Power Penalty Research Articles

Time scrambling and decoy-state quantum key distribution for optical physical layer encryption

We propose an optical physical layer encryption method based on real-time optical signal temporal scrambling and decoy-state quantum key distribution. The real-time optical signal processing is operating with an array of tunable Fabry-Perot cavities by using the updating and synchronization keys. Based on this scheme, an experimental demonstration is given to realize secure communication for optical physical layer in a standard 10 Gbps data transmission with quantum key distribution in real time. An on-line transmitted data over 100 km of a standard single mode fiber is realized with power penalty of as low as 3.45 dB, where the average key generation rate is better than 800 bps. The experimental results indicate that, the proposed encryption scheme of dynamic scrambling with quantum keys exhibits significantly potential for improving the confidentiality of optical physical layer.

Ultrawide-band Low Polarization Sensitivity 3-µm SOI Arrayed Waveguide Gratings

An ultrawide-band (UWB), O- to L- band, polarization insensitive (PI) 1 × 12 100 GHz channel spacing arrayed waveguide grating (AWG) is designed and realized in 3-μm Silicon-on-Insulator (SOI) platform. PI and UWB operations are achieved by directly exploiting the UWB 3-μm PI silicon waveguide as the arrayed waveguide. The PI AWG can be employed as demultiplexer and multiplexer in photonic integrated circuits (PIC)s, such as UWB wavelength selective switches (WSS)s. Experimental results demonstrate UWB (O- to L- band) and PI 1 × 12 AWG operation with −0.82 dB to −1.52 dB insertion losses, <−35 dB average cross-talk, 0.18 dB to 1.27 dB polarization dependent loss (PDL), and 0.006 nm to 0.041 nm polarization dependent wavelength shift (PDWS). Error-free operation at 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−9</sup> BER were measured with power penalties <0.1 dB, <0.2 dB, and <0.8 dB for 10 Gb/s, 20 Gb/s and 35 Gb/s NRZ-OOK PRBS 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">31</sup> -1 multi-band data, respectively.

SDM-WDM ROADM Based on Direct-Laser-Writing SDM Core Separator

Weakly-coupled space division multiplexing (SDM) techniques based on multi-core fibers (MCF) have attracted great attention for the capacity enhancement of optical interconnect systems and networks. In this paper, we propose a novel direct-laser-writing (DLW) core separator device and apply it in a reconfigurable optical add/drop multiplexer (ROADM) structure for two-dimensional SDM and wavelength division multiplexing (WDM) switching. The proposed core separator matching an 8-core MCF is fabricated. Then assisted with MCF rotators, independent adding and dropping functionalities for arbitrary core are experimentally demonstrated with slight power penalty for both core and wavelength dimensions. The influence of crosstalk for cascading core separators is also investigated and below 0.35-dB receiving sensitivity penalty is obtained when three cores are dropped one by one. The compact DLW core separators can reduce the complexity of SDM nodes and will be beneficial for high-speed optical interconnects.

Experimental Demonstration of a 100-Gbit/s 16-QAM Free-Space Optical Link Using a Structured Optical “Bottle Beam” to Circumvent Obstructions

We experimentally demonstrate a free-space optical (FSO) communication link using an optical &#x201C;bottle&#x201D; beam to help circumvent obstructions. At the transmitter, an optical &#x201C;bottle&#x201D; beam is generated by spatially structuring a Gaussian beam with a transmitter beam diameter of 7 mm. During propagation, the energy of the &#x201C;bottle&#x201D; beam evolves in a three-dimensional (3-D) shell which creates a &#x201C;bottle&#x201D;-like low-intensity region, allowing the beam to circumvent an obstruction located inside this region. Subsequently, the beam evolves back to its original shape and propagates in its original direction. In our demonstration, we use a 100-Gbit&#x002F;s, 16 quadrature amplitude modulation (16-QAM) data signal. Experimental results show that a &#x201C;bottle&#x201D; beam with a &#x201C;bottle&#x201D; size of 5 mm could help circumvent a circle-shaped obstruction with a diameter of &#x223C;4.5 mm and suffers &#x223C;10-dB less obstruction-induced power penalty as compared to a Gaussian beam. Additionally, we experimentally tailor the size and location of the &#x201C;bottle&#x201D; by changing the structuring pattern at the transmitter. Results after tailoring show that: (i) the beam with a larger &#x201C;bottle&#x201D; size could circumvent a larger obstruction but suffers more power loss when using a limited-size receiver aperture, and (ii) the location of the &#x201C;bottle&#x201D; in the propagation direction could be tuned to circumvent an obstruction more optimally at varying locations as compared to the case where the locations of the &#x201C;bottle&#x201D; and obstruction are not matched.

