JP2003069138A - Mode synchronization semiconductor laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a mode synchronization semiconductor laser which can be manufactured rather easily through expansion of the synchronization bandwidth. SOLUTION: The mode synchronization semiconductor laser 10 is provided with an optical waveguide layer 13 comprising a gain region 15, an intensity modulation region 14 to perform intensity modulation in the adjustable frequency to an induced light to realize synchronization among the modes of the induced and excited light generated in the gain region, and a diffraction grating region provided with a uniformly continuous diffraction grating 17 having the predetermined uniform grating interval to reflect the induced and excited light. The laser 10 is also provided with a heating means 24 for giving temperature distribution changing in the extending direction of the optical waveguide layer 13 to the diffraction grating region.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mode-locked semiconductor laser suitable for generating so-called ultrashort optical pulses for use in optical communication.

[0002]

2. Description of the Related Art In a conventional active mode-locked semiconductor laser or a hybrid mode-locked semiconductor laser combining active and passive, the basic repetition period determined by the resonator length of the laser is increased or decreased by increasing or decreasing the frequency of a modulator that gives external modulation. It is possible to adjust the phase of the pulsed light in a certain frequency range centered at, and it is possible to synchronize with the external pulsed light within the phase adjustment range called the locking bandwidth, that is, the synchronization bandwidth.

K.Sato, H.Ishii, I.Kotaka, Y.Kondo, and M.Yamamoto are added to conventional mode-locked semiconductor lasers of this type.
In 1977, the “Frequency range extension of
actively Mode-locked Lasers Integrated with elect
Roabsorption Modulators Using Chirped Gratings '', IEEE Journal of Selected Topics in Quantum E
There is an active mode-locked semiconductor laser announced in lectronics Vol.3, pp250-255.

According to the active mode-locked semiconductor laser described in the above publication, the penetration length is formed by forming the diffraction gratings, which are incorporated in the semiconductor laser and formed at a constant grating interval, with their phases shifted from each other. The substantial diffraction grating region length for light, referred to as, can be variable with respect to the wavelength of light. The diffraction grating provided with this phase shift causes the substantial resonator length to increase or decrease in accordance with the increase or decrease in frequency due to external modulation. Therefore, the synchronization bandwidth, which is referred to as the locking bandwidth, is expanded, and as a result,
It is possible to expand the synchronization adjustment range of the laser pulse light with respect to the external light pulse.

[0005]

However, it is not easy to accurately form a diffraction grating that is given the above-mentioned phase shift. Therefore, the object of the present invention is to
It is an object of the present invention to provide a mode-locking semiconductor laser which can increase the sync bandwidth and can be manufactured relatively easily. further,
Another object of the present invention is to provide a mode-locked semiconductor laser capable of varying the pulse width.

[0006]

The present invention employs the following constitution in order to achieve the above-mentioned object. <Structure 1> In a mode-locked semiconductor laser according to the present invention, a gain region for generating induced pump light and a mode of the induced pump light generated in the gain region are synchronized between a pair of cladding layers. A diffraction grating provided with an intensity modulation region for performing intensity modulation on the guided light at an adjustable frequency, and a diffraction grating having a uniform and uniform predetermined grating interval for reflecting the guided excitation light. A mode-locking semiconductor laser including an optical waveguide layer having a region, wherein heating means is provided for imparting to the diffraction grating region a temperature distribution that changes in the extending direction of the optical waveguide layer.

In the mode-locked semiconductor laser according to the present invention, when the temperature distribution in which the diffraction grating region changes in its extension direction is given by the heating means, the temperature distribution advances the optical waveguide layer by the temperature distribution. The grating spacing of the diffraction grating changes substantially with respect to the stimulated excitation light. Therefore, it is not necessary to form a diffraction grating having a special structure in which the phase is shifted as in the prior art, and it is possible to accurately and relatively easily form a diffraction grating having a uniform continuous uniform predetermined grating interval. By using a grating, the penetration length by the diffraction grating can be made variable in accordance with the increase or decrease in the frequency of the intensity modulation, whereby a relatively wide rocking bandwidth can be realized.

