JPH06302901A - Optical pulse generation control element - Google Patents

Abstract

PURPOSE:To provide an element wherein operation of higher repetition frequency is possible, control is easy (the repetition frequency is changeable), a higher output optical pulse train wherein not only the time width but also the spectrum width are narrower is simply generated, and the optical pulse train is subjected to coding and decoding. CONSTITUTION:In the optical pulse generation control element, a laser light source 12, a light modulation part 13, and a light control part 14 are integrally arranged on a semiconductor substrate, via an optical waveguide. The element has coding function which absorbs or transmits only specific optical pulses in a optical a pulse train by a light control part, after the optical pulse train is generated by modulating the intensity of the output light from the laser light source by a light modulation part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for generating and controlling a short optical pulse having a variable repetition rate at high speed as a light source in optical communication and optical measurement.

[0002]

2. Description of the Related Art A semiconductor laser has a feature that it is small and can be directly modulated, and has been used for generating an ultrashort optical pulse. The methods are roughly classified into three types: (1) Q switching method, (2) gain switching method, and (3) mode locking method. Among them, the Q switching method is not easy to manufacture an element. Although the gain switching method has the problem that the operation control is not easy and the gain switching method is simple and the repetition frequency is variable, it requires a narrow and high repetition frequency current pulse, and the semiconductor laser itself is fast. It is necessary to operate, and the generated optical pulse also has a drawback that the product of the pulse width and its spectral width becomes several times larger than the value specified by the Fourier transform because of the chirp characteristic peculiar to the semiconductor laser ( Usually, the amount of chirp is represented by the line width expansion coefficient α, and this product is obtained by using α (1
+ Α ² ) ^1/2 times larger). On the other hand, the mode-locking method has obtained a pulse width close to the theoretical limit, but requires a complicated external resonator configuration, and the repetition frequency is specified by this external resonator configuration, and is an integer multiple of the resonant frequency. I can only get it. Recently, in addition to the three methods described above, a method (4) for generating a high-speed short optical pulse using an electro-absorption type external modulator has been reported (Reference: M. et al.
Suzuki et al., CLEO '92 Post Dead
line Paper, CPD 26, pp. 56-57, 1992).

FIG. 10 shows the principle thereof. In an electroabsorption type bulk modulator, when an electric field is applied from the outside, the absorption coefficient changes as shown in the figure and the intensity of light passing therethrough can be modulated. , Its change is non-linear with respect to the applied voltage, so if continuous light is applied from the outside (for example, a semiconductor laser is operated by direct current) and a sine wave signal is applied to the modulator, a pulse of light narrower than half the wavelength of the signal Can occur. This method has an advantage that the repetition frequency can be freely set by using a sine wave voltage which is relatively easy to obtain, and an optical pulse having a narrow line width and a narrow spectrum width close to the Fourier transform limit can be obtained.

[0004]

However, when an optical pulse is generated as shown in FIG. 10, the width of the obtained optical pulse depends on the voltage dependence of the light intensity transmitted through the external modulator and the band of the external modulator. The problem is that the band is limited, the band is at most about 20 GHz (8-10 GHz in the above document), the driving voltage is not low, and the intensity of light is weak due to the large coupling loss between the modulator and the optical fiber. There is.

Further, when the optical pulse trains generated by the various optical pulse generation methods of the narrow line width and narrow spectral width described above are used for communication or the like, it is necessary to code or decode the pulse train in a desired form. However, there is a problem in that it is necessary to separately prepare a device for this purpose, which inevitably complicates the configuration and increases the coupling loss.

The present invention solves the problems existing in the conventional methods as described above, particularly the problem of the above method (4), and
It is an object to code or decode the pulse train described at the end.

That is, the object of the present invention is to operate at a higher repetition frequency and be easy to control (variable repetition frequency), and to simplify not only the time width but also the spectrum width, and higher output. Is to provide an element for generating an optical pulse train and coding or decoding the optical pulse train.

[0008]

According to a first aspect of the present invention, there is provided an optical pulse generation control element in which a laser light source, an optical modulation section and an optical control section are integrally formed on a semiconductor substrate via an optical waveguide. An optical pulse generation control element disposed in the optical pulse generation control device, wherein the light emitted from the laser light source is intensity-modulated by an optical modulator to generate an optical pulse train, and the optical pulse train absorbs only a predetermined optical pulse. Alternatively, it is characterized by having a transparent coding function.

