On-off Keying Signals Research Articles

Demonstration of optical de-aggregation of a single 10-Gbit/s QPSK signal to two 5-Gbit/s OOK signals using nonlinear wave mixing and constellation biasing.

Optical data format de-aggregation enables the conversion from a single higher-order phase-encoded data channel coming from a high-bandwidth network into two amplitude-modulated signals that may be commonly used in lower-bandwidth local information systems. We experimentally demonstrate the optical de-aggregation of a 10-Gbit/s quadrature phase-shift keyed (QPSK) signal into two 5-Gbit/s on-off keyed (OOK) signals. Using wave mixing in a highly nonlinear fiber (HNLF), we apply two optical effects simultaneously to the input signal: (a) constellation squeezing, in which the 10-Gbit/s QPSK signal is de-aggregated into two different 5-Gbit/s binary phase-shift keying (BPSK) signals, and (b) constellation biasing, in which the coherent addition of a continuous-wave (CW) bias and the two BPSK signals shifts the data constellation points, resulting in only amplitude modulation and two different 5-Gbit/s OOK signals. The optical signal-to-noise ratio (OSNR) differences at a bit error rate (BER) of 3.8·10-3 between the back-to-back (B2B) transmitted OOK signal and the two recovered OOK signals using direct detection are 1.9 dB and 3.2 dB.

Improved Frequency Sweep Keying CDMA Using Faster R-CNN for Extended Ultrasonic Crosstalk Reduction

Ultrasonic sensors are inexpensive and provide highly accurate measurements, even with simple hardware configurations, facilitating their use in various fields. When multiple ultrasonic sensors exist in the measurement space, crosstalk occurs due to other nodes, which leads to incorrect measurements. Crosstalk includes not only receiving homogeneous signals from other nodes, but also overlapping by other signals and interference by heterogeneous signals. This paper proposes using frequency sweep keying modulation to provide robustness against overlap and a faster region-based convolutional neural network (R-CNN) demodulator to reduce the interference caused by heterogeneous signals. The demodulator works by training Faster R-CNN with the spectrograms of various received signals and classifying the received signals using Faster R-CNN. Experiments implementing an ultrasonic crosstalk environment showed that, compared to on–off keying (OOK), phase-shift keying (PSK), and frequency-shift keying (FSK), the proposed method can implement CDMA even with shorter codes and is robust against overlap. Compared to correlation-based frequency sweep keying, the time-of-flight error was reduced by approximately 75%. While the existing demodulators did not consider heterogeneous signals, the proposed method ignored approximately 99% of the OOK and PSK signals and approximately 79% of the FSK signals. The proposed method performed better than the existing methods and is expected to be used in various applications.

Direct air–water communication by using an optical-acoustic method

Direct air–water communication by using an optical-acoustic method

All-optical wavelength and format conversion of DQPSK-to-PAM4 using DLI and pump assisted NOLM

All-optical wavelength and format conversion of DQPSK-to-PAM4 using DLI and pump assisted NOLM

An OOK and Binary FSK Reconfigurable Dual-Band Noncoherent IR-UWB Receiver Supporting Ternary Signaling

This article presents a multiband low-power and low-complexity impulse radio ultrawideband (IR-UWB) noncoherent receiver. The proposed receiver can be digitally reconfigured in three different modes of operation, including two single-band modes and one concurrent dual-band mode. In the two single-band modes, the proposed envelope detection architecture is capable of receiving and demodulating an on–off keying (OOK) pulse stream at RF center frequencies of 2.8 or 4.8 GHz. In the concurrent dual-band mode, the proposed architecture is able to demodulate binary frequency-shift keying (FSK), in addition to OOK demodulation, at center frequencies of 3 and 5 GHz. The receiver is composed of a reconfigurable low-power differential low noise amplifier (LNA), a fully differential squarer (self-mixer circuit), low-pass filter (LPF), and variable gain baseband (BB) amplifiers. The receiver is fabricated in TSMC 130-nm CMOS process technology. The receiver can operate at up to 150 Mb/s with the ternary signaling that is enabled by the binary FSK modulation combined with the OOK modulation in concurrent dual-band mode. At its maximum gain, the receiver achieves a sensitivity of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$-$</tex-math> </inline-formula> 72 dBm at a bit error rate (BER) of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10^{-3}$</tex-math> </inline-formula> at a 100-Mb/s data rate. It consumes 11.9 and 13.2 mW from a 1.2-V supply in the single-band modes and concurrent dual-band mode, respectively.