<Structure 2> Another mode-locked semiconductor laser according to the present invention comprises a gain region for generating induced pumping light between a pair of cladding layers, and a mode between the modes of the induced pumping light generated in the gain region. Diffraction grating provided with an intensity modulation region for performing intensity modulation on the guided light for the purpose of synchronizing the guided light and a diffraction grating having a uniform and uniform predetermined grating interval for reflecting the guided excitation light. A mode-locking semiconductor laser including an optical waveguide layer having a region, the heating device being provided with a heating means for imparting to the diffraction grating region a temperature distribution that changes in the extending direction of the optical waveguide layer so that its temperature gradient can be adjusted. Is characterized by.

In the other mode-locked semiconductor laser according to the present invention, since the temperature gradient of the temperature distribution changing in the extension direction of the optical waveguide layer is variable, the diffraction grating can be changed by changing the temperature gradient. The reflectance characteristics with respect to the wavelength of light can be changed. Since the bandwidth of the reflected light can be changed by changing the reflectance characteristic of the diffraction grating, the bandwidth can be increased or decreased by changing the temperature gradient. The decrease in the band width can increase the pulse width of the laser pulse light, and the increase in the band width can decrease the pulse width of the laser pulse light. Therefore, the pulse width of the pulsed light can be increased or decreased by adjusting the temperature gradient by the heating means regardless of whether the synchronous semiconductor laser is in the active synchronous mode, the passive synchronous mode or a hybrid synchronous mode that is a combination thereof. it can.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments. <Specific Example> FIG. 1 shows a specific example of the semiconductor laser 10 according to the present invention. Semiconductor laser 1 shown in FIG.
Reference numeral 0 denotes a so-called hybrid mode-locking semiconductor laser having both a passive mode-locking function and an active mode-locking function, which is a DBR (distributed reflection type: distributed reflection type: distributed reflection type:
d Bragg reflector) A semiconductor laser.

As is well known in the art, the semiconductor laser 10 has an n-type cladding layer 1 made of a semiconductor material.
1, a p-type clad layer 12 and an optical waveguide layer 13 between the clad layers 11 and 12 are provided. As is well known in the art, the optical waveguide layer 13 has a saturable absorption region 14 acting as an intensity modulation region, a gain region 15 for generating stimulated emission light, and a passive optical waveguide region 1
6 and a uniformly continuous diffraction grating 17 having a uniform predetermined grating spacing is provided.

For example, the n-type cladding layer 11 is formed of N-type In
By forming the P-type and p-type cladding layers 12 with P-type InP and the optical waveguide layer 13 with InGaAsP, respectively, a double hetero structure can be adopted for the laminated structure. Although not shown, a pair of well-known side clads for preventing light from leaking in the lateral direction of the optical waveguide layer 13 is provided on both sides of the optical waveguide layer 13.

A common electrode 18 to be grounded is provided on the n-type cladding layer 11, and the p-type cladding layer 1 is also provided.
In FIG. 2, electrodes 19 and 20 are formed corresponding to the saturable absorption region 14 and the gain region 15, respectively.

A DC power supply 21 is connected between the electrode 20 corresponding to the gain region 15 and the common electrode 18. The gain region 15 emits a predetermined stimulated emission light by the forward voltage from the DC power supply 21. This stimulated emission light is
The diffraction grating 17 provided at one end of the optical waveguide layer 13 is used as a reflection surface, and the cleaved surface at one end of the optical waveguide layer 13 is used as a reflection surface, and the optical waveguide layer has a resonator length defined between these reflection surfaces. It circulates in 13.

A reverse bias DC power supply 22 and an AC power supply 23 whose frequency can be adjusted are connected between the common electrode 18 and the electrode 19 corresponding to the saturable absorption region 14.
The saturable absorption region 14 is applied with a reverse bias voltage from the reverse bias DC power source 22, so that the optical waveguide layer 1
It efficiently absorbs a part of the above-mentioned stimulated emission light circulating in 3. This allows the stimulated emission light to be synchronized between its modes, as is well known in the art. When the synchronized stimulated emission light reaches a predetermined intensity, a wavelength corresponding to the mode-locking frequency f _ML basically defined by the resonator length is measured from at least one end surface of the optical waveguide layer 13. It is emitted as a λ laser beam. The AC power supply 23
_Applies a sine wave voltage having an adjustable frequency f _RF close to the mode-locking frequency f _ML to the saturable absorption region 14 to reduce the jitter of the laser light. Further, the AC power supply 23 enables adjustment of the phase of the pulsed light by adjusting its frequency.

