The invention relates to EMI shielding, and more particularly, to an EMI shield that prevents EMI leakage from one or more optical ports in an optical communications module.
The U.S. Federal Communications Commission (FCC), which is one of several such similar organizations around the world, defines and enforces standards directed at limiting the amount of electromagnetic interference (EMI) emissions out of various electronic and electrical products. EMI emissions are generally undesirable as they can lead to malfunctioning of other electronic and electrical products that are adversely impacted when exposed to interference from unwanted radio frequency (RF) signals. However, it is difficult and expensive to provide EMI shielding elements that entirely eliminate EMI emissions out of products, such as, for example, optical communications modules. The difficulty mainly arises from challenges associated with creating EMI shielding elements that effectively conform to the individual shapes and sizes of assorted holes and openings located at various places in these products.
For example, EMI emissions may take place out of a hole that has been provided in an optical communications module for inserting an optical cable used for propagating optical signals into or out of the optical communications module. While it may be relatively simple to seal such a hole for preventing moisture or air from entering the optical communications module, it is more complicated to provide an EMI shield that prevents EMI emissions generated by electrical circuitry that may be contained inside the optical communications module from leaking out through this hole.
As another example, EMI emissions may take place out of an opening formed between two mating parts of an optical communications module. The opening may have been specifically provided for purposes of accommodating a connector. However, EMI emissions can leak out from gaps between the body of the connector and the sides of the opening. It is desirable that such EMI emission leaks be prevented, or at least attenuated as much as possible.
Unfortunately, various traditional solutions for EMI shielding of holes and openings such as those described above, have proven inadequate or inefficient, and it is therefore desirable to address at least some of these traditional shortcomings.
Many aspects of the invention can be better understood by referring to the following description in conjunction with the accompanying claims and figures. Like numerals indicate like structural elements and features in the various figures. For clarity, not every element may be labeled with numerals in every figure. The drawings are not necessarily drawn to scale, emphasis instead being placed upon illustrating the principles of the invention. The drawings should not be interpreted as limiting the scope of the invention to the example embodiments shown herein.
Throughout this description, embodiments and variations are described for the purpose of illustrating uses and implementations of inventive concepts. The illustrative description should be understood as presenting examples of inventive concepts, rather than as limiting the scope of the concept as disclosed herein. It should be further understood that certain words and terms are used herein solely for convenience and such words and terms should be interpreted as referring to various objects and actions that are generally understood in various forms and equivalencies by persons of ordinary skill in the art. For example, it should be understood that the phrase “optical port” generally refers to a part of an optical communications module that is configured to mate with various external components such as, for example, an optical connector disposed at the end of an optical cable. It should also be understood that the word “example” as used herein is intended to be non-exclusionary and non-limiting in nature. More particularly, the word “exemplary” as used herein indicates one among several examples, and it must be understood that no undue emphasis or preference is being directed to the particular example being described.
Generally, in accordance with a first illustrative embodiment, an optical communications module includes an upper housing portion mated to a lower housing portion with two optical ports projecting through two openings in a front surface of the mated assembly. The lower housing portion accommodates an electronic circuit assembly that can lead to a leakage of electromagnetic interference (EMI) from the front surface, particularly from the two openings that accommodate the two optical ports. An electromagnetic interference (EMI) shield in accordance with the disclosure is used to provide EMI shielding on the front surface to address the EMI leakage.
Attention is now drawn to
The lower housing portion 110 and the upper housing 105 can be provided in the form of a pivot and snap feature that allows the two portions to be mated with each together. Such a mating can result in a gap 115 that extends around the periphery of the optical communications module 100. In some implementations, an adhesive material may be placed on the gap 115 and a curing procedure used for curing the adhesive material. Even if the adhesive material is applied in such a manner so as to block all portions of the gap 115, this adhesive material, which is typically non-metallic in composition, fails to operate as an effective EMI shield. Consequently, one or more external EMI shielding elements (not shown) can be used to block EMI leakage out of the gap 115.
However, EMI leakage is not limited to the gap 115, and can leak out through various other openings of the optical communications module 100 as well as directly through various non-metallic surfaces. One area of the optical communications module 100 that is particularly vulnerable to EMI emissions is the front surface 132 of the front housing portion 130, which includes the first receptacle area 120 and the second receptacle area 125.
