GB2330425A - Fiber optic assembly with lenses, mirrors and alignment projections - Google Patents

Abstract

A fibre optic assembly has a housing receptacle 18 for mating with a ferrule 17, an optical assembly comprising, in order, a first lens, a first mirror, a second mirror and a second lens, and alignment projections adjacent the receptacle for aligning a light path to an optic fibre in the ferrule. Optical transmitter 20 and receiver 21 are shown. The optical axis of the transmitter and/or receiver may be perpendicular to the fibre optic axis (Fig.7).

Description

1 FIBER OPTIC ASSEMBLY 2330425 This invention relates to a fiber optic

assembly for use, for example, in small-scale transmitter, receiver, or transceiver fiber optic modules.

In filber optic communications, similar to other electronic applications, high-density packaging is a critical issue. The number of fiber optic modules that can be positioned along the edge of a Printed Circuit Board (PC13), as might be found inside a fiber optic based Local Area Network (LAN) hub, significantly impacts the per channel cost and therefore the cost of transferring data through the hub. The correlation between module width and cost is so strong that decreasing the module width by half can reduce the per channel cost by half, due to the ability to double the number of fiber connections to a given PCB. This has resulted in a strong need for narrower modules and narrower connectors to interconnect the modules.

In the prior art, fiber optic modules have been limited in size due to the physical size of the connectors and the need to separate the transmitter channel from the receiver in order to provide electrical and optical separation between the transmit and receive channels. Emerging connectors, i.e. the Mitil-Nlechanically-transferable Pusli-On (Nllnl- MPO), are much smaller in size but present the fibers to the module with a small separation between transmit and receive channels, 750 im separation for the mini-MPO. The mechanical interface between the MPO connector or Mint-IMPO connector and the optical elements within the module has been a pair or precision alignment pins. These compact fiber optic connectors. though highly desirable, present a significant challenge because the optical paths are much closer together than it is practical to place the transmitter and receiver.

2 The present invention seeks to provide an improved fiber optic assembly.

According to an aspect of the present invention there is provided a fiber optic assembly for connecting to a ferrule having optical fibers comprising:

a house receptacle for mating to the ferrule.

an optical assembly, having a light path, including a first and second mirror, a first lens positioned adjacent the first mirror, a second lens positioned adjacent the second mirror, an optical device positioned adjacent the second mirror, and wherein the light path is defined as the path between the optical fibers to the first lens to the first mirror to the second mirror to the second lens to the optical device; and alignment projections, positioned adjacent the receptacle, for aligning the light path to the optical fibers within the ferrule. The preferred embodiment can provide a fiber optic module that is small and economically manufacturable, which is highly desirable. It is beneficial that the solution can separate transmit and receive signals while providing adequate spacing for ENfl shielding, environmental protection, and physical separation between the transn-dtter and receiver devices.

In addition, the preferred embodiment can enable the optical emitter and detector to be actively aligned to the fiber and lens system. Because of piece part tolerance problems, it is difficult to align the optical devices to the fiber in high volume manufacturing without an alignment system. Thus, it is further desirable for the optical devices to be packaged in Transistor Outline (TO) style cans. Thus, the emitter and receiver can be easily aligned along the x, y, z axes to optimize the optical path coupling 1 3 In the preferred embodiment, a compact fiber optic module is constructed by folding the internal light paths using mirrors and focusing the beams on either end. This design allows for six degrees of freedom in the position of the device with respect to the fiber since the devices can be located in any rotational position, e,,, ey, and ez.

In one embodiment, two optical devices within a housing are positioned close to one another using conventional mounting techniques. These two devices are too far apart to directly couple to the fibers contained within the Mini-MPO connector. Each device has a corresponding light path. For each device, the light path is folded using mirrors and collimated using lenses. An alignment plate is positioned between a the fiber optic cable and the collimating lens such that the light paths are aligned with the fibers to the micron level accuracy required for acceptable coupling efficiency.

Another embodiment integrates the lenses and the mirrors into a single optical element by using the internal surfaces of the optical element as Total Internal Reflectors (TIR) to fold the light path. In an alternate embodiment, no alignment plate is used and the alignment features are incorporated in the same piece as the lenses.

4 An embodiment of the present invention is described below, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 shows a prior art example of optical devices coupled to fibers.

Figure 2 schematically shows the optical elements and optical path of a preferred embodiment of transmitter.

