On-off Keying Signals Research Articles

Theoretical study of all-optical RZ-OOK to NRZ-OOK format conversion in uniform FBG for mixed line-rate DWDM systems

In this work we study all-optical multi-channel return-to-zero (RZ)–on-off keying (OOK) to nonreturn-to-zero (NRZ)–OOK format conversion in single uniform fiber Bragg grating (FBG) for mixed line-rate dense wavelength-division multiplexing systems using mathematical simulations. Forty and 20 Gbit/s RZ–OOK signals with 33% and 50% duty cycles are converted to NRZ–OOK signals in single uniform FBG with 21% reflectivity. Impact of amplitude noise from FBG contrast profile on modulation format conversion efficiency is also studied.

Estimation of the Threshold in Energy and Kurtosis Detectors for IR-UWB OOK Systems

In this paper, we propose a method to estimate the threshold value for energy detector (ED) and kurtosis detector (KD) in impulse radio ultra-wideband on-off keying (OOK) scheme. Estimation of threshold value is obtained from the parameters of the probability density functions (PDF) of two hypotheses in OOK signaling. Gaussian and lognormal distributions are used for ED receiver and KD receiver, respectively. Symbols are transmitted in packets and the PDF's parameters of the hypotheses are estimated by using training symbols in each packet. The approximation of the threshold value is obtained by using these parameters. Simulation results show that the estimated threshold has high accuracy for different amounts of signal to noise ratios and integration intervals.

Co-Channel Interference Mitigation Technique for Non-Coherent OOK Receivers

In this paper, we propose an interference mitigation technique for non-coherent on-off keying (OOK) receivers with respect to co-channel interference source. If the interfering signal (undecipherable at the receiver) is greater or equal to the desired signal, no reception is possible. A method is presented that mitigates this effect by inserting a blank space during the transmission of binary `1' in OOK signaling. Differential detection at the non-coherent receiver is employed to remove the symbol constant interference using the interference statistic from the initially inserted blank space. The proposed method not only mitigates the interference effect but uses the interfering signal power as another degree of freedom to detect the desired signal better.

Gaussian-like dual-wavelength prescaled clock recovery with simultaneous frequency-doubled clock recovery using an optoelectronic oscillator

A novel multifunctional frequency-doubling optoelectronic oscillator (FD-OEO) mainly based on a Mach-Zehnder modulator (MZM) cascaded with a phase modulator (PM) and a subsequent optical bandpass filter (OBPF) is proposed. We experimentally demonstrate simultaneous operations of frequency-doubled optical clock (FD-OC) recovery, low-duty-cycle dual-wavelength prescaled OC recovery and error-free fourfold time division demultiplexing with the proposed OEO injected with a 4 × 25-Gb/s optical time-division-multiplexing (OTDM) signal. We show that the proposed FD-OEO operates well for both the differential phase shift keying (DPSK) and on-off keying (OOK) modulation formats. The extracted dual-wavelength prescaled OC is proved to be nearly transform-limited with Gaussian-like shape. Furthermore, all four 25-Gb/s tributaries can be selectively demultiplexed by adjusting the phase shifters in the OEO loop. The power penalty at a bit error rate (BER) of 10(-9) is measured to be 2.4 dB, 1.2 dB for the best channel for DPSK signal and to be 2.5 dB, 1.1 dB for the best channel for OOK signal. In addition, as an extra benefit of the OEO, low-phase-noise prescaled electrical clock (EC) is also extracted.

