Volume 51 Issue 3
Apr.  2022
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He Qi, Wang Yaru, Chen Weicheng, Wan Dian, Chen Si, Gao Haoran, Guo Rongxiang, Gao Yisheng, Wang Jiaqi, Cheng Zhenzhou, Yu Yu, Liu Tiegen. Advances in short-wavelength mid-infrared silicon photonics (Invited)[J]. Infrared and Laser Engineering, 2022, 51(3): 20220043. doi: 10.3788/IRLA20220043
Citation: He Qi, Wang Yaru, Chen Weicheng, Wan Dian, Chen Si, Gao Haoran, Guo Rongxiang, Gao Yisheng, Wang Jiaqi, Cheng Zhenzhou, Yu Yu, Liu Tiegen. Advances in short-wavelength mid-infrared silicon photonics (Invited)[J]. Infrared and Laser Engineering, 2022, 51(3): 20220043. doi: 10.3788/IRLA20220043

Advances in short-wavelength mid-infrared silicon photonics (Invited)

doi: 10.3788/IRLA20220043
Funds:  National Natural Science Foundation of China (62175179,62161160335,61805164,61805175)
  • Received Date: 2022-01-11
  • Rev Recd Date: 2022-01-29
  • Accepted Date: 2022-02-10
  • Publish Date: 2022-04-07
  • Short-wavelength mid-infrared (mid-IR) (2-2.5 μm wavelengths) photonics has tremendous applications in optical communication, ranging, satellite remote sensing, disease diagnosis, and military defense. As key components of short-wavelength mid-IR optical systems, integrated optoelectronic devices have attracted great attention in the past decades. With the merit of the wide transparency window of silicon material, silicon photonic integrated circuits exhibit great potential in developing short-wavelength mid-IR optoelectronic devices. In this review paper, we briefly discuss potential applications of short-wavelength mid-IR silicon photonics, and review its history and frontier progress from three aspects, namely, passive waveguide devices, nonlinear optics waveguide devices, and optoelectronic waveguide devices.
  • [1] Thimsen E, Sadtler B, Berezin M Y. Shortwave-infrared (SWIR) emitters for biological imaging: A review of challenges and opportunities [J]. Nanophotonics, 2017, 6(5): 1043-1054. doi:  10.1515/nanoph-2017-0039
    [2] Zou Y, Chakravarty S, Chung C J, et al. Mid-infrared silicon photonic waveguides and devices [Invited] [J]. Photonics Research, 2018, 6(4): 254-276. doi:  10.1364/PRJ.6.000254
    [3] Lin H, Luo Z, Gu T, et al. Mid-infrared integrated photonics on silicon: A perspective [J]. Nanophotonics, 2017, 7(2): 393-420. doi:  10.1515/nanoph-2017-0085
    [4] Guo R, Gao H, Cheng Z, et al. Progress in mid-infrared germanium integrated optoelectronics [J]. Chinese Journal of Lasers, 2021, 48(19): 1901002. (in Chinese)
    [5] Ma H, Yang H, Tang B, et al. Passive devices at 2 µm wavelength on 200 mm CMOS-compatible silicon photonics platform [Invited] [J]. Chinese Optics Letters, 2021, 19(7): 071301. doi:  10.3788/COL202119.071301
    [6] Schliesser A, Picqué N, Hänsch T W. Mid-infrared frequency combs [J]. Nature Photonics, 2012, 6(7): 440-449. doi:  10.1038/nphoton.2012.142
    [7] Zhang M, Zhao H, Li N. Analysis of the influence of hyperspectral spectral resolution on the mineral recognition [J]. Infrared and Laser Engineering, 2006, 35(S4): 493-498. (in Chinese)
    [8] Wilson R H, Nadeau K P, Jaworski F B, et al. Review of short-wave infrared spectroscopy and imaging methods for biological tissue characterization [J]. Journal of Biomedical Optics, 2015, 20(3): 030901. doi:  10.1117/1.JBO.20.3.030901
    [9] Hu T, Dong B, Luo X, et al. Silicon photonic platforms for mid-infrared applications [Invited] [J]. Photonics Research, 2017, 5(5): 05000417.
    [10] Wysocki G, Kosterev A A, Tittel F K. Influence of molecular relaxation dynamics on quartz-enhanced photoacoustic detection of CO2 at λ =2 μm [J]. Applied Physics B, 2006, 85(2-3): 301-306. doi:  10.1007/s00340-006-2369-9
    [11] Refaat T F, Singh U N, Yu J, et al. Evaluation of an airborne triple-pulsed 2 μm IPDA lidar for simultaneous and independent atmospheric water vapor and carbon dioxide measurements [J]. Applied Optics, 2015, 54(6): 1387-1398. doi:  10.1364/AO.54.001387
    [12] Wu J, Yue G, Chen W, et al. On-chip optical gas sensors based on group-IV materials [J]. ACS Photonics, 2020, 7(11): 2923-2940. doi:  10.1021/acsphotonics.0c00976
    [13] Cai Y, Hu X. Short wave infrared imaging technology and its defence application [J]. Infrared and Laser Engineering, 2006, 35(6): 634-637. (in Chinese)
    [14] Liang Y J, Liu F, Chen Y F, et al. New function of the Yb3+ ion as an efficient emitter of persistent luminescence in the short-wave infrared [J]. Light: Science and Applications, 2016, 5(7): e16124.
    [15] Pisani M, Bianco P, Zucco M. Hyperspectral imaging for thermal analysis and remote gas sensing in the short wave infrared [J]. Applied Physics B-Lasers and Optics, 2012, 108(1): 231-236. doi:  10.1007/s00340-012-5015-8
    [16] Arnob M M P, Nguyen H, Han Z, et al. Compressed sensing hyperspectral imaging in the 0.9-2.5 μm shortwave infrared wavelength range using a digital micromirror device and InGaAs linear array detector [J]. Applied Optics, 2018, 57(18): 5019-5024. doi:  10.1364/AO.57.005019
    [17] Liu Z, Chen Y, Li Z, et al. High-capacity directly modulated optical transmitter for 2-μm spectral region [J]. Journal of Lightwave Technology, 2015, 33(7): 1373-1379. doi:  10.1109/JLT.2015.2397700
    [18] Soref R. Enabling 2 μm communications [J]. Nature Photonics, 2015, 9(6): 358-359. doi:  10.1038/nphoton.2015.87
    [19] Mashanovich G Z, Stankovic S, Topley R, et al. Silicon photonic waveguides and devices for near- and mid-IR applications [J]. IEEE Journal of Selected Topics in Quantum Electronics, 2015, 21(4): 407-418. doi:  10.1109/JSTQE.2014.2381469
    [20] Su Y K, Zhang Y, Qiu C Y, et al. Silicon photonic platform for passive waveguide devices: Materials, fabrication, and applications [J]. Advanced Materials Technologies, 2020, 5(8): 1901153. doi:  10.1002/admt.201901153
    [21] Soref R. Mid-infrared photonics in silicon and germanium [J]. Nature Photonics, 2010, 4(8): 495-497. doi:  10.1038/nphoton.2010.171
    [22] Bristow A D, Rotenberg N, van Driel H M. Two-photon absorption and Kerr coefficients of silicon for 850–2200 nm [J]. Applied Physics Letters, 2007, 90(19): 191104. doi:  10.1063/1.2737359
    [23] Cao W, Hagan D, Thomson D J, et al. High-speed silicon modulators for the 2  μm wavelength band [J]. Optica, 2018, 5(9): 1055-1062. doi:  10.1364/OPTICA.5.001055
    [24] Leo F, Kuyken B, Hattasan N, et al. Passive SOI devices for the short-wave-infrared [C]//16 th European Conference on Integrated Optics (ECIO), 2012.
    [25] Kitamura R, Pilon L, Jonasz M. Optical constants of silica glass from extreme ultraviolet to far infrared at near room temperature [J]. Applied Optics, 2007, 46(33): 8118-8133. doi:  10.1364/AO.46.008118
    [26] Miller S A, Yu M, Ji X, et al. Low-loss silicon platform for broadband mid-infrared photonics [J]. Optica, 2017, 4(7): 707-712. doi:  10.1364/OPTICA.4.000707
    [27] Chen W, Wu J, Wan D, et al. Grating couplers beyond silicon TPA wavelengths based on MPW [J]. Journal of Physics D:Applied Physics, 2021, 55(1): 015109.
    [28] Wang J Q, Cheng Z Z, Chen Z F, et al. Graphene photodetector integrated on silicon nitride waveguide [J]. Journal of Applied Physics, 2015, 117(14): 144504. doi:  10.1063/1.4917378
