Transmitter photonic integrated circuit (TxPIC) chip

A semiconductor chip having an output facet, the semiconductor chip comprising:

• a light source provided on the semiconductor chip;
• a photo diode provided on the semiconductor chip;
• an optical combiner provided on the semiconductor chip, the optical combiner having a first input and a second input, and an output, the first input being coupled to the light source and the second input being coupled to the photodiode, the output providing an output signal through the output facet of the semiconductor chip;
• and
• a coating provided on the output facet of the semiconductor chip, wherein a portion of the output signal is reflected by the output facet, the reflected portion of the output signal passing through the optical combiner and being output through the second input of the optical combiner to the photo detector, a thickness of the coating being one of a plurality of thicknesses, each of the plurality of thicknesses being associated with a corresponding one of a plurality of intensities of the reflected portion of the output signal, the thickness of the coating being associated with one of the plurality of intensities which is less than remaining ones of the plurality of intensities.