Note: Descriptions are shown in the official language in which they were submitted.
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HERMETIC OPTICAL SUBASSEMBLY
BACKGROUND OF THE INVENTION
1. Priority Claim
This application:
(1) claims the priority of U.S. Provisional Patent Application No. 62/245,878
filed on
October 23, 2015;
(2) is a continuation-in-part of U.S. Patent Application No. 15/236,390 filed
on August
12, 2016; and
(3) is a continuation-in-part of U.S. Patent Application No. 15/077,816 filed
on March 22,
2016.
These applications are fully incorporated by reference as if fully set forth
herein. All
publications noted below are fully incorporated by reference as if fully set
forth herein.
2. Field of the Invention
[0001] The present invention relates to optical subassemblies, particularly to
hermetically sealed
optical subassemblies.
3. Description of Related Art
[0002] There are many advantages of transmitting light signal via optical
fiber waveguides and the
use thereof is diverse. Single or multiple fiber waveguides may be used simply
for transmitting
visible light to a remote location. Complex telephony and data communication
systems may
transmit multiple specific optical signals. The data communication systems
involve devices that
couple fibers in an end-to-end relationship, including optoelectronic or
photonic devices that
include optical and electronic components that source, detect and/or control
light, converting
between light signals and electrical signals, to achieve high speed and high
capacity data
communication capabilities.
[0003] In an optical communication system, components on the transmission side
are typically
packaged in a transmitter optical subassembly (TOSA), and components on the
receiving side are
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typically packaged in a receiver optical subassembly (ROSA). For bidirectional
signal
transmission along a single optical fiber, components are packaged in a
bidirectional optical
subassembly (BOSA).
[0004] Heretofore, the TOSA consists of a laser diode (e.g., a distributed
feedback (DFB) laser),
optical interface, monitor photodiode, metal and/or plastic housing, and
electrical interface.
Depending upon the required functionality and application, other components
may be present as
well including filter elements and isolators. It is used to convert an
electrical signal into an optical
signal that is coupled into an optical fiber. The ROSA consists of a
photodiode, optical interface,
metal and/or plastic housing, and electrical interface. Depending upon the
required functionality
and application, other components may be present as well including trans
impedance amplifiers. It
is used to receive an optical signal from a fiber and convert it back into an
electrical signal. A
BOSA consists of a TOSA, a ROSA and a WDM filter so that it can use
bidirectional technology
to support two wavelengths on each optical fiber.
[0005] For the TOSA, semiconductor lasers used in fiber optics industry are
small, sensitive
devices. They are typically a few hundred microns long, with tiny pads for
cathode and anode
that need wire bonding for electrical connection. It is generally necessary to
strictly regulate the
operating temperature of the laser in order to stabilize the wavelength of the
light; this is typically
done using a thermoelectric cooler (TEC). Moreover, to couple the light
generated by them into
an optical fiber, focusing lenses with tight alignment tolerances are needed.
Because of these
delicacies, proper packaging is a crucial aspect.
[0006] With the TOSA, an optical subassembly fulfills several functions. It
provides a stable
mechanical platform for the laser chip along with the necessary electrical
interconnects. Inside the
TOSA, the interconnects are wirebonded to the laser's cathode and anode.
Practical TOSAs may
include a number of other electronic parts, such as power monitoring diodes,
TEC coolers, and
external modulators. The laser diode (and any additional device) is mounted on
a substrate.
[0007] In assembling a TOSA package, the laser is aligned with an optical
fiber so as to provide
sufficient coupling efficiency. The laser and the optical fiber may also need
to be aligned with
lenses disposed therebetween. It is often difficult and challenging to align
all of the optical
components to each other since three- dimensional alignment is typically
required. In addition, for
a variety of applications, it is desirable to hermetically seal the opto-
electronic devices within the
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housing of the TOSA package, to protect the components from corrosive media,
moisture and the
like.
[0008] Heretofore, in a hermetically sealed package, the opto-electronic
components (receiver
and/or transmitter and associated optical elements and electronic hardware)
are contained in an
opto-electronic package. The optical fiber is introduced from outside the
housing of the opto-
electronic package, through an opening provided in the housing wall. The end
of the optical fiber
is optically coupled to the opto-electronic components held within the
housing. A feedthrough
element supports the portion of the optical fiber through the wall opening.
Since the package of
the opto-electronic package must be hermetically sealed as whole, the
feedthrough element must
be hermetically sealed, so that the electro-optic components within the opto-
electronic package
housing are reliably and continuously protected from the environment.
[0009] Heretofore, hermetic feedthrough is in the form of a cylindrical
opening in the package
housing defining a relatively large clearance through which a section of the
optical fiber passes. A
sealing material such as glass frit or metal solder is applied to seal the
clearance space between the
optical fiber and the housing. Given the large clearance between the housing
and the optical fiber
and the use of sealant material and its clearance (i.e., a layer of material
between the external fiber
wall and the inside wall of the housing), the housing does not support the
optical fiber with
precise positional alignment with respect to the components inside housing.
The end of the
optical fiber is required to be positioned by a ferrule or other alignment
feature that is optically
aligned with the opto-electronic components provided in the package. To
optically couple the
input/output of the optical fiber to the opto-electronic components in the
package, optical
elements such as lenses and mirrors are required to collimate and/or focus
light from a light
source (e.g., a laser) into the input end of the optical fiber (or to
collimate and/or focus light from
the output end of the optical fiber to the receiver). To achieve acceptable
signal levels, the end of
the optical fiber must be precisely aligned at high tolerance to the
transmitters and receivers, so
the optical fiber is precisely aligned to the optical elements supported with
respect to the
transmitters and/or receivers.
