JPH04168431A - Wavelength converting element and ultra short optical pulse generating device - Google Patents

Abstract

PURPOSE:To efficiently obtain a second higher harmonic pulse having an optical period by connecting a high-speed single ultra-short optical pulse having a high peak output to a wavelength converting element, and selecting an optical pulse connected to an optical waveguide conducting wavelength conversion by a light switch. CONSTITUTION:The optical waveguide 12 of a wavelength converting element 10a is formed by proton converting method similarly to a light switch 13 and can convert the wavelength highly effectively. The semiconductor laser optical pulse of a peak output 1 W gained and switched by a sinusoidal wave current having a frequency 1.2 GHz is made into a parallel light by a collimator lens of NA=0.3, passed through lambda/2, and then connected to the wavelength converting element 10 by a light collecting lens of NA=0.6, whereby a second higher harmonic pulse having a wavelength 0.415 mum, a peak output 5 mW and a pulse width 12 ps can be obtained by Cerenkov radiation. The light switch 13 is switched by a voltage pulse synchronized with the high frequency current of 1.2 GHz, whereby the second higher harmonic pulse having a single pulse form of peak output 5 mW and the pulse width 12 ps can be obtained up to a minimum frequency of 10 MHz.

Description

[Detailed Description of the Invention] Industrial Field of Application The present invention 1 Optical information processing Optical meter Aim This invention relates to an ultrashort optical pulse generator in the visible to ultraviolet wavelength range that is applied to time-resolved spectroscopic measurements, etc. Conventional technology The generation of ultrashort light pulses in the visible to ultraviolet range has been achieved using dye laser mode-locking technology, but since it requires a high-output laser as the excitation light source, the equipment is large and maintenance is complicated. The problem was that the lifespan was short.In contrast, the power of a compact and long-life ultrashort optical pulse generator in the visible to ultraviolet range (Yoshiyuki Yamamoto, 49th Applied Physics for Picosecond Generation from a Blue Laser Light Source Using rSHG) As reported in Proceedings of Academic Conference 7 a-ZD-8, it is possible to obtain the results by combining an iQ semiconductor laser and a wavelength conversion element. The figure shows: 1 is a semiconductor laser;
2 is a wavelength conversion element, 3 is an optical waveguide 4.5 is a lens, and 6 is a λ/2 plate. Semiconductor lasers are gain switched by constant current pulses or high pressure RF signals.
The fundamental wave pulse 7 of the TE mode oscillation emitted from the semiconductor laser 1 is collimated by the lens 4, and the polarization direction is rotated by 90 degrees by the λ/2 plate 6. 5 and enters the optical waveguide 3 formed in the wavelength conversion element 2. At this time, the phase velocity of the fundamental wave guided in the optical waveguide 3 and the second harmonic 8 emitted by Cerenkov are equal. By switching the gain of a semiconductor laser with a wavelength of 0.84μ peak using a comb generator with a repetition frequency of 100MHz, the second harmonic wave can be efficiently generated without generating the second harmonic. Problems to be solved by the invention even when harmonics are obtained As mentioned above in the conventional technology, the semiconductor laser gain switching method uses a simple configuration to produce ultrashort light.

If the output is wavelength converted, the output of the second harmonic that can be obtained at present is only a small number.Increasing the output of the output light pulse of the semiconductor laser is a challenge4. Semiconductor laser output light pulse Cyo If the peak of the exciting current pulse is made higher, the force increases
When the repetition frequency is low, it is difficult to obtain a high peak current pulse with a pulse width of several hundred ps or less.Also, when the current pulse width becomes large, a second pulse of light appears due to the relaxation oscillation of the laser. The method of the present invention has been made in view of the above-mentioned problems.It is an object of the present invention to provide an ultrashort optical pulse generator capable of obtaining a high output and second harmonic of a single pulse at an arbitrary repetition frequency. Objects and Means for Solving the Problems The wavelength conversion element and friend of the present invention An optical switch formed by a three-dimensional optical waveguide having a control electrode is formed on a substrate having a nonlinear optical effect. The ultrashort optical pulse generator 1-L of the present invention has a structure including a coupled three-dimensional optical waveguide. The semiconductor laser has a structure in which the semiconductor laser device and the wavelength conversion element are optically coupled. gain-switched by a wave current to generate an ultra-short optical pulse; the optical switch of the wavelength conversion element is switched by an electrical signal of an arbitrary frequency synchronized with the high-frequency sinusoidal current; The ultrashort optical pulse coupled to the three-dimensional optical waveguide is wavelength-converted by the three-dimensional optical waveguide.The ultrashort optical pulse coupled to the three-dimensional optical waveguide is wavelength-converted by the three-dimensional optical waveguide.The gain switching method of the semiconductor laser using the high-frequency sinusoidal current described in the above means is used to convert the current pulse width to 11. Although it is possible to obtain a single optical pulse without relaxation oscillation because of the small value of oscillation, it is also possible to obtain an optical pulse with a large peak output by increasing the current amplitude.The optical pulse emitted from this semiconductor laser is wavelength converted. When coupled to the optical switch part of the element, when the optical switch is on, the optical pulse is coupled to a three-dimensional optical waveguide and wavelength converted, and no second harmonic pulse is generated.On the other hand, when the optical switch is off, the optical pulse is three-dimensional. Therefore, by switching the electrical pulse that operates the optical switch in synchronization with the high-frequency distorted sinusoidal current that performs the gain switch, it is possible to generate any second harmonic Figure 7 shows the relationship between the waveforms of the high frequency sinusoidal current, the semiconductor laser light pulse, the electrical pulse to the optical switch, and the second harmonic pulse.

