Patent ID: 12253725

DETAILED DESCRIPTION

The present disclosure is directed at an optical interconnection element that is capable of operation while immersed in a cooling liquid. Operation while immersed in a cooling liquid improves heat removal from the optical interconnection element, allowing the optical interconnection element to be operated at a lower temperature or increasing the packaging density of systems with multiple optical interconnection elements. Additionally, the sealed optical interconnection element may be used without immersion cooling. It is particularly advantageous for use in harsh environments, such as dusty environments or environments where either fresh or salt water spray may be present. The optical interconnection element can be configured as an optical transceiver. Thus, in this description the term optical transceiver will generally be used; however, the invention may equally be applied to any suitable optical interconnection element, such as an optical transmitter or optical receiver. Thus, each of the optical transmitter and the optical receiver, and thus the optical transceiver, can be generally referred to as an optical interconnection element.

As used herein, the terms “substantially,” “approximately,” “about,” and derivatives thereof and words of similar import as used herein recognizes that the referenced dimensions, sizes, shapes, directions, or other parameters can include the stated dimensions, sizes, shapes, directions, or other parameters and up to ±20%, including ±10%, ±5%, and ±2% of the stated dimensions, sizes, shapes, directions, or other parameters. Further, the term “at least one” stated structure as used herein can refer to either or both of a single one of the stated structure and a plurality of the stated structure. Additionally, reference herein to a singular “a,” “an,” or “the” applies with equal force and effect to a plurality unless otherwise indicated. Similarly, reference to a plurality herein applies with equal force and effect to the singular “a,” “an,” or “the.”

References herein to “one embodiment”, “an embodiment”, “an example embodiment”, etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to effect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

Referring toFIGS.1-2, a sealed optical transceiver100includes a substrate102, which can be configured as a printed circuit board (PCB), a riser108, an optical block110, and a plurality of optical fibers112. The optical fibers112can be fixed with respect to each other inside a fiber ribbon cable116. Alternatively, the optical fibers112can be loosely arranged in a loose fitting tube, and movable with respect to each other. Thus, the fibers112can be individually positionable with respect to the other fibers112when the fibers extend out the fiber ribbon cable116. Alternatively still, the fibers112can be individualized without being surrounded by the fiber ribbon cable116. In some examples, the optical transceiver100can be configured as a mid-board optical engine. As will be appreciated from the description below, various optical components are mounted to the riser108of substrate102. The riser108, in turn, is mounted to the substrate102. The transceiver100includes a transmitter and a receiver. The transmitter receives electrical signals, generates optical signals corresponding to the electrical signals, and emits and transmits light that ultimately travels to optical fibers112of the fiber ribbon cable116. The receiver receives optical signals, generates electrical signals corresponding to the optical signals, transmits the electrical signals to an electrical interface, that can be mated with a complementary electrical component. The electrical interface can be configured as electrical contact pads105of the substrate102.

The transmitter includes at least one electro-optical element104such as at least one light source. The at least one light source can be arranged as a plurality of light sources. The light source can be placed in electrical communication with a controller203, which can be configured as a microprocessor. The controller302can be mounted to the substrate202, and can be programmed to control the operation of either or both of the optical transmitter and the optical receiver. In one example, the light source can be directly modulated by modulating an electrical current driving the light source. In another example, the transmitter can include at least one photonic integrated circuit, such as a plurality of photonic integrated circuits. In particular, the light sources can emit a steady beam of light that is externally modulated. The external modulation may occur in the photonic integrated circuit. Thus, the photonic integrated circuit, if present, can be configured to receive at least one electrical transmit signal from the complementary electrical component, convert the electrical transmit signal to an optical transmit signal, and output the optical transmit signal. In one example, the photonic integrated circuit can be configured as a silicon photonics chip.

The light source can be configured as a laser array in some examples. The laser array may be configured as a plurality of vertical-cavity surface-emitting laser (VCSEL) a distributed feedback (DFB) laser or a Fabry-Perot (FP) laser. The laser can be mounted to the riser108. If a plurality of light sources are present, each light source may operate at a different wavelength or the light sources may be at substantially the same wavelength. The light source may be mounted directly on the photonic integrated circuit, if present, or can be mounted on the riser108or at some other location in the optical transceiver20. If the light source is located off the photonic integrated circuit, the transmitter can include optical waveguides that direct light from the light source to the photonic integrated circuit.

The light source can modulate the light based on the received electrical transmit signals so as to produce the optical transmit signals. In particular, the transmitter can include at least one modulator driver that defines a modulation protocol that determines the modulation of the light based on the electrical signals received from the complementary electrical component. The transmitter can include a plurality of modulator drivers, with each modulator driver being dedicated to a respective channel that receives the electrical transmit signal to be converted into a respective optical transmit signal. The modulator drivers may be fabricated on a single die. Each modulator driver can be configured to provide an electrical input to the modulation circuit appropriate for driving either the drive current of the light source or an external optical modulator.

One or more intervening optical elements may be situated between the photonic integrated circuit and the fiber ribbon cable116. These intervening optical elements may include one or more of mirrors, lenses, transparent substrates, transparent couplers, and optical waveguides that collectively serve to provide a light propagation path between the photonic integrated circuit waveguides and optical transmit fibers of the optical fibers112of the fiber ribbon cables116that are configured to receive the optical transmit signals.

