Sub-surface compound microlenses

A photonic device, comprising:

• a photonic integrated circuit (PIC);
• and
• a layer of glass, the layer of glass having a microlens portion monolithic with a bulk portion,
• wherein:
• the layer of glass is aligned with the PIC to receive a light beam from the PIC,
• the microlens portion includes regions stacked along an optical axis of the light beam,
• a refractive index of an individual region is substantially constant across a width of the individual region and is different from a refractive index of the bulk portion of the layer of glass by at least about 0.005, and
• at least one region of the regions is a biconvex lens.

A microelectronic assembly, comprising:

• a die;
• and
• a further component coupled to the die,
• wherein:
• the die includes a solid layer of glass rectangular in shape in a cross-sectional side view,
• the solid layer of glass has a first surface and a second surface opposite the first surface,
• the die further includes a stack of regions within the solid layer of glass,
• each region of the stack of regions has a refractive index different from a refractive index of the solid layer of glass,
• a first region of the stack of regions is a region closer to the first surface of the solid layer of glass than all other regions of the stack of regions,
• a second region of the stack of regions is a region closer to the second surface of the solid layer of glass than all other regions of the stack of regions,
• a non-zero distance separates the first region from the first surface solid layer of glass, and
• a non-zero distance separates the second region from the second surface solid layer of glass.

A photonic device, comprising:

• a photonic integrated circuit (PIC);
• and
• a layer of glass, the layer of glass comprising a microlens portion and a bulk portion,
• wherein:
• the layer of glass is aligned with the PIC to receive a light beam from the PIC,
• the microlens portion is unitary with the bulk portion,
• the microlens portion includes a region, and
• a refractive index of the region is substantially constant across a width of the region and is different from a refractive index of the bulk portion of the layer of glass by at least about 0.005.