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Abstract
All-optical devices used to process optical signals without electro-optical conversion plays a vital role in the next generation of optical information processing systems. We demonstrate an efficient all-optical modulator that utilizes a periodic dielectric atomic lattice produced in a gas of 85Rb vapor. Four orders of diffraction patterns are observed when a probe laser is passed through the lattice. The frequency shift of the peak of each diffraction order can be tuned by adjusting the control laser power and two-photon detuning, enabling this device to be used as a multi-channel all-optical modulator. Both theoretical simulations and experimental results demonstrate that this modulator can operate over a frequency band extending from about 0 to 60 MHz. This work may pave the way for studying quantum information processing and quantum networking proposed in atomic ensembles.
© 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
1. Introduction
All-optical signal processing, which is the processing of optical signals without passing into the electrical domain, has always been critical for the development of flexible optical networks [1]. The capability to transmit data over hundreds of $km$, at a very high bit rate, and without the need of any regeneration stage, makes this essential for the next generation of ultrafast, ultralow power-consumption optical information processing systems [2–4]. In order to realize all-optical signal processing, however, several types of all-optical devices are needed, including all-optical switches, all-optical flip-flops, all-optical logic gates, and all-optical modulators [5–8].
All-optical modulators, in which the modulation is produced by using a pump laser beam to control a probe beam, have great potential for use in optical communication networks [9,10]. With the development of quantum information technology, researchers need to explore new light modulation materials and device operating schemes to meet the new requirements for the integration, speed, and power consumption of modulating devices. Nonlinear optical materials, which are associated with broad wavelength operation, low optical loss, low fabrication cost, and integration compatibility with optical components, are required [11]. Recently, some exotic photonic platforms [12–14], especially for two-dimensional materials [15], have been applied to achieve all-optical modulation.
Dielectric atomic media have recently emerged as promising alternatives for all-optical modulation applications [16]. In addition to its advantage of being a pure substance, the linear and nonlinear optical properties of an atomic medium can be modified flexibly by utilizing various coherence control techniques enabled by electromagnetically induced transparency (EIT) [17]. Indeed, coherently prepared multilevel atoms with tunable optical properties are attractive systems for use in exploring novel optical devices, such as all-optical switching and routing [18], quantum storage [19], slow light [20], optical diodes [21], non-Hermitian physics [22], and non-reciprocal quantum optical systems [23]. Intriguingly, by applying a standing-wave field in an EIT medium, a probe field may diffract into higher orders, such periodic atomic medium can act as a practical diffraction device [24–27]. And the derived photonic graphene in atomic ensemble were also employed to study the interesting physical phenomenon like spin-orbit coupling and edge state [28,29]. The resulting photonic structure and diffraction patterns are highly tunable, which makes such a structure a good carrier for free space based all-optical switching [30]. However, to the best of our knowledge, the realization of an all-optical modulator using a periodic dielectric atomic lattice has not been reported previously.
In this work, we demonstrate a novel all-optical modulator that makes use of an optically induced atomic lattice in a three-level atomic vapor. Such a lattice is established by the interference of two control fields, and a probe field is launched into it. As a result, the probe field can be effectively diffracted into high-order directions. Remarkably, the frequency shifts of the maximum diffraction intensity of each order can be tuned by adjusting the control laser power and two-photon detuning, which enables the system to be used as a multi-channel all-optical modulator. Compared with a traditional modulator, this all-optical device has the following advantages. Firstly, the operating frequency band ranges from about 0 to 60 MHz, which is hard to achieve with traditional modulators. Secondly, this modulator can realize multi-channel information processing simultaneously. Thirdly, this modulator provides a novel approach for studying quantum information processing, and is also an essential element in the construction of quantum networks with atomic ensembles.
2. Experimental setup
A $V$-type three-level $^{85}$Rb atomic structure composed by $5S_{1/2}(F=2)-5P_{3/2}(F=3)$ and $5S_{1/2}(F=2)-5P_{1/2}(F=3)$ transitions shown in Fig. 1(a) is employed in this experiment. Figure 1(b) schematically depicts the principle of this all-optical modulator. The functional area of the modulator consists of a periodic dielectric atomic lattice inside a vapor, which is established by two control laser beams crossing at a small angle. An input probe field passing through this modulator is diffracted into multiple orders with different spatial positions, and the different order has different frequency shift.
