Since the invention of the laser, the field of photonics has progressed through the development of engineered materials which mold the flow of light. Photonic band gap (PBG) materials are a new class of dielectrics which are the photonic analogues of semiconductors. They represent a new frontier in quantum optics and offer many new technological application. Unlike semiconductors which facilitate the coherent propagation of electrons, PBG materials facilitate the coherent localization of photons. Our research suggests that PBG materials exhibit fundamentally new physics such as photon-atom bound states, lasing without a cavity mode, quantum optical spin-glass states of impurity atomic dipoles, and optical gap solitons. Applications include zero-threshold micro-lasers with high modulation speed and low threshold optical switches and all-optical transistors for optical telecommunications and high speed optical computers.

Our current research is aimed at developing a theoretical understanding of these novel materials. Specific calculations include N-atom collective spontaneous emission and laser activity. Light emission properties of photonic band gap materials differ dramatically from conventional lasers. The most fundamental novelty of these materials comes from the fact that when an atom or molecule, placed within the material, has an electronic transition which lies within the photonic band gap, spontaneous emission of light from the atom is inhibited. Instead, the photon forms a bound state to the atom! This has profound implications for laser activity. Spontaneous emission is the dominant loss mechanism in a conventional laser. In a PBG, lasing can occur with zero pumping threshold. Lasing can also occur without mirrors and without a cavity mode since each atom creates its own localized photon mode. This suggests that large arrays of nearly lossless microlasers for all-optical circuits can be fabricated with PBG materials.

Near a photonic band edge, the photon density of states exhibits singularities which cause  collective light emission to take place at a much faster rate than in ordinary vacuum.  . We have shown that this rate is proportional to the square of the number N of atoms rather than simply N itself as it would be in conventional systems. This demonstrates that microlasers operating near a photonic band edge will exhibit ultrafast modulation and switching speeds for application in high speed data transfer and computing.

Applications such as telecommunications, data transfer, and computing will be greatly enhanced through all-optical processing in which bits of information, encoded in the form of a photon number distribution, can be transmitted and processed without conversion to and from electrical signals. In this manner, the information contained in an entire encyclopedia can be transmitted over a fibre optic phone line in a matter of seconds. This relies on the development of ultra-low noise coherent light sources. We are evaluating the quantum statistics of photons produced by laser emission in a PBG material to evaluate the extent of signal noise reduction referred to as photon-antibunching and squeezing. These are crucial to lowering the bit error rate in optical telecommunication networks. In a PBG material the drastic reduction of spontaneous emission as well as the reduction of propagative pathways for photons, facilitates the realization of very low quantum noise.

A PBG material doped with impurity atoms also exhibits novel nonlinear optical properties  due to the resonance dipole-dipole interaction (RDDI) between atoms. Our current calculations show that under pumping by a weak external laser field, this system acts as a nearly lossless, nonlinear material which exhibits  optical bistability. We are currently investigating the possibility of using this system as a very low threshold, ultra-high speed optical switch. This low threshold nonlinearity is a consequence of a new equilibrium state of photons and atoms in a PBG which we refer to as a quantum optical spin-glass state. In this state, the atomic dipoles exhibit a spontaneous, frozen-in, random polarization. The light associated with this state is intermediate between coherent light from a conventional laser and chaotic light from an ordinary light bulb. We refer to this state as a  Bose-glass state of photons .

The photonic band gap is a frequency interval over which the linear electromagnetic propagation effects have literally been turned off. However, the PBG exhibits a rich variety of nonlinear optical propagation phenomena. These include classical gap solitons and quantum gap solitons . These solitons may be important in the transmission of information through the otherwise impenetrable PBG.

The PBG material provides dopant atoms with a high degree of protection from damping effects of spontaneous emission and dipole dephasing. In this case the two-level atom may act as a two-level quantum mechanical register or single photon logic gate for all optical quantum computing . We are currently studying two models for quantum computation within PBG materials. The first involves an atom which is laser-cooled in the void regions of a PBG material. In this case a polarized photon (flying qubit) with frequency just outside of the gap excites a protected atomic level inside the gap (stationary qubit) by resonant coupling to a third atomic level just outside the gap. The second and third atomic levels are coupled by an external laser field which drives a two-photon transition. This single atom acts as a phase sensitive quantum memory device. The resulting qubit is robust to decoherence effects provided that the Rabi frequency of the coherent laser field exceeds the rate of dephasing interactions. In effect, coherence is externally imposed on the system.


