Almeida, V. R., Q. F. Xu, and M. Lipson. “Ultrafast integrated semiconductor optical modulator based on the plasma-dispersion effect.” Optics Letters 30 (2005): 2403-2405. Abstract
We demonstrate integrated semiconductor optical devices with ultrafast temporal responses based on the plasma-dispersion effect. The geometry of the devices removes the dependence of the modulation time on the free-carrier dynamics. We present the theoretical analysis of the performance of such devices. We show that a silicon-based device with a free-carrier lifetime of 1.4 ns can be modulated on a time scale of only 20 ps. The ultrafast operation is verified experimentally.
Robinson, J. T., C. Manolatou, L. Chen, and M. Lipson. “Ultrasmall mode volumes in dielectric optical microcavities.” Physical Review Letters 95 (2005). Abstract
We theoretically demonstrate a mechanism for reduction of mode volume in high index contrast optical microcavities to below a cubic half wavelength. We show that by using dielectric discontinuities with subwavelength dimensions as a means of local field enhancement, the effective mode volume (V-eff) becomes wavelength independent. Cavities with V-eff on the order of 10(-2)(λ/2n)(-3) can be achieved using such discontinuities, with a corresponding increase in the Purcell factor of nearly 2 orders of magnitude relative to previously demonstrated high index photonic crystal cavities.
Almeida, V. R., C. A. Barrios, R. R. Panepucci, and M. Lipson. “All-optical control of light on a silicon chip.” Nature 431 (2004): 1081-1084. Publisher's Version Abstract
Photonic circuits, in which beams of light redirect the flow of other beams of light, are a long-standing goal for developing highly integrated optical communication components(1-3). Furthermore, it is highly desirable to use silicon - the dominant material in the microelectronic industry - as the platform for such circuits. Photonic structures that bend, split, couple and filter light have recently been demonstrated in silicon(4,5), but the flow of light in these structures is predetermined and cannot be readily modulated during operation. All-optical switches and modulators have been demonstrated with III-V compound semiconductors(6,7), but achieving the same in silicon is challenging owing to its relatively weak nonlinear optical properties. Indeed, all-optical switching in silicon has only been achieved by using extremely high powers(8-15) in large or non-planar structures, where the modulated light is propagating out-of-plane. Such high powers, large dimensions and non-planar geometries are inappropriate for effective on-chip integration. Here we present the experimental demonstration of fast all-optical switching on silicon using highly light-confining structures to enhance the sensitivity of light to small changes in refractive index. The transmission of the structure can be modulated by up to 94% in less than 500 ps using light pulses with energies as low as 25 pJ. These results confirm the recent theoretical prediction(16) of efficient optical switching in silicon using resonant structures.
Almeida, V. R., C. A. Barrios, R. R. Panepucci, M. Lipson, M. A. Foster, D. G. Ouzounov, and A. L. Gaeta. “All-optical switching on a silicon chip.” Optics Letters 29 (2004): 2867-2869. Abstract
We present an experimental demonstration of fast all-optical switching on a silicon photonic integrated device by employing a strong light-confinement structure to enhance sensitivity to small changes in the refractive index. By use of a control light pulse with energy as low as 40 pJ, the optical transmission of the structure is modulated by more than 97% with a time response of 450 ps. (C) 2004 Optical Society of America.
Xu, Q. F., V. R. Almeida, R. R. Panepucci, and M. Lipson. “Experimental demonstration of guiding and confining light in nanometer-size low-refractive-index material.” Optics Letters 29 (2004): 1626-1628. Abstract
We experimentally demonstrate a novel silicon waveguide structure for. guiding and confining light in nanometer-wide low-refractive-index material. The optical field in the low-index material is enhanced because of the discontinuity of the electric field at high-index-contrast interfaces. We measure a 30% reduction of the effective index of light propagating in the novel structure due to the presence of the nanometer-wide low-index region, evidencing the guiding and confinement of light in the low-index material. We fabricate ring resonators based on the structure and show that the structure can be implemented in highly integrated photonics.
Almeida, V. R., Q. F. Xu, C. A. Barrios, and M. Lipson. “Guiding and confining light in void nanostructure.” Optics Letters 29 (2004): 1209-1211. Abstract
We present a novel waveguide geometry for enhancing and confining light in a nanometer-wide low-index material. Light enhancement and confinement is caused by large discontinuity of the electric field at high-index-contrast interfaces. We show that by use of such a structure the field can be confined in a 50-nm-wide low-index region with a normalized intensity of 20 μm(-2). This intensity is approximately 20 times higher than what can be achieved in SiO2 with conventional rectangular waveguides.
Almeida, V. R., and M. Lipson. “Optical bistability on a silicon chip.” Optics Letters 29 (2004): 2387-2389. Abstract
We demonstrate, for the first time to our knowledge, optical bistability on a highly integrated silicon device, using a 5-μm-radius ring resonator. The strong light-confinement nature of the resonator induces nonlinear optical response with low pump power. We show that the optical bistability allows all-optical functionalities, such as switching and memory with microsecond time response and a modulation depth of 10 dB, driven by pump power as low as 45 μW. Silicon optical bistability relies on a fast thermal nonlinear optical effect presenting a 500-kHz modulation bandwidth.
Xu, Q. F., V. R. Almeida, and M. Lipson. “Time-resolved study of Raman gain in highly confined silicon-on-insulator waveguides.” Optics Express 12 (2004): 4437-4442. Abstract
We show time-resolved measurement of Raman gain in Silicon submicron-size planar waveguide using picosecond pump and probe pulses. A net nonlinear gain of 6 dB is obtained in a 7-mm long waveguide with 20.7-W peak pump power. We demonstrate an ultrafast all-optical switch based on the free-carrier dispersion effect in the silicon waveguide, whose transmission is enhanced by more than 13 dB due to the Raman effect.