Showing papers in "IEEE Photonics Journal in 2016"
TL;DR: In this paper, the authors proposed multilayer heterostructures on a SiO2 substrate, which provides multiple reflective bands with the very high reflective efficiency of nearly up to 100%.
Abstract: Quantum dots (QDs) show great promise for use in nanotechnology, owing to their high quantum efficiency, color tenability, narrow emission, and high luminescence efficiency. As a new generation of light-emitting devices (LEDs), QD-LEDs have attracted a great deal of attention in displays and lighting. To meet the commercial requirements, the brightness of QD-LEDs needs to be further improved. In this work, we propose multilayer heterostructures on a SiO2 substrate, which provides multiple reflective bands with the very high reflective efficiency of nearly up to 100%. Electric field distributes mostly in the superficial layer. The proposed structure provides highly multiband reflection covering the emission peaks of QDs in LEDs; hence, it can eventually enhance QDs' fluorescence and enhance the brightness of QD-LEDs. We investigate four typical emission wavelengths, mainly aiming for red QD-LEDs and infrared QD-LEDs, which correspond to the applications of displays, infrared illumination, optical communication, and so on. The total reflection bands can be adjusted according to practical requirements by tuning the thickness of every layer. One fabrication procedure can be used for different kinds of QDs or the same kind of QD with different sizes without changing their processing properties. The proposed structure has fewer flat layers compared with 1-D photonic crystals, which leads to lower cost and easier fabrications.
274 citations
TL;DR: A dielectric grating that can launch surface plasmon resonance (SPR) modes efficiently on the other side of flat metal films, which is similar to the conventional prism coupling mechanism, was proposed in this paper.
Abstract: We propose a dielectric grating that can launch surface plasmon resonance (SPR) modes efficiently on the other side of flat metal films, which is similar to the conventional prism coupling mechanism. Importantly, this structure can excite SPR under the normal incident light, which is particularly suitable for the integration with optical fiber tips. By launching the SPR mode near the wavelength of 1.55 $\mu\text{m}$ with a very narrow resonance line width (∼4 nm), this structure is promising for the development of high-performance portable, flexible, and real-time refractometric sensing applications.
266 citations
TL;DR: In this article, a pseudo-high-order GVLVS with a two-humped pulse along one polarization and a single-hump pulse along the orthogonal polarization was obtained.
Abstract: Manipulation of group-velocity-locked vector solitons (GVLVSs) is numerically proposed and experimentally demonstrated. A pseudo-high-order GVLVS could be generated from a fundamental GVLVS with the help of a polarization-resolved system. Specifically, a pseudo-high-order GVLVS with a two-humped pulse along one polarization and a single-humped pulse along the orthogonal polarization could be obtained. The phase difference between the two humps could be 180°.
198 citations
TL;DR: In this article, a long-distance UVLC system is designed, where the half power angle of light-emitting diode (LED) is narrowed to enhance the optical intensity at the transmitter, and a single photon avalanche diode is employed at the receiver to improve the detection sensitivity.
Abstract: Underwater visible light communication (UVLC) is of great interest to the military, industry, and the scientific community. In this paper, a long-distance UVLC system is designed, where the half power angle of light-emitting diode (LED) is narrowed to enhance the optical intensity at the transmitter, and a single photon avalanche diode (SPAD) is employed at the receiver to improve the detection sensitivity. A two-term exponential channel model of a long distance UVLC system with a SPAD receiver is established, and the channel parameters are obtained by Monte Carlo numerical simulation. Furthermore, the SPAD detection algorithm and the optimal detection threshold of the UVLC system are proposed. Simulation results show that the communication distance could be extended to 500 m in pure seawater.
159 citations
TL;DR: To reach a transmission performance of 54 Mb/s, which is standardized as the maximum data rate in IEEE 802.11p for V2X communication, a more advanced OCI-based automotive VLC system is described, which achieves a more than fivefold higher data rate by introducing optical orthogonal frequency-division multiplexing (opticalOFDM).
