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With high-speed space optical crosslink being a reality, the construction of an optical satellite network as part of a larger integrated space-terrestrial network is now feasible. This paper explores the architecture implications of the invention of such a radical technology building block. Not only can the satellite network performance and cost undergo quantum-leap improvements but also such a network can have profound transforming effects on space system architectures and data network user applications.

This book covers the technology of switching or modulating light in semiconductor optical waveguides. Currently a key function for optical communications systems is the conversion of data from an electrical signal to an optical signal for transmission in very low loss optical fibres and the converse process of optical to electrical conversion the O/E/O data conversion. It focuses on all-optical switching using second/third order optical nonlinearities in AIGaAs optical waveguides while covering a variety of device configurations including integrated nonlinear couplers and Mach-Zehnder interferometers. Supplementary Mathematica programs are available within Book Information.

This paper presents recent results in the design, fabrication, and demonstration of indium phosphide based integrated optoelectronic devices for applications in communications and signal processing. The underlying theme in the design and use of these devices is to exploit the parallelism that manifests itself owing to the availability of a set of stabilized, mutually coherent optical carriers, or optical frequency combs.

The high-performance server compute landscape is changing. The traditional model of building general-purpose enterprise compute boxes that end-users can configure with storage and networking to assemble their desired compute environments, has evolved to purpose-built systems optimized for specific applications. This tight integration of hardware and software components together with high-density midboard optical modules and an optical backplane allows for unprecedented levels of switching and compute efficiencies and has fueled the penetration of optical interconnects deep “inside the box,” particularly for switch scale-up. We briefly review earlier 40 G/port switching systems based on active optical cables, and present our newest system: An all-optically-interconnected 100 G/port 8.2 Tb/s InfiniBand packet switch ASIC with 41 ports running 100 Gb/s per port interconnected by 12-channel midboard optical transceivers with 25 Gb/s per channel per direction of optical I/O. Using a blind-mate optical backplane, these components enable systems with up to 50 Tb/s bandwidth in a 2U standard rack mount configuration with industry-leading density, efficiency, and latency. For even tighter co-integration of optical interconnects with switch and processor ASICs, we discuss photonic multichip module and interposer packaging technologies that will further improve system energy efficiencies and overcome impending system I/O bottlenecks.

We report on an ultrahigh-speed PAM-based IM/DD optical subsystem featuring compact signal generation and tractable digital-processing complexity. The proposed transceiver is based on two main technologies: an InP DHBT selector power DAC for electrical signal generation, and a complexity-optimized receiver processing chain. We show how the complexity of the feed-forward equalizer can be considerably reduced by stacking a

In the field of leading-edge techniques, such as broadband communications and large-scale radio interferometer applications, the need for a highly stable/wide-frequency-range photonic-microwave signal (continuous sine wave) is increasing. The main purpose of this research is to provide a highly stable photonic-microwave signal over a large broadband from microwave to terahertz frequencies using the same optical signal generation/transmission system. While transmitting signals through an optical cable, the transmission delay fluctuates and it suffers from chromatic dispersion that affects the distribution signal coherence. We have developed a postprocessing scheme transmission phase stabilizer. In the scheme, the measured phase of the round-tripped signal is acquired at time intervals at the optical transmitting port (an optical input port), and then the measured phase data are sent to the destination port (an optical output port) for the transmission phase compensation. The postprocessing method has advantages for a frequency dynamic range and compensation range issue. Theoretically, there is no upper frequency limit on the proposed phase stabilizer. We also discuss a high-frequency signal generator based on an optical comb signal generator up to terahertz frequencies.

Underwater optical wireless communications (UOWC) systems have recently received significant attention as an attractive solution for both research and commercial use because of their ability to provide high bandwidth communications over relatively short transmission spans along with their low operational cost. However, high absorption and scattering of optical transmission in the water limit the achievable range of underwater optical wireless links to only few metres. In this study, in an effort to increase the range and reliability of underwater optical wireless links, the authors propose to utilise semiconductor optical amplifiers at the receiver and discuss in a quantitative fashion the performance enhancements that can be achieved. After developing the required analytical framework, extensive numerical results are further provided to demonstrate the performance of the proposed scheme for different operating conditions. Specifically, assuming intensity modulation and direct detection schemes with on–off keying modulation, they evaluate the bit error rate of the proposed system configuration for different water types, link distances and forward error correction schemes. Performance evaluation results reveal that the use of optical amplification can significantly improve the quality of UWOC links.

