A receiver includes a waveguide defined in a layer of silicon positioned on a base. The waveguide is immobilized relative to the base along the length of the waveguide. The waveguide is unbranched and is a multi-mode waveguide. The receiver also includes a groove configured to receive an optical fiber. The groove is positioned such that when the optical fiber is positioned in the groove the waveguide receives a light signal that exits a facet of the optical fiber. The receiver also includes a light sensor configured to receive the light signal from the waveguide after the light signal is received by the waveguide, is guided through the waveguide, and exits the waveguide. The receiver also includes a tunable optical attenuator configured to attenuate the light signal as the light signal travels along the waveguide. The receiver can be formed on a chip such that the waveguide is the only optical waveguide on the chip.