend with a 1-μm bending radius for both polarizations. Our work opens new perspectives for high-density waveguide integration in PICs, which would benefit various applications with limited physical space, such as on-chip information processing and sensing.
A simple fiber-optic relative humidity sensor based on cellulose acetate butyrate (CAB) and Fresnel reflection is proposed and investigated theoretically and experimentally. The sensing system is only composed of one light source, three optical couplers, two photo-detectors and two fiber sensing ends. The operation principle is based on relative Fresnel reflection and water-absorption characteristic of the CAB which simultaneously contains hydrophilic and hydrophobic groups. The water absorption process will lead to variation of the CAB’s refractive index or permittivity. It has to be noted that the double-channel system can effectively eliminate the intensity fluctuation of the light source and the influence of the environment. In this paper, the relative humidity environments approximately ranging from 10 % to 100% are generated and measured both in the humidification and dehumidification processes, which shows a good repeatability and reveals a very good fitting feature with a high value of R2 above 0.99. It is of reflection type and can be simply extend to be a multi-point-monitoring system. The sensing system is of cost- effective, simple operation and high precision.
A long-range air-gaps assisted subwavelength waveguide is proposed and demonstrated. The configuration can be interpreted as a combination of a silicon waveguide and a metal–dielectric–metal (MDM) waveguide. Unlike the conventional MDM waveguide, the proposed waveguide is polarization insensitive because long propagation lengths can be achieved by both the transverse electric (TE) and transverse magnetic (TM) polarizations. The propagation length of this waveguide can even be up to decimeters. Moreover, this design is very compact with only a 1.05 μm center-to-center separation between two adjacent waveguides, while the waveguide isolation is >58 dB. Also, it is capable of guiding light effectively (>97% transmittance) through a 90 deg bend with a small bending radius (1 μm). These unique features make the proposed waveguide a promising candidate for the future large-scale photonic integrated circuits.
An innovative wavelength division multiplex-radio over fiber-passive optical network architecture for multiple access points (AP) based on multitone generation and triple sextupling frequency is proposed and demonstrated. A dual-drive Mach–Zehnder modulator (DD-MZM) is utilized to realize the multitone generation. Even sidebands are suppressed to make the adjacent frequency separation twice the frequency of the local oscillator by adjusting the modulation voltage of the DD-MZM. Due to adopting three fiber Bragg gratings to reflect the unmodulated sidebands for uplink communications source free at optical network unit (ONU), is achieved. The system can support at least three APs at one ONU simultaneously with a 30 km single-mode fiber (SMF) transmission and 5 Gb/s data rate both for uplink and downlink communications. The theoretical analysis and simulation results show the architecture has an excellent performance and will be a promising candidate in future hybrid access networks.
KEYWORDS: Radio over Fiber, Optical networks, Modulation, Radio optics, Modulators, Optical engineering, Single mode fibers, Oscillators, Clocks, Fiber Bragg gratings
We propose a duplex multiple-user radio over fiber-passive optical network (ROF-PON) system based on multitone generation and sextupling technique. A dual-drive Mach–Zehnder modulator (DD-MZM) is used to realize the multitone generation. By controlling the modulation voltage of the DD-MZM, the odd carriers can be suppressed which makes the adjacent frequency gap twice the frequency of the local oscillator frequency. Due to the multitone generation and pure carrier reuse technique, the base stations (BSs) are also source-free. The system can support more than one BS simultaneously for a transmission length more than 50 km. The proposed multiuser ROF-PON is scalable and cost-effective, and its feasibility is successfully verified by simulation.
KEYWORDS: Orthogonal frequency division multiplexing, Single mode fibers, Modulators, Dense wavelength division multiplexing, Optical amplifiers, Radio over Fiber, Receivers, Signal generators, Signal attenuation, Signal detection
We propose and demonstrate a full-duplex dense wavelength division multiplexing (DWDM) radio over fiber (ROF) system transmitting multibands wired and wireless orthogonal frequency division multiplexing (OFDM) signals. In a central station, an optical signal noise ratio (OSNR)-boosted multicarriers generator based on recirculation frequency shifter (RFS) is used to generate multicarriers. Sixty-six frequency-lock and coherent, 25 GHz frequency-spacing subcarriers with OSNR larger than 26 dB with an amplitude difference of 5 dB are generated and used to transmit downstream data. Since these subcarriers are coherent with each other, n-fold frequency optical millimeter-wave signals can be generated. Without using costly W-band components, a 20 Gbps downstream transmission operation at 75 GHz is experimentally validated. The power penalty of less than 3 dB was observed after a 50-km single mode fiber (SMF) and 4-m wireless transmission. In order to realize the full duplex system, a 1.2 GHz bandwidth reflective semiconductor optical amplifier (RSOA) is used to achieve 5 Gbps upstream traffic for 16QAM-OFDM signals. The measured power penalty of 3 dB is observed after a 50-km SMF transmission at the bit error rate of 3.8×10 −3 .
