Polarization-Maintaining Extinction Ratio Tester

A polarization extinction ratio (PER) tester measures the polarization extinction ratio and polarization angle of polarization-maintaining fibers or components, using a rotating polarizer and photodetector for precise alignment and characterization.

Overview

A polarization extinction ratio tester is an optical instrument designed to quantify the degree of linear polarization in a light beam, expressed as the ratio of maximum to minimum transmitted power through a polarizer. It also measures the polarization angle, which is critical for aligning polarization-maintaining (PM) fibers, connectors, and laser diodes. These devices are widely used in fiber optic component testing, PM fiber pigtailing, and quality assurance for optical systems.

Operating Principle

Most PER testers operate using a rotating polarizer in front of a photodiode detector. The photodiode measures the input light intensity as the polarizer rotates:

• Peak power occurs when the polarizer aligns with the input polarization axis.
• Minimum power occurs when the axes are perpendicular.
• The ratio of peak to minimum power determines the polarization extinction ratio.
• Unpolarized or circularly polarized light produces a low extinction ratio near 1, indicating minimal linear polarization contrast. Some instruments also measure insertion loss (IL) or output power simultaneously, and can handle single or multi-channel devices for high-throughput testing.

Key Features and Specifications

• Wavelength Range: Many testers cover 400 nm to 2500 nm, with specific models optimized for 400–700 nm, 600–1600 nm, or 1200–2500 nm (Thorlabs ERM2xx, Agiltron PERM) .
• Dynamic Range: High-end models like FIBERPRO ER2200 and Luna ERM-202 offer up to 50 dB dynamic range .
• Connector Compatibility: FC/PC, FC/APC, LC/PC, SC/PC, and bare fiber adaptors are commonly supported .
• Automation: Devices like Santec PEM-400 allow automated multichannel measurements, measuring a 12-fiber DUT in under 30 seconds .
• Data Interface: Many testers provide USB, GPIB, or RS232 connections for remote operation and data logging .

Applications

• PM Fiber Alignment: Ensures proper orientation of polarization axes during fiber pigtailing or connectorization.
• Component Testing: Measures PER and insertion loss of PM components, fiber array units, modulators, and laser diodes.
• Quality Assurance: Used in manufacturing of PM couplers, polarization beam splitters, and fiber gyros.
• Research and Development: Characterizes polarization properties in optical experiments and photonics labs.

Popular Models

• Thorlabs ERM2xx: Benchtop PER meters with monitor output for active alignment, covering 400–2500 nm .
• Santec PEM-400: High-speed multichannel PER tester for FAUs and ELSFPs, capable of automated measurements .
• FIBERPRO ER2200: 50 dB dynamic range, GPIB/RS232 interface, suitable for polarization axis alignment .
• Agiltron PERM: Push-button operation with GUI, measures PER and misalignment angle, supports bare fiber adaptors .
• Luna ERM-202: Rotating-polarizer PER meter with single or dual channel, 50 dB dynamic range, high-resolution angle measurement . These instruments provide fast, accurate, and repeatable measurements essential for both laboratory research and high-volume production environments.