    [29] Xiao T H, Cheng Z, Goda K. Graphene-on-silicon hybrid plasmonic-photonic integrated circuits [J]. Nanotechnology, 2017, 28(24): 245201. doi:  10.1088/1361-6528/aa7128
    [30] Zhou T, Jia H, Ding J, et al. On-chip broadband silicon thermo-optic 2×2 four-mode optical switch for optical space and local mode switching [J]. Optics Express, 2018, 26(7): 8375-8384. doi:  10.1364/OE.26.008375
    [31] Vlasov Y, McNab S. Losses in single-mode silicon-on-insulator strip waveguides and bends [J]. Optics Express, 2004, 12(8): 1622-1631. doi:  10.1364/OPEX.12.001622
    [32] Cheng Z, Tsang H K, Xu K, et al. Spectral hole burning in silicon waveguides with a graphene layer on top [J]. Optics Letters, 2013, 38(11): 1930-1932. doi:  10.1364/OL.38.001930
    [33] Zhang Y, Cheng Z, Liu L, et al. Enhancement of self-phase modulation induced spectral broadening in silicon suspended membrane waveguides [J]. Journal of Optics, 2016, 18(5): 055503. doi:  10.1088/2040-8978/18/5/055503
    [34] Cheng Z, Goda K. Design of waveguide-integrated graphene devices for photonic gas sensing [J]. Nanotechnology, 2016, 27(50): 505206. doi:  10.1088/0957-4484/27/50/505206
    [35] Wang J, Cheng Z, Chen Z, et al. High-responsivity graphene-on-silicon slot waveguide photodetectors [J]. Nanoscale, 2016, 8(27): 13206-13211. doi:  10.1039/C6NR03122F
    [36] Wang J, Zhang L, Chen Y, et al. Saturable absorption in graphene-on-waveguide devices [J]. Applied Physics Express, 2019, 12(3): 032003. doi:  10.7567/1882-0786/ab02ca
    [37] Zhou W, Cheng Z, Chen X, et al. Subwavelength engineering in silicon photonic devices [J]. IEEE Journal of Selected Topics in Quantum Electronics, 2019, 25(3): 1-13.
    [38] Chen W, Yue G, Hu H, et al. Dual-mode GVD tailoring in a convex waveguide [J]. IEEE Photonics Journal, 2020, 12(4): 1-6.
    [39] Sharma T, Rana V, Wang J Q, et al. Design of grating based narrow band reflector on SOI waveguide [J]. Optik, 2021, 227: 165995. doi:  10.1016/j.ijleo.2020.165995
    [40] Hattasan N, Kuyken B, Leo F, et al. High-efficiency SOI fiber-to-chip grating couplers and low-loss waveguides for the short-wave infrared [J]. IEEE Photonics Technology Letters, 2012, 24(17): 1536-1538. doi:  10.1109/LPT.2012.2208452
    [41] Rouifed M S, Littlejohns C G, Tina G X, et al. Low loss SOI waveguides and MMIs at the MIR wavelength of 2 μm [J]. IEEE Photonics Technology Letters, 2016, 28(24): 2827-2829. doi:  10.1109/LPT.2016.2623319
    [42] Hagan D E, Knights A P. Mechanisms for optical loss in SOI waveguides for mid-infrared wavelengths around 2μm [J]. Journal of Optics, 2017, 19(2): 025801. doi:  10.1088/2040-8986/19/2/025801
    [43] Li F, Jackson S D, Grillet C, et al. Low propagation loss silicon-on-sapphire waveguides for the mid-infrared [J]. Optics Express, 2011, 19(16): 15212-15220. doi:  10.1364/OE.19.015212
    [44] Cheng Z, Chen X, Wong C Y, et al. Mid-infrared suspended membrane waveguide and ring resonator on silicon-on-insulator [J]. IEEE Photonics Journal, 2012, 4(5): 1510-1519. doi:  10.1109/JPHOT.2012.2210700
    [45] Zhou W, Cheng Z, Wu X, et al. Fully suspended slot waveguides for high refractive index sensitivity [J]. Optics Letters, 2017, 42(7): 1245-1248. doi:  10.1364/OL.42.001245
    [46] Chen X, Xu K, Cheng Z, et al. Wideband subwavelength gratings for coupling between silicon-on-insulator waveguides and optical fibers [J]. Optics Letters, 2012, 37(17): 3483-3485. doi:  10.1364/OL.37.003483
    [47] Cheng Z, Chen X, Wong C Y, et al. Apodized focusing subwavelength grating couplers for suspended membrane waveguides [J]. Applied Physics Letters, 2012, 101(10): 101104. doi:  10.1063/1.4750071
    [48] Cheng Z, Chen X, Wong C Y, et al. Focusing subwavelength grating coupler for mid-infrared suspended membrane waveguide [J]. Optics Letters, 2012, 37(7): 1217-1219. doi:  10.1364/OL.37.001217
    [49] Cheng Z, Chen X, Wong C Y, et al. Broadband focusing grating couplers for suspended-membrane waveguides [J]. Optics Letters, 2012, 37(24): 5181-5183. doi:  10.1364/OL.37.005181
    [50] Cheng Z, Li Z, Xu K, et al. Increase of the grating coupler bandwidth with a graphene overlay [J]. Applied Physics Letters, 2014, 104(11): 111109. doi:  10.1063/1.4869219
    [51] Cheng Z, Tsang H K. Experimental demonstration of polarization-insensitive air-cladding grating couplers for silicon-on-insulator waveguides [J]. Optics Letters, 2014, 39(7): 2206-2209. doi:  10.1364/OL.39.002206
    [52] Zhou W, Cheng Z, Sun X, et al. Tailorable dual-wavelength-band coupling in a transverse-electric-mode focusing subwavelength grating coupler [J]. Optics Letters, 2018, 43(12): 2985-2988. doi:  10.1364/OL.43.002985
    [53] Kuyken B, Hattasan N, Vermeulen D, et al. Highly efficient broadband silicon-on-insulator grating couplers for the short wave infrared wavelength range [C]//Integrated Photonics Research, Silicon and Nanophotonics, 2011.
    [54] Zhou W, Tsang H K. Dual-wavelength-band subwavelength grating coupler operating in the near infrared and extended shortwave infrared [J]. Optics Letters, 2019, 44(15): 3621-3624. doi:  10.1364/OL.44.003621
    [55] Guo R, Gao H, Liu T, et al. Ultra-thin mid-infrared silicon grating coupler [J]. Optics Letters, 2022, 47(5): 1226-1229. doi:  10.1364/OL.449140
    [56] Wang J, Cheng Z, Shu C, et al. Optical absorption in graphene-on-silicon nitride microring resonators [J]. IEEE Photonics Technology Letters, 2015, 27(16): 1765-1767. doi:  10.1109/LPT.2015.2443051
    [57] Ke X, Wu Xinru, Sung Jiun-Yu, et al. Amplitude and phase modulation of UWB monocycle pulses on a silicon photonic chip [J]. IEEE Photonics Technology Letters, 2016, 28(3): 248-251. doi:  10.1109/LPT.2015.2494000
    [58] Wang J, Zhang X, Wei Z, et al. Design of a dual-mode graphene-on-microring resonator for optical gas sensing [J]. IEEE Access, 2021, 9: 56479-56485. doi:  10.1109/ACCESS.2021.3072134
    [59] Hu Yujie, Wang Shuxiao, Wang Dawei, et al. Research progress of mid-infrared micro-ring resonator and its application [J]. Laser & Optoelectronics Progress, 2020, 57(23): 230004. (in Chinese)
    [60] Wong C Y, Cheng Z, Chen X, et al. Characterization of mid-infrared silicon-on-sapphire microring resonators with thermal tuning [J]. IEEE Photonics Journal, 2012, 4(4): 1095-1102. doi:  10.1109/JPHOT.2012.2204734
    [61] Li J, Liu Y, Meng Y, et al. 2 μm wavelength grating coupler, bent waveguide, and tunable microring on silicon photonic MPW [J]. IEEE Photonics Technology Letters, 2018, 30(5): 471-474. doi:  10.1109/LPT.2018.2799194
    [62] Xu Ke, Chen Yimin, Li Chao, et al. An ultracompact OSNR monitor based on an integrated silicon microdisk resonator [J]. IEEE Photonics Journal, 2012, 4(5): 1365-1371. doi:  10.1109/JPHOT.2012.2210278
    [63] Zhang L, Dai D. Silicon subwavelength-grating microdisks for optical sensing [J]. IEEE Photonics Technology Letters, 2019, 31(15): 1209-1212. doi:  10.1109/LPT.2019.2922230
    [64] Xing Z, Li C, Han Y, et al. Waveguide-integrated graphene spatial mode filters for on-chip mode-division multiplexing [J]. Optics Express, 2019, 27(14): 19188-19195. doi:  10.1364/OE.27.019188
    [65] Li C, Liu D, Dai D. Multimode silicon photonics [J]. Nanophotonics, 2018, 8(2): 227-247. doi:  10.1515/nanoph-2018-0161
