Input Optical Power Research Articles

Vulnerabilities in the quantum key distribution system induced under a pulsed laser attack

Quantum communication protocols are considered secure provided that all devices included in the system are fully characterized, and side channels are closed. However, as a result of laser radiation exposure, it is possible to change quantum communication systems components’ characteristics. This leads to vulnerabilities appearing in the quantum key distribution system. In this paper, we consider the effect of pulsed laser radiation on fiber-optic isolators used in quantum communication systems. Isolators protect the source of the system from attacking optical radiation coming from the “eavesdropping” side via the quantum channel. Lowering the isolation factor can bring the entire system out of a secure state. This gives an eavesdropper access to information about the secret key. The scenario of the most probable attack to the source of the quantum key distribution system via a pulsed laser was simulated. The experimental setup provided exposure of fiber isolators with pulsed laser radiation at a wavelength of 1064 nm (within the transparency window of the isolators) with a mean power up to 840 mW in four different pulse generation modes. The isolation factor and throughput of tested samples were monitored using a laser diode with a wavelength of 1550 nm and average power of 10.5 mW. Spectrally selective splitters were used to separate the lasers. It is shown that the isolation factor (isolator attenuation in the direction from the quantum channel to the system) at a wavelength of 1550 nm decreases from the initial value of 59.1 dB to 24.5 dB. The throughput (in the direction from the system to the quantum channel) at the same wavelength decreases from 0.6 dB to 1.2–12.3 dB or remains the same, depending on the acting pulsed laser radiation parameters. Temperature monitoring showed that the temperature of the isolator body changes insignificantly when exposed to pulsed radiation. The obtained effects of changing the isolation coefficient and throughput can be explained by the presence of nonlinear effects in the magneto-optical crystal of the isolator. The results of the work can be applicable in the practical evaluation of quantum communication systems security, in particular, the security evaluation of quantum key distribution systems. The results can be used to prepare the standards for certification procedures for assessing the security of quantum communication systems. The work gives recommendations for enhancing signal source unit security in quantum communication systems. Namely, as countermeasures to protect against the effects of pulsed laser radiation, it is proposed to set optical fuses with a limited threshold power, detectors for monitoring input optical radiation power, and narrow-band optical filters at the entrance of the quantum communication system.

Efficient Optically-Pumped Semiconductor Optical Amplifier in a Coupled-Waveguide Configuration: A Novel Proposal

We propose an efficient scheme of optical pumping and a compact design of an optically-pumped semiconductor optical amplifier (OP-SOA), with gain characteristics which are qualitatively similar to that of conventional (electrically-pumped) SOA. The optical pump is coupled into the ‘active waveguide’ from an adjacent channel waveguide, called ‘pump waveguide’; by suitably tailoring the coupling between the two waveguides, selective transfer of pump power all along the active waveguide can be achieved. We show that optical pumping through the coupled-waveguide configuration is efficient over the existing schemes of optical pumping in semiconductors. The optical pump can be coupled into the pump waveguide through a separate fiber-pigtail, just as the signal is coupled to the active waveguide in commercially available SOA. Thus, the OP-SOA would be a stand-alone 3-port integrated optical device, without any electrical connections. The proposed scheme enables optical-to-optical gain control, in place of the current-controlled gain in conventional SOA. Performance characteristics of the OP-SOA are simulated for an InGaAsP/InP heterostructure device using a well-established model. It is found that for an input optical pump power of 25 dBm at the wavelength of 1310 nm, a small signal gain >30 dB is achieved at the wavelength of 1550 nm.

