23 Sep 2003
The pick of this week’s patent applications including a way to improve the beam quality of a high-power laser diode.
• Title: A laser diode with an amplification section that has a varying index of refraction
Applicant: Quintessence Photonics Corporation, US
International application number: WO 03/077387
Introducing a stripe with a varying refractive into the structure of a high-power laser diode can reduce self-focusing and result in a high-quality beam, according to the authors of patent application WO 03/077387. The inventors say that the refractive index of the so-called “pumped stripe section” can be varied in several ways. The first is to control structural characteristics such as the doping or thickness of the layer. Other alternatives include generating a thermal gradient across the device or creating an unequal current flow through the section.
• Title: Refractive projection objective for immersion lithography
Applicant: Carl Zeiss SMT, AG, Germany
International application number: WO 03/077037
High-precision optics firm Carl Zeiss is trying to patent a refractive projection objective lens for use in immersion lithography. The company says the lens is designed as a single-waist system made up of five lens groups - two with a negative refractive power and three with a positive refracting power. The lens is said to have a numerical aperture greater than one. “Pattern widths substantially below 100 nm can be resolved when immersion fluids are used between the projection objective and substrate for operating wavelengths below 200 nm,” say the inventors.
• Title: Method for organizing a mode-locked pulse train by pumping modulation
Applicant: Optoelectronics Research Centre, US
International application number: WO 03/077420
Patent application WO 03/077420 describes a way to stabilize the repetition rate of a passively mode-locked fiber laser using semiconductor saturable absorbers (SESAMs). The inventors say that the repetition rate is stabilized by electrically modulating the amplifier pump source, which in turn optically modulates the saturable loss of the SESAM. They add that this technique can also generate an actively mode-locked pulse train. “We expect that this approach combined with the use of regenerative modulation and polarization-maintaining fiber components will permit the generation of drop-out-free pulse trains at GHz repetition rates with good long-term stability and minimal cost,” conclude the authors.
Jacqueline Hewett is news reporter on Optics.org and Opto & Laser Europe magazine.
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