Ultralow sidelobe-level integrated acoustooptic tunable filtersusing tapered-gap surface acoustic wave directional couplers

We propose a new weighted-coupling scheme using tapered-gap surface acoustic wave directional couplers for realization of ultralow sidelobe-level integrated acoustooptic tunable filters (IAOTF's). Appropriate design analysis has been carried out for 30-mm-long filters operating at an optical wavelength of 1.55 μm in an X-cut Y-propagating LiNbO₃ substrate. New synthesized weighting functions have been used for the improvement of sidelobe level suppression over existing single-stage filters by as much as 27 dB. The -20 dB mainlobe width of the resulting IAOTF's varies from 2.7 to 3.9 nm only for the worst sidelobe levels ranging from -30.6 to -44.7 dB, respectively. It has also been shown that further suppression of sidelobe levels by 3-9 dB is possible if the filter is underdriven at 80% mode-conversion efficiency     

Resonant couplers acting as add-drop filters made withsilica-on-silicon waveguide technology

Add-drop filters are demonstrated using silica-on-silicon optical waveguide technology. This device consists of a full directional coupler subdivided by Mach-Zehnder sections. Tapering of the coupling coefficients is experimentally shown to dramatically reduce the filters' sidelobes. Only one photolithographic step is required using the silica planar waveguide technology, yielding accurate wavelength control of the filters. Excellent agreement between measurement and design was achieved     

Evaluation of absorption and emission cross sections of Er-dopedLiNbO3 for application to integrated optic amplifiers

The polarization-dependent absorption and emission spectra of the ⁴I_13/2-⁴I_15/2 transition (λ~1.5 μm) in single crystal bulk Er:LiNbO₃ have been measured. Low-temperature (10 K) measurements of the Stark split energy levels of these two manifolds indicate at least two Er³⁺ sites. McCumber theory is applied to determine the Er:LiNbO₃ absorption and emission cross sections. These values are used to calculate the gain characteristics of Er:LiNbO₃ channel waveguides. Calculations indicate that a gain of 10 dB is achievable in a waveguide of several centimeters using ~20-mW pump power     

Dynamic range of coherent analog fiber-optic links

We investigate the performance of coherent analog optical links employing amplitude modulation (AM), phase modulation (PM), and frequency modulation (FM). The performance of these coherent links is compared to that of AM direct-detection (DD) links. The signal-to-noise ratios, nonlinearities, and-spurious-free dynamic ranges (SFDR's) of the foregoing links are evaluated. We calculate the SFDR for links using DFB and Nd:YAG lasers with typical linewidths of 10 MHz and 5 kHz, respectively. The performance of PM and FM links is dominated by phase noise above a critical value of received optical power. For a linewidth of 10 MHz, and SFDR's of PM and FM links are 30 and 31 dB, respectively, for a received optical power above -27 dBm in a 1 GHz bandwidth. For a linewidth of 5 kHz, the corresponding SFDR's above a received power level of 0 dBm are 51 and 53 dB. The performance of DD and AM links is dominated by RIN above a critical value of received optical power. For a RIN level of -155 dB/Hz, the SFDR's of DD and AM links are 49 and 47 dB, respectively, for a received optical power of 10 dBm in a 1 GHz bandwidth. The SFDR's of the DD and coherent links used for transmission of subcarrier-multiplexed (SCM) signals are also derived. We evaluate target laser parameters needed by a number of different applications. For AM video and antenna remoting applications, linewidths of <1 and <3 kHz are required to use PM and FM links, respectively. For FM video, linewidths of <150 and <350 MHz are required to use PM and FM links. For SCM digital applications, linewidths of <80 and <200 MHz are required to use PM and FM links. The paper concludes with a discussion of system implementation issues, including linearization, optical frequency modulation, balanced receivers, and IF issues     

A time domain approach for avoiding crosstalk in optical blockingmultistage interconnection networks

Crosstalk in multistage interconnection networks can be avoided by ensuring that a switch is not used by two connections simultaneously, in order to support crosstalk-free communications among N inputs and N outputs, a space domain approach dilates an N×N network into one that is essentially equivalent to a 2N×2N network. Path conflicts, however may still exist in dilated networks. This paper proposes a time domain approach for avoiding crosstalk. Such an approach can be regarded as “dilating” a network in time, instead of space. More specifically, the connections that need to use the same switch are established during different time slots. This way, path conflicts are automatically avoided. The time domain dilation is useful for overcoming the limits on the network size while utilizing the high bandwidth of optical interconnects. We study the set of permutations whose crosstalk-free connections can be established in just two time slots using the time domain approach. While the space domain approach trades hardware complexity for crosstalk-free communications, the time domain approach trades time complexity. We compare the proposed time domain to the space domain approach by analyzing the tradeoffs involved in these two approaches     

Reduction of optical beat interference in SCM/WDMA networks usingpseudorandom phase modulation