Here, the above-mentioned optical modulator, optical controller and optical waveguide may be formed in a semiconductor multiple quantum well structure.

A diffraction grating may be included in the optical waveguide of the laser light source described above.

[0011]

The basic structure and operation of the optical pulse generation control element of the present invention will be described with reference to FIG. FIG. 1 (A) is a schematic top view schematically showing a main part of the configuration as seen from the functional side of the optical pulse generating element of the present invention. In the present invention, a laser light source (laser unit) 12, a light modulation unit 13, and a light control unit 14 are integrally disposed on a substrate (not shown) via an optical waveguide (not shown). Light modulator 1
3 constitutes an optical pulse generator, and an optical pulse train as shown in FIG. 1B is generated. This pulse train is controlled by the light controller to generate a coded pulse train as shown in FIG.

Even if the semiconductor laser itself is used to generate a narrow optical pulse by the Q-switching or gain-switching method, its line width has a large product with the spectral line width due to its chirp characteristic (usually, the chirp amount is It is represented by the line width expansion coefficient α, and α is 2-6 in the semiconductor laser,
This product is increased by (1 + α ² ) ^1/2 times using α), but since an external modulator with a small line width expansion coefficient α (0.2-1.0) is used, the line width is close to the theoretical limit. A light pulse having a narrow spectral width can be obtained. Since the semiconductor modulator with a multiple quantum well structure uses exciton absorption, it is possible to lower the driving voltage compared to the one using the forbidden band absorption of the bulk semiconductor crystal (Kordish effect in France). . That is, 10 ⁵ V / cm perpendicular to the MQW layer
Even if a high electric field is applied to the excitons, the excitons are unlikely to dissociate, and a steep absorption peak wavelength associated with the optical absorption of the excitons is observed. Shift to (Quantum-Confined
Stark Effect). Therefore, the MQW structure is expected to be a modulator having a large change in absorption coefficient due to application of an electric field and high efficiency. In fact, with the MQW structure,
The highest performance modulator with 3 dB band of 40 GHz has been reported (Reference: Odaka et al., IEICE Transactions C-
1, J74-C-1, Vol. 11, pp. 414-420, November 1991), its broadband property has been verified. If the band is widened, the modulation frequency can be increased accordingly and the width of the optical pulse can be narrowed. Further, the modulator needs to be driven with a large amplitude operation, but the driving voltage is small in the multiple quantum well structure modulator, and the burden on the high-frequency signal source is lightened. Furthermore, as shown in FIG. 4 later, in the multiple quantum well structure, the extinction ratio changes non-linearly with respect to the modulation voltage, and the degree of the change is larger than that of the bulk modulator described above.
As a result, the application of the sine wave voltage enables generation of a narrow optical pulse even under irradiation of CW light.

Further, monolithic integration with a semiconductor laser is also possible, and it is possible to reduce an increase in loss by coupling the light source and the modulator via the optical fiber, which was a problem of the method (4). it can. Further, since the optical pulse train generated by the above method is monolithically integrated with a semiconductor optical control unit having a traveling waveform whose absorption characteristic can be changed by an applied voltage, another device for transmitting an optical pulse carrying a desired signal is provided. You can get it without preparing.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure of a light emission control element according to one embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 2 shows an MQW-DF according to an embodiment of the present invention.
It is a schematic perspective view of an integrated light source of a B laser, an MQW light modulator, and an MQW light controller of a traveling waveform. Figure 3
It is an expanded sectional view which follows the II-II tip of the coupling | bond part of the element structure of FIG. 2 and 3, 10 is an optical pulse generation control element (MQW-DFB laser element), 11 is an optical waveguide, 12 is a distributed feedback semiconductor laser section, 13 is an optical modulation section, 14 is an optical control section, and 15 is an optical control section. A first semiconductor portion, 16 is a second semiconductor portion, 17 is an optical coupling region, 18 is an interface, 2
Reference numeral 0 is a substrate, 22 is an etching stop layer, 24 is a first lower cladding layer, 26 is an active layer (first multiple quantum well structure), 26A is a well layer, 26B is a barrier layer, 28 is a guide layer, and 29 is Diffraction grating (grating), 30 is a first upper cladding layer, 31 is a protective layer, 32 is a second lower cladding layer, 34 is a second multiple quantum well structure, 34A is a well layer, and 34B is a barrier layer, 36 is a second upper cladding layer, 38 is a third cladding layer, 38A is a thin portion, 38
B and 38C are clad layer portions, 40 is a separation portion, 42 is a cap layer, 44, 46 and 47 are buried portions, 38 is a laser portion electrode, 49 is a light modulation portion electrode, and 50 is a light control portion electrode. , 62 are n-type electrodes, and 64 is an antireflection coating.