Fig. 1. (a) The relevant energy levels of the V-type configuration of $^{85}$Rb atoms. (b) The schematic diagram of the principle of the all-optical modulator. (c) The sketch of the experimental setup. DL, diode laser; HWP, half-wave plate; PBS, polarization beam splitter; SAS, saturation absorption spectroscopy; AOM, acousto-optic modulator; M, high reflection mirror; QWP, quarter-wave plate; BB, beam block; EIT, electromagnetically induced transparency; AP, anamorphic prism; BS, beam splitter; CCD, charge-coupled device; L, lens; PD, photodetector.
Figure 1(c) shows the sketch of the experimental setup. The control laser corresponding to the hyperfine transition $5S_{1/2}(F=2)-5P_{1/2}(F=3)$ at 795 nm is provided by a diode laser (DL pro, Toptica). A weak beam that is split from the main beam first passes through a double-pass configuration based on an acousto-optical modulator (AOM), and the resulting beam is then used to lock the frequency by saturation absorption spectroscopy. After the main beam frequency is shifted by another AOM, the shape of the beam is adjusted into an elliptical profile by an anamorphic prism pair. The two shaped beams, each with same intensity and profile, intersect at the center of the rubidium cell with an angle of $2\varphi \approx 0.4^{\circ }$ to construct the periodic dielectric atomic lattice. The spatial periodicity of the standing-wave control field is $d=\lambda _{c}/(2sin\varphi )\approx 114$ µm, where $\lambda _{c}$ is the wavelength of the control laser. The other diode laser (DL pro, Toptica) operating at $^{85}$Rb D2 line (780 nm), serves as the probe field, is frequency locked in the same way as the control laser. The diffraction patterns of the probe beam passing through the vapor are observed in real-time with a charge coupled device (CCD). In addition, the multiple spatially separated diffraction signals are recorded by different photodetectors (PDs).
3. Experimental results and discussions
Figures 2(a) and 2(b) are the spatial intensity distributions of probe beam passing through the vapor without and with the standing-wave control field observed by a CCD, respectively. The powers of the control and probe beams are respectively 20.0 mW and 3.0 mW, and the two-photon detuning is -20 MHz. The atomic density remains at about $9.93\times 10^{12}$ cm$^{-3}$ throughout the experiment. Figure 2(b) shows that a clear diffraction pattern is observed with high resolution up to fourth order from this periodic dielectric atomic lattice. In order to obtain real-time changes in the intensity of different orders, we employed four photodetectors to record the diffraction intensity distributions. Figure 2(c) shows the detected intensity signals for the zeroth-, first-, second-, and third-order as a function of the two-photon detuning. Interestingly, the peak intensity for each diffraction order corresponds to a different two-photon detuning, and the frequencies of the higher order is gradually shift away from the two-photon resonant frequency. Moreover, higher orders have lower peak diffraction intensities.
Fig. 2. Experimental observations of the output profile of a probe beam passing through the vapor (a) without and (b) with the control beam, respectively. (c) The diffraction intensities of each order versus two-photon detuning.
