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This research work proposed and experimentally demonstrated beyond-100GBd probabilistically shaped coherent optics that support the transmission of a ~1.2 Tbps coded line rate and a ~0.9 Tbps net bit rate per optical carrier over metro-regional distances. Pursuing next-generation transmission systems having both high capacity approaching terabits per wavelength and high spectral efficiency require engineering efforts from different aspects, which may include the enhancement of analog-to-digital or digital-to-analog interfaces, the improvement of channel characteristics, and also the realization of better receiver sensitivities, preferably through DSP techniques such as probabilistic shaping (PS). By doing so, this work achieved a single-channel and a 112.5-GHz WDM transmission of 900G wavelengths over 800 and 400 km, respectively, which employed a PS DP-64QAM modulation format at 105 GBd, yielding a net spectral efficiency of 8.05 bits/s/Hz. Such a high symbol rate was demonstrated using a commercially available DAC unit without band-interleaving. The enhanced optical channel consists of ITU-T G.654 compliant Terawave SLA+ fiber spans with the backward-pumped Raman amplifiers. In addition, with the same PS DP-64QAM modulation format and the same enhanced channel, this research work also demonstrated that 400G wavelengths can be delivered over 2800 km supporting long-haul applications.

Forward error correction (FEC) performance down to 10−15 bit error rate (BER) of a concatenated staircase and Hamming code (CSHC), which was recently proposed for the first 400G inter-data center interconnect standard, is verified with a 50-piece field-programmable gate array (FPGA) implementation at a record 200-Gb/s throughput. The effect of digital noise tail accuracy on the FEC emulation results is investigated. A converging criterion is proposed and demonstrated for achieving high confidence in artificial digital-noise-source-based FPGA emulations. The CSHC performance as a function of decoding iterations of the outer staircase code is investigated, and emulation results show that six staircase decoding iterations is the optimal choice. The FPGA emulations also reveal the existence of an error flare of the CSHC at 10−10 BER, which corrects the predicted BER threshold from 1.25 × 10−2 to 1.21 × 10−2. Further investigations on the effects of interleaving processes and staircase decoding buffer size show that the error flare behavior of the CSHC depends on the decoding buffer size of the outer staircase code. To remove the CSHC error flare, a proper choice of the staircase decoding buffer size is shown to be 6, which also moves the FEC threshold to 1.27 × 10−2.

Digital signal processing (DSP) with both linear equalization and nonlinear compensation for the single-carrier 400G system based on 84-GBaud polarization-division multiplexing 8QAM signals is studied in this paper. The 8QAM signals are generated and preprocessed with pre-equalization and lookup table predistortion at the transmitter (Tx)-side. The implementation principles of training-based adaptive equalization and predistortion are presented in this paper with experimental studies on the tap and memory length. At the receiver (Rx)-side, fiber-nonlinearity compensation based on digital backward propagation is also utilized to further improve the transmission performance. Thanks to the Tx-side and Rx-side DSPs, eight channels of 400G are successfully transmitted over 2125 km SSMF with EDFA-only amplification.

Digital signal processing is the core functional block in beyond-100G transmission systems with a high symbol rate and/or high spectral efficiency. We review recent progress on high symbol rate signal generation and detection, and corresponding advanced algorithms for signal equalization and compensation at the transmitters (Tx) and the receivers (Rx), respectively. Thanks to the joint Tx-side optical pre-equalization (pre-EQ) and Rx-side partial response maximum likelihood sequence estimation, significant performance improvement can be achieved by reducing the penalty caused by bandwidth limitations of the optical and electronic components. A joint pre-EQ and look-up table predistortion technique is also reviewed in this paper, which is demonstrated to be an effective method for mitigating devices' nonlinearity impairment. We exemplify how these advanced algorithms enable high symbol rate beyond-100G transmission systems with signal generation based on either electronic time-division multiplexing or digital-to-analog converters.

