Periodically Poled Lithium Niobate Waveguide Research Articles

160 Gb/s Time-Domain Channel Extraction/Insertion and All-Optical Logic Operations Exploiting a Single PPLN Waveguide

160 Gb/s all-optical signal processing is demonstrated exploiting pump depletion in addition to sum and difference frequency generation (SFG/DFG) in a single periodically poled lithium-niobate (PPLN) waveguide. 160 Gb/s time-domain extraction and insertion operations of channels are obtained in an optical time division multiplexing (OTDM) system. Moreover, 160 Gb/s digital operations including half-adder, half-subtracter and AND/OR/XOR functions are carried out. The use of pump depletion effect allows to process ultrafast signals due to its high efficiency and ultrafast dynamics. 160 Gb/s bit error rate (BER) measurements confirm the effectiveness of all presented functionalities.

Soliton formation and collapse in tunable waveguide arrays by electro-optic effect

Light propagation in periodically poled lithium niobate (PPLN) waveguide arrays is numerically investigated. By employing the concept of a linear focusing effect, we propose a brand new method to control discrete diffraction and spatial solitons in PPLN waveguide arrays by electrical field. Simulated results are presented, and the principle is discussed to demonstrate the feasibility of the method.

Tunable dual-channel multicasting all-optical 40 Gbit/s logic AND operation and format conversion for CSRZ signals

Proposed and demonstrated is a novel approach of tunable multicasting simultaneous logic AND operation and format conversion for carrier-suppressed return-to-zero (CSRZ) signals. By exploiting cascaded sum- and difference-frequency generation in a periodically-poled lithium niobate waveguide, tunable dual-channel multicasting all-optical 40 Gbit/s CSRZ logic AND operation and CSRZ-to-RZ format conversion is successfully observed in the experiment.

All-optical UWB pulse generation using sum-frequency generation in a PPLN waveguide

We propose and demonstrate a novel approach to optically generate ultrawideband (UWB) monocycle pulses by exploiting the parametric attenuation effect of sum-frequency generation (SFG) in a periodically poled lithium niobate (PPLN) waveguide. The SFG process changes the continuous-wave pump into dark optical pulse pump with undershoot, resulting in the generation of UWB monocycle through the combination of input signal and output pump with proper relative time advance/delay. Pairs of polarity-inverted UWB monocycle pulses meeting the UWB definition of U. S. Federal Communications Commission (FCC, part 15) are successfully obtained in the experiment.

Wavelength-multiplexed distribution of highly entangled photon-pairs over optical fiber

We report the first experimental demonstration of wavelength-multiplexed entanglement distribution over optical fiber. Forty-four channels of polarization-entangled photon-pairs were produced from a single pulse-pumped, short periodically-poled lithium niobate waveguide and distributed over 10 km of dispersion-shifted optical fiber. Entanglement fidelities of the distributed photon-pairs exceeded 0.86 for all selected channels.

Stable source of high quality telecom-band polarization-entangled photon-pairs based on a single, pulse-pumped, short PPLN waveguide

We demonstrate a stable source of high quality telecom-band polarization-entangled photon-pairs based on a single, pulse-pumped, short periodically-poled lithium niobate (PPLN) waveguide. Full quantum state tomographic measurement performed on the photon-pairs has revealed a very high state purity of 0.94, and an entanglement fidelity exceeding 0.96 at the low-rate-regime. At higher rates, entanglement quality degrades due to emission of multiple-pairs. Using a new model, we have confirmed that the observed degradation is largely due to double- and triple-pair emissions.

SOA-Assisted Data-Polarization-Insensitive Wavelength Conversion in a PPLN Waveguide

We demonstrate a novel method of wavelength conversion in a periodically poled lithium niobate (PPLN) waveguide using polarization modulation and amplitude modulation of its pump. Polarization-insensitive, all-optical, intensity-to-polarization conversion in a semiconductor optical amplifier (SOA) is used to reduce the waveguide's polarization sensitivity from >30 dB to <1 dB. We demonstrate BER measurements of the converted signal at 2.5 Gb/s. We also demonstrate polarization modulation of the PPLN waveguide pump using cross-polarization modulation in highly nonlinear fiber (HNLF) at 10 Gb/s.

All-optical dual-direction half-subtracter based on sum-frequency generation

We report a simple method to realize all-optical dual-direction half-subtracter at 40 Gb/s based on sum-frequency generation (SFG) using only one periodically poled lithium niobate (PPLN) waveguide. The SFG process generates the Borrow outputs and the combination of the outputs from PPLN after SFG results in the Difference. The operation performance of the proposed scheme is simulated, including eye diagrams, Q-factor, extinction ratio, and tunability. For different input optical powers, the length of the PPLN waveguide is optimized.

