Paul Kolodner

Optical measurement of the Soret coefficient of ethanol/water solutions

We have employed a laser‐beam‐deflection technique to measure the Soret coefficient of ethanol/water solutions with ethanol weight fractions ranging from 0.02 to 0.39, over the temperature range 10 to 40 °C. This technique also allows precise determination of the mass‐diffusion coefficient and of the index of refraction. These results have permitted us to obtain a quantitative understanding of recent experiments on oscillatory traveling‐wave convection in binary fluid mixtures.

Wavelength-selective 1/spl times/K switches using free-space optics and MEMS micromirrors: theory, design, and implementation

The design and performance of several generations of wavelength-selective 1/spl times/K switches are reviewed. These optical subsystems combine the functionality of a demultiplexer, per-wavelength switch, and multiplexer in a single, low-loss unit. Free-space optics is utilized for spatially separating the constituent wavelength division multiplexing (WDM) channels as well as for space-division switching from an input optical fiber to one of K output fibers (1/spl times/K functionality) on a channel-by-channel basis using a microelectromechanical system (MEMS) micromirror array. The switches are designed to provide wide and flat passbands for minimal signal distortion. They can also provide spectral equalization and channel blocking functionality, making them well suited for use in transparent WDM optical mesh networks.

Low-cost, low-loss microlens arrays fabricated by soft-lithography replication process

This letter describes a soft lithographic approach for fabricating low-cost, low-loss microlens arrays. An accurate negative reproduction (stamp) of an existing high-quality lens surface (master) is made by thermally curing a prepolymer to a silicone elastomer against the master. Fabricating the stamp on a rigid backing plate minimizes distortion of its surface relief. Dispensing a liquid photocurable epoxy loaded to high weight percent with functionalized silica nanoparticles into the features of relief on the mold and then curing this material with UV radiation against a quartz substrate generates a replica lens array. The physical and optical characteristics of the resulting lenses suggest that the approach will be suitable for a range of applications in micro and integrated optics.

Molecular dissociation of SF6 by ultra-short CO2 laser pulses☆

Abstract We have measured the absolute dissociation probability of SF6 gas irradiated by CO2 laser pulses varying in duration from 0.5 nsec to 100 nsec. We find a threshold for dissociation of ≃ 1.4 J/cm2, independent of pulse duration. For fixed energy density, the dissociation probability increases as the pulse duration decreases, but not nearly to the degree expected from theory. We have also determined the dissociation probability in the ν2 + ν6 combination band and find it to be 103 times less than in the ν3 band, in contradiction to some conclusions recently reported by Ambartzumian et al. The dissociation mechanism takes place without collisions, and if collisions occur, they tend to be detrimental to the dissociation rate.

1100 x 1100 port MEMS-based optical crossconnect with 4-dB maximum loss

We present a microelectromechanical systems-based beam steering optical crossconnect switch core with port count exceeding 1100, featuring mean fiber-to-fiber insertion loss of 2.1 dB and maximum insertion loss of 4.0 dB across all possible connections. The challenge of efficient measurement and optimization of all possible connections was met by an automated testing facility. The resulting connections feature optical loss stability of better than 0.2 dB over days, without any feedback control under normal laboratory conditions.

Microscopic fluorescent imaging of surface temperature profiles with 0.01 °C resolution

We have exploited the temperature‐dependent fluorescence quantum efficiency in europium thenoyltrifluoroacetonate (EuTTA) to make high‐resolution, noncontact temperature measurements on the surface of an integrated circuit chip. The EuTTA is spun onto the chip in a polymer film. The chip is illuminated with long‐wave UV light, and the orange fluorescence is imaged onto a charge‐coupled‐device (CCD) camera. Digital image processing completely removes the optical features in the image, leaving a purely thermal map of the surface temperature profile with a measured temperature resolution of better than 0.01 °C and a spatial resolution of 15 μm. With a different camera and optics, 1‐μm resolution should be possible, allowing thermal imaging of the smallest high‐speed integrated circuits.

Remote thermal imaging with 0.7‐μm spatial resolution using temperature‐dependent fluorescent thin flims

We have applied the recently developed technique of fluorescent thermal imaging to measure the surface temperature profile of a test sample with unprecedented temperature and spatial resolution. A particularly simple temperature profile was produced by passing an electrical current through a long, unresolvably thin metal stripe on a glass substrate. The sample was coated with a fluorescent thin film whose fluorescence efficiency decreases with increasing temperature. Digital processing of the fluorescence image produces a quantitative surface temperature map with simultaneous temperature and spatial resolutions of 0.08 °C and 0.7 μm, respectively. This spatial resolution approaches for the first time the dimensions of state‐of‐the‐art integrated circuits. Extension of this technique into the nanosecond time domain will allow new advances in the fields of photothermal microscopy, integrated circuit diagnostics, and thermal transport measurements.

1296-port MEMS transparent optical crossconnect with 2.07 petabit/s switch capacity

A 1296-port MEMS transparent optical crossconnect with 5.1dB/spl plusmn/1.1dB insertion loss at 1550 nm is reported. Measured worst-case optical crosstalk in a fabric was n38 dB and nominal switching rise/fall times were 5 ms. A 2.07 petabit/s switch capacity was verified upon cross-connecting a forty-channel by 40 Gb/s DWDM data stream through a prototype fabric.

Oscillatory convection in viscoelastic DNA suspensions

Recent experiments on the response of individual, long DNA strands to externally-applied tension and fluid shear suggest that semi-dilute, aqueous suspensions of these molecules should behave as viscoelastic fluids with an elastic relaxation time of seconds and a viscosity comparable to that of water. I present experimental observations of the convective flow produced by heating a horizontal layer of such viscoelastic fluids from below, in a long, narrow, annular geometry. The convection patterns take the form of spatially-localized standing and travelling waves which exhibit small amplitudes and extremely long oscillation periods. The threshold Rayleigh numbers for the onset of oscillations are lower than the value measured for steady convection in a Newtonian fluid in the same apparatus and exhibit a decreasing trend with increasing elastic relaxation time. This behavior agrees with the predictions of theories of the linear instability of viscoelastic convection. However, the low frequencies are in gross quantitative disagreement with these analyses.

Wavelength-selective 1/spl times/4 switch for 128 WDM channels at 50 GHz spacing

We present a reconfigurable wavelength-selective switch that independently distributes 128 input WDM channels to four output ports. The switch is based on bulk optics and MEMS micro-mirrors, exhibits <5 dB insertion loss and flat-top pass-bands, and is well suited for transparent switching of 10 Gb/s signals.