Narek Karapetyan

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.

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.

Optical signal processing can provide high-speed operation on optical data and avoidance of optical-to-electrical-to-optical conversion. In many networking scenarios, the optical data may be encoded as quadrature-phase-shift-keying (QPSK) for spectral efficiency and noise tolerance. One signal processing function is pattern matching between two data streams, which directly compares their data patterns and can be useful for network security and improving data transmission. In this work, we experimentally demonstrate optical pattern matching between two independent QPSK data inputs using nonlinear wave mixing. The QPSK channels and their delayed copies are combined at the input of a highly nonlinear fiber (HNLF) along with a continuous wave pump. The data channels and pump undergo four-wave mixing in the HNLF to generate a 9-ary quadrature amplitude modulation (9-QAM) output. The output symbols correspond to the matched, partially matched, and mismatched 2-symbol patterns between the two QPSK inputs. The 9-QAM output constellation has an error-vector-magnitude of 8.4% and 8.9% at 3-Gbaud and 5-Gbaud rates, respectively, resulting in error-free optical pattern matching between the two QPSK inputs over 1536 symbols.

Optical data format de-aggregation enables the conversion from a single higher-order phase-encoded data channel coming from a high-bandwidth network into two amplitude-modulated signals that may be commonly used in lower-bandwidth local information systems. We experimentally demonstrate the optical de-aggregation of a 10-Gbit/s quadrature phase-shift keyed (QPSK) signal into two 5-Gbit/s on-off keyed (OOK) signals. Using wave mixing in a highly nonlinear fiber (HNLF), we apply two optical effects simultaneously to the input signal: (a) constellation squeezing, in which the 10-Gbit/s QPSK signal is de-aggregated into two different 5-Gbit/s binary phase-shift keying (BPSK) signals, and (b) constellation biasing, in which the coherent addition of a continuous-wave (CW) bias and the two BPSK signals shifts the data constellation points, resulting in only amplitude modulation and two different 5-Gbit/s OOK signals. The optical signal-to-noise ratio (OSNR) differences at a bit error rate (BER) of 3.8·10⁻³ between the back-to-back (B2B) transmitted OOK signal and the two recovered OOK signals using direct detection are 1.9 dB and 3.2 dB.

Performing pattern recognition via correlation in the optical domain has potential advantages, including: (i) high-speed operation at the line rate and (ii) tunability and scalability by operating on the optical wave properties. Such pattern recognition might be performed on quadrature-phase-shift-keying (QPSK) data transmitted over an optical network, which generally requires using coherent detection to distinguish the phase levels of the correlator output. To enable simpler detection, we combine optical correlation with optical biasing to experimentally demonstrate tunable and scalable QPSK pattern recognition using direct detection. The pattern is applied by adjusting the relative phases of the local pumps. Delayed QPSK signals, a coherent bias tone, and local pumps undergo nonlinear wave-mixing in a periodically poled lithium niobate (PPLN) waveguide to perform optical correlation and biasing. The biased correlator output is captured using direct detection, where the highest power level corresponds only to the pattern. Multiple QPSK pattern recognitions are achieved error-free over 3072 symbols using power thresholding values of (i) 0.78 at a 5-Gbaud rate and 0.73 at a 10-Gbaud rate for 2-symbol pattern recognition and (ii) 0.81 at a 5-Gbaud rate and 0.79 at a 10-Gbaud rate for 3-symbol pattern recognition.

Compared to its electronic counterpart, optically performed matrix convolution can accommodate phase-encoded data at high rates while avoiding optical-to-electronic-to-optical (OEO) conversions. We experimentally demonstrate a reconfigurable matrix convolution of quadrature phase-shift keying (QPSK)-encoded input data. The two-dimensional (2-D) input data is serialized, and its time-shifted replicas are generated. This 2-D data is convolved with a 1-D kernel with coefficients, which are applied by adjusting the relative phase and amplitude of the kernel pumps. Time-shifted data replicas (TSDRs) and kernel pumps are coherently mixed using nonlinear wave mixing in a periodically poled lithium niobate (PPLN) waveguide. To show the tunability and reconfigurability of this approach, we vary the kernel coefficients, kernel sizes (e.g., 2 × 1 or 3 × 1), and input data rates (e.g., 6–20 Gbit/s). The convolution results are verified to be error-free under an applied: (a) 2 × 1 kernel, resulting in a 16-quadrature amplitude modulation (QAM) output with an error vector magnitude (EVM) of ∼5.1–8.5%; and (b) 3 × 1 kernel, resulting in a 64-QAM output with an EVM of ∼4.9–5.5%.