Ultrafast Measurement of Optical DPSK Signals Using 1-Symbol Delayed Dual-Channel Linear Optical Sampling

We propose and demonstrate a 1-symbol delayed dual-channel linear optical sampling for observing optical differential phase-shift keying (DPSK) signals. As this technique is based on optical gate processing by means of interference with local short pulses, its performance allows ultrafast measurement for a symbol rate of greater than 100 Gsymbol/s. Moreover, as the new measurement apparatus employs a two-series interferometer system with a 1-symbol delay, the measured phase distribution reflects the signal quality between adjacent symbols of the optical DPSK signals. In our experiment, we successfully observe the waveform degradation caused by the coherence of the light source and the pattern effect of the phase modulator. The measurement system noise is also discussed.     

Ultrafast optical pulse-pattern signal measurement usingoptoelectronic techniques

A novel ultrafast optical pulse-pattern signal measurement technique using a fast photodetector and electro-optic sampling is demonstrated. The technique can measure 100 Gbit/s optical pulse-pattern signals with high sensitivity and polarisation independence     

Generation and transmission of millimeter-wave data-modulated optical signals using an optical injection phase-lock loop

Generation and transmission of millimeter-wave data-modulated optical signals is presented using an optical injection phase-lock loop (OIPLL). Millimeter-wave signal generation is demonstrated with wide locking range, 30-GHz low phase noise level, -93 dBc/Hz, and a wide frequency tuning range, 4-60 GHz generation demonstrated using optical injection locking only, verified by using OIPLL in the 26-40 GHz range. The OIPLL is also used to transmit error-free 140-Mb/s amplitude shift keying and 68-Mb/s differential phase-shift keying (DPSK) modulated millimeter-wave signals over up to 65 km of uncompensated standard singlemode fiber. The DPSK system uses reference frequency modulation, eliminating the need for optical amplification.     

Modulation and demodulation techniques in optical heterodyne PSKtransmission systems

Modulation and demodulation techniques are described for an optical PSK heterodyne transmission system operating at 560 Mb/s and 1.2 Gb/s. Performance limitations affecting the receiver sensitivity in a 1.2-Gb/s DPSK system, such as laser phase noise, phase modulation depth, IF center frequency deviation, and local laser power, are studied. High receiver sensitivities for PSK systems were achieved. The applicability of the Mach-Zehnder modulator as a phase modulator for 1.2-Gb/s DPSK is also demonstrated. A 1.2-Gb/s DPSK transmission of over 100 km, using polarization diversity with novel polarization-insensitive automatic frequency control in an attempt to overcome signal fading caused by polarization fluctuation in the transmitting fiber, is also described. A receiver sensitivity of less than -42.8 dBm and varying within 1.4 dB for all states of polarization was achieved. A multichannel high-definition TV (HDTV) transmission experiment using a DPSK polarization-diversity tunable receiver is described     

1-Gsymbol/s 64-QAM Coherent Optical Transmission Over 150 km

Quadrature amplitude modulation (QAM) is an excellent modulation format for realizing optical communication systems with a high spectral efficiency of much greater than 1bit/s/Hz. We describe QAM coherent optical communication that we achieved by using heterodyne detection with a frequency-stabilized fiber laser and an optical phase-locked loop (OPLL) technique. The phase error variance of the intermediate frequency signal of the OPLL was 6.1times10^-3 rad. A 1-Gsymbol/s 64-QAM coherent signal was successfully transmitted over 150km     

Transmission Performance Comparison of Direction Detection‐Based 100‐Gb/s Modulation Formats for Metro Area Optical Networks

Transmission performances of direct detection‐based 100‐Gb/s modulation formats are investigated and compared for metro area optical networks. The effects of optical signal‐to‐noise ratio sensitivity, chromatic dispersion, cross‐channel nonlinearity, and transmission distance on the performance of differential 8‐ary phase‐shift keying (D8PSK), differential phase‐shift keying plus three‐level amplitude‐shift keying (DPSK+3ASK), and dual‐carrier differential quaternary phase‐shift keying (DC‐DQPSK) are evaluated. The performance of coherent dual‐polarization quadrature phase‐shift keying (DP‐QPSK) with block phase estimation and coherent DP‐QPSK with digital differential detection are also presented for reference. According to our analysis, all three direct detection modulation formats could transmit a 100‐Gb/s signal over several hundred kilometers of a single‐mode fiber link. The results also show that DC‐DQPSK outperforms D8PSK and DPSK+3ASK, and the performance of DC‐DQPSK is comparable to that of coherent DP‐QPSK with digital differential detection. The maximum transmission distance of DC‐DQPSK is over 1,000 km, which is enough distance for metro applications.     

