Coherent light generators – Particular beam control device – Tuning
Reexamination Certificate
2000-01-31
2003-09-23
Scott, Jr., Leon (Department: 2828)
Coherent light generators
Particular beam control device
Tuning
C372S009000, C372S098000, C372S092000, C372S107000
Reexamination Certificate
active
06625183
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention pertains generally to tunable laser devices and methods, and more particularly to an external cavity laser apparatus which provides high tuning speeds and highly predictable, constant change in laser output wavelength with respect to time.
2. Description of the Background Art
Optical communication and optical data storage technologies increasingly rely on use of tunable semiconductor lasers. The output of semiconductor lasers can be often tuned over a range of output wavelengths by adjusting the angular configuration of an external laser cavity. Typical external laser cavity arrangements utilize a retroreflective dispersive device, such as a diffraction grating, together with a movable end mirror which can be adjusted in angular position. Common external laser cavity configurations include the “Littrow” arrangement, in which the retroreflective dispersive element itself serves as a resonator end minor, and the “Littman-Metcalf” arrangement, wherein the retroreflective dispersive element is positioned between the end mirrors of a “folded” resonator cavity. The end mirror and/or retroreflective dispersive element are varied in angle with respect to each other to control tuning or selection of desired laser output wavelengths.
The evolving uses for tunable solid state lasers has increasingly required precise systems and methods for optical frequency or wavelength control. In the field of photonics, and particularly in the filed of passive optical components, the optical characteristics of components must be tested for manufacturing, quality control and other purposes. These characteristics typically vary with the wavelength of the light input to the component, and tunable solid state lasers have been used for evaluating such optical characteristics throughout the wavelength ranges of the components.
An important deficiency of presently available tunable solid state lasers is the lack of smooth, constant, accurate tuning action to provide highly predictable tuning speeds and output wavelengths during tuning. Even relatively small amounts of wear or machining error in parts and/or low levels of vibration make accurate tuning difficult to achieve. The tuning inaccuracies of currently available solid state lasers increases the time and expense required for characterization of optical components, and can result in reduced component quality.
Various tuning mechanisms for external cavity diode lasers have been designed and implemented to improve tuning accuracy through control of external laser cavity configuration. Currently available tuning mechanisms, however, have not provided the needed increases in tuning accuracy. These tuning mechanisms also tend to be relatively complex and are subject to increased wear and require a high level of maintenance. Tuning mechanisms which have achieved some smoothness in tuning have done so at the expense of undesirable reductions in tuning speeds.
Corrective measures have also been implemented to overcome the low tuning accuracy of currently available solid state lasers. One such approach has been use of a high-precision wavelength meter control system together with the tunable laser. The wavelength meter typically comprises a high-finesse interferometer and a reference optical wavelength provided by an atomic or molecular emission or absorption feature. The tunable laser is stepped through a series of measurements, with the laser output wavelength being set or calibrated using the wavelength meter as a provider of feedback. This allows adjustment of the output wavelength of the tunable laser in precise amounts or increments to provide equally spaced, accurate measurement of the optical properties of components under test. Corrective measures of this type, however, are time intensive and result in considerable increase in the testing costs for optical components.
There is accordingly a need for an external cavity laser apparatus and method which provides highly accurate and predictable tuning speeds for tunable solid state lasers, which provides for rapid tuning, which provides output at precisely known wavelengths, which is of simple, wear-resistant construction, and which allows for quick and accurate wavelength-dependent characterization of optical components. The present invention satisfies these needs, as well as others, and generally overcomes the deficiencies found in the background art.
An object of the invention is to provide an external cavity laser apparatus and method which allows highly linear or highly predictable change in output wavelength.
Another object of the invention is to provide an external cavity laser apparatus and method which allows fast tuning speeds.
Another object of the invention is to provide an external cavity laser apparatus and method which operates with low tuning noise.
Another object of the invention is to provide an external cavity laser apparatus and method having a simple tuning mechanism which is easy to manufacture and implement.
Another object of the invention is to provide an external cavity laser apparatus and method having tuning mechanism which provides low friction, low wear and low-hysterysis tuning movement.
Another object of the invention is to provide an external cavity laser apparatus and method which delivers highly predictable output wavelengths without requiring complex corrective measures or control systems.
Another object of the invention is to provide a constant tuning speed micropositioning apparatus and method which allows quick and precise characterization of wavelength dependent properties of optical components.
Further objects and advantages of the invention will be brought out in the following portions of the specification, wherein the detailed description is for the purpose of fully disclosing the preferred embodiment of the invention without placing limitations thereon.
SUMMARY OF THE INVENTION
The present invention is a high precision, high tuning speed external cavity laser apparatus and method for tunable solid state lasers and the like. The invention provides for fast, highly predictable tuning of laser output wavelength or frequency and allows quick and easy wavelength- or frequency- specific characterization of optical components.
In its most general terms, the invention comprises an external cavity laser apparatus and method for use that provides an output wavelength which varies linearly and/or with high predictability over time, and which can provide tuning speeds of greater than 100 nanometers per second. More specifically, the invention comprises a laser resonator cavity having first and second reflective elements, at least one of which is movable to provide a constant or highly predictable change in output wavelength with respect to time. A tuning assembly associated with the movable reflective element is structured, configured and positioned to positionally adjust the movable reflective element such that constant changes in output wavelength and high tuning speeds are provided.
In a first presently preferred embodiment of the invention, the tuning assembly comprises a cam body, a motor or like rotating drive source which rotatably drives the cam body, an actuator arm which is mechanically interfaced with the cam body, and a low friction cam interaction surface associated with the mechanical interface of the cam body and the actuator arm. The actuator arm is coupled to the movable reflective element of the resonator cavity, and rotational movement of the cam body is transferred to the movable reflective element via the actuator arm such that the movable reflective element undergoes positional adjustment responsive to movement of the cam body. The output wavelength can be tuned with high linearity and/or predictability with respect to the rotational speed of the drive motor.
By way of example, and not of limitation, the actuator arm preferably is pivotally mounted to a base or surface at a pivot point such that the optical element undergoes positional adjustment which is pivotal in nature with r
Do Khiem
Hand Carter F.
Jenket Bruce
Pieterse Jan-Willem
Wippich Mark
Cannon Alan W.
Jr. Leon Scott
New Focus Inc.
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