Project Overview
The mid-infrared (MWIR) and long-wave-infrared (LWIR) optical phase arrays (OPAs) are attractive for gas-sensing or thermal LIDARs and for FSOC with lower sensitivity to turbulence and scintillation. While exploiting the transparent transmission window of the atmosphere and high eye-safety optical power at the operating mid-IR wavelengths, the range of the OPA devices can be further increased. The emergence of quantum cascade laser (QCL) made easier to address MWIR and LWIR spectral range. QCL sources are achieving high-efficiency and high continuous wave-power. However, the mature silicon photonic platform used for advanced and complex PICs is incompatible with MWIR. In this project, we pursue MWIR and LWIR OPAs based on Germanium-Silicon based 3D Photonic and Electronic Integrated Circuits (EPICs).
The fabrication process involving Ge on silicon can utilize the CMOS fabrication platform to achieve tolerance and resolution sufficiently large creating subwavelength (λ/2) MWIR structures needed for high-performance LIDARs

Current Research Activities
As in the SiPhotonic LIDARs, we are particularly interested in development of such systems in the area of 3D EPIC development where each cell includes emitters/receivers, and the control electronics.
Cell-based emitters/receivers:
As in the SiPhotonic LIDARs, we utilize the waveguides with phase shifters steer in lateral direction (N controls) and tunable laser + fixed grating (1 control point) steers in longitudinal direction to reduce the complexity of the unit cell scaling. The key building blocks of the unit cell includes dense waveguide array, compact and low-loss interlayer optical coupling structures, uniform emitting grating up to 10 mm scale, low power consumption phase modulators and wide range wavelength tunable lasers. Figure 1 shows a schematic view of the MWIR/LWIR Ge-Si OPA Photonic Integrated Circuit, and Figure 2 shows photographs of fabricated chips, and Figure 3 shows normalized far-field patterns of the beam steering experimental results.

Figure 1: Schematic view of an OPA PIC based on grating emitter for 2D beam-steering
Figure 2 (a) SEM picture of grating emitter waveguide array (b) Detailed view of a Ge waveguide with SiNx grating on top (c) SEM picture of a MMI 1×2 beam splitter (d) Microscope picture of a packaged 12 channels OPA based on Germanium photonic chip
Figure 3: (a) Normalized far-field scans along the θ axis for different input wavelength from 4500 nm to 4670 nm, the insert shows the steering angle as a function of the input wavelength (b) 2D plots of the beam profile obtained with the Ge-MIR OPA for different wavelengths and phase tuning settings

A.3. Recent Group Publications

  1. Mathias Prost, Yi-Chun Ling, Semih Cakmakyapan, Yu Zhang, Kaiqi Zhang, Junjie Hu, Yichi Zhang, and S. J. Ben Yoo, “MWIR Solid-State Optical Phased Array Beam Steering using Germanium-Silicon Photonic Platform,” IEEE Photonics Journal, 2019
  2. Mathias Prost, Yi-Chun Ling, Semih Cakmakyapan, Yu Zhang, Kaiqi Zhang, Junjie Hu, Yichi Zhang, and S. J. Ben Yoo, “MWIR Solid-State Optical Phased Array Beam Steering using Germanium-Silicon Photonic Platform“, OFC , Mar 2019

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