Long period bragg grating optical signal attenuation

An apparatus in one example comprises one or more light sources, one or more long period Bragg gratings that are optically coupled with the one or more light sources, and one or more amplification fibers that are optically coupled with the one or more long period Bragg gratings. The one or more light sources send one or more pump optical signals to one or more of the one or more long period Bragg gratings. The one or more of the one or more long period Bragg gratings transmit the one or more pump optical signals to one or more of the one or more amplification fibers. The one or more of the one or more amplification fibers absorb one or more of the one or more pump optical signals and emit one or more output signals. The one or more of the one or more long period Bragg gratings attenuate one or more of the one or more output signals.

TECHNICAL FIELD

The invention relates generally to fiber optics and more particularly to attenuation of optical signals.

BACKGROUND

Optical components, for example, a fiber optic gyroscope, use optical signals generated by broadband fiber sources. In one design of a backwards pumped broadband fiber source, a light source sends pump light through a wave division multiplexing (“WDM”) fiber to a rare-earth doped fiber. The rare-earth doped fiber absorbs the pump light and emits the output signals. This design suffers shortcomings from the use of the wave division multiplexing fiber to transmit the light for transmission to the rare-earth doped fiber. As one example, the wave division multiplexing fiber adds a significant cost to manufacture of the broadband fiber source. As another example, the wave division multiplexing fiber adds undesirable effects such as polarization splitting.

In one design of a forward pumped broadband fiber source, the light source sends the pump light directly to the rare-earth doped fiber. The forward pumped broadband fiber source omits the wave division multiplexing fiber of the design of the backwards pumped broadband fiber source discussed above. However, the light source comprises a facet face that, in this design, backreflects one or more of the output signals toward the fiber optic gyroscope. The backreflection of the output signals causes an oscillation in the broadband fiber source, which disrupts operation of the fiber optic gyroscope.

Thus, a need exists for attenuation of optical signals to promote a reduction of backreflection. A further need exists for attenuation of optical signals with a reduced cost of manufacture.

SUMMARY

The invention in one implementation encompasses an apparatus. The apparatus comprises one or more light sources, one or more long period Bragg gratings that are optically coupled with the one or more light sources, and one or more amplification fibers that are optically coupled with the one or more long period Bragg gratings. The one or more light sources send one or more pump optical signals to one or more of the one or more long period Bragg gratings. The one or more of the one or more long period Bragg gratings transmit the one or more pump optical signals to one or more of the one or more amplification fibers. The one or more of the one or more amplification fibers absorb one or more of the one or more pump optical signals and emit one or more output signals. The one or more of the one or more long period Bragg gratings attenuate one or more of the one or more output signals.

Another implementation of the invention encompasses a method. A reduction of backreflection of one or more output signals from one or more amplification fibers of a broadband fiber source is promoted through employment of one or more long period Bragg gratings.

DETAILED DESCRIPTION

Turning toFIG. 1, an apparatus100in one example comprises a plurality of components such as hardware components. A number of such components can be combined or divided in the apparatus100.

The apparatus100in one example comprises one or more light sources102, one or more long period Bragg gratings104, and one or more amplification fibers108that provide light to an optical component110. In a further example, the apparatus100comprises one or more long period Bragg gratings106. The light sources102, long period Bragg gratings104and106, and amplification fibers108in one example are optically coupled with one another, for example, by a fiber optic cable or waveguide. For example, the light source102is optically coupled with the long period Bragg grating104, the long period Bragg grating104is optically coupled with the amplification fiber108, and the amplification fiber108is optically coupled with the optical component110. In another example, the amplification fiber108is optically coupled with the long period Bragg grating106, and the long period Bragg grating106is optically coupled with the optical component110. In one example, the light source102, the long period Bragg gratings104and106, and the amplification fiber108are fusion-spliced to be optically coupled, as will be appreciated by those skilled in the art. The light source102, long period Bragg gratings104and106, and amplification fibers108in one example comprise a portion of a broadband fiber source112.

The light source102in one example comprises a pump diode laser, for example, an indium gallium arsenide (“InGaAs”) laser diode. A front facet of the light source102in one example comprises a surface that reflects optical signals. The light source102in one example converts electricity into light, for example, one or more pump optical signals114. The pump optical signals114in one example comprise a substantially same pump wavelength λp.

The long period Bragg gratings104and106comprise an optical core and a cladding that covers the optical core. For example, the optical core comprises a higher refractive index than the cladding to promote total internal reflection of light within the optical core. The long period Bragg gratings104and106comprise corresponding wavelength attenuation ranges. For example, the optical core of the long period Bragg grating104couples optical signals with a wavelength within the wavelength attenuation range to the cladding to attenuate the optical signals. The long period Bragg gratings104and106in one example attenuate the optical signals by twenty decibels, as will be appreciated by those skilled in the art.

The wavelength attenuation range of the long period Bragg gratings104and/or106in one example comprises a plurality of wavelength attenuation sub-ranges. For example, the long period Bragg grating104is represented by a plurality of long period Bragg gratings. The plurality of long period Bragg gratings comprise the plurality of wavelength attenuation sub-ranges. The plurality of long period Bragg gratings are optically coupled in series to provide the wavelength attenuation range of the long period Bragg grating104.