All-optical aggregation and de-aggregation between OOK, QPSK and 8QAM signals based on nonlinear effects

All-optical aggregation and de-aggregation between OOK, QPSK and 8QAM signals based on nonlinear effects

All-Optical Format Conversion for Star-8QAM Signals Based on Nonlinear Effects in Elastic Optical Networks

An all-optical format conversion (AOFC) scheme for star-octal quadrature amplitude modulation (star-8QAM) signals is proposed and numerically simulated based on nonlinear effects in the high nonlinear fiber (HNLF). In the first stage AOFC processing, the input 30 Gbit/s star-8QAM signal is firstly de-aggregated into one 20 Gbit/s quadrature phase shift keying (QPSK) signal and one 10 Gbit/s typical on-off keying (OOK) signal by deploying the self-phase modulation (SPM), cross-phase modulation (XPM) and parametric amplification (PA) effects. In the second stage AOFC processing, the 20 Gbit/s QPSK signal and the 10 Gbit/s typical OOK signal are aggregated into one 30 Gbit/s star-8QAM signal again by utilizing the XPM and PA effects. Moreover, the amplitude ratio (AR) between the outer ring and inner rings of the aggregated star-8QAM signal can be adjusted flexibly by changing the QPSK and OOK signals power. Other octal modulation formats can also be generated through changing the QPSK and OOK signals power, including the rectangular 8QAM signals, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\pi$</tex-math></inline-formula> /4-8QAM signals and 8-ary phase shift keying (8PSK) signals. Error vector magnitude (EVM) and bit error ratio (BER) for star-8QAM signals before and after AOFC are measured to analyse the scheme performance. The AOFC scheme provides the flexibility to adopt the appreciate modulation formats at the optical nodes to connect different optical networks.

Robust neural network-assisted conjugate orbital angular momentum mode demodulation for modulation communication

Orbital angular momentum shift-keying (OAM-SK), which enables modulation of digital signals by rapidly switching OAM modes, is promising in improving the modulation ability and confidentiality. Robust identification of conjugate OAM modes of VBs perturbed by atmospheric turbulence is critical for efficient demodulation of OAM-SK signals. We experimentally investigate a convolutional neural network (CNN) approach to detect OAM modes from diffraction patterns of turbulence-induced vortex beams. By introducing the hybrid-turbulence with variable turbulence strengths, this approach possessed high robustness against turbulence and low computational complexity in conjugate OAM mode identification, achieved 99.53 % mode detection accuracy in the −8 to 8 range for the hybrid-turbulence of Cn2=10-14∼10-12m-2/3. Mapping and encoding a grayscale image to the OAM modes, an OAM-SK communication link was built and the demodulated bit-error-rate (BER) was only 6.85 × 10−3. We show that this approach also can effectively assist in demodulating the conventional modulation signals, promoting the communication transmission capacity. By combining OAM-SK with on–off keying (OOK) and quadrature phase shift-keying (QPSK) to construct joint-modulation links, and OOK (QPSK) signals were successfully demodulated with the BER of 8.2 × 10−9–9.1 × 10−3 (3.34 × 10−6–2.8 × 10−3) with the assistance of CNN. Our results indicate that the proposed robust CNN is not only effective for demodulating OAM-SK signals, but is also compatible with conventional modulation signals, which is very promising for OAM-SK communication applications that require OAM mode identification.

Ultra-compact lithium niobate microcavity electro-optic modulator beyond 110 GHz

A lithium-niobate-on-insulator (LNOI) electro-optic (EO) modulator based on a 2 × 2 FP-cavity was designed and realized with an ultra-compact footprint and an ultra-high bandwidth. A comprehensive analysis on the present LNOI FP-cavity modulator was conducted to reveal the dependence of modulation bandwidth and modulation efficiency on the cavity Q-factor and the operation wavelength detuning to the resonance. In particular, the 2 × 2 FP cavity was designed to achieve an optimal Q factor by reducing the reflectivity of reflectors and the cavity length, thus reducing the photon lifetime in the cavity . An ultra-short effective cavity length of only∼ 50 µm was achieved for the designed LNOI FP-cavity modulator, with itsfootprint being as compact as ∼ 4 × 500 µm2. It was demonstrated theoretically that the modulation bandwidth could be improved significantly to be over 200 GHz by utilizing the peaking enhancement effect. The fabricated device exhibited an excess loss of ∼ 1 dB and an extinction ratio of ∼ 20 dB in experiments, while the measured 3-dB bandwidth was higher than 110 GHz (beyond the maximal range of the facilities in experiments). Up till now, to our best knowledge, this has been the first LNOI microcavity modulator with a bandwidth higher than 110 GHz. Finally, high-quality eye-diagrams of 100 Gbps on-off keying (OOK) and 140 Gbps 4-pulse amplitude modulation (PAM4) signals were demonstrated experimentally, and the energy consumption for the OOK signals was as low as 4.5 fJ/bit.

