We evaluate the potential of single crystal PTS (p-toluene sulfonate) for all-optical applications at the 1.32 mum communications wavelength by measuring the electronic and thermo-optic nonlinearities, and the multiphoton absorption with picosecond pulses. With appropriate heat sinking, duty cycles greater than 25% should be possible without significant cumulative thermal effects for 1 W operating powers

Baker, G.

Kim, Dug. Y.

Lawrence, Brian L.

Meth, J.

Stegeman, George I.

Torruellas, William E.

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University of Central Florida STARS Faculty Bibliography 1990s Faculty Bibliography 1-1-1994 Assessment Of Single-Crystal P-Toluene Sulfonate As An All-Optical Switching Material At 1.3-Mu-M Dug. Y. Kim University of Central Florida Brian L. Lawrence University of Central Florida William E. Torruellas University of Central Florida George I. Stegeman University of Central Florida G. Baker See next page for additional authors 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 Kim, Dug. Y.; Lawrence, Brian L.; Torruellas, William E.; Stegeman, George I.; Baker, G.; and Meth, J., "Assessment Of Single-Crystal P-Toluene Sulfonate As An All-Optical Switching Material At 1.3-Mu-M" (1994). Faculty Bibliography 1990s. 2953. https://stars.library.ucf.edu/facultybib1990/2953 Authors Dug. Y. Kim, Brian L. Lawrence, William E. Torruellas, George I. Stegeman, G. Baker, and J. Meth This article is available at STARS: https://stars.library.ucf.edu/facultybib1990/2953 Appl. Phys. Lett. 65, 1742 (1994); https://doi.org/10.1063/1.112902 65, 1742© 1994 American Institute of Physics.Assessment of single crystal p-toluenesulfonate as an all-optical switching materialat 1.3 μmCite as: Appl. Phys. Lett. 65, 1742 (1994); https://doi.org/10.1063/1.112902Submitted: 10 May 1994 . Accepted: 27 July 1994 . Published Online: 04 June 1998Dug. Y. Kim, Brian L. Lawrence, William E. Torruellas, George I. Stegeman, G. Baker, and J. MethARTICLES YOU MAY BE INTERESTED INStructural, vibrational, thermal and optical studies of organic single crystal: Benzotriazolium p-toluene sulfonate (BTPTS)AIP Conference Proceedings 1728, 020508 (2016); https://doi.org/10.1063/1.4946559Assessment of single crystal p -toluene sulfonate as an all-opticalswitching material at 1.3 mmDug. Y. Kim, Brian L. Lawrence, William E. Torruellas, and George I. StegemanCREOL, University of Central Florida, Orlando, Florida 32826G. BakerDept. of Chemistry, Michigan State University, East Lansing, Michigan 48824J. MethE. I. Dupont de Nemours & Co., Central Research and Development Department, Experimental Station,Wilmington, Delaware 19898~Received 10 May 1994; accepted for publication 27 July 1994!We evaluate the potential of single crystal PTS~p-toluene sulfonate! for all-optical applications atthe 1.32 mm communications wavelength by measuring the electronic and thermo-opticnonlinearities, and the multiphoton absorption with picosecond pulses. With appropriate heatsinking, duty cycles greater than 25% should be possible without significant cumulative thermaleffects for 1 W operating powers. ©1994 American Institute of Physics.Materials must satisfy a series of figures of merit to beuseful for ultrafast all-optical switching and relatedapplications.1 First, they must exhibit a large, nonresonant,optical Kerr-like response~n2.10212 cm2/W! for theintensity-dependent refractive index in order to operate atwatt peak powers in centimeter long devices. Second, a non-linear phase shift of at leastp should be possible over 1/eattenuation distances for reasonable device throughput. Thisrequirement is embodied in two figures of meritW5n2I SW/a1l.1 andT5a2l/n2,1 ~for 2p phase shift!,where a1 and a2 are the one and two photon absorptioncoefficients respectively, andI SW is the intensity required fora 2p phase shift. Finally, absorption leads to index changesvia the thermo-optic effect which accumulate