Koichi Maru

2.5%-/spl Delta/ silica-based athermal arrayed waveguide grating employing spot-size converters based on segmented core

We describe a novel structure for super-high-/spl Delta/ athermal arrayed waveguide gratings (AWGs) employing spot-size converters based on a segmented core formed in the slab region, to reduce the diffraction loss in resin-filled trenches. This structure requires no depth-tapering process. We demonstrated a compact 16-channel athermal AWG based on the 2.5%-/spl Delta/ silica waveguides. The excess loss due to athermalization was reduced to 0.9 dB with the proposed structure, whereas the excess loss was 2.4 dB using a conventional one. The measured results of the proposed structure show no degradation of the crosstalk and passband shape.

Demonstration of Flat-Passband Multi/Demultiplexer Using Multi-Input Arrayed Waveguide Grating Combined With Cascaded Mach–Zehnder Interferometers

We demonstrate multi/demultiplexers with a very flat passband and small excess loss using a multi-input arrayed waveguide grating combined with a cascaded Mach-Zehnder interferometer structure. We also analyze the impact of coupling between input waveguides just before the input slab on chromatic dispersion and investigate a waveguide structure for reducing the chromatic dispersion. We fabricated flat-passband multi/ demultiplexers with 100-GHz channel spacing using 2.5%-Delta silica waveguides and experimentally investigated the dependence of their optical characteristics on design parameters to demonstrate the effectiveness of the proposed theoretical model. We obtained a very flat passband response having a 1-dB bandwidth of 0.645-0.658 nm and 20-dB bandwidth of 0.944-0.960 nm with a loss penalty due to the passband-flattening of 0.9-1.0 dB and chromatic dispersion of -22.1-17.5 ps/nm over 0.5 nm in the passband. The measured passband shape and chromatic dispersion generally agreed with the simulation results.

Athermal and center wavelength adjustable arrayed-waveguide grating

Athermal and center wavelength adjustable AWGs with flat-top spectral responses are proposed. Low temperature sensitivity /spl sim/0.0013 nm//spl deg/C and precise center wavelength control less than 0.02 nm are demonstrated without additional loss and crosstalk penalty.

Dynamic gain equalizer using proposed adjustment procedure for thermooptic phase shifters under the influence of thermal crosstalk

A dynamic gain equalizer (DGE) is required to automatically compensate for gain variations related to fiber amplifiers. This paper proposes a DGE with thermooptic (TO) phase shifters based on a single-filtered-arm interferometer. A design procedure was newly developed for the control of the TO phase shifters, which could be used to accurately control the intended attenuation profile in one adjustment. In this procedure, the Taylor series method was used as an optimization algorithm, and thermal crosstalk was taken into account. From the point of view of thermal crosstalk, the behavior of phase shifters in an array and the effect of three-dimensional (3-D) trenches formed around the phase shifters were precisely investigated. A DGE module based on 1.5%-/spl Delta/ planar lightwave circuits and the 3-D trench structure are demonstrated. The measured spectra were found to be in good agreement with arbitrarily designed profiles under open-loop control, even when there was some thermal crosstalk between phase shifters. The results indicate that the design procedure and the estimation of the thermal crosstalk are effective for accurate control of the DGE.

Improved Heat Treatment for Wafer Direct Bonding between Semiconductors and Magnetic Garnets

The optical propagation loss of rib waveguides fabricated on magnetic garnet films increased upon annealing in H2 ambient during wafer direct bonding. The heat treatment in wafer direct bonding between InP and Gd3Ga5O12 was investigated with the aim of circumventing the loss increase. The bonding was achieved by heat treatment in H2 ambient at temperatures of 330° C or in N2 ambient.

Axial scanning laser Doppler velocimeter using wavelength change without moving mechanism in sensor probe

A scanning laser Doppler velocimeter (LDV) without any moving mechanism in its sensor probe is proposed. In the proposed scanning LDV, the measurement position is axially scanned by change in the wavelength of the light input to the sensor probe, instead of using a moving mechanism in the sensor probe. For this purpose, a tunable laser and diffraction gratings are used, and the sensor probe including the gratings is separated from the main body including the tunable laser. To demonstrate the scanning function based on the proposed concept, an experiment was conducted using optical fibers, a commercial tunable laser and a setup of the sensor probe consisting of bulk optical components. As the experimental result, it is found that the measurement positions estimated from the measured beat frequencies are in good agreement with the theoretical values. The scan ranges over a wavelength range of 30 nm are estimated to be 29.3 mm when the beam angle to the measurement position at the wavelength of 1540 nm is 10° and 20.8 mm when the beam angle is 15°. The result indicates that the scanning function by means of changing the wavelength input to the sensor probe is successfully demonstrated for the first time. The proposed method has the potential for realizing a scanning LDV with a simple, compact and reliable sensor probe.

Multi-point differential laser doppler velocimeter using arrayed waveguide gratings with small wavelength sensitivity

A multi-point laser Doppler velocimeter (LDV) using the arrayed waveguide gratings (AWGs) with small wavelength sensitivity (less than 1/10 of that for a conventional LDV without the AWGs) is proposed, in which velocities at different points in the depth direction can be simultaneously measured with compact optical systems. The design and characteristics of the proposed LDV are investigated with the model using the grating equation of the AWGs. From our simulation results, the wavelength sensitivity for multiple measured points can be reduced to less than 1/10 of that for a conventional LDV without an AWG.

Modeling of Multi-Input Arrayed Waveguide Grating and Its Application to Design of Flat-Passband Response Using Cascaded Mach–Zehnder Interferometers

We present a theoretical model of a multi-input arrayed waveguide grating (AWG) based on Fourier optics and apply the model to the design of a flattened passband response. This modeling makes it possible to systematically analyze spectral performance and to clarify the physical mechanisms of the multi-input AWG. The model suggested that the width of an input/output mode-field function and the number of waveguides in the array are important factors to flatten the response. We also developed a model for a novel AWG employing cascaded Mach-Zehnder interferometers connected to the AWG input ports and numerically analyzed its optical performance to achieve low-loss, low-crosstalk, and flat-passband response. We demonstrated the usability of this model through investigations of filter performance. We also compared the filter spectrum given by this model with that given by simulation using the beam propagation method

Low-loss, flat-passband and athermal arrayed-waveguide grating multi/demultiplexer.

We successfully demonstrated a low-loss, flat-passband, and athermal arrayed-waveguide grating (AWG) multi/demultiplexer with a Mach-Zehnder interferometer (MZI) as an input router. Resin-filled trenches were formed in the longer arm of the MZI as well as the slab in the AWG to compensate for the temperature dependence. A 32-channel athermal multi/demultiplexer was fabricated using silica-based planar lightwave circuit (PLC) technology. A small temperature-dependent wavelength shift of 0.02 nm was obtained over the temperature range of -5 to 65 degrees C with low-loss (3.3-3.7 dB) and flat-passband spectra.

Integrated Wavelength-Insensitive Differential Laser Doppler Velocimeter Using Planar Lightwave Circuit

In this paper, a design of an integrated wavelength-insensitive laser Doppler velocimeter (LDV) has been proposed using planar lightwave circuit (PLC). The proposed LDV uses arrayed waveguide gratings (AWGs) that can be fabricated using PLC technology. Its characteristics are simulated using a design model based on grating equations for AWGs. The simulation results indicate that wavelength-insensitive operation can be almost obtained by optimizing the design parameters of the proposed structure without assembly of bulk diffractive gratings or other optical elements.