Jean-Louis Gutzwiller

Design and construction of an optoelectronic crossbar switch containing a terabit per second free-space optical interconnect

The completed detailed design and initial phases of construction of an optoelectronic crossbar demonstrator are presented. The experimental system uses hybrid very large scale integrated optoelectronics technology whereby InGaAs-based detectors and modulators are flip-chip bonded onto silicon integrated circuits. The system aims to demonstrate a 1-Tb/s aggregate data input/output to a single chip by means of free-space optics.

Lossy Hyperspectral Images Coding with Exogenous Quasi Optimal Transforms

It is well known in transform coding that the Karhunen-Loève Transform (KLT) can be suboptimal for non Gaussiansources. However in many applications using JPEG2000Part 2 codecs, the KLT is generally considered as the optimal linear transform for reducing redundancies between components of hyperspectral images. In previous works, optimal spectral transforms (OST) compatible with the JPEG2000 Part 2 standard have been introduced, performing better than the KLT but with an heavier computational cost. In this paper, we show that the OST computed on a learningbasis constituted of Hyperion hyperspectral images issuedfrom one sensor performs very well, and even better thanthe KLT, on other images issued from the same sensor.

Low-Complexity Hyperspectral Image Coding Using Exogenous Orthogonal Optimal Spectral Transform (OrthOST) and Degree-2 Zerotrees

We introduce a low-complexity codec for lossy compression of hyperspectral images. These images have two kinds of redundancies: 1) spatial; and 2) spectral. Our coder is based on a compression scheme consisting in applying a 2-D discrete wavelet transform (DWT) to each component and a linear transform between components to reduce, respectively, spatial and spectral redundancies. The DWT used is the Daubechies 9/7. However, the spectral transform depends on the spectrometer sensor and the kind of images to be encoded. It is calculated once and for all on a set of images (the learning basis) from (only) one sensor, thanks to Akam Bita et al. s OrthOST algorithm that returns an orthogonal spectral transform, whose optimality in high-rate coding has been recently proved under mild conditions. The spectral transform obtained in this way is applied to encode other images from the same sensor. Quantization and entropy coding are then achieved with a well-suited extension to hyperspectral images of the Said and Pearlmans SPIHT algorithm. Comparisons with a JPEG2000 codec using the Karhunen-Loève transform (KLT) to reduce spectral redundancy show good performance for our codec.

Operation of an optoelectronic crossbar switch containing a terabit-per-second free-space optical interconnect

The experimental operation of a terabit-per-second scale optoelectronic connection to a silicon very-large-scale-integrated circuit is described. A demonstrator system, in the form of an optoelectronic crossbar switch, has been constructed as a technology test bed. The assembly and testing of the components making up the system, including a flip-chipped InGaAs-GaAs optical interface chip, are reported. Using optical inputs to the electronic switching chip, single-channel routing of data through the system at the design rate of 250 Mb/s (without internal fan-out) was achieved. With 4000 optical inputs, this corresponds to a potential aggregate data input of a terabit per second into the single 14.6 /spl times/ 15.6 mm CMOS chip. In addition 50-Mb/s data rates were switched utilizing the full internal optical fan-out included in the system to complete the required connectivity. This simultaneous input of data across the chip corresponds to an aggregate data input of 0.2 Tb/s. The experimental system also utilized optical distribution of clock signals across the CMOS chip.

Lossy compression of MERIS superspectral images with exogenous quasi optimal coding transforms

Our research focuses on reducing complexity of hyperspectral image codecs based on transform and/or subband coding, so they can be on-board a satellite. It is well-known that the Karhunen-Loève Transform (KLT) can be sub-optimal in transform coding for non Gaussian data. However, it is generally recommended as the best calculable linear coding transform in practice. Now, the concept and the computation of optimal coding transforms (OCT), under low restrictive hypotheses at high bit-rates, were carried out and adapted to a compression scheme compatible with both the JPEG2000 Part2 standard and the CCSDS recommendations for on-board satellite image compression, leading to the concept and computation of Optimal Spectral Transforms (OST). These linear transforms are optimal for reducing spectral redundancies of multi- or hyper-spectral images, when the spatial redundancies are reduced with a fixed 2-D Discrete Wavelet Transform (DWT). The problem of OST is their heavy computational cost. In this paper we present the performances in coding of a quasi optimal spectral transform, called exogenous OrthOST, obtained by learning an orthogonal OST on a sample of superspectral images from the spectrometer MERIS. The performances are presented in terms of bit-rate versus distortion for four various distortions and compared to the ones of the KLT. We observe good performances of the exogenous OrthOST, as it was the case on Hyperion hyper-spectral images in previous works.