The optical pulse generating element of the present invention, that is, M
The QW-DFB laser device 10 includes an optical waveguide 11 and a substrate 20.
It is provided above. The optical waveguide 11 is composed of a distributed feedback semiconductor laser section (laser light source) 12, an optical modulation section 13 and an optical control section 14 coupled to the semiconductor laser section. In other words, the laser light source 12, the light modulator 13, and the light controller 14 are integrally arranged via the optical waveguide 11. The distributed feedback semiconductor laser section 12 includes a first semiconductor section 15, and the light modulation section 13 and the light control section 14 include a second semiconductor section 16. The above-described first and second semiconductor portions 15 and 16 are provided on the substrate 20 via the etching stop layer 22. The first semiconductor portion 15 has a first lower cladding layer 24, an active layer 26 (first multiple quantum well structure), a guide layer 28, and a first upper cladding layer 30, which are stacked in this order. . A diffraction grating (grating) 29 is formed in the guide layer 28 in the distributed feedback semiconductor laser section. First upper and lower cladding layers 3
0 and 24 are doped to have different conductivity types, and sandwich the active layer 26 and the guide layer 28. The active layer 26 constitutes a first multiple quantum well structure including a well layer 26A and a barrier layer 26B. The light control unit 14 is composed of the second semiconductor portion 16 and has the same structure as the light modulation unit so that only the applied voltages can be applied independently of each other. The first semiconductor partial diffraction grating described above may be provided in the active layer 26.

On the other hand, the second semiconductor portion 16 included in the optical modulator 13 has a second lower cladding layer 32, a second multiple quantum well structure 34, and a second upper cladding layer 36, which are laminated in this order. I am doing it. Like the first upper and lower cladding layers, the second upper and lower cladding layers 36 and 32 are doped to have different conductivity types and sandwich the second multiple quantum well structure.
The second multiple quantum well structure 34 is composed of a well layer 34 and a barrier layer 34B, like the first multiple quantum well structure. The semiconductor laser section 12 is optically coupled in the optical coupling region 17 facing each other via the lower cladding layer 32 of the optical modulation section 13.

A continuous clad layer 38 is provided on the first and second semiconductor portions 15 and 16, and the clad layer 38 forms an interface 1 between the first and second semiconductor portions 15 and 16.
8 has a separating portion 40 whose upper portion is cut off along a region including the opposing end portions 15A and 16A sandwiching 8 therebetween. That is, the interface 18
The thin portion 38A extending over the portion 38A of the clad 38 existing in the DFB laser section 12, the optical modulation section 13, and the optical control section 14
B and 38C are in contact with each other. Optical waveguide 11 is DF
It has a ridge structure that penetrates the B laser unit 12, the light modulation unit 13, and the light control unit 14. Each side of the DFB laser unit 12, the light modulation unit 13, and the light control unit 14 has an embedded portion 44,
46 and 47 are provided at the same height as the cap layer 42. An electrode 48 of the laser portion, an electrode 49 of the light modulating portion 13, and an electrode 50 of the light controlling portion 14 are provided on the cap layer 42 and the embedded portions 44, 46, 47, respectively. The laser unit 12, the light modulator 13, and the light controller 14 are separated from each other by a separating unit 40.
Due to this, the insulation is improved.

Next, the operation principle of the optical modulator of the optical pulse emission control element of the present invention will be described.

As shown in FIG. 4, when a sine wave voltage having an amplitude Va centering on a certain DC voltage V ₀ is applied as the applied voltage, the intensity of light changes as shown in the left part of the figure. By properly selecting the bias position and amplitude conditions, a pulse narrower than the half wavelength of the applied sine wave can be obtained.
An optical control unit extracts a pulse from the optical pulse train generated in this manner. That is, a pulse train is generated by the combination of the laser light source and the next light modulator, and a voltage having a different frequency is applied to the next light controller, which is synchronized with the voltage applied to the previous light modulator. Then, the pulse train is coded according to the cycle.

