Micromechanical modulator having enhanced performance

• US 5,870,221 A
• Filed: 07/25/1997
• Issued: 02/09/1999
• Est. Priority Date: 07/25/1997
• Status: Expired due to Term

• Current Assignee: Avago Technologies General IP PTE Limited (Broadcom, Inc.)
• Original Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Inventors: Goossen, Keith Wayne
• Primary Examiner(s): Epps, Georgia
• Assistant Examiner(s): BURKE, MARGARET A
• Application Number:
  US08/901,050
• Time in Patent Office: 564 Days
• Field of Search: 359/290, 359/291, 359/318, 359/302, 359/263, 359/298
• US Class Current: 359/290
• 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: G02B 26/0833 the reflecting element being a micromechanical device, e.g. a MEMS mirror, DMD G02B26/0825 takes precedence; micromechanical devices in general B81B

Abstract

A modulator having low insertion and a broad operating bandwidth is disclosed. The modulator has a movable membrane that is spaced from a substrate. The reflectivity of the movable membrane, and the reflectivity of the subtrate/gap interface are unequal. In particular, relative to the membrane, the substrate has a lower reflectivity. Device finesse is dictated by the lower reflectivity "mirror," i.e., the substrate. The substrate configuration thus provides a broad operating bandwidth while the higher reflectivity membrane provides low insertion loss.

Claims

1. A device for modulating an optical signal comprising:

a substrate and a movable membrane separated by a gap, the gap defining an optical cavity, wherein,

the substrate and the membrane are physically adapted to receive a voltage for generating a force sufficient for moving the movable membrane from a first position, maintained in the absence of the voltage, toward a second position closer to the substrate when voltage is applied, the change in position of the membrane causing a change in the gap and a change in device reflectivity,

characterized in that, the membrane has a first reflectivity and the substrate has a second unequal reflectivity, the first and second reflectivities being selected to result in the device having an insertion loss of less than about 1.4 dB and an operating bandwidth greater than about 142 nm.

2. The device of claim 1, and further wherein the movable membrane is a single layer of material characterized by a first refractive index and having a thickness of about one-quarter of wavelength of the optical signal, and wherein the substrate is characterized by a second refractive index and the first and the second refractive indices are about equal.

3. The device of claim 1, and further wherein the movable membrane comprises an overlayer characterized by a first refractive index and an underlayer characterized by a second refractive index and wherein the substrate is characterized by a third refractive index wherein the second and the third refractive indices are about equal and the first refractive index is within the range of from about 0.8 to 1.2 times the square root of the third refractive index.

4. The device of claim 1, and further wherein the device has an on-state reflectivity of at least about eighty percent and an off-state reflectivity of less than about six percent over an operating bandwidth of 60 nm.

5. The device of claim 1, and further wherein the device has an on-state reflectivity of less than about six percent and an off-state reflectivity of at least about eighty percent over an operating bandwidth of 60 nm.