JPS61124187A - Semiconductor laser oscillating wave length controller - Google Patents

Abstract

PURPOSE:To suppress the disorder of a wave surface of a diffracted light and the loss of light quantity by using zero order light passage of a hologram for feedback, thereby using the primary passage light as directly diffracted light. CONSTITUTION:When zero order passage light is used for feedback entirely contrary to the conventional case and the primary passing light is used as scanning diffracted light in a hologram 18 which is also used as scanning hologram scanner, the primary passing light 24 becomes directly the scanning diffracted light, thereby removing the influence of the disorder of the system light or the loss of the light quantity due to the disposition of the conventional hologram for feedback. When the zero order passing light is used for feedback, the hologram for feedback an the hologram scanner for scanning can be commonly used to suppress the disorder and the loss of the light quantity. A diffraction grating 20 is used for feedback, but a pitch (d) and a set angle theta are readily decided as compared with the set of pinhole as advantages.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Technical Field of the Invention The present invention relates to a semiconductor laser device, and particularly to an oscillation wavelength control device thereof.

(2) Background of the technology Semiconductor lasers have a lower output than gas lasers, etc., but they can be made smaller and cheaper, and they can be directly modulated, so they are used for optical fiber communication.
It is widely used in DADs, VDs (video discs), optical scanning devices, optical measurement devices, etc., and is attracting attention.

(3) Conventional technology and problems Conventional semiconductor lasers (hereinafter abbreviated as LD).

There is a problem in that a phenomenon called mode hopping occurs in which the oscillation wavelength shifts depending on the flowing current, temperature, etc.

A first conventional example for eliminating such problems is shown in FIG. In this system, the monitor light 2 from the LDI is made into parallel light by a lens 3, and the parallel light is made incident on a reflection type diffraction grating (hereinafter simply referred to as a diffraction grating) 4. In this state, by adjusting the pitch and direction of the diffraction grating 4, the monitor light incident on the second diffraction grating 4 has a specific wavelength λ.
Only the zero diffracted light is reflected as parallel light in the opposite direction of the incident light and returns to the LDI. Thereby, the oscillation wavelength of the system light 6 from the LDI via the lens 5 can be stabilized at λ0. However, although this method requires monitor light 2 from the LDI, it is difficult to guide the monitor light to the outside of the LD in a normal LD, and the above conventional example cannot be directly applied.

In addition, Fig. 3 shows another conventional example (Japanese Patent Laid-Open No. 58-60590
). In this method, the output light 9 from the LD 7 is made incident on the hologram 10 via the lens 8, without using the monitor light as shown in FIG. Then, the hologram 10 is adjusted so that the primary transmitted light 11 from the hologram 10 has convergence.

The light is made incident on a mirror 13 through a pinhole 12. At this time, by setting the pinhole 12 so that only the diffracted light of a specific wavelength λ0 is transmitted, the mirror 1
The diffracted light of the specific wavelength λ0 reflected by 3 becomes the hologram 1 again.
It returns to LD7 via 0. And hologram 10
O from? ! R, by using transmitted light as the system light 14.

Its wavelength is stabilized at λ0. However, when this method is applied to an optical scanning device or the like, the system light 14, which is the zero-order transmitted light of the hologram 10, is further incident on a hologram scanner for scanning. Therefore, since the system light 10 is transmitted through the hologram 14, the wavefront of the system light 14 may be disturbed when it enters the hologram scanner for secondary scanning, and the wavefront of the system light 14 may be disturbed when it enters the hologram scanner for secondary scanning. There is also a problem in that the loss of light amount due to Furthermore, there was a problem in that the setting of the pinhole 11 for determining the wavelength λ0 was difficult.

(4) Purpose of the invention In order to eliminate the above problems, the present invention aims to
By using the secondary transmitted light for feedback to the LD and the primary transmitted light as direct scanning light.

It is an object of the present invention to provide a semiconductor laser oscillation wavelength control device that can supply stable waveforms, wavefronts, and light intensity outputs.

(5) Structure of the Invention In order to achieve the above object, the present invention provides an optical device using a semiconductor laser as a light source, which includes a hologram in the optical path of light emitted from the light source, and an optical path of zero-order transmitted light from the hologram. There is provided a semiconductor laser oscillation wavelength control device characterized in that it has a feedback means for returning only light of a specific wavelength to the semiconductor laser.

(6) Examples of the invention Hereinafter, one embodiment of the present invention will be described in detail.

FIG. 1 is a basic configuration diagram of a semiconductor laser oscillation control device according to the present invention. Semiconductor laser (hereinafter referred to as

The output light from the LD (abbreviated as LD) 15 is converted into parallel output light 17 via a lens 16 and enters a hologram 18 .

Zero-order transmitted light 19 from the hologram 18 enters a reflection type diffraction grating (hereinafter simply referred to as a diffraction grating) 20. The reflected diffracted light 23 from the diffraction grating 20 returns to the LDI 5 via the hologram 18 and the lens 16. Also hologram 1
The first-order transmitted light 24 from 8 is directly used as diffracted light.

