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  High efficiency, wavelength stabilized laser diode using awg's and architecture for combining same with brightness conservationUSPTO Application #: 20070223552Title: High efficiency, wavelength stabilized laser diode using awg's and architecture for combining same with brightness conservation Abstract: The invention relates to high power semiconductor lasers based on a laser diode array waveguide grating (DAWG) in which the wavelength is stabilized using an array waveguide grating (AWG) in an external cavity configuration. Another aspect of the present invention relates to techniques for efficiently coupling optical gain element arrays to an AWG. Another feature provides for the efficient and brightness-conserving combination of multiple high power DAWG lasers into a single output. (end of abstract) Agent: Allen, Dyer, Doppelt, Milbrath & Gilchrist P.A. - Orlando, FL, US Inventors: Martin H. Muendel, David J. Dougherty, Matthew Glenn Peters, Victor Rossin, Robert B. Sargent, Len Marabella, Kuochou Tai, Bruno Acklin, Yongan Wu, Kenneth M. Dzurko USPTO Applicaton #: 20070223552 - Class: 372050120 (USPTO) Related Patent Categories: Coherent Light Generators, Particular Active Media, Semiconductor, Injection, Monolithic Integrated, Laser Array The Patent Description & Claims data below is from USPTO Patent Application 20070223552. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application claims priority of U.S. Provisional Application No. 60/737,925 filed Nov. 18, 2005, entitled "WAVELENGTH STABILIZED LASER DIODE" which is incorporated herein by reference for all purposes. TECHNICAL FIELD [0002] The present invention relates to wavelength stabilized semiconductor laser sources in which array waveguide gratings (AWG) are used as the optical wavelength stabilizing element in an external cavity, in particular to broad-area (multimode) semiconductor laser diode arrays and, more particularly, to a system for scaling power to a 10 watt to kilowatt level into a single fiber output by combining outputs of multiple laser sources using wavelength and polarization multiplexing to conserve brightness. BACKGROUND OF THE INVENTION [0003] Semiconductor high power lasers are interesting as replacements of today's commercially available CW fiber lasers (FL's) for many reasons, among which compact size and high efficiency are among the most attractive. High-power single-mode fiber-coupled (FC) modules potentially have advantages of wavelength versatility (most FL's are based on Yb at 1050-1100 nm), compactness, improved efficiency, and enhanced reliability due to the elimination of the double-clad fiber. [0004] High-power multimode modules are of interest in less demanding applications, where output powers in the 100 W range from a 25-100 micron core fiber would be adequate. They would have the added advantage of lifting the constraint of single-mode operation, making these devices smaller, lower cost, and easier to manufacture than their single-mode counterpart. [0005] For applications demanding pulsed output or extremely high brightness, high-power modules can serve as a very cost-effective pump for Yb fiber lasers or disk lasers. One particular area of interest is a pump source for amplifying picosecond or femtosecond pulses in double-clad fiber, where the fiber length must be kept extremely short to mitigate pulse distortion, and therefore a very high brightness pump is required. [0006] A narrow wavelength high brightness pump technology will improve the fiber laser efficiency in a number of ways. Firstly, tight wavelength control will allow pumping of the narrow 976 nm Ytterbium absorption line which has a better quantum defect and higher absorption than the broader 915 nm line. Secondly, a high brightness source will enable pumping into a smaller diameter fiber. Conventional bars and single emitters, with relatively low brightness, require fiber with a large inner cladding (typically 400-600 microns), while a high-NA polymer outer clad fiber ends up having a much higher loss per unit length and very long (typically >50 m). Thirdly, the combination of these improvements will translate to a shorter overall fiber length with lower overall absorption and scattering and lower threshold power requirements. Fourthly, lasing in the 1040 nm band will be support, which has a lower quantum defect. For example the impact of pumping at 976 nm and lasing at 1050 nm, versus 915 nm and 1100 nm, will be to improve the quantum defect from 83% to 93%. The net effect of such pump laser improvements will enable a fiber laser optical-to-optical efficiency in the 80% range. [0007] Finally spectral multiplexing of either the single-mode or the multimode modules will enable reaching even higher output powers without impacting beam quality. For example, spectrally multiplexing multiple multimode modules could permit the construction of