Optical waveguides – With optical coupler – Switch
Reexamination Certificate
2000-07-19
2003-12-02
Hgo, Hung N. (Department: 2633)
Optical waveguides
With optical coupler
Switch
C385S017000, C385S020000
Reexamination Certificate
active
06658177
ABSTRACT:
FIELD OF INVENTION
The present invention relates to the fields of wave and optical communication switching and, more particularly, to switching devices using arrays of switches, and in particular microelectromechanical switches.
BACKGROUND OF INVENTION
In fiber-optic communication systems, information is transmitted as a light or laser beam along a glass or plastic wire, known as a fiber. A significant amount of electronic communication and information transfer is effected through fiber-optic lines due to their much broader bandwidth and lower susceptibility to electromagnetic interference compared to conventional copper or metal wires. For example, much of the Internet and many long distance telephone communication networks are connected with fiber-optic lines. However, fast and efficient switching between optical fibers in a fiber-optic network has been difficult to achieve. Switches are needed to route signals at the backbone and gateway levels of these networks where one network connects with another, as well as at the sub-network level where data is being transported from its origin or to its destination. In particular, in a wavelength division multiplexed (WDM) optical fiber network, many channels, each occupying a distinct wavelength of light, are multiplexed within the same fiber. In a WDM network, optical multiplexers and demultiplexers are need to combine component wavelength signals into the main optical fiber path and/or separate the optical channels from the main fiber path.
Various prior art switching technologies have been employed in fiber-optic systems. For example, in electrical cross-connect (or electro-optical) switch technology, the optical signal is transformed into an electrical signal, a switching operation is performed with an electronic switch, and the electrical signal is then transformed back into the optical domain. Another prior art solution is to use an optical switch or cross-connect (OXC) capable of connecting and disconnecting optical fibers in the optical domain. Integrated optical OXC devices have been used for this purpose. These devices are constructed of a material, such as lithium niobate, generally in a planar waveguide configuration that allows switching action to take place between various input and output ports. More recently, optical switches based on emerging microelectromechanical system (or MEMS) technology have received considerable attention. MEMS, including micromechanical or micromachined systems, boast considerable promise for overcoming many of the limitations associated with alternative prior art fiber-optic switching technologies, especially those limitations relating to cost, efficiency, size, wavelength dependence, cross-talk, and signal attenuation. As used herein, the term microelectromechanical (MEMS) device is intended to embrace devices that are physically small and have at least one component produced using micromachining or other microfabrication techniques, and the term MEMS device includes microactuators, micromechanical devices, and micromachine devices.
Optical MEMS systems, also referred to as microoptoelectromechanical systems (MOEMS), use microoptical elements that reflect, diffract, refract, collimate, absorb, attenuate, or otherwise alter or modulate the properties and/or path of a light beam or signal. These types of optical switches can be made very compact and small, typically within the micrometer to millimeter range. The insertion loss of a MOEMS switch interface is comparable to alternative technologies, and occurs mainly at the entry port of the switch where light leaves a first optical fiber and at the exit port of the switch where light re-enters a second optical fiber. These losses are due to the enlargement of the beam dimensions in free space, and generally the greater the distance travelled by a light beam in free space, the greater the insertion loss of the switch will be (lenses may be used to help decrease this effect). The medium of a MOEMS switch is typically air, but a vacuum, inert gas, or other suitable fluid may also be used. The transmission of light within the switch medium, if kept relatively small, amounts for only a small portion of the overall attenuation. Additionally, the non-blocking medium of the switch ensures that no interference occurs when different light paths cross, enabling light beams to traverse without mutual effect, attenuation, or cross-talk: see generally, Hecht J., “Optical switching promises cure for telecommunications logjam”,
Laser Focus World
, page 69, (September 1998), the contents of which are incorporated herein by virtue of this reference.
For example, micromachined optical switches often use small mirrors that move to perform a switching operation. By actuating the mirror or moving element between a first position in which a light beam is allowed to pass unaffected by the mirror and a second mirror position in which the moving element reflects or interferes with the light beam, the path of an input light beam can be redirected into different outputs or otherwise interfered with. The use of mirrors, in particular, is advantageous since they operate independently of wavelength when reflecting an optical beam. However, MEMS switches or valves may also use other types of moving elements such as attenuators, filters, lenses, collimators, modulators, and absorbers to perform a desired switching operation. In general, to achieve low attenuation losses in a micromachined optical switch, the mirror or other optical element should be very smooth and of optical grade. In addition, the principle and means used to actuate the moving element of a MEMS device should be fast, simple, and provide reproducible and accurate alignment of the moving element. Furthermore, the actuator must be able to move that element by a sufficient amount to accomplish the switching task. An improved MEMS device capable of advantageously acting as such an optical switch is disclosed in applicant's co-pending U.S. patent application Ser. No. 09/619,013, filed concurrently herewith and entitled “Microelectromechanical Device with Moving Element”, the contents of which are incorporated herein by reference.
To increase the capacity of fiber-optic communication networks, there is a growing desire and need to expand the number of fibers used in the network and/or the number of wavelength channels in a WDM fiber system. It is desirable and often necessary in these networks to have the capability to switch a given one of a plurality of inputs to a specific output. Consequently, the expansion of fiber-optic network capacity requires the use of high capacity switches capable of handling an increasing numbers of input and output ports. Such switches should be fast, efficient (i.e. have low losses), and compact. In addition, it is also desirable that the switching configuration be “non-blocking” so that the switching of one input fiber to an output fiber does not interfere with the transmission of any other input fiber to any other output fiber.
Prior art optical cross-connects (also referred to as cross-bar configurations) typically perform the desired switching between input and output ports in a single two-dimensional rectangular array. For example, Lin in U.S. Pat. No. 5,960,132 describes an array of optical micromachined switches each comprising a reflective panel. An M-input by N-output cross-connect of the type taught by Lin, requires M·N switching elements. Furthermore, for a uniformly spaced array of switching elements each separated by the distance d, the maximum possible free space switching distance between an input and output port is given as (M+N)×d. As a result, as the number of inputs and/or outputs in these optical cross-connects increases, the number of switches required to maintain full (non-blocking) switching flexibility rises rapidly, as does the size or footprint of the switching array. The insertion loss and cross-talk for certain input-output combinations in these two-dimensional cross-connects may also become unacceptably high due to a lengthening of the
Hgo Hung N.
Memlink Ltd.
Pennie & Edmonds LLP
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