It is expected that opto-electronic printed wiring board (OE-PWB) will appear very soon. We study optical coupling schemes to multi-layer and multi-channel OE-OWB, and propose several optical coupling devices fabricated by using UV-curable resin. The “optical pin” is a vertical optical pillar, and that is one promising approach to achieve optical coupling with 90-deg path conversion between surface devices and optical wiring. Analysis using Optical Ray Tracing method shows that optical pin has potential to achieve higher optical coupling efficiency and larger positional tolerance. The optical pin can be fabricated by the Mask-Transfer Self-Written Waveguide (SWW) method using UV-curable resin. Next we propose optical coupling device with micro lens array. The advantage of using micro lens is that there will be no interaction between the beams crossings which means no crosstalk and noise will not occur. In addition, micro lens is flexible for fabrication. Starting fabrication of a single micro lens on tip of fiber, we succeeded in fabrication of micro lens array on patterned substrate.
Doppler Laser Velocity measurement by self-mixing effect using direct modulation laser diode is proposed to distinguish the direction of the object movement. To distinguish the movement direction in conventional way, it is needed to assemble a frequency shift device such as an acoustic optic cell in the optical system. However, the self-mixing scheme cannot satisfy this condition this due to its simple system. Therefore, we applied triangularwave modulation current with repetition frequency of 250Hz directly to the laser diode emitting at a wavelength of 780nm. Target speed of 0.1 - 0.4 cm/s is measured and its movement direction forward and/or backward can be distinguished successfully. Both the velocity and moving direction of the target are obtained.
Laser Doppler Velocimeter (LDV) with a laser diode and Self-mixing effect is a new type of downsized and low cost LDV with high precision measurement. We propose a new LDV using a 3-beam fiber irradiation scheme. The sensor head consists of 3-fibers which are intersected perpendicularly each other. This new LDV enables three-dimensional velocity measurement. That is, the magnitude and direction of the velocity vector of the moving object can be measured independent on the relative position between the moving object and the 3-beam sensor head. We also study the case that these 3 beams are not right-angled each other. Operation principle and experimental results for both cases are reported.
Recently the importance of optical interconnect is increasing particularly in board-to-board interconnection. The success
of smart optical interconnects for practical use strongly depends on the development of sophisticated coupling
technologies achieving both high coupling efficiency and easy alignment. One promising technology for solving these
problems is self-written waveguide (SWW) method which uses light-curable resin. This method is flexible and may
allow substantial advances in the practical application of optical interconnect technology. We fabricated a micro 90°
light-path converter on the top of MT connector. Four channel SWWs are fabricated by irradiating a blue laser beam
(406nm wavelength) from a multi-mode fiber in light-curable resin. The SWWs are covered by cladding resin. This
converter is useful for connecting between fibers and an optical wiring board. We have further developed this fiber-
SWW technology into a new technology we call the “Mask-Transfer SWW method”. The Mask-Transfer SWW
technology involves contact exposure of UV-curable resin through a photomask. Alignment of the photomask pattern
with the target can be precisely accomplished by employing a conventional mask-aligner. We proposed a new Vgrooving
method by applying the Mask-Transfer SWW method. V-grooves are a well-known technique for aligning
optical fibers for coupling. Unlike the conventional methods and material, this new method has an advantage that Vgrooves
can be easily fabricated precisely on various kinds of substrates as designed. Therefore, optical coupling
between fibers and devices is achieved simply and efficiently. We believe that these devices will be a key for smart
optical interconnects in near future.
The introduction of optical interconnect technology is expected to solve problems of conventional electric wiring. One of
the promising technologies realizing optical interconnect is the self-written waveguide (SWW) technology with lightcurable
resin. We have developed a new technology of the "Mask-Transfer Self-Written (MTSW)" method. This new
method enables fabrication of arrayed M x N optical channels at one shot of UV-light. Using this technology, several
new optical interconnect devices and connection technologies have been proposed and investigated. In this paper, first,
we introduce MTSW method briefly. Next, we show plug-in alignment approach using optical waveguide plugs (OWP)
and a micro-hole array (MHA) which are made of the light-curable resin. Easy and high efficiency plug-in alignment
between fibers and an optoelectronic-printed wiring board (OE-PWB), between a fiber and a VCSEL, so on will be
feasible. Then, we propose a new three-dimensional (3D) branch waveguide. By controlling the irradiating angle through
the photomask aperture, it will be possible to fabricate 2-branch and 4-branch waveguides with a certain branch angle.
The 3D branch waveguide will be very promising in the future optical interconnects and coupler devices of the multicore
optical fiber.
For the use in cost-effective optical interconnection of
opt-electronic printed wiring boards (OE-PWBs), we have
developed novel optical interconnect devices and coupling methods simplifying board to board optical interconnect. All
these are based on the self-written waveguide (SWW) technology by the mask-transfer method with light-curable resin.
