Delivery of single-mode and multi-mode therapeutic laser light using a single and dual cladding optical fiber for a scanning fiber endoscope

The integration of thermal and photodynamic therapy into a scanning fiber endoscope (SFE) for the purpose of pixel accurate laser therapy during an endoscopic procedure has been examined using two distinct methods: combining R-635nm, G-532nm, B-440nm (RGB) laser light for imaging with high-power 405nm single-mode or multi-mode laser light for therapy. The single-mode system utilizes a SIFAM 405/635nm fused fiber device to combine single-mode 405nm and 635nm laser light into the core of a single output fiber. The multi-mode system uses a custom combiner (Lightel Technologies) to guide single-mode RGB light from one fiber into the core of a custom single-mode dual cladding fiber (DCF, Coherent) and places multi-mode 405nm light from a second input optical fiber into the inner cladding of the DCF. This multi-mode system has a higher output power measured at 300mW compared to the single-mode system measured at 30mW before the addition of combiners. A lens system from the SFE at the distal tip of each therapeutic system was used to focus the light without scanning. The resulting minimum spot diameters were 77microns for the single-mode system and 311microns for the multi-mode system, which equates to fluence rates of 644W/cm2 and 395W/cm2 respectively. Future studies will integrate a scanning fiber probe to the outputs of each system allowing the therapeutic light to be directed throughout an entire image as well as the ability to use wide-field fluorescence imaging with 405nm excitation.