KR100492846B1 - Semiconductor light source of optical transmitter with output control - Google Patents

Abstract

The present invention provides an output control optical transmitter of a semiconductor light source capable of sending part of an output of a semiconductor light source to a photodetector for output observation and output correction, wherein a window having a reflective curved surface is formed to reflect and collect light incident from the light source. A central axis on the traveling path of the light passing through the reflective curved surface while forming the exterior of the TO can, the inclined support plate on which the light source and the photodetector are inclinedly seated so as to prevent interference of the optical path reflected and incident on the reflective curved surface. And a housing for integrally supporting the focusing lens and the optical fiber so as to coincide with each other. The concave and inclined shapes of the reflecting surface of the TO-can window allow the light to be reflected to reach the absorption region of the photodetector. Coupling efficiency of optical transmitter by increasing the utilization efficiency of reflected light and minimizing the amount of light required for output observation In addition, it is possible to prevent the disturbance of the light source due to the light reflected mostly toward the light detector.

Description

Output control optical transmitter of semiconductor light source {SEMICONDUCTOR LIGHT SOURCE OF OPTICAL TRANSMITTER WITH OUTPUT CONTROL}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an output controlled optical transmitter of a semiconductor light source capable of sending part of the output of the semiconductor light source to the photodetector for output observation and output correction. The present invention relates to an output control optical transmitter of a semiconductor light source that focuses light to reach an absorption region of a photodetector.

 Recently, with the increase of data to be transmitted through the Internet, the existing communication system by an electric signal has been converted into an optical communication system that can exchange a large amount of data using an optical signal. Representative optical devices used in such optical communication systems are optical fibers, optical transmitters, and optical receivers. In the case of an optical transmitter, high speed, miniaturization, low cost, and ease of mass production have become important factors for commercialization.

In general, a semiconductor light source such as a vertical cavity surface emitting laser device (VCSEL) is affected by changes in external environment such as use time and temperature rise during use. For example, when the outside temperature increases, the temperature in the VCSEL rises together to reduce the intensity of output light despite the same driving voltage. This change in the output light intensity severely affects the bit error ratio (BER), causing a decrease in communication quality. Accordingly, there is a need for a feed-back system that detects a change in the output light intensity of the VCSEL and feeds back a signal corresponding thereto to the driving circuit of the VCSEL to make the output light intensity of the VCSEL constant. . Often, the feedback system includes a photodetector for monitoring that absorbs a portion of the output light of the VCSEL and outputs an electrical signal in accordance with the absorbed light intensity.

The structure of a device for observing and correcting changes in output light intensity, which is generally used, is to put a part of a light source output into a photodiode as a photodetector to monitor the trend of the output. Particularly when directing a surface-emitting photodiode for surface-emitting lasers and photodetectors directly onto a plane, a partial reflector, beam splitter, or diffraction grating is output between the light source and the optical fiber to direct a portion of the light source output to the photodiode. Put on the path. Among the most widely used and industrially interesting structures, as shown in FIG. 1, the TO can sealing the light source 1 and the photodetector 2 as a structure registered in US Patent No. 6,069,905 at Honeywell, Inc. The window 4 of the transistor outlet 3 is used as a reflective surface to partially reflect the VCSEL diode beam 5 into the photodetector 2. The main light axis of the VCSEL diode 1 and the window 4 of the TO can 3 are directed so that the center of distribution of the light 6 reflected from the window 4 of the TO can 3 is directed to the photodetector 2. It is not parallel and is inclined about 10 °. This directs the center of distribution of the light 6 reflected from the window 4 of the TO can 3 towards the photodetector 2 while being irradiated back to the light source 1 to impair the operation of the light source 1. prevent.

However, this prior art has the following problems.

First, in the structure having a symmetry around the light output main optical axis of the light source, the highest density of photons reflected from the reflection window is irradiated back to the light source, which may cause an obstacle to the operation of the light source. On the other hand, the amount of reflected light distributed to the photodetector becomes small, and the amount of reflected light is inevitably increased to put enough light into the photodetector. This reduces the amount of light directed to the receiving end, which in turn reduces the coupling dfficiency to the optical fiber.

