JPH04296830A - Optical second harmonic generator - Google Patents

Abstract

PURPOSE:To ensure phase adjustment by matching temperature characteristic of phase adjusting wavelength and temperature characteristic of the wavelength of semiconductor laser with each other. CONSTITUTION:An optical second harmonic generating device, or SHG device 2 having a phase adjustment means 1, i.e., a refractive factor cyclic pattern or a domain reversal cyclic pattern, and a semiconductor laser 3 of its basic wave light source are provided. The temperature characteristic of the phase adjustment wavelength of the SHG device 2 and the temperature characteristic of the oscillating wavelength of the semiconductor laser 3 are almost identical in that the same temperature characteristic is obtained in a predetermined operating temperature region. By diffusing Ti and so on preferentially on a primary surface 4a of a non-linear optical crystal 4 comprising Z-plate of LN of mono-region, as indicated by an arrow (a), a phase adjustment means 1 by means of cyclic polarization reversal is formed. Otherwise, by forming a local electric field and whereby reversing the electrode, a phase adjustment means 1 by means of polarization reversal cyclic pattern is formed.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to an optical second harmonic generator (hereinafter referred to as an "SHG element") having a semiconductor laser as a fundamental wave light source and an optical second harmonic element (referred to as an SHG element) that shortens the wavelength of the light emitted from the semiconductor laser. (referred to as SHG equipment).

0002

2. Description of the Related Art The need for short wavelength light is increasing for purposes such as high-density recording and high-resolution reproduction of optical discs, magneto-optical discs, etc.

[0003] Semiconductor laser light with a wavelength λ0, for example, about 840 nm, is introduced as fundamental wave light into an SHG element using a nonlinear optical crystal as an optical device capable of extracting this short wavelength light, and the second harmonic of this fundamental wave light is generated. For example, an SHG device that converts green light with a wavelength of 420 nm is attracting attention. This SHG device, for example, as shown in FIG. 1, forms a high refractive index region by selectively exchanging protons with an optical waveguide 5 in the form of a stripe on one main surface 4a side of a nonlinear optical crystal 4. It consists of

Then, a laser beam having a wavelength λ0 from the semiconductor laser 3 is inputted from one end 5a of the optical waveguide 5, and
A configuration is adopted in which a short wavelength light having a second harmonic of λ0/2 is extracted from the other end 5b together with the fundamental wave light, and this output light is passed through a filter (not shown) to extract only the short wavelength light. It will be done.

[0005] When such a waveguide type SHG element is used, in order to obtain a high SHG output, it is necessary that the fundamental wave and the second harmonic in the optical waveguide 5 are phase matched.

However, since the nonlinear optical crystal 4 has a high nonlinear optical constant d33, when using LiNbO3 (referred to as LN), which is suitable for use as this type of SHG element, the fundamental wave from which high output can be obtained is: For example, the oscillation wavelength of a normal semiconductor laser is 780 to 9
Since phase matching is achieved at a wavelength longer than 000 nm, for example about 1000 nm, it is inappropriate to use a semiconductor laser as a fundamental wave light source. For this reason, in this type of SHG element, a phase matching means 1 for achieving quasi-phase matching is provided in the forming portion of the optical waveguide 5.

This phase matching means 1 periodically aligns, for example, along an optical waveguide 5 on the main surface 4a side of a nonlinear optical crystal 4 whose polarization is made into a single domain, as shown by arrow a in FIG. A phase matching means 1 is formed by selectively doping Ti so that its polarization direction is periodically reversed or its refractive index is periodically changed, and the phase matching means is based on periodic polarization inversion or refractive index change. 1, a configuration is adopted in which the wavelength of the required input fundamental wave and its second harmonic are matched.

However, such a phase matching means 1 is
In fact, it has a temperature dependence, and on the other hand, the oscillation wavelength of the semiconductor laser 3 as a light source of the input fundamental wave light also has a temperature dependence. Even if the matching wavelength is set according to the input fundamental wave wavelength to be used, the original phase matching function will be inhibited due to variations in the matching wavelength depending on the surrounding temperature or temperature during operation, making it impossible to obtain high SHG output. Problems arise.