Wavelength reuse has been proposed as an effective solution to realize colorless optical network units (ONUs) for next-generation passive optical network with simplified maintenance and reduced cost. In this paper, we propose a wavelength reused mode-division-multiplexing (MDM) scheme for bidirectional short-reach optical access network with low mode-crosstalk multiplexer/demultiplexer (MUX/DEMUX) and few-mode fiber (FMF). In downstream (DS) transmission, one of the spatial modes in FMF is used to transmit optical carriers, while the others are used as DS signal channels. In upstream (US) transmission, the carrier is split to all the ONUs for US remodulation. By utilizing low mode-crosstalk mode MUX/DEMUX and FMF, the carrier and each signal channel can be effectively separated. Compared with other wavelength reused schemes in which the DS and US transmission are modulated in orthogonal dimension, the signal qualities on two transmission directions are independent in the proposed scheme, and symmetrical bidirectional transmission without residual remodulation crosstalk can be achieved. What is more, to reduce bidirectional Rayleigh backscattering noise, we propose to use different optical sidebands for DS and US transmission. With the proposed scheme, we experimentally demonstrate symmetrical bidirectional 2 × 12.5-Gb/s quadrature phase-shift keying (QPSK) orthogonal-frequency-division-multiplexing (OFDM) intensity-modulation and direct-detection transmission over 11.5-km four-mode FMF. With Rayleigh backscattering noise mitigation, a Q-factor improvement of 2 dB is achieved for the US signal at the DS signal-to-carrier power ratio of -27 dB.

A microwave photonic signal processor that is capable of simultaneously realizing sub-harmonic frequency down conversion and IF signal phase shifting operation is presented. The IF signal generated by the frequency down conversion process is obtained by the beating of the second-order local oscillator (LO) sideband with the fundamental RF signal sideband at the photodetector. The phase of the IF signal can be tuned continuously from 0° to 360° by controlling the optical phase of the RF signal sideband. The optical carrier is eliminated at the signal processor output to achieve high conversion efficiency mixing operation. The signal processor can be designed to have a very wide bandwidth as it only involves optical components. Experimental results are presented that demonstrate frequency down conversion with > 8.8 dB conversion efficiency over 6 to 40 GHz RF signal bandwidth and 0.05 to 10 GHz IF signal bandwidth, and a continuous 0° to 360° phase shift on the output IF signal.

An optical approach to implement radio-frequency (RF) self-interference cancellation using an integrated dual-parallel Mach–Zehnder modulator (DP-MZM) is proposed and demonstrated experimentally. The received signals and the reference signal are converted into optical domain via the sub-MZMs (MZM1 and MZM2) in the DP-MZM, which are biased at the quadrature point and the minimum point with the output of double sideband with carrier signal and double sideband with carrier-suppressed signal, respectively. It avoids the optical interference at the combining Y branch waveguide. The time and the amplitude matching conditions for cancellation between the reference signal and the interference signal are completed by the electrical tunable time delay line and the phase shifter in the MZM2 path. A cancellation depth larger than 80 dB is obtained for the single-frequency signal of 2.4, 5, 8, and 10 GHz. For the bandwidth of 100 MHz, cancellation depths as high as 35.8, 33.1, and 38.3 dB are realized at frequencies of 2.4, 5, 8, and 10 GHz, respectively.

Generation of optical vector millimeter-wave (mm-wave) signal based on Mach-Zehnder intensity modulator with frequency multiplication can reduce bandwidth requirement of optical and electrical components. A phase precoding scheme with constellation optimization is experimentally demonstrated in one 144-GHz mm-wave signal generation system with frequency sextupling. The bit-error-ratio (BER) performance at one BER of 3.8 × 10-3, hard-decision forward-error-correction threshold, is improved by over 3 dB using this novel scheme for 4-Gbaud quadrature-phase-shift-keying signal at D-band (110-170 GHz).

We propose and demonstrate a novel all-optical virtual private network (VPN) using a microwave photonic filter, which enables inter-communications among optical network units in a passive optical network system. In our scheme, an optical coupler based recirculating delay line is used at optical line terminal as an optical subsystem to implement a microwave photonic-bandpass filter (MP-BPF). The periodic passbands of an MP-BPF are used to transmit VPN signal, whereas stopbands are used for conventional upstream transmission. The proposed system has two critical issues, optical phase-induced intensity noise in the MP-BPF and Rayleigh back-scattering interference by a single-fiber loop back link. To overcome the issues, an RF clipping tone based spectrum-broadening technique is applied to uplink transmitter. The proposed all-optical VPN system is tolerant to wavelength of VPN optical carrier, and enables multi-VPN data transmission using multi-passbands of MP-BPF.

All optical 3R regeneration of 100-Gb/s return-to-zero on-off-keying (OOK) signal based on cross gain compression effect using semiconductor optical amplifiers is experimentally demonstrated for the first time. The shape of optical filters and signal powers are carefully adjusted to obtain the regenerative result. Bit error rate (BER) measurement is performed, and the receiving sensitivity is improved by 2 to 3 dB in the regenerative signal, compared with the degraded signal. Regenerative capability for different degrees of degradation has been studied.

