Hiroyuki Uenohara

Demonstration of All-Optical Divider Circuit Using SOA-MZI-Type xor Gate and Feedback Loop for Forward Error Detection

We investigated the feasibility of using an optical divider circuit with a semiconductor optical amplifier Mach-Zehnder interferometer (SOA-MZI)-based exclusive or (XOR) gate for an all-optical forward error detection and correction scheme with a cyclic code. We employed a conventional cyclic code scheme: the same divider circuit acts as both encoder and decoder with a given generator polynomial. The divider circuit consists of cascaded XOR circuits and feedback lines. Therefore, the performance of the XOR circuit is one of the key factors for realizing an all-optical scheme. We numerically investigated the operation performance of the SOA-MZI-based all-optical XOR gate. Dynamic operation was simulated using rate equations via the transfer matrix method. The XOR function was also investigated experimentally. The eye diagram obtained from the simulation at a bit rate of 10 Gb/s showed good qualitative agreement with experimental results. Additionally, we confirmed that the optimal condition for a high quality factor (Q-factor) is obtained with equal power for each signal. Next, we demonstrated all-optical divider processing with the SOA-MZI-based XOR circuit and a feedback line that forms the generator polynomial x + 1. The preliminary results for division operation could be verified.

Static and dynamic response of multiple-quantum-well voltage-controlled bistable laser diodes

We have simulated the static and dynamic characteristics of voltage-controlled multiple-quantum-well (MQW) bistable laser diodes. To investigate the time response of the saturable absorber under applied electric field, we performed pump-probe measurements with picosecond resolution. The obtained differential transmission signals indicate the reduction of the carrier escape time for the saturable absorber with increasing applied electric field. The field screening effect caused by spatial change of the carrier distribution is an important factor, as is phase space filling due to the photogenerated carriers. On the basis of the time response measurements, we have designed an MQW bistable laser by solving the modified rate equation including the recovery time response of the absorption saturation, A saturable absorption region narrower than 10 /spl mu/m is suitable for obtaining a low threshold device. To achieve low switching power and high switching speed, it is important to optimize the bias conditions and the MQW structures. We can expect a turn-off time of less than 10 ps, and a repetition rate of over 5 GHz from the calculations.

GaAlAs/GaAs MOCVD growth for surface emitting laser

A GaAlAs/GaAs Metalorganic chemical vapor deposition (MOCVD) has been introduced for growing GaAlAs/GaAs wafers with a thick active layer (d\cong3 µm) and multilayer Bragg reflectors for surface emitting lasers. A nominal threshold current density as low as 3.6 kA/cm2 µm was obtained in stripe cleaved lasers with a cavity length of 400 µm. GaAlAs/GaAs surface emitting lasers were fabricated by using these MOCVD grown wafers. The room-temperature pulsed operation of an MOCVD grown laser was obtained with a threshold current of 300 mA as a primary demonstration. In addition, a reflectivity of 97% was achieved by a Zn-doped 30 layer Ga0.9Al0.1As/AlAs Bragg reflector. These experimental results suggest the possibilities of a low-threshold surface emitting laser grown by MOCVD and potential applications toward integrated optics based on surface emitting lasers.

An 850-nm InAlGaAs strained quantum-well vertical-cavity surface-emitting laser grown on GaAs (311)B substrate with high-polarization stability

The polarization stability of 850-nm InAlGaAs strained quantum-well (QW) vertical-cavity surface-emitting laser (VCSEL) grown on GaAs (311)B substrate was investigated by comparing it with that of GaAs unstrained QW VCSEL grown on GaAs (311)B substrate. Photoluminescence measurement showed that strained QWs grown on GaAs (311)B substrate had larger anisotropy in optical gain than unstrained QWs. The VCSEL with strained QWs showed an orthogonal polarization suppression ratio (OPSR) as high as 21 dB under CW operation. Time-dependent OPSR measurement indicated that the strained QW VCSEL had higher polarization stability than the unstrained QW VCSEL under zero-bias modulation.

