fig5 y 1 and y 2 represent the distances between the front and back openings of alignment hole 406 to the bottom surface 404 respectively using the reference symbols of fig5 the difference between y 1 and y 2 should be preferably and approximately less than or equal to 10 um of course another aspect of parallelism is that the alignment holes should be parallel to each other in some manufacturing processes the alignment holes 406 are used as reference points by the cameras of alignment systems in order to properly position for example the circuitry set 408 and the photonic devices onto the backing block however osa 400 contains fiducials 410 which can also be used by alignment systems during manufacturing processes alignment systems can more easily utilize fiducials 410 rather than alignment holes 406 because fiducials 410 are sized more closely to the features of other reference points e g the anode pad of a photonic device alignment processes using fiducials 410 are easier to utilize because the cameras of alignment systems can focus on similarly sized objects in comparison it is more difficult to adjust a camera of an alignment system to sequentially focus on objects having very different sizes for example an alignment hole and an anode pad of a photonic device can have very different respective diameters of 700 and 70 um fiducials 410 can be easily formed on a surface of osa 400 during the injection molding manufacturing process of backing block circuitry set 408 includes a metal pad 412 that serves as a cathode and individual traces 414 photonic devices are attached to metal pad 412 such that their cathode contact surfaces make contact with metal pad 412 cathode traces 416 connect metal pad 412 to cathode contact pads 418 on the bottom.