JP2001160642A - Integrated variable wavelength laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact and inexpensive integrated variable wavelength laser. SOLUTION: In an integrated variable wavelength laser, an optical waveguide 13 constituted of a laser medium is provided with cyclic refractivity controllable from the outside part, and distribution feedback is obtained so that a laser medium, an optical resonator, and a wavelength tuning element are integrated on a single substrate 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an integrated tunable laser integrated on a single substrate.

[0002]

2. Description of the Related Art A conventional tunable laser has the following configuration.

FIG. 5 is a schematic view of such a conventional variable wavelength laser.

As shown in FIG. 1, a conventional variable wavelength laser comprises a laser medium 1 for amplifying light and two mirrors 2.
It comprises four parts (elements) of an optical resonator 2 composed of A and 2B, a wavelength tuning element 3, and an excitation laser 4 as an excitation light source.

[0005]

However, since the above-mentioned conventional variable wavelength laser has four elements, it is unavoidable that the size is increased and the cost is increased.

SUMMARY OF THE INVENTION It is an object of the present invention to eliminate the above-mentioned problems and to provide a compact and low-cost integrated tunable laser.

[0007]

In order to achieve the above object, the present invention provides: [1] In an integrated type variable wavelength laser, an optical waveguide constituted by a laser medium is provided with an externally controllable periodic refractive index. A laser medium, an optical resonator, and a wavelength tuning element are integrated on a single substrate by providing a distribution and obtaining a distributed feedback.

[2] The integrated tunable laser according to [1], wherein a semiconductor laser or a solid-state laser excited by a semiconductor laser is combined with the substrate as an excitation light source.

[0009]

Embodiments of the present invention will be described below with reference to the drawings.

Here, the variable wavelength laser is a laser such as a dye laser, an alexandrite laser, a titanium / sapphire laser, a color center laser, an optical parametric oscillator, etc., which can continuously change the wavelength of emitted light by controlling it over 10 nm or more. Means This type of laser is used for applications such as spectroscopic analysis. Semiconductor lasers are also tunable lasers in a broad sense.

On the other hand, a laser having good monochromaticity is produced by making use of a phenomenon in which periodic irregularities are formed along the optical waveguide and light propagating through the waveguide is reflected at a specific wavelength determined by the period of the irregularities. The technique to obtain is distributed feedback (DFB: Distr)
The method is called an “Improved Feedback” method and is applied to a semiconductor laser, which contributes to the improvement of monochromaticity.

According to the present invention, a waveguide laser is formed by thinning the medium of a tunable laser, and the laser medium, the optical resonator, and the wavelength tuning element are made several millimeters long by using the distributed feedback method. (About 10 mm).

In addition, instead of providing periodic irregularities fixed to the waveguide as in the prior art, a wave of an acoustic wave, a light wave, or an electron beam is given from outside to induce a periodic structure of a refractive index in the waveguide. , Thereby achieving a distributed feedback operation.

As a result, the oscillation wavelength can be continuously and widely changed by externally controlling and changing the period of the induced periodic structure.

FIG. 1 is a schematic view of an integrated type variable wavelength laser showing an embodiment of the present invention.

As shown in this figure, this integrated type variable wavelength laser is obtained by integrating the respective elements and integrating them on a flat optical waveguide. That is, the substrate 11
Above the excitation laser 12 and externally control the period,
A thin film laser medium (optical waveguide) 13 having a periodic structure of refractive index is provided.

With the above configuration, it is possible to realize a remarkably small and low-cost variable wavelength laser as compared with the conventional one.

Here, in order to integrate the laser medium, which is the four elements of the variable wavelength laser, and the four elements of the optical resonator, the wavelength tuning element, and the excitation laser, in the present invention, the optical waveguide is formed by the laser medium 13. And periodically changes the refractive index from the outside along the waveguide 13 to cause optical feedback at a specific wavelength. Further, it is achieved by using a semiconductor laser (LD) or a semiconductor laser-excited microchip solid-state laser as an excitation source as the excitation laser 12 and coupling its output to the optical waveguide 13.

More specifically, first, a tunable laser medium (waveguide) 13 is placed on a substrate 11 having a slightly different refractive index.
Thin and deposit to a thickness of ~ 5 microns. The waveguide 13 is irradiated with the excitation laser 12 to excite it, and at the same time, the waveguide 13 is given a refractive index change of a period that is an integer fraction of the wavelength to be oscillated, so that only light of a predetermined wavelength is fed back. Then, laser oscillation is obtained with a narrow spectrum width due to the filter effect.

As a method of changing the refractive index along the optical waveguide and controlling the period from the outside, there are a method of transmitting ultrasonic waves along the waveguide, and a method of causing excitation light or an electron beam to interfere. In the case of ultrasonic waves, the frequency is controlled, and in the case of light or electron beams, the incident angle is changed to control the oscillation wavelength.

