Optoelectronic assembly with coupling features for alignment

Optical signals are increasingly used in communication networks to carry data. These communication networks use optoelectronic modules (such as optical transmitters, receivers, and transceivers) to transmit and receive optical signals.

In an optoelectronic module, a light source (such as a laser in a transmitter or an optical fiber in a receiver) must be accurately aligned with a lens and a target (such as an optical fiber in a transmitter or a photodiode in a receiver) in order for the optical signals to be properly routed through the communication network.

FIG. 1 shows a diagram of a conventional optical path in an optoelectronic transmitter 11 . The optoelectronic transmitter 11 includes a laser 13 , coupling optics 15 , and an optical fiber 17 . The coupling optics 15 receives light from the laser 13 and focuses it onto the optical fiber 17 . The coupling optics 15 is a single unit having a first lens surface 19 and a second lens surface 21 . Positioning the coupling optics is difficult because the first lens surface 19 must be aligned with laser 13 while simultaneously aligning the second lens surface 21 with the optical fiber 17 .

Consequently, active alignment is needed to carefully place each component such that the light from the light source will be focused exactly on the target. For example, during active alignment of the optoelectronic transmitter 11 , the laser 13 is switched on while the positions of the coupling optics 15 and optical fiber 17 are adjusted. The power of the optical signal received by the optical fiber 17 is measured. The laser 13 , coupling optics 15 , and optical fiber 17 are considered to be at an optimal alignment when the optical power measured is at a maximum level. At this point, the positions of the laser 13 , coupling optics 15 , and optical fiber 17 are fixed in place with respect to one another.

Active alignment is time consuming and expensive. It requires precision mechanical equipment to achieve the alignment, as well as optoelectronic test equipment to power and monitor the system.

In accordance with an aspect of the present invention, an optoelectronic assembly uses a lens system comprising a first lens to collimate light from a light source, and a second lens to focus the collimated light onto a target. The first lens is fixed in position relative to the light source, and the second lens is fixed in position relative to the target. The first and second lenses are aligned using components with features designed to couple together.

One specific embodiment of the invention is an optoelectronic assembly that includes an optical lens element (OLE) coupled to a substrate. The substrate includes a transducer, a standing structure on the transducer, a transducer lens supported by the standing structure over the transducer, and alignment features. The OLE includes an OLE lens and co-alignment features that couple with the alignment features on the substrate. When the substrate is coupled to the OLE, the transducer lens is aligned with the OLE lens.

In one embodiment, the alignment features on the substrate are plugs and the co-alignment features on the OLE are sockets. In another embodiment, the alignment features on the substrate are sockets and the co-alignment features on the OLE are plugs.

Further features and advantages of the present invention, as well as the structure and operation of preferred embodiments of the present invention, are described in detail below with reference to the accompanying exemplary drawings.

FIG. 1 shows a diagram of a conventional optical path in an optoelectronic transmitter 11 .

FIG. 2 illustrates an embodiment of an optoelectronic assembly.

FIGS. 3A–3C illustrate the optical lens element from several perspectives. FIG. 3A is a top view, FIG. 3B is a side view, and FIG. 3C is a rear view.

FIGS. 4A–4B illustrate the substrate from different perspectives. FIG. 4A is a top view, and FIG. 4B is a cross-sectional view taken through the dotted line 48 – 48 ′ in FIG. 4A .

FIGS. 5A–5C illustrate the assembled optoelectronic assembly. FIG. 5A illustrates a cross-sectional view of FIG. 2 taken through the dotted line 36 – 36 ′. FIG. 5B illustrates a cross-sectional view of FIG. 2 taken through the dotted line 37 – 37 ′. FIG. 5C shows an exploded view of the dotted box 63 of FIG. 5B .

FIGS. 6A–6B show an optoelectronic assembly in another embodiment made in accordance with the teachings of the present invention. FIG. 6B illustrates a cross-sectional view of FIG. 6B taken through the dotted line 82 – 82 ′.