We demonstrate the generation and wavelength-division multiplexing (WDM) transmission of single-carrier 120-GBd electronic time-division multiplexing (ETDM) polarization division multiplexed 16-ary quadrature amplitude modulation (16 QAM) optical signals. Both transmitter-side optical preemphasis and receiver-side maximum likelihood sequence estimation are utilized to mitigate the impairments caused by bandwidth limitation of the optoelectronic components. Thanks to the preemphasis and post equalization, we have successfully transmitted 12 WDM channels on 150-GHz grid, each loaded with 960-Gb/s (800 Gb/s data signals + 20% FEC emulated overhead bits) over 1200-km link based on 100 km/span TeraWave terrestrial optical fiber. The achieved data rate interface ensured spectral efficiency of 5.33 b/s/Hz. To the best of our knowledge, this is the first experiment with the highest symbol rate reported for ETDM-based 16 QAM signals.

We experimentally demonstrate a coherent transmission system with a high symbol rate using up to 110-GBaud PDM-QPSK signals. Super-Nyquist-filtering technology is used to narrow down the bandwidth of a single channel on a 100-GHz grid. The performance of the high baud rate electronic time division multiplexed-based super-Nyquist-filtered signal is also studied under the aggressive optical filtering elements in multiple reconfigurable optical add-drop multiplexers (ROADMs) nodes during transmission. We successfully transmit 100-GHz-grid, 20 channel single-carrier 440-Gb/s super-Nyquist 9-QAM-like signal over 3600-km ultralarge effective-area fiber (ULAF) at a high net SE of 4 b/s/Hz (after excluding the 7% hard-decision FEC overhead). The highly filtering tolerant performance of the 9-QAM liked super-Nyquist signal is also experimentally demonstrated. Using this scheme, we then successfully transmit ten channel 440-Gb/s signal over 3000-km ULAF and ten cascaded 100-GHz-grid ROADMs based on the 110-GBaud QPSK. Such signal is coherently detected and processed after a real-time oscilloscope at 160-GSa/s sampling rate with 65-GHz bandwidth.

We propose a joint digital preequalization scheme for a Nyquist wavelength division multiplexing (N-WDM) system to compensate for the intersymbol interference caused by a limited channel bandwidth or aggressive prefiltering. A digital raised-cosine pulse filter is implemented before the reference-based preequalization scheme to enhance the tolerance of the signal to the crosstalk from adjacent channels. The experiment illustrates eight-channel digital-analog-converter generation of the polarization division multiplexing quadrature phase shift keying system at 112 Gb/s per channel on a 25-GHz grid, adopting the reference-based digital preequalization considering narrow-band optical filtering effect at the transmitter. The experimental results show that the proposed preequalization scheme allows for an ultradense channel spacing of 0.89 times of the baud rate in the super N-WDM system with a as large as 5-dB optical signal-to-noise ratio improvement.

We have realized the first field transmission of 8 × 216.8-Gb/s Nyquist wavelength-division-multiplexing (N-WDM) signals over 1750-km G.652 fiber consisting of 950-km real and 800-km lab fibers with erbium-doped fiber amplifier (EDFA)-only amplification. The average loss per span is 21.6 dB. Each channel is modulated with 54.2-Gbaud (216.8-Gb/s) polarization-division-multiplexing carrier-suppressed return-to-zero quadrature-phase-shift-keying (PDM-CSRZ-QPSK) data on a 50-GHz grid giving a record spectral efficiency (SE) of 4 b/s/Hz. Digital post filtering and 1-bit maximum likelihood sequence estimation (MLSE) are introduced into the offline digital signal processing (DSP) at the receiver to suppress noise, linear crosstalk and filtering effects. We have also investigated the co-transmission of 200 G PDM-CSRZ-QPSK and 200 G PDM 16-ary quadrature-amplitude-modulation (PDM-16 QAM) signals on a 50-GHz grid, and found that PDM-CSRZ-QPSK signals have better bit-error-rate (BER) performance for both back-to-back and 700-km transmission cases. Meanwhile, PDM-16 QAM signals are subject to larger crosstalk from the neighboring Nyquist QPSK channels.

