Utilizing a type II interaction for second-harmonic generation in a crystal of potassium titanyl phosphate, we experimentally demonstrate the all-optical action of a light modulator with both signal and output at the same optical wavelength. This modulator is controlled by the intensity of the injected signal, a characteristic that makes it a suitable candidate for all-optical transistor action and ultrafast analog processing in transparent networks for telecommunications

Assanto, G.

Hagan, D. J.

VanStryland, E. W.

Wang, Z.

English

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University of Central Florida STARS Faculty Bibliography 1990s Faculty Bibliography 1-1-1995 All-Optical Modulation Via Nonlinear Cascading In Type-Ii 2Nd-Harmonic Generation G. Assanto University of Central Florida Z. Wang University of Central Florida D. J. Hagan University of Central Florida E. W. VanStryland University of Central Florida Find similar works at: https://stars.library.ucf.edu/facultybib1990 University of Central Florida Libraries http://library.ucf.edu This Article is brought to you for free and open access by the Faculty Bibliography at STARS. It has been accepted for inclusion in Faculty Bibliography 1990s by an authorized administrator of STARS. For more information, please contact STARS@ucf.edu. Recommended Citation Assanto, G.; Wang, Z.; Hagan, D. J.; and VanStryland, E. W., "All-Optical Modulation Via Nonlinear Cascading In Type-Ii 2Nd-Harmonic Generation" (1995). Faculty Bibliography 1990s. 1274. https://stars.library.ucf.edu/facultybib1990/1274 Appl. Phys. Lett. 67, 2120 (1995); https://doi.org/10.1063/1.114739 67, 2120© 1995 American Institute of Physics.All-optical modulation via nonlinearcascading in type II second-harmonicgenerationCite as: Appl. Phys. Lett. 67, 2120 (1995); https://doi.org/10.1063/1.114739Submitted: 01 May 1995 . Accepted: 04 August 1995 . Published Online: 04 June 1998G. Assanto, Z. Wang, D. J. Hagan, and E. W. VanStrylandARTICLES YOU MAY BE INTERESTED INTunable optical bistability at the graphene-covered nonlinear interfaceApplied Physics Letters 104, 051108 (2014); https://doi.org/10.1063/1.4863927Resonant second harmonic generation in a gallium nitride two-dimensional photonic crystalon siliconApplied Physics Letters 106, 081105 (2015); https://doi.org/10.1063/1.4913679Second harmonic generation in phase matched aluminum nitride waveguides and micro-ringresonatorsApplied Physics Letters 100, 223501 (2012); https://doi.org/10.1063/1.4722941All-optical modulation via nonlinear cascading in type II second-harmonicgenerationG. Assanto,a) Z. Wang, D. J. Hagan, and E. W. VanStrylandCenter for Research and Education in Optics and Lasers, University of Central Florida, Orlando,Florida 32826~Received 1 May 1995; accepted for publication 4 August 1995!Utilizing a type II interaction for second-harmonic generation in a crystal of potassium titanylphosphate, we experimentally demonstrate the all-optical action of a light modulator with bothsignal and output at the same optical wavelength. This modulator is controlled by the intensity of theinjected signal, a characteristic that makes it a suitable candidate for all-optical transistor action andultrafast analog processing in transparent networks for telecommunications. © 1995 AmericanInstitute of Physics.All-optical effects constitute an active area of interestwhich is beginning to expand into the research and develop-ment community. Transparent networks and all-optical real-time reconfigurable systems have become common conceptsin those areas of investigation dealing with ultrafasttelecommunications.1 Recently, a new spur of activities innonlinear optics for all-optical applications has been pro-moted by the novel, although physically well understood,concept of large phase shifts via cascading of second-ordernonlinear effects,2,3 partly because of the mature technologyavailable in second-order materials in comparison to third-order systems. The cascading nonlinearity, however, is notonly being investigated as a potentially more suitable mecha-nism for producing phase shifts in all those configurationsfor which the optical Kerr effect used to be considered theoptimum candidate,4,5 but it is revealing its peculiar poten-tials in other areas, such as new solitarylike solutions inspace and time6–8 and analog processing. For the latter, vari-ous all-optical modulator schemes have been proposed whichrely on the coherent nature of cascading nonlinearinteractions.9–12 One of them, utilizing a weak phase-modulated second-harmonic seed signal to produce largethroughput changes in the fundamental frequency pump in apotassium titanyl phosphate ~KTP! crystal, has been recentlyreported by us.13In this letter we report, to the best of our knowledge, thefirst experimental demonstration of a KTP all-optical transis-tor which, in contrast to the schemes previously