Figure 3 schematically shows the optical elements and optical path of a preferred embodiment of receiver.

Figure 4 illustrates a Transceiver (Transmitter and Receiver) Module in which the optical devices are contained in windowed TO Cans.

Figure 5 illustrates a Transceiver Module in which the optical devices are contained in lensed TO Cans.

Figure 6 shows an alternative embodiment where the lens and mirror functions are combined into curved, reflecting surfaces.

Figures 7A and 7B show an alternative embodiment where the optical axis of the transmitter and/or receiver is perpendicular to the optical axis of the fibers.

Figure 1 Illustrates the prior art connection between a solid-state optical device 1 and an optical fiber 4. In this sketch. the optical device 1 represents a transmitter. The light 2 is shown in dashed arrows while lens 3 is shown in cross section. Typically, the lens 3 can be either a simple lens or a compound lens. The inherent optical axes of device 1, the lens 3, and the fiber 4 are aligned passively or actively to maximize optical coupling.

In the prior art, the device must be on, or close to, the optical axis of the fiber. The position of the device in the package is fixed with respect to the position of the fiber in the mating fiber optic cable. The z-axis position can be modified by changing the design of the lens but the position in the x and y axes is constrained to be on the optical axis of the fiber. Similarly, the rotational orientation is severely constrained in the prior art. The device can be placed at any orientation in Q, but the optical axis of tile device must always be parallel to the optical axis of the fiber so the 0, and OY rotations are entirely constrained.

Figure 2 silo-vs,s a schematic illustration of one embodiment of the invention, as it pertains to coupling an optical transmitter 5 to an optical fiber 10. Light emanating from the transmitter 5 is collimated by lens 6 to a parallel, or near parallel beam. A parallel beam is used in this embodiment for simplicity and ease of explanation, although any beam profile that results from the positioning of the optical elements of the invention and ultimately couples the light source 5 to the Fiber 10 can be implemented. The optical transmitter 5 can be a Surface Light Emitting Diode (SLED). Edge Light Emitting Diode (ELED), Vertical Cavity Surface Emitting Laser (VCSEL), or edge emitting laser.

To aid product manufacturability, the lens 6 may take the form of a compound lens, wherein the first lens is attached to the transmitter's packaging (e.g. a lensed TO-Can header, to facilitate hermetic scaling of the LED against the environment) and the second lens is used to collimate the light from the focussed spot proceeded by the lensed can. Light is then ultimately coupled to the fiber 10.

Two mirror surfaces 7. 8 affect the three dimensional translation of the beam emanating from lens 6. These mirror surfaces may be at whatever angle is needed to achieve the coupling 6 between the transmitter 5 and fiber 10. The transmitter 5 may not necessarily be in the same orthogonal plane as the fiber 10. Lens 9 focuses the beam reflected from mirror 8 to the fiber 10. By positioning the first mirror 7 and the second mirror 8, the transmitter may be placed in any position or orientation within the housing (not shown).

Figure 3 illustrates the equivalent embodiment for the coupling of light from a fiber 16 to an optical receiving device 11. Lens 12 may also be a compound lens and mirror surfaces 13 and 14 affect the three dimensional beam translation. A second lens 15, positioned near the fiber, may be a collimating lens.

Figure 4 illustrates an alternative embodiment, the Mini-Mechanically Transferable (Mini-MT) ferrule 17 as it mates with the Optical SubAssembly (OSA) of a transceiver module. The OSA includes a plate 18, the optical piece part 19, TO style cans 22, 24, the TO style headers 23, 25, an optical transmitter 20, and an optical receiver 2 1. The OSA is contained within the housing (not shown) of the transceiver module (not shown). The transceiver module is defined as the elcctro-optical component that converts electrical signals to optical signals and includes the housing, OSA, electronics and a connector which mates with the Mini-MPO connector. The Mini-MT feiTtile 17 houses the two fibers that are spaced apart by 750 gm. This NAini-MT ferrule would be part of the Mini-MPO connector (not shown) on the optical cable which provides the interconnection between transceiver modules or between transceiver modules and other optical cables. A plate 18, with suitable protrusions for location with the lvllnl-MT ferrule, is used to ensure correct alignment between the fibers and the optical element 19. This assembly performs the functions shown in Figures 2 and 1 In this embodiment, both the transmittim, device 20 and receiving device 2 1 are protected from the environment by TOstyle window cans 22, 24 atlached to TO-style headers 23, 25. In this embodiment, all of tile optical surfaces are molded in a single transparent plastic lens piece 19. The lens surfaces are molded in the plastic lens piece 19 and the mirrors are TIR surfaces i-nolded into this optical part 19.

