# Integrated Photonics on Glass: A Review of the Ion-Exchange Technology Achivements
## 3 Telecom Devices
### Waveguide Amplifiers and Lasers  
Active devices have been linked to the development of ion-exchanged devices since the beginning of this technology. Indeed, [PERSON] et al. demonstrated in 1973 a laser made with an optical amplifier based on a buried multimode ion-exchanged waveguide realized in a neodymium-doped borosilicate glass [65]. However, research on active devices really became a major field of research with a strong competition at the beginning of the 1990s when a lot of studies were carried-out. Work was first concentrated on Nd-doped amplifiers and lasers emitting at 1.06 \(\upmu\)m since the four energy levels pumping scheme of this transition made it easier to achieve a net gain with the 800 nm pumping diodes available at the moment [66; 67; 68; 69; 70]. With the rise of Wavelength Division Multiplexing systems, optical amplifiers and sources operating in the C+L band (from 1525 nm to 1610 nm) became key devices and research on rare-earth doped integrated devices switched to the use of erbium ions whose transitions from the \({}^{4}I_{13/2}\) level to the \({}^{4}I_{15/2}\) one is broad enough to cover this wavelength range. Dealing with Er\({}^{3+}\) active ions, the main issue was to realize waveguides with low-losses and a good overlap of the pump and signal modes. Indeed, the pumping scheme of this rare earth being a three levels one, the \({}^{4}I_{15/2}\) ground state absorbs the optical signal when it is not sufficiently pumped. [PERSON] et al. managed to solve this problem by developing a silver-sodium ion-exchange in their Er/Yb co-doped P1 glass [42]. 41 mm-long buried waveguides achieved 7 dB of net gain in a double pass configuration. This work has been followed by the demonstration of an amplifying four wavelength combiner [71] and the qualification of Erbium Doped Waveguide Amplifiers (EDWAs) in a 160 km-long WDM metro network [72]. This work has been completed by packaging and qualification developments in order to create a product line commercialized by TeemPhotonics. Meanwhile the phosphate glasses developed by [PERSON] also gained a lot of attention. [PERSON] et al. achieved a record high gain of 13.7 dB/cm in a 3 mm-long waveguide realized by a silver film ion-exchange [73]. Such a gain per length unit was made possible by a high doping level of the glass in Er (8 wt. %) and Yb (12 wt. %). Er-doped waveguide amplifiers being available, Er-doped lasers followed. Actually, the first proof of concept of an ion-exchanged waveguide laser was obtained on a modified BK7-silicate glass containing 0.5 wt. % of Er, with a potassium ion-exchange and two thin-film dielectric mirrors bonded to the waveguide's facets forming a Fabry-Perot cavity [74]. Nonetheless, from a strict point of view, this device was not a fully integrated laser because the mirrors were not integrated on the chip. Therefore, the next generation of Er-laser relied on the use of Bragg gratings as mirrors. In Distributed FeedBack (DFB) or Distribute Bragg  
Figure 8: Vertically integrated broadband duplexer (**a**) fabrication steps; (**b**) measured transmission (the insets display the observed device output’s mode at specific wavelengths). Top and bottom branches are separated by 28 \(\upmu\)m [36]. Reflectors configurations, these lasers presented a single frequency emission compatible with their use as transmitters in WDM systems. Similar for waveguide amplifiers, the use of phosphate glass entailed a major breakthrough in the performances. DBR lasers were demonstrated by [PERSON] et al. using a potassium ion-exchange [41], while [PERSON] et al. manufactured similar devices with a silver thin film [75]. These approaches allowed integrating several lasers on a single chip to provide arrays of multiwavelength sources with one single grating, the wavelength selection being made by tuning the effective indices of the waveguides through their dimensions. Thanks to the use of highly concentrated molten salt of silver nitrate and a DFB configuration, [PERSON] et al.