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Chapter 10
Appendix
10.1 Bias Circut (”Bias-T”)
10.1.1 General
The Bias-T allows to apply a constant (DC) cur-
rent to the laser in addition to the pulsed current
(therefore a Bias-T is useless in CW mode). The
current is drawn fro m the external (user supplied)
power supply through the laser . This current can
be controlled electrically.
Since tuning of a QC laser is done by changing
the temp e rature of the active zone, the DC Bias c ur-
rent can be used to control the emission wavelength
of the lase r via its heating effect. The Bias-T there-
fore allows for electrically controlled rapid scanning
of the emission wavelength. The achievable shift is
of the order of 0.1%, with a Bias frequency of up to
100Hz.
10.1.2 Description
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 con-
nector in the former case (positive voltage on yellow
wire). This version has no monitor connection.
Supply
Power
User
DC
+VDC
R
Q
LDD100
L
Bias−T
R
i_b
U_mon
T1
U_in
LLH
Control "IN"
Monitor "MONI"
Low Impedance Line
GND
Fig.53: Bias circuit diagram block
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