All-fiber wavelength-tunable acoustooptic switches based on intermodal coupling in fibers

In this paper, we demonstrate a novel all-fiber wavelength-tunable acoustooptic switch utilizing intermodal coupling in a two-mode fiber (TMF). Its all-fiber configuration consisting of a fiber acoustooptic tunable filter and a mode-selective coupler results in the low loss (<2 dB) operation. The operating bandwidth >50 nm, the switching time of 40 /spl mu/sec, and the crosstalk of 20 dB were achieved. By controlling the design parameters of the two-mode fiber, the 3-dB bandwidth of the switched signal was varied from 2.5 nm to >35 nm. A novel all-fiber dynamic optical add-drop multiplexer is also demonstrated using two acoustooptic switches in series.     

High-finesse laterally coupled organic-inorganic hybrid polymer microring resonators for VLSI photonics

We produced laterally coupled optical microring resonators having high finesse (F/spl sime/17 at 1.5-/spl mu/m wavelength) using a two-step patterning technique based on optical photolithography. The technique used allows us to separately control the height of both ring and port waveguides and structure submicrometer gaps. The resonance spectrum of microrings with radii of 50 /spl mu/m made of an organic-inorganic hybrid polymer have an extinction ratio of about 12 dB and a filter bandwidth /spl delta//spl lambda//spl sime/0.28 nm (full-width at half-maximum) at a wavelength /spl lambda/=1547.78 nm. We show that the resonances can be thermooptically tuned by 0.2 nm//spl deg/C, thus allowing us to modulate the transmission of the through port signal.     

Electron beam direct-write tunable polymeric waveguide grating filter

We report a tunable electron beam direct-write polymeric waveguide Bragg grating filter based on a negative tone epoxy, The waveguide filter, with a 5-mm-long first-order grating, exhibits a transmission peak of -27 dB and a 3-dB bandwidth of /spl sim/0.8 nm, and there is an excellent agreement between experimental data and simulation results. The temperature response of the filter is also characterized. The rate of change of refractive index dn/dT is /spl sim/ -1.8 /spl times/ 10/sup -4///spl deg/1C at 1550-nm wavelength for both transverse electric and transverse magnetic polarizations, and the rate of change of peak wavelength d/spl lambda//dT is /spl sim/ -0.14 nm//spl deg/C. The tuning performance is comparable to other grating devices fabricated using multiple processing steps.     

Miniature broadband bandpass filters using double-layer coupled stripline resonators

A novel double-layer coupled stripline resonator structure is introduced to realize miniature broadband bandpass filters. Filters with relative bandwidth up to 60% and size less than /spl lambda//8/spl times//spl lambda//8/spl times/h (/spl lambda/ is wavelength at the midband frequency; h is the substrate height, which is much smaller than /spl lambda//8) can be fulfilled using such resonators. Two possible filter configurations are proposed in this paper: combline and interdigital. The filter synthesis procedure follows the classical coupling matrix approach that generates very good initial responses. Optimization by the mode-matching method and fine tuning in Ansoft's High Frequency Structure Simulator are combined to improve the filter performance. Two filter design examples are given to validate the feasibility. Low temperature co-fired ceramic (LTCC) technology is employed to manufacture the filters. Experimental results of the two manufactured filters are presented. The effects of LTCC manufacturing procedure on the filter performance are also discussed.     

Fabrication of ultrathin and highly flexible InP-based membranes for microoptoelectromechanical systems at 1.55 /spl mu/m

In this letter, tunable microcavities have been fabricated to evaluate their tunability in dependence on the membrane thickness. The membrane thickness has been decreased from 615 nm down to a record thickness of 123 nm yielding in a maximum mechanical tunability of 15.15 nm/V/sup 2/. Furthermore, a three-period /spl lambda//4 InP/air-gap high reflective mirror (R > 99.8% at 1.55 /spl mu/m) with a record wide stopband of more than 1100 nm has been fabricated. These results are achieved thanks to specific metal-organic vapor-phase epitaxy growth parameters.     

