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NOMA-CoMP based space frequency block coding is firstly proposed and experimentally demonstrated for 28 GHz MMW fiber wireless integration fronthaul system. The end-to-end experiment reveals enhanced cell edge user signal quality and improved spectral efficiency.

We demonstrate a radial basis function network equalizer for 112-Gb/s IM-DD PAM4 inter-datacenter transmissions with gain-clamped SOA pre-amplifiers. The results outperform VNLE and FFE in receiving sensitivity, dynamic range and BER with >4dB power margin.

A neural-network based machine learning joint CFO-SCO equalizer is proposed for 5G multi-service mobile fronthaul. Up-to 100 ppm CFO and 100 ppm SCO are compensated without conventional synchronization on time or frequency domain.

For fixed services such as hybrid fiber-coaxial and passive optical network with deployed fiber networks, it is desirable to exploit the potentials to support wireless services in fifth-generation (5G) mobile data communications on the top of the existing fixed networks. We propose a polarization-division multiplexing (PDM) scheme to achieve the co-delivery of independent signals for fixed-mobile convergence. This is achieved by removing unwanted optical carrier in each polarization, and thus the proposed system can resolve the polarization-tracking issue in conventional PDM. It has been demonstrated in this letter that the polarization-tracking-free PDM system can support the co-transmission of respective 70-Gbps digital and analog signals over 20-km single mode fiber. Experimental results have shown low crosstalk between two polarizations. The proposed PDM system is compatible with wavelength-division-multiplexing (WDM) network and is capable of enhancing the spectral efficiency of WDM channels. The inherent single-sideband feature of the proposed PDM also enhances long-range services.

This letter proposes a polarization-tracking-free polarization division multiplexing (PDM) in an intermediate frequency over fiber mobile fronthaul system based on multiband direct detection optical orthogonal frequency division multiplexing (DDO-OFDM) with adaptive modulation. The use of two orthogonally polarized optical carriers with a simple optical filter at each radio access unit is sufficient to perform passive demultiplexing of the corresponding multiband signals in PDM schemes without transmission efficiency loss in training signal, which is commonly found in conventional PDM demultiplexing schemes. We experimentally achieved a multiband OFDM signal with adaptive modulation, which maximizes signal capacity, in a PDM scheme with the data rate of 49.64 Gb/s, which doubles that of corresponding single polarization schemes, over a 25-km single mode fiber. We also achieved a 6-dB power margin which is sufficient for the wireless transmission part.

Performance of multicarrier code division multiple access (MC-CDMA) long reach passive optical network (LR-PON) implemented with colorless laser diode transmitter is evaluated and compared with the same system under typical orthogonal frequency division multiplexing (OFDM) format. The relative amount of the multicode interference (MCI) in the MC-CDMA PON can be efficiently suppressed by applying the minimum mean square error based MCI cancellation processing and be analyzed in term of the error vector magnitude deviation. Due to the double sideband nature of the directly modulated colorless laser diode, both OFDM and MC-CDMA formats suffer from severe power fading after fiber transmission. Partial subcarriers in the OFDM-PON fail to reach the specified forward error correction (FEC) threshold, causing a huge performance deviation among subcarriers and a 3% data loss after 75-km transmission. In contrast, a distance transparency transmitter design for subscribers ranging from back-to-back to 50 km is achieved in the MC-CDMA PON scheme, and the received performance among subcarriers are equalized under the FEC criterion even after 75-km transmission. Therefore, the MC-CDMA exhibits superior performance when comparing with the OFDM format in the directly modulated colorless laser diode based LR-PONs.

A 520-nm GaN green gLED-based for visible light communication is experimentally demonstrated. By optimizing the PAPR and bit-power allocation of QAM-OFDM signals, the capacity achieves 10.05 Gbps with single gLED over air transmission.

A PDM-RoF mechanism is firstly experimentally demonstrated for MMW coordinate multi-point transmission system with a polarization-track-free RAU design. Without additional latency for PDM demultiplexing, we evaluate various coordinate multi-point joint transmission scenarios.

