We propose a novel method to optimize the transmission performance of the UWB-over-fiber system. In the proposed
UWB-over-fiber system, an UWB signal generator based on microwave photonics is used as the signal source in the
central unit. The UWB signal generator is used to generate high-order UWB signal. Direct sequence binary phase shift
keying (DS-BPSK) modulation and convolutional coding are applied to the baseband UWB signal. The dispersion and
transmission loss of the fiber can be compensated by a chirped fiber Bragg grating and an erbium-doped fiber amplifier,
respectively. The coherent receiving technology is applied for demodulation, and the Viterbi decoding technique is used
for channel decoding. The feasibility of the proposed scheme is demonstrated by simulations. At the forward error
correction (FEC) threshold of 3.8×10×−3 , the receiver sensitivity is around −16 dBm and the power penalty is around 0.2 dB,
after 25-km fiber transmission.
We propose and demonstrate an approach to generating a frequency-hopping (FH) microwave signal using an optoelectronic oscillator (OEO) based on stimulated Brillouin scattering (SBS). An SBS-based OEO is utilized to generate pure microwave signals as local frequency signal, and a dual-drive Mach–Zehnder modulator is employed to generate the FH signal. During the experiment, the local frequency generated by the OEO is 9.2 GHz with a power of 0 dBm and the FH signal hopping between 9.2 and 18.4 GHz is generated with FH speed up to 2 GHz.
A triple frequency- and phase-tunable optoelectronic oscillator based on stimulated Brillouin scattering effect and carrier phase-shifted single sideband (CPS-SSB) modulation is proposed and theoretically analyzed. In the structure, three pump lights are used to generate an oscillator signal in which the frequency is equal to triple the Brillouin frequency shift through the Brillouin gain–loss compensation. Benefiting from the wavelength-dependent characteristic of Brillouin shift, the triple frequency-tunable signal can be realized by directly tuning the laser source. The CPS-SSB modulation signal lies in the combination of a dual-parallel Mach–Zehnder modulator (DPMZM) and a tunable bandpass filter. The phase of the output microwave signal is changed by controlling the direct current bias voltage of DPMZM. Ultimately, a microwave signal, with a tunable frequency range from 26.3925 to 28.3425 GHz and a tunable phase from 0 deg to 360 deg, is obtained in theory. In addition, the theoretical simulation of the phase noise is below −110 dBc / Hz at the 10-kHz offset when tunable laser source is set at 1550 nm.
A bandwidth reconfigurable and passband switchable filter is proposed and experimentally demonstrated. Based on the same structure, the filter can realize a single broadened response, two passbands with tunable bandwidth or multiband filter. A single broadened response adopts binary phase-shift keying modulation, in which the bandwidth is related to the modulation data pattern. By using the programmable single-sideband suppression carrier signals, the position of the optical lines can be settled down properly and the corresponding arbitrary passbands are constructed. The proposed filter is flexible, which offers possibilities to process multitype microwave signals simultaneously.
The micro-actuator with the torsion beam and the cantilever beam on silicon is designed and analyzed, which is actuated by electrostatic force. Based on the torsion dynamics theory, the technique and relative formula are presented for analyzing the actuating voltage and the switching time, on which the effect of the air squeeze film damping is already considered. The optimized results of the structural parameters are compared between this technique and the finite element modeling (FEM). The optimized result of parameters is as: length, width and thickness of the torsion beam are 700, 12, and 10μm, length and width of the cantilever beam are 1900 and 1000μm, length and width of the balance beam are 100 and 1000μm, and distance of the upper and lower electrodes is 55 μm, respectively. The actuating voltage is about 50 V, and the switching time T off and T on are about 5 and 12 ms, respectively. The computed results show that the air squeeze film damping is an important factor for the study of dynamic response on micro-actuator. Finally, an optical technique is described for the measurement of the actuating voltage and switching time of the device, and the difference between the experimental results and theoretical datum is discussed.
Optical switch is one of key supporting technologies in all-optical-network (AON). And electrostatic MOEMS (Micro-Optical-Electro-Mechanical Systems) switch plays a very important role in all the researched switches, because of their excellent features, including low insertion, low crosstalk and scalability. But the packaging technology has been limiting the development of optical switch. In this paper, the authors study the laser beam propagating during the free space and select collimator, design the pedestal to packaging and address aspects of the insertion loss that are most important loss mechanisms for the 2D cross-connect switch.