  1. Sajeev John, H. Sompolinsky and Michael J. Stephen, Phys. Rev. B 27, 5592 (1983) "Localization in a Disordered Elastic Medium Near Two dimensions".  ABSTRACT  PDF
  2. *Sajeev John and Michael J. Stephen, Phys. Rev. B 28, 6358 (1983) "Wave Propagation and Localization in a Long Range Correlated Random Potential".  ABSTRACT  PDF
  3. Sajeev John, Phys. Rev. Lett.  53, 2169 (1984) "Electromagnetic Absorption in a Disordered Medium near a Photon Mobility Edge".    ABSTRACT  PDF
  4. S. John, Phys. Rev. Lett. 58, 2486 (1987) "Strong Localization of Photons in Certain Disordered Dielectric Superlattices".   ABSTRACT   PDF
  5. S. John and R. Rangarajan, Phys. Rev. B38, 10101 (1988) "Optimal Structures for Classical Wave Localization: An Alternative to the Ioffe-Regel Criterion".   ABSTRACT   PDF
  6. S. John and J. Wang, Phys. Rev. Lett. 64, 2418 (1990) "Quantum Electrodynamics Near a Photonic Band Gap: Photon Bound States and Dressed Atoms". ABSTRACT   PDF
  7. S. John, Physics Today, May 1991 (cover story) and page 32 "Localization of Light".
  8. Sajeev John and Jian Wang, Phys. Rev. B 43, 12, 772 (1991) "Quantum Optics of Localized Light in a Photonic Bandgap".   ABSTRACT   PDF
  9. S. John and N. Akozbek, Phys. Rev. Lett. 71, 1168 (1993) "Nonlinear Optical Solitary Waves in a Photonic Band Gap".  ABSTRACT   PDF
  10. S. John and T. Quang, Phys. Rev. A50, 1764 (1994) "Spontaneous Emission near the Edge of a Photonic Band Gap".   ABSTRACT PDF
  11. S. John and T. Quang, Phys. Rev. Lett. 74, 3419 (1995) "Localization of Superradiance near a Photonic Band Gap".  ABSTRACT   PDF
  12. Sajeev John and Tran Quang, Physical Review A 52, 4083 (1995) "Photon Hopping Conduction and Collectively Induced Transparency in a Photonic Bandgap''.    ABSTRACT    PDF
  13. S. John and T. Quang, Phys. Rev. Lett. 76, 1320 (1996) "Quantum Optical Spin-Glass State of Impurity Two-Level Atoms in a Photonic Band Gap".   ABSTRACT    PDF
  15. S. John and T. Quang, Phys. Rev. Lett. 76, 2484 (1996) "Resonant Nonlinear Dielectric Response in a Photonic Band Gap Material".  ABSTRACT   PDF  POSTSCRIPT
  16. S. John and T. Quang, Phys. Rev. A 54, 4479 (1996) "Optical Bistability and Phase Transitions in a Doped Photonic Band Gap Material".  ABSTRACT   PDF
  17. Sajeev John and Tran Quang, Physical Review Letters, 78, 1888 (1997) "Collective Switching and Inversion without Fluctuation of Two-Level Atoms in Confined Photonic Systems''.   ABSTRACT PDF  POSTSCRIPT
  18. Sajeev John and Valery Rupasov, Physical Review Letters 79, 821 (1997) "Multi-photon Localization and Propagating Quantum Gap Solitons in a Frequency Gap Medium".   ABSTRACT PDF   POSTSCRIPT
  19. Tran Quang, M. Woldeyohannes, Sajeev John and G.S. Agarwal, Physical Review Letters 79, 5238 (1997) "Coherent Control of Spontaneous Emission Near a Photonic Band Edge: A Single-Atom Optical Memory Device". ABSTRACT PDF   POSTSCRIPT
  20. Tran Quang and Sajeev John, Physical Review A, 56, 4273 (1997) "Resonance Fluorescence near a Photonic Band Edge: Dressed-State Monte Carlo Wave-function Approach".   ABSTRACT PDF   POSTSCRIPT
  21. Sajeev John, Nature, 390, 661 (1997) "Frozen Light".  ABSTRACT
  22. Neset Akozbek and Sajeev John, Physical Review E 57, 2287 (1998) "Optical Solitary Waves in Two- and Three-Dimensional Nonlinear Photonic Band-Gap Structures".   ABSTRACT  PDF   POSTSCRIPT
  23. Neset Akozbek and Sajeev John, Physical Review E 58, 3876 (1998) "Self-Induced Transparency Solitary Waves in a Doped Photonic Band Gap Material".   ABSTRACT  PDF   POSTSCRIPT
  24.  Kurt Busch and Sajeev John, Physical Review E 58, 3896 (1998) "Photonic Band Gap Formation in Certain Self-Organizing Systems". ABSTRACT PDF   POSTSCRIPT
  25. Nipun Vats and Sajeev John, Physical Review A 58, 4168-4185 (1998)  "Non-Markovian Quantum Fluctuations and Superradiance Near a Photonic Band Edge".   ABSTRACT PDF   POSTSCRIPT
  26. Sajeev John and V. Rupasov, Europhysics Letters 46 (3), 326 (1999)  "Quantum Self-Induced Transparency in Frequency Gap Media".  ABSTRACT
