Fider optics (Возникновение волоконной оптики) — страница 5

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Baird and Hansell patents, and Moeller Hansen was unable to interest companies in his invention. Nothing more was reported on fiber bundles until 1954, when Abraham van Heel of the Technical University of Delft in Holland and Harold. H. Hopkins and Narinder Kapany of Imperial College in London separately announced imaging bundles in the prestigious British journal Nature. Neither van Heel nor Hopkins and Kapany made bundles that could carry light far, but their reports the fiber optics revolution. The crucial innovation was made by van Heel, stimulated by a conversation with the American optical physicist Brian O'Brien. All earlier fibers were "bare", with total internal reflection at a glass-air interface. Van Heel covered a bare fiber or glass or plastic with a

transparent cladding of lower refractive index. This protected the total-reflection surface from contamination, and greatly reduced crosstalk between fibers. The next key step was development of glass-clad fibers, by Lawrence Curtiss, then an undergraduate at the University of Michigan working part-time on a project to develop an endoscope to examine the inside of the stomach with physician Basil Hirschowitz then working at the American Optical Co., made glass-clad fibers at about the same time, but his group lost a bitterly contested patent battle). By 1960, glass-clad fibers had attenuation of about one decibel per meter, fine for medical imaging, but much too high for communications. Meanwhile, telecommunications engineers were seeking more transmission bandwidth. Radio and

microwave frequencies were in heavy use, so they looked to higher frequencies to carry loads they expected to continue increasing with the growth of television and telephone traffic. Telephone companies thought video telephones lurked just around the corner, and would escalate bandwidth demands even further. The cutting edge of communications research were millimeter-wave systems, in which hollow pipes served as waveguides to circumvent poor atmospheric transmission at tens of gigahertz, where wavelengths were in the millimeter range. Короткая история волоконной оптики. Часть 2 В 1951, Holger Moeller {или Moeller, o имеет разрез через это}, Hansen просил датский патент на оптическом

волокном отображении. Однако, датское патентное бюро отрицало его заявление, цитируя патенты Baird и Hansell, и Moeller Hansen был неспособен интересовать компании его изобретением. ни о чем больше не сообщали относительно связок волокна до 1954, когда Пятка фургона Абрахама Технического Университета Дельфта в Голландии и Гарольда. H. Hopkins и Narinder Kapany Имперского Колледжа в Лондоне отдельно объявили связки отображения в престижном британском

журнале Природа{Характер}. Authentication (модуль 2) Do you know if the user logged in is really that person? It is an all to common practice for people to use other people's accounts to authenticate themselves to the server. In most wireless network, businesses often configure one account, "Wireless User," and that account can be used by several different devices. The problem is that a hacker (with his own wireless device) could easily log onto to this general account and gain access to your network. To prevent an unauthorized user from authenticating himself into your network, you can set your router to permit only connections from authorized wireless network cards. Each wireless network card has a Media Access Control (MAC) adress that

uniquely identifies it. You can tell your router only to authenticate those wireless users with a network card that is pre-authenticated to use your network. This protects you against users who are trying to gain access to your system by roaming around the perimeter of your building looking for good reception to log onto your local area network. Установление подлинности (модуль 2) Вы знаете, загружался ли пользователь - действительно тот человек? Это - все к общей{обычной} практике для людей, чтобы использовать счета других людей, чтобы подтвердить подлинность себя к серверу. В