Radiation Mode Tailored Semiconductor Laser

Abstract

The present disclosure relates to index guided semiconductor laser devices supporting wide single lateral mode operation for high power operation. A narrow channel ridge waveguide structure is presented which devices can be configured as single lateral multi-spectral high power semiconductor lasers, single frequency lasers, gain chips and semiconductor amplifiers. More specifically it relates to a means for increasing the lateral mode size over that of conventional index guided structures to increase the average output power typically limed by Catastrophic Optical Damage (COD) at the laser facet or by intensity related effects. This potentially allows the overall laser cavity length to be shortened for a given output power level to stabilize frequency locking with internal or external gratings to improve single frequency operation.

Claims

1. A semiconductor laser apparatus with a narrow channel waveguide structure comprising: a multi-layered epitaxy grown on a suitable substrate consisting of an active layer stacked in the perpendicular dimension between first and second layers, said first layer including a dopant one of n-type and p-type and said second layer doped the other n-type or p-type supporting a gain confining region, an optical waveguide for formation of perpendicular, lateral and longitudinal modes, a laser resonator cavity of length (CL) defined by the region between two opposing mirror facets which may have applied optical coating ether of high or low reflectivity, said optical waveguide supporting a single perpendicular mode established by the epitaxial layers with significant modal overlap with the gain region, a plurality of lateral modes established by a narrow channel waveguide structure, a plurality of longitudinal modes defined by the CL of the laser resonator, said narrow channel waveguide structure supporting a plurality of modes each with modal overlap with regions outside the channels causing modal loss difference between the supported modes with the fundamental mode having the lowest loss, electrical contacts for providing current for the active layer, wherein said gain confining region has a geometry which is substantially matched to intensity profile of a fundamental lateral mode, thereby providing a modal gain difference and attenuation loss difference between the fundamental mode and remainder of said mode plurality with the fundamental mode having the highest modal gain, thereby favoring wide fundamental mode operation for high power application.

2. The laser apparatus of claim 1 wherein said lateral optical waveguide includes a distributed Bragg reflector grating centered upon the waveguide section and or outer region to establish single frequency operation.

3. The laser apparatus of claim 1 wherein said lateral optical waveguide includes a distributed feed back grating to establish single frequency operation.

4. The laser apparatus of claim 1 wherein said lateral waveguide structure includes a tapered amplifier region for optical amplification.

5. The laser apparatus of claim 1 wherein said optical coatings include one facet with antireflection coating forming a gain chip coupled to an external grating by an optical element.

Description

[0013] The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. The accompanying drawings, which are incorporated into and constitute a part of the specification, illustrate specific embodiments of the apparatus, systems, and methods and, together with the general description given above, and the detailed description of specific embodiments serve to explain the principles of the apparatus, systems, and methods.

[0014] In the drawings:

[0015] FIG. 1 shows a cross sectional view of a narrow channel ridge waveguide semiconductor structure.

[0016] FIG. 2 shows simplified drawing of a narrow channel ridge waveguide semiconductor structure.

[0017] FIG. 3 shows a simplified drawing of a narrow channel ridge waveguide semiconductor gain chip coupled to an external grating to form an external laser resonator.

[0018] FIG. 4 shows a simplified drawing of a narrow channel ridge waveguide semiconductor laser coupled to an on chip tapered amplifier section.

[0019] FIG. 5 shows a simplified drawing of a narrow channel ridge waveguide distributed Bragg reflector (DBR) laser.

[0020] FIG. 6 shows a sketch of the lateral waveguide refractive index profile with supported mode profiles illustrating modal overlap of modes with the outer regions (regions outside the channels).

DETAILED DESCRIPTION

[0021] Example embodiments will now be described more fully with reference to the accompanying drawings.

[0022] Referring to the drawings, to the following detailed description, and to incorporated materials, detailed information about the apparatus, systems, and methods is provided including the description of specific embodiments. The detailed description serves to explain the principles of the apparatus, systems, and methods described herein. The apparatus, systems, and methods described herein are susceptible to modifications and alternative forms. The application is not limited to the particular forms disclosed. The application covers all modifications, equivalents, and alternatives falling within the spirit and scope of the apparatus, systems, and methods as defined by the claims.

[0023] The present invention includes a semiconductor laser structure with diode configuration including a n-type and p-type doped regions with a central active layer, electrical contacts and two parallel optical mirrors forming a laser resonator with a narrow channel lateral waveguide supporting a set of lateral modes with mode tails extending past the channel regions causing higher order modes to experience attenuation loss thereby favoring single lateral mode operation.

