52. Zi Jing Wong, Ye-Long Xu, Jeongmin Kim, Kevin O'Brien, Yuan Wang, Liang Feng and Xiang Zhang, "Lasing and anti-lasing in a single cavity, " Nature Photonics 10, 796–801 (2016).
    51. Han Zhao, William S. Fegadolli, Jiakai Yu, Zhifeng Zhang, Li Ge, Axel Scherer, and Liang Feng, "Metawaveguide for Asymmetric Interferometric Light-Light Switching, " Physical Review Letter 117, 193901 (2016).

      Light-light switching typically requires strong nonlinearity where intense laser fields route and direct data flows of weak power, leading to a high power consumption that limits its practical use. Here we report an experimental demonstration of a metawaveguide that operates exactly in the opposite way in a linear regime, where an intense laser field is interferometrically manipulated on demand by a weak control beam with a modulation extinction ratio up to approximately 60 dB. This asymmetric control results from operating near an exceptional point of the scattering matrix, which gives rise to intrinsic asymmetric reflections of the metawaveguide through delicate interplay between index and absorption. The designed metawaveguide promises low-power interferometric light-light switching for the next generation of optical devices and networks.

    50. Li Ge and Liang Feng, "Optical-reciprocity-induced symmetry in photonic heterostructures and its manifestation in scattering PT-symmetry breaking, " Physical Review A 94, 043836 (2016).
    49. Si-Yuan Yu, Xiao-Chen Sun, Xu Ni, Qing Wang, Xue-Jun Yan, Cheng He, Xiao-Ping Liu, Liang Feng, Ming-Hui Lu and Yan-Feng Chen, "Surface phononic graphene, " Nature Materials 15, 1243–1247 (2016).
    48. Pei Miao, Zhifeng Zhang, Jingbo Sun, Wiktor Walasik, Stefano Longhi, Natalia M. Litchinitser, Liang Feng, "Orbital angular momentum microlaser, " Science 353, 464-467 (2016).

      Structured light provides an additional degree of freedom for modern optics and practical applications. The effective generation of orbital angular momentum (OAM) lasing, especially at a micro- and nanoscale, could address the growing demand for information capacity. By exploiting the emerging non-Hermitian photonics design at an exceptional point, we demonstrate a microring laser producing a single-mode OAM vortex lasing with the ability to precisely define the topological charge of the OAM mode. The polarization associated with OAM lasing can be further manipulated on demand, creating a radially polarized vortex emission. Our OAM microlaser could find applications in the next generation of integrated optoelectronic devices for optical communications in both quantum and classical regimes.

    47. Cheng He, Xiao-Chen Sun, Xiao-Ping Liu, Ming-Hui Lu, Yulin Chen, Liang Feng, Yan-Feng Chen, "Photonic topological insulator with broken time-reversal symmetry, " Proceedings of the National Academy of Sciences 113.18, 4924-4928 (2016).




    35. Ye-Long Xu, Liang Feng, Ming-Hui Lu and Yan-Feng Chen, "Optical Isolation by Time-Dependent Sinusoidal-Shaped Structures, " Chinese Physics Letters 30, 094202 (2013).
    34. Xuefeng Zhu, Liang Feng, Peng Zhang, Xiaobo Yin, and Xiang Zhang, "One-way invisible cloak using parity-time symmetric transformation optics, " Optics Letters 38, 2821-2824 (2013).
    33. Liang Feng, Ye-Long Xu, William S. Fegadolli, Ming-Hui Lu, Jose E. B. Oliveira, Vilson R. Almeida, Yan-Feng Chen and Axel Scherer, "Experimental demonstration of a unidirectional reflectionless parity-time metamaterial at optical frequencies, " Nature Materials 12, 108-113 (2013).

