Expanded Beam Fiber Optic Connectors: Their Working and Significance in Mission-critical Applications Analyzed

Fiber optics technology has paved its way to almost every industrial sector. The industries like defense and military, aerospace, geophysics, etc widely employ fiber optics in their applications. All these industries are known for their mission-critical applications that are exposed to harsh environments. This means the fiber optics cables and fiber optic connectors are also exposed to elements like dust, dirt, moisture, high-temperatures, oil, water, and even chemicals. Yet utilization of fiber optics cables and fiber optics connectors cannot be overruled in such industrial applications. Therefore, the expanded beam fiber optic connectors are designed and developed specifically for fiber-based applications under harsh environments.

To understand the working of expanded beam fiber-optic cables and connectors in industrial applications, it is essential to know why the conventional fiber optics connectors are not suitable for operations in harsh environments. Further, it is essential to know the expanded beam principle and the significance of expanded beam connectors in certain applications.
This white paper discusses the conditions of using fiber optics in harsh environments, the drawbacks of physical contact fiber optics connectors, and the significance of expanded beam connectors in certain applications.

An Overview of Conventional Physical Contact Fiber Optic Connectors

The physical contact fiber optic connectors are the devices that terminate the ends of fiber optic cables or help connect two ends of fiber optic cables. The process of connecting two ends of fiber optic cables is known as splicing. In these fiber optic connectors, the fiber optic cable splicing is done by mechanically joining the fibers via the polished ferrules. However, the conventional physical contact fiber optics connectors are subjected to insertion losses or attenuation due to the mechanical or spliced linkage between the connector ferrules.

Despite the slight amount of data losses, these physical contact fiber optic connectors are suitable for industries like telecommunication, multimedia transmission, security, and surveillance, etc provided they are not exposed to harsh environmental conditions. Commonly known types of physical contact fiber optics connectors are ESCON, ferrule connectors (FC), lucent connectors (LC), media interface connectors (MIC), mechanical transfer connectors (MT), MT-RJ, obsolete connectors, etc.
However, when it comes to industrial applications like marine, aerospace, military, and defense, etc, the physical contact connectors may suffer the loss of linkage between the ferrules due to harsh environmental conditions like high pressure, temperature, dust, radio frequencies, etc. The loss of linkage between the ferrules further gives the pathway for interruption of dirt, dust, oil, moisture, etc act the point-of-contact, which leads to additional losses during optical signal insertion and overall data leakage.
Generally, the tactical industrial applications in military and defense, marine, geophysics, aerospace, etc are sensitive to data security. The loss of sensitivity may cause fatal damage or jeopardize the security concerns, therefore, even the minor data loss cannot be tolerated. In certain cases, the fiber optics connectors with higher performance ratings and negligible data loss must be utilized. To serve certain purposes, the expanded beam connectors are designed.
The expanded beam fiber optics connectors are designed and developed as harsh environment fiber optic connectors (HEFO) and certainly they offer more reliable data transmission in tactical fiber optics operations exposed to harsh environments.
Prior to getting into what expanded beam fiber optic connectors (HEFO) are, it is essential to understand the principle of the expanded beam.

Phenomenon or Principle of Expanded Beam

The phenomenon of the expanded beam occurs when the light rays are collimated from one spherical lens to another. The working principle of any device based on the expanded beam phenomenon includes two different spherical lenses, which are placed at a specific distance from each other. The source light is emitted from the optical fiber which is further collimated or scattered into the number of parallels, equidistant radiations by the first spherical lens. The collimated radiations are collected by the second lens and then are unified to transmit via an optical fiber on the receiving end.

Note: The collimated light rays travel through the air-gap between two ferrules of the fiber optics connectors, which tackles with insertion and return losses in conventional connectors.
The principle of the expanded beam is adopted in the expanded beam fiber optic connectors in order to reduce the insertion and return losses. This reduction of insertion losses helps reduce the attenuation of optical signals during transmission.