In order to understand these results, we performed a theoretical simulation. The transmission function of the modulated probe laser at $z=L$ is given by
where $E_{p}(x,0)$ is the profile of the input probe beam, $k_{p}=2\pi /\lambda _{p}$, $\lambda _{p}$ is the wavelength of the probe field, $\chi '$ and $\chi ''$ are the real and imaginary parts of the system susceptibility, respectively. The susceptibility, which is associated with the dispersion and absorption of the probe field, can be expressed asUnder the assumption that the field of the input probe is a plane wave, the diffraction intensity distribution can be written as
Using Eq. (4), we can simulate the intensity variation of each order with the two-photon detuning $\Delta =\Delta _{p}+\Delta _{c}$ as shown in Fig. 3(a), which shows the same change as the experimental results. Then, we define the frequency shift of the diffraction peak from the zero two-photon detuning case as $\delta _{n}$. When scanning the detuning of control laser $\Delta _{c}$, from Eqs. (1)–(3), $\delta _{n}$ is sensitive to the probe laser detuning and control laser Rabi frequency, i.e., $\delta _{n}\varpropto (\Delta _{p},\Omega _{c})$. Figure 3(b) is the first-order frequency shift $\delta _{1}$ as a function of $\Delta _{p}$ and $\Omega _{c}$. As either the probe detuning or the control Rabi frequency increase, the shift $\delta _{1}$ first increases and then approaches saturation. The other orders exhibit similar variations.
Fig. 3. (a) The diffraction intensity of each order as a function of the two-photon detuning. Here, $\Delta _{p}=3\Gamma _{2}$ and $\Omega _{c}=1.5\Gamma _{2}$. (b) The frequency shift of the first-order diffraction peak as a function of the probe laser detuning and the control laser Rabi frequency.
In other words, by controlling either the probe laser detuning or the control laser power, the frequency shift of each order can be modified in the proposed atomic system. We first study the effect of probe laser detuning on the behavior of the diffraction peak frequency shift when the power of the control laser is 20 mW. Figure 4 shows the diffraction intensities of the zeroth-, first- and second-order vary with the control laser detuning for different probe laser detunings, respectively. The dots are experimental frequency shifts, and the dotted lines represent frequency detunings of 0, 25 MHz, and 50 MHz for frequency reference, respectively. As expected, the frequency of the maximum intensity of each diffraction order exhibits a different shift, and the higher the diffraction order, the larger the diffraction frequency shift. We also find that, as the probe laser frequency detuning increases, the frequency of the diffraction peak shifts more and eventually saturates, as shown in Figs. 4(b) and 4(c), which is in good agreement with the theoretical simulation shown in Fig. 3(b).
Fig. 4. The diffraction intensity as a function of the control laser detuning with different probe laser detunings of (a) the zeroth-order, (b) the first-order and (c) the second-order, respectively. The gray dots are the experimental results, and the three dotted lines represent frequency detunings of 0, 25 MHz, and 50 MHz for frequency reference, respectively.
We have also studied the effect of the control laser power on the behavior of the diffraction frequency shift for a probe laser detuning of 160 MHz. Figure 5 shows the diffraction intensities of the zeroth-, first- and second-order vary with the two-photon detuning for different control laser powers, respectively. The dots are again the experimental results, and the dotted lines represent the frequency detunings of 0, 25 MHz and 50 MHz for frequency reference, respectively. The frequency shifts of different orders first increase with increasing control laser power, and they reach saturation when the power is about 25 mW, just as the theory predicts.
Fig. 5. The diffraction intensity as a function of the two-photon detuning for different control laser powers of (a) the zeroth-order, (b) first-order, and (c) second-order, respectively. The gray dots are the experimental results, and the three dotted lines represent frequency detunings of 0, 25 MHz, and 50 MHz for frequency reference, respectively. Points A$_{k}$, B$_{k}$, and C$_{k}$ ($k=0, 1, 2$) are selected experimental data points that correspond to control laser powers of 20 mW, 25 mW, and 20 mW with two-photon detunings of -50 MHz, -50 MHz, and 0 MHz, respectively.
Precision optical measurements require frequency shifts of an optical beam, which can be achieved using an AOM that shifts the frequency of the diffracted beam by the acoustic frequency (from several tens of MHz, typically). Low frequency shifts can only be achieved using two consecutively placed modulators driven at slightly different frequencies [32]. This configuration, however, results in lower efficiency and higher complexity. In contrast the all-optical device described in this paper solves this problem effectively and with good performance. The typical shift ranges of the zeroth-, first-, and second-order in this experiment are about $0\sim 15$ MHz, $0\sim 40$ MHz, and $0\sim 55$ MHz, respectively. These frequency ranges suggest that we can implement an all-optical modulator with small frequency offsets. Points A$_{k}$ and B$_{k}$ in Fig. 5 correspond to the two different control laser powers of 20 mW and 25 mW with the two-photon detuning of -50 MHz, and point C$_{k}$ corresponds to two-photon detuning of 0 MHz with the control laser power of 20 mW. Here, $k=0, 1, 2$ denotes the diffraction orders of the zeroth, first and second.
