JP3022437B2 - Mode-locked semiconductor laser - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to optical communication, optical measurement,
The present invention relates to a mode-locked semiconductor laser that generates a highly repetitive ultrashort optical pulse train useful for optical information processing and the like.

[0002]

2. Description of the Related Art In recent years, there has been an increasing demand for a technology capable of generating an optical pulse train having a repetition frequency of several tens of GHz as a basic technology of ultra-high-speed optical communication, optical measurement, and optical information processing. Further, in optical measurement, a wide range of wavelength variability and frequency variability is required. An example of a light source that satisfies these requirements is an external cavity mode-locked semiconductor laser using a two-electrode semiconductor laser having a saturable absorption region and a gain region.

[0003] This technique is disclosed, for example, in Japanese Patent Laid-Open No. 5-9 / 1993.
As disclosed in Japanese Unexamined Patent Application Publication No. 5152, in FIG. 3, a short-circuit in which a saturable absorption region 74, an optical waveguide region 72, an optical amplification region 71, and an optical modulation region 73 are connected in series on the substrate 21. There is a light pulse light source 70.

Further, for example, the IEE Journal of Quantum by Derrickson et al.
Electronics, Vol. 28, pp. 2186-2202 (DJ Derickson et al., IEEE Journal of Quantum El
ectronics Vol. 28, pp. 2186-2202). In this conventional example, as shown in FIG. 4, a semiconductor laser 101 having a saturable absorption region 111 and a gain region 112 is used.
And lenses 131 and 132, an optical filter 133, and a reflecting mirror 150 which are arranged in series therewith. In the mode-locked semiconductor laser configured as described above,
A reverse bias and a high-frequency signal are applied to the saturable absorption region 111 via the bias tee 145, and the gain region 11
By injecting a direct current into the device 2, a mode-locked operation can be realized under appropriate conditions.

[0005]

Generally, in a mode-locked semiconductor laser, in order to improve the accuracy of the repetition frequency of an optical pulse train and the stability of operation for optical communication applications, an electric control using a stabilized high-frequency power supply is required. In the above-described conventional mode-locked semiconductor laser, a method of superimposing a high-frequency signal and a bias voltage on either the saturable absorption region or the gain region is used. In this high frequency superposition method, it is necessary to optimize a high frequency circuit by reducing parasitic capacitance and impedance matching in order to inject a high frequency signal efficiently.

However, the mode locking has an optimum region length and an optimum bias condition. In the above-described conventional semiconductor device, it is very difficult to optimize the high-frequency characteristics due to a limitation in device design. It was difficult. Therefore, there is a problem that the load on the high-frequency signal source is large.

An object of the present invention is to eliminate the above-mentioned drawbacks of the conventional external cavity mode-locked semiconductor laser, to increase the efficiency of high frequency signal injection, to reduce the load on the high frequency signal source, and to cover a wide wavelength range. Another object of the present invention is to provide a mode-locked semiconductor laser which is variable and has a variable repetition frequency.

[0008]

A mode-locked semiconductor laser according to a first aspect of the present invention comprises a saturable laser provided on a first base.
A semiconductor laser having an absorption region and a gain region;
An electro-absorption type optical modulator provided on a base of
Optical coupling between a conductor laser and the electroabsorption optical modulator
And an optical coupling means for making the semiconductor laser.
The output side end face of the optical resonator and the electroabsorption optical modulator.
An external resonator is constituted by the end face.
You .

In the above case, the semiconductor laser has an optical resonance
Saturable absorption area on the output end face side of the vessel, the other end face side
A gain region, and an antireflection film is provided on an end face on the gain region side.
Wherein the electroabsorption optical modulator is formed with the external resonator
A high reflection film is formed on one end surface of the
An anti-reflection film is formed on the other end face facing the end face on the acquisition region side.
The configuration may be modified .

In addition, laser oscillation in the external resonator
It further has a wavelength control element for controlling the wavelength
It may be. In this case, the optical coupling means is the wavelength
A configuration including an optical filter as a control element may be employed .

Further, the optical coupling means may include a semiconductor laser.
Coaxially between the laser and the electroabsorption optical modulator.
It may include a pair of optical lenses arranged in series.
No. In this case, one of the pair of optical lenses is the first lens.
And the other is fixed on the second base.
May be set .

A mode-locked semiconductor laser according to the first aspect of the present invention.
In any of the above aspects, the first and second bases
The distance between the sources may be adjustable .

