A Switch/Variable Optical Attenuator (SVOA) includes a die including at least one 2×2 optical switch and a respective integral variable optical attenuator for each of the at least one 2×2 optical switch. Each of the at least one 2×2 optical switches includes an INPUT optical port, an OUTPUT optical port, an ADD optical port, and a DROP optical port. The INPUT optical port is connected to the OUTPUT optical port in one state of the switch, and the ADD optical port is connected to the OUTPUT optical port in a second state of the switch. A single air gap exists between the ports. The VOA is mounted on the die and is associated with the switch for selectively attenuating optical signals transiting the air gap from one port to another.

RELATED APPLICATIONS

The present application is related to U.S. patent application Ser. No. 09/794,773, filed Feb. 27, 2001, entitled “Bi-stable Micro-actuator and Optical Switch”, and that application is hereby incorporated by reference in its entirety into the present specification. Any document incorporated by reference into application Ser. No. 09/794,773 is also hereby incorporated into the present specification.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to optical switches and variable optical attenuators, and, more particularly, to a Switch/Variable Optical Attenuator (“SVOA”) including an integrated Micro-Electro-Mechanical System (“MEMS”) optical switch and MEMS Variable Optical Attenuator (“VOA”).

2. Description of the Related Art

In the past few years, the demand for telecommunications services has increased the bandwidth requirements placed on the major carriers. Accordingly, these major carriers have had to add equipment to handle the increased load. This increases the total board space needed for such equipment, thereby resulting in a need for a reduced product footprint; that is, it would be advantageous to decrease the size of the needed equipment. One method used to decrease equipment size is to develop new-technology products that are inherently smaller and more compact. For example, the industry standard in small-part-count optical switches had been opto-mechanical actuators. These opto-mechanical actuators are being replaced by new devices, based on MEMS technology, that are smaller in size and more reliable.

Integrating several functions into the same package can also effect a size reduction. Unlike electrical components, in which the electrical connections are obtained simply by soldering the components into a circuit board, optical components have fibers that must be connected either by attaching connectors at the ends of the fibers or by fusion spicing the fibers together. Also, room must be left to coil or wrap any extra fiber in such a way that it will not be damaged or kinked. This effectively increases the required board space for each component. Eliminating the fiber and the connection between two components, and integrating the components into a common enclosure, can save board space. A good example of this concept is the technology of planar waveguides. By providing waveguide patterns on a substrate material, various functions can be realized on the same chip.

The advantages of planar waveguide devices do not come without drawbacks. For example, optical switches using planar waveguides tend to be slower and more lossy than MEMS devices. Although the MEMS devices have better performance characteristics, they are generally considered more difficult to integrate. MEMS devices typically depend on free space propagation and mirrors to change the light path. Thus, MEMS devices are limited in the number of functions that can be integrated into a given space. Ideally, it would be desirable to have a device that has the performance characteristics of MEMS devices and the integration factor of planar waveguides.

In the expanding telecommunication field, several combinations of components are becoming standardized. One such combination is the Reconfigurable Optical Add Drop Multiplexer (“ROADM”), illustrated inFIG. 1. ROADMs are being used in almost every node of major optical networks, and will find more uses in other applications, such as inter-office networks.

As illustrated inFIG. 1, a multiplexed optical input signal IN is inputted to an optical demultiplexer100where it is demultiplexed into sixteen optical signals, for example. The sixteen optical signals are respectively inputted to sixteen optical switches, indicated at120, whose respective outputs are provided via respective Variable Optical Attenuators (VOAs)130to an optical multiplexer140. The output of the optical multiplexer140is inputted to an optical splitter150having one output, OUT, which is the output of the ROADM, and having another output which is inputted to an Optical Channel Monitor (OCM)160having Voltage Outputs that may be used for monitoring purposes, these Voltage Outputs reflecting the characteristics of the optical signal inputted to the OCM160from the optical splitter150.

One technique for implementing the ROADM illustrated inFIG. 1is to use arrayed waveguides for the multiplexer140and demultiplexer100, and to use commercially-available MEMS devices for the switches120and the VOAs130.

The add/drop function of the ROADM is usually performed with a 2×2 switch220, as illustrated inFIG. 2. Such a 2×2 switch220has an Inserted State and a Bypass State. In the Bypass State, the input In is connected to the output Out. In the Inserted State, the ADD input is connected to the OUT output while the input IN is connected to the DROP output. Thus, an incoming signal can either be allowed to pass through, or be dropped out and a new signal inserted in its place. In either case, fluctuations occur in the signal power, and the added signal almost never has the same signal power level as the incoming signal. Accordingly, it is necessary to equalize and level the signal power level. This may be effected by connecting a VOA130between the output of the switch220and the multiplexer140(not shown inFIG. 2). Unfortunately, a connector or fusion splice210must be provided between the switch220and the VOA130.

If the switch220and VOA130ofFIG. 2could be combined, the combination thereof would be simplified by eliminating one package and one connector or splice, and the resulting combination would have a reduced footprint and reduced assembly time, as well as improved reliability. On the manufacturing side, the integration of these two devices would eliminate four fiber end-face preparations and would eliminate one entire device packaging process.

SUMMARY OF THE INVENTION

In view of the above, it is an object of the present invention to provide a Switch/Variable Optical Attenuator (SVOA) by integrating a MEMS Optical Switch and a MEMS Variable Optical Attenuator (VOA).

These and other objects may be effected by providing a Switch/Variable Optical Attenuator (SVOA) including: a die including at least one 2×2 optical switch and a respective integral variable optical attenuator for each 2×2 optical switches. Each 2×2 optical switch includes an INPUT optical port, an OUTPUT optical port, an ADD optical port, and a DROP optical port. The INPUT optical port is connected to the OUTPUT optical port in one state of the associated optical switch, and the ADD optical port being connected to the OUTPUT optical port in a second state of the associated optical switch. A single air gap exists between the ports. The VOA is mounted on the die and is associated with the switch for selectively attenuating optical signals transiting the air gap from one port to another.

