Aki Takei

A wavelength-tunable short-cavity DBR laser with active distributed Bragg reflector

The incorporation of an active single-quantum well in the tuning layer of a DBR laser is proposed as a way of compensating for optical loss and achieving stable single-mode operation during wavelength tuning. Experimental results demonstrate that the structure achieves these goals while maintaining the efficiency of tuning. In application to a short-cavity DBR laser with a gain region 35-µm long, continuous wavelength gtuning over a broad 4.8nm is achieved with stable lasing properties (more than 40dB of side-mode suppression). Fast wavelength switching less than 10ns to cross a wavelength spacing of 2nm is also confirmed.

Wide-tuning (65 nm) Semi-cooled (50°C) operation of a tunable laser based on a novel widely tunable filter

A tunable laser based on a medium wavelength selectivity tunable filter named a lateral-grating-assisted lateral-co-directional-coupler was developed. A wide tuning range of over 65 nm with SMSR of over 35 dB was demonstrated at 50°C.

Wavelength-Tunable Short-Cavity DBR Laser Array With Active Distributed Bragg Reflector

With the aim of developing a fast wavelength-tunable laser for advanced dynamic network reconfigurations or optical burst switching, a short-cavity (SC) distributed-Bragg-reflector (DBR) laser array with an active-DBR (ADBR) structure (SC-ADBR laser) was fabricated. First, it was experimentally confirmed that the ADBR structure compensates for optical loss and achieves stable single-mode operation during wavelength tuning. An artificial-laser-phase-adjustment technique in the SC-ADBR laser by precise adjustment of a DBR mirror was then proposed. By applying this technique to a six-channel SC-ADBR laser array, perfect wavelength accessibility across a 21-nm range was attained

Temperature tuning of dispersion compensation using semiconductor asymmetric coupled waveguides

Two vertically coupled asymmetric InGaAsP ridge waveguides were fabricated and tested as a tunable dispersion compensator. In this waveguide, two coupled modes, symmetric and antisymmetric, exist simultaneously and have a significant amount of group-velocity dispersion (GVD), making it possible to reduce the size of the dispersion compensators. Since the GVD can be continuously controlled by changing the temperature of the asymmetric coupled waveguide, a semiconductor asymmetric coupled waveguide has great potential as a basis for a compact tunable dispersion compensator. To demonstrate tunable dispersion compensation, we carried out an experiment on the pulse compression of frequency-chirped pulses by using the InGaAsP asymmetric coupled waveguide at various temperatures of the waveguide. We observed a change in the compression ratio, ranging from 42.7% to 84.2%, as the temperature of the waveguide changed from 8to48.9°C. A theoretical study showed that the observed change in the compression ratio was we...

Wide-wavelength-range and high-output-power short-cavity DBR laser array with active distributed Bragg reflector

We demonstrated a wide-wavelength (1533-1568 nm), high-output power (30 mW) operation in a short-cavity DBR laser array by incorporating an active single quantum well in DBR mirrors.

Semiconductor Dispersion Compensator Based on Two Vertically Coupled Asymmetric Ridge Waveguides

A semiconductor dispersion compensator based on two vertically coupled asymmetric InGaAsP/InP ridge waveguides was designed and fabricated. This device consists of a dispersion-compensation region sandwiched between two mode converters. Two types of coupled modes, symmetric and antisymmetric, simultaneously exist in the dispersion-compensation region and have significant group-velocity dispersion (GVD) with opposite signs, making shrinkage of the device possible. The mode converters serve as mode selectors, exciting only the coupled mode needed for dispersion compensation with a high degree of efficiency. The compression of a 5.4-ps down-chirped pulse was demonstrated by the device; the pulse compression ratio was 55%. A theoretical study showed that the observed pulse compression was explained well by the dispersion compensation caused by the GVD of the coupled modes, and that the selectivity of the mode converter was approximately 80% for the symmetric coupled mode.

Large-Tolerant Direct Coupling to an SMF Array With a Lens-Integrated Surface-Emitting Laser

As a solution to provide a small-size and low-cost 100-Gb/s optical module, direct optical coupling between a lens-integrated surface-emitting DFB laser (LISEL) array and a single-mode fiber (SMF) array is demonstrated. A very-small far-field angle (~2°) was obtained by monolithic integration of an InP lens with a laser chip. As a result, each channel of the LISEL array can directly couple to an SMF without any additional external optical components. The measured misalignment tolerance between the LISEL array and an SMF array was sufficiently large, namely, ±5.5 μm, at excess loss of 1 dB over all four channels with the maximum coupling efficiency of 8.4 dB. These measurement results are in good agreement with a theoretical calculation based on Gaussian optics. These results demonstrate that high coupling efficiency (-3 dB) can be achieved while large misalignment tolerance (±4.5 μm) at excess loss of only 1 dB is maintained.

Non-blocking 4×4 InAlGaAs/InAlAs Mach-Zehnder-type optical switch fabric

We demonstrated the full-interport connection of a non-blocking 4x4 InAlGaAs/InAlAs Mach-Zehnder-type optical switch (MZ-OS) fabric. This switch fabric is consisted of six 2x2 MZ-OS elements in a cascading configuration, and it successfully operated with high-extinction ratios of about 20dB and polarization independence.

Cost-Effective Optical Sub-Assembly Using Lens-Integrated Surface-Emitting Laser

A cost-effective optical sub-assembly (OSA) for high-speed optical interconnections using lens-integrated surface-emitting lasers (LISELs) is demonstrated. Two concepts of the OSA, one based on a direct-modulation (DM)-LISEL and the other based on a continuous-wave (CW)-LISEL for a silicon-photonics (SiP) platform, are proposed. The design parameters of the integrated lens that enable low fiber-coupling loss and the SiP platform are described. Coupling losses, as low as 4.9 dB for the single mode fiber and 4 dB for the SiP platform, were experimentally confirmed. Furthermore, theoretical and experimental evidence that demonstrates the OSA does not require an optical isolator (i.e., it is “isolator-free”) is presented. A DFB laser used for the LISEL had a low relative intensity noise (less than -140 dB/Hz), even with a back reflection of more than -20 dB. For non-Hermetic packaging, 500 h, 85°C/85% relative humidity storage tests experimentally demonstrated no degradation in the lasing characteristics.

Capability of high optical-feedback tolerance and non-hermetic-packaging for low-cost interconnections using lens-integrated surface-emitting laser

Low-cost optical assemblies for optical interconnections using lens-integrated surface-emitting laser are proposed. High coupling efficiency with single-mode-fibers of over -1.9dB and RIN below -140dB/Hz with large back reflection and 85°C/85% storage test are demonstrated.