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This work demonstrates a record 160 m long visible light communication (VLC) link using LED transmitters and an image sensor-based receiver, for distance-critical applications. This marks the longest VLC distance achieved to date, using a combination of novel modulation technique at the transmitter and an undersampling-based receiver incorporating adaptive threshold decisioning. Experimental results demonstrate low bit error rate (BER) performance at the achieved communication distance.

To enable high-speed long-distance underwater optical wireless communication (UOWC) supplementing traditional underwater wireless communication, a low-power 520 nm green laser diode (LD) based UOWC system was proposed and experimentally demonstrated to implement maximal communication capacity of up to 2.70 Gbps data rate over a 34.5 m underwater transmission distance by using non-return-to-zero on-off keying (NRZ-OOK) modulation scheme. Moreover, maximum data rates of up to 4.60 Gbps, 4.20 Gbps, 3.93 Gbps, 3.88 Gbps, and 3.48 Gbps at underwater distances of 2.3 m, 6.9 m, 11.5 m, 16.1 m and 20.7 m were achieved, respectively. The light attenuation coefficient of ~0.44 dB/m was obtained and the beam divergence angle is 0.35°, so the aallowable underwater transmission distance can be estimated to be ~90.7 m at a data rate of 0.15 Gbps with a corresponding received light-output power of -33.01 dBm and a bit-error rate (BER) of 2.0 ×10-6. In addition, when the data rate is up to 1 Gbps, the UOWC distance is predicted to be ~62.7 m for our proposed UOWC system. The achievements we make are suitable for applications requiring high-speed long-distance real-time UOWC.

This paper investigates an adaptive threshold decision (ATD) scheme without the knowledge of channel state information (CSI) for optical wireless communication (OWC). Based on the low-pass characteristic of atmospheric turbulence channels, a low-pass filter is designed for the received signals, and the filtered signal can be employed as decision threshold. Theoretical analyses show that performance of ATD is very close to that with perfect CSI. Monte Carlo simulations demonstrate that the proposed scheme shows only 0.0221dB signal-to-noise (SNR) loss at most with Rytov variance of 0.05 and SNR of 21dB. An indoor experiment results are presented, which match well with that of theoretical prediction. The scheme is simple and without CSI, hence the efficient scheme makes the real-time implementation of high-speed transmissions for OWC based on ATD feasible.

We demonstrate PAM-4 and OOK operation of a novel silicon photonic modulator. The modulator design is based on two phase-shifts in a Bragg Grating structure driven in a push pull configuration. Back-to-back PAM-4 modulation is demonstrated below the FEC threshold at up to 60 Gb/s. OOK modulation is also shown up to 55 Gb/s with MMSE equalization and up to 50 Gb/s without equalization. Eye diagrams and BER curves at different bit rates are provided for both PAM-4 and OOK modulations. To our knowledge, this structure is the fastest silicon photonic modulator based on Bragg gratings, reaching modulation speed comparable to the fastest Mach-Zehnder modulators and micro-ring modulators.

The multiple-code (MC) and multicode-keying (MK) schemes were recently proposed to support multirate multimedia services in asynchronous optical code-division multiple-access (O-CDMA) systems. A user in the MC scheme simultaneously conveys multiple codewords to represent the transmission of multiple data bits of 1. While the MK scheme only transmits one codeword at a time, each codeword represents a symbol (of multiple data bits of 0 and 1). In this paper, a hybrid multirate asynchronous O-CDMA system model that comprises the conventional single-rate scheme and these two multirate schemes is studied. The bit error probability (BEP), spectral efficiency (SE), and throughput of the proposed hybrid systemare formulated. The conditions and combinations of simultaneous users from these three schemes that can optimize the system’s BEP, SE, and throughput are investigated. Finally, the new analytical models are validated with numerical examples and computer simulations.

A detailed analysis and comparison is carried out for optical wireless communications (OWCs) with coherent and subcarrier-intensity-modulation-based systems, which are the two major implementations for detection-threshold-free operation without irreducible error floors. Error rate performance is studied for communications with binary phase-shift keying, differential phase-shift keying, and noncoherent frequency-shift keying over weak-to-strong (gamma-gamma distributed) turbulence conditions. Series-form error rate expressions are also derived for diversity reception schemes, including maximum ratio combining, equal gain combining, and selection combining. Based on our analysis, it is found that coherent OWC systems typically outperform subcarrier intensity modulation systems, with 24-30 dB improvements in sensitivity, mainly due to their elimination of thermal and background noise effects. The performance improvements of coherent systems are confirmed through numerical studies. The findings can offer significant benefits for future OWC systems that are subject to transmitted power limitations.

