Analysis of novel cascaded /spl chi//sup (2)/ (SFG+DFG) wavelength conversions in quasi-phase-matched waveguides

A novel cascaded second-order nonlinear interaction (/spl chi//sup (2)/), which is simultaneously based on sum frequency generation (SFG) and difference frequency generation (DFG) processes, is proposed and analyzed in quasi-phase-matched wavelength converters. Analytical expressions with clear physical insights are derived for the converted light. It is shown that the same conversion efficiency can be achieved by employing two pump sources with lower output power (P/sub p1/,P/sub p2/) in this novel scheme as compared with the conventional cascaded wavelength conversion technique based on second-harmonic generation and difference frequency generation (SHG+DFG) with a single higher power pump beam (P/sub p/=P/sub p1/+P/sub p2/). The theoretical results are consistent with the experimental ones. It is found that the pump wavelength difference can be separated by a span as large as 75 nm, while large 3-dB signal conversion bandwidth is retained. The results show that the novel cascaded /spl chi//sup (2)/ wavelength conversion scheme is very attractive for practical applications.     

All-optical signal processing using /spl chi//sup (2)/ nonlinearities in guided-wave devices

The authors present a review of all-optical signal-processing technologies based on /spl chi//sup (2)/ nonlinear interactions in guided-wave devices and their applications for telecommunication. In this study, the main focus is on three-wave interactions in annealed proton-exchanged periodically poled lithium niobate waveguides due to their suitable properties with respect to nonlinear mixing efficiency, propagation loss, and ease of fabrication. These devices allow the implementation of advanced all-optical signal-processing functions for next-generation networks with signal bandwidths beyond 1 THz. In this paper, integrated structures that will allow for improvements of current signal-processing functions as well as the implementation of novel device concepts are also presented.     

Comparative determinations of the /spl chi//sup (2)/ spatial distribution induced in thermally poled silica planar samples

We herein report the comparison of two independent reconstructions of the distribution of the /spl chi//sup (2)/ nonlinear susceptibility induced by thermal poling in planar silica samples. Both nonlinear profiles are quantitatively in good agreement in terms of /spl chi//sup (2)/ magnitude and nonlinear thickness; and qualitatively in agreement in terms of shape. We conclude that both characterization methods used are efficient for the determination of the /spl chi//sup (2)/ susceptibility spatial distribution in bulk samples.     

Wavelength conversions in quasi-phase matched LiNbO/sub 3/ waveguide based on double-pass cascaded /spl chi//sup (2)/ SFG+DFG interactions

Based on the cascaded nonlinear interactions (/spl chi//sup (2)/:/spl chi//sup (2)/) of sum- and difference-frequency generation (SFG+DFG), a novel all-optical wavelength conversion scheme is proposed for the first time in periodically poled LiNbO/sub 3/ (PPLN) waveguide, in which a double-pass configuration is introduced. The performance of this scheme is thus different from the previous single-pass SFG+DFG scheme. The concept of the "balance condition" is presented to optimize the power and frequencies of the two pump sources. Under this condition, the energy is transferred irreversibly from the pump waves to the SF wave during the forward propagation. The equations describing the SFG can be solved analytically under this condition. Subsequently, the DFG equations are solved under the assumption that the SF wave would be constant during the backward propagation. Theoretical expressions are derived and are found to be consistent with numerical calculations. Compared with the conventional converter based on the cascaded /spl chi//sup (2)/:/spl chi//sup (2)/ interactions of second-harmonic generation and difference frequency generation SHG+DFG, the same conversion efficiency can be achieved in our scheme by employing two pump sources with lower power, or conversely higher conversion efficiency can be reached using two pump sources similar to that used in SFG+DFG scheme. The profile of the conversion efficiency can be further improved by adjusting the wavelengths of the two pump sources. In addition, compared with the single-pass SFG+DFG scheme, the main advantage of this new scheme rests on the fact that the conversion efficiency can be enhanced significantly. The advantages of the double-pass SHG+DFG scheme and the single-pass SFG+DFG scheme are combined in this new design to a great extent.     

Broadband 180/spl deg/ bit phase shifter using a /spl lambda//2 coupled line and parallel /spl lambda//8 stubs

In this paper, a broadband 180/spl deg/ bit phase shifter using a new switched-network was presented. The new network is composed of a /spl lambda//2 coupled line and parallel /spl lambda//8 open and short stubs, which are shunted at the edge points of a coupled line, respectively. According to a desired phase shift, it provides a controllable phase dispersive characteristic by the proper determination of Z/sub m/,Z/sub s/, and R values. The 180/spl deg/ bit phase shifter operated at 3 GHz was fabricated and experimented using design graphs which provide the required Z/sub m/,Z/sub s/ values, and I/O match and phase bandwidths. The experimental performances showed broadband characteristics.     

