Enhanced four-wave mixing in a high-finesse highly nonlinear fiber Fabry-Perot resonator

We have achieved a four-wave mixing process in a high-finesse highly nonlinear fiber Fabry-Perot resonator, where the amplified signal and idler were enhanced in transmission by 6 dB and 10 dB respectively comparing with those in a single fiber. We used a 6 m long low-loss Fabry-Perot resonator with two high-reflectivity fiber Bragg gratings written directly into a highly nonlinear fiber provided by Sumitomo Electric Inc., where the minimised intracavity loss resulted in the finesse in excess of 100. The resonator length was locked for 30 min by means of a modified Pound-Drever-Hall technique. The maximum intracavity power was increased by 14.3 dB by increasing the stimulated Brillouin scattering threshold with periodic phase modulation by a pseudo-random bit sequence, with length matching that of the cavity.     

An investigation of a fiber-optic air-backed mandrel hydrophone

In this work, a optical-fiber air-backed mandrel hydrophone is proposed and investigated both analytically and experimentally. The two-dimensional and three-dimensional quasistatically theoretical models of the hydrophone is created and compared, and the phase sensitivity of the hydrophone is analyzed. The theoretical result of phase sensitivity with three-dimensional model is −153.3 dB re rad/μPa. Twenty-two hydrophones of this type according to the model presented are constructed and tested. The experiment results show that experimental results of mean values of phase sensitivity are about −153 ± 0.5 dB re rad/μPa and have the close agreement with the estimation of theoretical models. The size of the fiber sensor is ∅12 × 55 mm, the normal phase sensitivity achieves −308 dB re 1 μPa⁻¹, the 3 dB effective bandwidth of the frequency response is 30 kHz, and the responsivity decreases less than 0.5 dB when static pressure is 2 MPa (200 m water depth). The hydrophone is easy to constructed at low cost with simple structure, and some new type of it with the required performances could be designed according to the model presented.     

Numerical simulation of transfer and attenuation characteristics of soft-tissue conducted sound originating from vocal tract

A non-audible murmur (NAM), a very weak speech sound produced without vocal cord vibration, can be detected by a special NAM microphone attached to the neck, thereby providing a new speech communication tool for functional speech disorders as well as human-to-machine and human-to-human interfaces with inaudible voice input for use with unimpaired. The NAM microphone is a condenser microphone covered with soft-silicone impression material that provides good impedance matching with the soft tissues of the neck. Because higher-frequency components are suppressed severely, however, the NAM detected with this device can be insufficiently clear. To improve NAM clarity, the mechanism of NAM production as well as the transfer characteristics of the NAM in soft neck tissues must be clarified. We have investigated sound propagation from the vocal tract to the neck surface, using a finite difference time domain method and a head model based on magnetic resonance imaging scans. Numerical results show that, compared to air-conducted sound detected in front of a mouth, soft-tissue-conducted sound attenuates 50 dB at 1 kHz, which consists of 30 dB full-range attenuation due to air-to-soft-tissues transmission loss and −10 dB/octave spectral decay due to a propagation loss in soft tissues. The decay agrees well with the spectral characteristics of the measured NAM.     

Microfabrication of stacks of acoustic matching layers for 15 MHz ultrasonic transducers

This paper presents a novel method used to manufacture stacks of multiple matching layers for 15 MHz piezoelectric ultrasonic transducers, using fabrication technology derived from the MEMS industry. The acoustic matching layers were made on a silicon wafer substrate using micromachining techniques, i.e., lithography and etch, to design silicon and polymer layers with the desired acoustic properties. Two matching layer configurations were tested: a double layer structure consisting of a silicon–polymer composite and polymer and a triple layer structure consisting of silicon, composite, and polymer. The composite is a biphase material of silicon and polymer in 2-2 connectivity. The matching layers were manufactured by anisotropic wet etch of a (1 1 0)-oriented Silicon-on-Insulator wafer. The wafer was etched by KOH 40 wt%, to form 83 μm deep and 4.5 mm long trenches that were subsequently filled with Spurr’s epoxy, which has acoustic impedance 2.4 MRayl. This resulted in a stack of three layers: The silicon substrate, a silicon–polymer composite intermediate layer, and a polymer layer on the top. The stacks were bonded to PZT disks to form acoustic transducers and the acoustic performance of the fabricated transducers was tested in a pulse-echo setup, where center frequency, −6 dB relative bandwidth and insertion loss were measured. The transducer with two matching layers was measured to have a relative bandwidth of 70%, two-way insertion loss 18.4 dB and pulse length 196 ns. The transducers with three matching layers had fractional bandwidths from 90% to 93%, two-way insertion loss ranging from 18.3 to 25.4 dB, and pulse lengths 326 and 446 ns. The long pulse lengths of the transducers with three matching layers were attributed to ripple in the passband.     

