An apparatus for manufacturing an optical transmission module

Abstract: A manufacturing apparatus comprises a heating device (7) for heating a semiconductor laser in an optical transmission module package (1), a temperature sensor (3) for measuring a temperature of the semiconductor laser, an optical power meter (5) for measuring an optical output of the semiconductor laser, a manipulator (10) for positioning an end of an optical fiber (2) to a desired position and a control unit (13) for controlling the heating device (7) and the manipulator (10). The control unit (13) reads data measured by the temperature sensor (3) and the optical power meter (5) and stores the data as a temperature-optical output characteristic of the semiconductor laser while driving the heating device. The control unit (13) also derives data of the optical output of the semiconductor laser produced through the optical fiber (2) from time to time while solder is fused and solidified when the end of the optical fiber 2 is soldered and fixed to the predetermined position in the package (1). The measurement of the optical output is modified, in accordance with the temperature-­ optical output characteristic and the temperature of the semiconductor laser, and the manipulator (10) is driven based on the modified measurement so that the position of the end of the optical fiber (2) is finely adjusted. In this manner, the optical fiber (2) is fixed at a maximum light coupling efficiency position.

Description: The present invention relates to an apparatus and a method for manufacturing an optical transmission module, and more particularly to an apparatus and a method for manufacturing an optical transmission module used in light communication systems such as optical LAN or optical CATV systems. An output laser beam from a semiconductor laser has a spread angle of ±20 degrees vertically and ±5 to ±10 degrees horizontally. Accordingly, when a semiconductor laser and an optical fiber are coupled together to manufacture an optical transmission module, they are usually coupled by lens coupling systems. In a module structure called a pigtail type, the optical fiber is fixed to an optical fiber mount in the vicinity of the semiconductor laser which is fixed on a stem. In the pigtail type module, a position precision of ±0.2 to ±0.5 µm is required particularly for a single mode ball lens fiber. In fixing the optical fiber, fusing metal such as solder is used and the optical fiber is finely positioned to a maximum output position while the optical output from the optical fiber is monitored. However, when the optical fiber is soldered, the adjacent semiconductor laser is also heated and the optical output of the semiconductor laser changes with the temperature rise as shown in Fig. 3. Accordingly, it is not possible to discriminate the change of the optical output due to the displacement of the optical axis from that due to the temperature change of the semiconductor laser, by monitoring the optical output. Accordingly, in the past, it has been difficult to fix the optical fiber at an optimum position. EP-A-0 234 057 discloses an apparatus and method as defined in the pre-characterizing part of claims 1 and 2, respectively. Various measures are proposed for eliminating thermal influences onto the alignment between a laser and the end face of an optical fibre. Specifically, visual location markers indicate approximately the position to be occupied by the injection laser header. Though it is indicated that prior to a soldering step used to fix the end portion of the fibre to a mount the optimum position is located, the optimum position of the end portion of the fibre and the optical output of the semiconductor laser as well are affected by the heat produced during the soldering step, so that an optimum position of the end face of the optical fibre cannot be obtained. It is an object of the present invention to provide an apparatus and a method for manufacturing an optical transmission module which permit fixing of the optical fiber at an optimum position. This object is solved by the features of claims 1 and 2, respectively. In particular, the manufacturing apparatus of the present invention comprises a heating device for heating a semiconductor laser in an optical transmission module package, a temperature sensor for measuring the temperature of the semiconductor laser, an optical power meter for measuring the optical output of the semiconductor laser, a manipulator for holding the optical fiber and positioning an end of the optical fiber to a desired position and a control unit for controlling the heating device and the manipulator. The control unit reads data measured by the temperature sensor and the optical power meter and stores the data as a temperature-optical output characteristic of the semiconductor laser while drivingthe heating device. The control unit also derives data of the optical output of the semiconductor laser produced through the optical fiber from time to time while solder is fused and solidified when the end of the optical fiber is soldered and fixed to the predetermined position in the