Packaging assembly for high-speed vertical-cavity surface-emitting laser

A packaging assembly for a high-speed vertical-cavity surface-emitting laser (VCSEL) mainly applies a lens assembly consisted of several prisms to split a laser beam emitted by a VCSEL element so as to guide a small portion of the laser beam back to a monitor photodiode (MPD) and the rest of the laser beam to travel away along an optical axis. Such a spectacular design of the lens assembly can not only relieve the VCSEL element from a position right under the optical axis, but can also reduce signal loss by shorting a length of a bonding wire for a corresponding pin through disposing the VCSEL element further close to the corresponding pin. Thereupon, a defect of lights reflected from a lens or a translucent plate on a cap can be substantially improved.

This application claims the benefit of Taiwan Patent Application Serial No. 106130839, filed Sep. 8, 2017, the subject matter of which is incorporated herein by reference.

BACKGROUND OF INVENTION

1. Field of the Invention

The invention relates to a packaging assembly for a high-speed vertical-cavity surface-emitting laser, and more particularly to the laser packaging assembly that mainly applies a lens assembly to split a laser beam emitted by a laser element so as to guide a small portion of the laser beam back to a monitor photodiode, thereby to relieve the laser element from a position right under the optical axis, thus able to dispose the laser element further close to a pin, and to shorten a length of a corresponding bonding wire.

2. Description of the Prior Art

Different to a conventional laser manufactured from an isolated cutout diode that emits a laser beam from an edge thereof, a vertical-cavity surface-emitting laser (VCSEL) is a semiconductor component that emits a laser beam perpendicular to a top surface thereof. In the art, to a conventional TO-CAN package for a VCSEL element, the VCSEL element is disposed at a center of the assembly, i.e. a position right under an optical axis. Thereupon, the laser beam emitted vertically from a top surface of the VCSEL element can travel directly along the optical axis. Nevertheless, the conventional TO-CAN package has two following defects. One of the defects is that, since a lens or a translucent plate is usually disposed on an optical window of a cap at the TO-CAN packaging assembly, and also since laser beams emitted by the VCSEL element disposed right under the TO-CAN packaging assembly travel vertically upward, thus a small portion of laser beams would be reflected back to the VCSEL element by the lens or the translucent plate on the cap, and thereby optical interference arises. The other defect thereof is that, since the VCSEL element is disposed right at the center of the packaging assembly, the distance between the VCSEL element and a signal-transmitting pin of the packaging assembly is rather too long. Namely, it is inevitable to introduce longer golden bonding wires to electrically connect corresponding pins of the packaging assembly. Thereupon, loss of signal transmission is substantially increased. Hence, the conventional TO-CAN package is hard to satisfy a rising demand for a higher transmission speed upon the VCSEL element of the light communication industry. Definitely, a further improvement upon the package of the VCSEL element for resolving the aforesaid shortcomings in the transmission speed is definitely welcome to the art.

SUMMARY OF THE INVENTION

Accordingly, it is the primary object of the present invention to provide a packaging assembly for a high-speed vertical-cavity surface-emitting laser, that mainly applies a lens assembly to split a laser beam emitted by a laser element so as to guide a small portion of the laser beam back to a monitor photodiode, thereby to relieve the laser element from a position right under an optical axis, thus able to dispose the laser element further close to a pin, and to shorten a length of a corresponding bonding wire. Thereupon, signal loss of the packaging assembly can be reduced, and the problem in the reflected light from a lens or a translucent plate on a cap can be substantially improved.

In the present invention, the packaging assembly for a high-speed vertical-cavity surface-emitting laser includes a header, a cap, a laser element, a monitor photodiode (MPD) and a lens assembly.

The header has an upper surface and a lower surface.

The cap, covering the header and thus forming an accommodation space between the cap and the header, is furnished thereon with an optical window. An optical axis is defined to penetrate the optical window by being perpendicular to the upper surface of the header.

The laser element, located on the upper surface of the header, is to emit a laser beam.

The monitor photodiode (MPD), located on the upper surface of the header, is to receive a portion of the laser beam emitted by the laser element for monitoring and feedback-controlling a luminous power of the laser element.

The lens assembly is located above the upper surface of the header by being positioned between the laser element and the optical window and also between the monitor photodiode and the optical window.

In the present invention, both the laser element and the monitor photodiode are not located on the optical axis, the lens assembly has thereinside a half-reflecting half-transmitting surface, the laser beam emitted by the laser element is directed into the lens assembly so as to split into a first light beam and a second light beam by the half-reflecting half-transmitting surface, the first light beam travels along the optical axis to leave the packaging assembly via the optical window, and the second light beam is directed to the monitor photodiode.

