Study Of Optical Comb Filters And Multi-Function Composite Module

Optical fiber communication network plays an important role in the construction of "Information highway". As we know, it is made up by backbone network, metropolitan network and access network. Meanwhile, each main node in the network involves a lot of optoelectronic components and various function modules. Performance of them will influence on the operation stability of the network directly.Optical filter represents a big class of key photonic components and its function is evident, which is usually used for dispersion compensation of the optical fiber links, for gain spectrum flattening of the optical amplifiers, for wavelength channel selection, for channel power equalization and so on. Thus, it is useful and meaningful to select optical comb filter and multi-function composite module as the main research topics and as the title of this dissertation.The main research methods adopted in this paper are math-physical modeling, characteristics simulation, theoretical analysis and experimental verification.The main research topics involve optical all pass filter (OAPF, periodic phase comb filter), multi-waveguide directional coupler, a novel type DWDM (dense-wavelength-division multiplexer) called as interleaver (periodic amplitude comb filter) and multi-function composite module. All these topics are stated in detail as follows.1. Design methods and applications of thin film Gires-Tournois interferometer (GTI) type OAPF. GTI is a reflective Fabry-Perot interferometer, and it is made up by partial reflective mirror, resonant cavity and total reflective mirror. Firstly, An iterative formula to calculate the reflectivity of the multi-layer thin film is given and its effectiveness in the design of thin film OAPF is proved. Secondly, omitting the concrete thin film structure of the mirror, analytical expressions of the phase, group delay and dispersion are deduced. Finally, transmission matrix method is adopted to design thin film OAPF appropriate for multi-channel dispersion compensation, and its characteristics is simulated numerically and analyzed in detail. For example, influence of the thin film structure of the mirrors on single-cavity GTI'sperformance, polarization splitting phenomena for oblique incident light, optimization of the dispersion compensation bandwidth et al. Design and analysis of multi-cavity GTI are involved as well.2. Multi-function double ring resonant optical comb filter. Analytical expression for the resonator composed by equilateral structure 3x3 fused fiber coupler is deduced, considering insertion loss and splitting ratio of the coupler; transmission loss, gain coefficient and length of the optical fiber delay line. Its characteristics is simulated in detail, the results reveal its multi-function performance such as multi-channel bandpass, bandstop and amplification. The relationship between the structure parameters and its dynamic changing laws is shown as well. An interesting dynamic changing course of double resonant peaks is found, which may be caused by the extra phase shift related with loss and gain. In addition, dispersion characteristics, Vernier effect and applications such as optical delay line and optical interleave filter are discussed also.3. Infinite impulse response (IIR) type interleave filter. It is made up by thin film OAPF and asymmetric Mach-Zehnder interferometer (MZI) with 3x3 fiber coupler. Its transmission characteristics and influence from parameter detuning are theoretically analyzed and simulated. At last, some conclusions are given which can be useful for further practical design and exploring related experimental techniques.4. Systematic study of multi-function optical filter composite module. Using 3x3 fiber coupler as a key unite to form finite impulse response (FIR) type bi-directional interleave filter based on two stage cascaded all-fiber MZI. Added by optical circulator, isolator, all-fiber DWDM, fiber grating dispersion compensator, F-P channel monitor and some other optical components, its function is strengthened. Related problems such as additional phase shift adjustment in DWDM, and fiber grating analogue to thin film GTI et al are discussed.5. Multiwaveguide directional coupler. There are two main parts in this chapter as follows.â–  Analytical solutions of scalar coupled-mode equations (CMEs) formultiwaveguide coupling system are obtained by Chebyshev polynomials and generalized Chebyshev polynomials for "weak coupling" (considering mode coupling between neighbored waveguides only) and "strong coupling" (otherwise) cases individually. The first kind of and the second kind of Chebyshev polynomials are appropriate for linearly distributed and circularly distributed multi-waveguide structure respectively. General steps to solve the CMEs and examples such as 2x2, 3x3, 4x4 and 5x5 directional couplers are given in detail.â–  Based on composite waveguide theory, analytical solution to a novel structure 2x6 fused fiber coupler is deduced, its power coupling characteristics are simulated numerically, which is proved by Xu Qiang's initial experimental result.In addition, new ideas and possible valuable results are shown as follows. First, to our knowledge, it is a new try in mathematics and physics to obtain analytical solutions of CMEs for multi-waveguide system by Chebyshev and generalized Chebyshev polynomials. But it should be pointed out that further development and perfection are needed. Second, a novel structure 2x6 fused fiber coupler is analyzed theoretically, which is proved experimentally by Xu Qiang. Third, using thin film OAPF and multi-port fiber coupler to form a novel structure bi-directional IIR type interleaver and multi-function composite module. Fourth, adopting three mathematical methods (iterative formula, analytical expression, and transmission matrix) to design thin film OAPF appropriate for multi-channel dispersion compensation. The fifth is embodied in the simulation results and discussions. For example, in the part of multi-function double-ring resonant optical comb filter, the dynamic changing laws of the double peaks; additional phase shift adjustments in multi-stage cascaded all fiber MZI type DWDM channel demultiplexer.This paper is organized as follows. The first chapter is a summary about optical filter (OAPF, interleaver, et al) applied in optical network; the second chapter focuses on the design and analysis of thin film GTI-OAPF used for multi-channel dispersion...