In order to increase the phase adjustment range by adjusting the frequency f _RF of the AC power supply 23, that is, the synchronization bandwidth called the locking bandwidth, the semiconductor laser 10 corresponds to the diffraction grating 17 on the cladding layer 12. The heating means 24 is provided in the area to be heated.

In the illustrated example, the heating means 24 is formed in a predetermined region on the clad layer 12 via an electrically insulating layer 25 such as a silicon dioxide layer along the extending direction of the optical waveguide layer 13. A strip-shaped conductor 26 made of, for example, platinum (Pt) having a substantially uniform thickness dimension, and a power supply 27 supplying electric power between both ends of the conductor. Power 27
In the illustrated example, a DC power supply is used, but an AC power supply can be used instead.

As shown in FIG. 2, the conductor 26 has a Z-axis along the cavity length, which coincides with the extension direction of the optical waveguide layer 13, as a longitudinal direction, and a width direction perpendicular to the longitudinal direction. The dimensions gradually decrease. In the illustrated example, the width dimension of the conductor 26 ranges from one end corresponding to the boundary between the diffraction grating 17 and the optical waveguide region 16 to the other end corresponding to the end of the optical waveguide layer 13, that is, the outer end of the diffraction grating region. It gradually decreases toward. Therefore, since the conductor 26 linearly gradually decreases its cross-sectional area from the one end to the other end, when the power supply 27 is energized between the both ends, the conductor 26 is reduced in accordance with the decrease in the cross-sectional area. The electric resistance value is gradually increased in the Z-axis direction. Resistance value per unit length of the conductor 26 in the Z-axis direction
dR is given by the following equation.

DR = σ / (W × d) (1) where σ is the specific resistance of the conductor 26, and W is the conductor 2
6 is a width dimension, and d is a thickness dimension of the conductor 26.

Due to the gradual increase of the electric resistance value of the conductor 26, in the diffraction grating region where the diffraction grating 17 is provided, as shown by the characteristic line 28 in the graph of FIG. Joule heat (i ² dR,
Here, i represents the value of the current flowing through the conductor 26. ), Along the extension direction of the diffraction grating 17 and the optical waveguide layer 1
The temperature increases curvilinearly toward the other end of 3. With the temperature change of the diffraction grating region, as shown by the characteristic line 29 of the graph of FIG. 3B, the refractive index (n) of the diffraction grating 17 with respect to the guided light around the optical waveguide layer 13 is
It increases due to its temperature-dependent characteristic (Δn / n is approximately 6 × 10 ⁻⁵ / ° C.).

Due to this change in the refractive index, the Bragg wavelength of the diffraction grating 17 increases as the temperature distribution increases, as indicated by the characteristic line 30 in FIG. 3 (c).
The increase in the Bragg wavelength along the extension direction of the diffraction grating 17 means a substantial increase in the equivalent refractive index with respect to the guided light. In addition, this increase in the equivalent refractive index causes the diffraction grating 17 to have a so-called chirp similar to that in the diffraction grating described in the above-mentioned document, even though the diffraction grating 17 has a uniform predetermined uniform grating interval. Since the grating function is imparted, the penetration length of the diffraction grating 17 with respect to the guided light according to the change of the frequency fRF of the AC power supply 23 is substantially increased or decreased.

FIGS. 4 (a) and 4 (b) show that the width dimension of the conductor 26 is linearly or linearly reduced toward the other end as shown in FIG. 6 is a graph showing the results of calculation of the respective changes in the equivalent refractive index of the diffraction grating 17 when the diffraction grating 17 is gradually decreased.

The parameters used in this calculation are as follows. The diffraction grating 17 has a coupling coefficient of 100 cm ⁻¹ , its coupling loss is 10 cm ⁻¹ , the length dimension of the diffraction grating 17 is 300 μm, and its grating period is 243.
The thickness is 7 nm, and the equivalent refractive index of the diffraction grating 17 when the conductor 26 is not energized is 3.1904. The conductor 26 is platinum (Pt) having a thickness of 0.25 μm.
And the width dimension W ₁ at the base end as shown in FIG.
Is 26 μm, and the width dimension W ₂ at the tapered tip is 6
The length dimension L from the base end to the tip along the Z-axis is 300 μm.

