Integrated multiplexer/demultiplexer having offset transmitters and receivers for use in an optical transceiver module

An apparatus for use in an optical transceiver module that incorporates an integrated multiplexer/demultiplexer for high speed data transfer applications. One example embodiment includes a transmissive block arranged to interface with a transmit optical port, a receive optical port, and a plurality of optical subassemblies. The transmit optical port may transmit a first multiplexed optical signal and the receive optical port may receive a second multiplexed optical signal. Filters may be positioned between the transmissive block and one or more of the optical subassemblies to transmit signals at predetermined wavelengths while reflecting other signals incident thereon.

BACKGROUND

1. Technology Field

The present invention generally relates to optical communication modules. In particular, the present invention relates to an integrated assembly for use in an optical transceiver module that incorporates an integrated multiplexer/demultiplexer for high speed data transfer applications. A unique laser and detector arrangement may enable the assembly's use in compact transceiver module form factors.

2. The Related Technology

While the use of light transmissive blocks in multiplexing or demultiplexing optical signals is generally known, such designs suffer from various limitations. For example, the size of the blocks is relatively large, making them too large to be used in some transceiver package form factors, such as Xenpak, X2, etc. Also, assemblies using such transmissive blocks typically have prevented a preferred alignment to be achieved, such as between transmit and receive ports of the transceiver, or between these ports and the optical transmitters or optical detectors that are optically coupled to the block. Such blocks also usually require an isolator to be coupled to each optical transmitter in the case of a multiplexer. Use of multiple isolators in this manner can increase the relative size, complexity, and cost of the device.

In addition, such transmissive blocks have typically been utilized for either multiplexing or demultiplexing optical signals in a device, but not for both operations. As such, two separate devices must often be included in a device, such as a communications module, to perform the requisite multiplexing and demultiplexing operations.

In light of this, a need exists in the art for a single device that can perform both multiplexing and demultiplexing operations in a communications module. Further, any such solution should permit its use within modules having prevalent form factors, such as Xenpak, X2, etc.

BRIEF SUMMARY

In general, embodiments of the invention are concerned with apparatuses for multiplexing and demultiplexing optical signals. While disclosed embodiments are described as having particular applicability for use in high data-rate applications of 100 G/s, it will be appreciated that the embodiments would have equal applicability in applications of other data rates as well.

One example embodiment of the present invention is directed to an integrated multiplexing and demultiplexing assembly that comprises a transmissive block and a plurality of optical transmitter and detector subassemblies each being arranged to interface with a transmit optical port and a receive optical port through the transmissive block. A first optical subassembly may be associated with a first wavelength, a second optical subassembly may be associated with a second wavelength, and so on.

A first filter may be positioned between the transmissive block and the first optical subassembly to transmit signals associated with the first wavelength while reflecting other signals incident thereon. Likewise, a second filter may be positioned between the transmissive block and the second optical subassembly to transmit signals associated with the second wavelength while reflecting other signals incident thereon. Thus, optical signals comprising multiple wavelengths may be multiplexed and transmitted to the transmit optical port. Similarly, optical signals comprising multiple wavelengths may be received from the receive optical port and demultiplexed.

DETAILED DESCRIPTION OF SELECTED EMBODIMENTS

Reference will now be made to figures wherein like structures will be provided with like reference designations. It is understood that the drawings are diagrammatic and schematic representations of exemplary embodiments of the invention, and are not limiting of the present invention nor are they necessarily drawn to scale.

FIGS. 1-6depict various features of embodiments of the present invention, which are generally directed to an integrated multiplexer (“mux”)/demultiplexer (“demux”) assembly for use in a communications module, such as an optical transceiver module. The integrated mux/demux assembly is a single device and as such can perform both the optical signal multiplexing and demultiplexing functions of the transceiver module, especially in high data-rate applications of 100 G/s. Further, the integrated mux/demux assembly is a compact solution that can be housed in various transceiver and device form factors, including Xenpak, X2, LX4, etc.