Complete elastic characterization of viscoelastic materials by dynamic measurements of the complex bulk and Young's moduli as a function of temperature and hydrostatic pressure

Two independent systems to measure the dynamic complex Young's and bulk moduli of viscoelastic materials as a function of temperature and hydrostatic pressure are described. In the Young's modulus system, a bar-shaped sample is adhered to a piezoelectric shaker and mounted vertically inside an air-filled pressure vessel. Data are obtained using both the traditional resonant approach and a wave-speed technique. In the bulk modulus system, the compressibility of a sample of arbitrary shape immersed in Castor oil and placed inside a pressure chamber is measured. Data can be obtained at frequencies typically ranging from 50 Hz to 5 kHz, at temperatures comprised between −2 and 50 °C and under hydrostatic pressures ranging from 0 to 2 MPa (Young's), or 6.5 MPa (bulk). Typical data obtained with both systems are presented, and it is shown how these data can be combined to completely characterize the elasticity of the material under investigation. In particular, they can be used to obtain experimental values of the complex Poisson's ratio, whose accurate measurement is otherwise quite challenging to perform directly. As an example, the magnitude and loss tangent of Poisson's ratio are presented for a nearly incompressible rubber.     

Optical loss measurements in femtosecond laser written waveguides in glass

The optical loss is an important parameter for waveguides used in integrated optics. We measured the optical loss in waveguides written in silicate glass slides with high repetition-rate (MHz) femtosecond laser pulses. The average transmission loss of straight waveguides is about 0.3 dB/mm at a wavelength of 633 nm and 0.05 dB/mm at a wavelength of 1.55 μm. The loss is not polarization dependent and the waveguides allow a minimum bending radius of 36 mm without additional loss. The average numerical aperture of the waveguides is 0.065 at a wavelength of 633 nm and 0.045 at a wavelength of 1.55 μm. In straight waveguides more than 90% of the transmission loss is due to scattering.     

The influence of temperature on magnetic and microwave absorption properties of Fe/graphite oxide nanocomposites

Fe/graphite oxide nanocomposites were prepared by inserting Fe³⁺ into layers of graphite oxide and then reducing Fe³⁺/graphite oxide compound at different reduced reaction temperatures in H₂. The composition, crystal structure, magnetic and microwave absorption properties of Fe/graphite oxide nanocomposites were investigated using elemental analysis, transmission electron microscope (TEM), X-ray diffraction (XRD), magnetic hysteresis curve and electromagnetic parameter analysis. The results show that the densities of samples are 2.43–2.47 g/cm³ and the nanocomposites are soft magnetic materials. The optimum reduced reaction temperature for preparing Fe/graphite oxide nanocomposites is 600 °C. With the increase of the thickness of the sample, the matching frequency tends to shift to the lower frequency region, and theoretical reflection loss becomes less at the matching frequency. Microwave absorption property of Fe/graphite oxide nanocomposites prepared at 600  °C (FeGO600) is the best. When the thickness is 1 mm, the maximum theoretical reflection loss of FeGO600 is −9 dB and the frequency region in which the maximum reflection loss is more than −6.0 dB is 11–18 GHz. In conclusion, FeGO600 is a good candidate for microwave absorbent due to its low density, wide frequency region for microwave absorption and large reflection loss.     

