JPH09230280A - Method to couple laser diode to multiplex channel modulator and multiplex channel modulator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multiplex channel laser diode system, which is difficult to be adversely affected by back reflection, by image forming each emitter on a linear light valve and stacking up all these images regardless of any individual emitter. SOLUTION: A mirror 13 reflects the tilted portion of the one tip of a high intensity profile 12 to a second mirror 14. The mirror 14 stacks up the portion reflected from the mirror 13 to the tilt profile of the other tip of illumination profile in the manner shown in a graph 15. The graph 15 indicates the intensity profile of the light beams immediately after the emission from the mirror 14. By adjusting the angle of the mirror 14 so that the tilt portion of the intensity profile is overlapped on a light valve 6 and a profile 16, which has an approximately rectangular shape on the valve 6, is obtained. This method makes the spread angle of the light beams slightly larger. However, the degree of the utilization of the laser power is considerably increased.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to multi-channel modulators as an alternative to individually addressable (individually addressable) multi-element laser diodes and methods for coupling laser diodes to multi-channel modulators. And equipment.

[0002]

2. Description of the Related Art In order to increase the emissivity and data rate obtained from a laser diode (hereinafter, also simply referred to as "diode"), a multi-element type individually addressable laser diode array (array) is used. is there. The laser diode arrays are, for example, diffraction-limited (diffraction limited resolution) single-mode type, or wide-emitter arrays. The wide emitter is diffraction limited on one side, called the "narrow" dimension, and acts as a large area emission source on the other side, called the "wide" dimension.

[0003]

The advantages of wide emitters, also called "striped" laser diodes, are:
That is, extremely high output power (laser power) can be obtained. These devices (laser diode)
Has a high power, and is manufactured by bonding its positive (positive) side surface to a heat sink (radiator). This is because the heat transfer coefficient of the device substrate is much lower than that of the heat sink. However, the connection to the individual diodes must also be brought out from the positive side, so a compromise must be found between the heat sink (heat dissipation) requirements and the interconnection requirements between the diodes.

Another problem with multi-element, individually addressable diodes is reliability. Since each diode is focused on a separate modulator cell and then on the photosensitive member or sensor, the presence of a defect in any one of a large number of elements will cause the entire device to be defective. . Prior art attempts to solve these problems by coupling a wide laser diode to a multi-channel modulator require a high degree of collimation of the light beam in both axes, and thus have been quite successful. Couldn't fit. This is because the wide laser diode can be collimated only in one axis. As an example of the prior art, U.S. Pat. No. 4,577,932 teaches the use of a wide laser diode and an acousto-optic modulator whose configuration is compared to operation in pulsed mode. Limited to diodes with narrow width.

Accordingly, it is an object of the present invention to use a wide laser diode in conjunction with an electro-optical multichannel modulator to provide the equivalent of a multi-element, individually addressable laser diode, and to such a device. To get the equivalent without any associated restrictions.

Another object of the present invention is to provide multi-element, individually addressable by eliminating the trade-off between heat sink requirements and interconnection requirements between diodes as described above, and eliminating the effects of data dependent thermal cycling. It is to provide a device with higher reliability than a simple laser diode. The reliability of this device is that near-field radiation from the diode is not imaged along the long dimension of the diode,
It is further enhanced by having tolerance to local defects and malfunctions.

Yet another object of the present invention is to provide a multi-channel laser diode system that is less susceptible to back reflection (reflection from the material on the exposed side) as compared to a laser diode having a narrow emitter. .

[0008]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides a wide emission surface (having a wide emission surface or a light emitting surface) composed of multiple emitters operating in parallel with a linear light valve. A method and apparatus for coupling a laser diode to a linear light valve is provided. According to the method of the present invention, each of the emitters is imaged onto a linear light valve, and any individual emitter is imaged of all of its emitters to increase their insensitivity to the defects present (immunity). Polymerize.
(Here, "imaging the emitter onto the light valve" means forming an image of the emitter (light emitted from the emitter) as an image onto the light valve, that is, forming an image.)

The imaging of the emitters is preferably performed by using an array of lenslets placed in close proximity to the laser diode (ie the array of emitters). The lenslet array may have a pitch that is slightly smaller than the pitch of the emitters of the emitter array. The focal length of the lenslet array is equal to the distance from each emitter to the part where the light beams from each emitter (hereinafter also simply referred to as “beam” or “light”) start to overlap (intersect) with each other. be able to. By using a lenslet array, it is possible to obtain a significantly higher number of channels than is possible by producing a multi-element individually addressed laser diode.

