Currently, the dominant method to generate ultrafast laser pulses passively is to use semiconductor saturable absorber mirrors (SESAMs). This type of passive mode locker produces exceptional results but is difficult to fabricate, expensive, and limited in bandwidth. In contrast, a graphene-based saturable absorber is easier to produce and has the advantages of much wider bandwidth, lower saturation intensity, tunable modulation depth, ultrafast recovery time, and much higher optical damage threshold, thus producing higher energies.
A process for transferring graphene to suitable optical substrates, as well as tips of optical fiber, was developed by growing large-area graphene using a low-pressure chemical vapor deposition (LPCVD) technique. In addition, a second process was developed for depositing multiple graphene layers on the same substrate. Using these new processes, engineers developed a process to make a saturable absorber with single-layer as well as multilayer graphene.
High energy (10s nJ) and femtosecond pulses with repetition rate on the order of hundreds of MHz have been demonstrated using graphene as a saturable absorber in developing a graphene-based mode-lock device for a laser transmitter. This work has also led to the development of other novel photonics devices. Aside from the applications as a laser transmitter, the saturable absorber can be used as a scalable graphene-based bolometer.