Introduction of Expanded Beam Connectors

The expanded beam fiber optic connectors are the devices that feature a minute set up to perform the expanded beam phenomenon. These connectors feature two spherical lenses fixed between the two ferrules of the fiber optic connector. The lenses used in these connectors are either graded index rod lenses (GRID) or ball/spherical lenses. These lenses perform expansion, collimation, and refocusing of optical rays emitted by an optical fiber. The refractive index of both these lenses is essential to be uniform and the focal distance between both the lenses must be calculated. If the spherical lenses are utilized, the light ray scatters in multiple radiations and changes directions along the curved surface of the spherical lens. In the case of GRID lenses, the refractive index across the surface of the lens is not constant but has a cylindrical form factor. Thus, the ray distribution can vary according to the refractive index itself. Due to the variation of refractive index in a parabolic profile, the collimation of the optical ray takes place. At the receiving lens, all the parallel yet equidistant rays are collected at a focal point, and then transferred to the delivering optical fiber.    
As discussed earlier, the lenses are located between the ferrules, and these ferrules are mounted to align the fibers. Since these types of fiber optic connectors do not involve spliced-contact of the fibers, ceramic ferrules do the job of fiber alignment. The optical signals are transmitted through an air-media, thus, the mechanical wear is prevented because there is no actual contact between the fibers. Also, the gap can be cleaned to remove dirt, dust, etc.

Components of Expanded Beam Fiber Optic Connectors

The essential components of expanded beam connector assembly are listed below.

• Ball/ GRID lenses (Note: Number of lenses varies based on number of channels in the connector)
• Termination ferrules
• Connector insert tip
• Expanded beam termini
• Connector shells

Types of Expanded Beam Fiber Optic Connectors

The types of expanded beam fiber optic connectors are decided based on the number of channels. The types are listed as follows.

Single Channel Expanded Beam Connectors:

• The single-channel expanded beam connectors feature single pair of lenses, which means a single stream of scattered radiations is transmitted via one channel of the connector.

Multi-Channel Expanded Beam Connectors:

• In the multi-channel extended beam connectors, the number of lenses is twice the number of channels, one pair of lenses creates one channel. For example, 8 channel extended beam connector would feature 16 ball lenses to create 8 pathways for contactless optical transmission. Each channel is terminated by a pair of termination ferrules.  The insertion tip remains single in these connectors.

Benefits of Expanded Beam Fiber Optic Connectors

Although the application of expanded beam fiber optic connectors is more significant in different industrial applications exposed to harsh environments, it is essential to acknowledge the benefits offered by these connectors in tactical applications.

• Effective Fiber Alignment: The expanded beam fiber optic connectors feature the ferrules for aligning the fibers. Therefore, issues like misalignment due to defective splicing, fiber cut, etc can be avoided. Since the ferrules used are made of ceramic or rubber material, the fiber strands remain at set alignment.
• Less Impact of Misalignment: Although the alignment of fibers is an essential factor and it remains accurate throughout the operation, the slight misalignment of fibers does not impact the function of expanded beam connectors. In case of factory errors existing in the expanded beam connectors, the operators can still use the connectors as misalignment does not cause a considerable error in the operation. Focal correction can be made during the operation. However, it is essential to adjust the fibers in proper alignment in order to get the best results.
• Less Blocking Effects: Since extended beam connectors are not subjected to problems like dirt and dust, optical signal blocking is not a concern. Due to no optical signal blocking path-way reflection, refraction and data loss is prevented in these types of fiber optic connectors. Since the beam expansion is wider in expanded beam connectors, any existence of dust particles is negligibly significant which prevents the data losses.
• Reduced Losses: Having accurately aligned fibers, ferrules, and lenses, the focal alignment of the light signal is precisely done in expanded beam connectors. Due to the same, the signals enter the fiber strand at an expected insertion angle. This reduces the insertion losses in the transmission. Due to minimal insertion losses, scattering of an optical signal, refraction, and partial reflection is reduced which minimizes the return losses.
• Contactless Operations: Since there is no direct contact between the ferrules or fibers, the transmission is contactless. This prevents wear and enhances the life expectancy of the connectors.

