The History of Free Space Optics

FSO in Ancient Times

Optical wireless communication dates back thousands of years. Ancient Greeks, including Cleoxenus, Democleitus, and Polybius, used torches for coded alphabetic signalling. In the modern era, semaphores and heliographs (wireless solar telegraphs) employed coded signals to communicate.

Alexander Graham Bell and the Photophone

In the late 19th century, Alexander Graham Bell pioneered FSO with his photophone, a device that transmitted voice via light beams. Developed with Charles Sumner Tainter at the Volta Laboratory in Washington, DC, the photophone achieved the first wireless telephone transmission over 213 meters (700 feet) between two buildings in 1880.

Military applications of FSO

FSO found practical use in military communication decades later, beginning with optical telegraphy. During the 1904 Herero and Namaqua genocide in German South-West Africa (now Namibia), colonial troops used heliograph transmitters.

In World War I, German forces used optical Morse transmitters (Blinkgerät) for communication over 4 km in daylight and 8 km at night. Optical telephone communications were tested late in the war but were not widely adopted.

By World War II, the German army used the Lichtsprechgerät 80/80, an optical speaking device, in anti-aircraft units and Atlantic Wall bunkers. This replaced Morse code by modulating optical waves in speech transmission.

More recently, FSO has been used by the military and NASA for high-speed, non-radio communication between satellites, drones, and other vehicles.

Lasers transform FSO

The development of lasers in the 1960s revolutionised FSO, with military organisations driving advancements. However, FSO’s commercial growth slowed during the peak of optical fibre network deployment for civilian use.

Consumer applications of FSO

In consumer IR technology, FSO powers consumer applications through infrared (IR) light, commonly used in low-speed remote controls for household devices like televisions. The Infrared Data Association (IRDA) standardised IR-based data transfer between laptops and mobile phones, achieving data rates up to 1 Gbps today.

Modern Terrestrial Free Space Optics

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

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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