From: jl@glen--canyon.com   
      
   On Sat, 6 Dec 2025 14:32:58 -0800, wmartin  wrote:   
      
   >On 12/6/25 14:00, john larkin wrote:   
   >> On Sat, 6 Dec 2025 13:06:18 -0800, wmartin  wrote:   
   >>   
   >>> Greetings,   
   >>> Just musing here. How might I couple a fiber optic cable to the optical   
   >>> window on a Lidar chip? Wondering if it's possible to do Lidar through a   
   >>> twisty path, like routed around an arbitrary light blocking "thing". Are   
   >>> there going to be intractable reflections at one or both ends of the   
   >>> fiber? I do have a use for this if it is possible...   
   >>> Regards,   
   >>> Bill M.   
   >>   
   >> If the lidar chip has a window, and the beam is expanded to some   
   >> modest diameter, you'd need a lens to get any amount of useful   
   >> coupling.   
   >>   
   >> Got a link to the part?   
   >>   
   >> There are lots of cheap OTDRs around, so there must be   
   >> fiber-compatible parts.   
   >>   
   >>   
   >> John Larkin   
   >> Highland Tech Glen Canyon Design Center   
   >> Lunatic Fringe Electronics   
   >   
   >The Lidar chip is ST VL53L4CD, a low power gadget for 1 to 1200mm   
   >ranging. Nothing elegant, but it's cheap. I only need about 1.5" worth   
   >of sensing range, just monitoring the position of an air cylinder shaft.   
   >Yes, there are cylinders with built-in position read out, but I don't   
   >get to use those...I'm looking at an add-on to existing installation(s).   
   >I'm suspecting that the Lidar to fiber connection is not the real   
   >problem here, the moving target reflector may be the bigger issue, I   
   >can't introduce a critical mechanical alignment. It's going to get   
   >shaken vigorously...in a race car.  Looking into the optical fiber as a   
   >way out of the also nasty electrical noise environment. Alternative is   
   >to level shift the Lidar chip signals to 12v and mount the chip on the   
   >air cylinder, not too keen on running an i2c bus over 3 or 4 feet of   
   >cable at low level signal.   
   >Anyway, just kicking around possiblities for now. Have a couple of the   
   >Lidar chips to play with, that may drive the solution one direction or   
   >another...or nowhere.   
   >Thanks for the reply!   
   >-bill   
      
   Cool part.   
      
   You might be able to use the clunky large-diameter plastic fiber, the   
   ones used in audio links, and get usable coupling. Toslink. The core   
   diameter is about 1 mm.   
      
   You could glue the fibers right onto the tx and rx holes in the top of   
   the chip.   
      
   You can also buy glass fibers with a moulded-in teardrop lens on both   
   ends, the GRIN that somebody mentioned. That might work on both ends.   
      
   https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=1340   
      
   Ignore the Thorlabs pricing. They are insane.   
      
      
   The other end, at the cylinder, would be interesting. Could the fiber   
   ends face one another, with no reflector? That would give tons of   
   signal with no alignment issues.   
      
      
      
      
   John Larkin   
   Highland Tech Glen Canyon Design Center   
   Lunatic Fringe Electronics   
      
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