A high-density MIM capacitor (13 fF//spl mu/m/sup 2/) using ALD HfO/sub 2/ dielectrics

Metal-insulator-metal (MIM) capacitors with different HfO/sub 2/ thickness have been investigated. The results show that both the capacitance density and voltage coefficients of capacitance (VCCs) increase with decreasing HfO/sub 2/ thickness. In addition, it is found that the VCCs decrease logarithmically with increasing thickness. Furthermore, the MIM capacitor with 10-nm HfO/sub 2/ shows a record high capacitance density of 13 fF//spl mu/m/sup 2/ and a VCC of 607 ppm/V, which can meet the requirement of the International Technology Roadmap for Semiconductors. It can also provide a low leakage current of 5.95 /spl times/ 10/sup -8/A/cm/sup 2/ at room temperature at 1 V, low tangent values below 0.05, and a small frequency dependence. These results indicate that the devices are suitable for use in silicon integrated circuit applications.     

Very high-density (23 fF//spl mu/m/sup 2/) RF MIM capacitors using high-/spl kappa/ TaTiO as the dielectric

A very high density of 23 fF//spl mu/m/sup 2/ has been measured in RF metal-insulator-metal (MIM) capacitors which use high-/spl kappa/ TaTiO as the dielectric. In addition, the devices show a small reduction of 1.8% in the capacitance, from 100 kHz to 10 GHz. Together with these characteristics the MIM capacitors show low leakage currents and a small voltage-dependence of capacitance at 1 GHz. These TaTiO MIM capacitors should be useful for precision RF circuits.     

A 6.7-fF//spl mu/m/sup 2/ bias-independent gate capacitor (BIGCAP) with digital CMOS process and its application to the loop filter of a differential PLL

A linear bias-independent gate capacitor (BIGCAP) with large intrinsic capacitance and low parasitic capacitance is proposed. BIGCAP is composed of a pair of accumulation-mode n-poly gate capacitors in an n-well and a pair of pMOS gate capacitors, which requires no additional fabrication process steps. Measured results with 1.5-V 0.13-/spl mu/m digital CMOS technology show that the intrinsic capacitance is 6.7 fF//spl mu/m/sup 2/ (6.7 times bigger than that of typical MIM capacitors) and the parasitic capacitance is 1.9% of the intrinsic capacitance (1/5 that of typical MIM capacitors). The linearity is /spl plusmn/2.9% and capacitance variation across a wafer is as small as /spl sigma/= 0.096%. For a 0.1-V threshold voltage variation, the capacitance variation was only /spl sigma/= 0.69% and the linearity ranged from /spl plusmn/2.84% to /spl plusmn/2.93%. For three types of BIGCAP using 1.5-V, 2.5-V, and 3.3-V MOSFETs, less than /spl plusmn/4% linearity is achievable by optimizing the ratio (x) of the pMOS gate capacitors' area to the area of the n-poly gate capacitors, and the optimum x value is within a range of 15%-25%. BIGCAP has been applied to the loop filter of a differential phase-locked loop (PLL) and reduces the gate area of the largest loop filter capacitor to only 35% of that of the conventional design while achieving reasonable jitter of 7.0 ps (rms) and 74.4 ps (peak-to-peak) at 840 MHz with a 1.5-V supply.     

The /spl Delta//sup 2/-conjecture for L(2,1)-labelings is true for direct and strong products of graphs

A variation of the channel-assignment problem is naturally modeled by L(2,1)-labelings of graphs. An L(2,1)-labeling of a graph G is an assignment of labels from {0,1,...,/spl lambda/} to the vertices of G such that vertices at distance two get different labels and adjacent vertices get labels that are at least two apart and the /spl lambda/-number /spl lambda/(G) of G is the minimum value /spl lambda/ such that G admits an L(2,1)-labeling. The /spl Delta//sup 2/-conjecture asserts that for any graph G its /spl lambda/-number is at most the square of its largest degree. In this paper it is shown that the conjecture holds for graphs that are direct or strong products of nontrivial graphs. Explicit labelings of such graphs are also constructed.     

An O(k/sup 2//spl middot/log(n)) algorithm for computing the reliability of consecutive-k-out-of-n: F systems

This study presents an O(k/sup 2//spl middot/log(n)) algorithm for computing the reliability of a linear as well as a circular consecutive-k-out-of-n: F system. The proposed algorithm is more efficient and much simpler than the O(k/sup 3//spl middot/log(n/k)) algorithm of Hwang & Wright.     