This type of semiconductor device is shown in FIG.
As shown in (C), when a reverse voltage is applied, the absorption coefficient changes as shown by the dotted line.
71 shifts to the long wavelength side 72, 73. For this reason, light that was transparent (in a state where it is not absorbed) in the state where no voltage is applied is absorbed by the voltage application, and therefore the transmitted light intensity is modulated by the applied voltage. In the conventionally used one (bulk structure), the change in absorption coefficient with respect to the voltage is small as shown in FIG. 5 (A), as shown in FIG. 5 (B). On the other hand, in the device of the present invention having the MQW structure, the absorption edge is shifted as shown in FIG. 5C, but the absorption edge is also shifted to the long wavelength side by the voltage application. ), The change in absorption coefficient is extremely large. As can be seen from FIGS. 5B and 5D, the conventional device has a smaller change in absorptivity than the MQW structure according to the present invention. Therefore, in order to obtain a certain extinction ratio, the device length must be changed. It is necessary to lengthen (the extinction ratio is exp (-Δα
L). (Δα: change in absorption coefficient, L: sample length)
Since the capacity of the device is increased, the speed is limited.

Since the MQW element of the present invention has a remarkably large change in absorptivity as compared with the conventional element, as shown in FIG. 4, when a large amplitude sine wave is applied to the light modulating section, it is emitted from the laser section. The light is intensity-modulated to generate a pulse train having a steep light pulse characteristic. FIG. 6 shows an example thereof.

FIG. 6 is a diagram showing the characteristics of the optical pulse generating element by the integrated light source of the MQW-DFB laser, the MQW optical modulator and the MQW optical controller to which the present invention is applied. Figure 6
As shown in (A), a steep pulse train is generated. That is, the pulse width with a full width at half maximum of about 10 picoseconds is 20 GHz.
Is obtained at the repetition frequency of, and considering the time resolution of the measurement system (since it has a response speed of about 10 picoseconds)
The width is estimated to be 7 picoseconds or less. Actually the second
According to the measurement of autocorrelation by harmonics, the full width at half maximum was 7 picoseconds as shown in FIG. 6 (B). The optical output is also several mW, which is a sufficient value for this type of optical pulse. When a signal (for example, a sine wave) having a frequency different from that synchronized with the signal applied to the optical modulator is added to the MQW optical controller, a decoded signal is obtained as shown in FIG. This control signal is not limited to a sine wave and may be a random pulse voltage. Conventionally, this optical control unit had to be prepared separately from the pulse generation unit to modulate the optical pulse using an optical fiber, and there were problems of fiber coupling loss, stability, etc. The invention overcomes this.

As described above, the optical pulse generation control element of the present invention maintains the small size and robustness peculiar to the semiconductor laser,
The invention uses the ultra-high speed (ultra-wide band), low drive voltage external light intensity modulator and the light controller using the multi-quantum well structure that has been invented and demonstrated by the present inventor, without affecting the laser itself. Utilizing the low chirp property of the modulator itself,
A narrow optical pulse train is easily generated at a high repetition frequency that is easy to control, and this is controlled by an optical control unit provided on the same substrate and driven by a signal different from the optical modulation unit.

If the light source and the optical modulator, and the optical modulator and the optical control unit are separate elements, an optical fiber is interposed between them, so that a coupling loss is inevitably generated and the intensity of light is reduced. Moreover, a module is required for coupling with the fiber, the number of manufacturing steps is increased, and reliability is also a problem. In order to solve this, in the light generation control element of the present invention, as shown in FIG. 2, the light modulator, the light controller and the semiconductor laser are monolithically integrated. The outline of this configuration can be shown in FIG. 7A. In the laser section 12, the light intensity is constant as shown in FIG. 7B1, and the light after passing through the light modulation section 13 is shown in FIG.
As shown in (B2), since it is a simple optical pulse train and does not carry any signal, a semiconductor light control unit 14 having a traveling waveform is provided on the same substrate to absorb or transmit light through a voltage applied to the semiconductor light control unit 14, and the semiconductor light control unit 14 shown in FIG. As shown in B3), an optical pulse train is coded to generate a high-output optical pulse carrying a signal. The external light modulator employs a multiple quantum well structure, which is faster than the bulk type and is advantageous for low voltage driving, and utilizes the strong nonlinearity and low chirp with respect to the voltage of the light intensity modulator. Further, in the light controller, as shown in FIG. 7, the absorption characteristic changes depending on the applied voltage, so that a specific pulse in the light pulse train can be extracted and coded (FIG. 7C).

