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The efficient and accurate evaluation of the transmission performance of high-capacity optical communication systems has always attracted significant research attentions. The enhanced Gaussian noise (EGN) model is considered as an excellent solution to predict the system performance taking into account linear and nonlinear transmission impairments. Since the conventional form of the EGN model is complicated and intractable for a fast computation, the closed-form simplification has been regarded as a direction to significantly reduce the computational complexity. However, the accuracy of such a closed-form EGN model becomes a main concern in the application of ultra-wideband optical communication systems. In this work, we have investigated the accuracy of the closed-form EGN model for ultra-wideband optical fiber communication systems, where the performance of the system using electronic dispersion compensation, multi-channel nonlinearity compensation and full-field nonlinearity compensation has been evaluated in terms of symbol rate, number of channels and signal power. Our work will provide an insight on the application of the EGN model in next-generation ultra-wideband long-haul optical fiber communication networks.\ud

With an ever increasing amount of end user devices connected to the internet, the global data traffic, especially within data centers, increases significantly. In order to keep pace, the current 100 Gbps standard (4 lines x 25 Gbps) needs to be upgraded. There are several possibilities to increase the data rate per line. The easiest way is to use multilevel modulation formats such as PAM4 with 2 bit per symbol or PAM8 or 16. Furthermore, optical multiplexing should be taken into account to maximize the bandwidth usage. Especially, optical signal processing with Nyquist pulses shows no inter-symbol interference, exhibit a rectangular spectrum and enables transmission at the maximum possible symbol rate for a given bandwidth. Here we present a simplified concept for ideal Nyquist pulse generation and simultaneous data modulation using just a single modulator per channel. Thereby, a laser source is split into three branches and the data signal is mixed electrically with a sine wave and then transferred into the optical domain, leading to a modulated Nyquist pulse train. The time delay between each Nyquist Pulse sequence for multiplexing is realized by a simple phase shift of the sinusoidal signal. With 3 time-domain channels, the proposed method achieved an aggregate baud rate, which corresponds to the full optical bandwidth of the modulators. On the contrary, the electronics require only 1/3 of the bandwidth. Due to the simple setup, integration on a silicon photonics platform might be straight forward. Preliminary simulation results show data transmission with PAM4 modulation at low bit error rates.

We investigate the computational complexity of adaptive equalization in coherent receiver digital signa l processing (DSP) for data center interconnect (DCI) systems. We propose modified DSP procedures with a first-stage static filter and a second-stage short-length adaptive equalizer. Typically, coherent DSP requires 11 and 17 adaptive equalizer taps respectively for 60 Gbaud and 80 Gbaud signals in the 100 km fiber link. The modified DSP procedures combine matched filter, chromatic dispersion compensation (CDC), and non-ideal channel effects and polarization effect s in to a static filter. Since polarization demultiplexing is partially realized by the static filter, the size of the following adaptive equalizer is substantially reduced. Results showed 35% - 87% overall complexity reduction in adaptive equalization a s compared with the reference DSP, depending on link length and symbol rate.

We present a method for complex spectrum analysis of periodic optical signal with multi-level modulation format. The information of the complex spectrum can be extracted with ultra-low sampling rate in the proposed method, and the temporal information reconstructed by inverse Fourier transform can be used to monitor the performance of the optical signal. Besides, the proposed method is transparent to symbol rate and modulation format. The spectral amplitudes and phases are measured accurately in the simulation based on the proposed method for a 28 GBaud Quadrature-Phase-ShiftKeying (QPSK) signal with a 400-bit pattern and a 28 GBaud 16-Quadrature-Amplitude-Modulation(16QAM) signal with a 560-bit pattern. Moreover, we analyze the performance of the reconstructed signal under different linewidth and optical signal-to-noise ratio (OSNR) by simulation. The Q-factor of the reconstructed 28-GBaud QPSK signal reduces when the linewidth of laser increases and the OSNR of signal decreases.

In order to keep pace with the increasing data traffic, the next generation of optical server connections in a data center requires data rates of 400 Gbps at 100 Gbps per channel. Data center applications require highly integrated, low-cost solutions with very low power consumption and a very small package size. This can be achieved by co-integration of photonic and electronic function blocks. Optical signal processing with Nyquist pulses makes it possible to achieve very high data rates even at relatively low optical and electrical bandwidths. Nyquist pulses have the property of no inter-symbol interference and exhibit a rectangular spectrum, enabling transmission at the maximum possible symbol rate for a given bandwidth. Additionally, with one or two coupled modulators, pulse sequences with three or four times the RF-bandwidth of the single modulator can be achieved. This method neither requires a mode locked source, nor any other complicated equipment. Thus, the generation of Nyquist pulse sequences by integrated modulators is a very promising candidate for the integration on a silicon photonics platform. Within the proposed system modulators, receivers and electronics have only a bandwidth of 12.1 GHz, leading to Nyquist pulses with a bandwidth of 36.3 GHz that are modulated by PAM4 to reach a data rate of 72.6 Gbit/s. By interconnecting several such systems on one chip, the targeted 400 Gbit/s can be achieved in a single common transceiver module. Preliminary simulation results show the data transmission with low bit error rates.

