A Comprehensive Study on Crosstalk Suppression Techniques in Fiber Optical Parametric Amplifier by Modulation Format

With the presence of multiple-WDM input signals, ON-OFF keying (OOK)-modulated signals suffer from crosstalk in fiber optical parametric amplifier (OPA) due to cross-gain modulation (XGM) and four-wave mixing (FWM) effects. We demonstrated substantial crosstalk suppression in one-pump OPA by using return-zero differential phase-shift keying (RZ-DPSK) modulation format, which with its pattern-independent amplitude and subunity duty cycle would be effective in reducing the XGM and FWM effects significantly. By using the RZ-DPSK format, the power penalty was improved by at least 0.8 dB over RZ-OOK, non-RZ (NRZ)-DPSK, and NRZ-OOK formats with four 10 Gb/s channels, separated by 200 GHz spacing. With eight 10 Gb/s channels separated by 100 GHz spacing, a Q-factor penalty of the RZ-DPSK signal was reduced by 2.4 dB compared to RZ-OOK counterparts.     

Integrated optical 2 /spl times/ 2 switch for wavelength multiplexed interconnects

A highly compact integrated optical switch is proposed and demonstrated for broadband optical switching applications. Routing of 8 /spl times/ 10 Gb/s data channels is demonstrated using a low-cost 1250-Mb/s control scheme. The advantages of lossless operation, broad optical bandwidth, and nanosecond switching times are leveraged. Multichannel wavelength is exploited for reduced latency, enhanced capacity, and functionality, while retaining compatibility with existing off-the-shelf electronics and transceiver technology. The requirements for optical header processing, wavelength translation, and optical buffering are avoided. Low-penalty multiwavelength transmission is demonstrated for a highly compact sub-mm/sup 2/ amplifying 2 /spl times/ 2 switch. Pattern dependent gain and amplified spontaneous emission are minimized to facilitate 0.0-0.4 dB penalty. Mitigation techniques compatible with the architecture are deployed to reduce the penalty under adverse operating conditions. Control schemes are proposed and demonstrated to facilitate 8 /spl times/ 10 Gb/s optically switched networking.     

Optical Signal Processing Using Tunable Delay Elements Based on Slow Light

Tunable optical delay lines have many applications for high-performance optical switching and signal processing. Slow light has emerged as an enabling technology for achieving continuously tunable optical delays. Delay reconfigurability opens up a whole new field of nonlinear signal processing using slow light. In this paper, the authors review recent advances in slow-light-based optical signal processing, with a focus on the data fidelity after traversing the slow light elements. The concept of slow-light-induced data pattern dependence is introduced and is shown to be the main signal degrading effect. We then propose and experimentally demonstrate phase-preserving slow light by delaying 10 Gb/s differential phase-shift keying (DPSK) signals with reduced DPSK pattern dependence. Spectrally efficient slow light using advanced multilevel phase-modulated formats is further described. With this technique, doubled bit-rate signals can be transmitted through a bandwidth-limited slow light element. We finally show several novel slow-light-based signal processing modules. Unique features such as multichannel operation, variable bit-rate capability, and simultaneous multiple functions are highlighted.     

Optical Signal Processing by Phase Modulation and Subsequent Spectral Filtering Aiming at Applications to Ultrafast Optical Communication Systems

This paper describes optical signal processing based on optical phase modulation and subsequent optical filtering, which is applicable to 160-Gb/s optical time-division multiplexed (OTDM) subsystems. Ultrafast phase modulation of an optical signal is done by self-phase modulation (SPM) and cross-phase modulation (XPM) when an optical pulse passes through a nonlinear optical fiber. Such phase modulation induces the spectral shift of the optical signal. Various types of optical signal processing are realized simply by filtering out the spectral-shifted component. Using SPM-based pulse reshaping in a 500-m-long silica-based highly nonlinear fiber (HNLF), we demonstrate highly stable generation of a 10-GHz 2-ps optical pulse train tunable over the entire C band. A phase-locked loop (PLL) can suppress the slow phase drift of the output pulse train induced by fluctuations of the nonlinear fiber length, enabling the application of the pulse generator to a 160-Gb/s OTDM transmitter. Based on XPM in a 2-m-long photonic crystal fiber, optical time-division demultiplexing of 160-Gb/s optical signals is demonstrated. The long-term stability is drastically improved as compared with the device composed of a conventional silica-based HNLF, because the short fiber length reduces the phase fluctuation between the signal and control pulses. Instead of nonlinear fibers, an electrooptic modulator such as a (LN) modulator also performs the phase modulation in a more practical manner. We propose and demonstrate an optoelectronic time-division demultiplexing scheme for a 160-Gb/s OTDM signal, which consists of an LN phase modulator driven by a 40-GHz electrical clock and an optical bandpass filter (BPF). We also demonstrate base-clock recovery from a 160-Gb/s optical signal with an optoelectronic PLL. The phase comparator is simply composed of an LN phase modulator and an optical BPF, ensuring the stable and reliable operation in the 160-Gb/s receiver.     

