Fiber Optic Tapers Selection Guide
What is Fiber Optic Taper
Fiber optic tapers (FOT) are coherent glass fiber optic bundles made into a taper shape, it can be used to magnify or minify image signals. The function is very similar to a focusing lens. But you will not need to adjust the focus and it can be directly coupled to sensors. Which improves the light efficiency and simplify your optical design. Also make the whole design lighter and much smaller (compared with lens system).
Fiber Optic Taper (2x Magnification)
In the fiber optic taper manufacturing process, a cylindrical fiber optic block is premade, the central zone of the block is heated, then fiber optic block is stretched. This resulting an hourglass-shaped piece, then cut into two pieces of fiber optic tapers.
Fiber Optic Taper Drawing Process
Fiber optic tapers offer compact and lens-free solutions to applications such as CCD coupling, medical imaging, and scientific imaging.
Key Parameters of Fiber Optic Tapers
- Magnification Ratio:
The image magnification ratio is the ratio of the diameters of the large and small ends of the Taper. Since light can pass through the taper in either direction, it serves equally well as both a concentrator and magnifier. Magnification ratio could go up to 6x - Fiber size (diameter):
Also called fiber pitch, this refers to the single fiber diameter on the large end of Fiber optic taper. (Small fiber diameter means a higher resolution)
Fiber Optic Taper under microscope (160x)
- Taper Height:
The vertical length of the taper. Usually approximately equal to the diameter of the big end. - Numerical Aperture:
Fiber acceptance angle, the larger the Numerical Aperture, the greater of luminous flux will be entering the fiber optic image element
Numerical Aperture Illustration
- EMA
Known as Mural Absorption Fibers is used between the imaging fibers. Crosstalk” can also occur when unwanted light from one fiber optic strand scatters to another, when they are aligned side-by-side. EMA is used to eliminate that crosstalk.
Applications of Fiber Optic Tapers
Scientific Cameras
The basic structure of an intensified camera is sketched in Figure below. It consists of an image intensifier tube that is coupled to a solid-state array by means of a fiber optic taper or relay lenses. The signal amplification takes place in the image intensifier tube. Incoming photons are converted into photoelectrons at the photocathode on the inside surface of the input window. A voltage difference applied between the multi-channel plate (MCP) and the photocathode draws the photoelectrons towards the MCP. Within a channel of the MCP, the photoelectrons are further accelerated due to a high voltage across the MCP and create additional electrons by means of secondary emission. The electron gain of this process can be adjusted to some extent by the applied voltage difference.
Electrons emerging from the MCP are converted at the phosphor screen to visible photons, which are optically linked to a solid-state array, where they are detected as electronic signals.
Lens-less Microscope
The microscopic imaging platform based on fiber optic Taper coupled CMOS module utilizes a coupling medium to form a closed optical waveguide between the CMOS photosensitive surface and the large facet of a fiber optic taper. The mechanism reduces the scattering loss of light and make the pixels on the CMOS photosensitive surface correspond to the pixel of the imaging device connected to the large end of fiber optic taper to provide a high image resolution and clarity.
Xray Detector
an optical system (a fiber optic taper), and a high-resolution CCD camera. The scintillator is directly coupled to the image intensifier via a fiber optic window. With the detector operating in photon-counting mode, an X-ray interaction is seen as a cluster of signals spread over multiple pixels. Significant improvement in spatial resolution is achieved by estimating the interaction position through a centroid calculation for the cluster. A two-dimensional position estimation can also be achieved through the use of maximum likelihood techniques. Because scintillation light is amplified (via the image intensifier) prior to entering the imaging chain, the system is no longer limited by light loss in the optical path. This allows for the use of a low-cost, high-speed CCD. It also allows for the use of a low-cost optical system, which couples the output screen of the image intensifier directly to the photosensitive surface of the CCD. The optical coupling system of the detector is a fiber optic taper instead of lenses.
Xray Detector Based on Fiber Optic Taper
Different Configuration of Fiber optic Tapers and Accessories
1.5x – 3x Standard Fiber Optic Taper (sFOT) >
– Mature Product, Economic Pricing
– Lower Distortion
3.1x-6x High Mag Fiber Optic Taper (hFOT) >
– Experimental Product, Higher Pricing
– More Compact than sFOT
– Higher Distortion
Fiber Optic Taper Array (FOTA) >
– Suitable when you need a large surface (And single taper price goes too high)
– Bonding Multiple FOTs together to make a Taper array.
Fiber Optic Taper Coupling to CMOS/CCD >
– Remove Protection Window on Sensor
– Using suitable optical adhesive bonding Taper Small End to Sensory Surface
– Sourcing Equivalent CCD/CMOS (Optional)
Difference between sFOT and hFOT
sFOT and hFOT are made with different manufacturing procedure, material and machinery (fixture, furnace, cooling etc…)
sFOT:
sFOT are coming with magnification ratio from 1.5x-3.0x. Fabricating with standard materials and protocols.
Taper height is very close to the diameter of large end.
Low defect rate, prices are relatively low.
hFOT:
hFOT are coming with magnification ratio from 3.1x-6.0x. Using a modified material, special furnace and algorithm for temperature control.
Taper length could made lower than its large end diameter. (e.g., 70% ~ 90%).
Higher defect rate, and prices are higher.
How light is transmitted inside Fiber Optic Taper
The image below shows what happens to a light ray entering a tapered fiber at an angle θ1. If the ray meets criteria for total internal reflection, it is confined in the core.
However, it meets the core-cladding boundary at different angles on each bounce, so each total internal reflection is at different angles from the axis. The result is that it emerges from the fiber at a different angle, θ2. If input core diameter is d1 and output core diameter is d2, the relationship between input and output angles is:
The same relationship holds for the fiber’s outer diameter as long as core and outer diameter change by the same factor, d1/d2.
As a numerical example, suppose the input angle is 30° and the taper expands diameter by a factor of 2. The sine of the output angle θ2 would be:
Thus, θ2 would be about 14.5° and light exiting the broad end of a taper would emerge at a smaller angle to the fiber axis than it entered. Conversely, light going from the broad end to the narrow end would emerge at a broader angle.
Notes: Tapered bundles of fused fibers can be used as magnifiers if the narrow end is placed on a page, and you look at the top side. Each fiber expands or shrinks the spot of the image it transmits by the same amount. The eye sees this as each spot being spread over a larger area at the large end of the taper. This increases the size of the image, but not the clarity, because the transmitted image has only as many picture elements as the narrow end of the bundle.
