JPH01272181A - Manufacture of protective film for protecting end face of semiconductor laser - Google Patents

Abstract

PURPOSE:To obtain a method of monitoring reflectance directly by using a semiconductor laser oscillating at a wavelength similar to that of a semiconductor laser to be monitored as a monitoring light source. CONSTITUTION:An active layer is formed of GaAs, and Al2O3 is vapor-deposited on the end face of a semiconductor laser 104 oscillating at a wavelength of 870nm and on a GaAs substrate 105 for monitoring. For monitoring, a semiconductor laser oscillating at 870nm is used in constant optical output operation. An optical system 107 is used for making the laser beam parallel with the optical axis, which are projected onto the monitoring GaAs substrate 105, and the light reflected from the substrate 105 is received by a monitoring photodiode 108. Reflectance of the GaAs coated with Al2O3 can be controlled between 40% and 3% by altering the thickness of the Al2O3 film.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for controlling the reflectance of a facet protection film of a semiconductor laser.

[Prior Art] Conventionally, as a method for monitoring the reflectance of the end face protection film of a semiconductor laser, for example, when a vacuum evaporation method is used, a crystal oscillator is inserted together with the semiconductor laser, and the problem that occurs due to deposits adhering to the crystal oscillator is A known method is to detect a change in the emission frequency, calculate the film thickness, and calculate the reflectance for each wavelength from the value.

[Problem to be Solved by the Invention 1] However, the conventional reflectance monitoring method calculates the film thickness by calibrating coefficients such as the density of deposits attached to the crystal resonator, which inevitably results in large miscalculations of the reflectance. turn into.

Furthermore, although the original purpose is to control reflectance, there is a direct problem in that information regarding reflectance cannot be obtained using conventional methods.

Therefore, the present invention aims to solve these conventional problems and provide a method for directly monitoring reflectance.

[Means for Solving the Problems] In order to solve the above-mentioned problems, the method for manufacturing a semiconductor laser end face protection film of the present invention uses a monitoring light source as a means for monitoring the end face protection film thickness of a semiconductor laser. , a method for producing an end face protection film for a semiconductor laser, comprising means for emitting light emitted from the monitoring light source to a film thickness monitor; and means for detecting reflected light intensity or transmitted light intensity from the film thickness monitor; The present invention is characterized in that a semiconductor laser whose oscillation wavelength is approximately the same as the oscillation wavelength of the semiconductor laser is used as the monitoring light source.

[Example] Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an apparatus for manufacturing a semiconductor laser end face protection film using an electron beam evaporation method.

A vapor deposition system equipped with an electron beam heating device 103 in a vacuum container 101 was used, and the protective film material 102 was made of A 12 t O.
s is used.

Then, A I2 s On is deposited on the end face of the semiconductor laser 104, which uses GaAs as an active layer and oscillates at a wavelength of 870 nm, and on the monitoring GaAs substrate 105.

The monitor semiconductor laser 106 is one that oscillates at 870 nm and is operated in a constant light output operation, and an optical system 107 is used to convert it into parallel light, which is irradiated onto the monitor GaAs substrate 105 , and the reflected light is received by the monitor photodiode 108 . It takes a form.

In addition, GaAs coded with A 12 z Os
By changing the film thickness of AI2*Os, the reflectance of
At a wavelength of 870 nm, it exhibits reflectance characteristics as shown in Figure 2.
In this case, the reflectance can be controlled between 40% and 3%.

Next, the operation will be explained.

In order to create a high-power semiconductor laser, consider the case where the reflectance of the semiconductor laser end face is lowered and an end face protection film with a reflectance of 3% is created.

In this case, since the monitoring GaAs substrate 105 and the semiconductor laser 104 are vapor-deposited under the same conditions, the monitoring GaAs substrate 105 and the semiconductor laser 104 are deposited under the same conditions.
The reflectance of the aAs substrate and the end face reflectance of the semiconductor laser 104 show exactly the same change due to A m On deposition, so a change in the output from the monitor photodiode 108 directly becomes a change in the reflectance.

Here, the output of the monitor photodiode 108 is 100%.
is defined as the output value when a mirror is placed in place of the monitor GaAs substrate 105.

