Novel field installable optical fiber splice and connector for optical access networks

We have developed two types of field installable connection techniques. One is mechanical splicing, which is used to connect coated optical fibers without the need for stripping or cleaning procedures. The other is a field assembly connection technique, which employs a new type of field installable connector that makes it possible to realize a physical contact connection with chamfer grinding. Mechanical splicing is achieved by precisely aligning and directly connecting coated fibers with a capillary. The assembled splice is installed with 1.3-μm single-mode fibers that have an 80-μm cladding and a 125-μm coating and they exhibit good optical performance with a low average insertion loss of 0.2 dB. Connection is achieved with our developed field installable connector by using a chamfered fiber endface and the compression force of the buckled fiber. The assembled connectors achieve physical contact with the chamfered fiber endface, which provides good optical performance with a low insertion loss of 0.11 dB.     

光纤连接器反射特性的研究

主要研究常用的垂直端面连接器的光反射特性。通过测量光纤垂直端面的光反射分析光纤抛光端面上的高折射层厚度与反射比的关系,环境温度与反射比的关系特性;光纤端面不抛光而直接连接时的反射比与温度、空气隙度等的关系特性,给出垂直端面上的高折射率层的折射率和厚度计算与测量方法。实验结果与分析相吻合。     

Tool for inspecting faults from incorrectly cleaved fiber ends and contaminated optical fiber connector end surfaces

We investigated and analyzed faults in field installable connection due to incorrectly cleaved fiber ends and manufactured physical contact (PC)-type connectors with contaminated end surfaces in optical access fiber networks. The insertion and return losses of fiber connections using incorrectly cleaved fiber ends might be at worst more than 40 dB and less than 30 dB, respectively. With PC-type connectors whose end surfaces are contaminated, the insertion and return losses might be at worst 8.7 and 27 dB, respectively. We developed an inspection tool for cleaved fiber ends and connector end surfaces as a countermeasure. The proposed tool has a simple structure and does not require focal adjustment. It can be used to inspect and clearly determine whether a fiber has been cleaved correctly and whether there is contamination or scratches on the connector end surfaces. The tool requires a slight increase of 11% in operation time compared to conventional fiber end preparation and assembly procedures. The proposed tool provides a simple and cost-effective way to inspect cleaved fiber ends and connector end surfaces and is suitable for field use.     

Return loss characteristics of optical fiber connectors

This paper describes the return loss characteristics for four typical contact type connectors: perpendicular and oblique endface connectors employing either physical contact or contact via index matching material. The high index layer on the polished fiber endface and the index matching material, which are important connector parameters, are investigated by measuring the return loss from one perpendicular fiber endface coated with the material and by etching the fiber endface. It is useful to apply two materials with different refractive indices to derive the refractive index and thickness of high index layers on perpendicular fiber endfaces. The index matching material we use has a refractive index of 1.467 at 20°C and a thermal coefficient of -2.9×10^-4/°C at 1.3 μm. We performed return loss calculations and experiments of the four contact type connectors. The worst value at any temperature from -40 to 80°C can be estimated, by measuring the return loss of these connectors at room temperature     

Optical Characteristics and Reliability of Mechanical Splice Utilizing Solid Refractive Index Matching Material for Hole-Assisted Fiber Connection

We demonstrated that a mechanical splice utilizing solid refractive index matching material enables us to connect hole-assisted fibers with the same optical characteristics as the mechanical splice used with single-mode fibers. The optical characteristics remained stable in environmental and mechanical tests.      

Cost-effective and monitoring-active technique for TDM-passive optical networks

A reliable, detection-active and cost-effective method which employs the hello and heartbeat signals for branched node distinguishing to monitor fiber fault in any branch of distribution fibers of a time division multiplexing passive optical network (TDM-PON) is proposed. With this method, the material cost of building an optical network monitor system for a TDM-PON with 168 ONUs and the time of identifying a multiple branch faults is significantly reduced in a TDM-PON system of any scale. A fault location in a 1 × 32 TDM-PON system using this method to identify the fault branch is demonstrated.     

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 and analysis of a refractive index sensor based on dual-core large-mode-area fiber

We present a novel co-axial dual core large-mode-area (LMA) fiber design for refractive index sensing. In a dual-core fiber there is resonant coupling between the two cores, which is strongly affected by the refractive index (RI) of the outermost region. The transmittance of the fiber, therefore, varies sharply with the refractive index of surrounding medium. This characteristic of the proposed structure has been utilized to design a RI sensor. We have analyzed the structure by using the transfer matrix method. Our numerical results show that the proposed sensor is highly sensitive with the resolution of 2.0 × 10⁻⁶ around n_ex = 1.44376. Effect of design parameters on sensitivity of the proposed sensor has also been investigated.     

