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- ArticleCao T, Zou Y, Adawi AM, Cryan MJ.Opt Express. 2014 Sep 22;22(19):22699-706.We numerically demonstrate an impedance-matched multilayer stacked fishnet metamaterial that has zero index with flat high transmittance from 600 nm to 620 nm. The effective refractive index(n(eff)) is calculated to be -0.045 + 0.466 i and the normalize effective impedance(Z(eff)/Z(0)) is 0.956-0.368 i at 610 nm. The light emitted by a red conjugated polymer layer embedded in such a zero index metamaterial (ZIM) is concentrated in a narrow cone in the surrounding media, where the half-power beam width (HPBW) of the center lobe of the radiation pattern is around 25° in the wavelength range between 600 nm and 620 nm, giving directive emission in the visible region. This proposed light focusing system can be applied to sensing, beam collimating and filtering functionalities.
- ArticleZhang X, Zhang S, Wang C, Li L, Zhao J, Cui J.Opt Express. 2013 Sep 23;21(19):22699-704.We first report a diode-pumped continuous wave orthogonally polarized dual-wavelength single-longitudinal-mode laser with a single c-cut Tm,Ho:LuLiF₄ laser crystal. The simultaneous dual-wavelength single-longitudinal-mode laser near 2 μm is realized by using two uncoated intracavity Fabry-Perot etalons. The output wavelengths are 2064 nm in π-polarization and 2066 nm in σ-polarization respectively, which are orthogonal to each other. At the absorbed pump power of 1 W, the maximum single-longitudinal-mode output powers at 2064 and 2066 nm are 76 and 32 mW respectively. The orthogonally polarized dual-wavelength single-longitudinal-mode laser is possible to be applied to the 2 μm differential absorption lidar and the generation of THz radiation.
- ArticleSpencer A, Barr B, Bell A, Briggs J, Minty A, Sorazu B, Wright J, Strain K.Opt Express. 2022 Jun 20;30(13):22687-22699.Longer wavelength lasers will be needed for future gravitational wave detectors that use cryogenic cooling of silicon based test-mass optics. Diode lasers with a 1550 nm wavelength output are potential seed light sources for such a detector, however diode laser devices have a different spectral profile and higher frequency noise than the solid state lasers used in current detectors. We present a frequency stabilisation system for a 1550 nm external cavity diode laser capable of reducing the laser frequency noise to a level of 0.1HzHz up to 1 kHz with a unity gain frequency of 535 kHz using a hybrid analogue-digital servo with in-loop cancellation of resonant features. In addition, a method of high speed digital filter optimisation and automated design is demonstrated.
- ArticleSchmeltz M, Teulon C, Latour G, Ghoubay D, Borderie V, Aimé C, Schanne-Klein MC.Opt Express. 2019 Aug 05;27(16):22685-22699.Second harmonic generation (SHG) enables in situ imaging of fibrillar collagen architecture in connective tissues. Recently, Circular Dichroism SHG (CD-SHG) microscopy has been implemented to take advantage of collagen chirality to improve 3D visualization. It measures the normalized difference in the SHG signal obtained upon excitation by left versus right circular polarizations. However, CD-SHG signal is not well characterized yet, and quite different CD-SHG values are reported in the literature. Here, we identify two major artifacts that may occur in CD-SHG experiments and we demonstrate that thorough optimization and calibration of the experimental setup are required for CD-SHG imaging. Notably it requires a careful calibration of the incident circular polarizations and a perfect mechanical stabilization of the microscope stage. Finally, we successfully record CD-SHG images in human cornea sections and confirm that this technique efficiently reveals collagen fibrils oriented out of the focal plane.
- ArticlePerrone S, Vilaseca R, Masoller C.Opt Express. 2012 Sep 24;20(20):22692-9.We study numerically the dynamics of a vertical-cavity surface-emitting laser (VCSEL) with optical injection and show that the interplay of polarization bistability and noise yields a reliable logic output to two logic inputs. Specifically, by encoding the logic inputs in the strength of the light injected into the suppressed polarization mode of the VCSEL (the so-called 'orthogonal' injection), and by decoding the output logic response from the polarization state of the emitted light, we demonstrate an all-optical stochastic logic gate that exploits the ubiquitous presence of noise. It gives the correct logic output response for as short as 5 ns bit times when the dimensionless spontaneous emission coefficient, β(sp), is within the range 10(-4)-10(-1). Considering that typical values of β(sp) in semiconductor lasers are in the range 10(-5)-10(-4), the VCSEL-based logic gate can be implemented with nowadays commercially available VCSELs, exploiting either their intrinsic noise, or external and background noise sources.