Femtowatt Photoreceiver FWPR


  • Ultra-low-noise – NEP 0.7 fW/√Hz
  • Transimpedance amplifier with high gain up to 1012 V/A included
  • Wavelength range from 320 nm to 1700 nm
Photodiode1.1 x 1.1 mm2 Si0.5 mm Ø InGaAs-PIN
Spectral Range320 – 1100 nm900 – 1700 nm
Bandwidth (−3 dB)DC – 20 HzDC – 20 Hz
Rise/Fall Time (10 % - 90 %) 18 ms18 ms
Transimpedance Gain1 x 1012 V/A1 x 1011 V/A
Max. Conversion Gain 0.6 x 1012 V/W (@ 960 nm)0.95 x 1011 V/W (@ 1550 nm)
NEP (@ 1 Hz) 0.7 fW/√Hz (@ 960 nm)7.5 fW/√Hz (@ 1550 nm)

Output voltage ±10 V max (@ 100 kΩ load). Offset adjustable by potentiometer. Output short-circuit protected. Threaded M4 and 8-32 mounting holes for use with standard mounting posts. Power supply ±15 V via 3-pin Lemo® socket. A mating connector is provided with the device. Optional power supply PS-15 available. For further information please view the datasheet or contact FEMTO.

Ultra high sensitivity and very low noise

The series FWPR-20 photoreceivers combine low noise Si or InGaAs PIN photodiodes with a specially designed transimpedance amplifier with extremely high gain of up to 1012 V/A and very low noise. This unique combination results in a photoreceiver with Femtowatt sensitivity due to its exceptional low NEP of 0.7 fW/√Hz. Direct detection of optical powers down to about 50 fW is possible. In conjunction with an optionally available FEMTO lock-in amplifier, even power levels in the sub-femtowatt range can be detected.

Replace expensive APD, PMT or LN2 cooled IT detectors

Due to their very high sensitivity the FEMTO FWPR-20 series photoreceivers can replace APDs, PMTs and cooled Ge photodiodes in many applications. No expensive high voltage power supply or cooling is required.

The FWPR-20-SI offers high quantum efficiency in the visible and near infrared similar to that of APD based single photon counting modules. In applications where timing is uncritical, e.g. when the signal of a photon counter is integrated for a few 10 ms or more, the FWPR-20-SI photoreceiver achieves a comparable signal-to-noise ratio at a fraction of the cost.

For NIR spectroscopy the InGaAs model FWPR-20-IN achieves similar results as a much more expensive and complex system based on a liquid nitrogen cooled Germanium detector with external amplifier. As a result of the already integrated very low noise, high gain amplifier, signals in the Volt range can be achieved directly at the output of the FWPR-20 Femtowatt photoreceiver.

Compatible with optical bench (free space) and fiber optics

The free space input (FST) is designed as a 1.035″-40 threaded flange with a screw-on coupler ring. It opens up a broad compatibility with optical accessories from various manufacturers, such as lenses, tubes, cage systems, optical adapters etc.

The free-space input can be converted into fiber connections (FC, FSMA) easily by simply screwing on the fiber adapter of the PRA series.

The relatively large-area detector facilitates optical focusing in free-space applications and ensures a high and stable degree of coupling when using the optionally available fiber optic adapter.


  • Fluorescence measurements
  • Spectroscopy
  • Electrophoresis
  • Chromatography
  • Replacement for photomultiplier tubes (PMTs), avalanche photodiodes (APDs) and liquid nitrogen cooled germanium photodiodes

All FWPR photo receivers are equipped with UNC 8-32 and M4 threaded holes and can therefore be conveniently and stably integrated into optical systems on standard rod holders. The optionally available adapter plate PRA-PAP opens up further mounting options.

Related products / accessories

Power Supply


Post Adapter Plate