JP2765551B2 - Laser amplifying device and its use, and real-time optical measurement device and its use - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for realizing a real-time measurement of an ultra-high-speed repetition ultra-short optical pulse train which is useful for optical communication, optical information processing, and optical measurement, by amplifying the output of the pulse train.

[0002]

2. Description of the Related Art In recent years, a time width of several ps or less and several GHz to 100
There is an increasing demand for technology development for generating an optical pulse train having a repetition frequency exceeding Hz. One of the optical oscillators that generate high-speed optical pulses is a semiconductor laser that performs mode-locked operation.

[0003] With respect to evaluation and measurement of a device that generates an ultrahigh-speed optical pulse train, a method of measuring a combination of a PIN diode and a sampling oscilloscope or a method of measuring with a synchro scan streak camera are usually used. A combination of a PIN diode and a sampling oscilloscope can perform sampling measurement with a resolution of about 10 ps, and a synchro scan streak camera can perform sampling measurement with a resolution of several ps.

However, in any of the above-described measurement systems, since the trigger period is fixed, the measurable light is limited to light having a wavelength that is an integral multiple of the trigger period. Limited to those synchronized with the signal. Further, since sampling measurement is performed by integrating and averaging a large number of light pulses, the resolution is reduced.

The nonlinear correlation method using the second harmonic generation (SHG) or the sum frequency generation (SFG) can avoid the problems of resolution and synchronization. However, in the case of a semiconductor laser, the peak power is not so large. It takes a relatively long time to obtain one measurement trace.

The above SHG correlation measurement technique is described, for example, in Journal of Quantum Electronics IEEE J. J. et al., By YK Chen et al. Qua
ntum Electron. Vol. 28, No. 10, p. 2176 to p. It is stated in articles published over 2185.

[0007]

Another problem of the sampling measurement by integrating and averaging a large number of light pulses is that these are not real-time measurements in the true sense. Therefore, although averaged measurement information can be obtained, the temporal asymmetry, intensity,
There is a problem that information about timing fluctuations cannot be obtained.

[0008] For true real time measurements, measurements with a single sweep streak camera are currently the only means.
However, the single sweep streak camera has extremely low sensitivity to light in a wavelength region exceeding 1 μm and cannot be directly observed. To enable measurement with a single-sweep streak camera, it is necessary to perform nonlinear wavelength conversion of the optical pulse.However, in order to perform nonlinear wavelength conversion with high efficiency, the optical pulse is output to a sufficiently high output by some means. It needs to be amplified.

In recent years, optical fiber amplifiers in the 1.3 μm band and the 1.5 μm band have attracted attention. However, even with these amplifiers, it is usually impossible to amplify an optical pulse to a power sufficient for nonlinear wavelength conversion. Have difficulty. Therefore, there is a problem that it is difficult to perform real-time measurement.

The present invention has been made in view of the above-mentioned problems of the prior art, and has a means for easily amplifying light in a wavelength region exceeding 1 μm to a high output and a means for real-time measurement. The purpose is to provide.

[0011]

According to the present invention, there is provided a laser amplifying apparatus comprising: an optical gate element for intermittently switching a passing state of input laser light; and an optical fiber laser amplifier for amplifying an output of the optical gate element. And the following.

As a method of using the laser amplifying device configured as described above, there is a method of intermittently switching the optical gate element at a repetition frequency of 1 MHz or less and a time width of 100 ns or less.

A real-time optical measurement device according to the present invention comprises: an optical gate element for intermittently switching a passing state of an input laser beam; an optical fiber laser amplifier for amplifying an output of the optical gate element; A nonlinear optical crystal that receives a fiber laser amplifier output light and generates a second harmonic, a streak camera that observes the nonlinear optical crystal output light, and controls switching timing of the optical gate element and operation timing of the streak camera. And timing control means.

In this case, a converted light transmission filter that allows only the second harmonic to pass may be provided between the nonlinear optical crystal output and the streak camera.

As a method of using the real-time optical measurement device configured as described above, the optical gate element is switched intermittently with a repetition frequency of 1 MHz or less and a time width of 100 ns or less. Can be

(Function) The present invention intermittently causes the light to be amplified to enter the optical fiber amplifier by means of an optical gate element, so that the energy stored for a time close to the life of the laser medium in the optical fiber amplifier is obtained. Is used for amplifying the light pulse within the gate time, and the peak value of the amplified light output is increased by one digit or more as compared with the case of the amplification by the continuous incidence.

Also, by amplifying the optical signal to a level of several tens of watts or more by a peak using this method, and converting the optical output to the second harmonic with high efficiency, the single sweep streak camera can provide sufficient sensitivity. The light is converted into light having the same wavelength, and measurement based on the light can be performed.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram schematically showing a configuration of an embodiment of a laser amplifier according to the present invention and a real-time optical measurement device using the same.

The ultrafast light source 1 outputs light having a wavelength in the 1.5 μm band. The output light of the ultrafast light source 1 is collimated by the first lens 2, passes through the first optical isolator 3, and is coupled to the optical gate element 5 by the second lens 4.
The optical gate element 5 is driven by a gate pulse output from the gate pulse generator 21 and performs an operation of transmitting light only for a time during which the gate pulse is output.

The optical output from the optical gate element 5 is collimated by a third lens 6, passes through a second optical isolator 7, and is coupled to an optical fiber amplifier 9 by a fourth lens 8. The optical output from the optical fiber amplifier 9 is the optical fiber 1
0 leads to the measurement system shown in the lower part of the figure.

