Thermally Diffused Expanded Core Research Articles

Modeling the splice loss of ultra-low loss fiber and single-mode optical fiber in high altitude area

The application of Ultra-low loss (ULL) fiber in high altitude areas is gradually expanding, and the junctions between ULL fiber and single mode optical fiber (SMF) will continue to increase. More factors affect the fusion of SMF and ULL fibers in high altitude areas, and the harsh environments add a further complication to the fusion. Accordingly, a model of splice loss for fusion SMF and ULL fibers affected by altitude is proposed in this work. The model takes the splice losses caused by thermally diffused expanded core (TEC), lateral misalignment, and angular misalignment into account, as well as the effect of atmospheric pressure on TEC and angular misalignment, and the fusion experiments of SMF and ULL fibers are carried out at different altitudes. The results illustrate that the model established in this work shows a good agreement with the data of experiments, and the model can play a guidance role for splicing SMF and ULL fibers at high altitudes in the future.

The effect of fusion current on thermally diffused expanded core of splicing ultra-low loss fiber and traditional single-mode fiber

Ultra-low loss (ULL) optical fiber is already being used at high altitude in optical communication due to the stable performance in long haul links. Whereas, traditional single-mode optical fiber (SMF) is still used in most general areas since the high price of ULL fiber. Accordingly, there will be an increasing number of junctions between SMF and ULL fibers. The main contents of this work are to study the influence of fusion current on the splice loss caused by thermally diffused expanded core (TEC) of splicing SMF and ULL fibers, and the variations on the diffusion of core dopants and fusion time are also taken into account. Furthermore, the analysis was verified by experiment and simulation. The results illustrate that the changes in fusion current will cause varying degrees of changes in the core and lead to different splice losses due to diffusion, which plays a guidance role in the current calibration of fusion splicer in the future when splicing SMF and ULL fibers. The significance of this work is to reduce the splice loss of SMF and ULL fibers. If the method is applied in a modern fusion splicer, the splice loss of SMF and ULL fibers will be deduced further.

Propagation characteristics of thermally diffused expanded core fibers with complexrefractive index profiles

In this paper, we investigate the propagation characteristics of thermally diffused expandedcore (TEC) fibers with complex refractive index using the numerical Galerkin’s method.Complex modal profiles and propagation constants for TEC fibers of differentexpanded core radii are calculated. The imaginary part of the electric field resultsin wavefront distortion showing that the power flows out of or into the dopedregion according to the sign of the imaginary part of the refractive index. Thegain or loss as a function of both mode field radius and operating wavelength iscalculated numerically. Moreover, an approximate formula for the loss or gaincoefficient of these fibers is given and the obtained approximate results agree wellwith those from Galerkin’s method applied to the complex refractive index fiber.

Characteristics of Thermally Diffused Transit Areas of Single-Mode Telecommunication Fibers

The paper deals with diffusion processes of the core dopant during thermal connection (splicing in electric arc) of telecommunication fibers whose parameters vary considerably. A method for defining values of diffusion coefficients GeO2 in SiO2 in splicing temperature has been presented. Better consistence of the dopant Gaussian and diffusion distribution has been found the longer the diffusion time-that is, splicing time. Theoretical analysis of thermally diffused expanded core (TEC) transit area transmission properties was performed which revealed that it is possible to obtain splice loss of thermal connections (splice) of fibers with different parameters, such as of the type G.652 and G.655, below 0.08 dB, using classical connection in electric arc. Whereas, using connection methods that increase the length of TEC, for example, connection by means of gas micro-burners, zero attenuation of such a connection can be accomplished.

Modal and coupling characteristics of low-order modes in thermally diffused expanded core fibers

In this paper, the Galerkin's numerical method is applied in order to calculate propagation constants, optical intensity distributions and far-field-patterns of low-order LP-modes in thermally diffused expanded core (TEC) fibers. The problem of efficient coupling between Gaussian laser beams and single-mode TEC-fibers is also considered. It is demonstrated that TEC fibers are good candidates for Laser source-to-fiber optical coupling scheme with long working distance. The numerical results are compared with the corresponding ones obtained by a one-parameter variational method utilizing Laguerre–Gauss functions. Galerkin's method is generally stable and more accurate when the mode is away from the cut-off region. On the other hand, the variational method provides an explicit form of the modal fields if the variational parameter is accurately determined.

Variational analysis of propagation characteristics in thermally diffused expanded core fibers

We present a scalar variational method for the analysis of light-propagation characteristics in thermally diffused expanded core (TEC) fibers. The method leads to simple closed-form expressions regarding the mode field diameter, numerical aperture, waveguide dispersion as well as coupling losses produced by radial, longitudinal and angular misalignments. The dependence of coupling losses on the ‘taper ratio’ and normalized frequency is investigated and previous predictions that TEC fibers transmit light more effectively in free space over the order of millimeters, is confirmed. The coupling losses between small core diameter step-index fibers typically used in most erbium-doped fiber amplifiers and TEC-fibers is also considered.

