JPH1117257A - Method of generating light pulse - Google Patents

Abstract

PROBLEM TO BE SOLVED: To resolve various problems caused by the generated heat to enable the generation of an optical pulse with a narrower pulse width and higher optical power than those of the prior art by modulating a laser beam so as to input the beam with a max. intensity to a modulator when the light transmittance of the modulator is max. SOLUTION: For inputting the output light L1 of a single mode laser 11 through an optical fiber 15 to a field absorption type light modulator 13, the timing is adjusted so that the light L1 with a max. intensity is inputted to the modulator 13 when the light transmittance of the modulator is max. such that the timings of which an electric signal E1 is applied to the modulator 13 and the light L1 from the laser 11 is inputted to the modulator 13 are adjusted to make the peak of the light L1 11 coincident with that of the signal E1. The laser 11 is composed of a DFB type semiconductor laser, etc., and modulator 13 is composed of a modulator including an InGaAsP layer, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for generating a short optical pulse used in, for example, ultra-high-speed optical communication, optical soliton communication, and optical information processing.

[0002]

2. Description of the Related Art As an example of a conventional method for generating an optical pulse, for example, Reference I (Journal of Lightwave)
Technology (JOURNAL OF LIGHTWAVE TECHNOLOGY), VOL.1
1, No. 3, MARCH, 1993, PP. 468-473). In this method, a semiconductor laser as a laser light source and an electro-absorption modulator as a modulator whose light transmission changes in accordance with an electric signal are used. Specifically, a sine wave electric signal is applied to the above-described electro-absorption optical modulator. Of course, a constant output light is input from the above-described semiconductor laser to the electroabsorption optical modulator. In this electroabsorption type optical modulator, the degree of transmission of light changes according to the electric signal of the sine wave. Therefore, this electroabsorption type optical modulator
The light from the above-described semiconductor laser is intermittently transmitted (output) according to the electric signal of the sine wave. For this reason, a light pulse could be generated from this electro-absorption type optical modulator.

[0003]

By the way, in ultra-high-speed optical communication, an optical pulse having a narrow pulse width and a large output is required.

(1). In order to reduce the pulse width, a large amplitude electric signal may be applied to the electro-absorption optical modulator. This is because the pulse width is represented by twice the time required for the electric signal to decrease from its peak value by ΔV. Therefore, as the electric signal having a large amplitude is used, the voltage from the peak of the electric signal is sharply reduced, so that the pulse width can be narrowed.

However, when an electric signal having a very large amplitude is applied to the electro-absorption type optical modulator, Joule heat in a light absorption layer provided in the modulator and heat generated by resistance of an electrode provided in the modulator are generated. The modulator itself generates heat. Therefore, the modulation characteristics of this modulator deteriorate,
There is a problem that a pulse having a short pulse width and a large output cannot be obtained.

(2). Further, in order to increase the power of the optical pulse output from the electroabsorption modulator, the light intensity from the semiconductor laser input to the modulator may be increased. However, if the light intensity is too high, the temperature of the light absorbing layer rises due to Joule heat caused by the absorption current when the light absorbing layer included in the modulator absorbs light. When the temperature of the light absorbing layer increases, the band gap of the light absorbing layer itself decreases. Then, since the light absorption layer more easily absorbs light, there is a problem that the light output of the modulator is reduced.

Therefore, when generating an optical pulse by using a modulator and a laser light source whose light transmission changes in accordance with an applied electric signal, the above-described problems caused by heat generation can be reduced, and the present invention can reduce the above-described problems. Therefore, there is a demand for a method capable of generating an optical pulse having a narrow pulse width and an optical output equal to or greater than that of the conventional one.

[0008]

Therefore, according to the invention of the method for generating an optical pulse, a laser beam is input from a laser light source to a modulator whose light transmission degree changes in accordance with an applied electric signal. In the method of generating an optical pulse from the modulator, when the light transmission degree of the modulator is maximum, the laser light is in a state of maximum intensity (substantially near the maximum value and substantially The laser beam is modulated so as to be input to the modulator (including the maximum state).