    [66] Sun C, Ding Y, Li Z, et al. Key multimode silicon photonic devices inspired by geometrical optics [J]. ACS Photonics, 2020, 7(8): 2037-2045. doi:  10.1021/acsphotonics.0c00370
    [67] Yu Y, Chen G, Sima C, et al. Intra-chip optical interconnection based on polarization division multiplexing photonic integrated circuit [J]. Optics Express, 2017, 25(23): 28330-28336. doi:  10.1364/OE.25.028330
    [68] Ryckeboer E, Gassenq A, Muneeb M, et al. Silicon-on-insulator spectrometers with integrated GaInAsSb photodiodes for wide-band spectroscopy from 1510 to 2300 nm [J]. Optics Express, 2013, 21(5): 6101-6108. doi:  10.1364/OE.21.006101
    [69] Rouifed M S, Littlejohns C G, Tina G X, et al. Silicon photonic devices for the mid-infrared [C]//2017 Conference on Lasers and Electro-Optics Pacific Rim, 2017: s2264.
    [70] Rouifed M S, Littlejohns C G, Tina G X, et al. Ultra-compact MMI-based beam splitter demultiplexer for the NIR/MIR wavelengths of 1.55 μm and 2 μm [J]. Optics Express, 2017, 25(10): 10893-10900. doi:  10.1364/OE.25.010893
    [71] Zheng S, Huang M, Cao X, et al. Silicon-based four-mode division multiplexing for chip-scale optical data transmission in the 2  μm waveband [J]. Photonics Research, 2019, 7(9): 1030-1035. doi:  10.1364/PRJ.7.001030
    [72] Salzberg C D, Villa J J. Infrared refractive indexes of silicon germanium and modified Selenium glass [J]. Journal of the Optical Society of America, 1957, 47(3): 244-246. doi:  10.1364/JOSA.47.000244
    [73] Liu X, Kuyken B, Roelkens G, et al. Bridging the mid-infrared-to-telecom gap with silicon nanophotonic spectral translation [J]. Nature Photonics, 2012, 6(10): 667-671. doi:  10.1038/nphoton.2012.221
    [74] Kuyken B, Verheyen P, Tannouri P, et al. Mid-infrared generation by frequency down-conversion across 1.2 octaves in a normally-dispersive silicon wire [C]//Conference on Lasers and Electro-Optics (CLEO), 2013: CTh1 F. 2.
    [75] Liu X, Osgood R M, Vlasov Y A, et al. Mid-infrared optical parametric amplifier using silicon nanophotonic waveguides [J]. Nature Photonics, 2010, 4(8): 557-560. doi:  10.1038/nphoton.2010.119
    [76] Kuyken B, Liu X, Osgood R M, et al. A silicon-based widely tunable short-wave infrared optical parametric oscillator [J]. Optics Express, 2013, 21(5): 5931-5940. doi:  10.1364/OE.21.005931
    [77] Kuyken B, Liu X, Osgood R M, et al. Mid-infrared to telecom-band supercontinuum generation in highly nonlinear silicon-on-insulator wire waveguides [J]. Optics Express, 2011, 19(21): 20172-20181. doi:  10.1364/OE.19.020172
    [78] Singh N, Hudson D D, Yu Y, et al. Midinfrared supercontinuum generation from 2 to 6  μm in a silicon nanowire [J]. Optica, 2015, 2(9): 797-802. doi:  10.1364/OPTICA.2.000797
    [79] Kou R, Hatakeyama T, Horng J, et al. Mid-IR broadband supercontinuum generation from a suspended silicon waveguide [J]. Optics Letters, 2018, 43(6): 1387-1390. doi:  10.1364/OL.43.001387
    [80] Griffith A G, Lau R K, Cardenas J, et al. Silicon-chip mid-infrared frequency comb generation [J]. Nature Communications, 2015, 6: 6299. doi:  10.1038/ncomms7299
    [81] Yu M, Okawachi Y, Griffith A G, et al. Mode-locked mid-infrared frequency combs in a silicon microresonator [J]. Optica, 2016, 3(8): 854-860. doi:  10.1364/OPTICA.3.000854
    [82] Guo R, Chen W, Gao H, et al. Is Ge an excellent material for mid-IR Kerr frequency combs around 3 μm wavelengths [J]. Journal of Lightwave Technology, 2022, 40(7): 2097-2103. doi:  10.1109/JLT.2021.3134791
    [83] Van Camp M A, Assefa S, Gill D M, et al. Demonstration of electrooptic modulation at 2165 nm using a silicon Mach-Zehnder interferometer [J]. Optics Express, 2012, 20(27): 28009-28016. doi:  10.1364/OE.20.028009
    [84] Wang X, Shen W, Li W, et al. High-speed silicon photonic Mach–Zehnder modulator at 2 μm [J]. Photonics Research, 2021, 9(4): 535-540. doi:  10.1364/PRJ.417107
    [85] Cao W, Liu S, Littlejohns C G, et al. High-speed silicon Michelson interferometer modulator and streamlined IMDD PAM-4 transmission of Mach-Zehnder modulators for the 2 μm wavelength band [J]. Optics Express, 2021, 29(10): 14438-14451. doi:  10.1364/OE.418285
    [86] Wang J, Li Q, Huang D, et al. Design of graphene-on-germanium waveguide electro-optic modulators at the 2 μm wavelength [J]. OSA Continuum, 2019, 2(3): 749-758. doi:  10.1364/OSAC.2.000749
    [87] Yue G, Xing Z, Hu H, et al. Graphene-based dual-mode modulators [J]. Optics Express, 2020, 28(12): 18456-18471. doi:  10.1364/OE.394409
    [88] Zou H, Wang Y, Zhang X, et al. Optimal design and preparation of silicon-organic hybrid integrated electro-optic modulator [J]. Optics and Precision Engineering, 2020, 28(10): 2138-2150. (in Chinese) doi:  10.37188/OPE.20202810.2138
    [89] Zhong C, Ma H, Sun C, et al. Fast thermo-optical modulators with doped-silicon heaters operating at 2 μm [J]. Optics Express, 2021, 29(15): 23508-23516. doi:  10.1364/OE.430756
    [90] Nedeljkovic M, Soref R, Mashanovich G Z. Free-carrier electrorefraction and electroabsorption modulation predictions for silicon over the 1-14-μm infrared wavelength range [J]. IEEE Photonics Journal, 2011, 3(6): 1171-1180. doi:  10.1109/JPHOT.2011.2171930
    [91] Slater B, Johnson M H, Rosenfeld L, et al. Modelling waveguide-integrated superconducting nanowire single photon detectors at short-wave infrared [C]//2018 IEEE Photonics Society Summer Topical Meeting Series (SUM), 2018: 93-94.
    [92] Grote R R, Souhan B, Ophir N, et al. Extrinsic photodiodes for integrated mid-infrared silicon photonics [J]. Optica, 2014, 1(4): 264-267. doi:  10.1364/OPTICA.1.000264
    [93] Hattasan N, Gassenq A, Cerutti L, et al. Heterogeneous integration of GaInAsSb p-i-n photodiodes on a silicon-on-insulator waveguide circuit [J]. IEEE Photonics Technology Letters, 2011, 23(23): 1760-1762. doi:  10.1109/LPT.2011.2169244
    [94] Cong H, Xue C L, Zheng J, et al. Silicon based GeSn p-i-n photodetector with longwave cutoff at 2.3 μm [C]//2016 IEEE 13th International Conference on Group IV Photonics (GFP), 2016: 106-107.
    [95] Zhang J, Lv J, Ni Z. Highly sensitive infrared detector based on a two-dimensional heterojunction [J]. Chinese Optics, 2021, 14(1): 87-99. (in Chinese) doi:  10.37188/CO.2020-0139
    [96] Hu S, Tian R, and Gan X. Two-dimensional material photodetector for hybrid silicon photonics [J]. Chinese Optics, 2021, 14(5): 1039-1055. (in Chinese) doi:  10.37188/CO.2021-0003
    [97] Guo J, Li J, Liu C, et al. High-performance silicon-graphene hybrid plasmonic waveguide photodetectors beyond 1.55 μm [J]. Light: Science & Applications, 2020, 9: 1-11. doi:  https://doi.org/10.1038/s41377-020-0263-6
    [98] Souhan B, Grote R R, Chen C P, et al. Si+-implanted Si-wire waveguide photodetectors for the mid-infrared [J]. Optics Express, 2014, 22(22): 27415-27424. doi:  10.1364/OE.22.027415
    [99] Ackert J J, Thomson D J, Shen L, et al. High-speed detection at two micrometres with monolithic silicon photodiodes [J]. Nature Photonics, 2015, 9(6): 393-396. doi:  10.1038/nphoton.2015.81
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Advances in short-wavelength mid-infrared silicon photonics (Invited)