Embodiment FIG. 1 shows a schematic configuration of an ultrashort optical pulse generator according to a first embodiment of the present invention, in which 9 indicates a wavelength of 0.
An 83 μm semiconductor laser, 10 a wavelength conversion element, 11 a control electric machine 12, and an optical waveguide 13 an optical switch. The semiconductor laser 9 is biased to the threshold current and gain switched by superimposing a high frequency sine wave current.
The waveform of the light pulse emitted from the semiconductor laser when the frequency is 1.6 GHz is shown. The current amplitude was adjusted so that the average optical output from the semiconductor laser was the rated maximum output of 40 mW.At a frequency of 600 MHz, relaxation oscillation occurred because the current pulse width was large, and the peak output of the first pulse was also small. Above GHz, a single pulse is obtained, and at a frequency of 1.2 GHz, the maximum peak output is 11. An optical pulse with a pulse width of 201) S was obtained.If the frequency was further increased, the optical peak output would have to be reduced in order to maintain the average optical output at 401 m.

The optical switch 131 of the wavelength conversion element 10 is a branching interference type optical switch consisting of a three-dimensional optical waveguide formed by a proton exchange method using birophosphoric acid on a &Z-cut MgO-doped LiNbO5 substrate. The half-wave voltage of is 5V, and if a potential difference of 5cm is applied to the control electrode 11, the optical switch is in the OFF state, and the optical switch whose potential difference is set to Ov by the voltage pulse is in the ON state of the wavelength conversion element 10. Although the optical waveguide 12 is formed by the proton exchange method like the optical switch 13, the optical waveguide using proton exchange has a large difference in refractive index, so the light is forced to be confined, so efficient wavelength conversion is not possible. A semiconductor laser light pulse with a peak output IW that was gain switched with a .2 GHz sine wave current was set to NA-0°3.
Parallel light and i passed through a λ/2 plate with a collimating lens.
By coupling to the wavelength conversion element 10 with a condenser lens of NA-0.6, a peak output of 5 mW and a pulse width of 12
By switching the optical switch 13 with a voltage pulse synchronized with a high frequency current of 1.2 GHz obtained by Cherenkov radiation of a second harmonic pulse with a wavelength of 0.415 μm in pS, the minimum frequency of 10
It is possible to obtain a single-pulse second harmonic pulse with a peak output of 5 mW and a pulse width of 12 ps up to MHz. Fig. 3 shows a wavelength tunable ultrashort optical pulse generator according to a second embodiment of the present invention. This shows the schematic configuration of 14
is a diffraction grating and constitutes an external resonator by feeding back the light emitted from the semiconductor laser element 15.The other structure is the same as that of the first embodiment. The semiconductor laser element 15 is mode-locked by modulating with a sinusoidal current having a frequency of C/2L (C: speed of light, L: external resonator length) to generate ultrashort optical pulses. In the mode-locking method of an external cavity laser using a diffraction grating, it is possible to obtain an ultrashort optical pulse with a narrower pulse width and spectral width than in the gain switching method described in the first embodiment. By adjusting the angle, the oscillation wavelength of the external resonator laser can be changed. In this example, the external resonator length is approximately 16 cm.
By modulating the semiconductor laser element 15 at 0 MHz, an ultrashort optical pulse with a pulse radiation of 15 ps and a spectral width of 0.4 r+m was obtained. Furthermore, by adjusting the angle of the diffraction grating, the oscillation wavelength was changed from 0.8 μm to 0.84 μm. At this time, the external resonator length is finely adjusted so that the peak output is maximized.
By coupling to 0, the wavelength ranges from 0.405 μm to 0.
A second harmonic pulse variable up to 42 μm and a pulse width of 10 ps was obtained. FIG. 4 shows the spectrum of the second harmonic pulse obtained in the first and second examples. It can be seen that in the second embodiment, an ultrashort optical pulse with a narrow spectrum width and good coherence is obtained. FIG. 5 shows the configuration of the wavelength conversion element of the third embodiment. In this embodiment, even if the optical switch 13 of the wavelength conversion element 10 is a directional coupler type, the directional coupler requires a bend or an oblique waveguide like the branching interference type shown in the first embodiment. It is easy to fabricate, and there is no loss in the diagonal waveguide portion. Light can be efficiently coupled to the optical waveguide 12. Figure 6 shows the fourth implementation. The configuration of an example wavelength conversion element is shown. In this embodiment, the optical switch 13 of the wavelength conversion element 10 is T
It becomes an E-TM mode converter. When the optical waveguide 12i and the TM mode are coupled, the wavelength conversion force <, T
Although the E mode did not propagate, it was also possible to perform an optical switch to couple it to the optical waveguide 12 by using a TE-TM mode switch. In Examples 1 to 4, LiNbO5 was used as a substrate having a nonlinear optical effect. niLi
Ferroelectric i MN such as TaO5, KNbOs, KTP
It is also possible to use organic substances such as A.Also, it is possible to use a proton exchange optical waveguide as an optical waveguide.
Effects of the InventionAs is clear from the above explanation, the present invention is an optical waveguide that couples a single high-speed ultrashort optical pulse with a high peak output to a wavelength conversion element to perform wavelength conversion. By selecting the optical pulses to be combined using an optical switch, it has the effect of making it possible to efficiently obtain second harmonic pulses of arbitrary periods.In the case of high frequencies, it is possible to efficiently obtain second harmonic pulses with arbitrary periods. It is effective as a light source, and in the case of low frequencies, it is effective as an excitation light source for measurements of fluorescence lifetime, etc. The wavelength tunable ultrashort optical pulse generator is effective as a light source for optical memories using photochemical hole burning, etc. A4

