Yasuhiko Aoki

Hollow Optical Waveguide for Temperature-Insensitive Photonic Integrated Circuits.

We propose a hollow optical waveguide with metal coating or dielectric multilayer coating to achieve sufficient reflectivity at guiding walls. Low-loss and polarization-insensitive propagation characteristics are predicted. The propagation constant is independent of the temperature, resulting in temperature-insensitive photonic waveguide devices, such as optical filters and grating optical demultiplexers. We demonstrate a hollow optical waveguide with metal-coated walls on a GaAs substrate, which was fabricated using dry etching. The propagation loss including the coupling loss with an input fiber was 2.6 dB/cm and 7.3 dB/cm for transverse electric (TE) mode and transverse magnetic (TM) mode, respectively.

Micro-optical bench for alignment-free optical coupling

We propose an optical coupling module, the micro-optical bench, designed for the purpose of completely passive alignment of optical components. The principle is for one to position a planar microlens array, semiconductor device submounts, and optical fibers by using reference planes and V grooves made on a Si substrate. A prototype was fabricated, and we achieved an optical coupling loss of less than 3 dB; small deviations among channels as low as 1 dB were achieved without any precise alignment. For multimode fibers, a coupling loss of approximately 0.5 dB was obtained.

Fundamental Study of Parallel Moduling Scheme Based on a Micro-Optical Bench and Collimating Planar Microlenses

We have conducted a feasibility study of a parallel moduling scheme based on a collimating guide using planar microlenses. This optical subsystem consists of a stacked planar optical circuit and a micro-optical bench (MOB) for alignment. We measured the coupling loss of microlens collimation and determined that single-mode fiber-to-fiber coupling of approximately 2 dB is possible. We also investigated the optical crosstalk of the collimating optical system using planar microlenses (PMLs), and the crosstalk of less than -70 dB was achieved. As an initial subsystem experiment using vertical cavity surface emitting lasers (VCSELs), we fabricated a VCSEL array (λ=850 nm, Ith=1.8 mA at room temperature, CW) and bonded it on a Si MOB.

Parallel and bi-directional optical interconnect module using vertical cavity surface emitting lasers (VCSELs) and 3-D micro optical bench (MOB)

We propose a novel parallel and bi-directional optical interconnect module using VCSELs and a 3-D stacked planar optical circuit. As an initial experiment of the optical circuit, we fabricate a stacked optical circuit chip and achieve an optical coupling loss of 2.4 dB.

Evaluation of Numerical Aperture and Focusing Characteristics of Planar Microlens for Optical Interconnects

We evaluated the numerical aperture (NA) and focusing characteristics of a planar microlens (PML) for parallel optical interconnect systems. The NA of a PML of 250 µm in diameter was measured to be 0.07 using a 125 µm mask aperture to clean the beam profile. By stacking two PMLs, the NA was raised to 0.17 due to the elliptical index profile of the stacked PML. The spot diameter was 11 µm, which is nearly equal to the diffraction limit and is usable for single-mode application.

Parallel Optical-Transmission Module Using Vertical-Cavity Surface-Emitting Laser Array and Micro-Optical Bench (MOB)

In this paper, we present a scheme of a parallel optical transmission module using a vertical-cavity surface-emitting laser (VCSEL) array and a micro-optical bench (MOB). We have fabricated a prototype using a VCSEL array emitting at 850 nm and a MOB for the first time, and demonstrated the feasibility of a two-dimensional alignment-free optical interconnect module. No noticeable degradation of I–V, and I–L characteristics of the packaged VCSEL array was observed after the proposed packaging process. The excess loss of the MOB alignment scheme using a multi-mode fiber was evaluated to be about 0.5 dB.

Spot size dependence of filtering characteristics in dielectric multilayer filters for WDM applications

We investigated filtering characteristics of dielectric filters for use in wavelength division multiplexing systems by employing an improved transfer matrix method. It is pointed out that the spotsize should be larger than 3mm for 25Ghz channel spacing. The spot size of input Gaussian beam is very critical affecting the performance.

A Bidirectional Optical Module Based on Stacked Planar Optical Circuit

In this paper, a bidirectional optical module based on a stacked planar optical circuit (SPOC) concept to perform a wavelength division multiplexing (WDM) function is described. The module consists of an optical chip which incorporates planar microlens (PML) arrays and nonpolarizing 1.31/1.55 µm WDM dielectric-multilayer filters. Module design and theoretical estimation of loss tolerance were conducted. From preliminary experiments, the feasibility of SPOC modules was confirmed. A fabricated WDM filter showed a small polarization-dependent loss (PDL) of about 0.48 dB and 0.05 dB for the wavelengths of 1.31 µm and 1.55 µm, respectively. Channel crosstalk and PDL for the SPOC module were characterized by means of discrete filter devices. For the 1.55 µm downstream (1.31 µm downstream/upstream) channel, a crosstalk as low as -40 dB (-26 dB) and a PDL less than 0.23 dB (0.53 dB) were achieved.

An Optical Network Unit (ONU) Chip Based on Stacked Planar Optics

In this paper, an optical network unit (ONU) based on stacked planar optics is described. The ONU chip consists of planar microlens (PML) arrays and dielectric multilayered filters conveniently arranged to perform a wavelength division multiplexing (WDM) transmitter/receiver function. To avoid polarization dependence, nonpolarizing filters were designed for WDM filters, half-mirrors and mirrors. An insertion loss of less than 2.5 dB and a polarization-dependent loss (PDL) of less than 0.5 dB were obtained for the 1.3 ?m port. Crosstalk was estimated to be as low as -26 dB. For the 1.55 ?m port, both insertion loss and PDL of less than 0.08 dB were obtained.

Hollow optical waveguide with thin film coating for micromachined photonic integrated circuits

We propose a novel hollow optical waveguide with thin film coating for temperature insensitive photonic devices. Low-loss and polarization insensitive propagation characteristics are predicted. We fabricated a hollow waveguide with metal coated walls on GaAs substrate. The propagation loss was 2.6 dB/cm and 7.3 dB/cm for TE and TM modes, respectively.