[0010] It can be appreciated that for a TOSA, the connection and optical
alignment of the optical
fiber with respect to a transmitter must be assembled and the components must
be fabricated with
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sub-micron precision. In the past, it has been challenging for TOSAs to be
economical produced
in a fully automated, high-speed process. Similar challenges apply to ROSA and
BOSA.
[0011] U.S. Patent Application Publication No. U52016/0274318A1, commonly
assigned to the
assignee of the present invention, discloses an optical bench subassembly
including an integrated
photonic device. Optical alignment of the photonic device with the optical
bench can be
performed outside of an optoelectronic package assembly before attaching
thereto. The photonic
device is attached to a base of the optical bench, with its optical
input/output in optical alignment
with the optical output/input of the optical bench. The optical bench supports
an array of optical
fibers in precise relationship to a structured reflective surface. The
photonic device is mounted on
a submount to be attached to the optical bench. The photonic device may be
actively or passively
aligned with the optical bench. After achieving optical alignment, the
submount of the photonic
device is fixedly attached to the base of the optical bench.
[0012] What is needed is an improved hermetic optical subassembly, which
reduces package size,
and improves manufacturability, throughput, optical alignment tolerance, ease
of use, functionality
and reliability at reduced costs. The present invention improves on the
invention disclosed in U.S.
Patent Application Publication No. US2016/0274318A1.
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SUMMARY OF THE INVENTION
[0013] The present invention provides an improved hermetic optical subassembly
structure to
facilitate optical alignment of components within the subassembly, which
overcomes the
drawbacks of the prior art. The present invention provides a hermetic
subassembly comprising
three main structural components, including a first optical bench that directs
optical signals
to/from an optical waveguide, a carrier supporting at least one opto-
electronic or photonic device
(e.g., a laser or a photodiode), and a second, intermediate, optical bench
that directs optical
signals between the photonic device and the first optical bench. When
assembled, the
intermediate optical bench aligns the carrier to the first optical bench, such
that the photonic
device and the waveguide are optically aligned along a desired optical path.
[0014] In one embodiment, the first optical bench supports an optical
component in the form of
an optical wave guide (e.g., an optical fiber). In a more specific embodiment,
the body of the first
optical bench defines an alignment structure in the form of at least one
groove to precisely
support the end section of an optical fiber. An optical element (e.g., a lens,
a prism, a reflector, a
mirror, etc.) is provided in precise relationship to the end face of the
optical fiber. In a further
embodiment, the optical element comprises a structured reflective surface
(e.g., planar reflective,
convex reflective, or concave reflective (e.g., an aspherical mirror
surface)). The reflective
surface is optically aligned with the optical axis of the optical fiber along
the desired optical path.
[0015] In one embodiment, the photonic device is mounted on the substrate of
the carrier. In one
embodiment, the photonic device comprises at least one edge emitting laser
(EML). A thermos-
electric cooler (TEC) is provided between the EML and the carrier substrate
for cooling the
EML. The carrier may be provided with circuits, electrical contact pads,
circuit components (e.g.,
a driver for the EML), and other components and/or circuits associated with
the operation of the
photonic device.
[0016] The intermediate optical bench includes a structured reflective surface
(e.g., planar
reflective, convex reflective, or concave reflective (e.g., an aspherical
mirror surface)) that directs
optical signals between the carrier and the first optical bench. A planar
surface of the intermediate
optical bench is attached to the first optical bench with the reflective
surfaces optically aligned to
each other along the desired optical path. The body of the intermediate
optical bench is attached
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to the carrier with the reflective surface optically aligned with the photonic
device (i.e., its optical
axis) along the desired optical path.
[0017] Accordingly, after assembly, optical signals can be directed between
the photonic device
and the waveguide via the reflective surface of the first optical bench and
the reflective surface of
the intermediate optical bench.
[0018] The reflective surface of the first optical bench may be passively
aligned with the reflective
surface of the intermediate optical bench (e.g., relying on alignment surface
features and/or indicia
provided on first optical bench and/or the intermediate optical bench. In
addition, the photonic
device may be passively aligned to the reflective surface of the intermediate
optical bench.
Alternatively, the photonic device and the optical bench may be actively
aligned by passing an
optical signal between the reflective surface in the intermediate optical
bench and the photonic
device. The photonic device can be activated to allow for active alignment.
After achieving
optical alignment, the carrier of the photonic device is fixedly attached to
the body of the
intermediate optical bench. The optical benches and the carrier are structured
to be hermetically
sealed against each other to form a hermetic package.
[0019] The body of the first and second optical benches are preferably formed
by stamping a
malleable stock material (e.g., a metal stock), to form precise geometries and
features of the
optical benches (including reflective surfaces, optical fiber alignment
grooves, etc.). By using a
stamped single-solid-body for each of the benches, the optical components that
are not stamped
(e.g., fibers, ball lens) can be aligned passively using alignment features
defined within the
stamped benches. The stamped optical bench will minimize the number of
components that need
to be actively aligned, reducing production costs and increasing yield and
throughput.
[0020] In another embodiment of the present invention, the optical bench is
structured to support
multiple waveguides (e.g., multiple optical fiber), and structured reflective
surfaces (e.g., an array
of mirrors), to work with an array of photonic devices mounted on a carrier.
[0021] In a further aspect of the present invention, the hermetic optical
subassembly of the
present invention integrates multiplexers/demultiplexers (Mux/Demux), for
directing optical
signals between a single optical fiber and a plurality of photonic devices.
