Simultaneous measurement of strain and temperature based on a long-period grating with a polarization maintaining fiber in a loop mirror

Simultaneous measurement of strain and temperature using a long-period grating (LPG) and a polarization maintaining fiber (PMF) in a fiber loop mirror (FLM) is presented. The sensing head is formed by an LPG. The transmitted optical intensity from the FLM is linear with the variation of the strain. And the interference resonant dip has a blue shift with the increasing of the temperature. Experimental results show that the proposed sensor has the sensitivities of 0.0346 nm/°C and 1.82 × 10⁻³ dB/με within the strain range of 0–1300 με, respectively.     

Tailoring chromatic dispersion in chalcogenide–tellurite microstructured optical fiber

We report fabrication of a highly nonlinear hybrid microstructured optical fiber composed of chalcogenide glass core and tellurite glass cladding. The flattened chromatic dispersion can be achieved in such an optical fiber with near zero dispersion wavelength at telecommunication wavelengths λ = 1.35–1.7 μm, which cannot be achieved in chalcogenide glass optical fibers due to their high refractive index, i.e. n > 2.1. We demonstrate a hybrid 4-air hole chalcogenide–tellurite optical fiber (Δn = 0.25) with flattened chromatic dispersion around λ = 1.55 μm. In optimized 12-air hole optical fiber composed of the same glasses, the chromatic dispersion values were achieved between −20 and 32 ps/nm/km in a broad wavelength range of 1.5–3.8 μm providing the fiber with extremely high nonlinear coefficient 86,000 km⁻¹W⁻¹. Hybrid chalcogenide/tellurite fibers pumped with the near infrared lasers give good promise for broadband optical amplification, wavelength conversion, and supercontinuum generation in the near- to mid-infrared region.     

Design of a bending-insensitive single-mode photonic crystal fiber

We present a design of a bending-insensitive single-mode photonic crystal fiber (PCF) based on the existence of a triangular core formed by three neighboring air holes missing in the center of the fiber, and two cladding layers of air holes with different diameters. By optimizing the design parameters, the designed PCF with bending-insensitive characteristics can match the requirements of fiber to the home applications very well. Simulation results show that the designed PCF has an effectively single-mode operation, a small bending loss below 0.15 dB/m for the bending radius of 5 mm, as well as a stable effective mode area of 80 μm² whatever the designed PCF is straight or bent, which can connect well with conventional single-mode fibers (SMFs).     

Planar copper-tin inter-metallic film formation on strained substrates

This paper presents the results of four-point bending tests investigating the effects of substrate strain on the growth ɛ of interfacial Cu–Sn inter-metallic compounds (IMCs). Test specimens were cut into strips, 27.5 mm in length and 5 mm in width, from 4 in. double polished silicon wafers. A very thin adhesion layer (Ta) was deposited on the silicon substrate by sputtering followed by a 10 μm thick layer of copper using electroplating. Finally, a 30 μm tin layer was deposited over the copper film also by electroplating. Samples were then placed in a furnace at 200 °C to undergo bending in order to introduce in-plane strain under tension or compression. Control samples also underwent the same treatment without applied strain. Our aim was to investigate the influence of substrate strain and aging time on the formation of IMCs (1.54 × 10⁻⁴, 2.3 × 10⁻⁴ and 3.46 × 10⁻⁴). The thickness and separation of each phase (Cu₃Sn) and η (Cu₆Sn₅) are clearly visible in scanning electron microscope images. Compressive strain and tensile strain both increased the thickness of the IMC layer during the aging process; however, the effects of compressive strain were more pronounced than those of tensile strain. We hypothesize that the increase in IMC thickness is related to the strain enhanced out-diffusion of Cu towards the solder as well as strain in the underlying lattice at the diffusion interface.     

Nonlinear effect mitigation based on PAPR reduction using electronic pre-distortion technique in direct-detection optical OFDM system

The nonlinear effect induced by the Mach–Zehnder modulator (MZM) and optical self-phase modulation (SPM) in the presence of high peak-to-average power ratio (PAPR) is investigated theoretically. We theoretically and experimentally investigate the direct-detection optical orthogonal frequency-division multiplexing (DD-OOFDM) system with an electronic pre-distortion technique of companding transform (CT) to reduce the peak-to-average power ratio (PAPR) of OFDM signals and improve the receiver sensitivity. Experimental results show that the PAPR reduction can reach about 3 dB when the complementary cumulative distribution function is 1 × 10⁻⁴, which means the number of random OFDM signals is 1 × 10⁴, and the receiver sensitivity is improved by 0.7, 1.7, and 2.4 dB for the launch power of 2, 6 and 10 dB m, respectively, at the BER of 1 × 10⁻⁴ after transmission over 100-km single-mode fiber with the μ of 2. It shows that the PAPR reduction can mitigate not only the nonlinearity of MZM, but also the nonlinear phase noise in the fiber link when the optical power into fiber is high.     

