JPH11251625A - Method and device for connecting independently modulated laser diode array to optical fiber array - Google Patents

Abstract

PROBLEM TO BE SOLVED: To connect a laser diode array being independently modulated to a fiber array, by providing an array of wavelength plates for changing one part of the polarization direction of a radiated laser beam, and by superposing the radiation beam with the different polarization direction. SOLUTION: Supply is made by fiber bundles 40 and 42 for forming an array of light spots on an aligner 44. Each of laser subsystems 36 and 38 is provided with a number of independently modulated laser diode array packages where each laser is connected to an optical fiber. The laser subsystem 36 has a laser package 50 including a laser diode array with a number of light sources. Each light source is formed by one wide radiation source being driven as a whole or is formed as the sub-array of the radiation source. Light being radiated from the laser package 50 is polarized in an array direction, thus becoming the laser beam of P and S polarization passing through the clearance of a wavelength section 55.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates generally to the field of optical fibers. More particularly, the present invention relates to a method and apparatus for coupling a laser diode array to an optical fiber.

[0002]

BACKGROUND OF THE INVENTION Systems incorporating a laser light source optically coupled to an optical fiber are well known and are continually finding various applications. Such systems include fiber optic communication systems, fiber optic medical systems, laser copiers, laser printers, and facsimile machines.

[0003] For example, in the field of thermal transfer printing, it is known that dye or ink can be transferred from a donor medium to a receiving medium using the optical power of a laser. German Patent Application No. 69218090.7 and US Pat. No. 5,453,777 each describe examples of laser thermal transfer printers. In each case, the laser used is an individual diode laser packaged.

There are significant problems with the prior art systems described in German Patent Application No. 69218090.7 and US Pat. No. 5,453,777. That is, because of the high costs associated with packaging individual diodes, systems with packaged individual diodes are relatively costly.

[0005] One approach to solving the above problems is to replace the costly packaged individual diodes with a laser diode array having a large number of independently modulated lasers. The laser diode array has significantly reduced the package cost compared to individual diode lasers. An example of a system that employs this approach is “Multi-Beam
Optical System Using Len
slot Arrays in LaserMulti
-Beam Printer and Record
European Patent Application No. 954020 titled "r"
No. 3.2 (Kessler et al.). In that example, a multi-spot array is formed on a medium using one laser diode array and its associated lenslet array as described above.

However, European Patent Application No. 954202
There is also a problem with a system using a laser diode array as shown in No. 03.2. One such problem is that the number of independently modulated lasers that can be provided on a single laser diode substrate is limited. First, the number is limited by electrical reasons. If too many light sources are arranged, one light source may affect the radiation of an adjacent light source, i.e. interfere and cause interference.

[0007] The number is also limited by thermal reasons. Maximum length of commonly used array is 10-13mm
It is. Laser thermal transfer printing is based on the fact that the media used has no or small gain, and
Since it is necessary to expose at 0.500 J / cm ² , high power operation is performed. Typically, the power of each spot is 0.
5-1 W. Thus, each of the 10 1W spots provides 10 joules of energy per second to the media, and is thus capable of transferring dye over an area of approximately 10 cm ² . Due to the thermal load on the laser substrate, the number of lasers on one substrate is limited to approximately 10-20.

In printers, ten or more than twenty light sources are often desired as independently modulated light sources. This is because most printers use an external drum on which a medium is placed. Drums can be quite large, so generally the rotational speed is
It is limited to about 1000 RPM. For example, if the number of print spots is ten, only ten lines, ie, 10,000 lines per minute, would be printed at each rotation of the drum. For graphic arts, the usual resolution is 2,500 DPI. At this resolution and rotation speed of 1000 RPM, 10,000
The 0 line is applied to the area of 4 inches.
Therefore, the printer prints only the area of 4 inches per minute. This is too slow and cannot be used in many applications.

Another reason for the limited number of light sources available from an array relates to the lifetime and manufacturing yield of the array. If during operation one of the light sources is weakened or damaged, one print spot will be missed and the entire array will be unusable. The greater the number of light sources in the array, the greater the probability that one of the light sources will fail.

