JPH03185887A - External resonator type semiconductor laser oscillator - Google Patents

Abstract

PURPOSE:To prevent the direction of output light from being changed by a method wherein the title oscillator is provided with an external resonator, in which primary diffracted light of a wavelength selected by an angle to be set by a diffraction grating is made to feedback to a semiconductor laser to perform a narrowing of a spectral width, light reflected by a plane reflecting mirror is led out as the 0-order light of the diffraction grating and the output light is always outputted in a constant direction. CONSTITUTION:An external resonator is formed between a semiconductor laser 1B and a diffraction grating 3 via a plane reflecting mirror 4A and an oscillation spectral width is narrowed here. A grating surface 5 of the grating 3 and a reflective surface of a plane reflecting mirror 4B are fixed at an angle theta1 and even if the grating 3 is rotated in the directions shown by arrows, an angle that 0-order light reflected by the mirror 4B forms with incident light to the grating 3 is constant. In such a way, the 0-order light reflected totally by the mirror 4B is incident to a plane reflecting mirror 4C, but as the mirrors 4A and 4C are fixed in such a way that the reflective surfaces of both of the mirrors 4A and 4c make an angle theta2, the direction of output light 8 which is emitted from the mirror 4C is not changed and is constant even if the grating 3 is rotated in the directions shown by the arrows.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] This invention relates to an external cavity type semiconductor laser oscillator using a diffraction grating.

[Prior Art] Semiconductor laser oscillators have characteristics such as being extremely small compared to gas or solid-state laser oscillators, using current for pumping, easy handling, and high efficiency. It has been put into practical use in a wide range of fields, including communications, optical information processing, and optical measurement.

However, semiconductor laser oscillators have poor optical coherence compared to gas or solid state laser oscillators, and the oscillation spectrum width is narrowed in order to improve the coherence of light.

There are two methods for narrowing the oscillation spectrum width: one is to perform negative feedback control using electrical feedback, and the other is to provide an external resonator formed by a reflector or the like outside the semiconductor laser. It is easier to set up
This is easy to achieve.

A semiconductor laser oscillator equipped with an external cavity as described above (
(Hereinafter, this will be referred to as an external cavity type semiconductor laser oscillator)
In this case, the reflector consists of only a flat reflector, and
Some use diffraction gratings. The device using a diffraction grating has the advantage of not only narrowing the spectral width but also sweeping (variable) the oscillation wavelength.

Figure 2 shows the configuration of a conventional external cavity type semiconductor laser oscillator using a diffraction grating. In the figure, (1A) is a semiconductor laser oscillator mounted in an open package that emits laser light from both end faces. Below, we will refer to this as a semiconductor laser (
(abbreviated as 1A〉), (2) is a collimating lens, (
3) is the diffraction grating, <6) is the laser beam from the semiconductor laser (IA>), (7) is the first-order diffracted light from the diffraction grating (3),
(8) shows the output light. Next, the operation will be explained.

Laser light (6) emitted from one end face (a) of the semiconductor laser (LA) is turned into parallel light by a collimating lens (2), and is incident on a diffraction grating (3). Then, it is diffracted by the diffraction grating (3) at a diffraction angle corresponding to each wavelength, and the first-order diffracted light (7>) of the wavelength selected by the angle set by the diffraction grating (3) returns to the semiconductor laser (1A).

The resonator length of the external cavity formed between this semiconductor laser (IA) and the diffraction grating (3) is
) Since the resonator length is much longer than the resonator length of the chip itself, the laser resonator loss is small and the spectral width can be narrowed around the selected wavelength as the center wavelength.

Then, an output light (8>) with higher coherence than in the case of a semiconductor laser alone is oscillated and output from the end face (b).

Furthermore, by rotating the diffraction grating (3) in the direction shown by the arrow in the drawing, the wavelength of the light that returns to the semiconductor laser (IA) can be changed to perform a wavelength sweeping change.

[Problems to be Solved by the Invention] Since the conventional external cavity type semiconductor laser oscillator as described above is configured as described above, the semiconductor laser used is a so-called open type semiconductor laser that emits laser light from both end faces. It is necessary to use a type semiconductor laser.

However, there are only a few types of open-type semiconductor lasers, and most of the general-purpose semiconductor lasers on the market are of the type that emit light only from one end face, which is housed in a package called a cantaib, so it is difficult to use general-purpose semiconductor lasers as they are. Therefore, the device becomes expensive and the oscillation wavelength band, optical output, etc. are limited.

In addition, with open semiconductor lasers that emit light from both end faces, the chip is directly exposed to the outside air, so if used as is without hermetically sealing, the lifespan will be extremely short, and the electrodes and chip on the mount will be damaged. Since all the gold wires used to connect the wires were exposed, there were problems such as making it inconvenient to handle them.

This invention was made to solve this problem, and has a simple configuration that allows general-purpose commercially available semiconductor lasers to be used as they are, and even when the diffraction grating is rotated for wavelength sweeping, the output light remains It is an external cavity type semiconductor laser oscillator whose direction does not change! The purpose is to obtain.

[Means for Solving the Problems] An external cavity type semiconductor laser oscillator according to the present invention includes:
By arranging a diffraction grating and a plurality of plane reflecting mirrors in an appropriate combination, the first-order diffracted light of the wavelength selected by the angle set by the diffraction grating is returned to the semiconductor laser, and the spectral width of the laser light is The device is equipped with an external resonator that performs constriction, extracts the constricted laser beam as zero-order light of a diffraction grating, and outputs the constricted laser beam in a constant direction.

