Aston University

Aston Photonic Technologies Limited

Catherine Anne Sugden

Xuewen Shu

Ian John Murgatroyd

Karen Elizabeth Chisholm

Kevin C Byron

Ian Bennion

Lin Zhang

Lee Ann Kennedy

A Gires-Tournois etalon (GTE) () comprising an optical fiber () in which a primary chirped fiber Bragg grating (FBG) () is provided, an RF signal generator (), a piezoelectric transducer (), and a glass horn (), for coupling an acoustic wave (26) into the fiber (). The acoustic wave (26) causes a periodic compression within the fiber (), which induces a low frequency periodic refractive index modulation within the grating section () of the fiber (). This causes two side frequency components to be generated for each high-frequency component of the FBG (). Two secondary grating are thus excited, having the same spectral bandwidth as the FBG (), but a lower reflectivity and different central wavelengths. The free spectral range of the GTE () can be adjusted by varying the frequency of the acoustic wave (). The reflectivity of the excited secondary gratings can be adjusted by adjusting the amplitude of the acoustic wave ().

Gires-Tournois etalons and dispersion compensators

A first embodiment of the invention provides a Gires-Tournois etalon (DGTE)comprising a cladding mode suppressed optical fibre, including an etalon sectionin which a weakly reflective optical waveguide gratingand a strongly reflective optical waveguide gratingare provided. The two gratingsare chirped fibre Bragg gratings (FBGs). The chirped FBGsare arranged to together define an etalon cavity. Another aspect of the invention provides a dispersion compensatorcomprising two DGTEsaccording to the first embodiment of the invention. The DGTEshave a linearly varying dispersion over a selected optical bandwidth. The first DGTEhas a positive dispersion slope and the second DGTEhas a negative dispersion slope. The magnitudes of the dispersion slopes of the two DGTEsare substantially equal, so that the dispersion compensatorhas a constant dispersion across the selected bandwidth. The DGTEsare optically coupled to one another via a four-port optical circulator

Gires-Tournois etalons and dispersion compensation

Apparatus () for interrogating an optical signal (not shown) propagating in an optical waveguide, such as an optical fiber, having an input section () and a second section () through which light entering from the input section () will subsequently propagate. The second section () includes a grating portion, such as a tilted chirped fiber Bragg grating (). The grating () causes at least part of the optical signal to be coupled out of the optical fiber, through the fiber cladding. A photodetector () is provided generally alongside the grating (). The photodetector () is arranged to collect and detect substantially all of the outcoupled optical signal. The relationship between the optical power outcoupled by the grating () and the wavelength of the optical signal is known, allowing a measurement of the outcoupled optical power to be used to determine the wavelength of the optical signal propagating through the grating ().

Apparatus for interrogating an optical signal

An optical spectrum analyzer ( ), receiving a multi-channel optical signal ( ). The optical signal ( ) is passed through an optical isolator ( ) and a fiber coupler ( ) to a tunable optical filter. The tunable optical filter comprises one or more fiber Bragg gratings ( ) inscribed in a length of optical fiber. The optical fiber is mounted on a means operable to apply a variable strain to the fiber, to they tune the peak wavelength of the Bragg grating ( ) over a desired wavelength range, the tunable optical filter thereby reflecting each channel of the input signal ( ) in turn. The detector ( ) therefore detects a signal only if the input signal ( ) contains wavelengths corresponding to the reflection wavelength of a grating ( ).

Optical spectrum analyzer

A fiber optic grating sensor ( ) comprising an optical fiber ( ) in which a grating portion ( ) is provided, the refractive index ( ) of the fiber ( ) varying periodically along the grating portion ( ). The periodic variation of the refractive index ( ) has an amplitude envelope which includes, in this example, two regions ( ) in which the amplitude of the envelope is substantially reduced, and in this example is substantially nulled. The null regions ( ) give the grating portion a spectral profile ( ) within which there are, in this example two pass bands ( ).

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Birmingham, United Kingdom

Catherine Anne Sugden