Raman-induced slow-light delay of THz-bandwidth pulses

Abstract

We propose and experimentally demonstrate a scheme to generate optically-controlled delays based on off-resonant Raman absorption. Dispersion in a transparency window between two neighboring, optically-activated Raman absorption lines is used to reduce the group velocity of broadband 765 nm pulses. We implement this approach in a potassium titanyl phosphate (KTP) waveguide at room temperature, and demonstrate Raman-induced delays of up to 140 fs for a 650-fs duration, 1.8-THz bandwidth, signal pulse; the available delay-bandwidth product is ≈ 1. Our approach is applicable to single photon signals, offers wavelength tunability, and is a step toward processing ultrafast photons.The effective operation of communication networks requires the ability to buffer and control the movement of information, whether in a postal service [1], or a quantum network [2]. All-optical controls are particularly desirable for classical and quantum photonic communication systems because manipulations can be effected rapidly, enabling high-bandwidth operations. The need for photonic propagation controls has motivated much research toward the development of slow light devices. These technologies modify the dispersion relationship between photon energy and momentum to reduce the group velocity of optical pulses; for example, using dispersion close to a reflection resonance in periodically-structured photonic media, or material dispersion associated with optical resonance features causing gain or loss [3]. Potential network applications of slow light include optical switching, signal synchronization, and buffering for all-optical routers [4]. In addition, slow light offers the prospect of improved optical sensing [5], and enhanced nonlinear interactions [6][7][8].Periodically-structured media slow light near reflection resonances, where energy is transferred between strongly-coupled forward-and backward-propagating waves, thereby reducing the group velocity [6]. Bragg gratings offer a simple implementation, however, more sophisticated coupled resonator structures are necessary to reduce the group velocity while minimizing higher-order dispersion which distorts the shape of pulses. For example, cascaded Bragg gratings [9], Moiré gratings [10,11], ring resonators [12], and photonic crystal structures [13][14][15][16][17] have all been used to demonstrate slow light. However, such structures offer limited tunability and lack continuous optical control when compared with optical absorption and gain resonance techniques.Slow light has been achieved for pulses tuned between absorbing resonances in an atomic vapour [18][19][20][21][22]. In one demonstration, pulses as short as 275 ps were delayed by up to 6.8 ps [19]. Motivated by the desire for optical control of slow light, a variety of nonlinear phenomena have been exploited, including, stimulated Brillouin scattering (SBS) [23,24], stimulated Raman scattering (SRS) [25], and electromagnetically-induced transparency (EIT) [26,27]. In EIT, a control field opens a narrow transparency window wit...

Quantum memories: emerging applications and recent advances

“…In a related recent work, a modified Raman storage interaction was used to demonstrate optically controlled, continuously tunable slow light with femtosecond-duration pulses in a potassium titanyl phosphate waveguide [ 108 ]. Signal pulses were slowed by the dispersion created when a narrowband control pulse was applied near two-photon Raman resonance with a Raman absorption doublet.…”

Quantum teleportation from light beams to vibrational states of a macroscopic diamond

“…For example, quantum coherence is hard to survive in mechanical vibration of macroscopic solids, which involves collective motion of a large number of strongly interacting atoms. Despite this challenge, achieving quantum control for the optomechanical systems becomes a recent focus of interest with remarkable progress 19 20 21 22 23 24 25 26 27 28 29 30 . This is driven in part by the fundamental interest and in part by the potential applications of these systems for quantum signal transduction 25 26 27 , sensing 19 and quantum information processing 19 20 21 .…”

“…This is driven in part by the fundamental interest and in part by the potential applications of these systems for quantum signal transduction 25 26 27 , sensing 19 and quantum information processing 19 20 21 . There are typically two routes to achieve quantum control for the optomechanical systems: one needs to either identify some isolated degrees of freedom in mechanical vibrations and cool them to very low temperature to minimize their environmental coupling 19 28 29 30 , or use the ultrafast laser technology to fast process and detect quantum coherence in such systems 20 21 22 23 24 . A remarkable example for the latter approach is provided by the optomechanical control in macroscopic diamond samples 20 21 , where the motions of two separated diamonds have been cast into a quantum-entangled state 20 .…”