A high capacity data centre network: simultaneous 4-PAM data at 20 Gbps and 2 GHz phase modulated RF clock signal over a single VCSEL carrier

Optical fibre communication technologies are playing important roles in data centre networks (DCNs). Techniques for increasing capacity and flexibility for the inter-rack/pod communications in data centres have drawn remarkable attention in recent years. In this work, we propose a low complexity, reliable, alternative technique for increasing DCN capacity and flexibility through multi-signal modulation onto a single mode VCSEL carrier. A 20 Gbps 4-PAM data signal is directly modulated on a single mode 10 GHz bandwidth VCSEL carrier at 1310 nm, therefore, doubling the network bit rate. Carrier spectral efficiency is further maximized by modulating its phase attribute with a 2 GHz reference frequency (RF) clock signal. We, therefore, simultaneously transmit a 20 Gbps 4-PAM data signal and a phase modulated 2 GHz RF signal using a single mode 10 GHz bandwidth VCSEL carrier. It is the first time a single mode 10 GHz bandwidth VCSEL carrier is reported to simultaneously transmit a directly modulated 4-PAM data signal and a phase modulated RF clock signal. A receiver sensitivity of ?10. 52 dBm was attained for a 20 Gbps 4-PAM VCSEL transmission. The 2 GHz phase modulated RF clock signal introduced a power budget penalty of 0.21 dB. Simultaneous distribution of both data and timing signals over shared infrastructure significantly increases the aggregated data rate at different optical network units within the DCN, without expensive optics investment. We further demonstrate on the design of a software-defined digital signal processing assisted receiver to efficiently recover the transmitted signal without employing costly receiver hardware.     

Maximizing capacity,flexibility and efficiency in G-PON networks using VCSEL-based OOK and 2/4-PAM formats

This work experimentally demonstrates the potential of multi-level pulse amplitude modulation with direct detection to maximize carrier spectral efficiency and double the Gigabit passive optical networks (G-PON) network data rate. Three scenarios have experimentally been exploited. First, a 1310?nm vertical surface-emitting laser (VCSEL) has directly been modulated with a 10?Gbps OOK data. A receiver sensitivity of ?19.11?dBm is attained, and a successful error free transmission over 22?km SMF fibre achieved, with a transmission penalty of 0.46?dB. To maximize carrier spectral efficiency, 2/4 PAM modulation formats are adopted respectively. A receiver sensitivity of ?14.64 and ?11.63?dBm is attained for 2-PAM and 4-PAM formats respectively. However, a 3.21?km fibre transmission introduces a penalty of 0.64 and 3.30?dB for 2-PAM and 4-PAM formarts respectively. 2/4-PAM modulation formats significantly increase the aggregated data rate at different ONUs within the G-PON without expensive optics investment, though at the cost of reduced transmission reach due to the high bitrate attained. We further demonstrate the design of a software defined digital signal processing assisted receiver to recover the 2/4 PAM transmitted signal without employing costly receiver hardware.     

VCSEL-based differential modulation technique for high-speed gigabit passive optical networks

With the convergence towards 5G, optical networks need to be upgraded to support the emerging data tsunami. This work experimentally demonstrates the first real-time transmission of 20?Gbps over a class 10G 1550?nm vertical cavity surface emitting laser (VCSEL) in the context of on-off-keying (OOK) modulation format, by employing VCSEL differential drive mode technique, for adoption in high-speed gigabit passive optical networks (GPONs). Two OOK data streams each with 10?Gbps are differentially modulated onto a single VCSEL, therefore generating an aggregated data rate of 20?Gbps OOK signal. A receiver sensitivity of -13.36?dBm is experimentally achieved. Through extinction ratio optimization, an error free transmission over 24.7?km single mode fibre is attained, with a transmission penalty of 1.91?dB. Our proposed technique alleviates band-limitation of the VCSEL carrier, and doubles the channel data rate without replacing the transmitter optics.     