This letter investigates the performance of underwater optical wireless communication systems (UOWC) employing optical pre-amplification as well as multiple receivers to exploit the advantages of spatial diversity. Numerical results are further provided to evaluate the error performance of pre-amplified single-input multiple-output (SIMO) UOWC systems when onoff keying (OOK) modulation is utilized. Our results reveal that the proposed system configuration can indeed offer significant system performance enhancements in terms of the attainable bit error rate.

An effective theoretical analysis method is presented to analyze different linear optical signal processing functions with optical filters reported in literatures. For different applications, the optical filters are supposed to operate on the analog or digital part of the signal separately, namely analog spectrum conversion and digital spectrum conversion. For instance, the return-to-zero (RZ) to non-return-to-zero (NRZ) format conversion for intensity or phase modulated signals are based on the analog spectrum conversion process, while the (N)RZ to (N)RZ phase-shift-keying (PSK) format conversion, logic NOT gate and clock recovery for RZ signals are based on the digital spectrum conversion process. Theoretical analyses with the help of numerical simulation are used to verify the reported experimental results, and all the experimental results can be effectively analyzed with this analytical model. The effect of the transmission spectrum of the filter on the performance of the converted signal is investigated. The most important factor is that the theoretical analysis provides an effective way to optimize the optical filter for different optical signal processing functions.

We have demonstrated all-optical format conversion from ON-OFF-keying to multiple-level phase-shift-keying based on self-generating optical clock scheme. This scheme enables us to generate an optical clock synchronized with an input data signal without a clock recovery circuit and an optical pulse source. In this letter, we have evaluated and compared the format conversion performances using a conventional optical clock and the self-generating optical clock in terms of bit-error-rate measurement. As a result, we have successfully achieved the low power penalty to the conventional scheme of

In Elastic Optical Networks, advanced transmission techniques based on coherent detection strategies have been proposed and exploited to provide high flexibility in resource allocation. So far, these techniques have assumed the constraint of each optical signal being transmitted along a dedicated frequency slot, by carefully avoiding frequency overlap with other optical signals. In this study, an overlap technique, that enables uncorrelated optical signals to be superimposed along the same spectrum resources, is designed and validated through simulations, both in terms of performance bounds and bit-error rate in coded transmissions. In particular, it is demonstrated how this technique allows each overlapped signal to be correctly received and detected. The proposed technique is less spectrally efficient and more complex to implement than increasing the constellation size and using non overlapping frequency slots, but it warrants consideration for flexible networking. The proposed technique is first theoretically detailed and justified. Then, networking scenarios and implementation schemes suitable for its effective utilization are identified and applied in the case of two overlapped 112 Gb/s polarization-multiplexed quadrature phase shift keying signals. Simulation results show that, applying 3-dB optical signal-to-noise ratio margin on the achieved bounds, optical reaches of around 800 km can be successfully supported by the proposed overlap technique.

This letter introduces Free-Space Optical (FSO) Communication links in vehicular applications using potential guiding structures around a vehicle. An optical wireless communication system simulation is described which delivers received power, bandwidth, root mean square delay spread channel impulse response for purely diffuse and diffuse-specular materials with omnidirectional and directed transmitters. In the former case, a bandwidth of 225 MHz with a power deviation of 25% results at the exit. For the latter, a 75GHz bandwidth is available at best but with a power deviation of over 99% making receiver positioning critical. The impulse response is calculated using a Modified Monte Carlo algorithm taking into account up to 15 reflections. The effect of the pipe bend angle on the path loss is also presented and the simulation is supported with experimental work.

One of the major challenges of optical camera communication (CamCom) is the low sampling rate at the camera-based receiver side compared with the very high speed modulation of the LED lighting source. The recently emerging compressed sensing (CS) theory makes signal reconstruction at a low sampling rate possible if the signal has a sparse representation. This letter proposes a novel flicker-free CS-based optical CamCom scheme that can detect signals at a lower sampling rate than the Nyquist rate, while providing reliable signal detection and implementation flexibility. This can be achieved by designing the random projection structure based on pseudonoise codes at the transmitter, leading to a decrease in complexity on the camera-based receiver side. The numerical results show that the proposed scheme can detect the original signal with high probability at a much lower sampling rate than the Nyquist rate.

A cost-effective mode-division-multiplexing and time-division-multiplexing passive optical network (MDM-TDM PON) utilizing a self-coherent detection for upstream signal at optical line terminal (OLT) and a high-gain reflective semiconductor optical amplifier (RSOA) as an optical amplifier for a downstream signal at optical network units (ONUs) to enhance bidirectional power budget is proposed. Meanwhile, to further reduce the cost of ONU, RSOA is also used as upstream on-off keying (OOK) signal modulator by time compression multiplexing. A novel dual-modulus algorithm is proposed for OOK signal detection at the OLT. We experimentally verify the proposed MDM-TDM PON architecture with an upstream 1-Gb/s OOK signal and a downstream 10-Gb/s orthogonal frequency division multiplexing (OFDM) signal. Due to the high gain of RSOA and high receiver sensitivity of self-coherent detection, a 30-dB bidirectional power budget is achieved after 10-km few-mode fiber and a 20-km standard single-mode fiber at the bit error rate (BER) of 10-3. Optimal seed power and signal power that input to the RSOA are investigated in this paper.

