COOLED OPTICS ATTACHED TO A PRINTED CIRCUIT BOARD

An optical module includes a PCB having an electronic component mounted on a first side thereof. A heat sink is located along a second side of the PCB. A thermoelectric cooler (TEC) is disposed in an opening through the PCB and has a surface adjacent the heat sink. A laser is located at another surface of the TEC in a thermal contact therewith. An optical fiber mount is attached to the first side of the PCB to hold an optical fiber end in optical alignment with the laser.

FIELD

Various example embodiments relate to electrical and optical modules with cooling.

BACKGROUND

When fabricating optical transmitters and receivers, the electronics are typically assembled on a printed circuit board (PCB) while the optics are assembled inside a sealed package, typically a transistor outline (TO) can or a metal-ceramic box, which is then electrically connected to the printed circuit board. The electrical connection can be a flexible circuit or rigid electrical pins. A thermoelectric cooler (TEC) may be used to cool the optical components within the sealed package during operation.

SUMMARY

An aspect of the present disclosure provides an apparatus comprising: a printed circuit board having an electronic component mounted on a first side thereof; a heat sink located along a second side of the printed circuit board; a thermoelectric cooler (TEC) disposed in an opening through the printed circuit board and having a surface adjacent the heat sink; a laser on another surface of the TEC; an optical fiber; and an optical fiber mount attached to the first side of the printed circuit board to hold an end of the optical fiber in optical alignment with the laser.

In some implementations, the apparatus further comprises a bulk optical collimating and/or focusing element mounted upon the another surface of the TEC between the laser and the optical fiber mount. In some implementations, the bulk optical collimating and/or focusing element is a lens.

In any of the above implementations, the apparatus may further comprise another bulk optical collimating and/or focusing element mounted to the printed circuit board in an optical path between the laser and the optical fiber mount. In some implementations, the another bulk optical collimating and/or focusing element is another lens.

In any of the above implementations, the apparatus may further comprise an optical isolator mounted to the printed circuit board between the laser and the optical fiber mount. In some implementations, the optical isolator may be between the lens and the another lens.

In any of the above implementations, the apparatus may further comprise an optical filter mounted to the printed circuit board between the laser and the optical fiber mount. In some implementations, the optical filter may be between the bulk optical elements lens.

In any of the above implementations, the another surface of the TEC may be substantially flush with the first surface of the printed circuit board.

In any of the above implementations, the heat sink may be in a mechanical contact with the second surface of the printed circuit board.

In any of the above implementations, the laser and the bulk optical element may be the only optical components mounted to the TEC.

In any of the above implementations, the electronic component may be a laser driver of the laser.

Any of the above implementations may further comprise a digital signal processor mounted to the printed circuit board.

Any of the above implementations may further comprise a cover over the laser and the bulk optical component(s) attached to the printed circuit board. In some implementations, the electronic component may be outside of the cover.

A second, related aspect of the present disclosure provides an apparatus comprising: a printed circuit board having an optical fiber mount attached to a first side thereof, a heat sink located along a second side of the printed circuit board, a TEC disposed in an opening through the printed circuit board and having a surface adjacent the heat sink, a laser on another surface of the TEC, wherein the optical fiber mount is to hold an optical fiber end in optical alignment with the laser, and a lens mounted upon the TEC between the laser and the optical fiber mount. In some implementations, the apparatus further comprises an electronic component mounted to the printed circuit board. The apparatus may further comprise an optical fiber having the optical fiber end. The electronic component may be, e.g., a laser driver.

Some implementation of the apparatus according to the second aspect may comprise a second lens mounted on the first side of the printed circuit board in an optical path from the laser to the optical fiber end.

In any of the above implementations according to the second aspect, the apparatus may further comprise a cover over the laser and the lens. The electrical component may be on the first side of the printed circuit board outside of the cover.

DESCRIPTION

In the following description, for purposes of explanation and not limitation, specific details are set forth, such as particular circuits, circuit components, techniques, etc. in order to provide a thorough understanding of the present invention. However, it will be apparent to one skilled in the art that the present invention may be practiced in other embodiments that depart from these specific details. In other instances, detailed descriptions of well-known methods, devices, and circuits may be omitted so as not to obscure the description of the present invention. All statements herein reciting principles, aspects, and embodiments of the invention, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future, i.e., any elements developed that perform the same function, regardless of structure.

