Switch Recovery Time Research Articles

High-performance self-powered UV photodetectors using SnO2 thin film by reactive magnetron sputtering

Self-powered UV photodetector (UVPD) operates without the need for an external energy source and contributes to global energy conservation. With ongoing innovation, self-powered PDs are becoming increasingly appealing for industrial and innovation applications such as advanced environmental monitoring and communication devices. This study investigates the influence of varying working pressures (ranging from 3 to 15 mTorr) during reactive magnetron sputtering on the crystalline structure, surface morphology, and performance of SnO2 thin film photodetectors, aiming to fabricate self-powered UVPDs. The SnO2-based UVPD demonstrates exceptional self-powered UV photodetection capabilities, characterized by a sensitivity of 6.41×105%, responsivity of 0.09 mA/W, and detectivity of 2.99×1010 Jones. In addition, SnO2-based UVPD possesses a switching photo response and recovery time of 0.75 and 0.99 s. Henceforth, it was observed that 8 mTorr SnO2 thin film exhibits exceptional stability, superior photodetector performance, and remarkable repeatability, rendering them highly suitable for UVPD applications. Notably, these films demonstrate sustained functionality for approximately 100 days without necessitating encapsulation. These excellent results confirm that SnO2 thin films are suitable for fabricating future smart optoelectronics devices.

Ratiometric Sensor Based on PtOEP-C6/Poly (St-TFEMA) Film for Automatic Dissolved Oxygen Content Detection.

A ratiometric oxygen sensor based on a platinum octaethylporphyrin (PtOEP)–coumarin 6 (C6)/poly (styrene-trifluoroethyl methacrylate) (poly (St-TFEMA)) film was developed for automatic dissolved oxygen (DO) detection. The oxygen-sensing film according to the dynamic quenching mechanism was prepared by embedding platinum octaethylporphyrin (PtOEP) and coumarin 6 (C6) in poly (styrene-trifluoroethyl methacrylate) (poly (St-TFEMA)). The optical parameter (OP) was defined as the ratio of the oxygen-insensitive fluorescence from C6 to the oxygen-sensitive phosphorescence from PtOEP. A calibration equation expressing the correlation between the OP values and DO content described by a linear function was obtained. A program based on the Labview software was developed for monitoring the real-time DO content automatically. The influence of the excitation intensity and fluctuation on the OP values and the direct luminescence signal (integration areas) was compared, verifying the strong anti-interference ability of the sensor. The detection limit of the sensor was determined to be 0.10 (1) mg/L. The switching response time and recovery time of the sensor were 0.4 and 1.3 s, respectively. Finally, the oxygen sensor was applied to the investigation of the kinetic process of the DO content variation, which revealed an exponential relationship with time.

High-contrast and low-power all-optical switch using Fano resonance based on a silicon nanobeam cavity.

We experimentally demonstrate an ultra-compact all-optical switch involving Fano resonance based on a side-coupled Fabry-Perot (F-P) resonator and a silicon photonic crystal (PhC) nanobeam cavity, with an area of only 11 μm2. By optimizing the structure of the nanobeam cavity to increase its intrinsic quality factor (Q), we achieve a sharp asymmetric transmission spectrum, with an extinction ratio (ER) as high as 40dB and a peak loss as low as 0.6dB. As far as we know, this is the highest measured ER in PhC-based Fano resonance. These excellent properties enable us to realize an all-optical switch with shorter switching recovery time, lower power consumption, and higher contrast, compared to that involving Lorentzian resonance. For example, under signal trains of 2.5Gb/s, switching energy with a contrast of 3dB for the Fano case is 113fJ, which is 8dB smaller than that for the Lorentzian case. Furthermore, by performing blue-detuned filtering on the 15-Gb/s output signal light, the switching contrast of the all-optical switch based on Fano resonance is significantly improved from 0.67dB to 9.53dB.

Ultra-compact multi-channel all-optical switches with improved switching dynamic characteristics.