Reference is first made toFIGS. 1A and 1B, which show an integrated mux/demux assembly (“assembly”) in a simplified top view, according to one embodiment. The assembly may include 10 optical transmitters or lasers L1-L10. The lasers can be FP, DFB, or VCSEL laser type, or can be any other suitable light source. Each laser may include a lens suitably positioned adjacent thereto, as described further below. The lasers L1, L3, L5, L7, and L9may be arranged laterally and in parallel along a first surface of an optically transmissive block G1, while the lasers L2, L4, L6, L8, and L10may be arranged laterally and in parallel along a second surface of the transmissive block. So positioned, the lasers may be aligned along a common plane on either side of the transmissive block.

FIG. 1Aalso shows a set of optical receivers or detectors D1-D10, which can be PIN detectors, APDs, or other suitable photodetectors. Like their laser counterparts, each detector may include a lens suitably positioned adjacent thereto, as described further below. The detectors D1, D3, D5, D7, and D9may be arranged vertically and in parallel along the first surface of the transmissive block G1, while the detectors D2, D4, D6, D8, and D10may be arranged laterally and in parallel along the second surface of the transmissive block. Each detector D1-D10may be positioned proximate its similarly numbered laser L1-L10in a manner further described below. As shown inFIG. 1A, the above configuration results in 10 optical subassemblies, each comprising a laser/detector pair, arranged along the first and second surfaces of the transmissive block, with each detector being offset from its respective laser by an angle, e.g., approximately 90 degrees (best seen inFIG. 1B).

In the present embodiment shown inFIGS. 1A and 1B, each laser or detector may have an edge-to-edge spacing of approximately 0.5 mm or more to ensure sufficient mechanical stability. Also, a center-to-center distance between adjacent lasers or detectors may be at least 6.1 mm; in this embodiment the center-to-center spacing is approximately 6.54 mm. In this case, with five laser/detector pairs disposed on either side of the transmissive block, the required transmissive block length is at least 30.5 mm, approximately.

Ten filters F1-F10may be included in the integrated assembly, one for each laser/detector pair (e.g., see filters F1and F2inFIG. 1B). In one embodiment, each filter is a thin film filter attached to the transmissive block G1that is configured according to the particular wavelength emitted or absorbed by the respective laser and detector with which they are operably positioned. So configured, the particular thin film filter allows passage therethrough of the optical signal having a wavelength corresponding to the respective laser and detector to which it is operably connected while reflecting all other wavelengths.

Operably attached to each filter may be a reflective prism P1-P10configured to redirect a received optical signal transmitted from the transmissive block G1and through the filter to the respective detector of the laser/detector pair (e.g., see prisms P1and P2inFIG. 1B). Each detector and corresponding prism may be positioned slightly offset with respect to the laser in order to enable the transmit optical signal produced by each laser to enter the corresponding filter unimpeded. So configured, each filter and corresponding prism may form a filter/prism assembly. In one embodiment, each prism is attached to its respective filter by suitable adhesive having a similar index of refraction to the prism, filter and/or transmissive block.

As mentioned, the optical signal-transmissive block G1is included as the core of the integrated assembly. The filter/prism assemblies may be operably connected at predetermined locations to the block G1in order to transmit and pass optical signals to and from the block, as further described below.

Two master prisms, transmitter port prism TxP and receiver port prism RxP, may also be positioned with respect to and operably connected with the transmissive block G1in order to redirect multiplexed optical signals from the block into a respective transmitter port TX (FIG. 5A) or to the block from receiver port RX (FIG. 5A). Each of the TX port and the RX port can include a lens as needed, and the TX port may include a free space, dual stage isolator.

A high reflection coating R may be applied to the surfaces of the block G1where reflection of optical signals within the block is desired, namely, between the locations of the filters. Note that no reflective coating is applied at the points of operable attachment of the filters and the master prisms TxP, RxP to the block G1.

As described, the integrated assembly shown inFIGS. 1A-1Band described above simultaneously mutliplexes and demultiplexes optical signals as a single device. Multiplexing of optical signals by the integrated assembly proceeds in one embodiment as follows: laser L1emits a beam having a wavelength λ1, which passes through the attached lens and filter. As described, the filter for laser L1is configured so as to allow passage of the beam of laser L1having wavelength λ1.

