modes has been extensively studied, there is still a lack of experiments exploiting the energy degree of freedom to generate qudits for $d>2$. Thus far, qudits with $d=3,4$ were demonstrated via two-photon interferences in [@marcikic2002; @thew2004; @richart2012]. In these experiments, the entanglement was encoded in a time-bin basis realized by interferometers with multiple arms. Time bins have been preferentially used as a basis for entangled qudits because they can be coherently manipulated by interferometers. However, the scalability to higher dimensions becomes prohibitively complex in view of interferometric stability.

By *directly* manipulating the photon spectrum, we demonstrate the implementation of various discretization schemes to realize entangled qudits. For this purpose we coherently address selected spectral components of the entangled photons by a spatial light modulator (SLM) and make use of an ultrafast optical coincidence detection, i.e. sum-frequency generation (SFG) [@peer2005; @zaeh2008]. As compared to the aforementioned experiments using interferometric methods, this procedure is intrinsically phase stable and potentially scalable to very high dimensions. It has been used to investigate frequency-bin entangled qudits by quantum state tomography and Bell measurements [@bernhard2013]. In this paper, we demonstrate the versatility of the experiment by discretizing the continuous frequency space not only in frequency bins 