Patent Application
20060045530
The invention relates to the field of optoelectronics. More particularly, the present invention relates to the field of optical communications.
Infrared optical transceivers need to provide good link distance and wide field of view (“FOV”) between a variety of communicating devices such as laptop computers, personal digital assistants (“PDA”), printers and mobile phones. As these devices become smaller, it is also very important for the infrared optical transceivers to become more compact. Additionally, low power consumption is very important for these portable devices.
Optical transceivers often use hemispherical lenses to receive and focus incoming light. One prior-art solution for increasing the link distance between communicating devices is to increase the lens size of the hemispherical receiver lens. However, this solution increases the size of the transceiver package.
Optical transceivers often generate light using light emitting diodes (“LED”). Another prior-art solution for increasing the link distance is to increase the electric current driving the LED of the emitter to produce a more intense and further traveling light beam. However, this solution leads to high power consumption and shorter battery life.
U.S. Pat. No. 5,506,445 to Rosenberg illustrates an infrared optical transceiver module. Both an LED (104), for transmitting an infrared (“IR”) signal, and a photodiode (106), for detecting an incoming IR signal, are connected to a common leadframe (103). Also attached to the leadframe is an integrated circuit (101) (“IC”) which drives the LED and amplifies the photo-electric current of the photodiode. A transceiver body (105) is molded around the leadframe/LED/photodiode/IC combination. The transceiver body includes first and second hemispherical concentrator lenses (121, 123) molded over the LED and photodiode through which the IR signals are transmitted and received. The complete transceiver module is mounted on a PCB.
One result of Rosenberg's design is that the emitter, receiver and IC are all on the same side of the substrate, resulting in a relatively large footprint of the transceiver module on the PCB. Moreover, Rosenberg does not address the problems of providing a compact design, long link distance between devices, wide field of view between devices, and low power consumption.
Also, Rosenberg's use of a hemispherical concentrator lens for collecting the light and sending it to the receiver is not optimal. A receiver having a lens with improved optical gain and a wider field of view would be desirable because it would result in a long link distance between devices and wide field of view between devices. However, such a lens would be more complicated to manufacture and would not be easy to combine in a single mold with the leadframe/LED/photodiode/IC combination as done by Rosenberg with the combination of the hemispherical lens with the leadframe/LED/photodiode/IC in a single mold.
Also, Rosenberg does not address a design for improved manufacturing economy. It is difficult to provide a stable solder connection between the leadframe tabs (124) and the main PCB because the leadframe tabs are long and must be kept coplanar with each other during soldering. It is also expensive, inconvenient and slow to trim the leads in the complex arrangements of FIGS. 4-6 of Rosenberg. Also, a large amount of epoxy forms the transceiver body for housing the transceiver. This large amount of epoxy can result in reliability problems during thermal stressing.
It would be desirable to provide a compact optical transceiver module having a long link distance, wide field of view and low power consumption, while at the same time allowing an economical manufacturing process.
The optical transceiver of the present invention provides a compact optical transceiver module having a long link distance, wide field of view and low power consumption, while at the same time allowing an economical manufacturing process.
The optical transceiver includes a substrate having first and second sides. A light emitter mounted to the first side. A light receiver is mounted to the first side and comprises a dielectric totally internally reflecting concentrator directing light to a photodetector. Amplification circuits are mounted to the second side and are electrically connected to the light emitter and the light receiver through the substrate. The light emitter and the light receiver are housed in separate molded housings.
The method of manufacturing the optical transceiver comprising the steps of: mounting amplification circuits to a second side of a substrate having at least one electrical terminal passing through the substrate; and mounting a light emitter and a light receiver to a first side of the substrate using an SMT process so that they are electrically connected to the amplification circuits through at least one of the electrical terminals. In this method the light receiver comprises a dielectric totally internally reflecting concentrator directing light to a photodetector.
The light receiver is manufactured by mounting a photodetector to a leadframe; electrically connecting the photodetector to the leadframe; and enclosing the leadframe within the light receiver;
The light emitter is manufactured by mounting an LED to a leadframe; electrically connecting the LED through the leadframe; and enclosing the leadframe within the light receiver.
By mounting the light emitter 109 and light receiver 111 on the opposite side of the substrate 103 relative to the amplification circuits 113, the optical transceiver 101 has a smaller footprint than the transceiver of Rosenberg where the emitter, receiver and IC are all mounted on the same side of the substrate. Thus, in the present invention, a substrate having a smaller surface area and reduced length along the direction of the light emitter 109, light receiver 111 and amplification circuits 113 can be used.
The light emitter 109 mounted on the leadframe 128, and the light receiver 111 mounted on the leadframe 129 are housed in separate molded housings 115 and 117, respectively. The molded housing 117 can include a dielectric totally internally reflecting concentrator lens 119 for directing light to a photodetector 121 of the light receiver 111. The molded housing 115 can include a hemispherical concentrator lens 125 for directing light from an LED 123 of the light emitter 109. The separate molded housings 115 and 117 allow the use of mass-produced light emitters and receivers 109, 111 and the use of surface mount technology (“SMT”) processes for mounting the light emitter and receiver 109, 111 to the substrate 103. The separate molded housings 115 and 117 also provide an additional advantage over the unitary transceiver body (105) of the Rosenberg reference. The present invention, by having separate molding housings, requires less epoxy and no significant stress is induced across the substrate, resulting in better reliability during thermal stressing.