The electrically insulating layer 25 is made of a silicon dioxide film having a thickness of 0.3 μm, and the p-type cladding layer 12 has a thickness of 2 μm. The thickness dimension of the waveguide layer on which the diffraction grating 17 is formed is 0.2 μm, the width dimension thereof is 1.5 μm, and the thickness dimension of the laminated structure is 100 μm. In addition, the semiconductor laser 10 is placed on a heat sink of a constant temperature, the attenuation factor related to the exponential function used in the calculation is 80 μm, and the calculation is performed under the condition that the electric current of 150 mA is supplied from the power supply 27 to the conductor 26. Results were sought.

The horizontal axis of each graph in FIGS. 4A and 4B represents the distance (μm) from the base end of the conductor 26, and the left vertical axis of each graph represents the conductor 26. Width dimension (μm)
And the right vertical axis thereof shows the equivalent refractive index of the diffraction grating 17.

In the graph of FIG. 4 (a), the width dimension of the conductor 26 changes linearly from the base end to the tip as shown by the characteristic line 31 (in FIG. 2, the solid line shows a solid line). It represents that the equivalent refractive index in the longitudinal direction of the diffraction grating 17 (corresponding to the conductor 26 shown) changes nonlinearly as shown by the characteristic line 32.

On the other hand, the graph of FIG.
When the width dimension of the element changes non-linearly from the base end to the tip end, as indicated by the characteristic line 33 (corresponding to the conductor 26 shown by the chain line in FIG. 2). Grid 1
7 indicates that the equivalent refractive index in the longitudinal direction of 7 changes linearly as shown by the characteristic line 34.

FIG. 4A and FIG. 4 showing the respective calculation results.
As is apparent from the respective graphs of (b), the diffraction grating 1 can be formed by appropriately changing the width dimension of the conductor 26.
7 can be given a temperature distribution that changes along its longitudinal direction, and the diffraction grating 17 can be given a desired change in the equivalent refractive index in accordance with this temperature distribution. The chirp grating structure of can be added.

Therefore, according to the semiconductor laser 10,
As is well known in the art, when the conductor 26 is not energized, the phase of the laser light from the semiconductor laser 10 can be shifted by changing the frequency f _RF of the AC power supply 23. By energizing the conductor 26 of the heating means 24, it is possible to impart a substantial chirp grating structure to the diffraction grating 17 regardless of the fact that the diffraction grating 17 has a uniform and uniform grating interval. It is possible to expand the adjustment range of the frequency f _RF of the AC power supply 23 as compared with the energized state, and it is possible to expand the synchronization bandwidth, that is, the locking bandwidth.

FIGS. 5 (a) and 5 (b) are graphs showing measurement results obtained by experiments for the respective rocking band characteristics in the non-energized state and the energized state of the conductor 26 in the semiconductor laser 10. . The horizontal axis of each graph, and the frequency f _RF with respect to a change in the frequency f _RF of the alternating current power supply 23, the semiconductor laser 10
_Shows the difference (MHz) from the mode-locked frequency f _{ML of} . The right vertical axis of each graph shows the central wavelength (nm) of the laser light emitted from the semiconductor laser 10, and the left vertical axis of each graph shows the time jitter (ps) and the pulse width (ps) of the laser light. ps).

The semiconductor laser 1 used in this experiment
The conditions of 0 are as follows. Saturable absorption region 1
4 has a length of 75 μm, the gain region 15 has a length of 900 μm, the optical waveguide region 16 has a length of 980 μm, and the diffraction grating 17 has a length of 300 μm.
The length of the laminated body, that is, the length of the semiconductor laser 10 was about 2330 μm. The active layers of the saturable absorption region 14 and the gain region 15 are composed of 8 layers in which a compressive strain of about 0.8% is applied to the well layer.
An InGaAsP / InGaAsP multiple quantum well structure was adopted. The waveguide in which the optical waveguide region 16 and the diffraction grating 17 are formed is formed of a bulk InGaAsP layer having a bandgap wavelength of 1.3 μm.