doi: 10.3788/IRLA20220043
  • 1. School of Precision Instrument and Opto-Electronics Engineering, Tianjin University, Tianjin 300072, China
  • 2. Key Laboratory of Opto-Electronics Information Technology, Ministry of Education, Tianjin 300072, China
  • 3. College of Physics and Optoelectronics, Taiyuan University of Technology, Taiyuan 030024, China
  • 4. College of Physics and Optoelectronic Engineering, Shenzhen University, Shenzhen 518060, China
  • 5. Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan 430074, China
Fund Project:  National Natural Science Foundation of China (62175179,62161160335,61805164,61805175)

Abstract: Short-wavelength mid-infrared (mid-IR) (2-2.5 μm wavelengths) photonics has tremendous applications in optical communication, ranging, satellite remote sensing, disease diagnosis, and military defense. As key components of short-wavelength mid-IR optical systems, integrated optoelectronic devices have attracted great attention in the past decades. With the merit of the wide transparency window of silicon material, silicon photonic integrated circuits exhibit great potential in developing short-wavelength mid-IR optoelectronic devices. In this review paper, we briefly discuss potential applications of short-wavelength mid-IR silicon photonics, and review its history and frontier progress from three aspects, namely, passive waveguide devices, nonlinear optics waveguide devices, and optoelectronic waveguide devices.

    • 短波红外(Short-Wavelength Infrared, SWIR)是指波长在0.7~2.5 μm范围内的电磁波波段[1],跨越近红外(< 2 μm)[2]和中红外(≥ 2 μm)[3]两部分,其中短波中红外(2.0~2.5 μm)[4]光学具有很多独特的性质,在通信测距、卫星遥感、疾病诊断、军事国防等领域具有广泛的应用。首先,短波中红外是重要的大气透明窗口之一[5],基本不与水汽分子的主要吸收带(1.7~2.0 μm和2.4~3.3 μm)重叠[6],在大气中具有较强的穿透力,可以用于遥感和测距等应用。例如,在美国陆地卫星专题制图仪(Thematic Mapper)所采用的扫描影像中,TM-7(2.08~2.35 μm)位于此波段,可用于探测岩石类型和粘土矿物信息[7]。其次,相比近红外波段,短波中红外的光子能量较低,对应于化学分子的基频振动跃迁能量[8],其吸收光谱可用于探测化学分子,在分子光谱检测等方面具有广泛的应用[9]。以CO2气体为例,分子在2 μm波段的吸收线强可达到10−21 cm/molecule量级[10-11],比近红外波段(1.5~1.6 μm)高两个数量级以上,可实现更加灵敏的气体传感[12]。另外,短波中红外也是重要的夜视成像[13-14]和高光谱成像[15-16]波段,在军事和海洋应用中具有巨大的价值。相比可见光和近红外,短波中红外不但可以有效降低空气中小颗粒瑞利散射的光学损耗,使反射光更好地穿透雾霾和尘烟等极端环境,而且其吸收特性可用于观测海洋叶绿素和悬浊物等信息,可用于指导海上作业和海洋资源开发。最后,光通信也正在向短波中红外发展。随着传统行业数字化转型、无人驾驶汽车和增强现实等技术飞速发展,人们产生和传输的数据总量呈现指数型爆发增长,对光通信带宽的需求每年都在逐步提高。在未来十年里,现有的光通信技术将逼近1.5 μm波段单根光纤的香农极限[17],2 μm波段光通信被认为是未来解决通信容量需求的发展方向之一[18]。总之,由于具有广泛的应用前景,短波中红外光电器件的研发一直是一个热门的研究领域。

      在现有的集成光学技术中,硅基光子学在开发短波中红外集成光波导器件方面具有无可比拟的优势[2-3, 19]。首先,作为第一代半导体材料的代表,硅基材料和器件的设计、制备和表征技术的发展都非常成熟[20],且器件具备高集成度、高稳定性、高可靠性等优点[3, 21],在半导体产业中占绝对主导地位。其次,硅是一种间接带隙的半导体材料,其带隙宽度约为1.12 eV[22],在短波中红外波段透明度高(图1),非常适合开发光学波导器件[5]。并且,随着波导中传输波长的增加,波导侧壁粗糙引起的瑞利散射光学损耗逐渐降低[23],特别是,当波长大于2.15 μm时,硅基波导器件中双光子吸收引起的非线性光学损耗也可忽略不计[24],因此,硅基平台是开发高功率光电子集成器件的理想平台。最后,以硅-绝缘体晶圆(Silicon-on-Insulator,SOI)为基础,面向通信波段(1.3 μm和1.5 μm)应用所开发的硅基光子学经过多年发展已经取得了雄厚的技术积累。同时,作为氧化埋层(Buried Oxide,BOX)和波导包层的二氧化硅材料在短波中红外波段吸收较弱[18]图1),所以通信波段相关技术基本可以直接转移到短波中红外波段,无需针对短波中红外波段开发新的器件加工工艺。另外,随着波长的增加,光学器件对加工工艺的最小尺寸、设计容差、加工精度等要求还将进一步降低[27],相比通信波段,短波中红外有望实现更低的器件开发成本。因此,短波中红外硅基光子学近年来逐渐发展成为一个热门的研究课题。

      Figure 1.  Silicon waveguide devices based on SOI have low two-photon absorption and low BOX absorption in the short-wavelength mid-IR band[22, 25-26]

      文中,笔者简要回顾了短波中红外硅基光子学的发展历程,从无源波导器件、非线性光学波导器件和光电波导器件等三方面综述了该领域的前沿进展,并对该领域的发展前景做出了简要的展望。论文的具体结构安排如下:在第一节中,讨论了目前所报道的四类短波中红外硅基无源器件,包括波导、光栅耦合器、微型谐振腔、复用/解复用器;在第二节中,总结了短波中红外硅基非线性光学波导器件的研究,包括可用于开发片上集成的短波中红外相干光源和放大器;在第三节中,综述了短波中红外硅基波导集成的调制器和探测器的研究;在第四节中,对论文进行总结。

