Optical waveguides – With disengagable mechanical connector – Optical fiber to a nonfiber optical device connector
Reexamination Certificate
2001-06-27
2003-03-04
Kim, Robert H. (Department: 2882)
Optical waveguides
With disengagable mechanical connector
Optical fiber to a nonfiber optical device connector
C250S205000, C250S214100, C372S029020, C372S029021
Reexamination Certificate
active
06527460
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a light emitter control system, and in particular, to an optical element of a light emitter control system that reflects at least a portion of a light beam from a light emitter to a light-sensing device.
2. Background Information
Computer and communication fiber optic systems are now being developed in which optical devices, such as optical fibers, are used as a conduit for modulated light waves to transmit information. In these fiber optic systems, light emitters are used to produce the light that carries the information. The produced light is then directed to and transmitted by the optical fibers.
Typically, two different types of light emitters are utilized with fiber optic systems. These include, in general, edge emitters and surface emitters. Edge emitters, such as edge emitting lasers, typically have a light emitting portion which is located on an edge of a chip, and typically have an active area that may be, for example, half a micron by four microns in size, for a total area of about 2 square microns. In contrast, surface emitters, such as vertical cavity surface emitting lasers (VCSEL), conventionally have an active area that is substantially larger than the active area of an edge emitter. The active area of a surface emitter is typically around 20 microns in diameter, to provide for about, for example, 400 square microns of active area.
The optical power of a light emitter can vary with changes in the operating temperature or age of the light emitter. These variations can result in inconsistent transmissions.
As such, optical power control systems are used to provide consistent optical power of the light emitters, and thus, more consistent transmissions. In these systems, a portion of the light emitted from the light emitter is detected by a light-sensing device, such as a photodiode, for example, and used to generate a control signal having a signal strength proportional to the emitted optical power. The light-sensing device sends the control signal to control circuitry, which controls the optical power output of the light emitter based on the signal strength of the control signal. The light-sensing device varies the signal strength of the control signal in response to changes in the optical power output of the light emitter.
With edge emitters, such as edge emitting lasers, the control signal has been derived from light emitted from a rear facet of the laser, with a rear facet photodiode collecting and converting the rear facet light to the control signal. That is, the light emitted from the rear facet of the laser is monitored and used to control an output of the light emitted from the front facet.
In contrast, with surface emitters, it is conventional to space the surface emitter away from the end of the optical fiber. This space allows a portion of the emitted light to be collected and utilized for monitoring and controlling the output power of the light beam.
For example, with VCSELs, a portion of the light beam may be directed to a light-sensing device, such as a monitoring photodiode, while allowing the remaining portion of the light beam to be transmitted to the optical fiber. This may be accomplished by using a beam splitter, for example. Alternatively, it is also known to provide an angled glass lid of a TO-CAN package to reflect a portion of the light beam to a photodiode, with the photodiode collecting and converting the reflected light to the control signal.
However, the use of the aforementioned beam splitter disadvantageously increases the cost of the assembly, and reduces the signal strength of the emitted light beam available for transmission to the optical fiber.
Further, the use of the known angled lid in an optical power control system has associated problems. Use of an angled lid requires expensive tooling of equipment to manufacture the angled lids and TO-CAN packages. Further, the lid must be positioned at a precise angle relative to the emitted light beam, in order to allow the partial reflection of the light beam while allowing the rest of the light beam to pass therethrough and to the optical fiber. This requires that the lid be positioned using expensive active alignment techniques. Moreover, it has been shown that an increase in the light output power causes changes in the reflectivity of the angled lid, which may prevent the light from reaching the light-sensing device or optical fiber. Thus, the use of an angled, partially-reflecting glass lid is not an ideal monitoring solution.
Therefore, it would be desirable to provide an optical element for a light emitter control system that would overcome the above-mentioned problems.
It is also known to derive the control signal from light emitted from a VCSEL directly onto a photodiode “flip-chip” mounted to the VCSEL. For example, in a 1×2 VCSEL array, a photodetector has been flip-chip mounted to one of the VCSELs to monitor its power variations and adjust the power output of the other VCSEL.
“Flip-chip” refers to a surface mount chip technology where a chip is packaged in place on a board and then underfilled with an epoxy. Commonly, the chip is attached by placing solder balls on the chip, “flipping” the chip over onto the board and then melting the solder. Flip chips are also mounted on glass substrates, such as LCD drives and smart cards, for example, using a conductive paste.
However, flip-chip mounting photodiodes to VCSELs creates a risk that the VCSEL may be damaged due to contact of the surface of a VCSEL with the photo diode. Therefore, it would be desirable to provide an optical element for a light emitter control system that would not contact the surface of a VCSEL.
As mentioned above, it is conventional to provide a space between the light emitter and the end of the optical fiber. However, this space allows the light emitted from the light emitters to diverge. This divergence may cause some of the emitted light not to reach the optical fibers, thus decreasing the efficiency of the transmission. Further, the divergence of the light increases the difficulty in aligning the emitted light beam with the optical fiber. In order to reduce this divergence, and facilitate the alignment process, the light emitter may be moved to be immediately adjacent to, or even in direct contact with, the optical fiber. However, in such an arrangement, there is no space left between the light emitter and the optical fiber, and thus, no light is readily accessible for creating a photodiode signal. Therefore, it would be desirable to provide a light emitter control system which allows a light emitter to be monitored when the light emitter is directly connected to the optical fiber.
SUMMARY OF THE INVENTION
It is, therefore, a principal object of this invention to provide a light emitter control system.
It is another object of the invention to provide a light emitter control system that solves the above-mentioned problems.
These and other objects of the present invention are accomplished by the light emitter control system disclosed herein.
In one exemplary aspect of the invention, an optical fiber is positioned immediately adjacent, or directly coupled to an active light emitter using a fiber guide formed on a chip of the light emitter. The fiber guide includes a bore fabricated using photolithographic techniques. Further, the fiber guide structure will preferably have precisely determined bore diameters with straight, vertical walls. It is recognized, however, that this would be difficult to fabricate by way of ordinary lithographic measures. Thus, the present invention broadly contemplates, in accordance with at least one presently preferred embodiment, that special lithographic methods be employed in fabricating a fiber guide.
One conceivable way of accomplishing this task would involve patterning a photoresist using standard photolithographic techniques and using the developed resist itself as the final structure. Such a process provides a simple, inexpensive, yet effective method of fabricating the desired fiber gu
Cohen Mitchell Simmons
Gaio David Peter
Hogan William K.
Trewhella Jeannine Madelyn
Berdo, Jr. Robert H.
Gemmell Elizabeth
International Business Machines - Corporation
Kim Robert H.
Rabin & Berdo PC
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