[0022] In Summary, the present invention provides a hermetic optical
subassembly, comprising: a
first optical bench supporting an optical fiber, and comprising at least one
first mirror defined by
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stamping a first malleable metal stock material; a second optical bench
comprising at least one
second mirror defined by stamping a second malleable metal stock material; a
carrier supporting at
least one photonic device, wherein the optical fiber, the first mirror, the
second mirror and the
photonic device are in optical alignment, and the first mirror and the second
mirror directs an
optical signal between the photonic device and the optical fiber, and wherein
the first optical
bench, the second optical bench and the carrier are coupled to form a hermetic
package. Further,
the present invention provides wherein the first optical bench further
comprising a multiplexer that
combines a plurality of input optical signals each having a different
wavelength into a single
output optical signal to be directed to the optical fiber, wherein the
photonic device comprises a
plurality of transmitters each providing an optical signal of a different
wavelength, wherein the
first optical bench comprises a plurality of first mirrors and the second
optical bench comprises a
plurality of second mirrors corresponding to the plurality of first mirrors
and corresponding to the
plurality of transmitters, and wherein corresponding transmitter, first mirror
and second mirror are
in optical alignment, and corresponding first mirror and corresponding second
mirror directs
corresponding optical signal provided by corresponding transmitter to the
multiplex. The
multiplexer comprises a filter block supported on the first optical bench,
wherein the filter block
combines the optical signals provided by the respective transmitters into the
single output signal
to be directed at the optical fiber.
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BRIEF DESCRIPTION OF THE DRAWINGS
[0023] For a fuller understanding of the nature and advantages of the
invention, as well as the
preferred mode of use, reference should be made to the following detailed
description read in
conjunction with the accompanying drawings. In the following drawings, like
reference numerals
designate like or similar parts throughout the drawings.
[0024] Fig. 1A is a perspective diagram of a quad small-form-factor pluggable
(QSFP) transceiver
module incorporating a hermetic optical subassembly, in accordance with one
embodiment of the
present invention; Fig. 1B is another view of Fig. 1A with shading.
[0025] Fig. 2A is a sectional view of the hermetic optical subassembly of Fig.
1, Fig. 2B is
another view of Fig. 2A with shading.
[0026] Figs. 3A to 3E illustrate the structure of the first optical bench in
the hermetic optical
subassembly, in accordance with one embodiment of the present invention.
[0027] Figs. 4A to 4D illustrate the structure of the second, intermediate,
optical bench in the
hermetic optical subassembly, in accordance with one embodiment of the present
invention.
[0028] Figs. 5A and 5B illustrate the structure of the carrier including the
photonic devices, in
accordance with one embodiment of the present invention.
[0029] Figs. 6A to 6C illustrate the hermetic optical subassembly as assembled
with its
components.
[0030] Figs. 7A to 7D depict exemplary dimensions of the hermetic optical
subassembly and
installation thereof in the QSFP module.
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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0031] This invention is described below in reference to various embodiments
with reference to
the figures. While this invention is described in terms of the best mode for
achieving this
invention's objectives, it will be appreciated by those skilled in the art
that variations may be
accomplished in view of these teachings without deviating from the spirit or
scope of the
invention.
[0032] The present invention provides an improved hermetic optical subassembly
structure to
facilitate optical alignment of components within the subassembly, which
overcomes the
drawbacks of the prior art. The present invention provides a hermetic
subassembly comprising
three main structural components, including a first optical bench that directs
optical signals
to/from an optical waveguide, a carrier supporting an opto-electronic or
photonic device (e.g., a
laser or a photodiode), and a second, intermediate, optical bench that directs
optical signals
between the photonic device and the first optical bench. When assembled, the
intermediate
optical bench aligns the carrier to the first optical bench, such that the
photonic device and the
waveguide are optically aligned along a desired optical path.
[0033] Various embodiments of the present invention incorporate some of the
inventive concepts
developed by the Assignee of the present invention, nanoPrecision Products,
Inc., including
various proprietary including optical bench subassemblies for use in
connection with optical data
transmissions, including the concepts disclosed in the patent publications
discussed below, which
have been commonly assigned to the Assignee.
[0034] For example, U.S. Patent Application Publication No. US2013/0322818A1
discloses an
optical coupling device for routing optical signals, which is in the form of
an optical bench having
a stamped structured surface for routing optical data signals. The optical
bench comprising a
metal base having a structured surface defined therein, wherein the structured
surface has a
surface profile that bends, reflects, and/or reshapes an incident light. The
base further defines an
alignment structure, which is configured with a surface feature to facilitate
precisely positioning
an optical component (e.g., an optical fiber) on the base in precise optical
alignment with the
structured surface to allow light to be transmitted along a defined path
between the structured
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surface and the optical component, wherein the structured surface and the
alignment structure are
integrally defined on the base by stamping a malleable metal material to form
an optical bench.
[0035] U.S. Patent Application Publication No. US2015/0355420A1 further
discloses an optical
coupling device for routing optical signals for use in an optical
communications module, in
particular an optical coupling device in the form of an optical bench, in
which defined on a metal
base is a structured surface having a surface profile that bends, reflects
and/or reshapes an incident
light. An alignment structure is defined on the base, configured with a
surface feature to facilitate
positioning an optical component (e.g., an optical fiber) on the base in
optical alignment with the
structured surface to allow light to be transmitted along a defined path
between the structured
surface and the optical component. The structured surface and the alignment
structure are
integrally defined on the base by stamping a malleable metal material of the
base. The alignment
structure facilitates passive alignment of the optical component on the base
in optical alignment
with the structured surface to allow light to be transmitted along a defined
path between the
structured surface and the optical component.
