Relative limitations of increasing the number of modulation levels in computer generated holography

Phase and amplitude spatial light modulators (SLMs) capable of both binary and mull-level modulation are widely available and offer a wide range of technologies to choose from for holographic applications. While the replay fields generated with mull-level phase-only SLMs are of a significantly higher quality than those generated by equivalent binary phase-only SLMs, evidence is presented in this letter that this improvement is not as marked for amplitude SLMs, where mull-level devices offer only a small benefit over their binary counterparts. Heuristic and numerical justifications for this are discussed and conclusions drawn.