During operation, the laser array emits light and transmits the light into the optical block110. Light emitted by the laser array may be collimated by a first lens on a first surface of the optical block110where the emitted light from the laser array enters the optical block. The first surface of the optical block110can face the electro-optic element104. The optical block110reflects light off a reflective surface124changing its propagation direction. An optional second lens on a second surface of the optical block110. The second surface of the optical block110can define an exit surface of the optical block110in the transmitter. The second lens can focus light exiting the optical block110. Light exiting the optical block110is focused into the core of the optical transmit fiber positioned proximate to the exit surface of the optical block110. An index matching material can be disposed between the optical block110and the fiber end faces to eliminate or reduce back reflections from the fiber end faces.

The receiver can include at least one electro-optic element104such as at least one photodetector. The at least one photodetector can be configured as a plurality of photodetectors arranged as a photodetector array104a(seeFIG.3A) that is in optical alignment with a plurality of optical receive fibers of the optical fibers112of the fiber ribbon cable116. The photodetectors may be mounted to the riser108. The receiver can further include a current-to-voltage converter that is in electrical communication with the at least one photodetector. For instance, the optical receiver can include a plurality of photodetectors of the array104athat are in optical alignment with a respective one of the plurality of optical receive fibers. It can thus be said that the optical receive fibers are in data communication with the current-to-voltage converter.

The photodetectors are configured to receive optical receive signals from the respective optical receive fiber. As will be appreciated from the description below, the optical receive signals can travel from the optical receive waveguides to the photodetectors. The photodetectors may be surface sensitive photodetectors in which incoming photons strike an active region of the photodetector at a normal or near-normal angle of incidence. Such a detector architecture can be advantageous since it provides a small volume absorption region. Also, since the light is striking the active region at a normal or near-normal angle of incidence, the photodetector is polarization insensitive. The active region can have a low electrical capacitance, thereby allowing for high bandwidth operation. It should be appreciated, of course, that photodetectors having alternatively configured active regions are contemplated by the present disclosure. The surface sensitive active regions are configured to receive the optical receive signals from an output end of the respective one of the optical receive fibers.

One or more intervening optical elements may be situated between the optical receive fibers and the photodetectors. These intervening optical elements may include one or more of mirrors, lenses, transparent substrates, transparent couplers (polarization manipulators and filters), and optical waveguides that collectively serve to provide a light propagation path between the optical receive fibers112and the photodetectors64. While the light propagation path is more complex in the embodiments using multiple optical elements, they may improve mode matching and relax alignment tolerances between the optical receive fibers and the photodetectors. The high coupling efficiency may advantageously be maintained over a large operating temperature range.

In some embodiments, the first lens can be situated on the opposing side of the photodetector die from the active region. The incoming optical receive signals pass through the first lens, the photodetector die, and are absorbed in the active region. The photodetectors are further configured to convert the optical receive signals to corresponding electrical receive signals. The electrical receive signals can have current levels that are proportional with an optical power level of the received optical receive signal. Generally the photo generated current increases as the intensity of the incoming optical receive signal increases, and decreases as the intensity of the incoming optical receive signal decreases. It is recognized that the current levels of the electrical receive signals are not necessarily linearly proportional to the optical power level of the received optical receive signal, and that often the proportionality is nonlinear. Thus, optical receive signals having a high optical power level will be converted to an electrical signal having higher current levels than optical receive signals having a lower optical lower level. Data may be transmitted by this modulated optical and electrical signal.

The photodetectors output the electrical transmit signals to respective channels of the current-to-voltage converter. The current-to-voltage converter outputs conditioned electrical transmit signals from the respective channels to corresponding electrical contacts at the electrical interface. In one example, the current-to-voltage converter can be configured as a transimpedance amplifier (TIA).

During operation, the optical receiver propagates light in an analogous manner as described above with respect to the optical transmitter, except in the opposite direction. In particular, light is emitted by a fiber end face of the optical transmit fibers and propagates into the optical block110. In the optical block110, the light reflects off the reflective surface124and is directed toward the photodetector. The receiver can further include the first lens on the first surface of the optical block110, which can define an exit surface of the receiver. The first lens of the receiver focuses received light on to the photodetector. The receiver can further include the second lens on the second surface of the optical block surface where the light enters the optical block110from the optical fibers112. The second lens can be configured to collimate the light that enters the fibers112.

Referring now toFIG.2, the riser108may be formed from a metal, such as plated copper to facilitate heat transfer from heat generating elements, such as the laser array. In this regard, the riser108can also be referred to as a heat spreader. The riser has a riser hole170, which is covered by the optical block110when the transceiver100is assembled. The riser hole170a centrally located hole of the riser108. The optical block110may be formed from a molded polymer, such as ULTEM™.

Referring now toFIG.2, the optical transceiver100defines an optical path150between a fiber end face and the electro-optic element104. As will be appreciated from the description below, light traveling along at least a portion of the optical path150can undergo free space propagation in a gas such as air between the fiber end face and the electro-optic element104. As described above, the electro-optic element104can be configured as a light source of the transmitter, and can be configured as a photodetector of the receiver. In practice, the optical transceiver100can include a pair of electro-optic elements104, one of the electro-optic elements being configured as at least one light source, and the other electro-optic elements being configured as at least one photodetector. Thus, the electro-optic element104illustrated inFIG.2is intended to schematically illustrate both the light source and the photodetector. The optical transceiver100can thus define a transmit light propagation path and a receive optical path150of the type described above. The transmit light propagation path extends from the light source or laser to the fiber end face. The receive light propagation path extends from the fiber end face to the photodetector or photodiode. Thus, while the optical path150is described in more detail below with respect to the receiver of the optical transceiver100, the optical path150can be equally applicable to the transmitter of the optical transceiver100. Thus, reference is made below interchangeably to a receiver, transmitter, and transceiver. The optical path150defines a first section151that extends from the fiber end faces to the reflective surface124, and a second section152that extends from the reflective surface124to the electro-optical element104. Thus, the electro-optical element104is in alignment with the light propagation path, and in particular with the second section152of the light propagation path.