The diffraction grating 17 was formed by an interference exposure method, and a uniform and uniform grating with a period of about 2433.7 nm was adopted. Since the equivalent refractive index of the diffraction grating region, that is, the DBR region, by the diffraction grating 17 is 3.1904, the Bragg wavelength of the diffraction grating 17 when the conductor 26 is not energized is about 1555 nm. Al ₂ O ₃ is formed on one end face of the laminated body where the diffraction grating 17 is located.
A non-reflective coating process using a thin film of The thickness of the laminated structure is 100 μm,
The thickness of the p-type clad layer 12 was about 2 μm. The conductor 26 has a thickness of 0.25 μm, the width W ₁ at the base end is 30 μm, and the width W ₂ at the tip is 10 μm. A conductor tapering linearly toward the tip similar to that of conductor 26 shown in FIG. Also,
As the electrically insulating layer 25, a silicon dioxide film having a thickness of 0.3 μm was adopted.

The graph of FIG. 5A shows that the conductor 26
In the non-energized state, that is, in the non-operating state of the heating means 24,
Frequency f_RFAbout the laser light when changing
For each measured value of its center wavelength, pulse width and time jitter
The respective characteristic lines 35, 36 and 37 thus obtained are shown.
ing. It is shown by the characteristic line 37 showing the jitter characteristic.
The frequency f of the AC power supply 23 _RFThe mode synchronization frequency
Wave number f_MLFrom about -30MHz and about +4
Even if it is changed in the range of 0MHz, it is large in the laser pulse light.
There is no significant jitter fluctuation.
Within the adjustment range, the frequency f_RFThe laser pulse
Characteristic line 35 showing the variation of the center wavelength of the laser beam and the laser beam.
If it is shown by the characteristic line 36 showing the fluctuation of the pulse width of the loose light
Fluctuations in the center wavelength and pulse width of the laser light
Does not occur. Therefore, the diffraction grating 17
Heating without any change in temperature distribution along the direction
In the non-operating state of the means 24, the above-mentioned modulation of about 70 MHz is performed.
The phase of the laser pulse light can be adjusted well within the adjustment range.
Nothing more than

On the other hand, in the graph of FIG.
6 is turned on, that is, by the operation of the heating means 24,
In the state that the power consumption of 0.1 W is supplied to the conductor 26 of
The frequency f_RFAbout the laser light when changing
Each of its center wavelength, pulse width and time jitter measurements
The respective characteristic lines 38, 39 and 40 obtained by the values are shown.
Has been done. It is shown by the characteristic line 40 showing the jitter characteristic.
So that the frequency f of the AC power supply 23 _RFThe same as the above mode
Period frequency f_ML-60 MHz and about
Even if changed in the range of + 60MHz, laser pulse light
Large jitter fluctuation does not occur, this 120M
The frequency f in the adjustment range of Hz_RFEven if you change
The characteristic line 38 showing the variation of the central wavelength of the pulsed light and
The characteristic line 39 showing the variation of the pulse width of the laser pulse light is shown.
As shown in the table,
There is no significant fluctuation. Therefore, the diffraction grating 17
To change the temperature distribution along the length of the
When the means 24 is in operation, the heating means 24 is operated as described above.
Within twice the frequency adjustment range compared to the non-operating state
The phase of the laser pulse light can be adjusted well.

As is apparent from the above description, according to the semiconductor laser 10 of the present invention, the diffraction grating 17 which can be manufactured relatively easily is used, and the diffraction grating region formed by this diffraction grating is arranged in the longitudinal direction thereof. By applying the changing temperature distribution by the heating means 24, the rocking band characteristic showing the adjustable region of the phase of the laser pulse light can be greatly increased.

Graphs I to VI of FIG. 6A are the same as those of the semiconductor laser 10 used in the experiment for obtaining the graphs of FIGS. 5A and 5B.
The calculation result of the change in the transmittance of the diffraction grating 17 with respect to the wavelength of light when the power consumption (W) due to the energization of the conductor 26 is changed is shown. A graph I in FIG. 6A shows the calculation result of the transmittance change of the diffraction grating 17 when the power consumption W by the heating means 24 is zero, that is, when the heating means 24 is in the non-operating state. In addition, graphs II to VI of FIG.
The power consumption W by the heating means 24 is 0.05, 0.2,
The transmittance changes of the diffraction gratings 17 when sequentially increased to 0.25, 0.3 and 0.4 are shown.

