Compact fiber-coupled distributed bragg reflector laser diode package

Abstract

A single-frequency, fiber-coupled, optically isolated laser diode includes a laser diode that produces an elliptical light beam, a combination of VPS and collimating lenses that convert the elliptical beam into cylindrical light beam, which passes through an isolator to a focusing lens that projects the light into a single mode fiber cable with a Bragg grating. The laser system is contained within a butterfly-like housing with a front pedestal secured to the front base of the housing which supports the laser diode, VPS lens and collimating lens. Two side pedestals secured to opposite side walls near the middle of the housing are used to mount the isolator. A rear pedestal secured to the rear base of the housing supports focusing lens and fiber cable.

Description

COMPACT FIBER-COUPLED DISTRIBUTED BRAGG REFLECTOR LASER DIODE PACKAGECross-Reference to Related Patent Applications

[0001] This application claims the benefit of priority to U.S. Provisional Application No.63 / 751, 717 filed January 20, 2025, the contents of which are incorporated herein by reference in their entirety.Field of the Invention

[0002] The present invention relates to tunable single-frequency laser systems and, more particularly, to a tunable single-frequency laser systems with a distributed Bragg reflector.Background of the Invention

[0003] A wide variety of applications require tunable single -frequency operation of a laser system. In the world of diode lasers, one of the main configurations to obtain a single -frequency output utilizes a distributed Bragg reflector (DBR) feedback configuration. The (DBR) Lasers incorporate an internal grating structure outside active region (gain region). The Bragg grating has a periodic variation so that only the wavelength of light that satisfies the Bragg condition for the grating is reflected back into the laser cavity, which results in a laser with extremely wavelength-stable emission.

[0004] In one version of DBR laser, the Bragg grating is in the form of an exceptionally long fiber Bragg grating (FBG), e.g., about 1 meter. They are designed to create a laser cavity that provides the laser with a very narrow line width and low relative intensity noise. The FBG reflects a portion of the light emitted from the gain medium while remaining thermally isolated from it. The grating period can be changed by introducing thermal stress to the fiber, allowing users to temperature tune the laser output while being able to independently stabilize the gain medium's temperature.

[0005] In a typical arrangement the system includes a laser diode with an output beam followed by collimating lenses that shape the beam into a cylindrical column. The cylindrical beam is then focused by a further lens into the end of an extended fiber bundle that has a Bragggrating reflector. The output of the system is emitted from the other end of the fiber. An isolator can be used after the collimating lenses to protect the laser diode from off frequency back-reflected light, ensuring stable operation and preventing damage to the diode.

[0006] A butterfly package is an industry-standard, hermetically sealed housing for high-performance optoelectronic components, such as laser diodes and photodiodes, featuring leads on both sides that resemble butterfly wings. Designed for high-speed fiber-optic communication, they provide superior heat dissipation, thermal management, and structural stability in harsh environment. They often including an internal thermoelectric cooler (TEC) for temperature control and integrated fiber optics for efficient light coupling.Summary of the Invention

[0007] The present invention is a single -frequency fiber-coupled, optically isolated laser diode package. The invention uses a proprietary integrated Bragg reflector to form a Distributed Bragg Reflector (DBR) semiconductor laser housed in a compact butterfly-like package. It does not have side extending leads. This design provides improved optical isolation and power output.

[0008] In a preferred embodiment the invention is a single-frequency, fiber-coupled, optically isolated laser diode comprising a laser diode that produces an elliptical light beam, a Virtual Point Source (VPS) lens that intercepts the elliptical light beam and converts it into a circular expanding cone light beam, a collimating lens that intercepts the expanding cone light beam and turns it into a relatively cylindrical light beam, an isolator through which the cylindrical light beam passes in a forward direction, but which blocks light at non-selected frequencies from passing in a backward direction, a focusing lens that turns the forward light beam from the isolator into a focused beam of light, and a single mode fiber cable with a Bragg grating receives the focused beam of light at one end and produces a light beam at is other end. The Bragg grating reflects light of the selected frequency back through the focusing lens, the isolator, collimating lens and VPS lens to the laser diode so as to form a lasing cavity and the other end of the fiber cable produces the light beam at the single selected frequency.

