Optimization of 1.5 mu m band LiNbO3 quasiphase matched wavelength converters for optical communication systems

1.5 mu m-band LiNbO3 quasiphase matched (QPM) wavelength converters consist ing of a periodical domain inverted structure and a proton exchanged wavegu ide, have been studied in detail both theoretically and experimentally. Opt imum device fabrication conditions are investigated with respected to waveg uide propagation loss, coupling loss to a single-mode fiber and wavelength conversion efficiency. A normalized conversion efficiency as high as 200 %/ W (by a SHG measurement) and a fiber-to-fiber insertion loss of less than 3 .5 dB (@ 1.55 mu m) is obtained for a wavelength converter module with a de vice length of 40 mm. It is shown that a highly uniform periodical domain i nverted structure and a uniform proton exchange waveguide are key to obtain ing efficient wavelength conversion. The tolerance of the waveguide width f luctuation is found to be very critical and is less than 20 nm for a 40 mm- long device. Future optimization of LiNbO3 QPM wavelength converters and th e possible device applications in future optical communication systems are also presented.