Abstract: As a new technology for next-generation vehicle-to-everything (V2X) communication, visible-light communication (VLC) using light-emitting diode (LED) transmitters and camera receivers has been energetically studied. Toward the future in which vehicles are connected anytime and anywhere by optical signals, the cutting-edge camera receiver employing a special CMOS image sensor, i.e., the optical communication image sensor (OCI), has been prototyped, and an optical V2V communication system applying this OCI-based camera receiver has already demonstrated 10-Mb/s optical signal transmission between real vehicles during outside driving. In this paper, to reach a transmission performance of 54 Mb/s, which is standardized as the maximum data rate in IEEE 802.11p for V2X communication, a more advanced OCI-based automotive VLC system is described. By introducing optical orthogonal frequency-division multiplexing (optical-OFDM), the new system achieves a more than fivefold higher data rate. Additionally, the frequency response characteristics and circuit noise of the OCI are closely analyzed and taken into account in the signal design. Furthermore, the forward-current limitation of an actual LED is also considered for long operational reliability, i.e., the LED is not operated in overdrive. Bit-error-rate experiments verify a system performance of 45 Mb/s without bit errors and 55 Mb/s with $\text{BER}\ .
148 citations
TL;DR: In this paper, a photonic crystal fiber surface plasmon resonance biosensor was proposed, where both the metal layer and the sensing layer are placed outside the fiber structure, which makes the sensor configuration practically simpler and makes the sensing process more straightforward.
Abstract: We propose a photonic crystal fiber surface plasmon resonance biosensor where the plasmonic metal layer and the sensing layer are placed outside the fiber structure, which makes the sensor configuration practically simpler and the sensing process more straightforward. Considering the long-term stability of the plasmonic performance, copper (Cu) is used as the plasmonic material, and graphene is used to prevent Cu oxidation and enhance sensing performance. Numerical investigation of guiding properties and sensing performance is performed by using a finite-element method. The proposed sensor shows average wavelength interrogation sensitivity of 2000 nm/refractive index unit (RIU) over the analyte refractive indices ranging from 1.33 to 1.37, which leads to a sensor resolution of $5\times 10^{-5}\ \text{RIU}$ . Due to the simple structure and promising results, the proposed sensor could be a potential candidate for detecting biomolecules, organic chemicals, and other analytes.
147 citations
TL;DR: The results show that in communication environments with frequent fog, FSO is typically a short-range data transmission technology and will have its preferred market segment in future wireless fifth-generation/sixth-generation (5G/6G) networks having cell sizes that are lower than a 1-km diameter.
Abstract: Fog is considered to be a primary challenge for free space optics (FSO) systems. It may cause attenuation that is up to hundreds of decibels per kilometer. Hence, accurate modeling of fog attenuation will help telecommunication operators to engineer and appropriately manage their networks. In this paper, we examine fog measurement data coming from several locations in Europe and the United States and derive a unified channel attenuation model. Compared with existing attenuation models, our proposed model achieves a minimum of 9 dB, which is lower than the average root-mean-square error (RMSE). Moreover, we have investigated the statistical behavior of the channel and developed a probabilistic model under stochastic fog conditions. Furthermore, we studied the performance of the FSO system addressing various performance metrics, including signal-to-noise ratio (SNR), bit-error rate (BER), and channel capacity. Our results show that in communication environments with frequent fog, FSO is typically a short-range data transmission technology. Therefore, FSO will have its preferred market segment in future wireless fifth-generation/sixth-generation (5G/6G) networks having cell sizes that are lower than a 1-km diameter. Moreover, the results of our modeling and analysis can be applied in determining the switching/thresholding conditions in highly reliable hybrid FSO/radio-frequency (RF) networks.
144 citations
TL;DR: Numerical simulation results indicate that the length difference between the upper waveguide and the under waveguide can change the output spectrum characteristics of the device, which acts like a Mach–Zehnder interferometer (MZI).
