Fiberoptic Technology--DALSA Life Sciences

Fiber Optics

Experience, expertise, and attention to detail let us provide better-quality, more reliable fiber-to-sensor interfaces

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Why use fiber optics in digital radiography?

better image resolution
more efficient light collection and transmission
tapered, buttable modules can image larger areas

Done properly, fiber optic faceplates placed between x-ray scintillators and CCD or CMOS imagers provide vastly improved image resolution compared to lenses. Light from an x-ray scintillator tends to scatter, but a faceplate made from coherent fiber optic strands minimizes scatter and preserves image intensity and resolution. No glass (lenses included) has perfect, 100% transmission, but by demagnification, fiber optic tapers can boost the light collected onto a imager by 10x compared to f/1.2 lens. And buttable fiber optic-to-imager modules can allow seamless imaging of large areas.

What are the challenges?

transmission efficiency
precise, robust attachment
distortion and response non-uniformity degrading image quality

The advantages of fiber optics are clear, but there are also challenges. The fiber faceplate must be attached to the image sensor with extreme precision. Gaps, irregularities, or residue from the bonding process can introduce unacceptable distortions and reduce transmission efficiency. Sensor heat cycling can cause bonds to deteriorate. Insufficient fiber can cause "chickenwire" or moire patterns in the image. Inferior fiber or poor butting processes can show up as opaque "seams" where butted tapers meet. And while tapering can be very useful, transmission efficiency decreases with the degree of taper. Applications that require the highest transmission efficiency need expensive, large-area sensors with non-tapered faceplates.

Why does DALSA Life Sciences excel?

Higher transimission efficiency: There are several ways to couple a fiber optic reducer to an imager. The easy way is to bond a fiber optic faceplate to the sensor, and then oil-couple the reducer to the faceplate. While this method is easy, it causes about 40% light loss at the fiber-to-fiber interface. We bond the fiber optic reducer directly to the CCD or CMOS imager, which is more difficult to do, but eliminates this 40% fiber-to-fiber interface light loss. We also assure a uniformly thin layer of epoxy between the fiber and the imager (no more than 20 microns) to preserve resolution uniformity.
Precise, robust, reliable attachment: Again there are several ways to couple a fiber to the surface of the sensor. One way is to use oil coupling, the other is the use of a hard epoxy. DALSA uses a hard epoxy for better reliability during thermal cycling. Although many companies have problems with debonding of the fiber/sensor assembly, especially when the imager is cooled, DALSA has bonded over 1000 cameras with fiber/sensor assemblies with an excellent yield. Even when cooled to -45 degrees C, our debonding rate is very low. Having a good fiber/sensor assembly that works to such low temperatures gives us a tremendous edge, because sensors generally cannot be rebonded, making debonding failures very expensive.
Higher image quality: On the average we have 16 fibers delivering light to each sensor pixel (6 micron fiber diameter, 24 micron pixel). This assures the elimination of moire patterns. Our software can correct each image for all sources of fixed pattern noise (the strongest of which is the fiber optic chickenwire pattern) before the image display.

DALSA Life Sciences sources some of the best fiber optics available. Through experience and innovation we have developed considerable expertise in coupling faceplates and tapers to sensorss to maximize image quality and durability. Our process is effective, efficient, and robust, even for back-illuminated sensors. And it is scalable--we can handle large volumes without sacrificing quality or consistency. Fiber optics are just one of the core technologies, have enabled our products to prove themselves in hospitals, clinics, and laboratories around the world.

For more information, contact Sales.