HK1161359A - Modular optical transceiver - Google Patents

Abstract

An optical transceiver converting and coupling an information-containing electrical signal with an optical fiber including a housing conforming to the industry standard XENPAKTM form factor including an electrical connector for coupling with an external electrical cable or information system device and for transmitting and/or receiving an information-containing electrical communications signal, and a fiber optic connector adapted for coupling with an external optical fiber for transmitting and/or receiving an optical communications signal. At least one electro-optical subassembly is provided in the housing for converting between an information-containing electrical signal and a modulated optical signal corresponding to the electrical signal, along with a modular, interchangeable communications protocol processing printed circuit board in the housing for processing the communications signal into a predetermined electrical or optical communications protocol, such as the IEEF 802.3ae 10 Gigabit BASE LX4 physical layer.

Description

Modular optical transceiver

The present application is a divisional application of the invention patent application of the applicant's ondol corporation, 2004/7/27, application No. 200410071023.8, entitled "modular optical transceiver".

Reference to related applications

The present application is co-pending (copend) US patent application serial No. 10/866,265, filed on 6/14/2004, assigned to the common assignee.

Technical Field

The present invention relates to optical transceivers, and more particularly to modules that couple accessories or provide a communication interface and optical fibers between computers or communication units having electrical input/output connectors or interfaces, as used in fiber optic communication links.

Background

Various optical transceivers are known in the art that include an optical transmitting portion that converts electrical signals to a conditioned optical beam coupled to an optical fiber, and a receiving portion that receives optical signals from the optical fiber and converts them to electrical signals. Traditionally, the light receiving portion contains a light combination to concentrate or direct light from the optical fiber onto a photodetector, which in turn is connected to an amplifier/limiter circuit on a circuit board. The photodetector or photodiode is typically packaged in a hermetically sealed package in order to protect it from harsh environmental conditions. Photodiodes are typically semiconductor chips hundreds of microns to a few millimeters wide and 100-500 microns thick. The packages in which they are installed are typically 3-6mm in diameter, 2-5mm long and have some electrical leads from the package. These electrical leads are then soldered to the circuit board containing the amplifier/limiter.

Disclosure of Invention

It is an object of the present invention to provide an improved optical transceiver using modular, interchangeable transmitter and receiver subassemblies.

It is another object of the present invention to provide an optical transceiver for use with optoelectronic assemblies via different optical transmission systems.

It is another object of the present invention to provide an optical transceiver for use in an optical transmission system through an industry standard XENPAK housing.

It is another object of the present invention to provide an optical transceiver for use in an optical Wavelength Division Multiplexed (WDM) transmission system for short range and long haul applications.

It is another object of the present invention to provide an optical transceiver that is capable of both field upgradeable hardware and software modules.

It is another object of the present invention to provide improved heat dissipation from a transmitter subassembly to a housing or case by using a heat conduction path in an optical transceiver.

It is another object of the present invention to provide improved EMI shielding in an optical transceiver through the use of interdigitated or intermeshing metal castellations (castellations) on the housing and cover assembly, respectively.

It is another object of the present invention to provide an optical transceiver for use in an optical transmission system that protects the primary components from exposure to environmental conditions by encapsulating them in a hermetically sealed enclosure.

Another object of the present invention is to provide an optical transceiver that is easily manufactured by using a simplified optical component mounting and arranging technique.

Briefly, and in general terms, the present invention provides an optical transceiver for converting and coupling electrical signals containing information through an optical fiber including a housing including an electrical connector for coupling with an external cable or information system device and a fiber optic connector adapted to couple with an external optical fiber; at least one electro-optical subassembly in the housing for converting between an electrical signal containing information and an adjusted optical signal corresponding to the electrical signal; and a communication protocol processing subassembly in the housing for processing the communication signal to a predetermined electrical or optical communication protocol.

In another aspect of the invention, there is provided a transmitter subassembly comprising first and second lasers operating at different wavelengths and being modularized with first and second electrical signals for emitting first and second laser beams, respectively; and an optical multiplexer for receiving the first and second optical beams and multiplexing the respective optical signals into a single multi-wavelength optical beam, coupled to the fiber optic connector for transmitting the optical signals to an external optical fiber.