[Function] Since the present invention includes the external resonator as described above, it is possible to use a commercially available general-purpose semiconductor laser as is.

[Example] Hereinafter, an example of the present invention will be described with reference to the drawings. 1st
The figure shows an embodiment of the present invention, and in the figure (1B
) is a general-purpose semiconductor laser (hereinafter abbreviated as semiconductor laser (1B)) that is housed in a package called a cantaib or the like that emits laser light from only one end face. (
2) is a collimating lens, (3) is a diffraction grating, (4A)
, (4B) and (4C) are plane reflecting mirrors, (5> is the grating plane of the diffraction grating (3), and (6) is the semiconductor laser (1B).
), (7) is the first-order diffracted light from the diffraction grating (3), and (8) is the output light.

Note that the diffraction grating <3) has a small number of diffraction orders,
For example, a blazed lattice (echelette) in which the grooves have a blaze angle
) lattice) is preferable.

Next, the operation will be explained. The laser beam (6) emitted from the semiconductor laser (1B) is turned into parallel light by the collimating lens (2), enters the plane reflecting mirror (4A>), is totally reflected there, and enters the diffraction grating (3).

Then, it is diffracted by the diffraction grating (3) at a diffraction angle corresponding to each wavelength, and the first-order diffracted light (7) of the wavelength selected by the angle set by the diffraction grating (3) follows the path of the incident light <6). It goes backwards and returns to the semiconductor laser (1B). That is, an external resonator is formed between the semiconductor laser (1B) and the diffraction grating (3) via the plane reflecting mirror (4A), and the oscillation spectrum width is narrowed here.

The light whose spectral width has been narrowed is passed through the diffraction grating (3)
The light enters the plane reflecting mirror (4B) as zero-order light, and is totally reflected there.

The grating surface (5) of the diffraction grating (3) and the reflective surface of the plane reflecting mirror (4B) are fixed at an angle θ1, so even if the diffraction grating (3) rotates in the direction of the arrow in the drawing, Reflector (4B)
The angle formed by the zero-order light reflected by the diffraction grating (3) and the incident light on the diffraction grating (3) is constant at θ1×2.

In particular, if θ1=90'', then 90°×2=180°, which means they are parallel to each other.

The 0th order light totally reflected by the plane reflector (4B) in this way is incident on the plane reflector (4C), but both the plane reflector (4A) and the plane reflector (4C) Since the reflecting surface of is fixed at an angle of θ2, even if the diffraction grating (3) is rotated in the direction shown by the arrow in the drawing, the direction of the output light (8) emitted from the plane reflector (4C) will change. does not change and remains constant.

In particular, by setting θ1=90° and θ2=270°, the optical axis of the laser beam from the semiconductor laser (1B) and the optical axis of the output light (8) can be made to coincide.

Therefore, even if the diffraction grating (3) is rotated to perform wavelength sweeping by changing the wavelength of the light that returns to the semiconductor laser (1B), the direction of the final output light (8) is always constant. Therefore, the problem that the output light (8) moves can be solved.

[Effects of the Invention] As explained above, the present invention allows use of commercially available general-purpose semiconductor lasers, so the device can be constructed at low cost, and conditions such as oscillation wavelength band and optical output can be adjusted. The effect is that various selections can be made and a wide variety of high coherence light can be obtained.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention, and FIG. 2 is a diagram showing the configuration of a conventional device. (1B> is a general-purpose semiconductor laser, (2) is a collimating lens, (3) is a diffraction grating, (4A), (4B), (4C)
) are plane reflecting mirrors, (5) are lattice surfaces, (6) are light from a semiconductor laser, (7〉 is first-order diffracted light, and 8〉 is output light. In addition, the same symbols in each figure are the same - or Showing the corresponding part 1
1B = General-purpose semiconductor laser 2: Collimating lens 3: Diffraction grating 4A, 4B, 4C: Plane reflecting mirror 5: Grating surface 6: Rade light from semiconductor laser 7/1st-order diffracted light 8: Output light Diagram

Claims (1)

[Claims] Laser light emitted from a semiconductor laser is made incident on a diffraction grating as parallel light, and the first-order diffracted light of a wavelength selected by the set angle of the diffraction grating is returned to the semiconductor laser to determine the oscillation spectrum width. In an external cavity type semiconductor laser oscillator having an external cavity that performs constriction, a first plane reflecting mirror (
4A), the parallel light reflected by this first plane reflecting mirror (4A) is incident, and the first-order diffracted light of the wavelength selected by the set angle is made to travel backwards in the optical path of the parallel light, and is reflected by the semiconductor laser (1).
B), the oscillation spectrum width is narrowed, and the laser light with the narrowed spectrum width is emitted again from the semiconductor laser (1B) and enters as the parallel light, and its zero-order light is A diffraction grating (3) is set to diffract at a predetermined diffraction angle, and a reflection surface is set at an angle θ1 to the grating plane (5) of this diffraction grating (3). a second plane reflecting mirror (4B) that totally reflects the zero-order light incident thereon; a second plane reflecting mirror (4B) having a reflecting surface set at an angle θ2 with respect to the first plane reflecting mirror (4A); A third plane reflector (4C) that totally reflects the 0th order light reflected by the reflector (4B)
), comprising means for rotating the diffraction grating (3) together with the second plane reflecting mirror (4B) to change the incident angle of the parallel light incident on the diffraction grating (3), the angle θ1 and By appropriately adjusting θ2, even if the diffraction grating (3) is rotated, the direction of the output light (6) whose spectral width is narrowed from the third plane reflecting mirror (4C) is always constant. An external cavity semiconductor laser oscillator characterized by: