Non-return-to-zero Research Articles

High-speed performance evaluation of ultra-flexible polymer waveguides supporting meter-scale optical interconnects.

We demonstrate bandwidth measurement and high-speed data transmission of meter-scale connectorized ultra-flexible multimode waveguide links with a maximum length of 180 cm. The pulses propagating through the waveguides broadened linearly with the increase of the length from 20 cm to 240 cm and the estimated mode delay from the pulse broadening was 0.093 ps/cm. The corresponding waveguide bandwidth decreased inversely with the increase of waveguide length, leading to a bandwidth-length product of 42 GHz·m. Degradation in bandwidth due to the introduction of bending or twisting was small when the samples were bent with a bending radius as small as 1 mm for 3 turns or twisted for 4 full turns, respectively. Error-free transmission of 30 Gb/s non-return-to-zero (NRZ) signal was achieved with a record link length up to 140 cm to the best of our knowledge. Our results show that the demonstrated flexible waveguides have both excellent optical and mechanical properties and are ideal for high-speed optical interconnects application especially those have a strict requirement on flexibility.

Comparison of pre and post-dispersion compensation schemes with RZ, NRZ and Gaussian modulations for 10 GBPS and 40 GBPS transmission rates / Comparação de esquemas de compensação pré e pós-dispersão com modulações RZ, NRZ e Gaussina para as taxas de transmissão de 10 GBPS e 40 GBPS

In this paper, we investigate two dispersion compensation methods: post-compensation, and pre-compensation for transmission rates from 10Gbps to 40Gbps with return to zero (RZ), non-return to zero (NRZ) and Guassian modulations using single fiber mode-fiber (SMF) and dispersion compensating fiber (DCF). The influence of the DCF compensator dispersion with different transmission rates was studied in order to evaluate the performance of the proposed systems. The simulation results were validated through the analysis of the quality factor (Q-factor) and the bit error rate (BER), where it was verified that the post-compensation system with Gaussian modulation offered better performance results in function of the transmission rate variation.

Research of fiber nonlinear effects in WDM-PON based 5G fronthaul networks

In fifth-generation (5G) fronthaul networks, the wavelength division multiplexing passive optical network (WDM-PON) is considered as an important tool to address the advanced transmission requirements. The nonlinear effects occur when multiple wavelengths are transmitted simultaneously in the same optical fiber. In this paper, we investigate the four-wave mixing (FWM) and the cross-phase modulation (XPM) effects by using non-return-to-zero (NRZ), 4-level pulse amplitude modulation (PAM4), and optical duobinary (ODB) modulation formats in WDM-PON-based 5G fronthaul networks. The results show that ODB performs better when it comes to limiting the FWM and XPM effects because of its precoded attribute. Compared to the unpredictable sensitivity penalty based on NRZ and PAM4, the FWM-induced sensitivity penalty using ODB is reduced to 2[Formula: see text]dB. Moreover, the XPM-induced sensitivity penalty is measured as 1[Formula: see text]dB by adopting ODB, which is almost 5[Formula: see text]dB better than NRZ and PAM4 modulation formats.

High-speed waveguide Ge/Si avalanche photodiode with a gain-bandwidth product of 615 GHz

High-sensitivity and high-bandwidth receivers are always demanded for high-speed optical link systems. As a key element, an avalanche photodiode (APD) is often regarded as one of the most attractive options for achieving high sensitivity owing to the potential high internal gain. In this paper, a 48-GHz waveguide Ge/Si avalanche photodiode operating at the O-band (1310 nm) is designed with a lateral reach-through structure and fabricated with simplified processes. The fabricated APD shows a high primary responsivity of 0.93 A/W at the unit-gain voltage of−4.7V. It has an avalanche gain of 12.8 and a record gain-bandwidth product of∼615GHzwith an input optical power of−15dBmwhen operating at a bias voltage of−14V. The present Ge/Si APD is used successfully for high-speed data receiving, showing a sensitivity improvement about 7.6 dB for KP4-FEC operation (i.e., BER=2.4×10−4) with 50 Gbps non-return-to-zero (NRZ) data, compared with the case of using the reference PIN PD on the same chip. The sensitivity of the receiver with the present APD for NRZ signals is about−21.3dBm,−17.8dBm, and−12.6dBmfor KP4-FEC operation with different data rates of 50 Gbps, 80 Gbps, and 100 Gbps, while the sensitivity for four-level pulse amplitude modulation signals is about−13.2dBmand−11.3dBmfor KP4-FEC operation with different data rates of 25 and 50 Gbaud. Such high-performance APDs pave the way to achieve high-speed and high-sensitivity data transmissions.