Timing synchronization is critical in digital demodulation systems such as intradyne optical receivers. In this paper, a novel timing recovery method for all-digital coherent receivers is proposed. With the help of a parallel architecture, the new method can be implemented on ASIC or FPGA platform, especially when the symbol rate is much higher than the clock rate of FPGAs. Through adjusting the frame structure in the parallel interpolator, the receiver synchronizes its symbol rate with the transmitter. Different from existing parallel timing recovery methods, the proposed method does not adjust the period between adjacent frames of samples, which can be beneficial to the subsequent processing in hardware. The performance is tested by simulation in QPSK modulation. Under relative clock offset between ±50 ppm and jitter noise with 0.3% standard deviation, the proposed method shows almost no degradation compared with its serial equivalent. Combined with different timing error detection algorithms, this method can be used in kinds of modulation formats like MPSK and QAM.

Flexible multi-rate capabilities are attractive for communications over the dynamic free-space optical (FSO) channel since it enables links to be efficiently established over a variety of distances, channel conditions, aperture sizes, and transmitter power levels. Recently, multi-rate differential phase shift keying (DPSK) modulation has been shown to provide good performance with modest complexity over a wide range of data rates. For these reasons, multi-rate DPSK has become the high-rate baseline format for NASA’s Laser Communication Relay Demonstration (LCRD) and other space-based FSO systems currently in development, operating at channel rates from 72 Mbit/s to 2.88 Gbit/s. Here, we report WDM-scalable power-efficient optical-transceiver advances that can extend single-channel rates by a factor of four to 11.52 Gbit/s using LCRD-compatible waveforms. Transmitter waveforms are implemented using time-frequency-windowed directly modulated lasers (DMLs) that can generate burstmode 2-DPSK and 4-DPSK waveforms at the standard LCRD 2.88 GHz symbol rate and twice the rate at 5.76 GHz. At the receiver, standard 2.88 GHz delay-line-interferometer (DLI) based demodulation is implemented for 2-DPSK. For 4-DPSK, a second 2.88 GHz DLI is required to demodulate the 2-bit-persymbol format, with the pair of DLIs biased at ±/4. With proper precoding of the transmitter waveforms, the double-rate 5.76 GHz symbols may be demodulated using the same 2.88 GHz DLIs using non-adjacent DPSK demodulation. In this manner, a common DPSK receiver platform may be used to demodulate standard multi-rate LCRD waveforms as well as 4-DSPK waveforms at 1x and 2x the standard symbol rate.

The information rate (IR) of a digital coherent transceiver is constrained by the inherent practical signal-to-noise ratio (SNR) limit. Coded modulation, which is the combination of multi-level modulation and forward error correction, aims to maximize the IR within this SNR envelope. While probabilistic constellation shaping has enhanced this methodology by providing an increase in IR over conventionally employed square quadrature amplitude modulation (QAM) formats, it is the ability to eloquently tune the per wavelength IR by varying the symbol probabilities that has gained this scheme significant traction within optical communications in recent years. As commercial line cards continue their evolution towards 100 GBd and to modulation formats beyond 64QAM, we discuss the merits of probabilistic shaping for high symbol rate digital coherent transceivers in the presence of a practical SNR limit.

With the advent of the coherent age the implementation of massive digital signal processors (DSP) co-integrated with high speed AD and DA converters became feasible allowing for the realization of huge flexibility of transponders. Today the implementation of variable transponders is mainly based on variable programming of DSP to support different modulation formats and symbol rates. Modulation formats with high flexibility are required such as pragmatic QAM formats and hybrid modulation formats. Furthermore, we report on an implementable probabilistically shaping technique allowing for adjusting the bitrate. We introduce fundamental characteristics of all modes and describe basic operation principles. The modifications of the operational modes are enabled simply by switching between different formats and symbol rates in the DSP to adjust the transponders spectral efficiency, the bitrate and the maximum transmission distance. A fine granularity in bitrate and in maximum transmission distance can be implemented especially by hybrid formats and by probabilistically shaped formats. Furthermore, latter allow for ~+25% increase of the maximum transmission distance due their operation close to the Shannon limit as a consequence of their 2D Gaussian like signal nature. If the flexibility and programmability of transponders is implemented, it can be utilized to support different strategies for the application. The variability in symbol rate is mainly translated into variability in bitrate and in bandwidth consumption. Contrary the variable spectral efficiency translates into a variation of the maximum transmission reach and of the bitrate. A co-adjustment of both options will lead to a superior flexibility of optical transponders to address all requirements from application, transponder and fiber infrastructure perspective.

The high-speed train in Japan connects megalopolises through many tunnels or underground routes. To provide seamless internet connectivity to the hundreds of passengers on the train, a new backhaul communication system is proposed in a millimeter-wave band by Radio over Fiber. We have shown that a vector-modulated signal can be generated by multiplying the radio frequency in the optical domain to avoid effects of chromatic dispersion in an optical fiber. In this paper, we show characteristics of long distance transmission by Radio over Fiber. Also, we present our concept and report on the relationship between the symbol rate and the modulation accuracy of the 96 GHz band signal generated by frequency doubling using RoF.