A portion of each of the first optical port 128 and the second optical port 129 projects out of the front surface 132 via respective openings that have been provided for this purpose. Specifically, a cylindrical body portion of the first optical port 128 projects out of the optical communications module 100 through a first circular opening 126. In this exemplary embodiment, the first circular opening 126 is formed by abutting a semicircular opening provided in a wall of the upper housing portion 105 with a corresponding semicircular opening provided in a wall of the lower housing portion 110. Similarly, a second circular opening 127 is formed by abutting another semicircular opening provided in the wall of the upper housing portion 105 with another corresponding semicircular opening provided in the wall of the lower housing portion 110.
In view of manufacturing tolerances and other factors, a first gap can exist between the cylindrical body portion of the first optical port 128 and the inner periphery of the first circular opening 126. A second gap can be similarly present between the cylindrical body portion of the second optical port 129 and the inner periphery of the second circular opening 127. EMI emissions can leak out of the optical communications module 100 not only through these two gaps but through other gaps, such as, for example, a seam 131 where the upper housing portion 105 abuts the lower housing portion 110. Furthermore, in some cases, EMI emissions can also directly leak out of the front surface 132 when electronic circuitry contained inside the optical communications module 100 is operated at certain regions of the radio-frequency (RF) spectrum.
For example, in one example implementation, the optical communications module 100 may contain electronic circuitry operating in the Gigahertz (GHz) range of RF frequencies. Such frequencies can readily propagate out of non-metallic surfaces as well as some types of ungrounded metallic surfaces. For example, a portion of one or both of the first optical port 128 and the second optical port 129 (an ungrounded metal body portion, for example) may act as an RF radiator element that radiates EMI. It is therefore desirable that EMI shielding be provided to not only block EMI emissions out of the front surface 132 as well as various openings in the front surface 132, but to also ground various portions of the first optical port 128 and the second optical port 129.
Each of the first optoelectronic module 206 and the second optoelectronic module 207 performs operations that include signal conversion between the optical domain and the electrical domain. For example, when the optical communications module 100 is configured to transmit optical signals out of the first optical port 128, the first optoelectronic module 206 converts electrical signals received from the electronic circuit assembly 205 into optical signals that are propagated out of the first optical port 128. On the other hand, when the optical communications module 100 is configured to receive an optical signal via the first optical port 128, the first optoelectronic module 206 converts the received optical signals into electrical signals that are then provided to the electronic circuit assembly 205.
In accordance with this illustrative embodiment, the EMI shield 210, which is configured for blocking EMI emissions radiating from the electronic circuit assembly 205 as well as any that may radiate out of the first optoelectronic module 206 and/or the second optoelectronic module 207, is inserted into a slot 215 that is provided in the lower housing portion 110. Further details pertaining to the EMI shield 210 are provided below with reference to other figures.
In this exemplary embodiment, the various components of the electronic circuit assembly 205 are mounted on a printed circuit board (PCB) 225. The PCB 225 can be a multilayer PCB and include a ground layer. The ground layer is connected to a set of ground pins that are a part of an edge connector 220. The edge connector 220 has other pins that are connected to various other components of the electronic circuit assembly 205 for purposes of conducting various electrical signals that are operated upon by the electronic circuit assembly 205. Such signals include power signals that are used to power the various components of the electronic circuit assembly 205.
When the optical communications module 100 is inserted into a host device (not shown) such as a router or a communications switch, the edge connector 220 mates with a corresponding connector in the host device. Each of the set of ground pins that are a part of an edge connector 220 makes contact with a matching set of ground pins in the corresponding connector of the host device. The ground pins located in the corresponding connector of the host device are connected to ground potential (typically via a chassis connection of the host device to what is known in the industry as “earth” ground). The set of ground pins located in the edge connector 220 thus get connected to ground potential, consequently grounding any EMI signals that enter the ground layer of the PCB 225.
Each of the first optoelectronic module 206 and the second optoelectronic module 207 is typically implemented in the form of a metal enclosure. The metal enclosure may be connected to the ground layer in the PCB 225 via a set of wires contained in one or both of a first ribbon cable 230 and a second ribbon cable 235. Thus, the metal enclosure of each of the first optoelectronic module 206 and the second optoelectronic module 207 is maintained at ground potential. The first optical port 128 and the second optical port 129 are each mounted on a respective wall of the first optoelectronic module 206 and the second optoelectronic module 207 as described below in further detail. Thus, the cylindrical body portion of each of the first optical port 128 and the second optical port 129 are maintained at ground potential, thereby operative to suppressing EMI emissions leaking from around a periphery of each of the first optical port 128 and the second optical port 129.