Abstract: We propose and demonstrate a directed optical logic circuit that can perform the XOR and XNOR logic operations consisting of two cascaded microring resonators, i.e., an upper waveguide and an under waveguide. No waveguide crossings exist in the circuit, which is very useful to improve the signal quality and reduce the insertion loss of the device. As proof of principle, XOR and XNOR logic operations with the speed of 10 kb/s are successfully demonstrated. In addition, numerical simulation results indicate that the length difference between the upper waveguide and the under waveguide can change the output spectrum characteristics of the device, which acts like a Mach–Zehnder interferometer (MZI).
127 citations
TL;DR: In this paper, a two-stage injection-locked 680-nm red-light vertical-cavity surface-emitting laser (VCSEL) transmitter to enhance the frequency response and a laser beam expander to expand the collimated beam diameter over a 5m highly turbid harbor water link is proposed and practically demonstrated.
Abstract: A 25-Gbps underwater wireless optical communication (UWOC) system with a two-stage injection-locked 680-nm red-light vertical-cavity surface-emitting laser (VCSEL) transmitter to enhance the frequency response and a laser beam expander to expand the collimated beam diameter over a 5-m highly turbid harbor water link is proposed and practically demonstrated. In highly turbid harbor water link, the overall attenuation coefficient at 680 nm is smaller than that at 520 and 450 nm, thereby a 680-nm red-light VCSEL transmitter is adopted in this proposed 5 m/25 Gbps UWOC system rather than a 520-nm green-light laser diode (LD) transmitter or a 450-nm blue-light LD transmitter. A satisfactory bit error rate performance (3 × 10–9) and a clear eye diagram are acquired in real time. This proposed UWOC system with a two-stage injection-locked 680-nm VCSEL transmitter and a laser beam expander brings important improvements in the scenario characterized by high turbidity.
109 citations
TL;DR: It is shown that, under certain conditions, the OAM multiplexing technique provides higher security over a single-mode transmission channel in terms of the total secrecy capacity and the probability of achieving a secure communication.
Abstract: The physical-layer security of a line-of-sight (LOS) free-space optical (FSO) link using orbital angular momentum (OAM) multiplexing is studied. We discuss the effect of atmospheric turbulence to OAM-multiplexed FSO channels. We numerically simulate the propagation of OAM-multiplexed beam and study the secrecy capacity. We show that, under certain conditions, the OAM multiplexing technique provides higher security over a single-mode transmission channel in terms of the total secrecy capacity and the probability of achieving a secure communication. We also study the power cost effect at the transmitter side for both fixed system power and equal channel power scenarios.
106 citations
TL;DR: A low-cost prototype of spectroscopy-based noninvasive glucose monitoring system that demonstrates promising results in vitro and establishes a relationship between the optical signals and the changing levels of blood-glucose concentration is reported.
Abstract: Diabetes mellitus claims millions of lives every year. It affects the body in various ways by leading to many serious illnesses and premature mortality. Heart and kidney diseases, which are caused by diabetes, are increasing at an alarming rate. In this paper, we report a study of a noninvasive measurement technique to determine the glucose levels in the human body. Current existing methods to quantify the glucose level in the blood are predominantly invasive that involve taking the blood samples using finger pricking. In this paper, we report a spectroscopy-based noninvasive glucose monitoring system to measure glucose concentration. Near-infrared transmission spectroscopy is used and in vitro experiments are conducted, as well as in vivo . Our experimental study confirms a correlation between the sensor output voltage and glucose concentration levels. We report a low-cost prototype of spectroscopy-based noninvasive glucose monitoring system that demonstrates promising results in vitro and establishes a relationship between the optical signals and the changing levels of blood–glucose concentration.
TL;DR: In this paper, a passively Q-switched erbium fiber laser using titanium dioxide (TiO 2) as a saturable absorber was demonstrated, where the TiO 2 was fabricated as a polymer composite film and sandwiched between fiber ferrules.
