Green's function for examples with an isotropic media is obtained using the image-coefficient method. The method is based on the boundary conditions and the reciprocity relation. Using this Green's function and solving directly the charge distribution on the strip, the line capacitances per unit length of a microstrip and of an electrooptic light modulator are obtained. High accuracy of this method is demonstrated by comparing the present results with the results obtained using the conformal mapping and with other data appeared in the literature. The charge distributions are also illustrated. Of particular interest is the effective filling fraction of the dielectric material, which depends mainly on the shape ratio and only slightly on the relative dielectric constant. The effective filling fractions are tabulated for the microstrip with a homogeneous dielectric substrate.

Analysis of the Microstrip and the Electrooptic Light Modulator

Optical communications—that is, the transmission of information by means of light—has been a subject of interest to Bell Labs for a long time, but the invention of the laser made it a concern of considerable and immediate importance, providing the impetus for a range of studies on possible transmission media, principles, methods, and components for systems. This survey attempts to tell how the work started and grew at Bell Labs, in addition to providing references to the many papers that describe the work in detail.

Optics at bell laboratories-optical communications.

LiTaO3 optical modulators have been developed using the technique of self-compensation for therma stability. By using two crystals in cascade, with optic axes 180° apart, and a half-wave plate between them with axis at 45°, the birefringence of each crystal is equal but opposite and there is no net change in birefringence with temperature. Aside from thermal stability, the optical modulator described damps out mechanical resonances caused by the piezoelectric properties of the crystals, and its thin-film substrate mounting is applicable to wideband modulation. Experimental measurements show that 95% modulation depth can be attained over a 25° C temperature range with virtually no change in the amplitude or phase of the modulated signal.

Fabrication of a lithium tantalate temperature-stabilized optical modulator.

Candidate wide-bandwidth (1-Gbit/s) satellite laser communications systems are compared on two different bases. First, a comparison is made with projected component technology to establish relative performance between the various approaches based on the fundamental system parameters. From this comparison it appears that the CO 2 (10.6-μm) system offers a signal-to-noise advantage over the Nd:YAG (1.06-μm) or doubled Nd:YAG (0.53- μm) system for a comparable satellite burden. Second, a comparison is made based upon the concept that launch cost for equivalent systems comprises an optimizing criterion. From this comparison it appears that the launch costs for the CO 2 and doubled Nd:YAG systems can be similar, but the latter is very sensitive to the projected weight of a large lightweight "photon bucket" receiving aperture. In general, the relative deficiency in signal-to-noise ratio for the Nd:YAG system can only be accommodated through adoption of an open-loop pointing system with an accuracy of 1 μrad or less, as compared to a closed-loop pointing system with relaxed accuracy for the CO 2 system. The most critical technology problem for the CO 2 system is that of Doppler compensation. These and other critical technologies for both approaches are listed and discussed.

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Wide-band laser communications in space

This short paper describes a proposed structure of a broad-band electrooptical modulator and an application of existing microstrip analysis programs to determine dimensions of the structure for a broad-band property. Results of numerical computations indicate that it is possible to obtain a broad-band modulator by using LiNbO/sub 3/ or LiTaO/sub 3/.

Application of Microstrip Analysis to the Design of a Broad-Band Electrooptical Modulator (Short Papers)

An optical communications system is described which is capable of transmission and detection of 1-Gbċs-1pulse-code modulation (PCM) word patterns. Modulation of an argon laser beam is obtained with a lithium tantalate (LiTaO 3 ) modulator rod using a traveling-wave interaction. The high-speed electrical modulation signal is obtained by a multiplexing of four separate information channels.

G. White

Papers

A one-gigabit-per-second optical PCM communications system