Realisation of flat FM response by directly modulating a phase tunable DFB laser diode

Phase Recovery in Interferometers by Optothermal Diode Laser Modulation

“…Cleaved coupled-cavity lasers are another optional source for both fibre sensor and communication applications, They provide constant amplitude frequency tuning, < 5% over about 50 GHz [24], and FM amplitudes of around 1-3 GHz mA -'with bandwidths up to 300 MHz [25] . However, we have shown that by using optothermal modulation, it is possible to provide a source with minimal power modulation for fibre sensor demodulation schemes using commercially available laser diodes .…”

FSK heterodyne transmission experiments at 560 Mbit/s and 1 Gbit/s

“…This has been demonstrated with a variety of techniques, including preequalization of the modulation signal with a passive network [12], [6], Manchester coding [ 131, and minimum shift-keying using an FM subcarrier (MSK-FM) [14]. An alternative approach uses a phase tunable DFB laser [15] as the FSK transmitter. This two section DFB laser has a flat FM characteristic from 1 kHz to 300 MHz, with a large frequency deviation of 1 to 3 GHz /mA, which is 5 to 10 times larger than that for conventional DFB lasers at modulation frequencies above 100 MHz.…”

Theory of direct frequency modulation of semiconductor lasers with integrated external cavity

“…Much work has been done to improve the FM responses of LD's. Up until now, the phase tunable DFB LD's [3] and other composite laser diodes with similar structures [4]- [9] have been most promising for FSK systems. The typical configuration of these two-section semiconductor lasers is shown in Fig.…”

“…The laser consists of two regions which are separately pumped by a dc current ZI (lasing region) and a biased modulation current Z2 (modulation region). The modulation region has the same structure as the lasing region but it may [3], [5] or may not [4], [6]- [9] have the active layer, and it acts as an external cavity to provide optical feedback to the lasing region. So either type (DFB or DBR) may be called integrated externalcavity semiconductor lasers [7].…”

“…So either type (DFB or DBR) may be called integrated externalcavity semiconductor lasers [7]. Flat FM responses for modulation frequency from 1 kHz to 300 MHz have been obtained in integrated external-cavity semiconductor lasers with a normalized frequency deviation of 1-3 GHz/mA [3], [9]. Furthermore, the frequency tuning of the integrated external-cavity semiconductor lasers can be easily performed by tuning the bias current of the modulation region [4], [6], [8], [9] with the spectral linewidth maintained almost constant.…”