Mode shape converter, method for fabricating the mode shape converter and integrated optical device using the mode shape converter
First Claim
1. A mode shape converter interposed between an input or output terminal of a function executing unit included in an optical device and an optical fiber and adapted to couple a mode of the optical fiber with a mode of the input or output terminal of the function executing unit, the mode shape converter comprising:
- a substrate;
a lower clad coated over the substrate, the lower clad having an etched portion in a desired region;
a lower rib waveguide formed on the etched portion of the lower clad;
a core formed over the entire upper surface of both the lower rib waveguide and the non-etched portion of the lower clad;
an upper rib waveguide formed on the core such that it is aligned with the lower rib waveguide, the upper rib waveguide having a desired shape; and
an upper clad formed over both the upper rib waveguide and a portion of the core not covered with the upper rib waveguide.
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Abstract
A mode shape converter, interposed between an input or output terminal of a function executing unit included in an optical device and an optical fiber and adapted to couple a mode of the optical fiber with a mode of the input or output terminal of the function executing unit, includes a substrate, a lower clad coated over the substrate, the lower clad having an etched portion in a desired region, a lower rib waveguide formed on the etched portion of the lower clad, a core. formed over both the lower rib waveguide and a non-etched portion of the lower clad, an upper rib waveguide formed on the core such that it is aligned with the lower rib waveguide, the upper rib waveguide having a desired shape, and an upper clad formed over both the upper rib waveguide and a portion of the core not covered with the upper rib waveguide.
93 Citations
18 Claims
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1. A mode shape converter interposed between an input or output terminal of a function executing unit included in an optical device and an optical fiber and adapted to couple a mode of the optical fiber with a mode of the input or output terminal of the function executing unit, the mode shape converter comprising:
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a substrate;
a lower clad coated over the substrate, the lower clad having an etched portion in a desired region;
a lower rib waveguide formed on the etched portion of the lower clad;
a core formed over the entire upper surface of both the lower rib waveguide and the non-etched portion of the lower clad;
an upper rib waveguide formed on the core such that it is aligned with the lower rib waveguide, the upper rib waveguide having a desired shape; and
an upper clad formed over both the upper rib waveguide and a portion of the core not covered with the upper rib waveguide. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
a coupling region having a mode coupled with the mode of the optical fiber; and
a conversion region having a width decreasing gradually from the width of the coupling region to zero such that it transmits the mode of the coupling region to the upper rib waveguide.
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3. The mode shape converter according to claim 2, wherein the width of the conversion region decreases gradually so that a radiation loss generated during the transmission of the mode from the conversion region to the upper rib waveguide is minimized.
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4. The mode shape converter according to claim 2, wherein the coupling region has, at an input end thereof, a cross section having a width and a thickness determined based on the thickness of the upper rib waveguide and the output-end width of the upper rib waveguide such that a coupling efficiency between the mode of the optical fiber and the mode of the coupling region is maximized.
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5. The mode shape converter according to claim 2, wherein the upper rib waveguide comprises:
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a coupling region aligned with the coupling region of the lower rib waveguide;
a conversion region aligned with the conversion region of the lower rib waveguide and adapted to convert the mode transmitted from the lower rib waveguide into a mode suitable for the function executing unit; and
a stabilization region for outputting the mode transmitted from the conversion region to the function executing unit.
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6. The mode shape converter according to claim 5, wherein the coupling region of the upper rib waveguide has an input-end width determined based on the thickness of the core, the thickness of the upper rib waveguide and the output-end width of the upper rib waveguide such that a coupling efficiency between the mode of the optical fiber and the mode of the coupling region in the lower rib waveguide is maximized.
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7. The mode shape converter according to claim 5, wherein the width of the coupling region in the upper rib waveguide varies so that a radiation loss generated during the conversion of the mode from the coupling region into the mode suitable for the function executing unit is minimized.
