Part of the book: Novel Applications of the UWB Technologies
Part of the book: Optical Communication
Part of the book: Advances in Optical Communication
All-optical signal processing is characterized by high bit-rate, power efficiency, high bandwidth, and transparency. All-optical logic gates are basic logic units for the all-optical signal processing implementation. Typically, all-optical gates are based on strong optical nonlinearities related in particular to semiconductor optical amplifiers (SOA). We briefly review the state of art in the field of all-optical logic gates and all-optical memory. In the original part, we discuss the ultrafast all-optical memory loop based on the Mach-Zehnder interferometer (MZI) with quantum dot (QD) semiconductor optical amplifier (SOA) in each arm.
Part of the book: Optical Fiber and Wireless Communications
Quantum dot (QD) laser devices can be successfully used in optical communications due to their unique properties caused by the carrier localization in three dimensions. In particular, quantum dot‐in‐a‐well (QDWELL) lasers are characterized by an extremely low threshold current density and the high modulation frequency. However, their operation rate is limited by the strongly nonlinear electron and hole scattering rates in and out of QD. We investigated theoretically the nonlinear optical phenomena in QDWELL lasers and amplifiers under the optical injection. We have shown that the synchronization of the carrier dynamics in QD and quantum well (QW) caused by the optical injection improves the QDWELL laser performance and, in particular, enhances the relaxation oscillation (RO) frequency. As a result, the QDWELL laser performance in the analogous optical link (AOL) is significantly improving. The optical injection also improves the performance of the QDWELL‐based semiconductor optical amplifiers (SOA).
Part of the book: Optical Communication Technology
Liquid crystals (LC) are the materials characterized by extremely high optical nonlinearity. Their physical properties such as temperature, molecular orientation, density, and electronic structure can be easily perturbed by an applied optical field. In particular, in smectic A LC (SALC), there is a specific mechanism of the cubic optical nonlinearity determined by the smectic layer normal displacement. The physical processes related to this mechanism are characterized by a comparatively large cubic susceptibility, short time response, strong dependence on the optical wave polarization and propagation direction, resonant spectral form, low scattering losses as compared to other LC phases, and weak temperature dependence in the region far from the phase transition. We investigated theoretically the nonlinear optical phenomena caused by this type of the cubic nonlinearity in SALC. It has been shown that the light self-focusing, self-trapping, Brillouin-like stimulated light scattering (SLS), and four-wave mixing (FWM) related to the smectic layer normal displacement are strongly manifested in SALC. We obtained the exact analytical solutions in some cases and made the numerical evaluations of the basic parameters such as the optical beam width and SLS gain.
Part of the book: Liquid Crystals
Quantum dot-semiconductor optical amplifiers (QD-SOA) attracted strong interest for applications in optical communications and in all-optical signal processing due to their high operation rate, strong nonlinearity, small gain recovery time of about few picoseconds, broadband gain, low injection current and low noise figure (NF). In this chapter, we present the theoretical investigation of the gain recovery time acceleration in DQ SOA; the specific features of the cross gain modulation (XGM) in QD-SOA; the influence of the optical injection on the dynamics of QD-SOA based on the QD in a well (QDWELL) structure. We describe the following applications of QD-SOA: the all-optical ultra-wideband (UWB) pulse generation based on the Mach-Zehnder interferometer (MZI) with a QD-SOA; the ultra-fast all-optical signal processor based on QD-SOA-MZI; the ultra-fast all-optical memory based on QD-SOA. The contents of the chapter are mainly based on the original results.
Part of the book: Optical Amplifiers
The phenomenon of superoscillation is the local oscillation of a band limited function at a frequency ω higher than the band limit. Superoscillations exist during the limited time intervals, and their amplitude is small compared to the signal components with the frequencies inside the bandwidth. For this reason, the wavelet transform is a useful mathematical tool for the quantitative description of the superoscillations. Continuous-time wavelet transform (CWT) of a transient signal ft is a function of two variables: one of them represents a time shift, and the other one is the scale or dilation variable. As a result, CWT permits the simultaneous analysis of the transient signals both in the time and frequency domain. We show that the superoscillations strongly localized in time and frequency domains can be identified by using CWT analysis. We use CWT with the Mexican hat and Morlet mother wavelets for the theoretical investigation of superoscillation spectral features and time dependence for the first time, to our best knowledge. The results clearly show that the high superoscillation frequencies, time duration, and energy contours can be found by using CWT of the superoscillating signals.
Part of the book: Wavelet Theory and Its Applications