Second, in order to be able to observe the output trend of the light source, the reflection performance of the absorbed light of the photodiode generally used as a photodetector is important. Generally, the avalanche-type photodiode has a reaction performance that is several times larger than that of a P-type-intrinsic-n-type (PIN) type photodiode, but the manufacturing cost is high and the circuit required for driving the photodiode is high. There is a design difficulty. When using a PIN type photodiode having a relatively low reaction performance, the active area absorbing the reflected light must be enlarged to compensate for the low reaction performance. If the active area of the photodiode is limited, there may be a problem in packaging, and the accuracy of output stability may be degraded.

Third, in the case of using the light output main light axis of the light source and the inclined reflecting surface, the light output passes through the reflecting surface and the path is refracted or the spatial light cross-sectional distribution is distorted, thereby reducing the optical connection efficiency to the optical fiber.

Accordingly, the present invention is to solve the above disadvantages, concave and inclined the shape of the reflective surface of the TO can window to collect the reflected light to reach the absorption region of the photodetector to improve the utilization efficiency of the reflected light The output control optical transmitter of the semiconductor light source can increase the coupling efficiency of the optical transmitter by minimizing the amount of light required to observe the output, and prevent the operation disturbance of the light source due to the light reflected mostly toward the optical detector. The purpose is to provide.

In order to achieve the above object, the present invention provides an output control optical transmitter of a semiconductor light source capable of sending part of an output of a semiconductor light source to a photodetector for output observation and output correction, so as to focus and reflect light incident from the light source. A TO can having a reflective curved window formed thereon, an inclined support plate on which the light source and the photodetector are inclinedly seated so as to prevent interference of the optical path reflected after the incidence with respect to the reflective curved surface, and a transparent curved surface which forms the exterior of the TO can And a housing integrally supporting the focusing lens and the optical fiber such that the central axis coincides on the path of the light.

  The above objects and various advantages of the present invention will become more apparent from the preferred embodiments of the invention described below with reference to the accompanying drawings by those skilled in the art.

Hereinafter, with reference to the accompanying drawings will be described in detail an embodiment of the present invention.

2 and 3 are sectional views showing the output observation of the photodetectors according to the first and second embodiments of the present invention, wherein a window of a TO outlet (transistor outlet) 19 of light output by the light source 16 is shown; 18 shows progress through. The light source 16 is located at the rotationally symmetric center of the entire structure, and the output is configured to direct to the window 18 of the TO can 19. The window 18 of the TO can 19 may be formed as a borosilicate, fused silica or optical polymer, and has a concave curved surface toward the light source 16. The concave curved surface may be made by a method of injection molding by heating the material for the lens to a pre-designed TO can 19 at a high temperature. The window 18 of the TO can 19 is configured to reflect a part of the beam output of the light source 16 to be irradiated in the direction in which the photodetector 17 is located. In FIGS. 2 and 3, reference numerals 14 and 15 denote lower support plates for electrically insulating the photodetector 17 and the light source 16, respectively, and reference numerals 11, 12 and 13 denote the photodetector 17 and the light source ( 16) Input and output terminals for driving.

The first embodiment shown in FIG. 2 is a case where the light source 16 and the photodetector 17 are integrated on the same lower support plate 14, and the second embodiment shown in FIG. 3 is the light source 16 and the light. The case where the detector 17 is integrated using the lower support plate 15 in the separated form is shown.

A part of the light output of the light source 16 reflected from the concave curved surface has a Gaussian distribution of the light source 16 and is concentrated by the photodetector 17. The beam waist of the output irradiated to the photodetector 17 is finally determined by the degree of concaveness of the TO can 19. The amount of light reflected can be changed using a metal coating or the like that can increase the reflectivity on the reflective surface. The radius of curvature of the window 18 of the TO can 19 is designed to receive all the beam waist reflected from the window 18 of the TO can 19 in the active region of the photodetector 17. Condensing all the reflected light with the photodetector 17 reduces the amount of reflected light required for monitoring, since the use efficiency of the light reflected from the window 18 of the TO can 19 is significantly improved compared with the conventional art. This means that the amount of light transmitted to 20 is increased.

