Design of an integrated electro-optically tunable filter for
tunable laser purposes
Citation for published version (APA):
Tilma, B. W., Bente, E. A. J. M., & Smit, M. K. (2008). Design of an integrated electro-optically tunable filter for tunable laser purposes. In Proceedings of the ePIXnet Spring School 2008, May 11-17 Elba, Italy (pp. 68-)
Document status and date: Published: 01/01/2008 Document Version:
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Design of an integrated electo-optically tunable filter
for tunable laser purposes
B.W. Tilma, E.A.J.M. Bente, M.K. Smit COBRA, Eindhoven University of Technology Den Dolech 2,
P.O. Box 513, 5600 MB, Eindhoven, The Netherlands e-mail: b.w.tilma@tue.nl
In this contribution we present the design of integrated electro-optically tunable filters to be realized in the InP/InGaAsP system. The filter is based on the interference principle in a tunable arrayed waveguide grating (AWG). They are to be used as tunable intracavity filters in a monolithic fast scanning ring laser for frequency domain optical coherence tomography (FD-OCT). In FD-OCT a continuous scan over up to 200 nm around 1700nm at a rate of several tens of kHz is required. This tuning range can be achieved using two tunable AWGs in sequence. The first is a high resolution AWG that selects a single laser cavity mode. Since this needs to be a sufficiently narrow bandwidth filter to suppress the neighboring laser modes, it will also have a free spectral range (FSR) of approximately 10nm. The second AWG selects a single peak of the high resolution AWG transmission. The combination is optimized to be tuned over 200nm of bandwidth around 1700nm. The AWG can be tuned by electro-optical phase shifters that are integrated in the different arms of the AWG. A single voltage controls the effective refractive index in one of the phase shifters. A set of voltages thus controls the optical path length differences in the arms of the AWG and therefore its tuning.
The design contains three different filters (Figure 1). The first tunable AWG has a 3dB point at 0.25nm (0.1dB at 0.05nm which is a possible mode spacing in an integrated ring-laser structure) and a FSR of 10nm. The other two tunable AWGs have a 3dB point at 14nm (1.5dB at 10nm) and a FSR of 210nm but different topologies. Specific aspects of the tuning control and design issues relating to the technological limitations will also be presented.
Figuur 1:Mask layout of the tunable AWGs and some test structures. The tunable AWGs can be
controlled by the electrical contact pads.
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