In some cases, the method of the present invention includes means for superimposing a portion of the combined image of each emitter onto the other portion of the combined image to enhance the illumination uniformity of the light valve. It is advantageous to include.

According to another aspect of the present invention, there is provided a multi-channel modulator including an incident light modulating light valve for modulating light from a wide emitting surface laser diode comprising multiple emitters. The light valve modulates light incident on the light valve in response to input data introduced at its control input and focuses the modulated light from the light valve onto a heat-sensitive or photosensitive member. To do.

By polymerizing the light from each emitter as described above, even if one emitter malfunctions, it is not necessary to discard the entire laser diode, and the loss of the malfunctioning emitter is lost. The power output from multiple emitters may be increased slightly to compensate for

The light from the laser diode is directed in a first dimension such that light from each lenslet of the lenslet array is superimposed on the light valve with light from each of the other lenslets of the lenslet array. The elongated cylindrical microlenses can be used to collimate and focus light from the lenslet array in a second dimension perpendicular to the first dimension.

The laser diode has a plurality of emitters connected in parallel relationship, the lenslet array has one emitter for each lenslet of the array, and each lenslet is the elongated lens. Cylindrical surface can be a cylindrical surface concentric with the axis of the microlens. The pitch of each lenslet may be slightly smaller than the pitch of each emitter of the laser diode.

The light forming the sloped portion on one side of the light intensity profile (hereinafter also simply referred to as the "intensity profile" or "illumination profile") is superposed on the light forming the sloped portion on the other side of the intensity profile. The light valve is provided with mirror means for reflecting the light from the focusing means so as to set a substantially rectangular intensity profile. By arranging to utilize the inclined portion at the end of the intensity profile, the usable portion of the output light from the diode can be increased, and therefore, the utilization efficiency of laser power can be significantly increased.

To achieve the above object, all the elements in the laser diode are connected in parallel to form a single laser diode. Image this laser diode on a multi-channel electron-optical modulator,
The modulator subdivides the image of the diode into multiple independent channels.

To increase the coupling efficiency between the laser diode and the modulator, a cylindrical surface lens is used on the "narrow" dimension side and a lens array is used on the "wide" dimension side to improve the illumination or intensity profile. A folding mirror is used to form a rectangular shape. With these means,
The coupling efficiency between the laser diode and the modulator can be improved to close to 90%.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Referring to FIG. 1, a broad emitting surface laser diode 1 for emitting an intense laser is
It emits a light beam 2, which is collimated in the vertical dimension by a microlens 3 in the form of an elongated cylinder. In the preferred embodiment, the lens 3 is made up of US Pat.
A pultruded aspherical lens as described in No. 80,706. The second microlens 4 is a linear array (linear array) of cylindrical lenslets 4'matched to the multiple emitters 1'of the laser diode 1, respectively.
It is. The light from each small lens 4'is the cylindrical surface lens 5
Are collimated by and are imaged or imaged as lines of light on the linear light valve 6.

If a high intensity laser is used, the linear light valve 6 is a PLZT device and its PLZ
When a voltage is applied to the electrode of the T material, the polarization state of light is rotated. The polarization prism 7 has a function of horizontally polarized light (that is, PL
Light transmitted through the inactive PLZT cell of the ZT linear array 6)
And the light 11 whose polarization state has been changed by passing through the active PLZT cell is reflected. The image 10 on the thermosensitive or photosensitive member 9 is the PLZT of the light valve 6.
A voltage is applied to the electrodes of the cell and has non-illuminated portions corresponding to many portions. The light valve 6 does not form part of the present invention and will not be described further, however, the present invention is not limited to the deformable magneto-optical mirror device or any type of light such as a ferroelectric liquid crystal. A valve can be used. Such linear light valves are available from Cemetex (Trance, California, USA), Motorola (Albuquerque, New Mexico, USA), DisplayTech (Boulder, Colorado, USA), Texas Instruments (Texas, USA). Sold by companies such as the state of Dallas. The imaging lens 8 focuses the light valve 6 on the heat-sensitive or photosensitive member 9 to form an image 10.
To create. The image 10 on the member 9 is the linear light valve 6
Is a reduced image of.