Performance evaluation of MDM-FSO transmission system for varying atmospheric conditions

Abstract We report the designing of a free-space-optics (FSO) transmission system capable of transmitting high rate information by utilising novel mode division multiplexing (MDM) transmission technique. In the work reported, 2-channels transmitting 10 Gbps data, using either non-return-to-zero (NRZ) encoding scheme or return-to-zero (RZ) encoding scheme are modulated by using different Hermite–Gaussian (HG) modal beams of the single laser beam to realize of 20 Gbps transmission system. The system proposed is simulative analysed under the effect of different weather states. Also, we have compared the bit error rate (BER) and Quality factor (Q Factor) performance for RZ and NRZ encoding schemes in the system for varying weather states. The results reported show that NRZ encoding exhibits a superior performance. Also, we have analysed the system performance by taking into consideration atmospheric scintillation effect and the reported results show notable signal degradation in the presence of scintillation.

Micro-LED with red-green-blue super-pixel integration for simultaneous display and optical near field communication.

This work presents a novel all-in-one Micro-LED pixel (µLEDP) technology by integrating red-green-blue super-pixels (RGBSP) in a single unit cell. Measurement results show that the proposed µLEDP delivers excellent optical and electrical characteristics, including wide color gamut (109% NTSC), wide correlated color temperature range (2831.7-10016.8 K), and high modulation system bandwidth (58-62 MHz). To the best of our knowledge, the proposed integrated µLEDP achieves the highest data rate compared to published results based on other multi-color low-capacitance high-bandwidth LEDs. The maximum simulated non-return-to-zero (NRZ) and 4-level pulse-amplitude-modulation (PAM-4) data rates of 0.3-Gb/s and 1.1-Gb/s, respectively.

Modulation bandwidth improvement of III-V/Si hybrid MOS optical modulator by reducing parasitic capacitance.

In this work, we numerically and experimentally examined the impact of parasitic capacitance on the modulation bandwidth of a III-V/Si hybrid metal-oxide-semiconductor (MOS) optical modulator. The numerical analysis revealed that the parasitic capacitance between the III-V membrane and the Si slab should be considered to achieve high-speed modulation, particularly in the case of a thick gate oxide. We also fabricated a high-speed InGaAsP/Si hybrid MOS optical modulator with a low capacitance using a SiO2-embedded Si waveguide. The fabricated device exhibited a modulation efficiency of 0.245 Vcm and a 3 dB bandwidth of up to 10 GHz. Clear eye patterns with 25 Gbps non-return-to-zero (NRZ) modulation and 40 Gbps 4-level pulse amplitude modulation (PAM-4) were obtained without pre-emphasis.

A 5 Gb/s Time-Interleaved Voltage-Mode Duobinary Encoding Scheme for 3-D-Stacked IC

A time-interleaved duobinary encoding scheme for the low-power high-bandwidth memory (HBM) I/O interface is proposed with a 65-nm CMOS process. To reduce power consumption in HBM I/O using multiple through-silicon via (TSV) I/Os, a transmitter (TX) that performs duobinary signaling with a voltage-mode driver is proposed. A small area encoder is implemented to generate duobinary output and an edge-boosted pre-driver is proposed to improve the slew rate and the robustness against the process, voltage, and temperature (PVT) variations of the duobinary voltage-mode driver. To convert the duobinary signal into a non-return-to-zero (NRZ) signal, a one-tap decision feedback equalizer (DFE) is used at the receiver (RX). NRZ signal conversion is proposed using one reference voltage and one PMOS switch to reduce the hardware complexity caused by additional reference voltages. An eight-stacked TSV is emulated in the 65-nm CMOS process, and the emulated capacitance of each stack is 100 fF. The energy efficiency of the proposed transceiver chip is 0.373 pJ/b/pF with a 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> – 1 pseudorandom binary sequence at 5 Gb/s.

