Semiconductor ring lasers (SRLs) are miniature

ring laser Ring lasers are composed of two beams of light of the same polarization traveling in opposite directions ("counter-rotating") in a closed loop. Ring lasers are used most frequently as gyroscopes (ring laser gyroscope) in moving vessels like car ...

devices with potential applications in

optoelectronics Optoelectronics (or optronics) is the study and application of electronic devices and systems that find, detect and control light, usually considered a sub-field of photonics. In this context, ''light'' often includes invisible forms of radiatio ...

photonics Photonics is a branch of optics that involves the application of generation, detection, and manipulation of light in form of photons through emission, transmission, modulation, signal processing, switching, amplification, and sensing. Though ...

and all-optical circuits. The first SRLs were developed in the 1980s. Recently, they have been of interest as potential random-access memory storage devices for all-optical computers. Semiconductor ring lasers are literally ring-shaped

optical waveguide An optical waveguide is a physical structure that guides electromagnetic waves in the optical spectrum. Common types of optical waveguides include optical fiber waveguides, transparent dielectric waveguides made of plastic and glass, liquid light g ...

s with a

lasing A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word "laser" is an acronym for "light amplification by stimulated emission of radiation". The firs ...

medium. They have the ability to trap light in a ring, and recirculate it continuously as long as they remain powered. The material of choice for SRLs is

indium phosphide Indium phosphide (InP) is a binary semiconductor composed of indium and phosphorus. It has a face-centered cubic ("zincblende") crystal structure, identical to that of GaAs and most of the III-V semiconductors. Manufacturing Indium phosphide ca ...

. SRLs can be square with corner reflectors, or, as is more common with the smaller designs, have a curved, "racetrack" shape. Devices are currently on the order of a 100

micrometre The micrometre ( international spelling as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American spelling), also commonly known as a micron, is a unit of length in the International System of Unit ...

s, but further miniaturization should be possible using existing silicon microelectronics technology. In the summer of 2010 researchers Dr. Muhammad Maqbool and Kyle Main of Ball State University and Dr. Martin Kordesch of Ohio University were able to successfully develop the first Aluminum Nitride SRL on the order of 20 micrometers in diameter. This SRL was constructed by depositing a 4 micrometer thick semi conducting Aluminum-Nitride film doped with Ti+3 ions onto a stretched fiber optic cable of 12 micrometer diameter. This SRL was shown to have considerable gain and a low threshold pump power, making it a highly efficient laser system. The light was confined only to the film and did not reflect off of the outer surface of the optical fiber. Such an arrangement is called a "Whispering Gallery Mode".Muhammad Maqbool, Kyle Main, and Martin Kordesch, "Titanium-doped sputter-deposited AlN infrared whispering gallery mode microlaser on optical fibers," Opt. Lett. 35, 3637-3639 (2010) Maqbool and Main plan to expand their work to include the development of nano scale SRLs on carbon nanotubes. SRLs may serve as the basis of a new form of optical

random access memory Random-access memory (RAM; ) is a form of computer memory that can be read and changed in any order, typically used to store working Data (computing), data and machine code. A Random access, random-access memory device allows data items to b ...

. The direction of circulation of light (clockwise or counterclockwise) would indicate the polarity of the bit (0 or 1). Due in part to the bistable and highly non-linear nature of the devices, they can be fed a starting signal from either direction. The directionality is maintained as long as the device remains powered. Other potential applications include "a digital response device that reshapes optical signals that have become distorted, effectively acting as a

gate A gate or gateway is a point of entry to or from a space enclosed by walls. The word derived from old Norse "gat" meaning road or path; But other terms include ''yett and port''. The concept originally referred to the gap or hole in the wall ...

." and a device for resynchronizing optical signals to eliminate timing "jitter". A European research project formed in 2006 to study potential applications of SRLs. It is known as IOLOS, (Integrated optical logic and memory using ultra-fast micro-ring bistable semiconductor laser), and will receive funding of €1.25 million over three years. Intense Photonics and

Siemens Siemens AG ( ) is a German multinational conglomerate corporation and the largest industrial manufacturing company in Europe headquartered in Munich with branch offices abroad. The principal divisions of the corporation are ''Industry'', '' ...

are also providing a further €100,000.

References

{{reflist

References

See also