Optical communications – Optical transceiver
Reexamination Certificate
2000-05-18
2004-06-15
Chan, Jason (Department: 2633)
Optical communications
Optical transceiver
C398S129000, C398S131000
Reexamination Certificate
active
06751420
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates to optoelectronic transceivers used in optical communication systems, and more specifically to an optical transceiver configured for transmission and reception of infrared optical signals within an asymmetrically shaped optical profile.
BACKGROUND OF THE INVENTION
Some previous optical transceivers used optical profiles that were uniform or broad. Some previous transceivers used narrow optical profiles by using emitter and receiver lenses oriented in different angles aimed in different directions in relation to each other to reduce optical signal interference to improve communication. However, this increased manufacturing costs and the size of the transceiver package, as well as limiting utility.
The Infrared Data Association (IrDA) published a standard titled
Infrared Data Association Serial Infrared Physical Layer Specification
(V1.3, Oct. 15, 1998) which contained the Advanced Infrared (AIr) communications standard. This standard defines a physical link layer protocol having infrared (IR) detectors, such as a photodetector for detecting received infrared light, and an emitter, such as a light emitting diode (LED) for emitting light up to a transfer rate of 4 Mb/s within a predetermined asymetrically-shaped optical profile having orthogonal minor and major axes with concentric centres. Along the major axis, the half power level of the profile shape is located at the outward edges of a cone which subtends an angle of 60 degrees that straddles a line normal to the major axis, and along the minor axis, the half power level of the profile shape is located at the outward edges of a cone which subtends an angle of 15 degrees that straddles a line normal to the minor axis. The shape of the optical profile is designed to maximize the ‘reach space’ along a direction orthogonal to the major axis, and minimize the ‘reach space’ along a direction orthogonal to the minor axis. It was originally conceived that the major axis would be aligned in a horizontal direction relative to a floor surface so that optical communications could occur within a collaborative workplace environment.
Prior art optical transceivers have a photodetector and an LED positioned adjacent to each other on the same plane using dedicated lenses or surfaces disposed over the photodetector and the LED. The lenses typically had a circular-shaped outer perimeter. A problem with prior art devices when using a photodetector is excessive Link Turn Around Time (LTAT) which slows the communications. An LED can transmit enough light or optical rays to saturate an adjacent photodetector, thus rendering the photodetector temporarily unable to receive optical rays. The saturated photodetector requires a predetermined amount of time (i.e., LTAT) to recover and become normalized enough to then be ready to reliably detect incoming optical rays. With prior art configurations, the communication process was required to wait for the saturated photodetector to normalize each time the adjacent LED completed a transmission cycle. A familiar example of a saturated optical sensor is a human eye that is exposed to too much light. This causes the retina to become temporarily blinded (i.e., saturated). Before the eye can once again detect images, the eye must normalize during a recovery time after the light is removed.
Therefore, it is desirable to find a solution to overcome the problem of optically isolating the photodetector from the LED to avoid saturating the photodetector when the LED is adjacent to the photodetector for maintaining continued communication by eliminating the wait or idle time while the photodetector normalizes. Some prior art methods addressed this by interposing a physical barrier between the photodetector and the LED to block light or optical rays from leaving the LED and reaching the photodetector. However, this causes a transceiver to become larger and more complicated. This is undesirable for portable computers or small-sized computing devices like laptop computers or hand-held personal digital devices which require an optical transceiver of a small size or form factor. Therefore, another objective of this invention is to configure a transceiver having a small physical size for use in portable computing devices and the like.
Maurin et al in U.S. Pat. No. 5,811,798 Sealed Photoelectric Detector dated Sep. 22, 1998, along with Isaksson in WO patent 09201 6021A Optoelectronic Component dated Feb. 27, 1991, discloses using a solid barrier that is interposed between the transmitter (emitter) and receiver (photodetector) for preventing the transmitter from radiating light or optical rays into the adjacent receiver when using the transceiver in free-space condition. Apparently, there is no concern or regard to the overall physical size of the transceiver which is an important issue if the transceiver is to be used with small-sized electronic systems nor the optical profile.
Johnson et al in U.S. Pat. No. 5,359,446 Wide-angle, High-speed, Free-space Optical Communications System dated Oct. 25, 1994 discloses using an interposing solid barrier for preventing a transmitter (emitter) from radiating light into an adjacent receiver (photodetector). This appears to be designed for a limited-space condition that is isolated from true free space by a shroud in order to achieve full duplex mode communications in which the receiver and the adjacent transmitter operate simultaneously or asynchronously. It does not address optical profiles nor appear to be capable of operation in free field conditions. It appears that the asynchronous communication occurs in a limited space within the boundaries of an opaque shroud, and does not occur within true free space or unrestricted space.
Rosenberg in U.S. Pat. No. 5,506,445 Optical Transceiver Module dated Apr. 9, 1996 discloses a structure for an ordinary optical transceiver, and does not disclose a structure that can satisfy the AIr communications standard.
The above listed prior art does not suggest how to prevent degrading a transceiver's communication performance while satisfying limitations on size for use with a portable PC, especially when the transceiver communicates within an asymmetrically shaped optical profile. The transceiver's communication ability may be degraded by several factors that are not addressed in combination by the prior art, such as:
(a) optical rays from an LED lens that enters into the photodetector lens because of the relative positions of the lenses with respect to each other;
(b) an LED saturating an adjacent photodetector that causes communication delays; and
(c) a photodetector lens that partially blocks the optical rays emitting from the LED lens thus creating a shadow that blocks optical rays being emitted from the LED.
To overcome these problems, the lenses could be separated further apart to keep the profiles of the emitter (LED) and receiver lenses from interfering with each other; however, the transceiver size will then be larger and thus less desirable for use in a portable PC.
Therefore, a solution should address, balance, and satisfy several technical problems in combination, such as:
(a) isolating the specific optical profiles for optimum condition of transmission and reception of optical rays;
(b) preventing a photodetector from becoming saturated by an adjacent LED, thus not allowing the communication process to idle unnecessarily;
(c) minimizing the transceiver's package size; and
(d) communicating optical rays freely within the specified optical profiles.
The prior art does not suggest a solution for simultaneously addressing the above-mentioned problems in combination.
A lens may be used with an emitter (such as an LED) and a detector (such as a photodetector) to define the shape of the optical profile of light being emitted from or received by those devices. The profile resembles a spatial conduit having a non-contact, non-reflecting boundary in which the optical rays of communication are spatially confined while being directed to and from the emitter and detector. This
Kerklaan Albert John
Kienzle Michael
Cameron Douglas W.
Chan Jason
Dougherty Anne V.
International Business Machines - Corporation
Leung Christina Y
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