WO2006071075A2

WO2006071075A2 - Optical subassembly for array transmitter and array receiver

Info

Publication number: WO2006071075A2
Application number: PCT/KR2005/004605
Authority: WO
Inventors: Tae Hyung Rhee; Hyung Jae Lee; Tae Hun Kim
Original assignee: Pointek Incorporation
Priority date: 2004-12-29
Filing date: 2005-12-28
Publication date: 2006-07-06
Also published as: KR20050007276A; WO2006071075A8

Description

OPTICALSUBASSEMBLYFORARRAYTRANSMITTERAND

ARRAYRECEIVER

Technical Field

[1] The present invention relates to an optical array sub-assembly which is an essential part in an optical transmitter array or an optical receiver array required in the parallel optical transmission. Many discrete optical transceivers as many as the number of the channels of the parallel signals, may be used to for the parallel optical transmission, it requires the large package volume and the high system cost. In the present invention, an optical array sub-assembly for an optical transmitter array in which the discrete light source dies are integrated and an optical array sub-assembly for an optical receiver array in which the discrete detector dies are integrated are performed and the manufacturing method is preformed. Background Art

[2] An optical transceiver, as an optical module with a combination of an optical transmitter unit and an optical receiver unit, is widely used in the optical transmission as well as optical data transmission. This kind of an optical transceiver have a standard receptacle for an optical connector such as SC or LC, or it has an optical fiber pigtail instead of having a optical connector receptacle. Figure 1 shows a schematic illustration of a conventional optical sub-assembly for an optical transceiver. A laser diode as a light source die or photo-detector as a detector die is placed inside of the TO Can package (101) which is a cylindrical metallic package with a plane glass window or a spherical optical lens (102) in order to pass the in-and-out optical signal. Then, it has the metallic leads (105) to have the electric signal connection to the optical dies. A TO Can package (101) with an laser diode or with an photo-detector are aligned and attached with an optical connector receptacle of a metallic or plastic cylindrical fixture housing (103), in order to connect to an optical fiber. In this alignment process, the active alignment method is used. In the active alignment, the light source die emits the light to the optical fiber and its position is precisely controlled to locate the maximum light intensity. The best alignment is preformed when the maximum light intensity is reached, and then TO Can package (101) and the cylindrical fixture housing are attached.

[3] In case of the parallel optical transmission link, which has the multiple channels, a standard MT connector and optical ribbon fiber are used in general. Because the spacing between the optical fibers in an optical ribbon fiber is 250um, it is necessary to have a chip of the light source die array with the same 250um spacing between the dies or to have a chip of the detector die array with the same 250um spacing between the dies, or it is necessary to have an optical waveguide to keep the optical paths. However, this approach is an expensive approach because of the using a chip of the die array and the waveguide array. In Figure 2, a schematic illustration of such conventional optical transmitter array or such conventional optical receiver array is shown. In the case of Figure 2, a die array chip (201) is aligned to an optical waveguide array (202) having the 45° angled slant for the optical coupling, and the optical waveguide array (202) is connected to an optical ribbon fiber (206) in a MT optical connector (205). It is recommended have the metal thin film deposition on the 45° angled slant to reflect the coupled lights with 90° angle. In addition, an additional supporting structure (207) is required to have the optical coupling between an optical waveguide array (202) and a MT optical connector (205).

[4] In the present invention, the discrete dies are used to form an array to have low cost assembly as well as the plastic molding platforms with alignment pins and alignment holes are used to perform the passive alignments. Therefore, it can provide the low cost production and the mass-production. The application area of this invention is to have the multiple-channel transmissions at the same time. The examples of such application are the image signal transmission to display devices, like a monitor or LCD panel, from a computer, and the high speed signal transmission using a parallel data port, like IEEE 1394. When the large bandwidth signal is transmitted with the electric system, the transmission distance is limited. To overcome this limitation, it is widely used: the electric signal is converted to the optical signal; the optical signal is then transmitted; and the optical signal is detected being converted to the electric signal. Disclosure of Invention Technical Problem