Drawings are not to scale. Use of the same reference numbers in different figures indicates similar or identical elements.

FIG. 2 illustrates an embodiment of an optoelectronic assembly 31 , made in accordance with the teachings of the present invention. The optoelectronic assembly 31 includes an optical lens element (OLE) 33 coupled to a substrate 35 .

FIGS. 3A–3C illustrate the OLE 33 from several perspectives. The OLE 33 includes an array of OLE lenses 55 and male alignment features that align the OLE 33 to the substrate 35 . In an exemplary embodiment, the alignment features are plugs 59 that protrude from the OLE 33 , and are formed as an integral part of the OLE 33 . Although only two plugs 59 are shown in FIG. 3B , as few as one or more than two alignment features may be used to provide the same alignment functionality.

The positions of the OLE lenses 55 in the OLE 33 are fixed relative to the location of the plugs 59 . Preferably, the OLE lenses 55 are formed as an integral part of the OLE 33 . In an exemplary embodiment, the OLE 33 and integral OLE lenses 55 are molded out of Ultem or a similar optically transparent material. The OLE lenses 55 may also be formed in a separate component that is subsequently attached to the OLE 33 .

A tab 57 protrudes from the OLE 33 , and may be used to keep the OLE lenses 55 at a predetermined distance from the substrate 35 when the OLE 33 is coupled to the substrate 35 . However, the distance of the OLE lenses 55 from the substrate 35 is not critical to the design of the OLE 33 , as will be discussed later.

The OLE 33 includes connectors 61 for coupling with a fiber optic ferrule (not shown). The positions of the connectors 61 are fixed relative to the OLE lenses 55 . When a fiber optic ferrule is coupled to the connectors 61 , the fibers within the fiber optic ferrule are aligned to the OLE lenses 55 in the OLE 33 . Although the connectors 61 are shown as posts, other types of connectors may also be compatible with a fiber optic ferrule. In an exemplary embodiment, the fibers used with the optoelectronic assembly 31 are multi-mode fibers.

FIGS. 4A–4B illustrate the substrate 35 . The substrate 35 can be a printed circuit board, flexible printed circuit board, ceramic, silicon, a stainless steel leadframe, or a similar substrate. The substrate 35 has female co-alignment features that couple with the male alignment features on the OLE. In an exemplary embodiment, the co-alignment features are sockets 51 in the substrate 35 . Although only two sockets 51 are shown in FIG. 3B , as few as one or more than two co-alignment features may be used to provide the same alignment functionality.

An array of optoelectronic transducers 43 (“transducers”) is located on the substrate 35 . The transducer 43 may be a light source (such as a laser) or a photodetector (such as a photodiode). In an exemplary embodiment of the invention, each transducer 43 is a Vertical Cavity Surface Emitting Laser (VCSEL). Although a plurality of transducers 43 is shown in FIG. 3 , the present invention includes embodiments with only a single transducer as well. The position of the transducers 43 is fixed relative to the location of the sockets 51 .

Each transducer 43 has a standing structure 45 formed upon its surface. A transducer lens 47 is attached to each standing structure 45 and is held in place over the active region of each transducer 43 , wherein “active region” is defined to be the light-emitting or light-detecting portion of the transducer 43 . The standing structure 45 is designed to position the active region with great precision at the focal point of the transducer lens 47 . In an exemplary embodiment of the invention, the transducer lens 47 is a ball lens.

To achieve such precise positioning of the standing structure 45 and the transducer lens 47 , the standing structure 45 is typically formed using photolithographic techniques, such as those used in semiconductor fabrication and processing. The standing structure may be formed of photoresist, polyimide, or other material that can be formed and patterned by photolithographic techniques.