A PDM mobile fronthaul was demonstrated with doubling capacity via a polarization tracking-free de-multiplexing module. 59.2-Gb/s data rate and 32.5-dB power budget were achieved even signals suffering from rapid SOP changing rate of 2,000 degrees/ms.

We implemented a two-hidden-layer dynamic complex deep neural network nonlinear equalizer which outperforms the linear equalizer, static and dynamic single hidden layer CDNN-NLE by 1.38-dB, 1.01-dB and 0.62-dB for a 34-GBaud/s, 64-QAM signal over 1200-km.

A timing synchronization free multi-user OFDM-RoF system is proposed and experimentally demonstrated. With Gold sequence multiplexing, two user signals separately transmitted and demultiplexed possess negligible performance variances with up to 25 km SMF transmission difference.

A multiband direct-detected optical orthogonal frequency-division multiplexing (DDO-OFDM) system effectively enhance data capacity without high-end electrical devices. However, signals are optical-to-electrically converted with only one photodetector in a direct detecting scheme, signal–signal beating interference (SSBI) is meanwhile introduced. Traditionally, a large guard band can be applied to evade SSBI, however, it seriously restricts the precious spectral efficiency (SE). In this letter, we propose an iterative digital signal processing (DSP) in the receiving end of a multiband DDO-OFDM system to cope with the SSBI. With this iterative DSP, the corresponding SE theoretically approach to that of single polarization coherent optical OFDM systems. A total 65.4-Gb/s data rate is experimentally demonstrated with a three-band DDO-OFDM signal in 16-QAM format, and the SSBI reduction DSP saturates within two iterations. Various bandgaps and carrier-to-signal power ratios settings are also evaluated to investigate the feasibility of the proposed iterative DSP.

We propose and experimentally demonstrate an optical modulation format converter from a 25-Gbps quadrature phase-shift keying (QPSK) signal to two 12.5-Gbps binary phase-shift keying (BPSK) signals in a double-pass configuration, which is achieved by four-wave mixing in a single highly nonlinear fiber. The phase logic of the original QPSK signal is preserved on both of the converted BPSK signals. The clear constellation diagrams and the satisfactory bit-error-rate (BER) performance are successfully obtained both in numerical simulation and experimental demonstration. Moreover, the tolerance of phase mismatch among pumps and signals in the proposed format converter is also investigated.

We proposed and experimentally demonstrated an all-optical modulation format conversion mechanism by applying bidirectional cross-phase modulation in a single highly nonlinear fiber. In our experiment, four individual 12.5 Gb/s nonreturn to zero ON–OFF keying signals are successfully converted to a 50-Gb/s polarization division multiplexed return to zero quadrature-phase shift keying signal within a satisfactory power penalty. The performance and feasibility of the proposed converter are both numerically and experimentally investigated. Moreover, the timing-mismatch tolerance among all the signals in the proposed format converter is also analyzed.

A point-to-multipoint PDM spectral aggregation and cell densification in 5G mobile fronthaul is proposed without requiring laborious polarization tracking in RAUs. A 25-km SMF transmission experiment shows less-than-1-dB power sensitivity differences between two polarization signals.

We experimentally demonstrate a multi-LED VLC system with low complexity Gold sequence multiplexed OFDM signals. Without time synchronization or uplink feedback mechanism, the received signal qualities are uniform and ubiquitously isolated from wireless multipath interferences.

For the first time, a period-one (P1) nonlinear dynamic modulated MMW OFDM signal is employed to mobile fronthaul uplink. A proof-of-concept experimental demonstrations show successfully retrieved signals after 1.5-m wireless and 25-km SMF transmissions.

We experimentally apply MC-CDMA based on OFDM to a 2-meter transmission phosphor-based LED VLC system. MC-CDMA provides highly uniform per-user performances and thus enhances the available communication bandwidth.