      Invisibility by metamaterials is of great interest, where optical properties are manipulated in the real permittivity–permeability plane. However, the most effective approach to achieving invisibility in various military applications is to absorb the electromagnetic waves emitted from radar to minimize the corresponding reflection and scattering, such that no signal gets bounced back. Here, we show the experimental realization of chip-scale unidirectional reflectionless optical metamaterials near the spontaneous parity-time symmetry phase transition point where reflection from one side is significantly suppressed. This is enabled by engineering the corresponding optical properties of the designed parity-time metamaterial in the complex dielectric permittivity plane.The demonstrated unidirectional phenomenon at the corresponding parity-time exceptional point on-a-chip confirms the feasibility of creating complicated on-chip parity-time metamaterials and optical devices based on their properties.



    31. Cheng He, Xiao-Liu Zhang, Liang Feng, Ming-Hui Lu and Yan-Feng Chen, "One-way cloak based on nonreciprocal photonic crysta, " Applied Physics Letters 99, 151112 (2011).
    30. Liang Feng, Zhaowei Liu and Yeshaiahu Fainman, "Direct Observation of Plasmonic Index Ellipsoids on a Deep-Subwavelength Metallic Grating, " Applied Optics 50, G1-G6 (2011).
    29. Liang Feng, Maurice Ayache, Jingqing Huang, Ye-Long Xu, Ming-Hui Lu, Yan-Feng Chen, Yeshaiahu Fainman and Axel Shcerer, "Nonreciprocal light propagation in a silicon photonic circuit, " Science 333, 729-733 (2011).

      Optical communications and computing require on-chip unidirectional light transport to various asymmetric optical components, for example, optical network analyzers. We have designed and fabricated a metallic-silicon waveguide system in which the optical potential is modulated along the length of the waveguide such that asymmetric light propagation is obtained on a silicon photonic chip. Unidirectional light transport at the quantum parity-time exceptional point is demonstrated at the wavelength of 1.55 micrometers in both simulations and experiments. Our system is compatible with conventional complementary metal-oxide-semiconductor processing for optical communications and computing.

    28. Liang Feng, Amit Mizrahi, Steve Zamek, Zhaowei Liu, Vitaliy Lomakin and Yeshaiahu Fainman, "Metamaterials for Enhanced Polarization Conversion in Plasmonic Excitation, " ACS Nano 5, 5100-5106 (2011).

      Surface plasmons efficient excitation is typically expected to be strongly constrained to transverse magnetic (TM) polarized incidence, as demonstrated so far, due to its intrinsic TM polarization. We report a designer plasmonic metamaterial that is engineered in a deep subwavelength scale in visible optical frequencies to overcome this fundamental limitation, and allows transverse electric (TE) polarized incidence to be strongly coupled to surface plasmons. The experimental verification, which is consistent with the analytical and numerical models, demonstrates this enhanced TE-to-plasmon coupling with efficiency close to 100%, which is far from what is possible through naturally available materials. This discovery will help to efficiently utilize the energy fallen into TE polarization and drastically increase overall excitation efficiency of future plasmonic devices.

    27. Xue-Feng Li, Xu Ni, Liang Feng, Ming-Hui Lu, Cheng He and Yan-Feng Chen, "Tunable unidirectional sound propagation through a sonic-crystal-based acoustic diode, " Physical Review Letters 106, 084301 (2011).

      Nonreciprocal wave propagation typically requires strong nonlinear materials to break time reversal symmetry. Here, we utilized a sonic-crystal-based acoustic diode that had broken spatial inversion symmetry and experimentally realized sound unidirectional transmission in this acoustic diode. These novel phenomena are attributed to different mode transitions as well as their associated different energy conversion efficiencies among different diffraction orders at two sides of the diode. This nonreciprocal sound transmission could be systematically controlled by simply mechanically rotating the square rods of the sonic crystal. Different from nonreciprocity due to the nonlinear acoustic effect and broken time reversal symmetry, this new model leads to a one-way effect with higher efficiency, broader bandwidth, and much less power consumption, showing promising applications in various sound devices.

