History of Free Space Optics

The History of Free Space Optics

FSO in Ancient History

Optical Wireless Communications, in various forms, have been used for thousands of years. The Ancient Greeks used a coded alphabetic system of signalling with torches developed by Cleoxenus, Democleitus and Polybius. In the modern era, semaphores and wireless solar telegraphs called heliographs were developed, using coded signals to communicate with their recipients.

Alexander Graham Bell pioneers FSO

HIstory of Free Space Optics - The FSO Photophone Concept
HIstory of Free Space Optics – The FSO Photophone Concept

Early experiments in FSO included demonstrations by Alexander Graham Bell, which preceded his invention of the telephone. Bell used beams of light to transmit voice conversations through the air, which he dubbed the ‘photophone’. Though Bell’s experiment never translated into a commercial device, the principle of FSO was proved.  In 1880, Alexander Graham Bell and his assistant Charles Sumner Tainter created the photophone, at Bell’s newly established Volta Laboratory in Washington, DC. Bell considered it his most important invention. The device allowed for the transmission of sound on a beam of light. On June 3, 1880, Bell conducted the world’s first wireless telephone transmission between two buildings, some 213 meters (700 feet) apart.

Its first practical use came in military communication systems many decades later, first for optical telegraphy. German colonial troops used heliograph telegraphy transmitters during the Herero and Namaqua genocide starting in 1904, in German South-West Africa (today’s Namibia) as did British, French, US or Ottoman signals.

WW I German Blinkgerät
WW I German Blinkgerät 

FSO used in times of conflict

During World War I when wire communications were often cut, German signals used three types of optical Morse transmitters called Blinkgerät, the intermediate type for distances of up to 4 km (2.5 miles) at daylight and of up to 8 km (5 miles) at night, using red filters for undetected communications. Optical telephone communications were tested at the end of the war, but not introduced at troop level. In addition, special blinkgeräts were used for communication with airplanes, balloons, and tanks, with varying success.

A major technological step was to replace the Morse code by modulating optical waves in speech transmission. Carl Zeiss, Jena developed the Lichtsprechgerät 80/80 (literal translation: optical speaking device) that the German army used in their World War II anti-aircraft defense units, or in bunkers at the Atlantic Wall.

More recently, Free Space Optics has long been used by the military and space agencies such as NASA to provide high-speed wireless communications using non-radio media, including between satellites, drones and other vehicles.

Lasers revolutionise Free Space Optics

The invention of lasers in the 1960s, revolutionized free space optics. Military organizations were particularly interested and boosted their development. However the technology lost market momentum when the installation of optical fiber networks for civilian uses was at its peak.

Consumer applications of Free Space Optics

Many simple and inexpensive consumer remote controls use low-speed communication using infrared (IR) light. This is known as consumer IR technology.  Almost every household has an infrared controller for television or other domestic appliance.

Data transfer between laptops and mobile phones was standardised with IRDA (Infrared Data Association) technology modules, with data rates up to 1Gbps today.

Modern Terrestrial Free Space Optics

CableFree Free Space Optics installed in the British Virgin Islands
CableFree Free Space Optics installed in the British Virgin Islands

Early commercial applications for FSO were to provide CCTV video connections and remote LAN-extension services.

Over the past 20 years, FSO has emerged from a niche to provide mainstream network infrastructure for corporate, government, education, wireless carrier and telecom networks.

Vendors such as CableFree: Wireless Excellence have pioneered Free Space Optics for terrestrial communications. Starting in 1996 the CableFree team pioneered FSO for reliable transport of data communications, CCTV, telecommunications and other applications.

World First achievements: CableFree were the first vendor with commercial 622Mbps (1997) and 1Gbps (1999) Free Space Optics anywhere in the world.

Beyond Free Space Optics

CableFree UNITY installation: FSO and Radio
CableFree UNITY installation: FSO and Radio

Beyond FSO:  Recognising the limits of “Optical Only” terrestrial FSO, CableFree pioneered UNITY solutions which combine FSO and radio or MMW to provide highest uptime and availability anywhere in the industry.
CableFree UNITY ensures that weather effects such as thick Fog and Snow which can affect FSO are overcome with diverse path resilient media, to increase uptime, range, availability and capacity


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