Meeting Measurement Challenges For Low-Power, Pulsed, Or ...

Recent developments in power meter technology have now enabled decent temporal signalmeasurements, eliminating the need for multiple instruments. One of the most advanced power metersin the market has been designed by Newport Corporation, Model 2936-C. This state-of-the-art, dualchanneloptical power meter has several sophisticated features that allow the user to achieve variousmeasurements, including frequency measurements of pulses up to 250 kHz (see figure 1).Figure 1: Newport Corporation’s optical power meter Model 2936-C with the 918D Series Photodiodes allowsvarious measurements for pulsed or modulated light input as well as continuous wave.Analog And Digital FilteringThe analog filter is an electronic, low-pass filter implemented on an optical power meter while thedigital filter averages the most recent 10, 100, 1,000, or 10,000 samples. The 2936-C optical powermeter has selectable 5 Hz, 1 kHz, 12.5 kHz, and 250 kHz low-pass filters. An optical power meter isessentially an amp meter with very low noise and high accuracy. Therefore, the proper filter settingwould make a huge impact on the signal response of the optical meter. For the best CW measurementor average power measurement of a modulated/pulsed light source, the heaviest filtering would beutilized, i.e., the 10,000 point digital filter with the 5 Hz analog filter. For a modulated or pulsed signal,an appropriate analog filter must be selected to obtain the best waveform, while the digital filter mustnot be used at all. Moreover, applying the digital and the analog filters on the pulsed or modulated inputsignal effectively averages out the signal.As seen in the 11/16/11 edition of the Photonics Online (www.photonicsonline.com) newsletter.