Energy Efficient Access Point Placement for Distributed Massive MIMO

Distributed massive multiple-input multiple-output (D-mMIMO) is one of the key candidate technologies for future wireless networks. A D-mMIMO system has multiple, geographically distributed, access points (APs) jointly serving its users. First of all, this paper reports on where to position these APs to minimize the overall transmit power in actual deployments. As a second contribution, we show that it is essential to take into account both the radiation pattern of the antenna array and the environment information when optimizing AP placement. Neglecting the radiation pattern and environment information, as generally assumed in the literature, can lead to a power penalty in the order of 15 dB and 20 dB, respectively. These results have been obtained by formulating the AP placement optimization problem as a combinatorial optimization problem, which can be solved with different approaches where different channel models are applied. The proposed graph-based channel model drastically lowers the computational time with respect to using an ray-tracing simulator (RTS) for channel evaluation. The performance of the graph-based approach is validated via the RTS, showing that it achieves 5 dB power saving on average compared with a Euclidean distance-based approach, which is the most commonly used approach in the literature.

Enhancement of Optical-Feedback Tolerance of SOA-Integrated EML (AXEL) by Introducing DBR-Type Laser

A DBR-laser-based SOA-assisted extended-reach EML (AXEL) was investigated in order to improve the optical feedback tolerance. The performance was tested in relative intensity noise measurement and fiber transmission experiment. A superior optical feedback tolerance was obtained in comparison with a conventional AXEL. The excess RIN induced by optical feedback is suppressed at 3-dB higher feedback power for the DBR-AXEL. 40 km fiber transmission of 10-Gbit/s signal with a feedback factor of −15 dB was achieved. The power budget was 41.3 dB. The feedback-induced power penalty was 0.52 dB.

Integrated Tunable Sideband Suppressor for Optical Carrier Reuse in Millimeter-Wave Radio-Over-Fiber Transmission

An integrated Si photonic tunable sideband suppressor is presented for application of remote optical carrier reuse. This tunable sideband suppressor is constructed by a two-rings-coupled Mach Zehnder interferometer with a tuning function to synthesize a box-like, narrow band-pass filter through dual Fano resonance interference. By varying the resonant wavelengths of the ring resonators, we can tune the suppression band adapted to the working millimeter wave (mmWave) frequency. We demonstrate a suppression ratio more than 25 dB on both 28 and 39 GHz downlink mmWave radio-over-fiber (RoF) signals. By applying this component in a bi-directional mmWave RoF system, we observe the quality of the uplink signal modulated on the recycled optical carrier is almost the same as that modulated on a clean laser source without extra power penalty. Since the sideband suppressor is made by Si photonic circuits, it potentially can be integrated with other high-speed Si photonic components to implement an on-chip mmWave radio-over-fiber transceiver.

Direct modulation bandwidth enhancement of uncooled DFB laser operating over a wide temperature range based on groove-in-trench waveguide structure

Uncooled direct modulation DFB laser offers high speed transmission rate over a wide temperature range with high reliability and low cost, making it a cost-effective light source choice for 5G fronthaul and data center applications. However, a significant 3dB bandwidth decrease can be observed in high temperature for conventional DFB lasers. We present an uncooled DFB laser operating up to 85°C with extended direct modulation bandwidth and high reliability based on a novel groove-in-trench ridge waveguide structure, where two narrow grooves penetrating the active layer are etched symmetrically in the two conventional trenches by deep wet etching, respectively. By optimizing the distance between the groove and the mesa stripe, we obtain a 3dB bandwidth of 15.3 GHz at 85°C, which is a 3.7 GHz improvement compared with the conventional ridge waveguide DFB laser. Transmissions of 25 Gb/s NRZ signal at 25°C and 85°C with clear eye openings have been demonstrated. It also achieves 25 Gb/s transmission over 10 km optical fiber with a low power penalty of 0.5 dB for a bit error rate of 10-12 at 85°C. In addition, the result of 2000-hour aging test shows that the proposed groove-in-trench structure DFB lasers have the same excellent reliability as the conventional ones.

