ASK heterodyne receiver sensitivity measurements with two in-line 1.5 ?m optical amplifiers

A heterodyne amplitude shift keying configuration was used to evaluate the performance of resonant-type optical amplifiers in a coherent lightwave communication system. With two in-line amplifiers, each with a gain of 25 dB, the total loss between the transmitter and the receiver was 95 dB at 10-9 bit error rate. At a 100 Mbit/s data rate, the receiver sensitivity without amplifiers was -49.3 dBm. With two amplifiers the receiver sensitivity could be maintained at -49.0 dBm.     

3 Gbit/s optically preamplified direct detection DPSK receiver with 116 photon/bit sensitivity

For the first time experimental bit error rate curves are presented for an optically preamplified direct detection differential phase and shift keying (DPSK) communication link. DPSK offers approximately 6 dB peak power sensitivity improvement over more traditionally optically preamplified on/off keying (OOK). Using an erbium doped fibre preamplifier, a fibre Fabry-Perot filter, an optical DPSK demodulator consisting of a fibre-optic Mach-Zehnder interferometer with a 1 bit differential delay, and a balanced receiver, a sensitivity of 116 photon/bit was obtained. To the authors' knowledge these results represent the first demonstration of optically preamplified DPSK with better sensitivity than previously reported multigigabit per second heterodyne DPSK and approximately 3 dB more sensitivity on a peak power basis than previously reported preamplified OOK systems.<>     

10 Gbit/s optical PSK homodyne transmission experiments using external cavity DFB LDs

10 Gbit/s optical PSK homodyne transmission experiments using a modified decision-driven optical phase locked loop with 1.55 mu m external cavity laser diodes were conducted. A receiver sensitivity of -34.2 dBm or 297 photon/bit was experimentally achieved. There was no degradation in receiver sensitivity after signal transmission through 151 km of dispersion shifted fibre.<>     

Optical phase-locked PSK heterodyne experiment at 4 Gb/s

A 4 Gb/s phase-locked optical PSK (phase shift keying) heterodyne communication system is demonstrated. The receiver was implemented with a single 100-Ω loaded p-i-n photodiode and a 1320-nm diode-pumped miniature Nd:YAG laser as a local oscillator. For a 2⁷-1 PRBS (pseudorandom bit sequence), the receiver sensitivity was -34.2 dBm or 631 photons/bit. The corresponding power on the surface of the detector was -37.3 dBm or 309 photons/bit. With a 2¹⁵-1 PRBS, a 2.6 dB additional sensitivity degradation was observed due to the nonideal frequency response of the phase modulator and the receiver amplifiers     

Rayleigh scattering influence on performance of 10 Gb/s opticalreceiver with Er-doped optical fiber preamplifier

The achievement of -30.8 dBm (630 photon/bit) receiver sensitivity at 10 Gb/s, with an Er³⁺-doped optical fiber preamplifier, is discussed. This is an 8.3-dB sensitivity improvement over the avalanche-photodiode/FET receiver. Power penalties caused by a noise increase due to Rayleigh backscattering by the transmission optical fiber have been evaluated. Approximately -30-dB Rayleigh scattering from a 20-km optical fiber resulted in a 3.5-dB power penalty for a 25-dB-gain optical amplifier     

Phase diversity techniques for coherent optical receivers

In the present state of the art, coherent optical receivers most often operate in the heterodyne mode. Here a photodiode-amplifier combination having bandwidth greater than twice the bit rate (B) is needed: indeed bandwidths considerably greater than2Bare preferably employed to ease design of the bandpass filter needed for noise limitation, and to avoid demodulator penalties in some modulation schemes. For the high bit rate systems now coming into service (560 Mbit/s-2.4 Gbit/s), the optical receiver design requirements become more stringent for coherent heterodyne operation. The various modes of "zero IF" operation, however, require only baseband receiver module bandwidth. The options available are either homodyne (phase locked) operation, or phase diversity (multiport) techniques. In this paper, we compare these options, and show that phase diversity techniques are capable of good performance for high bit rate coherent receivers. In phase diversity operation, not only is phase locking avoided, but also the necessary frequency locking does not have high stability requirements. Furthermore, there are advantages in operating with a small frequency offset from zero (of the order of 1 percent of the bit rate). An experimental receiver has been operated at 320 and 680 Mbit/s, demodulating both amplitude shift keying (ASK) and differential phase shift keying (DPSK). Operation with FSK is also possible. Sensitivities so far achieved of -47.5 dBm (320-Mbit/s ASK) and -42 dBm (680- Mbit/s ASK) with limited local oscillator power are capable of substantial improvement when higher power local oscillators and lower noise receive modules become available. Demodulation of DPSK at 320 Mbit/s has also been achieved and shows a measured receiver sensitivity improvement of over 4 dB over ASK at the same bit rate and local oscillator power. These practical results show clearly that phase diversity is a very realistic option for high bit rate systems.     

