Datasheet

CHAPTER 3. STARTER KIT (PULSER, TEMPERATURE CONTROLLER, ETC...) 12
3.2.2 What is the ”external power supply” used for?
The ”external power supply” is a DC power supply provided by the user; it is connected
(via banana plugs) to the pulse driver LDD100 and is delivering the electrical power
feeding the laser. Any standard laboratory power supply can be used, as long as it is
ripple-free (≤1%), voltage regulated, with variable voltage from 0V to at least 35V, and
capable of delivering 1A DC for duty cycles up to 2%. For higher duty cycles, contact
Alpes Lasers SA, since not all lasers are capable of working at more than 2%.
3.3 Low-impedance line
3.3.1 How to connect the low-impedance line
The low-impedance line LBI100 has a locating pin to avoid false connection on the LLH
laser housing and on LDD100. The LBI100 has to be connected with ”NEG” up unless
specifically told to connect with ”POS” up. Do not twist the LBI100.
3.4 Low-frequency bias current for modulation
This section describes use of a bias-T circuit for electrically controlled modulation of
peak emission wavelength.
For modulation of a CW QCL, please refer to section 4.2 (CW modulation),p.16.
3.4.1 What are function and purpose of a bias-T circuit?
What is the function of the bias-T?
The bias-T allows to apply a constant (DC) current to the laser in addition to the pulsed
current (therefore a bias-T is useless in CW mode). The current is drawn from the
external (user supplied) power supply through the laser.
This current can be controlled electrically. Alpes Lasers SA specifies use up to of
0.1kHz, but several clients have used the bias-T successfully at frequencies of up to
several kHz.
What is the purpose of using a bias-T?
Since tuning of a QC laser is done by changing the temperature of the active zone,
the DC bias current can be used to control the emission wavelength of the laser via its
heating effect. The bias-T therefore allows for electrically controlled rapid scanning of
the emission wavelength.
Why is using a bias-T better than changing base temperature?
Tuning can also be achieved by changing the temperature of the whole laser but at
much lower speed, due to the high thermal capacity of the laser submount and laser
base. Heating of the active zone alone by applying a DC bias current is affecting
only the active zone and the surrounding parts of the laser chip, and due to the small