Ultrafast optical switching and data encoding on synthesized light fields

Abstract

Modern electronics are founded on switching the electrical signal by radio frequency electromagnetic fields on the nanosecond time scale, limiting the information processing to the gigahertz speed. Recently, optical switches have been demonstrated using terahertz and ultrafast laser pulses to control the electrical signal and enhance the switching speed to the picosecond and a few hundred femtoseconds time scale. Here, we exploit the reflectivity modulation of the fused silica dielectric system in a strong light field to demonstrate the optical switching (ON/OFF) with attosecond time resolution. Moreover, we present the capability of controlling the optical switching signal with complex synthesized fields of ultrashort laser pulses for data binary encoding. This work paves the way for establishing optical switches and light-based electronics with petahertz speeds, several orders of magnitude faster than the current semiconductor-based electronics, opening a new realm in information technology, optical communications, and photonic processor technologies.

Fig. 1.. The basic principle of the attosecond optical switching based on the strong field interaction with dielectric.

The pump light field induces the instantaneous reflectivity change in the dielectric (fused silica) system following the shape of the incident pump pulse waveform in real time. The reflectivity modification is detected by measuring the reflected probe beam’s change using a photodetector (e.g., photodiode) as a function of the time delay between pump and probe beams. The detected reflected signal is switched OFF/ON (presented by 0 and 1), depending on the field intensity at the time τ, in the real time. The switching resolution is equal to the duration of the half-cycle field (900 as) of the pump pulse and can be controlled by tailoring the pump field waveform using the attosecond light field synthesis approach. The attosecond optical switching and control allow to encode data on ultrafast laser pulse and open the door for establishing the ultrafast optical switches.

Fig. 2.. Attosecond optical switching.

The reflectivity of SiO₂ is modulated in real time due to the interaction with a strong (pump) light field. (A) The measured spectrogram (average of three scans) of the reflected probe beam as a function of the time delay between the pump and probe pulses. (B) The obtained spectrogram by subtracting the probe spectrum in the absence of pump field from the measured spectrogram [shown in (A)]. The reflectivity switches between maximum to minimum alternatively in 900-as time scale. (C) The normalized total reflectivity modulation (TRM) of the SiO₂ in the strong field is retrieved from the measured spectrogram [in (A)] by the integration of the probe spectrum at each instance of time. (D) The probe beam’s spectrum reflected from the SiO₂ in the equilibrium state (in the absence of pump field) is shown as the black line. In contrast, reflected spectra intensities of the probe beam [outlined from the spectrogram in (A)] at τ = 0 and 0.9 fs are plotted in the red and blue lines, respectively. arb. un., arbitrary units.

Fig. 3.. Simulated reflectivity dynamics of fused silica in a strong light field.

(A) The retrieved reflectivity behavior of fused silica in strong field extracted from the measured spectrogram (see Discussion section) in frequency and time domains. (B) The amplitude of the reflectivity oscillation as a function of wavelength is shown as blue line calculated by halving the difference between maximum and minimum of an oscillation cycle [shown as white dashed rectangle in (A)]. The offset is calculated by averaging the maximum and minimum in an oscillation cycle and is shown as the red line. The transient reflectivity change of SiO₂ under no influence of the pump pulse is shown as the black line. (C and D) The simulation of the measured spectrograms in Fig. 2 (A and B) are calculated by the developed simple model considering the effect of the spectral phase of the driver pulse as explained in the Discussion section.

Fig. 4.. Ultrafast light field encoding.

(A) (I to III) The measured spectrograms of the reflected probe beam triggered by three different synthesized waveforms after subtracting the probe spectrum in the absence of the pump field. (B) (I to III) The positive value of the probe spectra integration as a function of time, representing the measured light signal by a photodetector in real-time, after subtracting the background. The light signal switches ON/OFF alternatively every half-cycle. (C) (I to III) The detected light signals above a 60% threshold. The light signals are switched ON and OFF at different time intervals. In the insets, the slots present the signal’s detection status in real time as follows: Black (0) means that no signal was detected above the threshold, while white (1) means the signal is above the threshold and seen by the detector. This control of the optical switching signal would enable the binary data encoding on light fields with petahertz speed.