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Browse Prior Art Database

Auto-Aligning Collection and Transmission Optics

IP.com Disclosure Number: IPCOM000104810D
Original Publication Date: 1993-Jun-01
Included in the Prior Art Database: 2005-Mar-19
Document File: 4 page(s) / 123K

Publishing Venue

IBM

Related People

Cato, RT: AUTHOR [+2]

Abstract

This article describes an optical design that will allow light collection or transmission optics to automatically align themselves. This could reduce manufacturing costs and improve reliability and performance. Wireless Infrared Communication Links would have the signal-to-noise advantage of extreme directivity without the problems and touch alignment.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 50% of the total text.

Auto-Aligning Collection and Transmission Optics

      This article describes an optical design that will allow light
collection or transmission optics to automatically align themselves.
This could reduce manufacturing costs and improve reliability and
performance.  Wireless Infrared Communication Links would have the
signal-to-noise advantage of extreme directivity without the problems
and touch alignment.

      Whenever a light collection system (such as used in a scanner
or wireless infrared communication system) is manufactured, there
always must be care given to carefully align the collection optics so
that the collected light hits the photodetector.  This is usually a
manual process, thus expensive.

      Solid-state photodetectors and emitters have become inexpensive
and are becoming even less expensive.  The concept of this disclosure
is to place an array of photodetectors in the collection system in
the place of the single unit previously used.  The center
photodetector of the array would be located where the optical axis of
the system would nominally be.

      Each photodetector in the array would be enabled or disabled
under microprocessor control.  Upon powering up, the processor would
systematically enable the individual detectors in the array,
searching for the detector with the strongest signal.  The detectors
with the weaker signals would be turned off, preventing them from
contributing noise to the signal.  The effect of this would be the
same as moving the collection lens until alignment is achieved.

      Referring to Fig. 1, when light parallel to the optical axis is
incident on a collection lens, it is focused at the focal point of
the collection lens.  Parallel light that is not parallel to the
optical axis (but within paraxial angles) is focused to a point that
is off the optical axis, but nearly in a plane perpendicular to the
optical axis that is through the on-axis focal point.  The detectors
in the array that are off axis will detect the light that is coming
in at an angle to the optical axis.

      One way in which a microprocessor could select individual
detectors in the array is with the circuit of Figure 2.  The figure
depicts a current-steering circuit that operates in the following
way.  The enable/disable signals from a microprocessor are presented
to the bank of inverters.  A low level presented to an inverter
causes its output to be high, and steers the signal current from the
associated detector out to the transimpedance amplifier.  A high
level presented to an inverter drives its output low, and sinks the
signal current from the associated detector in the inverter output
stage.  Thus, by presenting high-level inputs to all but one of the
inverts, a single detector will provide signal current to the
transimpedance amplifier.  Because the signal currents can be quite
small, the current-switching diodes should exhibit extremely low
leakage current.

      This...