Optical CDMA technology has shown promise in optical communications, particularly in local-area optical fiber networks. We present a novel O-CDMA scheme with programmable and reconfigurable bipolar code capability using liquid crystal (LC) Spatial Light Modulators (SLMs). The key to our system performance depends on constructing a decoder that implements a true bipolar correlation using only unipolar signals and intensity detection. This has been accomplished using two unipolar correlations that can be performed optically, followed by a subtraction. In our coding system, the power spectrum of a broadband light source is encoded and decoded by programming the SLMs. The high polarization selectivity of these components coupled with the polarization rotation ability of liquid crystal elements makes switching possible with high extinction ratio and low crosstalk. Experimental results including the correlation measurements are presented. Good contrast between the autocorrelation and cross correlation values shows that a binary information symbol can be recovered by an appropriate threshold operation.
Optical CDMA technology has shown promise in optical communications, particularly in local-area optical fiber networks. We present a novel O-CDMA scheme with programmable and reconfigurable bipolar code capability using liquid crystal (LC) Spatial Light Modulators (SLMs). The key to our system performance depends on constructing a decoder that implements a true bipolar correlation using only unipolar signals and intensity detection. This has been accomplished using two unipolar correlations that can be performed optically, followed by a subtraction. In our coding system, the power spectrum of a broadband light source is encoded and decoded by programming the SLMs. The high polarization selectivity of these components coupled with the polarization rotation ability of liquid crystal elements makes switching possible with high extinction ratio and low crosstalk. Experimental results including the correlation measurements are presented. Good contrast between the autocorrelation and cross correlation values shows that a binary information symbol can be recovered by an appropriate threshold operation.
Summary form only given.There been increasing interest in realizing optical signal processing functions in optical communication systems based on nonlinear optical parametric processes. In the proposed ultrashort pulse optical code-division multiple access (CDMA) systems, in order to realize multiplexing and demultiplexing for multichannel operation, a nonlinear element is needed to distinguish between correctly decoded signals and incorrectly decoded multiaccess interference, which have comparable average optical power but carry different spectral information. It had been proposed to realize all-optical recognition of optical phase-coded ultrashort waveforms by using second-harmonic generation in long nonlinear crystals, which could have advantages in contrast ratio, operating power and detection efficiency over other proposed schemes. While high contrast ratios have been demonstrated based on such a scheme using bulk periodically poled lithium niobate (PPLN) crystals, the high efficiency has not yet been demonstrated. We use a simple combination of PPLN SHG waveguides and conventional photodetectors to realize all-optical recognition of spectrally phase coded optical pulses, which shows the potential of much higher conversion efficiency compared to previous bulk experiments, which is crucial for real-time operation with a high signal to noise ratio.
Rapid and programmable shaping of light fields is central to modern microscopy, display technologies, optical communications and sensing, quantum engineering, and quantum information processing. Current wavefront shaping technologies face a fundamental dichotomy: liquid-crystal-on-silicon spatial light modulators (LCoS-SLMs) offer high pixel count but suffer from low refresh rates, while acousto-optic deflectors (AODs) provide moderate speed with restricted optical beam geometries. Though recent advances in photonic integrated circuits achieve fast switching, there is currently no tool that provides MHz-rate, continuous motion, and arbitrarily reconfigurable control over a set of diffraction-limited spots. Here we introduce a new class of spatial light modulator that provides both 2D pixel geometry and high speed. The device operates by encoding spatial information in frequency bins via a broadband optical phase modulator, and decoding them via a first-of-its-kind, high-resolution 2D spectrometer. The spectrometer, based on the architecture which we call the Re-Imaging Phased Array (RIPA), achieves its sensitivity through long path-lengths, enabled by intra-spectrometer re-imaging lens-guides. We demonstrate site-resolved optical pulsing with a 44(1)~ns rise time, corresponding to frame rates exceeding 10 million frames per second, as well as arbitrary, reconfigurable 2D addressing and multi-site operations, including asynchronous, independent beam motion, splitting, and recombination. Leveraging these tools opens new horizons in rapid optical manipulation of matter across science, from fast, scalable control that approaches the inertial and radiation limits of atoms in quantum processors, to dynamically programmable, microsecond-resolved illumination in microscopy and neuro-biological imaging.
