2068 THE BELL SYSTEM TECHNICAL JOURNAL,SEPTEMBER 1969 resistance filter.Alternatively,a multiple-line grating could be used in place of the resonant cavities as the reflecting element to refectf only,and the output positions of fa and f,fe would interchange. In filters of this kind the intrinsic loss of the substrate is of course important.Good quality glasses have bulk losses as low as 1 dB per m, which corresponds to an intrinsic of about 30 million;this would allow filters with band widths of a few hundred megacycles in the visible region;therefore,intrinsic substrate loss should not be too limiting. VIII.CONCLUSIONS This paper outlines a prospect for laser circuitry and devices which, if realized,would have many attractive features.Photolithographic processes would simplify reproducing complicated circuits,once the original was developed.Small size would facilitate isolating the com- pleted circuit assembly from thermal,mechanical,and acoustic am- bient changes.For communication purposes,low laser power levels are adequate so that the heat to be dissipated hopefully will not be large.In the very small laser beam cross sections,nonlinear effects needed for modulation and frequency changing should be achievable with only a few volts of drive. Finally,a word of caution is needed.Work is just beginning in the directions indicated,and we have identified goals rather than accom- plishments.We recognize these are difficult goals;but we believe they are worth the serious effort required to achieve them. IX.ACKNOWLEDGEMENT The helpful comments of J.K.Galt and numerous other colleagues are gratefully acknowledged. REFERENCES 1.Marcatili,E.A.J.."Dielectric Rectangular Waveguide and Directional Coupler for Integrated Optics,"B.8.TJ.,this issue,pp.2071-2102. 2.Goell,J.E."A Circular-Harmonic Computer Analysis of Rectangular Dielectric Waveguidcs,"B.S.TJ.,this issuc,pp.2133-2160. 3.Marcatili,E.A.J.,"Bends in Optical Dielectric Guides,"B.S.TJ.this issue, pp.2103-2132. 4.Schlosser,W.,and Unger,H.G.,"Partially Filled Waveguides and Surface Waveguides of Rectangular Cross Section."Advances in Microwaves,New York:Academic Press,1966,pp.319-387. 5.Miller,S.E.,"Light Propagation in Generalized Lens-like Media,"BS.TJ. 44,No.9(November1965),pp.2017-2064. 6.Pierce,J.R.,"Modes in Sequences of Lenses,"Proc.Nat.Acad.Sci.,47,No.11 (November1981),pp.1808-13.2068 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1969 resistance filter. Alternatively, a multiple-line grating could be used in place of the resonant cavities as the reflecting element to reflect f„ only, and the output positions of fa and ft,, fc would interchange. In filters of this kind the intrinsic loss of the substrate is of course important. Good quality glasses have bulk losses as low as 1 dB per m, which corresponds to an intrinsic Q of about 30 million; this would allow filters with band widths of a few hundred megacycles in the visible region; therefore, intrinsic substrate loss should not be too limiting. VIII. CONCLU.<*IONS This paper outlines a prospect for laser circuitry and devices which, if realized, would have many attractive features. Photolithographic processes would simplify reproducing complicated circuits, once the original was developed. Small size would facilitate isolating the com￾pleted circuit assembly from thermal, mechanical, and acoustic am￾bient changes. For communication purposes, low laser power levels are adequate so tha t the heat to be dissipated hopefully will not be large. In the very small laser beam cross sections, nonlinear effects needed for modulation and frequency changing should be achievable with only a few volts of drive. Finally, a word of caution is needed. Work is just beginning in the directions indicated, and we have identified goals rather than accom￾plishments. We recognize these are diflBcult goals; but we believe they are worth the serious effort required to achieve them. IX. ACKNOWLEDGEMENT The helpful comments of J. K. Gait and numerous other colleagues are gratefully acknowledged. REFERE^iCES 1. Marcatili, E. A. J., "Dielectric Rectangular Waveguido and Directional Coupler for Integrated Opücs," B5.TJ. , this issue, pp. 2071-2102. 2. Goell, J. E., "A Circular-Harmonic Compute r Analysis of Rectangular Dielectric Waveguides," B.S.TJ., this issue, pp. 2133-2160. 3. Marcatili, E. A. J., "Bends in Optical Dielectric Guides," BS.TJ. , this issue, pp.2103-2132. 4. Schlosser, W., and Unger, H. G., "Partially Filled Waveguide s and Surface Waveguide s of Rectangular Cross Section." Advances in Microwaves, Ne w York: Academic Press, 1966, pp. 319-387. 5. Miller, S. E., "Light Propagation in Generalized Lens-like Media," BS.TJ. , U, No . 9 (Novembe r 1966), pp. 2017-2064. 6. Pierce, J. R., "Mode s in Sequences of Lenses," Proc. Nat. Acad. Sei., 47. No . 11 (Novembe r 1961), pp. 1808-13