[5] Because the high speed digital data transmission is requested in the high speed parallel data transmission between a computer and the peripheral devices, as well as the image signal transmission in the large bandwidth display devices, the transmission distance has been a bottle-neck in the conventional copper wire based data transmission. To resolve such limitation, it is common approach to improve the quality of the signal and the transmission distance by the optical transmission based on the electrical-and-optical conversion. Although these O/E and E/O conversions can be performed by using the conventional optical transceivers, it is not suitable for the system requirements such as compact device package and for the parallel transmission. In the present invention, an optical array sub-assembly for an optical transmitter array or an optical array sub-assembly for an optical receiver array with low cost and compact size is preformed to meet the system requirements. Technical Solution

[6] In this invention, the appropriate optical array sub-assemblies for an optical transmitter array and an optical receiver array, which are suitable for the parallel optical transmission, are prepared by using the passive alignments between the plastic platforms of optical array sub-assemblies, and then it results the low cost production and the mass-production. The discrete VSCEL is used for the light source. The VCSELs are attached into the designated appropriate positions in a lead frame inserted plastic molding body of a light source die-mount platform by using a conductive adhesive, so that a light source die array is prepared. As well, the discrete photodiode die is used for the detector. The photodiode dies are attached into the designated appropriate positions in a lead frame inserted plastic molding body of a photodiode die- mount platform by using a conductive adhesive, so that a photodiode die array is prepared. This kind of a light source die array or a photodiode die array is coupled with optical lens array formed in each plastic molding body to be effectively aligned with the optical fibers, and then the optical fibers in an array are connected to a plastic molding optical connector platform. A light source die array or a photodiode die array are passively aligned by using the alignment pins and alignment holes formed in the plastic molding bodies of the platforms. Also, The optical coupling between a lens array and a optical connector array like MT connector is performed by the passively aligned by using the alignment pins and alignment holes formed in the plastic molding bodies of the platforms. In the present invention, it is suitable for the low cost production and mass-production due to using the platforms based on the plastic molding process as well as using the simple assembly process based on optical coupling between the alignment pins and the alignment holes formed in the plastic molding bodies. Advantageous Effects

[7] In accordance of this present invention, the optical array subassembly array can provide the optical transceiver array with the size of the conventional electric connector in the field of parallel optical transmission because of its compact size capability. It is very feasible to be used in the application of the reliable optical transmission with enough nMong distance because optical transmission can substitute the distance-limited electric parallel transmission with the large bandwidth. The present invention eliminates the additional optical alignment in accordance with the illustrated embodiments, so that the precision alignment equipments and the alignment process time, which are required in the conventional optical subassembly manufacturing process, are not necessary as well as the process cost is reduced as a result. In addition, it is feasible to have the easy manufacturing process as well as the mass- production because the plastic molding body is used. 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 an optical transceiver.

[10] Figure 2 is a schematic illustration of a conventional optical transmitter array or a conventional optical receiver array.

[11] Figure 3 is a schematic illustration of an optical array sub-assembly for an optical transmitter array or an optical receiver array in accordance with the present invention.

[12] Figure 4 is another schematic illustration of an optical array sub-assembly for an optical transmitter array or an optical receiver array in accordance with the present invention.

[13] Figure 5 is a schematic illustration of a die-mount platform for an optical array sub- assembly in accordance with the present invention.

[14] Figure 6 is a schematic illustration of an optical platform for an optical array sub- assembly in accordance with the present invention.

[15] Figure 7 is a schematic illustration of an optical connector platform for an optical array sub-assembly in accordance with the present invention.

[16] Figure 8 is a schematic illustration of an optical platform for an optical array sub- assembly, shown in Figure 3, in accordance with the present invention. Best Mode for Carrying Out the Invention

[17] Figure 3 is a schematic illustration of an optical array sub-assembly for an optical transmitter array or an optical receiver array in accordance with the present invention. An optical array sub-assembly consists of a die-mount platform (301), in which the light source dies or the photodiode dies are mounted, prepared by the lead-frame insertion plastic molding process, an optical platform (302), in which the optical lenses are formed by using an the optically transparent plastic molding process for the effective optical coupling between dies and optical fibers, and an optical connector platform (303), in which the optical fiber array connector part is prepared.

