Studies On Controlled Air Hole Collapse In Photonic Crystal Fiber

Controlled air hole collapse in totally internal reflection photonic crystal fiber (TIR-PCF) make PCF more popular and powerful in optics, especially in the manufacture of anamorphic core-shape PCF and mode converters. This thesis describes this technique in detail, and studies anamorphic core-shape PCF and mode converters based on controlled air hole collapse theoretically and experimentally. The main points are listed as follows:First, the differential air hole collapse technique is described in detail, involving equipments, processes and improved methods. A brief introduction to PCF post-processing technique and adiabatic tapered structure are presented.Second, several kinds of anamorphic core-shape PCFs are calculated by finite difference beam propagation method (FD-BPM) and manufactured by controlled air hole collapse technique, the mode field patterns and energy loss during core transitions are reported respectively.Third, the way of coupling between rectangular laser and conventional step index fiber (SIF) by anamorphic core-shape PCF is proposed, that the end with round core connect to SIF, and the other end connect to the rectangular laser, comparing to directly coupling 3.9dB is achieved by this new method.Fourth, mode converter based on air hole collapse is studied in detail by null coupler theory, and several necessary principals making mode convert are presented, which inform that the two different cores, not splice-like part as mentioned by K. Lai (Optics Letters, 2007, 32(4),328-330), make mode convert. Several LP₀₁-LP₁₁ satisfied the conditions are proposed by these principals, and numerical results support the deduction .Fifith, the mode evolution in LP₀₁-LP₀₂ and LP₀₁-LP₁₁ mode converters are calculated, the mode field patterns and extinction ration are achieved; and the two mode converters are fabricated by controlled air hole collapse. The near field pattern at output end is achieved.