A miniaturized net-type microstrip bandpass filter using /spl lambda//8 resonators

A novel miniaturized three-pole net-type bandpass filter using /spl lambda//8 resonators has been proposed. Asymmetric frequency characteristics of this filter exhibit a single transmission zero on the lower side of the passband at finite frequency, which is attributed to multi-path effect. Full-wave simulator IE3D is used to extract the coupling coefficients and external quality factor in order to determine the physical dimensions of this filter. The measured results are in good agreement with the simulated predictions. The overall size of the filter is only about 0.22/spl lambda//sub g/ by 0.2 /spl lambda//sub g/. As a result, the filter has not only a small size but also a wider upper stopband up to 6.5 f/sub 0/.     

Uniplanar compact wideband bandstop filter

A uniplanar wideband bandstop filter is proposed using two bent open-end stubs. The proposed filter consists of the bent connecting line of /spl lambda//sub g//2 between two bent /spl lambda//sub g//4 stubs, which results in wideband design with a rejection bandwidth of 90% at 2.05 GHz. Further, the connecting line and stubs have the same characteristic impedance. The proposed filter compared to the conventional one is also more compact. The area of the novel filter is (/spl lambda//sub g//4)/sup 2/ at the center frequency of the stopband, while the area of the filter realized using the nonbent stubs and connecting line is 2(/spl lambda//sub g//4)/sup 2/ for the same stopband characteristics.     

Compact microstrip bandpass filter with two transmission zeros using a stub-tapped half-wavelength line resonator

A compact microstrip bandpass filter is developed using a half-wavelength (/spl lambda//2) transmission line resonator with a pair of tap-connected open-ended stubs. Such paired stubs with total length of about /spl lambda//2 constructs an equivalent line resonator. Together with two separated /spl lambda//4 line resonators, the three transmission poles can be achieved inside the passband. Meanwhile, two stub lengths are adjusted slightly longer and shorter than /spl lambda//4 to realize the two transmission zeros at both low and high rejection bands. Further, the long tapped-stub is kept wider than its short counterpart to improve the low rejection behavior. A filter sample is designed and fabricated to provide an experimental verification on the proposed filter.     

On the development of a multifunction millimeter-wave sensor for displacement sensing and low-velocity measurement

A new multifunction millimeter-wave sensor operating at 35.6 GHz has been developed and demonstrated for measurement of displacement and low velocity. The sensor was realized using microwave integrated circuits and monolithic microwave integrated circuits. Measured displacement results show unprecedented resolution of only 10 /spl mu/m, which is approximately equivalent to /spl lambda//sub 0//840 in terms of free-space wavelength /spl lambda//sub 0/, and maximum error of only 27 /spl mu/m. A polynomial curve-fitting method was also developed for correcting the error. Results indicate that multiple reflections dominate the displacement measurement error. The sensor was able to measure speed as low as 27.7 mm/s, corresponding to 6.6 Hz in Doppler frequency, with an estimated velocity resolution of 2.7 mm/s. A digital quadrature mixer (DQM) was configured as a phase-detecting processor, employing a quadrature sampling signal-processing technique, to overcome the nonlinear phase response problem of a conventional analog quadrature mixer. The DQM also enables low Doppler frequency to be measured with high resolution. The Doppler frequency was determined by applying linear regression on the phase sampled within only fractions of the period of the Doppler frequency. Short-term stability of the microwave signal source was also considered to predict its effect on measurement accuracy.     

Narrow-band light source with acoustooptic tunable filter for optical low-coherence reflectometry

An electrically-tunable narrow-band light source with no moving parts is constructed for jaggedness-free optical low coherence reflectometry. The source incorporates a double-path acoustooptic tunable bandpass filter module whose two passbands automatically agree to within 0.2 nm during wavelength tuning from 1529-1568 nm. The source emits narrow-band light with an FWHM of 1.8/spl plusmn/0.1 nm, a power of >0 dBm and a suppressed background spectrum. The entire wavelength range can be swept electrically within 100 ms by using a variable RF source.     

Complex-coupled quantum cascade distributed-feedback laser

Quantum-cascade distributed-feedback lasers (QCDFB) with a grating close to the active region are reported. Feedback is provided by the grating in a refractive index-dominated coupling scheme. Reliable single-mode emission at /spl lambda//sub cm//spl ap/5.4 /spl mu/m with a side-mode suppression ratio (SMSR) /spl ap/30 dB is observed. The laser is continuously tunable over 40 nm with a coefficient of /spl Delta//spl lambda///spl Delta/T/spl ap/0.37 nm/K in the temperature range from 200 K to 300 K. Comparison with Fabry-Perot QC lasers shows an overall improved performance of QC-DFB lasers.     

