S.A. Hamilton

Comparison of an in-line asymmetric directional coupler modulator with distributed optical loss to other linearized electrooptic modulators

The transfer function of an external modulator is the critical factor that determines the spurious free dynamic range, signal power gain, and noise figure of a wide-band analog RF-photonic link. We present an in-line asymmetric directional coupler modulator with distributed optical loss capable of providing a transfer function linearized to the fourth order for multioctave bandwidths. This modulator compares favorably with multiple modulator suboctave linearization techniques consisting of series symmetric directional coupler and series Mach-Zehnder modulators and superoctave parallel Mach-Zehnder, and cascaded sections containing series Mach-Zehndersymmetric directional coupler modulators. The optimum bias point for the asymmetric directional coupler modulator is determined by device dimensions and material parameters with relative insensitivity to errors introduced during fabrication. Optical insertion loss imposes significant limitations on modulator performance. An implementation of an in-line asymmetric directional coupler modulator is discussed that eliminates excess loss due to fiber coupling in order to achieve a large RF power gain and competitive noise figure compared to the linearization configurations.

Polymeric in-line fiber modulator using novel processing techniques

Summary form only given. We have designed and fabricated a polymeric in-line fiber modulator using novel fabrication techniques. This device is based on evanescent coupling from a fiber half-coupler to a nonlinear polymer waveguide and takes advantage of a unique polymer deposition process.

High bandwidth traveling wave polymeric in-line fiber modulator

the p-substrate laser resistances. A power law fit shows the resistance is proportional to the (diameter)-”, where n = 1.0 for the p-substrate devices and n = 1.16 for the n-substrate devices. This exponent indicates that in both cases the resistance is dominated by contact, lateral, and spreading resistances as opposed to the vertical resistance of the mirror.2 Thus the low lateral resistance of the n-doped mirror is effective in decreasing the overall resistance of the p-substrate lasers. In addition to a lower differential resistance, the p-substrate lasers also have a lower extrapolated voltage at zero current. This voltage is usually dominated by the inversion potential required to achieve lasing at a particular wavelength, which is 1.47 V for 840 nm. Additional contributions come from nonohmic voltage drops across heterojunction barriers in the structure. While the doping profile of the mirrors is nominally symmetric within a period, growth kinetics may alter the doping profile and thus change the residual barriers differently for different heterojunctions. In summary, p-substrate VCSELs with characteristics equal to or better than similar n-substrate devices have been demonstrated. This work was supported by the United States Department of Energy under Contract DEAC04-94AL85000 and by the U.S. Air Force Phillips Laboratory. *University of New Mexico, Center for High Technology Materials, Albuquerque, New Mexico 87131-6081 **On leave from Ecole Nationale Supkrieure des Tklkcommunications, Paris, France 1. C. Lei et al., “High Performance OMVPE Grown 850 nm VCSELs on Both N-type and P-type Substrates” at the High-speed Opto-Electronics for Communications I1 conference, Snowbird, Utah, August

18 GHz traveling wave polymeric in-line fiber modulator

A radio frequency (RF) modulated optical fiber link is an attractive alternative to coaxial cables to distribute large bandwidth analog RF signals. A critical component necessary for applications such as antenna remoting is a fiber optic modulator with a large dynamic range. The dominant modulator in use today is the Mach-Zehnder which requires linearization schemes to achieve a large dynamic range. We present an alternative modulator configuration which can be tuned to an operating point where the second, third, and fourth order intermodulation products are minimized, thus yielding a large dynamic range without linearization schemes. This inline fiber modulator consists of an electro-optic (EO) waveguide deposited directly onto single mode fiber half coupler block.

