What is an Optical Power Meter?
An optical power meter (OPM) is a type of electronic test device used to measure the power output of fiber optic equipment or the power or loss of an optical signal transmitted through a fiber cable. An OPM uses a photodiode to generate an electrical current proportional to optical power. This allows the OPM to determine the average output power level of the light source.
Portable fiber optic power meters are routinely used for the installation, commissioning, and maintenance of fiber network links. In addition to standalone, handheld power meters, OPM functionality is often integrated into more comprehensive optical test solutions such as OTDR equipment.
Optical power meters are calibrated to measure the light output accurately at designated wavelengths. Four of the commonly utilized OPM wavelength settings are 850nm and 1300nm for multimode fiber and 1310nm and 1550nm for single mode fiber. During testing, wavelength settings are chosen to match the actual service transmission wavelength.
How to Use an Optical Power Meter?
Handheld optical power meters are known for being extremely intuitive and easy to use. Although setup and operation vary by manufacturer and model, many basic functions of optical power or optical loss testing remain consistent across platforms. Control buttons on a standard handheld OPM include power (ON/OFF), wavelength selection, memory functions, unit display, and zero/reference buttons to establish baseline values.
A fiber power meter can be used in conjunction with an optical light source (OLS) to form an optical loss test set (OLTS). This capability is particularly useful during the construction phase before system turn on. Patch cords, adapters, or direct connection is used to connect the OPM and OLS to the ends of the fiber link. The OPM is powered on, followed by the OLS, and the correct wavelength is selected. By measuring the power output power from a calibrated light source, the insertion loss (attenuation) of the link can be quantified and compared to the loss budget.
During the commissioning of a fully powered-on network, an optical power meter is used to validate the output power of the transmission equipment. This determines whether design specifications have been achieved. Because the loss inherent to the link itself has already been determined, the actual output-input power of the receiving equipment can be calculated, and receive power levels can also be measured if required. Test results can then be stored or uploaded as a requisite part of the network commissioning test data set.
What Does an Optical Power Meter Reading Show?
An optical power meter displays two key test parameters that allow fiber design specifications like insertion loss or low attenuation to be evaluated. The first is the wavelength setting in nanometers (nm) and the second is the power level in deciBels (dB or dBm). Optical loss is measured in dB, a dimensionless unit which is a ratio of the measured value to a reference value. Power measurement can be displayed using dBm as the unit of measure at a specific resolution. The dBm unit quantifies the power level based on a reference value of 1 milliwatt for 0 dBm.
The versatility of an optical power meter allows it to be utilized for other basic fiber testing functions such as continuity testing. Establishing the presence of signal across a fiber is important for quick fiber link verification in the field with minimal equipment changes. When deployed as part of an optical loss test set, an optical light meter reading can also be used to conveniently ascertain fiber length and send/receive polarity.
How to Choose the Right Optical Power Meter for Field Testing
Selecting the right handheld fiber meter for field testing applications often becomes a daunting task. A wide variety of OPM solutions are available as fiber optic networks continue to grow in complexity. Variables that account for accuracy, versatility, and form factor needs should be carefully weighed. For example, an OPM that will be used for cable TV hybrid fiber coax (HFC) service testing must be capable of accurate measurement within the appropriate power range because these networks typically operate at much higher power levels than telco fiber networks.
Variable use applications could be better suited to broadband optical power meters. Whereas a passive optical network (PON) OPM includes wavelength selective measurements, connections, and other features that optimize loss testing over PON. An ongoing test need, such as light output verification at an optical add drop multiplexer (OADM or MUX), might call for a more specialized solution. Other applications require double-ended testing or loss testing with a companion OLS device.
Budgets are a primary concern when it comes to optical loss. This adherence to budgetary constraints is equally important when it comes to test equipment expenditures. Mini optical power meters now pack full power and loss testing capabilities over common wavelengths into convenient handheld or thumb-sized form factors. At the same time, the industry-leading VIAVI portfolio of optical power meters and integrated fiber test solutions have evolved to accommodate emerging technologies like XGS-PON and xWDM.
Types of Optical Power Meters
Optical power meters come in all shapes and sizes. For each specific application, user, and budget, VIAVI has developed user-friendly solutions that accelerate commissioning, maintenance, and troubleshooting activities.
- Basic Optical Power Meters
Compact fiber power meters with outsized capabilities have revolutionized the fiber testing landscape. The MP-60/-80 Miniature USB 2.0 Power Meters exemplify this trend by putting power and loss testing into the palm of your hand. A convenient USB optical power meter interface connects to a laptop or test device such as an OTDR. Dedicated mini optical power meters are available for all common single-mode and multimode wavelengths.
