Forms Optical communication

1 forms

1.1 semaphore line
1.2 semaphore signal flags
1.3 optical fiber
1.4 signal lamps
1.5 photophone
1.6 free-space optical communication
1.7 heliograph

forms

visual techniques such smoke signals, beacon fires, hydraulic telegraphs, ship flags , semaphore lines earliest forms of optical communication. hydraulic telegraph semaphores date 4th century bce greece. distress flares still used mariners in emergencies, while lighthouses , navigation lights used communicate navigation hazards.

the heliograph uses mirror reflect sunlight distant observer. when signaler tilts mirror reflect sunlight, distant observer sees flashes of light can used transmit prearranged signaling code. naval ships use signal lamps , morse code in similar way.

aircraft pilots use visual approach slope indicator (vasi) projected light systems land safely, @ night. military aircraft landing on aircraft carrier use similar system land correctly on carrier deck. coloured light system communicates aircraft s height relative standard landing glideslope. well, airport control towers still use aldis lamps transmit instructions aircraft radios have failed.

in present day variety of electronic systems optically transmit , receive information carried pulses of light. fiber-optic communication cables employed send great majority of electronic data , long distance telephone calls not conveyed either radio, terrestrial microwave or satellite. free-space optical communications used every day in various applications.

semaphore line


a replica of 1 of chappe s semaphore towers (18th century).

a semaphore telegraph , called semaphore line , optical telegraph , shutter telegraph chain , chappe telegraph , or napoleonic semaphore , system used conveying information means of visual signals, using towers pivoting arms or shutters, known blades or paddles. information encoded position of mechanical elements; read when shutter in fixed position.

semaphore lines precursor of electrical telegraph. far faster post riders conveying message on long distances, far more expensive , less private electrical telegraph lines later replace them. maximum distance pair of semaphore telegraph stations can bridge limited geography, weather , availability of light; thus, in practical use, optical telegraphs used lines of relay stations bridge longer distances. each relay station require complement of skilled operator-observers convey messages , forth across line.

the modern design of semaphores first foreseen british polymath robert hooke, first gave vivid , comprehensive outline of visual telegraphy in 1684 submission royal society. proposal (which motivated military concerns following battle of vienna preceding year) not put practice during lifetime.

the first operational optical semaphore line arrived in 1792, created french engineer claude chappe , brothers, succeeded in covering france network of 556 stations stretching total distance of 4,800 kilometres (3,000 mi). used military , national communications until 1850s.

many national services adopted signaling systems different chappe system. example, britain , sweden adopted systems of shuttered panels (in contradiction chappe brothers contention angled rods more visible). in spain, engineer agustín de betancourt developed own system adopted state. system considered many experts in europe better chappe s, in france.

these systems popular in late 18th 19th century not compete electrical telegraph, , went out of service 1880.

semaphore signal flags


a naval signaler transmitting message flag semaphore (2002).

semaphore flags system conveying information @ distance means of visual signals hand-held flags, rods, disks, paddles, or bare or gloved hands. information encoded position of flags, objects or arms; read when in fixed position.

semaphores adopted , used (with hand-held flags replacing mechanical arms of shutter semaphores) in maritime world in 19th century. still used during underway replenishment @ sea , acceptable emergency communication in daylight or, using lighted wands instead of flags, @ night.

the newer flag semaphore system uses 2 short poles square flags, signaler holds in different positions convey letters of alphabet , numbers. transmitter holds 1 pole in each hand, , extends each arm in 1 of 8 possible directions. except in rest position, flags cannot overlap. flags colored differently based on whether signals sent sea or land. @ sea, flags colored red , yellow (the oscar flags), while on land, white , blue (the papa flags). flags not required, make characters more obvious.

optical fiber

optical fiber common type of channel optical communications. transmitters in optical fiber links light-emitting diodes (leds) or laser diodes. infrared light, rather visible light used more commonly, because optical fibers transmit infrared wavelengths less attenuation , dispersion. signal encoding typically simple intensity modulation, although historically optical phase , frequency modulation have been demonstrated in lab. need periodic signal regeneration largely superseded introduction of erbium-doped fiber amplifier, extended link distances @ lower cost.

signal lamps


an air traffic controller holding signal light gun can used direct aircraft experiencing radio failure (2007).

signal lamps (such aldis lamps), visual signaling devices optical communication (typically using morse code). modern signal lamps focused lamp can produce pulse of light. in large versions pulse achieved opening , closing shutters mounted in front of lamp, either via manually operated pressure switch or, in later versions, automatically.

with hand held lamps, concave mirror tilted trigger focus light pulses. lamps equipped form of optical sight, , commonly deployed on naval vessels , used in airport control towers coded aviation light signals.

aviation light signals used in case of radio failure, aircraft not equipped radio, or in case of hearing-impaired pilot. air traffic controlers have long used signal light guns direct such aircraft. light gun s lamp has focused bright beam capable of emitting 3 different colors: red, white , green. these colors may flashing or steady, , provide different instructions aircraft in flight or on ground (for example, cleared land or cleared takeoff ). pilots can acknowledge instructions wiggling plane s wings, moving ailerons if on ground, or flashing landing or navigation lights during night time. 12 simple standardized instructions directed @ aircraft using signal light guns system not utilized morse code.

photophone

the photophone (originally given alternate name, radiophone) communication device allowed transmission of speech on beam of light. invented jointly alexander graham bell , assistant charles sumner tainter on february 19, 1880, @ bell s 1325 l street laboratory in washington, d.c. both later become full associates in volta laboratory association, created , financed bell.

on june 21, 1880, bell s assistant transmitted wireless voice telephone message of considerable distance, roof of franklin school window of bell s laboratory, 213 meters (about 700 ft.) away.

bell believed photophone important invention. of 18 patents granted in bell s name alone, , 12 shared collaborators, 4 photophone, bell referred greatest achievement , telling reporter shortly before death photophone greatest invention [i have] ever made, greater telephone .

the photophone precursor fiber-optic communication systems achieved popular worldwide usage starting in 1980s. master patent photophone (u.s. patent 235,199 apparatus signalling , communicating, called photophone), issued in december 1880, many decades before principles came have practical applications.

free-space optical communication

free-space optics (fso) systems employed last mile telecommunications , can function on distances of several kilometers long there clear line of sight between source , destination, , optical receiver can reliably decode transmitted information. other free-space systems can provide high-data-rate, long-range links using small, low-mass, low-power-consumption subsystems.

more generally, transmission of unguided optical signals known optical wireless communications (owc). examples include medium-range visible light communication , short-distance irda, using infrared leds.

heliograph

heliograph: australians using heliograph in north africa (1940).

a heliograph (error: {{lang-xx}}: text has italic markup (help), meaning sun , , γραφειν graphein, meaning write ) wireless solar telegraph signals flashes of sunlight (generally using morse code) reflected mirror. flashes produced momentarily pivoting mirror, or interrupting beam shutter.

the heliograph simple effective instrument instantaneous optical communication on long distances during late 19th , 20th century. main uses in military, surveys , forest protection work. standard issue in british , australian armies until 1960s, , used pakistani army late 1975.