Waveguide PIN photodiodes with different absorber thicknesses and lengths were fabricated and characterized for linearity. Device A has a thicker absorber and shorter length, resulting in a bandwidth of 20 GHz while device B reduces the absorber by half while maintaining the intrinsic layer thickness and almost doubles the length, resulting in a smaller optical overlap factor and a bandwidth of 10 GHz. Device B shows a significant enhancement in OIP3 with a record high maximum value for a PIN waveguide photodiode of 42.4 dBm at 28 mA and -4V bias compared to device A which has a maximum OIP3 of 32.7 dBm at 10 mA and -4V bias. The increased linearity in device B is attributed to the reduction in optical overlap factor and increase in device length resulting in an easing of the front facet photocurrent density and overall device heating. The DC saturation points are about 75 mA and >160 mA for device A and B at -2V bias.