over manypulses and compete with the all-optical index changes. As-suming thatN pulses,Dt in width, are required for a cumu-lative thermal index change equal to 10% of the electronicindex change, then the maximum allowed duty cycle isD510N Dt/t% for any pulse width wheret is the thermalrelaxation time of the device structure.2 We have recentlyshown that the one-dimensional conjugated polymer PTS,poly@2,4-hexdiyne-1,6-diol-bis-p-toluene-sulfonate#, shows arecord high, nonresonant, nonlinear response of 231023cm2/GW at 1.6mm and satisfies theT parameter as well.3Here we show that PTS in the other important telecommuni-cation window around 1.3mm should satisfy all of the abovestated requirements.PTS has already been grown in an integrated waveguideformat with low losses in the near infrared.4 Here we con-centrate on predevice linear and nonlinear measurements in abulk single crystal approximately 210mm thick. Lineartransmission was limited by Fresnel losses at the surfaces ofthe crystal, and exceeded 80% for radiation polarized alongthe conjugation axis. Nonlinear losses were measured with aversatile parametric laser system with theZ-scan technique.An example of our experimental results for both the openand closed apertureZ-scan is shown in Fig. 1 for inputpulses at 1.30mm. As a result of the fits, also shown in Fig.1, a two-photon absorption coefficient of 2064 cm/GW~a2!is obtained. In addition, a positive intensity dependent refrac-tive indexn2 of 3.260.331023 cm2/GW is measured fromthe closed aperture data. The latter result was reconfirmedwith a hybrid Mach–Zehnder interferometer, which has beendeveloped to measure nonlinearly induced phase shifts assmall asp/100.5 In this case, just as previously observed forthe measurements at 1.6mm, a weak linear dependence~Fig.2! of both nonlinear coefficients on input intensity was ob-served, suggesting the presence of higher order effects atinput peak intensities used which ranged between 0.5 and 7GW/cm2, i.e.,Dn5n2I1n3I2 andDa5a2I1a3I2. From themeasured variations versus intensity we deduced the nexthigher order loss coefficient and intensity dependent refrac-tive index to be respectivelya355.260.3 cm3/GW2 andn3521.531024 cm4/GW2. Similar effects have been re-ported at other wavelengths previously in poly-diacetylenes.6,7 These higher order effects are negligible fortypical device switching intensities~.l/n2L.20 MW/cm2for L52 cm and a 2p phase shift!. We directly evaluate avalue of T50.75. Based on linear loss measurements re-ported by Thakuret al. and our experimental estimate of 10GW/cm2 for the damage threshold intensity, we estimate thatW.100.4 Therefore both loss-related figures of merit are ac-ceptible for PTS at this wavelength.An important issue which is frequently overlooked inassessing materials is the possibility that cumulative~overmany pulses!, large, optically induced index changes can ex-ceed the instantaneous, Kerr-effect index changes at highd ta rates. This effect is quantified by the duty cycle definedpreviously. For example, in the case of semiconductorwaveguides, Gabrielet al.demonstrated that both free carrierabsorption and thermo-optic phase drifts can play an impor-tant role.2 Here we employed a nonlinear Mach–Zehnderinterferometer developed to measure both the instantaneous~single pulse! refractive nonlinearity and the accumulatedthermal phase shift generated by a 76 MHz train of 100picosecond pulses. Figure 3 shows the phase shift induced by1742 Appl. Phys. Lett. 65 (14), 3 October 1994 0003-6951/94/65(14)/1742/3/$6.00 © 1994 American Institute of Physics2000 pulses of varying intensity. The induced phase shiftvaries quadratically with input intensity, implying a two pho-ton absorption origin for the thermal phase shift. At the high-est intensity used, 170 MW/cm2, the two photon inducedabsorption is 3 cm21, much larger than the typical linear lossof 0.2–0.3 cm21. We therefore conclude that two-photon ab-sorption is the dominant loss mechanism forI.15 MW/cm2.The maximum allowed duty cycle is estimated from theinterferometrically measured phase shifts. A single pulsemeasurement of the electronic nonlinearity with 170MW/cm2 input intensity showed a positive phase shift ofp/5in our 210mm platelet.