Optical cross connection switch using voltage-controlled interferometric optical switching elements

This application claims benefit of 60/331,796 filed Nov. 20, 2001.

This invention relates to optical communications, and more particularly to an optical cross-connection device using micro-mirror elements.

Global communications traffic in the form of voice, data, and video has grown tremendously in the past decade. To meet demand, communications bandwidth capacity and geographic coverage have been substantially expanded. Optical signals sent over optical fiber have been a key factor in enabling these advances.

A growing number of communications carriers are deploying optical switches, that is, switches that steer light pulses among different fiber spans without converting them into electrical signals at any point. The advantages of all-optical switching are significant. Optical switches promise to relieve bottlenecks, reduce costs, and provide good scalability.

Researchers are at work on various technologies for optical switching. These include the use of tiny micro-mirrors, liquid crystals, bubbles, holograms, and thermo- and acousto-optics. It may be that different of these technologies are suitable for different applications. For example, some switching fabrics may be better for large scale applications such as optical cross connects, whereas other technologies may be more appropriate for optical add-drop multiplexers or gear used in metro as opposed to long haul networks.

One aspect of the invention is an optical switch for switching a beam of light from an input fiber to an output fiber, the input fibers being parallel to the output fibers. The switch comprises an array of voltage-controlled interferometric optical switching elements. The elements are arrayed such that the axis of each input fiber and each output fiber is incident on an element at an angle of substantially 45 degrees. The array has two rows of elements such that each input beam and each output beam have an associated pair of elements, one in each row. The array also has an additional pair of elements at one end operable to reflect an input beam from one direction across the second row to the opposite direction across the first row. The array's configuration permits the elements to be electronically operated such that the output beam is outgoing in a direction parallel to the path of the input beam.

An advantage of the invention is that it provides for an optical switch for numerous applications, such as for communications, laser displays, projection displays, hologram memory writers, switching between storage networking devices, DWDM signal separation, and others. Applications for optical communications routing are especially promising.

FIG. 1 illustrates a typical voltage-controlled interferometric (VCI) optical switch.

FIG. 2 illustrates the operation of the switch of FIG. 1 .

FIG. 3 is a top plan view of a first embodiment of a cross connection switch in accordance with the invention.

FIG. 4 is a perspective view of the switch of FIG. 3 .

FIG. 5 is a top plan view of a second embodiment of the cross connection switch in accordance with the invention.

FIG. 6 illustrates how the switch of FIG. 5 may be operated in a one-to-many mode.

The following description is directed to various embodiments of an all-optical switch, suitable for dense wavelength division multiplexing (DWDM). DWDM is a fiber-optic transmission technique that employs light wavelengths to transmit data parallel-by-bit or serial-by-character.

Various embodiments of the invention are described, each being a high speed optical cross connection comprising a plurality of voltage-controlled interferomeric optical switches.

Voltage-Controlled Interferometric Optical Switches

FIG. 1 illustrates a voltage-controlled interferometric (VCI) optical switch 10 . Switch 10 may be made using semiconductor fabrication techniques, and FIG. 1 is a cross sectional view of the layers of switch 10 .

A first transparent electrode 12 is fabricated over a substrate 11 . The next layer 13 is a dielectric mirror, which may itself be comprised of multiple layers. An electro-optic polymer layer 14 separates the first mirror layer 13 from a second dielectric mirror layer 15 . The final layer is a second transparent electrode layer 16 .

The electro-optic polymer layer 14 is made from a material whose optical reflective index varies in response to a change in electric field magnitude. As illustrated schematically by power source circuit 17 , a voltage difference is applied to the two electrode layers 12 and 16 .

FIG. 2 illustrates the operation of switch 10 , including circuitry 21 for applying a voltage to operate switch 10 . When an optical length of electro-optical polymer layer 14 is equal to one-half wavelength of incident light, switch 10 is transparent for that wavelength. Therefore, switch 10 operates in response to changing the applied voltage.

In FIG. 2 , the incoming beam of light is incident on switch 10 at an angle. For purposes of this invention, it will be assumed that the angle of incidence is approximately 45 degrees. Because the axis of the incoming beam is not perpendicular to the face of switch 10 , the switching property of switch 10 depends on polarization. Thus, a polarizer 22 is placed in the path of the beam of light reflected from switch 10 . If the incident beam has been polarized, polarization at the output would not be necessary.

Optical Switching Arrays, Using VCI Elements

As explained above, a VCI optical switch 10 works as a simple optical switch, having either a reflection or transmission mode for a specific wavelength depending on an applied voltage. As explained below, an arrangement of an array of switches 10 , with a proper tilting angle, can be used as an optical cross connection switch.

FIGS. 3 and 4 illustrate a first embodiment of a cross connection switch 30 , comprising an array of VCI switching elements, such as switch 10 . FIG. 3 is a top view, and FIG. 4 is a perspective view of switch 30 .

The VCI elements 10 are arrayed with a tilting angle of 45 degrees. Input/output optical fibers 32 , which transmit laser beams, are installed parallel to each other and such that their optical axes are adjusted to elements 10 . Elements 10 are configured to operate as being transparent in an “off” state and reflective in an “on” state for a specific wavelength.

Switch 30 has two rows of elements 10 . Each fiber 32 has an associated element 10 in the first row 30 a and an associated element in the second row 30 b.

In operation, an input beam enters switch 30 via an input fiber 32 and is transmitted through the corresponding element 10 in the first row 30 a . The beam is then transmitted across the second row 30 b by “off” elements 10 , and back up to the first row 30 a by two “on” end elements 10 . The beam then traverses the first row 30 a , through all appropriate “off” elements 10 , until it reaches the element 10 corresponding to an output fiber 32 . This element 10 is “on” so that the beam is reflected into the output fiber 32 . In this manner, the signal from any input fiber 32 may be routed to an output fiber 32 .

As indicated in FIG. 3 , various optics 33 may be placed in the path of the incoming beam. These optics 33 may include various lenses and prisms, as well as a polarizer. As discussed above, polarization is used because of the angle of incidence of the face of switching elements 10 relative to the incoming beam. Similarly, optics 34 may be placed in the path of the outgoing beam, including a polarizer when the incoming beam is not polarized.

FIG. 4 further illustrates switch 30 . Each switching element 10 is installed with an angle of 45 degrees against the optical axis of the input/output fibers 32 . The output beam is transmitted in parallel with the input beam.

FIG. 5 illustrates a second embodiment of the invention, a cross connection switch 50 having the beam paths in a perpendicular configuration. Switch 50 has as many rows as output fibers 52 . In the example of FIG. 5 , there are four output fibers 52 and thus four rows of switch 50 . An input beam enters switch 50 and is transmitted to the row corresponding to the desired output fiber 52 . It is then reflected at a right angle toward the output fiber 52 and transmitted by intervening elements 10 so that it may enter the output fiber 52 . In this manner, input beams are transmitted perpendicularly towards output fibers 52 .

FIG. 6 illustrates how switch 50 may be operated in a one-to-many mode. By adjusting the applied voltage between the “on” state and the “oil” state, the beam can be split. Each element 10 in the path of the input beam that corresponds to a desired output fiber 52 is adjusted to this “mid-level” state so as to both transmit and reflect the signal.

Other Embodiments

Although the present invention has been described in detail, it should be understood that various changes, substitutions, and alterations can be made hereto without departing from the spirit and scope of the invention as defined by the appended claims.