Dual-channel-output all-optical logic AND gate at 20 Gbit/s based on cascaded second-order nonlinearity in PPLN waveguide

Proposed and demonstrated is a novel scheme of a dual-channel-output all-optical logic AND gate. Using cascaded sum- and difference-frequency generation in a periodically poled lithium niobate (PPLN) waveguide, 20 Gbit/s logic AND operation with dual-channel outputs is successfully observed in the experiment.

Fiber-feedback continuous-wave and synchronously-pumped singly-resonant ring optical parametric oscillators using reverse-proton-exchanged periodically-poled lithium niobate waveguides

We describe guided-wave singly-resonant reverse-proton-exchanged (RPE) periodically-poled lithium niobate (PPLN) waveguide ring optical parametric oscillators (OPOs) in which the feedback was provided via a single-mode fiber pigtailed to the waveguide. Wavelength selection was achieved by means of a fiber Bragg grating inside the feedback loop. The SRO threshold for the synchronously-pumped OPO was below 1 mW of average coupled pump power.

Analysis of picosecond-pulse wavelength conversion based on cascaded sum-frequency generation and difference-frequency generation in quasi-phase-matched LiNbO3 waveguides

Wavelength conversion based on the cascaded sum-frequency generation and difference-frequency generation (cSFG+DFG) process in quasi-phase-matched (QPM) periodically poled lithium niobate (PPLN) waveguides has the advantage of no pump occupation in the communication band, compared to the traditional cascaded second-harmonic generation (SHG) and DFG process. In cSFG+DFG-based wavelength conversion, two pump waves and a signal wave are required. The input pulse train, as a carrier of information, can be applied to either the signal or one of the two pump waves. Though the converted wave is in the form of pulses, its temporal and spectral characteristics are dependent on the arrangement of the pulsed wave. In this work, we target the wavelength conversion of 40-GHz picosecond pulse trains, and systematically analyze the temporal and spectral characteristics of the pump, signal, converted, and sum-frequency waves during their propagations in PPLN waveguides by using numerical simulation. In particular, pulse shapes, optical spectra, phases and conversion efficiency are compared when the picosecond pulse train is used as the signal and pump waves, respectively.

Generation of continuous-wave broadband entangled beams using periodically poled lithium niobate waveguides

Continuous-wave light beams with broadband quantum entanglement are created with two independent squeezed light beams generated by two periodically poled lithium niobate waveguides and a symmentric beam splitter. The quantum entanglement is confirmed with a sufficient criterion ΔA,B2=⟨[Δ(x̂A−x̂B)]2⟩+⟨[Δ(p̂A+p̂B)]2⟩&amp;lt;1 and the observed ΔA,B2 is 0.75 over the bandwidth of 30MHz. Although the bandwidth is limited by that of the detector so far, it would be broadened up to 10THz which would be only limited by the bandwidth of phase matching for the second-order nonlinear process.

Proposal for All-Optical Switchable or/xor Logic Gates Using Sum-Frequency Generation

All-optical logic gate based on parametric processes in periodically poled lithium niobate (PPLN) waveguides is a promising technique in future high-speed all-optical signal processing. A simple realization of switchable or/xor logic gates at 40 Gb/s is proposed and numerically demonstrated using sum-frequency generation in a PPLN waveguide. By appropriately adjusting the input signal power and choosing the waveguide length, or and xor logic gates can be obtained. The operation performance is simulated, including eye diagrams and Q-factor. The input signal powers and waveguide length are optimized, providing a theoretical basis for achieving the optimal performance for the switchable or/xor logic gates

Highly Stable 160-Gb/s OTDM Technologies Based on Integrated MUX/DEMUX and Drift-Free PLL-Type Clock Recovery

This paper reports 160-Gb/s optical time-division-multiplexed (OTDM) technologies including an all-optical integrated multiplexer (MUX) providing all-channel independent modulation, an all-optical integrated demultiplexer (DEMUX) that offers all-channel simultaneous demultiplexing, and a drift-free phase-locked-loop (PLL)-type clock recovery circuit for ultrahigh-speed OTDM signals. We present the configuration of each technology and the results of experiments on those technologies. Highly stable operation is successfully demonstrated by using a MUX based on periodically-poled lithium niobate (PPLN) hybrid integrated planer lightwave circuit (PLC), a DEMUX based on semiconductor optical amplifier hybrid integrated PLC, and clock recovery circuit based on a PLL with an optical phase modulator and a PPLN waveguide