In the semiconductor laser oscillation control device configured as described above, the pitch of the first diffraction grating 20 is d, and the optical axis 2 of the zero-order transmitted light 19 is
2 and the normal 23 of the diffraction grating 20 is θ, and the wavelength to be fixed is λ0, the setting angle θ can be determined as θ-5in-' (λo/2d) (A). Thereby, the wavelength of the primary transmitted light 24 can be fixed to λ0.

This primary transmitted light 24 is used, for example, as diffracted light for direct scanning. That is, whereas the conventional example shown in FIG. 3 uses the first-order transmitted light for feedback and the zero-order transmitted light as system light, a hologram scanner for scanning is placed at the subsequent stage, whereas the embodiment shown in FIG. Completely opposite to the case in FIG. 3, the zero-order transmitted light is used for feedback. Since the primary transmitted light is originally used as diffracted light for scanning, if the hologram 18 is also used as a hologram scanner for scanning, the primary transmitted light 24 becomes diffracted light for direct scanning, and the third transmitted light 24 becomes diffracted light for direct scanning.
It is possible to eliminate effects such as disturbance of the wavefront of the system light 14 and loss of light amount due to the arrangement of the feedback hologram 10 as in the conventional example shown in the figure. As described above, according to the present invention, by using zero-order transmitted light for feedback, a hologram for feedback and a hologram scanner for scanning can be used in common, and wave front disturbance and loss of light amount can be suppressed. Can be done. Although the diffraction grating 20 is used for feedback, determining the pitch d and setting angle θ for setting the wavelength λ0 based on equation (A) is easier than setting the pinhole 11 in FIG. There is an advantage.

Next, FIG. 4 is a block diagram of an optical scanning device using a hologram scanner using the present invention. Parallel output light 26 from the LD optical device 25 enters a hologram scanner 27 . Zero-order transmitted light 29 from the hologram scanner 27 enters the diffraction grating 28, and its reflected diffracted light 30 returns to the LD optical device 25 via the hologram scanner 27. Further, as the hologram scanner 27 rotates, its primary transmitted light is scanned as 32-1.32-2.32-3. An optical scanning device having such a configuration is similar to the basic embodiment of the present invention shown in FIG. 1 in which the hologram 18 is replaced with a concrete hologram scanner 27, and can obtain exactly the same effect. In other words, hologram scanner 2
As 7 rotates, its primary transmitted light becomes 32-1.3
It is scanned as 2-2°32-3 and used as a diffracted light for direct scanning. In this case, the nine diffraction gratings 28 are set based on the equation (A) as in the case of FIG.

Further, here, the reflected diffracted light 30 of the specific wavelength λ0 from the diffraction grating 28 is first-order transmitted light from the diffraction grating 28 (the meaning is different from the zero-order transmitted light from the hologram scanner),
The 0th order diffracted light from the diffraction grating 28 containing other components becomes specularly reflected light as shown in FIG.
Since it is not fed back to 5, it does not become a factor of instability of the LD. Note that the optical scanning device has applications such as a laser printer.

Note that in the above embodiments, when the amount of reflected diffraction light is weak, the ability to fix the wavelength becomes weak. In such cases, especially when the hologram scanner is of a surface relief type, it is possible to increase the light intensity of the 0th-order transmitted light by changing the incident polarization characteristics to the hologram scanner. (See Figure 11).

In FIG. 5, in the optical scanning device of FIG. 4, the output light from the LD optical device is not parallel output light 26.

This is an example in which the output light is a convergent output light 26'. In this case, a concave lens 33 is placed in the optical path of the zero-order transmitted light between the hologram scanner 27 and the diffraction grating 28. As a result, the zero-order transmitted light from the hologram scanner 27 is converted into parallel zero-order transmitted light 29'. At this time, the reflected diffraction light 301 from the 9-diffraction grating 28 enters the concave lens 33 again as parallel light, and returns to the LD following an optical path opposite to the convergent output light 26'. In this case, the primary transmitted light 3
2, the hologram scanner 27 is set to produce convergent light.

! ! Similarly, FIG. 86 shows an example in which the output light from the LD optical device is a diverging output light 26''. In this case, a convex lens 34 is arranged as shown in the figure. As a result, the hologram scanner 27 The zero-order transmitted light of the glass is converted into parallel zero-order transmitted light 29''. Then, the reflected diffracted light 30'' from the diffraction grating 28 enters the convex lens again as parallel light and returns to the LD following an optical path opposite to the two divergent output beams 26''.

In this case as well, the hologram scanner 27 is set so that the primary transmitted light 32 becomes convergent light.

Similar to FIG. 5, FIG. 7 shows an embodiment in which no concave lens is used in the case where the output light from the LD optical device is convergent output light 26'. At this time, as shown in FIG.
Then, the focus is set at point B, and the convergent spherical wave 41 is focused at point 0, and the pinch is adjusted so that their focal lengths are the same distance 1i111f. As shown in FIG. 7, the arrangement is such that the zero-order transmitted light 35 is focused at the zero point and the distance between the diffraction grating 37 and the zero point is the focal length f. As a result, the reflected diffraction light 36 having the wavelength λ0 can completely follow the optical path opposite to the convergent output light 26' and be returned to the LD.