According to the light pulse generation method of the present invention,
When the modulator is in a state where the laser beam is easily transmitted, a laser beam having a high intensity is input to the modulator. On the other hand, when the modulator is in a state that hardly transmits the laser beam, a laser beam having a small intensity (including a case where the intensity is zero) is input to the modulator. Therefore, the extent to which the modulator generates heat is reduced as compared with the conventional method in which light of a constant intensity is input to the modulator. Therefore, it is possible to reduce the problems caused by the heat generation of the modulator as compared with the conventional art, and thus it is possible to obtain an optical pulse having a pulse width narrower than that of the conventional art and an output equal to or more than that of the conventional art.

In practicing the invention of the method of generating an optical pulse, the modulation for modulating the laser light source is preferably an electric signal synchronized with the electric signal applied to the modulator. Preferably, the laser light source is driven by an electric signal having a rectangular shape or a waveform close thereto.

When a laser light source is driven by an electric signal having a rectangular waveform or a waveform close thereto, the laser light source outputs light having a rectangular waveform or a waveform close thereto (typically a trapezoidal waveform). That is, compared to the light having the sine waveform, the modulated light having a constant intensity for a longer time when the modulator is in a state where the laser light is more likely to be transmitted is output. Therefore, in this modulator to which such light is input, an optical pulse is generated from a portion where the light intensity is constant (that is, for example, a portion on the upper side of the trapezoidal waveform (see FIG. 4)).
Although details will be described later, an optical pulse having a smaller time-bandwidth product, that is, a high-quality optical pulse can be obtained as compared with the case where the laser light source is driven by a sinusoidal electric signal.

Further, in carrying out the invention of the method for generating an optical pulse, the laser light source and the modulator may include:
It is preferable to use a laser light source and a modulator integrated on the same substrate. The reason is as follows.

When a laser light source and a modulator are separately prepared, the two are connected by a suitable waveguide means, typically an optical fiber. On the other hand, according to the light pulse generation method of the present invention, when the light transmission degree of the modulator is maximized,
Since it is necessary that the laser light be input to the modulator with its intensity being maximum, the electric signal applied to the modulator and the modulated light input to the modulator from the laser light source have a predetermined value. Need to meet timing. However, when a wave guide is provided between the two, for example, the refractive index of the wave guide may change due to a change in the outside air temperature or the like. Then, there is a possibility that the electric signal applied to the modulator and the modulated light input to the modulator from the laser light source are shifted from a predetermined timing. On the other hand, in the case of the preferred embodiment using the laser light source and the modulator integrated on the same substrate as the laser light source and the modulator, such a timing shift can be reduced.

Further, a modulator often has polarization dependence. In such a case, if the laser light source and the modulator are separated, the waveguide means for connecting the two needs to be a waveguide means capable of maintaining polarization. However, configuring a polarization-maintaining device requires more time and effort than a device that does not. On the other hand, in the case of the preferred embodiment using the laser light source and the modulator integrated on the same substrate as the laser light source and the modulator, the light from the laser light source directly enters the modulator, so that the problem of polarization dependence is taken into consideration. There is no need to do it.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Some embodiments of the present invention will be described below with reference to the drawings. However, the drawings used in the description are merely schematic views so that the present invention can be understood. Further, in each of the drawings, the same components are denoted by the same reference numerals, and the duplicate description thereof may be omitted.

1. First Embodiment First, a first embodiment will be described with reference to FIG. In the first embodiment, a single mode laser 11 is used as a laser light source, an electro-absorption optical modulator 13 is used as a modulator, and an output light from the single mode laser 11 is used using an optical fiber 15. Electroabsorption optical modulator 13
An example of inputting to ".

The single mode laser 11 can be composed of a conventionally known semiconductor laser, for example, a DFB type semiconductor laser. The electro-absorption optical modulator 13 is described in, for example, the latter half of the right column on page 468 of document I (II: DEVICE CHARAC).
TERISTICS), and any suitable device such as a modulator including an InGaAsP layer or the like.

In the same manner as in the prior art, for example, an electric signal E1 having a sine wave waveform
For example, an electric signal of V _b + V sin (2πf ₀ t) is applied. Here, _Vb is a bias voltage.

