WO2020068260A1

WO2020068260A1 - Laser module having multiple component lasers

Info

Publication number: WO2020068260A1
Application number: PCT/US2019/043494
Authority: WO
Inventors: Guthrie Partridge; Richard P. Tella
Original assignee: Agilent Technologies, Inc.
Priority date: 2018-09-30
Filing date: 2019-07-25
Publication date: 2020-04-02
Also published as: CN112789773A; JP7398437B2; DE112019004915T5; JP2022501806A

Abstract

A laser module having a plurality of component lasers is disclosed. Each component laser is characterized by a gain chip, a diffraction grating structure, a pivot point, and an output laser beam traveling in an output beam direction. A drive shaft is coupled to each of the pivot points and causes each of the diffraction granting structures to rotate about the pivot point associated with the that component laser. The module also includes a plurality of reflectors, each reflector being positioned to receive the output laser beam from one of the plurality of component lasers and to direct the output laser beam along an output path that is common to all of the component lasers". A controller controls an angle of rotation of the drive shaft.

Description

Laser Module having Multiple Component Lasers

Background of the Invention

[0001] Many measurements of interest involve measuring the response of a sample to a light beam of a known wavelength as a function of wavelength. The light source for many of these measurements is a tunable laser. However many measurements require a tuning range that is beyond that achievable with a single gain chip in the laser. Prior art solutions to the limited tuning range have been suggested. One class of solution extends the amplification range of the gain section of the laser by utilizing multiple gain chips that process the light in series with each gain chip providing amplification in a corresponding band of wavelengths. These solutions have problems related to the non-active gain chip absorbing light that was amplified by another chip.

[0002] Other solutions utilize gain chips that have multiple active layers with each active layer providing gain in a different spectral range. These solutions have problems with multiple active layers providing gain at the same time.

Summary

[0003] The present invention includes a laser module having a plurality of component lasers, each component laser is characterized by a gain chip, a diffraction grating structure, a pivot point, and an output laser beam traveling in an output beam direction. A drive shaft is coupled to each of the pivot points and causes each of the diffraction grating structures to rotate about the pivot point associated with that component laser. The laser modules also includes a plurality of reflectors, each reflector bek g positioned to receive the output laser beam from one of the plurality of component lasers and to direct the output laser beam along an output path that is common to all of the component laser beams. A controller controls an angle of rotation of the drive shaft.

[0004] In one aspect of the invention, the diffraction grating structures of the plurality of component lasers are positioned such that no more than one of the component lasers lases for any given rotational angle of the drive shaft. [0005] In another aspect of the invention, one of the reflectors includes a partially reflecting mirror.

[0006] In another aspect of the invention, one of the reflectors includes a dichotic reflector that reflects light generated by a corresponding one of the component lasers and passes light generated by another one of the component lasers.

[0007] In another aspect of the invention, one of the reflectors rotates about an axis on the reflector such that the reflector does not block light along the output path, the rotation is controlled by the controller.

[0008] In another aspect of the invention, one of the component lasers includes first and second diffraction gratings having different grating spacings positioned such that at most one of the diffraction gratings reflects light from the gain chip in the component laser for any given rotation of the diffraction grating structure about the pivot point.

Brief Description of the Drawings

[0009] Figure 1 illustrates a component laser according to one embodiment of the present invention.

[0010] Figure 2is a side view of one embodiment of a laser module according to the present invention.

[0011] Figure 3 is a side view of a laser module according to another embodiment of the present invention.

[0012] Figure 4 illustrates a component laser with two gratings.

Detailed Description

[0013] The present invention addresses the above-described problems by providing a laser module instructed from a plurality of component lasers that are tuned together. Refer now to Figure 1, which illustrates a component laser according to one embodiment of the present invention. Component laser 10 includes a gain chip 11 and a grating 16 which provides a wavelength selected filter for the light amplified by gain chip 11. Gain chip 11 has a reflective coating on end 12 and antireflective coating on end 13. The light from gain chip 11 is expanded into a beam 15 by lens 14 and strikes diffraction grating 60. The light diffracted back to gain chip 11 is in a narrow band of wavelengths determined by the angle between the gradient and beam 15. Light which is reflected off of the grating into a beam 17 is reflected from mirror 18 which is at right angles to grating 16. The light reflected from mirror 18 is directed to a reflector 12 along path 19 which reflects that light in a direction perpendicular to the plane of the drawing.

[0014] Grating 12 and mirror 18 are structurally connected such that they moved together about an axis 21, which is perpendicular to the plane of the drawing. Component laser 10 is tuned by rotating grating 12 and mirror 18 about axis 21. There is a range of angles for grating 16 for which component laser 10 will lase. When grating 16 is rotated out of this range, component laser 10 will cease to lase.

[0015] To simplify the following discussion, a component laser will be defined to be a laser having a gain chip and a diffraction grating in which the diffraction grating is mounted in a grating structure that includes a planar mirror mounted at right angles to the plane of the diffraction grating such that the diffraction grating and the planar mirror are fixed relative to one another and rotate together about a pivot point such that light reflected back to the gain chip from the diffraction grating has a wavelength that depends on the angle between the plane of the diffraction grating and the path from the gain chip to the diffraction grating and light reflected from the planar mirror forms the output light beam from the component laser.

[0016] Refer now to Figure 2, which is a side view of one embodiment of a laser module 30 according to the present invention. The individual component lasers are shown at 31, 32, and 33. The individual reflectors corresponding to component lasers 31 - 33 are shown at 25 - 27, respectively. In the example shown in the figure, component laser 33 is lazing and generating an output beam 27A. When each laser module is lazing, the

corresponding output beam is coincident with beam 27A. The rotational angle of the grating of each of the component lasers is controlled by a motor 29 that is under the control of a controller 35 which sets the angle of the gratings to conform to the wavelengths specified by a user by setting the rotational angle of shaft 28.

