Managing back-side processing of photonic integrated circuits

An article of manufacture comprising:

• a bottom volume of a photonic integrated circuit, the bottom volume comprising
• a first region composed of a first material characterized by a first index of refraction and having a first thickness, and
• one or more thinned regions in which at least a portion of the first material is absent or has a thickness less than the first thickness;
• a middle volume of the photonic integrated circuit, located on top of the bottom volume, the middle volume comprising a second material characterized by a second index of refraction smaller than the first index of refraction;
• and
• a top volume of the photonic integrated circuit, located on top of the middle volume, the top volume comprising
• one or more alignment structures, and
• a first photonic structure in a set of photonic structures;
• where the top volume and the middle volume are in contact at an interface plane;
• where a first set of spatial coordinates specify one or more two-dimensional positions, with respect to the alignment structures, of one or more portions of the first photonic structure in a first plane that is parallel to the interface plane;
• where the first set of spatial coordinates specify one or more two-dimensional positions, with respect to the alignment structures, within at least one thinned region in a second plane that is parallel to the interface plane;
• and
• where at least one of the one or more thinned regions is formed by removing a portion of the first material based at least in part on
• an optical signal detected after the optical signal traverses through the middle volume, and
• a first set of spatial coordinates specifying one or more two-dimensional positions, with respect to the alignment structures, of one or more portions of the first photonic structure.