  27.  PDF
  28. Mesfin Woldeyohannes and Sajeev John, Physical Review A60(6), 5046-5068 (1999) "Coherent control of spontaneous emission near a photonic band edge: A qubit for quantum computation". ABSTRACT  PDF POSTSCRIPT
  29. "Large-scale synthesis of a silicon photonic crystal with a complete three-dimensional bandgap near 1.5 micrometres", Alvaro Blanco, Emmanuel Chomski, Serguei Grabtchak; Marta Ibisate, Sajeev John, Stephen W. Leonard, Cefe Lopez, Francisco Meseguer, Hernan Miguez, Jessica P. Mondia, Geoffrey A. Ozin, Ovidiu Toader and Henry M. van Driel, Nature 405 (6785), 437-440 (2000). ABSTRACT   PDF
  30. "Attenuation of Optical Transmission within the bandgap of thin two-dimensional macroporous silicon photonic crystals", S. W. Leonard, H. van Driel, K. Busch, S. John et al., Applied Physics Letters 75, 3063 (1999). ABSTRACT   PDF   POSTSCRIPT
  31. "Tunable two-dimensional photonic crystals using liquid-crystal infiltration", S. W. Leonard, J. P. Mondia, H. van Driel, O. Toader, S. John et al., Physical Review B, Phys. Rev. B 61, R2389 (2000). ABSTRACT  PDF  POSTSCRIPT
  32. "Resonance Raman Scattering in Dispersive Media and Photonic Band Gaps", M. Woldeyohannes, Sajeev John and V. Rupasov, Physical Review A 63, 13814 (2001).   ABSTRACT PDF  POSTSCRIPT
  33. "Radiating Dipoles in Photonic Crystals", K. Busch, N. Vats, Sajeev John and B. Sanders, Physical Review E 62, 4251 (2000).   ABSTRACT   PDF POSTSCRIPT
  34. "Optical Trapping, Field Enhancement, and Laser Cooling in Photonic Crystals", Ovidiu Toader, Sajeev John and K. Busch, Optics Express vol.8, no. 3, pg 271- (2001). ABSTRACT PDF
  35. "Single Atom Switching and NonMarkovian Dynamics in a Coloured Vacuum", M. Florescu and Sajeev John, Physical Review A 64, 033801 (2001).   ABSTRACT  PDF POSTSCRIPT
  36. "Proposed Square Spiral Microfabrication Architecture for Large Three-Dimensional Photonic Band Crystals", Ovidiu Toader and Sajeev John, Science vol. 292, 1133 (2001).   ABSTRACT   PDF
  37. "Photonic Band Gap Materials: Towards an All-Optical Micro-Transistor", Sajeev John and Marian Florescu, Journal of Optics A: Pure and Applied Optics 3, S103 (2001). ABSTRACT   PDF
  38. "Photonic Bandgap Engineering in Germanium Inverse Opals by Chemical Vapor Deposition", H. Miguez, E. Chomski, F. Garcia-Santamaria, M. Ibisate, S. John, C. Lopez, F. Meseguer, J. P. Mondia, G. A. Ozin, O. Toader, H. M. van Driel, Advanced Materials 13, No.21, 1634 (2001). ABSTRACT
  39. "Fabrication of Tetragonal Square Spiral Photonic Crystals", Scott Kennedy, Michael Brett, Ovidiu Toader, and Sajeev John, Nano Letters Vol. 2, No. 1, 59, (2002).   ABSTRACT  PDF
  40. "Theory of Fluorescence in Photonic Crystals", Nipun Vats, K. Busch, Sajeev John, Physical Review A 65, 043808 (2002). ABSTRACT   PDF  POSTSCRIPT
  41. "Enhancement of two-photon emission in photonic crystals ", Przemyslaw Markowicz, Christopher Friend, Yuzhen Shen, Jacek Swiatkiewicz, Paras N. Prasad, Ovidiu Toader, Sajeev John, Robert W. Boyd, Optics Letters 27, no. 5, 351 (2002).   ABSTRACT   PDF
  42. "Semi-classical Theory of Lasing in Photonic Crystals", Lucia Florescu, Kurt Busch, and Sajeev John, J. Optical Society of America B19, 2215 (2002). ABSTRACT PDF
  43. "Square spiral photonic crystals: Robust architecture for microfabrication of materials with large three-dimensional photonic band gaps", Ovidiu Toader and Sajeev John, Physical Review E 66, 016610 (2002), ABSTRACT  PDF  POSTSCRIPT
  44. "Diffractionless Flow of Light in All-Optical Micro-chips", A. Chutinan, Sajeev John, and O. Toader, Physical Review Letters 90, 123901 (2003) .   ABSTRACT PDF POSTSCRIPT
  45. "Photonic Band Gap Materials based on Tetragonal Lattices of Slanted Pores", O. Toader, M. Berciu, and Sajeev John, Physical Review Letters 90, 233901 (2003). ABSTRACT   PDF POSTSCRIPT
  46. "Photonic Band Gap Synthesis by Holographic Lithography", Ovidiu Toader, Tim Chan, and Sajeev John, Physical Review Letters 92, 043905 (2004).