The increase in power consumption by the heating means 24 increases the degree of inclination of the change in the temperature distribution along the longitudinal direction of the diffraction grating 17, that is, the gradient of the change in temperature along the longitudinal direction of the diffraction grating 17. Means increase.

To compare graphs I to VI of FIG. 6A, increase in power consumption by the heating means 24 described above,
In other words, it can be understood that the spectrum width of the light whose transmittance by the diffraction grating 17 is lowered increases as the gradient of the temperature change along the longitudinal direction of the diffraction grating 17 increases. Further, since this transmittance has an increasing / decreasing relationship with the reflectance of the diffraction grating 17, the spectral width of the light with which the reflectance of the diffraction grating 17 increases is equal to the above-mentioned heating means 2.
It can be understood that the power consumption increases as the power consumption of 4 increases.

The increase in the above-mentioned spectral width of the laser beam by the diffraction grating 17 means a decrease in the pulse width of the pulsed laser beam obtained from the semiconductor laser, as is well known in the art. That is, each of graphs I to VI in FIG. 6A shows that the pulse width of the pulsed laser light obtained from the semiconductor laser 10 can be adjusted by adjusting the power consumption by the heating unit 24 described above. ing.

Graphs I to VI of FIG. 6B are the same as those of the semiconductor laser 10 used in the experiment for obtaining the graphs of FIGS. 5A and 5B.
Spontaneous emission light (A) from the semiconductor laser 10 when the power consumption (W) due to energization of the conductor 26 is changed.
The measurement result of the intensity regarding the wavelength of SE light) is shown.

Graph I in FIG. 6B shows the measured value of the transmittance change of the diffraction grating 17 when the power consumption W by the heating means 24 is zero, that is, when the heating means 24 is in the non-operating state.
Graphs II to VI in FIG. 6B are heating means 2
The power consumption W by 4 is 0.02, 0.1, 0.14,
The intensity changes of the spontaneous emission light from the respective semiconductor lasers 10 when sequentially increased to 0.17 and 0.3 are shown.

To compare the graphs I to VI of FIG. 6B, the diffraction with the increase in the temperature change gradient along the longitudinal direction of the diffraction grating 17 due to the increase in the power consumption by the heating means 24 is performed. The spectrum width in which the intensity of the spontaneous emission light by the grating 17 decreases, that is, the spectrum width in which the reflectance by the diffraction grating 17 increases increases. The tendency by this experimental result is in agreement with the tendency of the calculation result obtained from each graph I-graph VI of FIG.

FIGS. 7 (a) and 7 (b) show consumption of the spectrum width and pulse width of the laser pulse light from the semiconductor laser 10 similar to that used in the experiment described above by the heating means 24. 6 is a graph of experimental results showing the dependence of the saturable absorption region 14 on the reverse bias DC power supply 22 when the power is changed.

The horizontal axis of the graph of FIG. 7A shows the voltage value (V) of the reverse bias DC power supply 22, and the vertical axis thereof shows the spectral width (nm) of the pulsed light. The characteristic line 41 is the spectral width when the reverse bias DC power supply 22 is changed in the non-operating state of the heating means 24, that is, in the state where the temperature distribution along the longitudinal direction of the diffraction grating 17 is substantially equal to room temperature and is uniform. Shows the change of. Also, the characteristic line 42 and the characteristic line 4
3, the characteristic line 44 and the characteristic line 45 show the reverse bias DC power source 22 when the power consumption W by the heating means 24 is 0.02, 0.1, 0.14 and 0.17, respectively.
The change of the spectrum width when is changed is shown.

According to the graph of FIG. 7A, the relationship between the change in the power consumption W by the heating means 24 and the change in the spectral width when the reverse bias DC power supply 22 shows a value of 1.4 V, for example. Looking at it, the power consumption W is 0.02, 0.
It can be understood that the spectral width increases with the sequential increase of 1, 0.14, and 0.17.

