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Entry  Wed Jul 7 13:05:07 2021, Paco, DailyProgress, 1418 nm AUX ECDL, New aspheric flexures 
    Reply  Fri Jul 9 11:40:42 2021, Paco, DailyProgress, 1418 nm AUX ECDL, New aspheric flexures IMG_1773.jpeg
       Reply  Wed Jul 14 12:21:08 2021, Paco, DailyProgress, 1418 nm AUX ECDL, ECDL lases... and MZ locked mid-fringe selfhomodyne_1418.jpg
          Reply  Wed Aug 4 11:36:30 2021, Radhika, DailyProgress, 1418 nm AUX ECDL, 1419 nm ECDL with 2um AOM tests rf_setup.jpgdiffraction_levels.png
             Reply  Tue Aug 10 09:51:44 2021, Paco, DailyProgress, 1418 nm AUX ECDL, 1419 nm ECDL AOM diffraction at 95 MHz rf_setup.jpg
                Reply  Thu Aug 12 11:49:59 2021, Radhika, DailyProgress, 1418 nm AUX ECDL, 1419 nm ECDL AOM diffraction at 95 MHz zeroth_order_contour.pdffirst_order_contour.pdf
                   Reply  Tue Aug 17 11:09:29 2021, rana, DailyProgress, 1418 nm AUX ECDL, 1419 nm ECDL AOM diffraction at 95 MHz 
                   Reply  Wed Sep 1 13:12:02 2021, Radhika, DailyProgress, 1418 nm AUX ECDL, 1419 nm ECDL AOM diffraction at 95 MHz 
Message ID: 1916     Entry time: Wed Jul 14 12:21:08 2021     In reply to: 1915     Reply to this: 1917
Author: Paco 
Type: DailyProgress 
Category: 1418 nm AUX ECDL 
Subject: ECDL lases... and MZ locked mid-fringe 

[Paco]

Worked for a few hours to get the aspheric properly aligned. The procedure is quite finnicky, as the four 2-56 flexure screws have too much game and the fine thread setscrew that adds tension is too constrained. Anyways, it generally goes like this:

  1. With the grating out of the way, and the 2-56 screws slightly loose, move the aspheric flexure until a collimated beam (as round as possible) exits the centered round aperture in front of the SAF chip.
  2. Very carefully tighten the fine threaded setscrew in place to register the aspheric alignment.
  3. Check that the desired beam hasn't changed
  4. Insert grating careful not to touch the aspheric flexure (again, the mechanical registration is not great!)
  5. Manually rotate the grating while monitoring the power at the fiber output until non-ASE light appears. This is quite sensitive to alignment/angle and the better the mode is matched back into the fiber, the easier it is to find the right position.
  6. Fix the grating flexure.
  7. Slightly tweak the grating mirror knobs by hand to maximize said power (careful to avoid saturating PD)

After this, I installed a second amplified InGaAs detector, hooked up the unbalanced MZ beamsplitter output into the two PDs, adjusted the gains to equalize the output voltages and then hooked the two signals to the A and B inputs of an SR560 in "A-B" mode. The output (gain 1) was good enough to feed back in the HV PZT amplifier input modulation which allowed the MZ to lock mid-fringe. The lock is rough, as the balanced homodyne signal retains a tiny offset due to imperfect balancing... Attachment 1 shows the setup, including a typical scope trace after coarse current tuning (Ch1 and Ch2 in yellow and blue represent the photocurrents in the two MZ ports in the absence of feedback).

Indeed, scanning the nominal PZT voltage broke the lock, potentially after crossing a mode hopping region.

Tasks to be done:

  • Power characterization, including RIN, emission vs current.
  • Emission spectrum characterization; using the homemade spectrograph (grating + lens + camera) as the PZT is scanned
  • MZ feedback loop characterization, including optimizing the balancing stage
  • Self-homodyne phase noise spectrum

Next, as was suggested during yesterday's group meeting, we will transition into a self-heterodyne setup (with an AOM which I have yet to check out in the QIL).

Attachment 1: selfhomodyne_1418.jpg  4.475 MB  Uploaded Wed Jul 14 13:56:09 2021  | Hide | Hide all
selfhomodyne_1418.jpg
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