JPH0262955B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the manufacture of a laser diode module in which a laser diode chip, a condensing element, and an output optical fiber are mutually fixed in optimal positions.

<Prior Art> FIG. 1 shows an example of the configuration of a conventional laser diode module. The coupling end face of the output optical fiber 1 faces the condensing ball lens 2, and the condensing ball lens 2
faces the active layer of the laser diode chip 3. The laser diode chip 3 is mounted on a heat sink 4, and a current injection wire 5 is connected to the laser diode chip 3. When assembling these to manufacture a laser diode module, the following steps are performed. First, the laser diode chip 3 is mounted on the heat sink 4, the current injection wire 5 is attached to the laser diode chip 3, and a current is passed through it to cause the laser diode chip 3 to emit light. Next, the optical axis of the condensing ball lens 2 is set in three directions, that is, x, which are perpendicular to each other,
The active layer of the laser diode chip 3 is adjusted to the optimum position by finely adjusting it in the y and z directions. Furthermore, by adjusting the optical axis of the output optical fiber 1 in three directions, the optical axes of the output optical fiber 1, condensing ball lens 2, and laser diode chip 3 are aligned with each other, and the distance between them is adjusted. They are adjusted and fixed to each other so that they are optimized, that is, the maximum light output is emitted from the output optical fiber 1.

In this way, in the past, the optical axis was adjusted and the fixing assembly was performed while the laser diode was oscillating, so adjustments had to be made with the heat sink 4 attached, and assembly had to be done with the power turned on. There were drawbacks such as problems with reliability due to various reasons, and poor manufacturing efficiency.
In other words, if the laser diode chip 3 is allowed to oscillate without hermetic sealing, it may deteriorate and its reliability may decrease. , it becomes difficult to adjust the condensing ball lens 2 and the laser diode chip 3 at the same time.

In addition to the so-called individual lens method in which the output optical fiber 1 and the condensing ball lens 2 are separated as shown in FIG. 1, the laser diode module can be configured using an output optical fiber 1
A configuration is known in which an element with a light condensing function, such as a microlens, is provided on the coupling end face. This type of construction method is called the advanced lens method, and for example, "Optical and Quantum Electronics Research Group Materials"
OQE76−85”. This method also has the same problems as the individual lens method, which arise from assembly with the laser diode chip emitting light.

Although the following embodiments will explain the tip lens method, the laser diode module can also be manufactured using the individual lens method using substantially the same procedure.

<Summary of the invention> In order to solve these problems, the purpose of the present invention is to interconnect the output optical fiber, the condensing element, and the laser diode chip so that the laser diode chip remains in a non-emitting state and is in an optimal state. An object of the present invention is to provide a method for manufacturing a fixed laser diode module.

According to this invention, a signal light modulated with a wavelength near the oscillation wavelength of the laser diode chip is input from the output end of the output optical fiber, and the signal light is transmitted from the coupling end face of the output optical fiber to the laser diode. The active layer of the laser diode chip is irradiated, and the modulation signal obtained by detecting the terminal voltage of the laser diode chip at that time is measured.
Adjust the optical axes of the condensing element and the output optical fiber, and the spacing between them.

<Embodiment> FIG. 2 shows a structural diagram illustrating an embodiment of the present invention, and parts corresponding to those in FIG. 1 are given the same reference numerals. In this example, as a condensing element between the output optical fiber 1 and the laser diode chip 3, a condensing element is attached to the coupling end face of the output optical fiber 1. A condensing element 6 having a condensing function, such as a microlens formed by etching or the like, is attached. The method of this invention will be explained below. Now, signal light having the same wavelength as the wavelength emitted from the laser diode chip 3 from the outside and whose brightness is modulated by a modulation signal is input into the output optical fiber 1 from its output surface side, and the light is focused by the condensing element 6. The active layer of the laser diode chip 3 is irradiated with the beam spot. Since the laser diode chip 3 is a Pn junction element, when light of the oscillation wavelength hits the active layer, the light is absorbed by the active layer, and a terminal voltage is generated by the photovoltaic effect. Therefore, the terminal voltage is measured through the current injection wire 5, and the optical axis of the output optical fiber 1 and the laser diode chip 3 are adjusted so that the terminal voltage is maximized. The axis, the optical axis of the laser diode chip 3, and the optical axis of the condensing element 6 are
The directions are also optimally matched, and the distance between them, that is, the distance between the condensing element 6 and the laser diode chip 3 in this example, is optimal. When detecting a change in the terminal voltage while modulating the signal light, that is, detecting the terminal voltage and detecting the modulated signal, it is normal that the detection sensitivity increases as the modulated signal increases because it is less affected by noise. This is the same as when using the selection level meter.

