In this work, we demonstrate an InGaAsP multiple quantum well tunable laser diode that amalgamates two gain sections with different bandgap energies. This is achieved using selective area intermixing of the multiple quantum wells, and impurity-free vacancy induced disordering. When different current combination is injected into each section, that leads to a laser wavelength peak whose position depends on the relative magnitudes of the two injected currents. The laser wavelength can be fine-tuned from 1538 nm to 1578 nm with relatively constant output power. The free spectral range FSR of the tunable laser found to be 0.25 nm. This tunable laser was launched into an optical surface plasmon resonance sensor head to provide an input light source for the SPR sensor. Using the tunable laser diode, we have demonstrated an optical surface plasmon resonance sensor head that is based on an inverted rib dielectric waveguide, in which the resonance wavelength of the surface plasmon excited at the gold metal-dielectric interface depends on the refractive index of the liquid in contact with it. The inverted-rib waveguide of the SPR sensor head is made of a layer of SU-8 polymer with a refractive index of 1.568. While the lower cladding layer consists of silicon oxynitride (SiOxNy) with a refractive index of 1.526. The top surface is coated with 20 nm of chromium followed by a 50 nm thick layer of gold or with 4 nm of titanium followed by a 25 nm thick layer of gold. The SPR sensor head was designed, to allow monitoring of analyte media with a refractive index, ranging from 1.43 to the 1.52. Using a set of reference liquids representing the analyte medium, the sensitivity of the SPR sensor was measured using the fabricated tunable laser, an optical spectrum analyzer, and a photodiode. It was found that with various calibrated sample liquids in contact with the gold metal, a sharp resonance dip in the transmission spectrum occurred, and its position shifted to a shorter wavelength when the refractive index of the sample liquids was increased. The average sensitivity of the SPR sensor devices was determined to be S = 334 nm/RIU.


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Graduation Date





Likamwa, Patrick


Doctor of Philosophy (Ph.D.)


College of Engineering and Computer Science


Electrical and Computer Engineering

Degree Program

Electrical Engineering









Release Date


Length of Campus-only Access

1 year

Access Status

Doctoral Dissertation (Open Access)