Cross-phase modulation induced performance degradation in nonlinear optical loop mirror switch

Ultrafast all-optical XOR and XNOR logic gates have been analyzed based on photonic crystal fiber (PCF) nonlinear optical loop mirror (NOLM). The performance of the logic operation is evaluated numerically using the coupled nonlinear Schrödinger equation and split step Fourier method. The wavelength allocation, peak power and the pulse width of signal with respect to the group velocity dispersion (GVD) and the nonlinearity of PCF affect the performance of logic gate. A highly nonlinear PCF with flattened dispersion is proposed to obtain 1 Tb/s operation.

High speed ultra short pulse fiber ring laser using photonic crystal fiber nonlinear optical loop mirror

Nonlinear polarisation rotation is shown experimentally to be an effective process to switch a fibre nonlinear optical loop mirror (NOLM). If interfering beams have different polarisations, no power imbalance is required. Contrary to standard NOLM designs, the proposed architecture combines high contrast with simultaneously low critical power and low insertion losses.

The role of the Advanced Air Transportation Technologies program undertaken at the NASA Glenn Research Centers has been focused mainly on the improvement of air transportation safety, with particular emphasis on air transportation communication systems in on-board aircraft. The conventional solutions for digital optical communications systems specifically designed for local/metro area networks are, unfortunately, not capable of transporting the microwave and millimeter RF signals used in avionics systems. Optical networks capable of transporting RF signals are substantially different from the standard digital optical communications systems. The objective of this paper is to identify a number of different communication link architectures for RF/fiber optic transmission using a single backbone fiber for carrying VHF and UHF RF signals in the aircraft. To support these architectures, two approaches derived from both hybrid RF-optical and all-optical processing methodologies are discussed with single and multiple antennas for explicitly transporting VHF and UHF signals, while the relative merits and demerits of each architecture are also addressed. Furthermore, the experimental results of wavelength division multiplexing (WDM) link architecture from our test-bed platform, configured for aircraft environment to support simultaneous transmission of multiple RF signals over a single optical fiber, exhibit no appreciable signal degradation at wavelengths of both 1330 and 1550 nm, respectively. Our measurements of signal to noise ratio carried out for the transmission of FM and AM analog modulated signals at these wavelengths indicate that WDM is a fiber optic technology which is potentially suitable for avionics applications.

In this work, we present a novel versatile fiber laser based on the scheme of bidirectional transmission, with a nonlinear optical loop mirror (NOLM) and a graphene-polyvinyl alcohol (G-PVA) as saturable absorbers (SAs), and demonstrate the generation of dispersion-managed soliton (DMS) and Q-switched pulse simultaneously or respectively for the first time to the best of our knowledge. In counter-clockwise (CCW) direction, the G-PVA is acted as a slow SA and used for obtaining Q-switched pulse trains, the DMS is achieved in clockwise (CW) direction by using NOLM. The proposed fiber laser can be switched in three cases by simply adjusting attenuator (ATT), pump power and polarizer controllers (PCs): (I) Only DMS is obtained. (II) Only Q-switched pulse trains are achieved. (III) The DMS and Q-switched pulse trains are established simultaneously. This versatile laser enables to generate two kinds of pulse, which is a potential candidate in communication system and industrial applications.

We examine the effectiveness of using nonlinear optical loop mirrors (NOLMs) to reduce the intersymbol interference in dispersion-managed (DM) fiber communication systems compensated by chirped fiber gratings (CFGs) with group delay ripples (GDR). We show that the use of NOLMs can enhance the transmission performance by more than one order of magnitude in the presence of amplifier noise and random variations in the parameters of the GDR in CFGs. We found that transoceanic transmissions can be achieved when NOLMs are included in the DM optical fiber transmission line compensated by CFGs with GDR whose parameters vary randomly along the transmission line.

We use a vector theory of cross-phase modulation to discuss how residual birefringence of the fiber loop affects the switching performance of a nonlinear optical loop mirror. It is found that the interaction between polarization-mode dispersion (PMD) and cross-phase modulation transfers spatial randomness of residual birefringence to temporal power fluctuations within the switching window. PMD reduces the switching contrast and the reduction depends on wavelength separation between the signal and control pulses as well as on the magnitude of the PMD parameter. Fluctuations in the switched power become worse for a wavelength separation for which the PMD diffusion length associated with birefringence fluctuations becomes comparable to the nonlinear length associated with cross-phase modulation.

We theoretically and experimentally demonstrate a novel scheme of bandwidth-variable ultra-wideband (UWB) monocycle generation, using a semiconductor-optical-amplifier (SOA)-based nonlinear optical loop mirror (NOLM). In our scheme, the probe light is split into two parts by the NOLM, and both of them are phase modulated by the pump light due to the cross-phase modulation in the SOA. An extra phase difference between these two parts is also introduced by tuning the polarization controller within the loop. When both parts interfere at the NOLM output port, the phase modulation is converted to the intensity modulation with a UWB monocycle waveform. In addition, the bandwidth of the UWB spectrum is variable by tuning the optical delay line within the loop.

