Alpes Lasers Cascade Laser Starter Kit Datasheet download pdf (Page 14)

CHAPTER 3. STARTER KIT (PULSER, TEMPERATURE CONTROLLER, ETC...) 13

thermal capacity of this tiny volume, the laser emission responds much faster to DC

bias current variations.

3.4.2 What are the connections of the bias-T circuit?

The bias-T circuit is either separately attached to the low-impedance line connecting

the pulser and the laser housing, or directly included in the pulser. Connections are

different in the two cases:

External circuit connected to low-impedance line

In this case, the bias-T box is soldered to the top contact of the low-impedance

line with the red wire. The black wire (with banana plug) must be connected to the

negative pole of the external user supply. The connector labelled IN receives the

control voltage (0.6...2.6V, center positive), the connector labelled MONI allows

monitoring of the bias current.

Circuit included in pulser unit

The circuit included in the LDD100 pulser unit is controlled by the twisted black

and yellow wires of the control cable (with the DSUB-9 plug). They correspond to

the shield and center of the IN connector in the former case (positive voltage on

yellow wire). This version has no monitor connection.

3.4.3 Dangers and disadvantages of using a bias-T circuit

• Since a bias-T only allows to heat the laser, the emission wavelength can only be

increased (or emission wavenumber decreased), and output power will decrease

with increased bias current, due to the additional heating. This means that the

laser should be operated initially at lowest possible temperature, and it reduces

the number of lasers available for reaching a given emission wavelength.

• Heating of the active zone will increase thermal stress of the laser, therefore the

expected lifetime will decrease more rapidly compared to increasing the tempera-

ture of the laser submount and base in total. If operation at only a ﬁxed wavelength

is needed, this should be adjusted with the overall temperature control.

• Too high a DC bias current can immediately destroy the laser due to catastrophic

thermal roll-over. Therefore set-up of the bias current has to be done only by

instructed personnel, and after checking with Alpes Lasers SA for allowed param-

eter ranges; otherwise warranty will be lost.

3.4.4 What has to be kept in mind before use?

• All use of a bias-T on a speciﬁc QC laser has to be accepted by Alpes Lasers SA

before; otherwise all warranty will be lost.

• The bias-T should never be used at the highest speciﬁed current or output power,

otherwise the risk of thermal roll-over failure is imminent.

• If optical output power can be monitored, this should be used during set-up of the

bias-T to make sure that thermal roll-over is not reached: Temporary increasing of

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Alpes Lasers Cascade Laser Starter Kit Datasheet Page 14