We propose and demonstrate a full duplex dense-wavelength-division-multiplexing radio-over-fiber (DWDM-ROF) system for transmitting 75-GHz W-band frequency multiple-input multiple-output orthogonal-frequency-division-multiplexing (MIMO-OFDM) signals with 12 Gbps downstream and 6 Gbps upstream. The downstream transmitting terminal is based on a three-channels sextupling-frequency scheme using an external modulation of a distributed feedback laser diode (DFB-LD) and dual drive Mach-Zehnder modulator (DD-MZM) for carrying downstream signals. MIMO-OFDM algorithms effectively compensate for impairments in the wireless link. Without using costly W-band components in the transmitter, a 12 Gbps downstream transmission system operation at 75 GHz is experimentally validated. For the downstream transmission, a power penalty of less than 3 dB was observed after a 50 km single mode fiber (SMF) and 4 m wireless transmission at a bit error rate (BER) of 3.8×10 −3 . For the upstream transmission, we use a commercially available 1.5 GHz bandwidth reflective semiconductor optical amplifier (RSOA) to achieve 6 Gbps upstream traffic for 16 QAM-OFDM signals. A power penalty of 3 dB was observed after a 50 km SMF transmission at a BER of 3.8×10 −3 . The frequency of the local oscillator is reduced due to the frequency sextupling scheme. The cost of the proposed system is largely reduced.
A simple fiber optic temperature sensor with a micro Fabry-Perot cavity constructed with a thin film coated on a fiber end is presented. Its operation principle is based on the temperature-dependent wavelength shift of the interference fringes formed by Fresnel reflections from both interfaces of the thin film. An analytical formula is derived from the theory of two-beam interference. Experimental temperature data agree with the theoretical result. A temperature resolution of 0.1 K within the range from 20 to 100 °C with good stability can be achieved. The proposed temperature sensor has a simple, solid, and compact structure.
In this paper, a scheme for all-optical AND gate which exploits the cross-phase modulation (XPM) effect in an
asymmetric semiconductor-optical-amplifier-assisted Mach-Zehnder Interferometer (SOA-MZI) has been proposed for
the first time. No additional input beam such as a clock signal or continuous light is employed in the design, which is
required in other AND operations. The scheme is validated and the system performance under various parameters is
investigated through numerical simulations. This logic gate is helpful for future all-optical signal processing
configurations.
Photonic crystals(PCs)have many potential applications because of their ability to control light-wave propagation. In
this paper, we theoretically investigate the tunability of light propagation in photonic crystal waveguides in
two-dimensional photonic crystals with square lattices composed of heat-resistant silicon resin. Waveguides can be
obtained by the infiltration of silicon resin into air regions in two-dimensional photonic crystals composed of air holes
with square lattices of dielectric cylinders. The refractive index of silicon resin can be changed by manipulating the
temperature of the sample. Numerical simulation by solving Maxwell's equations using the plane wave expansion(PWE)
method shows that the band gaps can be continuously tuned by silicon resin, accordingly the light propagation in
photonic crystal waveguides can be controlled. The band gap is analyzed in the temperature range of 20°C-120°C. In our
work, the gap map for a square lattice of dielectric cylinders is also simulated. The method can separate TM- and
TE-polarized modes in the waveguide. Such a mechanism of band gap adjustment should open up a new application for
designing field-sensitive polarizer in photonic integrated circuits.
The theoretical analysis of a flat-top AWG with multimode interference (MMI) power splitter at the input end is done. Several corrections to the former papers are made. For example, the field coupled into the arrayed waveguides is not treated with approximation, and domain of integration for coupling coefficient of an arbitrary waveguide in the array is chosen to be the waveguide spacing, which is coincident with the real optical propagation in AWG. Expressions for spatial distribution of field are obtained at the interfaces between waveguides, while an analytic expression for each channel response of AWG is derived. All of the expressions obtained are the functions of AWG configuration parameters. The output response of each channel is obtained by the analytic method much more quickly than by beam propagation method (BPM), and the period of optimization design of AWG is shortened greatly. Finally, a design example of flat-top AWG with good performance is presented, and its important specifications are calculated.
KEYWORDS: Mode locking, Mirrors, Resonators, Solid state lasers, Chemical elements, Crystals, Laser crystals, Nonlinear crystals, Gaussian beams, System on a chip
An analytical solution for hard-aperturing Kerr lens mode locking of compact three-element resonators is derived using nonlinear ABCD ray matrix method. The dependence of the hard-aperturing Kerr nonlinear strength on aperture position and other cavity parameters is discussed. Selection guidelines on aperture position, and other cavity parameters for effective KLM are provided.
Photoluminescence (PL), time-resolved photoluminescence (TRPL) and photoconductivity (PC) measurements were used to investigate the excitation transfer (ET) and charge transfer (CT) processes occurring in the poly(N- vinylcarbazole)(PVK)/C60 and poly(2-methoxy-5-(4-bromo- butoxy) phenylene vinylene)(MBB-PPV)/C60 combination films. The transferring excitation energy from the excited states of polymers to C60, PL intensity quenching and lifetime shortening of polymers were observed from PL and TRPL measurement while great enhancement in PC measurement of multilayer polymer/C60 film was also obtained.
