Our expertise in fiber optics fusion and tapering technology is at the core of Castor Optics' success. This precise process enables us to create highly specialized fiber optics components that ensure minimal optical losses and maximum sensitivity, even in low-photon and high-noise conditions. By leveraging this advanced technique, we help engineers and scientists push the boundaries of detection systems, ensuring every photon is captured and utilized effectively in their most demanding applications.
What Is the Fusion and Tapering Process?
The fusion-tapering technique involves precisely positioning two or more optical fibers into a specific arrangement and heating and tapering them to obtain the desired transfer function. The optical properties of this structure (how light behaves as it propagates to the output) are primarily influenced by the degree of fusion, the taper profile – or slope, and the alignment of each fiber core relative to the other(s). Minute control over these parameters results in couplers with superior performance and robustness compared to alternative technologies.
The results of a technology transfer from Polytechnique Montreal’s Laboratoire des Fibres Optiques [1] over 10 years ago, Castor expertise in fiber coupler fabrication has continuously been refined. The Castor team has developed novel fiber geometries and processing techniques to create increasingly sophisticated and performant fiber couplers.
Unlocking Endless Configurations
A Range of Fiber Types
Castor specializes in fabricating asymmetric couplers that may use different optical fibers. Single-mode fibers propagate a fundamental Gaussian mode through a small core, with a typical diameter between 2 to 11 microns, depending upon the operation wavelength. In contrast, multimode fibers have much larger cores, from 50 to hundreds of microns in diameter, and propagate light in thousands of modes, resulting in a flat top power distribution. Castor’s flagship product was developed around the double-clad fiber (DCF), which integrates the advantages of both previously described fiber types: a single-mode core surrounded by a multimode inner cladding. Castor’s expertise lies in seamlessly combining these fiber types into highly performing couplers.
Why Does our Technology Work for High Sensitivity Detection?
Castor’s primary objective in product design is always maximizing light transfer and transmission, which will have a direct impact on the signal-to-noise ratio (SNR) of a detected signal. This is achieved by minimizing insertion and excess losses. At the same time, all our packaging configurations are optimized to achieve the highest return loss performance, reducing the noise level. This dual optimization, together with our experts’ advice for system integration, enables Castor couplers to significantly improve the SNR of any detection system they are integrated into. Castor has developed specialized expertise to make this achievement possible. Explore our formula for success below.
Respecting the Adiabaticity Criterion
A critical fabrication parameter that we optimize for at Castor is the adiabaticity of the fused and tapered structures. When the process is adiabatic, no energy from the core is transferred to the cladding, resulting in a structure with minimal losses. To respect this criterion, fiber types, and fabrication parameters must be carefully chosen to obtain a structure with the right degree of fusion, steepness, and fiber alignment.
Conserving the Etendue
The etendue refers to the optical extent of a beam in surface area and angle. In fiber optics devices, it is defined as the product of the fiber’s numerical aperture (NA) squared and its area. Conserving the etendue results in conserving the optical power in a system, resulting in minimal losses. At Castor, we exploit this concept in fabricating our double-clad fiber couplers [2] and multimode circulators, allowing us to improve light transfer and overall performance.
Managing Noise Sources
Return losses primarily arise from back-reflections at fiber facet-to-air interfaces, contributing to background noise. Our products implement different strategies to reduce and manage these back-reflections at critical ports. We have developed solutions for both single-mode and multimode fibers, including high-return-loss beam dumps for unused ports and high-return-loss connectors for the sample port.
Key metrics
Insertion loss: The amount of signal loss a coupler induces from port to port, measured relative to the signal propagation in the same optical fiber without the coupler (i.e., an equivalent fiber length).
Excess loss: The total signal loss a coupler induces from the input port to all output ports, measured relative to signal power before entering the coupler.
Return loss: The proportion of light back-reflected to the input port for a given port, measured relative to the initial signal strength injected into that port.
References
1. Lacroix, S., N. Godbout, and X. Daxhelet. "Optical fiber components: design and applications of fused biconical tapered components." Optical fiber components: design and applications (2006).
2. Wendy-Julie Madore, Etienne De Montigny, Olivier Ouellette, Simon Lemire-Renaud, Mikael Leduc, Xavier Daxhelet, Nicolas Godbout, and Caroline Boudoux, "Asymmetric double-clad fiber couplers for endoscopy," Opt. Lett. 38, 4514-4517 (2013).