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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.

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

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.

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.

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).