The horizontal axis of the graph of FIG. 7B shows the voltage value (V) of the reverse bias DC power supply 22, and the vertical axis thereof shows the pulse width (ps) of the pulsed light. Similarly to the characteristic line 41, the characteristic line 46 shows the change in the pulse width when the reverse bias DC power supply 22 is changed in the non-operating state of the heating means 24. Further, characteristic lines 47, 48, and 49
And the characteristic line 50 indicates the power consumption W by the heating means 24.
Is 0.02, as in the graph of FIG.
In each state of 0.1, 0.14 and 0.17,
The change in pulse width when the reverse bias DC power supply 22 is changed is shown.

According to the graph of FIG. 7B, the relationship between the change in the power consumption W by the heating means 24 and the change in the pulse width when the reverse bias DC power supply 22 shows a value of 1.4 V, for example, is shown. Looking at it, the power consumption W is 0.02, 0.1,
It can be seen that the pulse width decreases with the sequential increase of 0.14 and 0.17.

Further, in the graph of FIG. 7A, when the reverse bias DC power supply 22 is 1.4 V and the power consumption W changes from 0.17 to 0.17, the spectral width of the pulse laser light is changed. Spreads from 0.38 nm to 1.0 nm. Similarly, in the graph of FIG. 7B, when the reverse bias DC power supply 22 is 1.4 V and the power consumption W changes from 0.18 to 0.17, the pulse width of the pulsed laser light becomes It has been reduced from 6.5 ps to 3.4 ps. Comparing the two shortest pulse widths at this time, the shortest pulse width is reduced from 6.5 ps to 2.6 ps, and a change of about 3 times is obtained.

The above-described relationship between the increasing tendency of the spectrum width obtained by the graph of FIG. 7A and the decreasing tendency of the pulse width obtained by the graph of FIG. 7B coincides with the theoretical one. .

Therefore, the semiconductor laser 1 according to the present invention.
According to 0, by adjusting the power consumption W of the heating means 24, that is, the amount of electricity supplied to the conductor 26, the temperature gradient that changes in the longitudinal direction can be changed in the diffraction grating region by the diffraction grating 17, Thereby, the pulse width of the pulsed laser light obtained from the semiconductor laser 10 can be adjusted.

In order to make the power consumption W of the heating means 24 variable, it is desirable to use a power source capable of voltage adjustment as the power source 27. Further, the semiconductor laser 10 whose pulse width is variable is not limited to the hybrid type described above, but can be applied to an active synchronous mode or passive mode synchronous semiconductor laser.

In the above description, the conductor 26 of the heating means is a conductor having a uniform thickness and a width gradually decreasing from the base end to the tip. From the end to the tip, the width dimension can be gradually increased, and in place of this, a conductor having a constant width dimension and changing the thickness dimension in the longitudinal direction can be used. Instead of the heating means provided with a power source for supplying electric power, various heating means capable of giving a temperature distribution changing in the longitudinal direction to the diffraction grating region or adjusting the temperature gradient thereof can be adopted.

[0053]

As described above, according to the mode-locked semiconductor laser of the present invention, the penetration length by the diffraction grating is set to the above-mentioned intensity by using the diffraction grating having a uniform and uniform grating spacing. It can be made variable according to the increase or decrease of the frequency of modulation, whereby a relatively wide locking bandwidth can be realized. Therefore, according to the semiconductor laser of the present invention, it is not necessary to form a diffraction grating having a complicated structure as in the conventional case, and the semiconductor laser can be manufactured relatively easily, and the locking band width is within a relatively wide range. It becomes possible to adjust.

Further, according to another mode-locked semiconductor laser of the present invention, as described above, the bandwidth of the reflected light by the diffraction grating can be varied by adjusting the temperature gradient by the heating means. Therefore, the pulse width can be increased or decreased by adjusting the temperature gradient. Therefore, according to the semiconductor laser of the present invention, the pulse of the pulsed light can be obtained with a relatively simple structure regardless of whether the synchronous semiconductor laser is a hybrid synchronous mode which is an active synchronous mode, a passive synchronous mode or a combination thereof. You can increase or decrease the width.

[Brief description of drawings]

FIG. 1 is a sectional view schematically showing a specific example of a mode-locked semiconductor laser according to the present invention.

2 is a plan view showing a conductor of a heating means provided in the mode-locked semiconductor laser shown in FIG.

FIG. 3 (a), FIG. 3 (b) and FIG. 3 (c) are
3 is a graph showing changes in heat distribution characteristics, refractive index change characteristics, and Bragg wavelength characteristics in a diffraction grating region by the heating means of the mode-locked semiconductor laser shown in FIG.

