共查询到20条相似文献,搜索用时 15 毫秒
1.
T.K. Liang L.R. Nunes K.S. Abedin D. Van Thourhout P. Dumon H.K. Tsang 《Optics Communications》2006,265(1):171-174
The switching speed of conventional silicon-based optical switching devices based on plasma dispersion effect is limited by the lifetime of free carriers which introduce either phase or absorption changes. Here we report an all-optical logic NOR gate which does not rely on free carriers but instead uses two-photon absorption. High speed operation was achieved using pump induced non-degenerate two-photon absorption inside the submicron size silicon wire waveguides. The device required low pulse energy (few pJ) for logic gate operation. 相似文献
2.
Free-carrier absorption (FCA) has proven to be an important obstacle in the development of a silicon-based laser; however, FCA may serve as a potential advantage in active silicon-based switches or modulators. In this work, we present FCA modulation in slot waveguides with silicon nanocrystals (Si-ncs) embedded in SiO(2) as the low-index slot material. Slot waveguides were fabricated with and without Si-ncs, and the presence of Si-ncs was shown to increase the pump-induced FCA loss in the waveguides by a factor of 4.5. We modeled the Si-nc material using a four-level rate equation analysis to estimate the excited population of Si-ncs, allowing us to extract a value of 2.6 × 10(-17) cm(2) for the FCA cross section of the Si-nc material. 相似文献
3.
Spälter S Hwang HY Zimmermann J Lenz G Katsufuji T Cheong SW Slusher RE 《Optics letters》2002,27(5):363-365
Single-mode planar waveguides were fabricated from chalcogenide glass compounds with large Kerr nonlinearities. Strong self-phase modulation of subpicosecond pulses along with low linear and nonlinear absorption losses demonstrates the potential for ultrafast, low-power, all-optical processing applications. 相似文献
4.
We present numerical investigations of ultrafast femtosecond (with time duration of 100 fs at 1/e intensity point) all-optical modulation of a pump-probe wave arrangement by using nondegenerate two-photon absorption (TPA),
namely cross absorption, inside silicon-on-insulator (SOI) optical waveguides. Our results show that when a pump pulse with
femtosecond duration and a continuous probe wave are co-propagating along the SOI, the probe wave can be modulated inversely
by the ultrafast pump pulse, whose modulation depth depends strongly on the system parameters such as the waveguide length,
the peak power and initial chirp of the pump wave, the group velocity dispersion (GVD), etc.; this means that the modulation
depth can be improved by an appropriate increase of the waveguide length, the pump peak, and the initial chirp, in addition,
which has a larger value for the probe wavelength in the normal dispersion regime compared with the case of abnormal dispersion
when the center wavelength of the pump wave is located at the zero-dispersion wavelength. 相似文献
5.
Ulmer TG Tan RK Zhou Z Ralph SE Kenan RP Verber CM SpringThorpe AJ 《Optics letters》1999,24(11):756-758
Performance-limiting asymmetric distortion is observed in the spectra of fundamental pulses transmitted through GaAs-Al(0.9)Ga(0.1)As multilayer waveguides designed for surface-emitted second-harmonic generation. This behavior is attributed to refractive-index changes resulting from the accumulation of free carriers created by two-photon absorption in the GaAs layers. Numerical simulations of the intensity-dependent spectra by use of the separately measured two-photon absorption coefficient are shown to be in good agreement with the observed spectra. 相似文献
6.
We demonstrate efficient self-phase modulation with a nonlinear phase shift of up to 3π, broadband cross-phase modulation, and four-wave mixing with a 14 nm tunability range in AlGaAs waveguides with a specially designed composition. The length of our sample is only 9 mm, but the efficiency of the observed effects is high. 相似文献
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A novel profilometry method based on two-photon absorption in a silicon avalanche photodiode is proposed. This method has a wide dynamic range, from millimeters to tens of meters. The principle is experimentally confirmed with a fiber-optic Mach-Zehnder interferometer. 相似文献
9.
We demonstrate a direct and sensitive technique for measuring two-photon absorption (TPA). An intensity-modulated femtosecond laser beam passes through a sample exhibiting TPA. A TPA signal at twice the modulation frequency is then generated and subsequently measured by a lock-in amplifier. The absolute TPA cross section of Rhodamine 6G at 800nm is found to be (15.3+/-2.0)x10(-50) cm(4) s/photon and agrees well with previously published results obtained with much higher intensity [J.Chem.Phys.112, 9201 (2000)]. Our method may be especially useful in measuring nonlinear absorptions of nonfluorescent materials. 相似文献
10.
