Fiber Optic Slabs

Generating a superdirective beam from metamaterials using Fourier optics

Metamaterials are artificial materials with structures specifically engineered to have optical properties that are not found in nature, such as a negative refractive index. We use thousands of coupled slabs of equal or almost equal thickness comprising air, which has a refractive index of 1, and metamaterial ‘anti-air’ with an effective refractive index equal to –1. The average refractive index is zero: a quasi-zero (QZAI) medium. The total effect of such complementary media is light transmission in the plane without diffraction, preserving the input source profile.

We have experimentally verified these theoretical predictions using a macroscopic sample with a length of 4mm. In our sample the metamaterial antimatter slabs are composed of a photonic crystal (PhC) made from silicon (n=3.45 for incident light at wavelength λ=1.55μm) with air holes arranged in a hexagonal lattice in the (x; z) plane. The holes have a radius r, lattice parameter a, and ratio r/a=0.38. This particular PhC shows an almost isotropic effective index n is the frequency normalized to a . For this polarization the electric field is directed along an axis that follows a line of the holes in the array. For λ=1.55μm, the parameters that render an effective index of –1 are r=180nm and a=472nm. The QZAI structure is obtained by alternating slabs of air with slabs of this PhC, and the side edges of the PhC are cut The grating period is , given by the distance between two air layers (see Figure 1 ), and acts as a virtual waveguide without a physical structure for the lateral and vertical confinement. A direct quantification of the propagation length and the angular spread of the mode are determined by measuring the angular and spectral width of the diffracted peaks.

High-accuracy experimental results have shown that the angular dispersion of the diffracted beam is as small as Δθ=0.06° as it propagates along the direction of the zeroth order of the diffraction grating composed by coupled slabs of air and anti-air metamaterial. This material exhibits low angular dispersion despite the high divergence of the input beam resulting from the strong focusing by the lensed fiber from which it is emitted. We have also experimentally verified with great accuracy that the wavenumber of the beam propagating in the QZAI plane is the wavenumber in air 2π/λ, i.e., the beam propagates without experiencing diffraction.

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Fiber optic network cable

The two most common outdoor fiber optic cable installations are pole line aerial installation and underground cable installation. Underground cable installation can be interred directly underground or placed into a interred duct.

Direct burial installation:

Direct burial installations ar most common for long cross-country installations. The cables ar ploughed in or interred in a trench the installation process can be very quick. The most common cables used for direct burial ar steel armored outdoor fiber cables.

Underground duct installation:

Fiber optic cables can also be pulled through underground ducts, which protect the cables from harsh environment. Underground duct installation also provides chance for future expansion without the need to dig. This is the most common practice in urban areas. Another benefit is that fiber cables without armor can be used which makes the installation even easier.

Preparation before underground cable installation:

1. Obtain right right-of-way permits 3. Investigate the soil condition in order to determine the installation depth, whether duct should be used, the type of fiber cable should be used and ploughing equipment needed

Cable Burial techniques:

1. Plowed under

Plowing in a fiber cable is faster than trenched. But this process has to be carefully monitored to prevent from damaging the cable .

2. Trenched

The fiber cable can also be trenched. This process is slower than plowing in however, it allows a much more controlled cable installation. Trenches can be dug by hand or by machine.

3. Directional boring

Directional boring technique is used where the surface cannot be worked on such as high, railway crossings, etc. Instead, a boring machine is used to bore a several inches diameter hole underneath the surface, a duct is pulling through the hole and then fiber cables pulled into the duct.

Important factors:

1.

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Solid state imaging arrays, August 22-23, 1985, San Diego, California

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