Optical mode sorters are a key enabling technology that have been widely used in communication and sensing systems. Conventionally, these are designed for a particular set of optical modes based on specific geometric transformation. We present a new approach for free-space optical mode sorting that can be tailored to measure any set of spatial modes or arbitrary superpositions of modes. Our approach is enabled by the combination of a reconfigurable photonics integrated circuit (PIC) interfaced with a Multiple-Plane-Light-Converter (MPLC) for pure optical mode processing. We have successfully sorted a range of high order spatial modes with crosstalk with a mean value -16dB and a reconfigurability greater than 12kHz.
Photonic crystal surface emitting lasers (PCSELs) are a new class of laser diode, offering control over emission (wavelength, polarisation, beam shape) through photonic crystal design, as well as power scalability and low beam divergence.
We present developments in 2D arrays of large scale (~150x150um) PCSELs, coherently coupled by 1mm long, 100 μm wide waveguides that can be electrically driven into loss or gain. By studying the spectral and current-power characteristics, we show coherent power scaling between multiple devices. We discuss injection locking between devices achieved through controllable 2D in-plane feedback and its effect on the near and far field emissions.
We fabricated and characterized a grating-coupled external cavity laser with gain chips including self-assembled InAs quantum dots (QDs) for swept-source optical coherence tomography applications. By controlling the emission wavelength of the self-assembled InAs QDs, tunable lasing at a wavelength band of 1–1.1 μm was obtained, which represents an optimal balance between absorption and scattering in biological tissues. Straight and J-shaped edgeemitting ridge waveguides (RWGs) were fabricated on a GaAs-based waveguide layer containing four InAs QDs layers. A diffraction grating with the quasi-Littrow configuration was employed as an external cavity for the fiber-coupled diodes. Electroluminescence spectra from the QD-based diodes revealed that broadband amplified spontaneous emissions appeared in a J-shaped RWG, whereas Fabry–Perot lasing occurred in the straight RWG. The external cavity was then introduced for the diode with a J-shaped RWG, and a tuning range of 65 nm centered at approximately 1100 nm was obtained from the QD gain chip with the J-shaped RWG.
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