MEMS variable optical attenuator

Details MEMS variable optical attenuator MEMS variable optical attenuator

2003-07-02

2004-11-09

Lester, Evelyn A. (Department: 2873)

Optical: systems and elements

Light control by opaque element or medium movable in or...

C359S230000, C385S140000, C385S025000, C385S016000, C385S018000, C385S015000

Reexamination Certificate

active

06816295

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a MEMS (Micro Electro Mechanical System) variable optical attenuator, and more particularly to a MEMS variable optical attenuator with an improved fine beam shutter for controlling the amount of an optical signal traveling between transmitting and receiving optical waveguides.
2. Description of the Related Art
An optical attenuator used in optical communication systems denotes an optical component, which comprises a pair of transmitting and receiving terminals, and serves to attenuate light inputted via the receiving terminal due to an optical loss and then to output the attenuated light via the transmitting terminal.
Individually, the level of optical reception and transmission varies according to the configuration of a system. For example, the level of optical reception and transmission is determined by the difference of transmission loss due to the length of transmission distance of an optical fiber, the number of connecting portions of optical fibers, the number and performance of optical components such as optical branches used in a transmission line. Accordingly, there is required an optical attenuator when light with an excessive amount is received by an optical receiver. Further, the optical attenuator can be widely applied in evaluation, adjustment, and correction of communication equipment and optical measuring equipment.
The optical attenuators are divided into a fixed optical attenuator, in which the amount of attenuation of optical light is fixed, and a variable optical attenuator (VOA), in which the amount of attenuation of optical light is variable. There is required an optical attenuator with excellent reliability and small size at a reduced cost.
In order to satisfy the above requirements, the optical attenuators have been developed so as to have a MEMS structure using a thin film technique. In the MEMS variable optical attenuator, an actuator with a fine structure is formed on a substrate made of silicon or etc. using the thin film technique. Generally, the actuator is driven using a thermal expansion force or an electrostatic force, thus causing an electric potential difference to a beam shutter. Thereby, the amount of light transmitted from a transmitting terminal (also, referred to as an “exit terminal”) to a receiving terminal (also, referred to as an “entrance terminal”) is controlled.
FIG. 1
is a schematic perspective view of a conventional MEMS variable optical attenuator using an electrostatic actuator. The conventional MEMS variable optical attenuator of
FIG. 1
comprises a substrate
11
provided with a transmitting terminal
20
and a receiving terminal
30
, an electrostatic actuator including driving electrodes
12
a
and
12
b
, a ground electrode
14
, a spring
15
and a mobile mass portion
16
, and a beam shutter
17
connected to the mobile mass portion
16
of the electrostatic actuator.
The driving electrodes
12
a
and
12
b
and the ground electrode
14
are supported on the substrate
11
by an oxide layer
19
(also, referred to as an “anchor”). The mobile mass portion
16
is connected to the ground electrode
14
by the spring
15
, and has a comb-type structure suspended from the substrate
11
. Portions
13
a
and
13
b
extended from the driving electrodes
12
a
and
12
b
have a comb-type structure interdigitated with the comb-type structure of the mobile mass portion
16
.
In
FIG. 1
, a driving signal is applied to the optical attenuator so that an electric potential difference occurs between the driving electrodes
12
a
and
12
b
and the ground electrode
14
. Then, an electrostatic force is generated at the interdigitated comb structure between the mobile mass portion
16
and the extended portions
13
a
and
13
b
, and the mobile mass portion
16
is moved to the extended portions
13
a
and
13
b
by the electrostatic force. As the mobile mass portion
16
moves, the beam shutter
17
is interposed between the transmitting terminal
20
and the receiving terminal
30
, thus partially cutting off light incident on the receiving terminal
30
.
The above-described MEMS variable optical attenuator requires the uniform amount of the attenuation of light at any usable wavelength, and the minimal variation of the attenuation of light due to disturbance such as variations of time, wavelength, polarization, and vibration.
However, the conventional variable optical attenuator has problems such as a great wavelength dependent loss (WDL) and a great polarization dependent loss (PDL).
FIGS. 2
a
and
2
b
are schematic views illustrating optical attenuation effect by a planar beam shutter of the conventional variable optical attenuator.
With reference to
FIG. 2
a
, light outputted from the transmitting terminal
20
and inputted to the receiving terminal
30
is partially cut off by the planar beam shutter
27
. Here, the beam shutter
27
is made of silicon the same as the conventional actuator.
A part (R) of light with a relatively large amount is reflected by the beam shutter
27
and prevented from being incident on the receiving terminal
30
. However, since the beam shutter
27
is made of silicon with excellent optical transmission, a further part (T) of light is incident on the receiving terminal
30
. Another part (S
1
) of light is scattered and then incident on the receiving terminal
30
, and yet another part (S
2
) of light is back-reflected and re-incident on the transmitting terminal
20
. In order to improve optical cut-off effect of the planar beam shutter
27
made of silicon, a beam shutter
37
, as shown in
FIG. 2
b
, coated with a metal with high reflectivity (not less than approximately 90%) such as Au, Ni, Cu, Al, and Pt.
FIG. 2
b
shows the beam shutter
37
coated with Au as a reflective metal. The beam shutter
37
provided with an Au coating layer
38
reflects the part (R) of light with a relatively large amount, and prevents the part (R) from being incident on the receiving terminal
30
, like
FIG. 2
a.
However, the beam shutter
37
provided with the Au coating layer
38
reflects parts of light, thus generating the scattered parts (S
1
and S
2
) of light. The scattered part (S
1
) of light is incident on the receiving terminal
30
, and the scattered part (S
2
) of light is incident on the transmitting terminal
20
. For example, when a beam shutter provided with an Au coating layer is used to cut off 50% of the total amount of light outputted from the transmitting terminal
20
to be inputted to the receiving terminal
30
, the amount of the cut-off part (R) of light is approximately 49% of the total amount of light, and the amount of the scattered part (S
1
+S
2
) of light is approximately 1% of the total amount of light.
Although the amount of the scattered part of light is small, the amount of the back-reflected part of light is increased by the scattered part of light, and sensitively varied according to variations of wavelength and polarization.
Accordingly, when the scattered part of light is incident on the receiving terminal, the WDL and PDL of the variable optical attenuator are increased.
As described above, in the conventional MEMS variable optical attenuator, the amount of the back-reflected part of light is increased by the imperfect cut-off effect of the beam shutter, and the WDL and PDL are increased, thus reducing the reliability of the attenuator.
Accordingly, there has been required a MEMS variable optical attenuator, which minimizes the amounts of back-reflected and scattered parts of light to reach the transmitting terminal, and cuts off the transmitted and scattered parts of light so as not to reach the receiving terminal.
SUMMARY OF THE INVENTION
Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide a MEMS variable optical attenuator, which minimizes the amount of back-scattered part of light due to the reflection of a beam shutter, and cuts off the transmitted and scattered parts of light so as not to

Affiliated with

Also associated with

Rating

MEMS variable optical attenuator does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with MEMS variable optical attenuator, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and MEMS variable optical attenuator will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3279564