This method enables fabrication of arrayed M × N optical channels at one shot of UV light. Very precise patterns, as an
example, optical rod with diameters of 50μm to 500μm, can be easily fabricated. The length of the fabricated patterns ,,
typically up to about 1000μm , can be controlled by a spacer placed between the photomask and the substrate.
Using these technologies, several new optical interfaces have been demonstrated. These are a chip VCSEL with an
optical output rod and new coupling methods of "plug-in" alignment and "optical socket" based on SWW.
By using 2-beam fiber laser Doppler velocimeter (LDV), velocity measurement can be conducted by using the offset angle between laser beams. Another unique feature in velocity measurement using 2-beam LDV is the appearance of the third spectrum that can be observed when 2 laser beams irradiate to the same spot on the measurement target. We demonstrated the application of third spectrum frequency to obtain moving object velocity within velocity distribution of liquid flow.
The success of optical interconnection for practical use is strongly dependent on the development of a sophisticated
packaging and coupling technology capable of both high coupling efficiency and easy alignment. We have developed
the photomask transfer method applying UV curable resin. This technology enables fabrication of arrayed M x N optical
patterns at one shot of UV light. It is also possible to fabricate very precise patterns by a conventional photomask. The
length/thickness of the fabricated patterns can be controlled by the thickness between the photomask and the substrate.
The maximum length reaches over 1,000μm. As applications using this method, two original devices are reviewed. One
is a chip optical device which consists of a VCSEL (vertical cavity surface emitting laser), optical rods as cores, and a
surrounding clad layer. These optical rods can be accurately fabricated on the emitting spot of the VCSEL. This VCSEL
device enables flexible packaging on OE-PWBs (opto-electric printed wiring boards). Another is a 90-degree light path
conversion device for coupling to an optical wiring on OE-PWBs. It features in hybrid comb-clad consisting of air and
polymer parts. This device has a large refractive index difference between the core and hybrid comb-clad, and enables
downsizing.
We have developed "tapered self-written waveguide (SWW)" for coupling of optical components in the board level optical interconnection. Tapered waveguides have a possibility of achieving larger alignment tolerance for optical coupling. The fabrication condition of tapered SWW was studied by adjusting both the optical power and irradiation time of curing resin, and tapered SWW was successfully realized. The optical tolerance vertical to the optical axis twice as compared with straight SWW was obtained.
The potential of the optical circuit packaging technology is discussed. Special attention has been paid to introduction of "Optical wiring" into the Printed Wiring Board level ("last 1 meter area") to overcome conventional electrical copper-based bandwidth limitations. Optical Surface Mount Technology (O-SMT) can be one of possible solutions in this field is reviewed. High efficiency and alignment-free coupling between optical wirings and optical devices is a key. O-SMT requires a method to change the beam direction from the horizontal to the vertical and vice verse in order to couple between optical wirings in an OE-board and OE-devices mounted on the board. A novel method using an "Optical Pin" has been proposed and investigated. Furthermore, an optical coupling method using a Self-Written Waveguide called "Optical Solder" has been investigated. Several applications of self-written waveguides using a green-laser and a photo-mask are demonstrated.
In the optical interconnection of board level, 45-degree micro mirrors are used to achieve 90-degree optical path change. These mirrors are often fabricated by using a rotating blade and this method has a serious problem of cutting other waveguides in the vicinity. A self-written waveguide ha been successfully applied to repari and connect these waveguides. So, it will be possible to allow optical signals to be input and output at a specific location on the board.
Fiber Bragg gratings have been studied intensively these years, because of their high potentiality in being applied in wavelength division multiplexing fiber transmission systems. As one of their useful characteristics, Bragg reflection wavelength can be changed by applying stress to the grating region. We obtained a maximum wavelength shift of 6.08 nm at 300 electric pulses to an electrically-driven micro-step stage. We investigated its possibility of optical wavelength switching. We achieved maximum extinction ratios of 26.0 dB and 25.9 dB for reflected and transmitted lights, respectively, and realized a switching time of 8 - 10 msec.
Information about the polarization state of light beam is of interest inmany areas. Several kinds of polarization analyzers have been already developed and commercially available. However most of themrequire an optical fiber to couple a laser beam into the analyzer. We have developed acompact polarization analyzer composed of a separated optical head and a personal computer. The optical head which is very thin and compact enables in-situ measurement of the polarization state of a free-space lightwave. This isimportant to study the polarization characteristics of optical devices, because the desired polarization informationmay be disturbed and/or loosen when a light beam is coupled to the head by using an optical fiber.
Polarization control photonic functional devices based on quantum well structures for application to advanced fiber communications are described. Two promising techniques are discussed: compositional disordering and strained-layer structures. TE/TM mode selective waveguides were successfully fabricated using polarization dependent index changes induced by the cap annealing. Enhancement of TM mode optical gain with tensile-strain enabled realization of high performance polarization-insensitive semiconductor optical amplifiers and superluminescent diodes.
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