from Hacker News

Optical Frequency Combs

by zafka on 1/30/25, 7:44 PM with 40 comments

• by mikewarot on 1/31/25, 5:10 AM

  This technology enables frequency counters for laser light.[1] Input a red laser, and you can directly measure its frequency in Hertz with 14 digits of precision.

  [1] https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=11...

• by high_priest on 1/30/25, 8:21 PM

  Nice to see some more posts about light communications on HN. I have had the pleasure talking with people who developed this tech & see it in action.

  Apparently, it is a big step towards purely optical network switching.

• by tzs on 1/31/25, 12:35 PM

  Does calibration of an optical frequency comb require that the speed of light be known, either directly or indirectly? By indirectly I mean the case where something you need to use to calibrate your comb depends, directly or indirectly, on knowing the speed of light.

  I'm curious because of something the professor did early on in the introduction to optics class I took in college. He picked up a metal ruler and said we were going to measure the speed of light. Everyone laughed (which was fine because he intended it as a joke).

  He then set the ruler on a table, directed a laser to reflect at a shallow angle off the ruler onto the blackboard.

  The ruler's lines were raised which made it act like a diffraction grating and there was a visible interference pattern on the blackboard.

  He then traced the pattern on the blackboard with chalk, turned off the laser, and used the ruler to (1) measure the distance from where it had been to the blackboard, and (2) the spacing of the lines in the diffraction pattern.

  From this and the known frequency of the laser and the known spacing of the lines on the ruler the speed of light is an easy calculation.

  This was meant as a joke because usually the frequency of light is calculated using methods that depend on knowing the speed of light, so all that was really happening was the he used a rule to very that the frequency calculation of the laser had been done correctly.

  But if you could accurately get the frequency without that depending on knowing the speed of light then you could actually measure the speed of light with a ruler.

• by packetlost on 1/30/25, 9:24 PM

  I worked closely with some of these devices at a previous employer. Might've even fried one at some point. I'm pretty excited about what other things they can be used for!

• by lutherqueen on 1/30/25, 8:26 PM

  > seamlessly connected to optical waves that oscillate at 10,000 times higher frequencies

  Somehow four orders of magnitude sound too less for the transition from radio to light, but it makes sense. A i9 processor works at ~6 GHz, and light is at the THz range

• by ziofill on 1/31/25, 4:30 AM

  There is also another type of comb that is extremely useful: the GKP qubit (introduced in https://arxiv.org/abs/quant-ph/0008040). Its wavefunction is a comb.

• by simojo on 1/31/25, 5:04 PM

  I had the privilege to attend a talk by Jun Ye, one of Hall's previous advisees, a few months back about frequency combs. I really felt honored meeting the person who is so tapped into the work being done at JILA. Lots of amazing, mind bending work.

• by londons_explore on 1/31/25, 12:26 PM

  What is the theoretical efficiency of these devices?

  Could it be used for example to combine multiple different frequencies of light into one higher frequency to excite a solar cell at exactly the bandgap energy so no energy is wasted?

• by dr_dshiv on 1/31/25, 9:41 AM

  Amazing! Check out the image of the methane leaks in a gas field.

• by dtgriscom on 1/30/25, 10:58 PM

  Perhaps I'm being pedantic, but in the video, when they show multi-spectral light coming in from the left, they show low-frequency light moving faster than high-frequency light. ("Survey says: EEEEEHHHHHNNNNNNK!")

  I was also hopeful the video would have actual info on how they work, but no such luck. Just a lot of "Are they cool, or what?".