Abstract
We revisit representative and widely used inverse-scattering fiber Bragg grating designs and shed physical insight into their characteristics. We first demonstrate numerically and experimentally that dispersionless square filters are actually dispersion compensated devices and we physically identify the spatially separated main (dispersive) reflector and dispersion compensator sections. We also look into the features of pure 2nd-order dispersion and 3rd-order dispersion compensator designs and discuss their physical importance. Finally, we use the gained physical insight to design strong symmetric gratings with dispersionless response from both sides. Using this knowledge we design and fabricate strong (>30dB) bidirectional dispersionless filters.
Highlights
Since their first demonstration in 1978 [1], fiber Bragg gratings (FBGs) have found widespread usage in lab experiments and a plethora of applications across the photonics domain [2,3]
Even with the current effectiveness of electronic dispersion compensation, FBG-based linear dispersion compensators are expected to continue to play a role in hybrid compensation schemes in future high speed optical systems [6,7]
Linearly chirped FBG have been extensively used for pulse stretching and recompression in chirped-pulse amplification high power fiber laser systems [8]
Summary
Since their first demonstration in 1978 [1], fiber Bragg gratings (FBGs) have found widespread usage in lab experiments and a plethora of applications across the photonics domain [2,3]. A much more efficient approach, is to use direct synthesis or inverse scattering (IS) of the required FBG [see Fig. 1)] This consists in defining first the required reflection coefficient or impulse response and work backwards to define the corresponding generalized coupling constant q(z) or refractive index distribution n(z) and local detuning ΔΛ(z). FBG device effectiveness took a leap forward with the introduction of efficient IS design algorithms Such advanced approaches allowed a number of FBG performance characteristics to be optimized simultaneously. A typical example is the multi-lobe FBG design with square dispersionless response, which enables dense wavelength-division-multiplexing (WDM) [30] and large number of concatenated adddrop functions without substantial penalty [31] Such gratings are uni-directional and cannot be used from both sides, which severely compromises their use as add AND drop multiplexers. We use the gained physical insight to design strong symmetric gratings with dispersionless response from both sides
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