After passage through the filter F1, the beam from laser L1enters the block G1and is then repeatedly reflected in a crisscross path along a reflective “transmit path” through the block by a selected combination of the reflective coatings R, filters, and prism TxP until its entry into the TX port. Specifically, the trace of this beam is: F1, F2, R1-3, R2-4, F3, F4, R3-5, R4-6, F5, F6, R5-7, R6-8, F7, F8, R7-9, R8-10, F9, F10, TxP, and TX port, wherein the numbers following the filter “F” designations indicate the laser/detector pair to which the filter is operably associated, and wherein the hyphenated numbers following the reflective coating designations indicate the portion of the reflective coating that is between the laser/detector pairs having those number designations.

Correspondingly, Laser L2emits a beam having wavelength λ2, which passes through the attached lens and filter F2. As described, filter F2is configured so as to allow passage of the beam of laser L2while reflecting all other incident beams having other wavelengths. After passage through the filter F2, the beam from laser L2enters the block G1and is then repeatedly reflected in a criss-cross path through the block by a selected combination of the reflective coatings R, filters F, and prism TxP until its entry into the TX port. Specifically, the trace of this beam is: F2, R1-3, R2-4, F3, F4, R3-5, R4-6, F5, F6, R5-7, R6-8, F7, F8, R7-9, R8-10, F9, F10, TxP, and TX port.

Laser L3emits a beam having wavelength λ3, which passes through the attached lens and filter F3. As described, filter F3is configured so as to allow passage of the beam of laser L3while reflecting all other incident beams having other wavelengths. After passage through the filter F3, the beam from laser L3enters the block G1and is then repeatedly reflected in a criss-cross path through the block by a selected combination of the reflective coatings R, filters F, and prism TxP until its entry into the TX port. Specifically, the trace of this beam is: F3, F4, R3-5, R4-6, F5, F6, R5-7, R6-8, F7, F8, R7-9, R8-10, F9, F10, TxP, and TX port.

Laser L4emits a beam having wavelength λ4, which passes through the attached lens and filter F4. As described, filter F4is configured so as to allow passage of the beam of laser L4while reflecting all other incident beams having other wavelengths. After passage through the filter F4, the beam from laser L4enters and traverses the width of the block G1and passes through prism TxP for its entry into the TX port. Specifically, the trace of this beam is: F4, R3-5, R4-6, F5, F6, R5-7, R6-8, F7, F8, R7-9, R8-10, F9, F10, TxP, and TX port.

In analogous manner, the beams of specified wavelength that are emitted by the lasers L5-L10follow along the corresponding portions of the reflective transmit path, which path is completely described by the path of the laser beam from L1, detailed above, until arrival at the master prism TxP, where they are passed into the TX port for transmission via an optical fiber (not shown) that is operably connected to the port. In this manner, the beams from each of the lasers L1-L10are combined via their introduction to the common reflective transmit path, resulting in a multiplexed optical signal that is transmitted from the TX port to the optical fiber.

The integrated assembly, as a single device, may also demultiplex incoming multiplexed optical signals that are received via the RX port. Demultiplexing of multiplexed optical signals may proceed in one embodiment as follows: a multiplexed optical signal containing wavelengths λ1, λ2, λ3, λ4, . . . , λ10is received through the RX port from an optical fiber (not shown) connected thereto. The multiplexed optical signal is reflected by prism RxP and into the transmissive block G1.

The optical signal having wavelength λ10may be transmitted in crisscross fashion across the block G1along a portion of a reflective “receive path” and to the filter F10corresponding to the laser/detector pair10. The filter F10may be configured so as to allow passage of the beam having wavelength λ10while reflecting all other incident beams having other wavelengths. Thus the optical signal having wavelength λ10may passthrough the filter F10, while the remainder of the multiplexed optical signal containing the wavelengths λ1-9may continue along the received path. After passage through the filter F10, the optical signal is redirected toward the detector D10by the prism attached to filter F10and is then is received by detector D10.