If only the window 18 of the TO can 19 is concave and has a symmetrical curved surface at the central axis 21, the reflected light is directed to the light source 16, which may cause a failure in driving the light source 16. A support inclining the light source 16 and the photodetector 17 to tilt the window 18 of the TO can 19 between the vertical plane of the light source 16 and the vertical plane of the window 18 of the TO can 19. For example, it is provided on the inclined support plate 22 so that the reflected light is directed only to the photodetector 17, thereby preventing the operation failure of the light source 16 due to the reflected light.

On the other hand, in the optical transmitter according to the present invention, the window 18 of the TO can 19 is inclined with respect to the main light axis of the light source 16, so that the light distribution transmitted through the window 18 to the optical fiber may be distorted. The propagation path of the chief ray axis is also refracted. The distortion of the spatial light distribution and the refraction of the chief ray axis can affect the coupling efficiency into the optical fiber.

In the present invention, the distortion of the light distribution is minimized by appropriately designing the center of curvature of the first concave reflection surface of the window 18 of the concave TO can 19 and the radius of curvature of the second concave surface. In addition, the coupling loss of the optical fiber due to the path deflection of the main optical axis was minimized by aligning the optical fiber with the new primary optical axis refracted.

In particular, as in the first embodiment shown in FIG. 2, the window of the TO can 19 when the spacing between the light source 16 and the photodetector 17 is a very small integrated chip with tens to hundreds of micrometers (μm). The tilt angle of (18) is small so that the light distribution distortion and the chief axis axis refraction are not large, so that the reduction in coupling efficiency can be further reduced.

In the present invention, since more than 90% or all of the reflected beams are directed to the active region of the photodetector 17, the coupling to the ultimate optical fiber may occur even if the reduction of the coupling efficiency due to distortion of the light distribution or path deflection of the chief ray axis occurs to some extent. The efficiency can be increased.

On the other hand, as in the second embodiment shown in FIG. 3, when the light source 16 and the photodetector 17 are used in separate forms using the lower support plates, it is difficult to reduce the interval to within 100 microns. Therefore, in such a case, the housing 33 has a structure in which the central axes of the optical fiber 20 and the condenser lens 24 are tilted and supported to coincide with the optical path irradiated from the light source 16, thereby minimizing the coupling loss. have.

The TO can 19 in which the optical transmitter is installed and the housings 23 and 33 in which the optical fiber 20 is to be mounted may be manufactured by using a mold designed in advance by an optical polymer.

Detailed description of the geometric position of the light source 16 and the photodetector 17 is as follows.

Since the light reflected by the window 18 of the concave TO can 19 must be put into the active area of the photodetector 17, the light collected by the window 18 of the concave TO can 19 is converted into a photodetector ( It should come to the center of the active area of 17). The distance between the light source 16 and the photodetector 17 has a correlation with the distance between the light source 16 and the window 18 of the TO can 19 as shown in equation (1).

Where L is the distance between the light source 16 and the photodetector 17, H is the vertical distance between the light source 16 and the window 18 of the TO can 19, and θ is the light source 16 and TO It is an angle of inclination made by each vertical plane of the window 18 of the can 19. The window 18 of the TO can 19 appropriately designs the radius of curvature of the reflective surface which is concave at the top so that the path refraction when the light output from the light source 16 is transmitted is minimized. The curvature of the housing focusing lens 24 is designed in consideration of the distance from the optical fiber 20 to be located behind the lens and the distance between the light source 16 and the focusing lens 24.

As in the first embodiment shown in FIG. 2, when the light source 16 and the photodetector 17 are integrated on the same lower support plate 14, the distance between the light source 16 and the photodetector 17 is several tens. The angle of inclination θ is within 2 ° when the height of the window 18 of the TO can 19 is about 2 to 4 mm. If the angle of inclination is less than 2 °, the output light distribution is distorted through the window 18 of the TO can 19, so that the coupling efficiency to the optical fiber is not seriously reduced.

