Erbium-doped fiber devices have been extraordinarily successful due to their broad optical gain around 1.5–1.6 μm. Er-doped fiber amplifiers enable efficient, stable amplification of high-speed, wavelength-division-multiplexed signals, thus continue to dominate as part of the backbone of longhaul telecommunications networks. At the same time, Er-doped fiber lasers see many applications in telecommunications as well as in biomedical and sensing environments. Over the last 20 years significant efforts have been made to bring these advantages to the chip level. Device integration decreases the overall size and cost and potentially allows for the combination of many functions on a single tiny chip. Besides technological issues connected to the shorter device lengths and correspondingly higher Er concentrations required for high gain, the choice of appropriate host material as well as many design issues come into play in such devices. In this contribution the important developments in the field of Er-doped integrated waveguide amplifiers and lasers are reviewed and current and future potential applications are explored. The vision of integrating such Er-doped gain devices with other, passive materials platforms, such as silicon photonics, is discussed.

Erbium-doped integrated waveguide amplifiers and lasers

Three different broadband sensitization concepts for optically active erbium ions are reviewed: 1) silicon nanocrystals, with absorption over the full visible spectrum, efficiently couple their excitonic energy to Er3+, 2) silver-related defect states in sodalime silicate glass have absorption in the blue and transfer energy to Er3+, and 3) organic cage complexes coordinated with well-chosen chromophores serve as broadband sensitizers in the visible. Energy transfer rates, efficiencies, and limiting factors are addressed for each of these sensitizers. Implications of the use of strong sensitizers for planar waveguide design are illustrated by using a model for the sensitizing effect of ytterbium.

Broadband sensitizers for erbium-doped planar optical amplifiers: review

In this paper, recent literature on the discussion on high-speed backplanes with optical, electrical, and mixed solutions, as well as on polymer-waveguide systems suitable for implementation on printed circuit boards (PCBs), is reviewed from the point of view of their optical losses. The reevaluation of the optical power budget for realistic high-speed optical polymer-waveguide links on backplanes showed that signal amplification is necessary to boost the signal, which resulted in an additional literature review on advances in optical amplifiers based on silicon bench technology available. Finally, a concept study of an active optical waveguide amplifier device, based on planar optical waveguide amplifiers and semiconductor optical amplifiers, was performed. The amplification device can be flip-chip mounted on the backplane to compensate for optical losses due to signal routing, which increases the overall degree of freedom in waveguide routing on high-density interconnects for backplanes. The hybrid concept design guarantees compatibility with the processes of the PCB industry.

Limitations to and solutions for optical loss in optical backplanes

Apparatus using mechanically-actuated evanascent wave coupling. At least a portion of an optical waveguide is integrated onto a substrate, and an optically active element is physically moved relatively to each other, with the result that propagation parameters for the waveguide are substantially altered. The optically active element may be a resonator or another waveguide. Altered propagation parameters can be used to cause an optical wave to be transformed in response to an electromagnetic signal. Physical parts of the apparatus can vary widely in both size and tolerance. The optically active element is mechanically actuated relative to a position of the optical waveguide.

Mechanically actuated evanescent-wave coupled optical devices

Energy transfer in erbium doped optical waveguides based on silicon This thesis describes the energy transfer processes
occurring in materials that can be used for the fabrication of silicon compatible optical integrated circuits, operating at 1.54 mm.The thesis consists of three parts: Part I discusses energy transfer in optical waveguide amplifiers on silicon. The waveguide amplifiers use an intra-4f transition of the rare earth ion erbium occurring at 1.54 mm. To achieve significant amplification, high
 Er concentrations (> 10 20 cm -3 ) are required. At these concentrations Er ions can interact, resulting in co-operative
 upconversion, in which one excited Er ion is excited into a higher energy state, while a neighboring Er ion returns to the ground
 state. In Part I this and other gain limiting effects are investigated. In particular, it is shown that the atomic-scale Er distribution
 is of crucial importance for the performance of Er doped waveguide amplifiers. Part II discusses the energy transfer processes
 occurring in Er doped silicon. It is shown that Er in silicon can be excited by electron-hole pair recombination in an
 impurity-Auger effect. This effect may be used to fabricate an electrically pumped Er doped waveguide amplifier. The reverse
 process can also occur: an excited Er ion can de-excite and generate an electron-hole pair in the silicon, due to a non-radiative
 backtransfer process. This process has an efficiency of 70% at room temperature. This observation enables the fabrication of an
 Er doped photo-detector in a Si waveguide operating at 1.54 mm. The performance of such a detector is discussed. Part III
 discusses the interaction between Er and silicon nanocrystals embedded in SiO2. Si nanocrystals efficiently absorb visible light,
 resulting in the generation of quantum confined electron-hole pairs. The electron-hole pairs efficiently transfer energy to Er.
 Due to the energy transfer, the effective Er absorption cross section is five orders of magnitude larger than for direct optical
 excitation. Silicon nanocrystals may thus be used to increase the pumping efficiency of an Er doped waveguide amplifier. It is
 shown that a single nanocrystal can excite ~1 Er ion at a time and that an optical gain of 0.6 dB/cm may be achieved in a typical
 nanocrystal sensitized waveguide amplifier. Due to the broad absorption band of Si nanocrystals, a broad band light source can
 be used as pump source in such a nanocrystal sensitized Er doped waveguide amplifier.

Energy transfer in erbium doped optical waveguides based on silicon

A novel scheme is presented that can be used to efficiently pump optical waveguide amplifiers. It is based on the coupling between two adjacent waveguides, where pump light is gradually coupled from a nonabsorbing pump waveguide into the amplifier waveguide. The coupling between the waveguides in such a configuration is calculated using an improved coupled mode theory (CMT). The proposed distributed coupling scheme can enhance the optical gain in systems that exhibit a reduced pumping efficiency at high pump power. A numerical example is given for a sensitized neodymium-doped polymer waveguide amplifier, in which the optical gain increases from 0.005 dB to 1.6 dB by changing from conventional butt-coupling to distributed coupling.

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A. Tip

Papers

Pumping planar waveguide amplifiers using a coupled waveguide system