The MOEMS 2×2 optical switch with slant lower electrode and with torsion beam on silicon is designed and analyzed theoretically. Analytical formulae for the squeeze film damping coefficient and the squeeze film damping moment on the cantilever beam of the optical switch are derived. Based on the torsion dynamics theory, the technique and relative results are presented for analyzing the actuating voltage and the switch time. The optimized result of parameters is as: length, width and thickness of the torsion beam are 700, 12 and 10 um, length and width of the cantilever beam are 1900 and 1000 um, length and width of the balance beam are 100 and 1000 um, shortest spacing between the upper and lower electrodes is 0.05 um, and highness of the lower electrode is 55 um, respectively. The actuating voltage is less than 10 V, and the switching time of Ton and Toff are 1.30ms and 1.25ms, respectively. The computed results show that the air squeeze film damping is an important factor for the study of dynamic response on MOEMS optical switch.
TiO2 and Mn0.2Ti0.8O2thin films were prepared by sol-gel process and their structural and optical properties were examined. The structural properties of samples were investigated by the X-ray diffraction (XRD) and auto force microscope (AFM). The XRD results showed that TiO2 thin film calcined at 650°C was anatase phase, and Mn0.2Ti0.8O2 thin films calcined at the same temperature was rutile. The AFM results of both samples showed quite a smooth surface. Optical properties of samples were examined by UV absorption spectrum. The absorption edge of Mn0.2Ti0.8O2 red-shifted.
The variable optical attenuator (VOA) has played very important roles in wavelength division multiplexed (WDM) systems, it is an essential optical component aimed to continuously adjust the optical power transmitting in optical networks. In this paper, we began to study a new type of variable optical attenuator using polymer liquid crystal material. We hanged the liquid crystal technologies and MEMS technologies together to design variable optical attenuator. This paper describes the methods and process of the preparation of polymer liquid crystal material, presents some experimental results obtained in laboratory.
We study insertion losses of optical switch when the laser beam is propagating during the free space between two single mode fibers (SMFs) and the related assemblage challenges; Then a new packaging structure is developed for the hybrid-integration of free-space MOEMS (micro-opto-electro-mechanical systems) chip with a silicon micromachined submount to improve alignment accuracy. The submount is designed to accommodate various free-space MOEMS chips with minimal active optical alignment, thus reducing the packaging cost. The silicon submount has a central recess to place the MOEMS chip in, sixteen V-grooves for optical fibers, and micropits for micro ball lenses, all bulk micromachined at the same time by a single anisotropic wet etching step. A corner compensation technique is employed to prevent erosion of the convex corners, where different geometries meet. Through this assembling method, the fiber, micro ball lens can be aligned preciously thus reduced lateral and angular misalignment between them. Then total insertion losses can be decreased.
Indium tin oxide (ITO) films as transparent conductors have caused a great deal of interest due to their prominent electro-optical behavior. This paper describes a study of the properties of ITO thin films that are used for a new type variable optical attenuator using polymer network liquid crystal (PNLC). The mechanism of PNLC optical attenuator operation is that the light from the input fiber is scattered when no voltage is applied, and the light passes through the attenuator when sufficient voltage is applied. So the ITO thin films can provide transparent electrodes for PNLC. They were deposited under various preparation conditions using the radio-frequency (rf) magnetron sputtering technique. Here discuss the results of the structural, electrical and optical properties of the ITO films. The paper presents some experimental results obtained in laboratory.
TiO2 thin films were prepared at various calcinations temperatures by sol-gel process and their structural and optical properties were examined. The influence of calcinations temperature on the structural properties of the prepared TiO2 thin films was investigated by the X-ray diffraction (XRD) and atomic force microscope (AFM). The XRD results showed that TiO2 thin film was transformed into the anatase phase at 350°C, and further into rutile phase at 850°C. The AFM results show quite a smooth surface and are in reasonably well agreement with the crystallite sizes estimated by XRD peak broadening. The influence of calcinations temperature on the optical properties of the prepared TiO2 thin films was investigated by UV-Vis spectrum and variable angle incidence spectroscopic ellipsometer (VASE). The results showed the both anatase phase and rutile phase of the TiO2 thin films prepared have good optical properties in UV region.
