JPH04343283A - Integrated semiconductor laser ray source - Google Patents

Abstract

PURPOSE:To provide an integrated semiconductor laser ray source whose optical system is mechanically stable and which is compact, small in line width (wave length spreading), and stabilized in oscillation wavelength. CONSTITUTION:In an integrated semiconductor laser ray source, a semiconductor laser 2 which oscillates in single wavelength and a waveguide type optical filter 5 which is wavelength-dependent in reflectivity are formed on the same semiconductor substrate 1 through the intermediary of a semiconductor optical waveguide 4.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser light source that generates light of a single wavelength and is used for purposes such as optical fiber communication or optical measurement.

0002

[Prior Art] In the fields of optical fiber communication and optical measurement, compact semiconductor lasers that generate light of a single wavelength are used, and the wavelength spread (hereinafter referred to as linewidth) of the generated light is narrowed. It is essential to do this in applied fields. Conventionally, distributed feedback lasers (hereinafter referred to as DFB lasers) and distributed reflection lasers (hereinafter referred to as DFB lasers) have been used to improve the single wavelength property of semiconductor lasers.
DBR lasers (DBR lasers) are being actively studied, and a linewidth of about 100 kHz has been obtained with a single device. (For example, M. Okay et al., IEEE Photonic
s Technology Letters, vo
l. 2, No. 8, pp. 529-530, 1990,
“Corrugation-pitch-modula
ted MQW-DFB laser with
narrow spectral line wide
th (170kHz)".) However, further linewidth reduction and stabilization of the oscillation wavelength are necessary from the viewpoint of improving the characteristics of the application field. Stabilization of the linewidth and oscillation wavelength of single wavelength semiconductor lasers There is a method in which a resonator is formed outside a semiconductor laser by a mirror having a wavelength-dependent reflectance (for example, B. Dahmani et al., Opti
cs Letters, vol. 12, No. 11,
pp. 876-878, 1987, “Frequenc.
y stabilization of semic
onductor lasers by res
onantoptical feedback”,H
．． Li et al., IEEE Journal of Q.
uantum Electronics, vol. 25
, No. 3, pp. 257-264, 1989, “Ef.
fficient frequency
reduction of GaAlAs se
micondactor lasers by o
physical feedback froman
external high-finesse
resonator”., and vol.25, N
o. 8, pp. 1782-1793, 1989, “An
lysis of the noise
pectra of a laser dio
with optical feedba
ck from a high-finesse
However, the method to realize this technology was to assemble an optical system using lenses, fine movers, etc. on an optical surface plate, which was extremely susceptible to mechanical vibration. It was not possible to modulate the optical frequency of the emitted light by direct modulation to a semiconductor laser.

Furthermore, in a method in which the output light wavelengths of several single-wavelength semiconductor lasers are set at specific optical frequency intervals and information is transmitted through the same optical fiber (hereinafter referred to as optical FDM method), several semiconductor lasers In order to fix the output light wavelength from a spectrometer to a specific optical frequency interval, a method has been used in which the resonance characteristics of the Fabry-Perot spectrometer are used to fix the output light wavelength to adjacent resonance peaks. (For example, H. Toba et al., Journal of Opt.
ical Communications, vol.
19, pp. 50-54, 1988, “A mult
i-channel laser diode
frequency stabilizerforn
arrowly spaced optical
frequency-division-multi
(plexing transmission).) Therefore, the light source is extremely large and is also extremely susceptible to mechanical vibrations and the like.

0004

[Problems to be Solved by the Invention] As mentioned above, conventional DFB lasers, DBR lasers, and optical FDM systems are susceptible to mechanical vibration, and it is difficult to modulate the stabilized frequency of light by direct modulation to a semiconductor laser. However, there were disadvantages in that it was not possible to do so, or the light source became very large.

The present invention solves these conventional drawbacks and provides a compact optical system that eliminates the mechanical instability of the optical system by forming a semiconductor laser and a waveguide optical filter on the same semiconductor substrate. An object of the present invention is to provide an integrated semiconductor laser light source with a narrow linewidth and a stabilized oscillation wavelength.

[0006]Furthermore, the waveguide type optical filter has a structure that allows an electric field to be applied or a current to be injected, thereby making it possible to modulate the optical frequency of the stabilized output light. The purpose is to provide a semiconductor laser light source.

In addition, in the light source according to the present invention, the waveguide semiconductor optical filter is a multiple interference type, and by arranging filters with the same length and shape, the optical frequency interval is constant and the line width is narrow. , and the light F whose oscillation wavelength is stabilized
The purpose is to construct a light source for DM system.

[0008]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a semiconductor laser that oscillates at a single wavelength,
A waveguide type optical filter whose reflectance is wavelength dependent is formed on the same semiconductor substrate via a semiconductor optical waveguide.

Further, in the present invention, a semiconductor laser that oscillates at a single wavelength and a waveguide optical filter whose reflectance is wavelength dependent are formed on the same semiconductor substrate via a semiconductor optical waveguide. It is characterized in that a plurality of semiconductor laser light sources are integrated, and the waveguide type optical filter is a multiple interference type, and has the same length and shape.