    • 无源波导器件是硅基光子学的基石[5],在过去的研究中,科研工作者们基于不同的硅基晶圆开发了多种类型的短波中红外硅基光学器件,包括波导、光栅耦合器、微型谐振腔、复用/解复用器件等。器件结构和性能的改进为实现低成本、高密度、多功能的短波中红外光电器件片上集成奠定了基础,有望惠及光通信、光互连、光学传感和非线性光学等多个领域。

    • 硅基波导具有光场限域能力强、光学损耗低、CMOS工艺兼容性好、可实现高密度器件集成等优点,是硅基光子学的研究重点[28-30]。相比于通信波段[31-39],短波中红外硅基波导器件发展较晚,但其具备开发超低光学损耗器件的强大潜力。2012年,Hattasan N等人[40]报道了基于SOI晶圆的单模条形波导(Strip Waveguide),在2.2 μm波长处测得其传输光学损耗低于0.6 dB/cm。随后,2016年, Rouifed M S等人[41]基于SOI晶圆制作了厚度为340 nm、宽度为600 nm、刻蚀深度为240 nm的单模脊形波导(Rib Waveguide),测得波导在2 μm波长处的传输光学损耗为(1.00±0.008) dB/cm。2017年,Hagan D等人[42]基于SOI晶圆制作了220 nm厚的单模条形波导和脊形波导,在2.02 μm波长处,测得条形波导和脊形波导的传输光学损耗分别为(3.3±0.5)、(1.9±0.2) dB/cm,如图2(a)所示。他们同时测量了弯曲半径为3 μm的波导弯曲损耗,条形和脊形波导的弯曲损耗分别为0.36 dB/90°和0.68 dB/90°。实验证明,与条形波导的传输损耗相比,脊形波导的传输损耗要更低。进一步,2021年, Chen W等人[27]基于多项目晶圆(Multi-Project Wafer,MPW)工艺制作了工作在2~2.5 μm波段的硅基波导器件,如图2(b)所示,为开发低成本、高密度集成的短波中红外片上系统提供了指导。2021年, Ma H等人[5]基于SOI晶圆研究了工作在2 μm波长处的波导交叉器件,通过级联多个波导交叉器件进行测量,得到单个波导交叉器件的插入损耗为(0.08±0.011) dB,交叉串扰小于 −34 dB。上述结果表明,氧化埋层对短波中红外的光学吸收损耗较低,SOI波导器件在光谱学和非线性光学中有广阔的应用前景。为了进一步降低波导器件基底对光的吸收,科研工作者还探索了除SOI波导外更多类型的短波中红外波导器件。2011年, Li F等人[43]基于硅-蓝宝石晶圆(Silicon-on-Sapphire, SOS)制作了条形波导,在2.08 μm波长处波导器件的传输光学损耗仅为1.4 dB/cm,其蓝宝石基底能有效避免对波导中长波段光的吸收,拓展波导器件的光谱范围至5.5 μm波长。2012年,Cheng Z等人[44]基于SOI晶圆开发了中红外悬空薄膜波导(Suspended Membrane Waveguide, SMW),见图2(c),实验测得传输光学损耗为(3±0.7) dB/cm,在理论上分析了该波导色散和非线性特性。2017年, Zhou W[45] 等人基于SOI晶圆开发了中红外悬空狭缝波导(Suspended Slot Waveguide),采用亚波长光栅包层(Subwavelength Grating Cladding)作为支撑,如图2(d)所示,在2.25 μm波长处的传输光学损耗为7.9 dB/cm。随着微纳加工工艺的不断改进,硅基波导器件的光学损耗将不断降低,这是大规模的片上系统集成的关键。在这一部分中,笔者主要总结了各类中红外波导器件的光学损耗,而其他方面的优势(例如,宽光谱透明窗口、高倏逝场占比、高光学非线性系数等)在后文的应用中进行了讨论。目前所报道的主要短波中红外波导器件性能对比如表1所示。

      Figure 2.  Silicon waveguides in the short-wavelength mid-IR band. (a) Measurement result of optical loss of the TE0-mode strip (left) and rib (right) silicon waveguides[42]; (b) Scanning electron microscope (SEM) images of the silicon waveguide fabricated with the MPW service[27]; (c) SEM image of the SMW cross section[44]; (d) Schematic of the subwavelength-grating-cladding suspended slot waveguide[45]

      No.WaferWavelength/
      μm
      Optical loss/
      dB·cm−1
      Waveguide typeRef.
      1SOI2.20.6Strip[40]
      2SOI21.00±0.008Rib[41]
      3SOS2.081.4Strip[43]
      4SOI2.021.9±0.2Rib[42]
      5SOI2.023.3±0.5Strip[42]
      6SOI2.257.9Suspended slot[45]

      Table 1.  Characteristics of the silicon waveguides in the short-wavelength mid-IR band

    • 光栅耦合器件用于在光纤与硅基芯片之间实现高效的光场耦合,是硅基光子芯片封装的关键技术之一,具有器件体积小、耦合位置灵活、易于进行片上测试等优点,在通信波段已经进行了广泛的研究和应用[37, 46-52],然而,工作在短波中红外的光栅耦合器仍需要进一步研究探索。一方面,由于波长的增加,短波中红外光栅耦合器的光栅周期比通信波段大1.5倍,而单模光纤在短波中红外的模场直径与通信波段几乎相同,因此,光纤与硅波导在长波段中的光场耦合不可避免地要使用更少的光栅周期实现。另一方面,随着波长的增加,器件的最小特征尺寸也相应增加,为开发光栅耦合器提供了更好的设计灵活性和器件制作容差。目前,科研工作者们对该波段的光栅耦合器件已经进行了初步的探索,并取得了一定的成绩。2011年,Kuyken B等人[53]基于SOI晶圆开发了适用于2.15 μm波段的浅刻蚀光栅耦合器(Shallow-Etched Grating Coupler, SEGC),光栅刻蚀深度为70 nm,如图3(a)所示,峰值耦合效率为−5.2 dB,3 dB光谱带宽为160 nm。该光栅耦合器的中心波长位于双光子吸收截止波长的边缘,覆盖了许多分子的特征吸收峰,可用于非线性光学器件和传感器件的开发。2012年,Cheng Z等人[48]基于SOI晶圆提出并实验验证了一种用于中红外光场耦合的聚焦亚波长光栅耦合器(Focusing Subwavelength Grating Coupler, FSGC),采用悬空结构去除氧化埋层对中红外光的吸收,实现了−6 dB的峰值耦合效率,并验证了该器件结构在偏振不敏感光场耦合中的应用[51]。同年,Hattasan N等人[40]基于SOI晶圆设计了一种采用多晶硅层增强耦合效率的光栅耦合器,总刻蚀深度为240 nm,如图3(b)所示。在2.1 μm波长处实现了峰值耦合效率为−3.8 dB、3 dB光谱带宽为90 nm的光栅耦合器。2019年, Zhou W等人[54]基于500 nm顶层硅SOI晶圆开发了两个双波段的聚焦亚波长光栅耦合器,在波长1.56 μm和2.255 μm处分别实现了−6.9 dB和−5.9 dB的耦合效率,在波长1.487 μm和2.331 μm处分别实现了−6.9 dB和−5.7 dB的耦合效率,该研究为通信波段和2 μm波分复用系统中芯片与光纤的耦合提供了新方法。为了克服电子束曝光(Electron Beam Lithography, EBL)工艺对大批量、低成本器件制作的局限性,2021年, Chen W等人[27]基于MPW工艺实验研究了短波中红外聚焦亚波长光栅耦合器,如图3(c)所示。该器件基于220 nm顶层硅SOI晶圆的标准工艺流片加工制作,刻蚀深度为70 nm,在中心波长2.36 μm处测得耦合效率为−7.77 dB,器件标准差为0.5 dB,平均3 dB光谱带宽为85 nm。他们还对耦合光纤的位置以及入射角度的容错性进行了测试,为基于MPW工艺开发短波中红外大规模系统集成应用奠定了基础。2022年, Guo R等人[55]基于220 nm顶层硅SOI晶圆开发了短波中红外超薄厚度的光栅耦合器用于短波中红外超薄波导的耦合,顶部硅层刻蚀深度为150 nm。该器件测试结果如图3(d)所示,在中心波长2.2 μm处,该器件耦合效率为−7.1 dB,1 dB光谱带宽为115 nm,此外研究者们根据光栅耦合器透射光谱的法布里-珀罗干涉条纹估计了该器件具有大约−19.9 dB的背向反射。与先前的工作相比,该器件在光谱带宽与背向反射方面具有优秀的表现,这主要归因于顶层硅层有效折射率的降低。未来根据实际应用,需要研发新结构的光栅耦合器件,以满足波导光场耦合在中心波长、耦合效率、光谱带宽、偏振特性、对准容差等方面的需求。目前所报道的主要短波中红外硅基光栅耦合器件性能对比如表2所示。