Furthermore, the following abbreviations and acronyms may be used in the present document:PCB: Printed Circuit BoardTO: Transistor OutlineTEC: Thermoelectric CoolerEML: Electro-absorption Modulated LaserFPGA: Field Programmable Gate ArrayDAC: Digital to Analog ConverterASIC: Application Specific Integrated Circuit

FIG.1illustrates an example apparatus100in a vertical cross-section. The apparatus100may include a part or all of an optical transceiver, e.g., in a small form-factor pluggable such as an SFP, QSFP, or the like. The apparatus100includes a printed circuit board110, which may have an electronic component115mounted on a first side111thereof. A heat sink130is located largely along a second side112of the printed circuit board110. A thermoelectric cooler (TEC)120is disposed in an opening117through the printed circuit board110. The TEC120has a surface (“back surface”)123adjacent to a surface of the heat sink130, e.g., in direct mechanical contact therewith to provide high thermal conduction there between. A laser140is mechanically mounted upon another surface (e.g., a “top surface”)121of the TEC120in good thermal contact therewith. In some embodiments, a highly thermally-conductive substrate142may be disposed between the laser140and the TEC120and in mechanical contact with nearby surfaces of both the laser140and the TEC120. An optical fiber mount160is mechanically attached to the first side111of the printed circuit board110to hold an optical fiber end165in approximate optical alignment with the laser140.

The laser140is electrically connected to the electronic component115with an electrical connection145, which may be flexible or rigid. In an embodiment, the electronic component115is a laser driver configured to drive the laser140in operation. The laser140may be e.g., an electro-absorption modulated laser (EML), or another suitable semiconductor laser device.

Some embodiments may use, in place of the laser140, another electrically-operated and/or electrically-energized optical device that in operation generates heat and/or is sensitive to temperature, such as an optical amplifier, e.g. a booster optical amplifier, or a photodetector, e.g. a photodiode, or an optical modulator.

In some embodiments, a lens151, or another bulk optical focusing or collimating element as may be suitable in some configurations, may preferably be mounted on the top surface121of the TEC120between the laser140and the optical fiber mount160, for coupling light emitted by the laser140into the optical fiber end165. The lens151(“first lens”) may be, e.g., a spherical lens or an aspheric lens. In a lens-less embodiment, the optical output of the laser140may be located very close to the near end of the optical fiber held by the optical fiber mount160to reduce optical coupling losses there between. In either of these embodiments, having the optical fiber mount160, which fixes the alignment of the end165of the optical fiber, off the surface121of the TEC120enables the footprint of the TEC120to be smaller than in devices where the large footprint, optical fiber mount160is over or on the surface121. The smaller surface121typically enables the TEC120to be operated at a lower power, for similar amounts of temperature cooling, than a TEC (not shown) on whose major surface both the laser140and an optical fiber mount are located.

In some embodiments, the top surface121of the TEC120may be substantially flush, e.g., with an accuracy within +/−50 micron (μm) or better, with the first side111of the printed circuit board110. In some embodiments, the heat sink130may have a mesa, as illustrated, or a cavity, upon or within which the TEC120may be mounted to level the top surface121of the TEC with the first side111of the printed circuit board110. In some other embodiments, the top surface121of the TEC120may be vertically offset from the first side111of the PCB as may be convenient for optically aligning the laser140with the lens151and the optical fiber mount160, i.e., the optical fiber end165.

FIG.2illustrates an apparatus200in a vertical cross-section. The apparatus200is an embodiment of the apparatus100and includes many of the elements described above with reference toFIG.1; these elements are indicated inFIGS.1and2with same reference numerals and may not be described here again. Compared to the apparatus100, the apparatus200includes another lens152(“second lens”) disposed between the (first) lens151and the optical fiber mount160in an optical path between the laser140and the optical fiber end165. The second lens152is mechanically mounted to the printed circuit board110on the first side111thereof. The second lens152may assist in forming a lower loss optical coupling between the laser140and the optical fiber end165, e.g., to make the laser-to-fiber optical coupling more tolerant to thermally-induced alignment variations between the optical fiber end165and the laser140. The second lens152may be spheric or aspheric.

