JP6763121B2 - Laser device - Google Patents

Description

The present invention relates to an optical fiber output type laser apparatus used in an application involving image processing.

In applications such as microscopes that observe and analyze an object using a laser beam, noise components contained in the laser beam deteriorate performance quality such as image quality and resolution. Therefore, the laser device is required to have stable light output and low noise.

As the laser light source mounted on the laser apparatus, semiconductor lasers having different wavelengths and outputs are often used depending on the application, and an optical fiber output form is desired from the viewpoint of handleability.

Known noises of semiconductor lasers include quantum noise caused by fluctuations in naturally emitted light, mode hopping noise caused by fluctuations in longitudinal mode, and the like.

Mode hopping noise is a phenomenon in which the return light from the outside of the laser is re-entered into the laser to induce fluctuations in the longitudinal mode, and the resulting output fluctuations appear as intensity noise. In applications, this effect dominates.

As a method of reducing mode hopping noise, there are a method of completely making the vertical mode into a single mode to eliminate mode fluctuation, and a method of making the vertical mode into multiple modes to create a multi-stable state.

As a semiconductor laser in which the longitudinal mode is changed to a single mode, a dynamic single-mode laser that maintains a single-mode operation even when current modulation or temperature change is known (Patent Document 1). As a method for converting a semiconductor laser into multiple modes, a method of superimposing a high frequency current of about several hundred MHz on the drive current of the semiconductor laser is known (Patent Document 2).

Further, apart from the noise reduction measures described above, there is a method of inserting an optical isolator between the semiconductor laser and the external reflection mechanism in order to avoid the return light itself to the semiconductor laser.

Patent No. 3226065 Patent No. 2532283

However, a method for reducing optical noise in a semiconductor laser that is easily affected by return light has the following problems. That is, in the above-mentioned dynamic single-mode laser, single-mode oscillation at the time of temperature change or modulation can be maintained, but when there is return light from the outside, there is a slight amount of side mode. Mode distribution noise is emphasized, which affects the performance of the application.

Further, in multimode using the high frequency superimposition method, when the frequency of noise required by the application extends over a wide band, the high frequency component of the superimposition current remains as optical noise. Further, in the method of avoiding the return light by the optical isolator, the applicable wavelength of the optical isolator is limited, and it becomes difficult to miniaturize the device. That is, the laser device becomes large and expensive.

An object of the present invention is to provide an inexpensive laser apparatus capable of reducing output fluctuation due to mode hopping and reducing the influence of return light.

In order to solve the above problems, the laser apparatus according to the present invention includes a laser light source, a condensing element that condenses the light of the laser light source, and an optical fiber that incidents light transmitted through the condensing element. A molding element for molding the emitted light of the optical fiber and a reflecting element having no wavelength selection characteristic in the wavelength region of the laser light source and reflecting a part of the light are provided, and the reflecting element is the laser light source. Of the reflected light, which is arranged between the light source and the light source, between the light source and the optical fiber, between the optical fiber and the molding element, and on the emission side of the molding element. A part of the light is incident on the laser light source or the light collecting element or the optical fiber or the molding element closest to the position of the reflecting element.

According to the present invention, a part of light is reflected by a reflecting element having no wavelength selection characteristic, and a part of the reflected light is reflected by a laser light source or a condensing element or an optical fiber or a molding element closest to the position of the reflecting element. The reflected light is re-incidented into the laser light source.

That is, in a semiconductor laser, stable multimode oscillation can be realized by adding a reflected wave to an incident wave. As a result, the output fluctuation due to mode hopping can be reduced, and the influence of the return light can be reduced.

It is a figure which shows the structure of the laser apparatus which concerns on Example 1 of this invention. It is a figure which shows the oscillation spectrum of a semiconductor laser. It is a figure which shows the oscillation spectrum which became unstable by the return light of the semiconductor laser of the laser apparatus which concerns on Example 2 of this invention. It is a figure which shows the oscillation spectrum of the semiconductor laser of the laser apparatus which concerns on Example 1 of this invention. It is a figure which shows the structure of the laser apparatus which concerns on Example 2 of this invention. It is a figure which shows the structure of the laser apparatus which concerns on Example 3 of this invention. It is a figure which shows the structure of the 1st modification of the laser apparatus which concerns on Example 1 of this invention. It is a figure which shows the structure of the 2nd modification of the laser apparatus which concerns on Example 1 of this invention.

Hereinafter, embodiments of the laser apparatus of the present invention will be described in detail with reference to the drawings.

