Castor Optics' Wideband Multimode Circulators (WMCs) are versatile in-fiber multimode light management components. These fused fiber components are three-port devices featuring a flat spectral response and high-efficiency multimode transfer and transmission. They can combine multiple signals or illumination/detection channels within a single fiber. Castor's co-president and WMC co-inventor, Nicolas Godbout, says:
The Wideband Multimode Circulators allow to efficiently illuminate and probe the light on a sample surface. They seemingly break the reciprocity law of optics by exploiting the properties of multimode light propagation. At Castor, we don't break the laws of physics, but we know how to bend them!
Castor Optics' is now expanding its product line by adding a 400-micron fiber core circulator. The all-fiber WMC family is an efficient solution with applications in diffuse reflectance spectroscopy, fluorescence spectroscopy, and optogenetics.
Exploiting the optical etendue for high-efficiency light transfer
Multimode circulators are a technology introduced on the market by Castor Optics. Unlike conventional multimode splitters, whose ratios are determined by the degree of fusion of the component, multimode circulators' high efficiency comes from fusing fiber optics with asymmetrical optical etendue. The optical etendue, also called throughput or optical extent, describes the cone of acceptance of an optical system. For a fiber optics system, it corresponds to the product between the fiber core area and its numerical aperture. The use of optical etendue to characterize multimode transmission and transfer was first used by Madore et al. to describe the behavior of double-clad fiber couplers. By conservation of the etendue, in a fused coupler, the light will split with a ratio proportional to the ratio of etendue of the fibers used. Using fibers of different etendue enables modulating the coupling ratio in favor of transfers from the fiber with a smaller etendue to the fiber with a larger one.
The newly launched WMC4H1 multimode circulator uses a 200-micron core fiber with a 0.22NA fused to a 400-micron core fiber with a 0.39NA, allowing a transfer from Port 1 to 2 of more than 80%. When light propagates from Port 2 to Port 3, "seeing" an optical etendue differential, most will be captured by Port 3 with a more than 80% transmission.
Exploiting asymmetrical optical etendues enables multimode components with a behavior equivalent to that of a single-mode circulator.
New fiber core size, new possibilities!
The WMC4H1 is particularly interesting in neuroscience, where fiber systems are increasingly popular to perform fiber photometry, used to infer brain functional activity via the excitation of fluorophores, and optogenetic manipulation. A high-efficiency system is critical to ensure enhanced sensitivity of the collected fluorescence emission. Using a larger collection fiber in combination with a high transmission circulator enables the recording of photometry signals in awake animals.
Multimode circulators have also been used for spectroscopy for applications ranging from single-fiber reflectance spectroscopy to multimodal imaging combining optical coherence tomography with spectroscopy, and ocular spectroscopy.
The WMC4H1 and the complete multimode circulator series are available on Thorlabs.com. To learn more about how Castor Optics' innovative fiber optics technology can enable faster, farther, and brighter sensing, contact our team at sales@castoroptics.com.
Écrit par Kathy Beaudette
Directrice du développement des affaires
