High-speed, burst-mode, packet-capable optical receiver andinstantaneous clock recovery for optical bus operation

This paper describes an enhanced performance version of a high-speed burst-mode compatible optical receiver and its application to 622-Mb/s optical bus operation in conjunction with an instantaneous clock recovery scheme. The receiver is fabricated in a 12 GHz f_t silicon bipolar technology and consists of a differential transimpedance amplifier with an auto-threshold level controller and a high-speed quantizer. Using an InGaAs avalanche photodiode, the typical burst mode sensitivity is around -34 dBm (10^-9 BER) at bit rates up to 1.5 Gb/s with a dynamic range of 26 db for both pseudorandom and burst signals. The results using a laser beam modulated by a high-speed external modulator indicate that the receiver can be operated at bit rates higher than 2 Gb/s. With a worst-case self-resetting time <50 ns for the threshold control circuit, the receiver is usable for optical packet communication where data signals with varying optical power are employed. This receiver was demonstrated in a 622-Mb/s optical bus application where the clock signal was recovered from the packet data signal using a novel high-speed CMOS instantaneous clock recovery IC     

Optical Clock Recovery Using a Polarization-Modulator-Based Frequency-Doubling Optoelectronic Oscillator

We propose and demonstrate a flexible optical clock recovery scheme using a polarization-modulator-based frequency-doubling optoelectronic oscillator (OEO). The proposed system can extract both prescaled clock and line-rate clock from a degraded high-speed digital signal using only low-frequency devices. A simple theory is developed to study the physical basis of the optical clock recovery. The OEO operation from a free-running mode to an injection-locking mode is investigated. The locking range is quantitatively predicted. An experiment is then implemented to verify the proposed scheme. A prescaled clock at 10 GHz and a line-rate clock at 20 GHz are successfully extracted from a degraded 20 Gb/s optical time-division-multiplexed (OTDM) signal. The locking range and the phase noise performance are also experimentally investigated. Clock recovery from data signals that have no explicit subharmonic tone is also achieved. The proposed system can be modified to extract prescaled clock and line-rate clock from 160 Gb/s data signal using all 40-GHz devices.      

All-Optical Clock Recovery for 40-Gb/s MZM-Generated NRZ-DPSK Signals Using a Self-Pulsating DBR Laser

All-optical clock recovery for the nonreturn-to-zero differential phase-shift-keying (NRZ-DPSK) modulation format is demonstrated experimentally at 40 Gb/s using a self-pulsating distributed Bragg reflector laser. The use of a Mach–Zehnder modulator to generate the NRZ-DPSK signal yields a modulated signal spectrum with a weak clock tone. The self-pulsating laser is able to directly recover a clock signal with a root-mean-square timing jitter of 760 fs and an extinction ratio of 13 dB; a preprocessing stage to enhance the clock tone is not required. The timing jitter of the recovered clock signal is characterized for different values of the input signal optical signal-to-noise ratio and for varying amounts of waveform distortion due to polarization-mode dispersion.      

K-means clustering-based data detection and symbol-timing recovery for burst-mode optical receiver

Burst-mode receivers are key components of optical transmission systems, including passive optical networks, and have received much attention in recent years. We present new, efficient methods for burst optical signal detection in burst-mode data transmission using a modified K-means clustering technique. We also develop a data-aided feedforward symbol-timing recovery method based on a polynomial interpolation and maximum-likelihood estimation theory. A performance criterion considering the error caused by the interpolation approximation is derived for this method. The proposed detection and timing recovery approaches can be implemented effectively and rapidly; therefore, they are very suitable for burst-mode receivers. We also provide some numerical examples to demonstrate the performance of the proposed methods.     

All-Optical NRZ-DPSK Clock Recovery Using Chromatic-Dispersion-Induced Clock Tone

All-optical clock recovery (CR) from 10-Gb/s nonreturn-to-zero differential phase-shift-keying (NRZ-DPSK) signal is demonstrated experimentally by introducing the chromatic-dispersion-induced clock tone into a free-running semiconductor optical amplifier (SOA)-based fiber ring laser for achieving mode-locking. Since no special component is required for NRZ-DPSK demodulation, our proposed method is very promising because of its simple configuration and better stability. The good performance of our proposed configuration is fulfilled with a 20-km standard single-mode fiber to regenerate clock tone of the NRZ-DPSK signal. The recovered clock signal with the extinction ratio of 17 dB and the root-mean-square timing jitter of 718 fs is achieved under 2³¹-1 pseudorandom binary sequence NRZ-DPSK signals measurement     