Cord identification technique for ultra-low bending loss fibers using higher order modes of visible light

We propose a cord identification technique for ultra-low bending loss fiber using higher order modes of visible light. With this kind of fiber, bending losses are greatly reduced and it is difficult to obtain sufficient leaked light with a conventional macro-bending technique. The bending loss of higher order modes is several orders larger than that of fundamental modes. Higher order modes can exist at shorter wavelengths and their guiding loss is small when the fiber is not tightly bent. As a result, higher order modes are suitable for cord identification purposes with ultra-low bending loss fiber. We determined that the LP₂₁ and LP₀₂ modes at 650 nm (red) and the LP₃₁ mode at 532 nm (green) are the most effective for cord identification purposes. We employed an offset launch technique to excite higher order modes, and achieved a sensitivity improvement of more than 14 dB. By using our method, a cord can be identified by red or green light even with the naked eye.     

A PAPR reduction technique using Hadamard transform combined with clipping and filtering based on DCT/IDCT for IM/DD optical OFDM systems

In Intensity Modulator/Direct Detection (IM/DD) optical OFDM systems, the high peak-to-power average ratio (PAPR) will cause signal impairments through the nonlinearity of modulator and fiber. In this paper, a joint PAPR reduction technique based on Hadamard transformation and clipping and filtering using DCT/IDCT transform has been proposed for mitigating the impairments in IM/DD optical OFDM system. We then experimentally evaluated the effect of PAPR reduction on the bit error rate (BER) performance and the results show the effectiveness of the proposed technique. At a bit error rate (BER) of 1 × 10⁻³, the receiver sensitivity of the proposed 2.5 Gb/s IM/DD optical OFDM system after 100-km standard single-mode fiber transmission has been improved by 0.8 dB, 1.3 dB and 3.1 dB for a launch power of 6.4 dBm, 8 dBm and 10 dBm respectively when compared with the classical system.     

Low-coherence interferometric fiber sensor with improved resolution using stepper motor assisted optical ruler

Low-coherence interferometric sensing is typically used to detect phase changes without simultaneous optical ruler calibration in order to by-pass light intensity fluctuations and the periodic nature of the interferometric signal. An interferogram from a two-staged optical low-coherence Mach–Zehnder interferometer is proposed to double the sensitivity improvement for fiber strain sensing. A 1310-nm wavelength distributed feedback laser implemented in an optical ruler achieved 655-nm resolved characterization from its high-coherence interferogram, which could further be enhanced to an average of 18.9 nm using a stepper motor assisted optical ruler. A 2.7-nε high strain resolution was then demonstrated on a 3-m long fiber sensing arm in a Mach–Zehnder interferometer. The relative movement distances between the interferograms were utilized to experimentally show the strain and force sensitivity as 6.8 μm/με and 8.5 μm/mN, respectively.     

Transmission performance of all-optical domain orthogonal frequency division multiplexing signals due to fiber nonlinearities for long-reach PON applications

This study examined the performance of 110 Gb/s all-optical domain orthogonal frequency division multiplexing (AO-OFDM) signal transmission systems using optical multi-carrier generation and optical 2-subcarrier modulation under the effects of chromatic dispersion and fiber nonlinearity. The numerical simulation results showed that the performance degradation of AO-OFDM signals lies in the inter-carrier interference between the subcarrier signals generated from the fiber nonlinearities. The numerical simulation showed that the calculated BER of the AO-OFDM channels has some power penalties at 10^?9 BER for the fiber chromatic dispersion effect. The calculated receiver sensitivity at 10^?9 BER showed additional degradation at the central subcarrier channel by applying a fiber launching power of 12 dBm after transmission over a 100 km standard single-mode fiber (SMF) link. The simulation results are expected to be useful for multi-service systems employing AO-OFDM technology in the future long-reach passive optical network (PON) applications.     