Real-time wavelength reuse based on Bragg trans-reflection for dynamic reference frequency and data transfer in Datacom

ABSTRACT

We experimentally demonstrate the first VCSEL-based all-optical wavelength reuse technique with reconfigurable fibre Bragg grating add and drop multiplexer. EDFA gain saturation and Bragg trans-reflection effect on a single FBG are respectively, adopted for full-duplex reference frequency and data transfer. A 1550 nm energy-efficient VCSEL is modulated with 1.7?GHz clock signal and transferred downstream over 26.6?km fibre OLT attain a phase noise stability of ?54.01 dBc/Hz at 10?kHz offset frequency. A saturated EDFA is exploited to optically reduce the peak-to-peak voltage of the incoming downstream RF, allowing for wavelength reuse with 10?Gbps upstream data. A 1.57 dB transmission penalty is incurred over the transmission fibre. An all-passive OADM is developed exploiting Bragg trans-reflection at 1549.45?nm. The reflected wavelength is routed over another 24.7?km fibre network attaining an extinction ratio of 6.1?dB and a SNR of 5.8?dB. This work provides an all-optical technique for routing and spectral management in flexible networks.     

All-optical wavelength reuse with simultaneous upstream data and PPS timing signal transfer for flexible optical access networks

All-optical wavelength reuse is a viable approach for realization of low cost colourless ONUs. We experimentally demonstrate a novel all-optical wavelength reuse technique with simultaneous upstream data and pulse-per-second signal transfer, exploiting EDFA gain saturation with a holding beam. A DFB laser is modulated with 8.5 Gbps data and transmitted downstream over 24.7 km fibre. A saturated EDFA located at the ONU is adopted to reduce the extinction ratio of the downstream data from 6.2 dB to 839.1 mdB. This allows for data rewrite and wavelength reuse for upstream transmission. Receiver sensitivities of ?20.19 dBm and ?19.60 dBm are achieved at back-to-back analysis and 24.7 km downstream link respectively. A holding beam is further exploited to attain simultaneous carrier reuse and PPS clock upstream transfer. PPS jitter stability of 1.01 × 10^-08 ns and 6.64 × 10^-08 ns are attained respectively. This work offers a convenient all-optical wavelength reuse solutions for optical access networks.     

Dynamic O-band to C-band wideband wavelength converter for integrated VCSEL-based optical interconnects

ABSTRACT

Real-time wavelength conversion and traffic routing at key network nodes is a fundamental requirement for current optical interconnects. This work experimentally demonstrates a broadband wavelength conversion from O-band to C-band employing commercially available, power efficient VCSELs. A 1310?nm VCSEL is directly modulated with 8.5 Gbps data and transmitted over 22?km G. 652 fibre with a 0.53 dB penalty. The received data is used to run a 1550?nm VCSEL located at the network integration node, achieving the first reported wavelength conversion from O-to-C-band. VCSEL wavelength tuneability with changing bias current functionality is further exploited to route the converted wavelength over 400?GHz spectra range for integration into wavelength flexible networks. The newly converted wavelength is transmitted over 24.7?km of G. 655 fibre, incurring a maximum penalty of 1.86?dB. Results from this work proves an enabling development technology for wavelength converters for transparent contention resolution in current and future optical Interconnects.     

10 Gbit/s tunable dual-wavelength nonreturn-to-zero-to-return-to-zero data-format transformer based on a non-direct-current-biased fabry-perot laser diode

We demonstrate the conversion of a nonreturn-to-zero (NRZ)-formatted electrical data stream into a wavelength-tunable return-to-zero (RZ)-formatted optical pulse code by externally seeding a synchronously sinusoidal-modulated Fabry-Perot laser diode (FPLD) with optical pseudorandom binary-sequence data at 10 Gbits/s (Gbps). The FPLD without a dc-biased current was modulated by use of a power-amplified sinusoidal wave signal (approximately 25.6 dBm) as an NRZ-to-RZ data-format transformer, which is regeneratively amplified by a closed-loop erbium-doped fiber amplifier. The gain switching and on-off keying operation of the FPLD is initiated under the seeding of self-feedback and external-injection signals. A maximum wavelength tuning range of 30 nm with a side-mode suppression ratio of greater than 36 dB is obtained. The power penalty of the NRZ-to-RZ data-format conversion at 10 Gbps is 1.5 dB.     

