Fabrication of planar beamsplitter integrated with Er-doped waveguide amplifier for optical fiber communication

Abstract

We developed planar beamsplitter integrated with an Er-doped waveguide amplifier to compensate for the loss of the beamsplitter. In thin-film waveguide, a vertical dimension is determined by an Er-doped layer thickness, whereas a lateral dimension is defined by a patterning process that usually involves photolithography and etching techniques. Etching of Er-doped glass is known to be a challenging process. Chemical etching usually results in rough surfaces. Dry etching of Er-doped glasses containing alkaline metals shows a low etch-rate problem. Some researchers have used an ion milling technique to form a ridge structure with variable success. However, high temperature reflow is still required to minimize side wall roughness. We have developed a new fabrication process for Er-doped 2D waveguides. The process does not require etching of an Er-doped film, and therefore is simple, economical, and highly reproducible in defining a lateral dimension of a waveguide. Under-cladding silica layer was grown by Microwave Plasma Assisted Chemical Vapor Deposition on silicon substrate. Patterning of waveguide was defined on the under cladding layer. After that, an Er-doped soda-lime silicate glass film was deposited with rf magnetron sputtering, and jointed with core layer region of waveguide beam splitter which has compatible mode profile with optical fiber.A 1.7-cm-long Er- doped waveguide shows 7.2 dB gain at 980 nm pump power of 40 mW. This demonstrates that the amplifier can provide an optical gain sufficiently to compensate for the splitter losses.