The MQW-DFB laser described above can be manufactured as follows. That is, molecular beam epitaxy (MBE) or metal-organic vapor phase epitaxy (MOVP)
E), the DFB laser portion (or light control portion, light modulation portion) formed on the substrate is selectively etched to the substrate by dry and wet etching methods, and then the light modulation portion, light control portion (or laser portion). ) Is grown using the MBE method. At this time, the height of the laser emitting portion measured from the substrate surface is made to match the height of the light modulation portion, the light control portion, and the optical waveguide portion measured from the substrate surface. The light modulator and the light controller are essentially the same except that the voltage can be applied independently.

FIG. 8 is a schematic sectional view showing a manufacturing process when the laser portion is formed first. In FIG. 8, the same reference numerals as those used in FIGS. 2 and 3 indicate the same members or portions, 52 is a SiO ₂ film, 54 is a patterned resist, and 56 is a SiO ₂ film eaves.

The method of manufacturing the light generation control element of the present invention will be described in detail below with reference to FIG.

The MQW-DFB laser described above can be manufactured as follows. That is, molecular beam epitaxy (MBE) or metal-organic vapor phase epitaxy (MOVP)
E), the DFB laser section 12 and the light control section 13 (or the light modulation section 14) produced on the substrate are selectively etched to the substrate by dry and wet etching methods, and then the light modulation section 13 (or the DFB laser). Part 1
2. The light control unit 14) is grown using the MBE method. At this time, the height measured from the substrate surface of the DFB laser unit 12 and the light control unit 14 is made to match the height measured from the substrate surface of the optical waveguide portion of the light modulation unit. The DFB laser unit 12 and the light control unit 14 are the same in all other configurations except for the presence or absence of a diffraction grating.

First, as shown in FIG. 8A, the p substrate 2
Etching stop layer 2 on the surface of 0 by MOVPE method
2, a first lower clad layer 24, and then an active layer 26 having a quantum well structure including a well layer (well layer) 26A and a barrier layer (barrier layer) 26B, and a guide layer 28 are sequentially grown. On top of that, the grating 2 is formed by interference exposure and etching only on the portion where the DFB laser portion is to be formed.
9 is formed, and the second lower cladding layer 30 is grown.

Next, Si is formed on the second lower cladding layer 30.
The O ₂ film 52 is formed by a sputtering device. A hole is opened in a desired portion (a portion where the light modulation portion is to be formed) by photolithography technique. That is, the SiO ₂ film 5
Lithography is performed using a two layer mask consisting of 2 and patterned photoresist 54. Thus, the structure shown in FIG. 8B is obtained.

Next, the photoresist 54 is removed, and the light modulating portion 13 is grown by the MBE method using the eaves portion 56 as a mask. The optical modulator 13 grows a second multiple quantum well structure 34 including a second lower clad layer 32, a well layer 34A, and a barrier layer 34B to form an optical waveguide, and a second upper clad layer 36 is formed thereon. To form. The protective layer 31 is formed on the second upper cladding layer 36. In this case, DF
The B laser unit 12 and the light control unit 14 are similarly laminated. In this way, the structure shown in FIG. 8C is obtained.

The portions (layers 32, 34, 36, 31) grown on the DFB laser portion 12 and the light control portion 14 are made of Si.
The O ₂ film 52 is removed by etching from the side to obtain the structure shown in FIG.

On top of this, as shown in FIG.
The cladding layer 38 and the cap layer 42 are formed by MOVPE method.

Next, the active layer 26 and the optical waveguide layer (second quantum well structure) 34 described above are etched to obtain DFB.
A ridge that penetrates the laser section, the light modulation section, and the light control section is formed (see FIG. 2).

After that, the embedded portions 44 and 47 are embedded in the DFB laser portion and the optical control portion, and the embedded portion 46 is embedded in the optical modulation portion, and finally, the electrodes 48, 50 and 49 are embedded in the respective portions.
(See Fig. 2).