20 Gbit/s long distance transmission using a 270 photon/bit opticalpreamplifier receiver

A 200 km nonrepeatered transmission experiment and a 400 km transmission experiment using three in-line amplifiers are carried out at 20 Gbit/s by using a simple but highly sensitive optical preamplifier receiver based on a 0.98 μm LD-pumped EDFA. High sensitivity of -31.6 dBm (270 photon/bit) at 20 Gbit/s is obtained     

Polarization independent coherent optical receiver

This paper describes an optical heterodyne receiver for DPSK signals which can receive an optical signal having an arbitrary polarization state. This is achieved by splitting the received signal between two orthogonal polarization axes and processing the resulting two signals as in a conventional DPSK heterodyne receiver. The sum of the two demodulated signals provides a baseband signal independent of the polarization state of the received optical signal. When the receiver noise is dominated by the shot noise of the photodetectors, the receiver provides a BER of 10^-9for an average number of 22 photon/bit. In comparison, a conventional optical heterodyne receiver requires under the same noise condition 20 photon/bit to achieve the same BER for a received optical signal polarized along the polarization axis of the local optical signal.     

2．4Gb／s50kmMach－Zehnder外调制／直接检测型光纤传输系统

本文介绍了国内首次利用国产Ｍａｃｈ－Ｚｅｈｎｄｅｒ型Ｔｉ：ＬｉＮｂＯ３外调制器进行２．４Ｇｂ／ｓ伪随机码信号光纤传输的系统实验。经过５０．７ｋｍ传输后接收机灵敏度为－３０．３ｄＢｍ。     

DC-1 Gb/s burst-mode compatible receiver for optical busapplications

The characteristics and performance of a high-speed, burst-mode compatible receiver for optical bus or packet communications are described. It employs an Si bipolar differential transimpedance amplifier, an auto-threshold tracking level control circuit, and a DC-coupled decision circuit (ECL compatible quantizer). To cope with intermittent data packets, the threshold control circuit can capture data amplitude and set the logic threshold in about 1 ns. Using an avalanche photodiode, the typical receiver sensitivity is -37.5 dBm (10 ^-9 BER) at bit rates up to 900 Mb/s, with a dynamic range of 23 dB for both pseudorandom and burst-mode signals. At 1 Gb/s, the sensitivity is -35 dBm. With a worst-case reset time <100 ns for the threshold control circuit, this receiver can be used for optical bus applications where data signals with varying optical power are employed     

Performance of homodyne detection of binary PSK optical signals

This study evaluates the performance of an optical receiver for binary phase shift keyed (BPSK) signals in the presence of noise originating from the photodetectors and the phase fluctuations of the optical sources. Analysis of the homodyne detection process shows that the performance is degraded by two effects: One due to the phase error fluctuations of the recovered carrier and the other due to reduction of the energy per bit available for data recovery. The resulting power penalty can be minimized by dividing in an optimal way the received optical signal between the carrier recovery and the data recovery circuits of the receiver. The minimum penalty thus obtained depends on the 3-dB linewidth and on the transmission rate. For example, a penalty of 0.5 dB, relative to the quantum limit of 9 photon bit needed to achieve a BER of 10^-9, imposes a minimum transmission rate of about 180 Gbit/s when the optical source has a 3-dB linewidth of 20 MHz.     

A high-performance optical receiver for 622 Mb/s direct-detectionsystems

A report is presented on the measurement of receiver sensitivity and noise characteristics of a high-performance optical receiver using a low-noise InGaAs avalanche photodiode (APD) and a low-noise high-electron mobility transistor (HEMT). At a bit rate of 622.08 Mb/s and a wavelength of 1.297 μm, the measured receiver sensitivity is -48.3 dBm. This is equivalent to a sensitivity of 155 photons/b and is about 12 dB away from the quantum limit of 10 photons/b     

A 10 Gb/s high sensitivity, monolithically integrated p-i-n-HEMToptical receiver

A high-sensitivity, monolithically integrated optical receiver, composed of a p-i-n-PD and high electron mobility transistors (p-i-n-HEMTs) is described. The receiver sensitivity is -17.3 dBm at a bit error rate of 1×10^-9 for a 10-Gb/s non-return-to-zero (NRZ) lightwave signal. This value is the best result yet reported for 10-Gb/s monolithically integrated receivers. The sensitivity is -30.6 dBm if an erbium-doped fiber amplifier (EDFA) is placed ahead of the p-i-n-NEMT receiver. A transmission experiment using a 150-km dispersion-shifted fiber (DSF) indicates no degradation in the bit error rate characteristics or the eye pattern. This verifies the practicality of the p-i-n-HEMT optical receiver for high-speed transmission systems     

交流耦合突发模式光接收机

本文对交流耦合突发模式光接收机进行了理论分析。这种接收机主要用于基于信元的时分复用系统中,工省了在直流耦合方式中为调整判决阈值而插入的开销,提高了传输效率。但理论分析表明这种接收机引入的灵敏度价比直流耦合模式接收机高。理论分析结果与模型仿真结果符合得很好。     