0010

[Operation] By forming on the same semiconductor substrate a structure in which a waveguide optical filter whose reflectance is wavelength dependent is coupled to a single wavelength semiconductor laser via a semiconductor optical waveguide,
It is possible to realize a light source in which the line width of the output light from the semiconductor laser is narrowed by the return light from the waveguide optical filter, and its wavelength is stabilized. In addition, there are light sources that can modulate the optical frequency of the output light from the light source by applying an electric field or injecting current to a waveguide semiconductor optical filter to change the equivalent refractive index and change the transmission band of the optical filter. realizable.

Furthermore, by making the waveguide semiconductor optical filter a multiple interference type, making the length and shape the same, and arranging the integrated semiconductor laser light source according to the present invention, the linewidth is narrow and the wavelength is stabilized. It is possible to realize an arrayed light source that outputs light at regular optical frequency intervals.

FIG. 1 is a diagram showing the principle of an integrated semiconductor laser light source according to the present invention. Curve A in the figure shows the optical frequency dependence of the reflectance of the optical filter. The light incident on the optical filter is reflected with a reflectance according to the optical frequency and returns to the single wavelength semiconductor laser. Consider the case where the wavelength of the semiconductor laser incident on the optical filter takes the value indicated by the black circle in the figure. At this time, a constant light intensity P is fed back to the semiconductor laser from an optical filter located a certain distance away, forming an external resonator. This effect causes
The oscillation wavelength of the semiconductor laser is stabilized to some extent, and the linewidth is narrowed to some extent. When the optical frequency of the light incident on the optical filter changes toward the higher frequency side by Δf, in the light source of this configuration, the intensity of the reflected light from the optical filter increases by ΔP. Therefore, the light intensity returned to the semiconductor laser increases,
Decrease the carrier density within the semiconductor laser. The decrease in carrier density increases the refractive index within the resonator, and the optical frequency of the generated light changes to the lower frequency side, achieving negative feedback.
The oscillation wavelength of the semiconductor laser is strongly stabilized, and the linewidth is narrowed. The frequency band in which this negative feedback occurs is determined by the intrinsic frequency modulation band of the semiconductor laser, and is 10G
The feedback frequency band is Hz or higher. Therefore, when the optical frequency of the optical filter's resonance peak is changed, the oscillation frequency of the semiconductor laser will follow and change, and the optical frequency of this light source will be modulated until the rate of change is about 10 GHz in terms of frequency. .

[0013]

【Example】

Example 1 FIG. 2 shows an example of the present invention. A laser light source 2 and a waveguide type optical filter 5 are formed on a semiconductor substrate 1 via an optical waveguide 4 . In this embodiment, a multiple interference Fabry-Perot interferometer 5 composed of a waveguide diffraction grating 51 and a high reflection film 52 formed on the end face of the element was used as the waveguide optical filter. The multiple interference type Fabry-Perot interferometer 5 has filter characteristics due to multiple interference of light between the waveguide type diffraction grating 51 and the high reflection film 52. The structure described in this example is all created on a semiconductor InP substrate 1,
As shown in FIG. 3, the optical waveguide 4 has an optical waveguide layer with a thickness of 1.3μ.
m-composition InGaAsP41, and p-InP42 and n-InP to satisfy the single mode condition.
It has a structure embedded with 43. The optical waveguide is p-
It has an n-junction and is formed so that voltage can be applied or current can be injected. Moreover, the waveguide type diffraction grating was created by chemically etching the optical waveguide layer to form irregularities. The pitch of the unevenness was about 2000 Å. The high reflection film 52 formed on the cleavage plane is made of SiO2
The dielectric film was prepared by depositing 20 dielectric films of TiO2 and TiO2. As the semiconductor laser 2 that oscillates at a single wavelength, a DFB laser whose substrate 1 is made of InP and has a diffraction grating inside is used here. In addition, the DFB laser and the optical waveguide are made of Indium with a composition of 1.55 μm in the DFB laser.
Active layer 21 made of GaAsP and optical waveguide layer 4 of the optical waveguide
1 and were joined by butting each other as shown in FIG. FIG. 5 shows the optical frequency dependence of the reflectance of this optical filter. The output optical frequency of this light source is stabilized at the optical frequency indicated by the black circle in the figure. The waveguide type optical filter 5 is coupled to the semiconductor laser 2 that oscillates at a single wavelength through the optical waveguide 4, and its components are formed on the same semiconductor substrate 1. The optical frequency (black circle point) in FIG. 5 at which the output optical frequency of this light source is stabilized is adjusted by adjusting the amount of current injected into the semiconductor laser. In this integrated semiconductor laser light source, when the amount of current injected into the semiconductor laser is changed, the optical frequency of the output light takes discontinuous values as shown by the black circles in Figure 5, and the line width at that time is 2.
0 kHz, and the oscillation wavelength fluctuation was 1 MHz or less in 30 minutes.

