Optical Pulse Position Research Articles

Optical continuous pulse position modulation-based analog RoF via frequency-domain position estimation.

Analog radio-over-fiber (A-RoF) solutions for mobile fronthaul are regaining wide attention due to their high spectral efficiency and low complexity. However, the performance of A-RoF is usually limited by the fiber link fidelity. In this Letter, we propose and experimentally demonstrate an optical continuous pulse position modulation-based analog radio-over-fiber (OCPPM-RoF) scheme, in which the amplitudes of wireless waveforms are mapped to the time-domain positions of optical pulses to decouple the additive noise. The de-modulation of OCPPM-RoF signals is performed by a frequency-domain continuous position estimation (FD-CPE) algorithm including cross-power spectrum calculation and weighted least square for accurate delay estimation. In the experiment, by adopting appropriate pulse width factors, the recovered signal-to-noise ratio (SNR) can be flexibly adjusted within a wide range from 31.8 to 54.0 dB, supporting the transmission of various formats from 256-QAM to 65536-QAM. The results indicate that OCPPM-RoF can be a promising candidate for future fronthaul.

BEP evaluation of 5G LDPC codes in a pre-amplified optical PPM receiver

We present results for the performance of a pre-amplified optical pulse-position modulation (PPM) receiver that utilizes the low-density parity-check (LDPC) correction codes of the 5G standard. The code construction is suitable for correcting burst errors that are introduced by PPM. Simulation results show that the LDPC codes can provide a very significant real gain, provided that the code rate is chosen appropriately. We find that the code rates that minimize the bit-error-probabilities (BEPs) of the system range between 2/3 and 22/26, with higher code rates being required in receivers that operate under increased optical noise. It is also shown that a comparable real gain is obtained for both the sum–product and min-sum decoders, while the power penalty of the latter one is only limited to 0.2 dB, when the aforementioned code rates are utilized.

A novel technique for secure transmission of two channels using a single optical pulse position modulated signal for free space optical communication

A novel technique for secure transmission of two channels using a single optical pulse position modulated signal for free space optical communication

Ground-to-Drone Optical Pulse Position Modulation Demonstration as a Testbed for Lunar Communications

Free-space optical (FSO) communication promises to bring fibre-like speeds to data transmissions between ground, sky and space. This is becoming more important in light of the increasing volume of data collected by aircraft and spacecraft. The University of Western Australia (UWA) is commissioning optical ground stations to support FSO communications payloads. We propose retroreflected laser links to drones as a useful step towards further ground-to-sky and ground-to-space FSO communications demonstrations. In this paper, we describe the operation of a hardware testbed for a high photon efficiency optical communication physical layer. This testbed was deployed over a slanted free space link to a drone to verify sub-systems required in communication between the ground station and a spacecraft in cis-Lunar space. Accomplishing this verification of the telescope pointing systems and communications systems would have otherwise been much harder or impossible without using a retroreflected drone link.

Likelihood based synchronization algorithms in optical pulse position modulation systems with photon-counting receivers.

Deep space optical communication (DSOC) is becoming a hot topic. Pulse position modulation (PPM) is an effective tool to realize DSOC benefiting from the feature of high sensitivity. In this paper, we analyze 2 × 1 optical PPM systems with photon-counting detectors, where the distance difference between the two links causes asynchronous superpositions at the receiving end. Two synchronization algorithms are proposed to estimate the time offsets of the two links, which are the optimal Global Maximum Likelihood Estimation (GMLE) and the suboptimal Integer Comparison - Fractional Likelihood Estimation (ICFLE). The complexities of the two methods are also compared. In order to measure the two proposed algorithms, the Cramer-Rao bounds (CRB) are derived. According to simulation results, both the two proposed algorithms approach the deduced CRBs. Furthermore, an equivalent experiment is designed to verify the feasibility and effectiveness of the proposed algorithms. It's also indicated that the proposed algorithms may be utilized in practical systems.

Performance analysis of optical spatial modulation over a correlated gamma-gamma turbulence channel.

In this paper, theoretical closed expressions for the symbol error rate (SER) of two optical spatial modulation (OSM) schemes in a free-space optical (FSO) communication system-optical spatial pulse amplitude modulation (OSPAM) and optical spatial pulse position modulation (OSPPM)-over correlated gamma-gamma fading channels are derived. To study practical optical channels affected by atmospheric eddies, the effect of arbitrary atmospheric channel correlation is considered particularly, and it is shown that the correlation can degrade system performance. The parameters of atmospheric turbulence and the number of optical antennas are also under consideration in performance analysis of the FSO multiple input, multiple output system. All analytical results are validated with Monte Carlo simulations, which clearly illustrate the effect of spatial constellation and signal constellation on the average SER. In addition, it is shown by comparison that turbulence fluctuation and channel correlation have less influence on the OSPPM system than the OSPAM system. Overall, the framework proposed in this paper is proven to be effective and conducive to algorithm research on reducing the effect of correlated channels on OSM FSO systems.

