with a fiber with lenses and discrete thin film filters. Figure 11.14 represents the section of a triplexer realized by micro-optics techniques. Integrated optics: Optical elements (both active and passive) are integrated mono- lithically or assembled directly in die on a single substrate. Different approaches have been proposed with different balances between monolithic and hybrid inte- gration [24-26]. Figure 11.15 represents an example of a triplexer realized by the planar lightwave circuit (PLC). Several industries have pushed integrated optics as the way to drastically reduce the cost of GPON optical interfaces. However, technology evolution has shown that the parallel between optics and micro- electronics cannot be perfect as discussed in some detail in Chapter 5, and microoptics triplexers and diplexers still hold the greater part of the market. Beyond the general discussion carried out in Chapter 5, two specific points differentiate access application optical components from electronic ones. Telecommunication Networks TO-CAN Mechanic holding Fiber TO-CAN laser Fiber Thin film filter Laser TO-CAN welding spot FIGURE 11.14 Section of a GPON triplexer implemented with a micro-optical mounting of discrete components. Fiber Filter 1 Digital coupling (1310/1500) groove bondings Optical chip Optical fiber Matching network Capacitor Taper Laser Outer (1310) Analog Electrical hermetic Filter 2 RX 1550 pinout package (1490/1550) FIGURE 11.15 Schematic layout of a GPON triplexer realized with hybrid integration technology. Filters are realized on a high index contrast chip where the location for a flip chip mounting of photodiodes, laser, and TIA is fabricated. Voltage and current sources can be integrated into electronic chips while lasers can- not be monolithically integrated into the PLC, whose waveguides are fabricated out of suitably doped glass. This forces the adoption of hybrid integration to accommodate the laser on PLC triplexers and diplexers. Moreover, even if interesting proposals exist at the research 