In another aspect of the invention, there is provided a receiver subassembly comprising an optical demultiplexer coupled to an optical fiber connector for receiving a multi-wavelength optical signal having a plurality of information-bearing signals, each having a different predetermined wavelength. The optical demultiplexer function is to convert the optical signal to a different (distint) optical beam corresponding to a predetermined wavelength. The subassembly includes a substrate forming an optical reference plane and including first and second photodiodes disposed thereon in the paths of the first and second optical beams, respectively.

In another aspect of the invention, the invention provides a protocol processing sub-assembly, such as an electrically variable programmable read only memory, that includes modular reprogrammable or interchangeable solid sub-elements. This sub-element enables simplified manufacturability and large-scale customization for a wide variety of different communication protocols. It also makes it possible to rapidly reconfigure the unit to handle different protocols. The layers of material, or the upper media access control layer, are programmed by simply moving one printed circuit board and replacing the other, or reprogramming the EEPROM on the circuit board.

Additional objects, advantages, and novel features of the invention will become apparent to those skilled in the art from this disclosure, including the following detailed description and by practicing the invention. While the invention will be described below with reference to preferred embodiments, it will be understood that the invention is not limited thereto. Those skilled in the art having access to the teachings herein will recognize additional applications, modifications, and embodiments in other fields, which are within the scope of the present invention, and with respect to which the present invention may be practiced, as disclosed and claimed herein.

Drawings

FIG. 1 is an exploded perspective view of an optical transceiver in an exemplary embodiment according to the present invention;

FIG. 2 is a high level simplified block diagram of the functional elements of the transceiver of FIG. 1;

FIG. 3 is an exploded perspective view of a transceiver subassembly;

FIG. 4 is a cutaway perspective view of a transmitter subassembly;

FIG. 5 is a top view of a flexible substrate for protecting optical fibers;

fig. 6 is a rear view of the flexible substrate of fig. 5.

Detailed Description

Details of the present invention, including exemplary aspects and embodiments thereof, will now be described. With reference to the figures and the following description, like reference numerals are used to identify similar or functionally similar elements and are intended to illustrate major features of the exemplary embodiments in simplified graphical form. Furthermore, the drawings are not intended to depict every feature of actual embodiments or relative dimensions of the depicted elements, and are not drawn to scale.

And in particular to fig. 1, there is provided an optical transceiver 100 for operating on an optical fiber of multiple photodetectors, and optical multiplexing and demultiplexing systems using multiple laser sources for both multimode (MM) and Single Mode (SM). This enables a single transceiver module to communicate across multiple protocols and at maximum distance from the target. The transceiver 100 and its housing 102 are designed to achieve maximum operating efficiency at an efficient cost and reduced electromagnetic interference (EMI) and thermal energy levels in industry standard form factor or package designs.

Transceiver 100 is advantageously manufactured in a modular fashion, preferably using three separately mounted circuit boards mounted on the housing transmitter subassembly, the receiver subassembly, and the protocol processing board, each board having specialized functionality and being electrically connected to each other using any flex circuit, mating multi-pin connectors, grounded gate arrays, or other electrical interconnect devices. This enables configuring the basic transceiver module to different protocols and can support the variation of different devices using simple subassembly configurations, thus minimizing manufacturing costs and eliminating the need to manufacture different transceivers for each different application. Additionally, the use of flex circuits or separable connectors to interconnect the boards allows for interchangeable board designs for the modules (e.g., receiver, transmitter, and PCS functionality, each on a separate board). Although the preferred design uses three plates, any two functions can be combined on a single plate for a more compact design.

The modular design of the board also enables the heat sensitive components to be placed in a desired location relative to the heat generating components (lasers and ICs) inside the module housing 102. It also makes it convenient and practical to independently test and inspect separate module subassemblies prior to final assembly. In addition, the bending or other interconnections allow for the fabrication of a wide variety of plates (PX, TX, PCS) to be performed in parallel instead of continuously, thus reducing the fabrication time for the entire cell.

Referring now to fig. 1 and 2, an exemplary optical transceiver module 100 has been shown in accordance with a preferred embodiment of the present invention. In this particular embodiment, the module 100 accommodates the IEEE 802.3ae 10GBASE-LX4 physical media dependent sublayer (PMD) and the XENPAK (TM) form factor. It should be noted, however, that the configurable transceiver module 100 operates under a wide variety of other compliant protocols (e.g., fibre channel or SONET) and is produced in a wide variety of alternative form factors such as X2. Module 100 is preferably a 10 gigabit Coarse Wavelength Division Multiplexing (CWDM) transceiver having four 3.125Gbps distributed feedback lasers and providing 300 meter transmission over conventionally installed multimode fiber and 10 to 40km transmission over standard single mode fiber.

