Composants en fibre optique à double gaine pour l'endoscopie à fibre unique

Double-Clad Fibres (DCFs) are a promising technology for single fibre endoscopy as their two claddings enable different injection/collection modes. The fabrication of a passive achromatic Double-Clad Fibre Coupler (DCFC) is explained and demonstrated in this master's thesis. Its application to Spectrally Encoded Endoscopy (SEE) is shown in a spectrally encoded benchtop setup. This coupler is obtained by fusing and tapering two DCFs. The core of the DCF is Single-Mode (SM) in the near infrared (9 microns diameter, NA = 0.12) and the inner cladding is Multimode (MM) (105 micron diameter, NA = 0.20). The fundamental mode is kept in the same branch of the coupler (same bre) (transmission of 95 %) while the inner cladding modes are statistically separated in each branch (40 % is transmitted in the other fibre). First, this coupler is used to obtain simultaneously SM and MM SEE 384 x 384 images in real time (26 fps) with a rapidly wavelength swept laser at 1310 ± 40 nm. In comparison with a traditional beam-splitter approach, the coupler increases the collected confocal SM signal by a factor 4 and the wide-field MM signal by a factor 2. Additionally, the DCFC is less sensitive to misalignments due to vibrations and transportation than the free space beam-splitter approach. The MM signal has a speckle contrast 4.6 times lower than the confocal SM signal. Also, using an all-fibre Mach-Zehnder interferometer in the SM path, a stereoscopic reconstruction equivalent have been obtained by superimposing the MM reflectance signal with the interferometric 3D reconstruction. Moreover, a Double-Clad Tapered Fibre (DCTF) for confocal endomicroscopy is demonstrated. This inherently achromatic DCTF, compatible with the DCFC, allows many injection/ collection modes depending on the final Inverse Taper Ratio (ITR). The point spread function of a spectrally encoded confocal microscope is optimized with the proper ITR. Compared to the SM signal, the MM signal showed a 3 times reduction in speckle contrast and a 5.5 times increase in signal collection while only increasing the optical sectioning by a factor of 1.7.