Abstract
We present a novel apodisation scheme for photo-induced waveguide gratings. The apodisation is implemented with double exposures that have reversely varying duty cycles. We have successfully applied the proposed scheme to remove the sidelobes of long period gratings (LPGs). We also observed for the first time super strong sidelobes in LPGs when creating them with only a single varying-duty-cycle exposure. The strong sidelobes can be well explained with a Mach-Zehnder interference model.
Highlights
Since the first discovery of photosensitivity of optical fiber, photo-induced grating devices have found extensive applications in optical communications and sensing [1]
It is seen that the unapodised long period gratings (LPGs) had sidelobes that result in an out of band loss of about 0.8dB
We have noted that the sidelobes for the varying-duty-cycle LPG with only a single exposure are located on the short wavelength side of the main peak. We found that such sidelobes can be much stronger than those of a normal LPG
Summary
Since the first discovery of photosensitivity of optical fiber, photo-induced grating devices have found extensive applications in optical communications and sensing [1]. Both short period gratings and long period gratings (LPG) with normal uniform coupling profile have strong sidelobes near the main reflection/transmission band, which are not desirable for most applications, such as add/drop filtering in wavelength-division multiplexing systems andoptical amplifier gain equalizing with cascaded gratings [2]. We demonstrated here that it is particular suitable for fabricating apodised long period gratings
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