As shown inFIG.2, the riser108is mounted onto a top surface of the substrate102, and the optical block110is mounted to a top surface of the riser108. Thus, the substrate102supports the riser108, and the riser108, in turn, supports the optical block110. The riser108can provide a thermal dissipation path for heat generated by the transceiver100. The sealed optical transceiver100can further include a fiber ribbon cable116having one or more optical fibers112that are supported relative to the optical block110, such that a first at least one of the fibers112are configured to transmit optical signals from the optical transmitter of the transceiver100, and others of the fibers112are configured to receive optical signals from the optical receiver of the transceiver100. The optical fibers112may be mounted in a fiber alignment structure to facilitate simultaneous alignment of multiple optical fibers112with the optical block110.

The optical block110defines a first cavity155that is disposed adjacent the reflective surface124, such that the reflective surface124is open to the first cavity155. The second lens can be disposed in the first cavity155. Thus, the first cavity115can also be referred to as a second lens cavity that includes the second lens. The optical block110defines an outer surface that defines an opening153to the first cavity155. The outer surface can be defined by a top surface of the optical block110opposite a bottom surface of the optical block110that faces the riser108. Of course, the opening153can be defined on any suitable surface of the optical block110as desired. The reflective surface124can be configured as a total internal reflection (TIR) surface. The first cavity155is typically occupied by a material having a refractive index near 1, such as air or dry nitrogen. Total internal reflection (TIR) on the reflective surface124occurs when the refractive index of the optical block110, typically in the range of 1.45 to 1.7, is larger than the refractive index in the first cavity155. If a liquid were to contact the reflective surface124when the reflective surface is configured as a TIR surface, it may spoil the TIR reflection and thus affect the operation of the optical transceiver100. When the reflective surface124is configured as a TIR surface, the first cavity155can be referred to as a TIR cavity.

In other examples, a portion of the optical block110can be coated with a metallic coating so as to define a metallic surface that, in turn, defines the reflective surface124. In one example, the metallic coating can be gold, though it is appreciated that any suitably optically reflective metallic material can be used. The light reflects off the metallic reflective surface changing its propagation direction. When the reflective surface124is metallic, the reflection is not spoiled by liquid contacting the reflective surface124.

With continuing reference toFIG.2, and as described above, the optical path150includes the first section151and the second section152. The reflective surface124redirects the light between the first and second sections151and152. The first section151of the optical path150can include a first portion that undergoes free space propagation portion from the end face of the optical fiber112to an internal surface of the optical block110. The first section151of the optical path150can include a second portion that extends from the internal surface of the optical block110to the reflective surface124. The second section152of the optical path150can include a first portion that resides in the optical block110, and extends from the reflective surface124to the bottom surface of the optical block110. The second section152of the optical path150can include a second portion that undergoes free space propagation from the bottom surface of the optical block110to the electro-optic element104.

Thus, the optical path150can define a first free space light propagation path, through a gas such as air, whereby the light undergoes free space propagation from the end face of the optical fibers112to the internal surface of the optical block110. The first free space light propagation path can be defined by the first portion of the first section151of the optical path150. The optical path150further defines an internal light propagation path, whereby the light undergoes free space propagation inside the optical block110. Collectively, the internal light propagation path can include the second portion of the first section151of the optical path150and the first portion of the second section152of the optical path150that each reside in the optical block110. The optical path150can further include a second free space light propagation path, through a gas such as air, that extends from the optical block110to the electro-optic element104, whereby the light undergoes free space propagation. The second free space propagation portion can be defined by the second portion of the second section152of the optical path. The second free space light propagation path can extend from a bottom surface of the optical block110to the electro-optic element104. Light is either emitted or absorbed by the electro-optic element (EO)104, which is mounted on the riser108. The second free space light propagation path is optically aligned with both the first light propagation path extending through the optical block110(and in particular the first portion of the second section152of the optical path150), and the electro-optic element104.

While the optical transceiver100defines the first free space light propagation path as described above, it is recognized that the end face of the optical fibers112can be butted against the optical block110in another example. Accordingly, in this example, the optical transceiver100can be constructed such that the optical path does not undergo free space propagation between the optical fibers and the internal surface of the optical block110. Thus, the optical path150can define the internal light propagation path that is defined by the first section151of the optical path and the first portion of the second section152of the optical path. Further, the optical path150can define a free space light propagation path that is defined by the second portion of the second section152of the optical path150as described above.

With continuing reference toFIG.2, the optical transceiver100defines a second cavity162, which can also be referred to as a component cavity. The component cavity162extends from the optical block110to the riser108, and also to the electro-optic element104that is mounted on the riser108. In the receiver, light travels from the optical block110and through the component cavity162to the electro-optic element104. In the transmitter, light travels from the electro-optic element104through the component cavity162to the optical block110. The component cavity162can be defined by the optical block110, and in particular the bottom surface of the optical block110, and the riser108, and in particular the top surface of the riser108. The first lens can be disposed in the component cavity162. Thus, the component cavity162can thus also be referred to as a first lens cavity.