[Brief explanation of the drawing]

Figure 1 is a schematic configuration of an ultrashort optical pulse generator according to a first embodiment of the present invention. A schematic diagram of the wavelength tunable ultrashort optical pulse generator according to the second embodiment. FIG. 4 shows the spectrum of the second harmonic pulse obtained in the first and second embodiments. Fig. 6 is a schematic perspective view of the wavelength conversion element according to the fourth embodiment. Fig. 7 is a schematic perspective view of the wavelength conversion element according to the fourth embodiment. FIG. 8 is a schematic diagram of a conventional ultrashort optical pulse generator. 9...Semiconductor LASAMI 10...Wavelength conversion element,
11... Control electric board 12... Optical waveguide 13...
- Optical switch, 14...diffraction grating, 15... semiconductor laser element. Name of agent: Patent attorney Akira Kodaji and 2 other people Illustrations - 2 illustrations (41#IpHHz 1Lb) /, 2 oaz 8ir question (C) / Otsu 6 ke 2 uff Fig. 4 P No. F Tora 1 box Iku 11; Two male two-hole l side 5i Φl-less suhe 0 ct I 4/5 41111
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Claims (4)

[Claims] (1) A substrate having a nonlinear optical effect is provided with an optical switch formed by a three-dimensional optical waveguide having a control electrode and a three-dimensional optical waveguide optically coupled to the optical switch. Wavelength conversion element. (2) The wavelength conversion element according to claim 1, wherein the optical switch is a branching interference type optical switch, a directional coupler type switch, or a TE-TM mode converter. (3) A structure is provided in which a semiconductor laser device and the wavelength conversion element according to claim 1 are optically coupled, and the semiconductor laser is gain-switched by a high-frequency sinusoidal current to generate ultrashort optical pulses. , the optical switch of the wavelength conversion element is switched by an electrical signal of an arbitrary frequency synchronized with the high frequency sinusoidal current, and the ultrashort optical pulse is coupled to the three-dimensional optical waveguide of the wavelength conversion element among the ultrashort optical pulses. An ultrashort optical pulse generator, characterized in that the wavelength of the optical pulse is converted by the three-dimensional optical waveguide. (4) A semiconductor laser device is provided with a structure in which a wavelength conversion element according to claim 1 is optically coupled, and the semiconductor laser device is an external cavity laser including a semiconductor laser device and a diffraction grating. The semiconductor laser element is mode-locked by modulating with a sinusoidal current of frequency C/2L (C: speed of light, L: external cavity length) to generate ultrashort optical pulses, and The oscillation wavelength of the external cavity laser is varied by controlling the angle, and the optical switch of the wavelength conversion element is switched by an electrical signal of an arbitrary frequency synchronized with the sine wave current, and the ultrashort optical pulse is A wavelength tunable ultrashort optical pulse generator, characterized in that an ultrashort optical pulse coupled to a three-dimensional optical waveguide of the wavelength conversion element is wavelength-converted by the three-dimensional optical waveguide.