Hongkun Lian

The full adder (FA) and full subtractor (FS) are key operations used in the arithmetic and logic units of digital processors. Performing the FA and FS optically may enable the direct line-rate processing of high-speed optical data. Previous demonstrations of optical FA and FS have not been shown for phase-encoded input and output data signals. Such phase-encoded data formats could offer improved noise tolerances and longer distances of transmission compared to amplitude-encoded data formats. In this work, we experimentally demonstrate an optical FA and FS for binary-phase-shift-keying (BPSK) data signals at 2.5- and 5-Gbit/s. Our approach utilizes input BPSK data signals and continuous-wave pumps that are encoded at different frequencies, in which one of the input BPSK data signals is negated for the FS case. The data and pumps undergo nonlinear wave mixing in a periodically poled lithium niobate (PPLN) waveguide to generate the FA or FS BPSK outputs at different frequencies. The experimental results show error-free logic operation for both the FA and FS outputs at 2.5- and 5-Gbit/s over 1536 captured bits.

This tutorial provides an overview of free-space optical (FSO) communications operating in the mid-infrared (mid-IR) wavelength bands. In the mid-IR region, there are two atmosphere transmission windows: (mid-wave infrared (MWIR) at 3–5 µm and long-wave infrared (LWIR) at 8–12 µm) with relatively low atmospheric absorption. Compared to near-infrared (near-IR) wavelengths (e.g., telecom C-band at ∼1.55 µm), mid-IR tends to be more resilient to atmospheric degradation effects (e.g., fog-induced scattering and atmospheric turbulence). Thus, using mid-IR wavelengths can enable more robust FSO links through challenging atmospheric conditions. This tutorial aims to review recent developments and advances in mid-IR FSO communications. Various devices and approaches for mid-IR data transmitters and receivers are discussed. Advanced demonstrations for single-channel and multi-channel-multiplexed high-capacity mid-IR FSO links are reviewed. This tutorial also discusses the challenges and limitations of current techniques, as well as the outlook for future research.

An optical-tapped-delay-line (OTDL) can implement various processing functions on data that is transmitted over an optical network, including format conversion, complex filtering, and pattern recognition. Previous demonstrations of OTDL functions have either processed: (i) one data channel with one or more OTDL functions, or (ii) multiple data channels with one OTDL function per channel. In this work, we experimentally demonstrate three OTDL functions simultaneously on two optical data channels to obtain six optical data outputs. The inputs include: (i) two quadrature-phase-shift-keying (QPSK) channels, and (ii) two on-off-keying (OOK) channels. In each case, delayed data copies and pumps encoded with the OTDL function weights undergo nonlinear wave mixing in a periodically poled lithium niobate (PPLN) waveguide. Six optical data outputs are simultaneously generated at six different frequencies. In the QPSK case, the average symbol correctness over 3072 symbols is: (i) ~99.5% at 7.5-Gbaud and ~98.8% at 10-Gbaud for format conversion, (ii) ~98.1% at 7.5-Gbaud and ~94.3% at 10-Gbaud for complex filtering, and (iii) 100% at both baud rates for pattern recognition. In the OOK case, the average symbol correctness at 7.5-Gbaud is ~99.8% for format conversion, ~99.9% for complex filtering, and 100% for pattern recognition.