Description
OPTICAL SUBASSEMBLY FOR BIDIRECTIONAL
TRANSCEIVER
Technical Field
[1] The present invention relates to the optical sub-assembly for bi-directional optical transceiver. In general, the optical transceiver consists of a transmitter part and a receiver part. For the optical communications between A point to B point, the optical transmitter part at A point is connected to the optical receiver part at B point by using a single optical fiber, and the optical transmitter part at B point is connected to the optical receiver part at A point by using another single optical fiber. In order to halve the numbers of installed optical fibers in such optical transceiver, an optical technology has been developed and allows the bi-directional optical transmission-reception by sharing a same single optical fiber. An optical bi-directional transceiver is preformed by operating the different transmitting and receiving wavelengths that share the same single line of an optical fiber.
[2]
Background Art
[3] Figure 1 represents the schematic illustration of the conventional optical sub- assembly, the most essential component to assemble an optical transceiver. For the general structure of the conventional optical sub-assembly, a metal fixture housing (101) is prepares and an optical fiber (106) is connected to the receptacle. A wavelength selective dielectric filter (102) is mounted with 45° angle to the optical path in the metal fixture housing (101). Then, the optical alignment from a light source (103) to an optical fiber (106) is preformed through passing the dielectric filter (102) when it transmits the light signal. When it receives the optical signal, the light signal from the optical fiber is reflected at the dielectric filter (102) and the reflected signal is connected to the photodiode (104). The TO-Can packaged light source (103) and the TO-Can packaged photodiode (104) are mounted in the metal fixture housing (101) by the laser welding process. In this alignment process, the light source (103) emits the light to the optical fiber (106) and its position is precisely controlled to locate the maximum light intensity at the fiber end. The best alignment is preformed when the maximum light intensity is reached, and this method is called the optical active alignment . To align the photodiode (104) to the optical fiber (106), the light from optical fiber (106) is launched into the photodiode (104) and the position of the photodiode (104) is precisely controlled to locate the maximum light intensity. The best alignment is preformed when the maximum light intensity is reached at the
photodiode (104). Such manufacturing method based on the active alignment requires an expensive optical alignment facility as well as a laser welding facility. In addition, this method requires the long process time. Therefore, the high manufacturing cost for the optical sub-assembly is easily expected when the conventional method is applied.
[4]
Disclosure of Invention Technical Problem
[5] The conventional method to manufacture an optical sub-assembly requires the long process time as well as the high manufacturing cost because it is necessary for the active alignment method, which requires the optimized optical alignment by monitoring the optical active devices, to use the expensive alignment facility and to take the long process time. Otherwise, the passive alignment method, which performs the optical alignment without using the optical active devices, can provide the sub¬ stantially low cost because the simple assembly of manufacturing an optical sub- assembly is possible. Technical Solution
[6] In the present invention, the passive alignment method between the optical platform and the die-mount platform is applied to replace the conventional active alignment method to manufacture the optical sub-assembly for the bi-directional optical transceiver. In addition, the optical platform, by the plastic molding process, and the die-mount platform, by the lead- frame insert plastic molding process, are prepared for the passive alignment purpose. In the die-mount platform, the optimized positions, to be mounted with the dies such as light source and photodiode die, are designated as well as the alignment structures are arranged for the passive alignment. In the optical platform, optical lenses, optical mirror, optical filter mount and optical connector receptacle to have the optical path coupling as well as alignment pins to be optically aligned with the die-mount platform are integrated as a plastic molding body. The optical alignment from the light source to the optical fiber and the alignment from the optical fiber to the photodiode die are preformed by the simple mechanical alignment between the alignment pins in the optical platform and the alignment structures in the die-mount platform.
Advantageous Effects
[7] With accordance of the present invention, the production cost for the optical sub- assembly can be lowered by eliminating the necessity of the optical active alignment process because the present invention can get rid of the precision alignment facility which requires in the optical active alignment process and because it can reduce the process time which takes long in the active alignment process. As well, by using the
plastic molding bodies, it is easier to make the platforms as well as to be more feasible for the mass-production than the conventional metallic fixture housing. Brief Description of the Drawings
[8] The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, both as to organization and method of practice, together with further objects and advantages thereof, may be best understood by reference to the following detailed description of the preferred embodiment(s) and the accompanying drawings in which:
[9] Figure 1 is a schematic illustration of a conventional optical sub-assembly for the conventional bi-directional optical transceiver.
[10] Figure 2 is a schematic illustration of the optical sub-assembly for the bi-directional optical transceiver in accordance with the present invention.
[11] Figure 3 is a schematic illustration of the plastic molding body for the optical platform in accordance with the present invention.
