Passive alignment frame using monocrystalline material

An apparatus for coupling an optical fiber to an optical device comprises a substrate and a passive alignment member. The substrate having a top surface and a bottom surface. The top surface having a fist groove disposed thereon for holding an optical fiber, and a second groove disposed on the top surface. The second groove being substantially orthogonal to the first groove. The passive alignment member disposed in the second groove. The passive alignment member having selectively etched forward and side pedestals for aligning the optical device to the optical fiber disposed in the first groove.

FIELD OF THE INVENTION 
The invention of the present disclosure relates to a collinear passive 
alignment apparatus for aligning both active and passive optical devices 
on a monocrystalline material. 
BACKGROUND OF THE INVENTION 
This invention is related to U.S. Pat. No. 5,420,953 assigned to the 
assignee of the present invention. 
The use of monocrystalline materials has enabled the passive alignment of 
optical devices to optical fiber for optical communication. The use of 
such materials to replace the requirements for active device alignment has 
great potential to effect the low cost, large production of optical links 
that have application to Fiber to the Home (FTTH) and Fiber to the Office 
(FTTO). Accordingly, the recent past has seen a great deal of interest and 
inventive activity in the development of passive alignment based on the 
use of monocrystalline materials. A common material for such use is 
monocrystalline silicon, as its crystalline properties are well known in 
the art. In U.S. Pat. No. 4,210,923 to North, et al., typical techniques 
for etching silicon is disclosed, and the disclosure of the North, et al. 
patent is specifically incorporated herein by reference. 
One of the preferred set of devices in the optical communication technology 
is the surface emitting and detecting device. To this end, the use of 
devices such as Vertical Cavity Surface Emitting Lasers (VCSELS) and 
photodetectors (such as PIN photodiodes) that have the photosensitive 
surface to receive or emit light on the top surface has required a great 
deal of modification to effect the alignment of the device to an optical 
fiber. In general, to effect the alignment between the device and the 
fiber using a silicon optical bench, it is required to have the device on 
a different plane that the fiber, with the light being communicated 
therebetween by a reflective surface. Examples of such techniques are 
found for example in U.S. Pat. Nos. 5,073,003 and 4,904,036, to Clark and 
Blonder, respectively, the disclosures of which are specifically 
incorporated herein by reference. While such technology has its merits in 
allowing passive alignment to some extent, it is nonetheless required that 
the device be actively aligned into position so that light is properly 
reflected by the reflective surface. Furthermore, the use of a reflective 
surface decreases coupling efficiency, since there are intrinsic losses 
incurred at each optical surface through dispersive effects. Accordingly, 
a more efficient system would allow for in-line coupling between the fiber 
and the device. 
U.S. Pat. No. 5,179,609 to Blonder, et al. discloses an example of the use 
of silicon waferboard technology to effect the coupling between the device 
and the fiber in a co-linear fashion. The disclosure of this patent is 
specifically incorporated herein by reference. This reference makes use of 
two pieces of monocrystalline material as mounting members that have 
etched therein detents in complimentary locations on each of the pieces of 
the mounting members. These detents receive microspheres to effect the 
alignment of the mounting members to effect the coupling of the device to 
the fiber. While the reference does disclose the use of other types of 
alignment fiducials, there are two substantive drawbacks to the invention 
disclosed in this reference. To effect alignment, there is required a 
separate member for holding the device to be coupled to the fiber, and 
another member to hold the optical fiber. Furthermore, the alignment 
fiducials are separated piece parts that are placed between the waferboard 
holding the fiber and the waferboard holding the device. 
As can be readily appreciated from a study of the disclosure of this 
reference, the alignment fiducials are an additional processing step 
requiring additional parts to effect alignment. Furthermore, the alignment 
fiducials of this reference are a potential source of misplacement and 
thereby misalignment of the members. Accordingly, what is needed is an 
apparatus that allows for direct attachment of the optical fiber and the 
device to a single alignment member. Furthermore, what is needed is an 
apparatus that enables passive alignment via alignment pedestals and 
standoffs that are integrally formed from and on the single alignment 
member. The alignment therebetween is thereby made simply and effectively 
at a lower cost in manufacture. 
SUMMARY OF THE INVENTION 
The present invention relates to a simple but fundamentally different way 
of aligning optical fibers and devices on monocrystalline material. To 
this end, a passive alignment frame has an etched surface for receiving an 
optical fiber for attachment therein. Also disposed on the passive 
alignment frame are alignment pedestals and standoffs that are formed or 
the frame by reactive ion etching. The pedestals allow for ready and 
accurate placement and bonding of the device to be coupled to the fiber. 
The device and the fiber are aligned and coupled passively. In the 
preferred embodiment, the device and the fiber are bonded to the passive 
alignment frame which is then readily packaged without substantial 
limitation. In another embodiment, the fiber is bonded first to a groove 
disposed on a substrate, and the surface emitting/receiving device is 
mounted on the passive alignment frame which is then mounted on the 
substrate and passively aligned to the fiber. Metallization is also 
provided on the passive alignment member (PAM) for electrical connection 
between the device and external circuitry. 
Objects, Features and Advantages of the Invention 
It is an object of the present invention to passively align an optical 
fiber with a surface emitting or receiving device in a collinear fashion. 
It is a further object of the present invention that the fiber and the 
device are bonded to a passive alignment member and passively aligned, 
forming an integral unit. 
It is a feature of the present invention to effect the collinear alignment 
of the optical device to the surface emitting or receiving device by the 
use of a single passive alignment member made of monocrystalline material 
selectively etched to effect the passive alignment of an optical device to 
an optical fiber. 
It is a further feature of the present invention that the proper placement 
of the device to effect accurate passive alignment is effected by 
pedestals that are integrally formed from the single passive alignment 
member. 
It is a further feature of the present invention that the selectively 
etched alignment pedestals are placed to efficiently locate the surface 
emitting/detecting optical device to two degrees of freedom, with the 
passive alignment member locating the third degree of freedom. 
It is an advantage of the present invention that the passive alignment 
members can be fabricated in large quantity and simultaneously from a 
single wafer by simultaneous processing techniques.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Turning to FIG. 1, we see an end view of the passive alignment member (PAM) 
101 having disposed thereon an optical device 102 and an optical fiber 110 
disposed therein (shown in outline form). There is also shown in FIG. 1, 
the forward alignment pedestals 103, and the side alignment pedestals 104 
which enable the accurate placement of the device 102. The device 102 is 
application driven, and is envisioned to be a VCSEL, a p-i-n photodiode or 
a hologram used for various applications such as focusing or wavelength 
division multiplexing. The particular device utilized need only be a 
surface emitting or receiving device. Finally, the metalization for 
effecting electrical connection 107 as well as the optional alignment 
standoffs 106 are shown. The apparatus in final mounted form is shown in 
FIGS. 3 and 4 in perspective view. 
The basic essence of the present invention is that the surface 
emitting/receiving device 102 can be passively aligned to the fiber to 
submicron precision using the inside edges of the passive alignment 
member. Turning to FIGS. 1 and 2, we see the preferred embodiment of the 
present invention. To this end, the alignment of the device 102 is 
effected by the alignment pedestals 103 and 104. As can be seen in FIG. 2, 
the device 102 is etched by RIE to have notches to receive the pedestals. 
In this way the device is precisely positioned with respect to the groove 
108 of the PAM 101. Thereafter, the fiber 110 is seated in the groove 108 
and the device 102 is aligned passively to the fiber 110. The device is 
then bonded to the PAM by solder reflow, and the vertical standoffs 106 
are used optionally in cases where solder on the device would impede its 
emission/reception of light. The geometry of the PAM having the fiber 
inserted therein and the device 102 missing is as shown in FIG. 6. As can 
be seen from a review of FIGS. 1 and 6 in particular, the optical fiber is 
disposed in the groove 108 and the device 102 is thereby oriented 
orthogonally with respect to the optical fiber 110. 
In an alternative embodiment shown in FIGS. 3 and 4, the optical fiber 110 
is shown mounted in a v-groove (not shown) that is etched by standard 
technique in the monocrystalline material that forms the substrate 302. 
Preferably, the substrate is made 100 Si and is etched by wet etching 
techniques as is discussed in the reference to North, et al. discussed 
supra. The PAM 101 is mounted in a cavity 303 in the substrate. This 
cavity is formed by diamond saw cutting in the substrate in a 
perpendicular fashion to the direction of the v-shaped groove that holds 
the fiber 110. Finally, the electrical connections for making contact 
between the device 102 and external electronics (not shown) is through the 
metalization 304 via metalization 107. As can be readily appreciated from 
a study of FIG. 6, the fiber 110 is readily aligned in the PAM. To be 
clear, the fiber is bonded in the v-groove on the substrate. The fiber is 
thus placed in a well determined relationship with the groove 303, and 
thereafter the PAM is mounted in a well determined relationship in the 
groove, seating the fiber in its groove 108. The device is thereby 
passively aligned to the fiber. In order to create the final assembly 
linking the device 102 to the fiber for communication, the fiber 110 is 
bonded to the v-groove as is shown in FIGS. 3,4 and 7. The bonding can be 
effected by soldering or other techniques such as electrostatic bonding 
techniques, as disclosed in U.S. patent application Ser. No. 08/269,302, 
which is now U.S. Pat. No. 5,553,158 Electrostatic Bonding of Optical 
Fibers to Substrates", and by solder techniques such as are described in 
U.S. patent application Ser. No. 08/269,300 "Solder Attachment of Optical 
Fiber to Semiconductor Waferboard." Both of these applications were filed 
Jun. 30, 1994 and are assigned to the assignee of the present invention. 