1 7 Figure 5 illustrates another embodiment using lensed TO cans 3 1, 33, instead of window cans 22, 24.

Figure 6 shows a schematic of another embodiment where the lens and the mirroring functions are combined into a single curved, reflecting surface 38 to couple the optical device 35 to the axis of the optical fiber 37.

Figures 7A and 713 show a schematic of another embodiment where the optical axis of the transmitter 38 and/or receiver 39 is perpendicular to the optical axis of the fibers 40. Figure 7A illustrates a front view while Figure 713 illustrates a top view. In this case, the transmitter 38 and the receiver 39 are placed on the Electrical SubAssembly (ESA) 41 within the module rather than being placed in separate TO Cans.

In all of the embodiments, a feature of the assembly is active aligrunent of the semiconductors in the TO cans to the images of the fibers as transferred by the lens assembly. This is typically accomplished by moving the cans in the x, y, and z directions to maximize the transmitted signal. The cans are then fixed in place with a quick curing adhesive.

The disclosures in United States patent application no 08/944,394, from which this application claims priority, and in the abstract accompanying this application are incorporated herein by reference.

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Claims (20)

1. A fiber optic assembly for connecting to a ferrule having optical fibers comprising: a housing receptacle for mating to the ferrule; an optical assembly, having a light path including a first and second mirror, a first lens positioned adjacent the first mirror, a second lens positioned adjacent the second mirror, an optical device positioned adjacent the second mirror; and wherein the light path is defined as the path between the optical fibers to the first lens to the first mirror to the second mirror to the second lens to the optical device; and alignment projections, positioned adjacent the receptacle, for aligning the light path to the optical fibers within the ferrule.

2. A fiber optic assembly as in claim 1, wherein the optical device is a receiver.

3. A fiber optic assembly as in claim 2, wherein the first lens is a collimating lens.

4. A fiber optic assembly as in claim 2 or 3, wherein: the first and second mirrors are total internal reflection surfaces; and the first and second mirrors, and the first and second lenses are integrated into a single transparent block.

5. A fiber optic assembly as in claim 4, wherein the alignment projections are integrated into the single transparent block.

6. A fiber optic assembly as in any one of claims 2 to 5, including an alignment plate, wherein the alignment projections are attached to the alignment plate.

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7. A fiber optic assembly as in any one of claims 2 to 6, wherein the first and second mirrors are parallel.

8. A fiber optic assembly as in claim 2, including a second optical subassembly, wherein the second optical device is a transmitter.

9. A fiber optic assembly as in claim 8, wherein: for each optical subassembly, the first and second mirrors are total internal reflection surfaces; and the first and second mirrors, and the first and second lenses are integrated into a single transparent block.

10. A fiber optic assembly as in claim 9, wherein the aligriment projections are integrated into the single transparent block.

11. A fiber optic assembly in any one of claims 8 to 10, including an alignment plate, wherein the alignment projections are attached to the alignment plate.

12. A fiber optic assembly as in any one of claims 8 to 11, wherein for each optical subassembly, the first and second mirrors are parallel.

13. A fiber optic assembly as in any one of claims 8 to 12, wherein the second lens of the second optical subassembly is a collimating lens.

14. A fiber optic assembly as in claim 1, wherein the optical device is a transmitter.

15. A fiber optic assembly as in claim 14, wherein the second lens is a collimating lens.

16. A fiber optic assembly as in claim 14 or 15, wherein: the first and second mirrors are total internal reflection surfaces; and the first and second mirrors, and the first and second lenses are integrated into a single transparent block.

17. A fiber optic assembly as in claim 16, wherein the alignment projections are integrated into the single transparent block.

18. A fiber optic assembly as in any one of claims 14 to 17, including an alignment plate, wherein the alignment projections are attached to the alignment plate.

19. A fiber optic assembly as in any one of claims 14 to 18, wherein the first and second mirrors are parallel.

20. A fiber optical assembly as in claim 1, wherein: the first lens and first mirror are combined into a first curved reflector; and the second lens and the second mirror are combined into a second curved reflector.

2 1. A filter optic assembly sustantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.