Integrated polarisation rotators

Bregenzer, Josef Johann (2010) Integrated polarisation rotators. PhD thesis, University of Glasgow.

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The ability to control and manipulate the state of polarisation of optical signals is becoming an increasingly desirable feature in numerous applications including integrated optical circuits, semiconductor optical amplifiers (SOAs) and optical communication systems.
This thesis introduces the design, optimisation, fabrication and operation of two novel integrated reciprocal single-section passive polarisation converter devices based upon mode-beating. The converter designs consist of asymmetric profiled waveguides, which were realised in a single reactive ion dry-etch process step. An in-situ custom built sample holder was utilised to place the samples at a predetermined angle to the incoming ions, which resulted in waveguide profiles with sloped sidewalls. This fabrication technique also allowed the incorporation of adiabatic taper sections within the device design.
The converter section waveguide profile of the first design consists of two sloped sidewalls. Devices realised on a GaAs/AlGaAs material structure achieved a converted transverse magnetic (TM) polarisation purity of 81.4% at a device length of 30 μm for a transverse electric (TE) polarised input signal at an operating wavelength of λ = 1064 nm. The convention used is that TE refers to light polarised in the plane of the wafer and TM refers to light polarised perpendicular to the plane of the wafer. The total optical loss imposed by this device was evaluated to be 1.72 dB. This design was also used for the monolithic integration of a passive polarisation converter incorporated within a Fabry-Perot semiconductor laser diode on an unstrained GaAs/AlGaAs double quantum well heterostructure material system. A predominantly TM polarised optical output from the converter facet of greater than 80% is demonstrated for a converter length of 20 μm at an emitting wavelength of 867.1 nm. The about 1.4 mm long fabricated device has a current threshold level of 100 mA and a side mode suppression ratio (SMSR) of 25 dB.
The second converter design is based on the modification of an already existing stripe waveguide structure. The converter section is defined by applying the above mentioned angled dry-etch process on a certain length of the stripe waveguide. The fabricated asymmetric waveguide core profile consists of a sloped undercut. A TM polarisation purity of 90% at a device length of 55 μm for a TE polarised input signal at an operating wavelength of λ = 1064 nm was achieved at the output. The total optical loss imposed by this device was evaluated to be 0.47 dB.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: integrated optics devices, polarisation rotation, semiconductor laser, optical device fabrication
Subjects: Q Science > QC Physics
T Technology > TK Electrical engineering. Electronics Nuclear engineering
Colleges/Schools: College of Science and Engineering > School of Engineering
Supervisor's Name: Hutchings, Prof. David Crichton
Date of Award: 2010
Depositing User: Mr. Josef Bregenzer
Unique ID: glathesis:2010-1573
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 30 Mar 2010
Last Modified: 10 Dec 2012 13:42

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