Coating processes – With pretreatment of the base – Etching – swelling – or dissolving out part of the base
Reexamination Certificate
2001-11-16
2003-12-02
Chen, Bret (Department: 1762)
Coating processes
With pretreatment of the base
Etching, swelling, or dissolving out part of the base
C427S534000, C427S576000, C427S255360, C204S192260
Reexamination Certificate
active
06656528
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the field of photonics, and in particular to a method of making specular infrared mirrors for use in optical devices, such as multiplexers and demultiplexers for use in wavelength division multiplex communication systems.
2. Description of Related Art
The manufacture of optical devices such as multiplexers and demultiplexers requires the fabrication of a highly reflective infrared mirror in the 1.55 &mgr;m and/or 1.30 &mgr;m optical bands. Such a highly reflective infrared mirror is typically required on the sidewall of deep vertical-etched optical components to reflect an infrared laser beam with maximum efficiency.
Typical fabrication techniques of infrared mirrors result in relatively poor surface quality, in lower reflectivity values at 1.55 &mgr;m wavelength and in significant optical losses from infrared light scattering from the surface defects.
Optical multiplexers and demultiplexers have been described in the scientific literature for at least 20 years. The following USA patents and published technical information will review the various manufacturing techniques used to produce the highly reflective infrared mirror of multiplexers, demultiplexers and other infrared optical devices:
U.S. Pat. No. 4,274,706, Hughes Aircraft Company
This patent describes the mirror of infrared multiplexers and demultiplexers shown in
FIGS. 1
a
and
1
b.
The multiplexers and demultiplexers incorporating the mirror allowing the reflection of infrared light are manufactured using a sodium glass microscope slide substrate; a planar wave guide produced by increasing the refractive index of the surface of this substrate to a depth of about 100 &mgr;m using an ion exchange process replacing the sodium atoms of the substrate by lithium atoms from a LiSO
4
salt heated at about 580° C. in oxygen; a grind-and-polished cylindrical shaped surface transverse to the surface of the glass substrate as to achieve the curved wave guide of radius R of
FIG. 1
a
(This cylindrical transverse surface is used to focus the light emanating from the input plane (identified as
14
in
FIG. 1
b
) back to the input plane and has a series of parallel grooves forming a series of pairs of facets of uniform spacing); a replica grating comprising a 0.005 inch thick acetate plastic film having 512 grooves/mm coated with an aluminum as to achieve high reflectivity; and an epoxy glue to bond this transversal cylindrical shaped surface to the replica grating.
This manufacturing technique involves the gluing of an aluminum coated thin flexible material such as an acetate plastic film onto a grind-and-polished sodium glass microscope slide. No further detail on the mirror characteristics and/or fabrication technique is given.
U.S. Pat. No. 4,786,133, Commissariat à l'énergie atomique
This U.S. patent describes the mirror of the infrared multiplexers and demultiplexers shown on
FIGS. 2
a
and
2
b
. The multiplexers and demultiplexers incorporating the mirror allowing the reflection of infrared light is manufactured using a silicon substrate, identified as
20
in
FIG. 2
b
; a stack of three transparent silica layers, identified as
22
,
24
and
26
in
FIG. 2
b
, with the intermediate 4 to 5 &mgr;m thick phosphorus-doped silica layer
24
having a 10-3 to 10-2 higher refraction index than the lower 6 to 8 &mgr;m thick undoped silica layer
22
and the upper 6 to 8 &mgr;m thick undoped silica layer
26
surrounding it; a plurality of optical microguides, identified as G
1
to G
N
in
FIG. 2
a
; a concave and elliptic shaped reflective diffraction grating, identified as R in
FIG. 2
a
, constituted by etched facets etched in the stack of three layers; and an aluminum metal layer, identified as
28
in
FIG. 2
b.
This manufacturing technique involves the vertical etching of facets through a three-layer optical waveguide followed by an aluminum coating. No detail is given on the aluminum coating fabrication technique.
U.S. Pat. Nos. 5,450,510, 5,608,826 and 5,793,912, APA Optics, Inc.
These three USA patents describe the mirror of similar variations of the infrared wavelength division multiplexed optical modulator shown in
FIGS. 3
a
and
3
b
. The infrared wavelength division multiplexed optical modulator incorporating the mirror allowing the reflection of infrared light is assembled using a wavelength dispersive multiplexer transmitter, identified as
21
in
FIG. 3
a
, and consisting of a laser power and laser temperature control circuitry, identified as
23
in
FIG. 3
a
, used to maintain the laser power and temperature at stable pre-set values; a directional coupler controller, identified as
24
in
FIG. 3
a
, used to control the integrated modulator; a semiconductor laser diode, identified as
26
in
FIG. 3
, maintained at constant temperature as to minimise wavelength variations of about 0.0005 &mgr;m/° C.; a first reflective holographic diffraction grating, identified as
27
in
FIG. 3
a
, used to demultiplex the various wavelengths from each other with a 0.0007 &mgr;m separation by using a series of 6190/cm parallel grooves replicated in its surface and overcoated with a reflecting material such as aluminum; a first collimating optics, identified as
28
in
FIG. 3
a
, used to collimate the output beam of the laser diode; a first focusing optics, identified as
29
in
FIG. 3
a
, used to inject the collimated output beam into the external integrated modulator; a mirror, identified as
30
in
FIG. 3
a
, used to reflect the laser diode beam toward the diffraction grating; an integrated modulator, identified as
31
in
FIG. 3
b
, used to attenuate the various wavelengths of the separated beam and used as a directional coupler of the separated beams into the optical fibre; an optical fibre, identified as
21
in
FIG. 3
a
, used to connect the wavelength dispersive multiplexer transmitter and the wavelength dispersive multiplexer receiver; a wavelength dispersive multiplexer receiver, identified as
22
in
FIG. 3
a
, and consisting of a detector array controller, identified as
25
in
FIG. 3
a
, used to control the detector array; a second reflective holographic diffraction grating, identified as
27
′ in
FIG. 3
a
, used to multiplex the various wavelengths together and also consisting in a series of 6190/cm parallel grooves ruled or replicated in its surface and overcoated with a reflecting material such as aluminum; a second collimating optics, identified as
28
′ in
FIG. 3
a
, used to focus the dispersed wavelengths onto the detector array; a second focusing optics, identified as
29
′ in
FIG. 3
a
, used to collimate the multiple wavelength light coming out of the optical fibre with a minimum angular dispersion; a detector array, identified as
32
in
FIG. 3
a
, used to detect the dispersed longitudinal modes; and the two reflective holographic diffraction gratings of this infrared wavelength division multiplexed optical modulator involve an aluminum coating. No detail is given on the aluminum coating fabrication technique.
The highly reflective infrared mirror from Newport Corporation
Newport Corporation, Irvine, Calif., is a worldwide manufacturer and distributor of precision components and systems used for development and application of laser and optical technologies in semiconductor manufacturing and testing, fiber optic communications and other commercial applications. The reflectivity spectra of the ER.1 enhanced aluminum coating near infrared mirror is shown in FIG.
4
.
These reflectivity spectra will be used as comparative reference the results for the present invention.
Marxer C. and Al, Vertical mirrors fabricated by deep reactive ion etching for fiber-optics switching applications. Journal of Microelectromechanical Systems, Vol 6 (3), pp. 277-285. September 1997
This paper describes the characteristics and performance of various metal-coated silicon mirrors to be used for electrostatic switches capable of switching 1.3 &mgr;m infrared light from optical fibres. The electrostatic switch
Ouellet Luc
Tremblay Yves
(Marks & Clerk)
Chen Bret
Dalsa Semiconductor Inc.
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