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projects:optics:log [2026/07/15 21:02] – [Day 2026-07-15 (rahix, guest)] rahixprojects:optics:log [2026/07/18 12:47] (current) – [Day 2026-07-18 (rahix, guest)] rahix
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 > //This page is a lab notebook. It documents the work done in the lab and our thoughts, theories, and findings related to it. Everything you read here is work in progress and not final results. We believe it is best to have our lab notes out in the open, because it gives more detailed insight into what worked for us and what didn't. Of course you can also use this page to follow our progress!// > //This page is a lab notebook. It documents the work done in the lab and our thoughts, theories, and findings related to it. Everything you read here is work in progress and not final results. We believe it is best to have our lab notes out in the open, because it gives more detailed insight into what worked for us and what didn't. Of course you can also use this page to follow our progress!//
  
 +==== Day 2026-07-18 (rahix, guest) ====
 +Cases are ready:
 +
 +{{:projects:optics:2026-07-18-cases.jpg?600|}}
 +
 +==== Day 2026-07-17 (rahix, guest) ====
 +Since we do not have a FAFO laser driver design yet (see techtree [[https://git.fa-fo.de/fafo/techtree/issues/85|#85]]), we are going to use an ''LD1100'' ([[https://www.thorlabs.com/oem-laser-diode-driver-constant-power?tabName=Overview|Thorlabs]]) module. We set up the module for the diode and verified everything works:
 +
 +{{:projects:optics:20260717_diode-test.jpg?600|}}
 +
 +Selected gain for the ''LD1100'' is max I<sub>mon</sub>=260µA. The diode monitoring current is specified for 150µA typ., but up to 400µA. With the selected gain and this diode, it works out well and the diode is easily driven at about 30mA.
 +
 +Wired up the diode socket to a 3-pin dupont header. The wires are labelled with 1, 2, 3 rings for pin 1-3 of the diode. For pin code A diodes like the one we are using, this means:
 +
 +{{:projects:optics:pin-code-a-diode-description.png?nolink&600|}}
 +
 +And it lines up with the pinning of the ''LD1100'' so you can connect it directly, as visible in the picture.
 +
 +----
 +
 +In the meantime, somewhere else, we machined the case(s) for the diode modules:
 +
 +{{:projects:optics:2026-07-17-diode-module-cases.jpg?600|}}
 +
 +The CAD really doesn't do it justice how small this is!
 +
 +==== Day 2026-07-16 (rahix, guest) ====
 +We decided to build two versions of the module case. Increasing the distance between lens and fiber end, we can much improve the theoretical coupling efficiency. But this comes at the cost of being much more sensitive to lens alignment (0.1mm shift of the lens moves the focus spot by 1.6mm). So we will need to see if we can pull it off.
 +
 +{{:projects:optics:2026-07-17_long_diode_module.png?400|}}
 +
 +[The longer module with more ideal coupling conditions]
 +
 +With this longer design, the TEM₀₀ beam diameter at the waist is 3.66µm which matches the MFD (mode field diameter) of the selected fiber.  With the shorter design, we are at 2.2µm.
 +
 +On the laser diode side, we capture 23° (half angle) of the emitted light (Compared to 18° with the shorter design).
 ==== Day 2026-07-15 (rahix, guest) ==== ==== Day 2026-07-15 (rahix, guest) ====
 Continued working on the diode module design. It lives here: [[https://git.fa-fo.de/rahix/FiberCoupledLaserModule]] Continued working on the diode module design. It lives here: [[https://git.fa-fo.de/rahix/FiberCoupledLaserModule]]
- 
-Current working state of the assembly: 
  
 {{:projects:optics:2026-07-15_diode-module.png?400|}} {{:projects:optics:2026-07-15_diode-module.png?400|}}
 +
 +Main changes of our assembly against the original design:
 +
 +  * Slightly larger to accommodate larger lens with longer focal distance
 +  * Diode is not press-fit into the housing but rather clamped from the back – we will also use the block clamping the diode to provide thermal control (Using a TEC + NTC)
 +  * Mounting solution for fixing the assembly to an optics breadboard
  
 Short list of selected components: Short list of selected components: