Wavelength Tunable Devices Research Articles

Estimation of absorption spectral shifts of cyano biphenyl liquid crystals: An impact of different solvents and oxygen substitution

Two nematic liquid crystals, viz. 4-octyl-4׳-cyanobiphenyl (CBP8) and 4-octyloxy-4׳-cyanobiphenyl (OCBP8) have been studied using CNDO/S and INDO/S approaches. The impact of different solvents (benzene, chloroform), and oxygen substitution on electronic origins of shifts in wavelengths have been summarized. The substituent and solvents induced shifts of the molecules in absorption maxima, extinction coefficient, and energy band gap have been analyzed. The changes in photosensitivity and conductivity of these compounds from the view point of these shifts have been analyzed. Other parameters such as ionization potential, chemical potential, electron affinity, electro negativity, hardness, softness of the molecules have also been reported. The solvent-specific alteration of optical and electro chemical properties have been discussed for wavelength tunable device and light modulation applications.

A tunable broadband bandpass filter based on quarter wavelength resonators

In this letter, a tunable broadband bandpass filter (BPF) based on quarter wavelength resonators was proposed. The resonators and coupling structures were mainly consisted of quarter wavelength transmission lines and tunable devices loaded at the two ends of the transmission lines. The resonant frequency of the BPF can be adjusted through changing the total capacitance at the both ends of the resonators. Especially, the coupling strength between resonators can be adjusted by adjusting the value ratio of the capacitor between the two ends. The tunable BPF in this scheme had the advantages of simply design. The bandwidth and center frequency of the tunable BPF can be tuned independently at the same time. As a demonstrator, an eight-orders filter was designed and fabricated on Rogers3006 substrate. The center frequency can be tuned in the range of 0.81 to 1.28 GHz, the relative tuning range was 45%. The relative bandwidth of the tunable filter can be tuned in the range of 14% to 38%. The simulated results were agreement well with the measured ones.

Position Dependence of Emission Wavelength of a SiO2 Colloidal Photonic-Crystal Laser

In this paper, a wavelength tunable colloidal-crystal laser with monodispersed silica particles was demonstrated. Silica particles were synthesized through the modified Stöber process and self-assembled into the colloidal photonic-crystal structure, which was then used to form the optic cavity of a wavelength tunable laser device. Due to Bragg’s diffraction of the colloidal photonic-crystal and the coffee ring effect, the forbidden energy gap of light varied with different lattice sizes at different positions of the colloidal photonic-crystal. When the pumping pulsed laser irradiated on the gain medium of the sample, the fluorescence was restricted and enhanced by the colloidal photonic-crystal. Lasing emission with a single peak occurred when the energy of the pumping laser exceeded the threshold energy. The threshold energy and the full-width at half-maximum (FWHM) of the proposed laser were 7.63 µJ/pulse and 2.88 nm, respectively. Moreover, the lasing wavelength of the colloidal photonic-crystal laser could be tuned from 604 nm to 594 nm, corresponding to the various positions in the sample due to the coffee ring effect.

Fabrication of a widely tunable fiber Bragg grating filter using fused deposition modeling 3D printing

The use of 3D-printing for designing a simple wavelength tunable device based on fiber Bragg gratings is demonstrated. Using fused deposition modeling (FDM), the fiber Bragg grating is embedded into a beam of polyethylene terephthalate glycol (PETG). Through bending, resulting in compression or tension of the optical fiber, the Bragg wavelength could be continuously tuned over a range of 60 nm, with maintained reflectivity and 3-dB linewidth.

Broadband coherent emission observed in polycrystalline CdSSe nanowires under highexcitation

Polycrystalline CdSSe nanowires were prepared with a low-temperature physicalevaporation method. Structural analysis combining HRTEM with XRD demonstrate thatthese as-prepared wires have a hexagonal wurtzite structure with a polycrystalline nature.Locally excited optical measurements show that though these wires can still act aswaveguide cavities, their polycrystalline nature will induce a significant redshift of theemitted light during its transportation along them. Power dependent photoluminescencemeasurement shows that these polycrystalline wires can achieve broadband coherentemission at the band-edge band under high excitation, which shows marked contrast withthe much narrower and multimode spectra observed in the single-crystalline nanowires withthe same elemental composition. Time-resolved photoluminescence further confirms theoccurrence of coherent emission in these wires, which originates from the electron–holeplasma (EHP) recombination of high-density carriers generated under high excitation.These kinds of polycrystalline alloy nanowires with broadband coherent emission shouldhave potential uses in nano-scaled wavelength tunable light-emitting devices.

Ultrafast switching by controlling Rabi splitting

We analyze the behavior of a quantum dot embedded in an add-drop filter for optical signal processing applications. The joint effects of dipole induced transparency and electromagnetic induced transparency, which shift the transparency peak induced by a dipole in an add-drop filter due to vacuum Rabi splitting, have been considered. The mathematical model and some different conditions for tuning the transparency peak are derived for application to all optical switching and wavelength tunable devices.