PAM-4 implementation study for future high-speed links

With the ever-increasing amount of data produced by the high energy physics experiments, the transmission rates from the detectors to the back-end stages must keep up. To mitigate the exponential growth of the total loss due to the increased bandwidth, the 4-Level Pulse-Amplitude Modulation (PAM4) could be envisaged. Where the line rate of Non-Return to Zero (NRZ) modulated signals is capping at 28 Gbps per lane, PAM4 allows the rate of 53.125 Gbps or above in extremely high-end applications. Investigating the implementation of such links in FPGA is one of the activities carried out by the Work Package 6 of the CERN EP Research and Development programme. A proof-of-concept system of high-speed links using PAM4-53.125 Gbps has been built, based on a Xilinx Virtex evaluation platform and various commercial optoelectronics transceivers. PAM4 standard Forward Error Correction (FEC) codes have also been implemented and characterized over electrical and optical layers in terms of coding gain and latency. Finally, the telecom and datacom markets were investigated to identify development perspectives for the research and development for future links. In this paper, the performance of the proof-of-concept implementing these high-speed links is presented and the current and future challenges for an error-free communication are discussed.

High-Performance Compensation Dispersion with Apodization Chirped Fiber Bragg Grating for Fiber Communication System

The effect of dispersion will interfere with the signal transmission. Several ways can be done in compensating the dispersion such as by utilizing dispersion compensator fiber (DCF) or chirp fiber Bragg grating (CFBG). The dispersion compensation schemes with DCF are expensive and it also causes nonlinear optical effects, meanwhile, the CFBG can reduce costs and promise better results. In this study, an Apodization Chirped Fiber Bragg Grating (ACFBG) has been developed as a dispersion compensator with Optisystem with non-return to zero (NRZ) 20 Gbps. It is found that the Gaussian Cubic-CFBG apodization with a size of 90 mm had the highest Q-factor evaluation of 20,776 dB for a 250 km dispersion compensation scheme. this result is much larger than the previous CFBG dispersion compensation scheme. This study also confirmed that the Gaussian Apodization was the best profile compared to Tanh Apodization, from the evaluation of the Q-factor, Tanh cubic-CFBG only obtained a Q-factor of 9.6 dB. Certainly, the high performance of ACFBG as a dispersion compensator is very useful to support optical communication systems

Total Internal Reflection Lens for Optical Wireless Receivers

This work considers the use of a freeform total internal reflection (TIR) lens for optical concentration and provides for the first time experimental results in the context of optical wireless communications (OWC). The lens is placed on a surface-mounted device (SMD) avalanche photodiode (APD) to minimize position tolerances and simplify assembly. The lens achieves a concentration ratio of go = 44.7 (16.5 dB) within the FOV center and exhibits an acceptance angle of ±5°. The TIR lens approach is validated by comparing eye diagrams and bit error ratios (BER) of a receiver with and without a TIR lens. For the measurements, non-return-to-zero (NRZ) on-off keying (OOK) signals are transmitted with a data rate of 1.289 Gbit/s.

A Receiver Front-End for VCSEL-Based Optical Links With 49 UI Turn-On Time

A fast turn-on front-end (FE) for a burst-mode nonreturn to zero (NRZ) receiver targeting vertical cavity surface-emitting laser (VCSEL)-based optical links operating at 10 Gb/s/ch is presented. Its bandwidth and power are reconfigurable for energy-efficient burst-mode operation. The circuit design for 4.9 ns power-ON time using a power-gating approach is presented. Rapid power-ON is achieved using the regeneration of a high-speed latch, activated by a quarter-rate clock. Implemented in a 65-nm CMOS technology, the proposed FE consists of a shunt-feedback transimpedance amplifier (TIA), a configurable one-stage or four-stage postamplifier (PA) and an offset compensation loop. By reconfiguring the number of stages in the PA from four to one, power dissipation, and the FE bandwidth are reduced during periods of link inactivity while still maintaining sufficient gain to allow the detection of an incoming burst. The presented work is supported by simulation and measurement results with optical inputs at 10 Gb/s. The results demonstrate a 4.9-ns turn-on time, corresponding to 49 unit intervals (UIs). The overall FE dissipates 5.7 mW at 10 Gb/s (0.57 pJ/bit) and 1.9 mW during idle periods. The complete receiver of each channel occupies an area of 95 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}\,\,\times81\,\,\mu \text{m}$ </tex-math></inline-formula> . A 5% area overhead is introduced by the burst sensing circuit.

