van der Waals (vdW) junctions provide a versatile platform to explore nonreciprocal superconducting phenomena, with the twist angle serving as a powerful knob to tune interfacial coupling and thereby modulate the superconducting diode effect (SDE). Here, we demonstrate twist-angle dependent modulation of Josephson coupling and the SDE in ${\mathrm{Nb}\mathrm{Se}}_2/{\mathrm{Nb}\mathrm{Se}}_2$ vdW junctions. By varying the twist angle, we observe a transition from a strongly coupled regime, characterized by large critical current density and a monotonic magnetic field dependence of critical current, to a weakly coupled regime with reduced critical current density and the emergence of a Fraunhofer pattern, indicative of a Josephson weak link. In the strongly coupled regime, the SDE efficiency remains below 1% within ±0.1 T, whereas in the weakly coupled regime it is markedly enhanced, reaching up to 10.4% at −35 mT. This distinct behavior reflects different microscopic origins of the SDE in the two coupling regimes. Our results reveal a direct correlation between interfacial coupling and SDE efficiency, opening avenues for twisted superconducting devices with customizable nonreciprocal functionalities.

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• Non-reciprocal transmission
• Transport phenomena
• Twistronics
• Diodes
• Josephson junctions
• Superconducting devices
• Transition metal dichalcogenides
• van der Waals systems