KEY WORDS: Nonlinear optical microscopy, double-clad photonic crystal fibre coupler

A double-clad photonic crystal fibre (DCPCF) has the unique dual function which can offer the efficient delivery of an excitation laser beam in the fibre core and signal collection through the inner cladding. The detection efficiency of the nonlinear optical microscopy system based on the DCPCF is approximately two orders of magnitude higher than that using a standard single-mode fibre [1]. To achieve an all-fibre microscopy system, a 1×2 DCPCF coupler has been fabricated to replace bulk optics and gain self-alignment. The DCPCF coupler is fabricated using the fused tapered method [2], showing a low excess loss of 1.1 dB and a splitting ratio of 97/3 over the entire visible and near-infrared wavelength range. In addition to the property of splitting laser power, the double-clad feature of the coupler facilitates the separation of a near-infrared single-mode beam from a visible multi-mode beam, which is ideal for nonlinear optical microscopy imaging. 2. CHARACTERIZATION OF A NONLINEAR OPTICAL MICROSCOPE BASE