Accurately modeling optical power supply with low optical input power

Accurately modeling optical power supply with low optical input power

Analysis of thermo-plasmonic lab-on-fiber probes in liquid environments

Lab-on-fiber (LOF) optrodes are recently emerging not only as valid platforms for biosensing, but also as promising light-controlled actuators in drug-delivery, optical trapping and thermo-ablation systems. In this regard, the thermo-plasmonic effect has been recognized as an intriguing tool for conferring to the optical fiber the capability of interacting with the external environment through the fine control of local overheating actuated by light in the range of few mW. However, the evaluation of the thermo-plasmonic overheating on small areas such as that of a standard single mode fiber tip is not trivial, especially in liquid solutions, where these probes typically operate. Here we demonstrate that by functionalizing the metallic nanostructure of LOF devices with a thermoresponsive smart materials, it is possible to measure the light-induced overheating on the fiber tip. Specifically, we monitored the plasmonic resonance wavelength shift induced by the temperature-dependent swelling dynamics of different microgel films deposited on the nanostructure. We find a local overheating of about 8 °C mW−1, i.e. also in line with our theoretical predictions based on numerical simulations. Our results demonstrate that the proposed approach is a valid methodology for the direct and continuous monitoring of the temperature changes in LOF devices induced by the input optical power in liquid environment. Our findings lay the basis for the analysis of thermo-plasmonic optical fiber probes exploitable in many applications, especially for the life science sector.

Magnetic-free silicon nitride integrated optical isolator

Integrated photonics enables signal synthesis, modulation and conversion using photonic integrated circuits (PICs). Many materials have been developed, among which silicon nitride (Si3N4) has emerged as a leading platform particularly for nonlinear photonics. Low-loss Si3N4 PICs have been widely used for frequency comb generation, narrow-linewidth lasers, microwave photonics and photonic computing networks. Yet, among all demonstrated functionalities for Si3N4 integrated photonics, optical non-reciprocal devices such as isolators and circulators have not been achieved. Conventionally, they are realized based on the Faraday effect of magneto-optic materials under an external magnetic field; however, it has been challenging to integrate magneto-optic materials that are not compatible with complementary metal–oxide–semiconductors and that require bulky external magnet. Here we demonstrate a magnetic-free optical isolator based on aluminium nitride (AlN) piezoelectric modulators monolithically integrated on low-loss Si3N4 PICs. The transmission reciprocity is broken by spatio-temporal modulation of a Si3N4 microring resonator with three AlN bulk acoustic wave resonators that are driven with a rotational phase. This design creates an effective rotating acoustic wave that allows indirect interband transition in only one direction among a pair of strongly coupled optical modes. A maximum of 10 dB isolation is achieved under 300 mW total radiofrequency power applied to three actuators, with minimum insertion loss of 0.1 dB. An isolation bandwidth of 700 MHz is obtained, determined by the optical resonance linewidth. The isolation remains constant over nearly 30 dB dynamic range of optical input power, showing excellent optical linearity. Our integrated, linear, magnetic-free, electrically driven optical isolator could be a key building block for integrated lasers and optical interfaces for superconducting circuits. An electrically driven, magnetic-free optical isolator is demonstrated. The device, based on aluminium nitride piezoelectric modulators and a silicon nitride microring resonator, may be useful for integrated lasers and other opto-electric systems.

Proposal of a Cascade Photonic Crystal XOR Logic Gate for Optical Integrated Circuits with Investigation of Fabrication Error and Optical Power Changes

A compact and simple structure is designed to create an all-optical XOR logic gate using a two-dimensional, photonic crystal lattice. The structure was implemented using three waveguides connected by two nano-resonators. The plane wave expansion method was used to obtain the photonic band gap and the finite-difference time-domain method was used to investigate the behavior of the electromagnetic field in the photonic crystal structure. Examining the high contrast ratio and high-speed cascade, all-optical XOR on a chip, the effects of fabrication error and the changes in the input optical power showed that the structure could be used in optical integrated circuits. The contrast ratio and data transfer rate of the cascade XOR logic gate were respectively obtained as 44.29 dB and 1.5 Tb/s. In addition, the designed structure had very small dimensions at 158.65 μm2 and required very low power to operate, which made it suitable for low-power circuits. This structure could also be used as a NOT logic gate. Therefore, an XNOR logic gate can be designed using XOR and NOT logic gates.