[12] Figure 4 is a schematic illustration of the plastic molding body for the die-mount platform in accordance with the present invention. Best Mode for Carrying Out the Invention
[13] As shown in Figure 2, the present invention represents an optical sub-assembly which consists of the two parts, the optical platform prepared by a plastic molding method using the an optically transparent plastic material and the die-mount platform prepared by the lead-frame insert molding method of a plastic material. A plastic molding body for the optical platform in which a receptacle part (201) to be connected to the optical connector ferrule, three optical lenses (204), an optical reflection mirror (203) to change the optical path, an optical filter mount to hold a wavelength selective dielectric filter (202), and the alignment pins (205) to have the optical path aligned with the die-mount platform (207) are integrated, is prepared and the resultant optical platform is embodied by attaching the wavelength selective filter (202) to the dielectric filter mount in the plastic molding body for the optical platform.
[14] A plastic molding body for the die-mount platform in which a designated pocket to position a light source (209) such as VCSEL die, a designated pocket to position a photodiode die (209), a designated pocket for a pre-amp chip die, a designated pocket for a decoupling capacitance, the designated alignment structures (210) to align with the alignment pins in optical platform, and the lead frame (211) inserted into the plastic molding body for the electric connection are integrated, is prepared and the resultant die-mount platform is embodied by attaching the VCSEL die, photodiode die, pre-amp chip die and decoupling capacitance into the designated pockets of the plastic molding body for die-mount platform. The die-mount platform is completed by attaching the
light source, photodiode, pre-amp chip die and decoupling capacitance into the designated pockets of the lead frame inserted plastic molding body for the die-mount platform with the conductive adhesives, followed by the gold wire-bonding between the electrode pads of the dies and the corresponding metal pads of the lead frames, and finally by attaching a dielectric optical filter at the top of the detection area of the photodiode die with an adhesive. This dielectric filter at the top the photodiode die is required to prevent the deterioration of the optical detection sensitivity due to the optical reflection sharing the optical path from the light source in the same die-mount platform. This specific dielectric filter has a function of passing the light source s wavelength from the corresponding optical sub-assembly as well as another function of blocking the light source s wavelength from the own optical sub-assembly.
[15] The optical path alignment between the resultant optical platform and the die-mount platform is performed by the coupling between the alignment pins in the optical platform and the alignment structures in the die-mount platform. The optical alignment from the light source to the optical fiber in the optical connector ferrule receptacle through a lens for paralleling the light, a WDM filter, and a lens for focusing the light, in the order, is preformed as transmitting the light signal, and the optical alignment from the optical fiber in the receptacle to the photodiode die through a lens for paralleling the light, a WDM filter, a reflection mirror and a lens for focusing the light, in the order, is performed as receiving the light signal. These alignments are preformed because every element in two plastic molding bodies is positioned in the places cor¬ responding to the alignment pins and alignment structures.
[16] Figure 3 is the schematic illustration of the plastic molding body for the optical platform by showing a front view, a side view and a plane view. As explained, the elements such as optical lenses (304), a reflection mirror (303), a dielectric filter mount (302) and an optical connector ferrule receptacle (301), in order to perform the optical path, and the alignment pins (305) to be passively aligned with the die-mount platform are integrated as a same body of the plastic molding body for the optical platform.
[17] Figure 4 is the schematic illustration of the plastic molding body for the die-mount platform by showing a plane view, a front view and a cross-section side view. As explained, a designated pocket (402) to position a light source such as VCSEL die, a designated pocket (403) to position a detector such as photodiode die, a mount (404) to attach a dielectric filter for photodiode die, wire-bonding pads (405), the leads (401, 406, 407) for the electric connection, a designated pocket (408) for a pre-amp chip die, a designated pocket (409) for a decoupling capacitance and the designated alignment structures (410) are integrated in a lead- frame inserted plastic molding body for the die-mount platform. The leads consist of the leads (401) to connect to the receiver part, the leads (406) to connect to the transmitter part, and the rest of the leads (407) for the
insertion molding that are eliminated after the molding process. Mode for the Invention
[18] The present invention represents an optical sub-assembly which consists of the two parts, the optical platform prepared by a plastic molding method using the an optically transparent plastic material and the die-mount platform prepared by the lead- frame insert molding method of a plastic material. The optical path alignment between the resultant optical platform and the die-mount platform is performed by the coupling between the alignment pins in the optical platform and the alignment structures in the die-mount platform. Also, the optical alignment from the light source to the optical fiber in the optical connector ferrule receptacle through a lens for paralleling the light, a WDM filter, and a lens for focusing the light, in the order, is preformed as transmitting the light signal, and the optical alignment from the optical fiber in the receptacle to the photodiode die through a lens for paralleling the light, a WDM filter, a reflection mirror and a lens for focusing the light, in the order, is performed as receiving the light signal. These alignments are preformed because every element in two plastic molding bodies is positioned in the places corresponding to the alignment pins and alignment structures. Industrial Applicability
[19] The embodiments in the present invention are able to provide the low cost manu¬ facturing of the optical sub-assembly for the optical transceiver required in the optical communications and data communications. As well, this invention can provides the effective use of the optical fiber lines due to the bi-directional optical transmissions and receptions through a single line of an optical fiber.
[20]