Ultrafast Forwarding Architecture Using a Single Optical Processor for Multiple SAC-Label Recognition Based on FWM

This paper investigates bidirectional transmission using four wave mixing (FWM) for wavelength division multiplex passive optical network (WDM-PON) applications. A semiconductor optical amplifier (SOA) is considered to generate FWM. A use of FWM makes it possible to convert a downstream data wavelength to a different wavelength, which is used for upstream transmission. The wavelength generated by FWM can realize bidirectional transmission with a single fiber. We assume intensity modulation (IM) for both up- and down-transmission. Both an injection locked Fabry-Perot laser diode (FP-LD) transmitter and a transmitter with an external modulator are considered for upstream transmission. In both cases, an extinction ratio (Ex) of downstream signal light is very important for both sending and receiving properties and the Ex influences the bit error rate (BER) property. This paper clarifies the relationship between the Ex of FWM and the power penalty ΔP. This paper also clarify the Ex value of FWM as a function of input signal Ex using a model SOA theoretically. Fundamental transmission experiments, 10 Gbit/s downstream and 2.5 Gbit/ s upstream, using both types of transmitters confirmed the possibilities of the bidirectional transmission using FWM.

Four-wave mixing (FWM) in semiconductor optical amplifiers (SOAs) has several important features, such as, high speed and high FWM conversion efficiency as well as optical demultiplexing (DEMUX) (Mecozzi et al., 1995; Mecozzi & Mrk, 1997; Das et al., 2000). The are several applications of FWM in SOAs for all-optical devices, such as, wavelength converters (Vahala et al., 1996), optical samplers (Inoue & Kawaguchi, 1998), optical phase conjugators (Kikuchi & Matsumura, 1998) and optical multiplexers/demultiplexers (Kawanishi et al., 1997; Kawanishi et al., 1994; Morioka et al., 1996; Uchiyama et al., 1998; Tomkos et al., 1999; Kirita et al., 1998; Buxens et al., 2000) have been demonstrated for optical communication systems. When a pulse of a time-multiplexed signal train (for example, a probe pulse) and a pump pulse are injected simultaneously into an SOA, gain and refractive index in the SOA are modulated and an FWM signal is generated by the modulations. Thus, we can obtain a demultiplexed signal as an FWM signal at the output of SOA. All-optical demultiplexing has been experimentally demonstrated up to 200 Gbit/s (Morioka et al., 1996). Tomkos et al., (Tomkos et al., 1999) suggested a number of ways to improve the performance of the dual-pump demultiplexer at 40 Gbit/s as follows; adjustment of the input wavelengths at the peak gain wavelength of the SOA under saturation conditions, the use of higher pump power at the input of the device, or/and the use of pulsed pumps with short pulsewidths. For the higher bit-rate, the overlap of the input to the FWM signal pulses may appear both in the time and spectral domain. The pattern effect may also appear in the FWM signal due to the slow components of the optical nonlinearities in SOAs (Saleh & Habbab, 1990). These effects degrade the usefulness of the FWM in SOAs as a practical DEMUX device in optical network/ communication systems. Therefore, it is very important to analysis the optical DEMUX characteristics based on FWM in SOAs for the ultrafast multi-bit input optical pulses.

All- optical phase encoded 4-to-1 phase multiplexer using four wave mixing in semiconductor optical amplifier

All-optical switching and wide-range wavelength conversion have been demonstrated at 160 Gbit/s using four-wave mixing in a semiconductor optical amplifier. We used the asymmetrical multiple-quantum-well semiconductor optical amplifier which allows for a wide 3 dB gain-bandwidth. The cross-correlation measurements show the high-speed switching capability for wavelength routing in optical time division multiplexing networks.