Abstract: We demonstrate a passively Q-switched erbium fiber laser using titanium dioxide (TiO 2) as a saturable absorber. The TiO 2 saturable absorber was fabricated as a polymer composite film and sandwiched between fiber ferrules. Q-switched pulsing starts with the assistance of physical disturbance of the laser cavity (by lightly tapping the cavity to induce instability) at 140 mW and lasts until 240 mW. The repetition rate increases with the pump power from 80.28 to 120.48 kHz. On the other hand, the pulsewidth decreases from $2.054\ \mu\text{s}$ until it reaches a plateau at $1.84\ \mu\text{s}$ . The Q-switched fiber laser exhibits two competing modes: at 1558.1 and 1558.9 nm as the pump power increases. A high signal-to-noise ratio of 49.65 dB is obtained.
TL;DR: This work considers the indoor positioning specified for a popular VLC scenario where the target device has multiple photodiodes (PDs) while having no help from other fixed receiving nodes with known coordinates.
Abstract: With the widespread use of light-emitting diodes (LEDs) for lighting, their ability to support communications through visible light has become promising for various wireless applications. In particular, visible-light communication (VLC) assisted indoor positioning enjoys its unique advantage of electromagnetic interference immunity and high accuracy. Instead of directly extending conventional wireless positioning using radio-frequency equipment, we consider the indoor positioning specified for a popular VLC scenario where the target device has multiple photodiodes (PDs) while having no help from other fixed receiving nodes with known coordinates. A general framework is presented for multi-PD device positioning by exploiting relative positions, as well as the received signal strength indications, of the multiple PDs. Moreover, the feasible condition for realizing effective positioning is also presented. Finally, we validate the accuracy of the proposed method via numerical tests.
TL;DR: In this article, the authors characterized the thermoptic properties of silicon nitride ring resonators between 18 and 300 K and found that the resonant modes show low temperature dependence at cryogenic temperatures and higher dependence as the temperature increases.
Abstract: In this paper, we characterize the Thermo-optic properties of silicon nitride ring resonators between 18 and 300 K. The Thermo-optic coefficients of the silicon nitride core and the oxide cladding are measured by studying the temperature dependence of the resonance wavelengths. The resonant modes show low temperature dependence at cryogenic temperatures and higher dependence as the temperature increases. We find the Thermo-optic coefficients of PECVD silicon nitride and silicon oxide to be $2.51 \pm 0.08\ \text{E}$ - $5\ \text{K}^{-1}$ and $0.96 \pm 0.09\ \text{E}$ - $5\ \text{K}^{-1}$ at room temperature while decreasing by an order of magnitude when cooling to 18 K. To show the effect of variations in the thermo-optic coefficients on device performance, we study the tuning of a fully integrated electrically tunable filter as a function of voltage for different temperatures. The presented results provide new practical guidelines in designing photonic circuits for studying low-temperature optical phenomena.
TL;DR: In this article, an analytical expression of the channel information capacity of an OAM-based free-space optical (FSO) communication system with non-diffraction Bessel-Gauss (BG) beams in weak turbulent ocean is derived.
Abstract: An orbital angular momentum (OAM)-mode transmission model of Bessel–Gauss (BG) beams is established to derive an analytic expression of the channel information capacity of an OAM-based free-space optical (FSO) communication system with non-diffraction BG beams in weak turbulent ocean. Effects of oceanic turbulence on the channel information capacity of this communication system are discussed in detail. Numerical results show that oceanic turbulence induces an evident spread of OAM-mode transmission probability spectrum and severely affects the channel information capacity of OAM-based FSO communication systems. The influences of beam parameter $\eta$ of BG and dual BG beams on channel information capacity are contrary to each other. BG beams show significant advantages over Laguerre–Gaussian beams in mitigating the effects of turbulence and improving the performance of OAM-based FSO communication links. The effects of oceanic turbulence on the channel information capacity become stronger with the increase in oceanic turbulence parameter, rate of dissipation of mean-squared temperature, and temperature–salinity balance parameter, as well as with the decrease in the rate of dissipation of turbulent kinetic energy per unit mass of fluid. Choosing an optimum blue–green wavelength and increasing $\eta$ of the BG beam can effectively improve the performance of an OAM-based FSO communication system in turbulent ocean.