The diffraction characteristics are analyzed for a polymer arrayed-waveguide grating (AWG) multiplexer around the central wavelength of 1.55 μm with the wavelength spacing of 1.6 nm. The diffraction loss and diffraction efficiency in the input and the output slab waveguide are investigated and discussed for different values of parameters, such as the core width, pitch of adjacent waveguides, the number of arrayed waveguides, taper end width of waveguides, and number of output wavelength. Finally, we give a set of parameters which have been optimized in this device.
Micromechanical optical switch has a good quality for free-space optical cross connects, particularly in terms of the low insertion loss, low crosstalk, low polarization dependent loss (PDL), wavelength-independence, and bit-rate transparency. In research of micromechanical optical switches, the electrostatic torsion beam actuator is widely used. But this actuator needs high-applied voltage. In this paper, the actuator with the slant counter electrode was proposed and fabricated with tilted 3° (111) silicon wafer.
The optical variable attenuators (VOA) play important roles in wavelength division multiplexing (WDM) transmutation systems, this paper describes a new type variable optical attenuator made by using fiber U-grooves in silicon wafer and polymer-network liquid crystal. Fibers are placed in the U-grooves of silicon wafer, and the
polymer-network liquid crystal is filled in the gaps between the ends of the docking fibers. The paper explains the principle of the attenuator operation and presents experimental method in laboratory.
Micromechanical optical switches have good quality for free-space optical cross connects, particularly in terms of the low insertion loss, low crosstalk, polarization and wavelength-independence, and bit-rate transparency. In micromechanical optical switches, the electrostatic torsion beam actuator is widely used. But this actuator needs high-applied voltage. In this paper, using mechanical and electric characteristic, the relation between the translocation at the end of upper electrode and the applied voltage was derived. The applied voltage is in direct proportion to the cube of the torsion beam thickness, and reduces with the shorten of original distance between two adjacent electrodes. The actuator with the inclined under electrode was proposed and fabricated with certain tilting angle (111) silicon. Theoretical analysis indicates that the drive voltage based on the slant under electrode actuator can decrease half of that based on the flat under electrode.
Using pure aqueous KOH solution and a one-level mask, the reflective micromirror in the direction <100> and the fibers self-aligned V-grooves in the direction <110> were fabricated on the (100) silicon. Reflective micromirror is a part of {100} family; the surface of the mirror is perpendicular at the optical axes. The deviation brought by manual assemble can be decreased by crystal orientation self-aligned between the micromirror and fibers. Using Atomic Force Microscope (AFM), the measured the surface roughness of the reflective micromirror is below 40nm, at a wavelength of 1550nm the reflectivity ofthe micromirror was measured to be higher than 80%.
An arrayed-waveguide grating multiplexer is demonstrated, which is successfully designed and fabricated . A wavelength channel spacing was 1 .6nm, a crosstalk of less than —20dB and the insertion loss was 7-12dB around 1.55?m. The polarization-dependent wavelength shift was very small without special compensation methods.
We designed some important parameters and analyzed loss characteristics of a 8X8 polymer arrayed waveguide granting multuplexer that operates around the wavelength of 1.55 micrometers and the wavelength spacing was 16nm. The total loss of the device includes the diffraction loss in the input and output (I/O) slab waveguides, bent loss caused by the AWG and 1/O channels, and leakage loss resulted from the high refractive index substrate. The effects of some structural parameters on the loss characteristics are investigated and discussed. The computed results show that when we select the core thickness as 4 micrometers , core width as 6 micrometers , pitch of adjacent waveguides as 15.5 micrometers , diffraction order number as 50, the number of the arrayed waveguides as 91, that the I/O channels as 8,confined layer thickness between the core and the substrate as 6 micrometers , distance between the focal point and the origin as 5500 micrometers , and central angle between the central waveguide and the vertical of the symmetrical line of the device as 60 deg, then the total loss of the device can be dropped to about 3.73 dB.
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