On the other hand, a forward bias current _Ib is supplied to the single mode laser 11. Further, an electric signal E applied to the optical modulator 13 is applied to the single mode laser 11.
Modulation current I _m sin as an electric signal E2 to synchronize to 1
The (2πf ₀ t), flow superimposed on the bias current I _b. Here, _Im is a 0 (zero) -P (peak) value of the sine wave current.

When a current is passed in this way, in order to suppress wavelength chirping in the single mode laser 11,
_{I b -I m> I th (} I th lasing threshold) so as to satisfy the condition, may be set to the current values.

When a current is supplied to the single mode laser 11 as described above, the single mode laser 11 outputs an output light having a sine wave waveform.

[0022] shown as L ₁ the state of the output light in Fig. Further, in FIG. 2 (A), the horizontal axis is the time, and the vertical axis represents the light intensity, showing how the output light L ₁ in greater detail. That is, in this first embodiment, the output light L ₁ from the single-mode laser 11 is higher in light intensity side is P1, and the sinusoidal light is lower side of the light intensity P0 Become.

[0023] In this case of generating a sinusoidal output light L _1, so that the light intensity P0 of the lower side is as close as possible to 0 is preferable to set the current I _b and I _m. P
If 0 = 0, the degree of modulation becomes 100%. Therefore, if the average optical power output from the laser 11 is the same as the conventional one, the peak power from the single mode laser 11 is maximized ( That is, the conventional constant light power of 2
Double). However, even when P0 is larger than 0, the effect of the present invention can be obtained.

The output light L ₁ of the single mode laser 11 described above.
Through the optical fiber 15 and the electroabsorption optical modulator 13
When entering the modulator 13 when the light transmission degree is maximum, the modulator 1 outputs light L ₁ is in its intensity maximum of the state
Adjust the timing so that it is input to 3. That is, in this case, as shown in FIG.
The peak of the electric signals E1 applied to 3, so that the peak of the output light L ₁ from the laser 11 is inputted to the modulator matches (including substantially identical), the application of an electric signal E1 to adjust the timing between the input of the output light L _1.

By controlling the timing in this manner, a unique effect is obtained in that a light pulse having a narrower pulse width and a higher intensity can be obtained as compared with the related art. The reason why such an effect is obtained will be described below.

(Point where the pulse width can be narrowed) First, the point where the pulse width can be narrowed will be described. In the prior art, the laser light input from the single mode laser 11 to the electro-absorption optical modulator 13 has a constant intensity. Therefore, the electric signal is supplied to the electroabsorption optical modulator 13 as −V _b + Vsin (2
The transmitted light intensity I through the modulator 13 when πf ₀ t) is applied is approximately I = I ₀ expｅｘ− (V _b + Vsin (2πf ₀ t))
/ V ₀ ).

Where I ₀ is the transmitted light power from the electroabsorption modulator 13 when the voltage applied to the modulator 13 is 0 V, and V ₀ is the extinction efficiency voltage. Is the voltage at which the transmitted light power becomes 1 / e with respect to the peak time.

On the other hand, in the method for generating an optical pulse according to the present invention,
The transmitted light intensity of the electroabsorption optical modulator 13 is: I = 0.5I ₀ (sin (2πf ₀ t) +1) × exp
｛− (V _b −Vsin (2πf ₀ t)) / V ₀ ).

This is because the intensity of transmitted light (time variation of output light power) of the electroabsorption optical modulator 13 is the product of the light from the single mode laser 11 and the modulation operation of the electroabsorption optical modulator 13. This is because Note that the coefficient of 0.5 is used to set the maximum value of the transmitted light power in the modulator 13 to I ₀ .

The light pulse width is determined as follows. The electro-absorption optical modulator 13, -V _b + Vsin (2
πf ₀ t) and f ₀ is, for example, 1
Consider a case where an electrical signal of 0 GHz is applied. Moreover,
Considering that V ₀ = −0.5 V, the voltage V applied to the modulator 13 is set to V = 5 sin (2π10 ¹⁰ t) −5.
Then, the obtained pulse width τ is, in the conventional example,
(Journal of Lightwave Technology (JL
ightwave Technol., vol. 13, pp. 2215 (1995)).