Transceiver module 100 includes a two-piece housing 102 having a base 104 and a cover 106. Additionally, the provision of contact strips 152 also grounds the module to the chassis ground. The housing 102 is constructed of die cast or milled metal, preferably die cast zinc, although other materials, such as specialty plastics and the like, may be used as well. Preferably, the use of special materials in the housing construction helps reduce EMI. Further reduction of EMI may be achieved by using castellations (not shown) formed along the edges of the housing 102.

The front end of the housing 102 includes a faceplate 132 for protecting the pair of receptacles 124, 126. The receptacles 124, 126 are configured to receive fiber optic connector plugs 128, 130. In the preferred embodiment, the connector receptacles 128, 130 are configured to receive industry standard SC duplex connectors (not shown). Likewise, keyed channels 132 and 134 are provided to ensure that the SC connectors are inserted into their proper orientation. Moreover, as shown in the exemplary embodiments and discussed further herein, connector receptacle 130 receives an SC transmit connector and connector plug 128 receives an SC receiver connector.

Specifically, the housing 102 possesses three circuit boards, including a transmit board 108, a receive board 110, and a material mode sublayer (PCS)/material media attachment (PMA) board 112, which is used to provide an electrical interface to an external electrical system (not shown). An optical Multiplexer (MUX)114 is bonded TO the transmitter board 108in the TO-can via a combination of four Distributed Feedback (DFB) lasers 116. A laser mount 118 is used to secure the laser 116 in place at the bottom of the housing 102. Laser mount 118 may also function as a heat sink for cooling laser 116. In addition, the transmitter board 108 and the receiver board 110 are connected to the PCS/PMA board 112 by separate flex interconnects 120, or other board-to-board connectors. Thermally conductive gap pads 160 and 161 are provided to route heat generated by the laser or other components to the base 104 or cover 106 of the housing, which acts as a heat sink. The receiver subassembly 110 is mounted directly on the housing base 104 using a thermally conductive adhesive to achieve heat dissipation. The different sub-assemblies thus distribute the heat to different parts of the housing for more uniform heat dissipation. The outputs of the four lasers 116 are then followed as illustrated in fig. 1, 5 and 6To the optical MUX 114. The MUX114 is mounted on the flexible substrate 140. The substrate 140 may be a photo-flexible flat material such as FlexPlane available from Molex, inc^TMBut other flexible substrates may be used. As shown, the optical fibers 117a, 117b, 117c, 117d originating from the laser assembly 116 and to be input to the MUX114 are mounted onto the substrate 140. The output of the MUX114 that is sent to the transmit connector insert 130 is also attached to the substrate 140. The transmission in this manner and the optical fibers 117a, 117b, 117c, 117d minimize abrupt bends in the optical fibers to avoid optical losses and mechanical failure.

The substrate 140 contains an opening 142 or hole in a portion of the material directly over the retimer IC or other heat generating component mounted on the PCS/PMA board 112, the general area of the opening 142 being the size of the unused portion of the substrate 140, allowing the heat sink on the lid to contact the heat transmitting gap pad 160 so that access to the board mounted components is provided. This area will normally be inaccessible if not for the reason of the opening 142. For example, heat sinks may be installed in the clock and data recovery components 202, 208 to allow access to the PCS/PMA board 112 without interference from fiber optic transmissions on the substrate 140 and without moving the mounted substrate 140.

Some additional advantages are realized when using a flexible substrate 140. Specifically, attaching the optical fibers to the substrate 140, rather than allowing the optical fibers to move freely within the transceiver module housing 102, neatly maintains the routing of the optical fibers to prevent unnecessary tangling and breakage during assembly of the transceiver. Furthermore, attaching the optical fiber to the substrate 140 greatly reduces the stress on the optical fiber, thus reducing the occurrence of micro-cracks formed in the optical fiber coating.