In order to make the laser diode 1 insensitive to local defects, the focal length of the lenslet 4'of the microlens 4 which images each emitter 1'of the laser diode 1 over the full width of the light valve 6. And pitch. The number of lenslets 4'is the same as the number of emitters 1'of the laser diode. The pitch of the cylindrical lenslets 4'is made slightly smaller than the pitch of the emitters 1 ', so that the images of all the emitters 1'of the laser diode overlap in the light valve 6. For best brightness, the focal length of each lenslet 4 ′ should be approximately equal to the distance from the face of the diode 1 to the point where the beams from the individual emitters 1 ′ intersect each other (overlap). Should.

Referring to FIGS. 2a and 2b in conjunction with FIG. 1, the images of all emitters 1'are overlapped on the light valve 6 in the form of a line. Since each emitter 1'of diode 1 is a wide emitter,
The strength of this line is uniform over most of its length.
These wide emitters typically radiate uniformly over their entire width and decay at both ends. This line is modulated by the light valve 6 and imaged on the thermosensitive or photosensitive member 9.

In most applications, diode 1 is
Infrared portion of the spectrum, typically 800 nm to 850 nm
Operating in the wavelength range of, the member 9 is heat sensitive rather than sensitive to a particular wavelength. It is also possible to operate this same device in the visible spectrum with visible laser diodes.

Referring to FIG. 3, the graph 12
Shows the intensity profile of the illumination obtained by superimposing the images of all the emitters 1 ′ of the laser diode 1 with the lenslet array 4. The same intensity profile applies to the embodiment of Figure 2a. This illumination profile is also the profile of each emitter 1 ', since the images from each emitter are exactly overlapped. Since the light valve 6 must be illuminated uniformly, only the flat part of this illumination profile can be used. The sloping edge of the illumination profile is 30-4 of the total laser power loss.
It accounts for 0% power loss. In order to utilize this laser power, the embodiment shown in FIG. 3 is used.

In FIG. 3, the mirror 13 reflects a tilted portion of one end of the intensity profile 12 to the second mirror 14, and the second mirror 14 graphs the tilted portion of the intensity profile reflected from this first mirror 13. Overlap the ramp profile at the other end of the illumination profile as shown at 15. The graph 15 represents the intensity profile of the light immediately after it emerges from the second mirror 14. By adjusting the angle of the second mirror 14 so that these sloped portions of the intensity profile overlap on the light valve 6, a substantially rectangular profile 16 is obtained at the light valve 6. This method slightly increases the divergence angle of the light compared to the method of FIG. 2a, but considerably increases the utilization of the laser power.

The line of light projected on the light valve 6 is
Because of the superposition of light from a large number (usually 10 to 40) of emitters 1'of the laser diode 1, no dark spot will occur on the light valve 6 even if any one of the emitters fails. It simply reduces the total illumination. By way of example, in the case of a laser diode 1 consisting of 20 emitters 1 ′, if one emitter fails, the illumination of the light valve 6 will be reduced by 5%. This uniform (overall) reduction in illumination can easily be compensated by increasing the current in the laser diode.

[0026]

EXAMPLES To give a specific example, the laser diode 1 is a 20 W C diode (part number OPC-B020-80-CS) manufactured by Opto-Power Corp. (Industry, California, USA). This diode is 787. It has 19 emitters, each 150 μm long, arranged with an inter-center distance of μ. Therefore, the spacing between each emitter is 637.5μ. Since the divergence angle of light in the width direction of this diode is about 10 °, the light beams from the individual emitters intersect each other at about 637.5 μ / tan 10 ° = 3.6 mm from the plane of the diode. This determines the focal length of the lens 4.

The cylindrical lens 3 has a blue
It is a pultruded cylindrical lens (part number SAC800) with a numerical aperture of 0.73 manufactured by Sky Research, Inc. (San Jose, Calif., USA). The second microlens 4 was manufactured by Teledyne Brown Engineering Co. (Huntsville, Alabama, USA) and manufactured by a 16-step (4 masks) method. 785μ, focal length 3.5mm). The cylindrical lens 5 has a focal length of about 250 mm. These dimensions are about 6 mm wide for the light valve 6 when using the configuration of FIG. 2b and about 10 mm when using the configuration of FIG.
Sufficient to illuminate the width light valve 6. The distance between the lens 5 and the lens 4 is about 250 mm. The distance between the lens 4 and the emitter of the laser diode is approximately 3.8 mm.