Performance optimization of RSOA based mm-wave radio-over-fibre access network

In this paper, a Reflective Semiconductor Optical Amplifier based, Radio-over-Fibre access network configuration has been proposed to feed future millimeter-wave radio systems. The system architecture combines several approaches to overcome the challenges of millimeter-wave signal transmission. Reflective semiconductor optical amplifier modulator realizes a colorless and relatively cost-effective Remote Antenna Unit. The same optical carrier is used for both downlink and uplink. Optical single-sideband modulation is used at the downlink, which is robust against chromatic dispersion, but the complex realization of this modulation format is not possible at the Remote Antenna Unit. Optical intermediate frequency transmission is applied at the uplink direction, and the required local oscillator signal originates from the central station. The critical element is the reflective optical amplifier, as it compensates for the optical loss and works as an external intensity modulator. The operation of the reflective optical amplifier is modeled by multisection rate and wave equation-based description. The amplification and modulation behaviors of an available reflective optical amplifier are also measured. The experimental work validated the colorless operation and the quality of the modulation versus bias current and input optical power. Finally, system simulation was realized. The uplink and downlink power budgets were balanced, and optimal values for the optical coupling rate and RSOA bias current have been selected.

Numerical analysis of dispersion and self-phase modulation for elimination of chaotic time delay

We mainly investigate the influence of group velocity dispersion (GVD) and self-phase modulation (SPM) in single-mode fiber on chaotic time delay signature (TDS) of single feedback semiconductor laser. In the simulation, the second-order dispersion coefficient and the average input optical power in fibers are adjusted to control GVD and SPM. The results show that after the fiber length reaches the dispersion length of the chaotic laser, the chaotic TDS caused by single optical feedback begins to be suppressed due to the significant enhancement of GVD, and then the value of the autocorrelation coefficient at the chaotic TDS descends at the fastest suppression rate of 0.5 dB/km. When chaos laser propagates about 20 km in the fibers, duo to the accumulation of SPM to the significant range of action, the chaotic TDS achieves the best stable suppression state, and the suppression effect can reach 11.6 dB.

High-performance germanium avalanche photodetector for 100 Gbit/s photonics receivers.

A high-bit rate and low-bias voltage waveguide-integrated vertical germanium avalanche photodetector is reported with doping optimization. This scheme alleviates the necessity of complex epitaxial single-crystal silicon layer and multiple ion implantation schemes. The optical absorption and carrier avalanche multiplication gain occur in the same germanium layer. The maximum gain is estimated to be 112.4 at an input power of -30.2dBm. With the input optical power of -16.1dBm, the gain-bandwidth product of nearly 141 GHz is obtained at 7.8 V bias. Meanwhile, a 4.6 dB sensitivity improvement for 60 Gbit/s signal reception is demonstrated with an avalanche gain of 5.1 at a soft-decision forward-error correction threshold (SD-FEC), i.e., bit-error-rate of 2×10-2. The absolute sensitivities of photonics receivers are -21, -18.6, -15.9, and -11.5dBm for 40, 60, 80, and 100 Gbit/s non-return-to-zero signals at the SD-FEC threshold. These demonstrated characteristics enable the reliable and robust on-chip photodetection for energy efficienct silicon photonic interconnects in the future.