In this paper, we describe an optical wireless communications system that uses light from an optical fibre access point to provide transparent and bi-directional optical links to nomadic terminals. Full localization and tracking is implemented, and a 50 Gb/s link is demonstrated. The link operates in an indoor environment, with a $ \pm 30^\circ $ field-of-view covering a distance of up to 3 m, and a localization accuracy of 0.05° (2.5 mm pointing accuracy at 3 m) is achieved. This demonstration shows that it is feasible to use an automated system to achieve the required alignment for an ultrahigh data rate fibre-wireless-fibre link.

Experimental results demonstrating the use of diversity combining in an optical wireless system using asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) are presented. A standard white lighting LED of the type often used in visible light communications (VLC) is used as the transmitter. The experiments show that diversity combining gives an improvement of 2–3 dB, and that uncorrected DC offset in the receiver can cause diversity combining to fail, but that DC correction methods are effective. It is shown that diversity combining changes the frequency distribution of noise received on the even subcarriers.

The recently reported high spectral efficiency (SE) and high-baud-rate signal transmission are all based on digital coherent optical communications and digital signal processing (DSP). DSP simplifies the reception of advanced modulation formats and also enables the major electrical and optical impairments to be processed and compensated in the digital domain, at the transmitter or receiver side. In this paper, we summarize the research progress on high-speed signal generation and detection and also show the progress on DSP for high-speed signal detection. We also report the latest progress on multi-core and multi-mode multiplexing.

A variable-gain current-amplifier-based feedback transimpedance amplifier (CA-TIA) with a gain-insensitive bandwidth is analyzed and designed for gigabit-per-second optical wireless communications. Implemented in 0.18- $\mu\text{m}$ CMOS, as the transimpedance gain varies from 55.8 to 69.3 $\text{dB}\Omega$ , the 3-dB bandwidth of the CA-TIA remains relatively invariable around 1 GHz.

The capacity of optical communication systems can be continuously scaled by utilizing spatial division multiplexing (SDM) technology. However, this scaling has significant impact on the required optical and electrical power as the number of EDFAs increase. This constraint is crucial in long-haul undersea optical systems where electrical power for the entire system is fed from the landing points. Successful implementation of SDM in undersea systems will require both signal modulation and amplification technologies with high power efficiency. In this work, we use 8-D coded modulation and simple EDFA design to demonstrate 100 Gb/s transmission over 9750 km with record high power efficiency as defined by the ratio of capacity-distance product to the total amplifier output power.

Present and next generation optical communication systems are constantly being developed to operate at higher baud rates and higher modulation formats. It then becomes inevitable to consider the various linear and nonlinear effects due to the imperfect components at the transmitter. State-of-the-art digital-to-analog converters, high bandwidth driver amplifiers, and dual-polarization (DP) Mach–Zehnder modulators are far from being ideal and present distortions in the form of bandwidth limitation, transmitter I/Q skew, and nonlinear effects. In this letter, we propose a new robust pre-distortion method to mitigate the undesirable linear and non-linear distortions of all electrical and optical transmitter components simultaneously. A step-by-step derivation and implementation of the algorithm are discussed and put forward. The performance of the algorithm is experimentally assessed across DP-4QAM, DP-8QAM, DP-16QAM, DP-32QAM, and DP-64QAM up to the signaling rates of 56 GBd. Significant improvements in the required optical signal-to-noise ratio at bit-error rate (BER) of $10^{-2}$ are demonstrated.

In this letter, we demonstrate a coherent radio frequency repeater. The repeater adds the appropriate phase shift to amplify or null a signal generated by another platform and directed to a target point. It leverages a high-accuracy microwave ranging system to estimate the range between platforms and maintain phase coherence when the platforms are moved without additional feedback from the receiver. A continuous beamforming gain operation is achieved without phase or frequency locking the repeater to the transmitter. We include measurements of the stability of the ranging system and discuss potential sources of the variations that limit system performance. Results from outdoor experiments demonstrating successful amplification and nulling of an existing communications link with the repeater are provided.