Light-enhanced electro-optic spectral tuning in annealed proton-exchanged periodically poled lithium niobate channel waveguides

We report the observation of light-enhanced electro-optic spectral tuning in annealed proton-exchanged, asymmetric domain-duty-cycle periodically poled lithium niobate (PPLN) channel waveguides for second-harmonic generation. The spectral tuning rate was increased rapidly from 0.07 nm/(kV/mm) to a saturated value of 0.32 nm/(kV/mm) in a 30%/70% domain-duty-cycle PPLN waveguide when the fundamental pump power near 1534 nm was increased from 0.6 to 46 mW. The second-harmonic laser power at 767 nm was identified to be the source enhancing the spectral tuning.

Second-harmonic generation in periodically poled lithium niobate waveguides fabricated by femtosecond laser pulses

The authors have demonstrated the second-harmonic generation (SHG) in optical channel waveguides which were fabricated in periodically poled lithium niobate (PPLN) by tightly focused femtosecond laser (781nm) pulses. The measured quasi-phase-matched wavelength and 3dB bandwidth for SHG in a 44.8-mm-long PPLN waveguide which has a domain period of 16.6μm were about 1563 and 0.25nm, respectively. The value of the index difference between the fundamental and harmonic wavelengths in laser written waveguide was inferred to be 0.047.

40-GHz picosecond-pulse second-harmonic generation in an MgO-doped PPLN waveguide

Second-harmonic generation (SHG) of 40-GHz picosecond optical pulses with different pulsewidths, pulse energies, and central wavelengths in a MgO-doped periodically poled lithium niobate (PPLN) waveguide is studied experimentally and theoretically. In the experiments, the picosecond pulses are generated from a 40-GHz mode-locked fiber laser and two tunable filters, with which the lasing wavelength can be tuned from 1530 to 1570 nm, and the pulsewidth can be tuned from 2 to 7 ps. The second-harmonic (SH) pulses are generated when the picosecond pump pulses pass through the MgO-doped PPLN waveguide. Dependences of SHG on pump pulsewidth, average pump power, and pump central wavelength are then investigated systematically. Meanwhile, dynamic behaviors of both pump and SH pulses in propagation are simulated numerically. Based on the temporal and spectral characteristics of SHG, a quantitative and systematic analysis on SHG efficiencies in terms of both pulse energy and spectral peak is presented. The simulation results are in good agreement with the measured data

Single-to-Multiple Channel Wavelength Conversions and Tuningof Picosecond Pulses in Quasi-Phase-Matched Waveguides

We report the single-to-multiple channel wavelength conversions of1.57-ps pulses based on cascaded second-harmonic generation anddifference frequency generation in quasi-phase-matched periodicallypoled lithium niobate waveguides. For single-to-single channelwavelength conversion, no external cavity laser is required with use of afibre ring laser. The conversion efficiency is about -21.44 dB. Theconverted idler wavelength can be tuned from 1526.4 nm to 1537.5 nm as thelasing pump wavelength is varied from 1566.1 nm to 1555.0 nm. By employingseveral input pumps, tunable single-to-dual and single-to-triplechannel wavelength conversions are experimentally demonstrated.

Flexible all-optical wavelength conversions of 1.57-ps pulses exploiting cascaded sum- and difference frequency generation (cSFG/DFG) in a PPLN waveguide

Flexible all-optical wavelength conversions of ps-pulses based on cascaded sum- and difference frequency generation (cSFG/DFG) are proposed and experimentally demonstrated using a periodically poled lithium niobate (PPLN) waveguide. The pulsed signal, with a 40 GHz repetition rate and a 1.57 ps pulse width is adopted. Fixed-in variable-out (tunable), variable-in fixed-out and variable-in variable-out wavelength conversions are successfully realized with three proposed tuning schemes. Both wavelength down- and up-conversion are simultaneously observed.

1.5- μm single photon counting using polarization-independent up-conversion detector

We report a 1.5- mum band polarization independent single photon detector based on frequency up-conversion in periodically poled lithium niobate (PPLN) waveguides. To overcome the polarization dependence of the PPLN waveguides, we employed a polarization diversity configuration composed of two up-conversion detectors connected with a polarization beam splitter. We experimentally confirmed polarization independent single photon counting using our detector. We undertook a proof-of-principle differential phase shift quantum key distribution experiment using the detector, and confirmed that the sifted key rate and error rate remained stable when the polarization state was changed during single photon transmission.