Fig. 2 illustrates an exemplary functional block diagram of the transceiver 100, as shown therein, the transceiver 100 includes a slave component (slave) MDIO/MDC interface 200 that interfaces to an off-board master (master) MDIO/MDC 190 in order to control the operation of the transceiver 100. The transmit section of the transceiver 100, which receives signals from the Media Access Controller (MAC)180, includes a clock and data recovery module 202 with lane alignment functionality, one or more laser drivers 204 for driving the DFB laser assembly 116 for output. The receive portion of transceiver 100, which provides signals to external MAC180, includes a clock and data recovery module 202 with XAUI lane alignment functionality.

The clock data recovery module 202 receives signals from a square transimpedance amplifier/limiting amplifier (TIA/LIA)210, and the square transimpedance amplifier/limiting amplifier (TIA/LIA)210 receives signals from a square InGaAs PIN 212. An optical demultiplexer 214 receives the light beam into the transceiver 100 and passes the demultiplexed light beam onto the InGaAs PIN 212. Transceiver 100 communicates with MAC180 via a 10 gigabit extended attachment unit interface (XAUI) compatible electrical interface 188. Communication between the XAUI interface 188 and the MAC180 is accomplished through an external IEEE 802.3ae compliant 10 gigabit media independent interface (XGMII)184, an XGMII extender sublayer (XGXS)186, and a Reconciliation (Reconciliation) sublayer 182.

The interchangeable PCS/PMA board 112 includes an MDIO/MDC 200, clock and data recovery retiming circuits 202, 208, and an on-board reference clock operating at 156.25 MHz. Other protocols such as fibre channel may be supported by similar boards. The slave component MDIO/MDC 200 is interfaced to the master MDIO/MDC 190 using IEEE45 electrical specifications and to the clock and data recovery modules 202, 208 using IEEE22 electrical specifications. The slave component MDIO/MDC 200 is also bonded to the square laser driver 204 and the square TIA/LIA 210. The functionality of the slave component MDIO/MDC may be implemented using a field programmable gate array (EPGA) or a microcontroller. Further, the MDIO/MDC 200 is bonded to EEPROM201 or other persistent memory for additional functionality. For example, EEPROM201 may be used to implement control and diagnostic capabilities, start configuration parameters, manufacture data, serial numbers, or other data within the transceiver itself.

The MDIO/MDC 200 enables highly secure operation of the transceiver 100, which is a slave to the off-board master MDIO/MDC 190. One particular advantage of the master/slave configuration of the MD 10 device in the present invention is that the EPGA allows the operator to control the laser and other transceiver functions and prevents reprogramming from outside sources by malicious programs or functions. This is possible because only predetermined functions or programs (which the operator considers to be approved) are executable on the dependent component MDIO/MDC 200.

The launch pad 108 contains a square laser driver 204, and the four DFB laser assemblies 116 are bonded to the launch pad 108 by the square laser driver 204. Advantageously, because a configuration of four separate lasers is used, a lower speed and lower cost driver can be used, and at a longer distance target, as opposed to a single laser. One of the transceiver form factor types used in the 10 gigabit ethernet market is the XENPAK LX4 transceiver. This transceiver is based on the extensive wavelength division multiplexing (WWDM) in which the optical signal consists of four widely spaced wavelengths transmitted over a single optical fiber. Receivers require light from a single fiber to be split, or demultiplexed, onto individual photodetectors. Each photodetector converts its respective optical signal into an electrical signal.

In the case of the WWDM receive section (section), there is a need for a separate photodetector for each wavelength. It is clear that the use of a photodetector in a separate sealed can results in a large receiving section for this multi-wavelength receiver. Alternatively, the present invention takes the approach of using a single empty multi-element photodiode array 220 mounted directly onto a circuit board 222 containing the amplifier/limiter circuitry.

Referring to fig. 1 and 3-6, a receiver subassembly 224 with a circuit board 222 serves as an optical bench for attachment and alignment of a demultiplexer 226 to the photodiode array 220. Specifically, there is shown a reduced optical demultiplexer 226 that corrects to the photodiode array 220, resulting in a compact receive section. The circuit board 222 serves not only as a substrate for the circuitry, but also as an optical bench for the optical elements. In particular, the surface of the circuit board 222 serves as an optical reference surface 228 for the optical assembly. Optionally, the receiver board 222 is a Printed Circuit Board (PCB) formed of PCB material having a higher glass content and providing less signal loss at high Radio Frequency (RF) operation than less expensive PCB material. A suitable material is Rogers RO4003 available from Rogers corp. of Chandler, Arizona. Which is less expensive than either ceramic or silicon. The use of ceramic or silicon provides the ability to compact the package.