[0036] U.S. Patent Application Publication No. U52013/0294732A1 further
discloses a hermetic
optical fiber alignment assembly having an integrated optical element, in
particular a hermetic
optical fiber alignment assembly including an optical bench that comprises a
metal ferrule portion
having a plurality of grooves receiving the end sections of optical fibers,
wherein the grooves
define the location and orientation of the end sections with respect to the
ferrule portion. The
assembly includes an integrated optical element for coupling the input/output
of an optical fiber to
optoelectronic devices in an optoelectronic module. The optical element can be
in the form of a
structured reflective surface. The end of the optical fiber is at a defined
distance to and aligned
with the structured reflective surface. The structured reflective surfaces and
the fiber alignment
grooves can be formed by stamping a malleable metal to define those features
on a metal base.
[0037] U.S. Patent No. 7,343,770 discloses a novel precision stamping system
for manufacturing
small tolerance parts. Such inventive stamping system can be implemented in
various stamping
processes to produce the devices disclosed in the above-noted patent
publications. These
stamping processes involve stamping a stock material (e.g., a metal blank), to
form the final
overall geometry and geometry of the surface features at tight (i.e., small)
tolerances, including
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reflective surfaces having a desired geometry in precise alignment with the
other defined surface
features.
[0038] U.S. Patent Application Publication No. U52016/0016218A1 further
discloses a
composite structure including a base having a main portion and an auxiliary
portion of dissimilar
metallic materials. The base and the auxiliary portion are shaped by stamping.
As the auxiliary
portion is stamped, it interlocks with the base, and at the same time forming
the desired structured
features on the auxiliary portion, such as a structured reflective surface,
optical fiber alignment
features, etc. With this approach, relatively less critical structured
features can be shaped on the
bulk of the base with less effort to maintain a relatively larger tolerance,
while the relatively more
critical structured features on the auxiliary portion are more precisely
shaped with further
considerations to define dimensions, geometries and/or finishes at relatively
smaller tolerances.
The auxiliary portion may include a further composite structure of two
dissimilar metallic
materials associated with different properties for stamping different
structured features. This
stamping approach improves on the earlier stamping process in U.S. Patent No.
7,343,770, in
which the stock material that is subjected to stamping is a homogenous
material (e.g., a strip of
metal, such as Kovar, aluminum, etc.) The stamping process produces structural
features out of
the single homogeneous material. Thus, different features would share the
properties of the
material, which may not be optimized for one or more features. For example, a
material that has a
property suitable for stamping an alignment feature may not possess a property
that is suitable for
stamping a reflective surface feature having the best light reflective
efficiency to reduce optical
signal losses.
[0039] U.S. Patent No. 8,961,034 discloses a method of producing a ferrule for
supporting an
optical fiber in an optical fiber connector, comprising stamping a metal blank
to form a body
having a plurality of generally U-shaped longitudinal open grooves each having
a longitudinal
opening provided on a surface of the body, wherein each groove is sized to
securely retain an
optical fiber in the groove by clamping the optical fiber. The optical fiber
is securely retained in
the body of the ferrule without the need for additional fiber retaining means.
[0040] International Patent Application No. PCT/U52016/046936 (PCT Publication
No.
________________________________________________________________________ )
discloses a multiplexer/demultiplexer (Mux/Demux) subassembly includes a
stamped optical bench, which includes an array of stamped reflective surfaces
for redirecting
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optical signals. Alignment features and components of the Mux/Demux
subassembly are
integrally formed on a stamped optical bench, defining a desired optical path
with optical
alignment at tight tolerances. The optical bench is formed by stamping a
malleable stock material
(e.g., a metal stock), to form precise geometries and features of the optical
bench.
[0041] The above inventive concepts are incorporated by reference herein, and
will be referred
below to facilitate disclosure of the present invention. The present invention
is disclosed in
connection with exemplary embodiments of hermetic transmitter optical
subassemblies (TOSA's),
which include Mux/Demux. It is understood that the present invention may be
adapted to
hermetic optical subassemblies for other applications (e.g., ROSA, BOSA), with
or without
Mux/Demux.
[0042] Fig. 1A is a perspective diagram of a quad small-form-factor pluggable
(QSFP) module
100 incorporating a hermetic optical subassembly 10, in accordance with one
embodiment of the
present invention; Fig. 1B is another view of Fig. 1A with shading. The QSFP
is a full-duplex
optical transceiver module with four independent transmit and receive
channels. It is designed to
replace four single-channel small-form-factor pluggable (SFP) and in a package
only about 30%
larger than the standard SFP. To equip a QSFP and similar transceivers
requiring multiple
wavelengths, a small Mux and/or DeMux device is very important. The hermetic
optical
subassembly 10 of the present invention provides a small footprint, broad
operating wavelength
range, enhanced impact performance, lower cost, and easier manufacturing
process.
[0043] Fig. 2A is a sectional view of the hermetic optical subassembly of Fig.
1, Fig. 2B is
another view of Fig. 2A with shading. These sectional views illustrate the
optical path defined by
the hermetic optical subassembly 10. Specifically, in the illustrated
embodiment, the hermetic
optical subassembly is a TOSA.
[0044] The hermetic optical subassembly 10 includes three main structural
components, including
a first optical bench 11 that directs optical signals to/from an optical
waveguide (e. .g., an optical
fiber 20), a carrier 13 supporting at least one photonic device 22 (e.g., an
electrically modulated,
edge-emitting laser (EML)), and a second, intermediate, optical bench 12 that
directs optical
signals between the photonic device 22 and the optical bench 11. When
assembled, the
intermediate optical bench 12 aligns the carrier 13 to the optical bench 11,
such that the photonic
device 22 and the optical fiber 20 are optically aligned along a desired
optical path L.
