A chaotic carrier of information can be considered a generalization of the more traditional sinusoidal carrier. In communication systems which use chaotic waveforms, as in many more conventional methods, information can be recovered from the carrier using a receiver which is “tuned,” or synchronized, to the dynamics of the transmitter. Communication methods using chaotic carriers have been studied for the past few years, and several methods have been experimentally demonstrated in electronic circuits [1]. While chaotic electronic circuits typically have bandwidths of 100 kHz or less [2], the optical system presented here has a bandwidth of at least several GHz. In those electronic chaotic communication methods that have been demonstrated, the chaos usually has been low dimensional. For certain low-dimensional chaotic communication methods, it has been shown previously that the message can be extracted from the transmitted signal by reconstructing the system’s chaotic attractor [3]. A communication method utilizing higher dimensional chaos is likely to provide enhanced privacy. Numerical analysis of our experimental data indicates that the dynamics of our system are indeed high dimensional, of order 10 or greater. Previously, Goedgebuer and colleagues have demonstrated chaotic communication of a 2 kHz sine wave using a hybrid electro-optic system to generate highdimensional chaotic fluctuations in wavelength [4]. Also in earlier work, we injected a small 10 MHz square wave optical message into a ring laser producing highdimensional chaotic light. The square wave message was masked by the chaotic intensity fluctuations of the light from the ring laser as it propagated to a receiver, where the message was recovered [5]. Here we describe several qualitatively new developments, in both concept and technique, over previous work. Rather than using the chaotic light to mask a message, an intracavity intensity modulator is used to directly encode the message onto an optical chaotic carrier. Unlike our previous work, the message signal does not have to be small compared to the carrier or slow compared to the bandwidth of the laser fluctuations; they can have comparable bandwidths. The message modulation drives the chaotic dynamics of the laser. The laser dynamics, in turn, incorporate the digital message into the chaotic waveform. Both transmitter and receiver have configurations that involve two separate time delays, thereby enhancing the privacy of the transmission —successful recovery of the message depends on multiple parameter settings and a matched geometric configuration in the receiver. Finally, the receiver utilizes the polarization properties of the light to recover the digital information by dividing two signals, rather than taking a difference. These innovations enable us to demonstrate recovery of a pseudorandom sequence of bits at 126 Mbitsysec, limited by the bandwidth of our photodiodes. Placing a 1.5 km communication channel between the transmitter and receiver did not cause any obvious degradation of performance. The experimental setup of the fiber-optic system is shown in Fig. 1. The inner ring of the transmitter includes EDFA 1 (erbium-doped fiber amplifier) and a polarizing lithium niobate sLiNBO3d intensity modulator which encodes the message onto the chaotic light. The inner ring is approximately 40 m in length. The outer loop contains EDFA 2, to adjust the amplitude of the light field, and a polarization controller. The polarization controller consists of three wave plates (ly4, ly2, and ly4, respectively) which allow control over the relative phase and polarization of the light fields in the inner ring and outer loop. The outer loop itself is approximately 36 m long and provides a time delay between these light fields. Light coupled out of the transmitter propagates through a fiber-optic communication channel to the receiver. Ten percent of the transmitted light is sent through an attenuator to photodiode A (3-dB roll-off at 125 MHz). The length of the fiber in the outer loop of the receiver has been matched to the length of the transmitter’s outer loop. The time delay between reception of a signal at photodiode A and reception at photodiode B (also 3-dB roll-off at 125 MHz) has been matched to the round-trip time in the inner ring of the transmitter. The signals detected by the photodiodes are recorded by a digital sampling oscilloscope at a rate of 1 3 10 9 samplesysec.