Low Bending Loss Research Articles

Profile structure of single-mode fibers with low nonlinear properties for long-haul communication lines

Special W-core ring (WCR) fiber profile structures with low nonlinear properties for long-haul communication lines are proposed. A single-mode dispersion-flattened fiber (DFF) design with effective core area larger than 55 μm 2 and low bending loss is presented. It is shown that based on this structure and small variation of outer diameter along the fiber length, it is possible to fabricate a continuous dispersion varying fiber (DVF) with average zero dispersion (less than 0.012 ps nm −1 km −1) in the spectral range 1.53–1.56 μm. Besides, a single-mode dispersion-shifted (DSF) fiber design with large effective core area over 75 μm 2 and low bending loss is proposed. By varying only the refractive index profile (RIP) of this fiber, a DSF with negative chromatic dispersion slope in the 1.55-μm range can be produced. It is shown that in this case an average chromatic dispersion of DVF, based on this DSF, does not exceed ±0.4 ps nm −1 km −1 in the spectral range 1.53–1.56 μm.

Directly UV written silica-on-silicon planar waveguideswith low loss

Planar waveguides have been fabricated in silica-on-silicon using a continuous wave UV laser beam. A propagation loss of <0.2 dB/cm and low bending loss are demonstrated. The authors' results show that the UV writing method permits high volume production of low loss waveguide components.

Optical properties of small-bore hollow glass waveguides

Hollow glass waveguides with a 250-µm i.d. have been fabricated with a liquid-phase deposition technique that uses silica tubing as a base material. The losses of the 250-µm-bore guide measured at CO(2) laser wavelengths are as low as 2.0 dB/m. The straight losses for the hollow guides are in good agreement with theoretically predicted losses as a result of the nearly ideal structure of the guides. It is also shown that the guides have low bending losses, a nearly pure-mode delivery, and good high-power laser transmission. By proper design of the dielectric thickness, the guide is also able to deliver Er:YAG laser energy with a low loss of 1.2 dB/m for the 320-µm-bore waveguide. Because the hollow glass waveguide is very flexible and robust, it is quite suitable for medical applications.

Deep-oxide planar buried-channel AlGaAs–GaAs quantum well heterostructure waveguides with low bend loss

Data are presented on planar S-bend waveguides fabricated in an AlxGa1−xAs–GaAs p-n quantum well heterostructure (QWH) crystal by a self-aligned process combining Si impurity-induced layer disordering and ‘‘wet’’ native oxidation. In the process, a deep, low-index (n∼1.7) oxide cladding structure is formed, creating a buried channel in the QWH core layers and defining the routing properties of ∼2.5-μm-wide guides. Deep-oxide S-bend waveguides with 100 μm offsets exhibit low excess bend losses with a 3 dB transition distance less than 140 μm for transverse electric polarization. These bend losses are significantly lower than those measured for oxide-only and disordered-only guides. Excellent optical isolation of the guided signal is observed, indicating very little crosstalk occurs between adjacent guides.

Depressed cladding single-mode fibres for 1300 nm operation

The design of depressed cladding single-mode fibres for operation at 1300 mm is investigated. The depressed cladding profile is the simplest structure which satisfies the requirement of low bending loss without compromising the dispersion characteristics of the fibre. Fibres can be designed with a cutoff wavelength close to the operating wavelength of 1300 nm and with a zero of dispersion coinciding with the operating wavelength. The fibres can have a large spotsize which does not compromise the splice loss. A significant advantage is the insensitivity of the performances of these fibres to changes in the structural parameters.

A quasi-single mode optical fiber for long-haul transmission in severe bending environments

We investigated the feasibility of a quasi-single mode optical fiber for low bending losses in long-haul transmission at 1550 nm. The advantage of a quasi-single mode fiber is that for comparable bending losses the relative index difference, /spl Delta/, can be smaller than the /spl Delta/ in a single-mode fiber. We demonstrated that a quasi-single mode fiber with /spl Delta/=0.72% and single-mode cutoff wavelength /spl lambda//sub c/ equal to 1630 mn exhibits bending losses as low as the losses in a single-mode fiber with P=0.93% and /spl lambda//sub c/=1259 nm. Modal noise and modal dispersion effects in the quasi-single mode fiber also were tested and found to be minimal. This letter describes the matched-clad, quasi-single mode fiber and presents the test results.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Low-loss optical waveguide-bend configuration with curved corner reflector

A new bend configuration with curved corner reflector in the form of a logarithmic spiral is proposed. It is shown that this structure has a small size and very low bend loss for a large bending angle and small refractive index difference at the reflector interface.

A novel design and analysis of low loss abrupt bends of dielectric slab waveguides

On the basis of the well-known laws of reflection and refraction of the plane electromagnetic waves, a concept for designing very low loss nonadiabatic junctions between tilted straight sections of dielectric waveguides is investigated. Combining the ray representation of the propagating modes with the equivalent source formulation of the dielectric waveguide excitation problem, a simple and accurate 2-D theory for treating such bends in slab waveguides is developed. Numerical results for typical cases are explained along with some new junctions for achieving large angle redirection of guided waves with very low bending loss.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Dispersion-shifted dual-shape core fibers. Optimization based on spot size definitions

Design features, for very low bend and splice losses, in dispersion-shifted dual-shape core (DSC) single-mode fibers are obtained in terms of characteristic mode spot sizes W responsible for splice loss, and W/sub infinity / responsible for bend loss. Dual-shape core fiber designs are given with W/sub infinity //W lying between 1.16 and 1.33 while maintaining the mode spot size between 4 and 5 mu m at the operating wavelength of 1550 nm. With this design goal it is shown that bending loss would be lower in a step-index than in a graded-index DSC fiber. Further, conventional single clad step-index or triangular-index dispersion-shifted fibers are seen to have higher bending loss than well-designed DSC fibers.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The performance of depressed-cladding single-mode fibers with different b/a ratios

Depressed-cladding single-mode fibers with a first cladding-to-core ratio (b/a) ranging from seven to one and relative refractive-index differences of the core from 0.25 to 0.35% and of the cladding from 0 to -0.2% are investigated experimentally with respect to the LP/sub 11/ mode cutoff properties, the mode-field diameter, the dispersion, and the bending attenuation. Numerical calculations based on actual profile parameters of the bend loss and the mode-field diameter agree well with experiment. It is demonstrated that low attenuation and bend losses independent of b/a can be obtained if the cutoff wavelength is kept constant by adjusting the core radius, the core index or the index of the first cladding.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Bend losses in GaAs/AlGaAs optical waveguides

Circular bends with low excess bend loss (≤ l dB) and radii of a few millimetres were fabricated using GaAs/AlGaAs single-heterostructure rib waveguides with propagation loss ≤ 1 dB/cm. The effect of rib geometry and roughness due to bend pattern quantisation on the excess bend loss at 1.52/μi was investigated.

Low-loss LiNbO_3 waveguide bends with coherent coupling

Low bending losses have been achieved in single-mode Ti:LiNbO(3) channel waveguides by utilizing coherent coupling effects between closely spaced abrupt bends. A variety of multiple-bend structures has been evaluated. Losses as low as 0.08 dB per coupled 1 degrees abrupt bend have been measured, as compared with 0.8 dB per isolated 1 degrees abrupt bend.