100 Gb/s NRZ OOK signal regeneration using four-wave mixing in a silicon waveguide with reverse-biased p-i-n junction.

A silicon waveguide with reverse-biased p-i-n junction is used to experimentally demonstrate all-optical regeneration of non-return-to-zero (NRZ) on-off keying (OOK) signal based on four-wave mixing. The silicon waveguide allows a high conversion efficiency of -12 dB. The 0.22 dB (1.1 dB) quality (Q) factor and 0.74 dB (6.3 dB) extinction ratio (ER) improvements on average are achieved for 100 Gb/s (50 Gb/s) NRZ OOK signal regeneration at different receiving powers via the optimal match between the input signal optical power and input-output transfer curve. To the best of our knowledge, this silicon-based all-optical regenerator exhibits superior regeneration performance, including large ER and Q factor improvements, and the highest regeneration speed of NRZ OOK signal, and it has wide applications in 5 G/6 G networks.

Experimental demonstration: Differential detection of 10 Gbps optical OOK signal over turbulent channel

In this paper, we experimentally demonstrate the bit error rate (BER) performance of fixed threshold differential detection for both 5 Gbps and 10 Gbps On-Off keying (OOK) signals over a turbulent channel, which induces slowly varying intensity fluctuation on the signals. The experimental results are also validated using numerical simulations. This study is significant for the terrestrial free-space optical (FSO) communication system in which the channel induces similar intensity fluctuation due to atmospheric turbulence. To show the efficiency of the differential detection scheme for the OOK signal two proof-of-principle systems are realized. In the first system, the effect of channel-induced intensity variation on the data is realized by passing a differentially coded OOK signal through a Mach–Zehnder modulator (MZM), which is driven by a low frequency sinusoidal electrical signal emulating slowly varying channel fluctuation. The amplitude of the sinusoid has been varied to create different levels of intensity fluctuation, mimicking different turbulent conditions in the optical link. In the second setup, we measure the BER performance of differential detection assisted OOK transmission over a short-range (10)m FSO channel, which is affected by turbulence-induced intensity fluctuations. The different turbulences are created by different heating levels of a blower, which injects hot air across the FSO channel. Experimental results show that in the presence of intensity fluctuation, differential detection of OOK signal using a fixed threshold offers a better BER performance at higher optical to signal ratio (OSNR) values compared to conventional direct detection (DD) scheme. Results obtained from numerical simulation of OOK transmission over turbulent FSO channels also confirm the similar behavior. Both simulation and experimental results show that differential detection can offer a BER of 10−3 at 5 Gbps and 10 Gbps data rates with slow varying channel-induced intensity fluctuation when the DD scheme fails to produce the same BER values.

Chaotic optical communications of 12.5-Gbaud OOK and 10-Gbaud QPSK signals based on mutual injection of semiconductor lasers.

Chaotic optical communications can provide a high level of security in data transmission. High-speed chaotic optical communications have hardly been implemented so far limited by the bandwidth of chaotic signals and the difficulties of wideband chaos synchronization. Here, we experimentally demonstrate all-optical wideband chaos synchronization and communications based on mutual injection of semiconductor lasers. Both 12.5-Gbaud on-off keying (OOK) signals and 10-Gbaud quadrature phase shift keying (QPSK) signals are successfully encrypted and transmitted over a 10-km and 2-km single-mode fiber (SMF), respectively.