[0009] The single-frequency, fiber-coupled, optically isolated laser diode system is packaged in a butterfly-like housing that includes a front pedestal secured to the base of the housing toward its front and upon which the laser diode, VPS lens and collimating lens are positioned in that order. The housing further includes two side pedestals secured to opposite11503 / 013393-WG0side wall of the housing towards its midsection and upon which the isolator is mounted. Also, the housing includes a rear pedestal secured to the base of the housing towards its rear and upon which the focusing lens and fiber cable are mounted.

[0010] The present invention utilizes a much more efficient isolator than the prior art, which isolator absorbs very little of the incident laser light, and has a transmission rate above 90% and up to 98%. The invention also utilizes a two lens system that collimates the laser beam and eliminates astigmatism for more efficient coupling into a single mode, and a polarization maintaining (PM) fiber which has a length of about 1 meter.

[0011] In a preferred the system uses an edge-emitting DBR with a monolithic single frequency Gallium Arsenide (GaAs) laser.Brief Description of the Drawings

[0012] The foregoing and other objects and advantages of the present invention will become more apparent when considered in connection with the following detailed description and appended drawings in which like designations denote like elements in the various views, and wherein:

[0013] FIG. 1 is a schematic front, right, top perspective view of the compact fiber-coupled distributed Bragg reflector laser diode package of the present invention;

[0014] FIG.2 is atopplan viewofthepackageofFIG. 1 according to the present invention;

[0015] FIG. 3 is a right-side elevation view of the package of FIG. 1 according to the present invention ;

[0016] FIG. 4 shows from left to right, cross-sectional views of the mechanical structure of the connector side, top view and fiber side, respectively, of the package according to the present invention;

[0017] FIG. 5 is a top view of the mechanical structure of the package according to the present invention showing the location of the optical devices, including the laser, lenses and fiber cable according to the present invention;

[0018] FIG. 6 is an enlarged view of FIG. 5 showing the location of the laser on a pedestal and the collimating lens according to the present invention;11503 / 013393-WG0

[0019] FIG. 7 is a side view showing the laser pedestal, laser, and collimating lens according to the present invention; and

[0020] FIG. 8 is a schematic of a fiber-coupled distributed Bragg reflector laser diode system.Detailed Description of the Invention

[0021] The present invention in its preferred embodiment is a single-frequency Gallium Arsenide (GaAs), fiber-coupled, optically isolated laser diode package, which can be referred to as the “IsoBragg.” The IsoBragg utilizes a proprietary integrated Bragg reflector to form a Distributed Bragg Reflector (DBR) semiconductor laser housed in a compact butterfly-like package without side leads. See FIGS.1 and 4. This design provides improved optical isolation and power output compared to the prior art such as the Thorlabs DBR, Single-Frequency Lasers, PM Butterfly Package (DBR780PN, DBR852PN, DBR1064PN). In particular, the IsoBragg utilizes a much more efficient isolator 18 that absorbs very little of the incident laser light and has a transmission rate above 90% and up to 98%. It also utilizes a two lens system 16 that collimates the laser beam and eliminates astigmatism for more efficient coupling into the single mode, polarization maintaining (PM) fiber.

[0022] FIG.8 shows the laser system without the packaging. In particular, DBR laser diode 12 produces a beam of light that is elliptical. VPS lens 14 turns it into a relatively circular expanding cone of light. This cone of light is converted into a cylindrical beam by collimating lens 16, which is passed through isolator 18. The cylindrical beam existing the isolator is intercepted by lens 20, which focuses it into single mode fiber cable 24. At least the first part of fiber cable 24 has a Bragg grating which reflects light of the selected frequency back through lens 20 and the isolator 18 to the laser diode 12 to set up a lasing cavity. The isolator 18 prevents frequencies other than the selected one from being reflected back into the cavity, making the arrangement operate at a single frequency. The output from the other end of the fiber or cable, which is about 1 meter long, is a ferrule, angle physical contact (FC / APC) male connector.