Τ / T = cos ⁻¹ (1-ln (2) / V _b ) / π (1) where T is the repetition frequency of the light pulse, and in this case, f ₀ is 10 GHz. Therefore, T = 1 / f ₀ = 1
00 ps. Further, _Vb is _calculated as V / V ₀ = 5 / 0.5 =
It is assumed to be 10. Also, cos ^-1 (1-ln (2) / V _b )
Is calculated by rad.

Then, τ ≒ 100 × cos ⁻¹ (1-0.
0693) /π≒11.9 ps.

On the other hand, in the method for generating an optical pulse according to the present invention,
Light L ₁ input from the single-mode laser 11 to the electroabsorption modulator 13, since a sine wave modulated light, the pulse width of the light L ₁ is already 50 ps. Further, when approximated to each Gaussian waveform output light L ₁ of the sine waveform and the electroabsorption modulator 13 a waveform shaping function according to a single axis mode laser 11, the electroabsorption modulator 13
Output waveform is exp (− (t / σ _t ) ² ) = exp
(− (T / σ ₁ ) ² ) × exp (− (t / σ ₂ ) ² ) =
exp (−t ² (1 / σ ₁ ² + 1 / σ ₂ ² ) Therefore, σ _t defining the pulse width is given by the following equation (2) (1 / σ _t ) ² = (1 / σ ₁₎ ) ² + (1 / σ ₂ ) ² (2) where σ ₁ = 11.9 ps, σ
_{Since 2} = 50 ps, (1 / σ _t ) ² = (1 / 11.9) ² + (1/50) ²
≒ 11.6 ps.

Therefore, according to the method of the present invention, the pulse width can be reduced by 0.3 ps as compared with the conventional method.

The above-mentioned effect that the pulse width is reduced by 0.3 ps is because the average optical power of the output light L ₁ from the single mode laser 11 is reduced by the conventional method (light of a constant intensity is applied to the modulator 13). It is obtained under the condition that it is the same as the average optical power of the input method (hereinafter, also referred to as “first condition”).

However, in the case of the method of generating an optical pulse according to the present invention, the single mode laser 1 is operated under the following second condition.
1 and the electro-absorption optical modulator 13 may be driven.

That is, the peak power of the output light L ₁ output from the single mode laser 11 (P in FIG. 2A)
1), so that the laser beam of said intensity of constant intensity is input to the modulator 13 and for example, the same in a conventional way, to generate an output light L _1, and inputs it to the modulator 13 This is a condition (second condition). In the case of this second condition,
The average optical power of the output light L ₁ from a single-mode laser 11 is half of the average optical power of the conventional methods. Then, under the second condition, the photocurrent in the electroabsorption optical modulator 13 is about half that of the conventional method. This means that even if the voltage applied to the modulator 13 is approximately doubled, the Joule heat generated in the modulator 13 can be made the same as in the related art. Therefore, even if the voltage applied to the modulator 13 is approximately doubled, the heat generation is the same as the conventional method. However, since the voltage applied to the modulator 13 can be approximately doubled, the pulse width of the optical pulse can be shorter than the first condition for the reason described in the section of the problem to be solved by the invention. Specifically, since the voltage applied to the modulator 13 is in the second condition which is twice the first condition, by changing the V _b in the above (1) to 20 (1), ( 2) Calculate the formula. Then, in the case of the second condition, the pulse width of the optical pulse is 8.3 ps, and the pulse width is 2 / ps as compared with the conventional case.
3 can be narrowed.

(Improvement of Light Output) Next, the reason why the light output is improved will be described. However, the output light L ₁ from a single-mode laser 11 consider the case to be supplied to the modulator 13 in the first of the above conditions.

As described above, in the electro-absorption type optical modulator 13 when a large RF signal is applied, the light output is increased due to the heat generated in the light absorption layer and the electrodes of the modulator 13. Indicates a saturation phenomenon. In other words, even escalated, the intensity of light input from single-mode laser 11 to the modulator 13, the light output decreases to a boundary certain input I _S.