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8. The mode shape converter according to claim 1, wherein the upper rib waveguide, the core, and the lower rib waveguide are made of the same material.
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9. A method for fabricating a mode shape converter interposed between an input or output terminal of a function executing unit included in an optical device and an optical fiber and adapted to couple a mode of the optical fiber with a mode of the input or output terminal of the function executing unit, said method comprising the steps of:
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(a) coating a lower clad over a substrate;
(b) patterning an etch mask on the lower clad, and etching the lower clad to a desired depth using the resultant pattern of the etch mask;
(c) coating a core material over the entire upper surface of the etched lower clad to form a lower rib waveguide and a core;
(d) patterning another etch mask on the core, and etching the core using the resultant pattern of the another etch mask to form an upper rib waveguide; and
(e) coating an upper clad on the core and the upper rib waveguide. - View Dependent Claims (10, 11)
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12. An integrated optical device including a function executing unit coupled to optical fibers at input and output terminals thereof, respectively, a first mode shape converter arranged at the input terminal of the function executing unit and adapted to convert an input optical fiber mode into a mode suitable for execution of desired functions of the optical device, and a second mode shape converter arranged at the output terminal of the function executing unit and adapted to convert a mode outputted from the function executing unit into an optical fiber mode, the output-end mode shape converter having an arrangement reverse to that of the first mode shape converter, wherein each of the first and second mode shape converters comprise:
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a substrate;
a lower clad coated over the substrate, the lower clad having an etched portion in a desired region;
a lower rib waveguide formed on the etched portion of the lower clad;
a core formed over the upper surfaces of both the lower rib waveguide and a non-etched portion of the lower clad;
an upper rib waveguide formed on the core such that it is aligned with the lower rib waveguide, the upper rib waveguide having a desired shape; and
an upper clad formed over both the upper rib waveguide and a portion of the core not covered with the upper rib waveguide. - View Dependent Claims (13, 14, 15, 16, 17, 18)
a coupling region having a mode coupled with the mode of the optical fiber; and
a conversion region having a width decreasing gradually from the width of the coupling region to zero such that it transmits the mode of the coupling region to the upper rib waveguide.
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14. The integrated optical device as set forth in claim 13, wherein the upper rib waveguide of the first and second mode shape converters comprise:
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a coupling region centrally aligned with the coupling region of the lower rib waveguide, said coupling region of said lower rib waveguide having a width greater than a width of said coupling region of said upper rib waveguide;
a conversion region centrally aligned with the conversion region of the lower rib waveguide and adapted to convert the mode transmitted from the lower rib waveguide into a mode suitable for the function executing unit, wherein the width of the conversion region of the lower rib waveguide decreases gradually to zero; and
a stabilization region for outputting the mode transmitted from the conversion region of the lower rib waveguide to the function executing unit, wherein the width of the stabilization region is less than the width of the coupling region of the lower rib waveguide and greater than the width of the coupling region of the upper rib waveguide, and wherein the width of the conversion region of the upper rib waveguide increases gradually from the coupling region of the upper rib waveguide to a width equal to the width of the stabilization region prior to reaching said stabilization region.
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15. The integrated optical device as set forth in claim 14, wherein the width of the conversion region of the lower rib waveguide of each of the first and second mode shape converters decreases gradually so that a radiation loss generated during the transmission of the mode from the lower rib waveguide to the upper rib waveguide is minimized.
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16. The integrated optical device as set forth in claim 12, wherein the upper rib waveguide, the core, and the lower rib waveguide of each of the first and second mode shape converters are made of the same material.
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17. The integrated optical device as set forth in claim 12, wherein the function executing unit has one of a modulation function, a switching function and filtering function.
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18. The integrated optical device as set forth in claim 12, wherein the lower rib waveguide and upper rib waveguide form a double rib waveguide such that the lower rib waveguide has a width and a depth adjusted to allow the fundamental mode of the double rib waveguide to well coincide with a circular mode of the optical fiber.
Specification