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Butterfly Laser Diode Mount Chapter 5: Operation
Rev E, May 8, 2018 Page 9
Chapter 5 Operation
5.1. RF Modulation
The LM14S2 has a Bias-T adapter to provide an RF input for modulating the laser with an external RF source up
to 500 MHz. The adapter has a 25 Ω input that is AC-coupled directly to the laser through a Bias-T network. This
adapter will only work with butterfly lasers specifically designed with an integrated blocking inductor and an
additional 25 Ω of input impedance (see Figure 5 below). The adapter makes its RF connection to Pin 12 of the
laser diode (typically an anode connection), and the return connection is made at Pin 13. This is a Type 2 laser,
therefore the TYPE 2 configuration option should be installed (see Section 4.1). The DC input to this type of laser
is applied to Pin 3 of the laser diode.
Install the Bias-T adapter as follows:
1. Install the laser diode as described in Step 7 of Section 4.1. Do not clamp the right side ZIF socket.
2. Remove the two black cap head screws on the right side ZIF socket. The socket will stay in place as it is
soldered to the main PCB below.
3. Orient the Bias-T adapter over the right side of the mount with the component side facing down.
4. Carefully place the adapter into the opening in the heat sink fins on the right side, orienting the two pins of
the adapter onto Pins 12 and 13 of the laser diode.
5. Install the two stainless steel cap head screws provided in the Bias-T kit. Do not over-tighten.
6. Clamp the ZIF socket down onto the remaining laser diode pins.
7. If the Bias-T adapter is removed, reinstall the black cap head screws removed in Step 2. Do not install the
stainless steel screws as they will interfere with the configuration card.
Figure 6 Installing the Bias-T Adapter
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 calculation:
LM14S2
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Laser On