With specific reference to
The second coaxial optical port 128 similarly includes a second elongated cylindrical portion 507 that has a larger diameter than the corresponding first elongated cylindrical portion 412 and further includes a second flange 510 that operates in conjunction with the EMI shield 210 in a manner similar to that described above with respect to the first flange 505.
The manufacturing procedure described above is directed at producing an EMI shield 210 that not only includes the first circular opening 126 and the second circular opening 127, but also various resilient metal fingers. Specifically, the first circular opening 126 of the EMI shield 210 is characterized by a first annular array of resilient metal fingers 605 and the second circular opening 127 is characterized by a second annular array of resilient metal fingers 610. Each individual resilient metal finger in the first annular array of resilient metal fingers 605 is configured to press against the first flange 505 (
Attention is drawn to a portion of
Furthermore, each of the individual resilient metal fingers of the first annular array of resilient metal fingers 605 incorporates a chamfer with respect to a major planar surface 640 of the EMI shield 210. For example, an illustrative first chamfer 605a is shown associated with a first resilient metal finger, and an illustrative second chamfer 605b is shown associated with a second resilient metal finger. The chamfer provided in each resilient metal finger of the first annular array of resilient metal fingers 605, coupled with the spring-like flexibility characteristics of the sheet metal from which the EMI shield 210 is manufactured, permits each resilient metal finger to provide positive contact force with the surface of the first flange 505. Each of the individual resilient metal fingers of the second annular array of resilient metal fingers 610 similarly incorporates a chamfer with respect to the major planar surface 640 of the EMI shield 210.
Each of the first annular array of resilient metal fingers 605 and the second annular array of resilient metal fingers 610 is further characterized by having an interdigital spacing between adjacent resilient metal fingers specifically defined on the basis of one or more EMI frequencies generated in the optical communications module 100. For example, the interdigital spacing can be selected to correspond to a fraction of a wavelength such as, for example, a fraction of the shortest wavelength corresponding to the EMI emissions generated when operating the electronic circuit assembly 205 at a data rate of 25 Gb/s. Such a fraction of wavelength can be, for example, one fifth or one tenth of a wavelength such as, for example, one fifth or one tenth of about 12 mm, or one fifth or one tenth of about 1.2 mm. In some example implementations, the interdigital spacing can be selected to correspond to fractions even smaller than one fifth or one tenth of a wavelength.
Turning now to another feature in accordance with the disclosure, the EMI shield 210 that is described in this exemplary embodiment has four outside peripheral edges. A top peripheral edge of the EMI shield 210 includes a first linear array of resilient metal fingers 615, and a bottom peripheral edge of the EMI shield 210 includes a second linear array of resilient metal fingers 620. As for the two sides, a first side edge of the EMI shield 210 includes a first bifurcated resilient metal member 625, and an opposing side edge of the EMI shield 210 includes a second bifurcated resilient metal member 630. Further details pertaining to the various resilient metal members of the EMI shield 210 are described below with reference to other figures.
To elaborate upon this aspect, attention is drawn to a first portion of
Attention is next drawn to a second portion of
Attention is next drawn to a third portion of
In one example implementation, an interdigital spacing 720 between the first resilient section 725 and the second resilient section 730 of the first bifurcated resilient member 625 is selected on the basis of one or more EMI frequencies generated in the optical communications module 100 (for example, in the electronic circuit assembly 205 shown in
In summary, it should be noted that the invention has been described with reference to a few illustrative embodiments for the purpose of demonstrating the principles and concepts of the invention. It will be understood by persons of skill in the art, in view of the description provided herein, that the invention is not limited to these illustrative embodiments. For example, the invention has been described with respect to a rectangular shaped EMI shield 210 that is defined with respect to a first optical port 128 and a second optical port 129. In other embodiments, the EMI shield can have shapes other than a rectangular shape and can be defined with respect to less than, or more than, two optical ports. Persons of skill in the art will understand that many such variations can be made to the illustrative embodiments without deviating from the scope of the invention.