Stand-alone, affordable, handheld optical power meter options with ruggedized designs and simple, four-button operation are hallmarks of the SmartPocket OLP-34/-35/-38 series of OPM. These meters feature automatic wavelength recognition, internal data storage, and long battery life.
- PON Optical Power Meters
The SmartPocket series also includes the dedicated OLP-37 PON power meter for downstream power testing of B-PON, E or G-PON, and 10G-EPON or XGS-PON networks. The SmartClass Fiber OLP-87 PON power meter is an advanced, wavelength selective power meter capable of simultaneous upstream and downstream power measurement over live PON networks. The OLP-87 is compatible with the same B, E, G-PON, and high-speed PON networks using 10G-EPON, XGS-PON, or NG-PON2 technologies.
The SmartClass OLP-88 TruePON tester is dedicated to G-PON upstream and downstream power level testing and PON-ID analysis. This makes it an ideal PON optical power meter for G-PON network acceptance, troubleshooting, and automatic power level certification. Like all SmartClass power meters, the OLP-88 provides a convenient visual display for an optional P5000i digital fiber microscope connection.
- xWDM Power Meters and Optical Channel Checkers (OCC)
Wavelength division multiplexing, including DWDM and CWDM methodologies, is an important tool for increasing fiber utilization and capacity. Lightweight and ruggedized optical channel checkers (OCC) effectively scan WDM channels while providing automated wavelength, frequency, and power level measurements for each.
The SmartClass OCC-55/-56 Optical Channel Checkers include the OCC-55 model for CWDM and OCC-56 for DWDM channel checking. The power of DWDM power meter is also provided in an optional OCC-4056 module for the T-BERD/MTS-2000, -4000 V2, and -5800 V2 platforms.
- MPO Power Meters
Multi-Fiber Push On (MPO) connectors continue to grow in popularity as data centers become more densely populated and fiber connections multiply. This makes an MPO power meter dedicated to Tier 1 MPO fiber network certification an increasingly advantageous option. The VIAVI SmartClass Fiber MPOLx provides native MPO connectivity. Length, loss, power, and polarity for all MPO fibers can be verified efficiently and accurately. Identical local and remote test units enable visibility, test initiation, and reporting from either end of the circuit.
- Optical Loss Test Set (OLTS) The versatility of the VIAVI optical power meter test offerings extends to full optical loss test sets (OLTS). SmartClass Fiber optical light sources are versatile companion tools with a full suite of fixed and multi-wavelength options. The OLTS-85/-85P series includes dedicated multimode, single-mode, and quad options. The OLS-85 features variable output power settings, real-time loss measurement, automated fiber end-face inspection, and a flexible adapter system.
The SmartPocket OMK-34/-35/-36/-38 optical test kit series is an affordable, highly compact OLTS option for essential single mode and multi-mode fiber test applications. This intuitive, easy-to-operate test set also provides auto-wavelength identification, permanent reference power storage, and report generation software.
- Power Meters for Optical Manufacturing Testing
The technology providing high-performance optical power testing in the field extends to the manufacturing test realm through the VIAVI optical manufacturing test platform. Each module in the LightDirect family is tailormade to address specific requirements for benchtop testing or high-volume, automated optical product manufacturing.
MAP Optical Power Meters (mOPM) provide simultaneous multi-channel testing, adjustable power thresholds, pre-event triggers, and an advanced, user-friendly software interface. Optical light source and amplifier modules include a tunable laser suitable for DWDM test functions, erbium doped fiber amplifiers, and general-purpose light sources with fixed wavelength emitters for common bands.
Next-Generation Optical Power Meters
The next generation of optical power meters incorporate cutting-edge connector, electronics, and wireless technology to meet the challenges of non-stop fiber network expansion. The progress that has allowed OPM speed and reliability to keep pace has also improved ease-of-use for a growing pool of network technicians with limited fiber experience.
A study by NTT-Advanced Technologies notes that 98% of cable installers report connector end-face contamination as a root cause of network failure. Combining fiber cleaning and inspection capabilities into optical power measurement devices is one approach to overcoming this challenge. Another is the elimination of test leads, a potential source of contamination or debris, through direct attachment connector designs. Fully adjustable test arms are another element of the next-generation optical power meter device. This feature allows bulkhead ports in crowded network hardware environments to be accessed more easily.
Technological advancements continue to improve battery life and Bluetooth communication for countless consumer and industrial products. These developments also find utility in next-generation handheld power meter designs. Increased charging intervals lead to uninterrupted fiber testing and reporting. Wireless features enable mobile device pairing and real-time reporting. The investment in these mainstays of fiber testing is protected through the continued application of highly durable and ruggedized optical power meter form factors.