Furthermore, by applying a voltage or injecting a current to the electrode 53 of the waveguide type optical filter 5, the optical filter 5 can be
The optical frequency of the resonant peak of the filter can be shifted, and the optical frequency of the light source stabilized at this resonant peak changes with the shift of the optical frequency of the resonant peak of the filter. The frequency that can be modulated by the light source of this example is determined by the modulation band of the component semiconductor laser, and modulation can be performed at a speed of 10 GHz or more.

Embodiment 2 FIG. 6 shows a second embodiment of the present invention. In this embodiment, a ring type optical filter 7 is used as a waveguide type optical filter.
is used. The ring type optical filter is a straight optical waveguide 73
and a ring-shaped optical waveguide 74, and adjacent waveguide portions of both form a directional coupler, forming a ring-shaped optical filter. A high reflection film 71 is formed on one end surface of the ring-shaped optical filter 7 to reflect light. The opposite end face of this filter is coupled to a semiconductor laser 2 that oscillates at a single wavelength, and the components are the same substrate 1.
formed on top. The device according to this example is Example 1
It operates on the same principle. Further, in the ring type optical filter 7 in this embodiment, the optical frequency of the resonance peak can be changed by applying a voltage or injecting a current to the waveguide from the electrode 72 formed in the ring portion in FIG. Thereby, the output optical frequency of the light source can be modulated.

Embodiment 3 FIG. 7 shows a third embodiment of the present invention. This embodiment is an array of integrated semiconductor laser light sources according to the first embodiment. The length and shape of the waveguide optical filters 5 of each of the constituent light sources are manufactured to be the same. Therefore, the reflection characteristics of all the waveguide optical filters 5 are the same. The distance from the end of the waveguide diffraction grating to the cleavage plane of the element was formed to be the same for all components. As a result, the filter characteristics of the optical filters of all the constituent elements became the same. By controlling the optical output frequency of each semiconductor laser, and by varying the resonance peak optical frequency of the optical filter to be stabilized in each integrated semiconductor laser light source that is a constituent element, the output optical frequency interval can be adjusted according to the optical filter. We have realized a narrow linewidth, wavelength-stabilized array light source with equally spaced optical frequencies matching the resonance peak spacing of .

Embodiment 4 FIG. 7 shows a fourth embodiment of the present invention. This embodiment is an array of integrated semiconductor laser light sources according to the second embodiment. The length and shape of the waveguide optical filters 7 of each of the constituent light sources are manufactured to be the same. Therefore, the reflection characteristics of all the waveguide optical filters 7 are the same. Furthermore, the sizes of the ring-shaped optical waveguides in all the components were made the same, so that the filter characteristics of the optical filters in all the components were made the same. By controlling the optical output frequency of each semiconductor laser, and by varying the resonant peak optical frequency of the optical filter used for stabilization in each integrated semiconductor laser light source that is a component, the output optical frequency interval can be adjusted. A narrow linewidth, wavelength-stabilized array light source with equally spaced optical frequencies matching the resonant peak spacing of the filter was realized.

[0018]

[Effects of the Invention] As described above with reference to specific examples, the present invention makes it possible to realize an integrated semiconductor laser light source that is compact, resistant to mechanical vibration, with a stabilized oscillation wavelength and a narrow linewidth. Ta. Further, according to the present invention, an array light source in which the oscillation wavelength interval is constant, the individual wavelengths are stabilized, and the line width is narrow can be realized.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the principle of an integrated semiconductor laser light source of the present invention.

FIG. 2 is a diagram showing an embodiment of the present invention.

FIG. 3 is a schematic cross-sectional view showing the structure of an optical waveguide.

FIG. 4 is a schematic cross-sectional view showing coupling between a semiconductor laser and an optical waveguide.

FIG. 5 is a diagram showing the optical frequency dependence of the reflectance of a waveguide type optical filter constituting an embodiment of the present invention.

FIG. 6 is a diagram showing a second embodiment of the present invention.

FIG. 7 is a diagram showing a third embodiment of the present invention.

FIG. 8 is a diagram showing a fourth embodiment of the present invention.

[Explanation of symbols]

1 Semiconductor substrate 2 Single wavelength semiconductor laser 3 Electrode for injecting current into the semiconductor laser 4 Optical waveguide 5 Fabry-Perot optical filter 51 Waveguide type diffraction grating 52 Highly reflective film 53 Electrode for applying voltage to the optical filter or injecting current 7 Ring Cavity type optical filter 71 High reflection film

Claims (2)

[Claims] [Claim 1] A semiconductor laser that oscillates at a single wavelength and a waveguide optical filter whose reflectance is wavelength dependent are formed on the same semiconductor substrate via a semiconductor optical waveguide. An integrated semiconductor laser light source. [Claim 2] A semiconductor laser in which a semiconductor laser that oscillates at a single wavelength and a waveguide optical filter whose reflectance is wavelength dependent are formed on the same semiconductor substrate via a semiconductor optical waveguide. An integrated semiconductor laser light source characterized in that a plurality of light sources are integrated, and the waveguide type optical filter is of a multiple interference type and has the same length and shape.