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We demonstrate reactively sputtered Al 2 O 3 :Er 3+ waveguide amplifiers with an erbium concentration of 3.9 × 10 20 ions/cm 3 , capable of achieving over 30 dB small signal net gain at 1532 nm using bidirectional pumping at 1480 nm. We observe on chip output powers of 10.2-13.6 dBm of amplified signal power at 1532 nm for a 12.9 cm waveguide amplifier considering -25.4 dB of lumped coupling losses per facet. Annealing was used to improve the performance of the devices, which were patterned using electron beam lithography and reactive ion etching. This result, to our knowledge, represents record breaking on-chip internal net gain for Al 2 O 3 :Er 3+ waveguide amplifiers, which show promise over other technologies due to wafer scalability and promise of easy monolithic integration with other material platforms to support a wide variety of applications.

We propose and experimentally demonstrate a modular microring laser (MML) cavity for sensing applications. The proposed MML permits much more design freedom compared with a traditional simple ring cavity by decoupling the performance parameters into several regions in the cavity. Thus, the different biosensor performance parameters can be optimized semi-independently limiting the need for trade-offs on the design of the biosensing device. The first generation MML has been fabricated and tested. A fiber-to-fiber slope efficiency of up to 1.2%, a temperature coefficient of 1.35 GHz/K and a 3σ limit of detection (LOD) of 3.1 × 10 -7 RIU without averaging and 6.0 × 10 -8 RIU with a 60 s averaging, has been measured for the MML sensor, which is a record-low LOD in on-chip ring cavity optical sensors. Further optimization is possible, capitalizing on the key advantage of the MML concept, namely the potential for designing the laser cavity to achieve the desired optimization goals.

Self-referenced biosensing based on mode-splitting on a microring resonator is experimentally demonstrated. A Bragg grating integrated on the surface of the ring provides coupling between the clockwise and counterclockwise travelling modes of the pristine ring resonator lifting their degeneracy. The amount of mode-splitting is directly related to the reflectivity of the grating and it is only affected by structurally modifying the grating. Environmental perturbations to the surroundings of the gratings, such as temperature and bulk refractive index variations, have a minor effect on the amount of mode-splitting. This principle allows the realization of a self-referenced sensing scheme based on the detection of variations of the mode-splitting induced by structural changes to the grating. In this work, a polymethyl methacrylate (PMMA) Bragg grating is integrated onto a ring resonator in Al 2 O 3 . It is shown both theoretically and experimentally that the amount of splitting of a resonance varies minimally under temperature or bulk refractive index perturbations. However, the structural change of attaching a layer of biomolecules inside the grating does affect its reflectivity and the amount of mode splitting present. This result represents the first proof-of-concept demonstration of an integrated mode-splitting biosensor insensitive to temperature and refractive index variations of the liquid matrix where the molecules to be detected are embedded. The reported results pave the road towards the realization of truly self-referenced biosensors.

TiO 2 channel waveguides were fabricated using a DC sputter deposition process, followed by photolithography and reactive ion etching. A SiO 2 cladding was deposited using evaporation. SEM, TEM and Raman measurements indicate the presence of both an amorphous and a crystalline phase. As the layer thickness increases, poly-crystalline structures start forming. Loss measurements were performed by imaging the scattered light from the top of the channel waveguides and fitting an exponential decay to the intensity profile. Propagation losses of 7.8 ± 0.52 dB/cm at a wavelength of 632.8 nm and 0.68 ± 0.46 dB/cm at a wavelength of 1010 nm were experimentally characterized.

Concentrations down to 3 nM of the rhS100A4 protein, associated with human tumor development, have been detected in undiluted urine using an integrated sensor based on microring resonators in the emerging Al 2 O 3 photonic platform. The fabricated microrings were designed for operation in the C-band (λ = 1565 nm) and exhibited a high-quality factor in air of 3.2 × 10 5 . The bulk refractive index sensitivity of the devices was ~100 nm/RIU (for TM polarization) with a limit of detection of ~10 -6 RIU. A surface functionalization protocol was developed to allow for the selective binding of the monoclonal antibodies designed to capture the target biomarker to the surface of the Al 2 O 3 microrings. The detection of rhS100A4 proteins at clinically relevant concentrations in urine is a big milestone towards the use of biosensors for the screening and early diagnosis of different cancers. Biosensors based on this microring technology can lead to portable, multiplexed and easy-to-use point of care devices.

We characterize the spectral response of a distributed-feedback resonator when subject to a thermal chirp. An Al 2 O 3 rib waveguide with a corrugated surface Bragg grating inscribed into its SiO 2 top cladding is experimentally investigated. We induce a near-to-linear temperature gradient along the resonator, leading to a similar variation of the grating period, and characterize its spectral response in terms of wavelength and linewidth of the resonance peak. Simulations are carried out, showing good agreement with the experimental results and indicating that the wavelength of the resonance peak is a result only of the total accumulated phase shift. For any chirp profile we are able to calculate the reflectivities at the resonance wavelength, and this information largely explains how the linewidth of the resonance changes. This result shows that the increase in linewidth is governed by the increase of the resonator outcoupling losses.

We demonstrate a fabrication procedure for the direct integration of micro-ball lenses on planar integrated optical channel waveguide chips with the aim to reduce the divergence of light that arises from the waveguide in both horizontal and vertical directions. Fabrication of the lenses is based on photoresist reflow which is a procedure that allows for the use of photolithography for careful alignment of the lenses with respect to the waveguides and enables mass production. We present in detail the design and fabrication procedures. Optical characterization of the fabricated micro-ball lenses demonstrates a good performance in terms of beam-size reduction and beam shape. The beam half divergence angle of 1544 nm light is reduced from 12.4 ° to 1.85 °.

Spiral-waveguide amplifiers in erbium-doped aluminum oxide on a silicon wafer are fabricated and characterized. Spirals of several lengths and four different erbium concentrations are studied experimentally and theoretically. A maximum internal net gain of 20 dB in the small-signal-gain regime is measured at the peak emission wavelength of 1532 nm for two sample configurations with waveguide lengths of 12.9 cm and 24.4 cm and concentrations of 1.92 × 10(20) cm(-3) and 0.95 × 10(20) cm(-3), respectively. The noise figures of these samples are reported. Gain saturation as a result of increasing signal power and the temperature dependence of gain are studied.

Monolithic integration of Al2O3:Er3+ amplifier technology with passive silicon-on-insulator waveguides is demonstrated. A signal enhancement of >7 dB at 1533 nm wavelength is obtained. The straightforward wafer-scale fabrication process, which includes reactive co-sputtering and subsequent reactive ion etching, allows for parallel integration of multiple amplifier and laser sections with silicon or other photonic circuits on a chip.