In one embodiment of the present invention, the lens assembly, formed as a trapezoidal structure in a cross-sectional direction, further includes a bottom surface, a first complete reflective surface, a top surface, a second complete reflective surface and the half-reflecting half-transmitting surface, the bottom surface is parallel to the upper surface of the header, one end of the first complete reflective surface is connected with an end of the bottom surface, the first complete reflective surface extends from the bottom surface toward the top surface by a first angle while another end of the first complete reflective surface is connected to the top surface, the top surface is parallel to the bottom surface, one end of the second complete reflective surface is connected with another end of the bottom surface, one end of the second complete reflective surface extends from the bottom surface toward the top surface by a second angle while another end of the second complete reflective surface is connected to the top surface, the half-reflecting half-transmitting surface is formed inside the lens assembly, and the half-reflecting half-transmitting surface is parallel to the first complete reflective surface.

In this embodiment, the laser beam emitted by the laser element is injected vertically into the lens assembly via the bottom surface, and then deflected to the half-reflecting half-transmitting surface by the first complete reflective surface; and, wherein, upon the laser beam hitting the half-reflecting half-transmitting surface, a large portion of the laser beam is reflected and deflected to travel through the top surface and then leave the packaging assembly via the optical window so as to form the first light beam, the rest of the laser beam penetrates the half-reflecting half-transmitting surface so as to form the second light beam, and the second light beam is further reflected and deflected by the second complete reflective surface, then leaves the lens assembly via the bottom surface, and is finally received by the monitor photodiode.

In one embodiment of the present invention, the lens assembly is consisted of a first prism and a second prism, the first prism is formed as a parallelogram structure in the cross-sectional direction, the second prism is formed as an isosceles triangular structure in the cross-sectional direction, and a junction surface of the first prism and the second prism is the half-reflecting half-transmitting surface.

In one embodiment of the present invention, at least one optical film is coated onto the half-reflecting half-transmitting surface so as to provide a function of half-reflection and half-transmission, and a refractive index of the at least one optical film is larger than that of any of the first prism and the second prism.

In one embodiment of the present invention, the first prism and the second prism are made of a BK7 borosilicate glass with the refractive index of 1.5168, the refractive index of the at least one optical film is within 1.52˜2.5, the first angle defined by the first complete reflective surface and the bottom surface is 45°, the second angle defined by the second complete reflective surface and the bottom surface is 45°, a light intensity of the first light beam is about 80%˜95% of the light intensity of the laser beam originally emitted by the laser element, and the light intensity of the second light beam is the rest of the light intensity of the laser beam originally emitted by the laser element.

In one embodiment of the present invention, the packaging assembly for a high-speed vertical-cavity surface-emitting laser further includes a light-transmitting component and a plurality of pins.

The light-transmitting component is furnished to the optical window.

The plurality of pins are furnished to the header by penetrating the upper surface and the lower surface of the header.

In this embodiment, the laser element is located close to one of the plurality of pins, and a bonding wire is applied to directly connect electrically the laser element and a bonding pad of the one of the plurality of pins.

In one embodiment of the present invention, the packaging assembly for a high-speed vertical-cavity surface-emitting laser further includes a sub-mount and a boss base.

The sub-mount, located on the upper surface of the header, is to mount the laser element and the monitor photodiode.

The boss base, located on the sub-mount by being disposed between the laser element and the monitor photodiode, is higher than the laser element and the monitor photodiode.

In this embodiment, the lens assembly is mounted on the boss base.

All these objects are achieved by the packaging assembly for a high-speed vertical-cavity surface-emitting laser described below.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The invention disclosed herein is directed to a packaging assembly for a high-speed vertical-cavity surface-emitting laser. In the following description, numerous details are set forth in order to provide a thorough understanding of the present invention. It will be appreciated by one skilled in the art that variations of these specific details are possible while still achieving the results of the present invention. In other instance, well-known components are not described in detail in order not to unnecessarily obscure the present invention.

In the present invention, the packaging assembly for a high-speed vertical-cavity surface-emitting laser (VCSEL) mainly applies a lens assembly consisted of several prisms to split a laser beam emitted by a VCSEL element so as to guide a small portion of the laser beam back to a monitor photodiode (MPD) and the rest of the laser beam lot to travel away along an optical axis. Such a spectacular design of the lens assembly can not only relieve the VCSEL element from a position right under the optical axis, but can also reduce signal loss by shortening lengths of bonding wires through disposing the VCSEL element further close to corresponding pins. In addition, a defect of lights reflected from a lens or a translucent plate on a cap can be substantially improved.

