THORLABS S4FC Series, Руководство пользователя

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S4FC Series Fiber Coupled Laser Source Chapter 5: Operation
Page 10 TTN051387-D02
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1 = Threshold: Sets the starting value to the laser diodes threshold value.

0 = Zero Power: Sets the starting value to nearly 0.1 mW power; or threshold if threshold is less than
0.1 mW.
5.8. Turning the Laser Off
WARNING
DO NOT turn the power key switch off until laser is disabled. Failing to disable the laser first can
damage the unit permanently.
When completely powering down an enabled unit, the operator needs to disable the output first to prevent
damage to the unit. Anytime the unit is turned OFF and then turned back ON, the laser will be disabled until the
ENABLE switch is pressed.

Press the ENABLE button to turn OFF the laser.

(Optional) Turn the power key counterclockwise to the off potion to power down the unit.
5.9. Modulating the Laser Output
The MOD IN input can be used to modulate the laser output or set the laser output remotely using a 5 V power
source. The 5 V maximum input corresponds to the maximum power, which operates using a constant current
drive technique. The resulting actual output power is dependent on the set current and operating temperature. In
addition, in order to eliminate a dead zone in the Power Adjustment knob (due to the lasing threshold current), the
output of the unit is offset to the threshold current of the coupled laser diode. Adjusting the knob below threshold
will immediately set the current to almost 0 mA.
Therefore there are two modes of modulation available in the control software. In the default mode,
From
Threshold , the control knob adjusts the laser from threshold to Max power. The analog Modulation voltage will be
limited to less than 5 V, but a DC offset will not be required. This should be kept in mind when using the
modulation input since it will limit the actual input voltage range. The second mode,
From Zero , allows the analog
modulation to utilize the full 0 – 5 volt input range. This allows more flexibility with the drawback that a minimum
voltage or DC offset will be required to operate above the laser threshold.

Connect a signal generator or 0 to 5 V power source to the unit using a BNC type connector.

Set the PWR ADJ knob on the front panel to its full counter clockwise setting, or increase slightly to the
threshold current mode.

Press the ENABLE switch to turn on the laser, wait for the safety delay to time out.
For Threshold Offset - To calibrate your input apply a DC voltage to the MOD IN and slowly increase until the
display reaches the maximum rated power, if exceeded the system will limit and may disable. This will be the max
voltage allowable. Then apply the appropriate signal to the MOD IN input. Increase to 5V, if too much voltage is
applied internal current limiting will prevent damage to the laser diode and the laser diodes will be immediately
disabled. If an internal threshold is set the acceptable drive voltage range will be less than 5V.
For Standby Operation – Apply and appropriate signal between 0 and 5 V to the MOD IN for the desired
channel. Determine the DC offset by increasing the voltage slowly until a large power jump is seen on the output.
An easier method it to apply a 1 Vpp sinusoid and adjust the DC offset until the sinusoid appears and then the
bottom edge is no longer clipping. This method requires applying the laser output to a photo-detector and
monitoring with an oscilloscope. Next maximize the amplitude so that the peak is 5 V or less as desired.
Modulation Maximum Frequency – The maximum modulation frequency is 100 kHz. Normally a sine wave is
used for modulation, if a square wave modulation is used instead; consider the bandwidth as a function of the rise
time:
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