Lastek Principals

Silicon and InGaAs for visible/nearIR

Thorlabs Free-Space Balanced Amplified Photodetectors act as balanced receivers by subtracting the two optical input signals from each other, resulting in the cancellation of common mode noise. This allows small changes in the signal path to be extracted from the interfering noise floor.

  • Wavelengths Covering the 190 - 2600 nm Range
  • DC to 1 MHz or DC to 100 MHz Bandwidths
  • Detectors with Diameters Up to 5 mm
  • Common Mode Rejection Ratio ≥30 dB

The PDB230x photodetectors have smaller active areas but wider bandwidth than the PDB220A2(/M), PDB210A(/M), PDB120C(/M), and PDB250x photodetectors (see Tables G1.1, G2.1, and G3.1).

Each detector uses two well-matched Si or InGaAs detectors and an ultra-low-noise transimpedance amplifier for improved noise reduction. An output voltage (RF-OUTPUT) is generated that is proportional to the difference between the photocurrents in the two photodiodes (i.e., the two optical input signals). The PDB250x series of detectors feature a switchable gain setting with eight steps and a range of 42 dB. Additionally, the photodetectors have two fast monitor outputs (MONITOR + and MONITOR -) to measure optical input power levels as well as RF modulated signals on each detector.

The detectors are spaced 2" apart, making beam alignment an easy task on an optical table. To further simplify the use of these detectors, the housing has external SM1 (1.035"-40) and internal SM05 (0.535"-40) threads around each detector to attach components such as lens tubes, cage systems, mounted optics, and fiber collimator adapters. For compatibility with other externally SM1-threaded items, two SM1T1 adapters are included with each detector.

Figure 1.1  Back of the PDB2xxx Detector Lists Important Specifications

Features

  • Common Mode Rejection Ratio: ≥30 dB
  • High Bandwidth: DC to 1 MHz or DC to 100 MHz
  • Fixed and Switchable Gain Options
    • Fixed Gain Item #'s: PDB220A2, PDB210x, PDB230x
    • Switchable Gain Item #: PDB250x 
  • Ultra Low Noise (See the Specs tab for Model-Specific NEPs)
  • Designed for Free Space Applications (Fiber Input Also Feasible)
  • Direct Detector Monitor Outputs
  • Includes Switchable Power Supply
  • External SM1 (1.035"-40) Threads and Internal SM05 (0.535"-40) Threads

Typical Applications

  • Spectroscopy
  • Heterodyne Detection
  • Optical Coherence Tomography
  • Optical Delay Measurements
  • THz Detection
Thorlabs Thorlabs Systems

Detection

Principals: Detection