A new approach is suggested to reduce the optical beat interference (OBI) in subcarrier multiplexed (SCM) wavelength-division multiple access (WDMA) networks. The idea is to deliberately introduce independent random polarization fluctuations in the electric fields transmitted on each optical channel. Random polarization results in an expanded OBI spectrum, and hence, less OBI power at the reference user receiving filter output. Electro-optic phase modulation is used to introduce polarization randomness in the fields before they are coupled into the fibers, A two-user system was simulated. Simulation results show the drastic reduction in OBI power spectral density using appropriate PN signals     

Performance and reliability enhancement for CVD tungsten polycidedCMOS transistors due to fluorine incorporation in the gate oxide

The impacts of CVD tungsten polycide (WSi_x) on MOSFET performance and reliability are studied in this letter. The WSi_x process is shown to enhance the S/D lateral extent for both N- and P-channel devices via C_GD and L_eff measurements, confirming previous suspicion. This enhanced S/D extent is found to be easily modulated by drain-to-gate bias, which is favorable for achieving both higher drive currents and higher S/D punch-through voltages than those of non-WSi_x devices. Both electron and hole mobility for the WSi_x device are also slightly higher and closer to the published data compared to the non-WSi_x case. These effects together yield about >5% improvement for nMOSFET and >10% improvement for pMOSFET in drive current at a given punch-through voltage. The channel hot-electron lifetime for the n-channel WSi_x device is about 10 times higher than that of the non-WSi_x one. These enhancements in both performance and reliability make the WSi_x device very attractive fog VLSI CMOS technologies     

Yeast sequencing reports. Isolation and sequence analysis of a gene from the linear DNA plasmid pPAC1–2 of Pichia acaciae that shows similarity to a killer toxin gene of Kluyveromyces lactis

The toxin-encoding linear plasmid systems found in Pichia acaciae and Kluyveromyces lactis yeasts appear to be quite similar, both in function and structural organization. By Southern hybridization, a linear plasmid of P. acaciae, pPac1–2, was found to hybridize to the second open reading frame (ORF2) of K. lactis plasmid pGKL1, known to encode the α and β subunits of the K. lactis toxin. A 1·7 kbp segment of pPac1–2 DNA was cloned, sequenced and shown to contain four regions of strong homology to four similarly oriented regions of K. lactis ORF2. This 1·7 kbp fragment also contained an ORF of 1473 bp that could encode a protein of ～ 55·8 kDa. Like the α subunit gene of K. lactis ORF2, a very hydrophobic region occurs at the N-terminus, perhaps representing a signal sequence for transport out of the cell. Unlike K. lactis ORF2, however, the encoded polypeptide is much smaller and lacks a recognizable domain common to chitinases. The structure of a toxin that includes the translation product of this P. acaciae ORF would likely be quite different from that of the K. lactis toxin. Analysis of the upstream region of the P. acaciae ORF revealed an upstream conserved sequence identical to that found before ORFs 8 and 9 of pGKL2. A possible hairpin loop structure, as has been described for each of the four K. lactis pGKL1 ORFs, was found just upstream of the presumed start codon. The similarity of the promoter-like elements found in the linear plasmid genes of these diverse yeasts reinforces the idea of the existence of a unique, but highly conserved, expression system for these novel plasmids. The sequence has been deposited in the GenBank data library under Accession Number U02596.     

Development of a Trans-Mucosal Controlled-Release Device for Systemic Delivery of Antianginal Drugs Pharmacokinetics and Pharmacodynamics

Oral mucosa is well-known to be one of the best routes for drug absorption. But very few R & D works have been initiated to investigate the feasibility of using this site to control drug delivery. A transmucosal controlled-release device, which is capable of achieving excellent absorption and controlled release of drugs, has been developed. The device is a tabletshaped mucoadhesive system which is composed of two layers. The upper layer is a fast-release layer and the lower layer is a sustained-release layer, and designed to be applied between buccal and gingival mucosae. Both layers are formulated from synthetic polymers to control the release of drugs.

Isosorbide dinitrate(ISDN), a well-documented antianginal drug, is known to be susceptible to extensive presystemic elimination when taken orally. It was used as the candidate drug and the systemic bioavailability was studied in human and observed to be improved by as much as 5 fold when compared to a marketed oral sustained-release tablet; On the other hand, much smaller amount of metabolites was formed. The plasma profile of ISDN has also been observed to be substantially prolonged (12 hrs as compared to less than 1 hr for sublingual tablet and spray product on the market). These observations have demonstrated that this device is capable of not only bypassing hepatic “first-pass” metabolism but also having a sustainedrelease property of prolonging the release of ISDN.

Clinical studies performed in the anginal patients for up to one year have demonstrated the therapeutic benefits of this device in achieving a substantial reduction in the frequency of anginal attacks.

This type of device was also applied to the systemic delivery of another antianginal drug, Nifedipine, by employing a formulation with longer sustained drug release property. Again, the clinical results demonstrated that a prolonged duration of therapeutic plasma concentration has also been accomplished.