Etching is performed by using the electrodes 48, 49 and 50 as a mask to form a separating portion 40 between the electrodes to strengthen the insulation between the light modulating portion, the DFB laser portion and the light control portion. Further, an antireflection coating 64 (see FIG. 3) is applied to the emission end face of the light control portion, and an n-type electrode 62 (see FIG. 2) is attached to the lower surface of the substrate 20. In this way, FIG.
The structure shown in (F) is obtained. This structure corresponds to the structure shown in FIGS.

Next, a specific manufacturing example of the element structure shown in FIGS. 2 and 3 will be described.

That is, M is formed on the surface of the n-InP substrate 20.
An n-InGaAsP layer is provided as an etching stop layer 22 by the OVPE method, an n-InP clad layer 24 is formed thereon to have a thickness of 0.1 μm, and 10 nm of InGaAs is used as a well layer (well layer) 26A, and an I corresponding to a wavelength of 1.3 μm.
Active layer 26 consisting of 6 layers of quantum well structure using nGaAsP 10 nm as barrier layer (barrier layer) 26B, wavelength 1.3 μm
An InGaAsP guide layer corresponding to m was grown to a thickness of 0.1 μm. A grating 29 is formed thereon by interference exposure and etching, a p-InP clad layer 30 is grown, and then a SiO ₂ film 52 is formed by a sputtering device, and a hole is formed in a desired portion by a photoremorphography technique. . That is, the patterned photoresist 54
Lithography is performed using the two-layer mask of

Next, using this as a mask, the light modulator 13 and the light controller 14 are grown by the MBE method. In the light modulator 13, the n-InAlAs cladding layer 32 is 0.3 μm thick, the InGaAs well layer 34A is 7.5 nm thick, and the I-layer is 5 nm thick.
A quantum well structure 30 layer composed of the nAlAs barrier layer 34B is grown to form an optical waveguide 34, and p-InA is formed thereon.
The 1As clad layer 36 is formed. A p-InGaAs protective layer 31 is formed on the clad layer 36. The portion grown on the laser portion 11 (layers 32, 34, 36, 31)
Is removed by etching the SiO ₂ film 52 from the side, and finally the p-InP clad layer 38, p-I
The nGaAs cap layer 42 is formed by the MOVPE method.

Next, the active layer 26 and the optical waveguide 34 described above are etched using a stripe having a width of 1.5 to 3.0 μm to form a ridge penetrating the laser portion, the light modulation portion, and the light control portion. After that, the laser section is changed to the InP layer (p-In
(Made of a combination of P and n-InP or semi-insulating InP) 44, the light modulator and the light controller are made of polyimide 46,
Each of them is filled with 47, and finally the electrode 4 is formed on each part.
Attach 8, 50, 49.

Etching is performed by using the electrodes 48, 49 and 50 as a mask to form a separating portion 40 between the electrodes to strengthen the insulation between the light modulating portion, the laser portion and the light controlling portion.

The length of the insulating portion between the laser portion, the light control portion and the light modulating portion, and each portion is 300 μm, 100 μm, 10
It was set to 0 μm and 50 μm. An antireflection coating (not shown) was applied to the emission end face of the light control section. Further, an n-type electrode 62 (see FIG. 2) is attached to the lower surface of the substrate.

Further, FIG. 9 is a schematic sectional view showing another embodiment of the light generation control element of the present invention. In FIG.
The same reference numerals as those used in FIGS. 2 and 3 indicate the same members or portions. A laser unit 12, a light modulation unit 13, and a light control unit 14 are provided on the n-InP substrate 20. The laser section 12 includes a laser active layer 26 and a light modulation section 1.
3, there are two layers including the core 34 of the waveguide layer of the light control unit 14,
The light modulator 13 and the light controller 14 have only one core 34, and the light emitted from the laser is the core 3 in the laser unit.
The structure is such that the light is guided to the optical waveguide 4 and is guided to the optical modulator and the optical controller. The optical pulse generation control element of this embodiment can be manufactured by manufacturing the laser portion first by a method similar to the method shown in FIG.

