Compact optical short-pass filters based on microfibers

We demonstrate a compact short-pass filter fabricated by integrating a microfiber (approximately 1 microm in diameter) with a low-index substrate. By varying the interaction length (from 0.65 to 3 mm) between the microfiber and the substrate for wavelength-dependent evanescent leakage, the cutoff wavelength has been tuned over a wide range of 400 nm. Typical rejection loss is higher than 40 dB with insertion loss as low as 0.3 dB. The fiber-diameter-dependent cutoff is also investigated, suggesting that the filter can be applied over a wide spectral range from 600 to 1500 nm. The microfiber-based short-pass filters demonstrated show advantages of compact size, wideband applicability, simple structure, high rejection loss, and compatibility with miniaturized fiber devices.