With the advent of the coherent age the implementation of massive digital signal processors (DSP) co-integrated with high speed AD and DA converters became feasible allowing for the realization of huge flexibility of transponders. Today the implementation of variable transponders is mainly based on variable programming of DSP to support different modulation formats and symbol rates. Modulation formats with high flexibility are required such as pragmatic QAM formats and hybrid modulation formats. Furthermore, we report on an implementable probabilistically shaping technique allowing for adjusting the bitrate. We introduce fundamental characteristics of all modes and describe basic operation principles. The modifications of the operational modes are enabled simply by switching between different formats and symbol rates in the DSP to adjust the transponders spectral efficiency, the bitrate and the maximum transmission distance. A fine granularity in bitrate and in maximum transmission distance can be implemented especially by hybrid formats and by probabilistically shaped formats. Furthermore, latter allow for ~+25% increase of the maximum transmission distance due their operation close to the Shannon limit as a consequence of their 2D Gaussian like signal nature. If the flexibility and programmability of transponders is implemented, it can be utilized to support different strategies for the application. The variability in symbol rate is mainly translated into variability in bitrate and in bandwidth consumption. Contrary the variable spectral efficiency translates into a variation of the maximum transmission reach and of the bitrate. A co-adjustment of both options will lead to a superior flexibility of optical transponders to address all requirements from application, transponder and fiber infrastructure perspective.

Recent developments for laser communication on CubeSats across interplanetary distances will be presented. A binary polarization-shift-keyed modulation scheme using dual gain-switched diode lasers is developed and demonstrated within an end-to-end link testbed to achieve signal acquisition under extremely poor signal-to-noise conditions (-43.5 dB average signal-to-noise power ratio at a 1-MHz symbol rate) to simulate direct-to-Earth links, while simultaneously targeting a limited SWaP footprint (1.5U envelope). Additional system design and constraints for the compact laser transmitter will be discussed.

To support the ever-increasing demand for high-speed optical communications, Nyquist spectral shaping serves as a promising technique to improve spectral efficiency (SE) by generating near-rectangular spectra with negligible crosstalk and inter-symbol interference in wavelength-division-multiplexed (WDM) systems. Compared with specially-designed optical methods, DSP-based electrical filters are more flexible as they can generate different filter shapes and modulation formats. However, such transmitter-side pre-filtering approach is sensitive to the limited taps of finite-impulse-response (FIR) filter, for the complexity of the required DSP and digital-to-analog converter (DAC) is limited by the cost and power consumption of optical transponder. In this paper, we investigate the performance and complexity of transmitter-side FIR-based DSP with polarization-division-multiplexing (PDM) high-order quadrature-amplitude-modulation (QAM) formats. Our results show that Nyquist 64-QAM, 16-QAM and QPSK WDM signals can be sufficiently generated by digital FIR filters with 57, 37, and 17 taps respectively. Then we explore the effects of the required spectral pre-emphasis, bandwidth and resolution on the performance of Nyquist-WDM systems. To obtain negligible OSNR penalty with a roll-off factor of 0.1, two-channel-interleaved DAC requires a Gaussian electrical filter with the bandwidth of 0.4–0.6 times of the symbol rate for PDM-64QAM, 0.35–0.65 times for PDM-16QAM, and 0.3–0.8 times for PDM-QPSK, with required DAC resolutions as 8, 7, 6 bits correspondingly. As a tradeoff, PDM-64QAM can be a promising candidate for SE improvement in next-generation optical metro networks.

In this paper the analysis of the transmission quality in Nyquist WDM transport system is presented. Results are presented of a system simulation carried out for different modulation format, symbol rates, channel spacing and filter characteristics of the transmitter and receiver. This paper also contains the comparison between results obtained for the N-WDM (Nyquist Wavelength Division Multiplexing) and DWDM (Dense Wavelength Division Multiplexing) system. Two quality indicators are taken into consideration: interchannel crosstalk and symbol error rate for both different system configurations.

We study the limitation of electrical bandwidth in QPSK optical coherent receiver with decision-aided maximum likelihood (DAML) carrier phase estimation. Before signal sampling, a low-pass rectangular filter is utilized to model the bandwidth limitation of electronic devices in the receiver. On one hand the limited bandwidth can reduce the power of additive noise, on the other hand it would distort the signal since inter-symbol interference (ISI) between adjacent symbols occurs. In this paper we discuss the effects on signal amplitude and phase caused by ISI and find original distribution of QPSK constellation points will shift due to ISI. When adjacent symbol interference, that is, the ISI effect of one previous symbol, is taken into account, the distribution changes into the form of 16-QAM, while changing as 4K+1-QAM if K previous symbols are considered. The impact on the subsequent DAML algorithm and the final bit error rate (BER) calculation due to constellation points shifts are analyzed intensively. Monte-Carlo (MC) simulation results show that 0.7 to 0.9 times symbol rate is a reasonable bandwidth range for different optical signal to noise ratios (OSNRs), and optimum bandwidth is often inside this range. Results also reveal that filter-induced ISI would degrade the BER performance of DAML receiver when OSNR is over 10 dB.

