Characteristic equations for the lasing Modes of infinite periodic chain of quantum wires

In this paper, we study the lasing modes of a periodic open optical resonator. The resonator is an infinite chain of active circular cylindrical quantum wires standing in tree space. Characteristic equations for the frequencies and associated linear thresholds of lasing are derived. These quantities are considered as eigenvalues of specific electromagnetic-field problem with "active" imaginary part of the cylinder material's refractive index - Lasing Eigenvalue Problem (LEP). ©2008 IEEE

Photonic Crystals with Alternate Arrays of Rods and Holes in a Low Dielectric-Index Material

This thesis theoretically deals with the propagation of electromagnetic waves (light beams) in periodically modulated dielectric material structures based on Maxwell’s equations. We are interested in novel light propagation characteristics in these man-made dielectric material structures for practical applications, especially on optical communications and computations. Since the wavelength range of light is on the same order of magnitude as the modulation periods of dielectric materials, an analogy of the light propagation in dielectric-constant modulated structures with the electron transport in solid-state crystals is used throughout my thesis by using a term “photonic crystals (PhCs)” referring to these dielectric structures. I started my work on two-dimensional (2D) PhCs. A new type of PhCs is proposed which consists of alternate arrays of rods and holes (AARH), embedded in a low dielectric-constant material such as ultravioletcurable polymer. By modeling them as 2D PhCs, it is discovered that this type of PhCs exhibits overlapped photonic band gaps (PBGs) for both transverse electric (TE) and transverse magnetic (TM) polarized light beams. This discovery is important for many practical applications related to light manipulation. It opens the door to more effective optical computing elements, as well as 1 better wave guides, LEDs and micro-lasers. It is also found that new AARH PhCs possess many interesting near-band-edge properties such as left-hand-material characteristics manifested by perfect reflection, negative refraction, and superlensing. I then extended my work to three dimensional (3D) counterparts of the discovered PhCs, which are called photonic crystal slabs (PCSs). I found that the overlapped TE and TM PBGs persist in these PCSs although they are restricted to a partial k-space. By manipulating certain structure parameters such as the thickness of PCS and its cladding, it is possible to achieve overlapping incomplete PBGs exactly in the frequency range predicted by 2D simulations. Hence, one can use fast and cheap 2D simulation instead of slow and expensive 3D and still engineer complex 3D photonic structures. The AARH PCSs also exhibit negative refraction and near zero effective refractive index. These effects allow for a strong control over the light propagation in PhCs. Additionally, the edge and surface modes of proposed PCSs are observed that effectively enlarge slabs’ PBGs

Tensilely strained germanium nanomembranes for infrared light emitting devices

Thesis (Ph.D.)--Boston Universitydevelopment of group-IV semiconductor lasers has attracted significant attention in recent years, since it represents the key missing ingredient for the large-scale monolithic integration of electronics and photonics in a CMOS-compatible fashion. The main challenge is to convert the indirect-bandgap group-IV materials into efficient light emitters. Many researchers have focused on improving the light emission efficiency of these materials in the near-infrared (NIR) spectral region, to replace the existing chip-to- chip communication technology with optical links. At the same time, group-IV lasers operating at mid-infrared (MIR) wavelengths also possess many important applications, mainly in the area of chemical and biological sensing, such as trace-gas detection, environmental monitoring, medical diagnostics, and industrial process control. Motivated by these applications, here I focus on improving the light emission efficiency of germanium (Ge). The small energy difference between its direct and indirect bandgaps can be further decreased with the introduction of tensile strain, leading to significantly improved radiative efficiency. At the same time, the bandgap energy shifts into the technologically important 2.1-2.5 µm MIR atmospheric transmission window. At 1.9% tensile strain, Ge even becomes a direct-bandgap semiconductor. In this work, tensile strain is introduced in Ge nanomembranes (NMs), i.e., single-crystal sheets with nanoscale thicknesses, through the application of mechanical stress. Our strain-resolved photoluminescence (PL) measurements performed on these NMs demonstrate a significant red-shift and enhancement in the emission spectra with increasing strain. PL measurement results obtained with a 24-nm-thick NM also reveal that the membrane is converted into direct-bandgap Ge with the application of 2% tensile strain. Furthermore, theoretical analysis of the high-strain PL spectra shows that population inversion can be achieved in these ultrathin NMs with gain values as high as 300 cm−1. Two-dimensional periodic structures fabricated on the top surface of such membranes result in further enhanced light collection through first-order diffraction of the in-plane emitted luminescence. Furthermore, the cavity modes of these periodic structures are also resolved in the strain-dependent PL spectra. These results are promising for the demonstration of Ge NM lasers operating in the technologically important 2.1-2.5 µm spectral region for potential applications in biochemical sensing and spectroscopy