Extinction Ratio Tester for Crystals

Extinction ratio testers measure the polarization extinction ratio (PER) and polarization angle of optical components, including crystals, using rotating polarizers and photodetectors.Overview of Extinction Ratio MeasurementThe polarization extinction ratio (PER) quantifies how well light is confined to a principal linear polarization mode. It is defined as the ratio of power in the principal polarization to the orthogonal polarization, expressed in dB. High PER values indicate strong linear polarization, which is critical for crystals, polarizers, and polarization-maintaining fibers. Typical PER values range from 18–20 dB for passive components to 50–60 dB for high-quality polarizers or waveguides. PER can also indicate the degree of polarization (DOP) for depolarized or low-polarization sources, where values approach 0 dB for unpolarized light .Measurement MethodsThe most common method for measuring PER is the rotating polarizer technique. A polarizer rotates in front of a photodiode or power meter, detecting the maximum and minimum transmitted optical power. The ratio of these values determines the extinction ratio. This method is simple, fast, and widely used for both fibers and crystal-based components .Commercial Extinction Ratio TestersThorlabs ERM2xx SeriesMeasures PER and polarization angle of polarization-maintaining (PM) fibers.Wavelength coverage: 400–2500 nm depending on model (ERM210, ERM200, ERM220).Features a rotating polarizer, photodiode detection, and monitor output for active alignment.Compatible with FC/PC, FC/APC, LC/PC, and SC/PC connectors .Santec PEM-400Designed for high-volume testing of PM components, fiber arrays, and laser pluggables.Measures PER up to 30 dB and polarization angle.Can perform automated multichannel measurements without repositioning the device under test.Supports multichannel polarized sources at 1310 or 1550 nm, with higher channel counts available .Agiltron PERMBenchtop PER meter for PM fibers and components.Wavelength range: 400–2500 nm.Features push-button operation, USB connectivity, and GUI-based data recording.Measures PER and misalignment angle using a rotating polarizer and photodiode detector.Supports multiple connector types and bare fiber adaptors .Application to CrystalsExtinction ratio testers can be used to evaluate crystals with polarizing properties, such as birefringent or polarizing crystals, by measuring the transmitted light along the crystal's principal axes. The tester determines how effectively the crystal maintains linear polarization, which is essential for optical experiments, laser systems, and polarization-sensitive devices.Key ConsiderationsWavelength range: Ensure the tester covers the operational wavelength of your crystal.Connector compatibility: For fiber-coupled crystals, check adapter availability.Automation: High-volume testing benefits from multichannel or automated systems.Accuracy: High PER components require meters capable of measuring up to 50–60 dB. Extinction ratio testers provide a reliable and quantitative method to assess the polarization performance of crystals and other optical components, ensuring proper alignment and high-quality optical output.