From: wwm@wwmartin.net   
      
   On 12/6/25 15:19, john larkin wrote:   
   > 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.   
      
   < That was my first thought, for a cheap experiment with easy to get parts.   
    >   
   >   
   > You could glue the fibers right onto the tx and rx holes in the top of   
   > the chip.   
      
   < Thinking to make a little alignment block that sits on top of the   
   chip, so I can play with the air gap distance to the fiber. Maybe   
   overkill? I can do the machining, so it will only cost a bit of time...   
    >   
   >   
   > 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.   
      
   < Insane? Close, I was thinking "Obscene"! :-) The individual parts look   
   like the way to go, but no way can this little fun project afford them.   
    >   
   >   
   >   
   > 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.   
   >   
   < That would be cool, but mechanically intractable, as the cylinder rod   
   may rotate a little bit as it travels in/out. I can't guarantee it will   
   stay aimed.   
    >   
      
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