Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
2002-05-23
2003-12-09
Dang, Hung Xuan (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C359S245000, C385S014000, C385S088000, C385S089000, C385S092000, C385S094000
Reexamination Certificate
active
06661554
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to electro-optical components, and specifically to electrical biasing of the components.
BACKGROUND OF THE INVENTION
In order for an electro-optical component, such as an Electro-Absorption Modulator (EAM) or a photo-diode detector (PDD), to function correctly, the element typically requires the ability to be independently DC biased and AC modulated. In addition to these electrical requirements, the element usually also needs to be aligned optically.
FIG. 1
illustrates apparatus, known in the art, for electrically and optically coupling an electro-optical component
10
. Component
10
is mounted on a first capacitor
24
, which typically has a capacitance of the order of 1 nF, so that a lower electrode
17
of the component mates with a first electrode
19
of the capacitor. Capacitor
24
is in turn mounted on a conductive optical bench
26
, so that a second electrode
11
of the capacitor is in electrical contact with the optical bench. A second capacitor
28
, typically having a capacitance of the order of 1 &mgr;F, is coupled in parallel with capacitor
24
, the two capacitors forming a low impedance path for low and high AC frequencies between the optical bench and the optical element. Optical bench
26
is electrically connected to a ground conductor
12
of a transmission strip-line
16
. A second conductor
14
of the transmission strip-line is bonded, by a wire
18
, to an upper electrode
22
of component
10
. Typically, a resistor
21
may be connected between electrode
22
and ground
12
. The resistor serves as an impedance match and as a DC return.
Electro-optical component
10
is aligned with an optical element
20
, such as a fiber optic, by adjusting optical element
20
. When alignment is achieved, optical element
20
is mechanically coupled to the optical bench.
The arrangement of elements as shown in
FIG. 1
provides DC isolation of electro-optical component
10
from ground conductor
12
, while enabling the component to be modulated by an AC voltage via capacitors
24
and
28
. Thus, electro-optical component
10
may be DC biased independent of any AC modulation provided to the element, by applying a DC bias level to electrode
17
and applying a ground potential to electrode
22
via resistor
21
. However, this method of arranging elements in order to be able to DC bias electro-optical component
10
separates the component from optical bench
26
, causing severe difficulties in aligning the component. An improved arrangement for aligning an electro-optical component is thus required.
SUMMARY OF THE INVENTION
It is an object of some aspects of the present invention to provide a method and apparatus for biasing and optically aligning an electro-optical component.
In preferred embodiments of the present invention, an electro-optical assembly comprises a transmission line which is coupled to an electro-optical component. The electro-optical component comprises a first and a second electrode coupled to an optical region, the optical region being aligned optically. The transmission line, preferably a micro-strip line, comprises a “live” conductor and a ground conductor, the ground conductor being divided into a first ground section and a second ground section by a non-conducting gap formed in the second conductor, so that the two ground sections are mutually isolated from a direct current (DC) point of view. The two ground sections are connected by one or more capacitors which effectively short-circuit the two sections from an alternating current (AC) point of view. The second ground section is bonded to a conductive optical bench, upon which the electro-optical component is positioned directly, the first electrode of the component being bonded to the optical bench. The second electrode of the electro-optical component is electrically connected to the live conductor of the micro-strip.
The assembly thus enables the electro-optical component to be DC biased independently of an AC level which feeds the component. Furthermore, since the electro-optical component mates directly with the optical bench, optical alignment of the component is significantly easier than electro-optical assemblies wherein the component is not in direct contact with the optical bench.
In some preferred embodiments of the present invention, the assembly is implemented as two sub-assemblies. A first sub-assembly comprises the transmission line implemented as described above and coupled with the one or more capacitors. A second sub-assembly comprises the electro-optical component mated with the optical bench. Preferably, the second sub-assembly is used to optically align the electro-optical component, and then the first sub-assembly is coupled to the second sub-assembly, to form the complete electro-optical assembly.
There is therefore provided, according to a preferred embodiment of the present invention, an electro-optical assembly, including:
an optical sub-assembly, including:
an electro-optical component including an optical region and a first and a second electrode coupled thereto; and
a conductive optical bench in contact with the second electrode of the electro-optical component, the optical bench being adapted to permit optical alignment of the electro-optical component while making such contact; and
a transmission line including:
a live conductor;
a ground conductor insulated from the live conductor; and
a port adapted to receive a signal, such that the live and ground conductors are coupled to the first and second electrodes of the electro-optical component so as to convey the signal between the port and the electro-optical component and to provide a direct current (DC) bias level to the electro-optical component independent of the signal.
Preferably, the conductive optical bench is in direct mechanical and electrical contact with the second electrode.
Preferably, the transmission line includes a micro-strip line which is adapted to operate at frequencies up to approximately 50 GHz.
Preferably, the ground conductor includes a first ground section and a second ground section separated from the first ground section by an insulating gap, wherein the first and second ground sections are coupled together capacitively, and wherein the first ground section is connected to the conductive optical bench.
Further preferably, the first and second ground sections are coupled by at least one capacitor so as to form an effective short-circuit between the two sections at alternating current (AC) frequencies in a range from approximately 1 kHz to approximately 50 GHz.
Further preferably, the transmission line and the at least one capacitor are fabricated as an electrical sub-assembly, and the electro-optical assembly is fabricated by coupling the electrical sub-assembly to the optical sub-assembly.
Preferably, the optical bench is adapted to permit the optical alignment after the live and ground conductors of the transmission line are coupled to the first and second electrodes of the electro-optical component.
Preferably, the assembly includes circuitry which matches an impedance of the electro-optical component to the impedance of the transmission line.
Further preferably, the circuitry includes a resistor connected between the first electrode and the ground conductor.
Alternatively or additionally, the circuitry includes a resistor and a capacitor connected in series between the first electrode and the conductive optical bench.
There is further provided, according to a preferred embodiment of the present invention, an electro-optical assembly, including:
an electro-optical component including an optical region and a first and a second electrode coupled thereto;
a conductive optical bench, in contact with the second electrode of the electro-optical component, the bench being adapted to permit optical alignment of the electro-optical component while making such contact;
a transmission line including a live conductor and a ground conductor insulated from the live conductor, the live conductor being bonded to the first elect
Cyoptics (Israel) Ltd.
Dang Hung Xuan
Darby & Darby
Tra Tuyen
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