TL;DR: In this paper, a new design approach for achieving quadband terahertz metamaterial absorber, formed by an asymmetric resonator and a metallic board separated by a certain thickness dielectric layer, is numerically studied and demonstrated.
Abstract: A new design approach for achieving quadband terahertz metamaterial absorber, formed by an asymmetric resonator and a metallic board separated by a certain thickness dielectric layer, is numerically studied and demonstrated. Results show that the absorber has four high absorption (greater than 98%) resonance bands (or peaks). The physical origin of the absorber is attributed to four different resonance modes of the single-patterned resonator. The proposed device resolves large unit size, complex resonance structure, and time-consuming and costly fabrication steps, which previously reported absorbers frequently encountered. Moreover, the five-band metamaterial absorber can be obtained by further optimizing the parameters of resonator. The proposed absorber has application prospects in many areas such as materials detection, thermal imaging, and biological sensing.
TL;DR: In this article, the authors demonstrate an ultrasensitive surface plasmon resonance sensor with 4-layer MoS2 and a monolayer graphene, which can achieve a sensitivity as high as 182°/RIU.
Abstract: In the conventional surface plasmon resonance biosensor, the sensitivity using angular interrogation is low. Graphene/MoS2 has been attached on the metal surface to improve the sensitivity; however, the ability to improve sensitivity is limited. Here, by sandwiching the MoS2 sheets between two gold films in the Kretschmann configuration, we demonstrate an ultrasensitive surface plasmon resonance sensor. By optimizing the structure of sensor, we find that the sensitivity as high as 182°/RIU can be realized with 4-layers MoS2 and a monolayer graphene. Moreover, it is indicated that the sensitivity can be tuned and controlled by changing the layer numbers of graphene and MoS2.
TL;DR: In this paper, a phase-noise-compensated optical time-domain reflectometry (φ$ -OTDR) was proposed for distributed fiber-optic vibration sensors.
Abstract: Distributed fiber-optic vibration sensors based on phase-sensitive optical time-domain reflectometry ( $\phi$ -OTDR) have found many applications in various fields. In this paper, we analyze the phase noise of $\phi$ -OTDR, which is the main limiting factor of the measurement range. We found that the laser phase noise and phase extraction error caused by the intensity noise in photodetection contribute to the total phase noise. By introducing a series of auxiliary weak reflection points along the fiber, we develop a phase-noise-compensated $\phi$ -OTDR and realize a long-range distributed vibration sensing based on the phase extraction. Furthermore, a statistical analysis was proposed to maintain the vibration measurement sensitivity along the whole fiber. In the experiment, vibrations at 30 km were measured with a linear response, which confirmed the validity of our proposed system.
TL;DR: In this article, the use of cyclic pulse coding for enhanced performance in distributed acoustic sensing based on a phase-sensitive optical time-domain reflectometry (φ$ -OTDR) using direct detection was proposed and experimentally demonstrated.
Abstract: We propose and experimentally demonstrate the use of cyclic pulse coding for enhanced performance in distributed acoustic sensing based on a phase-sensitive optical time-domain reflectometry ( $\phi$ -OTDR) using direct detection. First, we present a theoretical analysis showing that to make cyclic pulse coding effective in $\phi$ -OTDR, the laser linewidth and stability must be optimized to simultaneously guarantee intrapulse coherence and interpulse incoherence. We then confirm that commercial off-the-shelf distributed feedback (DFB) lasers can satisfy these conditions, providing coding gain consistent with theoretical predictions. By externally modulating such lasers with cyclic pulse coding, we demonstrate a distributed acoustic sensor capable of measuring vibrations of up to 500 Hz over 5 km of standard single-mode fiber with 5-m spatial resolution with ∼9-dB signal-to-noise ratio (SNR) improvement compared with the single-pulse equivalent. We also show that the proposed solution offers sensing performances that are comparable to similar sensors employing highly coherent and stabilized external cavity lasers and a single-pulse $\phi$ -OTDR.