Effective optical clock recovery and simultaneous fourfold demultiplexing of OTDM signal using an optoelectonic oscillator

We propose and demonstrate a novel scheme for clock recovery and simultaneous fourfold optical time-division demultiplexing using a dual-parallel Mach-Zehnder modulator based optoelectronic oscillator. 25-GHz prescaled optical clock with a 23% duty cycle and a 22-dB extinction ratio is successfully extracted from both 100-Gb/s on-off keying (OOK) and differential phase-shift keying (DPSK) optical time-division-multiplexing (OTDM) signal. The timing jitters (100 Hz to 10 MHz) are measured to be 195.9 fs and 125.6 fs for the optical clock extracted from the 100-Gb/s OOK and DPSK signal, respectively. Error-free optical time-division demultiplexing is also achieved simultaneously with clock recovery. By adjusting the phase shifter in the OEO loop, all four channels can be selectively demultiplexed. The power penalties at a bit error rate (BER) of 10⁻⁹ for the four demultiplexed channels are measured to be between 0.8 dB and 1.2 dB for the OOK signal and between 0.9 dB and 1.5 dB for the DPSK signal.

Design of Visible Light Communication Receiver for On-Off Keying Modulation by Adaptive Minimum-Voltage Cancelation

In this paper, a new design of visible light communication (VLC) receiver for on-off keying (OOK) modulation is proposed. The design is based on the cancelation of minimum offset voltage of the received OOK signal, using a novel minimum-voltage detection circuit. This circuit is capable of tracking the minimum voltage of an input signal even if its value increases with time. Experimental results show that the proposed receiver is immune to the interference from sunlight and indoor fluorescent lights.

A Crystal-Less Temperature-Independent Reconfigurable Transmitter Targeted for High-Temperature Wireless Acoustic Telemetry Applications

A reconfigurable acoustic telemetry transmitter that employs crystal-less temperature-independent frequency reference has been realized in a 1- μm silicon-on-insulator complementary metal-oxide-semiconductor process. The transmitter can be configured to transmit either a three-channel chirp signal or a six-channel on-off keying (OOK) signal to provide flexibility based on channel characteristics. Different frequencies derived from the crystal-less temperature-independent frequency reference are directly modulated by input data before being combined and sent through a multiple-feedback low-pass filter. The resulting three-channel chirp signal achieves a total data rate of 60 b/s, whereas the six-channel OOK signal achieves a total data rate of 120 b/s. The frequency reference is realized through a frequency-locked loop that employs a resistor-capacitor phase shifter with a resistor temperature coefficient cancellation technique. It achieves a frequency inaccuracy of ±1.94% over the temperature range of 175 °C ~ 275 °C. Consuming 9 mW and occupying 25 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , this brief is the first reported integrated solution targeted for high-temperature acoustic telemetry in oil-drilling applications with the highest reported data rate.

Ultra-Wideband and 60-GHz Generation and Transmission Over a Wavelength Division Multiplexing-Passive Optical Network

A novel scheme to simultaneously generate an on-off keying (OOK) impulse radio ultra-wideband (IR-UWB) signal, a 60-GHz millimeter-wave (mmW) signal, and a baseband signal in the optical domain using a Sagnac loop is proposed and demonstrated. In the proposed system, a polarization beam splitter (PBS), a fiber Bragg grating (FBG), and two back-to-back connected polarization modulators (PolMs) are incorporated in the Sagnac loop. An OOK Gaussian pulse signal is modulated on a clockwise transmitted optical carrier by the first PolM and then converted to an OOK UWB impulse signal at the FBG serving as an edge filter, and the counterclockwise transmitted optical carrier is simultaneously modulated by a baseband signal and a 30-GHz mmW signal at the second PolM. By introducing a ? phase shift between the clockwise and counterclockwise optical carriers, the optical carrier of the 30-GHz signal is suppressed when applied to a polarizer. As a result, a frequency-doubled mmW signal at 60 GHz is generated by beating the two first order sidebands at a photodetector. Due to the velocity mismatch between the counterclockwise light wave and the clockwise microwave carrier, the OOK signal and the baseband signal can travel through the other PolM with negligible modulation; thus no interference from another signal would be introduced. Error-free transmission of a UWB signal at 2.5 Gbps and a wired baseband signal at 2.5 and 5 Gbps over a 25-km single-mode fiber is achieved. A frequency-doubled mmW signal at 60 GHz is also obtained.

