1. The Field of the Invention
The present invention relates to optical transceivers. More particularly, the present invention relates to small form factor optical transceivers that couple light by defocusing the image in order to reduce or eliminate reflections back to the light source while still efficiently coupling the light.
2. Background and Relevant Art
Fiber optic networks often include a transmission side and a receiver side. On the transmission side, it is important that the light be efficiently coupled into the transmission fiber in order to achieve adequate transmission power with minimum laser output strength. On the receiver side, it is important to efficiently image the fiber output onto detectors with adequate margin for error. This is particularly true as the size of detectors decreases, often for cost reasons.
Effective coupling of the light into the fiber on the transmission side and effective coupling of the fiber output to a detector on the receiver side is often achieved through the use of small form factor optical transceivers or coupling elements that are often referred to as ports. Ports are also used for other purposes, such as coupling the output of an optical fiber to another optical fiber. Ports, which are often formed from ball lenses that are pressure fit to a housing body, are used because they are small and can typically be mass produced.
Optical transceivers or ports thus play an important role in optical networks. As the size of the optical ports decreases, attempts have been made to produce molded ports that incorporate the optical aspect or lens of the port into the molded design. This has proven to be a difficult task for several reasons. The molding process needs to support the integrity of the optical aspects of the port and the optical design of the port is typically limited by the mechanical limitations of the molding process.
In order to address these constraints, ports have been formed that assign optical power to each surface of the port lens. When the optical power of the port lens is divided between two surfaces, both making and designing the port become more difficult for several reasons. The surface accuracy of each surface, for instance, must be analyzed. Also, any positional error between the two surfaces of the port lens reduces the performance of the port lens due to aberrations that are caused by the positional error. In other words, it is more difficult to mold a port whose optical power is divided across two lens surfaces because there are more factors that can reduce the overall performance of the port.
Some optical transceivers incorporate ball lenses into their design. When the numerical aperture of the source light is low, a ball lens is usually able to couple the light effectively. Unfortunately, many light sources often generate most of the power into the higher angle light rays whose numerical aperture is higher than what the ball lens can effectively couple. The higher angle light rays are thus highly aberrated and are not effectively coupled by ball lenses, and ball lenses are unable to properly focus the higher angle light rays on an optical fiber or other light receiver.
Another problem with optical transceivers or ports is related to light reflections that interfere with the light source. When light rays from a light source are focused, for example, on an optical fiber, the image formed on the optical fiber is reflected back through the port lens to the light source. The reflection of light back into the light source may interfere with the data that is being transmitted over the optical network and may reduced the efficiency of both the light source and the lens. If the light source is an optical fiber, then the reflections may be transmitted back through the optical network.