Chapter 8 – Fiber Nonlinearities and Their Impact on Transmission Systems

Optical nonlinearlties are intended to generate newer frequencies as well as lead to the evolution of newer devices. The underlying mechanism in such devices may Include the stimulated Raman scattering, stimulated Brillouin scattering, Kerr effect, self phase modulation and four wave mixing besides the harmonics generation. These nonlinear processes and their effects in signal transmission through optical fiber are described. Optical amplifiers and their applications with special emphasis to doped fiber amplifiers are discussed. Soliton theory and its impact on optical fiber transmission Is also presented.

Nonlinear Effects in Optical Fiber Transmission System

With the advances in the field of ultrafast photonics occurring so fast, the demand for optical modulation devices with high performance and soliton lasers which can realize the evolution of multiple soliton pulses is gradually increasing. Nevertheless, saturable absorbers (SAs) with appropriate parameters and pulsed fiber lasers which can output abundant mode-locking states still need to be further explored. Due to the special band gap energy values of few-layer indium selenide (InSe) nanosheets, we have prepared a SA based on InSe on a microfiber by optical deposition. In addition, we demonstrate that our prepared SA possesses a modulation depth and saturable absorption intensity about 6.87% and 15.83 MW/cm2, respectively. Then, multiple soliton states are obtained by dispersion management techniques, including regular solitons, and second-order harmonic mode-locking solitons. Meanwhile, we have obtained multi-pulse bound state solitons. We also provide theoretical basis for the existence of these solitons. The results of the experiment show that the InSe has the potential to be an excellent optical modulator because of its excellent saturable absorption properties. This work also is important for improving the understanding and knowledge of InSe and the output performance of fiber lasers.

Nanosized indium selenide saturable absorber for multiple solitons operation in Er3+-doped fiber laser.

Demonstration of passively Q-switched and mode-locked operations through dispersion control in Er-doped fiber lasers with a cylindrite-based saturable absorber

Nonlinear vector rotation and depolarization of femtosecond laser pulses propagating in non-birefringent single-mode optical fibers

In our work, a new-type, to the best of our knowledge, ferromagnetic insulator and its nonlinear optical absorption characteristics and related ultrafast modulation applications were investigated. Cr2Si2Te6 saturable absorbers (SAs) with a modulation depth and a saturable intensity of 9.7% and 3.5MW/cm2 were fabricated. By adjusting the pump power to 120 mW and optimizing the polarization state, traditional soliton operations were obtained successfully; the corresponding duration of pulse and the fundamental repetition rate were ∼1.33ps and 6.70 MHz, and the signal-to-noise ratio was 50 dB. The experimental results reveal that Cr2Si2Te6 with excellent saturable absorption characteristics can be used as a SA to obtain ultrafast pulse lasers.

Passively mode-locked Er-doped fiber laser based on a ferromagnetic insulator Cr2Si2Te6 as a saturable absorber.

The interactions induced by the nonlinear refractive index in a single-mode optical fiber (Kerr effect) between a modulated wave and a carrier wave have been investigated for amplitude shift keying (ASK), frequency shift keying (FSK), and phase shift keying (PSK). The theoretical analysis, based on a time-domain solution, exploits the well-known formalism of self-phase modulation to describe the propagation of the input electric field in the fiber. The theoretical results were validated experimentally for amplitude- and phase-modulated waves with heterodyne detection techniques. These experiments mimic a coherent transmission system and allow the measurement of the spectrum of each of the waves that participate in the nonlinear interaction. >

Nonlinear Kerr interactions between modulated waves propagating in a single-mode fiber

The polarization changes induced by a strong wave on a copropagating weaker wave in a single-mode birefringent fiber are investigated. Quantitative analysis and measurements are presented for the dependence of these polarization changes on the relative input state of polarization of the two waves as well as on their frequency separation.

S. Tang

Papers

Passively mode-locked Er-doped fiber laser based on a ferromagnetic insulator Cr2Si2Te6 as a saturable absorber.

Nonlinear Kerr interactions between modulated waves propagating in a single-mode fiber

Cross-induced polarization changes in single-mode fibers.