In this work, we propose and implement a bi-junction depletion-type silicon electro-optic phase shifter. The phase shifter has a lateral profile of implants, that closely resembles that of a common bipolar junction transistor, and thus, has two polarities. These are acceptor-donor-acceptor (PNP) as well as donor-acceptor-donor (NPN). We realize both variants in IMEC ISIPP50G open-access silicon photonic technology and compare them to lateral and interleaved phase shifters. Both PNP and NPN phase shifters exhibit a VπLπ figure that is at least 14.47% and up to 45.1% lower than that of the lateral and interleaved phase shifters realized in the same technology. Bi-junction phase shifters can be implemented in any planar silicon photonic technology that offers bipolar implantations within silicon photonic waveguides.
Monolithic distributed feedback semiconductor lasers (1550 nm) for FMCW LiDAR applications have been designed, fabricated and tested. The strong optical frequency modulation distortion observed when a standard DFB laser is modulated with a triangular current waveform is significantly mitigated in our laser. A 100 kHz frequency modulation with amplitude of 0.9 GHz and nonlinear distortion of 0.3%, calculated as the standard deviation of the optical frequency after removal of a linear fit, was measured through an unbalanced fiber interferometer. This was achieved without electronic pre-distortion of the triangular waveform. The 60 kHz intrinsic linewidth of the laser was unaffected by the modulation. Two lasers were co-packaged in a 2.6 cm3 multi-layer ceramic package and coupled to fiber pigtails with micro-lenses. The pins of the ceramic package were soldered to a printed circuit board containing the current sources driving the lasers. This optical source was used in a two-channel LiDAR demonstrator built from off-the-shelf fiber optic components and a twodimensional gimbal scanning mirror. This demonstrator enabled detecting a target with 10 % Lambertian reflectivity up to a distance of >120 m and recording point clouds of different scenes. This shows that FMCW LiDAR in combination with highly coherent and linear DFB laser sources is a very promising technology for long range sensing. A version under development will include a silicon photonics chip for further integration and functionality including I/Q detection.
We have experimentally demonstrated the ability to couple an arbitrary polarization state from a fiber to the TE-mode of a single waveguide in an integrated silicon photonics circuit with an extinction ratio larger than 31 dB, measured between the output ports of the integrated photonic circuit. To achieve this we combined a 2D- grating coupler and a Mach-Zehnder Interferometer (MZI). After accounting for setup and coupling losses, for a 1 mW input into the 2D coupler, we obtain an average output power of 0.98 mW at the desired waveguide, with less than 1.2 dB variation across all input polarization states. The experiments were performed at a wavelength of 1.55 μm.
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