a 2-5 kW industrial cutting/welding direct diode system that would be extremely reliable and cost-effective. This would be an appealing alternative to current FL-based architectures currently being explored, in which a number of 100-200 W single-mode fiber lasers are combined spatially into a multimode output. [0008] The power achievable from a single laser module is limited to the range of several watt. To achieve the power levels demanded by various high-power applications mentioned above, a scaling scheme must be used that can efficiently combine the power from multiple laser sources. [0009] Simple optical combiners do not satisfy the efficiency requirement for fundamental physics reasons. In contrast, wavelength and polarization combiners can be made with zero theoretical optical losses. To implement such combining means, the laser source modules must fulfill certain properties. In addition to producing high output power and efficiency, their emission must be wavelength stabilized to within tight limits and be sufficiently narrow band, as well as possessing a high optical beam quality. [0010] To obtain high output power and efficiency, broad area laser diodes are generally used, however due to their dimensions they tend to oscillate in multiple transverse modes. The broad area output facet of these lasers also presents a challenge for coupling into a single mode optical fiber in applications where maximal brightness is called for. [0011] Wavelength stabilization techniques are well known in the art for single mode (narrow stripe) laser diodes. Distributed feedback gratings as well as distributed Bragg reflectors are commonly integrated into the laser structure, but these exhibit a relatively high wavelength shift with temperature, which can be problematic in high power environments. Other techniques are based on using thermally stable materials in an external cavity, such as Fabry-Perot etalons, free-space diffraction gratings and fiber Bragg gratings. [0012] Similar techniques have been developed also for broad area lasers, however coupling them into an external cavity with the required efficiency is still a major problem. Another stabilization method involves reflecting a spectrally narrow portion of the output emission back into the broad area laser. [0013] One such method has been disclosed by Bardia Pezeshki et al. in US Patent Application 20020085594 in the name of Santur, Inc. The embodiment shown in FIG. 1a has a plurality of DFB laser diodes as used in telecommunications, coupled into an array waveguide grating (AWG) for combining at a common output. A disadvantage of this arrangement is that it requires close tracking of the laser wavelength with the passbands of the WDM device under changing temperature conditions. [0014] Another method has been disclosed by Robert G. Waarts et al. in U.S. Pat. No. 6,212,310, assigned to SDL, Inc. An embodiment is shown in FIG. 1b where a plurality of optical fiber lasers, each with a different wavelength, is coupled through a WDM device such as a fused taper coupler, dichroic mirrors or grating mirrors into a single output. The output fiber has a Bragg reflector incorporated within it for providing some feedback to the fiber lasers. This has a similar disadvantage to the previous example. [0015] Thus, an object of the present invention is to stabilize the wavelength of broad area multi-mode laser diodes. [0016] Another object of the present invention is to provide an efficient coupling of such laser diodes to a single-mode waveguide or fiber. [0017] A further object of the present invention is to provide a device in which the optical outputs of an array of laser emitters is combined while conserving brightness, and furthermore to combine outputs of multiple arrays of laser emitters into one single-mode or multi-mode output to achieve high optical power levels in the tens to hundreds of watt. SUMMARY OF THE INVENTION [0018] Accordingly, the present invention relates to high power semiconductor lasers based on a laser diode array waveguide grating (DAWG) in which the wavelength is stabilized using an array waveguide grating (AWG) in an external cavity configuration. [0019] Another aspect of the present invention relates to efficiently coupling optical gain element arrays to an AWG. [0020] Another feature of the present invention provides for the efficient and brightness conserving combination of multiple high power DAWG lasers into a single output. Continue reading... Full patent description for High efficiency, wavelength stabilized laser diode using awg's and architecture for combining same with brightness conservation Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this High efficiency, wavelength stabilized laser diode using awg's and architecture for combining same with brightness conservation patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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