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The diffraction limit of light greatly limits the development of conventional optical devices, which are difficult to be miniaturized and integrated with high density. Surface plasmons, electromagnetic modes at the metal-dielectric interface, can concentrate light into deep subwavelength dimensions, enabling the manipulation of light at the nanometer scale. Surface plasmons can be used as information carrier to transmit and process optical signals beyond the diffraction limit. Therefore, nanodevices based on surface plasmons have received much attention. By modulating surface plasmons, the modulation of optical signals at nanoscale can be realized, which is important for the development of on-chip integrated nanophotonic circuits and optical information technology. In this article, we review the modulations of propagating surface plasmons and their applications in nano-optical modulators. The wave vector of propagating surface plasmons is very sensitive to the dielectric function of the metal and the environment. By tuning the dielectric function of the metal and/or the surrounding medium, both the real and imaginary part of the wave vector of surface plasmons can be modified, leading to the modulation of the phase and propagation length of surface plasmons and thereby modulating the intensity of optical signals. We first introduce the basic principles of different types of modulations, including all-optical modulation, thermal modulation, electrical modulation, and magnetic modulation. The all-optical modulation can be achieved by modulating the polarization and phase of input light, pumping optical materials, changing the dielectric function of metal by control light, and manipulating a nanoparticle by optical force to modulate the scattering of surface plasmons. The modulation based on thermal effect depends on thermo-optic materials and phase-change materials, and the temperature change can be triggered by photothermal effect or electrical heating. For electrically controlled modulation, Pockels electro-optic effect and Kerr electro-optic effect can be employed. Electrical modulation can also be realized by controlling the carrier concentration of semiconductors or graphene, using electrochromatic materials, and nanoelectromechanical control of the waveguide. The modulation of surface plasmons by magnetic field relies on magneto-optic materials. We review recent research progresses of modulating propagating surface plasmons by these methods, and analyze the performances of different types of plasmonic modulators, including operation wavelength, modulation depth or extinction ratio, response time or modulation frequency, and insertion loss. Finally, a brief conclusion and outlook is presented.
[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31] [32] [33] [34] [35] [36] [37] [38] [39] [40] [41] [42] [43] [44] [45] [46] [47] [48] [49] [50] [51] [52] [53] [54] [55] [56] [57] [58] [59] [60] [61] [62] [63] [64] [65] [66] [67] [68] [69] [70] [71] [72] [73] [74] [75] [76] [77] [78] [79] [80] [81] [82] [83] [84] [85] [86] [87] [88] [89] [90] [91] [92] [93] [94] [95] [96] [97] [98] [99] [100] [101] [102] [103] [104] [105] [106] [107] [108] [109] [110] [111] [112] -
Figure 4. based on thermo-optic effect: (a) Modulating surface plasmons based on thermo-optic effect of dye-doped polymer film[54]; (b) modulating surface plasmons on dielectric-loaded plasmonic waveguides based on thermo-optic effect of gold nanoparticle-doped polymer[57]; (c) modulating surface plasmons by thermo-optic effect of electrically heated polymer surrounding gold stripe waveguides[59]; (d) modulating surface plasmons by thermo-optic effect of the electrically heated polymer in dielectric-loaded plasmonic waveguides[61]; (e) modulating surface plasmons by thermo-optic effect of electrically heated polymer surrounding flexible silver stripe waveguides[64]; (f) modulating surface plasmons on silver nanowires based on thermo-optic effect of silver and glycerol[68].
Figure 6. based on electro-optic effect: (a) Modulating surface plasmons based on the Pockels electro-optic effect of polymer[85]; (b) plasmonic MZI modulator based on the Pockels electro-optic effect of DLD-164[86]; (c) modulating surface plasmons based on the Kerr effect of liquid crystal[90]; (d) modulating surface plasmons based on the Kerr effect of barium titanate film[92].
Figure 8. by tuning the carrier concentration of graphene: (a) Modulating surface plasmons on silver nanowire by tuning the carrier concentration of graphene[99]; (b) modulating the wedge plasmon mode of gold waveguide by tuning the carrier concentration of graphene[100]; (c) modulating surface plasmons on gold slot waveguide by tuning the carrier concentration of graphene[101].
调制类型 调制原理 全光调制 激发和干涉调制; 光学材料调制(增益/损耗介质调制、非线性光学材料调制、光致变色材料调制、光调制波导介电函数); 光学力操控调制 热调制 热光效应调制; 相变效应调制 电调制 电光调制(线性电光效应调制、二次电光效应调制); 载流子调制(电调制半导体载流子、电调制石墨烯载流子); 电致变色材料调制; 纳机电调制 磁调制 磁光效应调制 
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调制原理 工作波长/nm 消光比/dB 响应时间/调制频率 参考文献 全光调制 633 10 — [26] 633 12.6 — [27] 633 6 10 s [48] 633 9.5 — [30] 720—900 > 20 1 ms [44] 780 0.31 200 fs [50] 830 24 — [29] 1426 ~0.46 25 MHz [34] 热调制 442 — 40 Hz [65] 633 13 上升10 s, 下降2 s [54] 785 1.2 上升4.6 μs, 下降6.5 μs [68] 1520—1630 15 上升65 μs, 下降20 μs [60] 1525 — 100 Hz [61] 1530 0.48 8.3 kHz [66] 1530—1550 3 上升2 ns, 下降800 ns [67] 1550 35 0.7 ms [59] 1550 19 上升~ms, 下降60 μs [62] 1550 28 — [64] 1550 1.6 1 μs [76] 1588—1604 7.5 40 Hz [63] 电调制 633 14 2 s [103] 659 3 — [99] 688 0.71 — [92] 780 — 1 MHz [104] 1200—2200 20 — [97] 1460—1640 10 115 GHz [89] 1480—1600 — 65 GHz [85] 1500 0.36 — [100] 1500—1600 15 70 GHz [87] 1508—1516 0.64 上升1.3 s, 下降1 s [84] 1520—1620 6 70 GHz [86] 1520—1620 9 10 kHz [95] 1540—1560 2.1 200 kHz [101] 1550 — 170 GHz [88] 1550 4.6 100 kHz [94] 磁调制 808 — 690 Hz [106] DownLoad:
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[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31] [32] [33] [34] [35] [36] [37] [38] [39] [40] [41] [42] [43] [44] [45] [46] [47] [48] [49] [50] [51] [52] [53] [54] [55] [56] [57] [58] [59] [60] [61] [62] [63] [64] [65] [66] [67] [68] [69] [70] [71] [72] [73] [74] [75] [76] [77] [78] [79] [80] [81] [82] [83] [84] [85] [86] [87] [88] [89] [90] [91] [92] [93] [94] [95] [96] [97] [98] [99] [100] [101] [102] [103] [104] [105] [106] [107] [108] [109] [110] [111] [112]
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