This paper focuses on terabit superchannel transmission with enhanced network reach by using an emerging noise-suppressed Nyquist wavelength division multiplexing (NS-N-WDM) technique for polarization multiplexing quadrature phase shift keying subchannels at different symbol rate to subchannel spacing ratios up to 1.28, and for the first time, it was compared experimentally with the transmission capability of no-guard-interval coherent optical orthogonal frequency division multiplexing (NGI-CO-OFDM) on the same testbed. At 2 × 10-3 bit error ratio, the maximum reachable distance is 3200 and 2800 km SMF-28 with erbium-doped-fiber-amplifier-only amplification for NGI-CO-OFDM and NS-N-WDM terabit superchannels, respectively, at 100 Gb/s/ch. For 11 ntn112 and 11 × 128 Gb/s/ch NS-N-WDM transmission under assumption of different coding gain with hard-decision and soft-decision forward error correction, their maximum achievable distance was found to be equivalent, which are 2100 and 2170 km, respectively, both were achieved by using digital noise filtering and 1-bit maximum likelihood sequence estimation at the receiver DSP. In addition, the back-to-back characteristics of NS-N-WDM superchannel such as analog-to-digital converter bandwidth requirement and its tolerance to unequal subchannel power were experimentally evaluated and studied.

Successful joint experiments with Deutsche Telecom (DT) on long-haul transmission of 100 G and beyond are demonstrated over standard single-mode fiber (SSMF) and inline erbium-doped fiber amplifier-only amplification. The transmission link consists of eight nodes and 950-km installed SSMF in DT's optical infrastructure with the addition of lab SSMF for extended optical reach. The first field transmission of 8 × 216.8-Gb/s Nyquist-WDM signals is reported over 1750-km distance with 21.6-dB average loss per span. Each channel modulated by a 54.2-Gbaud PDM-CSRZ-QPSK signal is on 50-GHz grid, achieving a net spectral efficiency (SE) of 4 bit/s/Hz. We also demonstrate mixed data-rate transmission coexisting with 1 T, 400 G, and 100 G channels. The 400 G uses four independent subcarriers modulated by 28-Gbaud PDM-QPSK signals, yielding the net SE of 4 bit/s/Hz while 13 optically generated subcarriers from single optical source are employed in 1 T channel with 25-Gbaud PDM-QPSK modulation. The 100 G signal uses real-time coherent PDM-QPSK transponder with 15% overhead of soft-decision forward-error correction. The digital postfilter and 1-bit maximum likelihood sequence estimation are introduced at the receiver DSP to suppress noise, linear crosstalk, and filtering effects. Our results show the future 400 G and 1 T channels utilizing the Nyquist wavelength division multiplexing technique can transmit long-haul distance with higher SE using the same QPSK format.

We propose and demonstrate an integrated long- reach passive optical network (PON) and in-house graded-index plastic optical fiber (GI-POF) network architecture for hybrid community antenna television (CATV) and orthogonal frequency division multiplexing (OFDM) signals transmission. By reasonably multiplexing the OFDM and CATV signals into a CATV transmitter, both signals originated from a central office (CO) are successfully transmitted over a span of 60 km single mode fiber (SMF) and another span of 25 m GI-POF to consumers' devices. Although the SMF and GI-POF have different core sizes and attenuation features, no any bridge circuit or wavelength converter is utilized in the proposed architecture resulting in a transparent platform for the Internet service providers (ISPs) to directly manage their long-distance services toward suburban or rural areas. Since the optical signal generated at the CO can be transmitted straightforward to the consumers' devices, the average packet delay and packet overhead size can be greatly reduced and the quality of services (QoS) can be maintained easier. Good experimental performances of the CATV and OFDM signals transmission proof the practice and efficiency of this proposal to extend multimedia services from metro areas to suburban and rural areas.

A bidirectional three-band lightwave transport system is proposed and experimentally demonstrated for both fiber-to-the-X (FTTX) and radio-over-fiber (RoF) networks. By cascading a phase modulator (PM) and a Mach-Zehnder modulator (MZM) to generate multiple coherent lightwaves, hybrid 1.25 Gbps baseband (BB), 1.25 Gbps/20 GHz microwave (MW), and 1.25 Gbps/40 GHz millimeter-wave (MMW) downstream signals and a 1.25 Gbps BB upstream signal are simultaneously transmitted. Furthermore, with an assistance of an optical signal-to-noise ratio (OSNR) enhancement circuit, sufficient low bit error rate (BER) values are experimentally achieved for both down-link BB/MW/MMW and up-link BB signals. No additional high-frequency local oscillator, mixers and upstream laser diode are required in both transmitter and receiver sites. Under this architecture, both wire-lined and wireless clients can be simultaneously served without using any extra device/equipment to convert the downstream signals among BB, MW and MMW formats.

