Andong Wang

Demonstration of hybrid orbital angular momentum multiplexing and time-division multiplexing passive optical network

Mode-division multiplexing passive optical network (MDM-PON) is a promising scheme for next-generation access networks to further increase fiber transmission capacity. In this paper, we demonstrate the proof-of-concept experiment of hybrid mode-division multiplexing (MDM) and time-division multiplexing (TDM) PON architecture by exploiting orbital angular momentum (OAM) modes. Bidirectional transmissions with 2.5-Gbaud 4-level pulse amplitude modulation (PAM-4) downstream and 2-Gbaud on-off keying (OOK) upstream are demonstrated in the experiment. The observed optical signal-to-noise ratio (OSNR) penalties for downstream and upstream transmissions at a bit-error rate (BER) of 2 × 10(-3) are less than 2.0 dB and 3.0 dB, respectively.

Characterization of LDPC-coded orbital angular momentum modes transmission and multiplexing over a 50-km fiber

Mode-division multiplexing over fibers has attracted increasing attention over the last few years as a potential solution to further increase fiber transmission capacity. In this paper, we demonstrate the viability of orbital angular momentum (OAM) modes transmission over a 50-km few-mode fiber (FMF). By analyzing mode properties of eigen modes in an FMF, we study the inner mode group differential modal delay (DMD) in FMF, which may influence the transmission capacity in long-distance OAM modes transmission and multiplexing. To mitigate the impact of large inner mode group DMD in long-distance fiber-based OAM modes transmission, we use low-density parity-check (LDPC) codes to increase the system reliability. By evaluating the performance of LDPC-coded single OAM mode transmission over 50-km fiber, significant coding gains of >4 dB, 8 dB and 14 dB are demonstrated for 1-Gbaud, 2-Gbaud and 5-Gbaud quadrature phase-shift keying (QPSK) signals, respectively. Furthermore, in order to verify and compare the influence of DMD in long-distance fiber transmission, single OAM mode transmission over 10-km FMF is also demonstrated in the experiment. Finally, we experimentally demonstrate OAM multiplexing and transmission over a 50-km FMF using LDPC-coded 1-Gbaud QPSK signals to compensate the influence of mode crosstalk and DMD in the 50 km FMF.

Graphene-assisted nonlinear optical device for four-wave mixing based tunable wavelength conversion of QPSK signal.

We fabricate a nonlinear optical device based on a fiber pigtail cross-section coated with a single-layer graphene grown by chemical vapor deposition (CVD) method. Using such graphene-assisted nonlinear optical device, we experimentally demonstrate tunable wavelength conversion of a 10 Gbaud quadrature phase-shift keying (QPSK) signal by exploiting degenerate four-wave mixing (FWM) progress in graphene. We study the conversion efficiency as functions of the pump power and pump wavelength and evaluate the bit-error rate (BER) performance. The observed optical signal-to-noise ratio (OSNR) penalties for tunable QPSK wavelength conversion are less than 2.2 dB at a BER of 1 × 10(-3).

Full-duplex bidirectional data transmission link using twisted lights multiplexing over 1.1-km orbital angular momentum fiber.

We present a full-duplex bidirectional data transmission link using twisted lights multiplexing over 1.1-km orbital angular momentum (OAM) fiber. OAM+1 and OAM−1 modes carrying 20-Gbit/s quadrature phase-shift keying (QPSK) signals are employed in the downlink and uplink transmission experiments. The observed mode crosstalks are less than −15.2 dB, and the full-duplex crosstalks are less than −12.7 dB. The measured full-duplex optical signal-to-noise ratio (OSNR) penalties at a bit-error rate (BER) of 2 × 10−3 are ~2.4 dB in the downlink transmission and ~2.3 dB in the uplink transmission. The obtained results show favorable full-duplex twisted lights multiplexing data transmission performance in a km-scale OAM fiber link.

Demonstration of 20-Gbit/s high-speed Bessel beam encoding/decoding link with adaptive turbulence compensation

By mapping traditional amplitude modulation to spatial modulation and employing adaptive optics compensation technique, we propose and experimentally demonstrate a high-speed Bessel beam encoding/decoding free-space optical link through atmospheric turbulence. The Bessel beam encoding/decoding speed is not limited by the conventional slow switching response of a spatial light modulator (SLM) but is fully determined by the modulation rate of an intensity modulator, which easily supports tens of gigabits per second modulation and resultant encoding/decoding. We use an SLM loaded with a pseudorandom phase mask to emulate atmospheric turbulence in the laboratory environment. An adaptive optics closed loop is used to sense the phase distortion of an extra probe Gaussian beam and then compensate the distorted Bessel beams. A 20-Gbit/s Bessel beam encoding/decoding link with adaptive turbulence compensation is demonstrated in the experiment, showing favorable operation performance.

