JPH0593880A - Multiple light source unit - Google Patents

Abstract

PURPOSE:To provide the multiple light source unit for laser light which eliminates the problem point of conventional technology that the cost increases because the number of the constituent elements of a collimator lens is large. CONSTITUTION:The device consisting of plural light source parts 1 which emit laser light independently, fibers 2 as means which are connected to the light source parts 1 and carry the laser light, a light convergence optical system 3 which converges and projects plural laser beams, and an image formation optical system 5 which images the laser beams projected by the light convergence optical device on a recording medium 6 is provided with single-mode fibers 2 as the laser light carrying means, and at least the light convergence optical system is provided with an aspherical single lens.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light source for a recording apparatus, an inspection apparatus, etc., which uses a light source section for emitting a plurality of laser beams.

[0002]

2. Description of the Related Art Conventionally, a collimator lens that simultaneously collects a plurality of laser beams is constructed by combining two or three spherical lenses as shown in FIG. Is kept small.

[0003]

The above-mentioned prior art has the following problems. When a plurality of laser beams are to be condensed by a collimator lens, a good spot shape cannot be obtained on the recording medium unless the wavefront aberration in the condensing optical system is set to λ / 4 or less.

In particular, when the divergence angle of the emitted beam is as large as 30 ° or more (full angle at half maximum) like a semiconductor laser, two or more combined spherical lenses must be adopted in order to reduce the wavefront aberration λ / 4 or less. did not become. If the condensing optical system is composed of a plurality of spherical lenses, the transmission efficiency of the amount of light is naturally lowered, which causes an increase in cost due to an increase in the number of lenses.

It is an object of the present invention to provide a multiple light source device for laser light, which solves the problem in the prior art that the number of collimating lenses is large and the cost is high.

[0006]

In order to condense a plurality of laser beams by the same condensing optical system due to optical aberration, a plurality of light emitting light source parts do not pass through the center of the optical axis, so that the number of lenses is increased. It is necessary to suppress spherical aberration and coma aberration to a low level. However, if the emission angle is smaller than that of a semiconductor laser like a single mode optical fiber, the wavefront aberration required for a condenser lens is alleviated. In other words, in order to efficiently collect the beams emitted from multiple semiconductor lasers, it was necessary to combine many lenses and suppress the wavefront aberration to a low level. Wave element aberration λ / 4 with a single lens configuration by adopting an element and an aspherical lens
It became possible to collect light with the following.

As the light source conversion element, a relay lens may be used, but a single mode optical fiber is desired due to its compactness and freedom of arrangement of a plurality of light sources. By the way, the core diameter is 6
When a laser beam of 780 nm with a single mode fiber of 780 μm is incident, the emission angle can be exchanged to 10 ° or less. As the condensing lens, in order to suppress the wavefront aberration to λ / 4, one aspherical lens or a combination of an aspherical lens and a spherical lens can achieve this object.

[0008]

[Function] Lens coupling or direct incidence from a plurality of semiconductor laser light sources to a single mode fiber,
It is emitted from the other end of the fiber as a secondary light source while maintaining the shape of the Gaussian beam. At this time, the other end of the fiber is precisely arranged according to the light source arrangement determined by the magnification of the image forming optical system.

Gaussian beams are emitted from a plurality of arranged fiber emission ends, respectively, and a plurality of collimated light beams are formed by a condenser lens system formed of an aspherical surface. The image is recorded by forming an image on the medium.

[0010]

EXAMPLE An example of the present invention using four semiconductor lasers having a light source wavelength of 780 nm as a plurality of light sources will be described with reference to FIG. In the figure, 1 is a semiconductor laser, 2 is a single mode fiber, 3 is a condenser lens, 4 is a deflector, 5 is an imaging lens, and 6 is a recording medium.