A mode-locked semiconductor laser according to a second aspect of the present invention comprises:
An electro-absorption type light modulation area and a light modulation area provided on the first base.
Semiconductor laser having a gain region and a gain region, on a second base
Saturable absorber mirror with multiple quantum well structure
Optically connecting the semiconductor laser and the saturable absorption mirror
Optical coupling means for coupling, the saturable absorption mirror,
Difference in thickness distribution of multiple quantum wells in the in-plane direction of the mirror surface
Moving in the direction perpendicular to the optical axis of the optical coupling means.
Optical resonator configured to be capable of forming the semiconductor laser
An external resonator is formed by the output end face of
It is characterized by comprising .

In the above case, the laser in the external resonator
Further has a wavelength control element for controlling the oscillation wavelength
Alternatively, the configuration may be as follows. In this case, the optical coupling means is
Even if an optical filter as a wavelength control element is included.
Good .

Further , the optical coupling means may include a semiconductor laser.
And coaxially disposed between the
May be configured to include an optical lens. This place
If the optical lens is fixed on the first base,
Is also good .

The mode-locked semiconductor laser according to the second aspect of the present invention.
In any of the above aspects, the first and second bases
The distance between the sources may be adjustable .

[0017]

[0018]

[0019]

In the configuration of the first aspect , the optical modulator is provided separately from the saturable absorption region and the gain region which determine the mode locking condition, and an optical coupling means is provided therebetween. and the optical modulator separated, saturable absorption region
Since the gain and the gain region are mounted on separate bases and are movable in the axial direction, it is possible to independently optimize the mode locking condition and the high frequency characteristics. In other words, design the region length and material composition of the saturable absorption region and gain region to optimize the mode-locked state, and independently design the element length and material composition of the electroabsorption optical modulator to optimize the high-frequency characteristics. Is possible. Therefore, the burden on the high-frequency signal source can be reduced, and the accuracy of the repetition frequency of the ultrashort optical pulse train and the stability of the oscillation mode can be easily increased.

Similarly, in the configuration of the second aspect of the present invention, the optical modulation region is provided separately from the saturable absorption mirror and the gain region which determine the mode locking condition.
It is possible to optimize the mode locking condition and the high frequency characteristic independently. Further, since the optical system in the resonator of the mode-locked semiconductor laser can be simplified, the mounting cost can be reduced. Further, by utilizing the in-plane distribution of the material composition and the material film thickness of the saturable absorption mirror, it is possible to easily optimize the mode locking condition.

[0022]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a schematic longitudinal sectional view of a mode-locked semiconductor laser according to a first embodiment of the present invention.

The semiconductor laser 1 is a two-electrode parallel-plane Fabry-Perot type semiconductor laser, and has InGaAs with a saturable absorption region 11 having a length of 75 μm and a gain region 12 having a length of 500 μm. / InGaAs
It has an sP multiple quantum well structure. Further, an antireflection film 13 is provided on an end face of the Fabry-Perot resonator facing the gain area on the opposite end face. Saturable absorption region 11
Is connected to a DC voltage source 41 for applying a reverse bias, and the gain region 12 is connected to a DC current source 42 for injecting a forward current.

The electro-absorption type optical modulator 2 comprises a semiconductor laser 1
The laser resonators are formed in series and coaxially with a distance from each other. An antireflection film 23 is provided on an end surface of the optical modulator 2 facing the axial direction on the side of the semiconductor laser 1, and a high reflection film 24 is provided on an end surface on the opposite side.
Further, a DC voltage source 43 for applying a reverse bias to the optical modulator 2 and a stabilized high-frequency power supply 44 for superimposing a sine wave are connected via a bias tee 45.

Between the semiconductor laser 1 and the optical modulator 2,
As means for optically coupling the two, a pair of lenses 31 and 32 having an optical axis on the same axis as the two are provided, and an optical filter 33 as a wavelength control element is provided between the two lenses. . Here, the semiconductor laser 1 and the lens 31 are fixed on the base 1a, and the electroabsorption optical modulator 2 and the lens 32 are fixed on another base 2a. The bases 1a and 2a are movable relative to each other in parallel with the central axes of the semiconductor laser 1 and the optical modulator 2. Therefore, by changing the distance between the base 1a and the base 2a, the optical path length of the resonator can be changed, so that the circulating frequency of the light pulse can be changed over a wide range. Further, by changing the inclination of the optical filter 33 with respect to the optical axis, the center frequency of the filter 33 can be changed, so that the oscillation wavelength can be changed over a wide band.