We propose and demonstrate four-channel all-optical switches based on silicon photonic crystal (PhC) nanobeam cavities, with an area of only 31 μm2 per channel. For these switches, signal extraction and rejection functions have been successfully demonstrated while the signal speed is limited to 2.5 Gb/s due to the slow switching recovery process in silicon. In order to improve the signal speed, first, a blue-detuned filtering method is employed to suppress the slow switching recovery tails of the output signal light based on passive resonant devices. The suppressing mechanism relies on the extraction of the large blue-chirped component in the fast rising edge, while suppressing the red-chirped component in the slow switching recovery tail. A detailed theoretical model is established to analyze the improvement mechanism of the switching dynamic characteristics in the silicon PhC nanobeam cavity. Moreover, the simulated and experimental results have both shown that the switching recovery time of the output signal light is greatly reduced from 500 ps to 50 ps. Thus, the processing of 10-Gb/s optical signals has been experimentally demonstrated with the help of the blue-detuned filtering method.

High‐Performance Electrofluorochromic Devices Based on Electrochromism and Photoluminescence‐Active Novel Poly(4‐Cyanotriphenylamine)

A novel electrochromism (EC) and photoluminescence (PL)‐active poly(4‐cyanotriphenylamine) (CN‐PTPA) is prepared by oxidative coupling polymerization from 4‐cyanotriphenylamine (CN‐TPA) using FeCl3 as an oxidant. The high‐performance electrofluorochromic (EFC) devices using CN‐PTPA thin film with photoluminescent quantum yield of 21.9% as active layer are readily fabricated and reveal the highest fluorescent contrast ratio (I off/I on) of 242 between the fluorescent (neutral) state and the non‐fluorescent (oxidized) state, rapid response time shorter than 0.4 s, and excellent EFC stability longer than 9000 s. Furthermore, by introducing viologen into electrolyte as a counter EC layer for charge balance, the resulting EFC device exhibits notable improvement in reducing oxidation potential (from 2.30 V to 1.55 V) and switching recovery time (from 78 to 38 s) with enhanced fluorescent contrast ratio during pulse on/off multi‐cyclic scanning. These results demonstrate that incorporation of the EC and PL‐active CN‐PTPA is a facile and feasible approach to prepare highly efficient EFC devices.

Ultrafast optical control of terahertz surface plasmons in subwavelength hole arrays at room temperature

We demonstrate optical control of surface plasmon enhanced resonant terahertz transmission in two-dimensional subwavelength metallic hole arrays fabricated on gallium arsenide based substrates. Optically pumping the arrays creates a conductive layer in the substrate, reducing the terahertz transmission amplitude of both the resonant mode and the direct transmission. Under low optical fluence, the terahertz transmission is more greatly affected by resonance damping than by propagation loss in the substrate. An ErAs:GaAs nanoisland superlattice substrate is shown to allow ultrafast control with a switching recovery time of ∼10 ps.

Carrier Diffusion and Recombination in Photonic Crystal Nanocavity Optical Switches

Carrier dynamics in silicon photonic crystal (PhC) nanocavities are studied numerically. The results agree well with previous experimental demonstrations. It is shown that the presence of carrier diffusion makes fast switching possible, which is an advantage of nanocavity switches over other types of larger carrier based nonlinear optical switches. In particular, diffusion is effective in PhC nanocavity switches, which makes the switching recovery time even faster than that of silicon waveguide-based optical switches. In addition, calculations suggest that the thermo-optic effect can be reduced if the carriers are extracted within a few 100 ps by introducing a p-i-n structure.

Ultrafast optical switching of terahertz metamaterials fabricated on ErAs/GaAs nanoisland superlattices

We demonstrate optical switching of electrically resonant terahertz planar metamaterials fabricated on ErAs/GaAs nanoisland superlattice substrates. Photoexcited charge carriers in the superlattice shunt the capacitive regions of the constituent elements, thereby modulating the resonant response of the metamaterials. A switching recovery time of 20 ps results from fast carrier recombination in the ErAs/GaAs superlattice substrates.