An optical wireless communication system using subcarrier intensity modulation is analyzed for gamma-gamma turbulence channels with pointing errors. We study the error rate performance of such a system employing M-ary phase-shift keying, differential phase-shift keying, and noncoherent frequency-shift keying. Highly accurate error rate approximations are derived using a series expansion approach. Furthermore, outage probability expressions are obtained for such a system. Asymptotic error rate and outage probability analyses are also presented. Our asymptotic analysis reveals some unique transmission characteristics of such a system. Our findings suggest that pointing error compensation is necessary as pointing errors can severely degrade the error rate and outage probability performance of an uncompensated system.

A novel approach to photonically generate binary digital modulation radio frequency (RF) signals is proposed. In the proposed system, the short optical pulses are converted into high frequency RF signals based on optical pulse shaping followed by dispersion induced frequency-to-time mapping technique. And the generated signals are coded using a fast electro-optical switch based on polarization modulation. By properly configuring the system, binary digital modulation signals, including amplitude-shift keying (ASK), frequency-shift keying (FSK) and phase-shift keying (PSK) with required bit pattern are generated in the optical domain. A model describing the signal generation system is derived, which is verified via both simulations and a proof-of-concept experiment.

A regenerative all-optical grooming switch for interconnecting 130 Gbit/s on-off keying (OOK) metro/core ring and 43 Gbit/s-OOK metro/access ring networks with switching functionality in time, space, and wavelength domains is demonstrated. Key functionalities of the switch are traffic aggregation with time-slot interchanging functionality, optical time division multiplexing (OTDM) to wavelength division multiplexing (WDM) demultiplexing, and multi-wavelength 2R regeneration. Laboratory and field demonstrations show the excellent performance of the new concept with error-free signal transmission and Q-factors above 20 dB.

This paper focuses on the connectivity issues of a non-line-of-sight (NLOS) optical wireless network operating in the ultraviolet UV-C spectral region. NLOS UV-C transmitters have a limited effective coverage and, hence, a dense node distribution is required in order to efficiently cover a large geographical area. Under this assumption, the concept of connectivity is more than important since it provides a strong indication of the network reliability and robustness. In the present study, we consider transmission with on-off keying and pulse position modulation schemes assuming both Gaussian and Poisson noise and adopt an effective experimental path loss model. Then, we evaluate the k-connectivity properties in terms of several network parameters. More precisely, we present and analyze the trade-off between node density and the degree of k-connectivity against other parameters (i.e., transmitted power, supported data rate, and error probability). The derived results are depicted using appropriate figures and tables and constitute the theoretical basis for the design and implementation of a reliable UV-C network in practice.

In this paper, a power and bandwidth efficient pulsed modulation technique for optical wireless (OW) communication is proposed. The scheme is called optical spatial modulation (OSM). In OSM, multiple transmit units exist where only one transmitter is active at any given time instance. The spatially separated transmit units are considered as spatial constellation points. Each unique sequence of incoming data bits is mapped to one of the spatial constellation points, i.e., activating one of the transmit units. This is the fundamental concept of the spatial modulation (SM) technique. In OW communication systems, the active transmitter radiates a certain intensity level at a particular time instance. At the receiver side, the optimal SM detector is used to estimate the active transmitter index. An overall increase in the data rate by the base 2 logarithm of the number of transmit units is achieved. The optical MIMO (multiple-input multiple-output) channel and the channel impulse response are obtained via Monte Carlo simulations by applying ray tracing techniques. It will be shown in this paper that the optical MIMO channel is highly correlated if transmitter and receiver locations are not optimized, which results in a significant power penalty. The power efficiency can be improved by increasing the number of receive units to enhance receive diversity and/or by using soft and hard channel coding techniques. Conversely, it is shown that aligning transmit and receive units creates nearly uncorrelated channel paths and results in substantial enhancements in system performance even as compared to the diversity or coding gain. The resultant aligned scheme is shown to be very efficient in terms of power and bandwidth as compared to on-off keying, pulse position modulation, and pulse amplitude modulation. In this paper also, the upper bound bit error ratios of coded and uncoded OSM are analyzed. The analytical results are validated via Monte Carlo simulations and the results demonstrate a close match.