[0010] Yet another problem with the prior art is that the laser with the highest power is a multi-mode laser, and to achieve the required power levels, the laser is typically a multi-mode edge emitting laser.
laser). Typically,
One watt of power is obtained from an end face length of about 100 × 1 micron in the array parallel direction. A typical 1 watt laser light source may have one wide aperture or may be configured to be divided into multiple emission apertures. Using shorter light emitting end faces to achieve this power level increases the chance of surface damage due to high optical power density. The angular spread from such a light source in the array direction is typically about 14 full widths at the 1 / e ² level (ie, 13.5% of the peak value). Usually numerical aperture (NA)
Is used to measure the angular spread, and NA
Is the sine of half the full width value. Therefore, the NA of the laser in the array direction is sin (14/2) = sin (7) =
0.12. When the laser is imaged on the media and reduced by a factor of 5 to form a typical 20 micron spot, the NA in the media increases by this factor, ie, by a factor of 5, and the printing lens becomes It has an NA of 0.6 on a plane, which is a high value. This high NA value causes problems such as an increase in the cost of the printing lens and a reduction in the depth of focus associated with the high NA.

In view of the above, a number of developments have been made on techniques for coupling a laser light source to an optical fiber, but it is readily understood and appreciated that the prior art still has many disadvantages and disadvantages. Like.

[0012]

SUMMARY OF THE INVENTION It is an object of the present invention to overcome the disadvantages and disadvantages of the prior art by providing a method and apparatus for coupling an independently modulated laser diode array to a fiber optic array. It is to be.

[0013]

SUMMARY OF THE INVENTION An apparatus in accordance with the present disclosure comprises a plurality of independently modulated diode laser sources, an optical waveguide, for coupling each independently modulated diode laser source to an optical waveguide. A laser subsystem having a laser package composed of an array of waveguides as well as structures.

In an embodiment of the present invention, the connecting structure is
An array of wave plates for changing the polarization direction of a part of the emitted laser light is provided. Embodiments of the present invention also include a birefringent lens or Wollaston prism so that emitted beams having different polarization directions can overlap.

A method according to the present disclosure comprises the steps of generating laser light using an array of independently modulated diode lasers, changing the polarization direction of a portion of the generated laser light, A process in which the portion where the polarization direction of the laser light is changed can be superimposed, and a process in which the polarization direction of the generated laser light changes and the superposed portion is oriented in the optical waveguide.

It is an object of the present invention to reduce packaging costs associated with a laser light source incorporating the system.
Another object of the present invention is to reduce the manufacturing cost of a thermal transfer printing system by reducing the cost of printing optical equipment.

It is another object of the present invention to provide a thermal transfer printing system with increased depth of focus and improved resolution. Both the increased depth of focus and the increased resolution are at least partially provided by the reduced NA of the printing lens.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference is now made to the drawings, in particular to FIG.
The same reference numbers are used throughout the several figures,
Also, the components shown are not necessarily drawn to scale. FIG. 1 shows a high-level block diagram of a thermal transfer printer incorporating the present invention. In it, the printer 2 comprises a drum 4 mounted for rotation about a shaft 6 and driven by a motor 8. Drum 4
Is designed to support thermal transfer print media (not shown). Thermal transfer print media used with printers is, for example, the "Spacer BeadLa" granted March 10, 1993, assigned to the assignee.
ser For Dye-Donor Element
Used inLaser Induced The
It may be the medium disclosed in DE 3879136 entitled "rmal Dye Transfer", which is hereby incorporated by reference.

The print head 10 is movably supported adjacent to the drum 4 so as to slide along the main screw 12. The printhead 10 couples the optical fibers (line 2 in FIG. 1) into a laser diode array package 20 having a number of independently modulated lasers, each connected to an optical fiber.
4). For further details regarding the structure and operation of the printhead 10 and the array 14, see Assigned Assignee, Apr. 1996.
"Method and Appara" filed on March 27
tus forCoupling Light Emi
tted from a Multi-Mode La
ser Diode Array to a Multi
It is described in German Patent Application 196 17025.7, entitled "i-Mode Optical Fiber," which is hereby incorporated by reference.

Each independently modulated laser is independently modulated under the control of computer 22. When a voltage is thus selectively applied to an individual laser, the light rays emitted from that individual laser are coupled by a coupler 18 to individual optical fibers (e.g., into a coating labeled 24 in FIG. 1). And then transmitted over the length of the fiber until it reaches the end face of the fiber. Thereafter, the light is emitted from the optical fiber and strikes a print medium placed on the drum 4. Motor controller 26, control and timing logic 2 shown in FIG.
8, the D / A converter 30, the current driver 32, and the frame storage unit 34 are all conventional and well-known, and do not form a part of the present invention. I don't necessarily explain.