Finally, it is important to note that in addition to this bonding 
techniques, adhesives such as commercial are possible as bonding agents, 
and that all of the bonding techniques mentioned above are useful in 
bonding the fiber to the PAM as well as the substrate. The silicon 
substrate has a saw cut groove in the surface as shown at 303. The PAM 
having the device 102 mounted thereon are placed in the groove 303 and the 
fiber 110 then fi s through the v-groove 108 effected as described above. 
This is shown clearly in FIG. 6. The fiber is thereby passively aligned to 
the device 102. The PAM 101 may then be readily bonded to the groove 303 
by presolder in the groove. Solder may also be placed on the contact areas 
107 and 304 to enable electrical connection following reflow between the 
PAM and the silicon waferboard via the groove 303. 
The steps of manufacturing the device is discussed presently. Turning now 
to FIG. 5, we see the etched diamond shaped holes in quantity on a 
selected section of a wafer. The individual PAM's are then diced from the 
wafer. To this end, the wafer is preferably a monocrystalline Si wafer 
having a 110 plane on its top surface. This planar direction is chosen for 
purely illustrative purposes and it is understood that other planar 
orientations at variance with that chosen are within the purview of the 
skilled artisan and intended to be encompassed in the instant invention. 
To effect the structure shown, the diamond shaped holes are etched through 
the wafer by wet etching as described in the North, et al. reference. The 
side and forward pedestals, 103 and 104 respectively, as well as the 
standoffs 106 are formed by reactive ion etching (RIE). Details of RIE 
techniques can be found in Optoelectronic Integration: Physics, Technology 
and Applications, Chapter 4, p. 113-119, Kluwer Academic Publishers, 1994, 
the disclosure of which is specifically incorporated herein by reference. 
In production, the features made by RIE are effected first, then a mask 
such as SiN.sub.x which acts as a mask as well as a protective layer for 
the features etched by RIE. A photoresist is applied thereto the surface 
and the holes 501 are formed by revealing the preferred crystalline planes 
through the wet etching technique. Finally, the metallization patterns 107 
are placed on the wafer by vacuum evaporation, sputtering or plating of 
conductive metals, preferably gold. At this point, the device 102 is 
mounted and passively aligned to the alignment features 103 and 104 and 
thereafter diebonded using a passive alignment diebonder. Thereafter the 
individual PAM's having the devices 102 mounted thereon are diced from the 
wafer by the use of a diamond saw. 
The vertical standoffs 106 have particular application in the alignment 
when a VCSEL is the preferred device 102. To this end, in practice the 
fiber is fixed in position on the substrate 302 as described above, and 
the VCSEL is fixed in the x and y directions (assuming an orthogonal 
coordinate system) by the use of the side and forward pedestals. The 
height of the VCSEL in the z direction is carefully placed by the 
standoffs 106, as the VCSEL is bonded to the PAM with its epitaxial layer 
facing the fiber 110 (epi-side down), and as described above, the 
standoffs further have the inherent benefit to prevent solder from 
interfering with device emission/reception of light. 
The invention having been described for a single PAM coupling a single 
fiber to a single surface emitting/detecting device, we now turn to the 
applicability and manufacture of an embodiment in which the PAM is to 
effect the alignment of an array of fibers and devices. This embodiment is 
shown in FIGS. 8-11. FIGS. 8 and 9 are a perspective and top view of an 
array link. To this end, a PAM 801 is disposed in groove 802 saw cut into 
the silicon substrate having preferably a 100 crystalline on its top 
surface wherein v-grooves are etched for receipt of fibers 805. The fibers 
are thereby aligned to an array of surface emitting/detecting devices 804. 
The processes and techniques for effecting the forward and side alignment 
pedestals and standoffs as well as the etching of the PAM are identical to 
that described for a single fiber/PAM/device as described above. The PAM 
801 is shown on endview in FIG. 10, having forward and side alignment 
pedestals 901 and 902, respectively, as well as optional standoffs 904. 
The metallization 905 is effected as described above. Again, in large 
scale production, the PAM is fabricated on a wafer of (110) crystalline Si 
as is shown in FIG. 11, and the technique for the fabrication of the PAM, 
the mounting of the devices 804 and the separating of the individual array 
PAM are effected in an identical procedure as described above for a single 
PAM. FIG. 12 and 13 show the multiple fiber/multiple device configuration 
with the device 122 and fibers 123 mounted or the PAM 121 by forming an 
integral unit by techniques described for the single device/single fiber 
PAM as shown in FIGS. 1 and 2. 
The invention having been described to be readily understood by the artisan 
skill, it can be appreciated that variations in material and devices to 
effect the passive alignment members are considered within the purview of 
the ordinary skilled artisan. For example, it is clearly considered within 
the purview of the present invention that in a multiple device/multiple 
fiber PAM can be used as a transceiver. Such are considered within the 
scope if the invention.