Title: Dynamic alignment of optical fibers to optical circuit devices such as planar lightwave circuits
Abstract: An improved method and system of aligning an optical fiber or optical fiber array to an optical circuit device couples an optical signal source and an optical measuring device to the optical fiber array, the other side of which array is coupled to the same side of the optical circuit device, thereby forming an initial U-shaped optical path from the optical signal source to the optical fiber array to the optical circuit device to the optical fiber array and to the optical measuring device. The optical path is adjusted until the optical measuring device finds a characteristic of the optical signal to be satisfactory. At that time, the final alignment may be fixed or made permanent. The characteristic of the optical signal may include, for example, the intensity of the optical signal, which is preferably at a maximum or the insertion loss which is preferably at a minimum.
Patent Number: 6,937,335 Issued on 08/30/2005 to Mukai
| Inventors:
|
Mukai; Paul Victor (30 Via Lucca #F207, Irvine, CA 92612)
|
| Appl. No.:
|
094585 |
| Filed:
|
March 8, 2002 |
| Current U.S. Class: |
356/399; 356/400; 385/52 |
| Intern'l Class: |
G01B 011/00; G02B 006/26 |
| Field of Search: |
356/731,399,400,124.5
385/24,52,14,15
398/9-17,25-33
250/214.R,227.18,227.23,227.24,227.11,216
|
References Cited [Referenced By]
U.S. Patent Documents
| 5039191 | Aug., 1991 | Myszka.
| |
| 5596662 | Jan., 1997 | Boscher.
| |
| 5625450 | Apr., 1997 | Ikeno.
| |
| 5664033 | Sep., 1997 | Scheu et al.
| |
| 5926594 | Jul., 1999 | Song et al.
| |
| 5970192 | Oct., 1999 | Osugi et al.
| |
| 6024498 | Feb., 2000 | Carlisle et al.
| |
| 6108074 | Aug., 2000 | Bloom.
| |
| 6122423 | Sep., 2000 | You et al.
| |
| 6175675 | Jan., 2001 | Lee et al.
| |
| 6654523 | Nov., 2003 | Cole.
| |
| Foreign Patent Documents |
| 0 545 584 | Nov., 1992 | EP.
| |
| 10123373 | May., 1998 | JP.
| |
Other References
Bahadori, et al., Automated Fiber-Waveguide Array Alignment, Journal of
Optical Communications, Fachverlng Schiele & Schon, Berlin, Germany, vol. 10, No.
2, Jun. 1, 1989, pp. 54-55.
Haronian, D., Bottlenecks of Opto-MEMS, In Micro-Opto-Electro-Mechanical
Systems, SPIE vol. 4075:84-92 (2000).
|
Primary Examiner: Smith; Zandra V.
Assistant Examiner: Stock, Jr.; Gordon J.
Claims
1. A method of aligning an optical fiber array relative to an optical circuit
device, the optical fiber array being coupled to the optical circuit device, the
method comprising:
coupling an optical signal source to one end of the optical fiber array, the
other end of the optical fiber array being coupled to a side of the optical circuit
device, the optical signal source adapted to transmit an optical signal to the
optical fiber array;
coupling an optical measuring device to the one end of the optical fiber array,
the other end of the optical fiber array being coupled to the same side of the
optical circuit device, the optical measuring device adapted to measure a characteristic
of an optical signal received from the optical fiber array;
establishing an initial optical path from the optical signal source to the optical
fiber array to the optical circuit device to the optical fiber array and to the
optical measuring device;
measuring the characteristic of an optical signal received by the optical measuring
device from the optical fiber array; and
moving the relative position of the optical fiber array and the optical circuit
device to change the optical path until the measured characteristic indicates that
the alignment of the optical path is satisfactory.
2. The method of claim 1 wherein the optical path from the optical signal source
to the optical measuring device is "U"-shaped.
3. The method of claim 1 wherein the moving step changes the optical path until
the measured characteristic indicates that the alignment of the optical path is optimal.
4. The method of claim 1 wherein the moving step changes the optical path until
the measured characteristic indicates that the alignment of the optical path is
above a threshold.
5. The method of claim 1 further comprising fixing the relative positions of
the optical fiber array and the optical circuit device.