A multi-frequency fiber optic acoustic sensor based on graphene-oxide Fabry-Perot microcavity

A multi-frequency fiber optic acoustic sensor (FOAS) based on graphene-oxide Fabry-Perot microcavity (GO-FPM) is proposed and demonstrated. The micrometer-size FP cavity is formed by a single-mode-fiber end surface and a layer of GO diaphragm. The GO diaphragm is used as the acoustic sensitive diaphragm to realize the acoustic signal detection. The performance of the GO-FPM FOAS for single-frequency, dual-frequency and triple-frequency acoustic signal detection is experimentally investigated. The influence of the input optical power and wavelength on sensor performance is also investigated. As for single-frequency acoustic signal detection, the signal to noise ratio (SNR) can be as high as 65.2 dB, with a broad frequency response ranged from 400 Hz to 20 kHz and a high linearity of ≈1. The SNRs for the dual-frequency and the triple-frequency acoustic signal detection can be >65.1 dB and >61.8 dB, respectively. The proposed GO-FPM FOAS have potential applications in structural health monitoring, fiber hydrophone, pipeline leakage detection, biomedicine, etc.

Robust and flexible photodetector from a solution derived nanowire networks of organometallic charge transfer complex

An organometallic charge transfer (CT) complex, viz, silver- tetracyanoquinodimethane (Ag-TCNQ) has been synthesized through solution self assembly. The as synthesized product characterized through scanning electron microscope (SEM), X-ray diffraction (XRD) and Raman spectroscopy indicated that highly crystalline, unidirectional, nanostructure network of Ag-TCNQ has been grown. The thin film of Ag-TCNQ based CT complex on flexible substrate exhibited excellent photoresponse characteristics under white light illumination, which is 5-fold higher than the pristine Ag nanoparticle based photodetector (PD). The modulation in photocurrent and responsivity of Ag-TCNQ PD was controlled with variation in input optical power, electrode bias and illumination wavelength. The PD displayed highest responsitivity, ca. 13.8 mA/W and photo to dark current ratio, ca. 9.2 at an optical power of 10.2 mW/cm2. The photocurrent of the device showed insignificant degradation (2.1%) when the substrate was subjected to cyclic tensile stress with bending endurance upto 500 cycles. The device also displayed outstanding opto-mechanical and optoelectronics properties by exhibiting stable, fast and reversible photo switching behavior under various tensile stress on the flexible substrate with outward bending along the conduction channel.

50-GHz-Bandwidth Membrane InGaAsP Electro-Absorption Modulator on Si Platform

We fabricate a membrane InP-based electro-absorption modulator (EAM), in which an InGaAsP-based multiple-quantum-well (MQW) absorption region is buried with an InP layer, on Si-waveguide circuits. By optical coupling between the MQW absorption region and Si core, a low-loss and large-absorption-length (300-μm-long) supermode waveguide is designed to suppress electric-field screening at high optical input power. The EAM is fabricated by combining direct bonding of the MQW layer and regrowth of the InP layer on a thin InP template bonded on a silicon-on-insulator wafer. The fabricated membrane EAM shows an on-chip loss of less than 4 dB at wavelengths over 1590 nm and temperatures from 25 to 50 °C. Since the membrane lateral p-i-n diode structure is beneficial for reducing the RC time constant of a lumped-electrode InP-based EAM, the EO bandwidth of the EAM is around 50 GHz without a 50-ohm termination up to fiber-input power of 10 dBm. Using the device, we demonstrate clear eye openings for 56-Gbit/s NRZ and 112-Gbit/s PAM4 signals at temperatures from 25 to 50 °C.

Optically Feeding 1.75 W With 100 m MMF in Efficient C-RAN Front-Hauls With Sleep Modes

Using bundles of multimode optical fibers (MMF) as part of the 5G centralized radio access networks front-haul solutions for optically powering of low power consumption Remote Radio Heads (RRH) is proposed and experimentally demonstrated with 100 m of 200 μm core diameter MMF. From the 34.85 W electrical power provided to the system, 1.748 W are delivered to the load, giving an overall 5% efficiency, being the temperature controller of the High Power Lasers the most critical element. If intermediates results are considered, the efficiency from input optical power to electrical power after the PV cells is 43.4%. The RRH manages 2.34 W for control, battery charge, communications and the load operation. The system includes a low power bidirectional control channel that provides the capability of enabling different sleep modes and sending information about the status of the battery and sensing elements at RRH. The RRH has a minimum power consumption of 3.15 mW. Optimized design of different elements of the system are included. The system is tested by feeding a RF power amplifier at the RRH; providing a stable power supply and EVM performance below 17.8% with QPSK on a 20 GHz RF carrier.

