Reflection engineering / wavelength division multiplexing (WDM) geometric optical isolator

A transmitter, comprising:

• a photonic integrated circuit (PIC) comprising N WDM lasers and N modulators integrated on a common solid substrate, wherein N≥2, said WDM lasers and said modulators being interconnected via waveguides and a series of one or more combiner/splitter elements, each combiner/splitter element comprising at least one coupler;
• said common solid substrate controlling an optical phase within said PIC and within said WDM lasers, said modulators, said waveguides, and said series of one or more combiner/splitter elements;
• said waveguides and said series of one or more combiner/splitter elements forming a structure, said structure combining wavelengths from said N WDM lasers into N output waveguides, each of said N output waveguides comprising signals from all of said N WDM lasers, an optical power of each wavelength in each of said N output waveguides being reduced by a splitting factor, said splitting factor being determined by an amount of combiner/splitter elements and an amount of said WDM lasers, the N output waveguides providing inputs to the N modulators;
• wherein a power level of any inherent optical reflections occurring within said N modulators, or within said PIC optical circuit following said N modulators, returning through said series of one or more combiner/splitter elements is reduced by said splitting factor via said at least one coupler of said one or more combiner/splitter elements, plus excess loss due to said at least one coupler of said one or more combiner/splitter elements, thereby reducing a total optical reflection power returning to any one of said N WDM lasers.