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Entry  Tue Jan 22 19:12:24 2013, tara, Notes, EOM, EOM driver IMG_2209.jpgEOM.pdf
    Reply  Wed Jan 23 19:29:26 2013, tara, Notes, EOM, EOM driver IMG_2213.jpgIMG_2214.JPG
       Reply  Wed Aug 28 20:19:44 2013, tara, Notes, EOM, EOM driver: modification driver1.jpgdriver2.jpgdriver_TF.jpg
Message ID: 1092     Entry time: Wed Jan 23 19:29:26 2013     In reply to: 1090     Reply to this: 1317
Author: tara 
Type: Notes 
Category: EOM 
Subject: EOM driver 

The EOM driver is working. For the same modulation depth, it can drive a broadband EOM using less power.

==measurement and result==

I used PMC setup to test this EOM driver because its frequency range is only ~21 - 24 MHz, and the sideband for locking PMC is 21.5 MHz. So what I did:

  • Checked the performance of resonant EOM as a reference: Scanned the laser and measured the error signal, with resonant EOM. The input power to the EOM is 9 dBm (5.7 V on the RF power scale with phase shift = 3.297 + 180 degree phase flip). The error signal was 3.13 Vpk-pk.
  • Replaced the resonant EOM with a BB EOM equipped with the driver. Re-aligned the beam to the PMC. (I turned down the input power to min before I connected the RF input to the driver).
  • Scanned the laser again and increased the power until I got the same error signal. With the driver on BB EOM, the input power is reduced to -9.5 dBm (on the slider: 3.9V with 0.6707 phase shift, no phase flip) for the same error signal. So the board adds ~18.5 dBm.
  • PMC cavity can be locked and stable.

   From the schematic, the board is supposed to have 30V output from 0.15 V output (x200). In dBm that will be 20log(200)~ 23dBm. So It is roughly ok.

IMG_2213.jpg

fig1: BB EOM with the driver. One of the unused output is for output mon.

IMG_2214.JPG

fig2: Error signal from scanning the laser, with BB eom and the driver, measured at mixer out.

==conclusion==

 The board is definitely working and will benefit us, definitely for locking PMC. If we use a marconi to drive a BB EOM, the max output is 13dBm. The power is halved (one to the EOM, one to the mixer). That means ~ 10dBm to the EOM (we will probably split more some where for RFAM pickup, but we can do that on the line that goes to the mixer), so assuming we have ~ 10dBm for the EOM. With the board it will be ~ 10+18.5 dBm = 28.5dBm (~6V) . It should give modulation depth of 0.09, see psl:745, This might not be enough for locking the refcav( see,psl:929. where we have beta of 0.18), but we can add another RF amplifer, or use the board for PMC servo . I'll check what are the appropriate modulation depth for locking PMC and refcav.

 

 

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