Chirped rectilinear core longitudinally-graded optical fibers

Reported here is a straight-forward and flexible method to fabricate silica optical fibers of circular cladding cross-section and rectilinear cores whose aspect ratio and refractive index profile changes with position along the fiber in a deterministic way. Specifically, a modification to the process recently developed to produce longitudinally-graded optical fibers, LGFs [Opt. Express 20 (2012) 17394–17402], was employed. Herein reported are MCVD-derived germanosilicate fibers with rectangular cores where the aspect ratio changes by nearly 200% and the average refractive index changed by about 5%. Fiber losses were measured to be about 50 dB/km. Such rectangular core fibers are useful for a variety of telecommunication and biomedical applications and the dimensional and optical chirp provides a deterministic way to control further the modal properties of the fiber.     

Effect of thermal annealing on structural and optical properties of titanyl phthalocyanine thin films

Thin films of titanyl phthalocyanine (TiOPc) have been deposited on both fused quartz and glass substrates by the thermal evaporation technique. The structural and optical properties of the as-deposited and annealed films have been reported. The structural features of the as-deposited and annealed films have been studied by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), and Fourier-transform infrared (FT-IR) technique. The optical constants (refractive index, n, and absorption index, k) of the films have been presented for the first time in the wavelength range 200–2500 nm by using spectrophotometric measurements at nearly normal incidence. The band gaps of the as-deposited film at 1.48 eV and 2.5 eV corresponding to Q-band and B or Soret band were red-shifted to 1.15 eV and 2.19 eV, respectively, when the film annealed at 433 K.     

Optical waveguides fabricated on polymer substrate by electron beam

In the field of optical telecommunication, polymers are an interesting class of materials for the fabrication of passive optical devices. Electron beam (EB) irradiation appears as a promising method to achieve structures presenting a layer with a modified index of refraction, and therefore to generate optical waveguiding. The poly(diethylene glycol bis(allyl carbonate)) studied here fulfils the requirements of high transparency and is consequently widely used by the optical industry. A scanning electron microscope delivers the EB with a highest energy of 30 keV. The electrons induce an increase of the substrate refractive index (≥8×10⁻³ for an electronic fluence ≥5×10¹⁴ e/cm²) on a thickness corresponding to the penetration depth of the electrons in the material (≤10 μm for a 25 keV EB). Some optical characteristics are presented such as, the surface refractive index, the effective indices and, therefore, the index profile of the waveguides.     

Temperature and refractive index sensing characteristics of an MZI-based multimode fiber–dispersion compensation fiber–multimode fiber structure

We proposed an optical fiber sensor with simple multimode fiber (MMF)–dispersion compensation fiber (DCF)–multimode fiber structure based on Mach–Zehnder Interferometer (MZI) and researched its temperature and refractive index (RI) sensing characteristics. The sensing principle is based on the interference between core and cladding modes of DCF due to the large core diameter mismatch. Spectral analyses demonstrate that the transmission spectrum is mainly formed by the interference between the dominant excited cladding mode and core modes. The experimental results show that the proposed sensor has high temperature sensitivity of 0.118 nm/°C in the range of 20–250 °C and RI sensitivity of 66.32 nm/RIU within the linear sensing range of 1.33–1.39 RIU. Therefore, the characteristics of compact size, low cost, easy fabrication, high sensitivities, and good anti-interference ability make this sensor have extensive application prospects.     

Long-period grating inscription in hydrogen-free SMF-28 fiber by high-repetition-rate femtosecond UV pulses

Using femtosecond UV (258 nm) pulses, generated at high-repetition-rate (50 kHz), we managed to record high-quality long-period gratings in a number of fibers, including a standard telecommunication one, SMF-28. Along with the main grating, connected to the refractive index change in the fiber core, at the relatively high intensity of the inscribing UV radiation, I ～ 1.5 TW/cm², we recorded the formation of an additional long-period grating, based on the refractive index change induced in the fiber cladding. We have compared the temperature sensitivity and the thermal stability of both gratings.     

Structural and the optical dispersion parameters of nano-CdTe thin film/flexible substrate

CdTe thin films of different thicknesses were deposited on polymer substrates for flexible optical devices applications. X-ray diffractogram of different thicknesses for CdTe films are measured and their patterns exhibit polycrystalline nature with a preferential orientation along the (111) plane. The optical constants of CdTe films were calculated based on the measured transmittance spectral data using Swanepoel's method in the wavelength range 400–2500 nm. The refractive index n and absorption index k were calculated and the refractive index exhibits a normal dispersion. The refractive index dispersion data followed the Wemple–DiDomenico model based on single oscillator. The oscillator dispersion parameters and the refractive index no. at zero photon energy were determined. The possible optical transition in these films is found to be allowed direct transition with energy gap increase from 1.46 to 1.60 eV with the increase in the film thickness. CdTe/flexible substrates are good candidates in optoelectronic devices     

Tuning of an erbium-doped fiber ring laser based on heating a tapered fiber filter

An erbium-doped fiber ring laser (EDFRL) with wavelength tuning is reported. The laser has a Mach–Zehnder fiber interferometer (MZFI) based on tapers as an intracavity filter, which spectral interference transmission spectrum is modified by external refractive index changes induced by temperature variations in the 25–110 °C range. The MZFI is immersed in a glycerol solution, which refractive index is modified by controlled temperature changes, which allows the tuning of the laser wavelength determined by the interference fringes. Wavelength tuning of 12 nm was measured. This approach is very simple, portable and inexpensive over traditional methods to tune a fiber laser. In addition, the tuning mechanism do not require a solution replacement to operate.     