Intra-pulse analysis plays an important role in electronic warfare. Intra-pulse feature abstraction focuses on primary parameters such as instantaneous frequency, modulation, and symbol rate. In this paper, automatic modulation recognition and feature extraction for combined BPSK-LFM modulation signals based on decision theoretic approach is studied. The simulation results show good recognition effect and high estimation precision, and the system is easy to be realized.

We demonstrate silicon-organic hybrid (SOH) modulators for generating advanced modulation formats at high data rates and with low energy consumption. SOH integration combines slot waveguides on conventional silicon-on-insulator substrates with highly efficient electro-optic materials. With this approach we generate 16QAM signals at symbol rates of 28 GBd and 40 GBd leading to gross data rates (net data rates) of up to 160 Gbit/s (133 Gbit/s) for a single polarization. This is the highest value achieved by a silicon-based modulator up to now. With a maximum symbol rate of 28 GBd, low drive voltages of only 0.6 Vpp are sufficient and result in a record-low energy consumption of only 19 fJ/bit. This is the lowest energy consumption that has so far been reported for a 16QAM modulator at 28 GBd.

In traditional dimming control system using pulse width modulation (PWM) combined with M-QAM OFDM scheme, OFDM signal is only transmitted during “on” period. To guarantee the communication quality, reduction of duty cycle will cause increased symbol rate or added LED power. This means system BER performance degradation and power consumption. In order to solve the defects of the traditional dimming scheme, we propose a new dimming control scheme in indoor visible light communication, which combines OFDM signal and multi-pulse position modulation (MPPM) light pulse well with each other. By means of dividing traditional PWM pulses into MPPM pulses with the same duty cycle, the pattern effect of MPPM pulses is utilized, which makes excess signal transmission possible. Simulation results show that when reducing the brightness of LED the achievable symbol rate using dimming control patterns is not higher than the traditional PWM scheme and the LED power is also reduced, which satisfies both system reliability and energy effectiveness under constant high data rate and BER less than 10 -3 .

In this paper, we experimentally study DC-PM-BPSK, PM-QPSK, and PM-16QAM at 35 Gbaud for undersea transmission in a WDM environment with frequency spacing ranging from 50 GHz (DWDM) to 33 GHz (Super-Nyquist). The experimental study focuses on noise, linear cross-talk, and nonlinear tolerance in two undersea applications: (1) Legacy dispersion-managed submarine cables up to 5,000 km in length and (2) New uncompensated submarine cables up to 12,500 km in length. We experimentally demonstrate that a reduction in frequency spacing below the symbol rate can be achieved, and quantify the performance penalties. We also show a comparison of performance and reach between legacy dispersion-managed applications, and new uncompensated applications, as the frequency spacing is reduced below the symbol rate. It is shown that the constellation and line system dispersion map have a significant impact on the tolerance to linear and nonlinear interference generated by narrow frequency spacing.

With the development of ultrahigh speed optical communications, optical sampling oscilloscope is a promising candidate for the optical performance monitoring. In this paper, a periodically poled lithium niobate based optical sampling oscilloscope is demonstrated. In the optical sampling oscilloscope, the bit rate adaptive method and chirp Z transform synchronization method are adopted to realize bit rate transparency. The optical sampling is completed by the sum frequency generation effect in periodically poled lithium niobate waveguide. The sampled signal is processed by FPGA based digital signal processing hardware, the eye diagram and parameters such as Q factor are measured. Intensity modulated optical signals with symbol rate from 1.0~25Gbaud are measured with our optical sampling oscilloscope. The experimental results are compared with that measured with Agilent 86100A wide bandwidth optical to electronic (O/E) oscilloscope and EXFO PSO-100 optical sampling oscilloscope. The measurement results of our oscilloscope are much closer to Agilent 86100A oscilloscope. Besides, our optical sampling oscilloscope has the advantage of faster measurement speed and higher synchronization accuracy due to the novel methods we proposed. The operation stability is also measured for our optical sampling oscilloscope, and the steady state can be maintained for several hours.

Advanced modulation formats are an emerging area since they allow reducing the symbol rate while encoding more bits per symbol. This allows higher spectral efficiencies. In addition, we can achieve higher data rates using lower-speed equipment like in all-optical format conversion systems, an important step for the development of systems with high transmission rates. In this paper we study the impact of some impairments found in all-optical advanced format conversions based on cross phase modulation (XPM) on a highly nonlinear fiber (HNLF), such as amplified spontaneous emission (ASE), nonlinear fiber length and group velocity di spersion (GVD), and analyze its performance based on error vector magnitude (EVM) for different bitrate transmissions. This simulation study is applied on earlier proposed phase modulated format conversion where n nonreturn-to-zero on-off keying (NRZ-OOK) channels at 10 Gb/s are converted into a return-to-zero m phase shift keying (RZ-m PSK) at 20Gb/s. We extend the work with simulations and show the results for n NRZ-OOK channels at 20Gb/s, 40 Gb/s and 50Gb/s to RZ-PSK at 40Gb/s, 80 Gb/s and 100Gb/s, respectively. Keywords: modulation format conversion, cross-phase modulation, amplitude noise, phase noise, fiber nonlinearity, group velocity dispersion, quadrature phase shift keying

This paper presents a novel modulation scheme that is specifically designed for data of variable rate. Proposed design adopts 8PSK model and can processes signal with symbol rate even varying from 4.5Msps to 100Msps continuously. Realization on FPGA demonstrates the good performance of the proposed idea.