Thermal Lens Spectroscopy Gas Sensing Based on Etalon-Stabilized Wavelength Sweep Technique for Fiber Ring Laser

This article describe a thermal lens (TL) spectroscopy gas sensing apparatus based on a wavelength sweep technique for a fiber ring laser. The configuration of this apparatus is basically a fiber ring laser containing a TL sensor head composed of two spherical-lensed fibers and wavelength-tunable devices on the inside of the ring. The wavelength can be swept by slightly rotating an etalon plate so that the optical absorption spectrum of a gas can be synchronously captured with a sweep signal. We demonstrate that the measured dynamic range of our proposed apparatus is tenfold that of a conventional one. The limit of detection was estimated to be approximately 400 Pa for the measurement time when the ν1+ν3 band in the acetylene of a few seconds under our experimental condition when the ν1+ν3 band in the acetylene (12C2H2) molecules was applied.

Wavelength tunable device for neutron radiography and tomography

A special double monochromator system was tested for a conventional operating tomography setup in order to use a broad wavelength band of monochromatic neutrons for radiography and tomography. Scanning through the wavelength region of Bragg edges, it is possible to make series of radiographs and tomographs at different wavelengths from 2.0 until 6.5Å. So no beam hardening influences the measurements and is not to be corrected. With this instrument for cold neutron radiography and tomography, energy selecting quantitative radiography, stress and strain mapping, and phase radiography were performed.

Selective optical broadcast component for reconfigurable multiprocessor interconnects

Recent advances in the development of optical interconnect technologies suggest the possible emergence of optical interconnects within distributed shared memory (DSM) machines in the near future. Moreover, current developments in wavelength tunable devices could soon allow for the fabrication of low-cost, adaptable interconnection networks with varying switching times. It is the objective of this paper to investigate whether such reconfigurable networks can boost the performance of the DSM machines further. In this respect, we propose a system concept of a passive optical broadcasting component to be used as the scalable key element in such a reconfigurable network. We briefly discuss the necessary opto-electronic components and the limitations they impose on network performance. We show through detailed full-system simulations of benchmark executions, that the proposed system architecture can provide a significant speedup for shared-memory machines, even when taking into account the limitations imposed by the opto-electronics and the optical broadcast component.

Design and analysis of a scalable optical interconnection network for a computer cluster

This paper describes the dual-layer scalable optical intercon- nection network being developed at Tianjin University. The top layer of the network is a multiwavelength bidirectional optical bus, which has large bandwidth and low latency. The bus is made up of passive com- ponents. No wavelength-tunable devices are used. As a result, the bus has a low communication latency that is mainly determined by the optical fiber length. The sublayer of the network is a single-wavelength ring, which has low communication latency and high scalability. In each ring, a wavelength routing node is designed for data transmission between the ring and the optical bus. Each node computer is connected to the ring through an optical network interface card. The communication latency inside the ring is decreased by using synchronous pipelining transmis- sion. © 2001 Society of Photo-Optical Instrumentation Engineers.

Wavelength tunable fiber Bragg grating devices based on sputter deposited resistive and piezoelectric coatings*

Two all-fiber wavelength tunable devices, one utilizing thermal tuning and a second based on strain tuning, have been produced by combining resistive Ti/Pt and piezoelectric ZnO fiber coatings with fiber Bragg gratings (FBGs). The Ti and Pt coatings with thicknesses of 40 and 300 nm, respectively, were deposited by sequential magnetron sputter deposition. ZnO fiber coatings with a thickness of 18 μm were deposited by dual magnetron reactive sputtering. Joule heating of the Ti/Pt fiber coating was employed for the thermally tunable FBG device, which exhibited a tuning efficiency of 4.1 nm/W. The piezoelectric fiber Bragg grating device allowed for modulated tuning of the FBG wavelength through a strain modulation induced by the piezoelectric ZnO coating. A wavelength modulation amplitude of 0.044 nm was achieved at a driving potential amplitude of 1.26 V and frequency of 15.26 MHz.

LIGHTNING network and systems architecture

This paper describes a hierarchical WDM-based optical network testbed project that is being constructed to interconnect a large number of high performance computers to create a distributed shared memory environment. The objective of the architecture is to achieve scalability yet avoid the requirement of multiple wavelength tunable devices per node. It is a singlehop all-optical network; a packet remains in the optical form from source to destination. It features wavelength channel reuse at each level, allowing scalability to very large system sizes. It partitions the traffic between different levels of the hierarchy without electronic intervention in a combination of wavelength-division and space-division multiplexing. A significant advantage of this approach is its ability to vary dynamically the bandwidth provided to different levels of the hierarchy. Each node monitors the traffic intensities on each channel and can detect any temporal or spatial shift in traffic balance. LIGHTNING can dynamically reconfigure to balance the traffic at each level by reassigning wavelengths associated with each level in the hierarchy to a higher or lower level depending on need. Bandwidth reallocation is completely decentralized, achieving highly fault tolerant system behavior. This paper describes the system architecture, and the network and memory interface that have been developed in this project.