Laser light emitted from the semiconductor laser is directly incident on the end face of the fiber. The optical fiber is 78
In the case of 0 nm, a single mode fiber with a core diameter of 6 μm and a clutch diameter of 125 μm was adopted. The optical coupling from the semiconductor laser to the single mode fiber is precisely aligned with an accuracy of 1 μm or less, and the light transmission efficiency is 30% or more. Four fiber emitting ends are arranged with a main scanning pitch of 150 μm and a sub-scanning pitch of 7 μm, and a Gaussmann beam is emitted. The emission angle is 9.5 ° for a 6 μm core. A condensing optical element composed of one aspherical lens satisfying a focal length of 60 mm and an aperture F number of 5,
It is possible to collect the outgoing beam from the end of the fiber bar and emit it as a collimated beam. While the collimated beams are scanned in the main scanning direction by the deflector, a plurality of beams can be simultaneously recorded on the recording medium by the imaging lens.

When four fibers are arranged with a fiber emitting portion and a pitch of 150 μm, the ends of the fiber emit light at points 225 μm away from the center of the optical axis, but a biconvex spherical single lens (R ₁ = 35, R ₂ = 210, N = 1.
4855) has a wavefront aberration of 5λ, resulting in a lens system that cannot form an image with a predetermined beam diameter (FIG. 2). On the other hand, a biconvex aspherical lens (R ₁ = 3
3.6, aspherical surface coefficient is ε = 0.51, R ₂ = −211.
If 0 aspherical surface coefficient ε = −2.0, N = 1.4855) is adopted, the wavefront aberration is λ / 20, and the lens system can form an image with a predetermined beam diameter. (Figure 3). Usually wavefront aberration λ
If it is / 4 or less, it can be treated as an ideal Gaussian beam. A three-dimensional display of the point spread function of this aspherical mens is shown in FIG. 4, and a good Gaussian beam is obtained. Also shown in FIG. Compared with the conventional condenser lens composed of three spherical lenses,
The wavefront aberration of the aspherical single lens is within a range that practically causes no problems. In this way, by adopting the aspherical lens in the condensing optical system from the plurality of fiber bars, the number of constituent elements can be reduced.

An example of specifications of the aspherical lens used in the present invention shown in FIG. 7 is shown.

[0014]

In the recording apparatus having a structure in which a plurality of laser beams are simultaneously condensed, the condensing optical system plays an important role of condensing a plurality of light sources at the same time and making them incident on the imaging lens. The multiple light source device according to the present invention includes a plurality of light source units that independently emit laser light, a means for connecting each of the light source units to convey the laser light, and a light condensing unit that condenses and projects the plurality of laser lights. In an apparatus comprising an optical system and an image forming optical system for forming an image of a plurality of laser beams projected from the same condensing optical system on a recording medium, a single mode fiber bar is provided as the laser beam conveying means, and at least a collecting unit is provided. By providing the aspherical single lens in the optical optical system, the following effects are obtained.

In the prior art, in order to suppress the wavefront aberration to λ / 4 or less when the light is focused from the light source off the optical axis, it is necessary to have two or more spherical combination lenses.
However, according to the present invention, by adopting the aspherical lens, the wavefront aberration of the off-axis light source can be suppressed to λ / 4 or less even with a single lens. Therefore, the transmission efficiency of the amount of light can be improved and the cost can be reduced.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

FIG. 2 is a diagram showing off-axis wavefront aberration in a spherical single lens.

FIG. 3 is a diagram showing off-axis wavefront aberration of an aspherical single lens.

FIG. 4 is a diagram showing a point spread function of an aspherical single lens.

FIG. 5 is a diagram showing off-axis wavefront aberration in a set of three lenses.

FIG. 6 is a diagram showing specifications of a conventional spherical lens.

FIG. 7 is a diagram showing specifications of an aspherical lens used in the present invention.

[Explanation of symbols]

 1 semiconductor laser 2 single mode fiber 3 condenser lens 4 deflector 5 imaging lens 6 recording medium

Claims (1)

[Claims] 1. A plurality of light source units that independently emit laser light, a means that is connected to each of the light source units and conveys the laser light, and a condensing optical system that condenses and projects the plurality of laser lights. An image forming optical system for forming an image of a plurality of laser beams projected from the same condensing optical system on a recording medium, a single mode fiber is provided as the laser beam conveying means, and at least a condensing optical system is provided. A plurality of light source devices, characterized in that an aspherical single lens is provided in the.