Very high density RF MIM capacitors (17 fF//spl mu/m/sup 2/) using high-/spl kappa/ Al/sub 2/O/sub 3/ doped Ta/sub 2/O/sub 5/ dielectrics

Using high-/spl kappa/ Al/sub 2/O/sub 3/ doped Ta/sub 2/O/sub 5/ dielectric, we have obtained record high MIM capacitance density of 17 fF//spl mu/m/sup 2/ at 100 kHz, small 5% capacitance reduction to RF frequency range, and low leakage current density of 8.9/spl times/10/sup -7/ A/cm/sup 2/. In combination of both high capacitor density and low leakage current density, a very low leakage current of 5.2/spl times/10/sup -12/ A is calculated for a typical large 10 pF capacitor used in RF IC that is even smaller than that of a deep sub-/spl mu/m MOSFET. This very high capacitance density with good MIM capacitor characteristics can significantly reduce the chip size of RF ICs.     

Design of Luenberger state observers using fixed-structure H/sub /spl infin// optimization and its application to fault detection in lane-keeping control of automated vehicles

Lane-keeping control forms an integral part of fully automated intelligent vehicle highway systems (IVHS) and its reliable operation is critical to the operation of an automated highway. We present the design of a fault detection filter for the lane-keeping control systems onboard vehicles used by California-PATH, USA in its automated highways program. We use a Luenberger structure for the fault detection filters and tune the observer gains based on an H/sub /spl infin//-based cost. Such a choice of cost was motivated by the need to explicitly incorporate frequency-domain-based performance objectives. The linear matrix inequality (LMI)-based formulation of an H/sub /spl infin// optimization problem of Luenberger state observers does not allow for the augmentation with dynamic performance weightings in the optimization objective, since it makes the problem a nonconvex optimization problem. We present an algorithm to locally solve the problem of the design of Luenberger state observers using H/sub /spl infin// optimization by transforming the problem into an H/sub /spl infin// static output feedback controller problem. Experimental results demonstrate the efficacy of the tuning methodology by comparing the fault detection performance of filters that use H/sub /spl infin// Luenberger observers versus those that use Kalman filters. Implementation issues of the observers are also discussed.     

Bismuth-oxide-based nonlinear fiber with a high SBS threshold and its application to four-wave-mixing wavelength conversion using a pure continuous-wave pump

The unique and practical benefits of the use of bismuth-oxide-based nonlinear fiber (Bi-NLF) in implementing a four-wave-mixing (FWM)-based wavelength converter for fiber-optic-communication-system applications are experimentally demonstrated. First, the Kerr-nonlinearity and stimulated-Brillouin-scattering (SBS) characteristics of our fabricated Bi-NLF are experimentally investigated. The Bi-NLF is found to have the superior advantage of a significantly high SBS threshold in addition to its ultrahigh Kerr nonlinearity /spl gamma/ of /spl sim/1100 W/sup -1//spl middot/km/sup -1/, compared to the conventional silica-based highly nonlinear fiber. Next, the authors perform an experiment for the FWM-based wavelength conversion of a non-return-to-zero (NRZ) signal within a 40-cm length of the Bi-NLF fusion spliced to standard silica fibers by using a continuous-wave (CW) high-power pump beam. Error-free tunable wavelength conversion over a 10-nm bandwidth is readily achieved. No SBS-suppression scheme is employed for the pump due to the high SBS threshold, which simplifies the system configuration and improves the quality of the wavelength-converted signal.     

Fast transform for decoding both errors and erasures of Reed-Solomon codes over GF(2/sup m/) for 8/spl les/m/spl les/10

In this letter, it is shown that a fast, prime-factor discrete Fourier transform (DFT) algorithm can be modified to compute Fourier-like transforms of long sequences of 2/sup m/-1 points over GF(2/sup m/), where 8/spl les/m/spl les/10. Using these transforms, together with the Berlekamp-Massey algorithm, the complexity of the transform-domain decoder for correcting both errors and erasures of the Reed-Solomon codes of block length 2/sup m/-1 over GF(2/sup m/) for 8/spl les/m/spl les/10 is reduced substantially from the previous time-domain decoder. A computer simulation verifies these new results.     

Bending of a planar lightwave circuit 2/spl times/2 coupler to desensitize it to wavelength, polarization, and fabrication changes

We present a planar lightwave circuit curved 2/spl times/2 coupler. Its splitting ratio has a low sensitivity to wavelength, polarization, and fabrication yet is low-loss and compact. We present simple formulae for its design. We demonstrate a 50/50 version in silica-on-silicon waveguides. We discuss the tradeoff between amplitude accuracy and phase accuracy in such densensitized couplers.     

