2 Tbit/s free-space data transmission on two orthogonal orbital-angular-momentum beams each carrying 25 WDM channels.

We demonstrate a 2 Tbit/s free-space data link using two orthogonal orbital angular momentum beams each carrying 25 different wavelength-division-multiplexing channels. We measure the performance for different modulation formats, including directly detected 40 Gbit/s nonreturn-to-zero (NRZ) differential phase-shift keying, 40 Gbit/s NRZ on-off keying, and coherently-detected 10 Gbaud NRZ quadrature phase-shift keying, and achieve low bit error rates with penalties less than 5 dB.

Fiber structure to convert a Gaussian beam to higher-order optical orbital angular momentum modes.

We propose a fiber structure of a square core and ring refractive index profile that converts an input circular polarized Gaussian mode into optical orbital angular momentum (OAM) modes. By breaking the circular symmetry of the waveguide, the input circularly polarized fundamental mode in the square core can be coupled into the ring region to generate higher-order OAM modes, corresponding to the transference of spin angular momentum and orbital angular momentum. We show, by using simulation, the generation of OAM modes with a topological charge l up to 9 using <10 mm long fiber. The mode purity is above 96.4% and the extinction ratio can be 30 dB.

Fiber coupler for generating orbital angular momentum modes.

We propose a fiber coupler consisting of a central ring and four external cores to generate up to ten orbital angular momentum (OAM) modes. Four coherent input lights are launched into the external cores and then coupled into the central ring waveguide to generate OAM modes. By changing the size of the external cores, one can selectively excite a high-order OAM mode. The quality of the generated OAM modes can be enhanced by adjusting the polarization state and the phase of input lights. We show the generation of OAM modes with odd charge numbers of -9 to +9 (i.e., 10 modes totally) with mode purity of >99% using <2 mm long fiber. This fiber coupler design can be extended to enable all-fiber spatial-mode (de)multiplexing.

40 Gbit/s optical data exchange between wavelength-division-multiplexed channels using a periodically poled lithium niobate waveguide.

We propose a time- and channel-selective optical data exchange between wavelength-division-multiplexed (WDM) channels by exploiting the cascaded second-order parametric nonlinear interactions in a periodically poled lithium niobate (PPLN) waveguide. It is observed that the PPLN-based optical data exchange provides nearly symmetric performance with signals located in the short- and long-wavelength ranges. Optical data exchange between two WDM channels is realized with a power penalty of less than 1.5 dB at 10 Gbit/s and 3 dB at 40 Gbit/s at a bit-error rate of 10(-9). We demonstrate the 40 Gbit/s channel-selective optical data exchange between four WDM channels with a power penalty of approximately 4 dB.

Photonic processing of 320 Gbits/s based on sum-/difference-frequency generation and pump depletion in a single PPLN waveguide.

The possibilities and limitations of using nonlinearities in periodically poled lithium-niobate waveguides for ultrafast all-optical processing are experimentally investigated. A combination of the sum-/difference-frequency generation and pump depletion effect are exploited to obtain optical demultiplexing, add/drop multiplexing, and wavelength conversion of up to 320 Gbits/s.

Tunable 503 ns optical delay of 40 Gbit/s RZ-OOK and RZ-DPSK using a wavelength scheme for phase conjugation to reduce residual dispersion and increase delay.

We demonstrate a method for a tunable optical delay element that allows for minimal residual dispersion and double the relative delay. A tunable delay of 503 ns for 40 Gbit/s return-to-zero on-off keying and return-to-zero differential phase-shift keying is shown with a reduction in residual dispersion of approximately 95%.

Tunable 105 ns optical delay for 80 Gb/s RZ-DQPSK, 40 Gb/s RZ-DPSK, and 40 Gb/s RZ-OOK signals using wavelength conversion and chromatic dispersion.

We demonstrate a variable, optical-delay element using tunable wavelength conversion in a periodically poled lithium niobate waveguide, dispersion-compensating fiber and intrachannel dispersion compensation. A delay of up to 105 ns is demonstrated using 80 Gb/s return-to-zero differential-quadrature phase-shift keying, 40 Gb/s return-to-zero differential phase-shift keying, and 40 Gb/s return-to-zero on-off keying modulation formats. Bit-error rates <10(-9) are demonstrated for each waveform at various delay settings.

Time-slot interchange of 40 Gbits/s variable length optical packets using conversion-dispersion-based tunable delays.

We demonstrate tunable time-slot interchange of 40 Gbits/s optical data packets using a conversion-dispersion-based tunable optical delay element. Odd and even data packets are extracted from an input signal, delayed relative to one another in a highly dispersive medium, and then multiplexed back together. Tunability is demonstrated by operating with two different packet lengths, 182 and 288 bits/packet, and a bit error rate of <10(-9) is achieved.

Slow light on Gbit/s differential-phase-shift-keying signals.

We demonstrate, via simulation and experiment, slowing down of a phase-modulated optical signal. A 10.7-Gb/s NRZ-DPSK signal can be delayed by as much as 42 ps while still achieving error free via broadband SBS-based slow light. We further analyze the impact of slow-light-induced data-pattern dependence on both constructive and destructive demodulated ports. By detuning the SBS gain profile, we achieve 3-dB Q-factor improvement by the reduction of pattern dependence. Performance comparison between NRZ-DPSK and RZ-DPSK shows that robustness to slow-light-induced pattern dependence is modulation format dependent.

Optical data packet synchronization and multiplexing using a tunable optical delay based on wavelength conversion and inter-channel chromatic dispersion.

10 Gb/s non-return-to-zero (NRZ) on-off keyed (OOK) optical data packets are synchronized and time-multiplexed using a 26-ns tunable all-optical delay line. The delay element is based on wavelength conversion in periodically poled lithium niobate (PPLN) waveguides, inter-channel chromatic dispersion in dispersion compensating fiber (DCF) and intra-channel dispersion compensation with a chirped fiber Bragg grating (FBG). Delay reconfiguration time is measured to be less than 300 ps.