At this time, assuming that the duty ratio of the light pulse output from the modulator 13 is γ, the loss in the modulator 13 is α, and the element length of the modulator 13 is L, the light in the prior art is output P _out, from the law of beer, the _{P out = γI S exp (-αL} ).

On the other hand, in the method for generating an optical pulse according to the present invention, the output light L ₁ from the single mode laser 11 is set to the above first condition (ie, the average light power of the output light L ₁ is set to the same value as in the conventional method). Is supplied to the modulator 13 under the following condition:
The peak power of the light input to the modulator 13 is approximately 2I
Become _S. This is because the average light power of the input light input from the single mode laser 11 to the electro-absorption modulator 13 is the same between the conventional method and the method of the present invention.
If conditions of the modulation in the method of the present invention is 100% sinusoidal modulation, the intensity of the input light in the case of the present invention because changes between 2I _S and 0.

Accordingly, the light output P output from the electro-absorption type optical modulator in the case of the light pulse generation method of the present invention.
_out is a _{P out = 2γI S exp (-αL} ). That is, in the method of the present invention, the first
When the light of the laser 11 is input to the modulator 13 under the condition (1), the optical output can be improved by 3 dB (twice as large) as compared with the conventional method. This is preferable, for example, because the S / N ratio between the optical signal and the noise can be improved.

Incidentally, if you enter the light of the laser light source 11 to the modulator 13 in the above second condition in the present invention (conditions for the peak power of the output light L ₂ and the average optical power of the conventional method), light The power of the pulse becomes equivalent to the conventional one.

Further, as can be understood from the above description, it is understood that the pulse width narrowing effect and the light output increasing effect can be adjusted by modulating the output light L ₁ of the laser light source 11. That is, the modulated output light L ₁
Is P <P1 <2P with respect to the laser beam intensity P (constant intensity P) in the conventional method. That is, the average light level X of the output light L ₁ to the average light level Y of the conventional method, the Y / 2 <X <Y. Then, the voltage applied to the modulator 13 can be made higher than before, so that the pulse width can be made narrower than before, and the peak light level can be made higher than before because the peak level is higher than the conventional value P. .

2. Second Embodiment In the above-described first embodiment, the single mode laser 11 as a laser light source is modulated with a sinusoidal current. On the other hand, in the second embodiment, as shown in FIG. 3, an electric signal synchronized with an electric signal E1 applied to the electro-absorption optical modulator 13 by using a single mode laser 11 as a laser light source. And is modulated by the rectangular wave modulation current E21. Specifically, flowing bias current I _b in the forward direction in a single-mode laser 11, further superimposing the rectangular wave modulation current E21 of frequency f ₀ to the bias current I _b.

[0046] Also in the case of the second embodiment, in order to suppress the wavelength chirping, I _b - square wave modulation current E21> I _th (I _th lasing threshold) satisfy the condition It is better to set each current value so that

When the square-wave modulated current is supplied to the single-axis mode laser 11, the single-axis mode laser 11
As shown in FIG. 3, and outputs the output light L ₂ having an output waveform of the trapezoidal. Note that, as the light intensity of the low side of the output light L ₂ having a trapezoidal shape of the output waveform (intensity corresponding to P0 in FIG. 2 (A)) is as close as possible to zero, the above current value I _b and rectangles Preferably, the wave modulation current is set. The reason is the same as that of the first embodiment.

In the second embodiment, as shown in FIG. 4, the upper side of the optical output L ₂ having a trapezoidal waveform from the single mode laser 11 and the transmission of the electroabsorption optical modulator 13 Match when the condition becomes maximum (including substantially match)
Thus, the timing between the electric signal applied to the modulator 13 and the laser beam input from the single mode laser 11 to the modulator 13 is adjusted.

By adjusting the timing in this way, the first
As described in the first embodiment, narrowing of the light pulse can be achieved, and an output equal to or higher than the conventional one can be obtained.