Fast all-optical switching using ion-implanted silicon photonic crystal nanocavities

On-chip all-optical switching based on the carrier plasma dispersion in an argon ion (Ar+) implanted photonic crystal (PhC) nanocavity that is connected to input/output waveguides is described. A high dose of Ar+ is introduced, and annealing is used to recrystallize the silicon and thus create dislocation loops at the center of the PhC slab. Dislocation loops enable the fast recombination of the carriers, which allows a fast switching recovery time for PhC switches. The switching window (∼70ps) is three times smaller than that without ion implantation, while the required operating energy remains almost the same (<100fJ).

Wavelength conversion of 1.53-microm-wavelength picosecond pulses in an ion-implanted multiple-quantum-well all-optical switch.

An ultrafast high-contrast all-optical switch produced from a metal-organic vapor phase epitaxy-grown wafer incorporating a 50-period InGaAsP/InGaAsP multiple-quantum-well (MQW) saturable absorber (SA) and a distributed Bragg reflector is described. Postgrowth implantation with 4-MeV nitrogen ions reduces the MQW free-carrier lifetime, and hence the switch recovery time, to 5.2 ps. Incorporation of the MQW SA in an optical cavity results in switching contrast ratios greater than 10 dB. The all-optical switch is used to perform wavelength conversion of 2-ps pulses.

Spin relaxation and all optical polarization switching at 1.52 micrometres in InGaAs(P)/InGaAsP multiple quantum wells

The spin relaxation times of electrons in InGaAs(P)/InGaAsP multiple quantum wells have been directly measured as a function of well width using an ultrashort pulse colour centre laser. The times measured range from 20 to 5 ps, considerably faster than previously determined in GaAs quantum wells. In addition, a fast, all-optical polarization switch based on a spin-sensitive optical nonlinearity is demonstrated at a wavelength of . This operating wavelength and the observed switch recovery time of 5.5 ps make it a potentially useful element for future all-optical soliton communication systems.

130 ps recovery of all-optical switching in a GaAs multiquantum well directional coupler

A significantly improved recovery time of 130 ps has been achieved in an all-optical zero-gap directional coupler containing multiple quantum wells. The mechanism for the all-optical switching is due to free-carrier induced refractive nonlinearities at near-band-gap resonant frequencies. The large reduction in the switch recovery time was obtained by the application of an external dc bias which sweeps out the carriers from the quantum wells. From our experimental results on the laser pulse width limited switch-up time of 2 ps, we <m1;&37>deduce that the contribution of self-electro-optic effect nonlinearity is negligible in this case.

Optimal design of high current superconducting switches and the feasibility of their testing

We have designed a superconducting switch for optimum heat transfer from a high current carrying superconducting thin film to the substrate. This design is based upon the acoustical matching of the different layers of the compound substrate. The switch-recovery time is considered to be of the order of 1 μsec. The design of a magnetic triggering circuit that generate high current field (of approximately 1500 A/cm) pulses of 1 μsec duration has also been demonstrated. A simple LC circuit is employed to generate high current oscillations of 0.25 MHZ frequency. The optimum parameters of this circuit have been computed.

Broadband, high-power, coaxial arc discharge switch

This paper describes a new type of microwave coaxial gas switch tube which utilizes an electronically controlled pulsed hydrogen arc discharge. The device fires in a few tenths of a microsecond and recovers in a time of the order of 10 microseconds. It covers a frequency range extending from below 1 Gc/s to above 4 Gc/s. The tube operates over a wide range of pulsed peak input powers, from microwatts to hundreds of kilowatts, depending upon the particular application. Its unfired insertion loss and its arc loss are of the order of 0.1 db and 1 db respectively and its leakage isolation exceeds 50 db. The tube consists of a section of 7/8 coaxial line sealed off at each end by ceramic windows. Portions of the inner and outer conductors are gridded and together with a heated cathode and an anode provide an electrode structure similar to that in conventional hydrogen thyratrons. A number of tubes utilizing different electrode structures have been built and tested and are described. Switching is accomplished by creating an arc between the electrodes. Upon application of a trigger voltage, a previously charged pulse forming network discharges through the tube, The resultant electron density is of the order of 1012per cm3and acts like a short circuit to the incident microwaves. The results of measurements of the switch's firing time, recovery time, insertion loss, leakage, holdoff power and noise figure at both L and S-bands are presented and discussed.