Optical waveguides – With optical coupler – Input/output coupler
Reexamination Certificate
2000-09-21
2003-04-01
Sanghavi, Hemang (Department: 2874)
Optical waveguides
With optical coupler
Input/output coupler
C385S088000, C385S091000
Reexamination Certificate
active
06542669
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an enhanced coupling arrangement for an optoelectronic transducer, and in particular, to an enhanced coupling arrangement that reduces and/or controls a gap between an optical coupler for an optical device, such as an optical fiber, and a surface emitting device, such as a vertical cavity surface emitting laser, for example.
2. Background Information
Computer and communication systems are now being developed in which optical devices, such as optical fibers, are used as a conduit (also known as a wave guide) for modulated light waves to transmit information. These systems include at least a light emitter, and an optical coupler that connects the optical device to the light emitter. A generic term of either a light emitter or a light detector is an “optoelectronic transducer.”
As an example, optoelectronic transducers convert electrical signals to or from optical signals; the optical signals carry data to a receiver from a transmitter at very high speeds. Typically, the optical signals are converted into, or converted from, associated electrical signals using known circuitry. Such optoelectronic transducers are often used in devices, such as computers, in which data must be transmitted at high rates of speed.
In order to transmit the optical signals, the light emitter is typically either a light emitting diode (LED) or laser emitter. Conventionally, a photodiode is used to receive the optical signals. Optical fibers, which collectively form a fiber-optic cable, may be coupled to the respective LED or laser, and the photodiode, so that the optical signals can be transmitted to and from other optoelectronic transducers, for example.
The optoelectronic transducers are normally located on either input/output cards or port cards that are connected to an input/output card. Moreover, in a computer system, for example, the input/output card (with the optoelectronic transducer attached thereto) is typically connected to a circuit board, for example a mother board. The assembly may then be positioned within a chassis, which is a frame fixed within a computer housing. The chassis serves to hold the assembly within the computer housing.
Typically, there are two different types of light emitters which may be utilized with optoelectronic transducers. These include, in general, edge emitters and surface emitters. Edge emitters 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, so as to provide for about, for example, 400 square microns of active area.
Moreover, and in contrast to a typical edge emitter, the conventional surface emitter has an active area that is surrounded by inactive portions. This allows further devices to be placed immediately adjacent to the surface emitter, using the inactive portions as bearing surfaces. Moreover, and in contrast to a typical edge emitter, surface emitters commonly include coatings, such as silicon dioxide or other nitrides, which are utilized for passivation purposes.
Further, with the conventional VCSEL, the light is emitted in a conical beam vertically from the surface of the chip. Furthermore, the conventional VCSEL allows for integrated two-dimensional array configurations. For example, the VCSELs can be arranged in a linear array, for instance 12 surface emitters spaced about 250 microns apart, or in area arrays, for example, 16×16 arrays or 8×8 arrays. Of course, other arrangements of the arrays are also possible. Nevertheless, linear arrays are typically considered to be preferable for use with optoelectronic transducers, since it is generally considered easier to align the optical fibers which collect the light emitted from the VCSELs in a linear array, than in an area array. Moreover, it is also conventional not to arrange the VCSELs in any sort of array whatsoever, but instead utilize the VCSELs singly.
It is important to ensure that as much of the light emitted from the light emitters reaches the respective optical fibers. However, the light emitted from the light emitters always diverges. This divergence may cause some of the emitted light not to reach the optical fibers, thus decreasing the efficiency of the transmission. Thus, the gap that must be bridged between the emitter and the optical fibers must be carefully controlled.
Moreover, as the emitted light diverges, it becomes increasingly more difficult to align the emitted light with the respective optical fibers. That is, if the emitted light beam has a diameter that is smaller than a diameter of the respective optical fiber, there is a certain acceptable margin of error in the alignment process. For instance, the respective light emitter may be shifted slightly off-center relative to the respective optical fiber, with the emitted light still impinging completely upon the optical fiber. On the other hand, if the emitted light beam has a diameter that is, due to its divergence, the same as, or larger than the diameter of the respective optical fiber, any shifting of the light emitter away from center relative to the respective optical fiber will cause some of the emitted light to miss the optical fiber.
In order to reduce any misalignment between the optical fibers and the light emitters, so as to ensure that the emitted light does not partially or completely “miss” its intended target, the light emitters may be either actively or passively aligned. For a device to be actively aligned, the light emitter is typically turned on and the other elements aligned with the light emitter while the device is activated. By using this approach, each device produced is individually aligned. Obviously, this is not preferable if the devices are to be mass produced. However, when the positional tolerances are very small, active alignment may be the only acceptable way to ensure that the light emitters are aligned with the optical fibers, especially when there is a large divergence in the emitted light beams.
Alternatively, passive alignment techniques utilize jigs or other manual operations to align the light emitters to the respective optical fibers. Passive alignment techniques are less accurate that active alignment techniques, and thus work best when the positional tolerances are larger, that is, when some shifting of the light emitters relative to the respective optical fibers can be tolerated.
From the foregoing, it is clear that it is desirable to reduce the divergence of the light beam emitted from the light emitters as much as possible. One way to reduce the divergence of the light beam is to move the light emitter as close as possible to the optical fibers. However, due to the fragile nature of the light emitters, it is desirable that the surface of the light emitter does not directly contact the optical fibers, especially during the alignment process. Moreover, it is further desirable that the light emitters be fixed relative to the optical fibers, so as to maintain their relative positions to each other.
Referring to
FIGS. 1 and 2
, a known arrangement is illustrated, in which the light emitter
10
, such as a VCSEL, is attached to a carrier
12
, and the ends of optical fibers (not shown) are embedded within an optical coupler
14
. In this conventional arrangement, the carrier
12
, rather than the light emitter
10
, is directly attached to the optical coupler
14
. Moreover, it is understood that the light emitter is conventionally formed on a top surface of a chip. For explanatory purposes, both the light emitter and the associated chip are collectively referred to as light emitter
10
.
The carrier
12
is typically molded or otherwise constructed f
Hanley Michael Francis
Johnson Glen Walden
Malagrino Jr. Gerald Daniel
Berdo, Jr. Robert H.
International Business Machines - Corporation
Rabin & Berdo PC
Rojas Omar
Sanghavi Hemang
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