We may be looking at designing a diode laser current driver in the future. Comments and secondments welcome.

General notes

• Low-noise current controller for (low-power) laser diodes.
• Form factor TBD. May end up being a Stabilizer mezzanine or a separate board that interfaces with Stabilizer or a separate EEM
• Either two versions for 200-250mA and 1.5-2A range or variants or one design that fits both
• Different from the coil current driver in that it has smaller range, drives diode-like loads, doesn't need that much stability, but needs modulation features.
• Linkage to Thermostat: ethernet, Stabilizer: analog, and Zapper: analog
• Specifications and performance goals similar to the open designs:
  • Libbrecht-Hall
  • Libbrecht-Hall-Durfree
  • Libbrecht-Hall-Seck
  • JQI to be consolidated, based on Libbrecht-Hall-Durfree
• Compare to proprietary things:
  • Vescent
  • ILX Lightwave
  • Toptica
  • Koheron: uses LT3045, LT3261, OPA567, LT6655
  • MOGLabs
  • SISYPH SMC11
  • AOSense controller module

Variant A

• 250 mA
• 2V compliance
• single quadrant
• assumptions/requirements w.r.t cathode grounded, anode grounded TBD
• 0.5 µA resolution, digitally controlled (~100 kHz resolution, 200MHz/mA tuning), may be relaxed significantly to ~16 bit, depending on laser characterization
• 10 kHz small signal bandwidth
• RMS noise 10Hz-10MHz: 0.3 µA
• RMS noise 10Hz-10kHz: 0.05 µA
• Stability (<10Hz) TBD
• Linearity/absolute accuracy: 2% TBC
• tempco 5 µA/K (1 MHz/K, 20 ppm/K) TBC
• high demands on laser diode safety guarantees: no turn on/off transients, no chance of ESD/ground potential difference getting through to the diode, benign behavior and recovery from short circuits and open connections
• could be some coarse+fine additive or multiplicative hybrid solution to achieve resolution TBD
• has a modulation/error signal input that is both sampled by an ADC (at 100 kHz) and a high frequency bypass (10 kHz to 100 MHz) that goes onto a bias tee (together with the low frequency current output from the controller) on the output to the laser. Or alternative approaches TBD.

Variant B (otherwise same as A)

• 1.5A
• 3 V compliance
• bandwidth and resolution much less critical
• noise requirement at a similar relative level as A