Nadav Cohen

Ultrafast all-optical switching

We present innovative concepts related to the realization of ultrafast optical switches to be used for obtaining all-optical switching. We review the construction and the achievements of Civcom Incorporated during its research and development stages of constructing its ultrafast switch. Experimental measurements are exhibited.

Compact polarization-based all-optical interconnection systems with growth capability

All-optical communication requires all-optical interconnections, thus leading to reliable, fast, and flexible modular communication means in future systems. Free-space approaches are advantageous since they fully use the two dimensions optics offer. A folded architecture based on a polarization code is proposed for dynamic optical interconnection. The suggested systems are compact and appropriate for both intracomputer and intercomputer communication. The modularity of the proposed architecture is presented, and a growth rule for the fully connected versions of the system is introduced. The proposed approach significantly reduces both the price of the interconnection systems and their complexity. Presented are 4 x 4 and 8 x 8 fully connected switches, a rearrangeable nonblocking 4 x 4 switch, and a crossbar architecture.

Analytic approach for optimal quantization of diffractive optical elements

One of the most important factors that limit the performance of diffractive optical elements (DOEs) is the depth accuracy of the relief structure. A common procedure for fabricating DOEs is the binary optics procedure, in which binary masks are used for the fabrication of a multilevel relief structure. Here an analytic procedure for calculating the optimal depth levels of DOEs, the phase bias, and the decision levels is presented. This approach is based on the minimization of the mean-squared error caused by the quantization of the continuous profile. As a result of the minimization an optimal value for the etching depth of each photolithographic mask is determined. The obtained depth values are, in general, different from the depth values used by the conventional multilevel approach. Comprehensive mathematical analysis is given, followed by several computer simulations that demonstrate the advantages of the proposed procedure.

Complex Floating Point—A Novel Data Word Representation for DSP Processors

This work introduces a new floating point representation for complex numbers (“Complex floating point”), and compares it to the floating point representation defined in the IEEE 754 standard, with a reference to the common DSP fixed point representation. The new suggested representation uses fewer bits than the IEEE 754, while keeping the same dynamic range and precision. A number of common DSP building blocks have been implemented. Results show that for the new representation, the ASIC silicon footprint of the arithmetic modules is bigger, by a factor of more than 10%. However, the area of the registers and memories, which usually occupy most of the DSP subsystem footprint, is 10% less. This directly leads to reduction of the cost of the ASIC. The quantization noise introduced by both representations was evaluated by running a number of common DSP algorithms, on various inputs. Results show that both representations induce a negligible quantization noise level, and the difference between them is very small: up to 0.2 dB on high SNR scenarios or for small sized vectors, and up to 2 dB on low SNR scenarios with large sized vectors. These results indicate that effectively there is no difference in quantization degradation between the two representations. By using the results of this work, a DSP processor architect can decide whether to use the IEEE 754 floating point representation, or the suggested complex floating point representation, which allows smaller memories at the expense of bigger logic and negligible quantization degradation.

Multistage optical system for broadcasting and switching information

Conventional switching systems connect each input channel to one output channel. Broadcasting systems permit the connection of each input channel to more than a single output. A broadcast 2 x 2 switch is presented. This switch is an extension of the standard bypass-exchange switch. It allows for the broadcasting of the inputs in addition to the conventional modes. Multistage interconnection networks can be constructed with this switch as the basic building block. Such networks will extend their capabilities, allowing for broadcasting features. Three implementations of this type are described, and experimental results for the 2 x 2 switch are also presented.

Doppler-Based Flow Rate Sensing in Microfluidic Channels

We design, fabricate and experimentally demonstrate a novel generic method to detect flow rates velocity in microfluidic devices. The method is appealing for variety of applications where a simple and accurate speed measurement is needed.

Optical recursive implementation of the Cantor network

The spatial optical switch [or interconnection network (IN)] is one of the more successful optical elements in optical communication networks. In fact, it is one of the only commercially deployed all-optical elements and is probably the most widespread after optical fibers themselves and optical amplifiers. Low port-count switches are fairly easy to construct, but larger INs present interesting realization challenges, especially when strictly nonblocking connectivity is required. The Cantor network allows this high connectivity level, even for a large network, but it has not received much attention in the literature. Here optical implementation of the Cantor network is presented. The system is realized in a recursive manner, thus eliminating the complex static interconnection patterns usually required with this network.

Realization of temporal linear transformations by the use of a spatial-diffraction-based optical system

Signal processing in general, and optical signal processing in particular, make extensive use of linear transformations. The temporal nature of many optical signals (e.g., in optical communication systems) makes the realization of temporal transformations a desired extension. We present a system making possible the realization of arbitrary temporal linear transformation. The system supports real-time changes of the realized transformation. The mathematical analysis is derived, and computer simulations are presented.

Spurious-free dynamic range characterization of a χ 2 -based PPLN waveguide

We experimentally characterize the spurious-free dynamic range performance of a χ2-Based PPLN waveguide by measuring the distortion on a microwave photonic link of two RF tones around 9.9GHz and characterizing the SFDR of a generated idler in a PPLN waveguide.

Analog performance of multiple, discretely tunable time delays based on a frequency comb and a chromatic dispersion element

We demonstrate the analog performance of multiple, coherent, and discretely tunable time delays based on a frequency comb and a chromatic dispersion element. The amount of 0.6ns delay is measured between adjacent selected comb lines. The linear phase frequency response of the system is verified and the SFDR is measured.