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17874-D03
T-Cube Laser Diode Driver
3.3.3 Configuring The Unit to the Laser Diode
Before the laser diode controller can be used, it must be configured to operate with
the specific laser diode it is intended to drive. The following section explains why
certain parameters must be set for specific types of laser diode. The set up procedure
may be performed manu ally, using the top panel buttons (see Section 4.4.) o r
remotely via a PC (see Section 5.4.).
The configuration process consists of the following main steps:
- setting the laser diode polarity,
- setting the maximum laser current,
- adjusting the photodiode range and gain,
- optical power calibration.
These steps only need to be done once for a given laser diode. Once the setup has
been completed, the TLD001 stores the corresponding parameters in non-volatile
memory and they are loaded automatically at each power-up.
3.3.4 Laser Diode Polarity
Laser diodes are manufactured in a variety of packages and pin configurations, with
or without an internal photodiode. In addition, normally one terminal of the laser diode
is connected to the metal case and commoned with either the anode and cathode of
the photodiode.
The TLD001 has been designed to drive all the possible configurations but care is
needed to ensure that the l aser diode is connected to the controller correctly.
Although the TLD001 provides some protection against some common wiring errors,
some faults, such as accidentally swapping the laser diode and the photodiode or
connecting the laser diode with reverse polarity can still cause damage to the laser
diode module.
For the lowest noise and highest level of protection, the case of the laser diode
package should always be connected to the electrical system ground. Since normally
the case will also be electrically connected to either the anode or the cathode of the
laser diode, this results in two common configurations: anode grounded (AG) and
cathode grounded (CG). This can be established from the laser diode data sheet and
the device should be connected to the D-type connector on the TLD001 accordingly.
Additionally, in most cases either the anode or the cathode of the internal photodiode
(if there is one) is also connected to the case, resulting in four possible configurations,
as shown in Fig. 3.4.