[0045]

As described above, according to the present invention, M
It is possible to fabricate a light source in which a QW-DFB laser, an MQW optical modulator, and an MQW optical controller are integrated with good coupling efficiency.
Since the performance of each of the QW-DFB laser, the MQW optical modulator and the MQW optical controller can be optimized, it is possible to easily decode an optical pulse having a narrow line width and a high repetition frequency. It is also possible to operate with only two elements, the MQW light modulator and the MQW light controller.

The semiconductor laser forming the optical pulse generation section and the coupling form of the laser section and the optical modulation section of the optical pulse generation control element have been described above using the structure called a distributed feedback semiconductor laser and a butt joint. Similar characteristics can be obtained even if the semiconductor laser forming the pulse generating section is a distributed Bragg reflection type semiconductor laser.

[Brief description of drawings]

FIG. 1A is a schematic top view showing an outline of a main part of an optical pulse generation control element of the present invention, and FIGS. 1B and 1C are optical pulse waveform diagrams.

FIG. 2 is an MQW-DFB laser and MQ to which the present invention is applied.
It is a perspective view showing a schematic structure of a structure of an optical pulse generation control element by an integrated light source of a W light modulator and an MQW light controller.

3 is an enlarged cross-sectional view taken along line II-II of a junction interface between the MQW-DFB laser of FIG. 2, the MQW light modulator, and the MQW light controller.

FIG. 4 is a characteristic diagram showing characteristics when the light control section of the light pulse generation control element of the present invention is not operated.

5A is a characteristic diagram showing a wavelength shift of a conventional optical pulse generating element when a voltage is applied, FIG. 5B is a diagram showing a change in its absorption coefficient, and FIG. 5C is an optical pulse generation control of the present invention. FIG. 5 is a diagram showing characteristics when the light control unit of the element is operated, and FIG. 6D is a diagram showing changes in absorption coefficient thereof.

FIG. 6 is a diagram showing characteristics of the light generation control element of the present invention, where (A) shows optical signal intensity and (B) shows autocorrelation intensity.

FIG. 7 is a diagram showing an operating principle of an optical control unit of an optical pulse generation control element when the present invention is applied.

FIG. 8 is an MQW-DFB laser and MQ to which the present invention is applied.
It is a schematic sectional drawing which shows the manufacturing process of the optical pulse generation control element by the integrated light source of a W light modulator and an MQW light controller.

FIG. 9 is a schematic sectional view showing another embodiment of the optical pulse generation control element of the present invention.

FIG. 10 is a diagram showing an operating principle of a conventional optical pulse generation element.

[Explanation of symbols]

10 (MQW-DFB) Laser Element 11 Optical Waveguide 12 (Distributed Feedback Type Semiconductor) Laser Section 13 Light Modulation Section 14 Light Control Section 15 First Semiconductor Part 15A Opposing End 16 Second Semiconductor Part 16A Opposing End 17 Light Coupling region 18 Interface (diagonal etching surface) 20 Substrate 22 Etching stop layer 24 First lower cladding layer 26 Active layer (first multiple quantum well structure) 26A Well layer 26B Barrier layer 28 Guide layer 29 Diffraction grating (grating) 30 First upper clad layer 31 Protective layer 32 Second lower clad layer 34 Second multiple quantum well structure 34A Well layer 34B Barrier layer 36 Second upper clad layer 38 Third clad layer 38A Thin portion 38B, 38C Clad portion 40 Separation portion 42 Cap layer 44, 46, 47 Embedded portion 48 Ray Part electrodes 52 of the electrode 50 the light control unit of the electrode 49 the light modulation unit of the SiO ₂ film 54 patterned resist 56 eaves 58, 59, 60 p-type electrode 62 n-type electrode 64 antireflection film 71, 72, 73 and 74 the absorption edge

Claims (3)

[Claims] 1. An optical pulse generation control element in which a laser light source, a light modulation section, and a light control section are integrally arranged on a semiconductor substrate via an optical waveguide, and the light emitted from the laser light source is controlled. An optical pulse generation control element having a function of generating a light pulse train by intensity-modulating the light modulation unit and then coding the light pulse train by absorbing or transmitting only a predetermined light pulse by the light control unit. . 2. The optical pulse generation control element according to claim 1, wherein the optical modulation section, the optical control section and the optical waveguide are formed in a semiconductor multiple quantum well structure. 3. The optical pulse generation control element according to claim 1, further comprising a diffraction grating in the optical waveguide of the laser light source.