The role of the optical transmitter is to generate the optical signal, impose the information bearing signal, and launch the modulated signal into the optical fiber. The semiconductor light sources are commonly used in state-of-the-art optical communication systems. Optical communication systems has become one of the important systems after the advent of telephone, internet, radio networks in the second half of the 20th century. The development of optical communication was caused primarily by the rapidly rising demand for Internet connectivity. Orthogonal frequency-division multiplexing (OFDM) belongs to a wide class of multicarrier modulation. Orthogonal frequency-division multiplexing has succeeded in a wide range of applications in the wireless communication domain from video/audio digital broadcasting to wireless local area networks (LANs). Although their very low loss compared to that of the wireless counterpart, optical systems still need renovation for spans commonly less than150 Km. In this paper advantages of optical orthogonal frequency division multiplexing in communications systems will explained.

We report on the development of a free space, line of sight bidirectional optical wireless communication system for personal area networking. The system includes several transmitters mounted at the ceilings and attached directly to the optical communications cable. Each transmitter contains up to eight outlets connected to eight receivers through an infrared laser beam. Using a transmitted power of 5 dBm, the system transmits at 1.25 and 10 Gb/s and bit-error rates better than $10^{\mathrm {-12}}$ over the distance range of 2–12 m. To provide robustness against the environmental distortions, such as shock, vibration, and temperature fluctuations, an active repositioning is implemented by a closed-loop controlled steering of the laser beam by electrostatically actuated microelectro-mechanical system mirrors mounted within each of the outlets and allowing up to ±2° optical scanning angle. An algorithm based on the maximization of the transmitted optical power has been developed for automatic alignment between the central station and each of the user modules, enabling certain mobility of the system.

A symmetrical radio over a colorless wavelength-division multiplexing passive optical network with wavelength reuse based on polarization multiplexing and coherent detection incorporating digital phase noise cancellation is proposed and experimentally demonstrated. For the downlink, two optical signals are intensity modulated by two different 16-QAM downstream microwave vector signals that are polarization multiplexed at the optical line terminal (OLT). Then, the two orthogonally polarized optical signals are transmitted to the optical network unit (ONU). At the ONU, one of the two orthogonally polarized optical signals is selected to be reused for the uplink transmission. Then, the reused optical signal is split into two channels by a 3-dB coupler. One portion of the reused optical signal is phase modulated by a 16-QAM upstream microwave vector signal, while the other portion is intensity modulated by another 16-QAM upstream microwave vector signal. Again, the two portions of the optical signals are polarization multiplexed and transmitted back to the OLT. At the OLT, a coherent receiver with a digital signal processing (DSP) unit is used to detect the upstream optical signals. Two DSP algorithms are developed to recover the two 16-QAM upstream microwave vector signals. The transmission of two 2.5-Gb/s 16-QAM downstream microwave vector signals and two 2.5-Gb/s 16-QAM upstream microwave vector signals over a 10.5-km single-mode fiber is experimentally demonstrated. The error vector magnitudes for both the down and upstream transmissions are measured to be 7.3% and 8.65%, which are good enough to achieve error-free transmission with forward error correction.

The system tolerance to the dispersion of optical steganography and the deployment of dispersion to enhance secure transmission has been experimentally demonstrated and theoretically studied. Since the stealth signal is carried by amplified spontaneous emission noise, which has a much wider bandwidth compared with the laser carrier, the stealth channel is more sensitive to dispersion and has less tolerance to the uncompensated dispersion. On the other hand, the dispersion effect in the stealth channel can be employed to hide the stealth signal in the time domain. The extra dispersion at the transmitter and the receiver functions as a key pair for the optical encryption and the optical steganography.

This letter proposes and experimentally demonstrates a novel scheme to generate 10G/100G hybrid signal in a short-reach optical communication system. The optical transmitter, which serves 10 and 100-Gb/s channels simultaneously, is realized using Nyquist frequency-multiplexing independent-sideband (NFM-ISB) modulation. For each optical wavelength, there are as many as four 10-Gb/s and one 100-Gb/s NFM-ISB digital channels carried by subcarrier multiplexing scheme, which can be cost-efficiently generated using only one set of optical transmitter hardware. More importantly, compared with the conventional system with independent optical transmitter, the proposed system requires at least five times less downlink optical transmitters, which can be translated into savings in cost, power consumption, and footprint.

We propose and experimentally demonstrate a novel colorless full-duplex passive optical network (PON) access architecture. Utilizing orthogonal codes and correlation receiving methods, the novel PON can mitigate the optical beat interference (OBI) noise induced by Rayleigh backscattering (RB). A pair of electrical orthogonal codes is generated and modulated at the same wavelength in the optical line terminal (OLT). Then, modulated optical signals are transmitted from the OLT to the optical network units (ONUs). One of the codes is for downstream signal coding, and the other is used as the upstream seed. In the ONU, the upstream signal is remodulated without erasing the downstream signal. Neither extra centralized continuous wave (CW) light sources nor gain-saturated reflective semiconductor optical amplifier is required. By using these orthogonal codes, the spectral overlap between upstream signal and downstream signal in the full-duplex system is reduced, which can mitigate the OBI noise significantly. The performance of transmission and power margin is investigated through the experiments with different transmission distances. The remodulated upstream signals are recovered by correlation algorithm in the OLT. By correlation algorithm, we can get coding gain, which is important in long-reach transmissions. Because of coding gain and the OBI noise mitigation, a link power margin of 4−10 dB can be achieved for 5 Gb/s downstream and 1.25 Gb/s upstream, when the transmission distance is from 20 to 70 km.