Simultaneous distributed-boundary optimal control problems driven by nonlinear complementarity systems

The primary goal of this paper is to study a nonlinear complementarity system (NCS, for short) with a nonlinear and nonhomogeneous partial differential operator and mixed boundary conditions, and a simultaneous distributed-boundary optimal control problem governed by (NCS), respectively. First, we formulate the weak formulation of (NCS) to a mixed variational inequality with double obstacle constraints (MVI, for short), and prove the existence and uniqueness of solution to (MVI). Then, a power penalty method is applied to (NCS) for introducing an approximating mixed variational inequality without constraints (AMVI, for short). After that, a convergence result that the unique solution of (MVI) can be approached by the unique solution of (AMVI) when a penalty parameter tends to infinity, is established. Moreover, we explore the solvability of the simultaneous distributed-boundary optimal control problem described by (MVI), and consider a family of approximating optimal control problems driven by (AMVI). Finally, we provide a result on asymptotic behavior of optimal controls, system states and minimal values to approximating optimal control problems.

A Novel Inductorless Design Technique for Linear Equalization in Optical Receivers

To mitigate the trade-off between gain and bandwidth of CMOS multistage amplifiers, a receiver front-end (FE) that employs a high-gain narrowband transimpedance amplifier (TIA) followed by an equalizing main amplifier (EMA) is proposed. The EMA provides a high-frequency peaking to extend the FE’s bandwidth from 25% to 60% of the targeted data rate fbit. The peaking is realized by adding a pole in the feedback paths of an active feedback-based wideband amplifier. By embedding the peaking in the main amplifier (MA), the front-end meets the sensitivity and gain of conventional equalizer-based receivers with better energy efficiency by eliminating the equalizer stages. Simulated in TSMC 65 nm CMOS technology, the proposed front-end achieves 7.4 dB and 6 dB higher gain at 10 Gb/s and 20 Gb/s, respectively, compared to a conventional front-end that is designed for equal bandwidth and dissipates the same power. The higher gain demonstrates the capability of the proposed technique in breaking the gain-bandwidth trade-off. The higher gain also reduces the power penalty incurred by the decision circuit and improves the sensitivity by 1.5 dB and 2.24 dB at 10 Gb/s and 20 Gb/s, respectively. Simulations also confirm that the proposed FE exhibits a robust performance against process and temperature variations and can support large input currents.

K-Means algorithm-based detection for wavelength division multiplexed OOK PD-NOMA system over turbulent optical channel

We have experimentally demonstrated the efficacy of k-means algorithm-based detection scheme in a two-user-based wavelength division multiplexed (WDM) on-off keying (OOK) power-division non-orthogonal multiple access (PD-NOMA) system over turbulent free-space optical (FSO) channels. The proposed system utilizes both power and wavelength division multiplexing to enhance the capacity of the transmission system. The proposed system also incorporates successive interference cancellation technique that utilizes unsupervised machine learning technique, which is K-means clustering, to detect the signal. Two different weak turbulence conditions in the free-space optical channels have been realized in the laboratory environment having link lengths of 2.2 m (near user) and 3.2 m (far user). The results show that the measured probability density function of intensity fluctuation closely matches the log-normal distribution. The experimental results also show that the K-means-based detection provides the BER, which is well below the Pre-FEC limit. The maximum power penalty for the near (far) user is found to be 3.1 dB (4.2 dB) at a BER of 10 − 3 for weak turbulence conditions. The proposed and implemented k-means-based detection scheme for the WDM-OOK PD-NOMA system can also be used for FSO communication systems.

Enhanced Heat Transfer Performance of Multiple Triangular Air Flow Passages in Parallel With Inclined Fins for Flat Plate Solar Air Heater

Abstract This paper presents results of a study of heat transfer performance of multiple equilateral triangular parallel air flow passages below a uniformly heated flat plate having inclined fins of different thickness, length, and material covering a part of the side walls of the duct for transition to early turbulent regimes using appropriate experimental heat transfer coefficient and friction factor correlations from the literature. The heat transfer performance enhancement at equal pumping power has been measured in terms of a performance parameter (hA/hsAs), where hA is the product of heat transfer coefficient and total heat transfer area for the finned triangular duct, and hsAs is the product for the triangular duct with heated flat plate without fins and adiabatic side walls. The values of the performance parameter for steel fins integral with the heated plate are found to be 1.71–1.78 for 1.0 mm thick fins of 15 mm length and 1.94–2.04 for 1.5 mm thick fins of 20 mm length. For aluminum fins, the performance parameter is 2.36–2.54 for 30 mm long fins of 1–1.5 mm thickness. The results of the presented novel scheme of the finned heated plate can be utilized for the development of enhanced performance solar air heater with the finned absorber plate. Since the presented scheme enhances heat transfer without increased pumping power penalty, the existing smooth rectangular duct solar collectors can be modified for enhanced performance.