6. The method of claim 5 wherein the fixing step bonds or adheres the optical
fiber array to the optical circuit device.
7. The method of claim 1 wherein the optical fiber array is a single optical fiber.
8. The method of claim 1 wherein the optical fiber array includes an optical waveguide.
9. The method of claim 1 wherein the optical signal source and the optical measuring
device are coupled to different optical fibers of the optical fiber array.
10. The method of claim 1 further comprising using a mechanical reference to
assist establishing the initial optical path.
11. The method of claim 1 wherein the mechanical reference is a mark made on
the optical fiber array and the optical circuit device.
12. The method of claim 1 wherein the moving step moves the relative position
of the optical fiber array and the optical circuit device in a random manner.
13. The method of claim 1 wherein the moving step moves the relative position
of the optical fiber array and the optical circuit device in a systematic manner.
14. The method of claim 1 wherein the moving step rotates the relative position
of the optical fiber array and the optical circuit device.
15. The method of claim 1 wherein the moving step translates the relative position
of the optical fiber array and the optical circuit device.
16. The method of claim 1 wherein the moving step rotates and translates the
relative position of the optical fiber array and the optical circuit device.
17. The method of claim 1 wherein the characteristic is the intensity of the
optical signal.
18. The method of claim 17 wherein the moving step changes the optical path until
the intensity of the optical signal is a maximum.
19. The method of claim 17 wherein the moving step changes the optical path until
the intensity of the optical signal exceeds a threshold.
20. The method of claim 1 wherein the characteristic is the insertion loss of
the optical signal.
21. The method of claim 20 wherein the moving step changes the optical path until
the insertion loss of the optical signal is a minimum.
22. The method of claim 20 wherein the moving step changes the optical path until
the intensity of the optical signal is below a threshold.
23. The method of claim 1 wherein the optical circuit device comprises a planar
lightwave circuit.
24. The method of claim 23 wherein the optical path from the optical signal source
to the planar lightwave circuit is "U"-shaped.
25. The method of claim 23 wherein the moving step changes the optical path until
the measured characteristic indicates that the alignment of the optical path is optimal.
26. The method of claim 23 wherein the moving step changes the optical path until
the measured characteristic indicates that the alignment of the optical path is
above a threshold.
27. The method of claim 23 wherein the moving step rotates the relative position
of the optical fiber array and the optical circuit device.
28. The method of claim 23 wherein the moving step translates the relative position
of the optical fiber array and the optical circuit device.
29. The method of claim 23 wherein the moving step rotates and translates the
relative position of the optical fiber array and the optical circuit device.
30. The method of claim 23 wherein the characteristic is the intensity of the
optical signal.
31. The method of claim 30 wherein the moving step changes the optical path until
the intensity of the optical signal is a maximum.
32. The method of claim 30 wherein the moving step changes the optical path until
the intensity of the optical signal exceeds a threshold.
33. The method of claim 23 wherein the characteristic is the insertion loss of
the optical signal.
34. The method of claim 33 wherein the moving step changes the optical path until
the insertion loss of the optical signal is a minimum.
35. The method of claim 33 wherein the moving step changes the optical path until
the intensity of the optical signal is below a threshold.
36. The method of claim 23 further comprising fixing the relative positions of
the optical fiber array and the planar lightwave circuit.
37. The method of claim 36 wherein the fixing step bonds or adheres the optical
fiber array to the planar lightwave circuit.
38. A system adapted to align a first and second light-guiding element, the system comprising:
an optical signal source coupled to transmit an optical signal to the first light-guiding
element, the first light-guiding element being coupled to and adapted to propagate
the transmitted optical signal to an input of the second light-guiding element,
the second light-guiding element being adapted to propagate the transmitted optical
signal from its output to the first light-guiding element, the input and output
of the second light-guiding element being located on the same side of the second
light-guiding element;
an optical measuring device coupled to receive the transmitted optical signal
from the first light-guiding element, the first light-guiding element comprising
an optical fiber array, thereby forming an optical path from the optical signal
source to the first light-guiding element to the input of the second light-guiding
element to the output of the second light-guiding element to the first light-guiding
element and to the optical measuring device, the optical measuring device being
adapted to measure a characteristic of the received optical signal;
a control circuit coupled to the optical measuring device and to a movable structure,
the movable structure being coupled to move the relative position of the first
and second light-guiding elements, the control circuit processes information from
optical measuring device, determines whether the characteristic of the received
optical signal is satisfactory, and controls whether the movable structure moves
the relative position of the first and second light-guiding elements to change
the optical path;
wherein the relative positions of the first and second light-guiding elements
may be changed to alter the optical path until the optical measuring device determines
that the characteristic of the received optical signal is satisfactory.
