Optical power equalizer

• US 6,337,753 B1
• Filed: 12/21/1998
• Issued: 01/08/2002
• Est. Priority Date: 12/21/1998
• Status: Expired due to Term

• Current Assignee: WSOU Investments, LLC (WSOU Holdings, LLC)
• Original Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Inventors: Goossen, Keith Wayne
• Primary Examiner(s): Chan, Jason
• Assistant Examiner(s): Payne, David C.
• Application Number:
  US09/217,710
• Time in Patent Office: 1,114 Days
• Field of Search: 359/124-134, 359/110, 359/161, 359/174, 359/179, 359/245, 359/254, 359/251, 359/263, 359/267, 359/290, 359/291, 359/321, 359/292, 359/298, 359/140, 359/247, 359/237, 359/239, 359/577-590
• US Class Current: 398/79
• CPC Class Codes: G02B 26/001 based on interference in an adjustable optical cavity interference filters G02B5/28; devices or arrangements using multiple reflections in spectrometry or monochromators G01J3/26
• CPC Class Codes: G02B 26/02 for controlling the intensity of light G02B26/004 takes precedence
• CPC Class Codes: H04J 14/0221 Power control, e.g. to keep the total optical power constant

Abstract

The specification describes an optical power level equalizer device for compensating power tilt in a wavelength division multiplexed lightwave system. The device is a movable membrane device, similar in structure to a Mechanical Anti-Reflection Switch (MARS) device, but in which the movable membrane is made essentially transparent to the center wavelength of the multiplexed signal. Reflectivity increases on one side of the power band and decreases on the other, allowing tilt to be compensated without significant power loss in the center wavelengths. The degree of tilt compensation is dependent on the size of the air gap and can be adjusted dynamically to maintain equal power levels in each channel.

Claims

1. An electrooptic device comprising:

(a) a substrate,

(b) a membrane having an optically transparent portion and comprising at least one optically active layer with a refractive index η and

a thickness t,

(c) means for directing a beam of light on said optically transparent portion of said membrane, said beam of light having a range of wavelengths with a center wavelength λ

, where t=λ

/2η

,

(d) a flexible support for positioning the optically transparent portion of said membrane at a first position spaced from said substrate and defining an air gap d₁ between said optically active layer and said substrate, and a second position spaced from said substrate defining an air gap d₂ between said optically active layer and said substrate, and

(e) means for applying an electrical bias across said air gap to move said optically transparent portion of said membrane from said first position to said second position.

2. An electrooptic device comprising:

(a) a substrate,

(b) a membrane having an optically transparent portion and comprising at least two layers (i) and (ii), wherein layer (i) is an optically active layer with a refractive index η

₁ and a thickness t₁, and layer (ii) is a conductive layer with a refractive index η

₂ and a thickness t₂,

(c) means for directing a beam of light on said optically transparent portion of said membrane, said beam of light having a range of wavelengths with a center wavelength λ

, where t₁=λ

/2η

₁, and t₂=λ

/2η

₂,

(d) a flexible support for positioning the optically transparent portion of said membrane at a first position spaced from said substrate and defining an air gap d₁ between said layer (i) and said substrate, and a second position spaced from said substrate defining an air gap d₂ between said layer (i) and said substrate, and

(e) means for applying an electrical bias across said air gap to move said optically transparent portion of said membrane from said first position to said second position.

3. The device of claim 2 wherein layer (i) is silicon nitride.

4. The device of claim 3 wherein layer (ii) is polysilicon.

5. The device of claim 4 wherein λ

is approximately 1550 nm.

