The Research Of All-Fiber Filtering Technologies

As the key component of multiplexer/demultiplexer, optical filter technology has been fueling great interest with the emergence of wide range tunable laser source, all-wave fiber, and wide band optical amplifiers, which is promoting DWDM to a leading edge of optical fiber communication. The increasing of single channel capacities and evolution of optical networks topology, from simple point-to-point to intelligent optical networks, call for strict demands to optical filters. In this paper, the crucial technologies of optical filters such as Interleaver, optical digital filter, fused biconical taper all-wave coupler as well as polarization-pump combiner have been studied experimentally and theoretically, which include:1. A new process, cascaded FBT (fused biconical taper) with precise control as well as strict interference arm length difference, is proposed for the first time to our knowledge. The influences of couple ratio accuracy and twist stress of interference arms on device's isolation have been investigated theoretically and experimentally. The isolation can reach about 17.5dB. At the same time, the design of cascaded coupler with a given ratio distribution is proposed, which can lead to higher isolation by suppressing sidelobe.2. According to theoretical analysis and numerical simulation, the Interleaver can show flat-top and high isolation pass band characteristic when the two couplers' ratio is assigned to 15 percent. The experiment demonstrates that the simulated calculations are in good agreement with experimental results.. The conception and algorithm simulation of lattice digital filter in electronics are transplanted into optical filter, with a novice algorithm to resolve optical lattice array concrete parameter. Based on the Fourier series digital approximation method, the optimal design of flat-top and high isolation pass band frequency response Interleaver has been studied. At last a solution of high isolation ( >45dB )3 and flat pass band is introduced according to all fiber Interleaver scheme.4 . By theoretical analysis, numerical simulation and experiment research, the Interleaver based on optical all-pass filter technique is investigated. Group delay and dispersion characters are analyzed according to the above filter. In addition, the dynamic tunable feature is discussed.5 . All-wave coupler is proposed for the first time to our knowledge. This paper, on the basis of coupled-mode equations, analyzed the bandwidth characteristic of asymmetric FBT coupler, proposed and proved a solution of all-wave coupler (O+E+S+C+L band). We also succeeded in making all-wave couplers with a bandwidth of 390nm, while the excess loss is only 0.1 dB and the uniformity is about 1 dB. A specific solution to decrease the PDL (polarization dependent loss) of all-wave coupler is presented and demonstrated by experiment. Moreover, all fiber polarization-pump combiner is successfully developed with 16.5dB extinction ratio.