OOK-to-QPSK modulation-format conversion based on two gain-transparent SOAs

In this paper, the system scheme of on–off keying (OOK) to quadrature phase-shift keying (QPSK) format conversion is proposed, which is based on two gain-transparent semiconductor optical amplifiers (GT-SOA). GT-SOA is used as a simple all-optical phase modulator, which is no effects of cross gain modulation and four-wave mixing existing in conventional SOA. The assistant light is used to speed up the SOA carrier recovery time. The principles of OOK to QPSK format conversion are expounded. The influences of the assistant light power and signal light power on the conversions are numerically analyzed. The OOK signal can still be exactly converted to the QPSK signal with the power of OOK signal being changed within a certain range.

Optimal BER-Balanced Combining for Weighted Energy Detection of UWB OOK Signals

For the demodulation of ultra-wideband (UWB) on-off keying (OOK) signals, some weighted energy detection (WED) schemes have been proposed. However, the schemes available suffer from unbalanced bit error rates (BERs) for bits "0" and "1". Therefore, in this letter we will address the optimal BER-balanced WED. Specifically, we incorporate the BER balance requirement into the WED formulation and obtain the optimal weighting vector by solving a nonlinear convex optimization problem. To bypass the computational complexity required by the convex optimization, we derive a simple but near-optimal weighting vector. Simulations illustrate that the proposed BER-balanced WED schemes can achieve almost the same BER performance as the maximum likelihood (ML) demodulator, which is optimal in terms of BER performance but produces unbalanced BERs for different bits.

Improvement of OOK signals with a polarization-independent feed-forward control circuit using an electro-absorption modulator

An optical-and-electrical hybrid scheme for improving on–off keying (OOK) signals is described. It is a feed-forward (FF) control circuit composed of an optical coupler, a photo-detector, and an electro-absorption (EA) modulator, which works to suppress “on” level fluctuations. Owing to the use of an EA modulator, the circuit operates irrespective of the polarization state of the input signal. In addition, the scheme can also improve the extinction ratio (ER) of OOK signals. Experiments were conducted to demonstrate the noise suppression and the ER improvement.

Review on SOA-MZI-based photonic add/drop and switching operations

Semiconductor optical amplifier-Mach-Zehnder interferometer (SOA-MZI) is a technologically mature optical device that can be exploited for a wide range of operations on both amplitude and phase modulated signals, with performance limited by the carrier lifetime in the SOAs. Recent advances on SOA structures have demonstrated their suitability for high quality, ultra-fast photonic signal processing, making SOA-MZI a good candidate for elaborating signals in new generation high-capacity optical networks. Dynamic wavelength switching/routing and add/drop operations are expected to bring benefits in future optical networks in terms of improved system flexibility and efficiency. The capability of performing such operations directly in the optical domain can significantly reduce the number of opto/electrical and electro/optical conversions in the routing nodes, reducing their power consumption and their latency time. Moreover, since phase-shift keying (PSK) formats or other advanced modulation formats involving both amplitude and phase modulation, start to coexist in optical communication systems with the conventional on-off keying (OOK) modulation format, the availability of a single device, suitable for processing all these different signals, is mandatory. The SOA-MZI fits all these requirements for both OOK and constant-envelope phase-modulated signals, providing a compact and flexible solution. Here we review on the use of the SOA-MZI for carrying out alloptical switching operations, by realizing wavelength conversion and add/drop functionalities, both for OOK and differential binary phase shift keying (DPSK) signals up to 40 Gb/s. Power penalties lower than 2 dB are demonstrated in all cases.

