Introduction:

The negative effects of optical feedback on laser oscillators and laser diodes have long been know. Problems include frequency instability, relaxation oscillations, amplified stimulated emission, and in some cases, optical damage. As lasers have improved, the need to protect laser oscillators and laser diodes from optical feedback has increased. A Faraday isolators' ability to allow light to pass unimpeded in one direction, while strongly attenuating light traveling in the opposite direction, eliminates the negative effects of optical feedback. Figures 1 and 2 demonstrate this fact. Figure 1 illustrates noise emission displaced 60kHz from the actual laser frequency of a mode-locked laser due to reflections from an uncoated glass surface. The noise emissions correspond to relaxation oscillations in the laser being driven by residual feedback. Figure 2 illustrates the effectiveness of EOT's Faraday isolators in eliminating this problem.

At the heart of a Faraday isolator is a Faraday rotator. Faraday rotators utilize high strength, rare earth permanent magnets in conjunction with a high damage threshold optical element to provide a uniform 45° polarization rotation to light passing through the device. The amount of polarization rotation is, θ = V∫Hzdz where:

θ = polarization rotation angle
V = Verdet constant of optical element
Hz = longitudinal component of magnetic intensity vector
z = length of optical length of optical element

• Introduction
  
• Operation of a Faraday Isolator
  
• Broadband Isolators for Ti:Sapphire and Other Tunable Lasers
  
• Operation of Broadband Isolators
  
• Dispersion in Ultrafast Ti:Sapphire Lasers; Sellmeiers Equation for TGG
  
• Key Optical Components of a Faraday Isolator
  
• Optical Component Specifications
  
• Isolation Defined
  
• Pulsed Damage Threshold; Root “T” Scaling