In the mode-locked semiconductor laser configured as described above, a reverse bias of -1 V is applied to the saturable absorption region 11 of the semiconductor laser 1 by the DC voltage source 41, and a forward current of 100 mA is applied to the gain region 12 by the DC power supply 42. Injected. The electroabsorption optical modulator 2 is supplied with a reverse bias of −2 V by a DC voltage source 43 through a bias tee 45.
And a 10 GHz sine wave was superimposed at about +7 dBm by the stabilized high-frequency power supply 44. As a result, the optical pulse width is about 3 ps and the timing jitter is about 0.4 ps.
The ultrashort light pulse output was obtained.

Next, a mode-locked semiconductor laser according to a second embodiment of the present invention will be described with reference to a schematic longitudinal sectional view shown in FIG.

The semiconductor laser 10 is a two-electrode parallel-plane Fabry-Perot semiconductor laser, and is divided into an electro-absorption type optical modulation region 3 having a length of 250 μm formed by selective growth and a gain region 12 a having a length of 500 μm. Has an InGaAs / InGaAsP multiple quantum well structure provided with a patterned electrode. A DC voltage source 43 for applying a reverse bias via a bias tee 45 and a stabilized high-frequency power supply 44 for superimposing a sine wave are connected to the electroabsorption type optical modulation region 3. Is connected to a DC current source 42 for injecting a forward current.

The saturable absorbing mirror 50 disposed at right angles to the axis of the semiconductor laser 10 has InGaAs / InGaAsP.
One surface of the multiple quantum well has a mirror surface formed by depositing gold, and the other surface is provided with an antireflection film. Here, the saturable absorption mirror 50 can make a difference in the distribution of the film thickness of the multiple quantum well in the substrate surface by tilting the substrate at the time of manufacture and performing crystal growth.

A lens 32a is provided between the semiconductor laser 10 and the saturable absorption mirror 50 so that the axis of the semiconductor laser 10 coincides with the optical axis.
An optical filter 33, which is a wavelength control element, is provided between.

The semiconductor laser 10 and the lens 32a are fixed on the base 10a, and the saturable absorbing mirror 50 is
a, the base 10a and the base 50a are movable with each other in parallel with the axis of the semiconductor laser 10. Therefore, by changing the distance between the bases, the optical path length of the resonator can be changed, so that the circulating frequency of the optical pulse can be changed over a wide range. Furthermore, since the center frequency of the optical filter 33 can be changed by changing the inclination of the optical filter 33 with respect to the optical axis, the oscillation wavelength can be changed over a wide band.

Further, since a difference in the distribution of the thicknesses of the multiple quantum wells of the saturable absorption mirror 50 is provided, the saturable absorption characteristics can be changed by moving the saturable absorption mirror 50 in a direction perpendicular to the optical axis. Therefore, optimization of the mode synchronization condition can be performed.

In the mode-locked semiconductor laser configured as described above, a forward current of 100 mA is injected from the DC current source 42 into the gain region 12 a of the semiconductor laser 10, and the DC current is applied to the electro-absorption type optical modulation region 3 via the bias tee 45. A sine wave of 10 GHz was superimposed at about +7 dBm by the reverse bias -2 V from the voltage source 43 and the stabilized high frequency power supply 44. As a result, an ultrashort optical pulse output having an optical pulse width of about 3 ps and a timing jitter of about 0.4 ps was obtained.

In the above embodiment, InGaAs is used.
Although a semiconductor laser having a system multiple quantum well structure has been described, it is clear that the present invention is not limited to a particular material system from a theoretical viewpoint.

[0035]

As described above, according to the present invention, since the optical modulator is separated from the saturable absorption region and the gain region which determine the mode locking condition, the mode locking condition and the high frequency characteristic can be independently optimized. Therefore, the load on the high-frequency signal source can be reduced, so that the accuracy of the repetition frequency of the optical pulse train and the stability of the oscillation mode can be easily increased.

Further, in another invention of the present invention in which the light modulation region is provided separately from the saturable absorption mirror for determining the mode locking condition and the gain region, similarly to the above-mentioned invention,
Mode-locking conditions and high-frequency characteristics can be optimized independently, which has the same effects as described above. In addition, the optical system in the cavity of the mode-locked semiconductor laser can be simplified, reducing mounting costs. There is an effect that can be.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a mode-locked semiconductor laser according to an embodiment of the present invention.

FIG. 2 is a schematic sectional view of another mode-locked semiconductor laser according to an embodiment of the present invention.

FIG. 3 is a cross-sectional view showing one configuration example of a conventional mode-locked semiconductor laser.

