All-optical Routing Process By Light Storage In A Pr: YSO Crystal

All-optical routing by light storage in Pr:YSO crystal is a atomic coherence process based on light storage, which realizes the distribution or the total conversion of the optical information by using a series of pulses, which interact with an atomic or molecular system. We manipulate the open or the close of the control beams to realize the release of routing pulses,this is the all-optical routing process. When we change the intensity of the control beam,the energy and width of the released signals will also change.So far, most reports on all-optical routing process are in atomic vapor. For many potential applications, a solid-state medium is preferred. However, most solid materials have relatively broad optical linewidths and short relaxation times, which limits the achievable atom coherent effects. A notable exception to this general rule is Pr³⁺:Y²SiO⁵(Pr:YSO), which has narrow spectrum structure and long relaxation times. So far, electromagnetically induced transparency (EIT), four-wave mixing (FWM), and light storage based on EIT have been realized with these crystals. To our knowledge, however, all-optical routing process based on light storage has not been investigated with these crystals.In this thesis, we report experimentally the all-optical routing process in a Pr:YSO crystal. We consider a four-level double lambda system of Pr³⁺ irons shown in Fig 1. ³H₄ (±3/2), ³H₄ (±1/2), ¹D₂ (±3/2), and ¹D₂ (±1/2) are regarded as|1), |2), |3) and |4), respectively. The coupling fields ofω₁, andω₂ (with Rabi Fig 1 Energy level diagram of Pr:YSO frequenciesΩ₁ andΩ-2 interacts with the transitions |3> (?) |2>,|4> (?) |2>, respectively.The probe field interact with the transition|3> (?)|1>. The repump fieldω_r is on resonance with the transiton of³H₄ (±5/2) (?)¹D₂(±1/2). The repump field refills theholes burned by the coupling fields, and changes the large inhomogeneous broadening.The ionic state is initialized to|l> which can be achieved by optical pumping with these fields. We use the coupling pulseω_c1 initially couples the two empty states, |2>and |3>. Some time later another signal pulseω_p1 which is gauss shaped interact with the medium. After this process, the coherence is built between the the level |1?>and |2>.The next part is our experiment. The experimental arrangement is illustrated in Fig 2. We use a Coherent dye laser 899. The dye laser is continuous wave, and its linewidth is 0.5MHz, and its maximal output power is about 700mW in the wavelength of 605.977nm. We use acousto-optic modulators (AOM) to make four different coherent laser fields as shown. The four fieldsω_c1,ω_c2,ω_p1 andω_r areupshifted 189.8MHz,185.2MHz,200Mhz and 222.1MHz from the laser frequency, respectively. F i g 2 Schemat i c d i agram of the exper i mental setup of all -opt i ca l rout i ngprocessBS, beam spliter; L, lens; AOM, acousto-optic modulator; PD, photo-diode; OS, oscilloscope.Fig. 3—7 show the experimental results. Fig3 shows the group velocity of probe pulse is slowed down:Fig 3 slow light demonstration In our experiment, the width of gauss pulse is 43μs .in the slow light condition,the control fieldω_c1 and probe fieldω(p1) interact with the crystal, the control fieldω_c2 keep closed. The slow light is observed because of the EIT effect and it is slowed 37μs .When we we simultaneously switch on two retrieve control fields, we will see the following result:Fig 4 two retrieve control fields are simultaneously switched on (ω_c2 i s GmW)The process in the fig4 is the all-optical routing. When we stimultaneously swiched on control fieldsω_c1 andω(c2) after turning down control fieldω_ct sometime, the optical information will be contributed to two different optical channels. Note that the released signal have different propagation direction and different carried frequency, this is because the the four beams must satisfy the phase-matching condition(?). The process that optical information is separatedfrom one channel into two different channels is the All-optical routing process.Fig5 show the energy and temporary width of released signalω_p2 versus theintensity of the control-2 fieldω_c2 It is found that the energy of released signalincreases with the increment of the intensity of control-2field. This is because the intensity of the released signal is proportional to that of the associated control field. The increment of the intensity of the control-2 field leads to the result that the signal with more energy is released into the light channel with frequencyω_p2. So the intensity of the associated control field can control the distribution ratio of the signals between different light channels. The temporal width of the signal decreases with the increment of the intensity of the control-2 field. The solid curves in fig 5 are the theoretical fits.Fig 6 show the energy of released signalω_p1 increases with the increment of the intensity of control-2field. Like fig 5, The temporal width of the signal also decreases with the increment of the intensity of the control-2 field. The decrement of two released signals is because the spectral width of the EIT. The original system becomes a four-level double -lambda atomic system,where the width of the EIT widows is determined by the sum of the aquares of all control Rabi frequencies.Fig 6 the energy and temporary width of released signalω_p1 versus the intensity of the control-2 fieldω_c2We study the energy ratio of the released signals in the two light channels, by varying the intensity of the retrieve control-2 field and keep the intensity of the retrieve control-1 field constant. In such an EIT four-level double-lambda atomic system, the intensity of each released signal is linearly proportional to that of the associated retrieve control field. So the energy ratio (A_p2/A_p1) of the released signalsis determined by the intensity ratio (I_c2/I_c1) of the corresponding retrieve control fields.Fig 7 the energy ratio of the two released signalω_p2 andω(p1)Figure 7 shows the energy ratio (A_p2/A_p1) of the released signalsω_p2 andω(p1)as a function of the intensity of the control-2 field. We can see that the energy ratio of the releasedω_p2 andω(p1) is linearly proportional to the intensity of the control-2field. The increment of the control-2 intensity leads to the increment of the energy of the releasedω_p2 and decrement of the energy of the releasedω_p1 which isconsistent with the theoretical expectation. For the control-2 intensity of 25mW, the transfer efficiencies with respect to the original in put pulse and with respect to the slowed pulse with out storage are about 0.8% and 11%,respectively.In summary, we have experimentally demonstrated an all-optical routing based on the technique of light storage in a Pr:YSO crystal. By simultaneously switching on two retrieve control fields to rlease the stored optical information. The original optical information is distributed into two light channels. This all-optical routing by light storage may have many applications in quantum information and all-optical network.