Compact microstrip bandpass filter with two transmission zeros

A novel compact microstrip bandpass filter is proposed using a half-wavelength (/spl lambda//2) microstrip line resonator and an end-coupling resonator. The filter has two transmission zeros at both low and high rejection bands, as well as low insertion loss and compact design by giving two paths to the input signals. A demonstration filter has been designed and tested. Theoretical and experimental results are presented.     

SiC thin-film Fabry-Perot interferometer for fiber-optic temperature sensor

Polycrystalline SiC grown on single-crystal sapphire substrates have been investigated as thin-film Fabry-Perot interferometers for fiber-optic temperature measurements in harsh temperatures. SiC-based temperature sensors are compact in size, robust, and stable at high temperatures, making them one of the best choices for high temperature applications. SiC films with thickness of about 0.5-2.0 /spl mu/m were grown at 1100/spl deg/C by chemical vapor deposition (CVD) with trimethylsilane. The effect of operating temperature on the shifts in resonance minima, /spl Delta//spl lambda//sub m/, of the SiC/sapphire substrate has been measured in the visible-infrared wavelength range. A temperature sensitivity of 1.9/spl times/10/sup -5///spl deg/C is calculated using the minimum at /spl sim/700 nm. Using a white, broadband light source, a temperature accuracy of /spl plusmn/3.5/spl deg/C is obtained over the temperature range of 22/spl deg/C to 540/spl deg/C.     

Measurement of directional and spectral signatures of light reflectance by snow

The bidirectional reflection distribution functions (BRDF) of snow have been measured at high spectral resolution at various locations in Finland (Vuotso, Hyytia/spl uml/la/spl uml/, Sodankyla/spl uml/, Kilpisja/spl uml/rvi, Rovaniemi, Sodankyla/spl uml/ again). The measured snow types include fresh, new snow, both needle-like and hexagonal flakes, old, loose snow, and melting and refrozen snow. All snow types show strong forward scattering as previously reported, but there also appeared to be some enhancement in the backward directions that has not been reported in much detail. The grain size gives a clear signal at near-infrared, which was observed previously. A nontrivial dependence on grain shape was also observed, which has been ignored previously. Melting snow has a distinct forward feature not observable in dry snow: first a maximum in specular direction, a minimum after that, and then again brightening forward. There is a spectral signal at 1250/1350 nm that could be useful for wetness recovery in particular, even when the topography or BRDF model is not known. Density dependence was observed, partially contradicting earlier measurements. Microtopographic roughness slightly increases backscattering as expected. Much more detailed information about snow could be observed using hyperspectral, multidirectional remote sensing techniques than with current instruments. Measurements of more snow types need to be taken, especially dirty snow, snow/vegetation composites, and rough snow surfaces.     

Analysis and optimization of Q-switched operation of a Tm/sup 3+/-doped silica fiber laser operating at 2 /spl mu/m

Analysis and operation of a Q-switched Tm/sup 3+/-doped silica fiber laser in the wavelength region of 2 /spl mu/m is described when pumped with a Nd:YAG laser operating at 1.319 /spl mu/m. A large core of 17-/spl mu/m diameter was used to increase the laser gain volume, allowing high pump-power absorption and an output of high pulse energy and peak power. An acoustooptic modulator was used as Q-switching element and operated at repetition rates up to 30 kHz. A maximum peak output power of greater than 4 kW and a pulse duration at full-width at half-maximum of 150 ns has been obtained. This is the first report of high peak-power operation of the thulium-doped silica fiber laser.     

1 Gb/s system performance of an integrated,polarization-independent, acoustically-tunable optical filter

The first system demonstration of a polarization-independent acoustooptic filter centered at 1500 nm with a narrow bandpass (1.3 nm) and broad continuous tuning range (145 nm) is reported. It is shown that filtered transmission of 990-Mb/s pseudorandom data incurs less than 1 dB of additional noise penalty, less than 0.5 dB of which is dependent on the signal state of polarization. In addition, this versatile polarization-diversity configuration allows for multiple-channel selection and operation as a 2×2 wavelength-channel switch     

A new COG technique using low temperature solder bumps for LCD driver IC packaging applications