Further, in the case of the second embodiment,
An optical pulse having a small time-bandwidth product, that is, a high-quality optical pulse called a Fourier transform limited pulse can be obtained, which further provides a unique effect that cannot be obtained in the first embodiment. Hereinafter, this will be described in detail.

In the case of the first embodiment, since the current for driving the single mode laser 11 changes in a sinusoidal manner, the frequency of light fluctuates by several GHz even in the portion where the pulse is generated. Therefore, the spectrum of the light generated by the modulator 13 becomes wider by several GHz than when the stationary light is input to the modulator 13. When a pulse is cut out of such light, the pulse itself also has an inherent chirp, so that the time bandwidth product is not minimized. On the other hand, in the second embodiment, since a drive current having a rectangular waveform is used, the drive current is constant when an optical pulse is generated. Light pulses can be generated in a similar state. Therefore, it is possible to obtain an optical pulse having a smaller time bandwidth product than in the first embodiment.

3. Third Embodiment In each of the first and second embodiments described above, the laser light source 11 and the modulator 13 are separately provided, and the light L ₁ or L ₂ from the laser light source 11 is supplied to the modulator 13 has been described as an example of inputting at a predetermined timing. However, a laser light source and a modulator integrated on the same substrate may be used as the laser light source 11 and the modulator 13. Such a method has various advantages, which will be described later in detail. The third embodiment is such an example. This will be described with reference to FIGS.

In each of FIGS. 5 and 6, for example, a single mode laser 11 as a laser light source 11 and an electroabsorption type optical modulator 13 as a modulator 13 are integrated on the same substrate. . The output terminal of the integrated single mode laser 11 is directly connected to the input terminal of the integrated electro-absorption optical modulator 13. Such integration can be performed by using a known semiconductor laser manufacturing technique, and a specific description thereof is omitted here.

The difference between the embodiments described with reference to FIGS. 5 and 6 is that the single mode laser 1
1 is a difference between a sine wave current signal and a rectangular wave current signal.

That is, in the case of FIG. 5, the single mode laser 11 is driven by a sinusoidal current signal synchronized with a sinusoidal electric signal applied to the electroabsorption optical modulator 13. Specifically, the driving is performed by the sine wave current signal described in the first embodiment.

On the other hand, in the case of FIG.
1 is driven by a current signal having a rectangular wave or a waveform close thereto, which is an electric signal synchronized with a sine wave electric signal applied to the electroabsorption optical modulator 13. In detail, it is driven by the rectangular wave current signal described in the second embodiment.

Therefore, in the case of the example of FIG.
The same effect as described in the embodiment can be obtained, and
In the case of the example of FIG. 6, the same effect as that described in the second embodiment can be obtained.

Further, in each of the embodiments described with reference to FIGS. 5 and 6, unique effects described below, which cannot be obtained in the above-described first and second embodiments, are respectively obtained. can get.

In the first and second embodiments described above, the laser light source 11 and the modulator 13 are separately prepared, so that the optical output L ₁ or L ₂ is adjusted by the modulator. It was necessary to use the optical fiber 15 for inputting to the optical fiber 13. On the other hand, in the method of generating an optical pulse according to the present invention, when the degree of light transmission of the modulator 13 is maximum, the timing is set so that the laser light is input to the modulator 13 with the intensity being maximum. is important. However, since the refractive index of the optical fiber 15 fluctuates with the fluctuation of the environmental temperature, the speed of light propagating through the optical fiber changes when the environmental temperature changes. Then, in the case of using the optical fiber, even the timing was maintained some time, the speed of light output L ₁ or L ₂ for the environmental temperature changes is changed, as a result, the timing can not be maintained There is fear. That is, when an optical fiber is used, it is difficult to generate an optical pulse stably for a long period of time. . On the other hand, in the third embodiment, since no optical fiber is used, there is no shift in the timing due to the optical fiber. Therefore, in the case of the third embodiment, an optical pulse can be stably generated for a long period of time as compared with the first and second embodiments.

