Feature Articles

Silicon Photodiodes Matched to the CIE Photometric Curve Using Color Filter Glass

Color filter glasses are integrated with silicon photodiodes for spectral matching that correlates to the same visual sensitivity of a normal human observer. The actual response curve is defined by CIE (Commission Internationale de Eclairage), and is referred to as the Standard Photometric Observer. The response curve is based on several different studies from the 1910s and '20s using a statistical sample of individuals representative of the population at large. To match the relative response of the human eye to radiation at a given wavelength, unique subtractive color glass filters are prescribed to a thickness and installed in front of the detector. The filters mold the spectral response of the detector/filter combination to simulate the relative response of the human eye. The sensors may be manufactured on a production basis; however, careful attention must be paid to both detector and color glass filter variations.

by James P. Ritzel and Spike Sojourner
A Survey of Intellectual Property Rights in Optics

When asked why he had already spent $17,000 of his own money to file his patent application in the U.S. and in eight European countries under the Patent Cooperation Treaty, the engineer replied, "To become rich and famous." As he had, instead, become impoverished and obscure, he now had no kind words to say about the patent system in general, or his own lawyers in particular. I examined his documents and it appeared that he had gotten exactly what he paid for: a good patent with strong claims that, if enforced, can prevent all others from making, using, and selling his chromatographic invention in nine nations. What he did not seem to appreciate is that a patent is not a product, a product is not a business. And even a business is not a guarantee of fame and fortune. As his expectations were unrealistic in the first place, his disappointment was inevitable. So let us start at the beginning.

by Richard I. Miller
Hello, I'm Calling About a Manuscript

It had been a frustrating day in the lab. Hour after hour of labor and still no progress. I had tried everything, but still couldn't get the light to go through the pinhole. It wasn't as if I was working in the infrared. HeNe lasers are supposed to be simple to spatially filter and collimate. Then it dawned on me. I had forgotten the most basic of optics principles: light only travels from left to right! I was working from the wrong side of the optical table. Quickly, I ran around to the other side and—voilá—the red beam shot through the pinhole and down the length of the table. I was excited. This was groundbreaking research—experimental evidence confirming the previously only theoretically postulated left to right phenomenon.

by Michael W. Farn
The F-word in Optics

F-number was first found for fixing photographic exposure. But F/number is a far more flexible phenomenon for finding facts about optics. Douglas Goodman finds fertile field for fixes for frequent confusion for F/#.

by Douglas S. Goodman
Making Light of Stamp Collecting

With all the hoopla in past months over the Elvis stamps, one might easily forget that stamp collecting can be an enjoyable and educational hobby. Optical phenomena, optics devices, and the history of optics and photonics can all be found in the fascinating world of philately. Although the 1993 U.S. stamps to be issued include the circus, musicians, flowers, horses, and only one scientist—Percy Lavon Julian, an African American scientist and chemist whose work led to developments in the treatment of glaucoma—there is hope elsewhere for those seeking optics on stamps. In January 1993 alone, worldwide there were seven astronomy issues, three for light houses, and two for mathematics.

by Betsey Davis
Defining Reference Wavelengths: Is This Exercise Really Necessary?

Although we have written about the need for a reference wavelength in optics before, it is perhaps time to revisit it. There is a standard, ISO 7944, that defines two reference wavelengths for optics: the He "d" (yellow) line at 587.6 nm, and the Hg "e" (green) line at 546.1 nm. This standard is nearing another mandatory five-year review, and some parties want to see the Hg "e" line adopted exclusively as the reference wavelength: Some ophthalmic laboratories are rather upset with this idea because the diopter has been defined (historically) using the Na "D" line at 589.3 nm and a glass with an index of 1.53 at that wavelength. This means that if one desires to produce a plano-convex lens with a power of 1 diopter using a glass of index 1.53, the lens would have a 530 mm radius curve to give the required 1 meter focal length for light at 589.3 nm.

by Robert E. Parks
New Applications for Photorefractive Fibers

Our appetite for storing, retrieving, and transmitting large amounts of data appears to grow exponentially. Current communication and computer systems linked with copper wires are inadequate to satisfy this need, and are increasingly replaced by fiber optic-based networks. Fiber links have the bandwidths required for transmission of enormous volumes of data, that usually originate in electronic form, and are then converted into and transmitted as optical signals for subsequent backconversion into the electronic domain for further usage. These transformations are inefficient in terms of power consumption, and they are often the rate limiting steps in the overall system. Consequently, there is considerable interest in holographic data storage devices and other photonic devices having I/O bandwidths and processing rates commensurate with fiber optic networks.

by Lambertus Hesselink