Referring now to FIG. 2, a preferred embodiment of the present invention is shown. The embodiment shown comprises two laser subsystems, generally designated by the reference numeral 36.
And 38 to form an array of light spots on an aligner 44.
2 are joined. The aligner 44 is imaged by the printing lens 46 and forms a print spot 48 on the media plane mounted on the rotating drum 4. Although two laser subsystems 36, 38 are shown in FIG. 2, it should be clearly understood that any number of laser subsystems may be used in embodiments of the present invention.

The contents of each laser subsystem can best be understood by referring to FIGS. 3 is a cross-sectional view taken along line 3-3 of FIG. 2, and FIG. 4 is a cross-sectional view taken along line 4-4 of FIG.

Each of the laser subsystems 36, 38 includes a laser diode array package having a number of independently modulated lasers, each laser coupled to an optical fiber. More specifically, the laser subsystem 36
Includes a laser package 50 that includes a laser diode array with multiple light sources 52, 54, as shown in FIGS. Each light source is driven by a separate current source (not shown). Each light source is formed from one broad source that is driven as a whole, as shown in FIG. 3, or is formed as a sub-array of sources. For further details on the laser package 50,
Multi-Beam Optical System, filed July 18, 1995, assigned to the assignee.
m Using Lenslet Arrays In
Laser Multi-BeamPrinters
and Recorders "in European Patent Application No. 95420203.2,
Reference is made here to a part of the present invention.

Still referring to FIG. 3, it can be seen that the light emitted from the laser package 50 is properly polarized in the polarization direction of the array. In FIG. 3, this polarization is the polarization labeled P. Light emitted from the laser package 50 is transmitted to the wave plate section 55.
(Best shown in FIGS. 2 and 5)
There, either the state is left unchanged (due to the gap between the waveplate sections) or the state changes to the polarization in the array parallel direction, ie the polarization marked S in FIG. In other words, for clarity, as shown in FIG. 5, the laser light passing through the gap (eg, gap 56) in waveplate section 55 remains P-polarized, but the waveplate in waveplate section 55 Laser light passing through a section portion (eg, portion 57) is S-polarized.

Referring again to FIG. 3, each light source 52, 54
Begin to determine the optical channel,
Further, although the light pattern is shown in detail only for the channels of the light source 52 of FIG. 3, for example, for all the channels including the channel of the light source 54, a partially orthogonal polarization (cro
It should be further understood that ss polarization is applied.

Thereafter, the light passes through the lens element and lens 58, and immediately after passing through the birefringent lens plate 64, the lens element and lens 58 image a small lens plane 60 on the input end face of the fiber 62.

The birefringent lens plate 64 can best be understood with reference to FIG. In FIG. 7, from left to right, the lenslet plane 60, wave plate section 54 (with P gap light indicated by reference numeral 66A and S wave plate section light indicated by reference numeral 66B), lens 58, and multiple lenses. A refractive lens plate 64 is shown. The optical axis of the crystal is labeled 68 in FIG. The S-polarized light (indicated by a line slightly thicker than the P-polarized light) does not change so as to jump into 66B ′,
The light propagates through the birefringent lens plate 64. In other words, it follows substantially the same path as without a birefringent lens. On the other hand, the P-polarized light moves from the “original” position (that is, the position 66A ′ in FIG. 7 and jumps in the absence of the birefringent lens plate 64) to the position 66B ′ by the birefringent lens plate 64. Thus, both the P-polarized beam and the S-polarized beam effectively overlap each other at the fiber entrance plane 70 shown in FIG. In actual construction and operation, the movement by the birefringent lens plate 64 is designed so that the superimposed S and P beams are approximately equal to the diameter of the fiber core.

As shown again in FIG. 5, the half-wave plate array has a crystal axis direction 59 parallel to the input and output end faces and forming an angle of 45 °, for example, crystal quartz (crysta).
One of ordinary skill in the art will appreciate that it can be formed from quartz or lithium niobate.

Referring to FIG. 6, another wave plate 72 that can be used in an embodiment of the present invention is shown. Another wave plate 72 comprises an array of quarter wave plates, where wave plate 74 changes linear polarization to clockwise circular polarization and wave plate 76 changes linear polarization to counterclockwise circular polarization. , The crystal axis direction alternates between ± 45 °. As will be appreciated by those skilled in the art, by adding another quarter-wave plate to affect all generated light, the device 7
2 will give the same result as device 54.