Applications of Highly-Nonlinear Chalcogenide Glass Devices Tailored for High-Speed All-Optical Signal Processing

Ultrahigh nonlinear tapered fiber and planar rib Chalcogenide waveguides have been developed to enable highspeed all-optical signal processing in compact, low-loss optical devices through the use of four-wave mixing (FWM) and cross-phase modulation (XPM) via the ultra fast Kerr effect. Tapering a commercial As₂Se₃ fiber is shown to reduce its effective core area and enhance the Kerr nonlinearity thereby enabling XPM wavelength conversion of a 40 Gb/s signal in a shorter 16-cm length device that allows a broader wavelength tuning range due to its smaller net chromatic dispersion. Progress toward photonic chip-scale devices is shown by fabricating As₂S₃ planar rib waveguides exhibiting nonlinearity up to 2080 W^-1ldr km^-1 and losses as low as 0.05 dB/cm. The material's high refractive index, ensuring more robust confinement of the optical mode, permits a more compact serpentine-shaped rib waveguide of 22.5 cm length on a 7-cm- size chip, which is successfully applied to broadband wavelength conversion of 40-80 Gb/s signals by XPM. A shorter 5-cm length planar waveguide proves most effective for all-optical time-division demultiplexing of a 160 Gb/s signal by FWM and analysis shows its length is near optimum for maximizing FWM in consideration of its dispersion and loss.     

Two-Pump Parametric Optical Delays

Continuously tunable optical delay lines based on parametric process in optical fibers are described theoretically and demonstrated experimentally. Performance limits are outlined and compared to alternative approaches capable of continually adjustable delay management. The current record of 105 ns tunable optical delay at 10 Gb/s is presented, with a delay-bandwidth product of 1055.     

Benefit of SPM-based all-optical reshaper in receiver for long-haul DWDM transmission systems

The effectiveness of a self-phase modulation (SPM)-based all-optical reshaper with optically time-division-demultiplexing receiver was experimentally investigated using 42.7-Gb/s carrier-suppressed return-to-zero (CS-RZ) signals. We have confirmed that this scheme is quite effective to suppress the waveform degradation due to optical signal bandlimitation. We have demonstrated 80% spectral efficiency without using polarization demultiplexing by using the all-optical reshaper. We have also demonstrated 50-GHz-spaced 55/spl times/42.7 Gb/s signals transmission over 2500 km, using an optically bandlimited CS-RZ signal and the SPM-based all-optical reshaper in receiver without using polarization demultiplexing. A Q-factor improvement of about 1.5 dB was obtained by using the all-optical reshaper.     

Techniques for Polarization-Independent Cross-Phase Modulation in Nonlinear Birefringent Fibers

We present a theoretical, numerical, and experimental investigation of the polarization dependence of cross-phase modulation in nonlinear birefringent fibers. Two new methods are described for producing a polarization-independent spectral shift through cross-phase modulation of a weak probe signal by a copropagating strong optical pulse. The birefringence of the fiber and spectral separation between the pump and probe signals are shown to play a critical role in determining the polarization dependence of the cross-phase modulation process. The methods are experimentally verified in two different highly nonlinear fibers, and are used to achieve polarization-independent optical switching at speeds of up to 160 Gb/s.     

二阶拉曼和一阶遥泵组合的超长距技术在特高压工程中的应用

随着特高压输电网工程建设,超长距光纤通信传输技术应用也越来越多,10 Gb/s系统超长距光纤通信传输技术在很多特高压工程中都有应用。根据10 Gb/s传输系统的主要因素分析及国内外超长距光纤通信传输技术应用情况和可用技术,结合南方电网某多端直流工程给出了一段超长距光纤通信的试验电路方案。试验电路利用二阶拉曼和一阶遥泵组合方式的超长距光纤通信传输技术可实现470 km的传输距离,并给出了相应的设备配置方案和软件计算结论,为后续工程建设积累了经验。     

Optoelectronic Oscillators Using Direct-Modulated Semiconductor Lasers Under Strong Optical Injection

In this paper, optoelectronic oscillators (OEOs) are demonstrated by using direct-modulated edge-emitting lasers under strong optical injection. The optically injection-locked OEO (OIL-OEO) enables a stable optoelectronic oscillation by converting an optical signal to an electrical signal through a long optical fiber loop. Low RF threshold gain of 7 dB for loop oscillation is attained by utilizing the cavity resonance amplification of an injection-locked semiconductor laser. We investigated both the open- and closed-loop characteristics of the OIL-OEO link by varying the injection locking parameters. Using this novel technique with optimized locking parameters, a 20-GHz RF signal with a phase noise of $-$123 dBc/Hz is successfully achieved without sophisticated frequency or temperature stabilization.      