40Gbps甚短距离并行光传输系统接收电路的设计与实现

给出了符合OIF-VSR5规范的40Gbps甚短距离光传输系统接收电路的设计与实现。该接收电路实现简单,由一片转换芯片及光接收模块构成。其特点是充分利用现场可编程门阵列(FPGA)内嵌的高速收发器成功实现了16×2.488Gbps和12×3.318Gbps信号的发送和接收,并且在一片FPGA上实现了诸如时钟数据恢复、串/并转换、帧同步、通道对齐、12-16路映射等全部功能。基于二分查找法的帧同步电路则大大提高了转换芯片的工作速度。Signaltap Ⅱ逻辑分析仪的测试结果表明接收电路工作正常,性能良好。在此基础上,给出了VSR5实验系统的点到点测试方法,通过12通道垂直腔面发射激光器并行接收模块和7m 12芯多模带状光纤,将发送电路与接收电路相连,实现了OC768/STM-256 40Gbps的点到点测试,测试结果表明系统误码率小于10~(-12)。     

Reflectenna: a quasi passive on?off keyed microwave telemetry system for remote sensor applications

A method to transmit one-directional wireless data with low power consumption has been investigated. This system, called the 'reflectenna', works on the principle of transmitting information by modulating an incident continuous wave carrier signal prior to re-transmission and consists of two orthogonally linear polarised, micromachined microstrip patch antennas and a single-pole-single-throw switch that modulates the carrier signal. This quasi-passive method to transmit data has been tested with a transceiver system that transmits a 10 GHz carrier signal and demodulates the received signal reflected back from the reflectenna. The carrier signal was modulated with a 2 kHz square wave and a link with a range up to 25 m was achieved.     

Performance of burst-mode receivers for optical digital pulse position modulation in passive optical network application

A DC coupled burst-mode receiver for digital pulse position modulation (DPPM) is proposed for the first time. An analysis of the potential performance benefits of using such a receiver configuration in the upstream of a passive optical network is given. An optical pre-amplifier is assumed. Bit error rate expressions are derived and the performance is evaluated in terms of sensitivity and threshold acquisition penalty. Results are compared with a DC-coupled on?off keyed non-return-to-zero burst-mode receiver, and it is seen that DPPM?s continuous mode sensitivity advantage (about 8 dB for the optimal case) is only reduced to 7.7 dB when overhead preamble is restricted to 12 bits and 6 dB when restricted to 6 bits. Thus, if necessary, DPPM can almost recover its sensitivity advantage by a trade off with preamble length. As such DPPM can potentially offer an increase in optical network unit numbers by a factor of 4 or, alternatively, an increase in range of around 20 km.     

A simultaneous all-optical half/full-subtraction strategy using cascaded highly nonlinear fibers

Using non-linear effects such as cross-gain modulation (XGM) and cross-phase modulation (XPM) inside two highly non-linear fibres (HNLF) arranged in cascaded configuration, a simultaneous half/full-subtracter is proposed. The proposed simultaneous half/full-subtracter design is attractive due to several features such as input data pattern independence and usage of minimal number of non-linear elements i.e. HNLFs. Proof of concept simulations have been conducted at 100 Gbps rate, indicating fine performance, as extinction ratio (dB) > 6.28 dB and eye opening factors (EO) > 77.1072% are recorded for each implemented output. The proposed simultaneous half/full-subtracter can be used as a key component in all-optical information processing circuits.     

Feed-forward linearisation technique for impulse radar ultra-wideband over fibre

The authors present the linearisation of impulse radar ultra-wideband (IR-UWB) transmission system over fibre. The radio frequency signal of IR-UWB is transmitted over 50 km of the single mode fibre (SMF) using external Mach Zehnder modulator (MZM), amplified, linearised and detected by photodetector receiver. For improving the linearity and suppressing the four-wave mixing (FWM) caused by semiconductor optical amplifier (SOA) and 50 km SMF, the system uses feed-forward technique. Link performance was evaluated for two IR-UWB signals to suppress the FWM. The theoretical simulation results demonstrate a distortion cancellation that is produced by SOA of better than 25 dB over 1550 nm single mode optical fibre cable. In addition, the characteristic transmission of UWB pulse radio through 50 km single mode radio over fibre (RoF) system, such as BER measurements to evaluate the performance of the UWB with respect to different laser power output level, is investigated. This technique has been used to successfully transmit indirectly modulated data using laser diode at 10 GB/s light-wave transmission system.     