Generally, the component cavity162may be considered to be any volume or region which is filled with a gas, air, or evacuate, where an optical propagation path exists to or from an electro-optic element to an optical element. In this example, the optical element is defined by the optical block110. Within the optical block110light may travel in the first section151of the optical path150and in the first portion of the second section152of the optical path150. At the reflective surface124the propagation direction of light changes due to reflection off the reflective surface124.

In order for operation of the optical transceiver100to be unaffected by immersion of the transceiver100in liquid, particularly when the liquid is not optically transparent, the liquid is prevented from interfering with the first free space light propagation path between the end face of the optical fibers112and the internal surface of the optical block110. Further, as will be described in detail below, the liquid is prevented from interfering with the second free space light propagation path.

When the reflective surface124is configured as a TIR surface, the liquid can be prevented from entering the first cavity155. If a liquid were to enter the first free space light propagation path and contact the TIR surface, the optical properties of the first free space light propagation path would be altered, thereby affecting operation of the transceiver100. Accordingly, as described in more detail below in accordance with one example, the optical transceiver100can define a liquid impermeable first cavity seal that prevents the liquid from entering the first cavity155when the optical transceiver100is immersed in the liquid.

The first cavity seal can include a filler material118that can be in contact with both the optical block110and the optical fiber112in the first cavity155. In particular, the optical coupler defines a fiber opening, such that the optical fibers112enter the optical block110through the fiber opening. The filler material118can seal an interface between the optical fibers112and the optical coupler110, thereby providing a water impermeable seal that prevents liquid from entering the first cavity155through the fiber opening when the optical transceiver100is immersed in the liquid. The filler material118can be made of any suitable material. In one example, the filler118is an epoxy. It can be desirable for the epoxy to be dimensionally stable upon curing. Further, as described in more detail below, the optical transceiver100can include a closure member156that seals the opening153to the first cavity155. The closure member156in combination with the filler material118can define the first cavity seal, and prevents liquid from entering the first cavity155when the transceiver100is immersed in the liquid. Thus, the liquid is prevented from contacting the reflective surface124.

However, it is recognized that when the reflective surface124is metallic, contact between the liquid and the reflective surface124does not affect the reflection of the light between the first and second sections151and152of the optical path150. Therefore, liquid in the first cavity155does not affect the reflective properties of the reflective surface124when the reflective surface124is metallic. It would also be desirable to prevent liquid in the first cavity155from interfering with the first free space light propagation path, such that the first cavity155can be unsealed with respect to liquid when the optical transceiver100is disposed in the liquid. Thus, the optical transceiver100can be devoid of the closure member156when the reflective surface124is metallic.

Referring now toFIG.7, the fiber termination gap111can be sealed so as to prevent liquid in the first cavity155from traveling to the first free space light propagation path when the first cavity155is unsealed. In particular, the optical transceiver100can include an optically transparent filler material119that seals the fiber termination gap111. The optically transparent filler material119may be an optically transparent epoxy or adhesive that seals a fiber termination gap111that extends from the end face of the optical fiber112and one of the internal surface of the optical block110and the metallized reflective surface124. Thus, the first free space propagation path extends through the filler material119. It can be desirable for that optically transparent filler material119to be dimensionally stable to as to maintain alignment between the end faces of the optical fibers112and the reflective surface124. The optically transparent filler material119may be an index matching material such that optical reflections at the optical fiber end face and the second surface of the optical block110are sufficiently low or minimized. For instance, the optically transparent filler material119can have a refractive index between that of the optical fibers112and the optical block110. The optically transparent filler material119is configured to isolate the first free space light propagation path from its surrounding environment. Thus, if the first cavity155is not liquid sealed, the optically transparent filler material119prevents the liquid that enters the first cavity155from interfering with the free space propagation of light in the first cavity155. Thus, optical signals can propagate through the filler119selectively to the optical fibers112in the transmitter, and from the fibers112in the receiver.

Thus, it is recognized in some examples that the first cavity155can be unsealed with respect to liquid when the optical transceiver100is immersed in the liquid. Further, as will be described in more detail below, the first cavity155can be isolated from the component cavity162with respect to fluid flow therebetween in some examples. Thus, the liquid in the first cavity155is prevented from flowing from the first cavity to the component cavity162.

While it is appreciated that the optically transparent filler material119can have particular utility when the reflective surface124is metallic, it can nevertheless be desirable for the optical transceiver to include the optically transparent filler material119when the reflective surface defines a TIR surface and the first cavity155is sealed. Further, while the first cavity155can be unsealed when the reflective surface124is metallic, it is recognized that the first cavity155can also be sealed in the manner described herein when the reflective surface is metallic.

In order for light propagation through the transceiver100to be unaffected by immersion in liquid, particularly when the liquid is not optically transparent, the liquid is further prevented from interfering with the second free space light propagation path in the component cavity162. In one example, the optical transceiver100can define a liquid impermeable component cavity seal that prevents the liquid from entering the component cavity162when the optical transceiver100is immersed in the liquid. Thus, the liquid is prevented from entering the component cavity162, and is thus prevented from entering second free space light propagation path, thereby sealing the second free space light propagation path from the ambient environment such that environmental contaminants external to the optical block110are prevented from reaching the second free space light propagation path. The sealed optical transceiver100is configured to achieve liquid isolation from the light propagation path when the optical transceiver100is immersed in a liquid. For instance, as described in more detail below, the transceiver100can define a first liquid-impermeable seal between the riser108and substrate102, and a second liquid-impermeable seal between the optical block110and the riser108, thereby preventing liquid from traveling into the component cavity162, and thus into the second free space light propagation path, through both a first gap between the substrate102and the riser108, and a second gap between the riser108and the optical block110.