Transmitting ultra-high symbol rate optical signals remains a challenge due to their high sensitivity to fluctuations of GVD and higher orders of dispersion in the transmission link. Being able to cancel the impairments due to those fluctuations is a key requirement to make transmission of ultrashort optical pulses practical. We demonstrate an automatic compensation scheme able to keep an Optical Time Division Multiplexed (OTDM) signal stable at a bandwidth of up to 1.28 Tbaud in spite of external perturbations. Our approach is based on monitoring the signal with a photonic-chip-based all-optical RF-spectrum analyzer. The measurement of a single parameter extracted from the RF-spectrum is used to drive a multidimensional optimization algorithm. We apply the method to the real time simultaneous compensation for 2 nd , 3 rd and 4 th order dispersion using an LCOS spectral pulse shaper (SPS) as a tunable dispersion compensator.

Symbol rate is an important parameter in digital communication. In the area of non-cooperative communication, the precision of symbol rate estimation is essential to the success of subsequent signal processes such as demodulation. This paper proposes an approach for estimation of symbol rate for M-ary FSK signals. In this approach, an M-ary FSK signal is decomposed into M single tones, and the symbol rate is estimated by extracting the spectral line corresponding to the symbol rate in the spectrum of the summation of each single tone envelope signal. The implementation of the methodology does not require any apriori information. Computer simulations and analysis show that the approach provides high estimation accuracy and still keeps a good performance even at low input SNR.

Polarization multiplexing is an integral technique for generating spectrally efficient 100 Gb/s and higher optical links. Post coherent detection DSP-based polarization demultiplexing of QPSK links is commonly performed after timing recovery. We propose and demonstrate a method of asynchronous blind source separation using the constant modulus algorithm (CMA) on the asynchronously sampled signal to initially separate energy from arbitrarily aligned polarization states. This method lends well to implementation as it allows for an open-loop sampling frequency for analog-to-digital conversion at less than twice the symbol rate. We show that the performance of subsequent receiver functions is enhanced by the initial pol demux operation. CMA singularity behavior is avoided through tap settling constraints. The method is applicable to QPSK transmissions and many other modulation formats as well, including general QAM signals, offset-QPSK, and CPM, or a combination thereof. We present the architecture and its performance under several different formats and link conditions. Comparisons of complexity and performance are drawn between the proposed architecture and conventional receivers.

We propose a rate-adaptive optical transmission scheme using variable-rate forward error correction (FEC) codes and variable-size constellations at a fixed symbol rate, quantifying how achievable bit rates vary with distance. The scheme uses serially concatenated Reed-Solomon codes and an inner repetition code to vary the code rate, combined with single-carrier polarization-multiplexed -ary quadrature amplitude modulation with variable and digital coherent detection. Employing , the scheme achieves a maximum bit rate of 200 Gb/s in a nominal 50-GHz channel bandwidth. A rate adaptation algorithm uses the signal-to-noise ratio (SNR) or the FEC decoder input bit-error ratio (BER) estimated by a receiver to determine the FEC code rate and constellation size that maximizes the information bit rate while yielding a target FEC decoder output BER and a specified SNR margin. We simulate single-channel transmission through long-haul fiber systems with or without inline chromatic dispersion compensation, incorporating numerous optical switches, evaluating the impact of fiber nonlinearity and bandwidth narrowing. With zero SNR margin, we achieve bit rates of 200/100/50 Gb/s over distances of 640/2080/3040 km and 1120/3760/5440 km in dispersion-compensated and dispersion-uncompensated systems, respectively. Compared to an ideal coding scheme, the proposed scheme exhibits a performance gap ranging from about 6.4 dB at 640 km to 7.6 dB at 5040 km in compensated systems, and from about 6.6 dB at 1120 km to 7.5 dB at 7600 km in uncompensated systems. We present limited simulations of three-channel transmission, showing that interchannel nonlinearities decrease achievable distances by about 10% and 7% for dispersion-compensated and dispersion-uncompensated systems, respectively.

Numerical simulations were conducted to study the performance of a 112Gbit/s coherent polarization multiplexing (PolMux) quadrature phase-shift keying (QPSK) system. We addressed the bit resolution, bandwidth of analog-to-digital converters (ADC) in the presence of all chromatic dispersion, polarization-mode dispersion and imperfect laser frequency offset. Both return-to-zero (RZ) and non-return-to-zero (NRZ) QPSK waveforms are taken into account, while the filter type of ADC is assumed to have a Gaussian frequency response. An ADC with 6-bit resolution is found to be sufficient for 112Gbit/s PolMux QPSK transmission. And simulation results show that the ratio of optimum bandwidth of ADC to symbol rate is 0.5 for both RZ- and NRZ-QPSK formats when the 1st-order Gaussian frequency response of ADCs is assumed.