Thus, we conclude that the diffraction intensities and frequency shifts of each order can be manipulated by tuning the power and frequency of the laser fields in this controllable system. Such dynamical control of the intensity provides the intensity modulation of the all-optical modulator. To quantify the dynamic behavior of the device, we measured the resulting intensities of the output beams while varying the control laser power as shown in Fig. 6(a). The two-photon detuning is set as $\Delta =-50$ MHz. The power of the control laser is adjusted precisely by an AOM modulated with a square-wave signal. Obvious intensity-intensity modulation of each order is observed. As can be seen, the diffraction intensity of each order with low power of 20 mW (point A$_{k}$) is smaller than that with high power of 25 mW (point B$_{k}$), since the diffraction intensity increases with the increase of control laser power under the same two-photon detuning. Thus, the output intensity signals labeled as 0 and 1 for each order are synchronized with the input control laser power. We can realize multi-channel simultaneous intensity modulation by using the multi-order diffraction signals with different working powers.
Fig. 6. Dynamic behavior of the all-optical modulator for changing (a) control laser power and (b) two-photon detuning. The working points are chosen from Fig. 5.
It is even more interesting that, by selecting two suitable two-photon frequency detunings, such as $\Delta =-50$ MHz (point A$_{k}$) and $\Delta =0$ (point C$_{k}$), the variation in the diffraction intensity of each order is different. Figure 6(b) shows the resulting intensities of the output beams for changing the two-photon detuning. The control laser power is chosen as 20 mW. For zeroth-order, the output signal of the diffraction intensity is synchronized with the input two-photon detuning, since the diffraction intensity at low detuning point A$_{0}$ is smaller than that at high detuning point C$_{0}$. When the intensity at detuning point A$_{1}$ is approximately equal to that at detuning point C$_{1}$ for the first-order, the output signal always remains at about the same level. While the output signal is the opposite of the input signal for the second-order since the intensity at detuning point A$_{2}$ is higher than that at detuning point C$_{2}$. Therefore, by controlling the different two-photon detunings, we can use the output diffraction signal for each order to construct a multi-port asynchronous frequency-intensity modulated signal.
4. Conclusions
We have demonstrated an all-optical modulator based on a periodic dielectric atomic lattice formed in a three-level atomic vapor. With multiple tunable parameters and various coherence control techniques based on EIT, this novel modulator exhibits much higher tunability and can be realized with the use of a simple experimental setup. Compared with the traditional AOM, this all-optical modulator has the following advantages: The operating frequency band of this highly adjustable modulator extends from about 0 to 60 MHz, which is hard to achieve with traditional modulators. The feature that each channel can be independently tuned makes multi-channel information distribution possible, and this novel all-optical modulator can be employed to achieve stable and precise frequency chains with multiple independent lasers. Thus, the all-optical device demonstrated in this paper is useful for quantum information processing and for quantum networking proposed in atomic ensembles.
Funding
National Key Research and Development Program of China (2017YFA0304203); National Natural Science Foundation of China (61875112, 62075121, 91736209); Program for Sanjin Scholars of Shanxi Province; Key Research and Development Program of Shanxi Province for International Cooperation (201803D421034); 1331KSC.
Disclosures
The authors declare no conflicts of interest.
