Exciting Erbium-Doped Planar Optical Amplifier Materials
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ABSTRACT Erbium-doped planar optical amplifiers can find numerous applications in photonic integrated circuits operating at 1.5 gm. The challenge is to fabricate these devices with high gain, operating at low pump power, and having small overall size. In this paper a review is given of our recent work in the area of Er-doped waveguide materials and amplifiers based on three materials classes: oxidefilms (A120 3 , Y20 3, SiO 2), polymers, and silicon.
1. INTRODUCTION Erbium-doped materials are of great interest in optical communications technology, as they can serve as the gain medium in optical amplifiers operating at the standard telecommunications wavelength of 1.5 gam."12 Er 3, ions, when incorporated in a solid host, show well-defined energy levels of the 4f-shell electronic configurations (see Fig. l(a)).3 The transition from the first excited state to the ground state (4113/2 _) 4115/2) occurs at 1.53 p.m and is being employed to provide the gain in optical fiber amplifiers in long-distance telecommunication links worldwide. Medium- and long-distance optical communication is by now well established. The next development will be the introduction of optical links on a local scale, denoted as fiber-to-thehome technology. For this to become a reality, it is essential that a technology for the processing of optical signals on a local scale is established. Planar photonic integrated circuits are being
developed to perform functions such as guiding, splitting, switching, wavelength multiplexing and amplification of light. Figure 1(b) shows an example of the layout of such an optical chip, in which a variety of straight channel waveguides, waveguide bends and loops, splitters, and wavelength division multiplexers are integrated on one single chip with an area of 1 cm 2. At present, many of the materials and device concepts for this planar technology are still in the development stage. This paper will focus on one important component in planar integrated photonic circuits, i.e. the optical amplifier. Such a device can serve e.g. to compensate for coupling losses, waveguide losses, or the power division in optical splitters. As most planar waveguide devices are based on oxide materials or polymers, it appears of great interest to study the doping of such materials with erbium and to investigate the optical gain characteristics and prospectives. 4 This paper will also discuss the use of silicon as a planar waveguide material, in which both the guiding and semiconducting properties are combined. A schematic layout of an erbium-doped planar optical amplifier is shown in Fig. 2(a). Pump and signal beams are coupled into the device through separate input waveguides, and then combined in a wavelength division multiplexer (WDM). Next, an erbium-doped waveguide section is a
This paper is a slightly shortened version of an article published in Proc. SPIE, Vol. 3942 (2000).
Mat. Res. Soc. Symp. Proc. Vol. 597 © 2000 Materials Research Society
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