Analysis of a 1×32 polymer microring resonant wavelength de-multi/multiplexer assistant with interleave filter

A new 1×32 wavelength de-multi/multiplexer utilizing the microring resonator and interleave filter is proposed in this paper. A novel formula of transfer functions is presented, the parameters of microring are optimized, and the transmission characteristics of the system are analyzed. The channel spacing of the presented device is 0.4 nm. The analytical result shows that the crosstalk between adjacent channels can be reduced greatly and the filter response of the device can be improved by using the interleave filter. A bandwidth (3 dB) of 0.21 nm, an insertion loss less than 1.1 dB, and crosstalk below −32 dB were obtained for the optimized device. A method for compensating the manufacturing tolerances is discussed.     

Gain clamped L-band EDFA with forward–backward pumping scheme using fiber Bragg grating

The paper proposes a novel two stage L-band erbium doped fiber amplifier with forward–backward pumping scheme for transmission of 32 wavelength division multiplexed (WDM) channels. It is gain clamped with an in-line fiber Bragg grating (FBG) to provide flat gain over 45 nm by restricting and reutilizing amplified spontaneous emission (ASE). We demonstrate that it provides an efficient small signal gain with minimum noise figure of over 20 dB and 5.5 dB, respectively, in the L-band region (1565–1610 nm) by comparing with its forward and backward pumped counterparts with fixed Er³⁺ fiber length of 20 m for −30 dBm/channel input power. We also obtain the gain and noise figure dependence as a function of each of the Er³⁺ fiber lengths, pump power (both 1480 and 980 nm), and temperature. Hence a 10 nm region (1580–1590 nm) has been acknowledged where temperature variations become constricted for 30 °C variations (15–45 °C).     

Absorption properties of carbonyl-iron/carbon black double-layer microwave absorbers

Double-layer materials were devised in order to improve the absorbing properties of electromagnetic wave absorbing plates. The double-layer wave absorbing materials are composed of a matching layer and an absorption layer. The matching layer is the surface layer through which most of the incident waves can enter, and the absorption layer beneath it plays an important role in incident wave attenuation. The total thickness of the double layer is the sum of the thicknesses of these two layers. Carbonyl iron (CI) and carbon black (CB) were used as absorbents in the matching and absorption layers, respectively. The structures of the CI and CB particles were analyzed using scanning electron microscopy and transmission electron microscopy; the dielectric properties and absorption mechanisms were also studied. In the testing frequency range 2-18 GHz, the results show that the double-layer absorbers have two absorption peaks, and the positions and values of these peaks change with the content level of the absorbents. When the mass fraction of CI in the matching layer is 50% and the total thickness of the absorber is 4 mm, the effective absorption band (below −8 dB) reaches 5.5, 5.8, and 6.5 GHz. Where the mass fraction of CB is 50% or 60% and the mass fraction of CI is 70%, the bandwidth with reflection loss below −4 dB is larger than 10 GHz.     

Microwave absorption properties of Sr2FeMoO6 nanoparticles

The microwave absorption properties of nanosized double perovskite Sr₂FeMoO₆ and epoxy resin composites were investigated in the frequency range of 2-18 GHz using the coaxial method. The Sr₂FeMoO₆ composites with an optimal 20 wt% epoxy resin showed a strong electromagnetic attenuation of −49.3 dB at 8.58 GHz with a matching thickness of 2.15 mm. Moreover the optimum absorption frequency at which the reflection loss is less than −20 dB, which corresponds to 99% reflection loss of the incident microwave, is from 5.7 to 13.2 GHz with the matching thickness ranging from 3.0 to 1.5 mm. The excellent microwave-absorption properties are a consequence of a proper electromagnetic match due to the existence of the insulating matrix of anti-site defects and anti-phase domains, which not only contribute to the dielectric loss but also to the reduced eddy current loss.     