In the present description of the invention, the terms “optical” and “light” are used to describe the portion of the electromagnetic spectrum in or near the visible region. More particularly, this part of the electromagnetic spectrum is defined to include visible, infrared and ultraviolet radiation in the range from approximately 4 nanometers to 1000 nanometers.
Thus, by describing the invention as an “optical transceiver” what is meant is that it is not designed for the detection of electromagnetic radiation outside this range from approximately 4 nanometers to 1000 nanometers. Rather, the optical transceiver of the present invention has embodiments detecting electromagnetic radiation covering the entire approximately 4 nanometers to 1000 nanometers light spectrum and also has embodiments covering various sub-ranges of the light spectrum such as the infrared, ultraviolet or visible ranges.
In the present description of the invention, the term “infrared” is used to describe the range of invisible radiation wavelengths from about 750 nanometers to 1000 nanometers. The term “ultraviolet” is used to describe the range of invisible radiation wavelengths from about 4 nanometers to about 380 nanometers. The term “visible light” is used to describe electromagnetic radiation that has a wavelength in the range from about 400 nanometers (violet) to about 770 (red) nanometers and may be perceived by the normal unaided human eye. An embodiment of the present invention is said to operate within any of these ranges as long as it operates within a sub-range within the broader range.
The invention is now described in more detail with reference to
As illustrated at step 301 of
At step 303 the amplification circuits 113 are mounted to the second side 107 of the substrate 103. The amplification circuits 113 can, more specifically, be implemented by one or more integrated circuits (“IC”). The amplification circuits 113 are attached to the substrate using silver epoxy and are then wire-bonded with wirebonds 133 to the wire-bonding pads 131. Next, at step 305 the amplification circuits 113 and wirebonds 133 are encapsulated using glob top encapsulant epoxy 135 to protect against mechanical shock and vibration and to protect against environmental damage such as corrosion.
Alternatively, as illustrated in
At step 307 the light emitter 109 and the light receiver 111 are mounted to the first side 105 of the substrate using a surface mount technology (“SMT”) such as a pick and place machine and reflow process or using a wave soldering process.
The emitter and receiver housings 115, 117 can be made from epoxy such as MG-18 Hysol or can be made from Hysol OS4210 using a casting process. The use of the separately housed emitter 109 and receiver 111 allows for better mass production when the DTIRC 119 is integral with the receiver 111. It also allows for economical mounting of the emitter 109 and receiver 111 onto the substrate 103 using a surface mount technology (“SMT”) process such as a pick and place machine and reflow process or a wave soldering process. Another advantage is that the leadframe tabs 121 are relatively short and are directly aligned and soldered to the electrical terminals 127 without the need for trimming as in Rosenberg.
The DTIRC 119 can be obtained from the company Optical Antenna Solution. The DTIRC 119 is based on the internal reflection of IR rays on its lateral surface. Advantages of a DTIRC are described in Pavlosoglou et al., “A Security Application of the Warwick Optical Antenna in Wireless Local and Personal Area Networks”.
Compared with the hemispherical concentrator lenses used in the light receivers of the prior art, the DTIRC has improved optical gain and a wider field of view. This helps provide the optical transceiver of the present invention with a compact design, long link distance between devices, wide field of view between devices, and low power consumption compared to the prior art optical transceivers. Additionally, the use of the DTIRC 119 allows for the use of a smaller photodetector 121, resulting in decreased cost, allowing the use of smaller capacitors and improved receiver sensitivity.
Rosenberg combines the leadframe/LED/photodiode/IC along with the first and second hemispherical concentrator lenses (121, 123) in a unitary mold. However, the DTIRC 119 used by the present invention has a more complicated design than the hemispherical concentrator lenses (121, 123) used by Rosenberg. Therefore, it is not practical to mass-produce the DTIRC 119 in a single mold along with the leadframe/LED/photodiode/IC combination. Therefore, in the present invention the light emitter 109 mounted on the leadframe 128, and the light receiver 111 mounted on the leadframe 129 are housed in the separate molded housings 115 and 117, respectively. It is the molded housing 117 which includes the DTIRC 119. In this way the molded housing 117 with the integral DTIRC 119 can easily be mass-produced.
The amplification circuits 113 mounted to the second side 107 of the substrate 103 provide an electric current for driving the LED 123 to generate an output signal. The driving current is supplied to the LED 123 through the electrical connection provided by the wirebonds 133 of
The amplification circuits 113 also amplify the photo-electric current produced by the photodetector 121 in response to an optical input signal. The photo-electric current passes from the photodetector 121, through the wirebond 141, the leadframe 128, the leadframe tabs 137, the pads 131 on the first side 105 of the substrate 103, the electrical terminals 127, the pads 131 on the second side 107 of the substrate 103 and the wirebonds 133 to the amplification circuits 113.
Connections
In a preferred embodiment the optical transceiver 101 operates in the infrared light range. Thus, the light emitter 109 emits infrared light, the light receiver 111 receives infrared light and the amplification circuits 113 amplify infrared light received by the light receiver 111 and emitted by the light emitter 109.
In the foregoing specification, the invention has been described with reference to specific exemplary embodiments thereof. The specification and drawings are, accordingly, to be regarded in an illustrative sense rather than a restrictive sense.