package. The measurement of the optical output is modified in accordance with the temperature-optical output characteristic and the temperature of the semiconductor laser, and the manipulator is driven on the basis of the modified measurement so that the position of the end of the optical fiber is finely adjusted. In this manner the optical fiber is fixed at a maximum light coupling efficiency position. One embodiment of the invention will now be described by way of example with reference to the accompanying drawings, in which: Fig. 1 is a manufacturing apparatus for an optical transmission module in accordance with one embodiment of the present invention, Fig. 2 is a partially cut-away perspective view illustrating the inside of the optical transmission module, and Fig. 3 is a graph of the optical output characteristic relative to temperature change of a semiconductor laser. A heating device 7 is mounted on an anti-vibration table 8 with the intervention of a jig 9. An optical module package 1 which accommodates a semiconductor laser and a peripheral circuit is placed on the heating device 7. The semiconductor laser is mounted on a chip carrier 22 which is die-bonded to a hybrid IC substrate 21 as shown in Fig. 2. The peripheral circuit of the semiconductor laser is mounted on the hybrid IC substrate 21. The heating device 7 is powered from a power supply 12 to heat the package 1 placed thereon. The power to the heating device 7 is controlled by a microcomputer 13. A temperature sensor 3 measures the temperature of the semiconductor laser in the package 1. Manipulators 10 and 11 are mounted on the anti-vibration table 8, in addition to the heating device 7. The manipulator 10 holds one end of an optical fiber 2. The position of the end 24 of the optical fiber 2 is adjusted with a high precision through the drive of the manipulator 10. The other end of the optical fiber 2 is connected to an optical power meter 5, which measures the optical output of the semiconductor laser produced through the optical fiber 2. The manipulator 11 holds a soldering iron 6. The position of the soldering iron 6 is adjusted through the drive of the manipulator 11. The microcomputer 13 stores the optical output of the semiconductor laser measured by the optical power meter 5, under a predetermined condition. The microcomputer 13 also controls the heating device 7 and the manipulators 10 and 11 in accordance with the measurements of the temperature sensor 3 and the optical power meter 5. A process to manufacture the optical transmission module by the apparatus of the present embodiment is now explained. First, the end of the optical fiber 2 is inserted into the package 1 and the end plane thereof is approached to the optical output plane of the semiconductor laser in the package 1. The coating of the end 24 of the optical fiber 2 is removed and a metal film is vapor-deposited instead of the coating. The end 24 is arranged above a fiber mount table 23 placed on the hybrid IC substrate 21. A constant current which is about 10 to 30 mA larger than the threshold current of the semiconductor laser is supplied to the semiconductor laser in the package to cause the semiconductor laser to emit light. The position of the end of the optical fiber is changed by the manipulator 10 while the optical output of the semiconductor laser produced through the optical fiber 2 is measured by the optical power meter 5. The drive of the manipulator 10 is stopped at the position where the optical power meter 5 detects a maximum output. At this position, the optical fiber 2 and the semiconductor laser in the package 1 are in an optimum coupling state. Then, a current is supplied to the heating device 7 to start the heating of the package while the above constant current is supplied to the semiconductor laser. The optical output of the semiconductor laser produced through the optical fiber 2 is measured by the optical power meter 5 while the temperature of the semiconductor laser is measured by the temperature sensor 3. The microcomputer 13 reads and stores the data measured by the temperature sensor 3 and the optical power meter 5 at every temperature rise of 0.1 °C from the start of heating until the temperature of the semiconductor laser reaches approximately 60 °C. In general, the optical output of the semiconductor laser decreases with the temperature rise. Then, the heating device 7 is controlled in accordance with the data measured by the temperature sensor 3 such that the temperature of the semiconductor laser is stabilized around 45 °C. This is controlled by the microcomputer 13. This heating is effected to facilitate the fusion of the solder in the subsequent soldering process. Then, the solder is placed on the fiber mount table 23 across the end 24 of the optical fiber 2. Then, the heated soldering iron 6 is caused to approach to the solder on the fiber mount table 23 by driving the manipulator 11, and the solder is fused. The semiconductor laser is now in a light emitting state with the supply of the constant current. The end 24 of the optical fiber 2 has already been positioned to optically couple to the