Optical alignment tolerances in double-side irradiated self-written waveguide-induced fiber arrays packages

In this paper, we present our experimental study on the optical alignment tolerance between the couplings of single-mode fibers (SMFs) connected with a double-side irradiation-induced self-written waveguide (SWW). The study firstly focuses on the coupling of two SMFs and then on the two fiber arrays (FAs) for parallel optical communication. The SWW was formed in dye-dispersed epoxy materials by the photopolymerization technique. Rhodamine 6G dye was dispersed in epoxy, which is commonly used in the photonic packaging industry as a bonding adhesive. Using double-side irradiated SWW, we found the alignment tolerance for such optical interconnect to relax significantly. All the formed SWWs were evaluated in terms of optical loss. In our study, up to 4 µm misalignment tolerance was allowed for only 1 dB loss penalty. In addition, the optical interconnect formed by this technique was also able to tolerate up to ± 10 µm lateral shift with only 1 dB extra loss. The wavelength-dependent loss (from 1520 to 1610 nm) and polarization-dependent loss were less than 0.4 dB. The double-side irradiated SWW-induced couplings between two FAs also provided low optical loss. They were found to be less sensitive to temperature changes, and no significant distortion in the digital signal transmission test was observed. We believe that the findings are useful and applicable to other dye-dispersed epoxy material systems for relaxing the alignment tolerance of the optical interconnects in various photonic packaging situations.     

Impact of optical modulation formats on SPM-limited fiber transmission in 10 and 40 Gb/s optimum dispersion-managed lightwave systems

In this paper, 10 and 40 Gb/s optical systems have been investigated for nonreturn-to-zero (NRZ), return-to-zero (RZ), carrier-suppressed return-to-zero (CSRZ) and RZ-differential phase-shift-keying (RZ-DPSK) data formats. For the range of the optical signal power from −5 to 15 dBm, a maximum self-phase modulation (SPM)-limited transmission distance L_SPM is determined with eye-opening penalty (EOP) >1 dB .The observations are based on the modeling and numerical simulation of optimum dispersion-managed transmission link. Transmission over distances of the order of several hundreds of kilometers has been shown with and without amplified spontaneous emission (ASE) noise of the in-line erbium-doped fiber amplifiers (EDFAs).     

Add/drop applications in fiber ring networks based on a reconfigurable optical add/drop multiplexer in a re-circulating loop

A periodic add/drop system in a fiber ring network was investigated using a reconfigurable optical add/drop multiplexer (ROADM) in a re-circulating fiber loop. After seven cascaded add/drop nodes at every 150 km along the transmission, at bit error ratio (BER) equals to 10⁻⁹ and data rate of 10 Gbps, we observed a 2.5 dB power penalty for the passing through channels with 1050 km transmission distance, and 0.3 dB sensitivity penalty variation for the periodic add/drop channels at every 150 km, respectively.     

Fabrication of low OH loss holey fibers with varying air hole sizes and their optical properties

We experimentally investigate a flexible fabrication technique for low OH and transmission losses holey fibers with a Ge-doped core and air holes in a silica cladding region. Versatile holey fibers of different size, pitch, and shape of air holes were achieved by controlling the temperature and heating time of the holey fiber preform. In addition, we suppress the OH loss of less than ∼0.323 dB/km at 1383 nm. After fabricating holey fibers, we measure their optical properties including cut-off wavelength, mode field diameter, splicing loss, dispersion, bending loss, and polarization dependent loss based on the size of air holes. The total transmission loss was measured to be ∼0.226 dB/km at 1550 nm by improving the fabrication process. After fabricating optical patch cord based on holey fibers, we measured the long-term stability of the fabricated holey fiber by using the temperature cycling technique for 24 and obtained low power fluctuation of 0.2 dB. We achieve the high quality holey fiber with a low bending loss of ∼0.04 dB/turn under a bending radius of 2.5 mm at 1550 nm. We also obtain a tunable band rejection filter with a number of bending turns.     

