THORLABS LD2000R, Руководство пользователя

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OEM Laser Diode Driver Chapter 5: Operating the LD2000R
Page 12 0187-D01
1. The analog modulation voltage has a negative transfer function
characteristic. That is, at 0 V, the laser is fully on, at 2.5 V the laser should
be completely off.
2. The linear operating range of the analog modulation is determined by the
transimpedance gain of the PD Amplifier, R
F
. The appropriate
transimpedance gain for your laser can be calculated as follows:
𝑅
𝐹
=
2.5 V
𝐼
𝑀𝑂𝑁
Where I
MON
is the PD current specified by the laser manufacturer for the
maximum operating output power.
Note, the LD2000R includes an internal 20 kΩ resistor. R
F
is the net
resistance of the internal 20 kΩ resistor with any external resistance
added in parallel on pins 8 and 12. To calculate the external resistance
(R
F EXT
) needed to operate at a particular monitor current (I
MON
), use the
following equation:
𝑅
𝐹 𝐸𝑋𝑇
=
50,000
(20,000𝐼
𝑀𝑂
− 2.5)
5.3.3. External Modulation Operation
The laser output power can be controlled via an external modulation voltage while
operating in the Constant Power Mode. The laser output is inversely proportional
to the modulating voltage with 0 V being the laser fully on and 2.5 V turning the
laser fully off.
1. To use the external modulation, perform the following steps:
2. Set up the LD2000R for Constant Power.
3. Attach an external modulation source (e.g. function generator, D/A
converter, etc.) to the Analog Modulation Input (pin 3).
4. Apply power to the LD2000R and adjust the modulation input amplitude
and frequency for the desired output.
5. The laser output will now be controlled by the external modulation
voltage.
The graph above describes the characteristic of the modulation voltage. If the
LD2000R is set up to match a particular laser, the solid curve would represent the
output power of the laser as a function of the modulation voltage. A couple of notes
of interest: