Fiber-Optic Power Limiter Based on Photothermal Defocusing in an Optical Polymer

We describe the performance of a fiber-optic power-limiting component. The passive device is dynamically responsive to the input signal and has been shown to attenuate continuous-wave power with a dynamic range of up to 9 dB at 150 mW of input power at 1550 nm. The limiting threshold is approximately 30 mW from 1530 to 1565 nm and less than 10 mW at 1430 nm. The device is activated by a photothermal defocusing mechanism in an optical polymer fixed between two expanded core fibers that collimate light through the material. The magnitude and threshold of the limiting response is dependent on the absorption properties of the polymer and the size of the gap between the two fiber endfaces. Simple model calculations have been made to predict the limiting response, and they agree reasonably well with the performance of the actual device.