Prescaled clock recovery based on small timing misalignment of datapulses

A simple and robust prescaled clock recovery technique is analyzed and demonstrated. An electrical clock is extracted from an ultra-high-speed time-division multiplexed (TDM) RZ signal using a “classic” approach to clock recovery with a detector and a bandpass filter (BPF). A subharmonic tone at the base rate frequency is generated by inducing a small misalignment between adjacent pulses in the transmitted data. The subharmonic tone is recovered as a clock signal at the receiver. Numerical calculations clarify the effect of filter bandwidth, word length, and strength of timing shift on the received timing jitter. Furthermore, it is found numerically that correlated TDM channels will decrease the jitter of the recovered clock considerably. A clock recovery circuit is implemented into an experimental 40 Gb/s and 80 Gb/s optical TDM (O-TDM) system without any observed penalty. Measurements of the timing jitter of the recovered prescaled clock have been performed to verify the numerical results. A 10 GHz clock signal with subpicosecond root-mean-square timing jitter is recovered from a 40-Gb/s O-TDM sequence without a phase-locked loop (PLL) configuration. By using a PLL-configuration, the timing jitter is reduced further by 50%. A discussion on the influence on transmission capacity is performed in general and for nonlinear optical communication systems in particular     

Burst-mode clock and data recovery in optical multiaccess networks using broad-band PLLs

Broad-band phase-locked loops (PLLs) are proposed for burst-mode clock and data recovery in optical multiaccess networks. Design parameters for a charge-pump PLL-based clock and data recovery (CDR) with fast phase acquisition are derived using a time-domain model that does not assume narrow loop bandwidth or small phase errors. Implementation in a half-rate CDR circuit confirms a clock phase acquisition time of 40 ns, or 100 bits at 2.488-Gb/s rate, and data recovery at 1.244-Gb/s rate with a bit-error rate of 1/spl times/10/sup -10/ (2/sup 14/-1 pseudorandom binary sequence with Manchester-encoding). The CDR was fabricated in complementary metal-oxide-semiconductor 0.18-/spl mu/m technology in an area of 1/spl times/1 mm/sup 2/ and consumes 54 mW of power from a 1.8-V supply.     

A Standalone Burst-Mode Receiver With Clock and Data Recovery, Clock Phase Alignment, and RS(255, 239) Codes for SAC-OCDMA Applications

We demonstrate a standalone (no global clock) burst-mode receiver (BMRx) for a 7 times 622 Mb/s incoherent spectral-amplitude-coded optical code-division multiple-access system. The receiver provides the following functions: quantization (intensity noise filtering), clock and data recovery, burst-mode functionality (automatic phase acquisition) using a clock phase aligner (CPA), framing (for byte synchronization), and forward-error correction (FEC) using a (255, 239) Reed-Solomon decoder. The receiver provides an instantaneous (zero preamble bit) phase acquisition time for any phase step (plusmn2pi rads) between consecutive packets. With the CPA, we report a zero packet loss ratio (PLR) for up to four simultaneous users and more than a 300-fold improvement in the PLR for a fully loaded system. The BMRx also accomplishes more than 2.5 dB of coding gain, and achieves error-free (bit-error rate ) operation for a fully loaded system.     

A Burst-Mode 3R Receiver for 10-Gbit/s PON Systems With High Sensitivity, Wide Dynamic Range, and Fast Response

The burst-mode 3R receiver using monolithic ICs for 10-Gbit/s-class optical access networks is reported. In a point-to-multipoint access system like a passive optical network (PON), the receiver at the optical line terminal (OLT) must be able to handle burst-mode optical packets with significantly different powers and phases. An OLT receiver with high sensitivity with instantaneous response to burst inputs is desired for widening the accommodation area and for high efficiency in PON uplinks. Currently, the diffusion of high-speed Internet connection services represented by fiber to the home services at 1.25 Gbit/s is remarkable and the standardization of the next-generation system operating at 10 Gbit/s has started in IEEE. We first discuss the issues in the implementation of 10-Gbit/s-class PON systems, focusing on securing the accommodation area and the quality of the service comparable with those of the deployed system. Against that background, we propose target specifications for sensitivity, a dynamic range and response speed of the 10-Gbit/s-class burst-mode receiver so as to secure the power budget and the upstream efficiency comparable with those of the already-installed systems. Our burst-mode 3R receiver was designed to meet the above requirements and developed using monolithic ICs of transimpedance amplifier, limiting amplifier, and clock and data recovery circuit fabricated by using SiGe BiCMOS technologies along with a p-i-n photodiode. High sensitivity of , a wide dynamic range of over 16.5 dB, and quick response time of 75 ns were confirmed for burst inputs with extremely different powers.     

