IIA-4 GaAs p+n-n+directional couplers and electrooptic switches
1
1250 IEEE TRANSACTIONS ON ELECTRON DEVICES, NOVEMBER 1976 wiched between an A1.15Ga.85As lower layer and a 6.6 pm wide Al.15Ga.ssAsstrip on top, the psuedo index technique yields Rmin k 10 mil. The approachby Butler, et al., shows that low loss is obtained only if R 2 400 mil. In one set of measurements we have observed wave-guides in which the radius of curvature was varied between 40 and 400 mil. Our results are in agreement with the larger radius of curvature. We have also investigated waveguidw with abrupt small angle deviations (i.e., tilt). The angle, 6, is varied between .2O and 2O corresponding to an equivalent radilks of curvature of 5000 to 500 mil. We observe a steady degradaticn in the lateral confinement and the amount of guided light as 6 increases. The power is attenuated by l/e for 0.9' 5 6 I 1.2O. In conclusion, these measurements and our calculations confirin that although the stripline structure is advantageous for low 101s waveguides because of the inherent large bend radius, it is 1-111- suitable for the complex optical circuits that might be requircd for integrated optics. IIA-4 GaAs p+n-n+ Directional Couplers and Electroopt ic Switched-F. J. Leonberger, J. P. Donnelly andC. 0. Bozlcr, Lincoln Laboratory, Massachusetts Institute of Technology, Lexington, MA 02173. Two types of GaAs directional couplers and an electrooptic directional-coupler switchhave been successfully fabricated arid evaluated at 1.06 pm for use as IOC components. Thesedevic'3s were made from low-loss (-1 cm-l at 1.06 pm) single-mode p+n-n+ three-dimensional waveguides.2 Directional couplers with coupling lengths (for maximum power transfer) from 4 ;o 24 mm have been evaluated, and the dependence of the couplillg length on thedevice dimensions has been characterized. Bo';h types of couplers have exhibited 96% power coupling and ha'le shown a negligible (-0.1 dB) insertion loss relative to a single guide of the same dimensions as one of the coupled guides. The switch is characterized by 212 dB power isolation in both the switched and unswitched states and by anearly constant poww output. Specifically, at zero bias 96% of the power emerges from the coupled guide, while at the maximum switching voltage (!io V), 94% of the power exits fromthe input guide; the total outp It power from the switch varies 5 0.2 dB in this 0-50 V bias range. One type of directional coupler, the stripline coupler, was fabricated by formingtwo p+n-n+ optical striplines with a 3 Mrn spacing and the other type, the channel-stop coupler, used two p+n-n+ channel-stop strip guides, also with a 3 pm spacing. Both structures consist of an n+ (1 X lOl8 ~m-~) substrate, an 11- ~m-~) epitaxial guiding layer and ion-implanted p+ (2 - 3 X 1Ol8 ~m-~) regions to laterally confine the light. Multiple- energy Be+ implantations3 were used to yield regions of uniform concentration (and thus of uniform refractive index) to a depth of -2 pm. In the stripline coupler the p+ regions are formed into ribs and the light is guided beneath them. For guide widths of LO and 15 pm, coupling lengths of 9 and 22 mm, respectively, were measured for a 7 pm thick epitaxial layer. As the initial epitaw- ial-layer thickness increased from 5.5 to 8 pm, the coupling length was found to decrease about 20%. The channel-stop couplw, which has a planar structure, has three p+ regions: two that 1 ie along the outside edges of the nuidina channels and one that lies The optical switching was achieved in a channel-stop coupler by reverse-biasing the p+n- junction adjacent to one of t h e channels. The applied field destroys the phase synchronism of the two guides viathe electrooptic effect and therefore changes both the coupling coefficient and the maximum power coupled. In this respect it is similar to the switch formed with metal-gap waveguide^.