Phase modulated direct UV grating writing technique for ultrawide spectrum planar Bragg grating fabrication

Sima, C., Gates, J.C., Rogers, Helen, Mennea, Paolo, Holmes, C., Zervas, M.N. and Smith, P.G.R. (2013) Phase modulated direct UV grating writing technique for ultrawide spectrum planar Bragg grating fabrication. SPIE Photonics West 2013, , San Francisco, United States. 02 - 07 Feb 2013. (doi:10.1117/12.2001834).

Abstract

Direct UV Grating Writing (DGW) is an attractive technique for simultaneously fabricating integrated Bragg grating devices in a silica-on-silicon platform, yielding losses as low as 0.03dB/cm. Previously, an Acousto-Optical Modulator has been used for writing planar Bragg gratings; in this new work we demonstrate a new phase modulation fabrication technique that offers improved performance.
We report a novel phase control DGW method using an Electro-Optical Modulator for planar Bragg grating fabrication. We phase modulate one laser beam in a focusing interferometer as a photosensitive silica-on-silicon sample is translated under the spot to give a moving fringe pattern that allows high quality Bragg gratings and waveguides to be fabricated in a single step. This new approach has allowed us to achieve a 1mm long uniform Bragg grating with ~70% reflectivity and a 1.4nm 3dB bandwidth; while a 3mm long grating has 100% top flat reflectivity and a 1.22nm 3dB reflection bandwidth - refractive index changes of up to 0.001 can be achieved. Since there is neither laser power reduction nor writing speed variation, the method offers significantly faster writing speeds. The simplified optical layout offers greater laser power on sample and furthermore the design coding is simplified. By applying Gaussian apodisation to the grating design we can achieve sidelobe suppression of >15dB. Using grating detuning and this new phase control method we have shown that Bragg gratings can be written from 1200nm to 1900nm on a single chip under software control and with less than 3dB variation across a 250nm bandwidth high chemical stability, which makes these materials very interesting for active photonics applications. In particular, Yb³⁺-doped RTP exhibits a broad fluorescence spectrum that has been exploited to demonstrate ultrafast operation, with pulses as short as 155 fs being generated [1]. Recently, planar waveguiding has been demonstrated in an (Yb³⁺, Nb⁵⁺):RTP film grown by liquid phase epitaxy [2], opening the possibility of planar integrated devices based on this highly functional material.

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Contributors

Author: J.C. Gates

Author: C. Holmes

Author: M.N. Zervas

Author: P.G.R. Smith

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