6. An electrooptic device comprising:

(a) a substrate having at least two layers (i) and (ii) on the surface thereof, wherein layer (i) is an optically active layer with an index of refraction η

₁, and a thickness t₁, and layer (ii) is a conductive layer having an index of refraction η

₂ a thickness t₂,

(b) a membrane having an optically transparent portion and comprising at least two layers (iii) and (iv), wherein layer (iii) is a conductive layer with a refractive index η

₃, and a thickness t₃, and layer (iv) is an optically active layer with a refractive index η

₄ and a thickness t₄,

(c) means for directing a beam of light on said optically transparent portion of said membrane, said beam of light having a range of wavelengths with a center wavelength λ

, where t₁=λ

/4η

₁, t₂=λ

/4η

₂, t₃=λ

/2η

₃, and t₄=λ

/2η

₄,

(d) a flexible support for positioning the optically transparent portion of said membrane at a first position spaced from said substrate and defining an air gap d₁ between said layer (ii) and said layer (iii), and a second position spaced from said substrate defining an air gap d₂ between said layer (ii) and said layer (iii), and

(e) means for applying an electrical bias across said air gap to move said optically transparent portion of said membrane from said first position to said second position.

7. The device of claim 6 wherein layers (ii) and (iii) are polysilicon.

8. The device of claim 7 wherein layer (i) is selected from the group consisting of silicon dioxide and silicon nitride.

9. The device of claim 8 wherein λ

is approximately 1550 nm.

10. The device of claim 9 wherein said conductive substrate is a semiconductor.

11. The device of claim 10 wherein said conductive substrate is silicon.

12. The device of claim 6 wherein the movable membrane has an additional layer (v) of a conductive material having a thickness approximately equal to λ

/2, where λ

is measured in said material.

13. A WDM system comprising:

(a) WDM signal input means,

(b) optical amplifier,

(c) power spectrum analyzer,

(d) power spectrum equalizer comprising;

a substrate,

a membrane having an optically transparent portion and comprising at least one optically active layer with a refractive index η and

a thickness t,

means for directing a beam of light on said optically transparent portion of said membrane, said beam of light having a range of wavelengths with a center wavelength λ

, where t=λ

/2η

,

a flexible support for positioning the optically transparent portion of said membrane at a first position spaced from said substrate and defining an air gap d₁ between said optically active layer and said substrate, and a second position spaced from said substrate defining an air gap d₂ between said optically active layer and said substrate, and

means for applying an electrical bias across said air gap to move said optically transparent portion of said membrane from said first position to said second position,

(e) WDM signal output means,

(f) optical fiber interconnections between (a), (b), (c), (d) and (e), and (g) feedback means for transmitting a signal from said power spectrum analyzer to said power spectrum equalizer.

14. A WDM system comprising:

(a) WDM signal input means,

(b) optical amplifier,

(c) power spectrum analyzer,

(d) power spectrum equalizer comprising;

a substrate having at least two layers (i) and (ii) on the surface thereof, wherein layer (i) is an optically active layer with an index of refraction η

₁, and a thickness t₁, and layer (ii) is a conductive layer having an index of refraction η

₂ a thickness t₂,

a membrane having an optically transparent portion and comprising at least two layers (iii) and (iv), wherein layer (iii) is a conductive layer with a refractive index η

₃, and a thickness t₃, and layer (iv) is an optically active layer with a refractive index η

₄ and a thickness t₄,

means for directing a beam of light on said optically transparent portion of said membrane, said beam of light having a range of wavelengths with a center wavelength λ

, where t₁=λ

/4η

₁, t₂=λ

/4η

₂, t₃=λ

/2η

₃, and t₄=λ

/2η

₄,

a flexible support for positioning the optically transparent portion of said membrane at a first position spaced from said substrate and defining an air gap d₁ between said layer (ii) and said layer (iii), and a second position spaced from said substrate defining an air gap d₂ between said layer (ii) and said layer (iii), and

means for applying an electrical bias across said air gap to move said optically transparent portion of said membrane from said first position to said second position,

(e) WDM signal output means,

(f) optical fiber interconnections between (a), (b), (c), (d) and (e), and

(g) feedback means for transmitting a signal from said power spectrum analyzer to said power spectrum equalizer.