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Fiber coupling
Fiber coupling of the laser
According to operational needs, we can focus laser beams in free space and couple them into various optical fibers for transmission. For more fiber coupling products, click here to learn more.
Through the fiber coupling of the laser, the laser propagates in the fiber. It not only has advantages such as long-distance transmission, flexible bendable transmission and path interference avoidance, but also can achieve effects like mode selection, spot adjustment, optical field reconstruction and multi-wavelength beam combining.
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Free space output laser | Fiber coupled output laser |
Laser beams in free space need good beam quality, excellent spatial directivity and environmental stability. Only through precise adjustment of the focusing coupler can they be coupled into optical fibers accurately and efficiently. Especially when the core diameter of the used optical fiber is very small (e.g., the core diameter of general single-mode or polarization-maintaining fibers is only 3-5 μm), the requirements for the laser, coupler, adjustment accuracy and other aspects become more stringent.
Optical fiber
Laser transmission in optical fibers utilizes the principle of total internal reflection. These slender transmission media, made of glass or plastic, typically have a diameter ranging from several micrometers to hundreds of micrometers. They mainly consist of a core, cladding, and coating. The core is the central part where light propagates; the cladding has a lower refractive index than the core to enable total internal reflection, while the coating serves a protective function.
The Structure and Materials of Optical Fibers
In addition to the optical fiber material and core diameter, the numerical aperture (NA) of the optical fiber is also a very important parameter. It describes the size of the cone angle when laser light enters or exits the optical fiber.
As shown in the figure below, when laser beam is focused into the optical fiber through a coupler, not all the light incident on the fiber end face can be transmitted by the optical fiber—only the incident light within a certain angular range is feasible. The sine of this angle α determines the numerical aperture of the optical fiber (NA = nsinα). The NA range of commonly used optical fibers is generally between 0.10 and 0.25.
Fiber NA and the Cone Angle for Laser Coupling into Optical Fibers
Of course, we can also calculate the optical field cone angle when the laser exits the optical fiber based on the fiber's numerical aperture. For example, the divergence angle (half-angle) of the laser emitted by a silica fiber with NA = 0.12 is 6.8 degrees, while that of a silica fiber with NA = 0.22 is 12.4 degrees.
Commonly Used Types of Fiber Optic Couplers
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Connector | SMA905/ FC | SMA905/ FC | SMA905/ FC | SMA905/ FC | FC |
Features | Fixing screw | Fixing thread | Used for big beam spot | Power attenuable | Used for SM fiber and fiber removable |
Compatible Models | U, S | III, H, FN, F | N, W, D, SD, MD, HD, XD | DS, U, FN | DS, E, U, III, FN, F, N, W |
For specific models or parameters, please refer to www.
Commonly used types of optical fibers
Fibers for laser coupling/transmission are categorized by material, core diameter, structure/function into single-mode, polarization-maintaining, multimode, homogenizing fibers, fiber bundles, etc. Standard fiber connectors include SMA905 and FC.
(1) Single-mode fiber: Typically with a core diameter of only 3-5 μm, it generally has low laser coupling efficiency when entering the fiber, and the laser field mode exiting the fiber is an excellent TEM₀₀ mode (Gaussian distribution).
(2) Polarization-maintaining (single-mode) fiber: Ideal single-mode fiber has good geometric circular symmetry, but stress, bending, temperature, etc., cause asymmetry and birefringence in practice, leading to irregular polarization state changes in ordinary fibers during propagation. Polarization-maintaining fiber solves this via geometric design, generating stronger birefringence to reduce stress-induced polarization effects. It is thus used in polarization-sensitive applications like interferometers or laser-external modulator connections.
(3)Multimode fiber: A fiber that transmits multiple modes at a given operating wavelength. It is classified into step-index and graded-index types based on refractive index distribution. Standard multimode fibers have a numerical aperture (NA) of 0.2±0.02 and core diameters of 50μm, 100μm, 200μm, 400μm, 600μm, 1000μm, etc. Common standard fiber interfaces include FC and SMA905, with PVC and metal as the main jacket materials. CNI also offers multimode fibers with numerical apertures of 0.1 and 0.39.
(4) Liquid-core fiber: Using liquid as core (e.g., specific organic liquids, solutions, ionic liquids) and polymer as cladding, it overcomes traditional glass fiber transmission bottlenecks. Liquids' inherent refractive index, nonlinearity, and sensitivity to temperature/pressure enable higher duty cycle, coupling efficiency, and transmission efficiency in specific bands vs. traditional fibers.
CNI's Liquid-core fibers are widely used in UV curing, fluorescence detection, criminal forensics, and scientific research.
CNI's liquid-core optical fibers are widely used in UV curing, fluorescence detection, forensic investigations, and scientific research.
(5) Fiber bundle: Multiple fibers bundled in a specific arrangement, categorized into single-mode and multimode types. Multimode bundles include parallel-arranged ribbon fibers and bound bundled fibers. CNI’s laser-used multimode bundles are typically taper fused fiber bundles (TFB)—manufactured by stripping fiber coatings, arranging fibers, high-temperature melting, and bidirectional stretching to form tapered fused structures. TFB combines multi-wavelength lasers from multiple inputs for combined output via fusion technology.
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Single-mode Fiber | Multimode Fiber | Polarization-Maintaining (Single-Mode) Fiber | Liquid-Core Fiber |
For more detailed specifications of the fiber optic cable, please refer to www......
Fiber Collimator
Fiber output modes include free output and collimated output. Free output refers to direct fiber output, while collimated output involves attaching an end collimator to the fiber tip. Collimators are mainly used to collimate lasers, adjusting their beam diameter and divergence angle.
In laser processing, they collimate the laser beam before focusing it on the workpiece, improving processing precision and energy density. In optical imaging systems, they enhance imaging quality and reduce aberrations and blurring caused by beam divergence. At the receiving end of optical communication, collimators collimate received optical signals before coupling them into detectors and other receiving components, boosting the efficiency and accuracy of signal reception. This ensures the entire optical system can effectively process and utilize optical signals at the end stage, improving overall system performance and reliability. Collimators play a crucial role in numerous optical and optoelectronic applications, serving as key components to optimize and refine light source processing workflows.
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Single-mode Fiber | Multimode Fiber | Liquid-core Fiber |
There are several types of fiber collimators available. For details, please visit www.
Beam profiles of the fiber output
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Single-mode Fiber | Multimode Fiber | Liquid-core Fiber | Homogenized Square Spot Fiber |
CNI Laser offers fiber output modes such as flat-top and homogenized. Through specialized design, it can regulate the propagation mode of light beams in the fiber core while maintaining efficient light transmission and ensuring ultra-low insertion loss. Homogenizing fibers enable high-efficiency integration with existing optical systems and are suitable for applications including laser cladding, laser cleaning, laser welding, uniform illumination, spectroscopy, power supply, and medical treatment.
For detailed specifications, please refer to www......
Changchun New Industries Optoelectronics Technology Co., Ltd.
Address: No. 888 Jinhu Road, High-Tech Zone, Changchun, 130103, P.R.China
International Tel:+86-431-85603799
Email: sales@cnilaser.com
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