In an intensity-modulation direct-detection (IMDD) orthogonal frequency division multiplexing (OFDM) signal format, radio frequency (RF) power fading produces non-uniform receiving performance among the subcarriers due to chromatic dispersion. Hence each subscriber experiences distinct quality of service (QoS) in conventional frequency division multiple access (FDMA). In this paper, a multicarrier code division multiple access (MC-CDMA) signal along with multicode interference (MCI) cancellation process is proposed and experimentally demonstrated to enhance the receiving performance in an IMDD long reach passive optical network (LR-PON). With the proposed scheme, the receiving performance of each subcarrier can be equalized so that a universal transmitter design at central office (CO) can support all the subscribers with their locations ranging from back-to-back to 100 km. Our experimental results also reveal that, even under 20 dB RF power fading, the proposed scheme can still provide over 21.7 dB power budget and only approximately 2 dB sensitivity deviation is observed in an IMDD LR-PON system.

By utilizing the cyclic filtering and free spectral range characteristics of an arrayed waveguide grating (AWG), we propose and experimentally demonstrate a novel 3-D ring-mesh sensing system with comprehensive self-healing function. The Bragg wavelengths of the employed fiber Bragg grating-based optical sensors are periodically assigned, with respect to the AWG. The proposed ring-mesh topology is constructed by 2 × 2 optical switches to link the ring-based subnets in a meshed architecture. Moreover, a simple and cost-effective signal sensing processor, provided by the AWG, is employed for classifying the sensing signals and monitoring the sensing elements. With the same constructional building block, the proposed sensing system can be easily scaled up which provides more self-healing paths in a self-reproduced manner. In addition, we also bring up a routing algorithm to seek for an optimal sensing path that has the least accumulated power loss to deal with any possible sensing point outage when the sensing system is scaling up.

Two-way satellite time and frequency transfer (TWSTFT) is one of the main techniques used to compare atomic time scales over long distances. To both improve the precision of TWSTFT and decrease the satellite link fee, a new software-defined modem with dual pseudo-random noise (DPN) codes has been developed. In this paper, we demonstrate the first international DPN-based TWSTFT experiment over a period of 6 months. The results of DPN exhibit excellent performance, which is competitive with the Global Positioning System (GPS) precise point positioning (PPP) technique in the short-term and consistent with the conventional TWSTFT in the long-term. Time deviations of less than 75 ps are achieved for averaging times from 1 s to 1 d. Moreover, the DPN data has less diurnal variation than that of the conventional TWSTFT. Because the DPN-based system has advantages of higher precision and lower bandwidth cost, it is one of the most promising methods to improve international time-transfer links.

Precision of two-way satellite time and frequency transfer (TWSTFT) highly depends on the residual nonreciprocity delays; one of them is caused by the Sagnac effect. In this paper, we employ the satellite ephemeris data to compute the precise Sagnac effect and discuss the possible additive effect related to the Sagnac effect. We also describe a method to calculate the diurnal correction based on the time derivative of the Sagnac effect. Through the analysis of the link between the National Institute of Information and Communications Technology in Japan and the Telecommunication Laboratories in Taiwan, we demonstrate that the correction was useful to improve the TWSTFT data. The time deviation at an 8-h averaging time is reduced from 346 to 156 ps after the correction.

In this paper, we provide a numerical bit error rate (BER) estimation approach for direct-detected orthogonal frequency division multiplexing (OFDM) signals in the presence of optical preamplified receivers. The individual BER of each subcarrier is first computed by considering their electrical signal-to-noise ratio (SNR), and then the ensemble BER is derived simply by taking the average of all the subcarriers' BERs. The calculated BER is verified by the conventional error-counting approach with high precision and is still accurate with higher quadratic-amplitude modulation (QAM) formats, even under the influences of the optical filtering and polarization mode dispersion (PMD) effects. Based on our simulation approach, the required extra power budget for 16- and 64-QAM relative to 4-QAM format are found to be ~3.8 and 8.2 dB, respectively, at a BER of 10-9. Furthermore, we use this approach to compare the receiving sensitivities and PMD tolerances for the previous proposed gapped and interleaved radio-frequency (RF)-tone-assisted OFDM systems. The results show that the gapped OFDM has a better sensitivity while the interleaved OFDM has a more PMD-tolerable capability.