In one aspect, the optical block110defines a conduit159that extends from the component cavity162and the first cavity155. The conduit159places the component cavity162and the first cavity155in fluid communication with each other. Thus, the conduit159provides a path for gas exchange between the component cavity162and the first cavity155. The conduit159also allows the component cavity162to vent to the surrounding atmosphere through the opening153. The component cavity162, first cavity155and conduit159may be considered to form a contiguous, environmentally isolated, volume161where gas can be freely exchanged between them. Any method of making the component cavity162and first cavity155contiguous may be used.

The transceiver100can include the closure member156that is secured to the optical block110so as to seal the first cavity155with respect to the opening153. The closure member156can be configured as a plate157that extends across the first cavity so as to close and seal the first cavity155. In particular, the plate157can close the opening153to the first cavity155at the external surface of the optical block110. Thus, when the first cavity155and the component cavity162are in fluid communication with each other, the closure member156, the seal between the substrate102and the optical block, and the seal between optical block110and the riser108can combine to define the liquid impermeable component cavity seal.

The closure member156be sealed to the optical block110in a final assembly step. Accordingly, gasses produced during fabrication of the optical transceiver100can travel from the component cavity162through the conduit159, and out the first cavity155through the opening153. For instance, outgassing of water vapor or chemical components or solvents in the adhesive or any of the components such as the substrate102and the optical block110can occur. Once the gasses have evacuated the optical transceiver through component cavity162the conduit159, and the first cavity155, the opening153can be sealed by the closure member156. The closure member156is configured to isolate the reflective surface124from the surrounding environment. That is if the sealed optical transceiver100is immersed in a liquid, the closure member156will keep the reflective surface124free of contamination by the liquid. In particular, the closure member156will prevent the liquid from entering the first cavity155through the opening153when the optical transceiver100is immersed in the liquid. While the closure member156can be configured as a plate157in one example, the closure member156can be alternatively configured in any suitable manner as desired.

Referring now toFIG.7, it is recognized that the conduit159need not place the component cavity162in fluid communication with the first cavity155. Thus, the first cavity155and the component cavity162can be isolated from each other with respect to fluid flow therebetween. Instead, the conduit159can extend from the component cavity162to an external surface of the optical block110that is open to the ambient environment. The external surface can be defined by the top surface of the optical block110or any other suitable external surface. The conduit159can be open to the external surface of the optical block110, thereby placing the component cavity162in fluid communication with the ambient environment without passing through the first cavity155. Thus, during fabrication of the optical transceiver100, gas produced can travel from the component cavity162through the conduit159, and out the optical block110.

Whether the conduit159terminates at the external surface of the optical block or terminates at the first cavity155, it can be said that the conduit159is in fluid communication with the ambient environment. Once the gasses have evacuated the optical transceiver100through the conduit159, the conduit159can be sealed from the ambient environment with a liquid impermeable seal. In particular, the conduit159can be sealed at the external surface of the optical block110by a conduit closure member163. The conduit closure member163is configured to isolate the conduit159, and thus the component cavity162, from the surrounding environment. Thus, when the sealed optical transceiver100is immersed in a liquid, the conduit closure member163will keep the free space propagation that occurs in the component cavity162free of contamination by the liquid. In particular, the conduit closure member163will prevent the liquid from entering the conduit159, and thus, the component cavity162, when the optical transceiver100is immersed in the liquid. While the conduit closure member163can be configured as a plate in one example, the conduit closure member163can be alternatively configured in any suitable manner as desired.

As described above, the sealed optical transceiver100further seals the component cavity162from the liquid when the transceiver100is immersed in the liquid. In particular, the transceiver100can define a first liquid-impermeable seal between the riser108and substrate102. The transceiver100can further define a second liquid-impermeable seal between the optical block110and the riser108. The first and second seals are liquid-impermeable at least to the extent that when the transceiver100is immersed in the liquid, the first seal prevents the liquid from entering between the riser108and the substrate102, and the second seal prevents the liquid from entering between the optical block110and the riser108.

The first seal between the riser108and substrate102may defined by at least one or both of solder and adhesive.FIGS.3A-3Cshows an image of the riser108mounted to the substrate102of an optical receiver300.FIG.3Ashows the top surface of the riser108. The bottom surface of the riser108may be sealed to the top surface of the substrate102. The current-to-voltage converter, which can be configured as a transimpedance amplifier (TIA)174, may be disposed in a riser hole170of the riser108. The riser hole170can be a central hole of the riser108. The TIA174can be in electrical communication with electrical signal traces of the substrate102by wire bonds or any suitable alternative electrical connection. Similarly, the TIA174can be in electrical communication with the photodetector array104aby wire bonds or any suitable alternative electrical connection. The photodetector array104acan be supported by the riser108. For instance, in one example, the photodetector array104acan be adhesively attached to the riser108.

At least a portion of the bottom surface of the riser108may be soldered to the top surface of the substrate102so as to define a solder joint at a solder region. Thus, the optical transceiver100can provide a continuous, low thermal impedance, heat transfer path from the photodetector array104ato the substrate102to facilitate heat removal. The solder region may surround at least a portion of the riser hole170, such as a majority of the riser hole170up to an entirety of the riser hole170. The integrity of the solder joint may be assessed using x-ray or any suitable inspection.

