JPH07117675B2 - Short wavelength laser light source and optical information processing device - Google Patents

Description

TECHNICAL FIELD The present invention relates to the field of optical information processing utilizing coherent light,
Alternatively, the present invention relates to a short wavelength laser light source and an optical information processing device used in the field of optical measurement and control.

2. Description of the Related Art FIG. 7 shows a block diagram of a conventional short wavelength laser light source. 7th
In the figure, 21 is a semiconductor laser, 24 is a collimator lens, 25 is a focus lens, and 27 is a light wavelength conversion element. mount
The semiconductor laser 21 attached to 20 is driven by a CW power source 50 at a constant current and emits a fundamental wave P1. The generated fundamental wave P1 is collimated by the collimator lens 24 and converted into a half-wave plate.
After the polarization direction is rotated 90 degrees at 26, focus lens 25
Then, the light enters the optical waveguide 2 from the end of the optical waveguide 2 formed by the light wavelength conversion element 27. Harmonics in optical waveguide 2
It is converted to P2, passes through the filter 28, and is emitted to the outside. The generation of higher harmonics (wavelength 0.42 μm) with respect to the fundamental wave having a wavelength of 0.84 μm will be described below in detail with reference to FIG. [T. Taniuchi and K. Yamamoto, “Second harmonic
generation by Cherenkov radiation in proton−excha
nged LiNbO ₃ optical waveguide ", CLEO 86, WR3, 1986, reference]. Fig. 8 is a perspective view and a sectional view of the optical wavelength conversion element. Embedded type formed on the LiNbO ₃ substrate 1 When the light of the fundamental wave P1 from the semiconductor laser is incident on the incident surface 5 of the optical waveguide 2 of, the condition that the effective refractive index N1 of the guided mode of the fundamental wave and the effective refractive index N2 of the harmonic wave are satisfied is satisfied. The optical waveguide 2 to LiNbO ₃
The harmonic P2 light is efficiently radiated into the substrate 1 and operates as a light wavelength conversion element.

Such a conventional optical wavelength conversion element has an embedded optical waveguide as a basic constituent element. As a method of manufacturing this embedded optical waveguide, a LiNbO ₃ substrate 1 which is a ferroelectric substrate is used.
High refractive index layer (refractive index difference ΔNe = 0.13 with substrate) to be the optical waveguide 2 by vapor-depositing Cr or Al etc. on the substrate, heat-treating the one with slits of several μm width by photo process and etching in benzoic acid. Formed). [JLJa
ckel, GERice, and JJVeselka, “Proton exchange fo
r high−index waveguides in LiNbO ₃ “Appl.Phys.Let
t. (Applied Physics Letter), Vol41, No.7,
pp607-608 (1982)]. The optical wavelength conversion element manufactured by the above-mentioned benzoic acid treatment shows the maximum conversion efficiency at the optical waveguide thickness of 0.5 μm with respect to the fundamental wave P1 having a wavelength of 0.84 μm from the semiconductor laser. When the semiconductor laser was driven at 120 mW and the fundamental wave was P1 = 40 mW in the optical waveguide, a harmonic wave of P2 = 0.4 mW was obtained. The conversion efficiency P1 / P2 in this case is 1%.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention In the short wavelength laser light source based on the above semiconductor laser, it is difficult to use at 40 mW or more in consideration of the reliability of the semiconductor laser, and the loss of the lens and the coupling with the optical waveguide. Considering the loss, the usable fundamental wave output is about 20 mW. Therefore, the harmonic output is only 0.1 mW, which is 1 m, which is a practical level in the optical information processing field of short wavelength laser light sources.
It was difficult to stably obtain higher harmonics of W or higher.

Means for Solving the Problems The present invention enables higher output and stabilization of the harmonic emission power by adding a new device to the drive of the semiconductor laser.

Therefore, the short-wavelength laser light source of the present invention comprises an optical wavelength conversion element consisting of a substrate having an optical waveguide formed with an optical waveguide, a semiconductor laser and a power supply for driving the semiconductor laser, and the semiconductor laser is 500 MHz or more. It is driven by high frequency.