Marked Multi-Layer Optical Spatial Pulse Position Modulation

Marked Multi-Layer Optical Spatial Pulse Position Modulation

Optical Pulse Position Modulation Synchronization and Data Recovery Based on Multipixel Photon Counter

Optical Pulse Position Modulation Synchronization and Data Recovery Based on Multipixel Photon Counter

极低时间抖动的飞秒激光技术（特邀）

The time jitter of a femtosecond laser is the short-term deviation of the optical pulse position relative to its ideal equally spaced pulse position. Femtosecond lasers emit uniformly spaced ultrashort pulse train. The quantum-noise-limited timing jitter can be as low as few tens of attoseconds in millisecond time scale. This unique property and its advanced applications constitute a new branch of ultrafast research, Attosecond precision ultrafast photonics. In this paper, the recent advances in femtosecond laser timing jitter research, high-precision timing jitter characterization methods, and the ultralow timing jitter that can be achieved by different kinds of femtosecond laser sources were reviewed. Finally, the application of low-jitter femtosecond lasers in the fields of synchronization of large-scale scientific instruments, high-speed analog-to-digital conversion, absolute ranging technology and coherent beam combination are introduced.

Optical Spatial Modulation for FSO IM/DD Communications With Photon-Counting Receivers: Performance Analysis, Transmit Diversity Order and Aperture Selection

This paper investigates two pulse-based Optical Spatial Modulation (OSM) schemes as cost-efficient solutions for multi-aperture Free-Space Optical (FSO) communications with Intensity-Modulation and Direct-Detection (IM/DD). Namely, we consider Optical Space Shift Keying (OSSK) where information is encoded in the index of the pulsed optical source and Spatial Pulse Position Modulation (SPPM) where additional bits determine the position of the transmitted optical pulse resulting in higher transmission rates. A performance analysis is carried out over gamma-gamma channels with the exact Poisson photon-counting detection model. Exact Symbol Error Probability (SEP) expressions, simple upper bounds and the achievable transmit diversity orders are derived for both the open-loop and closed-loop scenarios. Based on the presented performance analysis, a transmit aperture selection scheme capable of maximizing the transmit diversity order is proposed for OSSK and SPPM in the closed-loop case. Results show that for open-loop OSSK, open-loop SPPM and closed-loop OSSK, the transmit diversity order does not depend on the severity of scintillation unlike the closed-loop SPPM case.

Range dependence of an optical pulse position modulation link in the presence of background noise.

We analyze the information efficiency of a deep-space optical communication link with background noise, employing the pulse position modulation (PPM) format and a direct-detection receiver based on Geiger-mode photon counting. The efficiency, quantified using Shannon mutual information, is optimized with respect to the PPM order under the constraint of a given average signal power in simple and complete decoding scenarios. We show that the use of complete decoding, which retrieves information from all combinations of detector photocounts occurring within one PPM frame, allows one to achieve information efficiency scaling as the inverse of the square of the distance, i.e. proportional to the received signal power. This represents a qualitative enhancement compared to simple decoding, which treats multiple photocounts within a single PPM frame as erasures and leads to inverse-quartic scaling with the distance. We provide easily computable formulas for the link performance in the limit of diminishing signal power.

基于脉冲展宽波形的光脉冲位置调制异步采样信号的数据恢复技术

基于脉冲展宽波形的光脉冲位置调制异步采样信号的数据恢复技术

基于光脉冲位置调制的异步时钟错位采样数据恢复技术

基于光脉冲位置调制的异步时钟错位采样数据恢复技术

SM/SPPM Aided Multiuser Precoded Visible Light Communication Systems

In this paper, we propose a multiuser precoded visible light communication (VLC) system utilizing optical orthogonal frequency division multiplexing (OFDM), where optical spatial modulation (OSM) and spatial pulse position modulation (SPPM) are invoked for supporting high-rate data transmissions without compromising uniform illumination across multiple light-emitting diodes (LEDs). Both OSM and SPPM exploit the index of data streams for carrying additional information bits, whereas the multiuser interference occurring between different user equipments is mitigated by the MIMO precoder. By evaluating the performances of the proposed VLC systems, we demonstrate that the OSM-aided system is capable of achieving high data rates at sufficiently high signal-to-noise ratios (SNRs). In contrast, the SPPM-aided system has a higher effective bandwidth efficiency at low SNRs, despite the fact that its attainable peak data rate is lower than that of the SM-aided counterpart. Such tradeoffs indicate the potential application scenarios of the proposed schemes for achieving diverse design prerequisites.