The second effect The operating characteristics of the electroabsorption optical modulator 13 have polarization dependence. In order to secure a stable light pulse generation operation by the method of the present invention, it is necessary to consider this point. For example, the first
When the laser light source 11 and the modulator 13 are separately prepared as in the second embodiment, it is necessary to use a polarization maintaining optical fiber as the optical fiber 15 provided therebetween. However, when the device is configured using the polarization maintaining optical fiber, it takes more time and effort than when the device is not used, and the device price increases. On the other hand, in the third embodiment, since the laser light source 11 and the modulator 13 are integrated, the output light from the laser light source 11 can be directly input to the modulator 13, so that special measures must be taken. The problem of the polarization dependence can be solved without using.

[0061]

As is clear from the above description, according to the present invention, laser light is input from a laser light source to a modulator whose light transmission degree changes according to an applied electric signal. In the method of generating an optical pulse from a modulator, when the light transmission degree of the modulator is maximum, the laser light is input to the modulator with its intensity being maximum, so that the laser light is Modulate. Therefore, compared to the conventional method in which light of a certain intensity is input to the modulator,
The extent to which the modulator generates heat is reduced. Therefore, it is possible to reduce the problems caused by the heat generation of the modulator as compared with the conventional art, and thus it is possible to obtain an optical pulse having a pulse width narrower than that of the conventional art and an output equal to or more than that of the conventional art.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram (part 1) of a first embodiment;
FIG. 3 is a diagram illustrating a relationship between a system that generates an optical pulse, an electric signal, and an optical signal.

FIG. 2 is an explanatory diagram (part 2) of the first embodiment;
(A) Figure explanatory diagram of the output light L ₁ from the laser light source,
(B) Figure is a view for explaining the relationship between the output light L ₁ to be inputted to the electric signal and the modulator is applied to the modulator.

FIG. 3 is an explanatory view (No. 1) of a second embodiment;
FIG. 3 is a diagram illustrating a relationship between a system that generates an optical pulse, an electric signal, and an optical signal.

FIG. 4 is an explanatory diagram (part 2) of the second embodiment;
Is a diagram illustrating the relationship between the output light L ₂ to be inputted to the electric signal and the modulator is applied to the modulator.

FIG. 5 is an explanatory view (1) of a third embodiment;
FIG. 4 is an explanatory diagram in a case where a laser light source and a modulator are integrated and a case where the laser light source is driven by a sine wave current.

FIG. 6 is an explanatory view (2) of the third embodiment;
FIG. 3 is an explanatory diagram in a case where a laser light source and a modulator are integrated and a case where the laser light source is driven by a rectangular wave current.

[Explanation of symbols]

11: Laser light source (for example, single mode laser) 13: Modulator (for example, electro-absorption type optical modulator) 15: Optical fiber E1: Electric signal applied to modulator E2: Electric signal applied to laser light source (Sinusoidal modulation) current) E21: electrical signal applied to the laser light source (square wave modulated current) L _1: the output light from the laser light source (sinusoidal light output) L _2: having a waveform of the output light (trapezoidal from the laser light source Optical output) L _OUT : Optical output from modulator

──────────────────────────────────────────────────続 き Continued on front page (51) Int.Cl. ⁶ Identification code FI H04B 10/06

Claims (5)

[Claims] 1. A method of inputting a laser beam from a laser light source to a modulator whose light transmission degree changes according to an applied electric signal and generating an optical pulse from the modulator, wherein: A method of generating an optical pulse, comprising: modulating the laser light so that the laser light is input to the modulator in a state where the intensity of the laser light is maximum when the degree of light transmission is maximum. 2. The method of generating an optical pulse according to claim 1, wherein the modulation is performed by driving the laser light source with an electric signal synchronized with the electric signal applied to the modulator. How to generate a light pulse. 3. The method of generating an optical pulse according to claim 1, wherein the modulation is an electric signal synchronized with the electric signal applied to the modulator, the electric signal having a rectangular shape or a waveform close thereto. A method for generating an optical pulse, wherein the method is performed by driving the laser light source. 4. The method for generating an optical pulse according to claim 1, wherein a laser light source and a modulator integrated on the same substrate are used as the laser light source and the modulator. 5. The method of generating an optical pulse according to claim 4, wherein the laser light source is a semiconductor laser, and the modulator is an electro-absorption optical modulator.