Liquid crystal displays (LCDs) are devices capable of manipulating properties of an incident light beam, such as amplitude, phase, and polarization, based on the voltage applied to their molecules. In this work, we will experimentally characterize the effect of an LCD on light polarization, aiming at its use as a programmable spatial light modulator (SLM) in optics and quantum information experiments. In the first part, we will determine the Mueller matrix of the device and, from it, its polarimetric properties. We will show that the LCD acts only approximately as an ideal retarder plate since it introduces depolarization to the incident light. In the second part, we investigate the behavior of the LCD through the formalism of quantum operations, treating its action as an operation on polarization qubit states. Through process tomography, we determine the matrix characterizing the device's operation and show that it is non-unitary. Next, we derive a general expression for the process matrix of an SLM, given by the combination of the LCD with wave plates. This expression will allow us to implement programmable operations on the polarization states of light based on the configuration of the wave plates and the voltage on the LCD. As an application, we will quantify the fidelity of the actual operation implemented by the SLM with an ideal unitary operation of interest in quantum information protocols.
Optical CDMA is being proposed as a suitable multiaccess technique to take advantage of the large bandwidth available in single-mode fiber-optic communications. In a CDMA system the communication link is shared by a number of users each of which has a unique address code, called signature. Recently an all-optical CDMA system based upon encoding and decoding coherent ultrashort pulses was introduced [l]. In the proposed optical CDMA system the transmitter consists of a bandhiited signal source, that generates a train of ultrashort light pulses. The output of the bandlimited source is multiplied by a data source that takes values 0 or 1 (ON-OFF Keying). If the data is 0, then no energy is transmitted. If the data is 1, then the ultrashort pulse is sent to the spectral-phase encoder which adds a determinate phase shift to each spectral component of the ultrashort pulse. When a pseudorandom set of spectral phase shifts is selected, spectral phase coding spreads the incident ultrashort pulse into a longer, lower intensity pseudonoise burst 111. The receiver is assumed to be a correlation receiver which is matched to the desired signal. The correlation process (optical decoder) is similar to that of the optical encoder, except that the decoder's spectral-phase code is the complex conjugate of the encoder's spectral-phase code. Thus a pulse is properly decoded when the encoding and decoding masks are a complex conjugate pair, in which case the spectral phase shifts are removed and the original pulse is recovered. On the other hand, when the encoding and decoding masks do not match, the spectral phase shifts are rearranged but not removed, and the output remains a low intensity pseudonoise burst. A threshold device is set to detect data corresponding to intense, properly decoded pulses and to reject low intensity, improperly decoded, pseudonoise bursts. An important factor in the performance of the proposed CDMA systrm is the peak intensity of the encoded signals. We consider using random signatures for the phase encoding of the phase pulses in the system and prove that they result in a fairly low peak intensity of the signals. We assume that the ultra-short light pulses are characterized by an ideal rectangular spectrum with bandwidth W. The ultrashort light pulse has peak intensity Po and duration t, $. Pulses of this form had been used in the experiments reported in [l]. The encodfng is taking place in the frequency domain. The signal
Optical CDMA is being proposed as a suitable multiaccess technique to take advantage of the large bandwidth available in single-mode fiber-optic communications. In a CDMA system the communication link is shared by a number of users, each of which has a unique address code called signature. Recently an all-optical CDMA system based upon encoding and decoding coherent ultrashort light pulses was introduced. An important factor in the performance of the CDMA system is the peak intensity of the encoded signals. We consider using random signatures for the phase encoding of the light pulses in this system and prove that they result in a fairly low peak intensity of the signals. In particular, we obtain an upper bound on the probability that the peak intensity of the encoded signal is greater than some value. This bound is strictly better than previously reported bounds and decreases exponentially with the length of the signatures. We also find a lower bound on the maximum number of minimally interfering signatures (or, to be more accurate, A-separated signatures, which will be defined) of length No that can be designed. Assuming that the communication is reliable if and only if any pair of signatures in the system is A-separated, a notion of capacity is defined and a lower bound on it is found.