By performing high-frequency drive to the semiconductor laser that generates the fundamental wave by the above means, it is possible to significantly improve the peak power of the fundamental wave without increasing the average power of the emitted fundamental wave by pulse-operating the semiconductor laser. Become. As a result, the conversion efficiency of the light wavelength conversion element into a harmonic can be improved and the average output of the harmonic can be greatly improved.

Example An example of the short wavelength laser light source of the present invention will be described with reference to the drawings. FIG. 1 shows a configuration diagram of a blue laser light source which is a kind of short wavelength laser light source explained by using a light wavelength conversion element. This blue laser light source is an optical wavelength conversion element 27 composed of a substrate having a nonlinear optical effect on which an optical waveguide 2 is formed.
It is basically composed of a semiconductor laser 21 and a high frequency power supply 100 which is a power supply for driving the semiconductor laser 21. As the manufacturing method, first, the surface of the optical wavelength conversion element 27 on which the optical waveguide 2 is formed is bonded to the mount 20. Next, the focus lens 25 having an NA of 0.6 and the half-wave plate 26 were inserted into the mount 20 and fixed. Next, collimator lens 24 with NA 0.3,
After inserting the semiconductor laser 21, the semiconductor laser 21 is driven to move the collimator lens 24 and the semiconductor laser 21 so that the fundamental wave P1 is focused on the incident portion 3 of the optical wavelength conversion element 27, and the maximum harmonic P2 emitted. After that, fixation was performed. After that, the absorption filter 28 for the fundamental wave scattered and emitted was attached to the mount 20. Figure 1 shows a semiconductor laser
21 is an oscillation wavelength of 0.78 μm, a constant current (hereinafter referred to as DC bias) is applied from the CW power supply, and a sine-shaped high frequency (1 GHz) is applied from the high frequency power supply.
A fundamental wave P1 of 40 mW is emitted. This fundamental wave P1 is incident on the optical wavelength conversion element 27 using the lenses 24 and 25 and the half-wave plate 26, and a harmonic wave P2 is generated. Half-wave plate 26 is a semiconductor laser
21 and the optical waveguide 2 formed in the optical wavelength conversion element 27 having a length of 6 mm were inserted to match the polarization directions. The emitting portion 4 of the optical waveguide 2 is roughened by a file so that the fundamental wave P1 is scattered. In this optical wavelength conversion element 27, the fundamental wave P1 of 25 mW was incident on the inside of the optical waveguide 2, a harmonic wave of 1.2 mW was obtained, and the total conversion efficiency was 3%. The stability of harmonics was ± 1% or less.

The electric waveform from the high frequency power source and the waveform of the fundamental wave emitted by the semiconductor laser 21 driven at high frequency are shown in FIGS. 2 (a) and 2 (b), respectively. Laser diode 21
Fails to respond to the high speed of the electric waveform (a), causes relaxation oscillation and oscillates like a pulse. And the semiconductor laser 21 in this case
The peak output is about 1W and the conversion efficiency to harmonics is 10%.
Will be exceeded. In this case, the average power of the semiconductor laser 21 is 40 mW, and there is no problem in terms of reliability. The power of the converted harmonics is about 5 to 10 times higher than that of CW.

FIG. 3 shows the relationship between the drive frequency and the harmonic output when the average power of the semiconductor laser 21 is 40 mW. In the frequency region shown by 22, that is, in the region of 500 MHz or more, the harmonic output increases in proportion to the drive frequency, and a high frequency output can be advantageously obtained. A higher frequency is more advantageous by increasing the output, and it is considered that the half width of the pulse waveform of the semiconductor laser becomes narrower as the frequency increases.
FIG. 4 shows the IL characteristic (current-output characteristic) of the semiconductor laser for explaining the difference in the driving method between the high frequency drive and the high frequency superposition. Since the high frequency superposition is used only for the purpose of stabilizing the semiconductor laser, it is used just _below the threshold I _th of oscillation of the semiconductor laser. That is, as shown in FIG. 4A, the difference between the peak current I _P and the operating current I _b (I _p −I _b ) is twice as large as the difference between the operating current and the threshold current (I _b −I _th ). It is a degree. On the other hand, in a high-frequency drive intended to increase the peak power of the semiconductor laser, at least (I _p −I _b ) is at least 3 (I _b −I _th ).
Times, usually 5 to 10 times. The peak power of the high frequency drive power increases especially when it is 1 W or more.
Moreover, the peak power is larger when the DC bias is applied than when it is not applied.