We propose and numerically investigate for the first time a novel all-optical on-off-keying to alternate-mark-inversion modulation format converter operating at 40 Gbps employing a semiconductor optical amplifier (SOA)-based Mach-Zehnder interferometer (MZI). We demonstrate that this SOA-MZI operates as a pulse subtractor, and in the absence of patterning will produce perfectly phase inverted pulses regardless of the individual SOA phase excursions. We use a comprehensive computer model to illustrate the impact of patterning on the output phase modulation, which is quantified through the definition of the phase compression factor.

In this paper, we present an interesting result of nonlinear light pulse propagation within a Mach-Zehnder Inteferometer (MZI) which can be used to extend the existed on off keying (OOK) techniques. The goal of this paper is OOK generation based on MZI incorporating a pumped nonlinear ring resonators system. We first analyze the principles of a phase modulation scheme using MZI incorporating the triple nonlinear ring resonators, which can be fabricated and used in practical communications. After that, we focus on the recent modulation schemes, where the all-optical on off keying and the phase shift control for phase shaped binary transmission (PSBT) are discussed in details. The novelty of this work is that the nonlinear ring resonators are used incorporating a MZI, where the extended switching generation can be achieved and seen.

We demonstrate a method for a tunable optical delay element that allows for minimal residual dispersion and double the relative delay. A tunable delay of 503 ns for 40 Gbit/s return-to-zero on-off keying and return-to-zero differential phase-shift keying is shown with a reduction in residual dispersion of approximately 95%.

We demonstrate a variable, optical-delay element using tunable wavelength conversion in a periodically poled lithium niobate waveguide, dispersion-compensating fiber and intrachannel dispersion compensation. A delay of up to 105 ns is demonstrated using 80 Gb/s return-to-zero differential-quadrature phase-shift keying, 40 Gb/s return-to-zero differential phase-shift keying, and 40 Gb/s return-to-zero on-off keying modulation formats. Bit-error rates10(-9) are demonstrated for each waveform at various delay settings.

We present and experimentally demonstrate a new method to generate optical carrier suppressed-differential phase-shift keying (OCSDPSK) modulation format in radio over fiber (RoF) systems. In our scheme, a single dual-parallel Mach-Zehnder modulator (DPMZM) is used to produce OCS-DPSK signal based on amplitude shift keying (ASK) to DPSK format conversion by suppressing the spectral tones of an OCS-ASK signal.

We propose a novel method for effective simulation of optical fiber transmission system performance with nonlinear interaction between the amplified spontaneous emission noise and the modulated optical signal employing on-off keying. The method enables a standard analytical description of the receiver operation even when the detected optical field obeys non-Gaussian statistics with a substantial amount of nonlinear phase noise accumulated along the fiber link due to strong signal-noise interaction.

The performance of the optical satellite communication links is degraded in atmospheric environment. The degradation is more in the case of an on-off keying (OOK) modulation scheme. The antenna aperture averaging method is used to improve system performance for different modulation schemes. With this method, it is found that improvement in system performance employing OOK modulation is higher as compared to subcarrier binary phase-shift keying and subcarrier quadrature phase-shift keying modulation schemes.

We examine the performance of optical 8-ary differential phase-shift keying transmission systems according to the type of receiver structure and modulation format. Compared with the approach based on a multilevel decision, we found that a bilevel receiver provides 3-dB gain in optical signal-to-noise ratio sensitivity and is more robust against chromatic dispersion for either nonreturn-to-zero or return-to-zero modulation.

We propose an optical initial phase control technique for external modulation in the format of minimum-shift keying (MSK). In this scheme, the optical phase discontinuities inherent to external frequencyshift- keying (FSK) modulation are compensated by use of an initial phase controller in conjunction with a FSK modulator. We present the principle of the control method and then numerically and experimentally prove that the signal has a modulation spectrum more compact than that of conventional binary phase-shift keying. 10-Gbit/s external modulation in MSK format was experimentally demonstrated.