2062 THE BELL SYSTEM TECHNICAL JOURNAL,BEPTEMBER 1969 TABLE II-ESTIMATED BENDING RADIUS Laser Beam Eatimated Acoeptable Width Bending Radius in m◆ 2a in mm a0.6334m) 14,500 0.1 14.5 0.01 0.0145 0.005 0.0018 .This estimate is obtained using equation(33)of Ref.9,and includes an allowance of 025 dB maximum loss resulting from a bend of any angle. III.FABRICATION OF SMALL WAVEGUIDES Tiny laser guides can be fabricated in the form of glass fibers. Previous work on fiber-optics for image transmission or incoherent light sensing has provided a considerable body of experience on which to build,not all of which is applicable.So-called "clad"fibers have two discrete regions of index as in Fig.1a.The n region (which car- ries little light)must be as thin as possible in image-transmitting fibers to minimize the"dead"region in the output image.For modulated laser beam transmission the cladding must be much thicker and the "core" (na of Fig.1a)much smaller to yield well-isolated single mode trans- mission. Whereas glass fibers may be used to connect repeater components and certainly are convenient as fexible connections,we can use an- other form of dielectric waveguide for miniature laser circuitry.Fig.2 n Fig.2-Planar waveguide formed using photolithographic techniques2062 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1969 TABLE II—ESTIMATED BENDING RADIUS Loser Beam EsUmatsd Acceptabla Width Bending Radiiu in m* 2a in mm (λ - 0.633 μιη) 1 14,500 0 . 1 14. 5 0.0 1 0.014 5 0.00 5 0.001 8 * This estimat e is obtained using equation (33) of Ref. 9, and includes an allowance of 02 5 dB maximu m loss resulting from a bend of any angle. ΠΙ. FABRICATION OF SMALL WAVBGTnDBS Tiny laser guides can be fabricated in the form of glass fibers. Previous work on fiber-optics for image transmission or incoherent light sensing has provided a considerable body of experience on which to build, not all of which is applicable. So-called "clad" fibers have two discrete regions of index as in Fig. la . The region (which car￾ries little light) must be as thin as possible in image-transmitting fibers to minimize the "dead" region in the output image. For modulated laser beam transmission the cladding must be much thicker and the "core" (na of Fig. la ) much smaller to yield well-isolated single mode trans￾mission. Whereas glass fibers ma y be used to connect repeater components and certainly are convenient as flexible connections, we can use an￾other form of dielectric waveguide for miniature laser circuitry. Fig. 2 Fig. 2 — Planar waveguide formed using photolithographic techniques