CWDM System Testing Process

With the explosion of CWDM, it is very necessary to formulate a basic testing procedure to certifying and troubleshooting CWDM networks during installation and maintenance. Today, one of the most commonly available test methods is the use of an OTDR or power source and meter, which is capable of testing the most commonly wavelengths, 1310, 1490, 1550 and 1625nm.

This article here is based on the pre-connectorized plug and play CWDM systems that allow for connecting to test equipment in the field:

In the multiplexing module of a pre-connectorized CWDM system, wavelengths are added to the network through the filters and transmitted through the common port. The transmitted wavelengths enter the COM port in the de-multiplexing module and are dropped. All other wavelengths present at the MUX/DeMux module are went through the express port.

Most of today's OTDRs have expanded capability for testing wavelengths in addition to 1310 and 1550 nm. The OTDR allows partial testing of such system offered in test equipment source. The OTDR allows partial testing of these systems by using the flexibility of pre-connectorized solutions. This is done by switching connections within the CWDM field terminal to allow for testing portions of the non-1310/1550 nm optical paths.

To test the 1310nm, the first step is to test the downstream portion of a system at 1310 nm by connecting the OTDR to the 1310 nm input on the CWDM MUX located at the headend. Then switch the test leads over the the upstream side and repeat. Test method is the same for both the downstream and upstream paths.

1550 nm testing is performed similarly by switching the test leads to the 1550nm ports. If additional wavelengths are present, you need to follow the procedures below:

Using the 1550 nm test wavelength, switch the OTDR connection to the 1550 nm input port on the headend MUX. Have a technician stationed at the field terminal connect the drop cable leg connectors for the 1570 nm customer to the 1550 nm port on the Mux/demux device. What should be noted is that in a play and plug solution this should not require repositioning where the drop cable passes through the OSP terminal. Test the downstream 1570 nm passive link at 1550 nm, and then repeat for the 1570 nm upstream side. When testing is complete, have the technician switch the connections for the 1570 nm drop back to the 1570 nm ports on the field MUX/DeMUX device as shown in Figure 6. Repeat this process for the 1590 nm, 1610 nm drop cables and other wavelengths present. Finally, test the 1550 nm path normally with the 1550 nm drop cable connected to the 1550nm MUX/DeMUX ports.

Since the OTDRs is able to test at 1490 or 1625 nm, the drop cables under test could be connected to the EXP port of the module and tested at 1490 or 1625 nm respective wavelength, without having to connect each to the 1550 nm port. Otherwise the procedure is the same.

As CWDM network become more and more common the data they carrying has also become critical. The procedure introduced here allows for testing modular pre-connectorized CWDM systems with standard optical test equipments. Relative channel power can be measured with a wide-band fiber optic power meter at the filter outputs or at other points in the network with the aid of a wavelength selective test device or with an optical spectrum analyzer.

Bare Fiber Adapter Installation Guide

Bare fiber adapter is a typical type of fiber optic adapters that places industry standard connectors on unterminated fiber. It is contained in a durable aluminum-alloy housing which is easy to stabilize any magnetic surface for hands free use. Bare fiber adapter provides a temporary connection that eliminates the time consuming process of splicing jumpers onto individual fibers to testing, allowing users to easily test and detect fiber damages anywhere, anytime.

Bare fiber adapters enable quick and easy temporary connections of single mode and multimode fibers. These adaptors are very useful for connecting fibers to fiber optic power meter, optical time-domain reflectometers (OTDRs) and a variety of other instruments, enabling in-situ functional testing without having to attach a permanent connector.

Bare fiber adapters provide a simple and effective way to use un-terminated fibers with commercial receptacles. Here is the installation guide for the bare fiber adapters.

Attaching the patch cord
Clean connectors on fiber jumper or launch reel. Position connector on fiber jumper or launch reel with bare fiber adapter connector port. Insert the connector into the bare fiber adapter connector port until hear a click.

Preparing the fiber
Remove 6 inches of jacket and Kevlar. Remove 1 inch of coating and cladding. Cut the fiber 12mm-15mm long with fibre cleavers

Inserting the fiber
Clean the bare fiber. Press and hold down the button (There is a button on the adapter) while slowly and carefully inserting the bare fiber into the fiber port. Open the window to visually see the proper alignment of the bare fiber in the V-groove. To prevent accidental breakage of the glass fiber, slowly insert 1/8 inch to 1/4 inch of fiber at a time. Rotate the fiber until the glass aligns with the v-groove to enter the connector port. Push the fiber until it stops in the connector port After that, releaser the button to secure the fiber.

Removing the fiber
Press and hold down the button while slowly and carefully pulling the bare fiber out of the fiber port. Be sure to check for any broken glass fiber pieces after removing the bare fiber from the adapter.

Removing the jumper cable
Slowing pull the fiber jumper connector out the connector port. Broken fibers are easily removed with piano wire, allowing hundreds of insertions.

FiberStore supply the largest selection of bare fiber adapters connector styles on the market including SC, ST and FC bare fiber optic adaptor with stable qualities. These adapters use high quality ceramic ferrules and precise fiber connector housing parts, they are used to quickly and easily terminate the fiber to the equipment.

Difference between Laser Light Source and LED Light Source

As the wide application of fiber optic system, optical light source plays a more and more important part in it. We known a basic optical fiber system consists of a transmitter, an optical fiber and a receiver. The fiber optic light source, as an important component of the transmitter is modulated by a suitable drive circuit in accordance with the signals to be transmitted. Optical light source are also needed for performing fiber optic network testing to measure the fiber optic loss in the cable plant. Light source are offered in a variety of types including LED, halogen and laser. Among which, LED and Laser light source are two types of semiconductor light sources. The following article will discuss about some differences between laser and Led light source.
Basically, both kind of light source must be able to turn on and off millions to billons of times per second while projecting a near microscopic beam of light into an optical fiber. During the working process of optical signals, they are both supposed to be switched on and off rapidly and accurately enough to properly transmit the signals.
General difference between them as that LEDS is the standard light source which is short for light-emitting diodes. Laser light source like gas lasers may be mainly used in some special cases. Lasers are more powerful and operate at faster speeds than LEDs, and they can also transmit light farther with fewer errors. Laser are also much more expensive than LEDs.
LED fiber optic light source are made of materials that influence the wavelengths of light that are emitted. A basic LED light source is a semiconductor diode with a p region and an n region. When the LED is forward biased, current flows through the LED. As current flows through the LED, the junction where the p and n regions meet emits random photons. LEDs emitting in the window of 820 to 870 nm are usually gallium aluminum arsenide (GaAIAs). Laser is also a semiconductor diode with a p and an n region like LED, but it provide stimulated emission rather than the simplex spontaneous emission of LEDs. The main difference between a LED and a laser is that the laser has an optical cavity required for lasting. The cavity is formed by cleaving the opposite end of the chip to form highly parallel, reflective, mirror like finishes.
VCSEL is a popular laser source for high speed networking, which consist of two oppositely oppositely-doped Distributed Bragg Reflectors (DBR) with a cavity layer. It combines high bandwidth with low cost and is an ideal choice for the gigabit networking options.
Different wavelengths travel through a fiber at different velocities as a result of material dispersion. What should always keep in mind is that both Laser and LED will not emit a single wavelength, but a range of wavelength that is known as the spectral width of the source. Fiber optic light source is always works with the fiber optic power meter. During the working process, it collimated beams of light and aim right down the center of the narrow single mode core and propagates in essentially a single mode transmission. By more questions about fiber optic test equipment, such as visual fault locators, optical power meter, OTDR testers, and more. please go for FiberStore webstore.