Rahman Nouroozi

Integrated Optical Devices in Lithium Niobate

Lithium niobate offers incredible versatility as a substrate for integrated optics. Researchers have developed an array of new optical devices based on this material, including waveguide structures, electro-optical wavelength filters and polarization controllers, lasers with remarkable properties, nonlinear frequency converters of exceptional efficiency, ultrafast all-optical signal processing devices and single photon sources.

Simultaneous Polarization-Insensitive Wavelength Conversion of 80-Gb/s RZ-DQPSK Signal and 40-Gb/s RZ-OOK Signal in a Ti:PPLN Waveguide

Simultaneous all-optical wavelength conversion of an 80-Gb/s return-to-zero differential quadrature phase shift keying (RZ-DQPSK) data signal and a 40-Gb/s return-to-zero ON--OFF keying (RZ-OOK) data signal using a Ti:PPLN waveguide in a polarization-diversity loop configuration are demonstrated. The wavelength conversion is fully transparent to polarization, data rate, modulation format, and modulation level. The conversion efficiency for the signals was -21 dB, which includes 9.2-dB passive losses in the whole Ti:PPLN subsystem. Error-free performance for both wavelength-converted signals was achieved for polarization-scrambled input data signals without additional penalty caused by the polarization scrambling.

High-Dimensional Single-Photon Quantum Gates: Concepts and Experiments

Transformations on quantum states form a basic building block of every quantum information system. From photonic polarization to two-level atoms, complete sets of quantum gates for a variety of qubit systems are well known. For multilevel quantum systems beyond qubits, the situation is more challenging. The orbital angular momentum modes of photons comprise one such high-dimensional system for which generation and measurement techniques are well studied. However, arbitrary transformations for such quantum states are not known. Here we experimentally demonstrate a four-dimensional generalization of the Pauli X gate and all of its integer powers on single photons carrying orbital angular momentum. Together with the well-known Z gate, this forms the first complete set of high-dimensional quantum gates implemented experimentally. The concept of the X gate is based on independent access to quantum states with different parities and can thus be generalized to other photonic degrees of freedom and potentially also to other quantum systems.

Polarization-Insensitive 320-Gb/s In-Line All-Optical Wavelength Conversion in a 320-km Transmission Span

Polarization-insensitive in-line all-optical wavelength conversion (AOWC) of a single-channel 320-Gb/s RZ-DQPSK data signal in the middle of a 320-km transmission span is reported. The technique is based on a Ti:PPLN waveguide in a polarization diversity scheme. The conversion efficiency of the signal was -21 dB, which includes 9.2 dB of passive losses in the whole Ti:PPLN subsystem. Error-free performance for the in-line wavelength converted signal after 320-km transmission was successfully achieved.

PPLN-Waveguide Based Tunable Wavelength Conversion of QAM Data Within the C-Band

Tunable optical wavelength conversion of a 40 Gb/s 16-ary quadrature amplitude modulated signal within the C-band is demonstrated by cascaded sum frequency generation and difference frequency generation in a periodically-poled lithium niobate module. System experiments with conversion efficiencies of ~ 7.5 dB (excluding module loss) are presented. Bit-error ratio measurements confirm excellent conversion performance.

Tunable All-Optical Wavelength Conversion Based on Cascaded SHG/DFG in a Ti:PPLN Waveguide Using a Single CW Control Laser

Tunable all-optical wavelength conversion (AOWC) of a 40-Gb/s RZ-OOK data signal based on cascaded second-harmonic generation (SHG) and difference-frequency generation (DFG) in a Ti:PPLN waveguide is demonstrated. Error-free performances with negligible power penalty are achieved for the wavelength-converted signal at 1535, 1538, 1541, 1551, 1554, and 1557 nm, respectively.

110 km transmission of 160 Gbit/s RZ-DQPSK signals by midspan polarization-insensitive optical phase conjugation in a Ti:PPLN waveguide

We demonstrate 160 Gbit/s return-to-zero (RZ) differential quarternary phase-shift keying (DQPSK) signal transmission over a 110 km single-mode fiber by taking advantage of mid-span optical phase conjugation (OPC). The technique is based on nonlinear wavelength conversion by cascaded second harmonic and difference frequency generation in a Ti:PPLN waveguide. Error-free operation with a negligible optical signal-to-noise ratio penalty for the signal after the OPC transmission without and with polarization scrambling was achieved. The results also show the polarization insensitivity of the OPC system using a polarization diversity scheme.

Phase control of double-pass cascaded SHG/DFG wavelength conversion in Ti:PPLN channel waveguides

Guided wave χ(2) nonlinear frequency conversion via cascaded processes such as frequency doubling and different frequency generation (cSHG/DFG) is an attractive means for wavelength conversion in high bit rate WDM-systems [1, 2]. The efficiency of corresponding devices strongly increases with the nonlinear interaction length (Fig. 1a). Therefore, longer devices are more efficient provided (quasi-) phase matching can be maintainned over the whole length. As alternative, a double-pass approach may be used to increase the interaction length. Such a configuration requires a broadband dielectric mirror on one end face of the waveguide. As it induces wavelength dependent phase-shifts of the reflected waves, the direction of energy transfer by the nonlinear interactions may be reversed in backward direction after reflection unless appropriate phase control allows readjustment.

Integrated optical modulator manipulating the polarization and rotation handedness of Orbital Angular Momentum states

Recent studies demonstrated that the optical channels encoded by Orbital Angular Momentum (OAM) are capable candidates for improving the next generation of communication systems. OAM states can enhance the capacity and security of high-dimensional communication channels in both classical and quantum regimes based on optical fibre and free space. Hence, fast and precise control of the beams encoded by OAM can provide their commercial applications in the compatible communication networks. Integrated optical devices are good miniaturized options to perform this issue. This paper proposes a numerically verified integrated high-frequency electro-optical modulator for manipulation of the guided modes encoded in both OAM and polarization states. The proposed modulator is designed as an electro-optically active Lithium Niobate (LN) core photonic wire with silica as its cladding in a LN on Insulator (LNOI) configuration. It consists of two successive parts; a phase shifter to reverse the rotation handedness of the input OAM state and a polarization converter to change the horizontally polarized OAM state to the vertically polarized one. It is shown that all four possible output polarization-OAM encoded states can be achieved with only 6 V and 7 V applied voltages to the electrodes in the two parts of the modulator.

Ultralong propagation of a surface plasmon polariton wave within an ultrawide bandwidth via phase-sensitive optical parametric amplification

The propagation length enhancement of surface plasmon polariton (SPP) waves could lead to practical applications. This Letter proposes the numerically verified phase-sensitive nonlinear χ(2)-based optical parametric amplification (OPA) for ultralong propagation of a SPP wave within an ultrawide bandwidth. The strong nonlinear interaction between the SPP mode and the hybrid guided mode, which limits the length enhancement, is mitigated in a silver-coated linearly chirped periodically poled lithium niobate planar waveguide via slowly phase-matched OPA. Obtained results indicate an ultralong propagation length for a SPP mode of about 4 cm when a 135 MW/cm pump intensity is launched. The acceptance bandwidth of the amplified SPP shows its dependency on the pump intensity; for a pump intensity range between 70 and 135 MW/cm, the acceptance bandwidth is still ultrawide, varying from 28 to 18 nm, respectively.