THORLABS INT-POL-1300, Operation Manual

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3 Detailed Description
INT-POL-1300 / page 8
3.3 Electrical Outputs
The INT-POL-1300 contains two separate balanced detectors. Each balanced detec-
tor has three SMA output connectors carrying monitoring signals (
/
MONITOR- ) and the balanced output signal ( RF OUTPUT ).
RF-OUTPUT delivers an output voltage proportional to the difference between the
photocurrents in the two photodiodes, i.e. the two optical input signals P
1OPT
and
P
2OPT
, detectors responsivity

(

) and transimpedance gain G given by:
 
G P P V
OPT OPT OUTPUT RF
   

) (
2 1

The responsivity

(

) for a given wavelength can be read from Figure 3 to estimate
the RF-OUTPUT voltage. The amplifier’s transimpedance gain G is 50x10
3
V/A.
Please note, that RF-OUTPUT voltage is reduced by a factor of 0.5 if connected to a
50

load.
The maximum output voltage swing of the RF-OUTPUT is

3.6 V for high impedance
loads (

1.8 V into 50

). Depending on wavelength responsivity

(

) of the detectors
the amplifier will reach saturation if the difference between the optical input powers at
the detector pair is greater than 80µW. The output signal should not exceed the max-
imum output voltage to avoid saturation. Please note, that the individual power at
each detector can be significantly higher, but not higher than damage threshold listed
in Specifications. The power differene can be adjusted by changing the input polari-
zation an each optical input.
The amplifier offset voltage is factory set to zero at 23°C ambient temperature. A
small drift during a short warm-up period (~5min) may occur. For exact DC light level
measurements a constant temperature environment is recommended.
The 3 dB bandwidth of the RF OUTPUT signal is DC-15 MHz. Figure 4 shows a
typical frequency response curve of INT-POL-1300 RF OUTPUT signal. For this
measurement a test signal was applied to one input port only.