[18] Figure 4 is another schematic illustration of an optical array sub-assembly for an optical transmitter array or an optical receiver array in accordance with the present invention with the similar construction. Figure 4 shows that an optical array sub- assembly consists of a die-mount platform (401), an optical platform (402), and an optical connector platform (403) like the one shown in Figure 3. Otherwise, unlike the coupling structure in Figure 3 that the optical platform (302) has the straight optical paths, the optical platform (402) in Figure 4 has the optical paths turned by 90° angle. [19] Figure 5 is a schematic illustration of a die-mount platform (301 or 401) for an optical array sub-assembly in accordance with the present invention. The pocket array

(501) in which the VCSEL dies or photodiode dies are attached, the wire-bonding pads

(502) for the electric connections to the attached die, the lead frames (503) which are inserted during the plastic molding process, and the alignment holes (504) for the optical alignment with the optical platform (302 or 402) are formed in the die-mount platform by using plastic molding process based on liquid crystal polymeric materials. The pockets (501), in which the dies are attached, are designed to exposure the lead frames (503) with the same area of each die, and are designed to have the 45° slant with wider opening in order to mount the dies into the pocket easily. The dies are attached by using a conductive adhesive and then the electric connections are completed by wire-bonding process between the bonding pads in the dies and the bonding pads (502) on the lead frames. Finally, the dies and boning wires are protected by coating a transparent silicone gel, followed by curing.

[20] Figure 6 is a schematic illustration of an optical platform for an optical array sub- assembly in accordance with the present invention, and the optical transparent polymers are required for the plastic molding process. For this purpose, poly- methylmethaacrylates (PMMA), Polycarbonates (PC), polyetherimides (PEI) are recommended. In the optical platform, the optical lenses (601) are formed as an array. The optical lens arrays (601) are formed at the both coupling surfaces of an optical platform, in order to have the effective optical coupling paths. A lens array at one side of an optical platform converts the out-going lights, with a certain radiation angle, from the light source die array to have the parallel lights, as well as it converts the incoming light to the photodiode die array to have the focused lights, so that the effective optical coupling is achieved. The lens array at the other side of an optical platform converts the out-going parallel lights, from the light sources passing through the first lens array, to the focused lights in order to be effectively coupled into the core of an optical fiber as well as it converts the in-coming lights, with a certain radiation angle, from the optical fibers to the parallel lights to be focused at the first lens array in order to be effectively coupled into the photodiode die array. The optical platform has the alignment pins (602) to align with the die-mount platform as well as alignment pins (602) to align with the optical connector platform at the both coupling surfaces. In addition, a matching key (603) to match the right optical fibers in order is formed in the optical platform when an optical connector platform is aligned together.

[21] Figure 7 is a schematic illustration of an optical connector platform for an optical array sub-assembly in accordance with the present invention. In an optical connector platform, the V-grooves (701) to hold the optical bare fibers to guide the precious alignment positions, the circular holes (702) to hold the optical fibers with the 900um buffer coating, and the epoxy pot (703) to fix the array of the optical fibers are formed. As well, the alignment holes (704) to be aligned with an optical platform and a matching lock (705) to lock the matching key (603) of an optical platform are formed to match the right optical fibers. The optical connector platform in the present invention is prepared from a plastic molding process. In order to package the optical fibers in the V-grooves (701), the fiber coatings at the optical fiber ends are removed, the bare optical fibers are inserted into the circular holes (702), an adhesive is applied, a lid plate is used to press, and then an adhesive is cured. A lid plat to press the optical fibers is made of a transparent plastic material in order to monitor that the optical fibers are well positioned in the V-grooves (701). An optical connector platform is completed by apply an adhesive in the epoxy pot (701), an adhesive is cured and finally the optical fiber end facet is polished.