    26. Cheng He, Ming-Hui Lu, Xin Heng, Liang Feng and Yan-Feng Chen, "Parity-time electromagnetic diodes in a two-dimensional nonreciprocal photonic crystal, " Physical Review B 83, 075117 (2011).
    25. Steve Zamek, Liang Feng, Mercedeh Khajavikhan, Dawn T.H. Tan, Maurice Ayache and Yeshaiahu Fainman, "Micro-resonator with metallic mirrors coupled to a bus waveguide, " Optics Express 19, 2417-2425 (2011).


    24. Yu Zhou, Ming-Hui Lu, Liang Feng, Xu Ni, Yan-Feng Chen, Yong-Yuan Zhu, Shi-Ning Zhu and Nai- Ben Ming, "Acoustic surface evanescent wave and its dominant contribution to extraordinary acoustic transmission and collimation of sound, " Physical Review Letters 104, 164301 (2010).

      We demonstrate both theoretically and experimentally the physical mechanism that underlies extraordinary acoustic transmission and collimation of sound through a one-dimensional decorated plate. A microscopic theory considers the total field as the sum of the scattered waves by every periodically aligned groove on the plate, which divides the total field into far-field radiative cylindrical waves and acoustic surface evanescent waves (ASEWs). Different from the well-known acoustic surface waves like Rayleigh waves and Lamb waves, ASEW is closely analogous to a surface plasmon polariton in the optical case. By mapping the total field, the experiments well confirm the theoretical calculations with ASEWs excited. The establishment of the concept of ASEW provides a new route for the integration of subwavelength acoustic devices with a structured solid surface.

    23. Maziar P. Nezhad, Aleksandar Simic, Olesya Bondarenko, Boris Slutsky, Amit Mizrahi, Liang Feng, Vitaliy Lomakin and Yeshaiahu Fainman, "Room Temperature Lasing from Sub-wavelength Metallo-Dielectric Lasers, " Nature Photonics 4, 395-399 (2010).

      We demonstrate room-temperature pulsed laser emission from optically pumped metallo-dielectric cavities that are smaller than their emission wavelength in all three dimensions. The cavity consists of an aluminum/silica bi-layer shield surrounding an InGaAsP disk in which the thickness of the silica layer is optimized to minimize the gain threshold of the laser. The lasers are pumped using a 1,064-nm pulsed fibre laser with a pulse width of 12 ns and repetition rate of 300 kHz. Lasing emission at 1.43 µm is observed from a laser with slightly elliptical gain core with major and minor diameters of 490 and 420 nm, respectively. Owing to the isolation provided by the aluminum shield, this laser design approach can be used to create arrays of uncoupled lasers with emitter densities that are close to the Rayleigh resolution limit.

    22. Steve Zamek, Amit Mizrahi, Liang Feng, Aleksandar Simic and Yeshaiahu Fainman, "Planar Dielectric Waveguide Cavity with Metallic Mirrors, " Optics Letters 35, 598-600 (2010).
    21. Liang Feng, Zhaowei Liu, Vitaliy Lomakin and Yeshaiahu Fainman, "Form birefringence metal and its plasmonic anisotropy, " Applied Physics Letters, 96, 041112 (2010).




    16. Jian Li, Ming-Hui Lu, Tian Fan, Xiao-Kang Liu, Liang Feng, Yue-Feng Tang and Yan-Feng Chen, "All-angle negative refraction imaging effect with complex two-dimensional hexagonal photonic crystals, " Journal of Applied Physics 102, 073538 (2007).
    15. Ming-Hui Lu, Xiao-Kang Liu, Liang Feng, Jian Li, Cheng-Ping Huang, Yan-Feng Chen, Yong-Yuan Zhu, Shi-Ning Zhu and Nai-Ben Ming, "Extraordinary Acoustic Transmission through a 1D Grating with Very Narrow Apertures, " Physical Review Letters 99, 174301 (2007).

      Recently, there has been increased interest in studying extraordinary optical transmission (EOT) through subwavelength aperture arrays perforated in a metallic film. In this Letter, we report that the transmission of an incident acoustic wave through a one-dimensional acoustic grating can also be drastically enhanced. This extraordinary acoustic transmission (EAT) has been investigated both theoretically and experimentally, showing that the coupling between the diffractive wave and the wave-guide mode plays an important role in EAT. This phenomenon can have potential applications in acoustics and also might provide a better understanding of EOT in optical subwavelength systems.

