JPH03195076A - External resonator type variable wavelength semiconductor laser - Google Patents

Abstract

PURPOSE:To obtain an end surface having a low reflectivity in a wide band by a method wherein a reflection-proof film is provided outside the window end surface structure of a semiconductor element and only lights having required wavelengths are selected from among lights emitted through the window end surface structure and the reflection-proof film and are made to return. CONSTITUTION:Photons created in an active layer 3 by applying a current between an electrode 1 and an electrode 2 are guided along the active layer 3. The photons guided to one direction are reflected by a cleavage plane 4 and return to the active layer 3. The photons guided to the other direction are transmitted through a window end surface structure 5 and a reflection-proof film 6. The transmitted photons are condensed by a convex lens 7 which is a light condensing means and reflected by a diffraction grating 8 selectively and return to the active layer 3 again. An oscillation is created by multireflection between the cleavage plane 4 and the deffraction grating 8. The oscillated lights are emitted from the cleavage plane 4. In order to emit only lights having required wavelengths selectively, the diffraction grating 8 is controlled by a deffraction grating scanning means 9. With this constitution, the reflectivity of a semiconductor end surface of the window end surface side can be returned and, further, the end surface having a low reflectivity in a wide band can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an external cavity type wavelength tunable semiconductor laser used as a light source for coherent optical communications, interference type optical fiber sensors, optical application measuring instruments, etc.

[Conventional technology]

External cavity type wavelength tunable semiconductor lasers, which are composed of a semiconductor laser with an anti-reflection film formed on one side of the active layer end face and a diffraction grating, have particularly low reflectance because the reflectance of the anti-reflection film depends on the thickness of the anti-reflection film. When trying to achieve reflection, it is difficult to control the film thickness during manufacturing.

For example, in the 1.3 μm band, in order to keep the reflectance below 0.1%, the error in the anti-reflection film thickness must be within ±60 (approximately 3%), and the wavelength bandwidth is set to the optimum film thickness. It was also about 40 nm. As a result, the reflectance of the antireflection film varies, making it impossible for external cavity type wavelength tunable semiconductor lasers to obtain stable performance characteristics.

[Problem to be solved by the invention]

When using a conventional semiconductor laser that only has an anti-reflection film applied to its end facets, it is necessary to achieve low reflectance with just the anti-reflection film. However, there are problems such as the permissible range of the film thickness of the antireflection film that can achieve low reflectance is narrow, the practical wavelength range is narrow, and the anti-load resistance is likely to vary. The gain cannot be fully utilized, and the wavelength range varies (
A lot of things happened.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an external cavity type wave-wound variable semiconductor laser using a window edge structure semiconductor laser having a wide band and low reflection.

[Means to solve the problem]

In order to solve the above problems, in the external cavity type wavelength tunable semiconductor laser of the present invention, (1) an active layer extending from the emission end face and a semiconductor element having a window end face structure in a region following the active layer, and (2) the semiconductor An antireflection film is provided on the outside of the window end face structure of the element, and a structure is adopted in which only a predetermined wavelength of light is selected and returned from the light emitted after passing through the window end face structure and the antireflection film.

Note that the wavelength selection means is controlled to select only a predetermined wavelength.

C effect] According to the external cavity type wavelength tunable semiconductor laser having the three structural requirements as described above, the relative reflectance can be reduced to 0.3% in the region of the window end face structure, so that the reflectance of the antireflection film can be reduced to 0.3%. performance requirements can be reduced. In other words, the tolerance range for the thickness of the anti-reflection film is widened; for example, if the reflectance of the anti-reflection film is 30% or less, the end face reflectance combined with the window end face structure can be reduced to 0.1%.
Since it is possible to do the following, variations in reflectance can be suppressed. In addition, it becomes possible to reduce the precision of the window end surface structure and the reflectance precision of the antireflection film during manufacturing. Specifically, the window end face structure can reduce the reflectance in a wide band, and in combination with an antireflection film, a reflectance of less than 0.000% can be obtained in a wavelength range of about 100 nm.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

(First Embodiment) FIG. 1 is a structural diagram showing a first embodiment of an external cavity type wavelength tunable semiconductor laser of the present invention. In the first embodiment,
A diffraction grating is used as the wavelength selection means, and a diffraction grating scanning means for rotating the diffraction grating is used as the control means.

