اتصالات بصرية

مصباح الإشارة بحري، شكل من أشكال الاتصال البصري يستخدم مصاريع ويستخدم عادة مع شفرة مورس (2002)

الاتصال البصري Optical communication، والمعروف أيضًا باسم الاتصالات البصرية عن بعد optical telecommunication، هواتصال على مسافة باستخدام ضوء لنقل المعلومات. يمكن إجراؤه بصريًا أوباستخدام أجهزة إلكترونية. تعود أقدم الأشكال الأساسية للاتصال البصري إلى عدة آلاف من السنين ، في حين حتى أقدم جهاز كهربائي تم إنشاؤه للقيام بذلك كان فوتوفون ، الذي تم اختراعه في عام 1880.

يستخدم نظام الاتصالات البصري مرسل ، الذي يشفر رسالة في الإشارة البصرية ، القناة ، التي ينقل الإشارة إلى وجهتها ، و جهاز استقبال ، الذي يعيد إنتاج الرسالة من الإشارة الضوئية المستقبلة. عندما لا يتم استخدام المعدات الإلكترونية ، فإن "جهاز الاستقبال" هوإنسان يراقب الإشارة ويفسرها بصريًا ، والتي قد تكون بسيطة (مثل وجود ضوء منارة) أومعقدة (مثل الأضواء التي تستخدم رموز الألوان) أوتومض في تسلسل شفرة مورس).

تم نشر الاتصال البصري في الفضاء الحر في الفضاء ، في حين حتى الأشكال الأرضية مقيدة بشكل طبيعي بالجغرافيا والطقس وتوافر الضوء. تقدم هذه الموضوعة مقدمة أساسية لأشكال مختلفة من الاتصالات البصرية.

نماذج

التقنيات البصرية مثل إشارات الدخان ، أضواء المنارة ، التلگراف الهيدروليكي ، أعلام السفن وخط الإشارة كانت أقدم أشكال الاتصال البصري. يعود تاريخ إشارات التلغراف الهيدروليكية إلى القرن الرابع قبل الميلاد في اليونان. لا يزال البحارة يستخدمون شعلة الاستغاثة في حالات الطوارئ ، بينما تُستخدم المنارة وضوء الملاحة لإبلاغ مخاطر الملاحة.

يستخدم المرسل مرآة لتعكس ضوء الشمس لمراقب بعيد. عندما يميل جهاز الإشارة المرآة ليعكس ضوء الشمس ، يرى المراقب البعيد ومضات ضوئية يمكن استخدامها لإرسال رمز إشارة تم ترتيبه مسبقًا. غالبًا ما تستخدم سفينة بحرية مصابيح الإشارة وشفرة مورس بطريقة مماثلة.

غالبًا ما يستخدم طياروالطائرات مؤشر المنحدر البصري للاقتراب (VASI) أنظمة الضوء المتسقطة للهبوط بأمان ، خاصة في الليل. تستخدم الطائرات العسكرية التي تهبط على حاملة الطائرات نظامًا مشابهًا للهبوط بشكل سليم على سطح الحاملة. ينقل نظام الضوء الملون ازدياد الطائرة بالنسبة لهبوط قياسي منحدر جليدي. كذلك ، أبراج مراقبة المطار لا تزال تستخدم مصباح Aldis لإرسال التعليمات إلى الطائرات التي تعطلت أجهزة الراديوالخاصة بها.

في الوقت الحاضر تقوم مجموعة متنوعة من الأنظمة الإلكترونية بنقل واستقبال المعلومات التي تحملها نبضات ضوئية بشكل بصري. تستخدم اتصالات الألياف الضوئية كابلات الآن لإرسال الغالبية العظمى من البيانات الإلكترونية والمكالمات الهاتفية البعيدة المسافة التي لا يتم نقلها عن طريق الراديوأو الأمواج الميكروية الأرضية أو قمر صناعي. كما يتم استخدام الاتصال البصري في الفضاء الحر جميع يوم في تطبيقات مختلفة.