All-Optical Aggregation and De-Aggregation Between 8QAM and BPSK Signal Based on Nonlinear Effects in HNLF

An all-optical aggregation and de-aggregation scheme between one 8-ary quadrature amplitude modulation (8QAM) signal and three binary phase shift keying (BPSK) signals is proposed and theory simulated based on nonlinear effects in high nonlinear fiber (HNLF). In this scheme, the input 8QAM signal is de-aggregated into three BPSK signals by deploying self-phase modulation (SPM), cross-phase modulation (XPM), four wave mixing (FWM) and parameter amplification (PA) effect. Firstly, an improved amplitude compression loop (ACL) is designed based on SPM effect to convert 8QAM signal into quadrature phase shift keying (QPSK) signal. A degenerate phase sensitive amplifier (PSA) based on FWM effect is used to decompose QPSK signal into the first two BPSK signals (BPSK-1 and BPSK-2). The third BPSK signal (BPSK-3) can be extracted from the probe light modulated in its phase by the input 8QAM signal thanks to XPM and PA effect. Secondly, BPSK-3 is converted into an atypical on-off keying (OOK) signal through a 1-bit delay interference (DI). BPSK-1 and BPSK-2 are recombined into one QPSK signal through a coupler. Finally, the recombined QPSK signal and the atypical OOK signal are aggregated into one 8QAM signal by using XPM and PA effect. The error vector magnitude (EVM) and bit error ratio (BER) of the 8QAM and BPSK signal before and after de-aggregation and aggregation are calculated to analyse the performance of the scheme. The scheme can be applied in the network node to connect different networks which explore to use 8QAM and BPSK signal respectively.

Optical adaptive power transmission using APC-EDFA for turbulence-tolerant FSO communications

This paper proposes a novel optical adaptive power transmission using automatic power control (APC)-erbium-doped fiber amplifier (EDFA) for turbulence-tolerant free-space optical (FSO) communications. Based on the quasi-stationary characteristics of turbulence channel and average power dependent optical gain features of EDFA, the channel state information (CSI) of the received upstream on-off keying (OOK) signal is optically conveyed to the orthogonally polarized transmitted downstream OOK signal with channel inversion via EDFA in APC mode. The performance is analyzed under various dynamic gain frequencies of APC-EDFA and different power ratios between downstream and upstream signals. Simulation results revealed that the power of downstream signal was adaptively transmitted according to the received upstream signal under effective turbulence suppression, transmitted power efficiency, and required SNR reduction without the estimation of CSI.

Tunable multiwavelength optical comb enabledRoF‐OFDM‐PONwith wavelength multiplex

AbstractWe propose a hybrid full duplex passive optical network with fusion of wavelength‐division‐multiplexing and orthogonal frequency‐division multiplexing (WDM‐OFDM) for a radio‐over‐fiber (RoF) system application. The key of the system is a tunable optical frequency comb (OFC) embedded cascading modulators and a parameter mixer. Moreover, 23 frequency components with 0.6 dB flatness generated by the OFC are used as light sources for each WDM channel. We utilize a 7.5 GHz OFDM wired signal and a 12.5 GHz OFDM wireless signal for downstream transmission and 10 Gb/s OOK (on–off keyed) signals for upstream traffic. Using polarization multiplexing technique, we extract a central optical carrier to bear the upstream signal so that no excess optical source is introduced into the ONU. Thus, the intricacy and costs of system are diminished. Moreover, successful transmission has been demonstrated since the bit error rates of the downstream and upstream signals are always under the adopted forward error correction limit. Furthermore, the proposed system can enhance power budget and reduce cost, which has a promising prospect for future wireless communication.

Integrated silicon reconfigurable optical transmitter.

We demonstrate an integrated silicon reconfigurable optical transmitter based on the reconfigurability of the Mach-Zehnder interferometer (MZI). By incorporating modulators into the tunable MZI structure and manipulating the operation states, different modulation formats, including amplitude/phase modulated binary/quaternary signals, as well as polarization multiplexed signals, can be generated as required, to accommodate different transmission links. For a proof-of-concept demonstration, the microring modulators are adopted, and we experimentally generate a 10 GBaud on-off keying (OOK) signal, four-level pulse amplitude signal, and polarization division multiplexing OOK signal using the same transmitter. The device is promising for a next-generation intelligent optical link.