Investigation of WDM-MDM PON employing different modulation formats

Advancement in the technology and optical communication sector has led to an increase in the demands of high bit rate and bandwidth, required for reliable data transmission. To meet such demands, future generation optical networks came into existence. In this paper, we propose a 100 Gbps, 4-channel WDM-MDM PON with two input wavelengths of 1550 nm and 1555 nm and using LP 01 and LP 11 modes. The system performance has been analyzed for different internal parameters considering return-to-zero (RZ), non-return-to-zero (NRZ), alternate mark inversion (AMI) and duobinary return-to-zero (DRZ) modulation schemes. DRZ modulation outperforms the other encoding schemes resulting in achievement of an acceptable bit error rate (BER) of ≤ 10−14 over 10 km of fiber length at a 25 Gbps data rate.

A Scalable 32–56 Gb/s 0.56–1.28 pJ/b Voltage-Mode VCSEL-Based Optical Transmitter in 28-nm CMOS

An optical transmitter (TX) data path is demonstrated in 28-nm CMOS which drives an 850-nm vertical-cavity surface-emitting laser (VCSEL) up to 56 Gb/s non-return-to-zero (NRZ). A dc-coupled single-ended voltage-mode driver employs area- and energy-efficient equalization techniques including slew-rate-based pulse-shaping at <40 Gb/s, active shunt peaking, and a three-tap feed-forward equalizer (FFE) at ≥40 Gb/s, for an optimum TX optical eye. At a 56 Gb/s data rate, the energy efficiency of 1.28 pJ/b from a 1.15 V supply is measured which is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$&gt; 2\times $ </tex-math></inline-formula> more energy- and area-efficient than optical TXs reported to date. The highly digital circuit architecture enables the supply scalability to 0.7 and 0.85 V to operate the TX at 32 and 40 Gb/s at 0.56 and 0.77 pJ/b, respectively, which is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\ge 4\times $ </tex-math></inline-formula> more energy-efficient than the prior art.

CMOS compatible ultra-compact MMI based wavelength diplexer with 60 Gbit/s system demonstration.

We design and experimentally demonstrate an ultra-compact 1310/1550 nm wavelength diplexer based on a multimode interference (MMI) coupler. The proposed device is designed at the first imaging length for 1550 nm wavelength resulting in an MMI length of only 41 µm. In order to improve the extinction ratio, the output ports are made asymmetric in width. A low insertion loss (< 1dB) and high extinction ratio (> 20 dB) is measured at the two operating wavelengths. It also displays a wide 3-dB bandwidth of 100 nm centered around 1310 nm and 1550 nm wavelengths. Furthermore, an on-chip wavelength demultiplexing experiment carried out on the fabricated device, with a non-return-to-zero (NRZ) on-off keying (OOK) signal at 60 Gbit/s, shows clear eye diagrams for both the wavelengths.

High-speed silicon microresonator modulators with high optical modulation amplitude (OMA) at input powers >10 mW.

A high-speed silicon photonic microdisc modulator is used with more than 10 mW optical power in the bus waveguide, extending the optical power handling regime used with compact silicon resonant modulators at 1550 nm. We present an experimental study of the wavelength tuning range and biasing path required to shift the resonant frequency to the optimal point versus on chip power. We measure the optical modulation amplitude (OMA) along different biasing trajectories of the microdisc under active modulation and demonstrate an OMA of 4.1 mW with 13.5 mW optical power in the bus waveguide at 20 Gbit/s non-return to zero (NRZ) data modulation.

Transporting MIL-STD-1553 Signals by Means of Optical Wireless Interfaces

Today, the on-board Spacecraft (SC) communication requires an impressive network of massive wires, both in flight and in the Assembly Integration and Test (AIT) phase. Here, we present the design and the experimental characterization of novel Optical Wireless Communication (OWC) transceivers compatible with MIL-STD-1553B, which is the shared bus predominantly deployed in SCs. Each transceiver works as an interface that transports the bipolar Manchester-coded signal by converting it to/from the optical domain. These OWC interfaces can effectively reduce the overall weight and cost of the SC and can also largely decrease the AIT time. Since they are fully analog and do not need any microprocessors or Digital Signal Processing, they have a small footprint and a very low power consumption. We initially characterize the transceivers using a non-return-to-zero (NRZ) signal, then we used them to replace a cable and connect a pair of test units, transmitting MIL-STD-1553B signals: the measurements show that our solution has a good power budget (+65dB), which will allow the interoperability with MIL-STD-1553B boards in a wide range of scenarios. Furthermore, it is realized by means of commercially available components; it could also be implemented by using proven space-graded devices.