The surface of the circuit board 222 is an optical reference plane 228. The top surface of the photodiode array 220 is set at a predetermined height by controlling its thickness within 50 μm and the thickness of its attachment material such as glue or solder 230. Also attached to this surface is a demultiplexer 226. Demultiplexer output 232 is thus at a predetermined height within 50 microns above photodiode array 220.

More specifically, the photodiode array 220 may vary in block-to-block thickness and be attached to the circuit board 222 by epoxy, soldering, or fusing (bonding) of variable thickness fusible metal. The frit material is fabricated to a thickness controlled such that the active surface of the photodiode is at a predetermined height above the surface of the circuit board so as to fit the focal point (focus) distance. The reduced optical demultiplexer 226 is then calibrated in a plane parallel to the photodiode array surface relative to the active area of the photodiode array 220. The demultiplexer 226 has a precise thickness such that when it is built on a light reference plane 228 defined by the surface of the circuit board, the light exit surface of the demultiplexer 226 is at the correct height above the photodiode array 226.

Utilizing and implementing the demultiplexer 226 in the present invention is preferably described in U.S. patent No. 6,542,306, and is hereby incorporated by reference herein, and includes a light block having an upper surface and a lower portion. The light block has at least one light element and a plurality of wavelength selective elements and reflectors. The optical block is specifically positioned on top of the beam directing member. In a preferred embodiment of the invention, both the light block and the beam directing means are optically transparent.

Specifically, at least one light element is typically disposed on an upper surface of the optical block, as described in the above noted U.S. patents. Its function is primarily to concentrate and direct the multi-wavelength optical signal along a designated optical signal path. In addition, the wavelength selective element is typically disposed below the upper surface of the optical block. The wavelength selective element is designed and operative to receive an optical signal from the optical element. Also, a plurality of reflectors are typically disposed on the upper surface of the optical block and opposite the wavelength selective element. Due to this strategic positioning and orientation, the reflector is capable of directing light signals from one wavelength selective element to an adjacent wavelength selective element. Thereafter. A guiding beam member, disposed at about the lower portion of the light block, operates to redirect and concentrate the light signal from the wavelength selective element to the photodiode array 220. Although the demultiplexer described above is preferred, other optical configurations for demultiplexing signals may be used, and such alternative configurations are within the scope of the present invention.

The present invention implements a transceiver 100, the transceiver 100 utilizing four standard, commercially available fiber pigtailed (Pigtailed) lasers 116 that are spliced to a fused double taper (FBT) coupler 114 to collect and multiplex the laser radiation into a single fiber. Optical fibers are used in the fiber pigtailed laser 116 and the FBT114 is attached to the flexible substrate material 140. This prevents the optical fibers from tangling and breaking but remains easily bendable and therefore works together easily. The flexible substrate material 140 may be an optically flexible planar material, such as Flexplane, available from Molex^TMInc, of Lisle, IL, or Kapton Delaware available from Dupont de Nemours and Company of Wilmington Delaware^TM. Other flexible substrates may also be used. A uniform coating is used throughout the bend 140 for protecting the fiber onto the bend 140.

As noted previously above, some additional advantages will be appreciated when using a flexible substrate 140 rather than allowing the optical fibers to move freely within the transceiver module housing 102, keeping the routing of the optical fibers uncluttered against unnecessary entanglement. Furthermore, attaching the optical fiber to the substrate 140 greatly reduces the stress on the optical fiber, thus reducing the occurrence of micro-cracks formed in the coating of the optical fiber. Routing and attaching the optical fiber in this manner causes a sharp bend in the optical fiber.