System Wide Implementation of Photonically Generated Impulse Radio Ultra-Wideband for Gigabit Fiber-Wireless Access

In this paper, we comprehensively review our research work on system wide implementation of photonically generated IR-UWB signals based on relaxation oscillations of a semiconductor laser. Firstly, we present our novel approach as a flexible method for photonic generation of high speed impulse radio ultra-wideband (IR-UWB) signals at 781.25 Mbps with on-off keying (OOK) and binary phase shift keying (BPSK) modulation formats. We further advance the state-of-the-art to include multi-Gigabit IR-UWB signal generation. Both OOK and BPSK signals comply with the Federal Communications Commission (FCC) regulation. Secondly, we implement UWB fiber transmission systems and study hybrid fiber-wireless transmission performance at a system level. This is accomplished by employing our digital signal processing (DSP) assisted receiver. The photonic generation method is superior to the state-of-the-art electronic generation method in terms of transmission bit-error rate performance. Moreover, photonic IR-UWB generation is shown to be capable of longer wireless reach due to its lower bandwidth limitation. Finally, we experimentally demonstrate the integration of a relaxation oscillations-based UWB photonic generation system into existing wavelength division multiplexing passive optical networks (WDM-PON) infrastructure. This provides converged Gigabit indoor wireless and wireline access services.

Broadband Modulation Performance of 100-GHz EO Polymer MZMs

We experimentally characterize the performance of 100-GHz electro-optical polymer Mach-Zehnder modulators in both dual-drive and single-drive versions using broadband modulation. For the dual-drive version, we measure bit-error rate (BER) at 80 Gbit/s for differential phase-shift keying (DPSK) and >; 90 Gbit/s for on-off keying (OOK). The eye diagrams of 100 Gbit/s OOK and S21 measurement of up to 110-GHz further indicate a response bandwidth of >;100 GHz. Tunable-chirp operation is also demonstrated by changing the phase and amplitude of each driving signal. For the single-drive version, a BER of 10-9 is achieved for both 100-Gbit/s OOK and DPSK signals without optical or electrical equalization. The single-drive version shows a 7-dB bandwidth of >; 110-GHz and a chirp factor of as low as -0.02.

All-Optical OOK to 16-QAM Modulation Format Conversion Employing Nonlinear Optical Loop Mirror

This paper proposes and numerically demonstrates an all-optical on-off keying (OOK) to 16 quadrature amplitude modulation (QAM) format conversion using nonlinear optical loop mirror (NOLM) based on cross-phase modulation (XPM) and parametric amplification in optical fibers. The 16-QAM signal is generated by the superposition of two quadrature phase shift keying (QPSK) signals with different amplitudes. OOK to QPSK modulation format conversion is achieved by XPM in one highly nonlinear fiber (HNLF). The amplitude ratio 2:1 of two QPSK signals can be realized by parametric amplification. The feasibility of OOK to 16-QAM modulation format conversion is confirmed at the symbol rate of 10 Gs/s by numerical simulation with the length of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$2^{7}-1$</tex></formula> pseudo random binary sequence (PRBS) input OOK signals. The tolerance of power deviation of the converter is also analytically evaluated.

Demonstrations of 10 and 40 Gbps upstream transmissions using 1.2 GHz RSOA-based ONU in long-reach access networks

Carrier-distributed long-reach passive optical network (LR-PON) is a promising candidate for future access networks. In this work, we analyze and compare the 4×2.5Gb/s and 4×10Gb/s upstream traffics in a carrier-distributed LR-PON using four wavelength-multiplexed 2.5Gb/s on–off keying (OOK) and 10Gb/s optical orthogonal frequency division multiplexing-quadrature amplitude modulation (OFDM-QAM) signals. Four commercial 1.2GHz bandwidth reflective semiconductor optical amplifiers (RSOAs) are used in each optical networking unit (ONU) for the generation of the upstream signal. Due to the limited bandwidth of the RSOA, only up to 2.5Gb/s upstream OOK signal can be generated. However, by using the spectral efficient modulation, such as OFDM-QAM, 10Gb/s data rate can be achieved. 20, 50 and 75km fiber transmissions are also compared using the two different kinds of modulation respectively.