By injecting a current between the electrodes 1 and 2, photons generated in the active layer 3 are guided along the active N3, one photon is reflected by the cleavage plane 4 and returns to the active layer 3, and the other photon is guided along the active layer 3. The photons pass through the window end surface structure 5 and the anti-reflection film 6, and the transmitted photons are focused by a convex lens 7 as a focusing means, selectively reflected by the diffraction grating 8, returned to the active layer 3, and cleaved. Multiple reflections occur between the surface 4 and the diffraction grating 8, resulting in oscillation. The oscillated light is emitted from the cleavage plane 4. Note that the diffraction grating 8 is controlled by a diffraction grating scanning means 9 so that only desired wavelengths can be selectively reflected. Specifically, the diffraction grating 8 is rotated to control the incident angle of light with respect to the normal line of the diffraction grating 8.

FIG. 2 is a diagram showing the manufacturing process of the semiconductor element of the external cavity type wavelength tunable semiconductor laser of the present invention.

For the first growth, liquid phase epitaxy (LPE) method, vapor phase epitaxy (
P-type I is deposited on p-type 1nP substrate 10 by VPE, MO-CVD) method, or molecular beam epitaxy (MBE) method.
nP buffer layer 11, non-doped InGaAsP active layer (λ: 1.3 μm composition) 3, and n-type InP layer thereon.
The cladding layer 12 is grown thinly (FIG. 2(a)), 5iNxll is deposited on the entire substrate surface, and 5iNxli is removed from the portion where the window end surface structure is formed.
Buttering the xll mask 13. n-type InP cladding layer 12 in a portion not covered by mask 13;
The non-doped InGaAsP active layer 3 is removed by etching (FIG. 2(b)), and after removing the mask 13 (
FIG. 2(c)), n-type 1nP is grown as a second growth, and the window end face structure 5 and thick cladding layer 12 are grown (FIG. 2(d)).

Next, in order to form a waveguide and a buried layer, SiNx
Film patterning, mesa etching, and third growth of buried current barrier layer (Figure 2 (e))
After the growth, electrodes 1 and 2 are deposited on both sides of the substrate (Fig. 2(f)), and an antireflection film 6 is formed by scribing into chips (Fig. 2(g)). The semiconductor element manufactured through the process is assembled into an external resonator to form an external resonator type wavelength tunable semiconductor laser.

(Second Embodiment) FIG. 3 is a structural diagram showing a second embodiment of the external cavity type wavelength tunable semiconductor laser of the present invention. The first embodiment utilizes wavelength selectivity depending on the incident angle of the diffraction grating, but the second embodiment uses a bandpass filter 14 and a reflection device 15 instead of the diffraction grating and the diffraction grating scanning means. Therefore, only a predetermined wavelength is selected and oscillation is performed at that wavelength.

By injecting a current between the electrodes 1 and 2, photons generated in the active layer 3 are guided along the active layer 3, one photon is reflected by the cleavage plane 4 and returns to the active layer 3, and the other photon is guided along the active layer 3. The photons pass through the window end surface structure 5 and the anti-reflection film 6, and the transmitted photons are focused by a convex lens 7 as a focusing means, a transmission wavelength is selected by a bandpass filter 14, and reflected by a reflection device 15. Returning to the active layer 3 again, the cleavage plane 4 and the reflection device 1
5 and undergoes multiple reflections and oscillates. The oscillated light is emitted from the cleavage plane 4. Note that the bandpass filter 14 is controlled to be replaced manually or automatically so that only a desired wavelength can be selectively transmitted and reflected by the reflection device 15. A specific example of the bandpass filter 14 is a multilayer interference filter. Further, as the spectral characteristics, there are a band pass filter, a long wave filter, a short wave filter, etc. It is also possible to use a continuously variable wavelength filter as the bandpass filter I4 and control the transmission center wavelength of the continuously variable wavelength filter to a predetermined value. Furthermore, an example of the reflective bag 215 is a total reflector.

