A delay line interferometer (DLI) can be a

Mach–Zehnder interferometer The Mach–Zehnder interferometer is a device used to determine the relative phase shift variations between two collimated beams derived by splitting light from a single source. The interferometer has been used, among other things, to measure pha ...

Michelson interferometer The Michelson interferometer is a common configuration for optical interferometry and was invented by the 19/20th-century American physicist Albert Abraham Michelson. Using a beam splitter, a light source is split into two arms. Each of those li ...

based on two-beam

interference Interference is the act of interfering, invading, or poaching. Interference may also refer to: Communications * Interference (communication), anything which alters, modifies, or disrupts a message * Adjacent-channel interference, caused by extr ...

, in which one beam is time-delayed to the other by a desired interval. Delay line interferometers are also known as

optical DPSK demodulator An optical DPSK demodulator is a device that provides a method for converting an optical differential phase-shift keying (DPSK) signal to an intensity-keyed signal at the receiving end in fiber-optic communication networks. It is also known as del ...

s. They convert a phase-keyed signal into an amplitude-keyed signal. In this application, an incoming

differential phase-shift keying Phase-shift keying (PSK) is a digital modulation process which conveys data by changing (modulating) the phase of a constant frequency reference signal (the carrier wave). The modulation is accomplished by varying the sine and cosine inputs at ...

(DPSK) optical signal is first split into two equal-intensity beams in two arms of a Mach Zehnder or Michelson interferometer, in which one beam is delayed by an

optical path difference In optics, optical path length (OPL, denoted ''Λ'' in equations), also known as optical length or optical distance, is the product of the geometric length of the optical path followed by light and the refractive index of homogeneous medium through ...

corresponding to ''1-bit'' time delay. After recombination, the two beams interfere with each other constructively or destructively. The resultant interference intensity is the intensity-keyed signal.

External links

Delay line interferometer and Optical DPSK demodulatorAll-Fiber Delay line interferometer and Optical DPSK demodulator
Fiber optics Photonics