4 (a) and 4 (b) respectively show calculated values of the refractive index change of the diffraction grating region with respect to the linear change and the non-linear change of the width dimension of the conductor of the heating means shown in FIG. It is a graph shown.

FIG. 5 (a) is a graph showing a rocking bandwidth characteristic of the mode-locked semiconductor laser according to the present invention when the conductor is not energized, and FIG. 5 (b) shows the present invention. 6 is a graph showing a rocking bandwidth characteristic of the mode-locked semiconductor laser according to the present invention when the conductor is energized.

6 (a) I to FIG. 6 (a) VI show changes in the transmittance characteristic with respect to the wavelength of the diffraction grating when the temperature gradient in the diffraction grating region is changed, which is obtained from the calculation results. It is a characteristic graph, FIG.6 (b) I-FIG.6 (b) VI.
[Fig. 4] is a similar characteristic graph showing light intensity characteristics obtained from experimental results.

FIG. 7 (a) is a graph showing changes in the spectral width of output pulsed light when the temperature gradient in the diffraction grating region of the mode-locked semiconductor laser according to the present invention is changed, and FIG. 10] is a graph showing a change in pulse width of output pulse light when a temperature gradient in a diffraction grating region of the mode-locked semiconductor laser according to the present invention is changed.

[Explanation of symbols]

10 mode-locked semiconductor laser 11, 12 Clad layer 13 Optical waveguide layer 14 Saturable absorption region (intensity modulation region) 15 Gain area 16 Optical waveguide area 17 diffraction grating 24 Heating means 25 electrical insulation layer 26 Conductor 27 power supply

Claims (10)

[Claims] 1. A gain region for generating induced pumping light between a pair of cladding layers, and a frequency adjustable to the guided light so as to achieve synchronization between modes of the guided pumping light generated in the gain region. An optical waveguide layer having an intensity modulation region for performing intensity modulation, and a diffraction grating region provided with a diffraction grating having a uniform and uniform predetermined grating interval for reflecting the induced excitation light is provided. A mode-locking semiconductor laser, comprising: heating means for applying a temperature distribution, which changes in the extension direction of the optical waveguide layer, to the diffraction grating region. 2. The mode-locking according to claim 1, wherein the temperature distribution substantially changes the lattice spacing of the diffraction grating in the extension direction of the optical waveguide layer with respect to the induced excitation light traveling in the optical waveguide layer. Semiconductor laser. 3. The mode-locked semiconductor laser according to claim 1, wherein an alternating voltage is applied to the intensity modulation region so that the phase of the pulsed light from the laser can be adjusted so that its frequency can be adjusted. 4. A gain region for generating induced pumping light between a pair of clad layers, and intensity modulation of the guided light so as to synchronize modes of the guided pumping light generated in the gain region. A mode-locking semiconductor laser having an optical waveguide layer having an intensity modulation region and a diffraction grating region provided with a diffraction grating having a uniform and uniform grating spacing for reflecting the induced excitation light. A mode-locked semiconductor laser is provided with heating means for applying a temperature distribution that changes in the extending direction of the optical waveguide layer to the diffraction grating region so that the temperature gradient can be adjusted. 5. The mode-locked semiconductor laser according to claim 1, wherein the intensity modulation region is a saturable absorption region. 6. The mode-locked semiconductor laser according to claim 1, wherein the semiconductor laser is a hybrid mode-locked semiconductor laser. 7. The heating means is formed in a portion of one of the cladding layers corresponding to the diffraction grating region so as to extend along the extension direction of the waveguide layer via an electrically insulating layer, and the longitudinal direction. 5. A strip-shaped conductor having a substantially uniform thickness and having a width-direction dimension changed, and a power supply for supplying a current to the conductor in its longitudinal direction. The mode-locked semiconductor laser according to any one of the above. 8. The mode-locked semiconductor laser according to claim 7, wherein the width of the conductor gradually decreases from one end of the conductor to the other end. 9. The mode-locked semiconductor laser according to claim 8, wherein the width of the conductor changes linearly. 10. The mode-locked semiconductor laser according to claim 8, wherein the conductor gradually decreases in width dimension toward the outer end of the diffraction grating region.