Polarization-controlled 850-nm-wavelength vertical-cavity surface-emitting lasers grown on [311]B substrates by metal-organic chemical vapor deposition

We demonstrate the polarization stability of 850-nm-wavelength vertical cavity surface-emitting lasers (VCSELs) grown on [311]B substrates under continuous-wave (CW) and dynamic operation. To clearly verify the polarization stability of VCSELs on [311]B substrates due to the anisotropic optical gain, the characteristics of both VCSELs on [311]B and [100] substrates were compared experimentally. Under CW operation, very small difference in both orthogonal polarization suppression ratio and the distribution of polarization direction was observed between VCSELs on [311]B and [100] polyimide-buried structures. On the other hand, significantly larger orthogonal polarization suppression ratio was obtained for VCSELs on [311]B substrates than those on [100] substrates under zero-bias modulation. Time-dependent orthogonal polarization suppression ratio measurements also showed that the orthogonal polarization suppression ratios of the VCSEL on [311]B substrates were more stable than those on [100] substrates. The data transmission characteristics also indicate large differences in the dependence of the bit error rate on bias current and the power penalty between polarization resolved and unresolved systems between VCSELs on [311]B and [100] substrates. The beneficial effect of the polarization stability of VCSELs on [311]B substrates due to their anisotropic optical gain is clearly demonstrated.

Investigation of high-speed wavelength routing and bit-error-rate performance of an optical packet switch with an optical digital-to-analog conversion-based header processor

Wavelength routing and bit-error-rate (BER) performance of an optical packet switch called a wavelength label switch consisting of an optical digital-to-analog conversion-based header processor, wavelength selection portion with an electrically tunable laser, a wavelength converter based on a semiconductor optical amplifier, and wavelength routing by use of an arrayed waveguide grating was realized. Wavelength selection for an electrically tunable laser was successfully achieved within a few tens of nanoseconds by using 2-b optical header processor and a field programmable gate array-based wavelength table. High-speed transfer performance of less than a few tens of nanoseconds and BER of less than 10/sup -10/ were verified in wavelength routing operation between three assigned wavelength.

Optical nonlinear characteristics of a side-injection light-controlled laser diode with a multiple-quantum-well saturable absorption region

A multiple-quantum-well bistable laser-diode structure in which the input signal is launched into the main laser through an orthogonally configured subwaveguide is proposed. Insensitivity to input light wavelength (28 nm of 3 dB bandwidth) and high isolation of input versus output (over 30 dB) are observed. In addition, reflection of input signal is negligibly small.<<ETX>>

Investigation of dynamic polarization stability of 850-nm GaAs-based vertical-cavity surface-emitting lasers grown on [311]B and [100] substrates

The polarization stability of 850-nm GaAs-based vertical-cavity surface-emitting lasers (VCSELs) under dynamic operation was investigated by comparing the characteristics of VCSELs grown on [311]B and [100] GaAs substrates. Significantly larger suppression ratios of the two orthogonal polarization modes was obtained for VCSELs on [311]B substrates than those on [100] substrates under zero-bias modulation. Time-dependent orthogonal polarization suppression ratio measurements also showed that the polarization direction was more stable in the VCSEL on [311]B substrates than that on [100] substrates. Error-free transmission was realized from VCSELs on [311]B substrates with and without a polarizer in both back-to-back and 100-m multimode fiber transmission.

Switching Characteristics of InGaAs/InP Multiquantum Well Voltage-Controlled Bistable Laser Diodes

Voltage-controlled optical bistability in In0.53Ga0.47As/InP multiquantum well (MQW) laser diodes is demonstrated for the first time by using the quantum confined Stark effect (QCSE) and saturable absorption of a two-dimensional exciton. Optical bistability is obtained in a wide range of control voltages from +0.7 V to -0.6 V. Switching operation is achieved by injecting a set light pulse and applying reverse bias reset voltage to the saturable absorption region. Turn-on time is 300 ps with input light of 6 mW, and turn-off time of 260 ps is obtained by reducing the stray capacitance in the saturable absorption region.

Wide range wavelength conversion experiments using a side-injection light-controlled bistable laser diode

Wavelength conversion has been demonstrated using a distributed feedback side‐injection light‐controlled bistable laser diode with an input wavelength range of 1496–1597 nm. Insensitivity to input light wavelength and a large separation ratio of output from input (more than 30 dB) are advantageous for a wavelength converter.