PSK optical homodyne detection using external cavity laser diodesin Costas loop

5-Gb/s optical PSK (phase-shift keying) homodyne detection experiments are discussed. In these experiments, the optical carrier is recovered by a Costas optical phase-locked loop using a multielectrode local oscillator (DFB) laser diode at 1.55 μm with a flat FM response. Although the beat linewidth of 80 kHz is broad compared to the loops in other phase-locked loop (PLL) experiments, phase locking with Costas loop is confirmed at 5 Gb/s by increasing the loop natural frequency. The receiver sensitivity is -42.2 dBm or 93 photon/bit for a 2⁷-1 pseudorandom bit sequence (PRBS) in front of a 90° hydride     

Numerical study of moderate distance high bit-ratealternating-amplitude soliton systems

We present a numerical investigation of alternating-amplitude soliton systems. We propagate 100 Gb/s, pseudorandom bit sequences of 2 ⁵-1 to 2⁷-1 solitons through fibers of different lengths and calculate the corresponding eye opening penalty at the receiver. The influence of different amplitude ratios, amplifier spacings, pulse widths, and dispersion slopes as well as of the soliton self-frequency shift are studied. We also study the effect of compression of the alternative-amplitude solitons with the larger amplitudes to preserve their soliton character and the impact of the relative initial phase between the alternating-amplitude solitons. When the amplifier spacing is 10 km the system length can be at least 400 km with alternating-amplitude solitons compared to only 200 km in the case of equal amplitude solitons with similar penalties. Our simulations show-that third-order dispersion and the soliton self-frequency shift limit the maximum allowable amplitude ratio     

2.488 Gb/s-318 km repeaterless transmission using erbium-dopedfiber amplifiers in a direct-detection system

The authors have achieved a 2.488 Gb/s, 318 km repeaterless transmission without any fiber dispersion penalty through a nondispersion-shifted fiber in a direct detection system. The system was loss limited with a T-R power budget of 57 dB. Three key components enabled the authors to achieve this result: (1) a Ti:LiNbO₃ external amplitude modulator enabling a dispersion-free transmission, (2) erbium-doped fiber amplifiers increasing the transmitting power to +16 dBm, and (3) an erbium-doped fiber preamplifier enabling a high-receiver sensitivity of -4.1 dBm for 10^-9 BER. To the author's knowledge, this result is the longest repeaterless transmission span length ever reported for direct detection at this bit rate. From the experimental results and a theoretical model, the authors identified the sources of the receiver sensitivity degradation from the quantum limit (-48.6 dBm) and estimated the practically achievable receiver sensitivity of ~-44 dBm (~-124 photons/bit) for 2.5 Gb/s optical preamplifier detection     

The BER theoretical model and properties of SiPM‐based receiver for OOK optical communication

The bit error rate (BER) theory of silicon photomultiplier (SiPM) based on‐off keying optical communication receiver, which introduces photon equivalent threshold is established. The optical crosstalk effect, the dark counts, the amplitude fluctuations of output pulses of SiPM, the baseline fluctuation, the shape of the incident light pulse, the adjacent symbol interference as well as the photon detection efficiency (PDE) are considered in the theory model. The numerical result shows that the average minimum optical power required is much smaller than that of the avalanche photodiode‐based receivers under the same conditions. The BER of SiPM‐based optical communication receiver is very sensitive to the PDE and optical crosstalk (OC) probability of SiPM. For the application of digital optical communication, a SiPM with high PDE but low OC probability and low dark count rate is a preference, under the premise that the output pulse is fast enough. For the state‐of‐the‐art SiPMs, the dark count rate is small enough to obtain adequate BER, and the OC effect is not a big limitation of the performance of SiPM‐based receiver. Moreover, the amplitude fluctuation and the baseline fluctuation of the SiPM‐based receiver are not bottlenecks of the performance in practice.     

1.25/10.3 Gbit/s dual-rate burst-mode receiver

A 1.25/10.3 Gbit/s dual-rate burst-mode receiver is proposed, which uses a tunable lowpass filter to change the sensitivity for each bit rate and an output-port selector to switch the output port according to the input bit rate. It is demonstrated that this receiver can realise a high sensitivity, a wide dynamic range, and a high-speed response with long consecutive identical digit signals.     

Four-Level Pulse Width Modulation for Fiber Optic Communications

The performance of a digital fiber optical system employing four-level pulse width modulation (PWM) is considered. It is shown that PWM may be an attractive alternative to pulse amplitude modulation (PAM), especially if a wide band channel is used. The probability density function (pdf) of the timing error is obtained in terms of the pdf of the noise amplitude, taking into account the thermal noise of the amplifier and the signal-dependent shot noise introduced by the photodiode detector. Near-Gaussian optical pulse edges at the receiver are assumed. Using typical system parameters, the variation of bit error rate (BER) with power level, and the effects of different bit rates, mean photodetector gain, and system bandwidths are calculated. It is observed that minimum BER's are achieved at moderate values of mean photodetector gain and that increased system bandwidth results in increased receiver sensitivity.