Multiplexed image storage by electromagnetically induced transparency in a solid

We report on frequency- and angle-multiplexed image storage by electromagnetically induced transparency (EIT) in a ${\mathrm{Pr}}^{3+}$:${\mathrm{Y}}_2{\mathrm{SiO}}_5$ crystal. Frequency multiplexing by EIT relies on simultaneous storage of light pulses in atomic coherences, driven in different frequency ensembles of the inhomogeneously broadened solid medium. Angular multiplexing by EIT relies on phase matching of the driving laser beams, which permits simultaneous storage of light pulses propagating under different angles into the crystal. We apply the multiplexing techniques to increase the storage capacity of the EIT-driven optical memory, in particular to implement multiplexed storage of larger two-dimensional amounts of data (images). We demonstrate selective storage and readout of images by frequency-multiplexed EIT and angular-multiplexed EIT, as well as the potential to combine both multiplexing approaches towards further enhanced storage capacities.

Figure 1

Coupling scheme in ${\mathrm{Pr}}^{3+}$:${\mathrm{Y}}_2{\mathrm{SiO}}_5$ for two frequency ensembles ${\epsilon }_1$, ${\epsilon }_2$ of dopant ions with a frequency separation of $\delta {\nu }_{\epsilon }$.

Figure 2

Experimental setup. The two control beamlines C1 and C2 pass the weak probe beamlines P1 and P2 under angles of ${\alpha }_1=1.5^{\circ }$ and ${\alpha }_2=2.7^{\circ }$ in air. In the experiments on frequency multiplexing we use the probe beamlines P1 and P2, as well as control beamline C1. In the experiments on angular multiplexing we use all four beamlines P1, P2, C1, and C2.

Figure 3

Preparation of two frequency ensembles in the doped solid by optical pumping. (a) Experimentally recorded absorption spectra. Black dotted line, spectral pit after the first preparation step with a frequency chirped pulse; blue solid line, spectrum after additional application of a single repump pulse and a single cleaning pulse; red dashed line, spectrum after application of two repump and cleaning pulses with frequency spacings of $\delta {\nu }_{\epsilon }=2\text{MHz}$. (b) Schematic pulse sequence for preparation of a single frequency ensemble (blue solid line). (c) Schematic pulse sequence for preparation of two frequency ensembles (red dashed line).

Figure 4

(Top) Pulse sequences (experimental data) for frequency-multiplexed light storage. Laser powers of control write and read pulses (red open squares), probe pulses (blue solid circles), and retrieved signal pulses (blue open circles). We denote single probe pulses by “p”, control write and read pulses by “w” and “r”, and retrieved signal pulses by “s”. The peak Rabi frequencies of the probe and control pulses are ${\Omega }_{\mathrm{p}1}=2\pi \times 264\text{kHz}$, ${\Omega }_{\mathrm{p}2}=2\pi \times 221\text{kHz}$ and ${\Omega }_{\mathrm{C}1}=2\pi \times 392\text{kHz}$. The frequency detunings of the probe and control pulses are $\Delta {\nu }_{\mathrm{p}1}=13\text{MHz}$, $\Delta {\nu }_{\mathrm{p}2}=15\text{MHz}$, $\Delta {\nu }_{\mathrm{w}1,\mathrm{r}1}=2.8\text{MHz}$, $\Delta {\nu }_{\mathrm{w}2,\mathrm{r}2}=4.8\text{MHz}$. In order not to overload the figure, we do not depict the RF rephasing pulses between the optical write and read processes. (Bottom) Image masks on the probe beams P1 and P2 (left). Sum of the spatial profiles of the signal pulses s1 and s2 after a storage time of $\Delta t=550\mu \text{s}$ (right). The gray shaded area illustrates the exposure time of the CCD camera.

Figure 5

Image storage by frequency multiplexed EIT. The matrices on the left show the input images (i.e., masks on the probe beams). The matrices on the right show the corresponding retrieved images (i.e., spatial profiles of the signal beams). We consider the cases (a) selective writing and simultaneous readout and (b) simultaneous writing and selective readout. As an example on how to read the graphics, we consider the first line of the matrices in case (b): We simultaneously write two different images with p1 and p2. We readout with r1, while r2 is switched off. On the signal beam s1 we correctly retrieve the image from p1 without cross-talk from the other image.

Figure 6

(Top) Pulse sequences (experimental data) for angle multiplexed light storage. Laser powers of control write and read pulses (red open squares), probe pulses (blue solid circles), and retrieved signal pulses (blue open circles). The peak Rabi frequencies of the probe and control pulses are ${\Omega }_{\mathrm{p}1}=2\pi \times 178\text{kHz}$, ${\Omega }_{\mathrm{p}2}=2\pi \times 127\text{kHz}$, ${\Omega }_{\mathrm{C}1}=2\pi \times 320\text{kHz}$, and ${\Omega }_{\mathrm{C}2}=2\pi \times 288\text{kHz}$. The frequency detunings of the probe and control pulses are $\Delta {\nu }_{\mathrm{p}1,\mathrm{p}2}=13\text{MHz}$ and $\Delta {\nu }_{\mathrm{C}1,\mathrm{C}2}=2.8\text{MHz}$. Image masks on the probe beams P1 and P2 (left). Sum of the spatial profiles of the signal pulses s1 and s2 after a storage time of $\Delta t=550\mu \text{s}$ (right). The gray shaded area illustrates the exposure time of the CCD camera.

Figure 7

Image storage by angular multiplexed EIT. The matrices on the left show the input images (i.e., masks on the probe beams). The matrices on the right show the corresponding retrieved images (i.e., spatial profiles of the signal beams). We consider the cases (a) selective writing and simultaneous readout and (b) simultaneous writing and selective readout. For an example on how to read the graphics, see caption of Fig. 5.

Figure 8

Pulse sequences (experimental data) for combined frequency-angle multiplexed light storage. Laser powers of control write and read pulses (red open squares), probe pulses (blue solid circles), and retrieved signal pulses (blue open circles). The peak Rabi frequencies of the probe and control pulses are ${\Omega }_{\mathrm{p}1,\mathrm{p}3}=2\pi \times 298\text{kHz}$, ${\Omega }_{\mathrm{p}2,\mathrm{p}4}=2\pi \times 212\text{kHz}$, ${\Omega }_{\mathrm{C}1}=2\pi \times 478\text{kHz}$, and ${\Omega }_{\mathrm{C}2}=2\pi \times 407\text{kHz}$.