In one example, the wavelength attenuation sub-ranges are staggered to cover the wavelength attenuation range. For example, none (i.e., zero) of the wavelength attenuation sub-ranges overlap. In another example, one or more of the wavelength attenuation sub-ranges overlap a portion of an adjacent wavelength attenuation sub-range. For example, a first long period Bragg grating provides a lower sixty percent of the wavelength attenuation range and a second long period Bragg grating provides an upper sixty percent of the wavelength attenuation range, and a central twenty percent of the first and second wavelength attenuation ranges is overlapped by the first and second long period Bragg gratings.

The amplification fiber108in one example comprises a rare earth doped fiber, for example, an erbium or neodymium doped fiber. The amplification fiber108receives and absorbs one or more optical signals and emits a plurality of output signals, for example, output signals116and118, through amplified spontaneous emission. In one example, the amplification fiber108directs the output signals116towards the long period Bragg grating104. In a further example, the amplification fiber108directs the output signals118towards the optical component110. The output signals116and118comprise a substantially same signal wavelength λs. The wavelength λpand the wavelength λscomprise different wavelengths, as will be appreciated by those skilled in the art.

The optical component110in one example comprises a fiber optic gyroscope. The optical component110employs one or more optical signals of wavelength λsto perform a task, for example, to determine a magnitude of rotation. The optical component110returns one or more of the optical signals to the broadband fiber source112. For example, the optical component110employs one or more of the output signals118to determine a magnitude of rotation.

An illustrative description of exemplary operation of the apparatus100is presented, for explanatory purposes. The light source102generates one or more pump optical signals114of wavelength λpand sends the pump optical signals114towards the long period Bragg grating104. The wavelength attenuation range of the long period Bragg grating104omits the wavelength λp, and the long period Bragg grating104transmits the pump optical signals114to the amplification fiber108.

The amplification fiber108absorbs one or more of the pump optical signals114. Through amplified spontaneous emission, the amplification fiber108emits a plurality of output signals, for example, output signals116and118. The amplification fiber108directs the output signals116towards the long period Bragg grating104and directs the output signals118towards the optical component110through the long period Bragg grating106.

The wavelength attenuation range of the long period Bragg grating104comprises the signal wavelength λsof the output signals116. The long period Bragg grating104attenuates the output signals116and creates one or more output signals122. The front facet of the light source102causes a backreflection of one or more of the output signals122, for example, output signals124, toward the long period Bragg grating104, as will be appreciated by those skilled in the art.

The long period Bragg grating104attenuates the output signals116to promote a reduction of backreflection of the output signals116incident on the front facet of the long period Bragg grating104. The long period Bragg grating104attenuates the output signals124and creates one or more output signals126. The long period Bragg grating104attenuates the output signals116and124to promote a reduction of oscillation of the output signals116, as will be appreciated by those skilled in the art.

The wavelength attenuation range of the long period Bragg grating106in one example omits the wavelength λsand the long period Bragg grating106transmits the output signals118to the optical component110, as will be appreciated by those skilled in the art. The optical component110employs the output signals118to perform a task, and returns one or more of the output signals118, for example, one or more output signals130, to the broadband fiber source112. The long period Bragg grating104attenuates the output signals130analogous to the output signals116.

The amplification fiber108in one example transmits one or more residual signals132of the pump optical signals114. The wavelength attenuation range of the long period Bragg grating106in one example comprises the wavelength λp. The long period Bragg grating106attenuates the residual signals132and creates one or more residual signals134. Where the optical component110comprises a fiber optic gyroscope, the long period Bragg grating106attenuates the residual signals132to promote a reduction of a scale factor linearity error of the fiber optic gyroscope.

Turning toFIG. 2, the apparatus100in another example comprises one or more light sources102, one or more long period Bragg gratings104and106, one or more amplification fibers108, one or more optical components202, and one or more optical couplers204that provide light to an optical component110. The optical component202in one example comprises a multi-function integrated optic chip and one or more portions of an optical fiber or waveguide. The optical component202redirects optical signals from the long period Bragg grating106back into the long period Bragg grating106. The optical coupler204redirects optical signals from the long period Bragg grating106to the optical component110.

The light source102generates pump optical signals114, analogous toFIG. 1. The amplification fiber108absorbs one or more of the pump optical signals114and emits the output signals118. The amplification fiber108transmits the residual signals132to the long period Bragg grating106. The long period Bragg grating106transmits the output signals118to the optical component202. The optical component202redirects the output signals118back into the long period Bragg grating106toward the optical coupler204. The optical coupler204redirects the output signals118to the optical component110.

The long period Bragg grating106attenuates the residual signals132and creates one or more residual signals134. Where the optical component110comprises a fiber optic gyroscope, the long period Bragg grating106attenuates the residual signals132to promote a reduction of a scale factor linearity error of the fiber optic gyroscope. The optical component202redirects the residual signals134back into the long period Bragg grating106toward the optical coupler204. The long period Bragg grating106attenuates the residual signals134and creates residual signals208. The optical coupler204redirects the residual signals208to the optical component110.

The steps or operations described herein are just exemplary. There may be many variations to these steps or operations without departing from the spirit of the invention. For instance, the steps may be performed in a differing order, or steps may be added, deleted, or modified.