      Figure 3.  Silicon grating couplers in the short-wavelength mid-IR band. (a) SEM image of the shallow-etched uniform grating coupler[53]; (b) Schematic of the polysilicon/silicon grating coupler[40]; (c) SEM image of the focusing subwavelength grating coupler fabricated with the MPW service[27]; (d) Measurement results of the ultra-thin focusing subwavelength grating coupler[55]

      No.WaferEtch depth
      /nm
      StructureWavelength/μmBandwidth
      /nm
      Efficiency
      /dB
      Ref.
      1SOI70SEGC2.15160 (3 dB)−5.2[53]
      2SOI240SEGC2.190 (3 dB)−3.8[40]
      3SOIN/AFSGC2.255/2.33138/54 (1 dB)−5.9/−5.7[54]
      4SOI70FSGC2.3685 (3 dB)−7.77[27]
      5SOI150FSGC2.2115 (1 dB)−7.1[55]

      Table 2.  Characteristics of the silicon grating couplers in the short-wavelength mid-IR band

    • 微型谐振腔是一类非常重要的硅基光学元件,在高灵敏度光学传感、光互连、光通信和非线性光学等领域有广泛的应用[56-59]。随着微纳制造技术和光刻技术的不断成熟,目前已经开发了许多不同结构的短波中红外微型谐振腔,包括微环谐振腔(Microring Resonator)、微盘谐振腔(Microdisk Resonator)等。2012年,Wong C Y等人[60]基于SOS晶圆设计开发了跑道型微环谐振腔(Racetrack Microring Resonator),如图4(a)所示,测得品质因子(Quality Factor)Q 值为11400±800。然而,相比SOI晶圆,SOS晶圆存在着器件制造工艺不标准和成本较高的问题。同年,Cheng Z等人[44]基于SOI晶圆研发了Q值约为8100的悬空薄膜微环谐振腔,可用于开发中红外非线性光学应用所需的低色散、高非线性和超低损耗器件,如图4(b)所示。2012年,Leo F等人[24]基于SOI晶圆开发了一种高Q值的硅基波导微环谐振腔,其周长为350 μm,微环与总线波导间隔450 nm,耦合长度20 μm。在2.3 μm波段,谐振腔Q值可达到75000,自由光谱范围(Free Spectral Range, FSR) 3.9 nm。2018年,Li J等人[61]基于MPW工艺开发了一种可热调谐的跑道型微环谐振腔,弯曲半径为10 μm,耦合长度为12 μm,如图4(c)所示。在2 μm波段处,实验测得Q值为1520,FSR约为12 nm,消光比超过20 dB。2021年,Ma H等人[5]基于SOI晶圆分别研究了未掺杂和轻p掺杂的微环谐振腔,微环直径为80 μm。在2 μm波段处,测得Q值分别为17000和11000,FSR分别为4.5 nm和4.47 nm。除了微环谐振腔,研究者们对微盘谐振腔[62-63]也进行了理论和实验研究。2019年,Zhang L等人[63]基于SOI晶圆开发了亚波长微盘谐振腔,微盘半径为6 μm,如图4(d)所示。在2 μm波段处,测得Q值为800,FSR为40 nm,为未来中红外传感提供了极具应用前景的器件。目前所报道的主要短波中红外硅基微型谐振腔性能对比见表3。总之,高品质因子的微型谐振腔为传感、非线性光学、光谱学等中红外应用提供了极具前景的开发平台,但仍需要进改进工艺,实现更高性能的微型谐振腔。

      Figure 4.  Silicon micro-resonators in the short-wavelength mid-IR band. (a) SEM image of the racetrack microring resonator[60]; (b) Schematic picture of the suspended membrane ring resonator[44]; (c) Microscope image of the tunable microring resonator[61]; (d) SEM image of the microdisk resonator with the subwavelength grating structure[63]

      No.WaferQ factorFSR
      /nm
      StructureRef.
      1 SOI 75000 3.9 Microring [24]
      2 SOI 17000 4.5 Microring [5]
      3 SOS 11400 N/A Racetrack microring [60]
      4 SOI 11000 4.47 Microring with p-type doping [5]
      5 SOI 8100 N/A Suspended membrane microring [44]
      6 SOI 1520 12 Racetrack microring [61]
      7 SOI 800 40 Subwavelength grating microdisk [63]

      Table 3.  Characteristics of the silicon micro-resonators in the short-wavelength mid-IR band

    • 复用/解复用器是用于高速数据通信和多参量传感领域的一类重要光学无源器件[58, 64-67]。首先,基于波导阵列光栅(Arrayed Waveguide Grating, AWG)的波分复用/解复用器具有波长间隔小、支持信道数多等优点,被广泛应用于密集波分复用和片上光谱分析系统中。2013年,Ryckeboer E 等人[68]首次基于220 nm顶层硅SOI晶圆设计开发了中心波长为2.2 μm的高分辨率六通道AWG。实验测得AWG的插入损耗为4 dB,串扰为−16 dB。2017年,Rouifed M S等人[69]基于340 nm顶层硅SOI晶圆设计并制作了九通道AWG,通道间距为200 GHz,器件结构和光谱响应如图5(a)所示。实验测得在2 μm波段处该器件的插入损耗为6 dB,串扰为−15.7 dB,可用作短波中红外波段解复用器。其次,中阶梯光栅(Echelle Grating, EG)和多模干涉仪(Multi-Mode Interferometer,MMI)也可以用作波分复用/解复用器。2013年,Ryckeboer E等人[68]基于SOI晶圆设计了中心波长为2.1 μm和2.3 μm的中阶梯光栅解复用器,如图5(b)所示。由于非最佳波导宽度,两个中阶梯光栅的插入损耗都较高,但都获得了低于−16 dB的串扰。2017年,Rouifed M S等人[70]基于340 nm顶层硅 SOI晶圆设计开发了一种可以实现1.55 μm和2 μm光波分复用的MMI。实验测得器件在1.55 μm和2 μm波段的插入光学损耗分别为0.14 dB和1.2 dB,两波长之间的串扰为−18.83 dB。该器件结构紧凑、光谱带宽宽、制作容差高,可作为多路复用/解复用器。最后,除波分复用器件外,模分复用器件在短波中红外硅基光子学中也得到了发展和应用。2019年, Zheng S等人[71]基于SOI晶圆设计开发了工作在2 μm波段的四模多路复用/解复用器,该复用器由三个锥形定向耦合器(Directional Coupler, DC)组成,如图5 (c)所示。在2 μm波段处,四个通道的平均插入损耗均小于5 dB,在1 950~2 020 nm的宽波长范围内,四个通道的平均串扰小于−18 dB。在误码率为3.8×10−3的情况下,测量到的光信噪比小于2.5 dB,如图5(d)所示,该研究在片上光互连和数据处理等领域具有广阔的应用前景。目前所报道的主要短波中红外硅基复用/解复用器性能对比见表4

