Hironori Sasaki

A comparison of optical second-harmonic generation efficiency using Bessel and Gaussian beams in bulk crystals

Abstract The conversion efficiencies of optical second-harmonic generation (SHG) of light by Bessel beams and Gaussian beams in nonlinear crystals are compared. A Bessel beam, which has a quasi-nondiffractive nature, is generated by illuminating an axicon lens with a Gaussian beam. The interaction path lengths are the same for both beams, and are set to be twice the confocal parameter of the Gaussian beams. The Bessel beam is found to have greater SHG efficiency than the Gaussian beam regardless of the interaction path length and the fundamental wavelength.

Wafer bonding technology for optoelectronic integrated devices

Abstract Wafer bonding has been investigated as a key technology to integrate InP lasers on Si for optoelectronic integrated circuits. The bonding process has been optimized to allow the integration of InGaAsP/InP double-heterostructures (DHs) on Si with keeping the crystal qualities good enough to realize the lasers. As a result, room temperature continuous-wave (CW) operation of InP edge-emitting lasers has been achieved. In addition, as one of the building blocks to implement the optimal interconnections between Si LSIs, InP optical devices on Si integrated with the back-surface diffractive lenses have been demonstrated. A novel bonding process which allows an integration on structured wafers, such as Si LSI wafers, has also been proposed. The wafer bonding is thought to be a promising technique to implement optical interconnections between Si LSI chips.

Bidirectional optical subassembly with prealigned silicon microlens and laser diode

We have succeeded in developing a low-cost bidirectional optical subassembly chip using a silicon microlens for fiber-to-the-home application. The main optical elements of the bidirectional function were automatically aligned and integrated on a silicon optical bench. The cost of subassembly was markedly lowered both by reducing the part number and simplifying the assembly process. The prototype bidirectional optical component was successfully fabricated on the basis of the proposed chip. A receiver minimum sensitivity of -28.5 dBm was experimentally demonstrated even at 75 degC

Scalability analysis of diffractive optical element-based free-space photonic circuits for interoptoelectronic chip interconnections

An interchip free-space optical interconnection module is investigated to solve the pin-input-output bottleneck at the interface of silicon integrated circuits. The scalability of the photonic circuit is theoretically analyzed by use of the minimum feature size requirement of each diffractive element used. The study showed that interconnection densities of 1000-2000 channels/cm is possible for a 40-mm interconnection length with a 3-mm-thick optical substrate. Diffraction-limited imaging capability has been demonstrated using a fabricated prototype, confirming its applicability for interchip free-space interconnections. Photonic circuit insertion losses of -23.4 dB for TE polarization and -25.9 dB for TM polarization as well as a polarization-dependent loss of 2.5 dB are found to be caused primarily by a pair of binary linear gratings used for beam deflections. Design modifications aiming at insertion loss reduction and further improvement of tolerance capabilities are also discussed.

Surface-mountable silicon microlens for low-cost laser modules

A surface-mountable silicon microlens that can be passively aligned in a silicon V-groove is proposed. The microlens has a diffractive optical element on the end facet of a semicylindrical structure whose diameter is identical to that of a single-mode fiber (SMF). The experimental result of coupling efficiency between a distributed feedback laser diode and SMF shows low loss (-3.0 dB) as determined using the microlens. Monte Carlo simulations indicate that the microlens is suitable for low-cost and high-performance optical modules for metro networks.

A low-cost micro-BOSA using Si microlens integrated on Si optical bench for PON application

We propose single TO-CAN type bi-directional optical subassembly in which. LD, PD chips, filter and Si microlenses are passively integrated on Si optical bench. High performance such as minimum sensitivity of -28 dBm was experimentally demonstrated.

CWDM multi/demultiplexer consisting of stacked dielectric interference filters and off-axis diffractive lenses

A compact coarse wavelength-division multi/demultiplexer based on a stack of dielectric interference filters and an array of off-axis diffractive lenses is reported. The prototype optical system was packaged in the volume of 6.4 (width) /spl times/ 2.5 (height) /spl times/ 8.2 mm (depth). The optical system is interfaced via a multichannel connector with single-mode fiber ribbons. Optical insertion losses are better than 5 dB. The worst channel crosstalk was -19 dB.

A low cost PON transceiver using single TO-CAN type micro-BOSA

A novel low-cost small-form-factor (SFF) optical transceiver using a micro-compact bi-directional optical sub-assembly (micro-BOSA) for passive optical network (PON) application is proposed. In this micro-BOSA, optical transmitting and receiving functions are incorporated in a single TO-CAN package. The BOSA is compact and its pin assignment provides fine connection to printed circuit board and fit in transceiver housing. Bi-directional optical transmission at 1.25Gbit/s with the receiver minimum sensitivity of -28.2dBm is demonstrated for the fabricated transceiver with the proposed micro-BOSA

DESIGN CONSIDERATIONS OF STACKED MULTILAYERS OF DIFFRACTIVE OPTICAL ELEMENTS FOR OPTICAL NETWORK UNITS IN OPTICAL SUBSCRIBER-NETWORK APPLICATIONS

The detailed design process and experimental results of stacked multilayer diffractive optical elements are reported for an optical network unit used in optical subscriber-network applications. The optical network unit accepts two incoming light beams of 1.3- and 1.55-microm wavelengths through a single-mode optical fiber. A laser diode is also placed for bidirectional communications. The optical network unit consists of five diffractive optical elements that perform the following functions: collimation of incoming beams, focusing of the outgoing 1.55-microm beam, 3-dB splitting of the 1.3-microm beam, focusing of the 1.3-microm beam onto the photodiode, and collimation of the light emitted from a laser diode. Possible cost reductions as a result of mass production and the ease of alignment of the stacked diffractive optical elements could be ideal for constructing low-cost optical network units.

Reduced alignment accuracy requirement using focused Gaussian beams for free‐space optical interconnection

The use of a focused Gaussian beam in the space variant micro-optical interconnection system is proposed for decreasing the alignment accuracy requirement. The relationship between both longitu- dinal and lateral misalignment of the light source and the power loss due to beam shift and beam spot size mismatch at the collimating lens and the photodetector are derived theoretically using ABCD matrices, and numerical simulation results are also given. A focused Gaussian micro- optical system is introduced by changing the beam radius ratio on the two lenses of the one-to-one Gaussian micro-optical system from unity. It is shown that the focused Gaussian micro-optical system with a smaller beam radius on the second collimating lens than on the first one has improved misalignment tolerances compared with the one-to-one Gaussian micro-optical system.