FIG. 4 is a schematic diagram similar to FIG. 3;

[Explanation of symbols]

 1, 10, 101 Semiconductor lasers 1a, 2a, 10a, 50a Base 2 Electroabsorption type optical modulator 3 Electroabsorption type optical modulation region 11, 74, 111 Saturable absorption region 12, 12a, 112 Gain region 13, 23, 23a , 113 Antireflection film 21 Substrate 24 High reflection film 31, 32, 32a, 131, 132 Lens 33, 133 Optical filter 41, 43, 143 DC voltage source 42, 142 DC current source 44, 144 Stabilized high frequency power supply 45, 145 Bias tee 50 Saturable absorption mirror 70 Optical pulse light source 71 Optical amplification area 72 Optical waveguide area 73 Optical modulation area 150 Reflecting mirror

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-51-77188 (JP, A) JP-A-4-56293 (JP, A) JP-A-8-321663 (JP, A) IEEE Journal of Quantum Electronics, Vol. 28, No. 10 (1992) p. 2186-2201 (58) Fields investigated (Int. Cl. ⁷ , DB name) H01S 5/00-5/50

Claims (13)

(57) [Claims] 1. A saturable absorber provided on a first base.
A semiconductor laser having an acquisition region and a gain region, an electro-absorption optical modulator provided on a second base , and an optically-absorbing semiconductor laser and the electro-absorption optical modulator.
Optical coupling means for coupling to the output side end face of the optical resonator constituting the semiconductor laser.
An external resonator is constituted by one end face of the electro-absorption optical modulator.
A mode-locked semiconductor laser characterized by being formed . 2. The mode-locked semiconductor laser according to claim 1,
In The, the semiconductor laser is Ka飽on the side of the output side end face of the optical resonator
A sum absorption region, and a gain region on the side of the other end face;
An anti-reflection film is formed on the end face on the region side, and the electro-absorption type optical modulator is configured such that one end face of the external resonator is formed.
A high-reflection film is formed on the constituent end face, and the
An anti-reflection film is formed on the other end face facing the end face.
And a mode-locked semiconductor laser. 3. The mode-locked semiconductor laser according to claim 1,
In The, for controlling the laser oscillation wavelength in the external resonator
A mode-locked semiconductor laser , further comprising a wavelength control element as described above . 4. The mode-locked semiconductor laser according to claim 3, wherein
In The, said optical coupling means, an optical fill as the wavelength control element
A mode-locked semiconductor laser comprising: 5. The mode-locked semiconductor laser according to claim 1, wherein
A mode-locked semiconductor laser , wherein the optical coupling means includes a pair of optical lenses arranged coaxially in series between the semiconductor laser and the electroabsorption optical modulator. 6. A mode-locked semiconductor laser according to claim 5, wherein
In The, one of said pair of optical lenses are solid on the first base
And the other is fixed on the second base.
And a mode-locked semiconductor laser. 7. The method according to claim 1, wherein
In the mode-locked semiconductor laser over THE, capable of configuration adjustment interval of the first and second base
A mode-locked semiconductor laser characterized in that: 8. An electro-absorption device provided on a first base.
Having a multiple quantum well structure provided on a second base and a semiconductor laser having an optical modulation region and a gain region
Saturable absorption mirror, and the semiconductor laser and the saturable absorption mirror are optically coupled.
Optical coupling means for causing the saturable absorption mirror to have multiple quantum in the in-plane direction of the mirror surface.
There is a difference in the thickness distribution of the wells, and
It is movable in the vertical direction against the output side end face of the optical resonator of the semiconductor laser and before
The fact that an external resonator was constructed with the saturable absorbing mirror
Characteristic mode-locked semiconductor laser. 9. The mode-locked semiconductor laser according to claim 8, wherein
In The, for controlling the laser oscillation wavelength in the external resonator
A mode-locked semiconductor laser , further comprising a wavelength control element as described above . 10. The mode-locked semiconductor laser according to claim 9,
In chromatography THE, said optical coupling means, an optical fill as the wavelength control element
A mode-locked semiconductor laser comprising: 11. The mode-locked semiconductor laser according to claim 8,
In chromatography The said optical coupling means, said saturable absorber and said semiconductor laser
Including an optical lens disposed coaxially with the mirror
A mode-locked semiconductor laser characterized by the above-mentioned . 12. The mode-locked semiconductor according to claim 11.
In a laser, the optical lens is fixed on the first base
A mode-locked semiconductor laser characterized by the above-mentioned . 13. The method according to claim 8, wherein:
In the mode-locked semiconductor laser described above, the distance between the first and second bases is adjustable.
A mode-locked semiconductor laser characterized in that: