Double hermetic package for fiber optic cross connect

Details Double hermetic package for fiber optic cross connect Double hermetic package for fiber optic cross connect

2000-04-14

2002-04-16

Schuberg, Darren (Department: 2872)

Optical waveguides

With optical coupler

Switch

C385S018000, C385S019000, C359S223100, C359S224200, C359S872000

Reexamination Certificate

active

06374007

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to fiber optic cross connects, and more particularly to the packaging for fiber optic cross connects.
BACKGROUND OF THE INVENTION
The use of optical cross connect (OXC) switching systems are well known in the art for directing a light beam from one optical port in an optical transmission system to another optical port. In a typical OXC, a plurality of input optical fibers, or ports, carry light beams into the OXC. The OXC then directs, or switches, the light beams to their respective plurality of output ports. Many conventional OXCs perform the switching utilizing numicromirrors, which are micro-machined onto a substrate. The micromirrors are used to reflect a light beam from an input port to a particular output port. In this specification, the words “input” and “output” are used to indicate a direction of travel for a light beam into and out of, respectively, a switch. In reality, the input and output ports can be used simultaneously for input and output, as is the case in bi-directional data transfer.
High port count switches utilizing micromirrors are of high demand in the industry. Such switches require a tight packing density of the micromirrors onto the substrate. Some conventional switches use a digital switching matrix for N input and N output ports with an N×N array of micromirrors. This requires a total of N
2
number of micromirrors. However, this architecture becomes impractical for switch port counts greater than a few hundred.
Some conventional switches use an analog switching matrix for N input and N output ports. This requires
2
*N micromirrors. In this configuration, two separate substrates, or one very large substrate, are necessary to accommodate port counts greater than a few hundred. However, the use of more than one substrate is cumbersome as they need to be aligned to each other within the package of the switch. This adds complexity to the assembly of the package and increases package size. Also, with a hundred or more micromirrors on a single substrate, or one half of a two-substrate OXC, device yield is compromised due to the large number of possible failure points. Additionally, the optical components of the OXC are typically hermetically sealed. Such hermetic sealing of the optical components requires additional complex steps in the manufacturing process, such as metallization of the fibers or optical component attached to the fibers.
For many conventional switches, each micromirror also utilizes different amounts of the Rayleigh Length for redirecting light beams. The Rayleigh Length is a maximum distance that a beam of light can be kept collimated. The Rayleigh Length depends on the wavelength and minimum diameter “waist” of the beam. The Rayleigh Length is well known in the art and will not be described in detail here. This “redirection length”, as used in this specification, is typically the length from a collimator to an input mirror and from an output mirror to another collimator. The remaining portion of the Rayleigh Length, i.e., the length from the input mirror to the output mirror, is available for scanning. Because the redirection length varies from micromirror to micromirror, the scanning length also varies. This requires the switch to be designed so that the longest redirection length is assumed for all micromirrors in the switch in order to minimize optical loss and crosstalk. However, in assuming the longest redirection length for all micromirrors, the density of micromirrors is compromised.
Accordingly, there exists a need for an improved OXC package which reduces the size of the package while still allowing a high port count. The improved package should also minimize optical loss and crosstalk and also allow a tight packing density of micromirrors. The present invention addresses such a need.
SUMMARY OF THE INVENTION
The present invention provides a double fiber optic cross connect (OXC) package. The double package includes a substrate with a first surface and a second surface; a micromirror array coupled to the second surface of the substrate; a first cap optically coupled to the micromirror array; and a second cap optically coupled to the micromirror array. The first cap, along with a substrate populated with a micromirror array and a set of sidewalls, form a volume which is preferably hermetically sealed. This volume is further packaged by the second cap with another set of sidewalls. With the first cap, only a short distance is used in redirecting the light. This short distance is uniform for each micromirror in the switch. The major portion of the beam is thus available for scanning. With the second cap, the light beam is folded during the switching operation, resulting in a smaller switch package. By folding the light in the switch architecture, the size of the switch package is reduced. Using the substrate in combination with a modular approach to substrate population allows for a single substrate switch with a higher device yield and scalability. Integrated circuits may be placed on the same substrate as the micromirrors, and the complexity of the assembly process is reduced.


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“Optical-layer Networking: Opportunities for and Progress in Lightwave Micromachines,” OFC 2000 Tutorials, Lih Y. Lin and Evan Goldstein, ATT Resaerch, (Mar. 10, 2000).

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