TL;DR: A 3 × 3 imaging multiple-input multiple-output (MIMO) VLC system is demonstrated and the original 1 MHz bandwidth commercially available phosphor white light LED can achieve 1 Gbps data rate over 1-m free-space transmission distance.
Abstract: The phosphor light-emitting diode (LED) has been widely used not only for indoor illumination but for the optical transmitter (Tx) as well in visible light communication (VLC). However, the transmission data rate is significantly limited by the modulation bandwidth of LED because of the low-speed response of phosphor. In order to enhance the data rate of the VLC system, we demonstrate a 3 × 3 imaging multiple-input multiple-output (MIMO) VLC system. Besides, the pre-equalizer circuit is used to extend the bandwidth of the LED Tx. Orthogonal frequency division multiplexing (OFDM) with bit-loading algorithm is used. By using the proposed scheme, the original 1 MHz bandwidth commercially available phosphor white light LED can achieve 1 Gbps data rate over 1-m free-space transmission distance.
TL;DR: A support vector machine (SVM)-based classification nonlinear equalizer (NLE) is demonstrated, for the first time, in coherent optical orthogonal frequency-division multiplexing (CO-OFDM).
Abstract: A support vector machine (SVM)-based classification nonlinear equalizer (NLE) is demonstrated, for the first time, in coherent optical orthogonal frequency-division multiplexing (CO-OFDM). For a 40-Gb/s 16 quadrature amplitude modulated (16QAM) CO-OFDM system at 400 km of transmission, SVM-NLE reduces the fiber-induced nonlinearity penalty by about 1 dB in comparison to the benchmark artificial-neural-network (ANN)-based and inverse-Volterra-series-transfer-function-based NLEs.
TL;DR: In this article, a compact broadband directional coupler using subwavelength gratings for silicon-on-insulator wafers with silicon layers of 220 nm is presented. But the dispersion properties of the optical modes are not considered.
Abstract: We experimentally demonstrate compact broadband directional couplers using subwavelength gratings for silicon-on-insulator wafers with silicon layers of 220 nm. The dispersion properties of the optical modes are engineered using subwavelength gratings, which allow broadband operation. Finite-difference time-domain (FDTD)-based band structure calculations, with significantly reduced simulation time, were used to analyze the design, which included both the structure and material dispersions. Compact broadband direction couplers, with device lengths shorter than 14 $\mu\text{m}$ , which cover a bandwidth of 100 nm for power splitting ratios of 50/50, 40/60, 30/70, and 20/80, are designed and fabricated for the fundamental transverse electric mode with a central operating wavelength of 1550 nm.
TL;DR: In this paper, a GeSn-based p-i-n photodetectors (PDs) with an active layer grown on n-type Si (100) substrate using molecular beam epitaxy (MBE) was reported.
Abstract: We reported an investigation of GeSn-based p-i-n photodetectors (PDs) with a ${\rm{Ge}}_{{\rm{0.92}}}{\rm{Sn}}_{{\rm{0.08}}}$ active layer grown on n-type Si (100) substrate using molecular beam epitaxy (MBE). The GeSn photodetector achieved a wide spectrum detection whose cutoff wavelength can reach to 2.3 μm. The PDs exhibited a high performance near 2.0 μm with a responsivity of 93 mA/W and a dark current of 171 μA under a reverse bias of 1 V at room temperature. This work represented a promising technology to develop Si-based short-wave infrared (SWIR) photodetectors.
TL;DR: By using spectral-efficient orthogonal frequency division multiplexing (OFDM) modulation with bit-and-power-loading algorithm, VCSEL-based transmission at 11.1 Gbps is successfully demonstrated over a free-space length of 1.2 m under small bias current.