That is, as shown schematically in FIG. 5, the dependence of the SHG output on temperature and wavelength shows a peak value at a certain temperature T0 and a certain wavelength λ.

Now, in the configuration of FIG. 1, when a proton exchange waveguide configuration is used and the second harmonic is generated by quasi-phase matching, and the waveguide length is 8 mm, the wavelength of the SHG output in FIG. The radius width Δλ is approximately 1 to 2 Å,
The temperature half width ΔT was about 1°C.

[0011] Therefore, the SHG output fluctuates greatly in response to fluctuations in the wavelength and temperature of the light source 3.

In order to suppress this fluctuation, it is necessary to individually precisely control the temperature of the semiconductor laser as a light source and the SHG element using an electronic temperature control element such as a Peltier element. It becomes extremely complicated.

For example, in FIG. 1, the temperature characteristics of the semiconductor laser 3 and the phase matching means 1 correspond to the characteristic curve 6L of FIG.
As shown in D or 6PM, when both characteristics intersect at a point at a predetermined temperature T0, the semiconductor laser and the SHG element must be maintained at this temperature T0 in order to obtain a high SHG output.

Further, as shown in FIG. 7, as shown in the temperature characteristics 7LD of the semiconductor laser and the temperature characteristics 7PM of phase matching, if the operating temperatures do not intersect with each other, the temperatures exhibiting a constant wavelength, respectively. It will be necessary to maintain the TLD and TPM at different temperatures.

[0015]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a stable and special temperature control means in an SHG device having an SHG element having the above-mentioned phase matching means and a semiconductor laser as a light source of fundamental wave light for the SHG element. To obtain high SHG output without providing any.

[0016]

[Means for Solving the Problems] As explained with reference to FIG. In an optical second harmonic generation device having a semiconductor laser 3 as a wave light source, the temperature characteristics of the phase matching wavelength of the SHG element 2 and the temperature characteristics of the oscillation wavelength of the semiconductor laser 3 are shown in FIGS. 2 and 3. As shown in FIGS. 1 and 2, they are configured to have substantially the same temperature characteristics in a predetermined operating temperature range, that is, temperatures T1 to T2, for example, 10° to 60°.

[0017]

[Operation] According to the configuration of the present invention described above, the required operating temperature T
1 to T2, as shown in FIGS. 2 and 3, the temperature characteristics of the phase matching wavelength and the temperature characteristics of the semiconductor laser wavelength are made to match, so that the fundamental wave, that is, from the semiconductor laser 3 at this temperature T1 to T2, The incident light is λ1
~λ2, its phase matching wavelength also changes to λ1
Since it changes with the same gradient at temperatures T1 to T2, phase matching is always ensured regardless of the temperature.

[0018] Therefore, a high SHG output of a predetermined wavelength λ can be maintained regardless of temperature.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A SHG apparatus according to the present invention will be explained with reference to FIG.

In the present invention, for example, by selectively diffusing Ti or the like onto, for example, one main surface 4a of the nonlinear optical crystal 4, which is made of a Z-plate of single-domain LN as shown by the arrow a, or The phase matching means 4 by periodic polarization inversion is formed by a well-known technique such as the Li out-diffusion method. Alternatively, the polarization of the single-domain LN crystal substrate is inverted by applying a voltage, forming a local electric field by electron irradiation, etc., and forming the phase matching means 1 with a periodic pattern of polarization inversion. Thereafter, a desired striped optical waveguide 5 is formed using a well-known technique such as a proton exchange method. In this proton exchange method, for example, a portion of one principal surface 4a of the nonlinear optical crystal 4 other than where the optical waveguide 5 is to be formed is
A striped window is formed only in the area where the optical waveguide is to be formed by using a lift-off method using a mask made of Ta or the like with a thickness of 220 Å, for example.
immersed in hot phosphoric acid at 350°C for 13 minutes, then exposed to air at 350°C.
By performing a heat treatment for about 2 hours at °C, a striped optical waveguide 5 having an interaction length, that is, a waveguide length of 8 mm, is formed.

[0021] A semiconductor laser, for example, with a wavelength λ0 of 8.0
A fundamental wave light having a wavelength λ0 is introduced into the optical waveguide 5 with the light emitting ends of the semiconductor laser 3 which oscillates a laser light of 40 nm facing each other.