[0023] As shown in FIGS. 4, 5 and 8, the size of the butterfly-like package is largely determined by the isolator 18. Larger or smaller isolators exist and could be used. The overall size of the package would shrink or grow depending on the isolator size chosen. The preferred size of the isolator was chosen to maximize the throughput, i.e., about a 98% transmission rate. Isolators conventionally used in legacy butterfly packages are very small and have transmission11503 / 013393-WG0rates typically around 50% at best. Typically, the package housing of the present invention is about 58.0 mm x 40.0 mm x 29.0 mm.

[0024] The laser diode and associated lens or lenses geometry is also restricted by the size of the Thermo-Electric Cooler (TEC) 32 as shown in FIGS.6 and 7 for temperature control of the optics. The TEC size for the preferred package was chosen to fit on the front mounting pedestal 30 located before the isolator 18. FIGS. 5 and 7. A larger or smaller TEC could also possibly be made to work in this package by changing the size of the mounting pedestal.

[0025] The beam profile exiting the laser diode 12 is highly elliptical. Therefore, prior to collimating the beam, the profile must be made as circular as possible. Two lenses 14 are used to collimate the beam. The first lens, called a Virtual Point Source (VPS) lens, makes the beam profile more circular. After the VPS lens, the beam looks like a circular expanding cone. The second lens, called the collimating lens, takes this expanding cone of light and collimates it. Since the two lenses collimate the beam exiting the laser diode, specific limitations are placed on the lens properties, which are further restricted by the size of the TEC. However, many different combinations of lenses are possible. A single lens may alternatively be used in place of the 2 lenses for collimating the beam.

[0026] The collimated beam passes through the isolator 18 and goes into the output fiber 24 supported on a rear pedestal 38 by way of a fiber lens sleeve 22. A GRaded INdex (GRIN) lens single mode fiber is preferred, in which the GRIN lens 20 is attached to the fiber by the manufacturer. The GRIN lens focuses the collimated beam into the fiber core 24. Focusing the beam into the fiber core takes extreme precision. Once the fiber is in position it is epoxied into place. Other methods, such as soldering, can also potentially be used to fix the fiber in position.

[0027] Instead of a GRIN lens fiber, a separate lens 20 could be placed after the isolator 18 that would focus the beam and allow it to be coupled to a single mode fiber 24 without the use of a GRIN lens.

[0028] As shown in FIG. 5, the isolator 18 is positioned between the two lenses 14, 16 for collimating the beam and the Grin lens 20 of the output fiber. The isolator is mounted on a mount within the package such that the isolator does not touch the bottom or base of the package so that less heat is transferred into the isolator. The mount comprises two pedestals 36 that extend from opposing side walls towards the middle of the interior of the package and which each include a groove that together serve as shelves to support the two side edges of the11503 / 013393-WG0isolator 18. The isolator is clamped to the pedestals at its four comers. The package is preferably made of aluminium but may be made of other materials with high heat conductivity.

[0029] Theoretically, a collimated beam would be a tube that is an infinitely long perfect cylinder. In that case, the only requirement for the lenses would be to produce a collimated beam because anywhere along the beam path would be equivalent to all other points along the beam path. However, that does not occur in practice. A collimated beam has what is known as a Gaussian profile. So instead of an infinitely long perfect cylinder, the tube initially gets narrower until it reaches a minimum somewhere along its length and then begins to expand after reaching this minimum. The two lenses 14, 16 are actually used to change the position of where this minimum occurs. However, exactly where this minimum occurs is not what is important. What is important is that a maximum amount of the total power coming from the laser is able to be focused into the fiber core. So, the function of the lenses is to position the beam minimum in such a location that maximum power is coupled into the fiber.

[0030] The lenses 14, 16 are chosen so that given the constraints of the package geometry and the available space, the beam minimum is positioned at a place that maximizes the amount of power that can be couple into the fiber core. In the preferred embodiment this translates to a collimating lens with a focal length of about 3-4 millimeters because that is how much distance there is between the two lenses. A single lens configuration would have to be able to mimic the performance of the two lenses.