The optical output of the optical fiber 10 is the fifth lens 11
After being collimated, the light is condensed on the nonlinear crystal 13 by the sixth lens 12, where the second harmonic light is generated. The light output from the nonlinear crystal 13 is collimated by a sixth lens 14 and then converted light transmission filter 15
, Only the second harmonic light is selected,
The light enters the light receiving section of the streak camera 41 in the single sweep operation by the seventh lens 16.

The trigger of the streak camera 41 and the trigger of the gate pulse generator 21 are set at appropriate timing by the timing controller 51.

In this embodiment having the above structure, a semiconductor laser amplifier is used as the optical gate element 5. In addition, a mode-locked semiconductor laser having an average output of 1 mW, an optical pulse width of 10 ps, and a repetition frequency of 10 GHz was used as the ultrafast light source 1. The optical fiber amplifier 9 contains an erbium (Er) -doped optical fiber and has an average output of about 100 mW.

By operating the optical gate element 5 with a gate time width of about 10 ns at a repetition frequency of about 10 kHz, the peak value of the light pulse from the optical fiber amplifier 9 is amplified to about 100 W and the nonlinear crystal 13 The conversion efficiency to the second harmonic light is about 10 ^-4 . The peak output of the converted light is about 10 mW and can be easily observed by the streak camera 41.

FIG. 2 is a diagram showing the configuration of an optical amplification system conventionally used as a comparative example. In FIG. 1, an ultrahigh-speed light source 1, a first lens 2, a first optical isolator 3, and a second lens 4, an optical gate element 5, a third lens 6, a second optical isolator 7, and an optical fiber amplifier 9.

In the optical amplification system shown in FIG. 2, the light output from the ultrahigh-speed light source 21 is supplied to a first lens 22 which is a condensing optical system.
The light enters the optical fiber amplifier 29 via the optical isolator 23 and the second lens, and is continuously amplified. With this configuration, the peak output of the 10 GHz mode-locked semiconductor laser reaches only about 1 W after amplification. Since the conversion efficiency is about 10 ^-6 , the peak output of the converted light is about 1 μm.
W and cannot be observed with a streak camera.

In the present embodiment described above, the mode-locked semiconductor laser is used for the ultrafast light source 1 and the semiconductor laser amplifier is used for the optical gate element 5. However, from a theoretical standpoint, this combination is used. It is obvious that the present invention is not limited to this, and a gain-switched semiconductor laser or the like may be used as the ultrahigh-speed light source 1 and the optical gate element 5 may be an optical modulator or the like having no amplifying action.

The switching of the optical gate element has been described as operating at a repetition frequency up to 10 KHz with a time width of about 10 ns. However, if the repetition frequency is 1 MHz or less and the time width is 100 ns or less, A sufficient amplification action can be obtained.

Further, the light wavelength is not limited to around 1.55 μm, which is the amplification band of the Er-doped fiber.
For example, at present, the present invention may be applied to a laser amplifying device and a real-time optical measuring device at a wavelength in the 1.3 μm band in which praseodymium (Pr) -doped fiber has an amplifying action.

[0030]

Since the present invention is configured as described above, it has the following effects.

According to the first aspect of the present invention, it is possible to intermittently input the light to be amplified into the optical fiber amplifier by the optical gate element. There is an effect that the light output peak value of can be increased by one digit or more.

In the method according to the second aspect, there is an effect that the effect of the intermittent incidence can be surely generated.

According to the third aspect of the present invention, a single sweep streak camera is provided by amplifying an optical signal by the effect of the first aspect and converting the optical output to a second harmonic with high efficiency. Real-time measurement of ultrashort pulses using the characteristics of a single sweep streak camera can be performed to convert to wavelength light with sufficient sensitivity.

According to the fourth aspect, the primary light contained in the light incident on the streak camera is eliminated, and the stray light removing effect is improved in addition to the above effect.

In the method according to the fifth aspect, of the above-mentioned effects, there is an effect that the effect of intermittent incidence can be surely generated.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of an embodiment of a laser amplification device and a real-time optical measurement device to which the present invention is applied.

FIG. 2 is a diagram illustrating a configuration of a comparative example of an optical amplification system.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ultra-high-speed light source 2 1st lens 3 1st optical isolator 4 2nd lens 5 Optical gate element 6 3rd lens 7 2nd optical isolator 8 4th lens 9 Optical fiber amplifier 10 Optical fiber 11 5th lens 12 6th lens 13 Nonlinear crystal 14 seventh lens 15 converted light transmission filter 16 eighth lens 21 gate pulse generator 41 streak camera 51 timing controller

Claims (5)

(57) [Claims] 1. A laser amplifying device comprising: an optical gate element for intermittently switching a passing state of input laser light; and an optical fiber laser amplifier for amplifying an output of the optical gate element. . 2. The method of using a laser amplifying device according to claim 1, wherein said optical gate element is switched intermittently at a repetition frequency of 1 MHz or less and a time width of 100 ns or less. To use laser amplifying device. 3. An optical gate element for intermittently switching a passing state of the input laser light, an optical fiber laser amplifier for amplifying an output of the optical gate element, and an optical fiber laser amplifier output light. A nonlinear optical crystal that generates a second harmonic, a streak camera that observes the nonlinear optical crystal output light, and a timing control unit that controls switching timing of the optical gate element and operation timing of the streak camera. A real-time optical measurement device characterized by the following. 4. The real-time optical measurement device according to claim 3, further comprising a conversion light transmission filter provided between the nonlinear optical crystal output and the streak camera and passing only a second harmonic. Real-time optical measurement device. 5. The method of using a real-time optical measurement device according to claim 3, wherein the optical gate element has a repetition frequency of 1 MHz or less and intermittently with a time width of 100 ns or less. A method for using a real-time optical measurement device, characterized by switching.