  48. "Direct Two-Photon Writing and Characterization of Slanted Pore Photonic Crystals", Markus Deubel, Martin Wegener, Artan Kaso and Sajeev John, Applied Physics Letters 85 (11), 1895 (2004).ABSTRACT  PDF
  49. "Photonic band gap enhancement in frequency-dependent dielectrics", Ovidiu Toader and Sajeev John, Physical Review E 70, 046605 (2004). ABSTRACT PDF
  50. ."Resonance Fluorescence in Photonic Band Gap Waveguide Architectures: Designing the Vacuum for All-Optical Switching", M. Florescu and Sajeev John, Physical Review A 69, 053810 (2004). ABSTRACT PDF
  51. "Engineering the Electromanetic Vacuum for Controlling Light with Light in a Photonic Band Gap Micro-chip", R. Z. Wang and Sajeev John, Physical Review A 70, 043805 (2004). ABSTRACT PDF
  52. "Sculpting the vacuum in a photonic band gap micro-chip", R.Z. Wang and Sajeev John, Journal of Photonics and Nanostructures 2, 137 (2004). ABSTRACT  PDF
  53. "Diffractionless Flow of Light in 2D-3D Photonic Band Gap Hetero-structures: Theory, Design Rules, and Simulations", Alongkarn Chutinan and Sajeev John, Physical Review E 71, 026605 (2005). ABSTRACT PDF
  54. "Pulse re-shaping in photonic crystal waveguides and micro-cavities with Kerr-nonlinearity: Critical Issues for all-optical switching", Dragan Vujic and Sajeev John, Physical Review A 72, 013807 (2005). ABSTRACT  PDF
  55. "Slanted Pore Photonic Band Gap Materials", Ovidiu Toader and Sajeev John, Physical Review E 71, 036605 (2005). ABSTRACT  PDF
  56. "Photonic Band Gap Synthesis by Optical Interference Lithography", Tim Chan, Ovidiu Toader, and Sajeev John, Physical Review E 71, 046605 (2005). ABSTRACT  PDF
  57. "Sub-nanometer precision tuning of the optical properties of three-dimensional polymer-based photonic crystals", G. von Freymann, V. Kitaev, T. Chan, Sajeev John, G. Ozin, M. Deubel, M. Wegener, Journal of Photonics and Nanostructures 2, 191-198 (2004). ABSTRACT PDF
  58. "Measurement of group velocity dispersion for finite size three-dimensional photonic crystals in the near infrared spectral region", G. von Freymann, Sajeev John, S. Wong, S. Kitaev, G. Ozin, Applied Physics Letters 86, 053108 (2005). ABSTRACT PDF
  59. "Enhanced coupling to slow photon modes of three-dimensional graded colloidal photonic crystals", Georg von Freymann, Sajeev John, Vladimir Kitaev, Geoffrey A. Ozin, Advanced Materials, Vol. 17, Issue 10, 1273-1276 (2005). ABSTRACT
  60. "Light Localization for Broadband Integrated Optics in Three Dimensions", A. Chutinan and Sajeev John, Physical Review B 72, 16, 161316 (2005). ABSTRACT PDF
  61. "Elastic Photonic Crystals: From Colour Fingerprinting to Enhancement of Photoluminescence", A. Arsenault, T. J. Clark, G. Von Freymann, E. Vekris, L. Cademartiri, S. Wong, V. Kitaev, I. Manners, Sajeev John, G. A. Ozin, Nature Materials 5 (3): 179-184 March (2006). PDF
  62. "New route towards three-dimensional photonic band gap materials: Silicon double inversion of Polymeric Templates", N. Tetreault, G. von Freymann, M. Deubel, M. Hermatschweiler, F. Perez-Willard, Sajeev John, M. Wegener, G.A. Ozin, Advanced Materials 18 (4): 457, Feb 17 (2006). ABSTRACT
  63. "Direct Laser Writing of Three-Dimensional Photonic Crystals in High Index of Refraction Chalcogenide Glasses", G. von Freymann, S. Wong, G. A. Ozin, Sajeev John, F. Perez-Willard, M. Deubel, M. Wegener, Advanced Materials Vol. 18, Issue 3, February, 2006, Pages: 265-269. ABSTRACT
  64. "3+1 Dimensional Integrated Optics with Localized Light in a Photonic Band Gap", A Chutinan and Sajeev John, Optics Express 14 (3): 1266-1279, Feb 6, (2006). ABSTRACT  PDF
  65. "3D-2D-3D photonic crystal heterostructures by direct laser writing", M. Deubel, M. Wegener, S. Linden, G. Von Freymann, and Sajeev John, Optics Letters 31 (6): 805-807 March 15 ( 2006) ABSTRACT  PDF
  66. "Photonic band-gap formation by optical-phase-mask lithography", Timothy Y. M. Chan, Ovidiu Toader, and Sajeev John, Physical Review E 73, 046610 (2006) ABSTRACT PDF
  67. ''Nonlinear Bloch waves in resonantly doped photonic crystals'', Artan Kaso and Sajeev John, Physical Review E 74, 046611 (2006) ABSTRACT  PDF
  68. "Localized light orbitals: Basis states for three-dimensional photonic crystal microscale circuits", Hiroyuki Takeda, Alongkarn Chutinan and Sajeev John, Physical Review B 74, 195116 (2006).   ABSTRACT  PDF  POSTSCRIPT
  69. "Diamond photonic band gap synthesis by umbrella holographic lithography", Ovidiu Toader, Timothy Y. M. Chan, and Sajeev John, Appl. Phys. Lett. 89, 101117 (2006); doi:10.1063/1.2347112 (3 pages)   ABSTRACT  PDF
  70. "Electromagnetically Induced Exciton Mobility in a Photonic Band Gap", Sajeev John and Shengjun Yang, Physical Review Lett. 99 , 046801 (2007).   ABSTRACT PDF
  71. "Exciton dressing and capture by a photonic band edge". Shengjun Yang and Sajeev John, Physical Review B 75, 235332 (2007).   ABSTRACT PDF
