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January 25, 2010

Major step towards low-power all-optical switching for optical communications


The January issue of the premier scientific magazine Nature Photonics publishes an ultra-small and fast, electrically pumped all-optical memory on a silicon chip with record low power consumption. This result achieved by imec and its associated laboratory INTEC at the Ghent University, paves the way for optical packet switching with drastically reduced overall power consumption in high-speed, high-data rate optical telecommunication systems.

The optical random access memory has been achieved with ultra-compact micro-disk lasers with a diameter of 7.5µm. The laser light can either propagate in the clockwise or counter clockwise direction and one can switch between these two laser modes using short optical pulses. The lasers, implemented themselves in Indium Phosphide membranes, are heterogeneously integrated onto passive silicon waveguide circuits. This allows to optically interconnect different memory cells using silicon wires. It also allows to use the strongly developed silicon-based microelectronics fabrication technology, making it a cost-effective solution.



Nature Photonics - An ultra-small, low-power, all-optical flip-flop memory on a silicon chip

Ultra-small, low-power, all-optical switching and memory elements, such as all-optical flip-flops, as well as photonic integrated circuits of many such elements, are in great demand for all-optical signal buffering, switching and processing. Silicon-on-insulator is considered to be a promising platform to accommodate such photonic circuits in large-scale configurations. Through heterogeneous integration of InP membranes onto silicon-on-insulator, a single microdisk laser with a diameter of 7.5 µm, coupled to a silicon-on-insulator wire waveguide, is demonstrated here as an all-optical flip-flop working in a continuous-wave regime with an electrical power consumption of a few milliwatts, allowing switching in 60 ps with 1.8 fJ optical energy. The total power consumption and the device size are, to the best of our knowledge, the smallest reported to date at telecom wavelengths. This is also the only electrically pumped, all-optical flip-flop on silicon built upon complementary metal-oxide semiconductor technology.

2 page pdf with supplemental information


Other Photonic Research

2. Are optical transistors the logical next step?
The idea of an optical transistor — and the associated optical logic circuits that may follow — conjures images of light controlling light in some sparkling, transparent computer. This dream resurfaces on a regular basis as new optical and optoelectronic technologies become available

3. Nature Photonics - Silicon photonics: On-chip OPOs
The potential for incorporating photonic functionality in silicon very-large-scale integrated (VLSI) circuits is extremely exciting, particularly for applications such as high-speed chip-to-chip data communication, spectroscopy and sensing. As a result, silicon photonics has attracted great attention from both academia and industry in recent years.


4. Nature Photonics - CMOS-compatible multiple-wavelength oscillator for on-chip optical interconnects
Silicon photonics enables the fabrication of on-chip, ultrahigh-bandwidth optical networks that are critical for the future of microelectronics. Several optical components necessary for implementing a wavelength division multiplexing network have been demonstrated in silicon. However, a fully integrated multiple-wavelength source capable of driving such a network has not yet been realized. Optical amplification, a necessary component for lasing, has been achieved on-chip through stimulated Raman scattering parametric mixing and by silicon nanocrystals or nanopatterned silicon. Losses in most of these structures have prevented oscillation. Raman oscillators have been demonstrated but with a narrow gain bandwidth that is insufficient for wavelength division multiplexing. Here, we demonstrate the first monolithically integrated CMOS-compatible source by creating an optical parametric oscillator formed by a silicon nitride ring resonator on silicon. The device can generate more than 100 new wavelengths with operating powers below 50 mW. This source can form the backbone of a high-bandwidth optical network on a microelectronic chip.

5. Nature Photonics - Synthesis of a single cycle of light with compact erbium-doped fibre technology
The advent of self-referenced optical frequency combs has sparked the development of novel areas in ultrafast sciences such as attosecond technology and the synthesis of arbitrary optical waveforms. Few-cycle light pulses are key to these time-domain applications, driving a quest for reliable, stable and cost-efficient mode-locked laser sources with ultrahigh spectral bandwidth. Here, we present a set-up based entirely on compact erbium-doped fibre technology, which produces single cycles of light. The pulse duration of 4.3 fs is close to the shortest possible value for a data bit of information transmitted in the near-infrared regime. These results demonstrate that fundamental limits for optical telecommunications are accessible with existing fibre technology and standard free-space components

6. Nature Photonics - An optical ultrafast random bit generator
The generation of random bit sequences based on non-deterministic physical mechanisms is of paramount importance for cryptography and secure communications. High data rates also require extremely fast generation rates and robustness to external perturbations. Physical generators based on stochastic noise sources have been limited in bandwidth to ~100 Mbit s−1 generation rates. We present a physical random bit generator, based on a chaotic semiconductor laser, having time-delayed self-feedback, which operates reliably at rates up to 300 Gbit s−1. The method uses a high derivative of the digitized chaotic laser intensity and generates the random sequence by retaining a number of the least significant bits of the high derivative value. The method is insensitive to laser operational parameters and eliminates the necessity for all external constraints such as incommensurate sampling rates and laser external cavity round trip time. The randomness of long bit strings is verified by standard statistical tests.




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