Referring now toFIG. 1andFIG. 2, which are schematically cross-sectional and top views of an embodiment of the packaging assembly for a high-speed vertical-cavity surface-emitting laser in accordance with the present invention, respectively. In this embodiment, the packaging assembly for a high-speed vertical-cavity surface-emitting laser20, formed as an optical transceiver, largely includes a header21, a VCSEL element22(or said briefly as a laser element), a monitor photodiode23(MPD), a lens assembly24, a plurality of pins251,252, a cap26, a light-transmitting component264, and a sub-mount27.

The header21for mounting, disposing and/or assembling other elements, has an upper surface211, a lower surface212, and a periphery213surrounding exteriorly the upper surface211. The cap26, formed as a hollow convex bowl member, is to cover the header21, such that an accommodation space can be formed between the cap26and the header21. In this embodiment, the cap26has an annular lower flange261, an annular sidewall262extending upward from the lower flange261, and a top surface263located on top of the sidewall262. The lower flange261of the cap26is engaged firmly with the periphery213of the header21by gluing, supersonic adhering, interference fitting, or welding. An optical window is formed on the top surface263of the cap26. An optical axis90is defined to penetrate the optical window and be perpendicular to the upper surface211of the header21. Practically, the optical axis90defines an optical path for laser beams emitted by the laser element22to leave the packaging assembly20. In this present invention, the optical axis90is perpendicular to the upper surface211of the header21. The light-transmitting component264, disposed at the optical window, is made of a transparent glass or plastics, and is not only to seal the optical window so as to reduce invasion of moisture to the accommodation space, but also to mount an optional optical member (a lens for example) on the light-transmitting component264.

The laser element22, located on the upper surface211of the header21, can emit a laser beam. In the present invention, the laser element22is a VCSEL element to emit the laser beam upward. The monitor photodiode23(MPD), also located on the upper surface211of the header21, is applied to receive a small portion of the laser beam emitted by the laser element22, which is provided for monitoring and feedback-controlling a luminous power of the laser element22. In the present invention, neither the laser element22nor the monitor photodiode23is located on the optical axis, but to opposing sides of the optical axis90. Individual centers of the laser element22and the monitor photodiode23are spaced to the optical axis90by normal distances of d1and d2, respectively. Namely, the laser beam emitted by the laser element22is not to go directly upward to leave the packaging assembly20exactly along the optical axis90, but rather to be deflected firstly by the lens assembly24so as to go toward the optical axis90and then to leave the packaging assembly20along the optical axis90.

In the present invention, the lens assembly24, located above the upper surface211of the header21, is disposed between the laser element22and the optical window (i.e. the light-transmitting component264), and also between the monitor photodiode23and the optical window (i.e. the light-transmitting component264). The lens assembly24has a half-reflecting half-transmitting surface. The laser beam emitted by the laser element22is projected into the lens assembly24, and splits into a first light beam and a second light beam via the half-reflecting half-transmitting surface inside the lens assembly24. As shown, the first light beam travels along the optical axis90to penetrate the optical window (i.e. the light-transmitting component264) and then leave the packaging assembly20. On the other hand, the second light beam is directed to the monitor photodiode23.

In the present invention, the sub-mount27is disposed on the upper surface211of the header21, and the laser element22and the monitor photodiode23are both mounted on the same sub-mount27. Practically, a boss base271is located on an upper surface of the sub-mount27by disposing between the laser element22and the monitor photodiode23. In addition, a height (or thickness) of the boss base271is larger than that of any of the laser element22and the monitor photodiode23. Further, since the lens assembly24is disposed on the boss base271, the lens assembly24is higher than each of the laser element22and the monitor photodiode23, so that the laser element22and the monitor photodiode23are located to a lower right side and a lower left side of the lens assembly24, respectively, by slightly deviating away from the lens assembly24.

