Despite all the beneficial factors listed above, there have been only a few demonstrations where high frequency operation and low timing jitter have been simultaneously achieved [
3-
6]. Moreover, these demonstrations often involve external cavity arrangements that are not readily scalable in terms of large scale manufacturing. To drive down cost, we need to integrate the external cavity elements on-chip. Two suggested substrates for integration include InP and Si. Although a variety of active and passive elements, viz. laser, amplifier, filter, multiplexer etc., have been integrated on InP substrates, the cost is still limited by the substrate sizes. The hybrid silicon platform [
7] based on oxygen plasma assisted wafer bonding [
8] allows for fabrication of both active and passive elements on large substrates (200 mm or more), and therefore has attracted many researchers to utilize this technology for various applications from telecommunications to sensing. It also allows for close integration with electronic integrated circuits to lower losses and increase performance [
9]. Figure 2(a) shows a photograph of a 200 mm silicon-on-insulator (SOI) wafer before bonding with pre-patterned waveguide circuits with long delay lines and Fig. 2(b)is a schematic of the cross-section of the gain section showing evanescent coupling to the quantum well active region. In this paper, we will review our progress in monolithic integration of mode locked lasers using the hybrid silicon platform and show the utility of long delay lines in reducing microwave phase noise. All the lasers have an eight quantum well (QW) active region sandwiched between two 125 nm 1.3Q separate confinement heterostructure (SCH) layers, with a photoluminescence (PL) peak around 1550 nm and allow for a reasonable one-to-one correspondence.