Dual logarithmic photodetector
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.
| Quantity | Price |
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Specifications
| PD10R | |
|---|---|
| Small signal bandwidth | 1.2 MHz at 3 dB (for input current > 100 µA) |
| Logarithmic slope | 300 mV / decade |
| Supply voltage | 3.3 - 15 V |
| Dimensions | 38 mm x 53 mm x 12 mm |
| InGaAs photodiodes | |
| Wavelength range | 900 - 1700 nm |
| Optical input power | -67 to 7 dBm (0 dBm = 1 mW) |
| Photodiode connector | FC |
| Photodiode active diameter | 300 µm |
| Photodiode peak responsivity | 0.90 A / W |
Characterization
Output voltage vs Optical power
Optical source is a Koheron LD101 1550 nm DFB laser followed by a variable optical attenuator and measured with a Thorlabs PM100D / S155C power meter.
We observe a linear behavior between -50 dBm (10 nW) and 7 dBm (5 mW).
Frequency response
Frequency response of the logarithmic amplifier for several input optical powers:
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.
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.