FIG. 5 shows a manufacturing process diagram of an optical wavelength conversion element which is a basic constituent element of a short wavelength laser light source. First, as shown in FIG. 3A, a protective mask Ta ₂ O ₅ is formed on the MgO-doped LiNbO ₃ substrate 1.
Film 12 was sputter deposited at 300A. After patterning the photoresist 11 of the thickness 0.7μm then in FIG (b), CF ₄
The protective mask 12 was dry-etched using gas to form slits. Next, after removing the photoresist 11,
In FIG. 2C, the LiNbO ₃ substrate 1 was heat-treated (proton conversion treatment) at 230 ° C. for 9 minutes in pyrophosphoric acid, which is a kind of phosphoric acid, to form an optical waveguide 2 having a thickness of 0.37 μm. After that, the protective mask 12 was removed as shown in FIG. Hydrofluoric acid was used to remove Ta ₂ O ₅ 12. After removal, a SiO ₂ film 14 was deposited as a protective film on the surface by 4000 A by sputtering. Finally, after optically polishing the surface perpendicular to the optical waveguide 2, AR coating was performed to further cut the emitting end of the fundamental wave. As a result, a light wavelength conversion element was manufactured. The length of this element is 6 mm. Further, in this embodiment, since the MgO-doped substrate is used, light damage can be prevented even for light having a short wavelength, and the output of harmonics does not fluctuate. Although Ta ₂ O ₅ is used in the examples, different ratios of Ta and oxygen may be used. The emission end is cut off in order to scatter at the emission part 4 most of the fundamental wave that propagated without being converted into the harmonic P2. As a result, the fundamental wave does not return to the semiconductor laser, so that the output and longitudinal mode of the semiconductor laser are stable, and accordingly, the output of harmonics is also stable. Further, when the semiconductor laser was driven with harmonics, the fluctuation of the harmonic output could be suppressed to ± 1% or less.

In addition, it was confirmed that the fundamental wave having a wavelength of 0.65 to 1.6 μm was used to generate harmonics by the optical wavelength conversion element.

Next, as a second embodiment, a short wavelength laser light source of the present invention constituted by a semiconductor laser having a fundamental wavelength of 1.3 μm, a semiconductor laser having a wavelength of 0.8 μm and an optical wavelength conversion element will be described. In FIG. 6, 31 is a semiconductor laser having a wavelength of 1.3 μm, 32 is a semiconductor laser having a wavelength of 0.86 μm, and 27 is an optical wavelength conversion element. In this embodiment, each semiconductor laser is directly coupled to the light wavelength conversion element. That is, the coupling is performed without using a lens. The fundamental waves P1 and P3 propagating through the incident waveguides 33 and 34 are combined by the Y branch 35, and the optical waveguide 2
It enters and is converted here and radiated as the sum frequency P2 (wavelength 0.52 μm). Fundamental wave that propagates through the optical waveguide 2 and reaches the end
P1 and P3 are scattered by the emission part 4, and the semiconductor lasers 31 and 32 do not return light and operate stably. The emission part 4 was processed using a CO ₂ laser so that the fundamental wave was scattered. By performing high frequency drive on each of the semiconductor lasers 31 and 32, the wave frequency P2 was obtained with high output and stability. The same 1.2 GHz high-frequency power source was used to drive the semiconductor lasers 31 and 32, and relaxation oscillation was simultaneously generated so that the peaks of the pulse waveforms of the fundamental waves were adjusted. As described above, this configuration is also effective for sum frequency generation. In this embodiment, the fundamental wave from the semiconductor laser is directly incident on the optical waveguide. However, this makes the light source extremely compact and is advantageous as an optical information processing apparatus such as a laser printer.

Next, as a third embodiment, an optical information processing apparatus in which the short wavelength laser light source of the present invention is applied to read an optical disk will be described. The harmonics obtained by the short-wavelength laser light source manufactured in Example 1 are beam-shaped by a shaping lens which is a shaping optical system so that the divergent light side becomes parallel light,
Both sides use parallel light. After passing through the polarization beam splitter, the collimated harmonics are condensed by a focusing lens to form a spot of 0.6 μm on the optical disc.
The reflected signal again passes through the polarization beam splitter and then enters the light receiver. By driving a semiconductor laser with a wavelength of 0.84 μm and an output of 40 mW at 960 MHz, a harmonic wave of 2 mW was radiated. The length of the light wavelength conversion element used is 12 mm.

