Off-axis pumping of air clad photonic crystal fiber lasers and amplifiers

We investigate a new, free space, off-axis pumping method for pumping PCF lasers and amplifiers. Experiments show that the lasing performance is improved compared to standard on-axis pumping, while maintaining all other advantages. Conventional methods for free space pumping of active double clad fibers involve mainly on-axis coupling of the pump beam through a dichroic mirror. In recent years there were many efforts to separate the laser and pump beam directions with various off-axis (sidewise) pumping configurations. With off-axis pumping the pump and laser beams are separated and do not share the same optical axis when coupled into the fiber (outside of the fiber). Most of the off-axis pumping methods are realized in all-fiber configurations by various methods [1, 2]. However, most of these methods are not suitable for air clad photonic crystal fibers (PCFs), often suffer from low damage threshold due to adhesives, mechanical instability and in many cases require special processing of the active fibers [1].