Zn-indiffused diced ridge waveguides in MgO:PPLN generating 1 watt 780 nm SHG at 70% efficiency

Abstract

We present a metallic zinc indiffused diced ridge waveguide in magnesium doped periodically poled lithium niobate (MgO:PPLN) capable of generating over 1 W of 780 nm with 70% efficiency. Our 40 mm long waveguide has near circular fundamental mode output with diameter 10.4 µm and insertion loss of -1.17 dB. Using a commercial 2 W EDFA-based system, the SHG output power did not exhibit roll-off at maximum available pump power.

CW demonstration of SHG spectral narrowing in a PPLN waveguide generating 2.5 W at 780 nm

“…The ND filter loss was measured with the silicon power sensor and verified with the thermal power sensor measurements; the ND filter was measured to have a -83.3±2.5% loss at 780 nm. The pump loss through our output coupling optics was measured as -17.6±1.2% [15]. These losses are accounted for in the data presented in the following sections.…”

“…Our approach to manufacturing PPLN waveguides is reported in our earlier works [14,15] and is based on three successive stages: zinc indiffusion to create a planar guiding layer, ultraprecision machining to form single-mode ridge waveguides, and preparation of the optical facets by dicing. The devices described in this paper were prepared in 1 mm-thick 5% magnesium-doped periodically-poled lithium niobate (MgO:PPLN) wafers (Covesion Ltd) each containing multiple 1.2 mm-wide 18.5 µm period gratings designed to access Type-0 1560-780 nm SHG via the d33 nonlinear coefficient.…”

“…Metallic zinc was sputtered with a thickness of 100 nm on to the +z surface of each MgO:PPLN wafer (Oxford Instruments Plasma Technology, Plasma Lab System 400) and indiffused at 950 ºC in an oxygen atmosphere to promote ZnO formation. To overcome any machining inaccuracy and facilitate high pump and SHG modal overlap at our chosen wavelengths, five ridge widths were cut into each PPLN grating ranging from 11-13 µm in 0.5 µm steps and parallel to the [100] X direction of the crystal [14,15]. Individual chips measuring 4.0 cm-long by 5 mm-wide were singulated from the wafers (Fig.…”

“…Finally, the input and output facets of each chip are anti-reflection (AR) coated for both the 1560 nm pump and 780 nm SHG wavelengths. Further details of the fabrication process, including optimisation of in-diffusion and dicing parameters for these wavelengths of operation are included in references [14][15][16]. Fig.…”

“…a) image of 4.0 cm PPLN ridge waveguide with AR coating held in tweezers. (b) SEM of two waveguide facets[15]. (c) micrograph of waveguide facet[14].…”