^ However, with this channel-stop switch, there is essentially no power loss at switching biases. The 12 dB switching with nearly constant total power wasobtained with 10 pm guides, spaced by 3 pmin a sample 7.8 mm long. Preliminary evaluation of channel-stop devices at 9350 .fi in- dicates a negligible (-0.1 dB) insertion loss relative to a single guide but a longer coupling length than obtained at 1.06 pm. Further investigation of these devices is planned, including a study of the effects of crystal orientation and bias configurations on switching performance. vol. 27, p. 202,1975. J. C. Campbell, F. A. Blum, D. W. Shaw, and K. L. Lawley, Appl. Phys. Lett., IIA-5 A Simple Beam-Splitter for Integrated Optics Ex- perimental Realization and Theory1-D. Vincent and J. W. Y. Lit, Laboratoire de Recherches en Optique et Laser Depart- ment de Physique, Universite Laval, Quebec, P.Q. Canada, G1K 7P4. A passive thin-film beam splitter hasbeen made, based on the principle that the effective index of a mode travelingin a thin- film optical waveguide varies with the thickness of the guide. The effect produced resembles that of total internal reflection in bulk optics or the tunneling effect across a potential barrier in quan- tum mechanics. The individual intensities of the two beams can be varied, from100%transmission to100%reflection. Thus the device can act as a mirror as well. Simple analytical expressions have been found for the coefficients of reflection and transmis- sion. The theoretical analysis is based on the WKBJ approxi- mation method, which applies very well to our case, because the rate of change in the effective index is very small. The effects of different physical parameters will also be discussed.Particular attention is drawn to the fact that the experimental method is extremely simple, and that most laboratories with thin-film de- position facilities should have no difficulty in making the de- vice. Research supported in part by the Defense Research Board of Canada. IIA-6 An Efficient Amplitude Modulator Using Diffused Ti-LiNbOs Branched Ridge Waveguides1-T. R. Ranganath and S. Wang, University of California, Berkeley, CA 94720. Various amplitude modulation schemes have been developed to date such as the Bragg deflector modulator,2 interferometric mod~lators,~,~J' polarization modulators with a polarizer6 and switched directional coupler^.^,^ Here we report an efficient amplitude modulator of the Mach-Zehnder interferometer type we have fabricated in a Ti diffused LiNb039 waveguiding system. in the pm 'pace theguide'* These P+ regions 1 Research sponsored by the U,S, Army Research Office, Durham, Grant opticalchannelstops by decreasing the effective guideind5x DAHCO4-74-GO070. outside the channels where the light propagates. For guide widths 2 J. M. Hammer, Appl. Phys. Lett., vol. 18, p. 147,1971. of 5 to 15 pm, the coupling length was found to vary from 4 to 14 J. C. Webster and F. Zernike, APP~. P~Ys. Lett., ~01.26, P. 465,1975. mm, respectively for a 5-pm-thick epitaxial layer. W. E. Martin, Appl. Phys. Lett., vol. 26, p. 562, 1975. Y. Omachi and J. Noda, Appl. Phys. Lett., vol. 27, p. 544,1975. This work was sponsored by the Department of the Air Force. M. Papuchon, Y. Combemale, X. Mathieu, D. B. Ostrowsky, L. Reiber, A. M. F. J. Leonberger, J. P. Donnelly, and C. 0. Bozler, Appl. Phys. Lett., May 15, H. Kogelnik and R. V. Schmidt, Topical Meeting on Integrated Optics, Jan. J. P. Donnelly, F. J. Leonberger, and C. 0. Bozler,Appl. Phys. Lett., June 15, S. Uehara, T. Izawa, and H. Nakagome, Appl. Optics, vol. 13, p. 1753, 1974. Roy, B. Sejourne, and M. Werner, Appl. Phys. Lett., vol. 27, p. 289,1975. 1976. 1976, Salt Lake City. 1976. R. V. Schmidt and I. P. Kaminow, Appl. Phys. Lett., vol. 25, p. 458,1974.