[22]

Mode for the Invention

[23] Figure 8 is another schematic illustration of an optical platform for an optical array sub-assembly, shown in Figure 3, in accordance with the present invention. Unlike Figure 6, the lens arrays (801) are formed in the lateral side and the base side. While an optical platform in Figure 6 has the straight optical path, an optical platform shown in Figure 8 has the optical path turned by a 90° right angle. In order to have an optical path with a 90° right angle turn, a 45° angled reflection surface (805) to an optical path is required. The operation principle at the 45° angled reflection surface is use the total internal reflection at the interface between the reflective indices of air and the plastic material of an optical platform. The total internal reflection is a phenomenon to have the loss-less reflection at the interface between the media when the light incidents from the higher reflective index medium to the lower reflective index medium with an angle larger than the certain degree. It is suitable for the production because it is not necessary for the total internal reflection to have an additional mirror coating for the reflection. Other elements except for the optical path, such as the alignment pins (802, 803) and a matching key (804), have to same operation principles as shown in Figure 6. Industrial Applicability

[24] The plastic molding process, in accordance of the present invention, is feasible for the mass-production as well as low cost production of the optical array sub-assemblies. These optical array sub-assemblies can be used in the image transmission of the remote display devices as well as the long distance-parallel data transmission.

Claims

[1] An optical array sub-assembly for an optical transmitter array or for an optical receiver array, which consists of an die-mount platform formed by the lead- frame insert plastic molding, an optical platform formed by an optical transparent polymer, and optical connector platform, comprising: An die-mount platform in which the light source dies like VCSELs or photodiode dies are assembled as an array form; and

An optical alignment structure which the alignment pins formed in the optical platform and the alignment holes formed in the die-mount platform and the optical connector platform are coupled to have an optical passive alignment.

[2] An optical platform to constitute the optical array sub-assembly, in which the elements are formed in the same plastic molding body, comprising: The optical lenses are formed in the said plastic molding body in order to convert the out-going lights, from the light source die array, to have the parallel lights, or in order to converts the in-coming light, form an optical fiber, to have the focused lights;

The optical total internal reflection mirror is formed in the said plastic molding body in order to change the optical paths;

The alignment pins are formed in the said plastic molding body in order to have optical passive alignment with an optical connector platform; and The alignment pins are formed in the said plastic molding body in order to have optical passive alignment with an die-mount platform.

[3] An die-mount platform to constitute the optical array sub-assembly, in which the elements are formed in the same lead-frame inserted plastic molding body, comprising:

The pocket array is forms in the said lead-frame inserted plastic molding body in order to position the light source dies like VCSELs, or photodiode dies; The wire-bonding pads for the electric connections between the lead frames and dies are integrated in the said lead-frame inserted plastic molding body; and The alignment holes are formed in the said lead-frame inserted plastic molding body in order to have the optical passive alignment with the optical platform.

[4] The method of manufacturing the die-mount platform, comprising the steps performed:

A step to conductively attach the said light source dies like VCSELs or photodiode dies into the designated pockets in the said molding plastic body by using a conductive adhesive; A step to have the electric connection from the said light source dies or photodiode die, or other die elements to the pads connected to the lead frames by using wire-bonding; and

A step to protect the said dies and bonding wires by applying and followed by curing the optically transparent silicone. [5] An optical connector platform in the Claim 1, in which the elements are formed in the same plastic molding body, comprising:

The said optical connector array in which V-grooves to hold the optical bare fibers to guide the precious alignment positions;

The circular holes to hold the optical fibers with the 900um buffer coating; and

The epoxy pot (703) to fix the array of the optical fibers. [6] The method of manufacturing the said optical connector platform in the Claim 1, in which the optical fiber is mounted into the said connector, comprising the steps performed:

A step to remove the fiber coating at the optical fiber end;

A step to insert the prepared optical bare fibers into the circular holes;

A step to position the optical fibers in the V-grooves

A step to apply the adhesive;

A step to place a transparent plastic lid plate; and

A step to cure the adhesive. [7] The said plastic molding body for the optical platform which is composed of a plastic material with good optical transparency, comprising: polymethylmethacrylates (PMMA); polycarbonates (PC); and

Polyetherimides (PEI). [8] The said plastic molding body for the die-mount platform which is composed of a plastic material with good thermal stability, comprising:

Liquid crystal polymers (LCP).