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Specifically, optical signal from the photonic device 22 is reshaped and
turned (redirected) by the
micro mirror 31 on the intermediate optical bench 12 towards the micro mirror
21 on the optical
bench 11, which in turn reshape and/or redirect the optical signal towards the
optical fiber 20
(though a ball lens 17).
[0045] Figs. 3A to 3E illustrate the structure of the optical bench 11 in the
hermetic optical
subassembly 10, in accordance with one embodiment of the present invention.
Fig. 3A shows the
structure of the optical bench 11 without the reflective surfaces 21 (shown in
Fig. 3C) and the
components for the Mux/Demux (e.g., filter block with thin-film filters and a
reflective film; see
discussions below in connection with Fig. 3E). Fig. 3B is a section view taken
alone line 3B-3B
in Fig. 3A. The optical bench 11 serves as a "cover" for the overall hermetic
optical subassembly
10. Defined on the body of the optical bench 11 are a through opening 14
adjacent a recess 15, a
dimple 16 (e.g., a spherical or tetrahedral depression) to support a ball lens
17 (see Fig. 3D), and
a groove 18 in a cavity 68 for aligning the optical fiber 20 (see Fig. 3D).
Fig. 3C illustrates a
block 19 in the shape of a plug or rivet, which is provided with a plurality
of micro mirrors or
structured reflective surfaces 21. In this particular illustrated embodiment,
there are four micro
mirrors 21 corresponding to four EML's (see Figs. 3E, 5A and 5B). The geometry
of the micro
mirrors 21 may conform to planar reflective, convex reflective, or concave
reflective (e.g., an
aspherical mirror surface). For example, in the illustrated embodiment, the
micro mirrors 21 may
be generally aspherical convex. The block 19 fits into the opening 14 in the
body of the optical
bench 11 (as will be explained later, the shape of the block 19 is formed in
place in the optical
bench 11 by a stamping operation, instead of it being separately formed and
inserted into the
opening 14).
[0046] Referring to Fig. 3D, the optical bench 11 is complete with the micro
mirrors 21, and the
components for the Mux/Demux (actually in this embodiment of TOSA, it is a Mux
23).
Referring also to Fig. 3E, the components and optical paths in the Mux 23 is
schematically
illustrated, in accordance with one embodiment of the present invention. In
the illustrated
embodiment, the Mux 23 is configured for input signals of four different
wavelengths to be
combined (i.e., multiplexed) into a single output signal (in reverse, a single
input signal can be
split (demultiplexed) into four output signals of different wavelengths). The
Mux 23 includes a
transparent block 24 having an array of thin film filters 25 (there are four
filters 25 in this
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embodiment, each having a particular transmissive wavelength to allow optical
signal from
respective EML 22 of the respective wavelength to pass through) and a mirror
26 (e.g., a
reflective coating) provided on opposing surfaces. The Mux 23 is supported in
the recess 15 in
the body of the optical bench 11, between the micro mirrors 21 and the ball
lens 17 and optical
fiber 20, with each micro mirror 21 positioned corresponding to a thin film
filter 25.
[0047] In a multiplexing operation, optical signals reflected from the micro
mirrors 21 (which
originated from the outputs of the EML's 22 via micro mirror 31) are passed
through the
respective filters 25, and the signals are reflected within the transparent
block 24 between the thin
film filters 25 and the mirror 26, with the thin film filters reflecting all
signals that do not
correspond to the respective the transmission wavelengths. As a result, the
optical signals are
effectively combined into a single output signal to the optical fiber 20. The
ball lens 17 focus this
output signal onto the end face of the optical fiber to improve optical
coupling. The particular
illustrated optical paths in Fig. 3E were configured in prior art systems,
except that none of those
systems incorporates the type of optical subassembly in accordance with the
present invention.
As shown, the "desired optical path L" would include various input optical
paths from the
EML'ss 22. (In a demultiplexer operation, the optical paths are in reverse.)
[0048] In accordance with one embodiment of the present invention, the array
of micro mirrors
21, and some or all of the alignment features for the optical fiber 20, the
ball lens 17, and the
components of the Mux 23 may be integrally formed on the body of the optical
bench 11 by
stamping, so as to define the desired optical path, with optical alignment at
tight tolerances.
These features may be integrally formed in a single stamping operation, after
the body of the
optical bench 11 is first provided with the recess 15, opening 14 and cavity
68 (e.g., from an
earlier stamping operation) as shown in Fig. 3A.
[0049] In the illustrated embodiment, the stamped optical bench 11 supports
the filter block 24
(having the thin film filters 25 and mirror 26), the lens 17, and the optical
fiber 20. The body of
the optical bench 11 defines an alignment structure in the form of the groove
18 to precisely
support the end section of the optical fiber 20. The body of the optical bench
11 also defines the
slot 16 (e.g., a spherical or tetrahedral depression) to support the ball lens
17 (or a reflector, a
mirror, etc.) in precise relationship to the end face of the optical fiber 20,
and further an additional
alignment feature (e.g., a step in the recess 15, not shown) for accurately,
and passively, aligning
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the filter block 14 along the desired optical path. The optical element
comprising the array of
structured reflective surfaces (e.g., micro mirrors 21, which may be planar
reflective or concave
reflective (e.g., an aspherical mirror surface)) is stamped formed with the
appropriate geometries
for routing optical signals along the desired optical path L.