      Figure 5.  Silicon multiplexing/demultiplexing devices in the short-wavelength mid-IR band. (a) The transmission spectrum image of different channels (left) and microscope image (right) of the AWG[69]; (b) Microscope image of the echelle grating[68]; (c) Schematic of the silicon multi-mode multiplexing/demultiplexing devices[71]; (d) Measured bit error rate (BER) of the silicon multi-mode multiplexing/demultiplexing devices as a function of the received optical signal-to-noise ratio (OSNR)[71]

      No.Wavelength
      /μm
      Insertion loss
      /dB
      Crosstalk
      /dB
      StructureRef.
      1 2 6 −15.7 AWG [69]
      2 2.1/2.3 High < −16 EG [68]
      3 2.2 4 −16 AWG [68]
      4 2 < 5 < −18 DC [71]
      5 2 1.2 −18.83 MMI [70]

      Table 4.  Characteristics of the silicon multiplexing/demultiplexing devices in the short-wavelength mid-IR band

    • 硅基材料具有高折射率(~3.45 @ 2 μm波长)[72]和高克尔非线性系数(~1.1$ \times $10−17 m2/W @ 2 μm波长)[22]的特点,并且在短波中红外波段的双光子吸收系数较低,因此,在短波中红外非线性光学器件的研发和应用方面潜力巨大。目前,多种非线性光学效应已经在短波中红外硅基器件中被研究探索,并用于研发新型的片上中红外光源,包括四波混频(Four-Wave Mixing, FWM)、光参量放大(Optical Parametric Amplification, OPA)、光参量振荡(Optical Parametric Oscillator, OPO)、超连续谱产生(Supercontinuum Generation, SCG)和克尔光频梳(Kerr Frequency Comb,KFC)等。例如,2012年,Liu X等人[73]在SOI晶圆上开发了螺旋波导(Spiral Waveguide),利用四波混频效应将2.4 μm波段的光转换到1.6 μm波段,实现了长达62 THz的频率转换,参量转换增益为19 dB,提高了对微弱中红外信号的探测灵敏度。2013年,Kuyken B等人[74]首次在正色散的硅基波导中利用四波混频实现了超过一个倍频程的波长转换,利用2.1 μm波长处的高功率泵浦和1.5 μm处的探测光,在3.6 μm波长附近产生中红外光,如图6(a)所示。实验证明,在峰值泵浦功率为18.3 W的情况下,片上参量增益峰值为13.1 dB。除了四波混频外,研究者们对光参量放大和光参量振荡也进行了相关研究。2010年,Liu X等人[75]开发了首个高增益带宽的短波中红外硅基波导光参量放大器件,在2.2 μm波段处利用一条4 mm长的硅基波导器件实现了增益系数高达25.4 dB的光信号放大。2013年,Kuyken B等人[76]实现了SOI波导集成的脉冲泵浦的光参量振荡器,在2 μm波段附近可以产生75 nm以上光谱调谐范围的短波中红外相干光输出。除了硅基波导集成的光参量振荡器外,短波中红外超连续谱光源也获得了广泛的关注。2011年,Kuyken B等人[77]研究了利用皮秒脉冲在SOI波导中实现短波中红外超连续谱产生,波长覆盖1.5~2.5 μm,测量光谱如图6(b)所示。该超连续谱源与各种分子的“指纹”振动吸收谱线重叠,在振动光谱学中有广泛的应用潜力。 为了克服SOI波导中二氧化硅衬底的吸收问题,2015年,Singh N等人[78]在SOS波导中实现了波长覆盖2~6 μm的超连续谱。这项研究是当时在硅基波导中实现的光谱最宽、波长最长的超连续谱,是在硅平台中实现连续跨倍频程超连续谱的标志性工作之一。随后,为了克服蓝宝石的吸收系数随波长的增加不断上升的问题,同时为了降低晶圆制作成本,2018年,Kou R等人[79]研究了基于空气包层的悬浮SOS波导超连续谱产生,光谱范围可覆盖2~5 μm 波段,该研究成果显示了空气包层的悬浮硅基波导在产生宽带超连续谱应用方面的巨大潜力。除超连续谱产生外,研究者也实现了片上克尔光频梳研究的突破进展。2015年,Griffith A等人[80]首次利用硅基波导微环谐振腔产生了光谱覆盖2.1~3.5 μm的宽带片上光频梳。2016年,Mengjie Yu等人[81]首次通过实验验证了利用硅基波导微环谐振腔产生锁模光频梳,提高了光频梳的相干性,光谱带宽覆盖2.4~4.3 μm,实现了40 %的高泵浦功率转换效率。除了硅基波导外,锗基波导器件的克尔光频梳也得到了关注。2021年,Guo R等人[82]理论研究了利用锗基和锗硅合金波导微环谐振腔在短波中红外产生克尔光频梳的可行性,如图6(c)所示。该工作的研究结果表明,利用锗硅合金波导可以有效减少双光子吸收的截止波长,从而使光频梳范围可覆盖到2.4~3.3 μm,如图6(d)所示。总之,开发波导集成的短波中红外非线性光学波导器件是一个非常前沿的研究方向,对推动光谱测量、生化传感、光通信测距等应用的小型化发展具有重要价值。

      Figure 6.  Nonlinear optical waveguide devices in the short-wavelength mid-IR band. (a) Wavelength conversion across more than one octave based on FWM[74]; (b) SCG based on the SOI waveguide[77]; (c) Schematic of the Kerr frequency comb generation in the microring resonator[82]; (d) Spectrum and intracavity power of the KFC based on the Si/Ge waveguide[82]

    • 短波中红外光电器件(包括调制器、探测器等)是实现通信、传感、测距等应用的关键核心组成部分,硅基光子学为开发调制器件和探测器件提供了极具发展前景的光电集成平台,近年来受到越来越多研究者的关注。此节将针对工作在2~2.5 μm波段的硅基波导集成的电光调制器、热光调制器和光电探测器的研究现状进行综述和讨论。

    • 目前所报道的短波中红外片上相移器件主要包括电光相移器件[23, 83-88]和热光相移器件[89]两类,并通过片上马赫-曾德尔干涉仪(Mach–Zehnder Interferometer, MZI)或微环谐振腔(Microring Resonators, MRR)两种结构实现相位到光强的转换。目前,基于自由载流子色散效应(Plasma Dispersion Effect)的硅基电光调制器在通信波段已经得到了广泛研究和应用,研究者们发现基于该效应的电光调制器还可应用于中红外波段[90]。2012年, Camp M 等人[83]首次开发了工作在短波中红外波段的、自由载流子注入型的、硅基波导集成的MZI电光调制器件,该器件具有1 mm长的p-i-n波导实现相移功能,其波导有源区截面示意图如图7(a)所示。该调制器对2.16 μm波段的光实现了3 Gbps的电光调制,消光比(Extinction Ratio, ER)为 23 dB,调制效率(Modulation Efficiency, ME)为0.12 V·mm。2018年,Cao W等人[23]基于自由载流子色散效应,开发了工作在2 μm波段的、硅基波导集成的MZI调制器件和MRR调制器件。其中,MZI调制器的调制速度可达20 Gbit/s,消光比5.8 dB,调制效率0.268 V·mm;MRR调制器的调制速度达到3 Gbit/s,消光比2.3 dB,功耗2.38 pJ/bit。该研究为实现2 μm波段的全硅片上收发器奠定了基础。2021年,Wang X等人[84]在2 μm波段开发了多电平调制的高速硅马赫曾德调制器件(Mach–Zehnder Modulator, MZM),如图7(b)所示,对四阶脉冲幅度调制(4-level Pulse Amplitude Modulation, PAM-4)信号实现了高达80 Gbit/s的调制速率。虽然电光调制器调制速度快,但其通常存在调制效率较低的问题,而热光调制器因其效率高、易于集成的优势也同样得到了广泛的关注。2021年,Zhong C等人[89]首次基于SOI晶圆开发了工作在2 μm波段的p++-p-p++型热光调制器,分别研究了MZI和MRR结构的调制器性能。基于MZI和MRR的热光调制器的调制效率分别为0.17 nm/mW和0.1 nm/mW,对应的半波功率损耗分别为25.21 mW和3.33 mW。两种热光调制器的上升/下降时间分别为3.49 μs/3.46 μs和3.65 μs/3.70 μs,是目前所报道的2 μm波段热光调制器件能达到的最快响应时间,对2 μm波段低损耗、低延迟光通信应用的发展起了重要推动作用。总之,调制器是集成光路应用的重要组成部分,是实现信号编码、交换、复用等功能的关键部件,为短波中红外波段的光通信和计算等应用起了重要的支撑作用。目前所报道的主要短波中红外硅基波导集成的调制器性能对比如表5所示。