A new chip on glass (COG) technique using flip chip solder joining technology has been developed for excellent resolution and high quality liquid crystal display (LCD) panels. The flip chip solder joining technology has several advantages over the anisotropic conductive film (ACF) bonding technology: finer pitch capability, better electrical performance, and easier reworkability. Conventional solders such as eutectic Pb-Sn and Pb-5Sn require high temperature processing which can lead to degradation of the liquid crystal or the color filter in LCD modules. Thus it is desirable to develop a low temperature process below 160/spl deg/C using solders with low melting temperatures for this application. In our case, we used eutectic 58 wt%Bi-42 wt%Sn solder for this purpose. Using the eutectic Bi-Sn solder bumps of 50-80/spl mu/m pitch sizes, an ultrafine interconnection between the IC and glass substrate was successfully made at or below 160/spl deg/C. The average contact resistance of the Bi-Sn solder joints was 19m/spl Omega/ per bump, which is much lower than the contact resistance of conventional ACF bonding technologies. The contact resistance of the underfilled Bi-Sn solder joints did not change during a hot humidity test. We demonstrate that the COG technique using low temperature solder joints can be applied to advanced LCDs that lead to require excellent quality, high resolution, and low power consumption.     

Low-loss LTCC cavity filters using system-on-package technology at 60 GHz

In this paper, three-dimensional (3-D) integrated cavity resonators and filters consisting of via walls are demonstrated as a system-on-package compact solution for RF front-end modules at 60 GHz using low-temperature cofired ceramic (LTCC) technology. Slot excitation with a /spl lambda/g/4 open stub has been applied and evaluated in terms of experimental performance and fabrication accuracy and simplicity. The strongly coupled cavity resonator provides an insertion loss <0.84 dB, a return loss >20.6 dB over the passband (/spl sim/0.89 GHz), and a 3-dB bandwidth of approximately 1.5% (/spl sim/0.89 GHz), as well as a simple fabrication of the feeding structure (since it does not require to drill vias to implement the feeding structure). The design has been utilized to develop a 3-D low-loss three-pole bandpass filter for 60-GHz wireless local area network narrow-band (/spl sim/1 GHz) applications. This is the first demonstration entirely authenticated by measurement data for 60-GHz 3-D LTCC cavity filters. This filter exhibits an insertion loss of 2.14 dB at the center frequency of 58.7 GHz, a rejection >16.4 dB over the passband, and a 3-dB bandwidth approximately 1.38% (/spl sim/0.9 GHz).     

Waveguide microcavity based on photonic microstructures

A waveguide based microcavity exhibiting a quality factor Q/spl ap/2500 has been realized by incorporating a /spl lambda//4 phase shift into a 1-D photonic microstructure. The microstructure has an overall length of 3 /spl mu/m, consists of a deeply etched grating with very narrow (75 nm) air-gaps and exhibits a third-order stop band in the 800-900 nm wavelength regime. A comparison between measurement and simulation suggests that there is a thin (approximately 18 nm) skin of oxidized material at the etched semiconductor-air interfaces.     

Breaking the feedback loop of a class of /spl Sigma//spl Delta/ A/D converters

/spl Sigma//spl Delta/ modulation is the currently successful technique used to perform high resolution analog-to-digital conversion. In spite of its practical success, its theoretical signal analysis has remained limited because a /spl Sigma//spl Delta/ modulator contains of a feedback loop that includes a nonlinear operation, i.e., the amplitude discretization or quantization. The feedback allows us to use oversampling to compensate for the limitations of the quantizer in resolution and in precision, which are typical of analog circuits. However, because of the lack of signal analysis, it is still not clear how much resolution of conversion can be gained as a function of the oversampling. We show that for a large class of /spl Sigma//spl Delta/ modulators, the feedback loop theoretically yields an equivalent feedforward signal flow graph, at least for constant inputs. This is possible thanks to remarkable modulo properties of these modulators. This equivalence can be asymptotically extrapolated to time-varying inputs with increasing oversampling. Although the exact components of the equivalent graph are not currently known in general, the theoretical structure of the feedforward graph is sufficient to point out misconceptions in the current knowledge on the final resolution of an nth-order /spl Sigma//spl Delta/ modulator. Specifically, except when the modulator is "ideal", the global resolution of conversion increases by n bits per octave of oversampling, instead of the currently believed rate of n+(1/2) bits/octave.