The generation of coherent and frequency-locked optical multi-carriers by using cascaded phase modulators and recirculating frequency shifter (RFS) based on an erbium doped fiber amplifier (EDFA) loop has been investigated theoretically and experimentally for a multi-terabit optical orthogonal frequency division multiplexing (OFDM) superchannel transmission. The phase and amplitude relationship between RF driving signals of two cascaded phase modulators and the impact of EDFA gain are analyzed. Experimental results are in good agreement with the theoretical analysis. The 112 coherent and frequency-locked subcarriers obtained after tilt filtering exhibit a tone-to-noise ratio of larger than 26 dB, a power fluctuation of less than 5 dB, and a frequency spacing of 25 GHz giving a 22.6 nm-wide optical OFDM signal spectrum. By using this method, we have successfully generated a 10-Tbit/s (112 × 100 Gbit/s) single optical OFDM polarization-division-multiplexing QPSK (PDM-QPSK) superchannel with an optical signal to noise ratio per OFDM subchannel greater than 20 dB at 0.1 nm bandwidth, and it has been transmitted over a 640-km SMF-28 and EDFA-only link with BER less than 2 × 10-3.

A new optical millimeter-wave generation scheme to triple the beating frequency based on subcarrier multiplexing in combination with single sideband technique is proposed, capable of high tolerance of fiber chromatic dispersion. The proposed scheme can be applied to two types of multiband 60-GHz wireless over fiber access systems: one with widely separated bands including millimeter-wave, microwave and baseband and the other one with multiple 60-GHz sub-bands. Experimental verification of the proposed system with widely separated bands is presented with the generation and error-free transmission of 2.1-Gb/s data on the 63-GHz mm-wave and 21-GHz microwave carriers over 50-km single-mode fiber (SMF-28) without dispersion compensation. The power penalties caused by 50-km fiber transmission for both signals are both less than 1.0 dB at BER of 10-9 Meanwhile, simultaneous generation and transmission of multiple services at 60-GHz sub-bands are also introduced. The experimental results demonstrate the successful delivery of the 1-Gbps data carried by 60-GHz millimeter-wave both over 50-km SMF-28 and wireless distance of 6-m without any dispersion compensation. The optical receiver sensitivity of the transmission with two sub-bands degrades by 2 dB compared with the single band 60-GHz signal, and the power penalty from 50-km SMF-28 transmission is 0.8 dB at BER of 10-9. From the theoretical analysis and experimental demonstrations of the two multiband systems, it is concluded that the proposed millimeter-wave generation scheme indeed increase the transmission distance for the system with 60-GHz signal, which normally having SMF transmission distance of few tens of kilometers, by utilizing optical and electrical components with low-bandwidth requirements.

We present two key system technologies on the two ends of RF spectrum to support optical-wireless access using radio-over-fiber (RoF) based distributed antenna system (DAS) for in-building environments. The proposed technologies can enable protocol-independent, multi-carrier broadband connectivity to the end users' devices deployed in the in-door facilities by supporting existing and emerging wireless services with lower radio frequency carrier (from 500 MHz up to 3 GHz) as well as future-proof very high throughput (VHT) gigabit wireless services using 60 GHz mm-wave band. For low frequency wireless services, a broad spectrum band-shifting technique is experimentally demonstrated to simultaneously transmit multi-service multiple input multiple output (MIMO) radio signals over in-building active DAS. This approach facilitates easy upgrading of existing non-MIMO services to MIMO services or adding future MIMO services in a simple and cost-effective way. For wireless-VHT service, for the first time to our knowledge, we demonstrate simultaneous all-optical up-conversion of multiple, separate gigabit wireless services at 60 GHz and 64 GHz mm-wave band using one single lightwave transmitter. This scheme can be used to achieve seamless convergence of very high throughput wireless personal area network (VHT-WPAN) with more conventional low frequency distributed antenna based optical-wireless access system.