Design of a colorless transmitter based on a low-resonant Fabry–Perot Laser for applications in WDM-PON

In this paper, we propose and numerically analyze a colorless transmitter based on a Fabry–Perot Laser Diode (FPLD) with an emission wavelength that is externally tuned using a spectral sliced super luminescent diode. The Fabry–Perot based colorless transmitter is designed to support 100 GHz spaced longitudinal modes with a central wavelength of 1552.525 nm. We study the cavity’s end-facets reflectivity, in order to determine a configuration that allows a low injection power requirement with high transmission performance. Finally, we analyze the transmission performance of the colorless transmitter in a Passive Optical Network (PON) at 2.5 Gbps bit rate with a Non-Return-to-Zero (NRZ) using the following configuration: transmission distances up to 120 km, seeding carrier with 3-dB bandwidths (12.5 GHz, 25 GHz and 50 GHz), two optical channels at 1552.525 nm (central mode) and 1550.125 nm (fourth side mode). The results show that reflectivities of 10% and 90% for the front-facet and the end-facet, respectively, allow a good trade-off between the injection power requirement for tuning the colorless source avoiding the inter-channel interference, and the transmission performance in terms of Bit Error Rate (BER). Thus, in all scenarios, it is possible to obtain Side Mode Suppression Ratios (SMSR) above 30 dB using injection power below to 0.3 mW. Besides, an error-free transmission is achieved for distances over 25 km, in the case with the injection carrier is less than 25 GHz 3-dB bandwidth. Hence, the proposed colorless source can be a suitable feasible solution to implement optical access networks.

Performance enhancement of hybrid fiber wavelength division multiplexing passive optical network FSO systems using M-ary DPPM techniques under interchannel crosstalk and atmospheric turbulence

The performance of moment generating function approaches, specifically Chernoff bound (CB) and modified Chernoff bound (MCB), is examined and improved in this study. We evaluates and enhances the performance of a wavelength division multiplexing (WDM) technique for free-space optical (FSO) fibre communications based on passive optical network (PON) using the M-ary digital pulse-position modulation (M-ary DPPM) schemes under amplified spontaneous emission (ASE) noise effects, interchannel crosstalk (ICC), and atmospheric turbulence (AT). We use a data rate of 2.5 Gbps for eight channels over a PON/DWDM-FSO optical fibre system in the C-band with 100 GHz channel spacing start from 1550 nm. The results achieve 20 Gbit/s transmissions (2.5 Gbps $$\times $$ 8 channels). This is a technology that can have extended leverage, higher data rates, power-efficient, and is considered an ideal option for the provision of bandwidth for potential access networks. When compared to the CB at a low gain (G = 8), the MCB outperforms the Gaussian approximation at high gain (G = 30). Because of its superior performance at a high gain (G = 30), the MCB offers the tightest limit on the bit error rate (BER). In comparison to an equivalent on–off keying (OOK) non-return-to-zero (NRZ), the M-ary DPPM scheme with a coding level (M) of 2 improves average power about by 2.9 dB at a data rate of 2.5 Gbps on the 1550 nm wavelength and BER of $${10}^{-{9}}$$ . The sensitivity of the M-ary DPPM modulation scheme remains improved over OOK in the presence of ICC. The lower power penalty is predicted to be approximately 0.2–3.0 dB in the DWDM-FSO systems for low coding level M $$=$$ 2. We achieve a lower power penalty at 0.2–3.0 dB for the hybrid fiber DWDM/PON-FSO optical communication system at a BER of $${10}^{-{9}}$$ . At a target BER of $${10}^{-{12}}$$ , the hybrid OOK-NRZ/M-ary DPPM offers about 4–8 dB of optical signal-to-noise-ratio improvements over the M-DPPM of the WDM-PON/FSO link for strong turbulence. The results demonstrated that the M-ary DPPM and the optical relaying amplification technique are powerful treatments for mitigating the impacts of ASE noise, AT, and ICC.

An optical access scheme with 1.25Gbit/s NRZ downstream signals over 6GHz subcarrier for next generation mobile systems application

In order to solve the problem of network frequency resource congestion from the central office (CS) to the base station (BS) in sixth generation (6G) mobile communication systems, we design a passive optical network (PON) access scheme. 1.25Gbit/s non-return-to-zero (NRZ) downstream signals over 6GHz subcarrier are successfully transmitted in the 20km single-mode fiber (SMF) and allocated to 4 optical network units (ONUs). The radio frequency (RF) spectrums, optical spectrums, eye-diagrams and bit error rate (BER) before and after transmission of NRZ signals in the system were measured and analysed. The results show that, this scheme can provide high-speed, stable and secure data communication.