Abstract: In this paper, we propose using an energy-efficient and low-cost 682-nm vertical-cavity surface-emitting laser (VCSEL) with 1-GHz modulation bandwidth for high-speed wireless visible light communication (VLC). Moreover, by using spectral-efficient orthogonal frequency division multiplexing (OFDM) modulation with bit-and-power-loading algorithm, we successfully demonstrate VCSEL-based transmission at 11.1 Gbps (10.2 Gbps in a raw data rate) over a free-space length of 1.2 m under small bias current of 3.5 mA. Furthermore, decreasing the bias current as low as 2 mA, we can also demonstrate 10.5 Gbps (9.7 Gbps in a raw data rate) OFDM VLC transmission over a 1.2-m free-space link. This proposed VCSEL-based OFDM transmission system could be viewed as a cost-effective and energy-efficient approach for high-speed (> 10 Gbps) laser diode wireless VLC application.
TL;DR: In this paper, a phase-change metasurface was used for multiband tunable active terahertz polarization control, which achieved linear-to-circular polarization at 0.45 and 1.10 GHz with an ellipticity of 0.998 and $-$ 0.971, respectively.
Abstract: Metasurfaces open up a low-dimensional artificial approach to tailor electromagnetic (EM) waves with unprecedented functionalities. However, the ability to actively control and manipulate EM waves via metasurfaces still faces challenges that need to be overcome. Here, we experimentally demonstrated a multiband switchable terahertz quarter-wave plate via inserting a phase-change material, i.e., vanadium dioxide (VO 2), into complementary electric split-ring resonators. Before the VO 2 phase transition, this phase-change metasurface achieves linear-to-circular polarization conversion at 0.45 and 1.10 THz with an ellipticity of 0.998 and $-$ 0.971, respectively. After the VO 2 phase transition, linear-to-circular polarization conversion is obtained at both 0.50 and 1.05 THz with an ellipticity of 0.999 and $-$ 0.999, respectively. This work reveals the feasibility of using phase-change metasurfaces for multiband tunable active terahertz polarization control, and such compact tunable devices can be designed for other frequency regimes as well.
TL;DR: This study aims to maximize the achievable rate for a visible light communication (VLC) downlink multiuser multiple-input-single-output (MISO) system deployed with zero-forcing (ZF) beamforming by exploiting the high signal-to-noise ratio (SNR) characteristic in VLC.
Abstract: In this study, we aim to maximize the achievable rate for a visible light communication (VLC) downlink multiuser multiple-input–single-output (MISO) system deployed with zero-forcing (ZF) beamforming. By incorporating the ZF, transmit signal's nonnegativity, and light-emitting diode (LED) maximum permissible current constraints, we formulate the rate maximization problem of interest, which possesses a complicated nonconvex form. To handle this challenging problem, we first employ the powerful concave–convex procedure to develop an iterative algorithm that converges to a locally optimal solution. Subsequently, by exploiting the high signal-to-noise ratio (SNR) characteristic in VLC, we simplify the primal nonconvex design problem into a solvable convex one that admits a high-quality solution. As an alternative approach, we impose a channel pseudoinverse structure on the beamforming matrix followed by power allocation optimization. Finally, we carry out simulations to investigate the performance of the proposed schemes under a VLC scenario.
TL;DR: In this article, a novel long-range surface plasmon with graphene was proposed to enhance the sensitivity and detection accuracy of the biosensor, and the authors demonstrated that the sensitivity has a nearly tenfold improvement with a huge increasing detection accuracy.