Next, the results of experiments conducted on actual laser diodes will be explained. Figure 3 shows adjacent wavelengths
This figure shows a measurement system for measuring the injection beam spot position dependence of the terminal voltage of a laser diode chip using two laser diodes that oscillate at 0.88 μm. The light source laser diode 7 oscillates when a current is injected from the DC power source 8 . This light source laser diode 7 is intensity-modulated by a tracking scope 9 using a modulation signal of, for example, 100 MHz. Light from the light source laser diode 7 is focused by a focusing lens 10, passes through an optical isolator 11, is focused by a focusing lens 12, and enters the active layer of the laser diode chip 3. A 10 MHz modulated signal component is extracted from the electrical signal obtained by the current injection wire 5 of the laser diode chip 3 by a filter 13, and then sent to a 22 dB amplifier 1.
4 and input to the tracking scope 9.

Now, the output light modulated at 100MHz from the light source laser diode 7 is injected into the active layer of the laser diode chip 3 using a 20x objective condenser lens 12, and the modulated signal power of the terminal voltage obtained at the current injection wire 5 is controlled. Measure with King Scope 9. FIG. 4 shows the dependence of the modulated signal power detected by the terminal voltage on the beam spot position and the measurement results. Here, Δy is the thickness direction of the active layer of the laser diode chip 3, Δx is the direction parallel to the active layer, and Δz
shows the variation in the modulated signal power when the beam spot is displaced in the optical axis direction. From this result, the displacement amount by which the modulated signal power drops by 3 dB is Δx, Δz
It can be seen that both are ±5 μm and Δy is ±1 μm. 20
The beam spot size focused by the double objective condenser lens 12 is thought to be about 5 μm. Therefore, if the beam spot size is narrowed down to this extent by the condensing element 6 formed at the end of the output optical fiber, it becomes possible to align the optical axis with extremely high sensitivity. By incorporating the modulated signal power into a feedback control system for optical axis alignment, optical axis alignment can be performed automatically.

As mentioned above, the present invention is also applicable to the case where the condensing element is separated from the output optical fiber 1 as shown in FIG. The alignment of the optical axes of No. 3 and their spacing can be optimized.

<Effects> As explained above, according to the present invention, the optical axes of the output optical fiber, the laser diode chip, and the condensing element are aligned in a state where no current flows through the laser diode chip (non-emission state), so the following effects can be achieved. It has the following advantages.

(1) There is no risk that the laser diode chip will deteriorate due to light emission, increasing reliability.

(2) Displacement detection sensitivity is high because it measures modulated signals.

(3) Optical axis alignment can be easily automated without the need to perform it in an inert gas atmosphere.

(4) Since the laser diode chip side can also be displaced for optical axis alignment, there is greater freedom in the manufacturing process.

[Brief explanation of the drawing]

Fig. 1 is a block diagram illustrating optical axis alignment of a conventional laser diode module, Fig. 2 is a block diagram illustrating optical axis alignment of the laser diode module manufacturing method of the present invention, and Fig. 3 is a block diagram illustrating optical axis alignment of a conventional laser diode module. FIG. 4 is a diagram showing the beam spot position dependence of the modulated signal power detected by the terminal voltage, which is the result of measurement using the measurement system of FIG. DESCRIPTION OF SYMBOLS 1... Optical fiber for output, 2... Ball lens for focusing, 3... Laser diode chip, 4... Heat sink, 5... Wire for current injection, 6... Focusing element.

Claims (1)

[Claims] 1. A coupling end face of an output optical fiber is arranged near the laser diode chip via a condensing element, and these laser diode chips and condensers are arranged so that the output light from the laser diode chip is coupled to the output optical fiber. In a method for manufacturing a laser diode module in which an optical element and an output optical fiber are fixed to each other, a modulated signal light having a wavelength near the oscillation wavelength of the laser diode chip is input from the output end of the output optical fiber. Then, the signal light is irradiated from the coupling end face of the output optical fiber to the active layer of the non-emitting laser diode chip, the terminal voltage of the laser diode chip at that time is detected, and a modulation signal of the terminal voltage is generated. A laser diode module characterized in that the optical axes of the laser diode chip, the condensing element, and the output optical fiber and the spacing therebetween are adjusted so that the modulation signal of the terminal voltage is maximized. manufacturing method.