Owing to certain benefits of expanded beam connectors, these connectors are highly significant in certain industrial operations exposed to harsh environments.

A General Introduction to Mission-critical Applications That Utilize Expanded Beam Connectors

In the following listed applications, the use of expanded beam connectors is highly significant.

• Military and Defense Operations: The military and defense industry utilizes fiber optics network for several tactical operations such as telecommunication, sensitive signal transmission, missile systems, radar systems, etc. However, such fiber optic networks are deployed in rugged situations. Fiber optics connections in certain applications are exposed to dust, dirt, extreme temperatures, and high pressure. Therefore, the use of expandable beam fiber optic cables and connectors is essential in military and defense operations.
• Marine Operations:  Marine operations are exposed to underwater pressure. Although the fiber optic cables and fiber optic products are immune to water, continuous exposure to this pressure may affect the lifecycle of products. The expandable fiber optic connectors can withstand the pressure, and wear can be prevented.
• Geophysical Operations: Geophysical operations like mining, oil exploration, submersible applications, etc are exposed to extremely high temperatures and pressures. In such operations, the pressure may raise up to 25000 psi and temperature up to 250° C. Also, the interruption of dust and dirt can be higher in geophysical operations, which can be tackled by using expanded beam connectors. To sustain certain applications expanded beam connectors are proven to be effective and efficient.
• Aircraft and Aerospace Operations: In aircraft and aerospace, the interruption of electromagnetic and radio frequencies may affect direct contact connections, which certainly increases the insertion and return losses in the fiber optics transmission. Also, the airborne sensors require higher bandwidth and minimum possible attenuation. Therefore, the use of expanded beam connectors is essential and beneficial in the tactical operations of the aircraft and aerospace industry.

These expanded beam fiber optic connectors must be partnered with the right fiber optic solutions for effective results. The next section discusses these solutions in detail.

Types of Fiber Optic Products to be Paired with Expanded Beam Fiber Optic Connectors Mission-critical Applications

The following fiber optic products will help you create strong connections using expanded beam fiber optic connectors.

• Media Converters: Copper to fiber media converters and fiber to fiber media converters are two types of devices that enable media conversion in different mission-critical applications. The copper to fiber media converters is used in infrastructure where copper and fiber cables are used together. Fiber to fiber media converters is widely used in applications, where multiple types of fibers exist together. While choosing for mission-critical applications ensure that you select the media converters with rugged construction and extended temperature range.
• Network Switches: Fiber optic network switches with SFP technologies have gained popularity in recent years. There are PoE switches, which helps in making reliable connections and minimize the use of accessories. These switches can be found in different designs and constructions to meet your application requirements. However, be specific about choosing industrial ruggedized fiber switches. Industrial Ethernet switches help to make the node-to-node connection between the two ends of fiber optic cables. This assures full usage of bandwidth during the transmission and minimizes signal loss, as well as ensures uninterrupted data connections.
• Modems: Ruggedized modems such as MicroModems by VERSITRON must be used in mission-critical applications. The MicroModems are designed for applications in the operating temperature range of -55°C to +100°C.  These modems are MIL-STD-199-114A compliant. They enable the secure transmission of signals over large distances.

Conclusion

The expanded beam fiber optic connectors are a type of contactless fiber optic connectors. In harsh environments, the application of extended beam connectors is of great importance. This white paper discusses the overview of conventional physical contact connectors and why the conventional connectors are not efficient for operations exposed to high temperature, pressure, dirt, etc. Further, the concept of an expanded beam in fiber optics is discussed followed by an introduction to the expanded beam connectors. Working, advantages, and industrial significance of extended beam connectors in fiber-based networks in harsh environments are discussed in this white paper. However, the expanded beam connectors are used along with different fiber optic products like expanded beam fiber-optic cables, media converters, fiber optic switches, modems, etc. The quality of certain products also impacts the overall performance of the network. Therefore, the fiber optics solutions for tactical industrial applications must be sourced from expert suppliers.

To know more about VERSITRON’s fiber optic solutions for different applications from industries like military and defense, aerospace, marine, etc, please visit https://www.versitron.com/.