Nyquist shaping UDWDM-PON combined with digital coherent optical systems has been recently proposed as a promising technology for future optical access networks. In this paper, we report real-time transmitter and receiver for a future coherent PON with high spectral efficiency and low-cost DSP implementation. Using field-programmable gate array (FPGA)-based 8-bit DSP, we experimentally demonstrate a high performance system based on 16 × 2.5 Gb/s QPSK signals in terms of receiver sensitivity and fiber transmission. An optimal transmitted power of –7 dBm per channel is achieved for 50-km standard single-mode fiber in a 2.5-GHz grid. The experimental results show the feasibility of coherent PON scenarios based on DSP supported by FPGAs.

Wavelength translation is one of the key functions to realize spectral defragmentation in an elastic optical add/drop network. Optically translating the wavelength of Terabit/s signals is challenging in the sense that it requires a signal processing scheme to be independent of the symbol rate and modulation format, wideband, and highly efficient simultaneously. In this paper, we present an all-optical wavelength translation for a single-carrier 1.376-Tb/s dual-polarization quadrature phase-shift keying (DP-QPSK) Nyquist optical time-division multiplexing (OTDM) signal by using an all-optical wavelength converter which fulfills all of the basic requirements. A seamless wavelength translation covering almost C-band is achieved with a boost in OSNR thanks to the improved conversion efficiency. The system performance is measured by a polarization-insensitive coherent receiver using linear sampling which implements simultaneously the demultiplexing of the time-domain tributaries, polarization demultiplexing, and carrier-phase recovery for the dual-polarization phase-modulated OTDM signal. The employed receiving scheme, therefore, resolves one of the most shortcomings of the conventional OTDM receiver, which is polarization sensitive due to the use of nonlinear sampling.

We propose a novel all-optical ultra-high-speed orthogonal frequency-division multiplexing (OFDM) to Nyquist wavelength-division multiplexing (Nyquist-WDM) conversion scheme, achieved by exchanging the temporal and spectral profiles using a complete optical Fourier transformation (OFT). This scheme enables high-speed OFDM to Nyquist-WDM conversion without complex optical/electrical/optical conversion. The all-optical OFDM transmitter is based on the generation of OFDM symbols with a low duty cycle by rectangular temporal gating, which in combination with optical time-division multiplexing yields a higher symbol-rate OFDM signal. In the receiver, the converted Nyquist-WDM super-channel is WDM demultiplexed into individual Nyquist-WDM channels using a rectangular optical bandpass filter, followed by optical sampling at the intersymbol-interference free point. In the experimental demonstration, a single-polarization 8-subcarrier 640 Gb/s differential phase-shift keying OFDM super-channel with a spectral efficiency (SE) of 0.8 symbol/s/Hz is generated. The OFDM super-channel is then converted to eight 80-Gb/s Nyquist-WDM channels by complete OFT. The complete OFT is based on two quadratic phase-modulation stages using four-wave mixing, separated by a dispersive medium. In the receiver, a BER < 10−9 is obtained for all channels. The SE remains unchanged after conversion.

We report the first successful field trial of up to 3 Tb/s real-time DP-16 QAM optical superchannel transport over 359-km EDFA-amplified fully managed flexible grid optical infrastructure using production grade hardware and management software from a live network operation center. The spectrum of the flexible grid ROADM was configured according to the requirement of the optical superchannel from a minimum of 37.5 up to 400 GHz with a resolution of 12.5 GHz. Spectral windows larger than 400 GHz were achieved by configuring multiple adjacent spectral slots enabling higher superchannel capacities. The optical superchannels of up to 3 Tb/s propagated alongside standard 50-GHz grid wavelength channels at 100 Gb/s. Stable error-free performance was measured for all sub-channel spacings down to 33.5 GHz, where a record net spectral efficiency of 5.97 b/s/Hz was achieved, an improvement of 49.25% over standard 50 GHz grid. We also show results on optical margin requirements when operating across a range of sub-channel spacings corresponding to different spectral efficiencies. Furthermore, a key technology building block for the 3-Tb/s optical superchannel, 200 G DP-16 QAM was trialed in a live WDM network to evaluate and demonstrate its applicability for deployment.