Then, from the other end 5b side of the optical waveguide 5, the short wavelength light of the second harmonic is extracted together with the fundamental wave, and is passed through a filter (not shown) to obtain the desired second harmonic. Extracts short wavelength light.

In particular, in the present invention, as shown in FIG. 3, an example of the temperature dependence of the semiconductor laser wavelength is as follows.
For example, the general operating temperature range of this SHG device is T1.
= 10° to T2 = 60°, for example, when the oscillation wavelength is assumed to be the wavelengths λ1, λR, λ2 at each temperature T1, TR, T2 in the range of temperature T, that is, T1 ≦T≦T2 (λ2 − λ1)
A semiconductor laser with a slope of /(T2 - T1 ) is used, and as shown in FIG.
-T2, the phase matching means 1 is assumed to have temperature dependence, the temperature gradient of which exhibits characteristics similar to the temperature dependence of the semiconductor laser wavelength in FIG.

In practice, for example, as a semiconductor laser, the distance is 80 m.
Single mode oscillation of W, wavelength 839 at 30℃
The slope of the temperature characteristic in the temperature range of 25° C. to 50° C. in a nm semiconductor laser is 6 nm/deg. On the other hand, as described above, a waveguide is formed by proton exchange, and the phase matching means 1 is configured by a domain inversion periodic pattern. The temperature dependence in this case can also be made to roughly match this.

As described above, according to the present invention, the temperature dependence of the semiconductor laser 3 as a fundamental wave light source and the SHG element 2
By matching the temperature dependence of the phase matching wavelength of
Stable output can be obtained.

In the example explained in FIG. 1, the light emitted from the semiconductor laser 3 is directly introduced into the SHG element 2, but in some cases, the optical system 10 is changed as shown in FIG. Can be introduced via placement.

The optical system 10 may have various configurations, such as a combination of a collimating lens 11 and a condensing lens 12, for example.

In the above example, the SHG element 2 made of a nonlinear optical crystal made of an LN Z plate is used, but the optical waveguide S made of KTP (KTiOPO4) or the like is used.
Various SHG elements such as a Cerenkov radiation type SHG element having an optical waveguide of a linear optical crystal provided on the nonlinear optical crystal 4 and a phase matching means as described above are used, and a semiconductor laser as its fundamental wave light source. The present invention can be applied when using.

[0029]

As described above, in the present invention, the temperature characteristics of the phase matching of the SHG element 2 having the phase matching means 1 and the temperature characteristics of the semiconductor laser 3 as its fundamental wave light source are almost matched within the required range. As a result, high S temperature can be maintained without any special temperature control means.
Optical second harmonic generator S capable of extracting HG output
An HG device can be obtained.

Therefore, an optical second harmonic generation device suitable for use as a short wavelength light source for optical disks and magneto-optical disks can be constructed.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram for explaining an apparatus of the present invention.

FIG. 2 is a characteristic curve diagram showing the temperature dependence of the phase matching wavelength of the SHG element.

FIG. 3 is a characteristic curve diagram showing the temperature dependence of a semiconductor laser wavelength.

FIG. 4 is a configuration diagram of another example of the device of the present invention.

FIG. 5 is a characteristic curve diagram showing the temperature and wavelength dependence of SHG output.

FIG. 6 is a temperature characteristic curve diagram of phase matching between a semiconductor laser and an SHG element.

FIG. 7 is a temperature characteristic curve diagram of a semiconductor laser and phase matching.

[Explanation of symbols]

1 Phase matching means 2 Optical second harmonic generation element (SHG element) 3 Semiconductor laser 4 Nonlinear optical crystal 5 Optical waveguide

Claims (1)

[Claims] 1. An optical second harmonic generation device comprising an optical second harmonic generation element having a phase matching means and a semiconductor laser as a fundamental wave light source thereof, wherein the temperature characteristic of the phase matching wavelength and the above 1. An optical second harmonic generator characterized in that the temperature characteristics of the oscillation wavelength of a semiconductor laser are substantially the same in a required operating temperature range.