Optical systems are disclosed which include one or more components such as an optical multiplexer, an optical demultiplexer, and, an optical amplifier. The average size of the graphene platelets is 50 nm or more and the number of layers of the graphene platelets is 9 or less. For some embodiments, a multiphase flowmeter includes an array of spatially distributed pressure sensors configured to determine a velocity of the mixture flow and hence the total flow rate, which is applied with information from a differential pressure meter to calculate the bulk density of the fluid mixture. in dry air, indicating significant thermoxidative stability with minimal or no aromatic content, thereby enabling use of Groups II and III base oils, in particular, without reduced toxicity andor quality concerns as compared with Group I base oil lubricants.