Tantalum oxide anti-reflective thin films for C-band travelling-wave semiconductor optical amplifiers

Travers-Nabialek, Josie 2023. Tantalum oxide anti-reflective thin films for C-band travelling-wave semiconductor optical amplifiers. MPhil Thesis, Cardiff University. Item availability restricted.

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Abstract

The work in this thesis describes an approach to suppressing cavity resonances in Travelling-Wave Semiconductor Optical Amplifiers (TW-SOA) by application of a single layer anti-reflective thin film, tuned for C-Band (1530-1565 nm) emission. A 215 nm layer of tantalum oxide (TaOx) is applied to both facets of AlGaInAs/InP ridge waveguide (RWG) Fabry-Pérot (FP) laser diodes (LD) via electron-beam (e-beam) evaporation. E-beam evaporation allows a dielectric layer, thicker than 200 nm, to be deposited onto many LD facets in a cost-effective and time efficient manner. This deposition technique is chosen as it allows the refractive index of the antireflection coating (ARC) to be tuned to produce a TaOx layer of the required refractive index, nfilm, by exploiting the relationship between nfilm and chamber pressure during evaporation. Monitoring the power-current characteristics and emission spectrum from the devices before and after coating demonstrates the successful realisation of a TW-SOA where lasing is no longer present. Remaining cavity resonances show gain ripple, Gr, values across the C-Band gain spectrum of ≤0.1 dB with a maximum of 0.5 dB at injection currents over three times the original laser threshold current. These values are competitive when compared to commercially available SOAs operating across the same wavelength region. The remaining FP fringes observed in the Amplified Spontaneous Emission (ASE) spectrum of the TW-SOA are consistent with geometric mean facet reflectivity, √ (R1 R2), values as low as 10-4 and 10-5 across the C-Band wavelength range (1530-1565 nm) of interest. The results in this thesis show promise for the future use of TaOx thin films to improve the performance of Distributed Feedback (DFB), and Distributed Bragg Reflector (DBR) laser diodes, or as an effective antireflection coating for different types of semiconductor optical amplifiers.

Item Type:	Thesis (MPhil)
Date Type:	Completion
Status:	Unpublished
Schools:	Physics and Astronomy
Subjects:	Q Science > QC Physics
Uncontrolled Keywords:	Tantalum oxide, Semiconductor Optical Amplifier, SOA, Semiconductor, Thin films, Antireflection coating, Reflectivity, Travelling-Wave, C-Band, Electron Beam Evaporation, Multiple Quantum Well , Lasers Diode, Gain ripple, ridge waveguide, Amplified Spontaneous Emission.
Funders:	EPSRC
Date of First Compliant Deposit:	11 January 2024
Last Modified:	11 Jan 2024 13:40
URI:	https://orca.cardiff.ac.uk/id/eprint/165404

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