Development of GPON upstream physical-media-dependent prototypes

This paper presents three new gigabit-capable passive optical network (GPON) physical-media-dependent (PMD) prototypes: a burst-mode optical transmitter, an avalanche photodiode/transimpedance amplifier (APD-TIA), and a burst-mode optical receiver. With these, point-to-multipoint (P2MP) upstream transmission can be realized in a high-performance GPON at 1.25 Gb/s. Performance measurements on the new burst-mode upstream PMD modules comply with GPON uplink simulations. The laser transmitter can quickly set and stabilize the launched optical power level over a wide temperature range with better than 1-dB accuracy. A burst-mode receiver sensitivity of -32.8 dBm (BER=10/sup -10/) is measured, combined with a dynamic range of 23 dB at a fixed APD avalanche gain of 6. Full compliance is achieved with the recently approved ITU-T Recommendation G.984.2 supporting an innovative overall power-leveling mechanism.     

All-optical enhancement of clock and clock-to-data suppressionratio of NRZ data

A scheme for all-optical enhancement of clock and clock-to-data suppression ratio of nonreturn-to-zero (NRZ) data based on self-phase modulation is proposed and demonstrated. More than 3-dB clock enhancement and 11-dB clock-to-data suppression ratio enhancement has been realized by a semiconductor optical amplifier (SOA) and fiber Bragg grating (FBG) in reflection. Clock enhancement of more than 6 dB is possible using a FBG in transmission. Using this technique, all-optical clock recovery from NRZ data has been demonstrated     

10Gb/s突发模式时钟数据恢复电路设计

突发模式的时钟数据恢复是10G EPON系统的关键技术之一。本文介绍了一种基于XNOR/XOR门的振荡器,分析了其工作原理与性能,以此为基础设计了半速率突发时钟恢复电路。设计采用SMIC 0.13?m CMOS工艺进行了流片验证,芯片面积为675?m ? 625?m。测试结果表明,该电路可以即时的实现10Gbit/s的突发数据恢复,恢复出的时钟数据符合IEEE 802.3av标准,锁定时间小于5bit。     

All-Optical Clock Recovery Using Erbium-Doped Fiber Laser Incorporating an Electroabsorption Modulator and a Linear Optical Amplifier

We demonstrated a 10-GHz all-optical clock recovery system using an erbium-doped fiber laser that incorporates an electroabsorption modulator and a linear optical amplifier. Stable pulses with peak power of 200 mW and pulsewidth of 6 ps are obtained. The output power and the pulsewidth of the recovered clock pulses are independent of the input data pattern. Stable optical clock can still be observed when the input data rate varies by more than 60% of the fundamental frequency without any optical tunable delay line inside the laser cavity. The scheme is essentially wavelength transparent for the whole C-band which recovers clock pulses from input data wavelength between 1525 and 1565 nm     

光接入网络中的数字信号处理技术

采用先进的数字信号处理(DSP)技术,在发射机和接收机分别引入预处理和后处理,以提高光接入网络的频谱效率并延长传输距离。研究了一种基于光超奈奎斯特(Super-Nyquist)滤波的类9状态正交振幅调制(9QAM)信号多模均衡(MMEQ)后端DSP算法,使用这种方案,能够有效提高频谱效率,实现了频谱效率高达4 bps/Hz的正交移相键控(QPSK)信号传输;还研究了一种基于数字SuperNyquist信号前端预处理的方案,此方案的优点是不需要光预滤波即可达到相同的频谱效率。使用一个采用直接调制激光器(DML)、直接探测和数字均衡技术的高速无载波幅度相位-64状态正交振幅调制(CAP-64QAM)系统,在20 km标准单模光纤(SSMF)上实现了创纪录的60 Gbit/s CAP-64QAM信号传输;使用相干探测,实现了速率高达100 Gbit/s的64状态正交振幅调制-正交频分复用(16QAM-OFDM)实时传输系统,解决了实时OFDM信号处理中的关键问题。     

Bit rate and wavelength transparent all-optical clock recovery scheme for NRZ-coded PRBS signals

All-optical clock recovery from 40-Gb/s nonreturn-to-zero (NRZ) pseudorandom binary sequence data streams based on self-pulsating lasers is presented. A compact preprocessing circuit is utilized to convert an NRZ signal to a pseudoreturn-to-zero sequence before injecting into the optical clock. It comprises a semiconductor optical amplifier followed by a periodical wavelength-division-multiplexing demultiplexer filter. A stable sinusoidal clock signal with a root-mean-square jitter below 700 fs is detected at the output of the self-pulsating laser within data dynamic range of more than 8 dB. The performance of the all-optical clock recovery scheme is investigated by varying the bit rates between 39.81 and 43.02 Gb/s as well as for various wavelengths in the C-band.     