Analysis of non-linear refractive index influences on four-wave mixing conversion efficiency in semiconductor optical amplifiers

Based on the single channel characterization of a Silicon Photonics (SiP) transceiver with Semiconductor Optical Amplifier (SOA) and semiconductor Mode-Locked Laser (MLL), we evaluate the optical power budget of a corresponding Wavelength Division Multiplexed (WDM) link in which penalties associated to multi-channel operation and the management of polarization diversity are introduced. In particular, channel cross-talk as well as Cross Gain Modulation (XGM) and Four Wave Mixing (FWM) inside the SOA are taken into account. Based on these link budget models, the technology is expected to support up to 12 multiplexed channels without channel pre-emphasis or equalization. Forward Error Correction (FEC) does not appear to be required at 14 Gbps if the SOA is maintained at 25 °C and MLL-to-SiP as well as SiP-to-SOA interface losses can be maintained below 3 dB. In semi-cooled operation with an SOA temperature below 55 °C, multi-channel operation is expected to be compatible with standard 802.3bj Reed-Solomon FEC at 14 Gbps provided interface losses are maintained below 4.5 dB. With these interface losses and some improvements to the Transmitter (Tx) and Receiver (Rx) electronics, 25 Gbps multi-channel operation is expected to be compatible with 7% overhead hard decision FEC.

An all-optical label recognition method is proposed, which is based on the fiber Bragg grating encoder/decoder and a semiconductor optical amplifier, employing multiple two-dimensional optical orthogonal codes for optical label in optical packet switching system. The program effectively reduces the code autocorrelation/cross-correlation requirements of label identification and removes the cross-correlation pulses after decoding, greatly increases the coding capacity and number of available labels, and improves the reliability of label identification, using the fiber Bragg grating as a decoder and four-wave mixing in the semiconductor optical amplifier. The feasibility of the method is validated by the simulation of OptiSystem software. The simulation also shows that the label has a relatively high extinction ratio and can be operated easily.

Implementation of optical logic gates at 160Gbps using nonlinear effect of single SOA

Summary form only given. In optical burst switching (OBS) networks, a short switching time is very important for handling fine grain packets such as TCP ACK packets, which are only 40 bytes in length. At data rate of 10 Gbps, such a data burst will occupy a period of only 32 ns. Therefore OXC (optical cross connector) with fast switching speed, for example < 100 ns, are generally required for OBS networks. There are many methods to configure an OXC. Tunable optical filters may used to build large scale OXC. In an optical filter, the tuning ability is usually achieved by introducing extra phase shift via the electro optic, thermo optic, or piezoelectric effect, etc. Up to date, the most commonly used tunable filter structures are interferometric such as Fabry-Perot (FP) and Mach-Zehnder (MZ) interferometers. They are usually poor in the performance of passband flatness and the crosstalk, and require robust electronics to stabilize the central wavelength. Hence, they are rarely practically used as switching elements in the dense wavelength division multiplexing (DWDM) optical networks. In recent years, digitally tunable optical filter (DTOF) has received increasingly attention. Structures based on the arrayed waveguide grating (AWG) and on-off switches have been reported. DTOF based on AWG may require precision thermal control for AWG usually suffers the problem of temperature dependence. In this talk, we present a novel approach to realize the DTOF (digitally tunable optical filter) based on DWDM thin film filters (TTF) and semiconductor optical amplifier (SOA). Apart from the outstanding feature being consistent with the wavelength comb suggested by international telecommunication union-telecommunication (ITU-T), the proposed DTOF is very stable in temperature performance. Furthermore it requires less SOAs in comparison with the reported structures.