A self-polarization diversity mechanism in a polarization division multiplexing direct detection optical OFDM radio-over-fiber system's backhaul is proposed and demonstrated to double the channel capacity and service coverage without polarization tracking mechanism and receiver modification.

A novel back propagation isolation module is firstly implemented at its powered remote node of the fiber-wireless convergence. Bi-directional multiband transmission, highly uniform receiving performance, and high compatibility are achieved in a long reach scheme.

We propose and experimentally demonstrate a novel bidirectional modulation format converter that can simultaneously phase multiplex and de-multiplex PSK signals between QPSK and BPSK formats all-optically by employing four-wave mixing (FWM) in a single HNLF.

This work demonstrates how electrical driving voltage of a Mach–Zehnder modulator and the bandwidth of electrical low-pass filters (LPFs) affect optical duobinary signals. The fact that a 100% driving voltage does not necessarily yield optimal results in duobinary systems is established both numerically and experimentally. Various filter bandwidths correspond to respective optimum driving voltages. In a 10 Gbps duobinary system, compared with the conventional condition of using a 2.5 GHz electrical LPF, a 2.5 dB sensitivity improvement is obtained by employing a 3 GHz LPF with an 88% driving voltage of fully driving. © 2007 Published by Elsevier Inc.

An iterative digital signal processing (DSP) for reducing signal-to-signal beating interference (SSBI) in a multiband direct-detection optical orthogonal frequency division multiplexing (DDO-OFDM) system is proposed and demonstrated experimentally. Without applying any optical/electrical filter in the receiver, all the OFDM signal bands can be almost uniformly recovered even under severely SSBI contamination. The aggregated data rate in the experimental demonstration achieves 65.4 Gb/s by employing 16-QAM format. Meanwhile, by applying a simulation aided investigation, the spectral efficiency of the proposed 16-QAM DDO-OFDM signals are enhanced to 3.4 b/s/Hz. The results indicate not only high spectral efficiency and high uniformity performance among all OFDM signal bands under different level of SSBI pollution, but also high potential of a multiband DDO-OFDM system to be widely employed.

The direct-detected optical OFDM spectral efficiency has been enhanced with three reviewed solutions, a multiband scheme, a receiver DSP scheme, and a PDM scheme. A self-polarization diversity PDM scheme guarantees SE enhancement with conventional receivers.

By using a widely wavelength lockable Fabry-Perot laser diode (FPLD) with low facet reflectance under intensity modulation and direct detection, a multicarrier code division multiple access (MC-CDMA) enhanced long-reach passive optical network (LR-PON) architecture is demonstrated to perform the dense-spectral-utilized transmission with orthogonal frequency division multiplexing (OFDM) format. Enlarging the power injected into the low-facet-reflectance FPLD enables the broadening of operational wavelength margins at a cost of slightly increased bit-error rate (BER). After LR-PON transmission, the signal-to-noise ratio among subcarriers strongly correlates with the frequency chirp of the wavelength-locked FPLD, which affects the allowable wavelength locking range. By substituting MC-CDMA for the typical OFDM format and using the minimum-mean-squared-error-based multicode interference cancellation processing, the BER degradation is minimized, accompanied by a 16% extension on the lockable wavelength margin achieved under 3 dBm injection. Such a widely wavelength lockable FPLD-based MC-CDMA enhances the LR-PON with a power penalty reduction of 1 dB as compared to the typical OFDM LR-PON after 60 km transmission.