39. The system of claim 38 wherein the optical fiber array is a single optical fiber.
40. The system of claim 38 wherein the movable structure moves the relative position
of the first and second light-guiding elements in a random manner.
41. The system of claim 38 wherein the movable structure rotates the relative
position of the first and second light-guiding elements.
42. The system of claim 38 wherein the movable structure translates the relative
position of the first and second light-guiding elements.
43. The system of claim 38 wherein the movable structure rotates and translates
the relative position of the first and second light-guiding elements.
44. The system of claim 38 wherein the optical path from the optical signal source
to the optical measuring device is "U"-shaped.
45. The system of claim 38 wherein the changes the optical path until the measured
characteristic indicates that the alignment of the optical path is optimal.
46. The system of claim 38 wherein the changes the optical path until the measured
characteristic indicates that the alignment of the optical path is above a threshold.
47. The system of claim 38 wherein the characteristic is the intensity of the
optical signal.
48. The system of claim 47 wherein the changes the optical path until the intensity
of the optical signal is a maximum.
49. The system of claim 47 wherein the changes the optical path until the intensity
of the optical signal exceeds a threshold.
50. The system of claim 38 wherein the characteristic is the insertion loss of
the optical signal.
51. The system of claim 38 wherein the control circuit changes the optical path
until the insertion loss of the optical signal is a minimum.
52. The system of claim 51 wherein the control circuit changes the optical path
until the intensity of the optical signal is below a threshold.
53. The system of claim 38 wherein the comprises a planar lightwave circuit.
54. The system of claim 38 wherein the optical signal source and the optical
measuring device are disposed on an optical device chip.
55. A system adapted to align a first and second light-guiding element, the system comprising:
an optical signal source coupled to transmit an optical signal to the first light-guiding
element, the first light-guiding element being coupled to and adapted to propagate
the transmitted optical signal to an input of the second light-guiding element,
the second light-guiding element comprising an optical circuit device, the optical
circuit device including a planar lightwave circuit, the second light-guiding element
being adapted to propagate the transmitted optical signal from its output to the
first light-guiding element, the input and output of the second light-guiding element
being located on the same side of the second light-guiding element;
an optical measuring device coupled to receive the transmitted optical signal
from the first light-guiding element, thereby forming an optical path from the
optical signal source to the first light-guiding element to the input of the second
light-guiding element to the output of the second light-guiding element to the
first light-guiding element and to the optical measuring device, the optical measuring
device being adapted to measure a characteristic of the received optical signal;
a control circuit coupled to the optical measuring device and to a movable structure,
the movable structure being coupled to move the relative position of the first
and second light-guiding elements, the control circuit processes information from
optical measuring device, determines whether the characteristic of the received
optical signal is satisfactory, and controls whether the movable structure moves
the relative position of the first and second light-guiding elements to change
the optical path;
wherein the relative positions of the first and second light-guiding elements
may be changed to alter the optical path until the optical measuring device determines
that the characteristic of the received optical signal is satisfactory.
56. The system of claim 55 wherein the movable structure moves the relative position
of the first and second light-guiding elements in a random manner.
57. The system of claim 55 wherein the first light-guiding element includes an
optical fiber array.
58. The system of claim 55 further comprising a single optical fiber coupled
to the first light-guiding element.
59. The system of claim 55 wherein the optical signal source and the optical
measuring device are disposed on an optical device chip.
Description
FIELD OF THE INVENTION
The field of the invention relates generally to the alignment of optical devices
and more particularly, to the alignment of optical fibers and/or optical fiber
arrays to optoelectronic devices in the form of planar lightwave circuits ("PLC").