  72. "Molding light flow from photonic band gap circuits to microstructured fibers", James Bauer and Sajeev John, Applied Physics Letters 90, 261111(2007).   ABSTRACT PDF
  73. "Nonlinear Bloch waves in metallic photonic band-gap filaments", Artan Kaso and Sajeev John, Physical Review A 76, 053838 (2007).   ABSTRACT PDF
  74. "Coherent all-optical switching by resonant quantum-dot distributions in photonic band-gap waveguides", Dragan Vujic and Sajeev John, Physical Rreview A 76, 063814 (2007).  ABSTRACT  PDF
  75. "Enhanced Photoconductivity in Thin-Film Semiconductors Optically Coupled to Photonic Crystals", Paul G. O'Brien, Nazir P. Kherani, Stefan Zukotynski, Geoffrey A. Ozin, Evangellos Vekris, Nicolas Tetreault, Alongkarn Chutinan, Sajeev John, Augustin Mihi, and Hernan Miguez, Advanced Materials 19, 4177-4182 (2007)  PDF
  76. "Broadband optical coupling between microstructured fibers and photonic band gap circuits: Two-dimensional paradigms", James Bauer and Sajeev John, Physical Review A 77, 013819 (2008)  ABSTRACT PDF
  77. "Compact optical one-way waveguide isolators for photonic-band-gap microchips", Hiroyuki Takeda and Sajeev John, Physical Review A 78, 023804 (2008)   ABSTRACT PDF
  78. "Light trapping and absorption optimization in certain thin-film photonic crystal architectures", Alongkarn Chutinan and Sajeev John, Physical Review A 78, 023825 (2008)   ABSTRACT PDF
  79. "Templating and Replication of Spiral Photonic Crystals for Silicon Photonics", Kock Khuen Seet, Vygantas Mizeikis, Kenta Kannari, Saulius Juodkazis, Hiroaki Misawa, Nicolas Tetreault, and Sajeev John, IEEE Journal of Selected Topics in Quantum Electronics, Vol. 14, No. 4, July/August (2008).  PDF
  80. "Circuits for light in holographically defined photonic-band-gap materials", Timothy Y. M. Chan and Sajeev John, Physical Review A 78, 033812 (2008)   ABSTRACT  PDF
  81. "Exceptional Reduction of the Diffusion Constant in Partially Disordered Photonic Crystals", Costanza Toninelli, Evangellos Vekris, Geoffrey A. Ozin, Sajeev John and Diederik S. Wiersma, Physical Review Letters, 101, 123901 (2008) ABSTRACT  PDF
  82. "Metallic photonic-band-gap filament architectures for optimized incandescent lighting", Sajeev John and Rongzhou Wang, Physical Review A, 78, 043809 (2008) ABSTRACT  PDF
  83. "Optical wavelength converters for photonic band gap microcircuits", Dragan Vujic and Sajeev John, Physical Review A 79, 053836 (2009). ABSTRACT  PDF
  84. "Ultrafast Population Switching of Quantum Dots in a Structured Vacuum", Xun Ma and Sajeev John, Physical Review Lett. 103, 233601 (2009). ABSTRACT  PDF
  85. "Switching dynamics and ultrafast inversion control of quantum dots for on-chip optical information processing". Xun Ma and Sajeev John, Physical Review A 80, 063810 (2009). ABSTRACT  PDF
  86. "Microscopic theory of multiple-phonon-mediated dephasing and relaxation of quantum dots near a photonic band gap", Chiranjeeb Roy and Sajeev John, Physical Review A 81, 023817 (2010). ABSTRACT  PDF
  87. "Self-consistent Maxwell-Bloch theory of quantum-dot-population switching in photonic crystals" Hiroyuki Takeda and Sajeev John, Physical Review A 83, 053811 (2011). ABSTRACT  PDF
  88. "Coherence and antibunching in a trapped interacting Bose-Einstein condensate" Shengjun Yang and Sajeev John, Physical Review B 84, 024515 (2011). ABSTRACT  PDF
  89. "Quantum-dot all-optical logic in a structured vacuum", Xun Ma and Sajeev John, Physical Review A 84, 013830 (2011). ABSTRACT  PDF
  90. "Optical pulse dynamics for quantum-dot logic operations in a photonic-crystal waveguide", Xun Ma and Sajeev John, Physical Review A 84, 053848 (2011). ABSTRACT  PDF
  91. "Anomalous flow of light near a photonic crystal pseudo-gap", Kyle M. Douglass, Sajeev John, Takashi Suezaki, Geoffrey A. Ozin, and Aristide Dogariu1, Optics Express, 19, No. 25 , 25321 (2011). ABSTRACT  PDF
  92. "Sculpturing of photonic crystals by ion beam lithography: towards complete photonic bandgap at visible wavelengths", Saulius Juodkazis, Lorenzo Rosa, Sven Bauerdick, Lloyd Peto, Ramy El-Ganainy and Sajeev John, Optics Express, 19, No. 7 , 5803 (2011). ABSTRACT  PDF
  93. "Effective optical response of silicon to sunlight in the finite-difference time-domain method", Alexei Deinega and Sajeev John, Optics Letters, 37, No. 1 112 (2012). ABSTRACT  PDF
  94. "Solar energy trapping with modulated silicon nanowire photonic crystals", Guillaume Demesy and Sajeev John, J. Appl. Phys., 112, 074326 (2012). ABSTRACT  PDF
  95. "Solar power conversion efficiency in modulated silicon nanowire photonic crystals", Alexei Deinega and Sajeev John, J. Appl. Phys. 112, 074327 (2012). ABSTRACT  PDF
  96. "Light-trapping in dye-sensitized solar cells", Stephen Foster and Sajeev John, Energy Environ. Sci., DOI: 10.1039/C3EE40185E (2013). ABSTRACT  PDF