[0024] Referring to FIG. 1 a narrow channel ridge waveguide semiconductor laser structure 100 is illustrated, the semiconductor epitaxy consisting of a n-type semiconductor substrate 101, a n-type cladding layer 102, a n-type waveguide layer 103, an active layer 104, a p-type waveguide layer 105, a p-type cladding layer 106 and a p-type cap layer 107, the n-type-p-type structure forms a diode structure and supports a single perpendicular mode with significant overlap with the active layer. A lateral waveguide is formed by etching channels 114 into the p-type layers defining a central waveguide region 113 between two parallel narrow channels 114, a dielectric coating 108 with top metal contact layer 109, a bottom contact layer 110, with opening in the dielectric coating 111 to allow electrical contact to the lateral waveguide region. Upon application of an applied bias between the top 109 and bottom 110 contacts current is injected into the active layer within a gain confining region 112 allowing radiative recombination to produce photons supporting a two dimensional modal profile defined by the lateral waveguide and perpendicular waveguides.

[0025] Referring to FIG. 2 a three-dimensional drawing of the a narrow channel ridge waveguide semiconductor laser is show. A laser resonator is formed by cleaving the semiconductor 100 into a chip 200 with parallel facets or mirrors 202,203 separated by a cavity length 201. The mirrors may include optical coatings defining a highly reflective coating at facet 203 and lower or antireflection coating on facet 202 to serve as the output mirror. The contact region 111 may be terminated short of the output creating a region 204 devoid of current injection extending from the output facet 202 along the contact region centered along the ridge defined by parallel narrow channels 114 to limit current recombination at the output mirror 202. Upon sufficient applied bias between electrodes 109,110 current injection threshold condition is satisfied and the device is capable of lasing with output out of one or both of the facets.

[0026] Referring to FIG. 3 a high level drawing of a narrow channel semiconductor external cavity laser 300 is shown. The semiconductor chip 200 has an anti-reflective coating applied to facet 202 and high reflective coating applied to facet 203 forming a gain chip, the narrow channel gain chip is coupled to an external wavelength selective grating 301 by a coupling lens 302 to enable single frequency operation.

[0027] Referring to FIG. 4 a narrow channel ridge waveguide semiconductor tapered amplifier 400 is shown, a narrow channel ridge waveguide section 200 is coupled to a tapered waveguide region 401 with provides optical amplification, facets 402 and 403 form the mirrors, with the mirror at the tapered end serving as the output facet 403. This device allows for high power single mode operation.

[0028] Referring to FIG. 5 a high level drawing of a narrow channel distributed reflector (DBR) semiconductor laser for single frequency operation. The (DBR) grating 501 is located at one end of the lateral waveguide region 113 external cavity laser 300 is shown.

[0029] Referring to FIG. 5, a sketch of the refractive index profile 600 is shown for the narrow channel ridge waveguide structure. The central waveguide region 113 is designed sufficiently wide to support a plurality of modes (the first two are sketched), with the dotted line 601 a sketch of the fundamental mode and 602 a sketch of the first order mode. Region 111 defines the lateral gain region 603 in the active layer 112, the confinement factor is given by the overlap of the gain region with the mode, as can be seen the confinement factor for the fundamental mode will be greater than that of the first mode (with the first mode having a null in the center of the waveguide region). The regions outside the channels 114 are defined by 604, the overlap of the modes with regions 604 define the modal radiation losses, as can be seen in the sketch the mode overlap of the first mode with regions 604 is greater than that of the fundamental mode causing comparatively higher loss. Overall the structure favors fundamental mode operation by supporting a higher confinement factor and lower radiation loss for the fundamental mode comparted to high order modes.

[0030] The foregoing description of the various embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.

[0031] Although the description above contains many details and specifics, these should not be construed as limiting the scope of the application but as merely providing illustrations of some of the presently preferred embodiments of the apparatus, systems, and methods. Other implementations, enhancements and variations can be made based on what is described and illustrated in this patent document. The features of the embodiments described herein may be combined in all possible combinations of methods, apparatus, modules and systems. Certain features that are described in this patent document in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable sub-combination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination. Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. Moreover, the separation of various system components in the embodiments described above should not be understood as requiring such separation in all embodiments.

[0032] Therefore, it will be appreciated that the scope of the present application fully encompasses other embodiments which may become obvious to those skilled in the art. In the claims, reference to an element in the singular is not intended to mean “one and only one” unless explicitly so stated, but rather “one or more.” All structural and functional equivalents to the elements of the above described embodiments that are known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the present claims. Moreover, it is not necessary for a device to address each and every problem sought to be solved by the present apparatus, systems, and methods, for it to be encompassed by the present claims. Furthermore, no element or component in the present disclosure is intended to be dedicated to the public regardless of whether the element or component is explicitly recited in the claims. No claim element herein is to be construed under the provisions of 35 U.S.C. 112, sixth paragraph, unless the element is expressly recited using the phrase “means for.”

[0033] While the apparatus, systems, and methods may be susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and have been described in detail herein. However, it should be understood that the application is not intended to be limited to the particular forms disclosed. Rather, the application is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the application as defined by the following appended claims.