Optical Power Meter

 

What is Optical Power Meter?

Optical power meter refers to an instrument used to measure absolute optical power or relative loss of optical power through a section of optical fiber. In the optical fiber system, measuring the optical power is the most basic measurement, like a multimeter in electronics; in the optical fiber measurement, the optical power meter is a heavy-duty common meter. By measuring the absolute power of the transmitter or optical network, an optical power meter can evaluate the performance of the optical device. Using an optical power meter in combination with a stable light source can measure connection loss, check continuity, and help evaluate the transmission quality of optical fiber links.

Why we need optical power meter?

With the rapid development of optical fiber communication technology, optical fiber communication has become the main transmission mode of various communication networks. Optical power is the most basic measurement parameter in optical fiber communication systems, and one of the most important parameters for evaluating the performance of optical end equipment and evaluating the quality of optical fiber transmission. The optical power meter is an instrument specially used to measure the absolute optical power or the relative loss of the optical power through a section of optical fiber. It is widely used in the laying of communication trunk lines, equipment maintenance, scientific research and production.

How to measure optical power with optical power meter?

Turn on the network optical device, just use an optical power meter and an optical fiber connector adapter to measure the power of the transmitter or receiver.Before measuring the power, the wavelength and other parameters of the optical power meter must be set within the specified range; after everything is ready, the optical power meter can be connected to the transceiver end to measure the power of the receiver, or it can also be connected to the light source end to measure the power of the emitter; finally write down the measured value and compare it with the power value specified by the device to see if it is within the specified floating range (determine the optical device failure).

How to measure fiber loss with optical power meter and light source

Fiber loss is the difference between the power when light is coupled from the transmitting end to the fiber and the power when the light reaches the receiving end. To measure fiber loss, not only an optical power meter, but also a light source is needed. Generally speaking, when measuring the fiber loss of a multimode fiber, you need to use an 850/1300nm LED light source, and when measuring the fiber loss of a single-mode fiber, you need to use a 1310/1550nm laser light source. In addition, in order to accurately measure the optical fiber loss, it is necessary to make the test environment and conditions of the optical fiber and the connector similar to the actual working conditions, that is, to select the appropriate light source and optical cable, and the optical cable has a standard transmitting power and has no effect on the power of the light source.

At present, there are two main methods for measuring fiber loss: one end loss measurement method and two ends loss measurement method. The single-ended loss measurement method uses only the transmitting optical cable, while the double-ended loss measurement method uses a receiving cable connected to the power meter in addition to the transmitting cable. The single-ended loss measurement method can be used to measure the loss caused by the connection between the connector and the transmitting cable as well as the loss caused within the fiber, connector or other connector. Therefore, you can test each connector individually, which is the best way to measure fiber jumpers; the double-ended loss measurement method can measure the loss in two connectors and all fibers, including the loss between the connectors. The following figure respectively reflects the specific information of the two measurement methods. Among them, the left side is the single-ended loss measurement method, and the right side is the double-ended loss measurement method.

In optical fiber measurement applications, in addition to the use of optical power meters and light sources, it is also necessary to use transmitting optical cables, adapters, visible light fault locators or optical tracers, and clean the detection toolbox.

How to choose an optical power meter

To choose a suitable optical power meter, consider the following four elements: 1. Choose the best probe type and connector interface type (LC, MPO or MTP, SC, ST, FC, MT-RJ). 2. Evaluate the calibration accuracy and manufacturing calibration procedures to match the requirements of optical fibers and connectors. 3. Make sure that these models are consistent with the measurement range and display resolution. 4. With the dB function of direct insertion loss measurement.

First of all, the optical probe is the most carefully selected component among all the performance of the optical power meter. The optical probe is a solid-state photodiode that receives coupled light from the optical fiber network and converts it into an electrical signal. You can use a dedicated connector interface to input to the probe, or use a universal interface UCI (using screw connection) adapter, UCI can accept most industry standard connectors. Based on the calibration factor of the selected wavelength, the optical power meter circuit converts the probe output signal and displays the optical power reading on the screen in dBm. The most important criterion for selecting an optical power meter is to match the type of optical probe with the expected operating wavelength range. It is worth mentioning that, when measuring, InGaAs has a good performance in all three transmission Windows. Compared with germanium, InGaAs has a more flat spectrum characteristic in all three Windows, a higher measurement accuracy in 1550nm window, and superior temperature stability and low noise characteristics.

Secondly, the performance standards of optical fibers and connectors are consistent with the requirements of the system. Should analyze what causes the uncertainty of the measured value with different connection adapters? It is important to fully consider other potential error factors. Although NIST (National Institute of Standards and Technology) has established American standards, the spectrum of similar light sources, optical probe types, and connectors from different manufacturers is uncertain.

Third, determine the optical power meter model that meets the measurement range requirements. Expressed in dBm, the measurement range (range) is a comprehensive parameter, including determining the minimum/maximum range of the input signal, so that the optical power meter can guarantee all accuracy, linearity (generally determined as +0.8dB) and resolution (usually 0.1dB or 0.01dB) to meet the application requirements. The most important selection criterion for optical power meters is that the type of optical probe matches the expected working range.

Finally, the optical power meter should have the dB function (relative power), and it is very practical to directly read the optical loss in the measurement. Without the dB function, the technician must write down the individual reference and measured values, and then calculate the difference. Therefore, the dB function provides users with a relative loss measurement, thereby improving productivity and reducing manual calculation errors.

Basic indicators of optical power meter

The basic indicators of the optical power meter are mainly four: 1. Wavelength range. This is related to the type of photodetector used inside the optical power meter. For example, the wavelength range of silicon detectors is generally 450 to 1000 nm; the wavelength range of gallium arsenide detectors is generally 800 to 1700 nm. 2. The detectable maximum and minimum power range, the typical power range is -100+3dBm. 3. Display resolution in dB or W. The typical resolution is 0.001dB or 10pW. 4. The internal noise generated by the power meter is typically 150pW.

Conclusion

For the manufacture, installation, operation and maintenance of any optical fiber transmission system, optical power measurement is essential. In the optical fiber field, without an optical power meter, no engineering, laboratory, production workshop or telephone maintenance facility can work. For example: optical power meter can be used to measure the output power of laser light source and LED light source; used to confirm the loss estimation of optical fiber link; most importantly, it is a key instrument for testing the performance indicators of optical components (optical fibers, connectors, attenuators, etc.).


Post time: 2021-01-15

Testimonials

Lomoveishiy – Finland

I needed those to connect my PC on the third floor to have internet access in that room, and ISP installed their modem on the first floor only. After dropping fiber patch cables, plugged in all cables into these media converters at both sides, and link came up instantly. Was much easier than I thought!

Raymond – USA

Great experience – units worked straight out of the box – just needed plug in cables and we were done. I also like the possibility to enable jumbo frames, while we do not have a need for this feature at the current moment it’s great to have this option.

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