Electromechanical optical modulator providing stray light...

Details Electromechanical optical modulator providing stray light... Electromechanical optical modulator providing stray light...

1999-10-08

2004-03-09

Epps, Georgia (Department: 2873)

Optical: systems and elements

Optical modulator

Light wave temporal modulation

C372S020000, C385S014000, C356S519000

Reexamination Certificate

active

06704130

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to electromechanical optical modulators and, in particular, to an optical modulator providing enhanced control of stray light.
BACKGROUND OF THE INVENTION
Electromechanical optical modulators (sometimes called MARS modulators) are useful in optical communication systems. A electromechanical optical modulator is basically a Fabry-Perot cavity comprising the air gap between an optical membrane and a substrate. Modulation of reflected light is based on voltage-controlled movement of the membrane in relation to the substrate. Such devices can provide high contrast reflection modulation at rates in excess of several Mbit/sec. They are particularly useful as optical equalizers, switches for wavelength Add/Drop modules and optical cross-connect mirrors. U.S. Pat. No. 5,500,761 issued to K. W. Goosen et al. on Mar. 19, 1996 describes a electromechanical optical modulator useful for power equalization, and modulator having low insertion loss and enhanced operating bandwidth is described in the copending U.S. patent application Ser. No. 08/901,050 filed by K. W. Goosen et al on Jul. 25, 1997 and entitled “Microelectromechanical Modulator Having Enhanced Performance”, now U.S. Pat. No. 5,870,221. Both U.S. Pat. No. 5,500,761 and application Ser. No. 08/901,050, now U.S. Pat. No. 5,870,221 are incorporated herein by reference.
Referring to the drawings,
FIG. 1
is a schematic cross section of a conventional electromechanical modulator
9
comprising a substrate
10
and a membrane
15
spaced from the substrate to define an air gap
20
. The substrate
10
is a conductive material such as doped silicon, and the has a top surface
21
(typically planar) and a back surface
22
(typically parallel or slightly inclined with respect to surface
21
). The membrane
15
comprises one or more layers of conductive material such as an overlayer
15
a
of silicon nitride and an underlayer
15
b
of polycrystalline silicon. The overlayer has an index of refraction approximately equal to the square root of the substrate refractive index and the underlayer has an index of refraction approximately equal to the substrate refractive index. The thicknesses of layers
15
a
and
15
b
are each less than one-quarter of the operating wavelength &lgr;. The membrane
15
and the substrate
10
are spaced apart by a peripheral support layer
12
of insulating material. Electrodes
1
and
2
permit connection of the membrane
15
and substrate
10
, respectively, to the terminals of a bias voltage source
29
.
The air gap
20
can be controlled by a bias voltage between the substrate
10
and the membrane
15
. Relative reflective maxima are produced when the gap
20
is an odd integer multiple of one-quarter of the operating wavelength &lgr;. Minima are produced when the gap
20
is 0 or an even integer multiple of &lgr;/4.
The modulator can employ mirrors of unequal reflectivity to provide broad operating bandwidth with low insertion loss. A high reflectivity membrane provides low insertion loss while a lower reflectivity substrate maintains the broader bandwidth of a low finesse device.
While these devices work well, stray light is a potential difficulty for some applications. Nonreflected light can be transmitted through the gap
20
into the underlying substrate. This light can be useful as a source of signals or information for feedback control, or it can be deleterious as a source of crosstalk through unwanted reflections or scattering. In either case there is a need to control the path of light transmitted into the substrate.
SUMMARY OF THE INVENTION
In accordance with the invention, a electromechanical optical modulator comprising an optical membrane, a substrate and Fabry-Perot air gap between them is provided with an improved structure for controlling light transmitted into the substrate. Specifically, an etched and coated cavity is formed in the backwall of the substrate underlying the air gap to receive transmitted light and redirect it onto controllable paths within the substrate. Advantageously the substrate is silicon, and the cavity is produced by anisotropic etching.


REFERENCES:
patent: 5500761 (1996-03-01), Goosen et al.
patent: 5943155 (1999-08-01), Goossen
patent: 6271052 (2001-08-01), Miller et al.
patent: 6356254 (2002-03-01), Kimura
patent: 6424450 (2002-07-01), Goossen
patent: 2001/0050707 (2001-12-01), Sasaki et al.
patent: 2002/0075483 (2002-06-01), Harris et al.
patent: 2002/0106871 (2002-08-01), Le et al.
patent: 2002/0126726 (2002-09-01), Flanders et al.
patent: 2002/0131458 (2002-09-01), Sirbu et al.

Affiliated with

Also associated with

Rating

Electromechanical optical modulator providing stray light... does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Electromechanical optical modulator providing stray light..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electromechanical optical modulator providing stray light... will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3274387