回折格子は波長や屈折率に依存して光ビームを偏向させるので,可変波長光源や屈折率制御機構(加熱 ヒーターなど)と組み合わせれば光偏向器として利用できる.ただし現実的な波長や屈折率の変化量に対する 偏向角が数度と小さい.我々は,フォトニック結晶導波路 (PCW) のスローライトがこれらの微小変化に対して 波数を大きく変える点に着目し,これと光回折機構を組み合わせた光偏向器を検討している .本研究では, 製作したシリカクラッド Si PCW に表面回折格子を形成した Fig. 1(a)のようなスローライト偏向器を報告する. 製作した PCW は,スラブ厚 210 nm,格子定数 400 nm,円孔直径 200 nm,上下シリカクラッドの厚さはそれ ぞれ約 2 m である.上側のクラッドを反応性イオンエッチングにより約 1 m まで薄膜化し,さらに集光イオン ビーム(FIB)を用いて周期 800 nm,深さ約 120 nm の回折格子を形成した.Fig. 1(b)には回折光の FDTD シ ミュレーション例(1 次元フォトニック結晶導波路を仮定した簡易的な断面 2 次元計算)を示す.また Fig. 1(c) は実際に上方向(鉛直が = 0°)に放射される光の遠視野像である.コリメートレンズ等を挿入していないので, 導波路と直交する方向には光が広がるが,導波路に沿った方向には 0.1°オーダーの狭いビームが観測された. また波長を変えると,約 1.2°/nm で偏向した.これは通常の回折格子の約 10 倍の感度である. より厳密な理論性能を予測するため,回折格子を含む 3 次元構造を考慮したフォトニックバンドと群屈折ス ペクトルを計算した.これより得られた偏向角と光放射量のスペクトルを Fig. 2 に示す.ここでは導波路上部の シリカクラッドの厚さ t を 300~400 nm,回折格子の幅を 400 nm,深さを 120 nm と仮定している.偏向角は 1.2°/nm であり,実験値とほぼ一致した.光の放射量は,元々の伝搬モードがシリカライトコーンに影響されな い波長 1550 ~ 1570 nm で t = 300 nm のときに約 100 dB/cm,t = 400 nm のとき,約 30 dB/cm である.最 終的な導波路長は 3 mm を想定しているが,これまでに製作したデバイスは 800 m なので,これで効率のよ い光放射を得るための設計と製作を行っていく. 参考文献 1) 竹内ら,本会
Complex photonic quasicrystals are designed theoretically in submicrometer scale by using a refractive interferometer. The calculated diffraction patterns prove their multi-fold rotational symmetry. Decagonal quasicrystals is prepared experimentally.
We demonstrated time-domain measurement and frequency domain measurement of continuous-variable (CV) entanglement with pulsed light source and waveguides. The experiment with pulsed light source has difficulty in temporal mode matching between the entangled beams and local oscillator (LO) beams. To break through this difficulty, we shorten the duration of LO pulse by optical parametric amplification (OPA) in a waveguide. We generated entanglement that satisfied EPR-Reid criterion in the time domain measurement.
Light carries spin (polarization) and orbital angular momentum (OAM). We review recent work on the stable propagation and nonlinear properties of such states in fibers, which have spawned applications ranging from telecommunications to biomedical imaging.
Early detection of skin cancer is fundamental to its successful treatment. Changes in the shape, including the relief, of skin lesions are an indicator of a possible malignancy l and image processing optical microtopographic inspection of skin lesions can be used to identify diagnostic patterns of benign and malignant skin lesions. Statistical parameters like the mean roughness (Ra) may allow the discrimination between different types of lesions and degree of malignancy. Fractal analysis of bi-dimensional and 3D images of skin lesions can validate or complement this assessment by calculation of its fractal dimensions (FD). In the study reported herein, the microtopographic inspection of the skin lesions was performed by using the optical triangulation based microtopographer developed at the Physics Department of the University of Minho, MICROTOP.03.MFC. Images of the skin lesions were digitized and processed in order to calculate fractal parameters. The patients that participated in this research study were men and women older with the clinical and histopathology diagnoses of: melanoma, basocellular carcinoma, epidermoide carcinoma, actinic keratosis, keratoacantosis and benign nevus.
Nonlinear directional couplers (NDCs) find wide interest in optical communication system because of its potential application in signal processing including optical switching and logic operation. In couplers, if any one of the channel of NDCs is replaced with negative index material (NIM), then the coupler is called as oppositely directed coupler (ODC) because of the opposite direction of input and output fields. The electromagnetic wave entering in one channel of the coupler leave through other channel in opposite direction. Optical bistability (OB) is a nonlinear phenomenon observed in optical systems such that, the system possesses two output intensities for the same input intensity. The importance of optical bistability arises due to its potential application for the development of devices such as optical switches, memories, and amplifiers. The primary requirements of OB are the intensity dependent refractive index and optical feedback mechanism. A two core directional coupler with channels made of nonlinear and homogeneous materials is not bistable. However, ODC shows the phenomenon of OB and admit gap solitons due to effective feedback mechanism in NIM channel arising as a result of opposite directionality of phase velocity and energy flow.
Fluorescence polarization microscopy (FPM) aims to detect the dipole orientation of fluorophores and to resolve structural information for labeled organelles via wide-field or confocal microscopy. Conventional FPM often suffers from the presence of a large number of molecules within the diffraction-limited volume, with averaged fluorescence polarization collected from a group of dipoles with different orientations. Here, we apply sparse deconvolution and least-squares estimation to fluorescence polarization modulation data and demonstrate a super-resolution dipole orientation mapping (SDOM) method that resolves the effective dipole orientation from a much smaller number of fluorescent molecules within a sub-diffraction focal area. We further apply this method to resolve structural details in both fixed and live cells. For the first time, we show that different borders of a dendritic spine neck exhibit a heterogeneous distribution of dipole orientation. Furthermore, we illustrate that the dipole is always perpendicular to the direction of actin filaments in mammalian kidney cells and radially distributed in the hourglass structure of the septin protein under specific labelling. The accuracy of the dipole orientation can be further mapped using the orientation uniform factor, which shows the superiority of SDOM compared with its wide-field counterpart as the number of molecules is decreased within the smaller focal area. Using the inherent feature of the orientation dipole, the SDOM technique, with its fast imaging speed (at sub-second scale), can be applied to a broad range of fluorescently labeled biological systems to simultaneously resolve the valuable dipole orientation information with super-resolution imaging.
Photonic microwave time delays using semiconductor lasers at period-one nonlinear dynamics is experimentally investigated. A wide tunable range of the microwave time delay, about 114 ps, over a broad frequency range of 4 GHz is realized by simply adjusting the power of an optical input.
