Table 1.

Comparison of different encoders.

Encoder	Typical Resolution	Typical Footprint	Advantages	Shortcomings
Fiber	<1 pm [27]	cm scale	Low cost, high resolution	Low-level miniaturization
Waveguides	<10 pm [42]	35 × 260 µm2 [42]	Low cost, structure variability	Relatively larger footprint
Random structure	<0.75 µm [46]	25 µm radius [46]	High resolution, smaller footprint	Large loss for scattering, structure uncertainty
Nanowires	<10 nm [56]	0.5 × 75 µm2 [56]	Very small size, easy to combine with CCD	Relatively lower resolution
PhC	<0.1 nm [64]	0.6 × 114 µm2 [64]	High resolution, cost effectiveness	Manufacture error sensitivity, larger footprint
QD	<1 nm [75]	cm scale, compatible with CCD	Easy to combine with CCD, small footprint	Similar responses function for QDs restrict resolution
Meta-surfaces	<0.8 nm [85]	cm scale, compatible with CCD	Large design freedom, structure variability	Relatively lower resolution
Tunable devices	<5 pm [131]	16 × 9 µm2 [136]	High resolution, small footprint	Environment sensitivity, more sophisticated manufacturing