NIST has developed highly accurate heterodyne techniques at 850 nm, 1319 nm, and 1550 nm for measuring frequency response of detectors. A calibration service has been established for frequency-response transfer standards operating at 1319 nm consisting of a photodiode combined with a microwave power sensor. This system is capable of measuring this type of standard from 300 kHz to 110 GHz or more. We have similar capabilities at 850 nm and 1550 nm, along with a service for calibrating the frequency-response magnitude of bare photodiodes to at least 50 GHz. Calibration of bare photodiodes is more complicated because it requires calibrated microwave power and scattering-parameter measurements.

Optoelectronic phase response, when combined with the magnitude response, is called the vector response. The vector frequency response of a photoreceiver is the Fourier transform of its impulse response. Vector response is required for design of high-speed optoelectronic systems but at present there are no accepted standard methods for this measurement.

Researchers in the High-Speed Measurements Project have demonstrated time-domain techniques for measuring optoelectronic vector response with verifiable accuracy up to 110 GHz using electro-optic sampling. By developing these measurements our project is pioneering a new paradigm for time-domain measurements with frequency-domain calibrations.

Plans:
We intend to have a Calibration Service for frequency response phase that uses these new calibration strategies, and by 2005 we will develop methods for extending frequency response calibrations beyond 110 GHz.

Frequency Response of Optical Waveform Measurement Equipment

Optical communications analyzers or reference receivers used for measuring digital eye-patterns on optical signals have many similarities to electrical oscilloscopes, but also have advantages of their own. In particular, they can be calibrated over a very high bandwidth because they do not require band-limited microwave calibrations. Use of this calibration on typical measurements, however, possesses some unique problems. For example, we must develop methods for removing time-base distortions and deconvolving the oscilloscope response. In collaboration with Divisions in EEEL and ITL, we are currently applying our expertise in receiver measurements to these problems.

Plans:
NIST will work with the IEC to document procedures developed at NIST for calibrating the frequency response of optical waveform measurement equipment. We will also develop methods that improve the accuracy of eye-diagram and other time-domain measurements by calibrating and removing instrument errors in optical oscilloscopes.