This section of the website covers a wide range of optical and
opto-electronic (optronic) devices that were used in covert operations,
ranging from infrared communication devices (photophone)
to long-range motion
detection systems. Such devices are also known as
Free Space Optics (FSO), and can be active as well as passive.
This section is currently under construction.
A Photophone is a speech communication device that uses a light beam for the
transmission of voice conversations, invented in
1880 by Alexander Graham Bell in the USA.
As light propagates in a straight line and can be obstructed by
objects in the transmission path, it is basically a
line-of-sight communication device.
In the German language it is known as a Lichtsprechgerät. 1
The Photophone was invented by Alexander Graham Bell 2 in the USA,
the same man who had invented the telephone
a few years earlier [1], and was first demonstrated on 3 June 1880 [2].
It used a light beam to transmit audio over a distance of 700 feet
(~213 metres). Although there was no immediate practical use for it
at the time, Bell would later call it his greatest invention.
The first practical implementations were developed during
World War I (WWI)
and World War II (WWII).
The German manufacturer Siemens & Halske
developed a device for the German Navy that could be used over distances
of more than 8 km by using current-modulated carbon arc lamps.
During WWII,
the German Army made practical use of optical transmission, with Lichtsprechgerät 80, a device that was
developed in 1935 by the
Carl Zeiss optics company and that allowed
line-of-sight communication over a distance of up to 5 km.
In the years following WWII — during the
Cold War —
several types of photophones were developed in the former DDR
(East-Germany) for virtually undetectable
covert communication across the East-German sector and state borders.
The Photophone can be seen as the precursor to the fibre-optic communication
systems that became popular in the 1980s and that are now used as the
backbone of our modern era internet.
Literally translated: light speech device.
Jointly with his assistent (and later associate) Charles Sumner Tainter.