References
1. P. Minzioni, C. Lacava, T. Tanabe, J. Dong, X. Hu, G. Csaba, W. Porod, G. Singh, A. E. Willner, A. Almaiman, V. T. Company, J. Schröder, A. C. Peacock, M. J. Strain, F. Parmigiani, G. Contestabile, D. Marpaung, Z. Liu, J. E. Bowers, L. Chang, S. Fabbri, M. R. Vázquez, V. Bharadwaj, S. M. Eaton, P. Lodahl, X. Zhan, B. J. Eggleton, W. J. Munro, K. Nemoto, O. Morin, J. Laurat, and J. Nunn, “Roadmap on all-optical processing,” J. Opt. 21(6), 063001 (2019). [CrossRef]
2. J. L. O’Brien, “Optical quantum computing,” Science 318(5856), 1567–1570 (2007). [CrossRef]
3. C. Koos, P. Vorreau, T. Vallaitis, P. Dumon, W. Bogaerts, R. Baets, B. Esembeson, I. Biaggio, T. Michinobu, F. Diederich, W. Freude, and J. Leuthold, “All-optical high-speed signal processing with silicon-organic hybrid slot waveguides,” Nat. Photonics 3(4), 216–219 (2009). [CrossRef]
4. M. Li, L. Wang, X. Li, X. Xiao, and S. Yu, “Silicon intensity Mach-Zehnder modulator for single lane 100 Gb/s applications,” Photonics Res. 6(2), 109–116 (2018). [CrossRef]
5. T. Tanabe, M. Notomi, S. Mitsug, A. Shinya, and E. Kuramochi, “Fast bistable all-optical switch and memory on silicon photonic crystal on-chip,” Opt. Lett. 30(19), 2575–2577 (2005). [CrossRef]
6. A. Shinya, S. Mitsugi, T. Tanabe, M. Notomi, I. Yokohama, H. Takara, and S. Kawanishi, “All-optical flip-flop circuit composed of coupled two-port resonant tunneling filter in two-dimensional photonic crystal slab,” Opt. Express 14(3), 1230–1235 (2006). [CrossRef]
7. A. Fushimi and T. Tanabe, “All-optical logic gate operating with single wavelength,” Opt. Express 22(4), 4466–4479 (2014). [CrossRef]
8. L. Stern, B. Desiatov, N. Mazurski, and U. Levy, “Strong coupling and high-contrast all-optical modulation in atomic cladding waveguides,” Nat. Commun. 8(1), 14461 (2017). [CrossRef]
9. H. M. Gibbs, Optical Bistability: Controlling Light with Light. (Academic, 1985).
10. Z. Chai, X. Hu, F. Wang, X. Niu, J. Xie, and Q. Gong, “Ultrafast all-optical switching,” Adv. Opt. Mater. 5(7), 1600665 (2017). [CrossRef]
11. M. Ono, M. Hata, M. Tsunekawa, K. Nozaki, H. Sumikura, H. Chiba, and M. Notomi, “Ultrafast and energy-efficient all-optical switching with graphene-loaded deep-subwavelength plasmonic waveguides,” Nat. Photonics 14(1), 37–43 (2020). [CrossRef]
12. V. R. Almeida, C. A. Barrios, R. R. Panepucci, and M. Lipson, “All-optical control of light on a silicon chip,” Nature 431(7012), 1081–1084 (2004). [CrossRef]
13. W. Chen, K. M. Beck, R. Bücker, M. Gullans, M. D. Lukin, H. Tanji-Suzuki, and V. Vuletić, “All-optical switch and transistor gated by one stored photon,” Science 341(6147), 768–770 (2013). [CrossRef]
14. L. Stern, M. Grajower, and U. Levy, “Fano resonances and all-optical switching in a resonantly coupled plasmonic-atomic system,” Nat. Commun. 5(1), 4856 (2014). [CrossRef]
15. Y. Fang, Y. Ge, C. Wang, and H. Zhang, “Mid-infrared photonics using 2D materials: status and challenges,” Laser Photonics Rev. 14(1), 1900098 (2020). [CrossRef]
16. J. T. Tippett, D. Berkowitz, L. C. Clapp, C. J. Koester, and A. Vanderburgh, Optical and electro-optical information processing. (MIT University, 1965).