The multiplexed signal having remaining wavelengths λ1-9may continue along the crisscross reflective receive path through the block G1, as shown inFIG. 1A, until arriving at the filter F9corresponding to the laser/detector pair9. The filter F9may be configured so as to allow passage of the beam having wavelength λ9while reflecting all other incident beams having other wavelengths. Thus the optical signal having wavelength λ9may pass through the filter F9, while the remainder of the multiplexed optical signal containing the wavelengths λ1-8may continue along the received path. After passage through the filter F9, the optical signal may be redirected toward the detector D9by the prism attached to filter F9and may then be received by detector D9.

The multiplexed signal having remaining wavelengths λ1-8may continue along the criss-cross reflective receive path through the block G1until each optical signal component having a particular wavelength is transmitted through a corresponding one of the filters F5-F7, redirected by the accompanying prism, and received by the corresponding detector D1-D8. Thus each optical signal having one of the predetermined wavelengths λ1-8is separated, or demultiplexed, from the multiplexed optical signal. Accordingly, the trace of the last optical signal to be demultiplexed, wavelength λ1, is as follows: RxP, R9, F10, F9, R8-10, R7-9, F8, F7, R6-8, R5-7, F6, F5, R4-6, R3-5, F4, F3, R2-4, R1-3, F2, F1. In this manner, all wavelengths of the multiplexed optical signal may be acceptably received into the corresponding detectors.

Note that the present design enables the TX and RX port (FIG. 5A) to be positioned in parallel relation to one another. Further, the current design enables the lasers and detectors to be positioned perpendicular to the TX and RX ports. Thus, as shown inFIG. 5A, multiplexed optical signal paths defined between the transmissive block G1and the TX and RX ports may be substantially parallel with the lateral surfaces of the transmissive block G1along which the lasers and detectors are positioned. This feature facilitates use of the integrated assembly within transceiver packages having established form factors. It is also noted that the present design may be designed for acceptable operation in environments having industrial temperature ranges (−40 to 85 degrees).

The design described above in connection withFIGS. 1A,1B may involve only one isolator included in the TX port, in contrast with previous designs, which typically use one isolator for each laser device. The use of only one dual-stage, free space isolator equates to lower assembly cost and may be possible where: 1) the optical signals produced by the lasers L1-L10are polarized; and 2) the wavelength interval of the optical signals produced by the lasers L1-L10is relatively small.

Together withFIGS. 1A and 1B, reference is now made toFIGS. 2A-2B, which compares a transmissive block having reflective coatings, such as the block G1of the integrated assembly ofFIGS. 1A-1B, to a block without the reflective coatings. As can be seen, the reflective coatings R inFIG. 2Benable the same center-to-center distance between filters, which correspond with the laser-to-laser or detector-to-detector spacing to be achieved in the small block as in the larger block by virtue of the total internal reflection of optical signals within the small block. In one embodiment the smaller block inFIG. 2Bis about four times smaller than the comparable block inFIG. 2A. Notwithstanding the small size of the transmissive block, however, suitable separation distances between the lasers and detectors are still achieved such that adjacent lasers or adjacent detectors are not in physical or overlapping contact with one another. In one embodiment the transmissive block G1is composed of fused silica, though other suitable compositions can also be used. Fused silica desirably has a small coefficient of thermal expansion (C.T.E.). Note also that the transmissive block provides ample surface area for bonding with a housing (seeFIGS. 5A-5F) in which the integrated assembly is housed. Thus, the smaller block represents two distinct advantages in that it allows for adequate spacing between the lasers and detectors while maintaining a relatively small size. However, though the smaller transmissive block may be desired in certain applications, either block can be employed in embodiments of the present invention.

The two sides on the small block ofFIG. 2Bmay be configured to be parallel within about 2 microns tolerance. In one embodiment wherein the total light path distance from laser to TX port is approximately 100 mm, a tolerance of about 2 microns is readily achievable. Further, it is noted that the transmissive block of the present invention may be designed to exhibit good temperature and mechanical stability.