A multibitrate burst-mode CDR circuit with bit-rate discriminationfunction from 52 to 1244 Mb/s

We fabricate and assess a clock and data recovery (CDR) circuit with a bit-rate discrimination (BRD) function that can receive burst-mode signals containing packets of different bit rates. The clock recovery circuit in the CDR circuit consists of gated oscillators (GOs) for handling the burst-mode signals, whose bit rates vary with each packet. Moreover, we improve the performance of the clock recovery circuit based on GOs against the bit rate unevenness around each bit rate. By combining an agile clock recovery circuit and a digital BRD circuit, the CDR circuit can handle multiplexed bit rates. Tests show that the circuit offers excellent performance for the multiplexed bit rates of nonreturn-to-zero 52, 155, 622, and 1244 Mb/s     

Enhancement of clock component in a nonreturn-to-zero signal through beating process

For optical clock recovery of nonreturn-to-zero (NRZ) signals of more than 40 Gb/s, we propose and experimentally demonstrate a simple clock recovery scheme through beating process between the carrier frequency component and one of the clock frequency components in modulated NRZ signals. The proposed scheme consists of a circulator, a variable optical attenuator (VOA), and two fiber Bragg grating (FBG) filters. With FBG filters and a VOA, the proposed scheme can equalize the amplitudes of two extracted frequency components for a maximum clock-to-noise ratio (CNR). Through this scheme, we have squared the adjustment range of the VOA and achieved an enhanced CNR of more than 15 dB before the receiver in experiment. Bit error rate (BER) curves for back-to-back and 80 km transmissions showed that BERs of less than 10⁻¹¹ can be obtained without error floors for both cases. We expect that the proposed scheme can operate as an efficient clock extraction system for high-speed optical communications.     

Time-transfer performance in burst-mode communication systems

This paper studies the performance of the clock transfer scheme for burst-mode communication systems for which data are received during short, equally spaced intervals. Its main focus is on satellite-based time-division multiple-access (TDMA) communication systems with data regeneration and switching onboard the satellite, although the results apply to other TDMA systems as well. The system reference clock is generated onboard from an incoming, very stable ground source, based on a burst-mode demodulator that extracts the clock from a discontinuous modulated carrier due to the bursty nature of TDMA signals. If good enough, this onboard regenerated clock avoids the use of bulky and expensive clocks in the satellite payload and can act as the master clock of the TDMA system     

40-Gb/s optical 3R regenerator using electroabsorption modulatorsfor optical networks

A 40-Gb/s optical retiming, reshaping, and retransmitting (3R) regenerator was proposed and demonstrated using wavelength converters based on electroabsorption (EA) modulators for effectively implementing 40-Gb/s-based or higher bit rate wavelength division multiplexing (WDM) optical networks. The proposed optical 3R regenerator is configured in a very simple architecture, consisting of two wavelength converters, a clock recovery section, and an optical clock generator section. Furthermore, the stable and polarization-insensitive operation, as well as simple adjustment of an optimal operation condition of our proposed optical 3R regenerator, were confirmed by conducting transmission experiments. To investigate the applicability of optical 3R regenerators to optical networks, it was evaluated by insertion between two 500-km-long segments of transmission line. A Q-factor improvement of about 1.5 dB was obtained after transmission over 1000 km, compared to evaluation without the regenerator. This type of optical 3R regenerator proves extremely useful in future high-speed and scaleable all-optical networks     

Optical Noise Tolerance in a Polarization-, Wavelength-, and Filter-Free All-Optical Clock Recovery System Based on a Monolithic Mode-Locked Laser

We experimentally investigated optical noise tolerance of a polarization-, wavelength-, and filter-free all-optical clock recovery system based on a monolithic mode-locked laser diode. The results showed that for input signal degradation, the jitter of the recovered clock did not degrade to approximately 8 dB/nm of the optical SNR. We also compared the clock recovery performance as functions of the wavelength and the modulation format (on-off keying and phase-shift keying) of the input data signals. We revealed that no significant changes were measured in the clock recovery performance despite such changes in the parameters of the input data signals, indicating that noise-tolerable clock recovery is expected, retaining the polarization- and the filter-free operations, regardless of the wavelength and the modulation format of the input data signals, by using our new scheme.