Optical Microfiber Fabrication And All-optic Microfiber Modulator

As important hardware base of micro-nano photonic integrated optical systems, optical microfibers are important realization ways for future all-optical integrated applications, such as all-optical communications, optical sensing and optical information processing etc.. In this thesis, the manufacture technique of optical microfibers is improved due to optical microfiber sensing application requirement; in-line optical monitoring system is set up to monitor the straight and the opposite light in the optical microfiber during the tapering process. The sudden change position in the intermodal interference spectrum is used to judge or calibrate the diameter of the fabricated optical microfiber so that an effective improvement of high quality microfiber tapering technique is realized. By heating and annealing temperature controlling, optical microfiber samples with stronger absorption and higher backscattering ability are achieved. Though these kinds of optical microfibers has sacrificed their low-loss property, we can achieve a partial reflector based on the backscattering-enhanced optical microfiber and an all-optical phase modulator based on the light absorption induced thermal effect by theoretical analyze and optimized design. Optical microfiber coupler is theoretical and experimental studied and the optical property difference between the optical microfiber coupler and the four ports optical microfiber has been determined. The coupling ratio controlling method in the optical microfiber coupler is studied according to the light absorption induced thermal effect. An all- optical intensity modulator based on the optical microfiber coupler is achieved. The main work of the thesis is introduced as follows:(1) The intermodal interference and the mode evolution are monitored during the optical microfiber tapering process by using a high coherence laser as the light source of the inline monitoring system. In the intermodal interference spectrum, the sudden change position, especially the cutoff position of LP02 mode, can be used to o judge or calibrate the diameter of the fabricated optical microfiber. The cladding’s absorption loss test method is also designed to judge the diameter of the optical microfiber so that we can assess the accordance property of the optical microfibers in the same bulk.(2) The characteristics of the microfiber’s back scattering are theoretically analyzed, the control method in the tapering process to regulate the back scattering characteristics is realized, and the back scattering enhanced microfibers are produced with reflectivity of 0.1-1%. By using the optical microfiber weak reflector with reflectivity of 0.5 % as a reflector of the F-P interferometer, it is demonstrated that the back scattering enhanced optical microfibers can be used as passive photonic devices with reflective function.(3) The characteristics of the optical microfiber’s phase modulation based on the light induced thermal effect are theoretically analyzed. The measurement system for the optical microfiber phase modulator is designed and fabricated. Under the modulation of 980 nm light with average power of 1.7 millwatts, the optical microfiber phase modulator can realize modulation frequency as ~20k Hz, and obtain a π modulation amplitude under 1k Hz modulation frequency and average power of 7.5millwatts.(4) The tapering technique and optical transmission characteristics of optical microfiber couplers that produced with two twisted optical fibers by direct draw method are introduced. The optical microfiber coupler with wavelength scale of waist region is manufactured and experimentally studied. Experimental results show that coupling capacity almost disappear when the diameter of the waist region is less than 2.5 μm at wavelength of 1.5 micrometer band. And the optical microfiber couplers serve as the “Four Ports Optical Microfiber”(FPOM). The characteristics of optical microfiber coupler’s thermal-optic modulation are theoretical analyzed and experimentally studied. The microfiber coupler based all-optical intensity modulator is produced. By using the structure optimized all-optical intensity modulator, the modulation of 1550 nm light is realized with frequency range of 50 k Hz under 980 nm pump light with power of 1.6 milliwatts. The modulation depth can reach ~75% under modulation frequency of ~1 k Hz and average power of 2.5 milliwatts...