Optical Network Components
There are many different active and passive components that make up an optical network. A solid understanding of the function of these components is vital when designing a cost-effective optical network that will meet the bandwidth needs for many years to come.
The Coupler
The optical coupler is often called a splitter and is depicted in Figure 1. It is a passive optical component (requires no power to operate) that can divide or combine light power between multiple fibers. There are many types of couplers available; the most commonly used are the 50/50, 80/20 and the 90/10. The numbers designate the percentage of light power divided between the outputs. Other coupler types split incoming optical signals among multiple outputs. Couplers are bi-directional and can combine multiple optical signals on to a single fiber, however this will introduce some loss in the system. Evertz’s passive optical couplers are available in many commonly used splitter types to meet the requirements for many optical systems.
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| Figure 1: A 50/50 passive optical coupler evenly distributes an incoming optical signal applied to its common port between its two output ports |
Optical Switch
The optical switch is an important component as it allows a network supervisor to selectively choose the input fiber. Intelligent switches are now being manufactured so that channel selection is automatic based on input optical strength. The optical switch will automatically change to input channels if the signal strength drops below a user set acceptable level. Optical signals can be lost should a fiber be damaged or disconnected. Evertz 7707BPX is an intelligent switch that can be set to automatically return to the original input if the optical link is restored.
Wavelength Division Multiplexors and Demultiplexors
Wavelength division multiplexing is used to combine/separate multiple wavelengths onto one fiber with minimum insertion loss. The internal make up of a WDM is shown in Figure 2 and is essentially a group of cascaded dichroic filters of different wavelengths. A dichroic filter is based on interferometric technology that reflects all light it does not transmit. Note the filter orders are reversed in the mux and demux to keep the insertion loss constant across all wavelengths.
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| Figure 2: Internal structure of a 4 Channel CWDM Mux and Demux. Notice how the filters on the Mux side are in the opposite order of the Demux side. This keeps insertion loss constant across all wavelengths |
Fiber Connectors
Many different styles of fiber connectors are available to the consumer; three popular connector types available on all Evertz products are the FC/PC, SC/PC and ST/PC.
FC/PC - A threaded optical connector that originated in Japan. Good for single-mode or multimode fiber and applications requiring low back reflection. The physical contact (PC) polish produces a slightly curved end face that forces the fibers in the mating connectors into contact. This reduces back reflection to about -40dB.
SC/PC - Abbreviation for subscription channel connector, this push-pull type of optical connector also originated in Japan. Features high packing density, low loss, low back reflection and low cost. The physical contact (PC) polish produces a slightly curved end face that forces the fibers in the mating connectors into contact. This reduces back reflection to about -40dB.
ST - Abbreviation for straight tip connector originally developed by AT&T. This connector closely resembles a BNC-type coax connector.
SC/APC - Abbreviation for subscription channel connector. The angled physical contact (APC) adds an 8° angle to a flat polish reducing back reflection to -70 dB. Its green colored body signifies Angle PC application. Caution: mating an angle polished connector with a flat polished connector will irreparably damage both connectors, DO NOT do it!