(Example 1)
FIG. 1 is a diagram showing a configuration of a laser apparatus according to a first embodiment of the present invention according to the first embodiment of the present invention. This laser device includes a semiconductor laser 1, a coupling lens 2, an optical fiber 3, a collimating lens 4, a reflector 5, a coupling lens 6, and an optical fiber 7.

The semiconductor laser 1 corresponds to the laser light source of the present invention, has an arbitrary spectrum, and obtains a desired light output by a supply current.

The coupling lens 2 corresponds to the condensing element of the present invention and serves as a condensing lens, and is coupled to the optical fiber 3 by condensing the laser beam from the semiconductor laser 1. The coupling lens 2 is provided with a antireflection film and is arranged at a predetermined angle with respect to the optical axis. As a result, the return light to the semiconductor laser 1 can be reduced.

The optical fiber 3 propagates the laser beam from the coupling lens 2 and emits it to the collimating lens 4. The incident end face of the optical fiber 3 is obliquely polished, and is arranged so that the end face reflected light does not return to the semiconductor laser 1.

The collimating lens 4 corresponds to the molded element of the present invention, and outputs the laser beam from the optical fiber 3 as parallel light.

The reflecting plate 5 corresponds to the reflecting element of the present invention, does not have a wavelength selection characteristic in the wavelength region of the laser light source, reflects a part of the light transmitted through the collimating lens 4, and transmits the reflected light through the collimating lens 4. It is incident on the fiber 3. The reflector 5 transmits the remaining light and emits it to the coupling lens 6. The reflector 5 is formed by coating quartz glass or sapphire with a metal such as a dielectric or aluminum.

The coupling lens 6 serves as a condensing lens, and is coupled to the optical fiber 7 by condensing the laser light from the reflector 5. The coupling lens 6 is provided with a antireflection film and is arranged at a predetermined angle with respect to the optical axis. As a result, the return light to the semiconductor laser 1 can be reduced.

Next, the operation of the laser apparatus of the first embodiment configured in this way will be described. First, the laser light oscillated by the semiconductor laser 1 is focused by the coupling lens 2 and coupled to the optical fiber 3. The laser light from the optical fiber 3 is collimated by the collimating lens 4, and a part of the laser light is reflected by the reflector 5. At this time, the amount of reflected light is adjusted by adjusting the angle of the reflector 5 with respect to the optical axis.

The reflected laser light whose reflected light amount is adjusted is incident on the collimating lens 4, further recoupled to the optical fiber 3, passed through the coupled lens 2, and is incident on the semiconductor laser 1. Therefore, in the semiconductor laser 1, reflected light is added to the incident light, and laser oscillation is performed.

At this time, a monitor is connected to the output side of the optical fiber 7, and the oscillation spectrum is monitored by the monitor. Then, the oscillation spectrum as shown in FIG. 4 can be obtained by adjusting the amount of reflected light by adjusting the angle of the reflector. That is, stable multi-mode oscillation can be realized.

FIG. 2 shows the oscillation spectrum of the semiconductor laser. FIG. 2 shows a spectrum close to a vertical single mode in the continuous wave drive (CW) of the semiconductor laser 1. FIG. 3 shows an oscillation spectrum when an arbitrary return light is applied from this state. The oscillation spectrum becomes unstable due to arbitrary return light, and the spectrum changes to the state shown in FIGS. 2 and 3 or other states in time.

FIG. 4 shows the oscillation spectrum of the semiconductor laser of the laser apparatus of Example 1. FIG. 4 is an example showing an oscillation spectrum when the angle of the reflector 5 is adjusted. The oscillation is in the same longitudinal mode as in FIG. 3, but in FIG. 4, the number of clear longitudinal modes is larger than that in FIG. 3, and the mode interval is uniform. From the longitudinal mode interval, it can be seen that the laser of the first embodiment oscillates in the resonator mode of the semiconductor laser 1 itself. Since the external resonator mode composed of the reflector 5 does not compete with each other, a stable oscillation state can be maintained.

As described above, according to the laser apparatus of the first embodiment, a part of the light transmitted through the collimating lens 4 is reflected by the reflecting plate 5 having no wavelength selection characteristic, and a part of the reflected light is reflected at the position of the reflecting plate 5. The reflected light is re-entered into the semiconductor laser 1 because it is incident on the collimating lens 4 closest to.

