This paper proposes a signal-to-noise-ratio (SNR) improvement by using an external phase modulator that allowed flexible control of the spectrum amplitude by varying the modulation index for linewidth measurements. Compared with the conventional self-heterodyne detection technique, the results obtained in this study showed an SNR improvement as high as 10 dB. This 10 dB improvement in SNR could help to reduce the usage of a particular length of a single mode fibre (normally about 50 Km) when measuring a linewidth in the region of 10 kHz.
The operating principle and the performance of chromatic dispersion (CD) measurement technique are discussed through developed numerical models. The performance of the CD measurement technique was studied in terms of the measurement range and sensitivity as the wavelength separation was varied. Based on the numerical model, the technique sensitivity increased with wavelength separation. However, this increase in sensitivity was traded off with a narrower measurement range. The measurement technique was optimized at 5.0 GHz wavelength separation with a sensitivity of 0.009 (dB/ps/nm) and measurement range of 2500 ps/nm.