The lens 3 is adjusted to image a sharp line on the light valve 6 in the vertical dimension. The pitch of the cylindrical microlenses of the lens 4 is slightly smaller than the pitch of the emitters of the laser diode 1 (77
From 6.3μ vs 787.5μ), images of all emitters are polymerized at a distance of about 250 mm. Because the cumulative displacement of the emitters at both ends is 9 × (787.5
μ-776.3 μ) ≈100 μ, and (100/36
This is because an image shift (displacement) of 250 mm≈7 mm occurs.

Although the present invention has been described with reference to the embodiments, the present invention is not limited to the structures and shapes of the embodiments illustrated here, but departs from the spirit and scope of the present invention. Rather, it should be understood that various embodiments are possible and that various changes and modifications can be made.

[Brief description of drawings]

FIG. 1 is a perspective view of a preferred embodiment of the present invention.

2a is a top plan view of the embodiment of FIG. 1. FIG.

2b is a side view of the embodiment of FIG. 1. FIG.

FIG. 3 is a top plan view of the embodiment of FIG. 1 showing the incorporation of intensity profile “folding” to increase power utilization.

[Explanation of symbols]

 1: Laser diode 1 ': Emitter 3: Micro lens 4: Small lens array 4': Small lens 5: Cylindrical free lens 6: Light valve 8: Imaging lens 13,14: Mirror 16: Light intensity profile

 ─────────────────────────────────────────────────── ─── Continuation of the front page (71) Applicant 596041652 3700 GILMORE WAY BURN ABY, B. C. V5G 4M1, CAN ADA

Claims (10)

[Claims] 1. A method of coupling a wide emission surface laser diode consisting of multiple emitters operating in parallel to a linear light valve to a linear light valve, wherein each of said emitters is imaged onto the linear light valve, A method characterized by polymerizing all images of any individual emitter in order to increase its insensitivity to defects present in it. 2. A focal length of a lenslet array having a pitch slightly smaller than the pitch of the emitters of the laser diode and being equal to the distance from each emitter to the point where the light beams from each emitter begin to overlap each other. 2. An array of lenslets having a lens is placed in close proximity to the laser diode and imaging of the emitter onto a linear light valve is performed by using the array of lenslets. The method described. 3. A means for superimposing a portion of the combined image of each emitter onto the other portion of the combined image to enhance the uniformity of illumination of the light valve. The method according to 1. 4. A multichannel modulator for modulating light from a wide emission surface laser diode comprising multiple emitters, comprising: (a) a control input end, and an input introduced to the control input end. A light valve for modulating incident light in response to data, and (b) focusing light from each emitter onto the light valve so as to superimpose light from each emitter onto light from all other emitters. A multi-channel modulator comprising focusing means for focusing and (c) focusing means for focusing the modulated light from the light valve onto a heat-sensitive or photosensitive member. 5. The multi-channel modulator of claim 4, wherein the focusing means for the emitter comprises a lenslet array located proximate to the laser diode. 6. The focusing means for the emitter comprises an elongated cylindrical planar microlens for collimating light from the laser diode in a first dimension, the lenslet array being the array. Light from each lenslet array is superposed on the light valve with light from each of the other lenslets of the lenslet array to a second dimension perpendicular to the first dimension direction. A multi-channel modulator according to claim 5, wherein the multi-channel modulator is adapted for directional focusing. 7. The laser diode has a plurality of emitters connected in parallel relationship, the lenslet array has one emitter for each lenslet of the array, and each lenslet has: The multi-channel modulator according to claim 6, wherein the multi-channel modulator has a cylindrical surface shape concentric with the axis of the elongated cylindrical surface microlens. 8. The multi-channel modulator according to claim 7, wherein the pitch of each lenslet is slightly smaller than the pitch of each emitter of the laser diode. 9. The light forming the sloped portion on one side of the light intensity profile is polymerized with the light forming the sloped portion on the other side of the light intensity profile to form a substantially rectangular intensity profile on the light valve. 5. The multi-channel modulator of claim 4, including mirror means for reflecting light from the focusing means to set. 10. The focal length of each lenslet array is equal to the spacing between the emitters equal to the tangent of the divergence angle of each emitter in the "wide" dimension. Multi-channel modulator.