Further, a semiconductor laser (LD) or a solid-state microchip laser using a semiconductor laser as an excitation source is used as the excitation laser 12, and the output thereof is directly or via the optical waveguide 13 to the above-mentioned integrated variable wavelength. By coupling to the waveguide 13 of the laser, an overall compact integration is achieved.

Hereinafter, a demonstration experiment performed so far will be described with reference to FIG.

The following operations have been confirmed for (1) a conventional method of providing a periodic structure with irregularities in a waveguide and (2) a method of causing excitation light to interfere.

(A) First, in a distributed feedback experiment in which a waveguide is provided with a periodic structure of irregularities, as shown in FIG. 2A, the excitation source 21 is a pulsed Nd: YAG solid-state laser, It is shaped into an elongated beam pattern.
Reference numeral 23 denotes a prototype integrated variable wavelength laser, which is an acrylic resin having a thickness of 5 μm and doped with an organic dye on a glass substrate. The surface is irradiated with ultraviolet laser light from two directions in advance, and the interference fringes are exposed and then etched to form a diffraction grating. When excitation light was applied to this element, distributed feedback occurred and laser oscillation occurred in a specific narrow spectrum as shown in FIG. In FIG. 3, the horizontal axis represents the wavelength (nm), the vertical axis represents the output (arbitrary scale) of the distributed feedback laser, and the dye is rhodamine 6
G1.28 × 10 ⁻² mol / l, the excitation intensity is 1.6 (mJ / cm ² ) for the dotted line, and 4.4 (mJ / cm ² ) for the solid line.
/ Cm ² ).

(B) FIG. 2B is an experiment of distributed feedback by a method of causing excitation light to interfere. Excitation light beam to mirror 2
By dividing into two by 4 and irradiating from two directions,
Interference fringes of excitation light are generated in the film, and distributed feedback is achieved.
In this case, unlike the above (A), the period of the fringes changes by changing the incident angle, and the oscillation wavelength can be controlled. FIG.
Is an experimental result showing that the oscillation spectrum was changed by changing the incident angle. In FIG. 4,
The horizontal axis represents the wavelength (nm), the vertical axis represents the output (arbitrary scale) of the distributed feedback laser, and the dye is rhodamine 6G.
3.5 × 10 ⁻² mol / l, waveguide length t = 5.4 μ
m, and the input energy is 203 μJ.

(C) FIG. 2C shows a method of inducing a periodic change in the refractive index in the waveguide by ultrasonic waves. That is, the ultrasonic oscillator 26 is driven by the electronic oscillator 25,
The distributed feedback is achieved by propagating the sound wave along the optical waveguide and simultaneously irradiating the excitation light. In this method, the wavelength can be electrically tuned by changing the frequency of the electronic oscillator. In addition, 27 is an ultrasonic absorber.

It should be noted that the present invention is not limited to the above embodiment, and various modifications are possible based on the spirit of the present invention, and these are not excluded from the scope of the present invention.

[0028]

As described above, according to the present invention, the following effects can be obtained.

(1) A compact and low-cost integrated tunable laser can be obtained.

(2) A semiconductor laser or a semiconductor laser-excited solid-state laser is combined with a substrate as an excitation light source. For example, ultrasonic waves induce periodic changes in the refractive index in the waveguide. That is, the ultrasonic oscillator is driven by the electronic oscillator, the sound wave is propagated along the optical waveguide, and the excitation light is irradiated at the same time, thereby achieving distributed feedback. By changing the frequency of the electronic oscillator, the wavelength can be electrically tuned.

[Brief description of the drawings]

FIG. 1 is a schematic view of an integrated tunable laser showing an embodiment of the present invention.

FIG. 2 is a diagram showing an experimental example of distributed feedback.

FIG. 3 is a diagram showing an example of a spectrum at the time of distributed feedback oscillation in the experiment of FIG. 2 (a).

FIG. 4 is a diagram showing an example of a spectrum at the time of distributed feedback oscillation due to interference of pump light in the experiment of FIG. 2 (b).

FIG. 5 is a schematic view of a conventional variable wavelength laser.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Substrate 12 Excitation laser 13 Thin-film laser medium (optical waveguide) 21 Excitation source 22 Lens system 23 Integrated tunable laser 24 Mirror 25 Electronic oscillator 26 Ultrasonic oscillator 27 Ultrasonic absorber

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) H01S 3/094 Z (72) Inventor Takayoshi Matsuoka 1-29-23 Hakozaki, Higashi-ku, Fukuoka, Fukuoka F-term (Reference) 5F072 AB20 AK10 JJ08 JJ20 MM20 PP07 PP10

Claims (2)

[Claims] 1. An integrated tunable wavelength laser, wherein an optical waveguide composed of a laser medium is provided with an externally controllable periodic refractive index distribution to obtain a distributed feedback, thereby obtaining a laser medium, an optical resonator, wavelength tuning. An integrated tunable laser, wherein the elements are integrated on a single substrate. 2. The integrated tunable wavelength laser according to claim 1, wherein a semiconductor laser or a semiconductor laser pumped solid-state laser is combined with the substrate as an excitation light source.