[0050] As shown in Fig. 3C, the block 19 having the micro mirrors 21 is shown
alone after stamp
forming. In actual stamping operation, before the micro mirror features are
formed by stamping,
a metallic "rivet", e.g., made from a soft material such as aluminum, is
inserted into the opening
14 in the body of the optical bench 11. Other surface features on the optical
bench 11 may also
be formed together after inserting the aluminum rivet into the opening 14 in
the body of the
optical bench 11. For example, the aluminum rivet is stamped with the desired
surface features
shown along with some of the other features (e.g., the groove 18 for receiving
a section of the
optical fiber 20; alignment features 65a to 65c on planar surface 61; see Fig.
3D). This "rivet"
type stamping approach and its features and benefits are disclosed in U.S.
Patent Application
Publication No. US2016/0016218A1, which has been commonly assigned to the
Assignee of the
present invention. Details of such stamping process is not discussed herein,
but incorporated by
reference herein.
[0051] The aluminum rivet is easily formable by stamping, and it has high
reflectance in the
wavelength range adopted in telecommunications and data communications. The
material of the
body of the optical bench 11 may be Kovar. Specifically, in the above
described embodiments,
pure aluminum is chosen for the rivet for forming the optical bench because it
is relatively softer,
and more malleable/ductile than Kovar chosen for the body of the optical bench
11, to obtain the
desired geometries, dimensions and/or finishes of critical features (e.g., the
micro mirrors 21) at
the optical bench 11. The harder and stronger frame material (e.g., Kovar) is
chosen to form
structures that require the integrity of a harder material, but stamping the
harder base material
would require larger forces and result in more springback, requiring multiple
hits of the stamping
punch to obtain the desire shape (especially for deeper profiles such as a
deep recess), which may
result in relatively higher tolerances. In contrast, the relatively softer
material chosen for stamping
the micro mirrors 21 requires less stamping forces and results in less
springback, requiring
relatively fewer hits (e.g., just one hit) of the stamping punch to obtain the
final stamped part.
Hence, micro features such as micro mirrors 21 can be stamped on the optical
bench 11 with very
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tight dimensional tolerances. The harder body material of the optical bench 11
also functions as
part of the die, which partially shapes the block 19 to define the micro
mirror 21 during stamping
operation. The coefficient of thermal expansion for Kovar material also
closely matches the
coefficient of thermal expansion of most semiconductor and glass materials so
that temperature
changes induce minimal misalignment between the components. Furthermore, the
melting
temperatures of the metallic optical bench are sufficiently high to allow for
compatibility with
soldering processes that are commonly used in electronic and photonic
packaging. Optionally, an
optical coating may be deposited onto the stamped micro mirrors 21 to increase
reflectivity.
[0052] While the above embodiment makes use of a ball lens 17 to focus output
light from the
Mux 23 to the optical fiber 20, instead of a ball lens 17, a micro mirror (not
shown) may be
stamped formed on the body of the optical bench 11, to focus output optical
signal from the Mux
23 to the optical fiber 20.
[0053] If at least the micro mirrors 21 and the fiber alignment groove 18 are
stamped in a single
stroke by the same tool when forming the optical bench 11, the alignment
precision between the
optical fiber 20 and the array of micro mirrors 21 could be on the order of
200 nanometers. This
provides completely passive alignment sufficient for single-mode optics, thus
avoiding the tedious
and more complex active alignment practice in the prior art. If the other
alignment features for
the ball lens 17 and the filter block 24 are also integrally stamped in a
single step along with the
micro mirrors 21 and the fiber alignment groove 2, further accurate passive
alignment of these
components are also possible.
[0054] An alternate embodiment of a Mux (and Demux) optical bench subassembly
is disclosed in
International Patent Application No. PCT/US2016/046936 (PCT Publication No.
___________ ), which may be adapted and replace the optical bench 11 in the
hermetic optical
subassembly of the present invention.
[0055] In view of the above disclosure, it can be seen that the stamped
optical Mux subassembly
in accordance with the present invention uses a stamped optical alignment
platform that uses non-
stamped thin-film filters to combine multiple sources of different wavelengths
(via a stamped
reflector) into a single beam and inject it into an optical fiber. By using
stamped micro mirror
arrays in combination with thin-film bandpass filters as part of the optical
system to do the optical
signal splitting/combining, the mirrors and the alignment optical bench will
be a stamped single-
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solid-body, and all of the optical components that are not stamped (fibers,
thin film filters,
possible ball lenses) can be aligned passively using features defined within
the stamped optical
bench. The stamped optical bench will minimize the number of components that
need to be
actively aligned, reducing production costs and increasing yield and
throughput.
[0056] A Mux/Demux having a stamped optical bench could have similar or
smaller overall size
and configuration, and similar or smaller footprint, compared to a prior art
Mux/Demux using,
e.g., a silicon optical bench. Stamped optical benches could be configured to
have a smaller
footprint and overall size than silicon optical benches. A stamped optical
bench can effectively
simplify the configuration of a silicon optical bench without compromising the
desired defined
optical path.
[0057] The Mux/Demux subassembly on the optical bench 11 discussed above is
suited for single-
mode, or multi-mode, and the sources may be fibers, or grating couplers, or
VCSEL's, or DFB
lasers. The receiver for the light output may be any kind of light sensitive
detector, or any kind of
fiber, or grating couplers, or any kind of waveguide. The Mux/Demux may
involve coarse
wavelength division multiplexing (CWDM) or dense wavelength division
multiplexing (DWDM),
and involve any number of wavelengths or channels, beyond the four channels
illustrated in the
embodiments.
[0058] Figs. 4A to 4D illustrate the structure of the second, intermediate,
optical bench 12 in the
hermetic optical subassembly 10, in accordance with one embodiment of the
present invention.
Fig. 4A shows the structure of the optical bench 12 without the micro mirrors
21 (shown in Fig.
4C). Fig. 4B is a section view taken alone line 4B-4B in Fig. 4A. The optical
bench 12 serves as
an intermediate adaptor to couple (as will be further discussed below,
hermetically couple) the
carrier 13 having the photonic devices and the optical bench 11 to form the
overall hermetic
optical subassembly 10. Defined on the body of the optical bench 12 is a
through opening 34 in a
recess 35 adjacent two prongs 36. The through hole is flanked by the main body
of the optical
bench 12, and a cross-member 33 between the prongs 36. A small through-hole 67
is provided at
a corner of the planar surface 62, at a location matching the location of the
cavity 68 in the optical
bench 11, for inserting hermetic sealing material to seal the optical fiber
section (as will be
explained later below).
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[0059] Fig. 4C illustrates a block 29 in the shape of a plug or rivet, which
is provided with a
plurality of micro mirrors or structured micro mirrors 31. In this particular
illustrated
embodiment, there are four micro mirrors 31 corresponding to the four EML's
(see Figs. 3E, 5A
and 5B). The geometry of the micro mirrors 21 may conform to planar
reflective, convex
reflective, or concave reflective (e.g., an aspherical mirror surface). For
example, in the illustrated
embodiment, the micro mirrors 21 may be generally aspherical concave.
Referring also to Fig.
5B, the output of the EML 22 does not cast a round beam spot, but instead an
oval beam spot
with fast and slow axes. Accordingly, the micro mirrors 21 and 31 have
geometry that reshapes
the oval beam into a round beam and turn the beam towards the filter 24 in the
cover optical
bench 11. The block 29 fits into the opening 34 in the body of the optical
bench 12 (as will be
explained later, and similar to the block 19 in the optical bench 11, the
shape of the block 29 is
formed in place in the optical bench 12 by a stamping operation, instead of it
being separately
formed and inserted into the opening 34).
[0060] Referring to Fig. 4D, the optical bench 12 is complete with the micro
mirrors 31. In
accordance with one embodiment of the present invention, the array of micro
mirrors 31, and
passive alignment features (e.g., alignment indicia and windows, protrusions
and/or recesses,
schematically represented by dotted squares 65a to 65c in Figs. 3D and 4D)
complementarily
provided on the facing planar surfaces 61 and 62 for passively aligning the
optical benches 11 and
12, may be integrally formed on the body of the optical bench 12 by stamping,
so as to define the
desired optical path, with optical alignment at tight tolerances. These
features may be integrally
formed in a single stamping operation, after the body of the optical bench 12
is first provided with
the prongs 36, the recess 35, the opening 34 and the opening 67 (e.g., from an
earlier stamping
operation) as shown in Fig. 4A.
[0061] As shown in Fig. 4C, the block 29 having the micro mirrors 31 is shown
alone after stamp
forming. In actual stamping operation, before the micro mirror features are
formed by stamping,
a metallic "rivet", e.g., made from a soft material such as aluminum, is
inserted into the opening
34 in the body of the optical bench 12 (which could be made of Kovar). Other
surface features on
the optical bench 12 may also be formed together after inserting the aluminum
rivet into the
opening 34 in the body of the optical bench 12. For example, the aluminum
rivet is stamped with
the desired surface features shown along with some of the other features
(e.g., passive alignment
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features 65 for aligning with the optical bench 11). Optionally, an optical
coating may be
deposited onto the stamped micro mirrors 31 to increase reflectivity.
[0062] This "rivet" type stamping approach and its features and benefits are
disclosed in U.S.
Patent Application Publication No. US2016/0016218A1, which has been commonly
assigned to
the Assignee of the present invention. Details of such stamping process is not
discussed herein,
but incorporated by reference herein. The design considerations using this
approach is similar to
those in connection with stamp forming the optical bench 11, and they will not
be repeated here.
[0063] Figs. 5A and 5B illustrate the structure of the carrier 13 including
the photonic device 22,
in accordance with one embodiment of the present invention. The carrier 13
serves as a "base" of
the overall hermetic optical subassembly 10, for mounting the hermetic optical
subassembly 10
onto, e.g., a standard "QFSP28" board 50 shown in Fig. 1A. The carrier 13
supports a
thermoelectric cooler (TEC) 41, on which at least one photonic device is
supported (in this
embodiment, the photonic device includes four EML's of different wavelengths).
Cooling of
EML's is essential for proper operation of the EML's. The EML's are mounted on
a sub-carrier
(e.g., in a chip on carrier (COC) configuration) on top of the TEC 41. The
temperature of the
carrier and hence the EML's need to be regulated to control the wavelength of
the optical signal
output of the EML's. The carrier 13 may be provided with circuits, electrical
contact pads,
circuit components (e.g., drivers for the EML's), and other components and/or
circuits associated
with the operation of the EML's.
[0064] It is noted that preferably, the electrical traces should be coplanar
with the lasers to
improve signal integrity. As can be seen from Figs. 1A, 2A, 6A and 6c, the
carrier 13 includes a
block 43 having a vertically extending wall 44. Patterned electrical traces 47
are provided
through and/or below the wall 44, so that sections 45 and 46 of the traces 47
are exposed beyond
both sides of the wall 44. The traces 45 provide for electrical access to the
hermetic optical
subassembly 10, or wire bonding to other components outside the hermetic
optical subassembly
10, and the traces 46 provide for wire bonding to the EML's. The traces are
substantially
coplanar with the EML's. Given the distal surface of the block 44 and the wall
44 of the carrier
13 are exposed to external environment, the material of the carrier 13 should
be chosen to be a
hermetic material with the electrical traces 47 running there-through. The
carrier 13 may be made
of hermetic materials such as Aluminum Nitrite (AIN), high temperature cofired
ceramic (HTCC)
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or low temperature cofired ceramic (LTCC), which are good hermetic packaging
material due to
its desirable electrical properties, high mechanical strength and good thermal
conductivity. These
materials are non-electrically conductive or electrically insulating, so as to
be able to support the
traces 47, as compared to the optical benches 11 and 12, which are made of
metal material(s).
