In this paper we elaborate on our work in the field of mid-infrared photonic integrated circuits for spectroscopic sensing applications. We discuss the use of silicon-based photonic integrated circuits for this purpose and detail how a variety of optical functions in the mid-infrared besides passive waveguiding and filtering can be realized, either relying on nonlinear optics or on the integration of other materials such as GaSb-based compound semiconductors, GeSn epitaxy and PbS colloidal nanoparticles.

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.

A 7.5µm-diameter InP microdisk laser, integrated on an SOI waveguide is demonstrated as all-optical flip-flop working in continuous-wave regime with an electrical power consumption of several mW, and allowing switching in 60 ps with pulses of 1.8fJ.

Abstract-We present high-efficiency grating couplers for coupling between a single-mode fiber and nanophotonic waveguides, fabricated both in silicon-on-insulator (SOI) and InP membranes using BenzoCycloButene wafer bonding. The coupling efficiency is substantially increased by adding a gold bottom mirror to the structures. The measured coupling efficiency to fiber is 69% for SOI grating couplers and 56% for bonded InP membrane grating couplers.

Abstract-The high index contrast silicon-on-insulator platform is the dominant CMOS 1 compatible platform for photonic integration. The successful use of silicon photonic chips in optical communication applications has now paved the way for new areas where photonic chips can be applied. It is already emerging as a competing technology for sensing and spectroscopic applications. This increasing range of applications for silicon photonics instigates an interest in exploring new materials, as silicon-oninsulator has some drawbacks for these emerging applications, e.g. silicon is not transparent in the visible wavelength range. Silicon nitride is an alternate material platform. It has moderately high index contrast, and like silicon-on-insulator, it uses CMOS processes to manufacture photonic integrated circuits. In this paper, the advantages and challenges associated with these two material platforms are discussed. The case of dispersive spectrometers, which are widely used in various silicon photonic applications, is presented for these two material platforms.

Laser frequency combs, sources with a spectrum consisting of hundred thousands evenly spaced narrow lines, have an exhilarating potential for new approaches to molecular spectroscopy and sensing in the mid-infrared region. The generation of such broadband coherent sources is presently under active exploration. Technical challenges have slowed down such developments. Identifying a versatile highly nonlinear medium for significantly broadening a mid-infrared comb spectrum remains challenging. Here we take a different approach to spectral broadening of mid-infrared frequency combs and investigate CMOS-compatible highly nonlinear dispersion-engineered silicon nanophotonic waveguides on a silicon-on-insulator chip. We record octave-spanning (1,500–3,300 nm) spectra with a coupled input pulse energy as low as 16 pJ. We demonstrate phase-coherent comb spectra broadened on a room-temperature-operating CMOS-compatible chip.

A review of recent progress in hybrid integrated platforms for silicon photonics is presented. Integration of III-V semiconductors onto silicon-on-insulator substrates based on two different bonding techniques is compared, one comprising only inorganic materials, the other technique using an organic bonding agent. Issues such as bonding process and mechanism, bonding strength, uniformity, wafer surface requirement, and stress distribution are studied in detail. The application in silicon photonics to realize high-performance active and passive photonic devices on low-cost silicon wafers is discussed. Hybrid integration is believed to be a promising technology in a variety of applications of silicon photonics.

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).