Multisection optical parametric–Raman hybrid amplifier for terabit+ WDM systems

We demonstrate flat-gain wide bandwidth Raman-Fiber optical parametric hybrid amplifier for wavelength division multiplexed systems (WDM). Raman-parametric amplifiers exploit system non-linearities which are otherwise inevitable in evolving WDM systems. Investigations show that the pumps of parametric amplifier and Raman amplifier can be carefully selected at wavelengths, to give gain over complementary bandwidth regions, resulting in wide bandwidth with low gain ripple. Results show a flat gain of 24.3 dB for 12 × 100 Gbps WDM system with lowest ripple of less than 2.78 dB reported over 220 nm bandwidth for Raman-FOPA hybrid.     

A PWM and PAM Signaling Hybrid Technology for Serial-Link Transceivers

A 1-Gb/s 0.18- mum CMOS serial-link transceiver using multilevel pulse-width and pulse-amplitude modulation (PWAM) signaling and a pre-emphasis technique is presented. Based on the PWAM technique, the transmit signaling is implemented to effectively push high data rates through bandwidth- limited channels. The clock is implicitly embedded in the 4-bit data stream, and the associated overhead needed in the clock-and-data recovery circuitry can be mitigated. In addition, the pin count can be reduced by transferring the data channels and the clock channel over a single transmitted channel. The recovered clock has an rms jitter of 5.9 ps at 250 MHz, and the retimed data have an rms jitter of 13.7 ps at 250 Mb/s. The occupied die area is 1.65 X 1.40 mm². The transmitter and receiver power consumption is 86 and 45 mW, respectively.     

A fully integrated high IP1dB CMOS SPDT switch using stacked transistors for 2.4 GHz TDD transceiver applications

A transmit/receive (T/R) switch is an essential module of every modern time division duplex (TDD) transceiver circuit. A T/R switch with high power handling capacity in CMOS process is difficult to design due to capacitive coupling of radio frequency signals to the substrate. This paper proposes a single-pole-double-throw (SPDT) T/R switch designed in a standard Silterra 130 nm CMOS process for high-power applications like RFID readers. The results reveal that, in 2.4 GHz ISM band, the proposed switch exhibits a very high input P1dB of 39 dBm with insertion loss of only 0.34 dB and isolation of 40 dB in transmit mode but 1.08 dB insertion loss and 30 dB isolation in receive mode. Stacked thick-oxide triple-well transistors, resistive body floating and negative control voltages are used to achieve such lucrative performance. Moreover, the chip size of the designed switch is only 0.034 mm² as bulky inductors and capacitors are avoided. The Monte-Carlo and corner analyses confirm that the performance of the switch is also quite stable and reliable.     

自由空间量子密钥分发中的信号同步解决方案

针对目前自由空间量子密钥分发（QKD）中的信号同步这一难点问题,提出一种采用外置光信号来解决信号同步问题的方案——光同步方案。在发送端利用声光调制器将外置激光器的连续激光分割成周期光脉冲序列,并作为同步光信号发送给接收端。接收端采用光电倍增管接收同步光脉冲信号,生成一个与发送端严格同步的信号,以此作为接收端的时基标准来进行单光子计数。采用高频的内部时钟信号来“监视”接收到的同步信号,从而提高计数准确性。该方案具有长距离性、无线性、低复杂度等特点,已成功应用于一个基于B92协议的自由空间QKD系统中。     

