# 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.

For free-space measurements, see Koheron PDX10R free-space logarithmic photodetector.

Quantity | Price |
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## Resources

## Specifications

PD10R | |
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Detector | |

Detector type | Dual InGaAs PIN photodiodes |

Active diameter | 300 µm |

Wavelength range | 900 nm to 1700 nm |

Optical input power | -67 dBm to 7 dBm (0 dBm = 1 mW) |

Peak responsivity (1550 nm) | 0.90 A/W |

Photodiode connector | FC |

Logarithmic amplifier | |

Small signal bandwidth | 1.2 MHz at 3 dB (for input current > 100 µA) |

Logarithmic slope | 300 mV/decade |

Intercept photocurrent | 100 pA |

Output impedance | 1 kΩ |

Power supplies | |

Supply voltage | 3.3 V to 13 V |

Quiescent current | 11 mA |

Max. current | 40 mA |

Other | |

Outside dimensions | 38 mm x 53 mm x 12 mm |

Operating temperature | 0 °C to 50 °C |

## More Photodetectors

## 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.