As described above, in the optical information processing apparatus of the present invention, by using the short-wavelength laser light source in which the semiconductor laser is driven at a high frequency, it is possible to stably extract high-power harmonics. Therefore, the spot can be narrowed down to a half of the reading system of the optical disc using the 0.8 μm band semiconductor laser which has been conventionally used, and the recording density of the optical disc can be increased four times. Since the driving is performed at an extremely high speed as in this example, it does not affect the signal recording / reproducing of the ordinary optical information processing apparatus.

In addition to the optical disc, it can be used for an optical information processing device such as a laser printer or a plate making machine.

Although the fundamental wave is scattered at the emitting portion in the embodiment, it is also effective to absorb the fundamental wave by applying an absorber to the emitting portion. Although LiNbO ₃ having a large nonlinear optical constant is used in the examples, other substrates such as LiTaO ₃ , ferroelectrics such as KNbO ₃ , organic materials such as MNA, or compound semiconductors such as ZnS having a large nonlinear optical constant are used. If it can be used.

As described above, according to the short wavelength laser light source of the present invention, it is possible to drive the semiconductor laser at a high frequency to increase its peak power and improve the conversion efficiency of the optical wavelength conversion element into a harmonic, As a result, the output of the harmonic wave or the sum frequency can be significantly improved.

Further, by driving a semiconductor laser that generates a fundamental wave at a high frequency, it becomes strong against the returning light to the semiconductor laser, and a stable harmonic wave output can be obtained.

As an optical information processing apparatus incorporating the above short wavelength laser light source, high output and stable short wavelength light can be used, and recording density and sensitivity are significantly improved.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a short wavelength laser light source of the present invention, FIG. 2 is an electrical waveform and a semiconductor laser waveform diagram, FIG. 3 is a graph showing drive frequency dependence of harmonic output, and FIG. 4 is a semiconductor laser. FIG. 5 is a manufacturing process diagram of an optical wavelength conversion element of the present invention, FIG. 6 is a configuration diagram of a short wavelength laser light source of a second embodiment of the present invention, and FIG. FIG. 8 is a block diagram of a short wavelength laser light source, and FIG. 8 is a block diagram of a conventional light wavelength conversion element. 1 ... LiNbO ₃ substrate, 2 ... Optical waveguide, 3 ... Incident part, 4
…… Emitting part, 21 …… Semiconductor laser.

Claims (7)

[Claims] 1. An optical wavelength conversion element comprising a substrate having an optical waveguide in which an optical waveguide is formed, at least one semiconductor laser, and a power supply for driving the semiconductor laser.
A short-wavelength laser light source characterized by driving the semiconductor laser at a high frequency of 500 MHz or more. 2. An optical wavelength conversion element comprising a substrate having an optical waveguide formed with a non-linear optical effect, at least one semiconductor laser, and a power supply for driving the semiconductor laser,
An optical information processing apparatus having a short wavelength laser light source for driving the semiconductor laser at a high frequency of 500 MHz or more and a shaping optical system. 3. LiNb _x T as a substrate having a nonlinear optical effect
a _1-x O ₃ (0 ≦ X ≦ 1) substrate or MgO-doped L
The short wavelength laser light source according to claim 1 or the optical information processing device according to claim 2, wherein an iNb _x Ta _1-x O ₃ (0 ≦ X ≦ 1) substrate is used. 4. The short wavelength laser light source according to claim 1 or the optical information processing device according to claim 2, wherein the fundamental wave from the semiconductor laser is directly incident on the optical waveguide. 5. A short-wavelength laser light source according to claim 1 or an optical information processing device according to claim 2, wherein an antireflection film is formed on the incident portion of the fundamental wave. 6. The short wavelength laser light source according to claim 1 or the optical information processing device according to claim 2, wherein the high frequency power is 1 W or more. 7. A short wavelength laser light source according to claim 1 or a light information processing device according to claim 2, wherein a DC bias is applied to the semiconductor laser.