We demonstrate a 160 Gb/s orthogonal frequency division multiplexing (OFDM) system using an all-optical symbol generator based on planar light circuit (PLC) technology. Excellent bit error rate (BER) is observed after long-distance transmission. The proposed symbol generator fundamentally eliminates the processing speed limits introduced by electronics and is suitable for high integration, making it physically realizable to build high-speed all-optical OFDM systems with a large number of subcarriers.

We propose and demonstrate a simple and flexible all-optical NRZ-DQPSK receiver based on optical detuned filtering. The proposed demodulator is quite flexible to input bit rates, which means it can be used for different bit rates without any change. With two given optical band-pass filters, simulation and comparison show that NRZ-DQPSK signals at 20, 40 and 80Gb/s (10, 20 and 40G symbol rate) can be demodulated to in-phase and quadrature data successfully by adjusting the detuning of two given filters.

The applications of Electronic Dispersion Compensation (EDC) have recently attracted attention for high speed long haul transmission. Moreover, recent progress in signal formats has gained interest in recent years such as Differential Quadrature Phase Modulation (DQPSK). This format has higher spectral efficiency and reduced symbol rate compared to binary modulation compared to binary modulation formats. In this paper, we investigate the application of different EDC schemes with DQPSK format against chromatic dispersion (CD). The schemes are nonlinear feed-forward equalizer (FFE) and Decision-Feedback equalizer (DFE) and butterfly FFE-DFE. We demonstrate that butterfly structure can mitigates nonlinearity of cross-coupling because of processing two DPQSK tributaries independently. A 40 Gb/s simulated transmission system over 160km length is established. Simulation results show that butterfly FFE-DFE has better performance than separate FFE-DFE.

Error rate performance of pulse position modulation (PPM) schemes for indoor wireless optical communication (WOC) applications is investigated. These schemes include traditional PPM and multiple PPM (MPPM). Study is unique in presenting and evaluating symbol error behaviour under wide range of design parameters such symbol length (L), number of chips per symbol (n), number of chips forms optical pulse (w). Effect of signal to noise ratio levels and operating bitrates on symbol error performance is also discussed. A comparison between studying modulation schemes is done. Relation with IrDA and IEEE 802.11 indoor WOC standardization is also investigated. Results indicate that PPM achieve great symbol error performance at reasonable signal to noise ratio and high bitrates with large symbol length.

For metro and regional 100-Gbps transmission, a transparent channel reach of 500-600 km is required and a 100-GHz channel grid is typically used. For these applications, a cost effective modulation format is introduced which can make use of electronic components designed for the already established 40-Gbps market, bypassing the requirements for novel electronic developments and therefore reducing the component cost. With this DPSK-3ASK modulation format, five information bits are transmitted in two consecutive symbols, leading to a symbol rate of 45 Gbaud, including overhead for framing and FEC. To minimize hardware requirements and to create a cost-effective solution, a single Mach-Zehnder modulator can be used to create the optical DPSK-3ASK signal after combining the phase and amplitude modulation signals into a 6-level modulator drive voltage. In this paper, it is demonstrated by numerical simulations that these voltage levels can be modified to adapt to varying signal distortions and thereby yield improved transmission performance. It is shown that by dynamically modifying the modulation levels based on the channel performance, dynamic signal impairments such as the non-linear effects from varying power levels, changes in chromatic dispersion, or varying PMD levels can be mitigated. Error-free performance (with FEC) can be obtained with 24 dB OSNR and 7ps DGD for a 112-Gbps (45-Gbaud) optical signal.

This paper demonstrates bandwidth requirement for optical DPQSK transmitter using one Dual-drive Mach Zehnder Modulator (DDMZM) for 100Gb/s physical transmission. The result shows that at receiver bandwidth of 40GHz, NRZ-DQPSK signal requires 60GHz modulation bandwidth at least, while RZ-DQPSK scheme demands less bandwidth, about 40GHz for 50 % duty cycle RZ-DQPSK signal. Keywords: differential quadrature phase-shift keying (DQPSK), dual-drive Mach Zehnder modulator (DDMZM), modulation bandwidth 1. INTRODUCTION Recent years 100G Ethernet has attracted much attention both on standardization and technical implementation issues due to the continuous growth of data traffic in provider networks over the decades. Of all the solutions imposed at present, 100Gb/s serial physical transmission using an optical differential quadrature phase-shift keying (DQPSK) modulation format has been proved as a preferable choice for implementation because of its high spectral efficiency as well as halved bandwidth requirement for electrical components. To further improv e the cost effectiveness, a simplified DQPSK transmitter scheme using single dual-drive Mach Zehnder Modulator (DDMZM) and two-level electrical driving signal was raised. However, the generated optical signal exhibits great ripples caused by the rise-fall edge of the drive signals, and an additional pulse carver is suggested by the author to mitigate the impacts [1, 2]. In this paper, the performances of DQPSK transmitter using one DDMZM with and without pulse carver for 100Gb/s back-to-back (B2B) transmission are evaluated, then the bandwidth characteristics of both NRZ-DQPSK and RZ-DQPSK with duty cycles of 33%, 50% and 67%, are examined respectively. First we introduce the principle of DQPSK transmitter using one DDMZM. Then the bandwidth characteristics of different DQPSK signals are analyzed in sequence. The result indicates that NRZ-DQPSK signal generated by one DDMZM demonstrates great demand for modulation bandwidth, which is beyond the symbol rate; while the RZ carved signals are able to reduce the bandwidth requirement effectively and approach to conventional transmitte r. This feature thus offers an alternative DQPSK scheme with simpler configuration and lower co st for 100Gb/s phys ical transmission.