Impact of Circular Layout on Characteristics in LSAMBM APD Based on SOI Film

Lateral separate absorption multi-buffer multiplication avalanche photodiode (LSAMBM APD) with rectangular layout based on SOI film had been investigated as a promising candidate in the high-speed weak-light detection application. In this article, the layout-dependent characteristics of LSAMBM APD were investigated furthermore. Comparing to rectangular layout, the circular layout could shorten the length and improve electric field intensity of absorption region under the same sensitive area. In this way, carriers’ drift velocity could be accelerated, and the photon-generated carriers would be more effectively separated to achieve high responsivity and fast frequency response in LSAMBM APD with circular layout. When the illumination wavelength was 400 nm and input optical power was 0.001 W/cm2, the circular layout could enhance LSAMBM APD to achieve high responsivity and fast frequency response under the reverse bias voltage of 8.11 V and 9.2 V, and reach to 1236.9A/W and 3.2GHz, respectively. All results revealed that the LSAMBM APD with circular layout was more appropriate to high-speed single photon detection systems.

Organic thin film thickness-dependent photocurrents polarity in graphene heterojunction phototransistor

To overcome the weak absorption deficiency of 2D materials, combining bilayer/bulk heterojunction and 2D materials in a photoconductive framework facilitates the separation and transfer of photo-generated carriers for prominent performance photo-detector. Nevertheless, apart from improving the inferior built-in electric field, the multilayer device may suffer a low efficiency due to depletion loss considering the effective exciton length limitation. Here, we demonstrate the thickness-dependent photocurrent polarity based on a bilayer enhanced graphene/C60/ZnPc phototransistor. A fast response time down to 7.29 μs and a responsivity of 6537 A/W are achieved in the device with the help of type-II band alignment and valid interfaces between organic layers. Moreover, three controlled thicknesses of intermediate charge transfer layer are investigated for the purpose of probing the transfer direction in multilayer heterojunction, which suggests that the photocurrent polarity is highly related to the thickness of C60 and even input optical power density. Owing to the phenomena of photocurrents polarity, a distinct bending curve of responsivity-power density relation is observed near the positive-negative altering point compared to general logarithm linear relation in most photoconductive devices. Our results may enable further exploration of charge transfer mechanism in multilayer system and development of high speed photoconductive transistor.

Self-monitored and optically powered fiber-optic device for localized hyperthermia and controlled cell death in vitro.

Localized hyperthermia therapy involves heating a small volume of tissue in order to kill cancerous cells selectively and with limited damage to healthy cells and surrounding tissue. However, these features are only achievable through real-time control of the tissue temperature and heated volume, both of which are difficult to obtain with current heating systems and techniques. This work introduces an optical fiber-based active heater that acts both as a miniature heat source and as a thermometer. The heat-induced damage in the tissue is caused by the conductive heat transfer from the surface of the device, while the heat is generated in an absorptive coating on the fiber by near-infrared light redirected from the fiber core to the surface by a tilted fiber Bragg grating inscribed in the fiber core. Simultaneous monitoring of the reflection spectrum of the grating provides a measure of the local temperature. Localized temperature increases between 0°C and 100°C in 10 mm-long/5 mm-diameter cylindrical volumes are obtained with continuous-wave pump power levels up to 1.8 W. Computational and experimental results further indicate that the temperature rise and dimensions of the heated volume can be maintained at a nearly stable level determined by the input optical power.