Comparison of Kurtosis and Fourth Power Detectors with Applications to IR-UWB OOK Systems

On-off keying (OOK) is one of the modulation schemes for non-coherent impulse radio Ultra-wideband systems. In this paper, the utilization of the kurtosis detector (KD) and fourth power detector (FD) receivers for OOK signaling is introduced. We investigate the effect of integration interval and the optimum threshold on the performance of energy detector (ED), KD and FD receivers. The semi analytic expression of BER is obtained by using generalized extreme value distribution function for KD and FD receivers. From performance point of view, the simulation results show that FD receiver outperforms KD and ED receivers. In contrast, the sensitivity to the optimum threshold is greatly reduced in KD receiver compared to ED and FD receivers.

A 2.4 GHz ULP OOK Single-Chip Transceiver for Healthcare Applications

This paper describes an ultra-low power (ULP) single chip transceiver for wireless body area network (WBAN) applications. It supports on-off keying (OOK) modulation, and it operates in the 2.36-2.4 GHz medical BAN and 2.4-2.485 GHz ISM bands. It is implemented in 90 nm CMOS technology. The direct modulated transmitter transmits OOK signal with 0 dBm peak power, and it consumes 2.59 mW with 50% OOK. The transmitter front-end supports up to 10 Mbps. The transmitter digital baseband enables digital pulse-shaping to improve spectrum efficiency. The super-regenerative receiver front-end supports up to 5 Mbps with -75 dBm sensitivity. Including the digital part, the receiver consumes 715 μW at 1 Mbps data rate, oversampled at 3 MHz. At the system level the transceiver achieves PER=10 (-2) at 25 meters line of site with 62.5 kbps data rate and 288 bits packet size. The transceiver is integrated in an electrocardiogram (ECG) necklace to monitor the heart's electrical property.

A novel combined WDM-PON with a single shared DI using downlink DPSK and uplink remodulated OOK signals

We propose a novel downlink optical carrier remodulated wavelength-division-multiplexed passive optical network (WDM-PON) architecture, in which two WDM-PONs whose wavelength locate in different wavebands share a single delay interferometer (DI) in remote node (RN) to demodulate the downlink data simultaneously. 10-Gb/s downlink differential phase-shift-keying (DPSK) signal and 1.25-Gb/s remodulated uplink On-Off keying (OOK) signal are generated and measured. Experiment results show that crosstalk between the two WDM-PONs is negligible even though the two PONs share a single DI. With our novel scheme, the single DI can be shared by more users in different PONs, which can reduce the cost of optical network unit (ONU). Meanwhile, Rayleigh backscattering noise is eliminated by combining these two PONs with different wavebands.

Adding channels with PSBT format at 40 Gbit/s in an existing 10 Gbit/s optical network

Until recently, the wavelength-division-multiplexed (WDM) transmission system has reached record capacities and distances due to innovations such as FEC (Forward Error Correction), distributed Raman amplification, new transmission fiber and advanced optical format. Optical-communication systems exclusively employed conventional On-Off Keying signals in either Non-Return-To-Zero (NRZ) or Return-To-Zero (RZ) format. Recently a number of advanced modulation formats have attracted attention. Some of these formats carry information through On-Off-Keying but also modulate the optical phase in order to enhance the robustness of signal to chromatic dispersion, optical filtering and non-linearities. Through extensive sets of simulation results, we showed that it is possible to replace a channel with higher bit-rate on existing DPSK or OOK at 10 Gbit/ s transmission link. Duobinary formats are ideal candidates to do it and are known for their low spectral range and high tolerance to residual chromatic dispersion. These particularities make them very attractive for both high bit rates and high distance-transmissions. Today, Phase Shaped Binary Transmission (PSBT) is considered as being the promising format for the deployment of 40 Gbit/ s technology on existing links at 10 Gbit/ s WDM long haul transmissions.