LDM9T
Chapter 5: Operation
Rev G, Jan 22, 2017
Page 9
Operation
5.1. General
Once the laser diode is mounted in the LDM9T and a Laser Diode Current
Controller is connected, the device is ready to operate. Please refer to the
operating instructions for the laser controller for specific operating instructions.
The LDM9T may be modulated at low bandwidth through the laser controller.
This mount includes a high bandwidth bias T circuit that allows RF modulated
signals to be added to the laser controller signal. See RF Modulation below for
more details.
The TEC control circuit is always active when powered. The cold plate
temperature will stabilize to the set point temperature indicated on the TEMP
ADJ knob. There is no tuning of PID setting for this system as long as the unit is
operated within the safe operating area as described in section 5.5, page 11.
5.2. RF Modulation
The LDM9T has an RF input for modulating the laser with an external RF source
from 200 kHz to 1 GHz. This is a 50 Ω input that is AC-coupled directly to the
laser through the Bias-T network. To calculate the desired RF power to modulate
the laser, determine the amount of modulating current needed from the laser
manufacturer’s data sheets and use the following calculations:
RF Voltage = (Laser Diode Modulating Current) x 50 Ω
It is strongly recommended that you start off conservatively by a factor of 10
below the calculated modulating voltage and slowly bring the RF power up until
the desired depth of modulation is reached.
Use the laser controller to establish the DC operating point of the laser.
WARNING
The RF input is directly coupled to the laser. Any excessive transients or noise
will be coupled into the laser and may cause the laser to be overdriven. Also,
the laser can be easily overdriven if excessive RF power is applied to this input.
Use the RF modulation input with care to avoid damaging your laser or mount.