investigated,does not rely on a specific phase relationship between signaland pump and, moreover, is capable of producing an ampli-fied signal at the same optical frequency as the input.The present scheme for all-optical modulation if basedon type II second-harmonic generation ~SHG!, in the case ofunbalanced input components along the spatial directionscorresponding to the allowed propagation eigensolutions inan anisotropic crystal.12 The equations governing the three-wave interaction for type II SHG are the classical set describ-ing parametric generation:idA j~v ,j!dj 5A32 j* ~v ,j!,B~2v ,j!1k jA j~v ,j!,~1!idB~2v ,j!dj 5A1~v ,j!A2~v ,j!1kBB~2v ,j!,j51,2,with A j and B slowly varying field amplitudes~in W1/2 m21), k j5b j(v)/xAP , kB5bB(2v)/xAP , j5zxAP , P the total input power, and x'4p/ldeff(2)A1/2ce0n3 the effective nonlinear coefficient.These equations, however, encompass a richer phenom-enology when the initial conditions on the fundamental fre-quency ~FF! waves are nonidentical, i.e., when one of theinput components is larger ~weaker! than the other one.12,14Under these circumstances, the well-known sech2(xz) solu-tion for the transmission of the FF wave is replaced by asolution where energy is periodically exchanged between FFand second harmonic ~SH!. This is illustrated in Fig. 1,where a small imbalance between the FF inputs results in-a!Visiting from the Department of Electronic Engineering, Terza Universityof Rome, Via Eudossiana 18, 00184 Rome, Italy. Electronic mail:assanto@diewshp1.ing.uniroma1.itFIG. 1. Total normalized fundamental intensityh(z)5(uA1(z)u21uA2(z)u2)/(uA1(0)u21uA2(0)u2) vs distance z/L at phase matching for r5uA2(0)u2/uA1(0)u251 ~solid line! and r50.9 ~short dashed!. In the lattercase the long-dashed line represents the weaker (uA2(z)u2) component. Totalinput excitation was L2x2P525 at v, and the calculation was carried outusing plane waves and cw fields.2120 Appl. Phys. Lett. 67 (15), 9 October 1995 0003-6951/95/67(15)/2120/3/$6.00 © 1995 American Institute of Physicscomplete switching of energy from SH to FF waves. Whilethe case r51 ~balanced FF inputs! corresponds to the stan-dard type II SHG case ~the standard configuration employedin KTP frequency doublers!, a large transmission change isintroduced for r close ~but not equal! to 1. Such occurrenceis more rapid with r and with better high/low contrast thesmaller the wave vector mismatch Db5bB(2v)2b1(v)2b2(v) characterizing the interaction.12 Moreover, thisthroughput variation, as also indicated by Hutchings et al.15in the framework of frequency nondegenerate interactions, isinsensitive to the phase offset of either FF input components,lending itself to all-optical transistor action with true ~rela-tive! intensity control.For the experimental demonstration of this all-opticalmodulation scheme, we utilized a 2-mm-thick flux-grownKTP crystal. The crystal was mounted in an three-axis go-niometric stage and placed at the waist of a focused Gaussianbeam from a 1.064 mm Q-switch mode-locked Nd:YAG laserproducing single, switched-out 26 ps pulses ~FWHM! at arep-rate of 10 Hz. The laser beam was linearly polarized anda l/2 waveplate allowed the angular shift of the FF inputfield at the entrance of the crystal, so as to control the pro-jection of the input onto the two orthogonal polarization di-rections involved in a type II interaction. First, the crystaland the electric field were aligned in order to maximizeSHG, with an angle of 45° at the input facet. This resulted ina substantial depletion of the fundamental. We verified that awaveplate rotation of 622.5° about this position resulted in anegligible amount of second harmonic, even at the largestpower available from the laser source. Then, after placing animaging system ~53! and a 100 mm pinhole at the output ofthe crystal in order to reduce ~or eliminate! the effects ofspatial averaging, we measured the total throughput versuswaveplate rotation. Such rotation corresponds to a variationin the ratio between the FF inputs. Figures 2~a! and 2~b!show the predicted and experimental results, for an inputbeam waist (1/e2) of 80 mm and an estimated FF intensityof 32 GW/cm2. The effective nonlinearity was taken deff(2)53.1 pm/V,16 and for the simulation we assumed that acertain phase mismatch was achieved over a pulse Gaussianin time but planar in space. The latter assumption is accept-able in view of the imaging geometry adopted for the mea-FIG. 2. Fundamental throughput h5(uA1(L)u21uA2(L)u2)/(uA1(0)u21uA2(0)u2) vs angle of polarization at the entrance facet of the crystal. 