AbstractThe layered insulator hexagonal boron nitride (hBN) is a critical substrate that brings out the exceptional intrinsic properties of two‐dimensional (2D) materials such as graphene and transition metal dichalcogenides (TMDs). In this work, we demonstrate how hBN slabs tuned to the correct thickness act as optical waveguides, enabling direct optical coupling of light emission from encapsulated layers into waveguide modes. We integrate two types of TMD monolayers (MoSe₂ and WSe₂) within hBN‐based waveguides and demonstrate direct coupling of photoluminescence emitted by in‐plane and out‐of‐plane transition dipoles (bright and dark excitons) to slab waveguide modes. Fourier plane imaging of waveguided photoluminescence from MoSe₂ demonstrates that dry etched hBN edges are an effective out‐coupler of waveguided light without the need for oil‐immersion optics. Gated photoluminescence of WSe₂ demonstrates the ability of hBN waveguides to collect light emitted by out‐of‐plane dark excitons and trions. In‐depth numerical simulations explore the parameters of dipole placement and total slab thickness, elucidating the critical design parameters and serving as a guide for novel devices implementing hBN slab waveguides that broaden the 2D material toolkit. Our results provide a direct route for waveguide‐based interrogation of layered materials, as well as a way to integrate layered materials into future photonic devices at arbitrary positions whilst maintaining their intrinsic properties.This article is protected by copyright. All rights reserved