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

100 Gb/s all-optical multifunctional AND, NOR, XOR, OR, XNOR, and NAND logic gates in a single compact scheme based on semiconductor optical amplifiers

In this paper we have implemented an all-optical OR-gate using simultaneous Four-Wave Mixing (FWM) and Cross-Gain Modulation (XGM) in a semiconductor optical amplifier (SOA).Which incorporates two semiconductor optical amplifiers (SOAs).The proposed OR logic is numerically simulated by solving nonlinear coupled equations that explain cross gain modulation(XGM) effect in individual SOAs.

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.

Future optical networks may require both wavelength conversion and bit shape regeneration in an all-optical domain. The possibility of pulse reshaping while providing wavelength conversion may support new demands over medium and large distances links (Kelly, 2001). Indeed, during propagation the optical data signal suffers deterioration due to the amplified spontaneous emission (ASE) from optical amplifiers, pulse distortion from intrinsic dispersion, crosstalk, and attenuation. All-optical regenerators may be important components for the restoration of these signals, providing complexity and cost reductions with the avoidance of optoelectronic conversions. The regeneration could be 2R (reamplification and reshaping) or 3R, which also provide retiming to solve jitter (Simon et al., 2008). Several 3R regenerators using the semiconductor optical amplifier (SOA) have been proposed, such as cascaded SOAs setups (Funabashi et al., 2006) or SOA based MachZehnder interferometers (MZI) (Fischer et al., 1999). However for small and medium distances systems, where the signal amplitude noise and distortions form the main problem and where jitter has fewer magnitudes, the simpler 2R processes can be adequate to keep signal quality (Simon et al., 1998). In addition, the SOA is a helpful device for both 2R-regeneration (Ohman et al., 2003) and wavelength conversion (Durhuus et al., 1996). Several techniques for 2R-regeneration based on SOAs have been proposed and tested, for example by using four-wave mixing (FWM) (Simos et al., 2004), cross-gain modulation (XGM) (Contestabile et al., 2005), integration within MZI (Wang et al., 2007), multimode interferometric SOA (Merlier et al., 2001), cross-phase modulation (XPM) with filtering (Chayet et al., 2004), and feed forward technique (Conforti et al., 1999). However, these techniques require complex designs and involve critical operation points, even the simplest ones based on XGM features. In addition, most of these techniques are not capable of wavelength conversion and regeneration simultaneously. Recently a regenerator based on cross-gain modulation was proposed using one SOA for wavelength conversion (in a counter-propagating mode) and another deeply saturated SOA (synchronized by an optical delay line) to achieve cross-gain compression (Contestabile 2005). This efficient approach has similarities with the all-optical feed-forward techniques. In addition, this regenerator could not done wavelength conversion if the wavelength of the

In this paper, we propose to use a semiconductor optical amplifier (SOA) in the optical network unit (ONU) to improve the loss budget in time and wavelength division multiplexed-passive optical network (TWDM-PON) systems. The SOA boosts the upstream signal to increase the output power of the electro-absorption modulated laser (EML) and simultaneously pre-amplifies the downstream signal for sensitivity improvement. The penalty caused by cross gain modulation (XGM) effect is negligible due to the low extinction ratio (ER) of upstream signal and the large wavelength difference between upstream and downstream links. In order to achieve a higher output power, the SOA is driven into its saturation region, where the self-phase modulation (SPM) effect converts the intensity into phase information and realizes on-off-keying (OOK) to phase-shifted-keying (PSK) format conversion. In this way, the pattern effect is eliminated, which releases the requirement of gain-clamping on SOA. To further improve the loss budget of upstream link, an Erbium doped fiber amplifier (EDFA) is used in the optical line terminal (OLT) to pre-amplify the received signal. For the downstream direction, directly modulated laser (DML) is used as the laser source. Taking advantage of its carrier-less characteristic, directly modulated signal shows high tolerance to fiber nonlinearity, which could support a downstream launch power as high as + 16 dBm per channel. In addition, the signal is pre-amplified by the SOA in ONU before being detected, so the sensitivity limitation for downstream link is also removed. As a result, a truly passive symmetric 40-Gb/s TWDM-PON was demonstrated, achieving a link loss budget of 51 dB.

An integrable all-optical clocked D type flip-flop is demonstrated exploiting SOA-based transparent all-optical SR latch. Nonlinear effects of four wave mixing and cross gain modulation are used for optical logic gate operations.

Ultra-wideband signal generator based on cross gain modulation effect in a distributed feedback laser

We propose and demonstrate all-optical format conversion from nonreturn-to-zero differential phase-shift-keying (NRZ-DPSK) to return-to-zero binary PSK (RZ-BPSK) at different bit-rates, using a tunable band-pass filter, a semiconductor optical amplifier (SOA) fiber ring laser and an SOA based Mach-Zehnder interferometer (SOA-MZI). The filter acts as the DPSK demodulator and also as the differential decoder. It converts the NRZ-DPSK into the RZ signals, which is equivalent to the data information before differential encoding. The SOA fiber ring laser is used to recover the clock signals from the demodulated RZ signals at different bit-rates. In the subsequent SOA-MZI, the RZ signal is used to modulate the recovered clock signal which is synchronous to the demodulated RZ signal. Thus, the amplitude information is encoded onto the phase of the clock signal, through cross gain modulation (XGM) and cross phase modulation (XPM) effects in the SOA-MZI. The converter can be operated at flexible bit-rates and used as the interface between long-haul WDM and OTDM systems.

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.

Techniques for all optical wavelength conversion and regeneration using semiconductor optical amplifiers are reviewed. In SOA based optical signal processing two (or more) signals are launched into the SOA where they interact due to the nonlinear properties of the active region in gain saturation, allowing the amplitude and phase of one optical signal to be controlled by another optical signal. Depending on the input conditions and topology, this can result in cross gain modulation, cross phase modulation or four wave mixing.

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

Optical chaotic communication using correlation demodulation between two synchronized chaos lasers

We have developed a theory of high-speed operation of quantum dot (QD) semiconductor optical amplifiers (SOAs), and showed that pattern-effect-free amplification of pulse trains, cross gain modulation (XGM) and cross phase modulation (XPM) can take place in QD SOA in the regime with maximum gain. Formulas, which relate the maximum bit-rate for the pattern-effect-free operation and the average SOA output power to the SOA pump current density, were derived. XGM without pattern effect can be realized in the regime with maximum gain due to spectral hole burning effects. Possibility of ultrafast frequency conversion and demultiplexing of data pulse streams through this nonlinearity is illustrated. Expression for the nonlinear refractive index η nl due to spectral hole burning in QD structure was obtained. The value of η nl in QD SOAs can be by 4-5 orders larger than η nl in silica; and efficient ultrafast XPM without pattern effects can be carried out in QD SOA through this nonlinearity. In whole, usage of the regime with maximum gain in QD SOAs can lead to development of new generation of high-speed devices for ultrafast optical processing and communications.

Microwave photonic filter with multiple taps based on single semiconductor optical amplifier