The recently developed digital coherent receiver enables us to employ a variety of spectrally efficient modulation formats such as $M$ -ary phase-shift keying and quadrature-amplitude modulation. Moreover, in the digital domain, we can equalize all linear transmission impairments such as group-velocity dispersion and polarization-mode dispersion of transmission fibers, because coherent detection preserves the phase information of the optical signal. This paper reviews the history of research and development related to coherent optical communications and describes the principle of coherent detection, including its quantum-noise characteristics. In addition, it discusses the role of digital signal processing in mitigating linear transmission impairments, estimating the carrier phase, and tracking the state of polarization of the signal in coherent receivers.

A novel dual-tone quadrature phase-shift keying (QPSK) optical millimeter (mm)-wave signal generation by frequency nonupling the radio-frequency QPSK signal via an optical phase modulator (PM) without phase precoding is proposed. To enable the generated optical mm-wave signal to resist the fiber chromatic dispersion degradation, the unmodulated −fourth-order and the QPSK-modulated +fifth-order sidebands are abstracted from the generated sidebands, considering the phase periodicity of a QPSK signal. The opto-electrical conversion efficiency is maximized by optimizing the modulation index of PM. An optical mm-wave generator along with a radio-over-fiber link is built, and the eye diagrams, constellations, and BER curves demonstrate that the frequency nonupling dual-tone QPSK optical mm-wave signal performs well. The simulated results agree well with the theoretical prediction.

High-speed long-haul wireless transmission links are required to meet the demand of mobile backhauling and emergency communications. We experimentally demonstrated ultra-high-speed 432-Gb/s polarization-division-multiplexing 16-ary quadrature amplitude modulation modulated W-band millimeter-wave (mm-wave) signal delivery over a 2-m horn antenna-based (HA-based) 4 × 4 multiple-input multiple-output (MIMO) wireless link, enabled by photonic mm-wave generation and optical/antenna polarization multiplexing. We further achieved the field trial demonstration of 80-Gb/s polarization-division-multiplexing quadrature phase shift keying modulated W-band mm-wave signal delivery over a 300-m Cassegrain antenna-based (CA-based) 4 × 4 MIMO wireless link, adopting photonic mm-wave generation, multi-band multiplexing, and optical/antenna polarization multiplexing. To the best of our knowledge, 80 Gb/s or 74.7 Gb/s after removing 7% forward-error-correction overhead is a record for W-band wireless signal delivery over a few hundred meters.

This report presents a novel method of generating an optical vestigial sideband (VSB) modulated signal without using optical bandpass filters. Using a modified Hilbert transformer based on digital signal processing, an optical VSB-modulated signal is generated using the phase-shift method. The proposed method is demonstrated experimentally for an optical binary phase-shift keying (BPSK) signal. The proposed method is wavelength-transparent compared to an optical bandpass filtering method, where the wavelength dependence of the optical bandpass filter limits applications. Furthermore, the optical bandwidth of the modulated signal is readily adjustable by changing the cutoff frequency of the high-pass Hilbert transformer. Fiber transmission characteristics of a single-channel optical BPSK-VSB signal are analyzed using a 100-km transmission link. Results of fiber transmission analysis show tolerance of the proposed modulation scheme to fiber nonlinearity-based signal distortions. For a 10 Gbit/s non-return-to zero(NRZ) sequence, a self-phase modulation threshold of 13 dBm is reported for the studied system.

We discuss the benefits and limitations of optical time-division multiplexing 22 (OTDM) techniques based on the optical generation of a periodic train of sinc pulses for 23 wavelength-division multiplexing (WDM) transmission at high baud rates. It is shown 24 how the modulated OTDM spectrum bandwidth is related to the optical comb parameters 25 and the pulse shaping of the modulating waveforms in the electrical domain. Such de- 26 pendence may result in broadening of the modulated spectra, which can degrade the 27 performance of Nyquist-WDM systems due to interchannel crosstalk penalties. However, 28 it is shown and experimentally demonstrated that the same technique of optical pulse 29 train generation can be allied with digital pulse shaping to improve the confinement of 30 the modulated spectrum toward the Nyquist limit independently of the number of OTDM 31 tributaries used. To investigate the benefits of the proposed approach, we demonstrate 32 the first WDM Nyquist-OTDM signal generation based on the periodic train of sinc pulses 33 and electrical spectrum shaping. Straight line transmission of five 112.5-Gbd Nyquist- 34 OTDM dual-polarization quadrature phase-shift keying (QPSK) channels is demon- 35 strated over a dispersion uncompensated link up to 640 km, with full-field coherent 36 detection at the receiver. It is shown that such a design strategy effectively improves the 37 spectral confinement of the modulated OTDM signal, providing a minimum intercarrier 38 crosstalk penalty of 1.5 dB in baud-rate-spaced Nyquist-WDM systems.

