Optical fiber drawing method with gas flow controlling system

A method for reducing the diameter variation of optical fibers during fiber drawing is described. The method is based on the control of gas flow and drawing speed. Rapid fluctuations in diameter are suppressed by adjusting the gas flow rate, and slower ones are controlled by changing the drawing speed. The efficiency of this method has been tested by applying stepwise disturbance of ±63% in preform feeding speed. Fluctuations of fiber diameter are controlled within ±1 μm despite the forced disturbance. By applying this method to high-speed drawing (30 m/min), a high-tensile-strength fiber, with diameter fluctuations within ±1 μm and transmission losses near the 0.85-μm wavelength region of approximately 3 dB/km, is achieved     

Optical time-domain reflectometry (OTDR) of diameter modulations insingle mode fibers

The influence of several types of diameter variations on the attenuation and on the optical time-domain reflectometry (OTDR) traces of specially prepared depressed cladding SM (single-mode) fibers is experimentally investigated. Depressed-cladding SM fibers have been prepared by the low-pressure plasma-induced chemical vapor deposition (PCVD) process. The core consists of GeO₂-doped SiO₂ and the cladding region of fluorine-doped silica. During drawing, the diameter of the fiber is controlled within ±0.3 μm for slow perturbations by adjusting the drawing speed (Anritsu M501A). Variations of the core diameter have been accomplished by changing the set point of the fiber diameter control. Core diameter changes give rise to steps or deviations in slope of the OTDR power trace of about 0.3 dB/μm. No indication of additional attenuation due to axial fiber parameter variations has been found up to core diameter changes of 12 μm/m, despite severe distortions of the OTDR traces     

Optical fiber characterization by simultaneous measurement of thetransmitted and refracted near field

An experimental setup is presented which permits, in a routine way for R&D purposes, simultaneous measurement of the transmitted near field at 1300 nm and 1550 nm, and the refracted near field at 820 nm. A new method for the calibration of the refractive index is proposed. The obtained accuracy for the refractive index is dn±0.0002. The reproducibility of measurements of geometrical parameters like the mode field diameter, the core and cladding diameters, and concentricity error, is ±0.1 μm. Measurements of the mode field as a function of polarization state for four different hi-bi fiber are presented     

Automatic geometric dimension measurements of single-mode fiberpreforms using a novel shadow method

A method is described in which a test preform is immersed in an index-matching liquid so as to detect optical signals from the core/cladding and cladding/index-matching liquid interfaces simultaneously. A light-beam sweeper with a mirror is used to sweep a He-Ne laser beam across a fiber preform, and the time intervals during which the preform intercepts the beam and casts a composite shadow on a photodetector are measured. The method is simple and accurate and has sufficient spatial resolution (better than 10 μm) to obtain detailed measurements of core eccentricity, core and cladding diameters and their ratio, and ellipticity in a step-index single-mode fiber preform for a subscriber line. On the basis of this principle, an automated geometry measurement system has been developed. The system is attractive for quality control applications in mass-production lines of single-mode fibers     

Frequency stabilized 622-Mb/s 16-channel optical FDM system and itsperformance in 1.3/1.55-μm zero-dispersion fiber transmission

A study has been conducted on a densely multiplexed 16-channel optical FDM system. A transmitter contains 16 two-section MQW DFB-LD's and a star coupler. An automatic optical multi-frequency controller stabilizes each LD of 10 GHz spacing within ±100-MHz accuracy. A receiver consists of heterodyne-delay-demodulators using a polarization diversity. Any desired channel can be tuned by a novel frequency discriminator with no insensitive frequency region. The system has successfully transmitted 622 Mb/s-16-channel HDTV signals through 110 km long 1.3 μm-zero-dispersion fiber. We have also studied error rate degradation due to four-wave mixing in a 1.55 μm-dispersion-shifted-fiber. Experimental results have revealed the allowable total input power to be +2 dBm for dispersion-shifted fibers     

Measured backscatter from conductive thin films deposited onfibrous substrates

The functional dependence of the electromagnetic backscatter by thin, straight, dielectric fibers with metallic coatings was measured as a function of coating thickness and conductivity at a wavelength of 0.86 cm (35 GHz). Cu and Ni coatings were applied to fibrous glass substrates (having a nominal diameter of 5.50 μm) using an evaporative process. The thicknesses of the thin films were directly measured by scanning electron microscopy (SEM) and ranged from 0.02 to 0.70 μm. Measurements were conducted using single fibers. Measured quantities agreed well with calculations based on previously developed theory     