Low-Latency Optical Wireless Data-Center Networks Using Nanoseconds Semiconductor-Based Wavelength Selectors and Arrayed Waveguide Grating Router

In order to meet the massively increasing requirements of big-data applications, data centers (DCs) are key infrastructures to cope with the associated demands, such as high performance, easy scalability, low cabling complexity and low power consumption. Many research efforts have been dedicated to traditional wired data center networks (DCNs). However, DCNs’ static and rigid topology based on optical cables significantly limits their flexibility, scalability, and even reconfigurability. The limitations of this wired connection can be addressed with optical wireless technology, which avoids cable complexity problems while allowing dynamic adaption and fast reconfiguration. Here, we propose and investigate a novel optical wireless data-center network (OW-DCN) architecture based on nanoseconds semiconductor optical amplifier (SOA)-based wavelength selectors and arrayed waveguide grating router (AWGR) controlled by fast field-programmable gate array (FPGA)-based switch schedulers. The full architecture, including the design, packet-switching strategy, contention solving methodology, and reconfiguration capability, is presented and demonstrated. Dynamic switch scheduling with a FPGA-based switch scheduler processing optical label and software-defined network (SDN)-based reconfiguration were experimentally confirmed. The proposed OW-DCN was also achieved with a power penalty of less than 2 dB power penalty at BER &lt; 1 × 10−9 for a 50 Gb/s OOK transmission and packet-switching transmission.

Visible Light Communication: An Investigation of LED Non-Linearity Effects on VLC Utilising C-OFDM

The electro-optic output of light-emitting diodes commonly used in visible light communication systems is generally nonlinear in nature. It is particularly problematic when using advanced modulation formats, such as orthogonal frequency-division multiplexing (OFDM), which have a high peak-to-average power ratio due to clipping and distortion. In this work, we introduce the so-called C-transform to the system architecture, which utilises a Walsh–Hadamard matrix in conjunction with a discrete cosine transform to deterministically spread the information and reduce the peak-to-average power ratio (PAPR). Several bias points along the electro-optic transfer function were selected for comparison purposes, and the new transform was compared with more traditional formulations of OFDM. This paper determines that the C-transform-based OFDM demonstrated the highest degree of independence from the non-linearity and yielded superior bit-error rate (BER) results. We note an improvement of ~2.5 dB in the power penalty at a BER of 10−4 in comparison to OFDM.

Numerical simulation for European and American option of risks in climate change of Three Gorges Reservoir Area

Abstract With the climate change processes over times, all professions and trades in Three Gorges Reservoir Area will be influenced. One of the biggest challenges is the risk of rising sea level. In this situation, a large number of uncertainties for climate changes will be faced in Three Gorges Reservoir Area. Therefore, it is of importance to investigate the complexity of decision making on investing in the long term rising sea level risk related projects in Three Gorges Reservoir Area. This paper investigates the sea level and the temperature as the underlying assets in Three Gorges Reservoir Area. A real option model is constructed to evaluate potential sea level rising risk. We formulate European and American real option models into a linear parabolic variational inequalities and propose a power penalty approach to solve it. Then we obtain a nonlinear parabolic equation. It shows that the nonlinear parabolic equation is unique and solvable. Also, the solutions of the nonlinear parabolic equation converge to the solutions of the parabolic variational inequalities at the rate of order O(λ −k/2). Since the analytic solution of nonlinear parabolic equation is difficult to obtain, a fitted finite volume method is developed to solve it in case of European and American options, and the convergence of the nonlinear parabolic equation is obtained. An empirical analysis is presented to illustrate our theoretical results.

Improved Metastability of True Single-Phase Clock D-Flipflops With Applications in Vernier Time-to-Digital Converters

This paper investigates the metastability of true single-phase clock (TSPC) D flip flops (DFFs) and its impact on the resolution of Vernier time-to-digital converters (TDCs). The mechanisms of the metastability of TSPC DFFs are investigated and the analytical expressions of setup time and hold time are obtained. A shunt capacitor technique capable of reducing setup time and hold time to zero with no power and delay penalty is proposed. The impact of PVT (process, voltage, temperature) on the effectiveness of the proposed technique is quantified using simulation. Vernier TDCs, both right-shifting and left-shifting, with untuned and tuned DFFs are designed in TSMC 130 nm 1.2 V CMOS technology and analyzed using Spectre with BSIM3V3 device models. Simulation results demonstrate TDCs with tuned DFFs enjoy zero conversion error while the right-shifting and left-shifting TDCs with untuned DFFs have 1-bit and 5-bit conversion errors or 11% and 56% error rates, respectively.

