Standard measurement of RF bandwidth, whether the device under test (DUT) is an optical receiver or an optical transmitter, requires the use of very expensive equipment. A vector network analyzer (VNA) is often used to characterize the frequency response of a DUT in both amplitude and phase from DC to high frequency. In the telecommunication industry, the test frequency upper limit is continually growing, which causes test challenges, both in terms of complexity and test equipment cost. It is proposed to look at testing components up to 110 GHz. Most of the times, from a production standpoint, only the amplitude response is needed for device screening purposes. A well-known technique for testing optical receivers is to use a heterodyne laser beating as an optical source for testing. This approach reduces test equipment cost significantly by avoiding the use of a VNA as the electrical source/detector for RF signals. A less known technique is the application of heterodyne to testing modulators. A version of this technique has been proposed. However, the approach used is rather complex, costly, and cannot be fast due to the use of an electrical spectrum analyzer (ESA). A novel approach is presented using the same basic concept (which is the use of a beating on a photodiode as an RF source to characterize a transmitter) that does not require frequency discrimination at the output, which allows the measurement over the whole RF band to be done in a few seconds, which is faster than a VNA approach and heterodyne techniques known.

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