A novel copolymer optical fiber with high azobenzene concentration is reported (more than 3.2 mol %). The orientation process of the preform was fitted with corrected bi-exponential equation. Compared with the doped one, the photosensitivity of this kind of copolymer optical fiber preform is analyzed. The influence of azobenzene concentrations and write conditions on photosensitivity of copolymerized PMMA was analyzed. Then, long-period of 120um birefringent grating was fabricated in the single mode fiber with core refractive index of 1.485 (at wavelength of 1.5um), and relative index difference delta of 0.008. The duty cycle is 50%, and the refractive index change in the exposed area is about 4*10-4 for the ordinary or extraordinary ray.
Inexpensive PMMA based Polymer Optical Fiber (POF) has the feature of a large core diameter, high numerical aperture and great flexibility, thus allow low connection cost and cheap LED source. These advantages make it a promising candidate for short distance communication. In this article, coarse wavelength division multiplexing (CWDM) test was performed with commercially available POF using its low loss transmission window. Light of two different wavelengths (650nm and 530nm) were sending on a single POF. Here 650nm red light was used for duplex IP data digital signal transmission and 530nm green light was used for voice signal transmission. Light sources are LEDs. A POF Coupler (Splitter) of 1:1 ratio was employed as multiplexer and prisms were used for demultiplexing. The channel isolation and insert loss of both channels were measured, for 650nm channel they are 20.5dB and 17.65dB, for 530nm channel they are 19.16dB and 20.55dB.
Birefringence gratings induced by 532nm polarized laser in an azobenzene doped polymethyl methacrylate (PMMA) fiber and perform block were investigated. Significant photo-induced birefringence has been observed from the fiber. The maximum induced index change is about 3.1x10+MIN5) from this material. The induced birefringence was attributed to the nonlinear absorption at 532nm wavelength. It is found there is the threshold intensity of 0.29mW/cm2. The birefringence decayed little by little when laser turned off, a certain amount of saturation was remained. The dynamics process of the birefringence was studied. This birefringent grating may apply in the polarization dispersion compensation of the fiber communication.
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