Orbital angular momentum (OAM) modes have emerged as a promising solution for enhancing the capacity of optical multiplexing systems, leveraging their theoretically unbounded set of orthogonal spatial modes. However, the generation and detection of OAM multiplexing signals are predominantly reliant on bulky optical components within complex optical setups. We introduce a compact solution for OAM information processing using laser-written glass chips, facilitating efficient multiplexing and demultiplexing of multiple OAM information channels. During the multiplexing process, OAM channels are managed via laser-scribed single-mode waveguides within a glass chip, with their modes converted using laser-written holograms on the side wall of the glass chip. The reciprocal process is employed for OAM demultiplexing. Our chips seamlessly interface with commercial optical fibers, ensuring compatibility with existing fiber-optic communication infrastructure. This work not only establishes, to our knowledge, a novel approach for OAM optical multiplexing but also underscores the potential of laser writing technology in advancing photonics and its practical applications in optical communications.