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Adjustment of Laser Optical Power and Adjustment of Photo Diode Monitor Current

IP.com Disclosure Number: IPCOM000105154D
Original Publication Date: 1993-Jun-01
Included in the Prior Art Database: 2005-Mar-19
Document File: 4 page(s) / 80K

Publishing Venue

IBM

Related People

Gagnage, A: AUTHOR [+2]

Abstract

Today, the above adjustments are done independently by active resistor trimming (impact on capital, yields, unit hours, design complexity).

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Adjustment of Laser Optical Power and Adjustment of Photo Diode Monitor Current

      Today, the above adjustments are done independently by active
resistor trimming (impact on capital, yields, unit hours, design
complexity).

      Laser power adjustment and laser power control can be done by a
unique movement of the monitor photo diode.

MONITOR PHOTODIODE SUBMOUNT - In a "T0 can" type of package, the
monitor submount is a block of metal.

      The photodiode is brased to the submount, the angle with the
laser being 90º+-15º  to avoid reflections.  To bring the
laser axis and the monitor diode in the same plan for wire bonding
purpose, the "T0 can" itself must be rotated.

      In our example, the photodiode is mounted on a copper foil (.3
mm thick), OFHC, with a flash of gold.

      The foil is grooved in such a way that, the foil being attached
at one end, moving the other end will force the monitor diode to
rotate around the AA axis.

      In the horizontal position, the diode can be wire bonded.  In
the vertical position, the diode is capable to capture some light as
it is shown in Fig. 2.

      The wire connecting the diode to the substrate can be soldered
as shown on Fig. 1 to avoid interference with the submount during the
rota tion.

      This rotating device is capable of bridging the monitor in the
proper location.  If needed, to increase the stability of the foil,
epoxy will reinforce the thinner parts.

MONITOR PHOTODIODE CURRENT ADJUSTMENT - In the classic approach, the
resistor trimming is there to compen sate for the large variations of
light emitted by the backside of the laser, the assembly tolerances,
the photodiode characteristics.

      Since the photodiode is now rotating, the quantity of light cap
tured by the photodiode varies continuously from near zero to max.
The current issued by the monitor varies from Imin.to Imax.  Assuming
that, per design, Imin.<Iref.<Imax., it is possible to reach Iref.
just by rotating the copper foil.

LASE...