Detecting a disturbance in the phase of light propagating in an optical waveguide
First Claim
1. An apparatus for detecting a disturbance in the phase of light propagating in an optical waveguide, the apparatus comprising:
- a light source for sending partially coherent successive light pulses along the waveguide;
a photodetector for generating signals representing the time distributed speckle pattern intensity of light backscattered in the waveguide as respective partially coherent light pulses travel along the waveguide; and
a processor for comparing the signals to identify differences in the intensity of light backscattered in the waveguide as the partially coherent respective light pulses travel along the waveguide,wherein the photodetector detects the backscattered light within a spectral width of the order of around 0.1 GHz to 100 GHz.
5 Assignments
0 Petitions
Accused Products
Abstract
A partially coherent Optical Time Domain Reflectometry (OTDR) apparatus has a light source comprising a directly modulated semiconductor Distributed FeedBack (DFB) laser diode for transmitting partially coherent light pulses along a monomode optical fibre. Light Rayleigh backscattered from the light pulses as they travel along the optical fibre is output from the end of the fibre into which the light pulses are transmitted to a Fibre Bragg Grating (FBG) filter. The FBG filter reduces the supectral width of light received at a photodetector. In one embodiment, the supectral width of the FBG filter is around one fifth of the supectral width of the light pulse after it has travelled around 1 km along the optical fibre. As a consequence of reducing the supectral width of the light received at the photodetector, the FBG filter increases the temporal coherence of the light. So, the FBG filter can ensure that the detected light is sufficiently coherent that a temporal supeckle pattern can be detected at the photodetector. At the same time, the light traveling in the optical fibre can be relatively supectrally broad so that non-linear effects in the optical fibre, such as Brillouin scattering, can be reduced.
-
Citations
32 Claims
-
1. An apparatus for detecting a disturbance in the phase of light propagating in an optical waveguide, the apparatus comprising:
-
a light source for sending partially coherent successive light pulses along the waveguide; a photodetector for generating signals representing the time distributed speckle pattern intensity of light backscattered in the waveguide as respective partially coherent light pulses travel along the waveguide; and a processor for comparing the signals to identify differences in the intensity of light backscattered in the waveguide as the partially coherent respective light pulses travel along the waveguide, wherein the photodetector detects the backscattered light within a spectral width of the order of around 0.1 GHz to 100 GHz. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 21, 22, 23, 24, 29, 30)
-
-
11. A method for detecting a disturbance in the phase of light propagating in an optical waveguide, the method comprising:
-
causing a light source to send successive partially coherent light pulses along the waveguide; generating signals representing the time distributed speckle pattern intensity of light backscattered in the waveguide and received at a photodetector as respective partially coherent light pulses travel along the waveguide; and comparing the signals to identify differences in the intensity of light backscattered in the waveguide as the respective partially coherent light pulses travel along the waveguide, wherein the generated signals are generated in response to backscattered light received at the photodetector within a spectral width of the order of around 0.1 GHz to 100 GHz. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19, 20, 25, 26, 27, 28, 31, 32)
-
Specification