Semaphore line

A replica of one of Chappe's semaphore towers (18th century).

A 'semaphore telegraph', also called a 'semaphore line', 'optical telegraph', 'shutter telegraph chain', 'Chappe telegraph', or 'Napoleonic semaphore', is a system used for conveying information by means of visual signals, using towers with pivoting arms or shutters, also known as blades or paddles. Information is encoded by the position of the mechanical elements; it is read when the shutter is in a fixed position.

Semaphore lines were a precursor of the electrical telegraph. They were far faster than post riders for conveying a message over long distances, but far more expensive and less private than the electrical telegraph lines which would later replace them. The maximum distance that a pair of semaphore telegraph stations can bridge is limited by geography, weather and the availability of light; thus, in practical use, most optical telegraphs used lines of relay stations to bridge longer distances. Each relay station would also require its complement of skilled operator-observers to convey messages back and forth across the line.

The modern design of semaphores was first foreseen by the British polymath Robert Hooke, who first gave a vivid and comprehensive outline of visual telegraphy in a 1684 submission to the Royal Society. His proposal (which was motivated by military concerns following the Battle of Vienna the preceding year) was not put into practice during his lifetime.

The first operational optical semaphore line arrived in 1792, created by the French engineer Claude Chappe and his brothers, who succeeded in covering France with a network of 556 stations stretching a total distance of 4,800 kiloمترs (15,700,000 قدم). It was used for military and national communications until the 1850s.

Many national services adopted signaling systems different from the Chappe system. For example, Britain and Sweden adopted systems of shuttered panels (in contradiction to the Chappe brothers' contention that angled rods are more visible). In Spain, the engineer Agustín de Betancourt developed his own system which was adopted by that state. This system was considered by many experts in Europe better than Chappe's, even in France.

These systems were popular in the late 18th to early 19th century but could not compete with the electrical telegraph, and went completely out of service by 1880.

Semaphore signal flags

A naval signaler transmitting a message by flag semaphore (2002).

Semaphore Flags is the system for conveying information at a distance by means of visual signals with hand-held flags, rods, disks, paddles, or occasionally bare or gloved hands. Information is encoded by the position of the flags, objects or arms; it is read when they are in a fixed position.

Semaphores were adopted and widely used (with hand-held flags replacing the mechanical arms of shutter semaphores) in the maritime world in the 19th century. They are still used during underway replenishment at sea and are acceptable for emergency communication in daylight or, using lighted wands instead of flags, at night.

The newer flag semaphore system uses two short poles with square flags, which a signaler holds in different positions to convey letters of the alphabet and numbers. The transmitter holds one pole in each hand, and extends each arm in one of eight possible directions. Except for in the rest position, the flags cannot overlap. The flags are colored differently based on whether the signals are sent by sea or by land. At sea, the flags are colored red and yellow (the Oscar flags), while on land, they are white and blue (the Papa flags). Flags are not required, they just make the characters more obvious.

الألياف البصرية

الألياف الضوئية هوالنوع الأكثر شيوعًا من القنوات للاتصالات الضوئية. تكون أجهزة الإرسال في روابط الألياف الضوئية بشكل عام الديودات الباعثة للضوء (LEDs) أوالديودات الليزرية التي تستخدم ضوء ذوالأشعة تحت الحمراء ، بدلاً من الضوء المرئي بشكل أكثر شيوعًا ، لأن الألياف الضوئية تنقل أطوال موجات الأشعة تحت الحمراء بأقل تخميد و تشتت] . عادةً ماقد يكون ترميز الإشارة بسيطًا تعديل الكثافة ، على الرغم من حتى الطور البصري تاريخيًا وتعديل التردد قد تم إثباته في المختبر. تم استبدال الحاجة إلى تجديد الإشارة الدورية إلى حد كبير بإدخال مضخم الألياف المدعم بالإربيوم ، الذي وسع مسافات الوصلة بتكلفة أقل بكثير.

