US 6,640,024 B1Granted

Add-drop wavelength filter using mode discrimination couplers and tilted bragg gratings

AssigneeKorea Advanced Institue of Science and Technology

InventorsByoung Yoon Kim, Hee Su Park, Seok Hyun Yun

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Abstract

An add-drop wavelength filter is described which separates specific wavelength components from optical signals propagating through an optical waveguide or adds specific wavelength components thereto. In general, add-drop wavelength filters serve to separate or add specific channels in channels comprising several different wavelengths in a wavelength division optical communication system, and require good wavelength selectivity, stability and etc. Up to now, several types of add-drop wavelength filters are proposed, however disadvantageously they were not stable or were difficult to fabricate. The add-drop wavelength filter of the present invention comprising a mode discrimination coupler, Bragg gratings in which mode conversion occurs and etc., utilizes mode conversion in a dual mode waveguide and has low loss and stability. Furthermore, devices included in the add-drop wavelength filter are conventionally used, thereby resulting in easy fabrication, and the application fields of the devices can be easily expanded by apodization, chirping, or etc. of the Bragg gratings.

Claims11

Dependent claims

An optical signal add-drop wavelength filter for separating optical signals having at least one wavelength λi(1≦i≦n) from input optical signals consisting of multiple wavelengths of λi, . . . , and λn (n is a positive integer more than 1) or adding optical signals having at least one wavelength λj to said input optical signals, said wavelength filter comprising:

a dual mode optical waveguide and a first optical waveguide in which input of the multiple wavelength optical signals and output of optical signals which experienced wavelength add-drop are performed in a mutually exchanging manner;
a mode discriminating directional coupler formed with a first portion of the dual mode optical waveguide and a portion of the first optical waveguide, the mode discriminating directional coupler characterized by energy transfer of at least 50% between a fundamental mode of said first optical waveguide and a higher-order mode of said dual mode optical waveguide and also by enabling the fundamental mode of said dual mode optical waveguide to propagate without change, in said input optical signal range;
and
a second portion of the dual mode optical waveguide for transmitting optical signals to and from said mode discriminating directional coupler and an arrangement of Bragg gratings, wherein
the arrangement of Bragg gratings is written within said second portion of the dual mode optical waveguide, and at least one Bragg grating in the arrangement of Bragg gratings is connected in series and tilted with an angle of more than 0.1 degree with respect to a plane perpendicular to a propagation direction of the optical signals, said at least one Bragg grating serving to perform both mode conversion and reflection of the optical signals propagating within said second dual mode optical waveguide portion at drop wavelength λi and add wavelength λj,
wherein said first and second portions of the dual mode optical waveguide are provided integrally without any splice,
wherein the fundamental mode of said first optical waveguide and the higher-order mode of said dual mode optical waveguide have a same propagation constant, and wherein said mode discriminating directional coupler utilizes coupling of one or more evanescent electric fields.

4 more elements

An optical signal add-drop wavelength filter for separating and simultaneously adding at least one wavelength signal from and to input optical signals consisting of multiple wavelengths of λi, . . . , and λn(n is a positive integer more than 1), said wavelength filter comprising:

a first dual mode optical waveguide portion and a first optical waveguide in which input of the multiple wavelength optical signals and output of optical signals which experienced wavelength drop are performed in a mutually exchanging manner;
a first mode discriminating directional coupler which causes energy transfer to occur at least 50% between a fundamental mode of said first optical waveguide and a higher-order mode of said first dual mode optical waveguide portion and also enables the fundamental mode of said first dual mode optical waveguide portion to propagate without change;
a second dual mode optical waveguide portion and a second optical waveguide in which input of optical signals to be added and output of optical signals which experienced wavelength add/drop are performed in a mutually exchanging manner;
a second mode discriminating directional coupler which causes energy transfer to occur at least 50% between a fundamental mode of said second optical waveguide and a higher-order mode of said second dual mode optical waveguide portion and also enables the fundamental mode of said second dual mode optical waveguide portion to propagate without change;
a third dual mode optical waveguide portion for propagating optical signals which passed through said first and second mode discriminating directional couplers;
and
an arrangement of Bragg gratings written within said third dual mode optical waveguide portion, in which at least one Bragg grating is connected in series which is tilted with an angle of more than 0.1 degree with respect to a plane perpendicular to the propagation direction of the optical signals, said Bragg grating serving to perform both mode conversion and reflection of the optical signals propagating within said third dual mode optical waveguide portion,
wherein said first, second and third dual mode optical waveguide portions are provided integrally without any splices, and
wherein a same propagation constant by at least one of:
a) the fundamental mode of said first optical waveguide and the higher-order mode of said first dual mode optical waveguide portion, and
b) the fundamental mode of said second optical waveguide and the higher-order mode of said second dual mode optical waveguide portion, and
wherein at least one of said mode discriminating directional coupler utilizes coupling of one or more evanescent electric fields.

9 more elements

Dependencies are inferred from the claim text.

Facts

Application: 09/700,245Filed 9 Nov 2000
Priority: KR 99-784710 Mar 1999
Granted: 28 Oct 2003
Term ends: Not estimatedThe source records don’t support an estimate.

Classification7 codes

G02B 6/0208
Refractive index modulation gratings, e.g. Bragg gratings: characterised by their structure, wavelength response
G02B 6/02085
Characterised by their structure, wavelength response: characterised by the grating profile, e.g. chirped, apodised, tilted, helical
G02B 6/29334
Wavelength selective couplers, i.e. based on evanescent coupling between light guides, e.g. fused fibre couplers with transverse coupling…
G02B 6/29344
With wavelength selective means: operating by modal interference or beating, i.e. of transverse modes, e.g. zero-gap directional coupler, MMI