Lossy and lossless compression of MERIS hyperspectral images with exogenous quasi-optimal spectral transforms

Our research focuses on reducing complexity of hyperspectral image codecs based on transform and/or subband coding, so they can be on-board a satellite. It is well-known that the Karhunen Loeve transform (KLT) can be sub-optimal for non Gaussian data. However, it is generally recommended as the best calculable coding transform in practice. Now, for a compression scheme compatible with both the JPEG2000 Part2 standard and the CCSDS recommendations for onboard satellite image compression, the concept and computation of optimal spectral transforms (OST), at high bit-rates, were carried out, under low restrictive hypotheses. These linear transforms are optimal for reducing spectral redundancies of multi- or hyper-spectral images, when the spatial redundancies are reduced with a fixed 2-D discrete wavelet transform. The problem of OST is their heavy computational cost. In this paper we present the performances in coding of a quasi-optimal spectral transform, called exogenous OrthOST, obtained by learning an orthogonal OST on a sample of hyperspectral images from the spectrometer MERIS. Moreover, we compute an integer variant of OrthOST for lossless compression. The performances are compared to the ones of the KLT in both lossy and lossless compressions. We observe good performances of the exogenous OrthOST.

Discrete Wavelet Transform and Optimal Spectral Transform Applied to Multicomponent Image Coding

These last years, research activities on multicomponent image compression have been expanded, due to the development of multispectral and hyperspectral image sensors which supply larger and larger amount of data. The end-users of such images become also more numerous and have various needs and various applications. The future earth observation systems, for instance, will use multi-, superand hyperspectral image sensors with higher resolutions leading to bigger amount of transmitted data. However the channel bandwidth for transmission is limited and therefore there is an interest of conceiving compression systems (onboard and on the ground) of multicomponent images which are not application dependent and which are compatible with the diversity of end-users’ needs. The components of a multicomponent image generally represent the same scene with different views depending on the wavelength. For data from different sensors, a preliminary step of image registration is therefore required as there is a high degree of dependence (or redundancies) between the various components: the usual spatial redundancy (between different pixels in each component) and the spectral redundancy (between the components). During the past two decades, different solutions have been proposed for multicomponent image coding. A solution currently adopted consists of using two different transformations, each with the goal of reducing only one of the two redundancies. In (Dragotti et al., 2000), a 2-D discrete wavelet transform (DWT) is used to reduce the spatial redundancies in each component while the Karhunen Loeve transform (KLT) is applied to reduce the spectral ones. In that paper, the quantization and entropy coding are achieved thanks to the well known SPIHT (Set Partitioning in Hierarchical Trees) codec by Said and Pearlman (Said & Pearlman, 1996) in its original version and in a modified version including VQ (vector quantization). In the same way, with the use of the 2-D DWT of (Antonini et al., 1992) (usually called the Daubechies 9/7), the authors of (Vaisey et al., 1998) use a lattice VQ with a stack run coder as quantization and entropy coding. More recently in (Rucker et al., 2005), the KLT associated with the Daubechies 9/7 2-D DWT and with EBCOT (Taubman, 2000; Taubman & Marcellin, 2002) for quantizing and entropy coding has been tested on Discrete Wavelet Transform and Optimal Spectral Transform Applied to Multicomponent Image Coding

Toward terabit/s input to silicon VLSI: a demonstrator experiment

The physical limit on electronic data communication rates between silicon chips is projected to be of the order of Tbit/s over cm-scale connections. The semiconductor industry predicts that this level of i/o is likely to be required in the near future. Free-space optical connections to silicon VLSI are potentially able to offer much higher data-rates than electrical interconnects and are promising for future high-performance electronic systems. We have assembled the components of an optoelectronic 15 Gbit/s crossbar switch designed to include, internally, an optical data rate to a hybrid InGaAs/silicon chip in the Tbit/s regime. Input to the demonstrator is by an 8 X 8 VCSEL array operating at 250 Mbit/s channel, and these 64 channels are fanned out 8 X 8 times to give the high data rate onto the hybrid chip. This chip includes an array of 4096 InGaAs-based detectors flip chip bonded to silicon CMOS. The custom- designed CMOS performs packet routing under the control of an optical clock and the routed signals are output via differential modulator pairs, interlaced between the detectors on the InGaAs chip.