  97. "Solar light trapping in slanted conical-pore photonic crystals: Beyond statistical ray trapping", Sergey Eyderman, Sajeev John, and Alexei Deinega, J. Appl. Phys. 113, 154315 (2013); doi: 10.1063/1.4802442. ABSTRACT  PDF
  98. "Finite difference discretization of semiconductor drift-diffusion equations for nanowire solar cells", Alexei Deinega and Sajeev John, Computer Physics Communications 183, 2128 (2012). ABSTRACT  PDF
  99. "Coupled optical and electrical modeling of solar cell based on conical pore silicon photonic crystals", Alexei Deinega, Sergey Eyderman, and Sajeev John, Journal of Applied Phys. 113, 224501 (2013); doi: 10.1063/1.4809982. ABSTRACT  PDF
  100. "Resonant dipole-dipole interaction in confined and strong-coupling dielectric geometries", Ramy El-Ganainy and Sajeev John, New Journal of Physics, 15, 083033 (2013). ABSTRACT  PDF
  101. "Macroscopic response in active nonlinear photonic crystals", Gandhi Alagappan,Sajeev John, and Er Ping Li, Optics Letters 38, No. 18, 3514 (2013). ABSTRACT  PDF
  102. "Light trapping and near-unity solar absorption in a three-dimensional photonic-crystal", Ping Kuang, Alexei Deinega, Mei-Li Hsieh, Sajeev John and Shawn-Yu Lin, Optics Letters 38, No. 20, 4200 (2013). ABSTRACT  PDF
  103. "Synergistic plasmonic and photonic crystal lighttrapping: Architectures for optical upconversion in thin-film solar cells", Khai Q. Le and Sajeev John, Optics Express, 22, Issue S1, pp. A1-A12, DOI:10.1364/OE.22.0000A1 (2014). ABSTRACT  PDF
  104. "Near perfect solar absorption in ultra-thin-film GaAs photonic crystals", Sergey Eyderman, Alexei Deinega and Sajeev John, Journal of Materials Chemistry A, DOI: 10.1039/c3ta13655h (2014). ABSTRACT  PDF
  105. "Light trapping design for low band-gap polymer solar cells," Stephen Foster and Sajeev John, Optics Express, Vol. 22, Issue S2, pp. A465-A480 (2014). ABSTRACT  PDF
  106. "Photonic Crystal Architecture for Room-Temperature Equilibrium Bose-Einstein Condensation of Exciton Polaritons," Jian-Hua Jiang and Sajeev John, Physical Review X 4, 031025 (2014). ABSTRACT  PDF
  107. "Photonic Architectures for Equilibrium High-Temperature Bose-Einstein Condensation in Dichalcogenide Monolayers," Jian-Hua Jiang & Sajeev John, Nature Magazine Scientific Reports 4, 7432 (2014). ABSTRACT  PDF  Supplementary Information
  108. "Optical Biosensing of Multiple Disease Markers in a Photonic-Band-Gap Lab-on-a-Chip: A Conceptual Paradigm," Abdullah Al-Rashid and Sajeev John, Phys. Rev. Applied 3, 034001 (2015). ABSTRACT  PDF
  109. "Light-trapping optimization in wet-etched silicon photonic crystal solar cells," Sergey Eyderman, Sajeev John, M. Hafez, S. S. Al-Ameer, T. S. Al-Harby, Y. Al-Hadeethi, and D. M. Bouwes, Journal of Applied Physics 118, 023103 (2015). ABSTRACT  PDF
  110. "Waveguide-mode polarization gaps in square spiral photonic crystals," Rong-Juan Liu, Sajeev John and Zhi-Yuan Li, EPL, 111 54001 (2015). ABSTRACT  PDF
  111. "Biosensor architecture for enhanced disease diagnostics: lab-in-a-photonic-crystal," Shuai Feng, Jian-Hua Jiang, Abdullah Al Rashid and Sajeev John, Optics Express, 24 No. 11, 12166 (2016). ABSTRACT  PDF
  112. "Light-trapping in perovskite solar cells," Qing Guo Du, Guansheng Shen and Sajeev John, AIP Advances 6, 065002 (2016). ABSTRACT  PDF
  113. "Light-trapping for room temperature Bose-Einstein condensation in InGaAs quantum wells," Pranai Vasudev, Jian-Hua Jiang and Sajeev John, Optics Express 24 No.13, 14010 (2016). ABSTRACT  PDF
  114. "Light-trapping and recycling for extraordinary power conversion in ultra-thin gallium-arsenide solar cells," Sergey Eyderman and Sajeev John, Nature Scientific Reports 6 28303 (2016). ABSTRACT  PDF
  115. "Achieving an Accurate Surface Profile of a Photonic Crystal for Near-Unity Solar Absorption in a Super Thin-Film Architecture," Ping Kuang, Sergey Eyderman, Mei-Li Hsieh, Anthony Post, Sajeev John and Shawn-Yu Lin, ACS, Nano 10 (6) 6116-6124 (2016). ABSTRACT  PDF
  116. "Probing the intrinsic optical Bloch-mode emission from a 3D photonic crystal," Mei-Li Hsieh1, James A Bur, Qingguo Du, Sajeev John and Shawn-Yu Lin, Nanotechnology 27 415204 (2016). ABSTRACT  PDF
  117. "Light-trapping design for thin-film silicon-perovskite tandem solar cells," Stephen Foster and Sajeev John, Journal of Applied Physics 120, 103103 (2016). ABSTRACT  PDF
  118. "Effectively infinite optical pathlength created using a simple cubic photonic crystal for extreme light trapping," Brian J. Frey, Ping Kuang, Mei-Li Hsieh, Jian-Hua Jiang, Sajeev John and Shawn-Yu Lin, Scientific Reports 7, Article number: 4171 (2017). ABSTRACT  PDF