Short pulsed laser sources have recently been under investigation for applications in high speed optical communications systems. Studies concerning short pulse laser sources based on Gain Switching techniques and compression devices have been made. Nonlinear Optical Loop Mirrors (NOLM) provide both compression and reshaping of the optical pulses. As achieved pulse widths become shorter, timing jitter becomes crucial. The present work turns the attention to the influence of timing jitter in the performance of the NOLM pulse compression device. The results obtained will be the basis for the design of a compact high quality ultrashort optical pulse source at 40 GBs with monolithic semiconductor compressor. This device is under investigation within the MONOPLA project.

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Recently, optical phase modulation has been widely used in microwave photonics (MWP) systems, such as radio over fiber systems, photonic microwave filters, optical microwave and millimeter-wave signal generators, and optical subcarrier frequency up-converters. An optical phase-modulated signal can be converted to an intensity-modulated signal in a dispersive optical fiber. Due to the intrinsic nonlinearity of optical phase modulation, for linear applications such as microwave signal distribution and filtering, the modulation index should be kept small to minimize the unwanted modulation nonlinearity. However, for nonlinear applications such as microwave frequency multiplication and subcarrier frequency upconversion, the modulation index should be large to maximize the frequency multiplication and upconversion efficiency. In this paper, for the first time to our knowledge, we develop a thorough theoretical framework for the characterization of phase-modulation-based MWP systems, in which the phase modulation to intensity modulation conversion is realized using a dispersive fiber. Analytical models for the distributions of single-tone and two-tone microwave signals and for microwave frequency multiplication and subcarrier frequency upconversion are developed, which are verified by numerical simulations. The analytical models for single-tone and two-tone transmissions are further confirmed by experiments. The developed analytical models provide an accurate mathematical tool in designing phase-modulation-based MWP systems. </para>

Broad-band microwave packaging of a traveling-wave amplifier with an on-chip bandwidth of 2-50 GHz is described. Techniques to reduce overall insertion losses and to extend the low-frequency cutoff of the amplifier while maintaining gain-flatness are discussed. The packaged amplifier modules exhibit excellent performance from 100 kHz to 50 GHz. They are demonstrated as modulator drivers and receiver amplifiers in a 30-Gbit/s digital optical communication system.

Optical amplifiers are important building blocks in nowaday's optical communication system. Their noise behavior differs considerably from that of electrical amplifiers. Theory is reviewed and supplemented by examples that allow to estimate the performance of optical transmission systems. In particular, a correct optical noise figure definition is explained.

Characterization and Modeling of SAGCM InP/InGaAs Avalanche Photodiodes for Multigigabit Optical Fiber Communications

The impact of the first-order and second-order PMD on the performances of optical switching with NOLM is studied by the split-step Fourier method (SSFM) based on the coupled nonlinear Schrodinger equation (CNLSE), including optical eye graphs, power transmission function of the NRZ code and the Q-factor penalty of different code patterns at different working speeds. The simulation results show that the switching performances are deteriorated badly by PMD, and using the right code pattern can reduce the impact of PMD partially. Furthermore, the compensation method of PMD by the polarization-maintaining fiber (PMF) inside the fiber loop of NOLM is put forward. It influences the original switching performances to the least extent when the PMF is located in the middle of the fiber loop.

Nonlinear optical loop mirror (NOLM) is one of the promising candidates for ultra-fast all-optical demultiplexers in future optical communication systems [1-3]. The highest switching bit rate achieved with NOLM demultiplexer was 64 Gbit/s as reported in Ref. [4] where a 64 Gbit/s data stream was switched by a 4 GHz control pulse train. This paper is intended to further investigate ultra-high speed performance (> 100 Gbit/s) of the NOLM demultiplexer. One of the problems associated with 100 Gbit/s operation has been synchronization errors between control and signal pulses caused by timing jitter. The 1st approach we have attempted is to produce sufficient amount of jitter tolerance of the NOLM demultiplexer by utilizing chromatic dispersion-induced pulse walk-off between control and signal pulses, which is controlled by using a wavelength tunable mode-locked Er3+-doped fiber ring laser (MLRL) [3, 5] as an optical signal source (gating-width control). Secondly, we incorporated a planar lightwave circuit (PLC) 6.3-100 Gbit/s time division multiplexer which makes it possible to suppress pulse-energy fluctuations and timing jitter of a densely multiplexed signal pulse stream. Based upon the two schemes 100 Gbit/s NOLM demultiplexing is successfully demonstrated for the first time and it has been found that fine gating-width control is essential for ultra-high speed demultiplexing over the 100 Gbit/s regime.