Broadband and efficient excitation of LP_0,<i>m</i> modes using fused silica binary phase plates

We demonstrate excitation of the circularly symmetric LP_0,<i>m</i> modes with microstructured monolithic binary phase plates etched in fused silica. The principles, design, and manufacturing of the phase plates are described. We show results of experimental mode excitation using the phase plates, resulting in total excitation efficiencies above 65% of the incident power and modal purities in the excess of 10 dB, which are comparable to the theoretically expected values. We also provide a numerical investigation of the bandwidth of the binary phase plates, which is shown to have an overlap integral of >70<i>%</i> to the target fiber mode in the wavelength range of 1363-1825 nm at an optimal wavelength of 1550 nm. Lastly, we describe how to shift the conversion wavelength by layering the phase plates. The fused silica phase plates can potentially enable applications for the LP_0,<i>m</i> modes in systems with high optical power.