Optical Wavelength Conversion by Cross-Phase Modulation of Data Signals up to 640 Gb/s

In this paper, all-optical wavelength conversion by cross-phase modulation in a highly nonlinear fiber is investigated. Regenerative properties of the wavelength converter are demonstrated, and the effect of adding Raman gain to enhance the performance of the wavelength converter is shown. The wavelength conversion scheme is demonstrated at the record-high bit rate of 640 Gb/s.     

Terabus: Terabit/Second-Class Card-Level Optical Interconnect Technologies

In the “Terabus” optical interconnect program, optical data bus technologies are developed that will support terabit/second chip-to-chip data transfers over organic cards within high-performance servers, switch routers, and other intensive computing systems. A complete technology set is developed for this purpose, based on a chip-like optoelectronic packaging structure (Optochip), assembled directly onto an organic card (Optocard). Vertical-cavity surface emitting laser (VCSEL) and photodiode arrays (4$,times,$12) are flip-chip bonded to the driver and receiver IC arrays implemented in 0.13-$mu$m CMOS. The IC arrays are in turn flip-chip assembled onto a 1.2-cm$^2$silicon carrier interposer to complete the transmitter and receiver Optochips. The organic Optocard incorporates 48 parallel multimode optical waveguides on a 62.5-$mu$m pitch. A simple scheme for optical coupling between the Optochip and the Optocard is developed, based on a single-lens array etched onto the backside of the optoelectronic arrays and on 45$^circ$mirrors in the waveguides. Transmitter and receiver operation is demonstrated up to 20 and 14 Gb/s per channel, respectively. The power dissipation of 10-Gb/s single-channel links over multimode fiber is as low as 50 mW.     

40 Gb/s Field-Modulated Wavelength Converters for All-Optical Packet Switching

We present a high-functionality photonic integrated circuit that performs field-modulated wavelength conversion. This device incorporates an on-chip sampled grating distributed Bragg reflector laser for wide tunability. Wavelength conversion is accomplished using a preamplified semiconductor optical amplifier photodiode receiver interconnected with a traveling-wave modulator to form a high-speed optical gate. This paper discusses the design and performance of this device, as well as its potential for optical packet switching applications. Error-free wavelength conversion is demonstrated at 40 Gb/s with 1–3 dB power penalty compared with back-to-back transmission over 22 nm of input and output tuning. Output extinction in all cases is greater than 9 dB, and conversion efficiency ranges from $-$2 to $-$ 6 dB over the tuning range. This device additionally demonstrates the capability for external 10 Gb/s modulation, which can be used for optical label encoding.      

640 Gb/s Timing Jitter-Tolerant Data Processing Using a Long-Period Fiber-Grating-Based Flat-Top Pulse Shaper

We report on the use of a novel all-fiber flat-top pulse shaping technique for improving performance and timing jitter tolerance of a switch made for 640-10 Gb/s signal demultiplexing. The jitter tolerance is increased to almost 30% of the one-bit time window, and an increase of the receiver sensitivity by 13 dB compared to a nonflat-top pulse is reported.     

新型多模光纤OM3及DMD测试

以多模光纤万兆传输方案为背景,对新型光缆OM3的传输原理进行了详细介绍,从而使用户可以更好地理解这种新型多模光缆以及相关DMD测试问题.重点介绍了康普SYSTIMAX综合布线系统DMD测试平台,并对DMD测试方法进行了简单的说明.     

EA-Modulator-Based Optical Time Division Multiplexing/Demultiplexing Techniques for 160-Gb/s Optical Signal Transmission

In this paper, 160-Gb/s optical-time-division-multiplexing (OTDM) techniques employing electroabsorption (EA)-modulator-based optical multiplexer are described. The optical multiplexer integrates four EA modulators with free-space optics and enables, stably, to generate an authentic 160-Gb/s OTDM signal. The optical multiplexer possesses a switching capability of modulation format, which originates in the thermo-optic effect in EA waveguide, so that it is possible to generate various phase-coded OTDM signals such as carrier-suppressed return-to-zero (CS-RZ) signal by tuning operation temperatures of the EA modulators. By employing the novel 160-Gb/s optical multiplexer, prototypes of 160-Gb/s OTDM transmitter and receiver were developed. EA modulators are also adopted to optical short pulse source at transmitter side, optical time division demultiplexer, and phase-locked loop (PLL) circuit for clock recovery at the receiver side. The 160-Gb/s system prototype exhibited a superior performance maintaining high stability, and its applicability to practical use is discussed, showing experimental results of 160-Gb/s 635 km field trial on Japan Gigabit Network II (JGN II) optical testbed     

