In the last years, mid-infrared (mid-IR) integrated nanophotonics, spanning from 2 µm up to 12 µm wavelengths, has been extensively researched due to its imminent potential for advanced on-chip applications in spectroscopy, material processing, chemical and bio-molecular sensing, security and communications, to name a few. Herein, the group-IV elemental semiconductors such as silicon (Si) and germanium (Ge) hold promisefor leveraging mature microelectronics facilities for the low-cost production of mid-IR circuits. Recent advances in mid-IR field include, but not limited to, low-loss waveguides, splitters, demultiplexers, and surface grating couplers. The latter are particularly critical devices to allow for successful implementations as well as further exploitations of mid-IR photonics [1-5]. In this work, we report on our recent advances in development of efficient fiber-chip surface grating couplers that operate at 3.8 µm mid-IR wavelengths. In particular, we demonstrate single-etch step surface grating couplersrealized on Ge-on-Si substrates. The coupling devices advantageously combine focusing geometry and an inversely tapered excitationaccessto achieve compact device footprint, improved fiber-chip light coupling up to-11 dB, and lowered back-reflections (<-15 dB). The reduced grating reflectivityis essential for spectroscopic scenarios, where absorption features of a few hundreds of megahertz in bandwidthneed to be precisely resolved [5].In addition, we study the potential of Ge-on-silicon-on-insulator (Ge-on-SOI) membrane waveguides to develop robust and efficient grating-coupled optical interfaces. Ge-on-SOI membranes are particularly attractive to implement surface grating couplers, since the platform provides a superior vertical index contrast between the waveguide core and surroundings. To this end, we propose Ge-on-SOI grating couplers engineered with sub-wavelength gratingmetamaterials to optimizeoverall fiber-chip coupling performance down to-1 dB.