Volume 4 Issue 8, August 2010

Silicon photonic devices can be built using commercial CMOS chip fabrication facilities, or 'fabs'. However, nearly all research groups continue to design, build and test chips internally, rather than leveraging shared CMOS foundry infrastructure.

Ingenious techniques are needed to extend group IV photonics from near-infrared to mid-infrared wavelengths. If achieved, the reward could be on-chip CMOS optoelectronic systems for use in spectroscopy, chemical and biological sensing, and free-space communications.

Mario Paniccia, Intel fellow and director of Intel's Photonics Technology Lab, talks to Nature Photonics about the company's progress in commercializing high-speed silicon photonics.

Common sense suggests that complex phenomena such as Bose–Einstein condensation require complicated experimental set-ups to be observed. But when it comes to the field of photonics, the simplest system may sometimes reveal the most unexpected surprises.

The demonstration of an integrated terahertz transceiver featuring a quantum cascade laser and a Schottky diode mixer promises new applications for compact and convenient terahertz photonic instrumentation.

Entangled photons are a key ingredient in optical quantum technologies, but researchers have so far been unable to produce a single pair of entangled photons. Now, two groups from China and Austria independently report just that, with a technique that avoids the need to infer entanglement from detection signatures.

Carefully designed nanophotonic silicon waveguides, when pumped at long wavelengths to avoid inherent losses, are opening the door to useful nonlinear processes in the mid-infrared.

The generation of entangled photon pairs is usually a complex process involving optically driven schemes and nonlinear optics. The recent demonstration of an electrically powered light-emitting diode that is capable of this task looks set to greatly simplify experiments in the field of quantum information processing.

Silicon lasers have long been a goal for semiconductor scientists. This Progress Article reviews the most recent developments in this field, including silicon Raman lasers, the first germanium-on-silicon lasers operating at room temperature, and hybrid silicon microring and microdisk lasers. Challenges and opportunities for the present approaches are also discussed.

CMOS-compatible silicon optical modulators with high modulation speeds, large bandwidths, small footprints, low losses and ultralow power consumption are needed for current optical communications systems relying on highly integrated on-chip optical circuits. This Review summarizes the techniques used to implement silicon optical modulators, gives an outlook for these devices, and discusses the candidate solutions of the future.

Owing to their excellent optoelectronic properties, Ge-on-Si photodetector can be monolithically integrated with silicon-based read-out circuits for applications such as high-performance photonic data links and low-cost infrared imaging at low power consumption. This Review covers the major developments in Ge-on-Si photodetectors, including epitaxial growth and strain engineering, free-space and waveguide-integrated devices, as well as recent progress in Ge-on-Si avalanche photodetectors.

The increasing capability for manufacturing a wide variety of optoelectronic devices from polymer and polymer–silicon hybrids, including transmission fibre, modulators, detectors and light sources, suggests that organic photonics has a promising future in communications and other applications.

Researchers demonstrate coherent control of an exciton qubit in a semiconductor quantum dot through optoelectronic means. Such state manipulation of single quantum systems is essential for the development of quantum information systems.

An efficient source of entangled photons generated in an event-ready manner by conditioned detection of auxiliary photons is reported. A fidelity better than 87% and a state preparation efficiency of 45% are obtained. The scheme could offer promising applications in essential photonics-based quantum information tasks, and represents a particularly important development in the realization of optical quantum computing.

Researchers present the first heralded generation of photon states that are maximally entangled in polarization with linear optics. Three photon pairs are generated by spontaneous parametric down-conversion from β-barium borate crystals. The coincident detection of four auxiliary photons unambiguously heralds the successful preparation of the entangled state.

By taking advantage of the absorption reduction at wavelengths approaching the two-photon absorption bandedge of 2,200 nm, scientists demonstrate a mid-infrared silicon optical parametric amplifier that exhibits broadband gain as large as 25.4 dB and a net off-chip amplification of 13 dB using only an ultra-compact 4-mm silicon chip.

Using probe and pump waves derived from ultra-compact telecom optical fibre sources, scientists perform four-wave mixing in silicon waveguides in the spectral region beyond 2 µm, achieving mid-infrared wavelength generation of 2388 nm over a bandwidth of 630 nm on a silicon chip.

A terahertz quantum cascade laser and diode mixer are monolithically integrated to form a simple microelectronic terahertz transceiver. The performance of this system — the transmission of a coherent carrier, heterodyne reception of an external signal, frequency locking and tuning — is as efficient as that of discrete component terahertz photonic systems.

Quasi-phase-matching (QPM) has always been thought of as a purely spatial phenomenon. Now, scientists show that QPM can be extended to the temporal domain, introducing temporal and spatiotemporal modulations of the nonlinear susceptibility. This concept paves the way for the manipulation of light through nonlinear interactions, and may have unique applications in nonlinear optics.

The development of efficient and convenient mid-infrared sources based on quantum cascade lasers and nonlinear optics is creating possibilities for spectroscopy and sensing, reports The Scott Partnership.

Can excitons be used to achieve scalable control of quantum light? Steffen Michaelis de Vasconcellos explained toNature Photonicsthat the optoelectrical control of exciton qubits in quantum dots offers great promise.

The field of silicon photonics is gaining significant momentum because it allows optical devices to be made cheaply using standard semiconductor fabrication techniques and integrated with microelectronic chips. This Focus Issue provides a comprehensive collection of articles that review up-to-date progress and the latest news in the field, as well as giving some ideas about what the future has in store and what challenges should be expected.