FIGS. 2 , 5 A– 5 B illustrate the alignment features on OLE 33 coupled with the co-alignment features on the substrate 35 to form the optoelectronic assembly 31 . In an exemplary embodiment, the plugs 59 on the OLE 33 couple tightly with the sockets 51 in the substrate to hold the OLE 33 to the substrate 35 . This coupling can be a snap-fit, slip-fit, or press-fit coupling. When the OLE 33 is joined to the substrate 35 , each OLE lens 55 is aligned with an optoelectronic transducer 43 , and also with a transducer lens 47 .

FIG. 5C shows an exploded view of the dotted box 63 of FIG. 5B . An optical fiber 71 has been added to this figure to help illustrate an exemplary light path 73 . The X-, Y-, and Z-axis directions are defined as shown in FIG. 5C . The Y-axis is defined to be pointing in a direction out of and perpendicular to the plane of the drawing.

The optoelectronic assembly 31 may be a transmitter or a receiver. When the optoelectronic assembly 31 is a transmitter, the transducer 43 is a light source such as a laser diode. The transducer lens 47 collimates the light from the transducer, and the OLE lens 55 focuses it onto the target optical fiber 71 . When the optoelectronic assembly 31 is a receiver, the transducer is a photodetector such as a PIN photodiode and the functions of the components are reversed: the optical fiber 71 functions as a light source; the OLE lens 55 collimates light emitting from the optical fiber 71 ; and the transducer lens 47 focuses the collimated light onto the target transducer 43 .

As previously described, the transducer lens 47 is already precisely aligned to the transducer 43 by the standing structures 45 . Consequently, there is more tolerance in the alignment between the transducer lens 47 and the OLE lens 55 . Furthermore, the light beam 73 is collimated between the transducer lens 47 and OLE lens 55 . If the alignment between the transducer lens 47 and the OLE lens 55 in the XY-plane is slightly off, only a small amount of light is lost, but the optical signal will still be focused on its target. Finally, the distance between the transducer lens 47 and the OLE lens 55 is not so critical, since the light beam 73 is collimated between the lenses.

This two-lens system introduces enough tolerance within the optoelectronic assembly 31 to allow the OLE 33 to be coupled to the substrate 35 without using active alignment. The amount of tolerance will vary depending on the coupling efficiencies needed. Lower speed or shorter distance applications will allow for larger tolerances, whereas higher speed or longer distance applications will require tighter tolerances.

FIGS. 6A–6B show an optoelectronic assembly 81 in another embodiment made in accordance with the teachings of the present invention. Optoelectronic assembly 81 is similar to optoelectronic assembly 31 except for the coupling mechanism. In this embodiment, the OLE 33 has female alignment features while the substrate 35 has male co-alignment features. The female alignment features on OLE 33 are sockets 83 . The male co-alignment features on the substrate 35 are bumps 83 designed to snap-fit, slip-fit, or press-fit with the sockets 83 . In an exemplary embodiment, the bumps 83 are solder balls.

To form the bumps 83 , solder balls with very accurate diameters are placed on the substrate 35 and reflowed, forming bumps 83 with precise dimensions. The substrate 35 can be flat with precisely formed metal features (e.g. traces) onto which the solder balls are placed, reflowed and thus attached to the metal features. Alternatively, the substrate 35 can have pits into which the solder balls are placed and attached. This method is especially effective if the substrate is formed of silicon, because the pits can then be precisely formed using semiconductor etching techniques.

In other embodiments of the invention, the coupling mechanism may be visual fiducials. For example, the alignment feature maybe an outline drawn on the substrate within which the optical element should be attached using adhesive, solder, or other attachment means. The coupling mechanism may also be magnetic. For example, the substrate 35 can have magnetic contacts 90 of one polarity, and the optical element 33 can have magnetic contacts 92 of the opposite polarity.

Although the present invention has been described in detail with reference to particular preferred embodiments, persons possessing ordinary skill in the art to which this invention pertains will appreciate that various modifications and enhancements may be made without departing from the spirit and scope of the claims that follow.