Enhancement of Multioctave Dynamic Range in a Push-Pull Modulated Analog Photonic Link

These past few years, there have been numerous research efforts concentrated on the spurious free dynamic range (SFDR) enhancement of analog photonic links (APLs). These efforts are driven by various applications, such as military radars [1] and phased-array antennas for radio astronomy [3], that impose stringent SFDR requirements to the APLs. To date, most efforts to increase the SFDR have been directed to externally-modulated APLs rather than directly modulated ones [2]. This, to some extent, is attributed to the fact that external modulation offers chirp-free operation and a higher modulation bandwidth compared to direct modulation. However, for applications in which a large number of APLs are required, employing external modulators might become too costly. In this case, directly modulated lasers (DMLs) are still very much preferred due to their low cost and simple operation. These DMLs, nevertheless, should provide sufficiently large SFDR. One of the main limitations of DMLs is the high second-order intermodulation distortion (IMD2) [2]. This prevents them to be implemented in broadband systems in which the signal has a bandwidth of more than one octave (i.e. multioctave). A solution to this problem is to suppress the IMD2 using a technique that combines push-pull modulation of DMLs with a balanced detection scheme [1, 3]. Using this technique, we recently reported one of the highest SFDR ever achieved with DMLs, shown at the frequency of 2.5 GHz [3]. In this paper, we optimize our system to operate in an extended frequency range beyond 2.5 GHz.