Path to the measurement of positive gain on the 1315-nm transition of atomic iodine pumped by O/sub 2/(a/sup 1//spl Delta/) produced in an electric discharge

Laser action at 1315 nm on the I(/sup 2/P/sub 1/2/)/spl rarr/I(/sup 2/P/sub 3/2/) transition of atomic iodine is conventionally obtained by a near-resonant energy transfer from O/sub 2/(a/sup 1//spl Delta/) which is produced using wet-solution chemistry. The system difficulties of chemically producing O/sub 2/(a/sup 1//spl Delta/) have motivated investigations into gas phase methods to produce O/sub 2/(a/sup 1//spl Delta/) using low-pressure electric discharges. We report on the path that led to the measurement of positive gain on the 1315-nm transition of atomic iodine where the O/sub 2/(a/sup 1//spl Delta/) was produced in a flowing electric discharge. Atomic oxygen was found to play both positive and deleterious roles in this system, and as such the excess atomic oxygen was scavenged by NO/sub 2/ to minimize the deleterious effects. The discharge production of O/sub 2/(a/sup 1//spl Delta/) was enhanced by the addition of a small proportion of NO to lower the ionization threshold of the gas mixture. The electric discharge was upstream of a continuously flowing supersonic cavity, which was employed to lower the temperature of the flow and shift the equilibrium of atomic iodine more in favor of the I(/sup 2/P/sub 1/2/) state. A tunable diode laser system capable of scanning the entire line shape of the (3,4) hyperfine transition of iodine provided the gain measurements.     

Fabrication of MOD-derived YBCO films on [001]LaAlO/sub 3/ and their application to /spl lambda//4 CPW SIR BPFs

Chemically derived epitaxial thin films of YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) are fabricated on [001]LaAlO/sub 3/ substrates by the metalorganic-deposition (MOD) process, which has advantages of high quality, nonvacuum, low-cost, and large-scale production of high-T/sub c/ superconducting films. The MOD-derived YBCO films have a sharp transition at the critical temperature (90.4 K) and a high-quality film with a surface resistance of 0.13 m/spl Omega/ (30 K, 9.98 GHz) is obtained. As a microwave application, simple and compact bandpass filters (BPFs) using /spl lambda//4 coplanar-waveguide. stepped-impedance resonators are demonstrated on the YBCO films. A two-stage Chebyshev BPF of center frequency of 5.731 GHz, bandwidth of 135 MHz, and insertion loss of 0.29 dB with little input power dependency in a power range less than 10 dBm is realized on the film.     

Extraction of /spl epsiv//sub r/(f) and tan/spl delta/(f) for printed circuit board insulators up to 30 GHz using the short-pulse propagation technique

In this paper, the self-consistent, frequency-dependent dielectric constant epsiv_r(f) and dielectric loss tandelta(f) of several materials are determined over the range 2 to 30 GHz using a short-pulse propagation technique and an iterative extraction based on a rational function expansion. The simple measurement technique is performed in the time domain on representative printed circuit board wiring. Broadband, fully causal transmission-line models based on these results are generated up to 50 GHz for card wiring using low loss materials including BT, Nelco N4000-13, and Nelco N4000-13SI. Simulation and modeling results highlight the need for the accurate frequency-dependent dielectric loss extraction. Signal propagation based on these results shows very good agreement with measured step and pulse time-domain excitations and provides validation of the measurement and model generation technique     

Design of complex-valued variable FIR digital filters and its application to the realization of arbitrary sampling rate conversion for complex signals

This brief studies the design of complex-valued variable digital filters (CVDFs) and their applications to the efficient arbitrary sample rate conversion for complex signals. The design of CVDFs using either the minimax or least-squares criteria is formulated as a convex optimization problem and solved using the second-order cone programming (SOCP). In addition, linear and convex quadratic inequality constraints can be readily incorporated. Design examples are given to demonstrate the effectiveness of the proposed approach.     

Cladding alignment of butted optical fibers using a diffraction alignment device (DAD) and its application to mode-spot concentricity-error measurement

A novel technique which uses the interference of diffraction patterns to establish the mechanical alignment of butted optical fibers is described, and its application to mode-spot concentricity-error measurement is demonstrated. Complete spatial alignment to within 0.2 μm of relative offset and about 7-min of arc of relative tilt is achieved. In conjunction with a straightforward optical transmission loss apparatus, the method, when applied to mode-spot concentricity-error measurements, provides good agreement with alternative techniques. Accuracies are estimated and improvements suggested.