Ultrafast modulation with subpicosecond recovery time in a GaAs/AlGaAs nonlinear directional coupler

Abstract

All-optical modulation is observed at room temperature in a GaAs/AlGaAs multiple quantum well nonlinear directional coupler using femtosecond pulses. The origin of the ultrafast (<500 fs) recovery of the device is attributed to the optical Stark effect.

Nonlinear Guided Wave Optics

“…Analytical solutions were first reported for Αβ = 0 by Maier and Jensen [58,59], and generalized later to Αβ Φ 0 by Wabnitz and Trillo [60], and by Maier and Sitarski [61]. Switching in nonlinear directional couplers (and their analogs) has been demonstrated in glass fibers [62][63][64], and in organic [28] and semiconductor [23][24][25][26][27]29] integrated optics waveguides. 9a.…”

“…The most desirable case for an all-optical switch is for Αβ = 0, as sketched in Fig. In the other cases, deleterious effects such as two-photon absorption [27], slowly relaxing nonlinearities [23,25,26], large linear losses [23][24][25][26][27]29], and saturation in the ail-optically induced index change [24] have spoiled the response. Switching in nonlinear directional couplers (and their analogs) has been demonstrated in glass fibers [62][63][64], and in organic [28] and semiconductor [23][24][25][26][27]29] integrated optics waveguides.…”

“…To date, the experiments have all been performed near the band gap with large throughput losses, and the dominant switching mechanisms have been electronic in nature, either exciton bleaching or band filling. In addition to switching due to refractive effects, switching due to absorption band bleaching or shifting have also been demonstrated [24,27]. For Δί > τ, carrier diffusion plays an important role, deteriorating the response of the coupler [65].…”

“…The response depends on whether the input pulses (Δί) are shorter or longer than the carrier recombination time (τ, typically 10s of nanoseconds for GaAs). 11, show switching on a femtosecond time scale with kilowatt input powers [27]. For Δί < τ, the index change caused by carrier excitation accumulates over the duration of the pulse, leading to pulse distortion and time varying switching response if the data rate is faster than τ -1 [66].…”

Valley-selective optical Stark effect probed by Kerr rotation

“…By harnessing the optical selection rules of materials, the Stark effect can be selectively applied to spinpolarized excitons [17][18][19], thereby splitting degenerate spin states without the use of external magnetic fields. This capability for all-optical state shifting can enable both classical applications such as ultrafast switches [20] and modulators [21] as well as quantum coherent control of spin [1][2][3][4][5][6]. The polarization-sensitive optical Stark effect can be generalized for coherent control of more exotic systems, evidenced most recently by the valley pseudospin in monolayer transition metal dichalcogenides (TMDCs) [22].…”