semiconductor laser in the measurement step of the temperature-optical output characteristic. However, the position is displaced during the step of fusing and solidifying of the solder. Thus, the position of the end 24 should be finely adjusted during the fusion and solidification of the solder such that the light coupling efficiency between the optical fiber 2 and the semiconductor laser reaches a maximum. During the fine adjustment, the semiconductor laser is affected by the heat of soldering and the optical output of the semiconductor laser varies even if the current supplied to the semiconductor laser is constant. Accordingly, a modification is made to eliminate the effect of the temperature from the optical output measured by the optical power meter 5 and a fine adjustment is made to bring the modified measurement of the optical output to a maximum. This fine adjustment is done by controlling the manipulator 10 by the microcomputer 13. The microcomputer 13 eliminates the change of the output of the semiconductor laser due to the change of temperature from the optical output measured by the optical power meter 5 and calculates a modified optical output which is free from the temperature-optical output characteristic of the semiconductor laser. The microcomputer 13 controls the drive of the manipulator 10 from the fusion of the solder to the solidification of the solder so that the calculated modified optical output is always kept maximum. In this manner, the optical fiber 2 and the semiconductor laser are optically coupled at the maximum coupling efficiency. In the present embodiment, the optical output of the optical laser is measured through the optical fiber 2 to obtain the temperature-optical output characteristic of the semiconductor laser. Alternatively, the optical power meter 5 may be approached to the semiconductor laser to directly measure the optical output, or it may be measured through a separate measuring optical fiber.

Claims: An apparatus for manufacturing an optical transmission module having a semiconductor laser (22) in a package (1) and an optical fiber (2) optically coupled to the semiconductor laser (22), said apparatus comprising: a heating device (7) for heating said semiconductor laser (22); a temperature sensor (3) for measuring the temperature of said semiconductor laser (22); an optical power meter (5) for measuring the optical power of said semiconductor laser (22); and a first manipulator (10) for holding said optical fiber (2) and positioning an end of said optical fiber (2) to a desired position; characterized by a soldering iron (6); a second manipulator (11) for positioning said soldering iron (6) to a predetermined position; a control unit (13) for controlling said heating device (7) and said manipulators (10, 11); said control unit (13) carrying out a first control operation of reading, from time to time, data measured by said temperature sensor (3) and said optical power meter (5) and storing the data as a temperature-optical output characteristic of said semiconductor laser (22) while the temperature of said semiconductor laser (22) is changed and a constant current is supplied to said semiconductor laser (22), and a second control operation of maintaining the current to the semiconductor laser (22) at the value used in the first control operation, deriving temperature data from said temperature sensor (3), deriving optical output data of said semiconductor laser (22) through said optical fiber (2) from said optical power meter (5), modifying the measurement of said optical output in accordance with said temperature-optical output characteristic and said temperature data to eliminate the effect of the temperature from the optical output measured, and driving said first manipulator (10) to bring the modified measurement to maximum. A method for manufacturing an optical transmission module having a semiconductor laser (22) in a package (1) and an optical fiber (2) optically coupled to the semiconductor laser (22), comprising the step of fixing the end of the optical fiber (2) by solder in said package (1); characterized by the following steps: measuring a temperature-optical output characteristic of said semiconductor laser (22) with a constant current being supplied to the semiconductor laser (22); measuring an optical output of said semiconductor laser (22) produced through said optical fiber (2) during a period from the fusion of the solder to the solidification of the solder; modifying the measurement of the optical output in accordance with the temperature-optical output characteristic and temperature of the semiconductor laser (22) to eliminate the effect of the temperature from the optical output measured; and adjusting the position of the end of said optical fiber (2) on the basis of the modified measurement, thereby the end of said optical fiber (2) is fixed at a maximum light coupling efficiency position.

Inventors: SHIGA NOBUO C O YOKOHAMA WORKS, SHIGA, NOBUO C/O YOKOHAMA WORKS
Applicants: SUMITOMO ELECTRIC INDUSTRIES, SUMITOMO ELECTRIC INDUSTRIES, LTD.
Application year: 1989
Main classification: G02B6
IPC codes: G02B6