In recent years, reconfigurable optical add drop multiplexers (ROADM) and multiple-dimensions optical cross-connection (OXC), as the essential devices of next-generation dynamic optical networks, have been attracted great interests by research institutions and relevant industry. 1×N Wavelength selective switches (WSSs) are one of the key components in current and next generation ROADM. Currently, WSS primarily rely on micro-electromechanical systems (MEMS) and liquid crystal on silicon spatial light modulators (LCOS-SLM) switches. LCOS-based WSSs have several advantages, including flexible spectrum coverage, adaptive alignment, and robustness. Based on a novel 2-f optical structure, we therefore propose 1×32 WSS system including a 1×32 fiber-coupling lenslet arrays, a collimating lens, a transmission grating, a cylindrical lens and a LCOS-SLM. By uploading the optimized phased holograms on the LCOS, we have successfully switched input signal with arbitrary wavelength in C-band into any output port. The output channel spacing can be adjusted flexibly and each port switches independently. Experimental results demonstrate the insertion loss is around 5~10dB and the switch crosstalk at 1550nm is -35dB. The 3dB-bandwidth of signal@100G is 40G.The research has established the theory and experiment foundation for the development of M×N WSS in future.
Multifrequency filtering characteristics of the two-dimensional square-lattice photonic crystal structures with rectangular microcavities are studied. Owing to the different sensitivities of the resonant frequencies to the variation of the rectangle’s side length, one resonant frequency can be flexibly adjusted only by changing one of the rectangle’s side lengths, while another frequency is immunizing to the variation. So, a two-output-channel frequency filter is designed to allow two frequencies to travel along different channels, and allow the third frequency to travel along both the channels. Based on the low spatial symmetry of rectangular defect, which supports localized modes with different symmetries, together with optimizing the coupling regions between the input waveguide and the rectangular microcavities, the two-output-channel and four-output-channel filters are both achieved, which can select different frequencies to travel along various channels, and share another frequency to travel along every output channel. These kinds of devices have both the abilities of information selecting and sharing carried out by different frequencies, and may have potential applications in the future complex all-optical integrated circuits.
We experimentally demonstrate and characterize an organic octagonal quasicrystal slab with a single-defect microcavity at low-index contrast. The gain medium is the conjugated-polymer, composed by two PPV derivatives, a BEHP-PPV and a MEH-PPV. By optical pumping, the lasing action is achieved at 607 nm with a FWHM of 1nm. The threshold of lasing is 9uJ/cm2. The intensity of the lasing peak depends linearly on the pump energy above the threshold.
A high stable wavelength-tunable fiber laser is experimentally demonstrated by using a digital-micromirror-device (DMD) processor and a polarization-maintaining erbium-doped fiber amplifier (EDFA).The electronic-addressed DMD processor is able to select and couple a waveband from of the polarization-maintaining EDFA back into the fiber ring to generate a narrow line-width laser output. The tunable fiber laser shows a line-width of 0.02nm, a tuning step of 0.08nm over the c-band and a side mode suppression ratio (SMSR) greater than 50 dB. The output power uniformity of 0.016dB is achieved by using the automatic power control (APC) system under room temperature. The center wavelength fluctuation during 1 hour is below 0.01 nm.
Unidirectional light transmission through composite structures, consisting of a square lattice of square metals with different sizes, is studied by the finite-difference time-domain method. Through adding two metallic slices into the lateral boundaries of the composite structures, the lateral light energy leak is avoided and unidirectional light propagations towards two opposite directions are obtained within two separate frequency regions based on the directional band gaps. Through the design of arranging metallic rods at the interface of two photonic crystals, the unidirectional light propagation, based on the different refractive and reflective behaviors at the frequencies within the pass bands, is also obtained.
The transmission characteristics of the electromagnetic waves through the coupled-resonator optical waveguides based
on the two-dimensional oval-rod photonic crystals are studied by the finite-difference time-domain method. The
simulated results show that the guided mode region can be controlled by partially changing the circular rods with oval
rods adjacent to the cavities, and the oval rods' rotating angles are set to be different. When the rotation angle of the oval
rods around one cavity is different from the rotation angle of the oval rods around the adjacent cavities, the group
velocities of the guided modes can be greatly reduced and high efficiency of light transmission is insured. And the
information of different frequencies can be shared and chosen at the same time by the waveguide branch based on the
above structures.
The low-frequency optical properties of CuS nanoparticles in the composite samples were
measured by the terahertz time-domain spectroscopy. Then, the power absorption, refractive index,
complex dielectric function and conductivity of pure CuS nanoparticles are extracted by applying
Bruggeman effective medium theory. The measured dielectric function and conductivity are consistent with
the Lorentz theory of dielectric response as well as the Drude-smith model of conductivity in the frequency
range from 0.2 to 1.5 THz, respectively. In addition, the extrapolation of the measured data indicates that
the absorption is dominated by the lattice vibration localized at 4.7 ± 0.2 THz and the time constant for the
carrier scattering is only 64.3 fs due to increased electron interaction with interfaces and grain boundaries.
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