Applications of Active Thin Film Coatings on Optical Fibers

ABSTRACTActive thin film coatings on optical fibers provide a variety of functions that are being used to develop active all-fiber optical devices. Two types of active coatings that are of interest for device development include resistive and piezoelectric coatings. Resistive coatings can be used to heat an optical fiber, while piezoelectric coatings can be used to strain the fiber. Localized changes in the fiber waveguiding properties can be achieved by electrically activating the fiber coating. These coated fibers show promise for applications such as optical phase shifters and modulators.Recent developments in the fabrication of diffraction gratings within the core of an optical fiber have provided the means for making a variety of intra-core reflection and band pass filters. By combining these passive intra-core fiber devices with active coatings, wavelength tunable devices have been demonstrated. Wavelength tunable devices are expected to have a variety of applications in telecommunications and sensing networks. A review of recent developments in fiber coating and analysis techniques, device fabrication, and applications of active all-fiber devices are presented along with a discussion of which coating materials are of interest in active devices.

Enhanced wavelength tuning in grating-assisted codirectional coupler filter

Wavelength-tunable devices based on grating-assisted codirectional coupler filters have been shown to possess enhanced wavelength tunabilities and are promising for use in multiwavelength communication networks. It was found theoretically that the enhancement factor can be estimated by the mismatch of group velocities between the two coupled models. We have confirmed this prediction via measurements of wavelength tuning for both the coupler filter and the Fabry-Perot filter in reverse bias. These measurements are accomplished with photonic-integrated devices. An enhancement factor of approximately 11 is measured on our device, which agrees very well with the theory. >

Hierarchical scalable photonic architectures for high-performance processor interconnection

Introduces two hierarchical optical structures for processor interconnection and compares their performance through analytic models and discrete-event simulation. Both architectures are based on wavelength division multiplexing (WDM) which enables multiple multi-access channels to be realized on a single optical fiber. The objective of the hierarchical architectures is to achieve scalability yet avoid the requirement of multiple wavelength tunable devices per node. Furthermore, both hierarchical architectures are single-hop: a packet remains in the optical form from source to destination and does not require cross dimensional intermediate routing. >

Switching Latency Impact on Star-Coupled WDM Photonic Network Pre-Allocation Protocol Performance

This paper evaluates the performance of two pre-allocation protocols when the switching latency of the wavelength tunable optical devices required for WDM networks is not negligible. The channels are pre-allocated to the nodes with the approach, where each node has a home channel that it uses either for all data packet transmissions or all data packet receptions. This approach reduces the resulting system complexity since both tunable transmitters and receivers are not required, and also has the advantage of being applicable to systems where there are many more nodes than wavelength channels. Switching latency is the time required by the tunable optical devices to tune to the required destination wavelength. The performance impact of switching latency on a generalized random access protocol is compared to an approach based on interleaved time multiplexing. Both protocols are designed to operate in a multiple-channel multiple-access environment and require each node to possess a tunable transmitter and a fixed (or slow tunable) receiver. Semi-markov analytic models are developed to investigate the performance of the two protocols. The analytic models are validated through extensive simulation. The performance is evaluated in terms of network throughput and packet delay with variations in the number of nodes, data channels, packet generation rate, and switching latency.

Devices for wavelength multiplexing and demultiplexing

Developments of optical fibre communication systems have until recently concentrated on increasing both the distances between repeaters and the intensity modulation bandwidths for single channel optical transmission. Tremendous achievements have been made in both areas such that, in the latter case, it is electronic component limitations which are starting to restrict the speed of operation of experimental systems. In this context, there is renewed interest in wavelength division multiplexing as a technique to upgrade the transmission bandwidth capacities of existing systems together with the possible future provision of broadband multichannel systems. A critical review of the component technology to enable wavelength division multiplexing is therefore useful at this stage. The major implementations of wavelength multiplexer/demultiplexer devices are discussed and compared with particular emphasis placed on their optical efficiency, spectral stability, crosstalk performance and the number of channels that may be provided. Passive devices ranging from the bulk optic implementations (i.e. prisms, gratings, filters) to integrated waveguide and fibre directional coupler realisations are considered. In addition developments associated with active devices including integrated source and detector arrays, wavelength tunable devices and optical amplifiers which may be employed within wave length multiplexed systems are outlined to provide an insight into possible future directions within the field.