Brillouin characterization of fiber strain in bent slot-typeoptical-fiber cables

A technique based on Brillouin gain spectroscopy is proposed to evaluate tensile and compressive strain variation in optical fibers. This technique is applied to characterize fiber strain in bent slot-type optical-fiber cables. Fiber ribbons containing four optical fibers each are stranded through the cable. When the cable is bent, two types of strain are created in the fiber. It was found from experimental results that the first strain, which was induced by the elongation and compression of the fiber ribbon along its length, was drastically reduced, while the second strain, which was created by bending the fiber ribbon in its plane surface, remained     

层绞式多芯光纤带的应变

主要研究层绞式带状光缆和边粘型大芯数光纤带。通过对光纤应变,光缆传输特性的分析和研究,结果表明,带状光缆特性受光纤带宽度和盘外径的影响。     

Solid-state sensing tip for zinc ion with double parallel optical fibers embedded in fluorescent hydrogel

A tip-shaped zinc ion solid-state sensor is made by two parallel optical fibers embedded closely in a sensing hydrogel film. The film is made of poly(2-hydroxyethyl methacrylate) (poly HEMA)hydrogel mixed with the selective fluorescent probe meso-2,6-Dichlorophenyltripyrrinone (TPN-Cl₂) with weight ratio of 0.025 wt%. A 405 nm laser output is sent from one fiber and the 622 nm fluorescence of the doped hydrogel is collected by the second fiber. Each fiber diameter is 370 μm (core is 300 μm), whose sum is roughly the tip diameter. The 0.4 cm by 0.5 cm tip has real-time response for zinc ion concentration over 10⁻⁶ M, with marginal signal for 10⁻⁷ M. The tip is inserted inside an oyster and successfully detects the zinc ions, showing that the sensor works in complex body fluid and tolerates certain mechanical stress. To show the potential application for medicine, the sensing film is applied for primary neuronal cultures. We report for the first time zinc ions release at concentration levels 10⁻⁶–10⁻⁷ M to the medium under stress conditions of ischemia, inflammation, and intoxication. Furthermore, this correlates with the zinc levels detected by biochemical assay. Such sensing tip has great potential for biomedical monitoring ex vivo or in vivo.     

Temperature-independent accelerometer using a fiber Bragg grating incorporating a biconical taper

An intensity-modulated optical fiber accelerometer is proposed and experimentally demonstrated by using a fiber Bragg grating (FBG) incorporating a biconical fiber taper. Acceleration-induced microbending of the fiber taper region introduces various attenuation to the light, so that acceleration can be measured from changes of the optical power of the reflected light from the FBG. This power detection method reduces the cost and complexity of the sensor setup since only photodetector is required for the signal detection. In the static measurement, a relatively large range of 5g (g is gravity, equals to 9.8 m/s²) with sensitivity of 4.85 nW/g is achieved. Vibration measurements have also been carried out with a frequency up to 20 Hz. The proposed accelerometer is nearly independent of temperature because the reflected optical power of the FBG is insensitive to temperature.     

Economic and system impact of hybrid Raman–EDFA amplification in a 40 × 40 Gbps optical transmission network with DPSK modulation

Demands of modern high-bandwidth services drive the need to constantly improve existing optical amplification technology beyond its current bounds. In this paper, we demonstrate a hybrid broadband amplification scheme which is capable of improving the system performance of a wavelength-division-multiplexed (WDM) network. We present the study of optical signals with differential-phase-shift keying (DPSK) modulation at 40 Gbps and its transmission in a 50-GHz spaced, 40-channel WDM system over an 80-km link with hybrid optical amplification. A comparison of the system and cost impacts of a Raman-only amplification scheme with two hybrid Raman–erbium doped fiber amplifier schemes (Hybrids I and II) is performed. It is shown that one of the proposed hybrid schemes (Hybrid II) outperforms the other by (i) improving the tolerance to signal input power by 17 dB and (ii) increasing the system reach by 55 km for input signal power of 5 dBm, for a bit error rate (BER) performance of 10⁻¹².     

