Single Stage Faraday Isolators

Technical Overview

Introduction

The compact Faraday isolators in this chapter use a single stage rotator. The length is kept to a minimum with the use of powerful permanent magnets in an optimized geometry. A 360° rotation of the exit polarizer provides a maximum extinction over a certain range around the central wavelength. The entrance and exit polarizers are polarizing beam splitter cubes. The blocked radiation is diverted by 90° and is readily available for other applications. At 30dB, the specification of the isolator is sufficient for most standard applications. For specialized applications, selected isolators with an extinction up to 45dB are available.

An even higher extinction is provided by the two stage isolator series.

Wavelength Tuning

The Verdet constant of the TGG crystal is dependent upon wavelength and temperature. In order to compensate for different temperatures or different wavelengths, it is possible to tune the isolator in order to achieve maximum extinction. Tuning the isolator is accomplished by rotating the holder of the exit polarizer with respect to an engraved angular scale.

The graph shows the typical reduction factor of the transmission (Δλ) that is due to the tuning of the isolator to a wavelength λ that is different from the design wavelength λ₀. The bar has a length that covers the wavelength range for which 0.95 < T(Δλ) < 1. The bullet indicates the design wavelength λ₀. The overall transmission of a Faraday isolator is equal to T_t = T₀ x T(Δλ), where T₀ is a factor that represents the transmission of the polarizers. At the design wavelength the overall transmission of the Faraday isolator is λ₀ > 90 %.

Broadband Option

On Broadband (BB) models the isolation is improved over a broadband spectrum by compensating rotational dispersion of the TGG. This renders the device usable over a wavelength range of ±50nm without additional adjustment. The isolators can be mounted on rods, cylindrical mounts or by using the assembly surfaces so that the laser polarization can be oriented horizontally or vertically.

Applications

The following single stage Faraday isolators are suitable for all lasers operating in the range especially:

• Ar+ and Kr+ lasers
• Other Ion lasers
• HeNe lasers
• Other gas lasers
• Dye lasers
• Diode lasers
• Ti: Sapphire lasers
• Cr: LiCAF lasers
• Short pulse lasers
• Mode-synchronized lasers
• Alexandrite lasers