Atmosphere Laser Communication (ALC) has the great capability, the better quality of anti-jamming and security, so ALC is adapt to the military application in particular. But because ALC's channel is atmosphere, ALC will be influenced by Atmospheric fading and turbulence, which reduce communication reliability. As a result, studying the suitable modulation and coding becomes the important problems for ALC. From these, people has put forward plenty of modulation and coding technologies, including On-off keying (OOK), pulse position modulation (PPM), digital pulse interval modulation (DPIM), dual-header pulse interval modulation(DHPIM) and so on. Among these, the mean transmit power and error symbol rate of PPM are all less than the others, so PPM has some applied advantage. People has also studied channel coding technology for PPM in ALC, George Stephen Mecherle applied RS code to PPM and analyzed error bit performance in 1986, Jon Hamkins and Meera Srinivasan analyzed the error bit rate of applying Turbo code to PPM through APD detecting in 1998, J. Hamkins analyzed the error bit performance of 256-ray PPM for Turbo code in 1999, and HU Hongfei analyzed the combined mode and applying approach of binary LDPC and multi-system PPM. But all of these have not involved the influence of atmosphere weak turbulence. The paper introduces LDPC as the channel code to ALC, and combines with PPM, discusses the error performance of LDPC in weak turbulence, then compares the performance in weak turbulence, Gauss channel and uncoded system. The emulation results indicate that the LDPC-coded performance of Gauss channel is better than that in weak turbulence channel, and introducing LDPC can efficiently improve the error performance in Gauss channel and weak turbulence channel, which has some applied value.

We report the BER performance characteristics of 16-ary Multi-level Amplitude-Differential Phase Shift Keying (MADPSK) modulation formats. The modulation scheme is bandwidth efficient with an effective transmission symbol rate equal to 1/4 of the bit rate. The BER performance of NRZ and RZ MADPSK formats are investigated for long haul optically amplified transmission in the presence of optical noise, fiber residual chromatic dispersion and non-linearity.

The performance of a Subcarrier Multiplexing (SCM) optical fibre system using QPSK modulation is analysed in this paper. Our results will show that it is possible to increase the system bandwidth by controlling the input optical power. Various fibre dispersion values and subcarrier channel spacing are used in order to check the bandwidth increase proportional to the optical power. The transmission bandwidth was studied in terms of fibre dispersion and input optical power. The frequency response was measured and computed. Limitations imposed by nonlinear distortions mainly due to interplay between dispersion and self-phase modulation are verified as well. The analysis to the SCM_QPSK transmission system such as the subcarrier channel spacing, signal input power, available frequency bandwidth under the fibre specifications and system conditions operation will be explored in a specific application. It means applying this technique after setting the requirements necessary to the operation of an optical ground-wire (OPGW) already installed system. The results showed an increase of the transmission bandwidth as the optical power increases. For QPSK modulation, power penalties smaller than 1 dB were obtained only for channel spacing higher than 1.2 multiplied by the symbol rate. Experimental measurements obtained in the literature were used to validate our results. Eye opening and received eye diagrams will be evaluated in order to have a simpler receiver layout and make the entire system more reliable, since it will become more robust to error disturbance, maintenance is easier and system upgrades will be facilitated.

Next generation high-capacity (> 40 Gb/s) optical communication systems, whether for fiber or free-space transmission, will likely require high spectral efficiency techniques that enable optimization of performance, SWAP (size, weight and power), as well as the support of critical features such as transmission security. Modulation techniques with high number of bits per symbol coding such as differential quaternary phase-shift-keying (DQPSK) at lower symbol rates are more advantageous than conventional binary on-off keyed format with one bit per symbol coding. DQPSK is more robust to impairments of the transmission medium such as fiber dispersion than 40 Gb/s on-off keying. DQPSK is also less vulnerable to eavesdropping than direct-detection of on-off keyed signals at the physical layer. We report results of a 2-bit/s/Hz spectral efficiency multi-channel transmission system with four bits per symbol coding using 12.5 Gsymbol/s DQPSK and polarization multiplexing by bit-interleaved orthogonal polarizations. Transmission of 14×40 Gb/s 20-GHz spaced optical channels over 4×102 km of standard SMF-28 optical fiber with bit-error-ratio below the forward-error-correction code threshold (10 -3 ) required for error-free operation was achieved. Key enabling components used in the transmission experiment are: DQPSK optical modulator and demodulator, channel demultiplexing tunable band-pass optical filter, and balanced photoreceiver.

In this paper we introduce a new structured channel impulse response (CIR) estimation method for sparse multipath channels. We call this novel CIR estimation method Time-Of-Arrival based Blended Least Squares (TOA-BLS) which uses symbol rate sampled signals, based on blending the least squares based channel estimation and the correlation and cleaning followed by TOA estimation. TOA estimation is accomplished in the frequency domain and is based on AR model parameter estimation via unconstrained least squares. Simulation examples are drawn from the ATSC digital TV 8-VSB system. The delay spread for digital TV systemscan be as long as several hundred times the symbol duration; however digital TV channels are, in general, sparse where there are only a few dominant multipaths.