[0017] In one exemplary embodiment, the angles of the gratings in the component laser are set such that only one grating is positioned to lase for any given rotational angle of shaft 28. The individual gain chips and starting grating positions are chosen such that the output wavelength varies continuously with the rotational angle of shaft 28.

[0018] In another exemplary embodiment, the angles of the gradients in the component lasers and the gain chips are chosen such that two of the component lasers have overlapping operational ranges. As the angle of the shaft changes, a first component laser begins to lase at the beginning of its operational range at a wavelength that is also supplied by a second component laser at the end of the second component laser’s operational range.

[0019] In the above-described embodiments, the output beam from each component laser is directed along a common path by a reflector that is part of that component laser, and hence, the output of the laser module appears to come from a single laser. For example, reflector 26 must pass light generated by component laser 31. In one exemplary embodiment, the reflectors are either partially reflecting mirrors or dichotic reflectors.

[0020] In another exemplary embodiment, the mirrors are hinged such that each mirror flips into place when its component laser grating is positioned to lase and flips out of the road when the laser module is no longer lasing. Refer now to Figure 3, which is a side view of a laser module 40 according to another embodiment of the present invention. Laser module 40 differs from laser module 30 shown in Figure 2 in that reflectors 25-27 have been replaced by moveable reflectors 45-47. Each moveable reflector pivots about a shaft 49 between a vertical position in which the reflector does not intercept light from the component lasers above it in the stack and a 45 degree orientation in which the reflector reflects light from the corresponding component laser and directs the light in a downward direction.

Reflector 45 of component laser 41 is in the 45 degree orientation while reflectors 46 and 47 of component lasers 42 and 43, respectively are in the vertical position. The angle of rotation of shaft 28 or controller 35 can control which reflector is positioned to deflect light from its component laser. In this configuration, a fully reflecting mirror can be used as the reflector provided only one component laser is operating at a time.

[0021] In the above described embodiments, only one of the component lasers was lasing at a time. However embodiments in which two or more lasers are generating light simultaneously can also be constructed. Such light sources can provide light with multiple wavelengths that could be utilized in Raman scattering or other spectral measurements.

[0022] In embodiments in which not all of the lasers are generating light

simultaneously, it may still be advantageous to power the gain chips in the lasers that are not lasing. This will maintain the temperature of all of the gain chips at their operating temperature and hence prevent shifts and wavelength due to the change in temperature of the gain chip as it heats up.

[0023] For some applications, it may be advantageous to provide lasers with different grating spacings even for the same gain chip. Altering the grating spacing alters the width of the spectral line generated by the laser. Hence, if a tunable laser with a different spectral width is desired for a particular application, a component laser with a different grating spacing can be utilized. In one embodiment, the grating spacing for the different component lasers is different. In such an embodiment, two component lasers with the same gain chip but different grating spacings could be utilized. However, this requires an additional component laser. Alternatively, a single component laser with multiple gratings can be provided.

[0024] In the above-described embodiment, each component laser included a single grating and its corresponding reflector mounted at 90° to the plane of the grating. However embodiments in which multiple gratings are used in a component laser can also be constructed. Refer now to Figure 4 which illustrates a component laser with two gratings. In this example, a second grating 88 is mounted at right angles to the plane of grating 16 shown in Figure 1. The back surface of grating 16 acts as the reflector for grating 88. Grating 88 is introduced into the optical path by rotating the grating structure about axis 21 in a manner analogous to that described above. [0025] The above-described embodiments had a particular number of compound lasers, namely three. However, it is to be understood that the number of compound lasers is not limited to three.

[0026] The above-described embodiments of the present invention have been provided to illustrate various aspects of the invention. However, it is to be understood that different aspects of the present invention that are shown in different specific embodiments can be combined to provide other embodiments of the present invention. In addition, various modifications to the present invention will become apparent from the foregoing description and accompanying drawings. Accordingly, the present invention is to be limited solely by the scope of the following claims.

Claims

WHAT IS CLAIMED IS:

1. A laser module comprising: a plurality of component lasers, each of said plurality of component laser being characterized by a gain chip, a diffraction grating structure, a pivot point, and an output laser beam traveling in an output beam direction; a drive shaft coupled to each of said pivot points, said drive shaft causing each of said diffraction grating structures to rotate about said pivot point associated with that component laser; a plurality of reflectors, each of said plurality of reflectors being positioned to receive said output laser beam from one of said plurality of component lasers and to direct said output laser beam along an output path that is common to all of said component laser beams; and a controller that controls an angle of rotation of said drive shaft.

2. The laser module of Claim 1 wherein said diffraction grating structures of said plurality of component lasers are positioned such that no more than one of said plurality of component lasers lases for any given rotational angle of the drive shaft.

3. The laser module of Claim 1 wherein one of said plurality of reflectors comprises a partially reflecting mirror.

4. The laser module of Claim 1 wherein one of said plurality of reflectors comprises a dichotic reflector that reflects light generated by a corresponding one of said plurality of component lasers and passes light generated by another one of said plurality of component lasers.

5. The laser module of Claim 1 wherein one of said plurality of reflectors rotates about an axis on said reflector such that said one of said plurality of reflector does not block light along said output path, said rotation being controlled by said controller.

6. The laser module of Claim 1 wherein one of said plurality of component lasers comprises first and second diffraction gratings having different grating spacings positioned such that at most one of said diffraction gratings reflects light from said gain chip in said component laser for any given rotation of said diffraction grating structure about said pivot point.