Robust and sensitive GFP-based cGMP sensor for real time imaging in intact Caenorhabditis elegans

cGMP is a ubiquitous second messenger that plays a role in sensory signaling and plasticity through its regulation of ion channels and kinases. Previous studies that primarily used genetic and biochemical tools suggest that cGMP is spatiotemporally regulated in multiple sensory modalities, including light, heat, gases, salt and odor. FRET- and GFP-based cGMP sensors were developed to visualize cGMP in primary cell culture and Caenorhabditis elegans to corroborate these findings. While a FRET-based sensor has been used in an intact animal to visualize cGMP, the requirement of a multiple emission system limits its ability to be used on its own as well as with other sensors and fluorescent markers. Here, we demonstrate that WincG2, a codon-optimized version of the cpEGFP-based cGMP sensor FlincG3, can be used in C. elegans to visualize rapidly changing cGMP levels in living, behaving animals using a single fluorophore. We coexpressed the sensor with the blue light-activated guanylyl cyclases BeCyclOp and bPGC in body wall muscles and found that the rate of WincG2 fluorescence correlated with the rate of cGMP production by each cyclase. Furthermore, we show that WincG2 responds linearly upon NaCl concentration changes and SDS presentation in the cell bodies of the gustatory neuron ASER and the nociceptive phasmid neuron PHB, respectively. Intriguingly, WincG2 fluorescence in the ASER cell body decreased in response to a NaCl concentration downstep and either stopped decreasing or increased in response to a NaCl concentration upstep, which is opposite in sign to previously published calcium recordings. These results illustrate that WincG2 can be used to report rapidly changing cGMP levels in an intact animal and that the reporter can potentially reveal unexpected spatiotemporal landscapes of cGMP in response to stimuli. Author Summary cGMP is a second messenger that plays an important role in sensory signaling and neural plasticity. Previous genetic and biochemical studies indirectly suggest that cGMP is spatiotemporally regulated in neurons to modulate neural activity. While a FRET-based sensor for cGMP has been used in intact Caenorhabditis elegans to examine its spatiotemporal regulation in neurobiological processes, its use has been limited due to the complicated setup required to image this type of sensor. Here, we describe a GFP-based cGMP sensor that has been codon optimized for use in C. elegans and demonstrate that it responds robustly and reliably to endogenously changing cGMP levels. We show that the sensor responds to cGMP production by coexpressing it with blue light-activated guanylyl cyclases, and we show that it responds to NaCl and sodium dodecyl sulfate when expressed in a gustatory and nociceptive neuron, respectively. We think that this sensor can be used to investigate the spatiotemporal regulation of cGMP in neurons and its relationship to neural activity.

Progress toward an efficient traveling wave in-line fiber analog modulator

An in-line fiber modulator is an asymmetric directional coupler consisting of a continuous single mode fiber interacting through the evanescent fields with an electro-optic (EO) waveguide. Such an asymmetric coupler can be described by coupled wave theory.

High-bandwidth polymer in-line fiber modulator

We are developing a traveling electro-optic modulator for analog microwave modulated fiber optic links used in radar applications. The modulator is a polymer in-line fiber device that has a rugged and low loss interface to single mode fibers and can be engineered to provide linear modulation over a large dynamic range. In the development of the modulator we take advantage of a variety properties available in polymers. The ability to deposit a conformal electro-optic thin film is used to fill the gaps between high-frequency co-planar electrodes and thus obtain a good overlap between the electric field produced by the the microwave electrodes and the fields in the optical fiber and the electro-optic waveguide. Reactive ion etching of the electro-optic polymer is used to trim the thickness of the polymer waveguide to obtain operation at a specific wavelength. The thermo-optic effect is used to fine tune the operation point of the modulator to obtain a large dynamic range. The geometry of the modulator permits operation close to the absorption peak of the electro-optic polymer and this provides the opportunity to take advantage of the resonant enhancement of the nonlinearity in the vicinity of an absorption band.

In-line fiber electro-optic modulators: Decal deposition of patches of poled nonlinear polymers

Summary form only given. We demonstrate the application of decal technique to electro-optic modulators. It allows the deposition of high-quality, corona-poled, nonlinear polymer films onto structures without subjecting them to spin coating, large electrostatic fields, and other nonlinear polymer processing steps that may damage the underlying device. Another distinct advantage of the decal deposition for devices where the film thickness determines the optical spatial resonances, such as Fabry Perot structures or waveguides, is that the thickness of the film is determined prior to deposition on the final substrate and since many identical patches are formed it ensures reproducibility between devices. The decal deposition technique significantly simplifies the fabrication of the in-line fiber electro-optic modulators.