The substrate102defines a bridge region172defined as a location whereby electrical signal traces of the substrate102pass under the riser108. The optical transceiver100can define a riser gap107between the riser108and substrate102that can be filled with a suitable adhesive, such as a low viscosity adhesive109. The adhesive109can be an epoxy in some examples. It can be desirable for the epoxy to be resilient against harsh environments, and further to have a low dielectric constant so as to not impede high speed performance of the optical transceiver100. As shown inFIG.3C, the adhesive109can seal the bridge region172with respect to liquid when the optical transceiver100is immersed in the liquid. In particular, the adhesive109can be applied to at least one of the top surface of the substrate102and the bottom surface of the riser108at a location adjacent the bridge region172. The riser108can then be mounted to the riser108, and the adhesive109can cure so as to define a liquid impermeable seal at the bridge region172. Thus, liquid is prevented from penetrating the seal and flowing into the bridge region172between the riser108and the substrate102when the transceiver100is immersed in the liquid.

The riser gap107can be defined along a vertical direction that separates top surfaces from bottom surfaces. The adhesive109can be introduced into the gap107in any suitable manner as desired. For instance, in one example, capillary action may be used to draw the adhesive into the gap107. Further, as shown inFIG.3B, the adhesive109can extend continuously and uninterrupted about the riser hole170. After introducing the adhesive into the gap107, the adhesive109may be cured. Alternatively, electrical traces on the substrate102can be buried beneath the top surface of the substrate102and a continuous seal can be formed around the riser hole170of the riser108. For instance, a solder joint can be formed around the riser hole170that joins the riser108to the substrate102. Thus, it may be said that the riser108may be mounted to the substrate102such that a liquid-impermeable seal surrounds the riser hole170in the gap107between the substrate102and the riser108. Thus, when the optical transceiver100is immersed in the liquid, the liquid is prevented from penetrating the liquid-impermeable seal and flowing into the gap107.

As described above, the transmitter of the transceiver can be liquid impermeable in the manner described herein with respect to the receiver. In particular, for a transmitter, the TIA174is replaced by a light source driver, and the photodetector array104as replaced by a light source. For instance, the light source can be defined by a laser array, and the light source driver can be configured as a laser driver. In the optical transceiver100, a photodetector array and laser array are both present, as are a laser driver and TIA. These components may be scaled in size so that both the laser driver and TIA fit within the riser hole170of the riser108. Both the photodetector array and the laser array may be scaled so that they both may be mounted adjacent the riser central hole170. Alternatively, the riser central hole170may be enlarged such that the photodetector array and the laser array both fit within the riser hole170of the riser108, such that the riser hole170accommodates the components for both the transmitter and the receiver. In still other embodiments, the riser108can define first and second riser holes. The laser driver can be disposed in the first riser hole, and the TIA can be disposed in the second riser hole.

Referring now toFIGS.4A-4B, the optical block110can be mounted to the riser108. For instance, the optical block110can be sealed to the riser108. In particular, an adhesive180can be applied to either or both of the top surface of the riser108or the bottom surface of the optical block110that faces the top surface of the riser108. The adhesive180surrounds the riser hole170of the riser108. In one example, the adhesive is applied to the top surface of the riser108as a continuous uninterrupted bead of adhesive180that surrounds an entirety of the perimeter of the riser hole170. The optical block110can be mounted on the top surface of the riser108such that the adhesive bead180is disposed between the optical block110and the riser108, thereby defining a sealed interface that attaches the optical block to the riser108. In one example, the optical block110can be positioned on the adhesive bead after the adhesive bead180has been applied to the top surface of the riser108.

The optical block110may be aligned with the riser108in accordance with conventional automated techniques used to assemble existing optical transceivers. Once the optical block110is properly aligned with the riser108and positioned on the riser108, the adhesive bead180may be cured, thereby fixing the position of the optical block110relative to the riser108. The adhesive bead180can be cured using any known method, such as ultra-violet light curing, heat curing, time curing, or any combinations thereof. The adhesive used in the adhesive bead180may have a relatively high viscosity, so that it will accommodate and conform to varying gap sizes between the optical block110and riser108arising from optical alignment of the optical block110. The adhesive can be an epoxy in some examples. It can be desirable for the adhesive bead180can be dimensionally stable after curing, thereby preventing substantial movement of the optical block with respect to the riser108and electro-optic component104. It can also be desirable for the adhesive bead180to be resilient to harsh environments. Thus, it may be said that the optical block110can be mounted to the riser108such that a liquid impermeable seal is disposed in a gap between the optical block110and the riser108and also surrounds the component cavity162. Thus, when the transceiver100is immersed in the liquid, the liquid is prevented from penetrating the seal and flow through the gap between the optical block110and the riser108and into the component cavity162. Excess adhesive can be evident along the entire perimeter of the optical block110indicating that the adhesive defines a continuous and uninterrupted seal.

As described above, the optical block110further defines the at least one conduit159that extends from the first cavity155to the component cavity162. In one example, the at least one conduit extends from the top surface of the optical block110to the bottom surface of the optical block110. Thus, the top end of the conduit159is open to the first cavity155(seeFIG.2), and the bottom end of the conduit159is open to the component cavity162. Accordingly, the conduit159provides a continuous passage from the component cavity162to the first cavity155. Further, as described above, the first cavity155is open to the ambient environment during assembly of the transceiver100. The first cavity155can be defined by the top surface of the optical block110. Thus, the at least one conduit159can similarly extend through the top surface of the optical block110. Further, the component cavity162can be defined by the bottom surface of the optical block110. Thus, the at least one conduit159can extend through the bottom surface of the optical block110. The component cavity162is sealed against the riser108by the adhesive bead180in the manner described above.