[0031] The preferred Grin lens single mode fiber that is used has a diameter of about 3 mm. The collimated beam must be less than this diameter otherwise a significant amount of the total laser output power would be lost. In this case, the beam diameter is less than 1 mm when it contacts the fiber lens. This ensures that nearly all of the laser light is being collected by the fiber lens.

[0032] The combination of the lasers, lenses, and highly efficient isolators allows the IsoBragg lasers of the present invention to attain previously unattainable power levels. The power output of the IsoBragg and the Thorlabs DBR, Single-Frequency Lasers, PM Butterfly Package (DBR780PN, DBR852PN, DBR1064PN) at various wavelengths are compared in Table 1 below, which demonstrates a multiple of increase of power output between 2.0 - 6.67 for the present invention over the ThorLabs DBR lasers.11503 / 013393-WG0

[0033] The above are only specific implementations of the invention and are not intended to limit the scope of protection of the invention. Any modifications or substitutes apparent to those skilled in the art shall fall within the scope of protection of the invention. Therefore, the protected scope of the invention shall be subject to the scope of protection of the claims.

[0034] Embodiments

[0035] A first embodiment is a single-frequency, fiber-coupled, optically isolated laser diode comprising:a laser diode that produces an elliptical light beam;a Virtual Point Source (VPS) lens that intercepts the elliptical light beam and converts it into a circular expanding cone light beam;a collimating lens that intercepts the expanding cone light beam and turns it into a relatively cylindrical light beam;an isolator through which the cylindrical light beam passes in a forward direction, but which blocks light at non-selected frequencies from passing in a backward direction;a focusing lens that turns the forward light beam from the isolator into a focused beam of light; anda single mode fiber cable with a Bragg grating receives the focused beam of light at one end and produces a light beam at its other end, andwherein the Bragg grating reflects light of the selected frequency back through the focusing lens, the isolator, collimating lens and VPS lens to the laser diode, whereby a lasing cavity is established, and the other end of the fiber cable produces the light beam at the single selected frequency.

[0036] A second embodiment, comprising any of the previously provided embodiments, and wherein the single-frequency, fiber-coupled, optically isolated laser diode of the first embodiment wherein the laser diode is a Gallium Arsenide (GaAs) diode.

[0037] A third embodiment, comprising any of the previously provided embodiments, and wherein is the single-frequency, fiber-coupled, optically isolated laser diode of has a transmission rate of above 90%.

[0038] A fourth embodiment comprising any of the previously provided embodiments, and wherein the isolator has a transmission rate of 98%.

[0039] A fifth embodiment, comprising any of the previously provided embodiments, and wherein the combination of the VPS lens and the collimating lens eliminates astigmatism.

[0040] A sixth embodiment, comprising any of the previously provided embodiments, and wherein the single mode fiber cable with a Bragg grating uses a single mode, polarization maintaining (PM) fiber.

[0041] A seventh embodiment comprising any of the previously provided embodiments, and wherein the collimating lens a focal length of about 3-4 millimeters.

[0042] An eighth embodiment is a single-frequency, fiber-coupled, optically isolated laser diode package comprising a butterfly housing and a laser according to of the first embodiment, wherein the housing includes:a front pedestal secured to the base of the housing toward its front and upon which the laser diode, VPS lens and collimating lens are positioned in that order;two side pedestals secured to opposite side wall of the housing towards its midsection and upon which the isolator is mounted; anda rear pedestal secured to the base of the housing towards its rear and upon which the focusing lens and fiber cable are mounted.

[0043] A nineth embodiment comprising any of the previously provided embodiments, and wherein the isolator does not touch the base of the housing.

[0044] A tenth embodiment is the laser diode package of the eight embodiment comprising any of the previously provided embodiments, and wherein the housing is made of aluminium.

[0045] An eleventh embodiment is the laser diode package of any previously provided embodiments further including a Thermo-Electric Cooler (TEC) for temperature control of the optics located on the front pedestal.

[0046] A twelfth embodiment is the laser diode package of the any of the previously provided embodiments further including a fiber lens sleeve for holding the fiber cable on the rear pedestal.

[0047] A thirteenth embodiment is the laser diode package of the previously provided embodiments further including a ferrule, angle physical contact (FC / APC) male output connector at the other end of the fiber cable.

