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Browse Prior Art Database

Novel Sensor Based on a Semiconductor Laser

IP.com Disclosure Number: IPCOM000115656D
Original Publication Date: 1995-Jun-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 2 page(s) / 76K

Publishing Venue

IBM

Related People

Broom, RF: AUTHOR

Abstract

Principle of Operation - A plan view of the proposed scheme is shown schematically in Fig. 1. A diode laser 4 of length LL has at its rear an additional mirror M sub 3 forming part of a flexible beam 5 attached to, or fabricated from the laser bar. Movement of the mirror M sub 3 parallel to the axis of the laser 4 (i.e., parallel to the x-axis in Fig. 2) changes the phase of the light reflected back into the optical cavity formed by the mirrors M sub 1 % 'and' % M sub 2, thus modulating the light output, which can be monitored by the photodiode P. Deflection of M sub 3 (dX) relative to M sub 2 can be achieved by several means, for example: 1. mechanical force, e.g., a gas flow or by a stylus pressing on the beam; 2. thermal differential expansion, as in a bimetallic strip.

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Novel Sensor Based on a Semiconductor Laser

      Principle of Operation - A plan view of the proposed scheme is
shown schematically in Fig. 1.  A diode laser 4 of length LL has at
its rear an additional mirror M sub 3 forming part of a flexible beam
5 attached to, or fabricated from the laser bar.  Movement of the
mirror M sub 3 parallel to the axis of the laser 4 (i.e., parallel to
the x-axis in Fig. 2) changes the phase of the light reflected back
into the optical cavity formed by the mirrors M sub 1 % 'and' % M sub
2, thus modulating the light output, which can be monitored by the
photodiode P. Deflection of M sub 3 (dX) relative to M sub 2 can be
achieved by several means, for example:
  1.  mechanical force, e.g., a gas flow or by a stylus pressing on
the
       beam;
  2.  thermal differential expansion, as in a bimetallic strip.

Realization - Si micromechanical techniques may be used to construct
the beam 5, which must then be attached to the laser 4, a non-trivial
operation.  More simply, the additional mirror can be formed
monolithically by milling the laser material (for example AlGaAs) by
focussed ion beam (FIB).  FIB has demonstrated its ability to create
accurately defined surfaces with minimum damage and minimum
degradation of the laser's threshold.  An example of its application
to the present problem is illustrated in Fig. 2.  In essence, three
orthogonal cuts in the z-, x-, and y-planes, labelled 1, 2, and 3,
are made as shown.  The outer surface 6 is the original cleaved
surface of the laser 4.  The dimensions of the beam 5, thickness t,
length L, width W, and the gap X between M sub 2 and M sub 3, are all
defined by the cuts 1 and 2.  Construction by this means is th...