As a result, the component cavity162can equilibrate with the pressure of the ambient environment through the conduit159and the first cavity155once the optical block110has been secured to the riser108. This avoids trapping gases in the component cavity162during the steps of aligning the optical block110and securing the optical block110to the riser108. Trapped gases could otherwise cause pressure differentials between the component cavity162and the ambient environment, which could cause misalignment and compromise the seal between the riser108and optical block110. The at least one conduit159can be made by laser machining, or any suitable alternative method as desired. The at least one conduit159is disposed at a location of the optical block110so that it does not interfere with any of the light propagation paths that pass through the optical block110. In one example, the at least one conduit159can include a pair of conduits159. The conduits can be positioned such that the optical fibers112are disposed between the conduits159with respect to a row direction along which the optical fibers112are arranged. That is, the optical fibers112can be arranged adjacent each other along the row direction. Each of the conduits159can be disposed outboard of the optical fibers112with respect to the row direction. However, it is appreciated that the conduits159can be alternatively positioned as desired. The conduits159can be cylindrical in shape in one example. However, the conduits159can define any suitable alternative shape as desired.

Referring now toFIG.5, and as described above, the upper end of the at least one conduit159can be sealed with respect to fluid flow. In particular, at least one closure member156can extend over the opening153of the first cavity155, thereby isolating the at least one conduit159from the ambient environment. In one example, the closure member156can be configured as a plate157that is secured to the top surface of the optical block110. The closure member156can extend over at least a portion of the first cavity155. Thus, the closure member156can isolate the transceiver optical path150(seeFIG.2) from contaminants or liquids that may be present in the ambient environment. In one example, the closure member156can have a coefficient of expansion that is substantially equal (e.g., within 25%) of that of the optical block, thereby avoiding warpage during fabrication of the optical transceiver100. For example, both the optical block110and the plate157may be made of Ultem™ material, a polyetherimide commercially available by Aetna Plastics having a place of business in Mantua, Ohio. The closure member156covers and seals the opening153to the first cavity155. In this regard, the closure member156isolates the first cavity155and the component cavity162, and the at least one conduit159from the ambient environment of the transceiver100.

In one example, an adhesive190can secure the closure member156to the top surface of the optical block110. The adhesive190can be applied to either or both of the top surface of the optical block110and the bottom surface of the closure member156that faces the top surface of the optical block110. The adhesive190can be applied as a continuous uninterrupted bead that surrounds an opening to the first cavity155. The opening can be defined by the top surface of the optical block110. The closure member156can then be mounted onto the top surface of the optical block110such that the adhesive190is configured to secure the closure member156to the optical block110. After the closure member156has been mounted to the optical block110, the uncured adhesive190can be cured by any known method, such as those previously described. The adhesive190can be an epoxy in some examples. It can be desirable for the epoxy to be dimensionally stable after curing and resilient in harsh environments.

Referring also again toFIG.2, when the closure member156has been mounted to the optical block110, and the optical block110has been mounted to the riser108, the first cavity155, the component cavity162, and the at least one conduit159define a sealed liquid-impermeable enclosed volume161. The closure member156can be sufficiently thin such that is flexible. As a result, the closure member156can selectively bow upward or downward as desired so as to equilibrate the pressure within the sealed continuous volume161with that of the ambient environment. Limiting the pressure differential between the enclosed continuous volume161and the ambient environment reduces the risk of motion of the optical block110, which could cause misalignment of the optical path150. For example, the closure member156may be substantially 0.005″ thick, although thinner and thicker closure members can be used. Such a thin plate may flexible and bow or slightly shift position in response to possible pressure differentials between the sealed continuous volume161and ambient environment to minimize that differential. Minimizing the pressure differential between the sealed continuous volume161and ambient environment reduces the risk of possible misalignment of the optical path between the electro-optic element104and fiber112. In one example, the closure member156can be configured as a plate157. In one example, the plate157can have substantially planar top and bottom surfaces, having the shape of a rectangular parallelepiped. It is recognized, however, that the closure member156can define any suitable size and shape as desired. The closure member156may be mounted to the optical block110such that a gap between the optical block110and the sealing member has an impermeable seal surrounding the first cavity155. While the closure member156is secured to the optical block with an adhesive in one example, it should be appreciated that the closure member156can be secured to the optical block110in accordance with any suitable alternative method as desired.

As described above, the second free space light propagation path can be sealed by sealing the optical block110against the riser108, and sealing the riser108against the substrate102. Further, when the conduit59joins the component cavity162with the first cavity155, the second free space light propagation path can be sealed by sealing the first cavity155. Alternatively or additionally, the second free space light propagation path can be sealed by placing an adhesive in the component cavity162, such that the adhesive extends from the electro-optic element to the first surface of the optical block110. The adhesive can be an epoxy. It can be desirable for the epoxy to be optically transparent epoxy or adhesive that seals a gap that extends from the first surface of the optical block110to the electro-optic element104. Thus, the second free space propagation path extends through the adhesive. The optically transparent filler material may be an index matching material such that optical reflections at the electro-optic element104and the first surface of the optical block110are sufficiently low or minimized. For instance, the optically transparent filler material can have a refractive index between that of the electro-optic element104and the optical block110. The optically transparent filler material is configured to isolate the second free space light propagation path from its surrounding environment. Thus, if the component cavity162is not liquid sealed, the optically transparent filler material prevents the liquid that enters the component cavity162from interfering with the free space propagation of light in the component cavity162. Thus, optical signals can propagate through the filler material selectively to the first surface of the optical coupler110from the electro-optic element in the transmitter, and from the first surface of the optical coupler110to the electro-optic element104in the receiver.