We conceptually propose and experimentally demonstrate a novel multifunction all-optical packet switch architecture with less active optical components and simpler traffic control by adopting a periodic wavelength arrangement between wideband fiber Bragg gratings and an arrayed waveguide grating in the optical buffering unit and output ports, respectively. Three functionalities of switch, including first-in-first-out multiplexing, switching, and add-drop are successfully exhibited by the proposed architecture with negligible power penalties.

By strictly assigning and periodically arranging the Bragg wavelengths of fiber Bragg gratings and composing three 2 × 2 optical switches to construct the links and replace the nodes, respectively, we theoretically propose and experimentally demonstrate a novel three-dimensional mesh-based sensing system with comprehensive self-healing functionality. Moreover, a simple and cost-effective sensing signal processor for the classification of sensing signals and the monitoring of sensing elements is also proposed by utilizing the cyclic filtering and free spectral range characteristics of an arrayed waveguide grating.

A novel bidirectional transmission system is proposed and experimentally demonstrated using a four-port interleaver to enable unidirectional amplification. Following bidirectional transmission through 210 km of standard single-mode fibers, sensitivity variations of less than 0.2 dB, with a bit-error rate level of 10/sup -9/ at 10 Gb/s, were observed between bidirectional and unidirectional transmissions.

We proposed and experimentally demonstrated a low-complexity and cost-effectiveness format converter using XPM in a single HNLF. Four individual 12.5 Gbps NRZ-OOK to one 50 Gbps PDM RZ-QPSK format conversion is successfully achieved.

A carrier centralized bi-directional 150/60 Gbps hybrid DDO-OFDM/Nyquist-WDM Long Reach PON is experimentally demonstrated. Uniform performance, high spectral efficiency, asynchronous upstream manipulation, and 1:1024 splitting ratio are achieved.

A multipurpose network which integrates the functionalities of single radio channel and baseband data distribution has been proposed recently. In this letter, we further propose and compare two possible combination schemes which combine multiple radio channel and single digital baseband data in electrical and optical domains. Linearity of multiple radio channels and performance of digital baseband data are studied in this externally modulated hybrid analog-digital link. It is found that signals combined in the optical domain, while with higher cost, will outperform that in the electrical domain on the carrier-to-noise and distortion ratio. In addition, the baseband data performance is also improved with optical combining scheme since the optimum required modulation index is lower.

A 50-GHz channel spaced dispersion-compensated interleaver pair for a metro add-drop network application was demonstrated using a recirculating loop. After five cascaded nodes (ten interleavers), a 2.5-dB sensitivity differential at bit-error-rate level around 10/sup -9/ was observed between the compensated and uncompensated pairs within a /spl plusmn/10-GHz detuning frequency window.

In this paper, we demonstrate a simple receiving system for decoding a >100-Gb/s double-sided multiband DDO-OFDM system. In a LR-PON system, with this simple receiving design, 120 Gb/s capacity and splitting ratio of 128 have been achieved.

A 120-Gb/s double-sided multiband DDO-OFDM based LR-PON architecture is proposed and experimentally demonstrated. With a simple receiver design, the implementation complexity can be reduced and the splitting ratio can be as high as 1:128.

In this paper, we’ll review some latest results in improving the spectral efficiency and receiving sensitivity in both the electronic and optical domains of a direct-detected optical OFDM signal.

Optoelectronic oscillators (OEOs) are used to generate low phase noise microwave signals. A high performance OEO may act as a local oscillator that could lock the output of the absolute reference frequency, provided by the atomic transition. This study investigates the relationship between the phase shifts of a reference injection locked OEO and its fiber delay fluctuation. The impact of fiber delay fluctuation and the method to realize a good injection-locked OEO are discussed.

A precise two-way satellite time and frequency transfer (TWSTFT) data by using the Dual Pseudo-random noise (DPN) signal was correspondingly compared with the regular TWSTFT and GPS Precise Point Positioning (GPSPPP) between the National Institute of Information and Communications Technology (NICT) and Telecommunication Laboratories (TL) in this study. Our result shows that the frequency stabilities of DPN are competitive with those of the GPSPPP. There was less obvious diurnal in the DPN time transfer data. Since the DPN system has advantages of higher precision and lower bandwidth cost when compared with the regular TWSTFT, it is one of the most potential methods to improve the international time transfer links.

