Enhanced all-optical tuning of leaky eigenmodes in photonic crystal waveguides

Abstract

We demonstrate all-optical switching in an active two-dimensional photonic crystal waveguide, observing as large as 16 nm blueshifts of a leaky eigenmode at 839 nm and switching ratios of almost 70%. These results are larger than those previously observed in similar experiments performed on passive photonic crystal waveguides; the enhancement is due to resonant photogeneration of carriers by In(0.12)Al(0.2)Ga(0.68)As quantum wells in the core of the waveguide. The effective change in the refractive index of the structure is approximately10(-2), with a rise time of approximately1 ps and a decay time of approximately10 ps, potentially allowing high-speed switching and fast modulation rates.

Ultrafast reflectivity modulation inAlxGa1−xAs∕Iny

“…In the case of real carriers excited by twophoton absorption, we expect a finite rise time as the hot carriers relax to the bottom of the bands. 16 This process is clearly observed as the rising edge for positive time delays in Fig. 5͑a͒.…”

“…In our previous work we have investigated the nonlinear shifts of the photonic coupling resonances induced by free carriers. [12][13][14][15][16] The free carriers can be excited by singlephoton absorption when the pump photon energy is above the band gap of the waveguide core, or by multiphoton absorption for smaller photon energies. These real-carrier effects occur over a very broad range of pumping conditions, making it somewhat challenging to observe the faster nonlinearities associated with virtual carriers.…”

“…17 In this paper, we demonstrate a subpicosecond reflectivity modulation in Al x Ga 1−x As/ In y Al x Ga 1−x−y As quantum well photonic crystal waveguides under both near-resonant and nonresonant pumping conditions. This is a significant development on our previous work, in which the response time was determined by the slower recombination dynamics of real carriers, [12][13][14][15][16] and also on ultrafast work by other groups, which has so far been restricted to bulk materials. 9,17 We have used the same time-resolved surface reflectivity pumpprobe technique as previously, but we now report an ultrafast response time that we attribute to virtual carrier effects.…”

“…1 The possibility of fast optical nonlinearities has been predicted theoretically [2][3][4][5] and demonstrated experimentally in several reports, [6][7][8][9][10][11] including earlier work within our own group. [12][13][14][15][16] Despite the significant work carried out to date, the nonlinear properties of PCs are still not fully understood, and there is considerable scope for improved control of the optical properties, especially as regards the response time.…”