Referring now toFIG.6, the sealed optical transceiver100can be immersed in a liquid201that is disposed in a container200. The liquid201can be a coolant liquid that is configured to remove sufficient heat from the optical transceiver100to prevent the optical transceiver100from overheating during normal operation. The liquid201can be configured as FC-43 liquid, commercially available from3M Inc. having a place of business in St. Paul, MN The liquid201could, of course, be any suitable alternative liquid as desired. The fiber ribbon cable116can terminate at an MT ferrule, which can also be immersed in the liquid201and still function according to specification. Alternatively, the fiber ribbon cable116can emerge from the liquid as it is directed away from the optical block110.

It is appreciated in some examples that the optical path150is sealed from the liquid201even though the optical block110is not encapsulated water tight housing. Thus, the liquid201is able to flow to and contact at least the external surface of the contact block110. In some examples, the seals of the optical transceiver100prevent the liquid201from entering the first cavity155and the component cavity162. Alternatively, in some examples described above, the liquid201can further be able to flow into the first cavity155. Alternatively or additionally, the liquid201can be able to flow into the component cavity162. In all examples, the liquid can be prevented from flowing into the optical path150, thereby affecting the free space propagation of the light traveling along the optical path150.

It has been observed that the optical transceiver100can be subject to 2000 hours of continuous immersion in the liquid201without any noticeable performance degradation of the sealed optical transceiver100. In addition, the optical transceiver100has passed the following the standard test of over pressure to 60 PSI, whereby the optical transceiver100is placed into a pressure chamber that is pressurized to 60 PSI to evaluate passively the integrity of the seals described herein. Further, the optical transceiver100was tested at 35 PSI by applying active pressure. In other words, the transceiver100is placed into a pressure chamber that is pressurized to 35 PSI and the transceiver100is activated and undergoes normal operation in the pressurized chamber. The optical transceiver has further been found to achieve sufficient radio frequency (RF) and optical performance. The optical transceiver100is further configured to be stored at low temperatures that can range down to −55 degrees Celsius. Further still, operation of the optical transceiver100was unaffected over the course of 100 temperature cycles from minus 45 degrees Celsius to 85 degrees Celsius.

While the sealed optical transceiver100may be immersed in a liquid during operation, this is not a requirement. The sealed optical transceiver100may be cooled by forced air flowing over an attached finned heat sink. Alternatively, the optical transceiver may be cooled by contacting it with a liquid cooled chill plate. An advantage of the sealed optical transceiver100is that it is insensitive to contaminants that might be present in the surrounding environment. Such contaminants include, but are not limited to, dust and salt water spray.

In some applications, the sealed optical transceiver100may be coated with a conformal layer to provide additional environmental isolation. For example, electrical components and/or electrical signal lines that may be present on the substrate102may be isolated from the surrounding environment by a conformal coating. Electrical contact areas of the sealed optical transceiver100may remain exposed so that electrical connections may be made to the sealed optical transceiver100. Generally, the conformal coating covering will cover a majority of the exposed surface area of the optical interconnection element. An advantage of the sealed transceiver100is that its optical path150is isolated from the environmental contamination without use of a costly metal housing or electrical feedthroughs. The conformal coating covering can be a urethane in certain examples.

In other applications, it has been found that an electrically nonconductive lubricant can be applied to exposed, or unsealed, metallic structures of the optical transceiver, such as the electrical contact pads105, so as to thereby define an electrically nonconductive protective coating. The lubricant can be thixotropic, such that the complimentary electrical component can mate with the electrical contact pads105, thereby establishing an electrical connection therebetween. Because the optical block110is sealed with respect to the ingress of liquid, the lubricant can be applied by immersing the optical transceiver in a bath of the lubricant. Because the optical block110is liquid impermeable, the lubricant is applied only to external surfaces of the optical block110and of the optical transceiver100. Alternatively, the lubricant can be sprayed onto a substantial entirety of the optical transceiver100or optical block110. It should be appreciated, of course, that the lubricant can be applied in any suitable manner as desired. Further, the lubricant can alternatively be selectively applied to desired structures to be coated with the lubricant. The lubricant can be anti-corrosive so as to prevent the metallic surfaces coated with the lubricant from corroding in the presence of salt spray, fog, and high humidity such as 95% humidity. Further, the lubricant can prevent fungus from growing on the underlying structures that are coated with the lubricant.

It should be noted that the illustrations and discussions of the embodiments shown in the figures are for exemplary purposes only and should not be construed as limiting the disclosure. One skilled in the art will appreciate that the present disclosure contemplates various embodiments. Additionally, it should be understood that the concepts described above with the above-described embodiments may be employed alone or in combination with any of the other embodiments described above. It should further be appreciated that the various alternative embodiments described above with respect to one illustrated embodiment can apply to all embodiments as described herein, unless otherwise indicated. Various orientation terms, such as top, bottom, upper, and lower, such be understood as relative to a typical orientation of the transceiver with the transceiver substrate resting on a horizontal surface.