Optics 101

What is a Periscope?

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A periscope is an optical instrument that allows objects that are not in direct line of sight to be viewed. Periscopes have proven to be of great help to submariners by allowing these professions to have a view above the surface of water and aid in navigation under water.

A simple periscope only requires mirrors, whereas a more complicated periscope utilizes prisms rather than mirrors. The periscopes used in submarine applications are complex, typically requiring the use of tubes that are at least 10 meters in length to achieve a greater range of scope.

Recent developments in science and technology have incorporated the use of fiber optics in periscopes. Fiber optic periscopes, such as cystoscopes and endoscopes, are used by medical physicians to view the organs of a human body without requiring invasive procedures. The working principle, construction and applications of periscopes are discussed in the sections below.

Working Principle

A periscope works on the Laws of Reflection which states that the light from the object falls on one mirror at a 45o angle from the object and is reflected. This reflected light then falls on another mirror and is again reflected until it reaches the human eye.


Periscopes can be constructed using a pair of flat mirrors or prisms and a rectangular hollow tube that has a viewing window at the top and bottom of the tube. The mirrors within this structure are fixed at an angle of 45o at the two ends of the rectangular hollow.


Periscopes are found in a variety of applications; however, they are almost synonymous with their use in submarines for general navigation and detection, as well as radar and their ability to determine potential nearby threats. In a similar 'threat detection' application, periscopes are often used on battlefields to look out of trenches safely without exposing the observer's body. One of the most widely used applications for periscopes is in medicine, as a result of their ability to be less obtrusive method diagnostic techniques as compared to surgical procedures.

Future Directions


For over 80 years, the United States Navy utilized the technology of the periscope within the control room of almost every submarine while at sea. As technology has advanced, the integration of sensors into submarine technology is expected to increase this market value from $230.48 million in 2016 to $315.17 million by the year 2025.

The growth in this market has been supported to an increase deployment of attack submarines by naval agencies around the world. One recent advancement in submarine sensor technology that was developed by Virginia-Class engineers is known as a “Fly-by-Wire” technology, which allows the submarine to quietly travel shallow waters without requiring the ship to rise to the surface3. Additionally, the software behind the “Fly-by-Wire” technology allows the user to direct the movement of the ship purely through the use of the software and electronics, thereby leaving the ship almost autonomously driven.


In an effort to further advance periscope technology within the medical field, the medical holography market has incorporated endoscopic technology, as well as several other imaging technologies, into this expanding field. A hologram, which can be in both the two- or three-dimensional medium, is a recording device that is a visual representation of the interference pattern that is formed when a reference light beam of a specified wavelength meets the light of the same wavelength as it hits the object beam4. Within the medical community, researchers are working towards improving this system that is still limited in its ability to precisely represent patient tissues and organs.

When connected with a rigid endoscope, this joint imaging system also incorporates three different object illumination source positions that provide information on the patient’s internal organs and tissue to a digital holography. To obtain the 3D hologram, the optical paths of each reference object beam pairs must match to allow for the three pulsed holograms to be recorded within a single frame of the charged-coupled device (CCD) sensor5.  

References and Further Reading

  1. How Does It Work? Binoculars, Periscopes, and Kaleidoscopes- Molecular Expressions
  2. Periscopes- National Museum of American History
  3. “Navy attack sub ‘fly-by-wire’ tech inspires strategy shift’” – Fox News
  4. “Medical Holography Market Evolving Technology, Trends and Industry Analysis by Medical Application as X-ray Holography, Endoscopic Holography etc. – Till 2023” – Med Gadget
  5. Saucedo, A. T., Santoyo, F. M., De la Torre-Ibarra, M., Pedrini, G., & Osten, W. (2006). Endoscopic pulsed digital holography for 3D measurements. Optics Express 14(4), 1468-1475. DOI: 10.1364/OE.14.001468.

This article was updated on 31st July, 2018.

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