Phase noise is a major performance limitation of modern electronic systems. When upgrading and designing new systems, phase noise evaluation is therefore a necessity. Phase noise evaluation is therefore a necessity when it comes to upgrading and designing new systems.
However, measuring phase noise is one of the more challenging tasks for an electrical engineer. Established measurement procedures rely on high-quality references. On the other hand, the delay line method enables the measurement of phase noise without the use of a reference, but this advantage comes at the cost of a lower noise bandwidth and more complex calibration.
The development of optical fiber and high-speed optoelectronics has given rise to a new field called microwave photonics. It has brought renewed attention to the process of measuring phase noise with a delay line. A phase noise meter implemented using microwave photonics techniques is the subject of this PhD thesis.
The meters developed in the framework of the doctoral thesis use an electro-optic delay line implemented as an optical link, using an optical fiber as the transmission line. The thesis is divided into two parts. The first part focuses on the automatic calibration of the meter.
To ensure correct operation, the quadrature at the input of the mixer must be guaranteed, and for a correct phase noise reading, a precise knowledge of the mixer factor and the frequency response of the FFT analyzer is also required. The new solutions are implemented with an electrically adjustable phase shifter and associated control circuitry, phase modulation with a calibration tone and calibration with a known noise spectrum.
In the second part, two implementations of a new approach to ensuring the quadrature at the mixer and thus the correct operating regime of the meter are presented. The new approach exploits the chromatic dispersion of the fiber resulting from the frequency dependence of the refractive index of the silica. This allows fine tuning of the delay time through the adjustment of the laser wavelength. The achieved phase shift required for quadrature condition is proportional to the frequency of the device under test. A single-fiber phase-noise meter requires a high chromatic dispersion coefficient fiber, which is available in the form of compensation modules to eliminate the effects of chromatic dispersion in telecommunications links. The limitations arising from the need for a dedicated fiber are overcome in the design of the phase-noise meter with two fibers of different chromatic dispersion coefficients, where the difference in chromatic dispersion determines the tunability of the delay. This design allows the use of standard telecommunication fibers which are affordable and compatible with each other. The quadrature tuning in the optics significantly increases the usable frequency range of the devices under test.
The meters designed and built in the framework of the PhD thesis are affordable because they use building blocks used in telecommunication equipment, easy to handle as they have built-in automatic calibration procedures, and robust enough to be suitable for use outside a laboratory environment.
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