Signal lamps

An air traffic controller holding a signal light gun that can be used to direct aircraft experiencing a radio failure (2007).

Signal lamps (such as Aldis lamps), are visual signaling devices for optical communication (typically using Morse code). Modern signal lamps are a focused lamp which can produce a pulse of light. In large versions this pulse is achieved by opening and closing shutters mounted in front of the lamp, either via a manually operated pressure switch or, in later versions, automatically.

With hand held lamps, a concave mirror is tilted by a trigger to focus the light into pulses. The lamps are usually equipped with some form of optical sight, and are most commonly deployed on naval vessels and also used in airport control towers with coded aviation light signals.

Aviation light signals are used in the case of a radio failure, an aircraft not equipped with a radio, or in the case of a hearing-impaired pilot. Air traffic controllers have long used signal light guns to direct such aircraft. The light gun's lamp has a focused bright beam capable of emitting three different colors: red, white and green. These colors may be flashing or steady, and provide different instructions to aircraft in flight or on the ground (for example, "cleared to land" or "cleared for takeoff"). Pilots can acknowledge the instructions by wiggling their plane's wings, moving their ailerons if they are on the ground, or by flashing their landing or navigation lights during night time. Only 12 simple standardized instructions are directed at aircraft using signal light guns as the system is not utilized with Morse code.

Photophone

The photophone (originally given an alternate name, radiophone) is a communication device which allowed for the transmission of speech on a beam of light. It was invented jointly by Alexander Graham Bell and his assistant Charles Sumner Tainter on February 19, 1880, at Bell's 1325 'L' Street laboratory in Washington, D.C. Both were later to become full associates in the Volta Laboratory Association, created and financed by Bell.

On June 21, 1880, Bell's assistant transmitted a wireless voice telephone message of considerable distance, from the roof of the Franklin School to the window of Bell's laboratory, some 213 meters (about 700 ft.) away.

Bell believed the photophone was his most important invention. Of the 18 patents granted in Bell's name alone, and the 12 he shared with his collaborators, four were for the photophone, which Bell referred to as his 'greatest achievement', telling a reporter shortly before his death that the photophone was "the greatest invention [I have] ever made, greater than the telephone".

The photophone was a precursor to the fiber-optic communication systems which achieved popular worldwide usage starting in the 1980s. The master patent for the photophone (U.S. Patent 235٬199 Apparatus for Signalling and Communicating, called Photophone), was issued in December 1880, many decades before its principles came to have practical applications.

Free-space optical communication

Free-space optics (FSO) systems are employed for 'last mile' telecommunications and can function over distances of several kilometers as long as there is a clear line of sight between the source and the destination, and the optical receiver can reliably decode the transmitted information. Other free-space systems can provide high-data-rate, long-range links using small, low-mass, low-power-consumption subsystems which make them suitable for communications in space. Various planned satellite constellations intended to provide global broadband coverage take advantage of these benefits and employ laser communication for inter-satellite links between the several hundred to thousand satellites effectively creating a space-based optical mesh network.

More generally, transmission of unguided optical signals is known as optical wireless communications (OWC). Examples include medium-range visible light communication and short-distance IrDA, using infrared LEDs.

هليوگراف

هليوگراف: الأستراليون يستخدمون صورة فوتوغرافية في شمال إفريقيا (1940).

هليوگراف (باليونانية: Ἥλιος هليوس, تعني الشمس, وγραφειν graphein, معنى "الكتابة") تعبير عن تلغراف شمسي لاسلكي يشير إلى ومضات من ضوء الشمس (باستخدام شفرة مورس بشكل عام ينعكس بواسطة مرآة. يتم إنتاج الومضات عن طريق تدوير المرآة للحظات ، أوعن طريق مقاطعة الشعاع بغالق.

