Case: PIC-to-FAU Alignment

Abstract

In silicon photonics assembly, accurate visual alignment between a photonic integrated circuit (PIC) and a fiber array unit (FAU) depends on more than magnification alone. A North American optical communications company approached VICO to evaluate a new imaging setup for PIC-to-FAU visual pre-alignment and feature recognition. The customer wanted to replace its existing microscope objective and ring light with a telecentric lens and coaxial illumination. Based on the required field of view, camera specifications and mechanical layout, VICO proposed two 4× solutions: the WWH40-63CTV3 object-space telecentric lens and the DTCA121-5C-GV2.1 bi-telecentric lens. A live online test was then arranged to compare their imaging performance under white and blue coaxial illumination.

Application Background

The customer’s existing system used an IDS UI-3080CP2-C-HQ camera with a Sony IMX250 sensor (2456 × 2054, 3.45 μm), paired with a Mitutoyo 3X compact objective and a ring light (FOV ≈ 2.8 × 2.35 mm).

Live Online Comparison

Live online test on a Sony IMX264 demo camera with representative samples; white and blue coaxial illumination demonstrated for contrast comparison.

MTF30 ≈ 285 lp/mm (WWH40-63CTV3) vs ≈ 310 lp/mm (DTCA121-5C-GV2.1). Customer also weighed FOV, DOF, telecentricity, illumination, mechanical space, and visual vs measurement intent.

Conclusion

Object-space telecentric can be practical for visual alignment with coaxial light; bi-telecentric adds stability when measurement accuracy matters. Live remote testing moved the customer from datasheet selection to application-based evaluation, then to quotation and procurement.

For the new top-down setup, coaxial illumination was needed to distinguish reflective PIC/FAU features. Ring lighting may create reflections or uneven illumination on small, highly reflective optical components.

Two Telecentric Solutions

WWH40-63CTV3 — 4× object-space telecentric with coaxial interface; stable magnification with slight Z variation; suited for flat reflective photonic features.

DTCA121-5C-GV2.1 — 4× bi-telecentric; stronger control of perspective error and magnification stability for precision dimensional/positional measurement.

Same nominal magnification, different optical structures and priorities — selection needs more than comparing the “4×” label.