Modeling of Ga1−xInxAs1−y−zNySbz/GaAs quantum well properties for near-infrared lasers

The aim of this work is to model the properties of GaInAsNSb/GaAs compressively strained structures. Indeed, Ga_1?xIn_xAs_1?y?zN_ySb_z has been found to be a potentially superior material to GaInAsN for long wavelength laser dedicated to optical fiber communications. Furthermore, this material can be grown on GaAs substrate while having a bandgap smaller than that of GaInNAs. The influence of nitrogen and antimony on the bandgap and the transition energy is explored. Also, the effect of these two elements on the optical gain and threshold current density is investigated. For example, a structure composed of one 7.5 nm thick quantum well of material with In=30%, N=3.5%, Sb=1% composition exhibits a threshold current density of 339.8 A/cm² and an emission wavelength of 1.5365 μm (at T=300 K). It can be shown that increasing the concentration of indium to 35% with a concentration of nitrogen and antimony, of 2.5% and 1%, respectively, results in a decrease of the threshold current density down to 253.7 A/cm² for a two well structure. Same structure incorporating five wells shows a threshold current density as low as 221.4 A/cm² for T=300 K, which agrees well with the reported experimental results.     

20 Gb/s WDM-OFDM-PON over 20-km single fiber uplink transmission using optical millimeter-wave signal seeding with rate adaptive bit-power loading

We experimentally demonstrate the use of millimeter-wave signal generation by optical carrier suppression (OCS) method using single-drive Mach–Zehnder modulator as a light sources seed for 20 Gb/s WDM-OFDM-PON in 20-km single fiber loopback transmission based on cost-effective RSOA modulation. Practical discrete rate adaptive bit loading algorithm was employed in this colorless ONU system to maximize the achievable bit rate for an average bit error rate (BER) below 2 × 10⁻³.     

Gain characteristics of quantum dot fiber amplifier based on asymmetric tapered fiber coupler

We theoretically analyzed the gain characteristics of an integrated semiconductor quantum dot (QD) fiber amplifier (SQDFA) by using a 2 × 2 tapered fiber coupler with a PbS QD-coated layer. The asymmetric structure of the fiber coupler is designed to have a maximum working bandwidth around 1550-nm band and provide a desired optical power ratio of the output signals. By using 600 mW of 980-nm pump, 10 dB gain of a 1550-nm signal is estimated with the gain efficiency of 4.5 dB/cm.     

Performance evaluation of (D)APSK modulated coherent optical OFDM system

Performance of amplitude and phase shift keying (APSK) modulated coherent optical orthogonal frequency division multiplexing (CO-OFDM) with and without differential encoding is investigated. Numerical simulations based on 40 Gbit/s single-channel and 5 ^* 40 Gbit/s wavelength division multiplexing transmission are performed, and the impacts of amplified spontaneous emission noise, laser linewidth, chromatic dispersion, and fiber nonlinearity on the system performance are analyzed. The results show that compared with conventional 16 quadrature amplitude modulation (QAM) modulated optical OFDM signal, although 16(D)APSK modulated optical OFDM signal has a lower tolerance towards amplified spontaneous emission (ASE) noise, it has a higher tolerance towards fiber nonlinearity such as self-phase modulation (SPM) and cross-phase modulation (XPM): the optimal launch power and the corresponding Q² factor of 16(D)APSK modulated OFDM signal are respectively 2 dB and 0.5 dB higher than 16QAM modulated optical OFDM signal after 640 km transmission, both in single-channel and WDM CO-OFDM systems. Although the accumulated CD decreases the peak-to-average power ratio (PAPR) during transmission, 16(D)APSK modulated OFDM signal will still remain an advantage compared with 16QAM modulated OFDM signal up to 1000 km single-channel transmission, meanwhile relaxing the needs for training symbols and pilot subcarriers and consequently increase the spectral efficiency.     

Low power flexible organic thin film transistors with amorphous Ba0.7Sr0.3TiO3 gate dielectric grown by pulsed laser deposition at low temperature

We deposited amorphous Ba_0.7Sr_0.3TiO₃ (BST) on silicon and plastic substrate under 110 °C by pulsed laser deposition (PLD) and use it as the dielectric of the organic transistor. Depends on the thickness of BST layer, the highest mobility of the devices can achieve 1.24 cm² V^?1 s^?1 and 1.01 cm² V^?1 s^?1 on the silicon and polyethylene naphthalate (PEN) substrate, respectively. We also studied the upward and downward bending tests on the transistors and the dielectric thin films. We found that the BST dielectric pentacene transistor can maintain the mobility at 0.5 cm² V^?1 s^?1 or higher while the bending radius is around 3 mm in both upward and downward bending. Our finding demonstrates the potential application of PLD growth high-k dielectric in the large area organic electronics devices.