FIG. 8 shows an example in which a convex lens is not used when the output light from the LD optical device is a diverging output light 26'' as in FIG. 6. In this case, one diffraction grating 37 is explained in FIG. 9 above. As shown in FIG.
and the focal length f. As a result, the zero-order transmitted light 38 that has entered the diffraction grating 37 is completely converted into a divergent output light 26'' as reflected diffracted light 39 with a wavelength λ0.
The light can be returned to the LD by following the optical path opposite to the above.

Finally, FIG. 10 shows an embodiment in which the hologram scanner of the optical scanning device in FIG. 4 is replaced with a surface relief type hologram scanner 43. Also, in the surface relief type hologram scanner 43.

As shown in FIG. 11, the diffraction efficiency η of the first-order transmitted light 52 and the zero-order transmitted light 53 changes depending on the polarization characteristics of the incident light. In a hologram scanner, the scanning light is 1
It is desirable that the diffraction efficiency η of the next transmitted light 51 (FIG. 10) be high. Therefore, the output light 42 of the LD incident on the nine-surface relief type hologram scanner 43 has the same S polarization characteristic as the grating direction of the hologram. At this time, the zero-order transmitted light 44 passes through the quarter-wave plate 45 and becomes circularly polarized zero-order transmitted light 46 and enters the second diffraction grating 47 . Then, the reflected diffraction light 48 is reflected again by the quarter wavelength plate 4.
5, it becomes P-polarized reflected diffracted light 49 and input into the surface relief type hologram scanner 43 again. Here, from FIG. 11, when the incident light to the hologram scanner is P-polarized, the diffraction efficiency of the 0th-order transmitted light is maximum, so most of the P-polarized reflected diffraction light 49 passes through the surface relief type hologram scanner, The feedback light 50 is substantially fed back to the LD, so that the oscillation wavelength of the primary transmitted light 51 can be controlled more strongly.

Although the present embodiment has been described above using a hologram scanner, it goes without saying that the present invention can also be applied to optical big amplifiers such as DADs and VDs, optical fiber communications, and the like.

(7) Effects of the Invention According to the present invention, since the 0th-order transmitted light of the hologram is used for feedback, the 1st-order transmitted light can be directly used as diffracted light, and a hologram exclusively for return can be newly created. Since this is not necessary, disturbance of the wavefront of the single diffracted light and loss of light amount can be suppressed. Furthermore, if a diffraction grating is used as the feedback means, the oscillation wavelength of the LD can be controlled more easily than in the past.

Furthermore, when a surface relief type hologram scanner is used, feedback efficiency can be improved by arranging a quarter wavelength plate between the hologram scanner and the feedback means.

[Brief explanation of the drawing]

FIG. 1 is a basic configuration diagram of a semiconductor laser oscillation control device according to the present invention. FIG. 2 is a configuration diagram of an example of a conventional semiconductor laser oscillation control device. FIG. 3 is a configuration diagram of another example of a conventional semiconductor laser oscillation control device. FIG. 4 is a configuration diagram of an embodiment of an optical scanning device using the present invention. FIG. 5 is a configuration diagram of a second embodiment of an optical scanning device using the present invention. FIG. 6 is a configuration diagram of a third embodiment of an optical scanning device using the present invention. FIG. 7 is a configuration diagram of a fourth embodiment of an optical scanning device using the present invention. FIG. 8 is a configuration diagram of a fifth embodiment of an optical scanning device using the present invention. FIG. 9 is an explanatory diagram of the embodiment of FIGS. 7 and 8. FIG. 10 is a configuration diagram of an embodiment in which the present invention is applied to an optical scanning device having a surface relief type hologram scanner. FIG. 11 is a diagram showing the relationship between the incident polarization characteristics and the diffraction efficiency of the surface relief type hologram scanner for explaining the embodiment of FIG. 10. 15... Semiconductor laser. 16...Lens. 18...Hologram. 20.2B, 37.47... Diffraction grating. 25... Semiconductor laser optical device. 27...Hologram scanner. 33...Concave lens. 34...Convex lens. 43...Surface relief type hologram scanner. Figure 1-C4 I-S Figure 2 Figure 3 Figure 6 Figure 7 Figure 8 Figure 9

Claims (2)

[Claims] (1) In an optical device using a semiconductor laser as a light source, a hologram provided in the optical path of light emitted from the light source;
A semiconductor laser oscillation wavelength control device comprising a feedback means for returning only light of a specific wavelength to the semiconductor laser in the optical path of zero-order transmitted light from the hologram. (2) The hologram is of a surface relief type, and includes a quarter wavelength plate in the optical path of the zero-order transmitted light between the hologram and the feedback means. The semiconductor laser oscillation wavelength control device according to item 1.