Referring again to FIG. 7, the overlap at region 66B 'allows the use of smaller core diameter fibers as compared to systems that do not utilize birefringent lenses. When imaged on media by such a fiber, the printing lens (element 46 in FIG. 2) is required to be further reduced, so that light can be coupled to a fiber with a smaller core diameter, As a result, there is an advantage that the NA on the medium plane is reduced.

Based on the foregoing, those skilled in the art will understand and appreciate that the present invention implements many configurations for coupling an array of independently modulated diode laser sources to an optical fiber. Embodiments of the present invention utilize means such as birefringent lenses to reduce the NA of the laser light, and thus improve resolution and depth of focus. Indeed, the fact that embodiments of the present invention utilize an independently modulated diode laser source reduces laser packaging costs and thus overall system costs.
Embodiments of the present invention are particularly suitable for use in thermal transfer printing systems.

Although the present invention has been described with respect to particular embodiments thereof, it is to be understood that alternatives, modifications,
Variations will be apparent to those skilled in the art. For example, each laser source in the array may be a large non-segmented radiation aperture, as opposed to a sub-array of lasers. Also, instead of using a birefringent lens between the fiber and the lens, a Wollaston prism is placed at the fiber end, thus entering the fiber as opposed to reducing the beam size at the fiber input end. The NA of light can be reduced. For purposes of illustration and support, the element 64 shown in FIGS. 3 and 4 may be considered a Wollaston prism in another embodiment of the present invention. Accordingly, the invention is intended to cover all such alternatives, modifications, and variations as fall within the spirit and scope of the appended claims.

[0033]

As described above, by using the structure for coupling a laser diode array and an optical fiber according to the present invention, it is possible to reduce the cost for packaging a laser, thereby reducing the cost of the entire system. By reducing the NA of the printing lens of the laser printer, a system with improved depth of focus and resolution can be provided.

[Brief description of the drawings]

FIG. 1 is a high-level block diagram of a thermal transfer printer incorporating the present invention.

FIG. 2 is a diagram showing an embodiment of the present invention.

FIG. 3 is a cross-sectional view of a first portion of the embodiment of FIG.

FIG. 4 is another cross-sectional view of the first portion of the embodiment of FIG.

FIG. 5 shows a first alternative embodiment of the second part of the embodiment of FIG. 2;

FIG. 6 shows another embodiment of the second part of the embodiment of FIG. 2;

FIG. 7 is a diagram illustrating an operation of a birefringent lens used for superimposing polarized light in the embodiment of the present invention.

[Explanation of symbols]

2 printers, 4 drums, 6 axes, 8 motors, 10
Print head, 12 main screws, 14 fiber optic array, 18 coupler, 20 laser diode array, 22 computer, 24 lines, 26 motor controller, 28 control and timing logic, 30 D / A converter, 32 current driver,
34 frame storage unit, 36 laser subsystem, 3
8 laser subsystem, 40 fiber bundle, 4
2 fiber bundle, 44 aligner, 46 print lens, 48 print spot, 50 laser package, 52 light source, 54 light source, 55 wavelength plate section, 56 wavelength plate gap, 57 wavelength plate section, 58 lens, 59 crystal axis direction, 60 small lens plane, 62 optical fiber, 64 birefringent lens plate, 66AP gap light, 66B S wave section light, 6
6A '"native" light position, 66B'"moved" light position, 68 crystal optical axis, 70 fiber entrance plane, 7
2 Another wave plate, 74 wave plate, 76 wave plate.

Claims (3)

[Claims] 1. A system comprising a laser subsystem, the laser subsystem comprising: a laser package including an array of independently modulated diode laser sources; an array of optical waveguides; Means for coupling the diode laser source to the optical waveguides of the array of optical waveguides. 2. A system comprising a laser subsystem, the laser subsystem comprising: a laser diode package array having a plurality of independently modulated lasers emitting laser light; and a plurality of laser diode package arrays each having an input end face. An optical fiber; and a laser / optical fiber coupler for coupling the radiated light from the plurality of independently modulated lasers to the input end face of the plurality of optical fibers. A wave plate section that changes the polarization of the alternating bands of the emitted laser light; and a birefringent medium that allows the alternating bands of the emitted laser light to overlap at the optical input end of the optical fiber. And a system comprising: 3. A method for using laser light to act on a thermal printing medium, comprising: generating a laser light using a plurality of independently modulated diode lasers; Changing the polarization direction of a part of the laser light, changing the polarization direction of the generated laser light to be superimposed, and changing the polarization direction of the generated laser light, and Orienting the superimposed portion to the optical waveguide.