Aberrative nonlinear transfer matrices are introduced to treat the propagation of laser beam in Kerr medium with thermal lensing. The dependence of mode-locking regions on cavity symmetry and the distance between the fold mirror and the crystal, and the optimal agreement for Kerr-lens mode- locking are discussed with ABCD matrix method.
Visible photoluminescence from crystallized a-Si:H/a-SiNx:H multilayers has ben observed at room temperature. Analyses using transmission optical microscopy, scanning electron microscopy, and x-ray diffraction show that the laser crystallization of multilayer samples take place in the solid-phase crystallization region and the average crystalline grain size is limited by the thickness of the a-Si:H well-layer. The photoluminescence peak position increases with the decrease of well thickness, while the spectral width decreases. Photoluminescence decay time decreases with the decrease of the well thickness. The experimental results are in agreement with those obtained by calculations based on the quantum confinement model.
A laser microbeam system has been set up for microsurgery on cell. The relations of laser wavelength, pulse duration and pulse energy to punching effects and self-healing are studied. The experimental results demonstrate that picosecond pulse laser microbeam offers many advantages in cell microsurgery. The mechanism of punching by picosecond microbeam is high field puncture instead of heat effect, and is irrelevant to cell kinds and colors. The diameter and depth of microsurgery can therefore be easily controlled by adjusting the laser pulse energy. The diameter of the minimum aperture is about 0.1 micrometers , much smaller than the theoretical limit ((lambda) /2) for optical microscope due to self- focusing effect. With ultrashort pulse laser microbeam, we can easily cut off any part of a cell. An example is that eight nuclei in the center of unicellular parasite Pneumocystis Carinii can be destroyed one by one by ultrashort pulse laser microbeam without cell wall injury. The holes can also be punched by ultrashort pulse laser microbeam from cell wall to cell nucleus. In a fraction of a second to several seconds after punching, the hole on cell wall or cell membrane can self-heal. Exogenous DNA can be introduced into the cell before its self- healing.
ABCD transfer matrix theory was utilized to study the stability of a solid state laser with a Brewster-angle-cut active medium in a Z-fold cavity consists of two spherical and two flat mirrors. Analytic solutions of stability regions for CW operation have been obtained. These solutions allow easy analysis of the behavior of the stability regions when the resonator parameters are varied.
In this communication, the electron tunneling process in GaAs/AlGaAs asymmetric double quantum wells with different barrier thickness and doping pattern were studied by picosecond photoluminescence spectrum technique. Impurity-assisted sequence tunneling and coherent tunneling were excluded. An electron and hole resonant/nonresonant tunneling model were considered to explain the experimental data obtained.
The result of experimental studies of Photoluminescence (PL) in cis-transoid and trans-cisoid polyphenylacetylene were presented. The samples were prepared by a. newly-developed method using rare-earth metal catalyst. In contrast to polyacetylenea, the obtained PPA samples were soluble in common organic solvents and can be proceaaed into thin film. Comparing the results of diferent form of samples: powder, film and toluene solution samples, we concluded that, the observed fut PL decay is caused by the polaronic exciton radiative recombination, which will diminished when the inter-chain charge transfer took place, while the slow PL decay is related to the intra-chain bipolaron recombination.
Experimental demonstration of optical pulse slicing and pulse shaping by pumping a large core, liquid-filled waveguide with picosecond radiation are reported. Steepening of the optical pulses to the extend that the peak of an input pulse catches up and overpasses the rising edge is observed, which results in the pulse shape with a 'negative-like' rising edge. Significant pulsewidth reduction by over 20 fold is obtained. Based on the experimental results, a new mechanism of self trapping of picosecond radiation in a waveguide structure is proposed, which is shown to agree well with our experimental results.
The results show that some nonlinear interaction procses (x2 and x3) occur in LiB305, the upper limits of temporal parameters of the refractive index grating are 35ps, and no optical coupling effect is observed.
The dynamics of the carrier recombination in a-Si:H/a-SiN3:H multilayers has been investigated with picosecond photoluminescence spectroscopy. The thermalization of photogenerated carriers is a direct hopping process. The decay time cutoff, the mobility edge and the bandtail width vary non-monotonously with a turning point near x=O.85, which is attributed to the changes of the build-in field and the multilayer structure with nitrogen content.
An investigation of the time-resolved photoluminescence decay in glow-dischargingly deposited hydrogenated amorphous carbon is presented, the dependence upon substrat temperature, emission energy, and excitation energy has been investigated. Our measurements suggest the exciton recombination rather than the pair process. The photoluminescence decay time decreases with increasing substrat temperature, as result of enhancing nonradiative recombination. Comparisons with hydrogenated amorphous silicon are also made.
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