(Third Embodiment) FIG. 4 is a structural diagram showing a third embodiment of the external cavity type wavelength tunable semiconductor laser of the present invention. A third embodiment uses an optical piezoelectric crystal 16 and a reflection device 1 as wavelength selection means.
7. A voltage supply device 18 is used as a control means. In other words, a lattice-shaped electrode is installed on the surface of the optical piezoelectric crystal 16, a voltage is applied, and light is passed through the lattice-shaped refractive index changing portion that occurs in the crystal directly under the electrode due to the electric field effect, resulting in a diffraction effect. The optical path is wavelength-selectively deflected by using the wavelength, and reflected by the reflection device 17 to cause oscillation at the selected wavelength.

By injecting a current between the electrodes 1 and 2, photons generated in the active layer 3 are guided along the active layer 3, one photon is reflected by the cleavage plane 4 and returns to the active layer 3, and the other photon is guided along the active layer 3. The photons pass through the window end surface structure 5 and the anti-reflection film 6, and the transmitted photons are focused by a convex lens 7 as a focusing means, a diffraction wavelength is selected by an optical piezoelectric crystal 16, and a reflection device 17
The light is reflected back to the active layer 3, undergoes multiple reflections at the cleavage plane 4 and the reflection device 17, and oscillates. The oscillated light is emitted from the cleavage plane 4. Note that by controlling the voltage between the electrode input terminals by the voltage supply device 18 so as to selectively deflect only the desired wavelength toward the reflection device 17,
The refractive index of the lattice-shaped portion formed within the crystal directly under the electrode changes.

〔Effect of the invention〕

As explained above, the external cavity type wavelength tunable semiconductor laser of the present invention includes an active layer extending from the emission end facet, a semiconductor element having a window end face structure following the active layer, and an anti-reflection device provided outside the window end face structure. A light collecting means that collects the light emitted after passing through the film, the window end surface structure and the anti-reflection film, and a light collecting means that enters the light collected by the light collecting means and selects only a predetermined wavelength. It is equipped with wavelength selection means for transmitting in the opposite direction, and control means for controlling the wavelength selection means to select a predetermined wavelength ρ. Therefore, the reflectance of the semiconductor laser end face on the window end face side can be reduced to about 0.003χ, and moreover, a wide band and low reflection end face can be stably realized. By using such a semiconductor laser with a window end facet structure, it is possible to stably produce an external cavity type wavelength tunable semiconductor laser having a narrow spectral linewidth, low noise, and a wavelength tunable over a wide band.

[Brief explanation of drawings]

Fig. 1 is a structural diagram showing the first embodiment of the present invention, Fig. 2 is a diagram showing the manufacturing process of the invention, Fig. 3 is a structural diagram showing the second embodiment of the invention, Fig. 4 (
a) and FIG. 4(b) are a side view and a plan view of a structural diagram showing a third embodiment of the present invention. Active layer, 4. Window end surface structure, 6. Light condensing means, 8. Control means.・cleavage plane, ... antireflection film, ・wavelength selection means,

Claims (1)

[Claims] A semiconductor element including an active layer extending from an output end face, a window end face structure following the active layer, an antireflection film provided on the outside of the window end face structure, and a semiconductor device that passes through the window end face structure and the antireflection film. a condensing means for condensing the light emitted by the condensing means, a wavelength selection means for inputting the light condensed by the condensing means, selecting only a predetermined wavelength, and transmitting it in the opposite direction to the incident light; 1. An external cavity type wavelength tunable semiconductor laser comprising: control means for controlling the selection means to select only a predetermined wavelength.