Multiple scattering of light in biological tissue provides a safe, inexpensive, and noninvasive probe of brain, breast, and skin tumors. Unlike, magnetic resonance imaging (MRI) which relies on very long wavelength radiation, or X-ray based tomography which relies on very short wavelength radiation, the optical method utilizes an intermediate wavelength window. This window is sensitive to the concentration of oxygenated haemoglobin in tissue, and thereby provides an early diagnostic image of metabolic processes leading to cancer, prior to structural damage caused by the tumor. We are developing a microscopic theory of the propagation of the Wigner coherence function (two-point electric field correlation function) of near infra-red light propagating and scattering in biological tissue which contains a statistical inhomogeneity (tumor). The inhomogeneity exhibits preferential absorption of light and may have different scattering characteristics than healthy tissue. The optical Wigner function is sensitive to these different absorption and scattering characteristics. The difficulty of the optical method is that, unlike X-ray and MRI techniques in which radiation propagates in a straight line, light undergoes a complicated multiple scattering path in the medium. Our work is aimed at unscrambling the information about tissue characteristics contained in the optical wave-field after it has been scattered many times. Most other researchers in this field have adopted the simplistic assumption that photons (particles of light) can be regarded as classical particles undergoing diffusion in the tissue. Using this assumption, tissue properties can only be resolved on the scale of a millimeter. Our approach, which for the first time solves the wave equation and relates the Wigner coherence function to the tissue dielectric constant, will improve the resolution of the optical method by several orders of magnitude. Our microscopic theory will facilitate the reconstruction of tissue images with a resolution on the scale of the optical wavelength. Imaging devices based on our theory will be safe, inexpensive, and suitable for use in the office of the general practitioner. Other applications include the ability to diagnose skin tumors without recourse to a biopsy and the ability to perform a blood test without having to draw blood.

Biological tissue is a weakly absorbing, multiple light scattering medium. A closely related problem is that of stimulated emission, optical amplification and lasing in a random medium with gain. Recent experiments have revealed that a multiple scattering medium doped with dye molecules can exhibit isotropic laser action when suitably pumped. We have developed a comprehensive microscopic theory of these "Random Lasers".


  1. S. John and M. Stephen, Phys. Rev. B28, 6358 (1983) "Wave Propagation and Localization in a Long Range Correlated Random Potential".  ABSTRACT  PDF
  2. Sajeev John, Phys. Rev. B 31, 304 (1985) "Localization and Absorption of Waves in a Weakly Dissipative Disordered Medium".   ABSTRACT   PDF
  3. S. Etemad, R. Thompson, M.J. Andrejco, Sajeev John and F. MacKintosh, Phys. Rev. Lett. 59, 1420, (1987) "Weak Localization of Photons: Termination of Coherent Random Walks by Absorption and Confined Geometry".  ABSTRACT   PDF
  4. Fred MacKintosh and Sajeev John, Phys. Rev. B 37, 1884 (1988) "Coherent Backscattering of Light in the Presence of Time Reversal Non-invariant and Parity Violating Media".    ABSTRACT    PDF
  5. F. MacKintosh and S. John, Phys. Rev. B40, 2383 (1989) "Diffusing-Wave Spectroscopy and Multiple Scattering of Light in Correlated Random Media". ABSTRACT    PDF
  6. S. John, G. Pang and Y. Yang, Journal of Biomedical Optics, Volume 1, No. 2, page 180 (1996) "Optical Coherence Propagation and Imaging in a Multiple Scattering Medium".   ABSTRACT
  7. Sajeev John and Gendi Pang, Physical Review A 54, 3642 (1996) ''Theory of Lasing in a Multiple Scattering Medium''.    ABSTRACT    PDF
  8. Sajeev John, Nature, 390 661 (1997) "Frozen Light".  ABSTRACT
  9. ''Theory of Photon Statistics and Optical Coherence in a Multiple-Scattering Random Laser Medium'', Lucia Florescu and Sajeev John, Physical Review E 69, 046603 (2004). ABSTRACT  PDF  POSTSCRIPT
  10. ''Lasing in a random amplifying medium: Spatiotemporal characteristics and nonadiabatic atomic dynamics'', Lucia Florescu and Sajeev John Physical Review E 70, 036607 (2004) . ABSTRACT  PDF
  11. ''Photon Statistics and Optical Coherence Properties of Light Emission from a Random Laser'', Lucia Florescu and Sajeev John, Physical Review Letters 93, 013602 (2004). ABSTRACT  PDF


The microscopic mechanism for high temperature superconductivity is one of foremost unsolved problems in solid state physics. A clear understanding of this mechanism may lead to the design of new materials which exhibit superconductivity at room temperature. This would lead to a technological revolution rivaling the semiconductor and the laser.

