Optical device formed with grating therein, add/drop filter using same, and method of fabricating same

An optical device formed with a low reflection grating therein, comprising:

• an optical waveguide comprising a core of a first refractive index and a cladding layer of a second refractive index, said core being imbedded in said cladding layer;
• a grating of a periodically striated distribution of refractive indices to be formed in said optical waveguide in a direction of a light propagation in accordance with a UV light radiation thereto;
• wherein a width W of said core is changed at a position z in said direction of said light propagation in accordance with an equation as defined below,
• w=w.sub.0 -W.multidot..vertline.sin(C.multidot.Z).vertline./.vertline.C.multidot.Z.v ertline.
• where w.sub.0 is an inherent and unchanged width of said core, .DELTA.W is a difference between said unchanged width w.sub.0 and a minimum width of said core, and C is a constant;
• and
• an envelope of said periodically striated distribution of refractive indices for said grating is changed in accordance with a value of ".vertline.sin(C.multidot.Z).vertline./.vertline.C.multidot.Z.vertline.", whereby a light of a specific wavelength to be transmitted through said optical waveguide is shifted in phase at said position Z meeting an equation as defined below,
• Z=m.pi./C(m=. . . -3,-2,-1,1,2,3, . . . ).

A method of fabricating an optical device formed with a low reflection grating, comprising the steps of:

• forming a core of a first refractive index having a width W which is changed at a position Z in a direction of light propagation in accordance with an equation as defined below,
• w=w.sub.0 -W.multidot..vertline.sin(C.multidot.Z).vertline./.vertline.C.multidot.Z.v ertline.
• where w.sub.0 is an inherent and unchanged width of said core, .DELTA.W is a difference between said unchanged width w.sub.0 and a minimum width of said core, and C is a constant,
• said core being embedded in a cladding layer of a second refractive index lower than said first refractive index;
• positioning a phase grating mask over said core, said phase grating mask having a grating striation which is shifted in phase at said position Z as defined below by .pi.,
• Z=m.pi./C(m=. . .-3,-2,-1,1,2,3, . . . );
• Scanning a UV light to be radiated via said phase grating mask to said core in said direction of said light propagation in accordance with a speed determined by a value of "1/(.vertline.sin(C.multidot.Z).vertline./.vertline.C.multidot.Z).vertline .", thereby providing a low reflection grating of a periodically striated distribution of refractive indices.

A method of fabricating an optical device formed with a low reflection grating, comprising the steps of:

• forming a core of a first refractive index having a width W which is changed at a position Z in a direction of light propagation in accordance with an equation as defined below,
• w=w.sub.0 -W.multidot..vertline.sin(C.multidot.Z).vertline./.vertline.C.multidot.Z.v ertline.
• where w.sub.0 is an inherent and unchanged width of said core, .DELTA.W is a difference between said unchanged width w.sub.0 and a minimum width of said core, and C is a constant,
• said core being embedded in a cladding layer of a second refractive index lower than said first refractive index;
• refracting a UV light to said core to derive an envelope of a periodically striated distribution of refractive indices, said envelope changing in accordance with a value of ".vertline.sin(C.multidot.Z).vertline./.vertline.C.multidot.Z).vertline.";
• and
• radiating UV lights of a fine spot surplusly to said core at said position Z to shift a phase of a light to be propagated in said direction by .pi. as defined below,
• Z=m.pi./C(m=. . .-3,-2,-1,1,2,3, . . . ).