That is, in the semiconductor laser 1, stable multimode oscillation can be realized by adding a reflected wave to the incident wave. As a result, the output fluctuation due to mode hopping can be reduced, and the influence of the return light can be reduced.

(Example 2)
FIG. 5 is a diagram showing a configuration of a laser device according to a second embodiment of the present invention. In FIG. 1, the reflector 5 is arranged on the exit side of the collimating lens 4, but in FIG. 5, the reflector 5 is arranged between the optical fiber 3 and the collimating lens 4.

As described above, in the case of the laser apparatus according to the second embodiment, the same effect as that of the laser apparatus according to the first embodiment can be obtained based on the principle of the multi-mode stable oscillation of the semiconductor laser described above.

(Example 3)
FIG. 6 is a diagram showing a configuration of a laser device according to a third embodiment of the present invention. The laser apparatus according to the third embodiment is an optical fiber output type laser apparatus having a multi-wavelength output. The laser device includes two semiconductor lasers 1a and 1b that output laser light having different wavelengths λa and λb, two coupled lenses 2a and 2b that collect the light of the semiconductor lasers 1a and 1b, and coupled lenses 2a and 2b. The two optical fibers 3a and 3b that incident the transmitted light, the two collimating lenses 4a and 4b that mold the emitted light of the optical fibers 3a and 3b, and the light that does not have wavelength selection characteristics in the wavelength region of the semiconductor laser. It is provided with two reflectors 5a and 5b that reflect a part of the light, a combiner 8a, and a combiner 8b that guides the light from the reflector 5b to the combiner 8a. The combiner element 8b is a reflection mirror or the like. The combiner element 8a is a half mirror or the like.

The combiner element 8a combines the light from the combiner element 8b and the light from the reflector 5a and guides them to the coupling lens 6. Since the configurations of the coupling lens 6 and the optical fiber 7 are the same as those shown in FIG. 1, the description thereof will be omitted.

In Example 3, the semiconductor laser, the coupling lens, the optical fiber, the collimating lens, and the reflector are each two, but three or more of each may be provided.

As described above, according to the laser apparatus according to the third embodiment, the vertical multi-mode can be realized and the multi-wavelength laser light can be combined with one optical fiber.

(First modification)
FIG. 7 is a diagram showing a configuration of a first modification of the laser apparatus according to the first embodiment of the present invention. In FIG. 1, the reflector 5 is arranged on the exit side of the collimating lens 4, but in FIG. 7, the reflector 5 is arranged between the coupling lens 2 and the optical fiber 3.

As described above, also in the case of the first modification, the same effect as that of the laser apparatus according to the first embodiment can be obtained based on the above-mentioned principle of multi-mode stable oscillation of the semiconductor laser.

(Second modification)
FIG. 8 is a diagram showing a configuration of a second modification of the laser apparatus according to the first embodiment of the present invention. In FIG. 1, the reflector 5 is arranged on the exit side of the collimating lens 4, but in FIG. 8, the reflector 5 is arranged between the semiconductor laser 1 and the coupling lens 2.

As described above, in the case of the laser apparatus according to the second modification, the same effect as that of the laser apparatus according to the first embodiment can be obtained based on the principle of the multi-mode stable oscillation of the semiconductor laser described above.

The laser apparatus of the present invention is not limited to the above-described first to third embodiments, the first modification, and the second modification. For example, Example 3 may be used in combination with the first modification. Further, for example, the second modification may be used in combination with the third embodiment.

The present invention can be applied to an optical fiber output type laser apparatus used in an application involving image processing.

1,1a Semiconductor laser 2,2a, 6 Coupling lens 3,7 Optical fiber 4 Collimating lens 5 Reflector 8a, 8b Combined element

Claims (1)

With a laser light source
A condensing element that condenses the light of the laser light source and
An optical fiber that incidents light that has passed through the condensing element,
A collimating lens that molds the emitted light of the optical fiber and
Wherein not have the wavelength selection characteristics in the wavelength region of the laser light source, Ru to reflect part of the light that is not wavelength selective, and a angle adjustable reflective elements,
The reflecting element may be located between the laser light source and the condensing element, between the condensing element and the optical fiber, between the optical fiber and the collimating lens, or on the exit side of the collimating lens. A part of the arranged and reflected light is incident on the laser light source or the condensing element or the optical fiber or the collimating lens closest to the position of the reflecting element, and the reflection is re-incidented on the laser light source. A laser device characterized in that the angle is adjusted so as to adjust the incident amount of a part of the emitted light.

Images