BACKGROUND
Optical fibers and/or optical fiber arrays may be connected to optoelectronic
devices in the form of planar lightwave circuits (PLC). The alignment of such connections
is important as it affects the quality of the transmitted optical signal (e.g.,
its intensity and/or insertion loss). Attaching optical fibers to PLC devices is
a fundamental aspect of the manufacturing and assembly process. The accuracy with
which this process is executed can affect the overall device performance. Present
alignment methodologies for a multi-ported optical device require the simultaneous
positioning, or alignment, of at least three independent physical units, in free
space. The complexity of this scheme is significant in that each unit must have
its own independent positioning system. The movement of each of the positioning
systems must be orchestrated in such a manner that a line-of-sight, or optically
conductive path, be established through all of the units.
A large class of products utilize PLC to fiber connections. These include both
active and passive photonic components such as arrayed wave gratings, lasers, filters
and amplifiers. Each of these components possesses input and output ports that
convey light. The best way to properly direct light to and from these ports is
to convey the light with a guided wave structure. This requires the use of optical
fibers or optical fiber arrays. The nature of this operation is inherently complex
and time consuming. At a minimum it requires the manipulation of at least two independent
fibers, each with six degrees of freedom while trying to obtain levels of precision
at the submicron level.
U.S. Pat. No. 5,926,594 describes an example of this methodology. Once the optical
path is established, the units' positions must be secured and made permanent relative
to the other units. This operation includes the application of a bonding material
that must be cured through the application of infrared radiation or thermal energy.
This type of curing process may impart stresses and relative displacement between
the units as the state of the curing material changes. The displacement may include
warping and twisting that will affect the planarity of the finished assembly. The
finished assembly itself is affixed to a rigid substrate to increase its overall
mechanical strength.
The prior art approach has several disadvantages. The approach is mechanically
complex because it requires a six degree-of-freedom positioning mechanism for each
of the three independent units. Further, the time required for the alignment process
to converge to the optimal alignment is long and extended due to an unconstrained
geometry and an inherently iterative, sequential process. Also, the optimal alignment
for the assembly, which comprises a series of optical paths, is no better than
the insertion loss of the optically worst path of the series of paths. For example,
in trying to align eight parallel optical paths, one finds that the optimal position
has 0 dB insertion loss on seven of the eight paths and that the eighth path has
an insertion loss of 5 dB. Assuming that this is the best one can do, the so-called
best path is limited by the path having the greatest insertion loss-the 5 dB path.
That path represents the worst-case insertion loss path, which is an inseparable
function of the alignment of all three units. Another issue is the accumulation
of mechanical tolerances. By cascading all of the alignment parameters into a single
operation, it is not possible to optimize sub-alignment tasks.
Therefore, there is a need for an improved method of aligning optical
fibers and/or optical fiber array structures to optoelectronic devices.
SUMMARY OF THE INVENTION
An improved method of aligning an optical fiber or optical fiber array to an
optical
circuit device couples an optical signal source and an optical measuring device
to the optical fiber array, the other side of which array is coupled to the same
side of the optical circuit device, thereby forming an initial optical path from
the optical signal source to the optical fiber array to the optical circuit device
to the optical fiber array and to the optical measuring device. The optical path
is adjusted until the optical measuring device finds a characteristic of the optical
signal to be satisfactory. At that time, the final alignment may be fixed or made
permanent. The characteristic of the optical signal may include, for example, the
intensity or insertion loss of the optical signal.
Other systems, methods, features and advantages of the invention will be or
will become apparent to one with skill in the art upon examination of the following
figures and detailed description. It is intended that all such additional systems,
methods, features and advantages be included within this description, be within
the scope of the invention, and be protected by the accompanying claims.
BRIEF DESCRIPTION OF THE DRAWINGS
The components in the figure are not necessarily to scale, emphasis instead being
placed upon illustrating the principles of the invention. All illustrations are
intended to convey concepts, where relative sizes, shapes and other detailed attributes
may be illustrated schematically rather than literally or precisely.
FIG. 1A is a block diagram representation of an example embodiment of an optical
alignment system for aligning an optical fiber array to an optical circuit device.
FIG. 1B is a block diagram representation of another example embodiment of an
optical alignment system for aligning an optical fiber array to an optical circuit device.