Wavelength Division Multiplexed Radio Over Fiber Links for 5G Fronthaul Networks

The ever-increasing demand for data rates by mobile users can be fulfilled by radio over fiber (RoF) combined with spectrally-efficient modulation techniques. Thus, RoF is critical to the design of the fronthaul for 5 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> generation (5G) mobile communication networks. We propose and experimentally demonstrate a low-cost directly modulated laser (DML)-based wavelength division multiplexing (WDM)-RoF transmission system for use in next-generation 5G networks. The proposed architecture provides flexible resource allocation as well, under low and high traffic loads at the remote radio heads (RRHs). We also present robust analytical models of the proposed DML-based WDM-RoF network with spectrally-efficient M-ary-quadrature amplitude modulation ( M-QAM), beneficial for system designers. In OptiSystem software, we evaluate the error vector magnitudes (EVM) as a function of the optical link lengths, input optical power, and the received optical power with 4/16/64-QAM over the optical link. The EVMs of the link for 4/16/64-QAM are below the 3GPP standards for 5G. We find good agreement between the simulations and the analytical results. We also experimentally demonstrate a small scale model of this network with resource allocation. Such a flexible architecture is suitable for meeting the demands of femtocells in 5G fronthaul networks.

Speed characterization of p-i-n photodiode based on GaSb/GaInAsSb/GaAlAsSb heterostructure with frontal bridge contact at 1.9 µm.

We report a study of the response function parameters (amplitude and rise/fall time) of a high-speed GaSb/GaInAsSb/GaAlAsSb photodiode operating at 1.9 µm as a function of optical input power and reverse bias voltage. The experimental measurement results yield the optimal pulse energy and optimal reverse bias voltage for the photodiode. The 44 ps minimal rise time of the response function and 3.6 GHz bandwidth are achieved under a 3 V reverse bias voltage and pulse energy in the 0.27-2.5 pJ range.

PAM-4 generation using an electrostatic doping aided single silicon microring modulator driven by two binary electrical signals

In this paper, we propose and analyze the performance of an on-chip electrostatic doping (ED) aided single silicon microring PAM-4 modulator driven by two binary electrical signals of different peak-to-peak voltages. The proposed ED-aided microring modulator (MRM) is realizable on the standard 220 nm silicon-on-insulator (SOI) platform and can operate over the C-band. The steady state and dynamic performance of the ED-aided MRM is estimated using commercial simulation tools. Also, we have analytically assessed the performance of the proposed PAM-4 modulator in terms of optical modulation amplitude (OMA), transmitter power penalty (TPP), level-deviation (LD), and dynamic energy consumption. Simulation results show that the proposed system can achieve pre-HD FEC bit error rate (BER) of 3.8 × 10−3 at 50 Gb/s over 1 km of standard single mode fiber (SSMF) which is promising for next generation high-speed silicon optic link. Simulation results also indicate that the proposed ED-aided MRM based PAM-4 modulator while operating at 50 Gb/s offers approximately 17.63 dB of extinction ratio (ER) with 2.2 dB of insertion loss (IL) and −2.7 dBm of OMA (for 0 dBm of input optical power). The 3-dB electro-optic bandwidth of such modulator is assessed to be 19.58 GHz. Estimated dynamic energy consumption per bit for 25 Gb/s OOK signal and 50 Gb/s PAM-4 signals are 110.63 and 40.18 fJ, respectively.

Compact seven-level optical power quantizer using silicon-based nonlinear ring resonators

In this paper, an all-optical quantization scheme using the nonlinear Kerr effect in silicon-based ring resonators is proposed. In this structure, silicon nanocrystals embedded in silica (Si-nc/SiO2) are used as the Kerr materials because of their high nonlinear coefficient at the wavelength of 1550 nm and complementary metal–oxide–semiconductor (CMOS) fabrication compatibility. Simulation results obtained by the three-dimensional finite difference time domain (FDTD) method show seven quantization levels corresponding to the range of 0 to 75 W/mm2 of the optical input power. This is the maximum number of quantization levels in similar recent structures to the best of our knowledge, while the total footprint is reduced to 300 μm2.