Additional modifications and improvements of the present invention will also be apparent to those skilled in the art. Accordingly, the particular combination of parts described and illustrated herein is intended to represent only a certain embodiment of the present invention and is not intended to serve as a substitute device limited within the spirit and scope of the present invention. The techniques and apparatus of the various aspects related to the protocol processing aspects of the invention may be implemented in digital electronic circuitry, or in computer hardware, firmware, software, or in combinations of them. The apparatus of the present invention may be implemented in a computer product, tangibly incorporated into a readable machine storage device for execution by a programmable processor, or incorporated in software located at a website or web site that may be downloaded to the transceiver automatically or on demand. The foregoing techniques may be implemented, for example, by a single central processing unit, multiple processors, one or more digital signal processors, a gate array of logic gates, or hardwired logic for executing a sequence of signals or programs as directed, to implement the functions of the present invention by operating on input data and generating output. The method may advantageously be implemented in one or more computer programs executable on a programmable system including at least one programmable processor coupled to receive data and instructions, to form, and to transmit data and instructions, a data storage system, at least one input/output device, and at least one output device. Each computer program can be implemented in a high-level procedural or object-oriented programming language, or in assembly or machine language if desired; and in any case, the language may be an editable or a translated language. By way of example, suitable processors include both general and special purpose microprocessors. Typically, a processor will receive instructions and data from a read-only memory and/or a random access memory. Memory devices suitable for tangibly embodying computer program instructions and data include all forms of persistent memory, including by way of example semiconductor devices, such as EPROM, EEPROM, and flash memory devices; magnetic disks such as internal hard disks and removable disks; magneto-optical disks; and CD-ROM disks. Any of the above may be supplemented by, or incorporated into, specially designed application-specific integrated circuits (ASICS).

It will be understood that each of the elements described above, or two or more together, may likewise find a useful application in other types of constructions differing from the types described above.

Although the invention has been described and illustrated as embodied in a transceiver for an optical communications network, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly establish the essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

Claims (10)

1. An optical transceiver for converting and coupling an electrical signal containing information through an optical fiber, comprising: a housing comprising an electrical connector for coupling with an external cable or information system device and for transmitting and/or receiving an electrical communication signal containing information; a fiber optic connector adapted to couple with an external optical fiber for transmitting and/or receiving an optical communication signal; and a base member and a cover member forming a pluggable module;

a transceiver subassembly in the housing, comprising: (i) first and second lasers operating at different wavelengths and being modularized by first and second electrical signals for emitting first and second laser beams, respectively; (ii) an optical multiplexer for receiving the first and second beams and multiplexing the optical signals into a single multi-wavelength beam, coupled to the fiber optic connector for transmitting the optical signal to an external optical fiber; and (iii) a first electrical interconnect;

a receiver in the housing, comprising: an optical demultiplexer coupled to the fiber optic connector for receiving an information-containing multi-wavelength optical signal having a plurality of different predetermined wavelengths, and demultiplexing the optical signal into different optical beams corresponding to the predetermined wavelengths; a plurality of photodiodes, each of the plurality of photodiodes disposed on a support in the path of a different light beam, the photodiodes functioning to convert the respective light signals into an electrical signal, and a second electrical interconnect for transmitting the electrical signal; and

a communication protocol processing subassembly in the housing for processing the communication signal into a predetermined electrical or optical communication protocol supporting at least a 10 gigabit data rate.

2. The optical transceiver of claim 1, further comprising a rigid electrical interconnect mounted on the communication protocol processing subassembly.

3. The optical transceiver of claim 1, the communication protocol processing subassembly comprising a third interconnect connected to the first interconnect of the transceiver subassembly and a fourth interconnect connected to the second interconnect of the receiver subassembly.

4. The optical transceiver of claim 3, wherein one of the first and third electrical interconnects and the second and fourth electrical interconnects comprise flexible electrical interconnects.

5. The optical transceiver of claim 3, wherein one of the first and third electrical interconnects and the second and fourth electrical interconnects comprise rigid electrical interconnects.

6. The optical transceiver of claim 1, comprising one or more thermally conductive gappads in contact with at least one of the lasers and at least one of the base member and lid member.

7. The optical transceiver of claim 1, comprising (1) at least one of one or more thermally conductive gap pads in contact with at least one heat generating component of the communication protocol processing subassembly and at least one of the base member and cover member, or (2) a thermally conductive gap pad between at least one of the subassemblies and the housing for dissipating heat from the at least one subassembly.

8. The optical transceiver of claim 1, wherein the multiplexer is mounted to a flexible substrate.

9. The optical transceiver of claim 8, comprising a plurality of optical fibers disposed within the housing extending between the first and second lasers and the multiplexer; wherein the plurality of optical fibers are mounted to the flexible substrate.

10. The optical transceiver of claim 1, at least one of the subassemblies being mounted directly to the housing using a thermally conductive material.