Karl M. Kissa

A review of lithium niobate modulators for fiber-optic communications systems

The current status of lithium-niobate external-modulator technology is reviewed with emphasis on design, fabrication, system requirements, performance, and reliability. The technology meets the performance and reliability requirements of current 2.5-, 10-, and 40-Gb/s digital communication systems, as well as CATV analog systems. The current trend in device topology is toward higher data rates and increased levels of integration. In particular, multiple high-speed modulation functions, such as 10-Gb/s return-to-zero pulse generation plus data modulation, have been achieved in a single device.

Acousto-optic tunable filters (AOTFs) for multiwavelength optical cross-connects: crosstalk considerations

Acousto-optic tunable filters (AOTF) have been investigated as a potential basis for multiwavelength cross-connects in optical networks. In this paper, we discuss crosstalk issues, some of which are common to other cross-connect technologies, and some of which are unique to the AOTF, which will determine the suitability of the AOTF technology for this application. In particular we show how the interactions between wavelength channels make the AOTF sensitive to switch architectures, we conclude that significant performance improvements will be required to diminish crosstalk if the AOTF is to be useful in any but small-size cross-connects, even when spare and wavelength dilation are used.

Simultaneous and independent switching of 8-wavelength channels with 2-nm spacing using a wavelength-dilated acoustooptic switch

We have used a wavelength-dilated acoustooptic cross-connect, for independent routing of 8-wavelength channels separated by 2 nm. The individual acoustooptic switches making up this cross-connect provide low-crosstalk switching only for channel spacings of at least 4 nm. Total loss through the dilated 2/spl times/2 crossconnect is 9 dB, and crosstalk ranges from -25 to -35 dB. Switch architectures of this kind will be needed in multiwavelength networks where channel spacings are too close to be accommodated by a single multiwavelength switch.

Modeling annealed proton-exchanged directional couplers with nonlinear diffusion theory

The coupling lengths of annealed proton exchanged directional couplers are calculated using a recently proposed nonlinear diffusion model and compared with experiment. The coupling lengths were predicted using the matrix effective refractive index (MERI) method and found to agree with experiment within measurement error for anneal times of 5 h. Some moderate amount of systematic error appears for longer anneal times; however, the new model is still far more accurate than the traditional linear diffusion model, which results in a large overestimation of the coupling length.<<ETX>>

Integrated optic frequency shifters for space heterodyne interferometry

Heterodyne interferometer laser gauges are used in space- based astronomical interferometers to very accurately measure and compensate for variations in starlight pathlength. Bragg cells have been traditionally used to generate the heterodyne signal by shifting the frequency of the laser light. This paper presents the development and qualification of an integrated optic frequency shifter (IOFS) which offers improved performance and reliability compared with Bragg cell technology. The most critical advantage of the IOFS for space applications is that it enables fiber optic metrology source integration, which facilitates the integration process and result in more reliable and compact heterodyne interferometer laser gauges.

Analysis of optical attenuators on proton-exchanged and annealed LiNbO3 waveguides

Optical attenuators for proton-exchanged and annealed waveguides in LiNbO3 are modeled by the matrix effective refractive index (MERI) method. It is shown theoretically and experimentally that an attenuation of 1.6 dB/mm can be expected for a titanium-gold metallic overlay. The theory indicates that this attenuation can be increased to nearly 4.5 dB/mm by placing a titanium dioxide layer between the waveguide surface and the metallization.