FIG.3illustrates an apparatus300in a vertical cross-section. The apparatus300is an embodiment of the apparatus200and includes many of the elements that are described above with reference toFIGS.1and2; these elements are indicated inFIGS.1,2, and3with same reference numerals and are not described here again. Compared to the apparatus200, the apparatus300includes another optical element170disposed between the (first) lens151and the optical fiber mount160in an optical path between the laser140and the optical fiber end165. The optical element170is mounted to the printed circuit board110on the first side111thereof. In the illustrated embodiment, the optical element170is between the two lenses151and152, but the optical element may alternatively, e.g., be locate between the lens152and the near end165of the optical fiber. In an example implementation, the optical element170is an optical isolator. The optical element170may also be, e.g., an optical filter, or some other optical element, or a combination of optical elements, which may be useful for a particular application of the apparatus300.

FIG.4illustrates a top view of the apparatus300ofFIG.3according to an embodiment. In the illustrated example, the apparatus300includes a digital processor410, e.g., an FPGA or an ASIC, optionally mounted upon the printed circuit board110. The electronic component115is a laser driver electrically connected to the processor410and the laser140for driving the laser140with a signal generated according to the processor410. In other embodiments, the processor410may be disposed outside of the printed circuit board110. A digital to analog converter (“DAC”, not shown) may be disposed in a signal path between the processor410and the laser driver115. In some implementations the DAC may be disposed on the printed circuit board110. In some embodiments, the processor410and the laser driver115may be implemented in a same integrated circuit, which may be mounted on the printed circuit board110.

FIG.5illustrates an apparatus500in a vertical cross-section. The apparatus500is an embodiment of the apparatus200and includes many of the elements that are described above with reference toFIGS.1and2; these elements are indicated inFIGS.1,2, and4with same reference numerals and are not described here again. The apparatus500includes a cover510locally encapsulating optical elements of the apparatus to protect them from dirt and humidity. In the illustrated example, the cover510is disposed over the laser140and the lenses151,152and at least a part of the optical fiber mount160. The cover510may be attached, e.g., glued or soldered, to the printed circuit board110. In some embodiments, the cover510may be disposed over the optical elements140,151attached to the TEC120, with the second lens151being outside thereof.

In any of the apparatus described above, the laser140and, possibly, the lens151may be the only optical components mounted onto the TEC120, allowing the TEC120to be suitably small and reducing the power consumption thereof. Positioning the TEC with the laser in an opening of a PCB, e.g., the printed circuit board110, where the laser driver is located allows the electrical connection145between the driver and the laser to be short, which is beneficial at high modulation rates. Some embodiments may include one or more temperature sensors (not shown) in thermal contact with the top surface121of the TEC120as known in the art. The apparatus may further include a TEC driver (not shown) in communication with temperature sensor for controlling the TEC120to maintain the laser140at a desired temperature during operation.

In various embodiments, the PCB110typically provides substantial thermal isolation the heat generating electronics, e.g., the processor410and/or the laser driver115ofFIG.4, and the laser140, which is laterally distant along the surface111of the PCB110. For this reason, the smaller footprint TEC120may typically still be able to adequately control the temperature of the laser140even when strong heat generators are located at different lateral positions on the surface111of the PCB110.

It will be understood by one skilled in the art that various changes in detail may be affected in the described embodiment without departing from the spirit and scope of the invention as defined by the claims. For example, any one of the apparatus100and the apparatus300may include a cover, such as the cover510, locally encapsulating the optical components of the respective apparatus. The apparatus100and/or the apparatus200may include a digital processor410, which may be mounted to the printed circuit board110. In some embodiments of the apparatus100,200,300, or400the lens151may be mounted to the printed circuit board110, so that the laser140is the only optical component mounted to the TEC120, e.g., as illustrated inFIG.6; this would allow to reduce the size and the power consumption of the TEC, but may provide less stable optical coupling. Furthermore, in some embodiments, the lens151, and/or the lens152where present, may be replaced with another bulk optical focusing and/or collimating element or device, including but not limited to a series of lenses.

Furthermore, in the description above, for purposes of explanation and not limitation, specific details are set forth such as particular architectures, interfaces, techniques, etc. in order to provide a thorough understanding of the present invention. In some instances, detailed descriptions of well-known devices, circuits, and methods are omitted so as not to obscure the description of the present invention with unnecessary detail. Thus, for example, it will be appreciated by those skilled in the art that block diagrams herein can represent conceptual views of illustrative circuitry embodying the principles of the technology. All statements herein reciting principles, aspects, and embodiments of the invention, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future, i.e., any elements developed that perform the same function, regardless of structure.

Thus, while the present invention has been particularly shown and described with reference to example embodiments as illustrated in the drawing, it will be understood by one skilled in the art that various changes in detail may be affected therein without departing from the spirit and scope of the invention as defined by the claims.