Frequently Asked Questions
How do I measure the bandwidth of an optical tunable filter?
To measure the spectral shape of a narrow bandwidth filter, you can use a tunable laser or an optical spectrum analyzer. For the latter, you have to apply a correction factor since the spectrum is the convolution of the input spectrum with the OSA filter spectral response.
|With an optical spectrum analyzer in combination with a broadband light source
The OSA makes a convolution between its transfer function and the transfer function of the filter.
|With a tunable laser in combination with a photodetector
The tunable laser acts as a Dirac function and provides directly the real transfer function of the filter.
If the filter bandwidth measurement is affected by the bandwidth of the analysis tool you can calculate the real filter bandwidth with the following formula:
= calculated filter bandwidth
= measured filter bandwidth
= bandwidth of the laser or OSA
Note that with an OSA the
can be a function of the wavelength.
Where do measurement issues come from in the E-band (1350-1420 nm)?
Ions OH-, often referred to as water absorption peak, are introduced during the fiber manufacturing process. This impurity creates extra loss in fiber component, in the 1385 nm region in particular.
This absorption is intrinsic to the fiber component itself.
Water vapor contained in the atmosphere has many absorption lines in the 1350-1420 nm spectral range and relative humidity determines the level of absorption: water vapor can degrade the measurement result of a DUT; the measurement method must be selected with care.
Choice of Measurement Devices
To measure power, loss or attenuation, commonly used devices are power meters and optical spectrum analyzers.
In the 1350-1420 nm region:
Power meters are suited because the air gap between fiber and detector is around 2 millimeters only. It is noted that an integrating sphere is less suited because of a longer path length in air.
OSAs have a major drawback since the internal monochromator has a long optical path in air: from the input fiber to the detector, this air gap is often around 1 meter.
So if you work on the 1350-1420 nm region, take care of the water peak absorption:
Favor the use of a laser and a detector
Avoid if possible the use of a broadband source in combination with an OSA
Limit the air gap in your set-up
How can I make my USB/GPIB Adaptor work with Yenista’s instruments?
Only single-vendor USB/GPIB controller(s) should be installed on your computer. You cannot use USB/GPIB adapters from different vendors at the same time on your computer:
If no USB/GPIB controller is installed on your computer:
1. Install the USB/GPIB controller’s driver.
2. Connect the USB/GPIB controller to your computer.
3. In the controller’s utility, make sure the GPIB interface is installed as the primary board 0 (GPIB0).
If another vendor’s USB/GPIB controller is already installed on your computer:
1. Remove all the USB/GPIB controllers connected to your computer.
2. Uninstall any existing USB/GPIB driver from your computer.
3. Install the new USB/GPIB driver on your computer.
4. Connect the corresponding USB/GPIB controller to your computer.
5. In the controller’s utility, make sure the GPIB interface is installed as the primary board (GPIB 0).