Abstract: A novel long-range surface plasmon with graphene is proposed to enhance the sensitivity and detection accuracy (DA) of the biosensor. Compared with the conventional long-range surface plasmon resonance (LRSPR) structure with Au, the coating of the metal surface with graphene is employed to increase the biomolecules adsorption, prevent oxidation, and enhance the sensitivity and DA. Furthermore, we demonstrated that the sensitivity has a nearly tenfold improvement with a huge increasing DA in the proposed LRSPR biosensor compared with the SPR biosensor. Finally, we discuss the influence of the refractive index of sensing medium on the LRSPR biosensor and find that the sensitivity is changing with the refractive index of the sensing medium and that an optimal sensitivity can be obtained at a suitable refractive index. We believe that this scheme could find potential applications in chemical examination, medical diagnosis, and biological detection.
TL;DR: In this paper, the design, fabrication, and optical characterization of the sensing element of a photonic InP-based gyroscope intended for applications in the field of aerospace and defense are reported.
Abstract: The design, fabrication, and optical characterization of the sensing element of a photonic InP-based gyroscope intended for applications in the field of aerospace and defense are reported in this paper. The sensing element is a spiral resonator coupled to a straight bus waveguide through a multimode interference coupler and exhibits a $Q$ factor of approximately 600 000 with a footprint of approximately 10 mm 2. The design of each component of the sensor is based on some well-established numerical methods such as the Finite Element Method, the beam propagation method, and the film mode matching method. The spiral cavity was designed using the standard transfer matrix method. The selected fabrication process, which is an enhanced version of the standard COBRA process, allows the monolithic integration of the sensing element with the other active components of the gyroscope, e.g., lasers, photodiodes, and modulators. Each component of the fabricated sensing element was optically characterized using an appropriate setup, which was also used for the optical characterization of the whole sensor. Based on the results of the characterization, the gyro performance was evaluated, and a way to improve both the resolution and the bias drift, i.e., down to 10 °/h and 1 °/h, respectively, was also clearly identified. The achieved results demonstrate, for the first time, the actual feasibility of a photonic gyro-on-chip through a well-established InP-based generic integration process.
TL;DR: By introducing a piecewise function with adaptive slopes according to the required optical power, the proposed eDCO-OFDM scheme has the potential to effectively eliminate the clipping noise.
Abstract: In visible light communication (VLC) systems, optical orthogonal frequency-division multiplexing (O-OFDM) is an appealing modulation scheme. Recently, a number of O-OFDM schemes have been proposed. Among them, direct-current O-OFDM (DCO-OFDM) is a widely used scheme for its high spectral efficiency and low complexity. Since VLC involves a combination of illumination and communication, different optical power is often required to achieve a certain illumination level. However, clipping noise will dominate a severe performance degradation of DCO-OFDM when a relatively high or low illumination level is imposed, and it restricts applications of DCO-OFDM in future VLC systems. To address this problem, an enhanced DCO-OFDM (eDCO-OFDM) scheme is proposed. By introducing a piecewise function with adaptive slopes according to the required optical power, the proposed eDCO-OFDM scheme has the potential to effectively eliminate the clipping noise. Furthermore, two parameter selection mechanisms with different complexities and performance gains are designed for the piecewise function in the eDCO-OFDM scheme. Simulation results verify the energy and spectral efficiency of the proposed scheme under the constraints of optical power.
TL;DR: In this paper, the authors investigated the nonlinear and ultrafast photonics of chemically processed black phosphorus quantum dots (BPQDs) synthesized by the solvothermal treatment approach, with an average lateral size of about 2.48 $\pm$ 0.4 nm.
Abstract: We have investigated the nonlinear and ultrafast photonics of chemically processed black phosphorus quantum dots (BPQDs) synthesized by the solvothermal treatment approach, with an average lateral size of about 2.48 $\pm$ 0.4 nm. BPQDs exhibit optical saturable absorption measured by the balanced twin-detector measurement system at the telecommunication band and have been demonstrated for the generation of passively mode-locking operation in an erbium-doped fiber laser. Either two-pulse or three-pulse bound state of soliton pulse has been obtained, making the best use of the BPQDs-based saturable absorber. Our work suggests that BPQDs might be developed as an efficient optical saturable absorber for ultrafast photonics applications.