Abstract:In this work we experimentally demonstrate laser erasable germanium implanted Bragg gratings in SOI. Bragg gratings are formed in a silicon waveguide by ion implantation induced amorphization, and are subsequently erased by a contained laser thermal treatment process. An extinction ratio up to 24dB has been demonstrated in transmission for the fabricated implanted Bragg gratings with lengths up to 1000µm. Results are also presented, demonstrating that the gratings can be selectively removed by UV pulsed laser annealing, enabling a new concept of laser erasable devices for integrated photonics.

-We present Bragg gratings with an effective index change introduced by implanting germanium at only 15KeV. An extinction ratio of 35dB at 1350nm is demonstrated for device lengths of 600μm, furthermore laser annealing is demonstrated. IntroductionIn the information age current technologies struggle to deliver the data rates required by modern communications and computer bus systems. Silicon photonics has the potential of overcoming some of these obstacles by relying on a well understood material system and technology [1]. However the full adoption of silicon based photonics would require complex integrated optoelectronic systems to be manufactured in high volumes at low costs. These requirements cannot be met without enabling a wafer scale testing [2] strategy in a similar fashion to what has been happening for many decades in the integrated electronics industry. The current challenge for silicon photonics in this area is represented by the inability of the light signal to access a processed wafer without substantially modifying the wafer surface. Most of the solutions presented for light coupling into test samples rely on substantially modifying the structure of the material to enable end fire coupling, prism coupling [3], inverted tapers [4], and cantilever structures [5]. Introducing these kinds of test points, or even wavelength selective test points such as etched or metal gratings on a processed wafer can potentially introduce undesired alterations of the light propagation, such as scattering and losses, as well as interfering with successive processing steps. In order for optical wafer scale testing to become a viable technology, optical wafer scale testing should be implemented as a minimally intrusive technology. The use of ion implanted optical structures is particularly suited for these applications, as the refractive index change can be introduced on the wafer surface without altering the general topography of the wafer. Furthermore, since the planarity of the wafer is retained, it could be possible to employ these structures for applications that require extensive surface interaction such as bonding or flip chip interactions, and sensing. The use of a low energy/low dose implant conditions (10 15 ion/cm 2 , as opposed to general doping densities which can reach 10 19 ion/cm 2 ) potentially allows minimal optical losses to be introduced by the implantation process.

Silicon photonics shows tremendous potential for the development of the next generation of ultra fast telecommunication, tera-scale computing, and integrated sensing applications. One of the challenges that must be addressed when integrating a "photonic layer" onto a silicon microelectronic circuit is the development of a wafer scale optical testing technique, similar to that employed today in integrated electronics industrial manufacturing. This represents a critical step for the advancement of silicon photonics to large scale production technology with reduced costs. In this work we propose the fabrication and testing of ion implanted gratings in sub micrometer SOI waveguides, which could be applied to the implementation of optical wafer scale testing strategies. An extinction ratio of over 25dB has been demonstrated for ion implanted Bragg gratings fabricated by low energy implants in submicron SOI rib waveguides with lengths up to 1mm. Furthermore, the possibility of employing the proposed implanted gratings for an optical wafer scale testing scheme is discussed in this work.

Neural connectionism is a common theoretical abstraction of biological neural networks (1-3) and a basis for common artificial neural networks (4) . Yet, it is clear that connectionism abstracts out much of the biological phenomena significant and necessary for many cognitive-driven behaviors, in particular intra-neuronal and inter-neuronal biochemical processes (5-8) . This paper presents a model which adds an abstraction of these processes to a standard connectionism-based model. Specifically, a sub-system determines the synaptic weights. The resulting network has plastic synapses during non-learning-related behavior, in sharp contrast with most common models in which synapses are fixed outside of a learning-phase. Some synapses introduce plasticity that is causally related with behavior, while in others the plasticity randomly fluctuates, in correspondence with recent data (9,10) . In this model the memory engram is distributed over the biochemical system, in addition to the synapses. The model yields better performance in memory-related tasks compared to a standard recurrent neural network trained with backpropagation.