Numerical analysis of eigenmodes and splice losses of thermally diffused expanded core fibers

Field distributions and far-field patterns (FFP's) of the eigenmodes of thermally diffused expanded core (TEC) fibers are clarified by numerical analysis. The spot size of the TEC fiber is estimated by using the FFP that can be measured more easily than the near-field pattern (NFP). Splice losses of two TEC fibers are analyzed numerically considering a single or composite effect of gap, offset, and tilt. The results are useful for estimating isolations of fiber-integrated optical isolators and insertion losses of other fiber-integrated type optical devices. Splice losses considering multiple reflection between two endfaces of the TEC fibers with gaps are also analyzed numerically. This is useful for the design of fiber-integrated tunable wavelength filters.

Fabrication of an expanded core fiber having MFD of 40 /spl mu/m preserving outer diameter

A thermally-diffused expanded core (TEC) fiber with the mode field diameter (MFD) of 40 /spl mu/m has been fabricated by improving the diffusion process using an electric furnace. The outer diameter of any TEC fiber is preserved and the excess loss (normal-TEC-normal) is as low as 0.1 dB. >

Erbium-doped optical fiber amplifiers pumped in the 660- and 820-nm bands

State-of-the-art erbium (Er)-doped optical fiber amplifiers (EDFA's) pumped in the 660- and 820-nm bands are described. We have demonstrated highly efficient EDFA's incorporating optimized 664- and 827-nm pump wavelengths and an Er-doped high numerical aperture (NA) fiber with thermally diffused expanded core (TEC) fiber ends. Gain coefficients of 3.8 and 1.3 dB/mW at respective wavelengths of 664 and 827 nm were achieved at a signal wavelength of 1535 nm. Noise figures of 3.1 and 4.1 dB at respective pump wavelengths of 670 and 827 nm were obtained at a signal wavelength of 1535 nm. A highly efficient Er-doped fiber amplifier module, in which an AlGaInP visible laser diode (LD) was used as the pump source, was successfully developed as a practical application of this technology. A maximum overall gain coefficient of 3.0 dB/mW was achieved at a signal wavelength of 1535 nm. The EDFA module realized a maximum overall signal gain of 33 dB at 1535 nm with a saturated output power of -1 dBm. A maximum saturated output power of 3.9 dBm was obtained at a signal wavelength of 1552 nm. The present EDFA design using a low-cost laser diode for optical disk memory use and a high NA Er-doped fiber has great potential for providing inexpensive, high-performance EDFA's.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Light-propagation characteristics in thermally diffused expanded core fibers

Characteristics of light propagation in thermally diffused expanded-core (TEC) fibers are analyzed. Changes in the modal-field distributions along fibers and transition losses are obtained by use of the propagating-beam method. It is found that a transition length sufficiently longer than the characteristic length is necessary to expand or reduce the field diameter with low losses. A simplified model for understanding the mechanism of light propagation in TEC fibers is presented. Transmission losses between TEC fibers having imperfect splices are measured, the results are compared with those obtained by a simple theory and an exact theory. >

Loss characteristics of thermally diffused expanded core fiber

The authors have clarified experimentally the dependence of loss characteristics on wavelength for thermally diffused expanded core (TEC) fiber applied to connectors. Based on the relationship between the loss characteristics and the expanded mode field diameter (MFD), they suggest a method for measuring the MFD in TEC fibers nondestructively. >

Optical coupling characteristics of laser diodes to thermally diffused expanded core fiber coupling using an aspheric lens

A discussion is presented of the optical coupling characteristics of a 1.3 mu m laser diode to a thermally diffused expanded core (TEC) single-mode fiber coupling using an aspheric lens. The misalignment tolerance width for a 0.5 dB loss increment of the expanded core fiber was enlarged to 8.4 mu m from 1.9 mu m of a nonexpanded core fiber without a remarkable coupling-loss increase. The TEC fibers will make the LD module assembly easier, and reduce the assembly cost. >

Connection loss reduction by thermally-diffused expanded core fiber

Connection loss reduction in ten fiber connectors prepared by the thermally diffused expanded core (TEC) method has been confirmed. The mode field diameters (MFDs) of conventional single mode (SM) fibers were expanded from 9.8 to 13 mu m by thermal treatment considering the influence of loss increase due to fiber axis misalignment. An average connection loss of 0.15 dB for 4-SM-fiber connectors was realized, which was improved by 0.22 dB compared with previous value of 0.37 dB without thermal treatment. The TEC method promises to reduce the coupling loss, which is caused by lateral offset of multifiber connectors, fiber/LD modules, and fiber/waveguide device modules. >