One-dimensional coupled cavities photonic crystal filters with tapered Bragg mirrors

The performance of one-dimensional (1D) coupled cavities photonic crystal (PC) filters has been analyzed by finite-difference time-domain (FDTD) simulation. It is shown that the addition of tapered Bragg mirrors at each side of the cavities, to create near-Gaussian field profiles for the cavity modes, results in the prediction of near flat-top passband filters with high out-of-band rejection ratio and near unity transmission. The tapered structures suppress the vertical radiation loss to allow optimization of the number of mirror periods for the best filter response whilst guaranteeing high transmission. A critical coupling condition (k = 2L_out/L_in = 1) for flat-top responses in doubly coupled cavities filters is proposed in the tapered structures. An optimized filter for 100 GHz optical communication system are demonstrated with 1 dB bandwidth of 0.17 nm, roll-off of 0.6 dB/GHz, out-of-band signal rejection of 33 dB and transmission of 95%. Further improvement of roll-off and out-of-band rejection is demonstrated in a triply coupled cavities filter.     

Comparison of the effects of particle shape on thin FeSiCr electromagnetic wave absorber

The raw materials of FeSiCr were processed in the ball mill for 30 h and the shape of the FeSiCr particles was changed from sphere to flake type, which was observed using a scanning electron microscope. And FeSiCr composite microwave absorbers were mixed with silicone for mobile phones and the effects of the thickness of the samples on the absorption were measured using a network analyzer in order to investigate the relationship between the microwave absorption and the material constants. The flake-type FeSiCr-rubber composite showed high reflection loss, which was due to the high complex permittivity and permeability. Also, the matching frequency shifted toward lower frequency range with microwave absorber thickness, and the maximum reflection loss of −8.7 dB was observed in 1.85 GHz for a 1.6 mm thickness.     

Enhanced microwave absorption in ZnO/carbonyl iron nano-composites by coating dielectric material

The microwave absorption properties of zinc oxide/carbonyl iron composite nanoparticles fabricated by high energy ball milling were studied at 0-20 GHz. Experiments showed that ZnO as a kind of dielectric material coating carbonyl iron particles made the bandwidth of reflection loss (RL)<−5 dB expanding to the low frequency, and enhanced absorption effect obviously. For a 3 mm thickness absorber of ZnO/carbonyl iron after 30 h milling, the values of RL<−5 dB and RL<−8 dB were obtained in the frequency range from 7.0 GHz to 17.8 GHz and from 9.8 dB to 14.9 dB, respectively, and its strongest RL peak was −29.34 dB at 13.59 GHz. The magnetic loss of carbonyl iron particles and the dielectric loss of ZnO particles were the main mechanisms of microwave absorption for the composites.     

Measurements of sound transmission through panels of locally resonant materials between impedance tubes

We present a method for the measurements of complex transmission coefficient through high transmission loss samples using three-sensors, two impedance tubes, monotonic wave excitation, and phase sensitive detection. Having demonstrated the effectiveness of the method on perforated plates measurements have been made on locally resonant sonic materials (LRSMs). The transmission losses of perforated plates are found to decrease with decreasing frequency down to 120 Hz, following the mass law. For the LRSM’s panels with the same area mass density but different compositions, the local resonance frequency (at which the transmission loss is maximum) is found to vary according to the predesigned value. Transmission losses as high as 96.5 dB at 630 Hz and 87 dB at 250 Hz can be measured with good accuracy, with corresponding phase spectra that match the theoretical prediction of LRSMs, confirming the reliability of the transmission data.     

Characterization of a tunable three-section slotted Fabry-Perot laser for advanced modulation format optical transmission

In this paper we report on the characterization of a narrow linewidth three-section tunable slotted Fabry-Perot laser. The SMSR of the 25 available 100-GHz ITU channels is above 30 dB, whereas their average linewidth is 538 kHz with a maximum below 800 kHz. The RIN spectra of six different channels are also measured and a maximum average RIN of −135 dB/Hz is obtained. The linewidth effect of the laser in a 1.25 Gb/s DPSK transmission system is investigated by comparing the performance between the slotted Fabry-Perot laser and a commercial SG-DBR laser respectively. Error free transmission of the slotted Fabry-Perot laser shows the benefit of the narrow linewidth of the device for systems employing advanced modulation formats.