Japanese version is also available.

Problem: how to realize integrated and pluggable free-space optoelectronic systems ?

 Ideas:

    1) Use an image relay optical system

Image relay based optoelectronic system. Module 1 and module 2 can be shifted laterally and longitudinally without changing the image position of chip 1 onto chip 2 and vice versa

ðThe connection of chip-lens modules is tolerant (to some extent) to lateral and longitudinal misalignments

 

    2) Butt-couple the optical and chip packages

Degrees of freedom when the chip and optical packages are butt-coupled

Butt-coupling scheme

          ðThe remaining degrees of freedom corresponds to the tilt and the lateral misalignment between chips

     3) Use a machine vision system to correct the remaining misalignments

 

Alignment & integration set-up

Image analysis process

ðThe chip is aligned with respect to a transparent "target" mask. A machine vision software analyses the misalignment between the targets and the image of the chip devices through the optical system.

 Integration process:

(a) A reference module composed of a target mask fixed to an optical package that contains half an image relay, is connected to an optical package.
(b) A chip package is mounted on translation and rotation stages and positioned just under the optical package.
(c) The image through the optical system of the chip devices and the targets are observed using a CCD camera. A machine vision software analyzes the misalignment between the target masks.  The chip package is then moved using the translation and rotation stages so that the device image are in the center of the targets.
(d) The chip package is fixed to the optical package to form a module. The stages are removed and the modules are disconnected.

 Experimental results

1) Componants

Target mask                           NTT VCSEL array               Hamamatsu photodetector array  GRIN lens (5mm diameter, 0.2 pitch)

2) Packages

 

VCSEL package

Hamamatsu photodetector package

 

Optical package

2) Alignement and integration setup

Alignment set-up for the fabrication of modules

3) Modules produced

Reference module	Test module (target mask instead of chip)
VCSEL module	Photodetector module

4) Validation of the integration technique

- VCSEL module connected to the test module
 

 Target mask from the test module with the image through the GRIN lens relay of the VCSEL array

The lateral misalignment between the VCSELs and targets was 20 ± 20µm.

- VCSEL module connected to the photodetector module

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Parallel optical interconnects have been successfully obtained at the bitrate of 10Mb/s.

Advantages of this novel integration technique:

Simple: no processing of the electronic chips and the optics such as a.o. alignment marks, micro pins, holes and grooves is required. No complex packages with multiple elements or sub-mounts are needed. Very few integration steps are necessary to merge the optics with the optoelectronic chips. The connector between modules have few constraining requirements.

• Flexible: : this integration method can be relatively easily and quickly adapted to different kind of chips (as demonstrated) and image relay based optical systems. A change of chip, chip carrier, optics or optical package can for instance only require a modification of the height of the spacers. Also, the optical package is not in contact with the chip what allows for example the use of wire bonding techniques.

• Modularity: when the modules are fabricated, they can be plugged or fix together. No additional optics or electro-mechanical components as e.g. Risley prisms or MEMs are needed to realize the alignment. Moreover, different components could be inserted between modules such as cube splitters or diffractive optical elements.

•  Accurate: we believe that the chip package can be integrated to the optical package with micron-precision if the machine vision system makes use of high magnification microscope objective. The precision will also depend on the imaging properties of the optical system and the development of suitable connectors to link the modules. With our quite simple packages, a lateral misalignment of only 20 ± 20µm was already obtained. Professional fabrication methods and package designs should greatly reduce it.

•  Easy to manufacturable:  this integration method could be automated using a machine vision system and motorized position stages as explained before. These are quite inexpensive  equipment..

•  Dust-free: : by choosing appropriate design for the optical and chip packages and the spacers, dust-free free-space systems can be easily realized.

•  Rugged: as all elements can be fixed or connected together, optoelectronic systems should remain stable.

Here is a demonstration mpeg file.

References

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