Optical fiber relative-humidity sensor with evaporated dielectric coatings on fiber end-face

An optical fiber relative-humidity sensor (OFRHS) with evaporated dielectric coatings is proposed and demonstrated. The sensitive coatings, composed of multilayers of Ti₃O₅ and SiO₂, form an extrinsic Fabry–Perot cavity on the distal end of the multimode fiber. As the effective refractive index of the porous coatings were correlated with the change of ambient Relative-humidity (RH), which will at last result in the shift of interference fringe. By monitoring the drift of reflected interference fringe under different RH levels, the information about RH of the environment under test can be extracted. Experimental results show that the average sensitivity is 0.43 nm/% RH when environmental RH changes from 1.8% RH to 74.7% RH. The proposed sensor was proved to be high repeatability, little hysteresis and especially highly sensitive to lower moisture measure.     

Morphologies and optical properties of mixed tin oxysulfide produced by evaporation condensation of SnS

The goal of the present study was to use the evaporation-condensation method of SnS to synthesize mixed novel tin oxysulfide nanostructures. Structural, morphological and optical properties of these nanomaterials were investigated. Synthesis was carried out in horizontal tube furnace using Au coated quartz and Si(100) substrates. The substrates were set along 1–25 cm from the centered alumina boat. The deposition was observed mainly in two regions. Region A was close to the boat and extended approximately 6 cm from it and region B started approximately 15 cm from the center of the boat and extended over 10 cm towards the end of the tube. EDAX and XRD analysis revealed formation of mixed tetragonal SnO₂ and tetragonal tin oxide sulfate, SnO₂SO₄, in region A whereas mixed orthorhombic SnS and tetragonal tin oxide sulfate in region B. SEM investigations showed randomly oriented nanowires and cotton candy morphologies for samples prepared in regions A and B, respectively. Moderate transmittance, high refractive index (2.218 at 550 nm) and two optical band gaps of 1.87 eV and 3.35 eV were obtained for samples prepared in region A whereas high transmittance, moderate refractive index and optical band gap of 1.82 eV were obtained for the samples prepared in region B. The obtained results, especially the new oxysulfide samples, may have find applications in various fields.     

Optical characteristics of wurtzite ZnTe thin films

The growth of wurtzite ZnTe thin films with thickness between 250 and 1000 nm on borosilicate glass substrates by electron beam evaporation is reported. The formation of the wurtzite structure was confirmed using X-ray diffraction. The films showed diffraction peaks originating from the (110), (016) and (116) planes, indicating absence of any preferred orientation. The transmission of all the films was of the order of 80% in the near IR region. The refractive index of the wurtzite ZnTe phase increased with increase in thickness from 3.0 at 250 nm to 4.2 for the 1000 nm thickness film at a wavelength of 1800 nm. The optical band gap of these films increased with thickness showing values of 0.85, 0.9 and 0.98 eV at 250, 400 and 1000 nm thickness, respectively. Chemical composition studies revealed that the films were mildly non-stoichiometric with excess Te. Comparison with the zinc blende structure of ZnTe shows that the wurtzite structure has a higher refractive index, lower band gap and lower charge carrier concentration.     

Properties of cobalt-doped zinc oxide thin films grown by pulsed laser deposition on glass substrates

Undoped and cobalt-doped zinc oxide (CZO) polycrystalline piezoelectric thin films (Co: 3, 5 at.%) using a series of high quality ceramic targets have been deposited at 450 °C onto glass substrates using a pulsed laser deposition method. The used source was a KrF excimer laser (248 nm, 25 ns, 2 J∕cm²). X-ray diffraction patterns showed that the Co-doped ZnO films crystallize in a hexagonal wurtzite type structure with a strong (0 orientation, and the grain sizes calculated from these patterns decrease from 37 to 31 nm by increasing Co doping. The optical waveguiding properties of the films were characterized by using a prism-coupling method. The distinct M-lines of the guided transverse magnetic (TM) and transverse electric (TE) modes of the ZnO films waveguide have been observed. With the aim of study the optical properties of the ZnO films, an accurate refractive index and thickness measurement apparatus was set up, which is called M-lines device. An evaluation of experimental uncertainty and calculation of the precision of the refractive index and thickness were developed on ZnO films. The optical transmittance spectra showed a good transparency in the visible region. Calculated optical band gap varying from 3.23 to 3.37 eV when the content of Co doping increases from 0 to 5 at.%.