In the first 18 months of this project development and fabrication of the set of 3 SG DBR lasers for 100-nm-band wavelength swept source have been taken place. Unfortunately, this goal has not been reached due to difficulties in SG DBR laser connected with their lifetime. Thus, most work was focused on defining the problem and finding a solution to overcome it. Development of optical power amplifier (OPA) based on semiconductor chip has been successfully finished. Progress with development of optical µ-assembly is in accordance with initial Project plan.
Furthermore a technological platform for fabrication of OCTchips with passive and active optical components has been provided. In the first months of the project, IMEC provided the necessary PDK (Process Development Kit) to AIT for simulations to define the waveguide height that will be used for passive photonic integrated components. Subsequently, once the components were designed, IMEC took the charge of fabrication of the photonic chips. The first run of the project, SLR1 (Short Loop Run 1), has been completed and tested. The SLR1 was used to evaluate the SiN passive components, the data obtained from the SLR1 has been fed into the FLR1 (Full Loop Run 1) which is currently being fabricated. It will contain active components (photodetectors) and the 1st prototypes of the OCTengine.
In addition project simulations were carried out to find the optimum waveguide cross section both regarding thickness and width. In the next step, simulation routines were established for the design of the required photonic building blocks. Two CAD mask layouts (one with waveguides only for the first short loop run (SLR) and one co-integrated with photodiodes for the first full loop run (FLR)) were elaborated comprising individual photonic building blocks and first OCTengines to be used by MUW to acquire OCT images. The short loop fabrication run with the layout containing only the waveguides was finished in M12 and the supplied PICs have been evaluated since then.
The body of packaging work done so far consisted in assessing different approaches in packaging the PIC engine optically and electrically, together with corresponding tests and measurements. This involved simulating and testing four different fibre options on different edge couplers, and making the first optical test package. On 3D-printed optics side, the most suitable edge couplers were selected and micro-lenses for the sample and reference arm were simulated, developed, printed and characterized. For electrical packaging, electrical requirements were evaluated, and three different TIA options were assessed, TIA-ADC connections were also researched.
System integration so far comprised the systems concept including the opto-mechanical concept the system electronics, firm-and software and the system integration concept. The integration options with respect to sensitivity and heat load in the handheld unit have also been analyzed.
Furthermore, validation of the PICs for OCT single components, such as the passive PICs have been tested. In addition, polarizing (PZ) fibers within an OCT setup have been evaluate if this introduces imaging artefacts and the coupling losses between first passive PIC and different fiber arrays (FA) were evaluated. Preliminary OCT measurements with the passive PIC, integrated in a fiber-based OCT setup were performed. All measurements in this WP show promising results: The PZ fiber does not introduce imaging artefacts and achieves the desired polarization stability. Coupling losses could be improved by the usage of a lensed FA, which seems to be a promising option for low loss coupling between fibers and PICs.