45°corresponds to balanced excitation, i.e., standard type II SHG. ~a! Numericalcalculation including time averaging over a Gaussian pulse and for variouswave vector mismatches; ~b! experimental results with 26 ps pulses.FIG. 3. Fundamental throughput h vs total FF input fluence for a fixed ratior>0.98 between the FF components in z50. ~a!Numerical simulation forDbL50, 0.05p , 0.1p , and time integration; ~b! experimental results. Anormalized excitation L2x2P530 corresponds to an intensity of 32 GW/cm2.2121Appl. Phys. Lett., Vol. 67, No. 15, 9 October 1995 Assanto et al.surement. The FF transmittance was normalized to its linearvalue, and no corrections were introduced for angular or tem-poral walk-off due to crystal birefringence. The results ex-hibit an abrupt switching feature about 45°, with a transmis-sion contrast of almost 7:1 for a 21° change in input angle~0.5° waveplate rotation!, i.e., a 1.7% variation in the size ofeach FF input component. This corresponds to a throughputmodulation Dh>~0.5–0.075! over 1° rotation ~>42.5%/degree! or an equivalent ~small signal! amplificationD(uA1(z5L)u21uA2(z5L)u2)/2D(uA2(0)u2)[14 dB. Theslight asymmetry visible in Fig. 2~b! is attributable to thealignment, but the overall comparison between our simplemodel and the experimental results is quite satisfactory for amismatch DbL between 0.05 and 0.1p. Similar results areobtained using two separate input beams.17 The measurementof an actual small signal amplification, distinguishing the‘‘pump’’ from the ‘‘signal’’ input, is under way and will bepresented elsewhere.In order to verify the validity of the model, a differentset of data was collected varying the input excitation to thecrystal, setting the FF component ratio ~or, equivalently, thewaveplate angle! to a value corresponding to a transmittanceof '0.3 in Fig. 2~b!. Figures 3~a! and 3~b! show the numeri-cal and experimental results which, also in this case, are ingood agreement in the same estimated range of wave vectormismatches.In summary, we have experimentally demonstrated afrequency-degenerate second-order nonlinear all-optical tran-sistor, based on a type II SHG interaction in a KTP crystal.This result, not yet optimized, is particularly relevant in theframework of all-optical analog signal processes where anFF signal coherent with the pump may not be available, andindicates the feasibility of other schemes based on an inher-ently ultrafast cascaded nonlinearity. Even though the inten-sities employed were relatively high, a substantially lowerpower budget will be required when employing materialswith higher ‘‘d (2),’’such as the organic crystal MMONS,18and/or guided-wave geometries.4,5 An order of magnitude in-crease in nonlinearity and/or interaction length would indeedallow for two/four orders of magnitude reduction in power,with further reductions possible when using smaller crosssections and/or shorter pulses.G. A. acknowledges support from the Italian MURST~40% and 60% ’94! and a NATO grant ~No. CRG931142!.He is also grateful to Professor G. Stegeman ~CREOL-UCF!for truly enlightening discussions. The work in CREOL wassupported by the National Science Foundation grant ECSNo. 9320398.1See, for instance, ‘‘Advanced Communication Technologies and Services -Workplan,’’ the European Commission, DGXIII-B-RA946043-WP ~1994!.2R. DeSalvo, D. J. Hagan, M. Sheik-Bahae, G. Stegeman, and E. W. VanStryland, Opt. Lett. 17, 28 ~1992!.3G. I. Stegeman, M. Sheik-Bahae, E. Van Stryland, and G. Assanto, Opt.Lett. 18, 13 ~1993!.4G. Assanto, G. I. Stegeman, M. Sheik-Bahae, and E. W. VanStryland,Appl. Phys. Lett. 62, 1323 ~1993!.5R. Schiek, J. Opt. Soc. Am. B 10, 1848 ~1993!.6Y. N. Karamzin and A. P. Sukhorukov, JETP Lett. 20, 339 ~1974!; M. J.Werner and P. D. Drummond, J. Opt. Soc. Am. B 10, 2390 ~1993!.7C. R. Menyuk, R. Schiek, and L. Torner, J. Opt. Soc. Am. B 11, 2434~1994!.8W. Torruellas, Z. Wang, D. J. Hagan, E. W. Van Stryland, G. I. Stegeman,L. Torner, and C. R. Menyuk, Phys. Rev. Lett. 74, 5036 ~1995!.9G. Assanto, G. I. Stegeman, M. Sheik-Bahae, and E. Van Stryland, IEEEJ. Quantum Electron. 31, 673 ~1995!.10P. St. J. Russell, Electron. Lett. 29, 1228 ~1993!.11G. Assanto, I. Torelli, and S. Trillo, Opt. Lett. 19, 1720 ~1994!.12G. Assanto, Opt. Lett. 20, 1595 ~1995!.13D. J. Hagan, M. Sheik-Bahae, Z. Wang, G. Stegeman, E. W. Van Stryland,and G. Assanto, Opt. Lett. 19, 1305 ~1994!.14A. L. Belostotsky, A. S. Leonov, and A. V. Meleshko, Opt. Lett. 19, 856~1994!.15D. Hutchings, J. S. Aitchison, and C. N. Ironside, Opt. Lett. 18, 793~1993!.16R. C. Eckardt, H. Masuda, Y. X. Fan, and R. L. Byer, IEEE J. QuantumElectron. QE-26, 922 ~1990!.17During revision of this manuscript, an experiment with separate beams hasbeen reported by L. Lefort and A. Barthelemy in Electron Lett. 31, 910~1995!.18 J. D. Bierlein, L. K. Cheng, Y. Wang, and W. Tam, Appl. Phys. Lett. 56,423 ~1990!.2122 Appl. Phys. Lett., Vol. 67, No. 15, 9 October 1995 Assanto et al.

All-Optical Modulation Via Nonlinear Cascading In Type-Ii 2Nd-Harmonic Generation

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All-Optical Modulation Via Nonlinear Cascading In Type-Ii 2Nd-Harmonic Generation

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