AC vs. DC Output Coupling

All of our high speed detector and receiver products are available with DC output coupling which allows the user to make DC optical measurements and high speed optical measurements with the same detector or receiver model. If the user desires to make AC-only measurements, we recommend adding an external DC-blocking capacitor to the output of the device. By selecting the capacitor value, the user can choose a low-frequency cut-off point that is best suited to his needs. Your Newport sales-engineer can help with these recommendations.

When DC-coupling to a receiver, the user must be aware of the output DC offset voltage that may be present. Most products have a zero-voltage output offset and pose no problem for output connection. Some receivers, however, do have a DC -level present at the output. This is dictated by the amplifier used in the product and is often tolerated so that DC measurements can be made. For some models that have a significant DC offset (up to 3 volts) we offer the user an AC-coupled version that integrates the DC-block within the receiver so no extra part needs to be used. With this option, the low-frequency cut-off is limited to about 1 MHz. If you need lower frequency performance, purchase the DC-coupled version and supply your own external DC-block.