Shaozhen Ma

High speed all optical logic gates based on quantum dot semiconductor optical amplifiers

A scheme to realize all-optical Boolean logic functions AND, XOR and NOT using semiconductor optical amplifiers with quantum-dot active layers is studied. nonlinear dynamics including carrier heating and spectral hole-burning are taken into account together with the rate equations scheme. Results show with QD excited state and wetting layer serving as dual-reservoir of carriers, as well as the ultra fast carrier relaxation of the QD device, this scheme is suitable for high speed Boolean logic operations. Logic operation can be carried out up to speed of 250 Gb/s.

High speed all-optical PRBS generation based on quantum-dot semiconductor optical amplifiers

A scheme to generate return-to-zero on-off keying (RZ-OOK) high speed all-optical pseudo random bit sequence (PRBS) based on quantum-dot semiconductor optical amplifiers (QD SOA) has been studied. By analyzing the performance of the core functional unit of this system, which is composed of QD SOA-based logic XOR and AND gates, as well as considering the saturation effect of the QD device and noise level of the system, we demonstrated the systems capability of producing stable high speed optical PRBS signals. Results show that the performance of the system depends on a number of parameters, including relaxation lifetime from QD excited state to ground state, injected current density, bit repetition rate, signal pulse width and single pulse energy. For devices with relaxation time approximately 1.0 ps, injected current density >1.8 kA/cm(2), single pulse energy <1.0 pJ with pulse width around 1.0 ps, the system is capable of PRBS generation at speeds of approximately 250 Gb/s.

Multiwavelength fiber ring laser based on a semiconductor and fiber gain medium.

We report a novel multi-wavelength laser source based on hybrid gain medium, with a semiconductor optical amplifier and erbium doped fiber amplifier, and a double-ring structure. More than 60 lines with more than 50 dB signal-to-noise ratio (SNR) have been achieved in our setup. The wavelength interval between the wavelengths is approximately 0.32 nm. The 3 dB spectral width of each lasing line is approximately 0.019 nm. The laser can be tuned from approximately 1526 nm to approximately 1562 nm by adjusting the loss in the cavity.

Dual-Wavelength Mode-Locked Erbium-Doped Fiber Ring Laser Using Highly Nonlinear Fiber

We demonstrate a stable dual-wavelength actively mode-locked erbium-doped fiber laser operating at 20 GHz. A highly nonlinear fiber is used to compensate the frequency chirp caused by regular single-mode fiber in the optical cavity. Dual-wavelength pulse trains with pulsewidths ~1.4 ps are obtained.

All optical logic gates based on two-photon absorption

When the two-photon absorption of a high intensity pump beam takes place in a semiconductor optical amplifier there is an associated fast phase change of a weak probe signal. A scheme to realize fast all-optical XOR logic function using twophoton absorption induced phase change has been analyzed. Rate equations for semiconductor optical amplifiers, for input data signals with high intensity, configured in the form of a Mach-Zehnder interferometer has been solved. The input intensities are high enough so that the two-photon induced phase change is larger than the regular gain induced phase change. The model shows that both XOR operation and pseudorandom binary sequence generation at 250 Gb/s with good signal to noise ratio is feasible.

All-optical latches based on two-photon absorption in semiconductor optical amplifiers

The design and performance of two optical latches, the set–reset (S-R) latch and D flip-flop have been studied. These latches are the building blocks of large optical processors. The latches are built using two optical logic operations NAND and NOT. Both NAND and NOT operations are realized by using the ultrafast phase response during two-photon absorption process in semiconductor optical amplifiers. Rate equations for semiconductor optical amplifiers, for input data signals with high intensity, configured in the form of a Mach–Zehnder interferometer, have been solved. The input intensities are high enough that the two-photon induced phase change is larger than the regular gain induced phase change. Results show that this scheme can realize the functions of the S-R latch and D flip-flop at high speeds (∼250  Gb/s) with good signal-to-noise ratio.

Coherence Properties of Supercontinuum Generated in Dispersion-Tailored Lead-Silicate Microstructured Fiber Taper

Abstract This article details the numerically studied coherence properties of the supercontinuum generated in a lead-silicate microstructured fiber taper, with an increasing core radius along the propagation distance that tailors the dispersion property. Simulations are conducted by adding quantum noise into the input pulse at 1.55 μm, and the complex degree of first-order coherence function and the overall spectral coherence degree are both calculated. Although the spectral broadening is comparable, the coherence degree is shown to vary with different pumping conditions. It decreases with higher peak power and longer duration due to the significant competition between the soliton-fission process and the noise-seeded modulation instability. By controlling the input pulse parameters, it is possible to generate a perfectly coherent supercontinuum with a flat broadened spectrum extending from ~1 μm to ~5μm in this fiber taper.

All optical logic NAND gate based on two-photon absorption

When the two-photon absorption of a high intensity pump beam takes place in a semiconductor optical amplifier there is an associated fast phase change of a weak probe signal. A scheme to realize fast all-optical NAND logic function using two-photon absorption induced phase change has been analyzed. NAND gate is important because other Boolean logic elements and circuits can be demonstrated using NAND gates as a basic building block. Rate equations for semiconductor optical amplifiers (for input data signals with high intensity) configured in the form of a Mach-Zehnder interferometer has been solved. The input intensities are high enough so that the two-photon induced phase change is larger than the regular gain induced phase change. The model shows that both AND and NAND operation at 250 Gb/s with good signal to noise ratio is feasible.

All-Optical Logic NOR Gate at 40 Gb/s Using SOA based Mach-Zehnder Interferometer

An all-optical logic NOR gate operating at 40 Gb/s has been demonstrated using an SOA-based Mach-Zehnder interferometer (MZI). An optical loop mirror is used as a delayed interferometer to reshape the return-to-zero (RZ) NOR sequence from the MZI output port. The performance of the NOR operation is numerically analyzed by solving the rate equation of an SOA. An increase in signal output power enhances the Q factor and extinction ratio. Faster SOAs such as quantum-dot SOAs can achieve higher Q value. The demonstrated technique has potential for optical logic operation at ultrahigh speed

Optical processors using semiconductor optical amplifiers

Semiconductor optical amplifiers are important for wide range of applications in optical networks, optical tomography and optical logic systems. For many of these applications particularly for optical networks and optical logic, high speed performance of the SOA is important. All optical Boolean operations such as XOR, OR, AND and NOR has been demonstrated using SOA based Mach-Zhender interferometers (SOA-MZI). A rate equation model for SOA-MZI has been developed. The model has been used to analyze the Set-Reset (S-R) latch, the gated S-R latch and the D-Flip-Flop devices. The modeling results suggest that the Flip-Flop circuits should work at high speeds. An optical pseudo-random bit stream (PRBS) generator is important for all-optical encryption circuits. A model of a PRBS generator using SOAMZI based devices has been developed. We show that a PRBS generator can work @ 80 Gb/s using regular SOAs and @ ~ 250 Gb/s or at higher speeds using two-photon absorption based processes in SOAs.