High-speed drawing of optical fibers with pressurized coating

To make progress in high-speed drawing of optical fibers, a pressurized coating method was developed on the basis of viscous flow behavior of the coating resin. In a pressurized die, when the shear rate at the fiber surface is minimized, the pressure which is affected by the resin viscosity reaches on optimum condition, resulting in the coating diameter being dependent only on fiber and die diameters. Coating tension is given as a function of pressure so that it is closely related to the optimum pressure through the viscosity. Based on these fundamentals, a 1200-m/min drawing speed was achieved, indicating a smooth and uniform coating with good concentricity. It is clarified that fiber transmission loss does not fundamentally change in relation to the speed.     

Transmission loss of a 125-μm diameter PANDA fiber with circularstress-applying parts

The transmission loss of a 125-μm diameter polarization-maintaining and absorption-reducing optical fiber (the PANDA fiber) with circular stress-applying parts (SAPs) has been investigated. The loss is calculated at a 1.55- μm wavelength for SAPs consisting of B₂O₃ doped silica glasses. The experimental measurements show the validity of the analysis. It is shown that, when the half distance between SAPs is more than 2.2 times the core radius, the additional transmission loss due to B₂O₃ absorption is less than 0.05 dB/km with normalized frequency of 2.2 to 2.4 and a B₂O₃ dopant concentration of 20 mol.%. As a result, it has been confirmed that transmission losses of 125-μm diameter PANDA fibers can be comparable to those of commercially available single-mode optical fibers     

All-silicon integrated optical modulator

The authors describe the operating principle, design, and performance of an all-silicon light modulator at 1.3 μm wavelength. The modulator is based on the plasma effect in silicon and the mode selectivity of single-mode optical fibers, resulting in low polarization dependence and the capability of handling high light intensities. Standard silicon IC technology is used in the fabrication process and the modulator has a vertical structure that takes up a small surface area (the active area matches the single-mode fiber core of 9 μm diameter), simplifying integration with other circuitry on the same chip. The modulator can be directly coupled to a single-mode optical fiber, without using lenses or other bulk optical components. Typical performance of the fabricated modulators is 6 dB insertion loss, 24% modulation depth, and 60 MHz bandwidth with a current drive of 22 mA rms     

Grating-assisted surface-emitting laser transmitter withimage-forming capability

A grating-assisted surface-emitting laser transmitter with image-forming capability has been fabricated. The laser transmitter consists of an InP-InGaAsP distributed Bragg reflector ridge laser emitting at 1.5 μm, a semiconductor optical amplifier and a computer-generated holographic out-coupler. The area of the out-coupler is 80 μm×80 μm. The image produced by the out-coupler is focused at 3 cm above the laser surface and each circular spot has a diameter of 0.6 mm     

Precision fabrication of D-shaped single-mode optical fibers by insitu monitoring

A technique has been developed to locally remove, over a distance of several millimeters of fiber length, the cladding layer of single-mode (at the 1300 nm wavelength) optical fibers with 1 μm depth precision by use of mechanical lapping and in situ optical transmission monitoring. A cylinder lap dressed with diamond is used to perform high-pressure mechanical lapping. The in situ monitoring technique is based on the specific different attenuations exhibited by higher order propagating modes (for 633 nm light) as the cylinder penetrates into the fiber. Advantages include relatively rapid overall processing, high lapping rate, good optical surface quality, and 1 μm precision. Experimental results are presented and analyzed by an approximate geometrical-optics model     

Fiber diameter measurements and their calibration

Seeks to establish a high level of confidence in fiber cladding diameter measurement by the use of three methods: white light interferometry, mechanical contact, and image inverting microscopy. Calibration with transfer fibers is considered unattractive because of the difficulty of maintaining the calibrated cleaved end. The uncertainties involved in calibrating other methods are investigated, namely image shear, grey scale digitization, and refracted near field, using chromium on glass circular patterns or lines. Their use is found to give consistent results with uncertainties not exceeding ±0.15 μm. Experimental arrangements are discussed. There are some sources of measurement error, but these can be overcome so that measurements of fiber diameter with an uncertainty of less than ±0.15 μm look feasible using chromium on glass calibration standards     