The central question in this field is the nature of the, parent, non-Fermi-liquid metallic state of a strongly interacting electron gas from which superconductivity emerges. This parent state differs from that of ordinary superconductors in a highly fundamental way. One aspect of the unconventional nature of the parent metal is the appearance of antiferromagnetism at very low charge carrier concentration and the disappearance of this magnetic state with increasing carrier concentration. Recently, our work has revealed the existence of  topological magnetic solitons  in such an electron gas as well as a novel magnetic phase of these systems, which we refer to as a  spin-flux phase. When electrons are added to this system, this background magnetic state causes the spin and the charge of the electrons to separate and become bound to magnetic vortex solitons. These vortex solitons are the 2-d analogues of domain wall solitons in 1-d polyacetylene. They induce mid-gap electronic levels in the Mott-Hubbard charge transfer gap . In this state the electron gas no longer acts as a Fermi liquid, in agreement with experiments. The appearance of these solitons also leads to the observed disappearance of long range antiferromagnetic order in the spin background. We are developing a microscopic theory of the anomalous metallic phase and superconducting phase of the high temperature cuprate superconductors based on these concepts. Our current work involves the calculation of the Hartree-Fock energies of various magnetic solitons, the determination of the spin, charge, and statistics of these solitons, and the nature of the thermodynamic phases formed by a finite density of these solitons. We are studying the linear and nonlinear response of charged and uncharged to solitons to external electromagnetic fields. A detailed comparison of our model with experimentally observed magnetic, optical, and electronic properties of high temperature superconducting materials is being performed.


  1. Sajeev John and T.C. Lubensky, Phys. Rev. B 34, 4815 (1986) "Phase Transitions in a Disordered Superconductor near Percolation".  ABSTRACT   PDF
  2. S. John, P. Voruganti and W. Goff, Phys. Rev. B43, 13, 365 (1991) "Electronic and Magnetic Features of Twisted Spin-Density-Wave States in the Two-dimensional Hubbard Model".   ABSTRACT   PDF
  3. P. Voruganti, A. Golubentsev and Sajeev John, Phys. Rev. B45 13945 (1992) "Conductivity and Hall Effect in the Two Dimensional Hubbard Model". ABSTRACT   PDF
  4. S. John and A. Golubentsev, Phys. Rev. Lett. 71, 3343 (1993) "Topological Magnetic Solitons in the Two-dimensional Mott-Hubbard Gap".  ABSTRACT   PDF
  5. S. John and A. Golubentsev, Phys. Rev. B51, 381 (1995) "Spin-flux and Magnetic Solitons in an Interacting Two-dimensional Electron Gas: Topology of Two-Valued Wavefunctions".  ABSTRACT   PDF
  6. S. John and A. Muller-Groeling, Phys. Rev. B51, 12989 (1995) "Mean-field Energies of Spin-flux Phases".   ABSTRACT    PDF
  7. Sajeev John,  Mona Berciu and A. Golubentsev, Europhysics Letters 41, (1), 31 (1998) "Midgap States of a Two-Dimensional Antiferromagnetic Mott Insulator: Electronic Structure of Meron-Vortices".   ABSTRACT PDF
  8. Mona Berciu and Sajeev John, Physical Review B57, 9521 (1998) "Charged Bosons in a Doped Mott Insulator: Electronic Properties of Domain Wall Solitons and Meron-Vortices".   ABSTRACT   PDF   POSTSCRIPT
  9. Mona Berciu and Sajeev John, Physical Review B 59, 15143 (1999) "Numerical study of multisoliton configurations in a doped antiferromagnetic Mott insulator".    ABSTRACT  PDF   POSTSCRIPT
  10. Mona Berciu and Sajeev John, Physical Review B 61 (15), 10015-10028 (2000) "Quantum dynamics of charged and neutral magnetic solitons: Spin-charge separation in the one-dimensional Hubbard model". ABSTRACT   PDF
  12. Mona Berciu and Sajeev John, Physical Review B 61 (24), 16454-16469 (2000) "A microscopic model for d-wave charge carrier pairing and non-Fermi-liquid behavior in a purely repulsive 2D electron system". ABSTRACT   PDF
  14. "Magnetic structure factor in cuprate superconductors: Evidence for charged meron vortices", Mona Berciu and Sajeev John, Physical Review B 69, 224515 (2004). ABSTRACT PDF

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Photon Localization and Photonic Bandgap Materials    |    Multiple Light Scattering, Medical Imaging and Random Lasers     |    Magnetism and Superconductivity    |
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