Optical filter and method of making the same

• US 6,337,937 B1
• Filed: 05/17/1999
• Issued: 01/08/2002
• Est. Priority Date: 05/18/1998
• Status: Expired due to Fees

• Current Assignee: Sumitomo Electric Industries Limited (Sumitomo Corporation)
• Original Assignee: Sumitomo Electric Industries Limited (Sumitomo Corporation)
• Inventors: Takushima, Michiko, Shigehara, Masakazu
• Primary Examiner(s): Healy, Brian
• Assistant Examiner(s): ROJAS, OMAR R
• Application Number:
  US09/313,005
• Time in Patent Office: 967 Days
• Field of Search: 385/37, 385/124, 385/127, 385/130, 385/359, 385/28, 359/341, 430/321
• US Class Current: 385/28
• CPC Class Codes: G02B 6/0208 characterised by their structure, wavelength response G02B6/02114, G02B6/02171, G02B6/02195 take precedence; multiple layer cores or claddings G02B6/036, protective coverings G02B6/4429
• CPC Class Codes: G02B 6/02095 Long period gratings, i.e. transmission gratings coupling light between core and cladding modes
• CPC Class Codes: G02B 6/02142 based on illuminating or irradiating an amplitude mask, i.e. a mask having a repetitive intensity modulating pattern

Abstract

The present invention relates to an optical filter having a plurality of long-period gratings, and a method of making the same. The optical filter according to the present invention comprises a plurality of long-period gratings having attenuation peaks different from each other in a core region thereof, whereas the order of cladding mode in the light attenuated by the plurality of long-period gratings to couple with the core mode thereof varies among these long-period gratings.

Claims

1. An optical filter comprising:

an optical waveguide having a core region which has a predetermined refractive index, and a cladding region which is provided on an outer periphery of said core region and has a lower refractive index than said core region;

a first filter region arranged at a predetermined position at least in said core region, and provided with a first long-period grating attaining an attenuation peak at a first wavelength by mode coupling, a refractive index of said first filter region varying with a first period; and

a second filter region arranged at a predetermined position at least in said core region, and provided with a second long-period grating attaining an attenuation peak at a second wavelength different from said first wavelength by mode coupling, a refractive index of said second long-period grating varying with a second period;

wherein the order of cladding mode in light attenuated by said first long-period grating to couple with a core mode thereof differs from the order of cladding mode in light attenuated by said second long-period grating to couple with a core mode thereof.

2. An optical filter according to claim 1, wherein said first and second filter regions are arranged where at least a part of said first filter region and at least a part of said second filter region overlap each other.

3. A method of making the optical filter of claim 1, said method comprising the steps of:

preparing an optical waveguide having a core region doped with an impurity for changing a refractive index, and a cladding region provided on an outer periphery of said core region and having a lower refractive index than said core region;

generating a refractive index fluctuation with a first period in a first grating forming region at a predetermined position in said core region, so as to form a first long-period grating attaining an attenuation peak at a first wavelength by mode coupling; and

generating a refractive index fluctuation with a second period in a second grating forming region at a predetermined position in said core region, so as to form a second long-period grating attaining an attenuation peak at a second wavelength different from said first wavelength by mode coupling;

wherein said first and second periods are set such that the order of cladding mode in light attenuated by said first long-period grating to couple with a core mode thereof differs from the order of cladding mode in light attenuated by said second long-period grating to couple with a core mode thereof.

4. A method according to claim 3 wherein said second grating forming region is set where at least a part thereof overlaps at least a part of said first grating forming region.

5. A method according to claim 4, further comprising the step of:

uniformly irradiating said first and second grating forming regions with grating forming light along a longitudinal direction of said core region before forming said first and second long-period gratings.

6. A method according to claim 3, further comprising the steps of:

measuring, after forming said first long-period grating, a transmissivity of thus formed first long-period grating at each wavelength within a predetermined wavelength band;

measuring, after said second long-period grating is formed subsequent to the forming of said long-period grating, a transmissivity of thus formed first and second long-period gratings at each wavelength within said predetermined wavelength band; and

computing differential data between first data concerning thus measured transmissivity of said first long-period grating and second data concerning thus measured transmissivity of said first and second long-period gratings as third data concerning said second long-period grating.

7. A method according to claim 6, further comprising the step of:

uniformly irradiating said first and second grating forming regions with grating forming light along a longitudinal direction of said core region before forming said first and second long-period gratings.

8. A method according to claim 6, wherein said predetermined wavelength band includes a range between said first and second wavelengths.