Hirofumi Morita

Microphotonics devices based on silicon microfabrication technology

This work presents our recent progress in the development of an Si wire waveguiding system for microphotonics devices. The Si wire waveguide promises size reduction and high-density integration of optical circuits due to its strong light confinement. However, large connection and propagation losses had been serious problems. We solved these problems by using a spot-size converter and improving the microfabrication technology. As a result, propagation losses as low as 2.8 dB/cm for a 400/spl times/200 nm waveguide and a coupling loss of 0.5 dB per connection were obtained. As we have the technologies for the fabrication of complex, practical optical devices using Si wire waveguides, we used them to make microphotonics devices, such as a ring resonator and lattice filter. The devices we made exhibit excellent characteristics because of the microfabrication with the precision of a few nanometers. We have also demonstrated that Si wire waveguides have great potential for use in nonlinear optical devices.

Improved line-defect structures for photonic-crystal waveguides with high group velocity

Through the analysis of the guided modes in simple photonic-crystal (PC) slab waveguides, we have established a simple and essential interpretation for the dispersion structure of the guided modes: the structure of the dispersion curves is the result of interactions between the index-confined mode and the gap-confined mode. This interpretation gave us guidelines for increasing group velocities near the zone boundary, or for solving the severe light-line problem in PC slab waveguides with dielectric claddings. Applying these guidelines, we proposed novel waveguide structures that promise fine transmission characteristics.

SOI-based photonic crystal line-defect waveguides

We have experimentally demonstrated single-mode light-wave transmission and tunable waveguiding characteristics in photonic crystal (PC) waveguides constructed on a silicon-on-insulator (SOI) substrate as is most likely to be used for the a large scale integration of photonic circuits. Although off-plane diffractive leakage has been a serious problem in SOI-PC waveguides, we have overcome this problem in our narrow line-defect and phase-shifted-hole line-defect waveguide structures. These devices were developed through intensive theoretical studies on PC line-defect waveguieds. We have also demonstrated low-loss mode profile converter that will enable efficient connection between conventional silica-based waveguides and PC line-defect waveguides. The converter features an inversely-tapered silicon wire waveguide with an ultra-thin tip constructed on an SOI substrate. In our experiments, this converter proved capable of coupling loss as low as 0.5dB per conversion. These SOI-based devices represent an important step towards practical large-scale integrated photonic crystal circuits.

Functional components in SOI photonic crystal slabs

We study various types of two-dimensional photonic crystal (PhC) waveguides (WG) on silicon-on-insulator (SOI) substrates for future photonic integrated circuit (PIC) applications. One of our goals is to realize a low-loss single-mode PhC WG. Off-plane diffractive leakage above the cladding layer light line is a serious problem in SOI-based PhC-WGs. We overcame this problem in width-varied line defect waveguides whose core-widths are changed by sliding PhC domains or deforming holes beside the waveguides. Narrow-core WGs have a wide transmission band below the cladding layer light line, and wide-core WGs can greatly suppress the diffractive leakage even above the cladding layer light line, and both types have a very low propagation loss. Another goal is to achieve a highly efficient coupling between SOI-based PhC WGs and single-mode fibers (SMFs). Normally, the loss of such a coupling system is very large, i.e. over 20 dB, because of the quite different mode profiles of the WGs and SMFs, and this loss is an obstacle to the development of PhC-based devices. Our system achieves a very small mode-profile-conversion loss of about 3-4 dB/connection from 1500 to 1600 nm wavelength.

Multi-beam mask writer MBM-1000 and its application field

NuFlare has started development of multi-beam mask writer MBM-1000 aiming to apply to N5 and to release in Q4 2017. MBM-1000 is based on large area projection optics with shaping aperture array plate, blanking aperture array (BAA) plate, single cathode and inline/realtime data path for vector data rasterization and bitmap dose correction. It is designed to accomplish higher throughput than EBM series (variable shaped beam (VSB) writers) with massive beam array, higher resolution by using 10-nm beam size and 10-bit dose control, and better writing accuracy with more write passes. Configuration of MBM-1000 and flow of data path processing are described. Write time estimation suggests MBM-1000 has advantage over VSB writer with shot count > 200 Gshot/pass and resist sensitivity >75 μC/cm2. Printing test of 20 nm hp 1:1 line and space pattern with ZEP-520 resist showed better beam resolution of MBM-1000 alpha tool than EBM series.