I once worked on SAC-OCDMA and I have some publication on its applications in vibration sensing. I have always used LED in simulations and I used Agilent ASE(Amplified Spontaneous Emission)for the experimental setup. I have never heard of Laser of Linewidth up to such (625GHz) before. Kindly check your references for more info.
However, u need to consider the fact that one of the advantages of SAE-OCDMA is possibility of using LED with broadband for multi-point which cuts cost of expensive laser. Using laser source means you have to use a separate light source for individual user and perhaps for each code chip (“1”) for encoding and decoding which then makes the system to be more expensive and at the same time more complex.
However, I am waiting to learn more