Dual logarithmic photodetector

Absorption measurements for spectroscopy setups
PD10R - Dual logarithmic photodetector
PD10R - Dual logarithmic photodetector Output voltage vs Optical Power Measurement of gas cell absorption Setup for measurement of gas cell absorption

345 €

Ref.: PD10R

Quantity Price
1+ 345 €
10+ 305 €
Koheron PD10R is a dual logarithmic photodetector for general purpose optical power measurements. In addition to two analog outputs log(A) and log(B), the PD10R gives the log-ratio log(A/B) with an adjustable offset and two gain settings (x1 and x10). The PD10R provides a fully-analog solution for direct absorption measurement in spectroscopy setups.

Product details

  • Operating wavelength: 900 - 1700 nm
  • Optical power: -67 - 7 dBm (0 dBm = 1 mW)
  • 3 dB bandwidth: 1.2 MHz (for optical power > -10 dBm / 100 µW)
  • Logarithmic slope: 30 mV / dBm (between -50 and 7 dBm)
  • Supply voltage: 3.3 - 15 V
  • Dimensions: 38 mm x 53 mm x 12 mm

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The figure below shows the voltage measured on the two outputs log(A) and log(B) vs. the optical power incident on photodiodes A and B respectively. Optical power was generated with a 1550 nm DFB laser followed by a variable optical attenuator and measured with a Thorlabs PM100D / S155C power meter.

Output voltage vs Optical Power

We observe a linear behavior between -50 dBm (10 nW) and 7 dBm (5mW).

Absorption measurement

The PD10R can perform accurate absorption measurements with small amounts of optical power. We used the setup below to observe the absorption lines of a HCN gas cell with 200 nW of total optical power. Optical source is a DFB laser whose temperature is increased linearly from 10 to 25 °C in 60 s. The absorption path and the reference path are connected respectively to the A and B inputs of the PD10R.

Absorption measurement setup

The three outputs log(A), log(B) and log(A/B) have been recorded simultaneously during the 60 s temperature sweep. Intensity variation observed on the log(A) and log(B) channels are nicely rejected on the log(A/B) output. Numerical computation of log(A/B) from log(A) and log(B) is represented in the cyan curve.

Gas cell absorption

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