SECURE HIGH-SPEED DATA TRANSMISSION WITH microFX!
Technical Background on Connector Design.
With data volumes and processing speeds continually on the rise, modern systems place ever greater demand on connection technologies. The key component for maintaining a connection is always the connector itself, since it is most susceptible to breaking down. A truly modern connector must therefore be able to meet a variety of stringent demands.
Connectors must often provide a reliable connection under extreme ambient conditions, among them heat, water and pressure, and be able to transmit data and power at once. Of course, many applications also demand that they be as small as possible. Ideally, connectors should be designed with parameters that meet recognized international standards (e.g., IEC).
To ensure functional transmission over longer distances and under threat of outside interference, such as magnetic fields, fiber-optic light guides are finding use today instead of copper cores. Special hybrid connectors are also available for transmitting both data - in the form light pulses - via light guides and electrical power via copper cores. For example, SOURIAU's M12-based microFX connector supports up to two each fiber-optic and copper contacts. Certainly, a high degree of know-how is required to engineer reliable transmission properties into a light-guide connector.
How to connect copper lines to copper contacts is fairly common knowledge, but how much do we really know when it comes to light guides? How are light rays transmitted across a contact point, anyway?
Seamless Transition
The ability to ensure a seamless transition of light pulses is especially vital for optical contacts. Whereas transmission is directionally independent for copper contacts, usually occurring radially from the connector to the sleeve, light guides require axial transmission - i.e., the contact area is made up of the frontal surfaces of the contact pins. Because light travels in the form of electromagnetic waves, the transmission medium must provide nearly straight-line transmission.
Light Guidance
The most important consideration for the transmission of light through a fiber-optic contact is that both ends of the fiber are centered. If not properly centered, some light will exit the cable (scatter) and signal attenuation (losses) will occur. In addition, light that is back-reflected from non-centered fiber edges causes noise interference.
A precision tube, called a "ferrule" and having a tolerance in the µm range, is used to guide the optical fiber. Even the smallest deviation outside the ferrule tolerance will directly impact the axial offset of the optical fiber contact area, thus increasing attenuation.
To unite the fiber and ferrule into an inseparable unit, the gap between them is sealed using a special adhesive. This adhesive settles evenly around the fiber's outer surface, thus also ensuring that the fiber is properly centered inside the ferrule.
Air Gap
An equally important factor for optimal transmission is to ensure that the air gap at the connecting point between individual light guide sections is practically non-existent, since a gap at the connection will otherwise reflect most of the light. This is due to the fact that air has a lower refraction index (n0=1) than the fiber (n1>1), which, depending on the light's angle of incidence, may lead to complete back-reflection. A tiny gap that would have virtually no impact with copper contacts can thus significantly deteriorate the attenuation characteristics of light-guide optical contacts. Also, the wider the core, the more negative will be the air gap's impact.
To ensure an ideal contact between ferrules, the latter are mounted on alignment springs that push the ferrules against each other. A so-called PC (physical contact) connection achieves back-reflection values as low as -40dB (approx.), thus minimizing back-reflected noise. Non-PC connections result in an air gap at the termination point and a back-reflection in the area of -14dB (roughly 4%). A follow-on development to the PC connection is the APC (angled PC) connection, whose termination end-face is at an 8° angle to the rounded cladding. This design ensures that light reflected back from the termination end-face moves away from the core and into the glass cladding, refracting to the air outside. Back-reflection is thus an even lower -70dB.
General Characteristics of Light Guides
There are many reasons for choosing light guides (LGs) over copper cables. One main advantage of LGs is their natural immunity to interference, which eliminates the need for shielding. LG connectors are also immune to magnetic/electrical or electro-magnetic fields, while copper solutions can never guarantee 100% shielding.
This factor especially comes into play near electrical machinery and high-voltage systems (both DC and AC) or environments susceptible to lightning strikes. What's more, LGs pose no signal interference to neighboring fibers. The combination of high immunity to interference, minimal line attenuation and a wide bandwidth means that a higher link/transmission rate ratio can be achieved.
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Another positive characteristic of LGs is that they use a non-conducting transmission medium (dielectric). For example, it acts as lightning protection, thus eliminating the need for additional potential-equalization cables between two distant systems or buildings. And, because the dielectric holds no potential for sparking, LGs are suited for use in explosive environments (e.g., chemical, mining, gas and wood industries).
Other material and mechanical advantages also exist and should not be underestimated: e.g., LGs are thin, light-weigh and highly flexible, and thus save significant space in cable conduits.
Finally, an increasingly important consideration for industrial network security, LGs provide inherent protection against electronic wiretapping.
General Outlook
The increasing trend toward fiber optics in industrial applications is further evidenced by the degree of interest expressed by working groups of such organizations as PROFInet, IAONA, ODVA and others, which have published planning and installation guides to assist users in the implementation of such systems.
Technical Data for microFX Connector:
• Suitable for Fast Ethernet (100Mbit/s)
• Suitable for multi-mode, single-mode, POF and HCS light guides
• Low insertion loss (< 0.3dB)
• High mechanical reliability (100 connection cycles)
• Low electrical contact resistance (15mOhm max.)
• Rated current of 4A
• Rated voltage: 250VAC/DC (connector); 60VDC (transceiver)
• Temperature range: -25 °C to +85°C
• Protection: IP 67
• Fire resistant: UL94V0
microFX makes it easy to put fiber-optic technology into practice
The microFX is a complete M12 system consisting of a connector, transceiver and 2 adapters. It is designed to connect directly to the physical layer as a Fast Ethernet (100BaseFX) solution and uses a 62.5/125µm cable as the light guide.
a) The connecting adapter is offered in two versions: As a freely connecting piece for connecting two unfixed light guide cables together or as a wall duct, e.g. for use inside a wiring cabinet.
b) The transceiver provides a compact interface between electrical and optical signals, and is suited for the wavelengths 650nm and 1300nm. As an option, it also offers electrical contacts for power transmission. When fastened to a separating wall using a central screw, one side of the transceiver can be soldered directly to a PCB, while the other side is equipped with an IP67 microFX coupling. The interface is in accordance with IEC 61076-2-101 (M12 Standard).
c) The microFX connector can be optionally configured with up to 2 each optical and electrical contacts that are easy to insert and remove. Coded markings furthermore preclude connecting errors.
The optical contacts (ferrules) are designed to leave no air gap between the contacting surfaces - i.e., the light guides of two microFX connectors are always in direct contact at the adapter junction. The two optional electrical contacts can, for example, be used to supply power to connected equipment, which eliminates the need for a separate power supply line. This is especially advantageous when considerable distance separates the connected systems.
The high degree of protection - IP67, to include salt water spray - is afforded by the various sealing rings used in the connector, adapter and transceiver.
The new classification of environmental durability in accordance with IEC24702 for rough operation also applies.
A strain relief mechanism protects the cable against shock and pulling forces, while the wide operating temperature range of -25°C to +85°C also fulfills the most stringent environmental criteria.
„microFX" is a registered trademark of the companies SOURIAU, Hirschmann and Harting.
For more details, please contact:
Gerhard Strobl, EXT 37
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