      Figure 7.  Optoelectronic waveguide devices in the short-wavelength mid-IR band. (a) Cross-sectional schematic diagram of the active region of the p-i-n diode phase-shifter[83]; (b) Optical microscope image of the MZM [84]; (c) Schematic of the racetrack microring resonator-enhanced WSi nanowire photodetector. The red line indicates the waveguide on which the WSi nanowire is integrated[91]; (d) SEM image of the cross-section of the Zn2+-implanted Si waveguide photodiodes [92]

      No.WaferWavelength/μmSpeed
      /Gbit·s-1
      ER
      /dB
      MEStructureRef.
      1SOI2.163230.12
      V·mm
      MZI[83]
      2SOI2205.80.268
      V·mm
      MZI[23]
      3SOI232.3N/AMRR[23]
      4SOI280N/AN/AMZI[84]
      5SOI2N/AN/A0.17 nm/mWMZI[89]
      6SOI2N/AN/A0.1 nm/mWMRR[89]

      Table 5.  Characteristics of the silicon-waveguide-integrated modulators in the short-wavelength mid-IR band

    • 光电探测器能将光信号转变为电信号以便进一步的处理和存储,是集成光学中非常重要的一类有源器件。目前,2~2.5 μm波段的光电探测器以Ⅲ-Ⅴ族材料、二维半导体材料、纳米线与硅基波导器件异质集成为主要实现方法。例如,2011年,Hattasan N等人[93]基于SOI晶圆提出了首个GaInAsSb p-i-n光电二极管探测器。该探测器在2.29 μm处的响应度为0.44 A/W,外部量子效率约24%,室温下工作的暗电流为1.13 μA。然而,Ⅲ-Ⅴ族材料一般存在成本高、器件与CMOS技术不兼容、材料制备污染较大等问题。为解决这些问题,2016年,Cong H等人[94]开发了Ge0.92Sn0.08合金的p-i-n光电探测器,其截止波长为2.3 μm。反向偏压为1 V时,探测器在2 μm波长处的响应度为93 mA/W,暗电流为171 μA,是当时所报道的响应度最高的GeSn p-i-n光电探测器。该研究为工作在短波中红外波段的光电探测器的开发提供了一种极具前景的技术。另一方面,二维材料,如石墨烯(Graphene)、黑磷(Black Phosphorus)等,因光谱响应带宽宽以及能够避免材料与硅基波导晶格失配的优点,成为了一类极具发展前景的短波中红外光电材料[95-96]。2020年,Guo J等人[97]开发了基于热辐射/光导效应的、波导集成的石墨烯光电探测器,在2 μm波长处该探测器的响应度为70 mA/W,3 dB带宽为20 GHz,该研究为短波中红外波段的高响应光电探测器的发展开辟了道路。除此之外,超导纳米线单光子探测器因其高灵敏度也得到了一定的关注。2018年,Slater B等人[91]首次报道了工作在2.1 μm波长处的波导集成超导纳米线单光子探测器,如图7(c)所示。为了增加光子的有效作用时间,该探测器利用硅化钨纳米线吸收光子,然后耦合进纳米线下方的跑道型微环谐振腔,实验测得探测效率高达90%以上。异质集成的光电探测器在短波中红外波段有较强的电光响应,是目前硅基波导器件集成的短波中红外光电探测器的主要实现方法,然而,异质集成的光电探测器仍存在着制作成本较高、不与CMOS工艺完全兼容等缺点。另一方面,纯硅光电探测器因其与COMS工艺完全兼容、易于单片集成的优点,同样获得了研究者们的关注。然而,受到硅基材料本征带隙的限制,短波中红外硅基光电探测器通常需要利用离子掺杂等技术引入中间能级,提升硅基材料的光电响应,目前这一技术仍存在响应度较低的问题。2014年,Grote R R等人[92]报道了工作在2.2~2.4 μm波段的Zn+离子注入型硅基波导光电二极管探测器,其响应度为(87±29) mA/W,暗电流小于10 μA,波导器件截面的扫描电镜图如图7(d)所示。该研究成果证明了在短波中红外波段利用硅基波导实现片上光电探测的可行性。同年,Souhan B等人[98]研究了工作在2.2~2.3 μm波段的Si+离子注入硅波导p-i-n光电探测器,在5 V反向偏压下测得最大响应度为10 mA/W,暗电流小于1 μA。2015年,Ackert J J等人[99]首次报道了工作在2 μm波段的高速单片硅雪崩光电二极管探测器。该器件在2 μm处的响应度为(0.3±0.02) A/W,工作速率超过了20 Gbit/s,暗电流小于1 μA,为此波段首个高速硅探测器,该成果为短波中红外光通信的发展提供了新的解决方案。目前所报道的主要短波中红外硅基波导集成的探测器性能对比见表6

      No.TypeWavelength
      /μm
      Responsivity
      /mA·W-1
      Dark current
      /μA
      Ref.
      1GaInAsSb p-i-n photodiode2.290.441.13[93]
      2GeSn p-i-n photodetector293171[94]
      3Silicon−graphene waveguide photodetector270N/A[97]
      4Superconducting nanowire single photon detectors2.1N/AN/A[91]
      5Zn+ implanted Si waveguide photodiode2.2-2.487±29< 10[92]
      6Si+-implanted Si-wire waveguide photodetector2.2-2.310< 1[98]
      7Silicon photodiode20.3< 1[99]

      Table 6.  Characteristics of the silicon-waveguide-integrated detectors in the short-wavelength mid-IR band

    • 文中主要介绍了硅基光子学在短波中红外波段近年来的研究现状,内容涵盖了无源波导器件、非线性光学波导器件和光电波导器件三部分。在无源波导器件部分,阐述了目前所报道的短波中红外硅基波导、光栅耦合器、微型谐振腔和复用/解复用器的结构和器件性能;在非线性光学波导器件部分,介绍了硅基波导集成的短波中红外非线性相干光源和放大器件的相关研究;在光电波导器件部分,总结了硅基波导集成的短波中红外调制器件和探测器件的研究进展。得益于硅基材料在短波中红外波段的高透明度、高光学非线性和成熟的CMOS制作工艺等优势,硅基光子技术有望为实现低成本、大规模单片光电子集成应用提供一种极具前景的解决方案。

      未来通过开展新型红外光电材料的片上异质集成、采用亚波长结构调控片上光场特性、改进微纳加工技术降低波导器件光学损耗等方面的研究,短波中红外硅基光子学器件和系统的性能有望得到进一步提升。首先,新型的低维材料(例如,石墨烯、黑磷、二硒化钯等)在中红外波段展现了出色的光电特性。并且,相比现有的中红外光电材料(例如,碲镉汞材料、量子阱材料、Ⅱ类超晶格材料等),其制备对环境相对污染小,同硅基波导器件结合研制异质集成器件不存在晶格失配的问题。因此,开展低维材料/硅基波导异质集成的光电探测器件和电光调制器件将是一个极具发展前景的方向。其次,基于超表面和逆向设计的方法开发波导集成的短波中红外器件有望得到快速发展。随着近年来人工智能算法和计算机算力的大幅提升,并有赖于硅基亚波长器件在中红外波段更大的特征尺寸,对利用亚波长结构调控波导中光场的强度和相位给予了更大的灵活性,有望使无源硅基波导器件的性能得到进一步提高。最后,不断改进的CMOS工艺与以量子理论为基础的原子及近原子尺度制造技术的结合,有望深度融合短波中红外片上光谱检测与纳米材料、凝聚态物理、化工等多交叉学科领域,实现颠覆性的重大创新应用。

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