Richard A. Hill

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.

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.