Double-Clad Fiber (DCF) transmit single mode in the core and multimode in the inner cladding layer efficiently. The diagram to the right depicts DCF cross-section structure. This unique feature can be utilized for sensor applications in which a laser beam is launched
through the small center core and the reflected lights are collected by the large cladding layer. This approach improves light collection efficiency. Photonwares produces couplers and circulators that separate the return lights and guide them into a detector via a large mode fiber. These 2×2 Double-Clad Fiber Couplers combine a double-clad fiber with a large core step-index multimode fiber. Light in the single mode core transmits with little loss over the 430 – 680 nm, 680 – 980 nm, 960 – 1260 nm, or 1250 – 1550 nm wavelength range. The multimode transfer efficacy, defined as the ratio of the output signal at large core multimode fiber Port 3 to the light intensity input at Port 2, is ≥60% over a wider wavelength range of 400 – 1750 nm, excluding the water absorption region around 1383 nm. Double-clad fiber couplers are well suited for applications at 530 nm, 780 nm, 1060 nm, or 1300 nm.These double-clad fiber couplers can be used for many imaging and sensing applications, including LiDAR, Optical Coherence Tomography (OCT), Fluorescence Imaging, Confocal Microscopy, Surface Plasmon Resonance (SPR) Sensing, Speckle-Free Single-Fiber Endoscopy. The inner cladding of the fiber behaves like a pinhole in a confocal microscopy setup, preserving optical sectioning while increasing collection efficiency and reducing laser speckle. Additionally, this coupler can be used to combine optical coherence tomography (OCT) with fluorescence imaging, spectroscopy, or confocal microscopy. The sensing end can be further configurated with multiple multimode fibers to collect signal lights in various locations/positions, as shown in Fig.2. Custom configurations using different DCF and coupling detector fiber are available.
Fig.1 application example- single mode probing laser, multimode reflection signal collection though a shared lens.