This paper presents the world's first field trial of a 40-km reach and over 512-split symmetric-rate 40-Gbit/s λ-tunable time and wavelength division multiplexing passive optical network (TWDM-PON) that utilizes our newly developed high-speed λ-tunable optical network unit transceivers and automatic gain controlled semiconductor optical amplifier-based PON extender for repeater and central office use. The upstream signals for C-band and downstream signals for L+-band in our developed λ-tunable TWDM-PON comply with the wavelength plan of ITU-T G.989 series. In a field trial, we successfully demonstrate error free λ-tunable transmission for the 40-km reach and 1024-split (maximum number) symmetric-rate 40-Gbit/s λ-tunable TWDM-PON over installed standard single-mode fiber links, and advanced network functions such as dynamic load balancing, incremental system upgrade, optical subscriber unit protection, and OLT equipment power saving are also confirmed.

In this paper, we proposed a cost-effective broadcast signal transmission scheme using a distributed feedback laser diode (DFB-LD) for wavelength-division-multiplexing passive optical network (WDM-PON) systems. The DFB-LD is directly modulated with a single-tone radio frequency signal to generate multiple optical carriers. An optical signal-to-noise ratio (OSNR) is enhanced using a delay interferometer as a double-pass interferometer. Orthogonal frequency division multiplexing (OFDM) and on-off keying (OOK) signals are experimentally demonstrated to test the broadcasting scheme. We measured the bit-error-rate (BER) and the power penalty after the broadcasting OFDM and OOK signals are transmitted through a 25-km single-mode fiber. An excellent performance of BER is achieved for both OOK and OFDM signals. The proposed scheme is a practical and cost-effective solution for broadcast signal transmissions in WDM-PON systems.

In this pajjer. we derive high-order Volterra based pre-distorters for a broad class of nonlinear am­ plifiers. The traditional problems associated with high-order Volterra kernels are bypassed by using the structure of the amplifier. It is seen that the problem of pre-distortion is mainly that of estimating the amplifier. Once this is completed, finding the pre-distorter is straightforward. The derived pre-distorters are actually high-order Volterra op>erators. The proposed method results in easily implemented, but high-order pre-distorters. The method is applicable to both pre-distorting RP and baseband signals. If baseband signals are used, the in-h)and distortion is cancelled while the out-of-band distortion is essentially unchanged. The work weis founded by Rockwell International. Cedar Rapids. Iowa, contract CF\VQ49.5-12.

We demonstrate the generation and detection of single-carrier electronic time division multiplexing 400 GE signal based on 120-GBd PDM PAM-4 signal. The signal performance is significantly improved by using our novel pre-equalization scheme. A line rate of 480-Gb/s is achieved, which enables 20% forward-error correction overhead to keep the record 400-Gb/s net information rate.

An energy-aware solution for physical-layer reconfigurability in metro-access networks is presented. The dynamicity of optical switching is introduced in nodes that are perceived as fully-passive by the network. Energy scavenging at low optical feed level of $- 10\;{\text{dBm}}$ supports field-deployment without local electrical power supply. Two types of network nodes are demonstrated experimentally. First, a resilience node is evaluated for fast protection switching in 10.7 ms at the feeder segment. Optical switching is further exploited for the purpose of dynamic allocation of spectral slices and routing in a new class of reconfigurable optical add-drop multiplexer. The spectral bandwidth of drop segments can be extended on demand while intranetwork communication among different segments of the access network is also enabled. Finally, we discuss the potential for realizing self-powering by means of tapping optical signals traversing the access network rather than utilizing a dedicated pump source.

A simple optoelectronic regenerator for differential quadrature phase-shift keying (QPSK) signals is demonstrated. The regenerator consists of two parallel delay interferometers followed by balanced detectors, limiting and driving amplifiers, and a dual-parallel Mach-Zehnder modulator that regenerates noise-suppressed optical QPSK signals. We experimentally show that the regenerator improves the receiver sensitivity by about 8 dB at an input optical signal-to-noise ratio (OSNR) of 19 dB at a signal speed of 10 Gbaud. Numerical simulation is conducted for higher speed operation at 56 Gbaud to study the impact of the bandwidth of electrical circuits inside the regenerator on the regenerator performance. Electrical power consumption of the regenerator is assessed, and it is shown that the optoelectronic regenerator consumes a similar amount of electrical power as that consumed by an all-optical version of the regenerator using semiconductor optical amplifiers as a nonlinear element.

We propose a novel and in-service method for in-band OSNR system margin and overall link impairment level monitoring based on the use of an optical coherent receiver. This technique relies on the estimation of the ESNR margin of the received optical coherent channel, scaled by a correction factor which depends on the modulation format and the overall link impairment level. This method is demonstrated experimentally for a 120 Gb/s DP-QPSK channel in both dispersion and nondispersion managed links with different impairment scenarios.