17. S. E. Harris, “Electromagnetically induced transparency,” Phys. Today 50(7), 36–42 (1997). [CrossRef]
18. J. T. Sheng, U. Khadka, and M. Xiao, “Realization of all-optical multistate switching in an atomic coherent medium,” Phys. Rev. Lett. 109(22), 223906 (2012). [CrossRef]
19. D. Ding, W. Zhang, Z. Zhou, S. Shi, G. Xiang, X. Wang, Y. Jiang, B. Shi, and G. Guo, “Quantum storage of orbital angular momentum entanglement in an atomic ensemble,” Phys. Rev. Lett. 114(5), 050502 (2015). [CrossRef]
20. A. H. Safavi-Naeini, T. P. Mayer Alegre, J. Chan, M. Eichenfield, M. Winger, Q. Lin, J. T. Hill, D. E. Chang, and O. Painter, “Electromagnetically induced transparency and slow light with optomechanics,” Nature 472(7341), 69–73 (2011). [CrossRef]
21. D. Wang, H. Zhou, M. Guo, J. Zhang, J. Evers, and S. Zhu, “Optical diode made from a moving photonic crystal,” Phys. Rev. Lett. 110(9), 093901 (2013). [CrossRef]
22. Z. Zhang, F. Li, G. Malpuech, Y. Zhang, O. Bleu, S. Koniakhin, C. Li, Y. Zhang, M. Xiao, and D. D. Solnyshkov, “Particlelike behavior of topological defects in linear wave packets in photonic graphene,” Phys. Rev. Lett. 122(23), 233905 (2019). [CrossRef]
23. C. Liang, B. Liu, A. Xu, X. Wen, C. Lu, K. Xia, M. K. Tey, Y. Liu, and L. You, “Collision-induced broadband optical nonreciprocity,” Phys. Rev. Lett. 125(12), 123901 (2020). [CrossRef]
24. Y. Zhang, Z. Wang, Z. Nie, C. Li, H. Chen, K. Lu, and M. Xiao, “Four-wave mixing dipole soliton in laser-induced atomic gratings,” Phys. Rev. Lett. 106(9), 093904 (2011). [CrossRef]
25. F. Wen, H. Ye, X. Zhang, W. Wang, S. Li, H. Wang, Y. Zhang, and C. Qiu, “Optically induced atomic lattice with tunable near-field and far-field diffraction patterns,” Photonics Res. 5(6), 676–683 (2017). [CrossRef]
26. J. Yuan, C. Wu, L. Wang, G. Chen, and S. Jia, “Observation of diffraction pattern in two-dimensional optically induced atomic lattice,” Opt. Lett. 44(17), 4123–4126 (2019). [CrossRef]
27. J. Yuan, S. Dong, C. Wu, L. Wang, L. Xiao, and S. Jia, “Optically tunable grating in a V + Ξ configuration involving a Rydberg state,” Opt. Express 28(16), 23820–23828 (2020). [CrossRef]
28. Z. Zhang, S. Liang, F. Li, S. Ning, Y. Li, G. Malpuech, Y. Zhang, M. Xiao, and D. Solnyshkov, “Spin-orbit coupling in photonic graphene,” Optica 7(5), 455–462 (2020). [CrossRef]
29. Z. Zhang, R. Wang, Y. Zhang, Y. V. Kartashov, F. Li, H. Zhong, H. Guan, K. Gao, F. Li, Y. Zhang, and M. Xiao, “Observation of edge solitons in photonic graphene,” Nat. Commun. 11(1), 1902 (2020). [CrossRef]
30. A. W. Brown and M. Xiao, “All-optical switching and routing based on an electromagnetically induced absorption grating,” Opt. Lett. 30(7), 699–701 (2005). [CrossRef]
31. H. Ling, Y. Q. Li, and M. Xiao, “Electromagnetically induced grating: Homogeneously broadened medium,” Phys. Rev. A 57(2), 1338–1344 (1998). [CrossRef]
32. M. Taglieber, A. C. Voigt, F. Henkel, S. Fray, T. W. Hänsch, and K. Dieckmann, “Simultaneous magneto-optical trapping of three atomic species,” Phys. Rev. A 73(1), 011402 (2006). [CrossRef]