Fischer MC Ye T Yurtsever G Miller A Ciocca M Wagner W Warren WS 《Optics letters》2005,30(12):1551-1553
We show that phase-sensitive detection of spectral hole refilling can yield information about self-phase modulation and two-photon absorption coefficients. We expect that, when applied to tissue microscopy, this technique will allow the study of endogenous molecular markers beneath the surface, even if those markers are nonfluorescent. 相似文献
11.
We study whether helium ion implantation can reduce the carrier lifetime and thus reduce the density of two-photon-absorption-generated free carriers. Our experiments and theoretical model show that helium ion implantation into silicon waveguides can successfully reduce the free-carrier losses and allow net gain to be attained by cw-pumped stimulated Raman scattering without requiring reverse bias to remove the photogenerated free carriers. 相似文献
12.
Self phase modulation is observed in a polymeric thin film for the first time. It is found that this effect can occur at relatively low laser intensity. Experimental results obtained are compared with theoretical predictions. 相似文献
13.
We present experimental measurements of the polarization dependence of two-photon absorption in silicon photodiodes at 1550 nm, and we offer a simple theory that explains our observations. Based on this theory, we propose and demonstrate that it is possible to construct an optical cross-correlation system that is polarization insensitive, provided that one of the two input polarization states can be controlled. 相似文献
14.
We demonstrate that chromatic dispersion and group delay ripple limit the performance of all-optical regeneration based on self-phase modulation. The level of degradation depends in detail on the type of phase distortions introduced. The regenerator performance is measured using the optical signal to noise ratio (OSNR) margin provided to the system for a given bit error ratio. The addition of chromatic dispersion and group delay ripple induces a significant reduction in this OSNR margin. 相似文献
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By employing a simplified nonlinear coupled mode theory, we discuss the influence of two-photon absorption (TPA) on the characteristics of bistable switching. It is revealed that the critical value of frequency detuning for bistability rises linearly with increasing TPA coefficient k (when k is less than 30), and eventually access to a saturated value. It is also found that TPA effect will be enhanced for a greater frequency detuning, especially when transmission reaches its peak value. As a result, the peak transmission will decrease monotonously with the increasing frequency detuning. Based on this simplified model, the TPA-induced temperature rise in microcavity is also estimated. The theoretical predictions show good agreement with the simultaneous results, as well as the proposed experimental phenomena. 相似文献
18.
Yue Y Huang H Zhang L Wang J Yang JY Yilmaz OF Levy JS Lipson M Willner AE 《Optics letters》2012,37(4):551-553
We propose and experimentally demonstrate ultrawideband monocycle pulse generation using nondegenerate two-photon absorption in a silicon waveguide. The free-carrier absorption induced pulse tail at the rising edge of inverted probe pulse is largely compensated by the overlapped pump pulse and results in a symmetric negative monocycle pulse. A 143 ps Gaussian monocycle pulse is successfully obtained with a 131.7% fractional 10 dB bandwidth using a 68 ps pulsed pump. The 10 dB bandwidth and center frequency of the RF spectrum for the generated monocycle pulse can be largely tuned using an optical delay line. An operational bandwidth of 30 nm is demonstrated experimentally with stable performance, and larger optical bandwidth is expected. 相似文献
19.
Time-resolved absorption spectra of the A exciton in CdSe are measured by using pico-second white-light pulses produced by a self-phase modulation technique. The absorption peak of the n = 1 A exciton shifts to the high-energy side due to the high-density effect. The magnitude of the shift reaches a maximum at 20 psec after the pulse excitation, which is considered to indicate that the time constant for the formation of the n = 1 excitons by band-to-band excitation is about 20 psec. 相似文献
20.
E. A. Gazazyan G. G. Grigoryan 《Journal of Contemporary Physics (Armenian Academy of Sciences)》2016,51(3):244-249
The possibility of formation of a coherent dark state in the five-level system in the entire volume of the medium in an adiabatic pulse propagation is investigated. It is shown that the dark state formation is independent on the value of the first two-photon detuning from the resonance, which may be changed during the propagation in the medium. In the case of the M-type system with the equal strengths of oscillators at the extreme transitions it is shown that the self-phase modulation does not influence the coherent effects while in the ladder-type system it may lead to the destruction of the dark state. The estimation of the length of the medium in which the propagation effects are negligible is obtained. 相似文献