    14. Ming-Hui Lu, Chao Zhang, Liang Feng, Jun Zhao, Yan-Feng Chen, Yi-Wei Mao, Jian Zi, Yong-Yuan Zhu, Shi-Ning Zhu and Nai-Ben Ming, "Negative birefraction of acoustic waves in a sonic crystal, " Nature Materials 6, 744-748 (2007).

      Optical birefringence and dichroism are classical and important effects originating from two independent polarizations of optical waves in anisotropic crystals Furthermore, the distinct dispersion relations of transverse electric and transverse magnetic polarized electromagnetic waves in photonic crystals can lead to birefringence more easily. However, it is impossible for acoustic waves in the fluid to show such a birefringence because only the longitudinal mode exists. The emergence of an artificial sonic crystal (SC) has significantly broadened the range of acoustic materials in nature that can give rise to acoustic bandgaps and be used to control the propagation of acoustic waves. Recently, negative ref raction has attracted a lot of attention and has been demonstrated in both left-handed materials and photonic crystals. Similar to left-handed materials and photonic crystals, negative refractions have also been found in SCs. Here we report, f or the first time, the acoustic negative-birefraction phenomenon in a two-dimensional SC, even with the same frequency and the same 'polarization' state. By means of this feature, double focusing images of a point source have been realized. This birefraction concept may be extended to other periodic systems corresponding to other forms of waves, showing great impacts on both fundamental physics and device applications.

    13. Liang Feng, Kevin Tetz, Boris Slutsky, Vitaliy Lomakin and Yeshaiahu Fainman, "Fourier plasmonics: Diffractive focusing of in-plane surface plasmon polariton waves, " Applied Physics Letters 91, 081101 (2007).
    12. Ming-Hui Lu, Liang Feng, Xiao-Ping Liu, Xiao-Kang Liu, Yan-Feng Chen, Yong-Yuan Zhu, Yi-Wei Mao and Jian Zi, "Experimental observation of both negative and positive phase velocities in a two-dimensional sonic crystal, " Physics Letters A 366, 523-527 (2007).
    11. Jian Li, Ming-Hui Lu, Liang Feng, Xiao-Ping Liu and Yan-Feng Chen, "Tunable negative refraction based on the Pockels effect in two-dimensional photonic crystals composed of electro-optic crystals, " Journal of Applied Physics 101, 013516 (2007).


    10. Liang Feng, Xiao-Ping Liu, Ming-Hui Lu, Yan-Bin Chen, Yan-Feng Chen, Yi-Wei Mao, Jian Zi, Yong-Yuan Zhu, Shi-Ning Zhu and Nai-Ben Ming, "Refraction control of acoustic waves in a square-rod-constructed tunable sonic crystal, " Physical Review B 73, 193101 (2006).
    9. Liang Feng, Xiao-Ping Liu, Ming-Hui Lu, Yan-Bin Chen, Yan-Feng Chen, Yi-Wei Mao, Jian Zi, Yong-Yuan Zhu, Shi-Ning Zhu and Nai-Ben Ming, "Acoustic Backward-Wave Negative Refractions in the Second Band of a Sonic Crystal, " Physical Review Letters 96, 014301 (2006).

      Acoustic negative refractions with backward-wave (BW) effects were both theoretically and experimentally established in the second band of a two-dimensional (2D) triangular sonic crystal (SC). Intense Bragg scatterings result in the extreme deformation of the second band equifrequency surface (EFS) into two classes: one around the K point and the other around the Γ point of the reduced Brillouin zone. The two classes can lead to BW negative refractions (BWNRs) but with reverse negative refraction dependences on frequencies and incident angles. Not only BWNR but BW positive refraction can be present at EFSs around the K point, so it is possible to enhance the resolution of acoustic waves with a subdiffraction limit regardless of refractions, which is no analogy in both left-handed material and SCs’ first band. These abundant characters make refractions in the second band distinguished.