Laser & Photonics Reviews

Envisioned lab-on-a-chip platform with on-chip detection using integrated optics-based transducers. In the figure, an array of Mach-Zehnder interferometers are integrated with individual microfluidics channels, grating couplers for the in- and output of the light in each sensing channel, read-out photodetectors and CMOS electronics for data processing. (Picture: M. C. Estevez et al., pp. 463–487, in this issue)

Photograph of a 3-inch Lithium Niobate on Insulator (LNOI) wafer. It consists of a 760-nm thick single crystalline LN film crystal bonded on a 1.3-µm thick silicon dioxide layer deposited by PECVD on a LN substrate. The inset is a scanning electron micrograph of a racetrack microring resonator in LNOI structured by laser lithography patterning and Ar⁺ ion etching. (Picture: G. Poberaj et al., pp. 488–503, in this issue

Solid-state organic amplifiers and lasers are attractive for hybrid integration due to their compatibility with different material platforms, ease of processing, and possibility to optimize their optical and electronic properties by molecular engineering. Advances in the gain medium design and synthesis in combination with new resonator architectures led to improvements in temporal and spectral properties, lifetime stability, gains produced and operating threshold powers, which triggered interest in their use for a broad range of integrated photonic applications.

The application of portable, easy-to-use and highly sensitive lab-on-a-chip biosensing devices for real-time diagnosis could offer significant advantages over current analytical methods. Integrated optics-based biosensors have become the most suitable technology for lab-on-chip integration due to their excellent properties. This review provides an extended overview of the state-of-the-art in integrated photonic biosensors technology including interferometers, grating couplers, microring resonators, photonic crystals and other novel nanophotonic transducers.

The state-of-the-art of high-refractive-index-contrast single-crystalline thin lithium niobate (LiNbO₃) films as a new platform for high-density integrated optics is reviewed. Sub-micrometer thin LiNbO₃ films are obtained by “ion-slicing”. They can be bonded by two different techniques to a low-index substrate to obtain “lithium niobate on insulator” (LNOI) even as wafer of 3'' diameter. Different micro- and nano-structuring techniques have been used to successfully develop micro-photonic devices.

Silicon photonics defines a significant advancement in the development of highly integrated devices on a single semiconductor substrate. As a revolutionizing technology it benefits from the vast infrastructure to service the burgeoning microelectronics industry and has found application in a range of areas such as telecommunications, sensing and optical interconnects. It is this latter application which is addressed primarily in this review. The potential for silicon photonics as a solution to high data rate transmission through the description of the devices and processes which have emerged in the last decade is discussed.

An overview is presented of recently developed light-mediated methods for ferroelectric domain engineering of lithium niobate single crystals. These methods include light-assisted poling, UV laser-induced inhibition of poling, and all-optical poling. In addition to the primary application of ferroelectric domain patterns, namely the realization of non-linear optical devices, the ability of transferring a domain pattern into a topographical structure by domain selective etching allows also for surface structuring of lithium niobate.

Integrated phased-array optical switches, having a high port-count scalability and broad spectral coverage, can potentially be used as building blocks of large-scale optical routers. In this article, recent works on monolithically integrated InP phased-array switches and their applications to optical packet switching (OPS) are reviewed. A series of OPS experiments, employing high-bit-rate optical packets with different modulation formats and a tunable optical buffering experiment are presented as potential applications of these switches.

This review article is concerned with the basic principles of photonic crystals (PhC) as well as topics such as PhC beam-splitters, slow-light structures, micro-/nano-resonators, coupled resonator optical waveguides (CROWs) and PhC-based semiconductor lasers. Emphasis is placed on both the conceptual and the practical matters that need to be addressed in order to fulfill the tasks of designing and realizing devices that exploit photonic crystal principles.