Phase Retrieval-Based Coherent Receivers: Signal Design and Degrees of Freedom

Kramers-Kronig (KK) detection exploits properties of minimum-phase, single-sideband signals to recover the phase of a signal from its intensity. It offers many of the benefits of standard coherent detection, while not requiring a local oscillator, quadrature hybrid, or balanced photodiodes. Adding a carrier to a transmitted signal to render it minimum-phase, however, causes a power penalty for KK detection relative to standard coherent detection. We study the mutual information (MI) achieved by KK detection and the impact of signal and system design parameters, including excess bandwidth, carrier-to-signal power ratio, modulation order, probabilistic shaping, and chromatic dispersion, making comparisons to standard coherent detection and standard direct detection. We study the effective degrees of freedom for KK detection, confirming that it tends towards unity at high signal-to-noise ratio (SNR), supporting the classification of KK detection as coherent detection. At low SNR, however, KK detection is outperformed by standard direct detection in terms of MI per symbol. This study focuses on the fundamental performance of the detection methods under comparison, by numerically approximating ideal continuous-time signals and signal processing operations. The results and conclusions reported here will be constrained, in practice, by limitations of practical implementation, including those addressed in the Discussion section.

Mitigation of Atmospheric Attenuations in Hybrid Fiber-optical and Free-space Optical Channel for Last-mile Communication System

The aim of this research is to investigate the performance of a hybrid fiber-optical (FO) and free-space optical (FSO) communication system to reach the last mile, as well as to propose a technique to overcome atmospheric attenuation. Installing transmission cables between buildings is costly and difficult, but FSO technology can be implemented where fiber-optic cables cannot be installed. This work considers attenuation effects in weather conditions such as haze, thin fog, thick fog, and heavy fog. A single FSO channel (1*1), dual FSO channels (2*2), and four FSO channels (4*4) are cascaded in a fiber optic channel to reach the last mile and to mitigate attenuation in signal transmission over free space. The Q-factor, bit error rate (BER) at the receiver, and eye diagrams were analyzed for all cases. This system is demonstrated up to 3.5km FSO channel range for haze and thin fog conditions and 2.2km and 1.7km range for thick and heavy fog conditions. The system results show improvement in BER as 4.93e-040 for 1*1 FSO channel, 1.07e-078 for 2*2 FSO channel, and 1.28e-154 for 4*4 FSO channel in case of 22dB/km atmospheric attenuation for 1.4km range with minimum power penalty. A data stream of 10 Gbps was transmitted under four attenuation conditions, and the results show that 4*4 FSO channels have a better Q-factor and BER than other systems.

A Bidirectional RoF System for the Multi-Band Signal with Mitigation of the Nonlinear Effects

A bidirectional full duplex radio over fiber (RoF) system is proposed for multi-band signal generation and transmission. A multi-band signal is generated at the central station (CS), which includes 10 GHz baseband, 40, and 70 GHz millimeter-wave (mm-wave) by optical frequency multiplication technique of radio frequency (RF) local oscillator (LO) with frequency of 15 GHz. The simultaneous transmission of the 16-QAM OFDM-based multi-band downlink signal and 4-QAM uplink signal over a single fiber is demonstrated. The carrier for uplink transmission is extracted from the unmodulated downlink signal with tunable FBG which is modulated by OFDM-based 4-QAM uplink data obtained from the user end via an antenna. The frequency reuse from the downlink signal makes the base station (BS) free from the laser source. At the user end, the multi-band signals for multi-serve application are obtained by heterodyne beating of multiple bands. An increase in launch power induces fiber dispersion and non-linearities like self-phase modulation (SPM) and cross phase modulation (XPM), which depends on the nonlinear refractive index of the fiber. Different industrial standard fibers with common specifications and modulation format along with co-shared components are deployed, and system performance is analyzed. The stimulated Brillouin scattering (SBS) can be mitigated by optimizing the launch power within the SBS threshold. The nonlinear effects are minimized at the system level without the requirement of additional digital signal processor (DSP) . The theoretical and simulation analysis shows that the designed bidirectional RoF link exhibits an improved system performance for bidirectional transmission with negligible power penalty.

Volterra predistorter for the dynamic nonlinearity of LED.

In this Letter, we propose the application of a Volterra predistorter to compensate for the second-order nonlinear distortion generated in light-emitting diode (LED) communication systems. We demonstrate that a predistorter dedicated specifically to the LED has linear (not quadratic) numerical processing complexity. Experimental investigation performed using pulse amplitude modulation (PAM-4) indicates that it achieves similar performance as the classical Volterra equalizer located at the receiver. The highest measured gain in electrical signal to noise and interference power ratio of predistortion over linear equalization was at 300 Mbaud and was approximately 3.5 dB. At the same baud rate, the unpredistorted signal had a received optical power penalty of up to 2.5 dBm compared with the predistorted signal.