Interlaboratory comparison of radiation-induced attenuation inoptical fibers. I. Steady-state exposures

A comparison of the losses induced at 0.85 μm in three all glass-pure silica core optical fibers by steady-state radiation exposures has been made among five laboratories. Both the growth of the attenuation during irradiation and the recovery following exposures of 3000 and 10⁵ rads have been measured. Although a standard set of parameters was attempted by all laboratories, the slight divergences (0.45⩽σ⩽0.99 dB/km) observed in some data indicate sensitivity of the results to factors such as photobleaching, injection conditions, and sample coil diameter     

Microelectrode arrays for electrophysiological monitoring ofhippocampal organotypic slice cultures

A three-dimensional platinum (Pt) microelectrode array embedded on a micromachined silicon (Si) substrate (porosity of 13%, via hole diameter of 40 μm) has been developed. Electrodes are 35-μm wide and 20-μm high, spaced 200 μm apart and arranged in an elliptic geometry. Integrated within a microperfusion chamber, the devices were used for stimulation and recording experiments of hippocampal slice cultures over a period of several days     

Efficient small-area GaAs-Ga1-xAlxAs heterostructure electroluminescent diodes coupled to optical fibers

A GaAs-Ga1-xAlxAs heterostructure prepared by liquid-phase epitaxy has been employed in the fabrication of efficient small-area (50-µm diameter) electroluminescent diodes, and the light output has been coupled into optical fibers. The light output through a short fiber was about 1 mW at a wavelength of 0.9 µm for a bias current of 200 mA dc. By comparison, the output from the most efficient diffused GaAs diodes of similar geometry was about 0.4 mW at this current.     

Optimum signal wavelength for a distributed erbium-doped fiberamplifier

Theoretical analysis of a 100-km-long transparent germanosilicate distributed erbium-doped optical fiber has been carried out. It is shown that the optimum signal wavelength is 1.554 μm both considering the noise performance and the necessary pump power for achieving unity gain when the distributed erbium-doped fibers are pumped at 1.48 μm     

An optical fiber amplifier for wide-band wavelength range around1.65 μm

The optical amplification characteristics of a 0.781-μm pumped thulium-doped fiber in the wavelength range of 1.6-1.7 μm are discussed. A maximum net gain of 2.0 dB was obtained for 1.69-μm operation. This optical fiber amplifier is suitable for in-service monitoring and identifying fibers operating at 1.2-1.6 μm     

Surface-micromachined gear trains driven by an on-chipelectrostatic microengine

Test results for a polysilicon, surface-micromachined, electrostatically-actuated microengine driving multiple gears are presented. The microengine provides output in the form of a continuously rotating output gear (50 μm in diameter) that is capable of delivering torque to additional geared mechanisms. The microengine can be operated at varying speeds and its motion can be reversed. A rotational speed of up to 200000 r/min while driving multiple gears has been obtained. Drive of a 1600 μm diameter optical shutter has also been demonstrated. The resultant microengine and gear train, produced by polysilicon surface-micromachining techniques, are completely batch-fabricated without the need for piece-part assembly     

Fiber-embedded in-line isolator

A fiber-embedded optical isolator with a low forward loss has been developed. The isolator consists of thermally diffused expanded core fibers, laminated polarizers, and a Faraday rotation garnet. Backward and forward losses at 1.3 μm wavelength are 44.0 and 0.9 dB, respectively. The isolator has a minute size, and its alignment is simple     

A monolithic three-channel LD-PD array with vertically staggeredfacets for autofocusing reflectivity sensors

A monolithic three-channel LD-PD array with vertically staggered facets is proposed for an autofocusing reflectivity sensor which uses light feedback. The focus-sensing characteristics are investigated using an array with a radiation facet displacement of 12 μm and an interchannel distance of 130 μm, fabricated on an 830-nm AlGaAs/GaAs multiple-quantum-well laser substrate with buried-heterostructure stripe geometry waveguides. High focus-sensing accuracy is achieved. A potential application of the array to optical heads for phase change media is discussed