We'll bring out our latest developments in improving the spectral efficiency and receiving sensitivity in a direct-detected OFDM transmission. The analytical model, numerical simulations and experimental results of the proposed architectures will be presented.

In this paper, we will review our latest developments in improving the spectral efficiency and receiving sensitivity in a direct-detected OFDM transmission system. An RF-tone assisted virtual single sideband (VSSB) OFDM modulation format is proposed to enhance the spectral efficiency in both electrical and optical domains for direct detected OFDM applications. The receiving sensitivity can be improved by using an iterative estimation and cancellation algorithm. Furthermore, the ultimate sensitivity limit using spectrally matched optical filters in direct detection scheme, which can theoretically approach to the performance limit of coherent OFDM systems, will also be discussed. The analytical model, numerical simulations and experimental results of the proposed architectures will be presented.

We propose and experimentally demonstrate a novel sensing system based on FBG sensors with comprehensive self-healing capability in a mesh-ring-based topology by utilizing the FSR and periodic filtering characteristics of the AWG.

We propose the generation, detection, and label swapping methods for DPSK-labelled almost no influence on the superior performance of OFDM payload.

Two-way satellite time and frequency transfer (TWSTFT) is one of the major techniques to compare the atomic time scales between timing laboratories. As more and more TWSTFT measurements have been performed, the large number of point-to-point 2-way time transfer links has grown to be a complex network. For future improvement of the TWSTFT performance, it is important to reduce measurement noise of the TWSTFT results. One method is using TWSTFT network time transfer. The Asia-Pacific network is an exceptional case of simultaneous TWSTFT measurements. Some indirect links through relay stations show better short term stabilities than the direct link because the measurement noise may be neutralized in a simultaneous measurement network. In this paper, the authors propose a feasible method to improve the short-term stability by combining the direct and indirect links in the network. Through the comparisons of time deviation (TDEV), the results of network time transfer exhibit clear improved short-term stabilities. For the links used to compare 2 hydrogen masers, the average gain of TDEV at averaging times of 1 h is 22%. As TWSTFT short-term stability can be improved by network time transfer, the network may allow a larger number of simultaneously transmitting stations.

We provide a fast and accurate BER calculation for a SSB-OFDM signal by considering the SNR of each subcarrier separately. The numerical results show that our scheme can accurately evaluate the BER for different QAM formats even under a strong optical filtering.

Two way satellite time and frequency transfer (TWSTFT) is an important method to compare the atomic time scales between time keeping laboratories. The aim of this paper is to analyze the Asia-Pacific TWSTFT network, in which the measurements are performed synchronously by using multi-channel modems. As a result of the synchronous measurements, the clock drift and the majority path instabilities could be neutralized in the calculation of the closure links. This paper discusses what kinds of noise could be cancelled and what kinds of noise would still be kept in the result of the closure links by taking all three stations at the same time into account. From the re-examination of TWSTFT equations, we deduced that the time difference between two laboratories could be obtained via relay stations without debasing the stability in the synchronous TWSTFT measurements. The results show that the noises of the closure links in the Asia-Pacific TWSTFT network are very low. The smallest standard deviation of triangle closure is only 121 ps for the data over four months. The closing errors are closed to zero after removing calibration values. The analysis of modified Allan deviation confirms that the stability of data via relay station is in competition with the direct TWSTFT link. This paper also shows that the stability of TWSTFT could be improved by the weighted mean of the redundant TWSTFT links.

We propose and demonstrate a virtual SSB-OFDM with direct detection that uses half the electrical bandwidth by employing an RF tone at the edge of the signal. We transmit 10 Gbps data with a 4-QAM over 340 km of SSMF with no penalty.