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.     

OSNR Monitoring Method for OOK and DPSK Based on Optical Delay Interferometer

We describe a simple method to measure the optical signal-to-noise ratio (OSNR) of on-off-keying (OOK) and differential phase-shift-keying (DPSK) signals by using an optical delay interferometer (ODI) having a sinusoidal and tunable passband. This OSNR monitoring method is independent of chromatic dispersion, polarization-mode dispersion, and noise polarization. We show experimentally that accurate OSNR measurements are made for a 10-Gb/s OOK signal by using a 1-bit ODI and a 40-Gb/s DPSK signal by using a partial-bit ODI with the OSNR ranging from 5 to 25 dB.     

Corona Based Optimal Node Deployment Distribution in Wireless Sensor Networks

This paper shows the trade off between different modulation techniques such as multi level quadrature amplitude modulation, multi level phase shift keying, and multi level differential phase shift keying for upgrading direct detection optical orthogonal frequency division multiplexing systems with possible transmission distance up to 15,000 km and total bit rate of 2.56 Tb/s. The 2.56 Tb/s signal is generated by multiplexing 64 OFDM signals with 40 Gb/s for each OFDM. Variations of optical signal to noise ratio (OSNR), signal to noise ratio (SNR), and bit error rate (BER) are studied with the variations of transmission distance. Maximum radio frequency power spectrum, and output electrical power after decoder are measured for different multi level modulation techniques with carrier frequency. It is observed that multi level QAM has presented better performance than multi level PSK and finally multi level DPSK in optical OFDM systems. Maximum output power after decoder is enhanced with both 32-PSK, and 64-QAM. Quadrature signal amplitude level at encoder is upgraded with 64-QAM. It is noticed that OSNR, SNR, and BER are improved using 4-QAM OFDM system than either QPSK or 4-DPSK.     

基于光纤差分相移键控的色散补偿方案的研究

为了研究光差分相移键控(DPSK)调制格式在光纤高速传输系统中的色散补偿, 利用色散补偿光纤(DCF)的色散补偿原理, 对40Gbit/s光纤传输系统进行色散补偿, 分析了40Gbit/s单通道光纤传输系统中3种DPSK调制格式信号的频谱特性; 仿真了3种码型的色散容忍度以及3种调制格式在考虑光纤的非线性下的色散补偿方案。结果表明, 光非归零码差分相移键控(NRZ-DPSK)信号具有最好的色散容忍度, 但其受非线性的影响比较大; 33%归零码差分相移键控(33%RZ-DPSK)信号的色散容忍度差, 但其色散补偿后的效果优于NRZ-DPSK; 而载波抑制归零码差分相移键控信号对色散和非线性效应都有较好的抑制; 3种DPSK调制格式均在对称补偿2方案中色散补偿的效果最佳。此仿真研究对光DPSK信号在光纤中的色散补偿具有参考意义。     

Optical DPSK heterodyne detection experiments using DBR laser diodes with external optical feedback

High receiver sensitivity, with 7 dB improvement over a direct detection system, has been achieved in a 400 Mbit/s optical DPSK heterodyne detection experiment using DBR laser diodes with external optical feedback. The influence of the laser output phase noise was evaluated experimentally in good agreement with theory.     

OSNR Monitoring Technique for DPSK/DQPSK Signals Based on Self-Heterodyne Detection

We describe a new method for monitoring the “in-band” optical signal-to-noise ratio (OSNR) of differential phase-shift-keying (DPSK) and differential quadrature phase-shift-keying (DQPSK) signals. This technique estimates the OSNR by analyzing the radio frequency spectrum obtained by the self-heterodyne detection. The results show that the performance of the proposed technique is not sensitive to the effects of chromatic dispersion and polarization-mode dispersion. In addition, this technique can be used for monitoring the polarization-scrambled signals. For a demonstration, we measure the OSNR of the polarization-scrambled 10-Gb/s DPSK and 20-Gb/s DQPSK signals in a 640-km-long transmission link.      