FIG. 2 is a flow chart representation for an example embodiment of an optical
alignment system.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1A is a block diagram representation of an example embodiment of an optical
alignment system for aligning an optical fiber or optical fiber array
20
to an optical circuit device
22 such as a PLC. The optical fiber or optical
fiber array
20 may also be referred to as an optical waveguide(s) or optical
element. Preferably, the optical circuit device
22 is a PLC. For convenience,
the optical circuit device
22 may be referred to as a PLC
22 even
though other types of optical circuit devices, such as one containing a light-guiding
element in an optical fiber array, are also contemplated. The optical alignment
system uses a loopback feature to provide an optical circuit path that allows an
active optical alignment of the optical fiber array
20 to the PLC
22
to occur independent of the state of the PLC
22. The optical alignment system
preferably is a "U"-shaped optically conductive path whose endpoints
34,
38 reside on the same side of the PLC
22. An optical signal source
32 is aimed at one endpoint
34; an optical measuring device
36
is directed to receive and measure the intensity of optical signals from the other
endpoint
38. Responding to the optical measuring device
36, a control
circuit
52 adjusts the alignment of the optical fiber or optical fiber array
20 by adjusting the fiber array header
40 relative to the optical
circuit device
22. When the optical measuring device
36 finds the
maximum intensity of the optical signal, the alignment is optimal and may be made
permanent. The optical source
32 and the optical measuring device
36
may be disposed on the same chip or on different and separate structures. If the
optical source
32 and the optical measuring device
36 are disposed
on the same chip, the U-shaped optical path may be optionally formed on the optical
fiber array
20 instead of the PLC
22. In other words, the location
of the U-shaped optical path relative to the optical source
32 and optical
measuring device
36 may switched so that either the U-shaped optical path
is on the PLC
22 (and the optical source
32 and optical measuring
device
36 are off the PLC
22), or the optical source
32 and
optical measuring device
36 are on the PLC
22 (and the U-shaped optical
path is on the optical fiber array
20). Other configurations may also be
possible, as a person of skill in the art would be able to discern from reading
this disclosure.
Referring to FIG. 2, to perform the improved alignment method, the following
may occur:
Referring to block
100 of FIG. 2, an optical signal source
32
and an optical measuring device
36 are connected to the optical fiber array
20. The optical source
32 may include a laser diode, a laser, a tunable
laser source, a light emitting diode, or any other kind of optical source used
in an optical network. The optical measuring device
36 may be, for example,
an optical detector, a photodiode, a charge coupled device, or any other kind of
optical source used in an optical network. This arrangement creates a source path
from the optical source
32 to the optical fiber array
20 to the PLC
22 and a return measure path from the PLC
22 to the optical fiber
array
20 to the optical measuring device
36. The source and measure
paths should be connected to unique optical fibers so that their signals do not
interfere with each other.
Referring to block
102 of FIG. 2, an initial alignment of the components
is established, which alignment will allow the completion of an initial optical
path from the optical source
32, to the optical fiber array
20, to
the PLC
22, back to the optical fiber array
20, and to the optical
measuring device
36. If desired, mechanical references, or fiducial marks,
may be made on the optical fiber array header
40 and the PLC
22 to
assist establishing the initial alignment.
Referring to blocks
104 and
106 of FIG. 2, the PLC
22
is moved relative to the optical fiber array
20 via rotation and/or translation,
or other movements, to change the optical path until the optical measuring device
36 determines that a characteristic of the optical signal received by the
optical measuring device
36 is such that indicates that the optical signal
transmission is satisfactory. The standards for what is satisfactory may, of course,
be varied as desired. For example, the highest standard may require that the optical
signal transmission is optimal. As another example, the optical signal transmission
may be considered satisfactory if the measured characteristic satisfies a certain
criteria or meets a specific threshold. Other standards are also contemplated.