Field demonstration of up to 640 gb/s (64 ch/spl times/10 gb/s) GWP switching networks with a QPM-LN wavelength converter in JGN II test bed

The first field experiment of virtual grouped-wavelength-path switching is successfully demonstrated by using polarization-independent multichannel wavelength conversion in a quasi-phase-matched lithium niobate waveguide and an 8/spl times/8 matrix switch. Contention resolution functionality is confirmed by using wavebands composed of 25GHz spaced, 8- or 64-ch, 10 Gb/s wavelength division multiplexing signals, transmitted through field-installed fibers in Japan Gigabit Network II optical test bed.     

A silicon MEMS optical switch attenuator and its use in lightwavesubsystems

A single-mode fiber connectorized microelectromechanical systems (MEMS) reflective optical switch attenuator operating in the 1550-nm wavelength region is described. The device consists of an electrostatically actuated gold-coated silicon vane interposed in a fiber gap yielding 0.81-dB minimum insertion loss in the transmit state and high transmission isolation in the reflection state with 2.15-dB minimum return loss. The switch attenuators also work as continuously variable optical attenuators capable of greater than 50-dB dynamic range and can be accurately regulated with a simple feedback control circuit. Switching voltages were in the range of 5-40 V and a switching time of 64 μs was achieved. The MEMS switch can be used in optical subsystems within a wavelength-division-multiplexed (WDM) optical network such as optical power regulators, crossconnects, and add/drop multiplexers. We used a discrete array of 16 switch attenuators to implement a reconfigurable 16-channel 100-GHz spacing WDM drop module of an add/drop multiplexer. Thru-channel extinction was greater than 40 dB and average insertion loss was 21 dB. Both drop-and-transmit of multiple channels (11-18-dB contrast, 14-19-dB insertion loss) and drop-and-detect of single channels (>20-dB adjacent channel rejection, 10-14-dB insertion loss) were demonstrated     

Continuous-phase frequency-shift keying with external modulation

A high-speed external modulation scheme for optical continuous-phase frequency-shift keying (CPFSK) is presented. In external frequency-shift keying (FSK) modulation using single-sideband modulation technology, an optical upper/lower sideband (USB/LSB) component with respect to a carrier frequency is selectively generated. However, the FSK-modulated signal has phase discontinuities at the timings of frequency shifts. To overcome the problem, we propose a synchronous control technique that enables continuous phase modulation. In the external CPFSK modulation, the USB/LSB is allowed to shift to the other state when their phases coincide with each other. It is shown that CPFSK with a zero-to-peak frequency deviation of 0.5/spl times/(bit rate) is achieved with this synchronous control. Occupant bandwidth is less than half that of the externally modulated incoherent FSK with phase discontinuities. At a modulation speed of 10 Gb/s, higher order sidelobes are highly suppressed by more than 20 dB at the 20-GHz offset, comparing to a conventional binary phase-shift keying (BPSK). By the use of a Mach-Zehnder interferometer with balanced photodetection, receiver sensitivity is 3-dB greater than that of an on-off keying, as well as a BPSK. In this paper, we report on the experimental demonstration of CPFSK modulation/demodulation. A six-channel wavelength-division-multiplexed, 10-Gb/s CPFSK modulation/demodulation was successfully demonstrated.     

1.3-$mu$m Four-Channel$,times,$10-Gb/s Parallel Optical Transceiver With Polymer PLC Platforms for Very-Short-Reach Applications

A four-channel$times10$-Gb/s parallel optical transceiver for high-capacity very-short-reach applications was developed. The transceiver module was fabricated with low-cost components such as polymer planar lightwave circuit (PLC) platforms and 1.3-$mu$m Fabry–Perot laser diodes (FPLDs). The polymer PLC platform enables the FPLDs or waveguide photodiodes (WGPDs) to be butt-coupled to the polymer waveguide by low-cost passive alignment. Using 1.3-$mu$m FPLDs and single-mode fibers (SMFs) achieves reliable transmission over 600 m. Widening the spacing between the waveguides up to 1 mm suppressed the interchannel crosstalk to below$-39$dB. The fabricated transceiver was operated at 10 Gb/s per channel and it successfully demonstrated 600-m error-free transmission. The sensitivity of each channel was better than$-14$dBm with an interchannel-crosstalk penalty of less than 0.7 dB.