On the other hand, as in the second embodiment shown in Figure 2, when using the light source 16 and the photo detector 17 in a separate form using the lower support plate 15, respectively, the spacing is reduced to within 100 microns Hard. In consideration of manufacturing convenience, when the distance between the light source 16 and the photodetector 17 is 1 mm and the height of the window 18 of the TO can 19 is about 2 to 4 mm, the inclined angle θ is about 10 It becomes about degree. In this case, the coupling loss to the optical fiber due to the distortion of the output light distribution through the window 18 of the TO can 19 and the path refraction of the chief ray axis is increased, and the optical fiber 20 is connected to the light source 16 by the housing 33. Coupling loss can be minimized by tilting it to align with the vertical plane.

Referring to the operation principle of the optical transmitter according to the present invention configured as described above are as follows.

The output of the light source 16 is partially reflected and partially transmitted through the window 18 of the TO can 19. The window 18 of the TO can 19 is positioned to be inclined with the light source 16 and to face the photodetector 17 so that the reflected light is collected by the concave surface of the window 18 of the TO can 19. Most of the collected light is absorbed in the active region of the photodetector 17. The intensity of the optical signal detected by the photodetector 17 is proportional to the output intensity of the light source 16 transmitted to the optical fiber. When the intensity of the optical signal detected by the photodetector 17 is lowered, the driving current of the light source 16 is increased to increase the light output of the light source 16, and when the intensity of the optical signal detected by the photodetector 17 is increased The output of the optical transmitter can be kept constant by reducing the driving current of the light source 16 to reduce the light output of the light source 16.

In the above description, it should be understood that those skilled in the art can only make modifications and changes to the present invention without changing the gist of the present invention as it merely illustrates a preferred embodiment of the present invention.

As described above, according to the present invention, there is no limitation on the size of the active area of the photodetector since the reflected light is focused on the photodetector to monitor the output of the surface emitting laser by placing a concave reflective surface in the window of the TO can. Even if the responsivity of is low, output observation can be performed.

In addition, since the light reflected from the window of the TO can is collected and absorbed in the active area of the photodetector, the amount of light reflected for output observation can be reduced, and as a result, the amount of light transmitted to the optical fiber with the same output light source can be increased. The optical transmitter of connection efficiency can be manufactured.

In addition, by using the inclined concave window of the TO can prevent the output light of the light source is reflected from the window of the TO can not be irradiated back to the active region of the light source to prevent driving disturbance of the light source due to the reabsorption of the reflected light. have.

It is also possible to use a standard TO can structure which is not tilted using a housing structure aligned with the inclined support plate.

1 is a cross-sectional view showing an output control optical transmitter of a semiconductor light source according to the prior art;

2 is a cross-sectional view showing output observation of the photodetector according to the first embodiment of the present invention;

3 is a cross-sectional view showing output observation of a photodetector according to a second embodiment of the present invention;

<Description of the symbols for the main parts of the drawings>

11, 12, 13; Terminals 14 and 15; Lower support plate

16; Light source 17; Photodetector

18; Genesis 19; TO can

20; Optical fiber 21; Central axis

22; Inclined support plates 23, 33; housing

24; Housing focusing lens

Claims (3)

In the output control optical transmitter of the semiconductor light source capable of sending part of the output of the semiconductor light source to the photodetector for output observation and output correction, A TO can having a window provided with a reflective curved surface for condensing while reflecting light incident from the light source; An inclined support plate on which the light source and the photodetector are inclined and mounted so as to prevent interference of the light path reflected after the incident light with respect to the reflective curved surface; A housing for integrally supporting the focusing lens and the optical fiber such that the central axis is coincident with the traveling path of the light passing through the reflective curved surface while forming the exterior of the TO can. Output control optical transmitter of the light source comprising a. The method of claim 1, Output control optical transmitter of a semiconductor light source, characterized in that the gap between the light source and the photodetector is set on the same lower support plate in the case of a very small integrated chip with tens to hundreds of micrometers (µm). The method of claim 1, And a light source and a photodetector, each of which is installed on a lower support plate in a separated form, so that the optical fiber is inclined to align the housing so that the optical fiber is aligned with the vertical plane of the light source.