A new optical millimeter-wave generation scheme to double the beating frequency without suppressing the carrier by taking advantages of the out-of-phase property between sidebands of a phase-modulated optical carrier is proposed for the first time. Theoretical analysis shows that the generated 60 GHz optical millimeter-wave (mm-wave) can tolerant ±0.016 nm wavelength drifting with filter bandwidth ranging from 70 to 100 GHz to sustain first to second harmonic suppression ratio of 18 dB. The doubled frequency is continuously tunable from 60 to 90 GHz within 100 GHz filter bandwidth with RF power variation of less than 2 dB. In addition, simultaneously generating and transmitting multi-band signal: millimeter-wave band, microwave band, and baseband leveraging the same concept is also proposed. Error-free transmission of 2.5 Gb/s wireless baseband signals carried by the generated 60 GHz mm-wave is successfully demonstrated in both single- and multi-band network environments over a combined optical fiber and wireless distance with a proper equivalent isotropically radiated power of about 20 dBm for in-building access. Moreover, dispersion effect on the generated frequency-doubled optical mm-wave is analyzed by experimentally comparing the link performance of both single mode fiber (SMF-28) and dispersion-shifted fiber cases. It is concluded that for single-band service delivery, the proposed scheme is immune to the interference from the dispersion-induced, redundant 1st harmonics; however, to deliver multi-band services, launching lightwave at zero-dispersion wavelength over SMF-28 is highly recommended to mitigate inter-band interference.

The broadband penetration and continuing growth of Internet traffic among residential and business customers are driving the migration of today's end user's network access from cable to optical fiber and superbroadband wireless systems The integration of optical and wireless systems operating at much higher carrier frequencies in the millimeter-wave (mm-wave) range is considered to be one of the most promising solutions for increasing the existing capacity and mobility, as well as decreasing the costs in next-generation optical access networks. In this paper, several key enabling technologies for very high throughput wireless-over-fiber networks are reviewed, including photonic mm-wave generation based on external modulation or nonlinear effects, spectrum-efficient multicarrier orthogonal frequency-division multiplexing and single-carrier multilevel signal modulation. We also demonstrated some applications in wireless-over-fiber trials using these enabling techniques. The results show that the integrated systems are practical solutions to offer very high throughput wireless to end users in optically enabled wireless access networks.

A novel radio-over-graded index-plastic optical fiber (GI-POF) transport system is proposed based on vertical-cavity surface-emitting lasers (VCSELs) and light injection-locking technique. Comparing with other light sources, VCSEL provide a good balance between its cost and quality for intrabuilding network applications. To further enhance its transmission performance, we are the first one to integrate VCSELs with light injection-locking technique in radio-over-GI POF intrabuilding network. Impressive upgrading of third-order intermodulation distortion to carrier ratio, spurious-free dynamic range, error vector magnitude, and bit error rate were experimentally obtained and discussed in the paper.

This work describes a concept of a hierarchical radio-over-fiber (RoF) network architecture that provides both intra- and inter-network connectivity for end user wireline and wireless terminals with high-bandwidth, in-building access applications. An intelligent gateway router (IGR) is proposed as a unified platform to accommodate multi-gigabit, millimeter-wave services at 60-GHz band as well as being backward compatible with all current wireless access technologies such as WiFi and WiMAX. In addition, we further present an advanced multi-band optical carrier generation technique that can simultaneously deliver independent 60-GHz mm-wave, 2.4-GHz WiFi, and 5.8-GHz WiMAX signals efficiently carried over the same wavelength, and is suitable for the proposed IGR. Finally, we report, for the first time to our knowledge, a campus-wide field trial demonstration of RoF system transmitting uncompressed 270-Mbps standard definition (SD) and 1.485-Gbps high definition (HD) real-time video contents carried by 2.4-GHz radio and 60-GHz millimeter wave signals, respectively, between two on-campus research buildings distanced over 2.5-km standard single mode fiber (SMF-28) through the Georgia Institute of Technology's (GT) fiber network.