This paper presents a free-space optical communication system that uses the orbital angular momentum (OAM) of light to encode and transmit information. The system uses spatial light modulators (SLMs) to generate and measure eight pure OAM states of a laser beam. The OAM states are encoded in the light beam's phase, and the information is resistant to eavesdropping because any attempt to measure the beam away from its axis introduces angular restrictions and lateral offsets, which result in measurement uncertainty. This demonstrates the uncertainty principle for OAM and the effects of aperturing and misalignment on OAM measurement. The system uses a HeNe laser and a computer-controlled SLM to generate OAM states. The transmitter unit converts a plane-wave input into a helical phase front using a hologram pattern. The receiver unit uses a similar setup to measure the OAM of the received beam. The system operates over a 15-meter distance and demonstrates that data recoverable by eavesdroppers is corrupted. The security of the system is enhanced by the inherent difficulty of reading OAM data without positioning the detector directly in the path of the intended receiver. The OAM data is difficult to recover from scattered light because the scattering process randomizes the phase structure of the beam. Additionally, the measurement of OAM is limited by the angular extent of the beam during measurement, as shown by the effect of inserting different segment masks into the path of an l=1 laser beam. The measured OAM values show a spread that increases with the size of the angular restriction. The system is also affected by alignment errors, which can result in beam broadening and a superposition of different OAM states. The security of the system is further enhanced by the fact that the OAM content of the beam is difficult to infer in such situations. The channel separation of Δl = 1 offers a higher degree of security than the configuration based on Δl = 4. The system is compatible with current free-space optical (FSO) techniques such as wavelength-division multiplexing, adaptive optics for atmospheric correction, and quantum cryptography with single photons. The paper also raises several interesting questions that need to be fully addressed before the system can be realized in a commercial FSO system.This paper presents a free-space optical communication system that uses the orbital angular momentum (OAM) of light to encode and transmit information. The system uses spatial light modulators (SLMs) to generate and measure eight pure OAM states of a laser beam. The OAM states are encoded in the light beam's phase, and the information is resistant to eavesdropping because any attempt to measure the beam away from its axis introduces angular restrictions and lateral offsets, which result in measurement uncertainty. This demonstrates the uncertainty principle for OAM and the effects of aperturing and misalignment on OAM measurement. The system uses a HeNe laser and a computer-controlled SLM to generate OAM states. The transmitter unit converts a plane-wave input into a helical phase front using a hologram pattern. The receiver unit uses a similar setup to measure the OAM of the received beam. The system operates over a 15-meter distance and demonstrates that data recoverable by eavesdroppers is corrupted. The security of the system is enhanced by the inherent difficulty of reading OAM data without positioning the detector directly in the path of the intended receiver. The OAM data is difficult to recover from scattered light because the scattering process randomizes the phase structure of the beam. Additionally, the measurement of OAM is limited by the angular extent of the beam during measurement, as shown by the effect of inserting different segment masks into the path of an l=1 laser beam. The measured OAM values show a spread that increases with the size of the angular restriction. The system is also affected by alignment errors, which can result in beam broadening and a superposition of different OAM states. The security of the system is further enhanced by the fact that the OAM content of the beam is difficult to infer in such situations. The channel separation of Δl = 1 offers a higher degree of security than the configuration based on Δl = 4. The system is compatible with current free-space optical (FSO) techniques such as wavelength-division multiplexing, adaptive optics for atmospheric correction, and quantum cryptography with single photons. The paper also raises several interesting questions that need to be fully addressed before the system can be realized in a commercial FSO system.