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 aluminum oxide integrated optical amplifiers were fabricated on silicon substrates, and their characteristics were investigated for Er concentrations ranging from 0.27 to 4.2ϫ 10 20 cm −3 . Background losses below 0.3 dB/ cm at 1320 nm were measured. For optimum Er concentrations in the range of 1 to 2 ϫ 10 20 cm −3 , an internal net gain was obtained over a wavelength range of 80 nm ͑1500-1580 nm͒, and a peak gain of 2.0 dB/ cm was measured at 1533 nm. The broadband and high peak gain are attributed to an optimized fabrication process, improved waveguide design, and pumping at 977 nm as opposed to 1480 nm. In a 5.4-cm-long amplifier, a total internal net gain of up to 9.3 dB was measured. By use of a rate-equation model, an internal net gain of 33 dB at the 1533 nm gain peak and more than 20 dB for all wavelengths within the telecom C-band ͑1525-1565 nm͒ are predicted for a launched signal power of 1 W when launching 100 mW of pump power into a 24-cm-long amplifier. The high optical gain demonstrates that Al 2 O 3 :Er 3+ is a competitive technology for active integrated optics.

A reliable and reproducible deposition process for the fabrication of Al 2 O 3 waveguides with losses as low as 0.1 dB/cm has been developed. The thin films are grown at 5 nm min deposition rate and exhibit excellent thickness uniformity within 1% over 50 50 mm 2 area and no detectable OH incorporation. For applications of the Al 2 O 3 films in compact, integrated optical devices, a high-quality channel waveguide fabrication process is utilized. Planar and channel propagation losses as low as 0.1 and 0.2 dB/cm, respectively, are demonstrated. For the development of active integrated optical functions, the implementation of rareearth-ion doping is investigated by cosputtering of erbium during the Al 2 O 3 layer growth. Dopant levels between 0.2-5 10 20 cm 3 are studied. At Er 3+ concentrations of interest for optical amplification, a lifetime of the 4 I 13 2 level as long as 7 ms is measured. Gain measurements over 6.4-cm propagation length in a 700-nm-thick Al 2 O 3 :Er 3+ channel waveguide result in net optical gain over a 41-nm-wide wavelength range between 1526-1567 nm with a maximum of 5.4 dB at 1533 nm.

We demonstrate amorphous and polycrystalline anatase TiO(2) thin films and submicrometer-wide waveguides with promising optical properties for microphotonic devices. We deposit both amorphous and polycrystalline anatase TiO(2) using reactive sputtering and define waveguides using electron-beam lithography and reactive ion etching. For the amorphous TiO(2), we obtain propagation losses of 0.12 ± 0.02 dB/mm at 633 nm and 0.04 ± 0.01 dB/mm at 1550 nm in thin films and 2.6 ± 0.5 dB/mm at 633 nm and 0.4 ± 0.2 dB/mm at 1550 nm in waveguides. Using single-mode amorphous TiO(2) waveguides, we characterize microphotonic features including microbends and optical couplers. We show transmission of 780-nm light through microbends having radii down to 2 μm and variable signal splitting in microphotonic couplers with coupling lengths of 10 μm.

We describe the fabrication and operation of an optical power monitor, monolithically integrated with a silicon-on-insulator rib waveguide. The device consists of a p+-v-n+ structure with a detection volume coincident with the single-mode supporting waveguide. Detection of optical signals at wavelengths around 1550nm is significantly enhanced by the introduction of midband-gap generation centers, which provide partial absorption of the infrared light. The most efficient device extracted 19% of optical power from the waveguide and showed a responsivity of 3mA∕W. These devices are fabricated using current standard processing technology and are fully compatible with silicon waveguide technology and integrated operational amplifier circuits.