Graphene-assisted multiple-input high-base optical computing.

We fabricate a nonlinear optical device based on a fiber pigtail cross-section coated with a single-layer graphene grown by chemical vapor deposition (CVD) method. We demonstrate 10-Gbaud three-input quaternary hybrid addition and subtraction (A+B−C, A+C−B, B+C−A) in the experiment.

Graphene-silicon microring resonator enhanced all-optical up and down wavelength conversion of QPSK signal

We fabricate a nonlinear optical device based on graphene-silicon microring resonator (GSMR). Using such graphene-assisted nonlinear optical device, we experimentally demonstrate up and down wavelength conversion of a 10-Gbaud quadrature phase-shift keying (QPSK) signal by exploiting degenerate four-wave mixing (FWM) progress in the fabricated GSMR. We study the conversion efficiency as a function of the pump power. In addition, the resonant wavelength of GSMR is tuned by changing the temperature from 20°C to 40°C. We evaluate the bit-error rate (BER) performance for up and down wavelength conversion. The observed optical signal-to-noise ratio (OSNR) penalties for QPSK up and down wavelength conversion are less than 1.4 dB at a BER of 1 × 10-3. The BER performance as a function of the pump power for up wavelength conversion is also assessed. The minimum OSNR penalty is less than 0.8 dB when the pump power is 13.3 dBm.

Experimental demonstration on two-input optical high-base hybrid doubling and subtraction functions in graphene

Optical signal processing is considered to be a promising technique to overcome the speed limitation of electronics and accelerate next-generation high-speed optical networks. Among various optical signal processing operations, optical arithmetic functions have attracted increasing interest. Here, by exploiting the degenerate four-wave mixing progress in graphene and adopting (differential) quadrature phase-shift keying signals, we experimentally demonstrate 10 Gbaud two-input (A, B) hybrid quaternary arithmetic functions of doubling and subtraction (2A-B, 2B-A) in the optical domain. The measured optical signal-to-noise ratio penalties at a bit-error rate of 2 × 10⁻³ are about 7.4 dB for 2A-B and 7 dB for 2B-A.

Direct fiber vector eigenmode multiplexing transmission seeded by integrated optical vortex emitters

Spatial modes have received substantial attention over the last decades and are used in optical communication applications. In fiber-optic communications, the employed linearly polarized modes and phase vortex modes carrying orbital angular momentum can be synthesized by fiber vector eigenmodes. To improve the transmission capacity and miniaturize the communication system, straightforward fiber vector eigenmode multiplexing and generation of fiber-eigenmode-like polarization vortices (vector vortex modes) using photonic integrated devices are of substantial interest. Here, we propose and demonstrate direct fiber vector eigenmode multiplexing transmission seeded by integrated optical vortex emitters. By exploiting vector vortex modes (radially and azimuthally polarized beams) generated from silicon microring resonators etched with angular gratings, we report data-carrying fiber vector eigenmode multiplexing transmission through a 2-km large-core fiber, showing low-level mode crosstalk and favorable link performance. These demonstrations may open up added capacity scaling opportunities by directly accessing multiple vector eigenmodes in the fiber and provide compact solutions to replace bulky diffractive optical elements for generating various optical vector beams.

Demonstration of data-carrying orbital angular momentum-based underwater wireless optical multicasting link

One-to-many data information transfer, also known as multicasting, is desired in underwater wireless communications when distributing signal between multiple users. In this paper, by exploiting the space domain (spatial phase structure) of lightwaves, we propose and demonstrate an orbital angular momentum (OAM)-based underwater wireless optical multicasting link. 2-meter underwater transmission of 4-fold green light (520 nm) OAM modes multicasting (OAM-6, OAM-3, OAM+3, OAM+6), each channel carrying 1.5-Gbaud 8-ary quadrature amplitude modulation (8-QAM) with orthogonal frequency-division multiplexing (OFDM) signal, is demonstrated in the experiment. The OAM spectrum after underwater propagation suffers some degradation with the crosstalk between multicasting OAM channels and other unwanted channels measured to be less than −6 dB. Bit-error rate (BER) performance is characterized with ~2 dB penalty. Higher-order modulation signals (16-QAM-OFDM, 32-QAM-OFDM) are also considered in free-space OAM multicasting link for comparison.