Control of spontaneously emitted light lies at the heart of quantum optics. It is essential for diverse applications ranging from miniature lasers and light-emitting diodes, to single-photon sources for quantum information, and to solar energy harvesting. To explore such new quantum optics applications, a suitably tailored dielectric environment is required in which the vacuum fluctuations that control spontaneous emission can be manipulated. Photonic crystals provide such an environment: they strongly modify the vacuum fluctuations, causing the decay of emitted light to be accelerated or slowed down, to reveal unusual statistics, or to be completely inhibited in the ideal case of a photonic bandgap. Here we study spontaneous emission from semiconductor quantum dots embedded in inverse opal photonic crystals. We show that the spectral distribution and time-dependent decay of light emitted from excitons confined in the quantum dots are controlled by the host photonic crystal. Modified emission is observed over large frequency bandwidths of 10%, orders of magnitude larger than reported for resonant optical microcavities. Both inhibited and enhanced decay rates are observed depending on the optical emission frequency, and they are controlled by the crystals’ lattice parameter. Our experimental results provide a basis for all-solid-state dynamic control
of optical quantum systems.

Controlling the dynamics of spontaneous emission from quantum dots by photonic crystals

Rare-earth ion doped TeO2 and GeO2 glasses as laser materials

A light energy delivery head is provided which, in one aspect, mounts laser diode bars or other light energy emitters in a heat sink block which is adapted to cool both the emitters and a surface of a medium with which the head is in contact and to which it is applying light energy. In another aspect, various retroreflection configurations are provided which optimize retroreflection of back-scattered light energy from the medium. The size of the aperture through which light energy is applied to the medium is also controlled so as to provide a desired amplification coefficient as a result of retroreflection.

Light energy delivery head

Photocosmetic device for use in medical or non-medical environments (e.g., a home, barbershop, or spa), which can be used for a variety of tissue treatments. Radiation is delivered to the tissue via optical systems designed to pattern the radiation and project the radiation to a particular depth. The device has a variety of cooling systems including phase change cooling solids and liquids to cool treated skin and the radiation sources. Contact sensors and motion sensor may be used to enhance treatment. The device may be modular to facilitate manufacture and replacement of parts.

Cooling System For A Photocosmetic Device

Over the last 20 years, silicon photonics has revolutionized the field of integrated optics, providing a novel and powerful platform to build mass-producible optical circuits. One of the most attractive aspects of silicon photonics is its ability to provide extremely small optical components, whose typical dimensions are an order of magnitude smaller than those of optical fiber devices. This dimension difference makes the design of fiber-to-chip interfaces challenging and, over the years, has stimulated considerable technical and research efforts in the field. Fiber-to-silicon photonic chip interfaces can be broadly divided into two principle categories: in-plane and out-of-plane couplers. Devices falling into the first category typically offer relatively high coupling efficiency, broad coupling bandwidth (in wavelength), and low polarization dependence but require relatively complex fabrication and assembly procedures that are not directly compatible with wafer-scale testing. Conversely, out-of-plane coupling devices offer lower efficiency, narrower bandwidth, and are usually polarization dependent. However, they are often more compatible with high-volume fabrication and packaging processes and allow for on-wafer access to any part of the optical circuit. In this paper, we review the current state-of-the-art of optical couplers for photonic integrated circuits, aiming to give to the reader a comprehensive and broad view of the field, identifying advantages and disadvantages of each solution. As fiber-to-chip couplers are inherently related to packaging technologies and the co-design of optical packages has become essential, we also review the main solutions currently used to package and assemble optical fibers with silicon-photonic integrated circuits.

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Coupling strategies for silicon photonics integrated chips [Invited]

We have demonstrated that the population feeding from the 4I11/2 level to the 1.5 μm fluorescence emitting 4I13/2 level of Er3+ ions in low phonon energy glass hosts can be enhanced by codoping with Ce3+ under optical pumping at 980 nm. The nonradiative energy transfer Er3+: 4I11/2; Ce3+: 2F5/2→Er3+: 4I13/2; Ce3+: 2F7/2, occurs in the form of phonon-assisted energy transfer, and therefore the feeding rates are faster in the tellurite glasses, which have a comparatively higher phonon energy than in the sulfide glasses. The cross-relaxation process for 4I13/2: 4I13/2→4I15/2: 4I9/2, which lowers the population density of the 4I13/2 manifold and causes a deleterious effect in the 1.5 μm fluorescence intensity, is more severe in the sulfide glasses. Population feeding rate from the 4I11/2 to the 4I13/2 level is significantly enhanced by way of cerium codoping into tellurite glasses, which promises an efficient 980 nm pumped broadband Er3+-doped fiber amplifier.

