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Sinko J.,University of Szeged | Dudas L.,University of Szeged | Gajdatsy G.,Furukawa Electric Institute of Technology Ltd. | Erdelyi M.,University of Szeged | And 3 more authors.
Optics Letters | Year: 2011

Line-scanning tomographic optical microscopy (LSTOM) requires precise rotation of the scanning line. We demonstrate a method that applies translation-invariant optical elements (polarizer and birefringent plate) to minimize the rotation error. An astigmatic line produced by means of a focused beam through a birefringent plate is used as line illumination. A comparative theoretical and experimental study is presented using an LSTOM system. © 2011 Optical Society of America. Source


Nyakas P.,Furukawa Electric Institute of Technology Ltd.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2010

We simulated the cold-cavity optical modes of coupled defect cavities in photonic crystal (PhC) vertical-cavity surface-emitting lasers (VCSELs). Holes were etched into the top distributed Bragg reflector of the COST benchmark structure in hexagonal pattern, leaving 2×1 or 2×2 positions intact. A lattice constant of 4 μm was selected, the hole diameter-to-lattice- constant ratio was varied from 0.5 to 0.7 outside the defect region and from 0.15 to 0.7 between the cavities. We used finite volume method to discretize the scalar Helmholtz equation, and finite element method to solve the vectorial Helmholtz equation, both in three dimensions. Prism elements were selected that fit the complicated contours of the PhC-VCSEL. In-phase and out-of-phase couplings were specified with different symmetry boundary conditions. The complex eigenvalues and optical field distributions were obtained with an in-house developed iterative algorithm. The real part of the eigenvalue determined the wavelength, its imaginary part was proportional to the cold-cavity modal loss. In-phase and out-of-phase coupled modes possessed almost equal properties when all holes had relatively large diameters, indicating uncoupled behavior. For a narrower hole between the defect cavities, the in-phase coupled mode exhibited slightly larger mode area than its out-of-phase counterpart due to its extending tails, but also showed considerably larger optical loss. This predicted out-of-phase operation. If one etched very small holes into the coupling region of the 2×2 PhC-VCSEL array, an additional lobe appeared between the holes, which resulted in enhanced overlap with the gain region. This confirmed in-phase operation. © 2010 SPIE. Source


Nyakas P.,Furukawa Electric Institute of Technology Ltd.
IEEE Photonics Technology Letters | Year: 2011

In this letter, the optical modes of a ring-defect photonic crystal vertical-cavity surface-emitting laser are calculated by the fully numerical solution of the scalar Helmholtz equation. We explain the experimentally observed higher order mode emission on the basis of optical loss discrimination. Special photonic crystal patterns that favor even higher order optical modes are designed and simulated. These modes are beyond the scope of previous simplified analysis. © 2011 IEEE. Source


Nyakas P.,Furukawa Electric Institute of Technology Ltd.
Journal of the Optical Society of America B: Optical Physics | Year: 2013

A new design is proposed to increase the single-mode current range of low threshold current, photonic crystal vertical-cavity surface-emitting lasers. Our method is based on the optical coupling between the usual central defect and six others of nearly identical sizes. The resulting honeycomb configuration aims to spread higher supermodes in transverse directions, and to reduce their overlap with a central current-injected region. Simultaneous confinement of the fundamental mode within the central cavity and the shift of higher modes toward outer trapping defects can lead to stable single-mode operation. Simulations confirm that either in-phase or out-of-phase coupled supermodes could be promoted by slightly modifying the areas of outer cavities, while thermal lensing always stabilizes the in-phase coupled supermodes. The single-mode current regime should be extended noticeably compared to the conventional single-defect lasers. © 2013 Optical Society of America. Source


Nyakas P.,Furukawa Electric Institute of Technology Ltd.
Proceedings of the International Conference on Numerical Simulation of Optoelectronic Devices, NUSOD | Year: 2011

A fully numerical solution of the scalar Helmholtz equation is applied for the optical mode calculation of a ring-defect photonic crystal vertical-cavity surface-emitting laser. It is shown that the diameter of the central hole determines which mode starts lasing at the threshold current. This confirms the result of a previous experimental work. © 2011 IEEE. Source

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