Polarimeter

Polarimeter — Photodiode Analog Front-End

A 4-layer mixed-signal PCB that reads optical polarization by measuring the photocurrent from a pair of photodiodes through a low-noise transimpedance signal chain. Designed in KiCad; this repository contains the full schematic, layout, fabrication outputs, and bill of materials.

📄 Full schematic (PDF) · 🖼️ board bottom

What it does

Light passing through a polarizing optical stage lands on two photodiodes (D1, D2). Each diode's photocurrent is converted to a voltage by a transimpedance amplifier (TIA), filtered, and buffered for acquisition. By comparing the two channels, the relative polarization / intensity of the incident beam can be recovered. The board carries its own low-noise power regulation and a precision voltage reference so the analog measurement is clean and ratiometric.

Signal chain

Power

• LT8609 synchronous step-down buck — primary rail regulation from the DC input jack.
• LP5912-3.3 low-noise LDO — clean 3.3 V rail for the precision analog section.
• Local decoupling throughout (0.1 µF / 1 µF / 10 µF) to keep the TIA front-end quiet.

Board

• 4 copper layers: F.Cu, In1.Cu, In2.Cu, B.Cu
• Surface-mount construction, 0603/0805 passives
• Gerbers and drill files included for direct fabrication

Repository layout

Polarimeter.kicad_pro      KiCad project
Polarimeter.kicad_sch      Root schematic
Power.kicad_sch            Power-supply sub-sheet (hierarchical)
Polarimeter.kicad_pcb      PCB layout (4-layer)
Polarimeter.csv            Bill of materials
Gerbers for AMO/           Fabrication outputs (Gerber + Excellon drill)
docs/                      Rendered schematic PDF + 3D board images

Bill of materials

The full BOM lives in Polarimeter.csv (designator, footprint, quantity, value). Key actives: OPA381, OPA320/OPA2320, REF3425, LT8609, LP5912-3.3.

Tools

Designed in KiCad. Open Polarimeter.kicad_pro to view or edit the schematic and layout.

Designed by Christian Hearn, with Malik Shaaban.