This paper further examines a computationally simple scheme for estimating the symbol period in the presence of multipath that was recently proposed by Breinholt and Zoltowski. The algorithm is not premised on the symbol pulse shape making it robust to multipath effects. This paper relates simplifications that facilitate real-time implementation of the algorithm in a per sample update mode. The algorithm is presented in the context of the 8-VSB digital TV modulation standard but is equally applicable to other modulation formats. Simulations show that the algorithm performs well in the presence of multipath. Comparisons with a Gardner timing recovery loop show a reduction of jitter and faster frequency acquisition than that of the Gardner loop. The algorithm can be used alone or to speed the acquisition of other timing recovery methods. As an example, the algorithm is combined in a simple manner with a Gardner loop to provide significantly faster timing acquisition.© (2002) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Microwave Fiber Optic (MFO) links have attracted much attention recently with their application in wireless access. When a wireless link is in series with the optical link, nonlinear distortion (NLD) of the MFO link becomes the biggest concern. The linearity requirement is high due to the large variations in the RF power through the link. Laser intrinsic nonlinearity is usually the major concern in a directly modulated link. However, in wireless applications significant amplification is required at the antenna site, which introduces additional NLD. In this paper a higher order adaptive fiber is proposed to model the entire MFO link considering all cascaded nonlinearities. The FIR filter runs at the baseband symbol rate and trains itself from the input/output amplitude and phase relationships of the microwave modulated symbols. Thus no accurate knowledge of the link physical parameters is required. The powerful recursive least square algorithm converges quickly, tracking any modification or drift in the link parameters. Simulation results show that, third order Volterra adaptive filters are adequate to model measured AM-AM and AM-PM characteristics of a MFL link under steady state conditions. The link consists of a directly modulated InGaAsP DFB laser and PIN diode receiver with a high gain amplifier.

We propose two methods to provide optimal image quality at a fixed image delivery rate for any given transmission channel condition. The first method, channel-controlled variable-rate (CCVR) image coding, employs adaptive-rate source coding and channel coding, while operating with a fixed modulation symbol rate. The second method, adaptive-rate coding-modulation (ARCM), extends the CCVR system by utilizing adaptive modulation. Both methods use a variable-compression-ratio image coder and variable-rate channel coding. The objective is to maximize the quality of the reconstructed image at the receiver when transmitted through Rayleigh fading and additive white Gaussian noise (AWGN). The CCVR system maximizes the reconstructed image quality through a bit-rate trade-off between the source and channel coders. The ARCM method provides a trade-off between the rates of source and channel coding, and the modulation rate. Both methods require knowledge of the channel state which is used by the receiver to inform the transmitter, via a feedback channel, of the optimal strategy for image compression, channel coding, and modulation format. The resulting system using ARCM achieves up to a 17 dB improvement over the peak signal-to-noise ratio (PSNR) performance of a system using a fixed-compression-ratio image coder and fixed-rate channel coding. We extend the adaptive image transmission system to video, and present a candidate system for wireless mobile video applications using orthogonal frequency division multiplexing (OFDM).

This paper presents a comparison of the two most common modulation systems for downstream digital transmission on hybrid fiber/coax: quadrature amplitude modulation (QAM), and vestigial sideband modulation (VSB). Both modulations use multiple signal levels to send multiple bits per Hertz with similar bandwidth efficiency. Detailed calculations of QAM and VSB performance on hybrid fiber/coax are reported here. It is shown that, since VSB has a higher symbol rate, it has at most one-half dB less received SNR than QAM because of dispersion and jitter. This difference is negligible. Proposals for VSB recover the carrier with a pilot tone and a PLL, and proposals for QAM use all-digital data-directed carrier recovery. Simulations reported here show that QAM and VSB have very similar carrier recovery performance. It is concluded that, for hybrid fiber/coax, the performance and inherent cost of QAM and VSB are very similar, although the two systems have many implementation differences and are incompatible.

In this paper, a VLC decoder IC based on the table-lookup technique is described. In this design, a barrel shifter is employed to shift a number of bits corresponding to the decoded codeword. This parallel approach lowers the hardware speed constraint and reduces the system buffer memory size as well. The barrel shifter in conjunction with a codeword table and a word-length table makes the one-step decoding possible. The table storage required by this approach is the type of associative memory which is most efficiently implemented in Programmable Logic Arrays (PLAs). A Content Addressable Memory (CAM) approach that facilitates programmability is also addressed. Design considerations for multiple code tables and tables containing escape codes are discussed for more general applications of the decoder IC. The important issue of decoder interface circuitry, often ignored by others, is also fully considered. Such circuitry can greatly reduce the system complexity. Finally, the implementation of a mask programmable VLC decoder IC is demonstrated using a silicon compiler. Based on our simulations, the output symbol rate for a VLC decoder with 64 entries is about 30 MHz. This speed is high enough for most real-time applications including CCIR 601 digital video (Y: 13.5 MHz, U and V: 6.75 MHz each).