Transcript of IIA-4 GaAs p+n-n+directional couplers and electrooptic switches
1250 IEEE TRANSACTIONS ON ELECTRON DEVICES, NOVEMBER 1976
wiched between an A1.15Ga.85As lower layer and a 6.6 pm wide Al.15Ga.ssAs strip on top, the psuedo index technique yields R m i n k 10 mil. The approach by Butler, et al., shows that low loss is obtained only if R 2 400 mil. In one set of measurements we have observed wave-guides in which the radius of curvature was varied between 40 and 400 mil. Our results are in agreement with the larger radius of curvature. We have also investigated waveguidw with abrupt small angle deviations (i.e., tilt). The angle, 6, is varied between .2O and 2O corresponding to an equivalent radilks of curvature of 5000 to 500 mil. We observe a steady degradaticn in the lateral confinement and the amount of guided light as 6 increases. The power is attenuated by l/e for 0.9' 5 6 I 1.2O. In conclusion, these measurements and our calculations confirin that although the stripline structure is advantageous for low 101s waveguides because of the inherent large bend radius, it is 1-111- suitable for the complex optical circuits that might be requircd for integrated optics.
IIA-4 GaAs p+n-n+ Directional Couplers and Electroopt ic Switched-F. J. Leonberger, J. P. Donnelly and C. 0. Bozlcr, Lincoln Laboratory, Massachusetts Institute of Technology, Lexington, MA 02173.
Two types of GaAs directional couplers and an electrooptic directional-coupler switch have been successfully fabricated arid evaluated at 1.06 pm for use as IOC components. These devic'3s were made from low-loss (-1 cm-l at 1.06 pm) single-mode p+n-n+ three-dimensional waveguides.2 Directional couplers with coupling lengths (for maximum power transfer) from 4 ;o 24 mm have been evaluated, and the dependence of the couplillg length on the device dimensions has been characterized. Bo';h types of couplers have exhibited 96% power coupling and ha'le shown a negligible (-0.1 dB) insertion loss relative to a single guide of the same dimensions as one of the coupled guides. The switch is characterized by 212 dB power isolation in both the switched and unswitched states and by a nearly constant poww output. Specifically, at zero bias 96% of the power emerges from the coupled guide, while a t the maximum switching voltage (!io V), 94% of the power exits from the input guide; the total outp It power from the switch varies 5 0.2 dB in this 0-50 V bias range.
One type of directional coupler, the stripline coupler, was fabricated by forming two p+n-n+ optical striplines with a 3 M r n spacing and the other type, the channel-stop coupler, used two p+n-n+ channel-stop strip guides, also with a 3 pm spacing. Both structures consist of an n+ (1 X l O l 8 ~ m - ~ ) substrate, an 11-
~ m - ~ ) epitaxial guiding layer and ion-implanted p+ (2 - 3 X 1 O l 8 ~ m - ~ ) regions to laterally confine the light. Multiple- energy Be+ implantations3 were used to yield regions of uniform concentration (and thus of uniform refractive index) to a depth of -2 pm. In the stripline coupler the p+ regions are formed into ribs and the light is guided beneath them. For guide widths of LO and 15 pm, coupling lengths of 9 and 22 mm, respectively, were measured for a 7 pm thick epitaxial layer. As the initial epitaw- ial-layer thickness increased from 5.5 to 8 pm, the coupling length was found to decrease about 20%. The channel-stop couplw, which has a planar structure, has three p+ regions: two that 1 ie along the outside edges of the nuidina channels and one that lies
The optical switching was achieved in a channel-stop coupler by reverse-biasing the p+n- junction adjacent to one of the channels. The applied field destroys the phase synchronism of the two guides via the electrooptic effect and therefore changes both the coupling coefficient and the maximum power coupled. In this respect it is similar to the switch formed with metal-gap waveguide^.^ However, with this channel-stop switch, there is essentially no power loss at switching biases. The 12 dB switching with nearly constant total power was obtained with 10 pm guides, spaced by 3 pm in a sample 7.8 mm long.