Comparative study of energy transfers from Er3+ to Ce3+ in tellurite and sulfide glasses under 980 nm excitation

We demonstrate a compactly integrated polarization beam splitter (PBS) with high polarization extinction ratios greater than 20 dB over the full C-band wavelength range based on a simple bridged silicon nanowaveguide directional coupler. The PBS device is designed via three dimensional finite-difference time-domain (3D-FDTD) simulation, and fabricated experimentally. The optimum dimension of the bridge waveguide is determined to be 7.5-μm-long and 500 nm-wide for 250-nm thick silicon core. At the 1,550-nm wavelength, the measured polarization extinction ratios (PERs) of the PBS device are 22.5 dB and 22.9 dB for TE and TM polarization modes, respectively, and its corresponding insertion losses (ILs) are about 2.1 dB and 1.8 dB, both PERs and ILs within the maximum error range of ± 2.0 dB.

Planar-type polarization beam splitter based on a bridged silicon waveguide coupler

Ge–Ga–As–S glasses were investigated to develop efficient host materials for the Er 3+ :2.7 μm fiber lasers. Ge30Ga1As9S60 and Ge30Ga2As6S62 (all in at.%) glasses show good thermal stability and high rare-earth solubility up to 0.3 mol%. Mid-infrared emission with a peak wavelength of 2.76 μm and bandwidth of ∼120 nm was observed in Er3+- and Er3+/Tm3+-doped Ge30Ga2As6S62 glasses. Codoping of Tm3+ significantly reduced the lifetime of the Er 3+ : 4 I 13/2 level due to the energy transfer of Er 3+ : 4 I 13/2 → Tm 3+ : 3 F 4 . Thus, the population inversion between the 4 I 11/2 and 4 I 13/2 levels in Er3+ became possible. In Er3+-doped glasses, the rate of cross-relaxation for the 4 I 11/2 level was approximately 11 times faster than that for the 4 I 13/2 level.

Emission properties of the transition in Er3+- and Er3+/Tm3+-doped Ge–Ga–As–S glasses

16 μm emission originated from Pr3+: (3F3,3F4)→3H4 transition in Pr3+- and Pr3+/Er3+-doped selenide glasses were investigated under an optical pump of a conventional 1480 nm laser diode The measured peak wavelength and full width at half maximum of the fluorescent emission were ∼1650 and >100 nm, respectively A moderate lifetime of the thermally coupled upper manifolds (∼212±5 μs) together with a high stimulated emission cross section of ∼(3±1)×10−20 cm2 promises to be useful for 16 μm band fiber-optic amplifier that can be pumped with an existing high-power laser diode Codoping of Er3+ significantly enhanced the emission intensity by way of a nonradiative Er3+: 4I13/2→Pr3+: (3F3,3F4) energy transfer

1.6 μm emission from Pr3+: (3F3,3F4)→3H4 transition in Pr3+- and Pr3+/Er3+-doped selenide glasses

Er 2 O 3 -doped PbO-Bi 2 O 3 -Ga 2 O 3 glasses were prepared through the conventional melt-quenching method, and the energy transfer mechanisms in Er 3+ were investigated. The fluorescent emission at 2.73 μm, which is normally quenched in silicate glasses, became evident because of the low phonon energy of PbO-Bi 2 O 3 -Ga 2 O 3 glasses. The measured lifetime of the upper level of 4 I 11/2 was 0.9 ms, and it decreased to ∼0.6 ms with increased Er 3+ concentration. When the concentration of Er 2 O 3 was 0.05 wt%, the coefficient of the cross-relaxation rate for the 4 I 11/2 level was -18 times larger than that of the 4 I 13/2 level. On the other hand, the interaction parameter of energy migration was considerably larger for the 4 I 13/2 level (-52 × 10 -40 cm 6 .s -1 ) compared with the 4 I 11/2 level (-3.1 × 10 -40 cm 6 .s -1 ). Therefore, the major energy transfer mechanism associated with the 4 I 13/2 level was migration induced, whereas that for the 4 I 11/2 level was direct cross relaxation of 4 I 11/2 : 4 I 11/2 → 4 F 7/2 : 4 I 15/2 .

Kyong Hon Kim

Papers

Comparative study of energy transfers from Er3+ to Ce3+ in tellurite and sulfide glasses under 980 nm excitation

Planar-type polarization beam splitter based on a bridged silicon waveguide coupler

Emission properties of the transition in Er3+- and Er3+/Tm3+-doped Ge–Ga–As–S glasses

1.6 μm emission from Pr3+: (3F3,3F4)→3H4 transition in Pr3+- and Pr3+/Er3+-doped selenide glasses

Spectroscopic Properties of and Energy Transfer in PbO–Bi2O3–Ga2O3 Glass Doped with Er2O3