~This corresponds ton254310212cm2/W, in good agreement with theZ-scan measurement ob-tained at intensities one order of magnitude larger.! Becausethe phase shift is linear in intensity, this would correspond toa phase shift ofp/5 @20/170#5p/42.5 at the typical switchingintensity of 20 MW/cm2 for a 2-cm-long device. It required3000, 170 MW/cm2, pulses to shift the fringes by-p/5 via thethermal process. Because this is a two photon activated pro-cess,N52.553104 pulses will be required to produce aphase shift ofp/42.5 at a 20 MW/cm2 switching intensity.Furthermore, with a well heat-sunk environment to dissipatethe heat, for example, a sapphire substrate for a waveguide, athermal decay time of 1ms is a conservative upper limit.This implies a 25% duty cycle, i.e., switching of pulses sepa-rated by three pulse widths is feasible at the stated intensitylevels with minimum cross talk due to thermal effects.In summary, our measurements show that single crystalPTS satisfies all of the important figures of merit for ultrafastall-optical devices at 1.3mm. its nonlinearity is orders ofmagnitude larger than that of other materials used in thecommunications spectral windows which also satisfy thesame figures of merit, for example, silica and chalcogenideglasses in fiber form, or AlGaAs.7–9 For example, a 2-cm-long PTS device with a 2mm guiding core would need asource of approximately 1 W peak~0.25 W average, 25%duty cycle! power. Such sources should become availablesoon at 1.3mm, making nonlinear devices viable and com-patible with current state of the art fiber technology. Finally,we note that the loss figures of merit are also very good at1.60 mm, allowing even larger duty cycles at thatwavelength.3FIG. 1. TypicalZ-scan data at 1.3mm. The open circles show the openapertureZ-scan showing the presence of two-photon absorption with pulsesof 5.66 GW/cm2. The filled circles show the result of a closed apertureZ-scan at 0.8 GW/cm2.FIG. 2. Variation in the effectiven2 ~a!, anda2 ~b!, with peak input inten-sity.FIG. 3. Accumulated thermal nonlinear phase change for a PTS sample for2000, 100 ps pulses as a function of the input intensity. Shown in the insetis a schematic of the nonlinear phase shift with number of pulses for boththe electronic and thermal nonlinearities.1743Appl. Phys. Lett., Vol. 65, No. 14, 3 October 1994 Kim et al.The research at CREOL was supported by AFOSR~91-0339!.1G. I. Stegeman and A. Miller, inPhotonics and Switching, edited by J. E.Midwinter ~Academic Press, London, 1994!, pp. 81–145.2M. C. Gabriel, H. A. Haus, and E. P. Ippen, J. Lightwave. Tech.LT-4 ,1482 ~1986!.3B. L. Lawrence, M. Cha, J. Kang, W. E. Torruellas, G. I. Stegeman, G.Baker, J. Meth, and S. Etemad, Electron. Lett.30, 447 ~1994!.4D. M. Krol and M. Thakur, Appl. Phys. Lett.56, 1406~1990!; M. Thakur,R. C. Frye, B. I. Greene, Appl. Phys. Lett.56, 1187~1990!.5K. B. Rochford, R. Zanoni, and G. I. Stegeman, IEEE J. Quantum Elec-tron.QE-28, 2044~1992!.6J. M. Nunzi and F. Charra, Nonlinear Opt.1, 19 ~1991!.7K. S. Kim, R. H. Stolen, W. A. Reed, and K. W. Quoi, Opt. Lett.19, 257~1994!.8A. Asobe, T. Kanamori, and K. Kubodera, IEEE Photon. Tech. Lett.PTL-4, 362 ~1992!.9A. Villeneuve, C. C. Yang, G. I. Stegeman, C.-H. Lin, and H.-H. Lin,Appl. Phys. Lett.62, 2465~1993!.1744 Appl. Phys. Lett., Vol. 65, No. 14, 3 October 1994 Kim et al.

Assessment Of Single-Crystal P-Toluene Sulfonate As An All-Optical Switching Material At 1.3-Mu-M

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Assessment Of Single-Crystal P-Toluene Sulfonate As An All-Optical Switching Material At 1.3-Mu-M

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