In the below linked research paper published on Nature.com, a team of researchers from the University of Virginia, Peking University, Shanxi University, and California Institute of Technology use a Yokogawa Test&Measurement Optical Spectrum Analyzer in order to achieve spectrum measurements above 1200 nm.
High Performance LONG WAVELENGTH
The AQ6375B is a bench-top optical spectrum analyzer covering the long wavelengths, 1200 to 2400 nm, with the added benefits of gas purging input ports / output ports, a built-in cut filter for high order diffracted light, and a novel double speed mode which increases the sweep speed up to 2 times compared to the standard sweep mode.
Measures the power intensity of light across different wavelengths in the electromagnetic spectrum.