[0065] With the optical bench 11, the intermediate optical bench 12 and the
carrier 13 pre-
assembled as respectively shown in Fig. 3D, Fig. 4D and Fig. 5A, the optical
bench 11 is first
attached to the intermediate optical bench 12. The planar surface 62 (see Fig.
4D) of the
intermediate optical bench 12 is mated to the planar surface 61 (see Fig. 3D)
of the optical bench
11, so that the reflective surfaces 21 and 31 are optically aligned to each
other along the desired
optical path L. As noted above, passive alignment of the optical benches 11
and 12 may be
achieved by making use of the alignment features 65a to 65b provided on the
facing planar
surfaces 61 and 62 of the optical benches 11 and 12, respectively. The optical
benches 11 and 12
may be fixedly attached by soldering, brazing, or laser welding along the
perimeter of the mating
surfaces to provide hermetic joints. A hermetic sealing material, such as a
glass solder, is inserted
into the opening 67 to fill the cavity 68 in the optical bench 11 (see Figs.
2A and 3D), so as to
hermetically seal the feedthrough section of the optical fiber 20. Hermetic
sealing may further be
based on the teaching of U.S. Patent Application Publication No.
US2013/0294732A1. After
hermetically assembling the first and second optical benches 11 and 12 and the
carrier together, a
hermetic package is formed.
[0066] After assembling the optical benches 11 and 12, the preassembled
carrier 13 shown in Fig.
5A is aligned and attached to the front of and below the intermediate optical
bench 12. The
adjoining mating surfaces are hermetically sealed, e.g., by soldering. The
photonic device 22 may
be passively aligned to the reflective surfaces 31 of the intermediate optical
bench 12 (e.g., by
providing additional passive alignment surface features on the mating surfaces
of the carrier 13
and the optical bench 12 (not shown). Alternatively, the photonic device 22
and the intermediate
optical bench 12 may be actively aligned by passing an optical signal between
the reflective
surfaces 31 in the intermediate optical bench 12 and the photonic device 22.
The photonic device
22 can be activated to allow for active alignment. After achieving optical
alignment, the carrier
13 having the photonic device 22 is fixedly attached to the base of the
intermediate optical bench.
The optical benches and the carrier are structured to be hermetically sealed
against each other.
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The resultant structure of the hermetic optical subassembly would include a 3-
tier structure,
including the top optical bench 11, the intermediate optical bench 12 and the
bottom carrier 13.
[0067] Fig. 6C is a sectional view illustrating the hermetic optical
subassembly 10 after assembly
as discussed above. The base of the carrier 13 is shown attached to the QSFP28
board 50. The
pigtail end of the optical fiber 20 may be terminated in a ferrule (not shown)
in an optical
connector to provide a connection to an external optical fiber.
[0068] After assembly, optical signals can be directed between the photonic
device 22 (e.g.,
EML's) and the optical fiber 20 via the reflective surface 31 of the
intermediate optical bench 12
and the reflective surface 21 of the optical bench 11. In the illustrated
embodiment, there are four
EML's, which output signal are multiplexed through the Mux 23 in the optical
bench 11. Given
the nature of EML's, their output is parallel to the carrier on which the
EML's are mounted.
Accordingly, the output signals would be transmitted horizontally, which need
to be turned
upwards to the level of the Mux 23 and optical fiber 20. The micro mirrors 31
serves to reshape
and turn or fold the output signal, which is then collimated before passing
through the Mux 23 to
be focused at the optical fiber 20. In the past, EML's were not effectively
used in TOSA, given
the difficulties in obtaining an acceptable optical path. In the illustrated
embodiments, the output
signals from the EML's are substantially parallel to the input signal to the
optical fiber 20 (at least
in a vertical direction). With the use of two sets of reflective surfaces, the
desired optical effect
and optical path can be achieved while maintaining the overall height of the
hermetic optical
subassembly to a minimum. With the stamped optical benches, it is now possible
to incorporate a
multiplexer into the hermetic TOSA (or a de-multiplexer in a hermetic ROSA).
The smaller and
more compact construction improves reliability and preserves optical alignment
by reducing the
magnitude of thermal expansion due to temperature changes while operating the
laser or due to
heat from other module components.
[0069] Figs. 7A to 7D depict exemplary dimensions of the hermetic optical
subassembly and
installation thereof in the QSFP module. (All dimension shown in mm.)
[0070] In accordance with the present invention discussed above, it can be
seen that a hermetic
optical subassembly can be configured with a small form factor, which can be
manufacture using
high throughput stamping processes. More specifically, the present invention
provides a hermetic
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TOSA having a small package size, with improved manufacturability, throughput,
optical
alignment tolerance, ease of use, functionality and reliability at reduced
costs.
* * *
[0071] While the invention has been particularly shown and described with
reference to the
preferred embodiments, it will be understood by those skilled in the art that
various changes in
form and detail may be made without departing from the spirit, scope, and
teaching of the
invention. Accordingly, the disclosed invention is to be considered merely as
illustrative and
limited in scope only as specified in the appended claims.
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