A novel non-equidifferent optical APPM mapping scheme for strong turbulent atmospheric channel

An optical Amplitude and Pulse Position Modulation (APPM) mapping scheme for strong turbulent atmospheric channel is proposed to optimize Bit Error Rate (BER) performance. In this scheme, a non-equidifferent amplitude series is designed based on quantitative BER analysis of the specific A×M APPM demapping procedures containing time slot selection and amplitude decision in selected time slot, which are different from traditional ones. Simulation results of 4×4, 4×8 and 4×16 APPM show 4, 3.4 and 6.9 dB SNR gain against traditional APPM scheme respectively. Thus significant BER performance improvement is achieved which helps to enhance reliability of free-space optical communication systems.

Numerical modeling of the temporal response of back-gated metal-semiconductor-metal photodetector in an equilibrium condition

We have simulated the carrier concentration and temporal response characteristics of a Back-Gated Metal-Semiconductor-Metal (BG-MSM) photodetector in one dimension as a function of optical pulse position on the active region in an equilibrium condition (without bias voltage to the photodetector). We have adopted a nonlinear ambipolar transport model to simulate the behavior of photo-generated carriers in the active region of the BGMSM photodetector. From the simulation results, it is observed that for optical pulse positions in the cathode region, the magnitude of the response current is exactly the same but opposite that of the anode region. The response of the photodetector is zero when a pulse is positioned at the center of the active region. This important feature of the device could make it attractive for micro-scale positioning of highly sensitive instruments. Our simulation results agreed well with the experimental results.

Numerical investigation of the effect of optical pulse position on the response of an unbiased BGMSM photodetector using ADI method

A numerical method for describing the electrical response of a Back-Gated Metal-Semiconductor- Metal Photodetector (BGMSM-PD) to an impinging optical pulse on the active region of the device is presented. In the absence of external voltage, the main mechanism for the transport of photo-generated carriers is diffusion mechanism. Two nonlinear differential equations describe the behavior of photocarriers’ densities in the device medium with respect to time and position. Having linearized the parabolic partial differential equations, the time evolution of carrier densities is calculated using the Alternating Direction Implicit (ADI) method. The numerical results show good agreement with the experimental data. Both experimental and numerical findings confirm that the electrical response of the device to optical pulses with spatial FWHM comparable with the width of the active region is dependent on pulse position on the active region. This feature of the device makes it to be a good candidate as position sensors in places where micro-positioning is required.

Numerical modeling of the effect of optical pulse position on the impulse response of a Metal-Semiconductor-Metal (MSM) photodetector (low field condition)

We present a numerical modeling of the effect of optical pulse position on the impulse response of a GaAs back-gated Metal-Semiconductor-Metal (MSM) photodetector at low bias voltages. The backside contact of the photodetector is set to the floating condition (disconnected from the external circuit). Experimentally the device response to the optical pulse is strong only when the position of the optical pulse is around the anode contact. We have used a one-dimensional time-dependent nonlinear ambipolar transport equation to model this behavior. Our numerical modeling results agree well with the reported experimental findings.

Approaching Helstrom limits to optical pulse-position demodulation using single photon detection and optical feedback

Optical pulse-position modulation (PPM) is one of the primary modulation formats being investigated for use in deep-space communications, as well as terrestrial fiber optical communications. We consider the problem of demodulating M-ary optical PPM waveforms, and propose a structured receiver whose mean probability of symbol error is smaller than all known receivers, and approaches the Helstrom (quantum) limit of the minimum probability of error (MPE) of discriminating between the coherent-state PPM signals. The receiver uses photodetection coupled with optimized phase-coherent optical feedback control through the PPM pulse slots and a phase-sensitive parametric amplifier. We present a general framework of optical receivers known as the ‘conditional pulse nulling receiver’, and present new results on ultimate limits and achievable regions of the trade-off space between the spectral versus photon efficiency of PPM, for the single-spatial-mode far-field pure-loss optical communication channel.

Investigation of higher order optical multiple pulse position modulation links over a highly dispersive optical channel

This study describes a performance analysis of eight different multiple pulse position modulation (PPM) systems with 4, 7, 12, 15, 17, 22, 28 and 33 slots operating over a plastic optical fibre (POF) channel. The receiver/decoder uses slope detection and a maximum likelihood sequence detector (MLSD). As the analysis of any multiple pulse position modulation (MPPM) system is extremely time consuming, especially when the number of slots is large, a software solution was used. A measure of coding quality that accounts for efficiency of coding and bandwidth expansion was applied and original results showed that the middle systems of these MPPM families are the most efficient for a wide range of bandwidths. Although the efficient Gray coding was used for this investigation, a close to optimum mapping is presented for MPPM systems of the families mentioned above. These mappings were found to be superior to the efficient Gray codes, linear coding and a series of random mappings.