Bit error rate performance of π/4-DQPSK in a frequency-selectivefast Rayleigh fading channel

The bit error rate (BER) performance of π/4-differential quadrature phase shift keying (DQPSK) modems in cellular mobile communication systems is derived and analyzed. The system is modeled as a frequency-selective fast Rayleigh fading channel corrupted by additive white Gaussian noise (AWGN) and co-channel interference (CCI). The probability density function of the phase difference between two consecutive symbols of M-ary differential phase shift keying (DPSK) signals is first derived. In M-ary DPSK systems, the information is completely contained in this phase difference. For π/4-DQPSK, the BER is derived in a closed form and calculated directly. Numerical results show that for the 24 kBd (48 kb/s) π/4-DQPSK operated at a carrier frequency of 850 MHz and C/I<20 dB, the BER will be dominated by CCI if the vehicular speed is below 100 mi/h. In this derivation, frequency-selective fading is modeled by two independent Rayleigh signal paths. Only one co-channel is assumed in this derivation. The results obtained are also shown to be valid for discriminator detection of M-ary DPSK signals     

Effects of chromatic dispersion on optical coherent-detection systems

Chromatic dispersion induces to a phase-modulated optical signal a constand phase rotation that was never included in most previous studies. When the constant phase shift is removed by a phase-locked loop, the dispersion tolerance of a coherent-detection system is increased. The dispersion tolerance of phase-shift keying (PSK) signal is compared with differential PSK (DPSK) signals by numerical simulation and experimental measurement. Contrary to conventional belief, PSK signal has larger dispersion tolerance than DPSK signal.     

基于光纤四波混频DPSK系统相位噪声提取检测和抑制

差分相移键控(DPSK）在长距离光纤通信系统中有高接收机灵敏度、高频谱效率以及抗非线性效应方面的优势,最近受到广泛关注。在DPSK通信系统中,线性相位噪声和非线性相位噪声是影响系统性能的主要因素。研究了如何利用光纤四波混频（FWM）效应来监测和抑制相位噪声,降低相位噪声对DPSK通信系统的影响。结果表明利用光纤FWM效应产物可以检测相位噪声值,并且基于光纤饱和FWM效应全光限幅器可以有效地降低非线性相位噪声,提高了DPSK系统性能。该结果对研究高速全光通信有重要意义。     

SSB Phase Noise Evaluation of Analog/IF Signals on Standard Digital ATE

This paper presents a low-cost solution for the evaluation of frequency-domain phase noise characteristics for analog/IF signals. The technique is based on 1-bit signal acquisition with a standard digital channel of an Automated Test Equipment (ATE) and a dedicated post-processing algorithm that permits to reconstruct the time-domain phase fluctuations of the analog/RF signal from the captured binary vector. Single SideBand (SSB) phase noise is then obtained based on FFT applied on the reconstructed phase fluctuations. Simulation results demonstrate a very good agreement between SSB phase noise obtained using the proposed digital method and the conventional analog method on a large range of measurement frequency offset. The digital method also permits spur detection and exhibits similar performance than the conventional method in terms of measurement variability. The technique is also validated through hardware measurements on a practical case study, i.e. SSB phase noise evaluation on the 1.3125 MHz sinusoidal signal delivered by the transceiver of a JN5168 wireless microcontroller.     

560 Mbit/s optical PSK heterodyne detection using carrier recovery

An optical PSK heterodyne synchronous detection experiment was performed at a bit rate of 560 Mbit/s using carrier recovery in the IF stage. A receiver sensitivity of -51.6 dBm was achieved, and the power penalty due to the phase noise of the laser diodes was suppressed to less than that of DPSK.<>     

An optical homodyne technique for measurement of amplitude and phase of subangstrom ultrasonic vibrations

An optical homodyne technique is utilized to measure sub-angstrom dynamic mechanical deformations. For measurement in the frequency domain, where synchronous detection is used both the amplitude and phase of the mechanical signal can be measured with a high sensitivity; displacements less than 10^-2Å were measured with normal environment acoustic noise. Measurement in the time domain is also feasible with reduced sensitivity.     

5 Gbit/s direct optical DPSK modulation of a 1530-nm DFB laser

5 Gb/s direct optical differential-phase-shift-keying (DPSK) modulation of a 1530-nm distributed feedback (DFB) laser is demonstrated using injection current modulation with a bipolar signal format. Delay demodulation is performed using an interferometer with a delay time T equal to the duration of one bit. The input and differentially encoded nonreturn to zero (NRZ) signals are shown. The bipolar modulation current signal is basically the time derivative of the NRZ signal. There was no degradation of the optical DPSK signal due to thermal frequency modulation of the laser. The direct DPSK modulation technique avoids the insertion loss and systems complexity of external DPSK modulators