The reflective coatings R in one embodiment are composed of Ta2O5 and SiO2. Other embodiments can use other acceptable coating materials, including metallic and broadband dielectric coatings.

With respect to the optical signal passage through the filters F1-F10and the transmissive block G1, note that the angle of incidence of the filters is approximately 13.5 degrees on the air side and approximately 9.3 degrees on the transmissive block side, owing to the respective differences in index of refraction. Such filters are commercially available, which further facilitates a lower production cost for the integrated assembly. Of course, the filter and/or block can be modified to produce different angles of incidence, if needed or desired for a particular application.

FIG. 3illustrates that the position of the transmitter port prism TxP or receiver port prism RxP can be adjusted with respect to the block G1in order to direct the optical beam either to or from the TX port/RX port accurately. In one embodiment the prisms TxP and RxP are composed of fused silica and have a minor angle of 49.6 degrees, +/−0.1 degree. The prisms TxP and RxP may be bonded to the surface of the block G1by an epoxy or other suitable adhesive having an index of refraction sufficiently close to that of the composition of the prism and/or the block.

FIG. 4graphically describes the respective positioning of the laser and lens of the lasers L1-L10in order to produce an optical signal that propagates at an angled direction of travel with respect to the emitting surface of the laser. In this configuration, the emission point of the laser is positioned at the focal point of the lens but off-center with respect to the central axis of the lens, thereby producing the angled beam propagation. This configuration can also be employed in the respective positioning of the lenses included with the detectors D1-D10.

It is noted that, because each laser in the illustrated embodiment produces a relatively small beam spot of approximately 3 microns, and thereby will produce a relatively large divergent angle, the focal length of the lens should also be small, such as approximately 0.8-1 mm, in order to produce a suitably sized and collimated beam. In the present embodiment, each laser and lens may be positioned so as to produce a beam having a tilted angle of approximately 13.5 degrees, equal to the angle of incidence of the air side of the filters F1-F10. For each detector D1-D10, the focal length can be about 2 mm, owing to the relatively larger size of the sensitive area of the detector, about 40 microns. Note that the lens type can be any suitable type, including A or D-lenses, a Grin lens or ball lens.

FIGS. 5A-5Fshow various views of a housing in which the integrated assembly ofFIGS. 1A-1Bcan be housed, according to one embodiment. Also shown with the housing are the TX and RX ports through which the multiplexed optical signals pass during transceiver operation.

FIGS. 6A-6Dshow various views of a Xenpak transceiver package into which the housed integrated assembly ofFIGS. 5A-5Fcan be received. As mentioned, the integrated assembly can also be included in transceiver packages having a variety of form factors as well, including LX4, X2, etc. Again, because of its relatively small displacement, the integrated assembly can be fit into module form factors that cannot house other multiplexer and demultiplexer solutions. This is due in part to the combined mux/demux functionality of the integrated assembly.

Thus, the structure and design of the integrated mux/demux assembly described herein offers several advantages, including small size due to the unique arrangement of the glass block, integration of both mux and demux functionality in a single component, lower cost and device complexity via reduction of part count, and preferred orientation and arrangement of device components, including the TX port, RX port, lasers, and detectors.

In one embodiment, each laser of the integrated assembly is a 10 Gb/s laser. When multiplexed in the manner described above, the multiplexed optical signal output therefore represents a 100 Gb/s data stream. Similarly, the detectors of the integrated assembly are capable of receiving and processing a 100 Gb/s incoming optical signal, wherein each detector receives and processes a 10 Gb/s optical signal. Of course, in other embodiments the composite data rate of the integrated assembly can be altered by choosing individual lasers having data rates greater or lower than 10 Gb/s. In addition, it is also possible in other embodiments to vary the total number of lasers and detectors from the ten of each shown in the accompanying drawings in order to produce a different composite data rate capacity. In yet another embodiment, it is possible to have a number of lasers that is different than the number of detectors in the integrated assembly. The above modifications in the total number of lasers and detectors would, of course, alter the overall size of the integrated assembly.