地震数据采集无线同步技术研究

针对地震勘探中时间同步问题和其他数据采集领域的采集同步问题,设计并完善基于GPS授时技术的同步技术方案,利用GPS授时信号全方位、实时性、连续性和高精度的特点,以GPS的PPS信号为基准来校准本地时钟,采用单片机和无线通信技术实现数据采集同步。通过对无线遥测各道地震数据进行同步处理,解决了当地震勘探仪采集的道数增多时数据采集和存储的实时性问题,特别是解决了未来数字式检波器中独立同步和分时处理等关键问题。     

All optical format conversion at 10 Gbps using SOA and optical band-pass filter

In this paper, an all-optical non return-to-zero (NRZ) and return-to-zero (RZ) modulation format converter using a single semiconductor optical amplifier (SOA) and an optical band-pass filter (OBPF) is proposed. The format converter consists of a single SOA which is acting as a nonlinear element to broaden the spectrum of the input signal and the OBPF which is used to extract the special spectrum from the broadened spectrum. By adopting the ultra-fast SOA model associated with optical system software, the 10 Gbps NRZ and RZ format conversion is successfully demonstrated with simulation. We also demonstrate the proof-of-principle experiment at 10 Gbps by using the test SOA and OBF converter. The converted NRZ is achieved with an output extinction ratio of 11.51 dB. The BER is 5.5 × 10^?9 while the power of NRZ is ?10 dBm and the BER is 1.0 × 10^?9 when the power of RZ is ?14 dBm. The experimental results coincide well with the simulated results. The proposed scheme is robust and has potential for applications in future optical networks.     

Frequency division transmission imaging and synthetic aperture reconstruction

In synthetic transmit aperture imaging only a few transducer elements are used in every transmission, which limits the signal-to-noise ratio (SNR). The penetration depth can be increased by using all transmitters in every transmission. In this paper, a method for exciting all transmitters in every transmission and separating them at the receiver is proposed. The coding is done by designing narrow-band linearly frequency modulated signals, which are approximately disjointed in the frequency domain and assigning one waveform to each transmitter. By designing a filterbank consisting of the matched filters corresponding to the excitation waveforms, the different transmitters can be decoded at the receiver. The matched filter of a specific waveform will allow information only from this waveform to pass through, thereby separating it from the other waveforms. This means that all transmitters can be used in every transmission, and the information from the different transmitters can be separated instantaneously. Compared to traditional synthetic transmit aperture (STA) imaging, in which the different transmitters are excited sequentially, more energy is transmitted in every transmission, and a better signal-to-noise-ratio is attained. The method has been tested in simulation, in which the resolution and contrast was compared to a standard synthetic transmit aperture system with a single sinusoid excitation. The resolution and contrast was comparable for the two systems. The method also has been tested using the experimental ultrasound scanner RASMUS. The resolution was evaluated using a string phantom. The method was compared to a conventional STA using both sinusoidal excitation and linear frequency modulated (FM) signals as excitation. The system using the FM signals and the frequency division approach yielded the same performance concerning both axial (of approximately equal to 3 wavelengths) and lateral resolution (of approximately equal to 4.5 wavelengths). A SNR measurement showed an increase in SNR of 6.5 dB compared to the system using the conventional STA method and FM signal excitation.     

Microwave generation with photonic frequency octupling using a DPMZM in a Sagnac loop

A photonic microwave signal generation scheme with frequency octupling is proposed and experimentally demonstrated. The scheme is based on bi-directional use of a dual-parallel Mach–Zehnder modulator (DPMZM) in a Sagnac loop. The two sub-modulators in the DPMZM are driven by two low-frequency signals with a π/2 phase difference, and the dc biases of the modulator are all set at the maximum transmission points. Due to the velocity mismatch of the modulator, only the light wave along the clockwise direction is effectively modulated by the drive signals to generate an optical signal with a carrier and ±4th order sidebands, while the modulation of the light wave along the counterclockwise direction is far less effective and can be ignored. By properly adjusting the polarization of the light wave output from the Sagnac loop, the optical carrier can be significantly suppressed at a polarizer, and then an optical signal with only ±4th order sidebands is generated. In the experiment, a pure 24-GHz microwave signal without additional phase noise from the optical system is generated using a 3-GHz local oscillator signal. As no electrical or optical filter is used, the photonic frequency octupler is of good frequency tunability.