MEMS tunable optical filter system with moisture getter for frequency stability

• US 6,776,538 B2
• Filed: 12/12/2001
• Issued: 08/17/2004
• Est. Priority Date: 12/12/2001
• Status: Expired due to Term

• Current Assignee: Excelitas Technologies Corporation (Excelitas Technologies Holdings LLC)
• Original Assignee: Axsun Technologies Incorporated
• Inventors: Pourmand, Raymond V., Miller, Michael F., Whitney, Peter S., Korn, Jeffrey A.
• Primary Examiner(s): Bovernick, Rodney
• Assistant Examiner(s): WONG, TINA MEI SENG
• Application Number:
  US10/021,765
• Publication Number:
  US 20030108306A1
• Time in Patent Office: 979 Days
• Field of Search: 385/92-94, 372/34-36
• US Class Current: 385/94
• CPC Class Codes: G02B 6/29362 Serial cascade of filters or filtering operations, e.g. for a large number of channels
• CPC Class Codes: G02B 6/29395 configurable, e.g. tunable or reconfigurable switching G02B6/35
• CPC Class Codes: G02B 6/4215 the intermediate optical elements being wavelength selective optical elements, e.g. variable wavelength optical modules or wavelength lockers G02B6/4246 takes precedence
• CPC Class Codes: G02B 6/4251 Sealed packages G02B6/4248 takes precedence
• CPC Class Codes: G02B 6/4265 of the Butterfly or dual inline package [DIP] type
• CPC Class Codes: G02B 6/4271 with thermo electric cooling
• CPC Class Codes: G02B 6/4285 Optical modules characterised by a connectorised pigtail
• CPC Class Codes: G02B 6/4286 Optical modules with optical power monitoring

Abstract

In optoelectronic systems, package moisture can affect stress levels in dielectric coatings on MEMS devices. Specifically, as the moisture content in these dielectric coatings changes, there are concomitant changes in the material stress. These changes in material stress can affect the operation of the overall MEMS device. Specifically, in the context of tunable filters, moisture can lead to a drift in the size of the optical resonant cavity over time as changes in material stress affect the MEMS structures. According to the invention, a getter is added to the package to absorb moisture, and thereby stabilize the operation of the optical filter, and specifically prevent uncontrolled drift in the size of its optical cavity.

Claims

1. An optical filter system, comprising

a package;

an optical filter installed within the package having at least two thin film mirrors that define an optical resonant cavity; and

a getter in the package that absorbs moisture to stabilize the optical filter.

2. A tunable optical filter system as claimed in claim 1, wherein the package is a hermetic package.

3. A tunable optical filter system as claimed in claim 1, wherein the optical filter is a tunable filter in which at least one of the thin film mirrors is disposed on a release structure.

4. A tunable optical filter system as claimed in claim 3, wherein the release structure is a membrane.

5. A tunable optical filter system as claimed in claim 1, wherein the getter absorbs moisture in the package to stabilize a material stress in the thin film mirrors and thereby stabilize dimensions of the optical resonant cavity.

6. A tunable optical filter system as claimed in claim 1, wherein the thin film mirrors comprise alternating layers including tantalum pentoxide.

7. A tunable optical filter system as claimed in claim 1, wherein the thin film mirrors comprise alternating layers including tantalum pentoxide and silicon dioxide.

8. A process for packaging an optical filter, comprising

installing an optical filter comprising at least two thin film mirrors, which define an optical resonant cavity, in a package;

placing a getter in the package to absorb moisture in the package during operation;

sealing the package with the optical filter and the getter inside.

9. A process as claimed in claim 8, further comprising drying the inside of the package to remove moisture prior to the sealing step.

10. A process as claimed in claim 8, wherein the step of sealing the package comprises sealing a lid onto the package.

11. A process as claimed in claim 8, further comprising applying the getter to the lid prior.