[0048] The foregoing description of the specific embodiments will so fully reveal the general nature of the disclosure that others can, by applying knowledge within the skill of the relevant art(s) (including the contents of the documents cited and incorporated by reference herein), readily modify and / or adapt for various applications such specific embodiments, without undue experimentation, without departing from the general concept of the present disclosure. Such adaptations and modifications are therefore intended to be within the meaning and range of equivalents of the disclosed embodiments, based on the teaching and guidance presented herein. It is to be understood that the phraseology or terminology herein is for the purpose of description and not of limitation, such that the terminology or phraseology of the present specification is to be interpreted by the skilled artisan in light of the teachings and guidance presented herein, in combination with the knowledge of one skilled in the relevant art(s).

[0049] Any patents, patent applications, publications or other references are herein incorporated by reference as if each was presented in its respective entirety.

[0050] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a", “an” and “the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and / or “comprising”, when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0051] While the invention is explained in relation to certain embodiments, it is to be understood that various modifications thereof will become apparent to those skilled in the artupon reading the specification. Therefore, it is to be understood that the invention disclosed herein is intended to cover such modifications as fall within the scope of the appended claims.

Claims

11503 / 013393-WG0Claims1. A single-frequency, fiber-coupled, optically isolated laser diode comprising: a laser diode that produces an elliptical light beam;a Virtual Point Source (VPS) lens that intercepts the elliptical light beam and converts it into a circular expanding cone light beam;a collimating lens that intercepts the expanding cone light beam and turns it into a relatively cylindrical light beam;an isolator through which the cylindrical light beam passes in a forward direction, but which blocks light at non-selected frequencies from passing in a backward direction;a focusing lens that turns the forward light beam from the isolator into a focused beam of light; anda single mode fiber cable with a Bragg grating receives the focused beam of light at one end and produces a light beam at is other end,wherein the Bragg grating reflects light of the selected frequency back through the focusing lens, the isolator, collimating lens and VPS lens to the laser diode, whereby a lasing cavity is established, and the other end of the fiber cable produces the light beam at the single selected frequency.

2. The single-frequency, fiber-coupled, optically isolated laser diode of claim 1 wherein the laser diode is an edge-emitting monolithic single -frequency Gallium Arsenide (GaAs) diode.

3. The single-frequency, fiber-coupled, optically isolated laser diode of claim 1 wherein the isolator has a transmission rate of above 90%.

4. The single-frequency, fiber-coupled, optically isolated laser diode of claim 3 wherein the isolator has a transmission rate of 98%.

5. The single-frequency, fiber-coupled, optically isolated laser diode of claim 1 wherein the combination of the VPS lens and the collimating lens eliminates astigmatism.

6. The single-frequency, fiber-coupled, optically isolated laser diode of claim 1 wherein the single mode fiber cable with a Bragg grating uses a single mode, polarization maintaining (PM) fiber.

7. The single-frequency, fiber-coupled, optically isolated laser diode of claim 1 wherein the collimating lens a focal length of about 3-4 millimeters.

8. A single -frequency, fiber-coupled, optically isolated laser diode package comprising a butterfly-like housing and a laser according to claim 1, wherein the housing includes:a front pedestal secured to the base of the housing toward its front and upon which the laser diode, VPS lens and collimating lens are positioned in that order;two side pedestals secured to opposite side wall of the housing towards its midsection and upon which the isolator is mounted; anda rear pedestal secured to the base of the housing towards its rear and upon which the focusing lens and fiber cable are mounted.

9. The laser diode package of claim 8 wherein the isolator does not touch the base of the housing.

10. The laser diode package of claim 8 wherein housing is made of aluminium.

11. The laser diode package of claim 8 further including a Thermo-Electric Cooler (TEC) for temperature control of the optics located on the front pedestal.

12. The laser diode package of claim 8 further including a fiber lens sleeve for holding the fiber cable on the rear pedestal.

13. The laser diode package of claim 8 further including a ferrule, angle physical contact (FC / APC) male output connector at the other end of the fiber cable.

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