كانت آلة التصوير الشعاعي أداة بسيطة ولكنها فعالة للاتصال البصري الفوري على مسافات طويلة خلال أواخر القرن التاسع عشر وأوائل القرن العشرين. كانت استخداماته الرئيسية في الأعمال العسكرية والمسوحات وحماية الغابات. كانت هذه قضية قياسية في الجيوش البريطانية والأسترالية حتى الستينيات ، واستخدمها الجيش الباكستاني في أواخر عام 1975.

References

Citations

^ Chapter 2: Semaphore Signalling ISBN 978-0-86341-327-8 Communications: an international history of the formative years R. W. Burns, 2004
^ Telegraph Vol 10, Encyclopædia Britannica, 6th Edition, 1824 pp. 645-651
^ "Nation Park Service Fire History Timeline".
^ "Lewis and Clark Journals, July 20, 1805".
^ Harris, J.D. Wire At War - Signals communication in the South African War 1899–1902. Retrieved on 1 June 2008. Note a discussion on the heliograph use during the Boer War.
^ Telegraph, Volume 17 of The Edinburgh encyclopaedia, pp. 664-667, 1832 David Brewster, ed.
^ Calvert, J.B. The Origin of the Railway Semaphore, Boston University, 15 April 2000, Revised أربعة May 2007.
^ McVeigh, Daniel P. An Early History of the Telephone: 1664-1865, Part 2 Archived 2012-11-28 at the Wayback Machine., Columbia University in The City of New York, Institute For Learning Technologies, 2000.
^ Bruce 1990, pg. 336
^ Jones, Newell. First 'Radio' Built by San Diego Resident Partner of Inventor of Telephone: Keeps Notebook of Experiences With Bell Archived 2006-09-04 at Archive.is, San Diego Evening Tribune, July 31, 1937. Retrieved from the University of San Diego History Department website, November 26, 2009.
^ Bruce 1990, pg. 338
^ Carson 2007, pg. 76-78
^ Groth, Mike. Photophones Revisted, 'Amateur Radio' magazine, Wireless Institute of Australia, Melbourne, April 1987 pp. 12–17 and May 1987 pp. 13–17.
^ Mims 1982, p. 11.
^ Mims 1982, p. 14.
^ Morgan, Tim J. "The Fiber Optic Backbone", University of North Texas, 2011.
^ Miller, Stewart E. "Lightwaves and Telecommunication", American Scientist, Sigma Xi, The Scientific Research Society, January–February 1984, Vol. 72, No. 1, pp. 66-71, Issue Stable URL.
^ Gallardo, Arturo; Mims III, Forrest M.. Fiber-optic Communication Began 130 Years Ago, San Antonio Express-News, June 21, 2010. Accessed January 1, 2013.
^ Clint Turner (October 3, 2007). "A 173-mile 2-way all-electronic optical contact". Modulated light web site. Retrieved June 28, 2011.
^ Wilson, K. (2000-01-04). "Recent Development in High-Data Rate Optical Communications at JPL". Jet Propulsion Laboratory (NASA Technical Reports Server).

Bibliography

Alwayn, Vivek. Fiber-Optic Technologies, Cisco Press, Apr 23, 2004.
Bruce, Robert V Bell: Alexander Bell and the Conquest of Solitude, Ithaca, New York: Cornell University Press, 1990. ISBN 0-8014-9691-8.
Carson, Mary Kay (2007). . Sterling Biographies. 387 Park Avenue South, New York, NY 10016: Sterling Publishing Co., Inc. pp. 76–78. ISBN . OCLC 182527281.
Mims III, Forest M. The First Century of Lightwave Communications, Fiber Optics Weekly Update, Information Gatekeepers, February 10–26, 1982, pp. 6–23.
Paschotta, Rüdiger. Encyclopedia of Laser Physics and Technology, RP-Photonics.com website, 2012.