Referring now toFIG. 3, a schematically cross-sectional view of an exemplary embodiment of the lens assembly ofFIG. 1is shown. In this embodiment, the lens assembly24, shaped as a trapezoidal structure as a whole in a cross-sectional view, includes a bottom surface, a first complete reflective surface2411, a top surface2413, a second complete reflective surface2422, and the half-reflecting half-transmitting surface2412. The bottom surface is consisted of a right-bottom surface2410and a left-bottom surface2423. In the following description, the term “bottom surface2410,2423” is used to stand for a combination of the right-bottom surface2410and the left-bottom surface2423. The bottom surface2410,2423is parallel to the upper surface211of the header21. One end (lower end) of the first complete reflective surface2411is connected with a right end of the right-bottom surface2410, and the first complete reflective surface2411is extended from the right-bottom surface2410toward the top surface2413in a first angle so as to have another end (upper end) of the first complete reflective surface2411to connect a right end of the top surface2413. The top surface2413is parallel to the bottom surface2410,2423. One end (lower end) of the second complete reflective surface2422is connected with a left end of the left-bottom surface2423, and the second complete reflective surface2422is extended from the left-bottom surface2423toward the top surface2413in a second angle so as to have another end (upper end) of the second complete reflective surface2422to connect or adjoin a left end of the top surface2413. The half-reflecting half-transmitting surface2412is constructed inside the lens assembly24, and the half-reflecting half-transmitting surface2412is parallel to the first complete reflective surface2411. The laser beam91emitted by the laser element22is firstly injected upward vertically into the lens assembly24from the right-bottom surface2410. Then, the incident laser beam91hits the first complete reflective surface2411, and is deflected to travel horizontally toward the half-reflecting half-transmitting surface2412(shown as the laser beam911ofFIG. 3). Thereafter, the laser beam911traveling inside the lens assembly24would finally hit the half-reflecting half-transmitting surface2412. Then, a large portion of the laser beam911would be reflected and deflected vertically upward to travel along the optical axis90and leave the lens assembly24from the top surface2413, shown as the laser beam912ofFIG. 3. The outgoing laser beam912would be directed to the optical window, and thus form the first light beam92. On the other hand, at the half-reflecting half-transmitting surface2412, a small portion (the rest) of the laser beam911would penetrate through the half-reflecting half-transmitting surface2412, and then the penetrating laser beam913would hit the second complete reflective surface2422. Then, the laser beam913would be deflected by the second complete reflective surface2422so as to form the second light beam93traveling vertically downward and finally leaving the lens assembly24after penetrating the left-bottom surface2423. The outgoing second light beam93would be finally received by the monitor photodiode23.

In this embodiment, the lens assembly24is consisted of a first prism241and a second prism242. Viewing from the cross-sectional direction, the first prism241is shaped as a parallelogram structure, while the second prism242is shaped as an isosceles triangular structure. The junction surface of the first prism241and the second prism242is exactly the half-reflecting half-transmitting surface2412. By properly coating at least one optical film, then the half-reflecting half-transmitting surface2412can thereby perform a function of half-reflection and half-transmission. The at least one optical film can be plated on the half-reflecting half-transmitting surface2412of the first prism241, or on the half-reflecting half-transmitting surface2421of the second prism242. In this embodiment, at least one of the optical films has a refractive index (n-index) larger than the refractive index of the material for producing the first prism241and the second prism242. In one embodiment of the present invention, one of many qualified materials for the first prism241and the second prism242is a BK7 borosilicate glass having a refractive index of 1.5168. In addition, at least one of the optical films has a refractive index (n-index) ranging within 1.52˜2.5. Further, the first angle is an angle defined by the first complete reflective surface2411and the right-bottom surface2410, preferably an angle of 45°; and, the second angle is an angle defined by the second complete reflective surface2422and the left-bottom surface2423, preferably an angle of 45°. In addition, a light intensity of the first light beam92is about 80%˜95% of the light intensity of the laser beam91originally emitted by the laser element22, while the rest of the light intensity is contributed to the second light beam93. In the present invention, the percentages of the light intensity for the first light beam92and the second light beam93can be determined by evaluating the structure and the refractive index of the at least one optical film coated on the half-reflecting half-transmitting surface2412.

As shown inFIG. 1andFIG. 2of the present invention, a plurality of pins251,252are furnished to the header21by firstly penetrating both the upper surface211and the lower surface212of the header21and then extending downward by a predetermined length. The plurality of pins251,252include at least one signal pin251for transmitting signals and one ground pin252. In the packaging assembly of the present invention, by including the lens assembly24, the horizontal position of the laser element22can be offset from the optical axis90and thus become closer to the signal pin251. In addition, the laser element22applies bonding wires215to electrically connect corresponding bonding pads214of the respective pins251. In comparison with the conventional packaging assembly whose laser element is located right on the optical axis, the packaging assembly of the present invention enables the laser element20to be disposed at a position much closer to the signal pin251, such that the required length of the bonding wire215can be reduced substantially so as to minimize the signal loss. Further, Since the laser element20of the present invention can be located away from the optical axis90, thus direct influence of the reflected light deflected from the light-transmitting component264(lens or translucent plate) on the cap26upon the laser element22would be substantially reduced due to the existence of the lens assembly24. Thereupon, related shortcomings in the art can thus be improved significantly.