Photonic integrated circuits (PICs) are considered as the way to make photonic systems or subsystems cheap and ubiquitous. PICs still are several orders of magnitude more expensive than their microelectronic counterparts, which has restricted their application to a few niche markets.

The application market for Photonic Integrated Circuits (PICs) is rapidly growing. Photonic integration is the dominant technology in high bandwidth communications and is set to become dominant in many fields of photonics, just like microelectronics in the field of electronics. PICs offer compelling performance advances in terms of precision, bandwidth, and energy efficiency. To enable uptake in new sectors, the availability of highly standardized (generic) photonic integration platform technologies is of key importance as this separates design from technology, reducing barriers for new entrants. The major platform technologies today are Indium Phosphide (InP)-based monolithic integration and Silicon Photonics. In this perspective paper, we will describe the current status and future developments of InP-based generic integration platforms.

A novel optical switch operating at a wavelength of 1.55 µm and showing a 12 dB modulation depth is introduced. The device is implemented in a silicon microring resonator using an overcladding layer of the phase change data storage material Ge 2 Sb 2 Te 5 (GST), which exhibits high contrast in its optical properties upon transitions between its crystalline and amorphous structural phases. These transitions are triggered using a pulsed laser diode at λ = 975 nm and used to tune the resonant frequency of the microring resonator and the resultant modulation depth of the 1.55 µm transmitted light.The ever-increasing demand for high speed optical communication networks is driving the development of new photonic devices that can process optical signals in a reliable, low-cost manner. Among competing technologies, Si-based devices have emerged as one of the main candidates for such applications, and several devices, including modulators 1-5 , add-drop filters 6 and wavelength division multiplexers (WDM) 7 have already been demonstrated. An important branch of this technology is the ability to program reconfigurable optical circuits. Indeed, a reprogrammable optical circuit that can hold its configuration without an external continuous source is extremely desirable for a multitude of applications ranging from photonic routers to optical cognitive networks. Recently, new solutions for non-volatile photonic memories have been proposed, involving the use of phase-change materials (PCM) and microring resonators 8,9 .Herein, a non-volatile Si microring resonator optical switch is demonstrated. A thin film of the phasechange material 10 (PCM) Ge 2 Sb 2 Te 5 (GST), which is commonly encountered in optical and electrical data storage applications [11][12][13][14] , is used to switch the resonant frequency and Q-factor of the microring resonator. GST shows high optical contrast between its amorphous, covalently bonded, and crystalline, resonantly bonded, structural phases 15-18 (n cryst − n amorph = 2.5 ; k cryst − k amorph = 1 at 1.55 µm) 19 . Moreover, transitions between the two phases can take place on a sub-ns timescale 20,22 while the resulting final state is stable for several years. These characteristics deem this material appropriate for application in reconfigurable optical circuits.The device, shown in Fig. 1, consists of a Si microring resonator with a bend radius of 5 µm and a coupling region of 3 µm, on top of which a GST thin film with an area of 3×1.5 µm 2 has been deposited. A second Si a) miquel.rude@icfo.es microring with identical dimensions but free of GST is used as a reference during the measurements. A 200 nm gap separates both microrings from a Si strip waveguide (220×440 nm 2 ) with grating couplers 23 at both ends, which are used to deliver light into the device and monitor the transmitted spectrum using single-mode fibers (SMF).

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Photonic integration in a micrometer-thick indium phosphide (InP) membrane on silicon (IMOS) offers intrinsic and high-performance optoelectronic functions together with high-index-contrast nanophotonic circuitries. Recently demonstrated devices have shown competitive performances, including high sidemode-suppression ratio (SMSR) lasers, ultrafast photodiodes, and significant improvement in critical dimensions. Applications of the IMOS devices and circuits in optical wireless, quantum photonics, and optical cross-connects have proven their performances and high potential.