Preliminary evaluation of channel-stop devices a t 9350 .fi in- dicates a negligible (-0.1 dB) insertion loss relative to a single guide but a longer coupling length than obtained at 1.06 pm. Further investigation of these devices is planned, including a study of the effects of crystal orientation and bias configurations on switching performance.
vol. 27, p. 202,1975. J. C. Campbell, F. A. Blum, D. W. Shaw, and K. L. Lawley, Appl. Phys. Lett.,
IIA-5 A Simple Beam-Split ter for Integrated Optics Ex- perimental Realization and Theory1-D. Vincent and J. W. Y. Lit, Laboratoire de Recherches en Optique et Laser Depart- ment de Physique, Universite Laval, Quebec, P.Q. Canada, G1K 7P4.
A passive thin-film beam splitter has been made, based on the principle that the effective index of a mode traveling in a thin- film optical waveguide varies with the thickness of the guide. The effect produced resembles that of total internal reflection in bulk optics or the tunneling effect across a potential barrier in quan- tum mechanics. The individual intensities of the two beams can be varied, from 100% transmission to 100% reflection. Thus the device can act as a mirror as well. Simple analytical expressions have been found for the coefficients of reflection and transmis- sion. The theoretical analysis is based on the WKBJ approxi- mation method, which applies very well to our case, because the rate of change in the effective index is very small. The effects of different physical parameters will also be discussed. Particular attention is drawn to the fact that the experimental method is extremely simple, and that most laboratories with thin-film de- position facilities should have no difficulty in making the de- vice.
Research supported in part by the Defense Research Board of Canada.
IIA-6 An Efficient Amplitude Modulator Using Diffused Ti-LiNbOs Branched Ridge Waveguides1-T. R. Ranganath and S. Wang, University of California, Berkeley, CA 94720.
Various amplitude modulation schemes have been developed to date such as the Bragg deflector modulator,2 interferometric mod~la tors ,~ ,~J ' polarization modulators with a polarizer6 and switched directional coupler^.^,^ Here we report an efficient amplitude modulator of the Mach-Zehnder interferometer type we have fabricated in a Ti diffused LiNb039 waveguiding system.
in the pm 'pace theguide'* These P+ regions 1 Research sponsored by the U,S, Army Research Office, Durham, Grant optical channel stops by decreasing the effective guide ind5x DAHCO4-74-GO070. outside the channels where the light propagates. For guide widths 2 J. M. Hammer, Appl. Phys. Lett., vol. 18, p. 147,1971. of 5 to 15 pm, the coupling length was found to vary from 4 to 14 J. C. Webster and F. Zernike, APP~. P ~ Y s . Lett., ~01.26, P. 465,1975. mm, respectively for a 5-pm-thick epitaxial layer. W. E. Martin, Appl. Phys. Lett., vol. 26, p. 562, 1975.
Y. Omachi and J. Noda, Appl. Phys. Lett . , vol. 27, p. 544,1975.
This work was sponsored by the Department of the Air Force. M. Papuchon, Y. Combemale, X. Mathieu, D. B. Ostrowsky, L. Reiber, A. M.
F. J. Leonberger, J. P. Donnelly, and C. 0. Bozler, Appl. Phys. Lett., May 15, H. Kogelnik and R. V. Schmidt, Topical Meeting on Integrated Optics, Jan.
J. P. Donnelly, F. J. Leonberger, and C. 0. Bozler,Appl. Phys. Lett., June 15, S. Uehara, T. Izawa, and H. Nakagome, Appl. Optics, vol. 13, p. 1753, 1974.
Roy, B. Sejourne, and M. Werner, Appl. Phys. Lett., vol. 27, p. 289,1975.
1976. 1976, Salt Lake City.
1976. R. V. Schmidt and I. P. Kaminow, Appl. Phys. Lett., vol. 25, p. 458,1974.