Then, if the vapor deposition is stopped when the output of the monitor photodiode 108 shows 3%, the end face reflectance of the semiconductor laser 104 will surely become 3%.

Further, Aj2, O and film thickness at this time were 1300.

Furthermore, when it is desired to select an appropriate value for the end face reflectance in order to obtain a semiconductor laser with high output and a low threshold current value, it is possible to ensure that the vapor deposition is stopped when the output of the monitor photodiode 108 reaches the desired value. Therefore, the desired end face reflectance can be obtained.

Above, we have described an example in which the end face reflectance of a semiconductor laser having a GaAs active layer was monitored using a GaAs substrate as a reflectance monitor. However, the reflectance monitor is not limited to GaAs substrates, and may be made of silicon, glass, etc. Of course, it is also possible to obtain sufficient monitor characteristics by performing some calibration.

Further, even if the wavelength of the monitoring semiconductor laser is slightly different from the wavelength of the semiconductor laser to be deposited, sufficient monitoring characteristics can be obtained by just performing some calibration.

Further, the semiconductor laser forming the end face protection film is not limited to GaAs-based semiconductor lasers, but can be applied to general semiconductor lasers such as InP-based ones. This is particularly effective for devices such as distributed feedback semiconductor lasers where reflection from the end face is to be avoided.

In addition, the protective film material is AI! , *In addition to Os, various materials such as amorphous Si and SiO□ may be used.

Further, the protective film is not limited to a single layer, and may of course be a multilayer film, and a high reflectance or, conversely, a low reflectance can be obtained.

In addition, it is preferable that the wavelength difference between the monitoring semiconductor laser and the semiconductor laser to be vapor-deposited is small;
If it is on the order of nm, errors due to refractive index dispersion etc. will be sufficiently small, allowing precise reflectance control. However, by performing sufficient calibration, the wavelength of the two lasers can be adjusted to 75
Sufficient accuracy is usually obtained between 0 nm and 1600 nm.

Of course, the monitor photodiode may be any other photodetecting element.

Alternatively, the output of the monitor photodiode may be fed back to the electron beam heating device to form a closed loop control system.

[Effects of the Invention] The method for manufacturing a semiconductor laser end face protection film of the present invention has the following advantages.

(i) Since direct reflectance control is performed, reflectance control can be performed with precision and high reproducibility no matter what material is selected for the end face protective film.

(ii) Since a laser having a wavelength similar to the oscillation wavelength is used for reflectance observation, measurement errors can be reduced.

In particular, if the film thickness monitor is made of the same material as the active layer material of the semiconductor laser and the monitoring semiconductor laser has the same oscillation wavelength, the reflectance error can always be kept within 2%.

(iii) Since the monitor semiconductor laser, the monitor photodiode, and the optical system are extremely small, they can be housed in a vacuum apparatus, and there is no need for trouble such as optical axis alignment.

Moreover, since the positional accuracy of the optical system has no effect on the measurement accuracy, the optical system is easy to manufacture.

(iv) Since optical measurement is used, there is no malfunction even in the presence of strong electromagnetic noise caused by gravel from electron beam heating, etc.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a semiconductor laser end face protection film manufacturing apparatus using an electron beam evaporation method for explaining an embodiment of the present invention. FIG. 2 shows GaA for explaining the embodiment according to the present invention.
Ai, 0. A graph showing the relationship between film thickness and light reflectance at a wavelength of 870 nm. 101... Vacuum container 102... Protective film material 103... Electron beam heating device 104... Semiconductor laser 105... GaAs substrate for monitor 106... Semiconductor laser for monitor 107... Optical system 108 ...Monitor photodiode and above Applicant: Seiko Epson Corporation

Claims (1)

[Claims] As a means of monitoring the thickness of the end face protection film of a semiconductor laser,
Manufacture of an end face protection film for a semiconductor laser having a monitoring light source, a means for emitting the film thickness of the light emitted from the monitoring light source to a monitor, and a means for detecting the reflected light intensity or transmitted light intensity from the film thickness monitor. 1. A method of manufacturing a facet protection film for a semiconductor laser, characterized in that the monitoring light source is a semiconductor laser whose oscillation wavelength is approximately the same as the oscillation wavelength of the semiconductor laser.