800 Gbit/s transmission over 1 km single-mode fiber using a four-channel silicon photonic transmitter

We demonstrate the optical transmission of an 800 Gbit/s ( 4 × 200 Gbit / s ) pulse amplitude modulation-4 (PAM-4) signal and a 480 Gbit/s ( 4 × 120 Gbit / s ) on–off-keying (OOK) signal by using a high-bandwidth (BW) silicon photonic (SiP) transmitter with the aid of digital signal processing (DSP). In this transmitter, a four-channel SiP modulator chip is co-packaged with a four-channel driver chip, with a measured 3 dB BW of 40 GHz. DSP is applied in both the transmitter and receiver sides for pre-/post-compensation and bit error rate (BER) calculation. Back-to-back (B2B) BERs of the PAM-4 signal and OOK signal are first measured for each channel of the transmitter with respect to a variety of data rates. Similar BER performance of four channels shows good uniformity of the transmitter between different channels. The BER penalty of the PAM-4 and OOK signals for 500 m and 1 km standard single-mode fiber (SSMF) transmission is then experimentally tested by using one channel of the transmitter. For a 200 Gbit/s PAM-4 signal, the BER is below the hard-decision forward error correction (HD-FEC) threshold for B2B and below the soft-decision FEC (SD-FEC) threshold after 1 km transmission. For a 120 Gbit/s OOK signal, the BER is below SD-FEC threshold for B2B. After 500 m and 1 km transmission, the data rate of the OOK signal shrinks to 119 Gbit/s and 118 Gbit/s with the SD-FEC threshold, respectively. Finally, the 800 Gbit/s PAM-4 signal with 1 km transmission is achieved with the BER of all four channels below the SD-FEC threshold.

Stochastic Properties and Outage in Crosstalk-Impaired OOK-DD Weakly-Coupled MCF Applications With Low and High Skew×Bit-Rate

Intercore crosstalk (ICXT) impaired weakly-coupled multicore fiber (MCF) systems using on-off keying (OOK) and direct-detection (DD) are experimentally assessed. The stochastic properties of the received bit amplitudes that depend on the relative propagation delay (skew) between two cores of the MCF and on the OOK bit-rate are discussed. For low skew×bit-rate ( $ 1): (i) the received amplitude of bits 0 or 1 of the interfered core are mainly characterized by two possible levels; (ii) when the short-term average crosstalk (STAXT) power increases (decreases), the fluctuations of the received amplitudes of bits 1 and 0 become larger (lower). For high skew×bit-rate ( $>>$ 1): (i) the received amplitudes of bits 0 and 1 present a noise-like behaviour; (ii) larger fluctuations of the received amplitudes of the OOK signal may not occur only for high STAXT powers. For both low and high skew×bit-rate, it is shown that the histogram of the received amplitudes of bits 1 or 0, and the histogram of the mean and variance of these amplitudes are reasonably well characterized by Gaussian distributions. Experimental results suggest that the rule of thumb to design emerging MCF applications with higher ICXT tolerance is to use cores with skew much longer than the symbol period.

Transmission characteristics of 24.5 Gb/s atmospheric laser communication based on optical frequency comb

Abstract Through cascading Mach–Zehnder intensity modulator (MZIM) and phase modulator (PM), an optical frequency comb (OFC) with 7 flat comb teeth is produced. The frequency interval of the OFC is 25 GHz and the flatness is less than 1.5 dB. The 7 channels of the OFC are used as the carrier source of the one-to-many free-space optical (FSO) communication system, and the atmospheric turbulence simulation pool is used to simulate the turbulence intensity in the real atmosphere to verify its feasibility for FSO communication. In the experiment, the bit error rate (BER) and eye diagram are measured under the back-to-back (BTB) conditions, and the temperature difference of atmospheric turbulence simulation pool are 80 °C, 150 °C and 220 °C. Each channel of the system can stably transmit the on–off keying (OOK) signal of 3.5 Gb/s, and the 7 channels can stably transmit the OOK signal of 24.5 Gb/s. Thereby, the OFC can be used in place of multiple lasers or laser arrays as a carrier source for a one-to-many FSO communication system.

All-Optical OOK -to-QPSK Modulation Format Conversion With Wavelength Multicasting Based on Cascaded SOA Configuration

An on–off keying (OOK) to quadrature phase shift keying (QPSK) format conversion scheme has been demonstrated in this paper. Two-channel OOK signals are converted into one-channel QPSK signal, and accompanied with a multicast function. The proposed scheme is based on a cascaded semiconductor optical amplifiers (SOA) configuration where the processes of cross phase modulation (XPM) and nonlinear polarization rotation (NPR) are properly controlled by OOK signals in each SOA. The experimental results show that after conversion, four-channel QPSK signals are successfully obtained with open eye-diagrams, and all the converted signals experience a small power penalty of less than 3.4 dB at a bit error rate (BER) of $10^{-9}$ compared to the original signal. In addition, the optical spectra and the constellation diagrams of the converted signal also indicate the high quality performance exhibited by the proposed format conversion scheme.