JPS6298320A - Phased array semiconductor laser optical system - Google Patents

Abstract

PURPOSE:To obtain the spot of a diffraction limit on a recording medium by converging a beam from a phase-locked array semiconductor laser and forming a single lobe through an optical system composed of a wavelength plate and a polarization beam splitter in combination. CONSTITUTION:The beam emitted by the phase-locked array semiconductor is collimated by a coupling lens 2. The far field pattern of the beam from the laser 1 is separated into two lobes 3 and 3'. One beam 3 is reflected by a total reflecting mirror 4 to reach a splitter 5. At this time, the planes of polarization of the beams 3 and 3' both correspond to P polarization to the mirror 4 and splitter 5. The beam 3 is therefore, transmitted through the splitter 5. The beam 3', on the other hand, is transmitted through the half-wavelength plate 6 to become an S- polarized beam 7, which is reflected by the splitter 5 to have the same optical axis with the transmitted beam 3 in common, so that they are put together into one composite beam. The composite beam 10 obtained through the prism 9 is guided to a stop-down lens 11 and image-formed in a spot on the recording medium 13.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an optical system suitable only for condensing a beam of a phased array semiconductor laser and focusing it onto a medium.

[Background of the invention]

A phased array semiconductor laser is made by arranging approximately 10 semiconductor lasers monolithically in a line as shown in Figure 1.
By shortening the adjacent distance, the phases are coupled and all are attempted to oscillate coherently with each other. However, in the case of, for example, 10 light emitting points, there are 10 types of oscillation modes. Among these modes, the one that is most likely to occur is the 18o degree out of phase (out of please) as shown in Figure 2, that is, the double lobe mode with two peaks in the far field (F or Field). 3) is well known. If such double-lobed laser light is focused onto a recording medium, it will not be possible to obtain a diffraction-limited spot determined by the wavelength of the laser and the NA (numerical aperture) of the optical system, and an optical system with high resolution will not be possible. [Object of the Invention] An object of the present invention is to overcome the above-mentioned drawbacks and to provide an optical system capable of obtaining a diffraction-limited spot on a recording medium even when using a phased array semiconductor laser.

[Summary of the invention]

That is, the present invention provides out-of-phase
The beam from the phase-locked array semiconductor laser oscillating in the phase is focused, and an optical system that combines a wave plate and a polarizing beam splitter is used to focus the beam into a beam in the far field (F or Fjeld). The aim is to finally obtain a narrowed-down spot with a diffraction limit.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG. A beam diverging from a phase-locked array semiconductor laser 1 is received by a coupling lens 3 and is collimated. As mentioned above, the far field pattern of the beam from the phase-locked array semiconductor laser 1 is divided into two lobes, 3 and 3'. One of these beams 3
is reflected by total reflection mirror 4 and polarized beam splitter 5
It comes to. At this time, the polarization planes of the beams 3 and 3' are both P-polarized within the plane of the drawing, that is, with respect to the reflecting mirror 4 and the polarizing beam splitter 5.

Therefore, beam 3 will pass through the polarizing beam splitter 56, while beam 3' will pass through the 172 wave plate 6.
The beam passes through and becomes an S-polarized beam 7, which is reflected by the polarized beam splinter 5, shares the optical axis with the beam transmitted by the beam 3, and becomes one combined beam. In this embodiment, the reflecting mirror 4, the wavelength plate 6, and the polarizing beam splitter 5 are integrated in close contact with each other.

Since the beam from the polarized beam splinter 5 has an elliptical shape, the prism 9 is used to shape the beam into a circular shape. In the figure, there is only one prism, but a combination of two or more prisms may be used.

The combined beam 10 thus obtained is directed to a focusing lens 11 and is imaged as a spot on a recording medium 1; 3 such as an optical disk, a photosensitive drum for a laser printer, or a liquid crystal.

FIG. 5 shows a second embodiment of the invention. The method of combining the beams is exactly the same as in the first embodiment, except that a set of cylinder lenses 14 and 15 is used to shape the elliptical beam. When the ratio of the long and short axes of the elliptical beam is r, the cylinder lens 14.1
Let r be the ratio of the focal lengths of 5 and 5. What needs to be noted here is that in general, gain-guided phase-locked array semiconductor lasers experience not only phase shift but also phase curvature. This is called astigmatism, but according to the embodiment of Suihiro 2, the relative positions of the two cylinder lenses are set to be shifted by an amount that cancels out the astigmatism difference of the light source.

For example, the astigmatism can be corrected at the same time.

〔Effect of the invention〕

According to the present invention, phase array semiconductor lasers oscillating in a mode with a phase shift of 180' are synthesized in the far field into a single beam, which is then used as a diaphragm lens. A diffraction-limited spot determined by NA will be obtained. Furthermore, another aspect of the present invention is that the beams 3 and 3', which are out of phase with each other by 180°, have their polarization planes perpendicular to each other after being combined, so that no interference effect occurs and they are combined as a scalar sum of intensities. This is one effect.

If the present invention described above is applied to an optical disk recording optical system, a laser beam printer, an image scanner, an optical system for a liquid crystal display, etc., a faster and higher resolution optical system can be realized.

[Brief explanation of drawings]

Figure 1 is a conceptual diagram of a phase-locked array semiconductor laser.
FIG. 2 is a diagram showing the oscillation mode, FIG. 3 is a diagram showing the far field baton of the phase-locked array semiconductor laser, FIG. 4 is a plan view of the first embodiment of the optical system according to the present invention, and FIG. 5 is a diagram showing the oscillation mode. FIG. 2 is a plan view of a second embodiment of the present invention. 1... Phase-locked array semiconductor laser, 2...
Coupling lens, 3...beam, 3'...beam, 4.
... Total reflection mirror, 5 ... Polarizing beam splitter, 6
...1/2 wavelength plate, 7...S polarized beam, 8...
Combined beam, 9... Prism, 10... Shaped beam, 11... Stopping lens, 12... Spot, 1
3... Recording medium (optical disk), 14... Cylinder lens, 15... Cylinder lens, 16... Recording medium (photosensitive drum). 1 prisoner, 2 Nagiyang, 3 prisoners, 40 grass, 50 grass.

Claims (1)

[Claims] An optical system consisting of a phased array semiconductor laser, a condenser lens that receives light beams of different phases from the laser, and an imaging lens that narrows the light beam condensed by the condenser lens onto a medium. In the optical path of the optical system,
A reflective mirror, liquid length plate, and polarizing beam splitter are arranged.
A phased array semiconductor laser optical system characterized in that the light beams having different phases are combined into one light beam.