The characteristic being measured by the optical measuring device
36 may
be any characteristic of the received optical signal, such as the intensity, insertion
loss, or some other characteristic of the optical signal. Preferably, the optical
measuring device
36 detects the maximum intensity of the optical signal
transmission (or in the alternative, detects a minimum insertion loss). Such movement
of the PLC
22 relative to the optical fiber array
20 may be random
or systematic, as desired. Preferably, when the intensity of the optical signal
transmission reaches its maximum (or in the alternative, the insertion loss reaches
its minimum), the optical alignment is deemed optimal so the PLC
22 need
not be moved anymore relative to the optical fiber array
20. Of course,
the method may be adapted to stop adjusting the alignment when the intensity is
satisfactory or exceeds a certain threshold. Likewise, the method may be adapted
to stop adjusting the alignment when the insertion loss is satisfactory or falls
below a certain threshold.
Optionally, a control circuit, with or without associated software, may
process information from the optical measuring device, determine whether the characteristic
of the optical signal is satisfactory, and control when to stop adjusting the alignment.
The control circuit and its software may be readily created by a hardware engineer
and software programmer.
As an example of controlling adjustments to the alignment, the control circuit
52 may control a movable structure
50 that is coupled to move the
relative position of the optical fiber array
20 and the PLC
22. FIG.
1B is a block diagram representation of another example embodiment of the optical
alignment system depicting movable structure
50 coupled with PLC
22.
Here, the PLC
22, fiber array
20, fiber array header
40, light
source
32 and optical measuring device
36 are all located on a common
structure such as an optical device chip
60.
Referring to block
108 of FIG. 2, the relative position of the PLC
22 to the optical fiber array
20 is fixed or made permanent. For
example, a bonding material may be applied between the PLC
22 and the optical
fiber array header
40 to secure the relative position of the optical fiber
array
20 and the PLC
22. The optimal relative position of the PLC
22 and the optical fiber array
20 are maintained until the bonding
material cures. Alternatively, other methods of fixation may be used, such as adhesives
or screws.
At this point, the optical alignment between the PLC
22 and the optical
fiber array
20 is optimal and fixed. The entirety or a portion of the above
process for aligning the PLC
22 and the optical fiber array
20 may
be performed manually by a person, or by a machine such as a robot controlled by
control circuitry and/or software.
This improved method for aligning optical fiber arrays
20 to a PLC
22
achieves optimal optical signal transmission even though the PLC
22 itself
is in an unknown state. This method also simplifies the alignment of an optical
fiber array with a multi-ported PLC
22 by reducing the need to align three
independent units (input optical fiber waveguide, PLC and output optical fiber
waveguide) to two units (optical fiber waveguide
20 and PLC
22).
The two-unit technique is made possible by providing an independent optical path
to and from the PLC device
22 where the input and output are on the same
side of the PLC device
22.
The improved alignment method provides several advantages. For example, the improved
method is mechanically simpler because it requires only two, six degree-of-freedom
positioning mechanisms to align any two units. Of course, the method may be adapted
for less than six degree-of-freedom movements if one is willing to arrive at a
possible alignment that may be less than optimal, but still desirable. Another
example advantage is that the shorter time required for the improved alignment
process to converge because the problem has been reduced from three units to two
units. Yet another example advantage may be an improvement in optical performance.
The overall optical performance of the composite structure may be improved because
the optical power transmission at each interface is optimized separately. There
is also a reduced accumulation of mechanical tolerances. By partitioning the three-unit
alignment process into two two-unit alignment processes, the accumulation of error
tolerances is reduced.
Further possible advantages in using the improved method for aligning optical
fiber arrays to PLCs include the ability to align a single-sided optical fiber
array to a PLC whose optical state is unknown, an alignment method that maximizes
signal transmission when the PLC device is not flat, and the provision of an active
optical path for performing connectivity testing and verification both during and
after the manufacturing process has been completed.
In the foregoing specification, the invention has been described with reference
to specific embodiments thereof. It will, however, be evident that various modifications
and changes may be made thereto without departing from the broader spirit and scope
of the invention. For example, the reader is to understand that the specific ordering
and combination of process actions shown in the process flow diagrams described
herein is merely illustrative, and the invention can be performed using different
or additional process actions, or a different combination or ordering of process
actions. As another example, each feature of one embodiment can be mixed and matched
with other features shown in other embodiments. Features and processes known to
those of ordinary skill in the arts of device alignment and optical devices may
similarly be incorporated as desired. Additionally and obviously, features may
be added or subtracted as desired. Accordingly, the invention is not to be restricted
except in light of the attached claims and their equivalents.
*
