Research On Key Intelligent Fiber Optoelectronic Techniques

Recently, the fiber optoelectronic technologies with rapid development have already become important high and new technologies in the21st Century, which have been valued widely in the world. The fiber optoelectronic devices and photon systems with various functions have already played important roles in scientific research field and various fields of national economy, particularly the high-speed information networks, sensor networks and new type of light sources. It is an inevitable trend to improve the performances of devices, put forward new techniques, and realize the intelligences of fiber optoelectronic systems, which is for the purpose of meeting the development of modern optical engineering. Fiber filter, fiber laser, and wavelength detection have important significances in fiber photoelectrons, which are deeply investigated theoretically and experimentally in this paper. Moreover, an intelligent tunable Erbium-doped fiber ring laser (EDFRL) system is designed and implemented based on these key techniques. The main works and contributions of this dissertation are as follows:First, the reflection spectrum characteristics of fiber Bragg gratings (FBGs) are discussed theoretically and analyzed numerically, which bring out the relationships between the line width of FBG reflection spectrum and the grating length as well as the "AC" coupling coefficient. After the characteristic that the reflection wavelength of FBG can be moved by axial stress has been analyzed theoretically, a package structure of tunable FBG filter that can be tuned by axial stress is designed, whose tunable range is greater than16nm by experimental tests. A sort of nonlinear chirped FBG with asymmetric reflection spectrum is proposed, whose theoretical model, the Riccati Equation, is numerically solved by the four-order Runge-Kutta method. The concrete forms of the phase modulation function and apodization function are given and a spectrum envelope slope parameter is defined in order to describe its asymmetric level. A novel narrow-bandwidth transmission tunable FBG filtering technique is put forward based on this sort of FBGs’characteristics and its filtering performances are discussed as well.Second, by theoretically analyzing the EDFRL’s output characteristics about output power, slope efficiency, threshold power, lasing spectrum line width and etc., a tunable single-longitudinal-mode EDFRL system is proposed, which have highly stable output, narrow line width, and fine tunable resolution. The EDFRL is designed using ring cavity to suppress the spatial hole burning (SHB) effect and high doping Erbium-doped fiber (EDF) as gain medium, whose3dB line width of single-longitudinal-mode lasing spectrum is only12pm and slope efficiency is17.9%, while the same parameters are respectively17pm and14.68%when using low doping EDF. The tunable FBG filter is utilized as the frequency selective element and a42stepper motor subdivided256times acts as the fine tuning mechanism, which brings out the laser’s mean tuning resolution of-1.41pm/pulse. The wavelengths with50GHz mode spacing are demonstrated, which are suitable for dense wavelength division multiplexing (DWDM) system and meet the International Telecommunications Union’s (ITU’s) recommendations and standards.Third, the spectral coupling ratio characteristic of fused tapered wavelength division multiplexing (WDM) with short half-wave oscillation cycle is analyzed theoretically and experimentally. Based on the experimental results, the functional relationship between the contrast parameter R(λ)(the output coupling ratio deference of two WDM arms) and wavelength change is fitted. Combining with the control system of EDFRL, a wavelength detector is designed and fabricated by using fiber isolator (ISO),1525/1575nm WDM and two InGaAs photo detectors. The communication between the computer and wavelength detector is established through serial ports and the upper computer software is designed to receive the wavelength data transferred from the wavelength detector. After the wavelength detector is calibrated experimentally, its theoretical wavelength resolution is1.72pm-5.28pm and single detection accuracy is±95pm@1554.452nm on the case of detecting the EDFRL’s single-longitudinal-mode lasing spectrum.Fourth, the way of extracting a fraction of light signal from the ring cavity is proposed, as well as the wavelength detector is applied as the detecting element, and then, the signal feedback loop is established. A closed-loop control scheme of the tunable EDFRL is designed. The control algorithm is put forward, which is used to compare the set wavelength value and output wavelength value based on the contrast ratio parameter R(λ) and compensate the output wavelength according to the difference. The tunable EDFRL’s intelligent control system that combines the open-loop control and closed-loop control systems uses the single chip MSP430(Texas Instruments) as the main controller and the control system software architecture is designed as a foreground-background framework. Finally, the prototype machine of intelligent tunable EDFRL system is implemented, which has various functions such as intelligent tuning output, wavelength tracking, wavelength adjustment, zero-scale calibration and etc.