In the SVOA described above, there may be n 2×2 optical switches and respective integral variable optical attenuators, n being an integer greater than 1. Each optical switch may be an Optical Micro-Electro-Mechanical System (MEMS) Switch.

Furthermore, in the SVOA described above, each respective variable optical attenuator may include a MEMS variable optical attenuator.

The foregoing, and a better understanding of the present invention, will become apparent from the following detailed description of an example embodiment and the claims when read in connection with the accompanying drawings, all forming a part of the disclosure of this invention. While the foregoing and following written and illustrated disclosure focuses on disclosing an example embodiment of the invention, it should be clearly understood that the same is by way of illustration and example only and that the invention is not limited thereto. This spirit and scope of the present invention are limited only by the terms of the appended claims.

DETAILED DESCRIPTION

Before beginning a detailed description of the subject invention, mention of the following is in order. When appropriate, like reference numerals and characters are used to designate identical, corresponding, or similar components in differing drawing figures. Furthermore, in the detailed description to follow, example sizes/models/value/ranges may be given, although the present invention is not limited thereto. Still furthermore, any clock or timing signals in the drawing figures are not drawn to scale but rather, exemplary and critical time values are mentioned when appropriate. When specific details are set forth in order to describe an example or embodiment of the invention, it should be apparent to one skilled in the art that the invention can be practiced with, or without, variations of these specific details. Lastly, it should be apparent that differing combinations of hard-wired control circuitry and software instructions may be used to implement embodiments of the present invention; that is, the present invention is not limited to any specific combination of hardware and software.

FIG. 3schematically illustrates an SVOA310. In such an SVOA, a VOA311, which is integrated with a 2×2 optical switch, is located upstream of the switch output OUT. It is to be noted that both the switch and the VOA311can be actuated by either electrostatic or thermal MEMS actuators, for example. These actuators have been omitted from some of the drawing figures for the sake of clarity. Furthermore, it is noted that the switch may be a bistable switch, that is, the switch may be latched in either a blocking or non-blocking mode.

As illustrated inFIG. 4, one possible arrangement for an SVOA310is to combine a MEMS switch with an optical attenuation vane450on the output side thereof. One switch design, having a switch actuator420and a VOA actuator430, uses a lensed fiber, for example, to collimate and transmit light across an air gap to another lensed fiber. A mirror blade440located between the fibers can be used to redirect the light to a third fiber. If sufficient room is provided between the face of the output fiber and the mirror blade440, it is possible to locate an attenuator vane450therebetween to block part of the light and thereby effect attenuation. The VOA actuator430moves the attenuator vane450so as to control the amount of attenuation. The IN terminal is at the end of fiber442, the DROP terminal is at the end of fiber441, the OUT terminal is at the end of fiber443, and the ADD terminal is at the end of fiber444. The switch actuator420selectively moves the mirror blade440so as to optically connect either the IN terminal with the OUT terminal, or the ADD terminal with the OUT terminal.

FIG. 5illustrates a pass-through switch operation with optical attenuation of an SVOA in accordance with an example embodiment of the present invention. As clearly illustrated inFIG. 5, the mirror blade440is out of the way, thereby allowing light to pass across the air gap from fiber442to fiber443. The attenuator vane450partially blocks the passage of light across the air gap and may be incrementally moved, thus providing different levels of attenuation in accordance with the amount of light being blocked.

FIG. 6illustrates a blocking function of a switch with optical attenuation of an SVOA in accordance with an example embodiment of the present invention. As clearly illustrated inFIG. 6, light is inputted into the air gap by fiber444and is reflected by the mirror blade440into fiber443. The attenuator vane450still partially blocks the passage of light across the air gap so as to still provide different levels of attenuation in accordance with the amount of light being blocked.

FIG. 7illustrates exemplary component spacing of an SVOA in accordance with an example embodiment of the present invention, andFIG. 8illustrates a component spacing detail of the SVOA ofFIG. 7. For example, as illustrated inFIG. 7, the distance across the air gap700may be on the order of 200 microns, while the horizontal distance710between distant corners of the fibers442and443may be on the order of 230 microns, and the horizontal distance720between adjacent proximate corners of the fibers442and443may be on the order of 53 microns.

Similarly, as illustrated inFIG. 8, the horizontal width800of half the mirror blade440may be on the order of 1.5 microns. The horizontal width830of the attenuator vane850, which includes a bent portion to improve back-reflection, may be on the order of 5 microns. The horizontal distance810between the mirror blade440and the attenuator vane850may be on the order of 10 microns and the distance840between the attenuator vane850and the face of the fiber443may also be on the order of 10 microns. Furthermore, the distance820between the centerline of the mirror blade440and the corner of the fiber443may be on the order of 26.5 microns.

FIG. 9is a schematic perspective view of an SVOA in accordance with an example embodiment of the present invention. By including both a switch and a variable optical attenuator on the same chip die (e.g., a silicon substrate), the overall size can be reduced significantly as compared with a switch and a variable optical attenuator on separate chip dies. Because of this, any chip layout currently designed for the switch alone, could be readily expanded to accommodate the added variable optical attenuator. This is particularly important in the case of multi-device modules, where, for example, sixteen SVOAs might have substantially the same footprint as sixteen switches by themselves. Furthermore, if the operating voltages for the SVOAs are low enough, a microprocessor and D/A (Digital/Analog) converter might be included in the same package so as to provide a completely digital interface. This is not to preclude the use of the inventive SVOA in other applications.