All-optical packet switching can overcome limitations of electronic switches in terms of power consumption, speed, cost, and footprint. Switch architectures combining wavelength converters and fiber delay lines provide tunable routing and contention resolution when used with an N×N arrayed waveguide grating (AWG), a key passive optical component to bypass electronic processing limitations. An AWG passively routes either single or multiple input port wavelengths to output ports. A single wavelength per port strategy reduces crosstalk within the AWG, but drastically increases the dimensionality of the device. AWG design constraints due to bandwidth limitations and fabrication processes limit the port number for the foreseeable future to under 100. In order to scale optical switches to emerging network requirements, we must use multiple wavelengths per port. In this paper, we examine several optical router architectures for data center applications using multiple wavelengths per port, and quantify the physical layer impairments. We consider not only the AWG crosstalk, but also Q-factor degradation caused by the multiple wavelength conversions occurring when a packet is buffered for contention resolution. We present the results as a function of the number of recirculations for on–off-keying (OOK) signal formats. While previous work has addressed this issue in terms of accumulated loss, we focus on accumulated intensity noise due to crosstalk and amplified spontaneous emission (ASE). We compare the routing performance of each architecture, and we point out that the AWG crosstalk and accumulated ASE noise during packet recirculation are both critical to the routing performance.

We have performed four wave mixing (FWM) measurements on a 2-section semiconductor optical amplifier (SOA) using CW and pulsed pump and probe beams. The FWM efficiency depends on the input pump power, the gain of the 2-section SOA and the wavelength separation between the pump and probe beams. A -19.1 dBm FWM signal power from the amplifier is achieved when the wavelength difference between the pump and probe beams is 2.5 nm. The pulse amplitude and pulse width of the FWM signal under the condition when the FWM signal is generated using pulsed pump and probe beams has been measured and analyzed. The results of the analysis are in agreement with the experimental data.

Chapter 8 - Semiconductor Optical Amplifiers (SOA)

The possibility to perform broad wavelength generation and conversion is of great interest in classical and quantum optics. With the introduction of integrated nonlinear silicon photonics, these tasks have been made even more viable thanks to the combination of the high nonlinear refractive index of silicon with the high confinement provided by the photonic waveguides. Exploiting this platform, several solutions for wavelength conversion have been investigated, for both optical processing [1] and applications in the Mid Infrared (MIR) [2]. The possibility to perform broad and controllable wavelength generation can be exploited also for creating integrated sources of quantum states of light based on single photons [3] or correlated photon pairs [4]. Both the generation and conversion can be accomplished by means of Four Wave Mixing (FWM). FWM is a nonlinear optical process in which two pump photons at frequency are converted into signal and idler photons at frequencies and ω/ respectively (with ω I /ω S ). In the particular case of wavelength conversion, FWM is stimulated by a seed wave at the same wavelength of the signal (idler) that will be converted to the wavelength of the idler (signal). FWM has to satisfy the energy conservation, according to which the relation ω P + ω P = ω S + ω I holds, and its efficiency is ruled by the phase matching condition. This latter condition is related to the phase mismatch among the waves involved in the FWM process, that is evaluated as Δk = k p + k p −k S −k I , where k P , k S , k I are the wavevectors for the pump, the signal and the idler, respectively. When Δk = 0, the phase matching condition is fulfilled and the efficiency of FWM is maximized. What is important for wavelength generation and conversion is the spectral position of the phase matching condition, which determines the wavelength at which the maximum efficiency of the conversion or generation process is achieved. Because of this, techniques for the control of the phase matching condition have been developed, focusing on the possibility to tailor the Group Velocity Dispersion (GVD) through a proper engineering of the waveguide geometry [5]. While these techniques consider only the first order waveguide mode, here we propose to exploit the higher order modes propagating inside a multimode waveguide. The dispersion of the higher order modes can be used to tune the spectral position of the phase matching condition for the FWM process, achieving controllable and large spectral translation in both Stimulated Four Wave Mixing (sFWM) and Spontaneous Four Wave Mixing (SFWM).

Ultrafast optical pulse shaping supports a broad number of applications, ranging from ultrafast time-resolved spectroscopy to RF photonics [1]. Conventional pulse shapers rely on bulk optics and use liquid crystal spatial light modulators, with reconfiguration times limited to milliseconds. Integrated optical pulse shapers offer not only size advantage but also the potential for much faster reconfiguration by using electro-optic pulse shaping elements. Integrated pulse shapers usually employ an arrayed waveguide grating (AWG) to separate the input light into its constituent wavelengths, process each wavelength band using an array of on-chip components, and then recombine the light again relying on AWG action. AWG-based integrated pulse shapers with independent thermo-optic amplitude and phase control have been demonstrated in silica, but the reconfiguration time remains limited [2]. Our group previously reported a 32-channel InP arrayed waveguide grating pulse shaper (AWGPS) with 25 GHz channel spacing and an array of semiconductor optical amplifiers (SOAs) for spectral amplitude control. This work demonstrated amplitude shaping fidelity good enough to apply to RF photonic bandpass filtering with sidelobe suppression >35 dB as well as microsecond-scale reconfiguration [3]. Other groups have also demonstrated pulse shaping with integrated InP with either amplitude or phase control but not both [4]. In this work we report preliminary characterization of a 48 channel InP shaper at 50 GHz channel spacing, provisioned with both channel-by-channel phase adjusters and SOA gain elements (Fig. 1). To our knowledge this constitutes the first demonstration of an operable integrated InP pulse shaper with independent intensity and phase control.

Four -Wave Mixing and Phase Conjugation in Plasmas Using Ionization NonlinearitiesJohn F. Federici' and Ernie J. ValeoPrinceton Plasma Physics Laboratory. Princeton UniversityP.O. Box 451, Princeton. New Jersey 08544ABSTRACTPlasmas have recently received considerable attention as potentially efficient long wavelength (infrared to mi-crowave) phase conjugators using degenerate four -wave mixing (DFWM). In such processes, two electromagnetic(EM) pump waves (`forward' and `backward') plus a `probe' electromagnetic wave interact through the nonlinear lowfrequency susceptibility of the medium to produce a fourth `signal' or `conjugate' electromagnetic wave. The processmay also be viewed as an Bragg scattering of an EM wave from a low frequency density grating. The density gratingis generated by the coupling of one pump wave to the probe wave via pondermotive or thermal pressure forces. Inthis paper, the possibility of using ionization nonlinearities in weakly ionized plasmas for wave mixing applicationsis discussed. By locally heating the weakly ionized plasma, one may selectively ionized portions of the plasma toproduce a low frequency density grating. The applicable wavelength regimes, plasma parameters, and response timesfor ionization nonlinearities will be discussed.I. INTRODUCTIONPhase conjugation has many applications for signal processing, beam combining, tracking and pointing, laserbeam clean up, phase distortion compensation, etc..1,2 It has long been recognized that plasmas are efficient longwavelength (infrared through microwaves to radio waves) nonlinear optical mediums for phase conjugation by four -wave mixing (FWM).3 -6 Recent experiments have demonstrated nonlinear thermal forces' as well as pondermotiveforces8 for FWM in plasmas. This paper focuses on a new nonlinearity for plasmas based on laser- induced ionizationimbalances within the plasma.In collisionless plasmas, the pondermotive force dominates the thermal force. When the electron collisional mean -free -path is short compared to the beat -wave wavelength, thermal pressure forces become important. If a plasmawere weakly ionized, there would be another nonlinear force in plasmas - the ionization 'force' - which may beexploited for wave mixing and other nonlinear optical effects. Like the thermal pressure force, the ionization forceresults from the heating of the plasma by the beat -wave. However, as the weakly ionized plasma is heated, moreneutrals are ionized; instead of pushing the electrons into a grating structure, the electron grating is created directlyby ionization.The nonlinear mechanism in the plasma which generates the electron density grating for FWM is similar tothe mechanism for ionization instability driven electron -density waves. These waves are also called `striations' or`ionization waves'. A common type of striations occur naturally in discharge plasmas.''Semiconductors exhibit an analogous `ionization nonlinearity' for FWM.12 In semiconductors, the coupled pumpand probe waves generate a large concentration of free carriers (electron -hole plasma) by optically induced transitionsof electrons between the valance and conduction bands. For laser wavelengths near a semiconductor bandgap, the