Coherent light generators – Particular beam control device – Tuning
Reexamination Certificate
1998-09-14
2001-08-28
Arroyo, Teresa M. (Department: 2881)
Coherent light generators
Particular beam control device
Tuning
C372S098000, C372S099000
Reexamination Certificate
active
06282213
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the field of tunable diode lasers, and particularly to tunable diode laser configured as a Littman-Metcalf laser cavity with high speed line selection capability.
BACKGROUND OF THE INVENTION
Tuning for a monochromatic light, such as emission from a laser diode, is most commonly realized by using the Littman-Metcalf external cavity configuration with a diffraction grating and a rotating mirror used to select the specific wavelength. Using this approach, a high degree of precision in the rotation mechanism is required for wavelength selection, and the tuning process is very slow. This original approach as applied to dye laser technology is described in detail in the following non-patent prior art: M. G. Littman and H. J. Metcalf, Applied Optics, vol. 17, no. 14, 2224-2227, Jul. 15, 1978, and P. McNicholl and H. J. Metcalf, Applied Optics, vol. 24, no. 17, 2757-2761, Sep. 1, 1985.
Recently, a variety of techniques have been applied to tuning diode lasers. Versatility and low cost are desired specifically in spectroscopic applications. For example, a variety of U.S. Patents exist for laser tuning with alternative configurations of the mirror at the cavity end. U.S. Pat. No. 4,896,325 discloses an alternative cavity configuration in which a pair of mirrors with narrow discontinuities to provide reflective maxima bound the active cavity. These narrow bands of reflective maxima provides means for wavelength tuning which is actively controlled by a vernier circuit. U.S. Pat. No. 4,920,541 discloses an external laser cavity configuration of multiple resonator mirrors used to produce multiple wavelength emission from a single laser cavity simultaneously or with a very fast switching time. U.S. Pat. No. 5,319,668 discloses a tunable diode laser with a diffraction grating for wavelength separation and a moveable mirror at the cavity end for wavelength selection. The pivot points are designed to provide an internal cavity length specific for the production of several wavelengths. Alternative tuning arrangements are possible. U.S. Pat. No. 5,771,252 discloses an external cavity continuously tunable wavelength source utilizing a cavity end reflector moveable about a pivot point for simultaneous rotation and translation for wavelength selection.
In addition, several U.S. Patents disclose the use of alternative components in the laser cavity configuration in order to achieve wavelength tuning. U.S. Pat. No. 4,216,439 discloses a spectral line selection technique that utilizes a spectral line selection medium in the gain region of an unstable laser resonator cavity. U.S. Pat. No. 4,897,843 discloses a microprocessor-controlled laser system capable of broadband tuning capabilities by using multiple tuning elements each with progressively finer linewidth control. U.S. Pat. No. 5,276,695 discloses a tunable laser capable of multiple wavelength emission simultaneously or with a very fast switching time between lines by using a laser crystal in the cavity and fine rotation of the cavity end reflective element. U.S. Pat. No. 5,734,666 discloses a wavelength selection apparatus for a laser diode eliminating mechanical motion of a grating by utilizing a laser resonator for wavelength range selection and a piezoelectric-controlled crystal for specific wavelength selection.
Recent non-patent prior art also discloses relevant technology. In SPIE vol. 2482, pp. 269-274 by Zhongqi, Zhang, et al., a microprocessor-controlled tunable diode laser that utilizes a stepper motor to rotate the grating for wavelength tuning is described. In addition, in SPIE vol. 3098, pp. 374-381 by Uenishi, Akimoto, and Nagoka, a tunable laser diode with an external silicon mirror has been fabricated with MEMS technology and has wavelength tunability.
All of the prior art described above is limited in its performance by one or more of the following: requiring mechanical motion, small wavelength range tunability, or specified or limited line selection order. Especially for applications in spectroscopy, broadband wavelength tuning, arbitrary or simultaneous line selection, and limited or no mechanical motion are desired characteristics.
OBJECTS OF THE INVENTION
Therefore, it is the object of the invention disclosed herein to provide a tunable diode laser with broadband digital line selection capability.
It is also an object of the invention disclosed herein to provide a tunable diode laser with fast, broadband, digital line selection capability in arbitrary order.
It is also an object of the invention disclosed herein to provide a tunable diode laser with fast, broadband, digital line selection capability in arbitrary order that allows discrete switching between a predetermined series of wavelengths.
SUMMARY OF THE INVENTION
The present invention provides an improved tunable diode laser configuration over the prior art. A focusing element, such as a concave mirror or a lens, used in combination with a micromirror array serves as the retroreflector in a typical Littman-Metcalf laser cavity. This configuration provides both arbitrary and simultaneous line selection capability over a very broad wavelength range. The use of individually controllable micromirrors within the micromirror array eliminates the high precision mechanical motion of the grating element and improves the overall durability and ruggedness of the device. The present invention can be universally adapted to any laser diode device. The advantages that the present invention provides over the prior art are particularly significant in various spectroscopic applications.
REFERENCES:
patent: 4216439 (1980-08-01), Pond et al.
patent: 4896325 (1990-01-01), Coldren
patent: 4897843 (1990-01-01), Scott
patent: 4920541 (1990-04-01), Baumgartner et al.
patent: 5230005 (1993-07-01), Rubino et al.
patent: 5276695 (1994-01-01), Scheps
patent: 5319668 (1994-06-01), Luecke
patent: 5524012 (1996-06-01), Wang et al.
patent: 5624437 (1997-04-01), Freeman et al.
patent: 5734666 (1998-03-01), Wada et al.
patent: 5771252 (1998-06-01), Lang et al.
M.G. Littman and H.J. Metcalf, “Spectrally Narrow Pulsed Dye Laser Without Beam Expander”, Applied Optics, vol. 17, No.14, Jul. 15, 1978, 2224-2227.
P. McNicholl and H.J. Metcalf, “Synchronous Cavity Mode And Feedback Wavelength Scanning in Dye Laser Oscillators with Gratings”, Applied Optics, vol. 24, No. 17, Sep. 1, 1985, 2757-2761.
K.C. Harvey and C.J. Myatt, “External-cavity Diode Laser Using a Grazing incidence Diffraction Grating”, Optics Letters, vol. 16, No. 12, Jun. 15, 1991, 910-912.
P. Zhongqi, Z. Hanyi, Y. Jinqiang, et al., “Programmable Tuning External Cavity Laser Diode”, SPIE Proceedings, vol. 2482, May 1995, 269-274.
Y. Uenishi, K. Akimoto, and S. Nagaoka, “Microelectromechanical Systems (MEMS) and Their Photonic Applications”, SPIE Proceedings, vol. 3098, Sep. 1997, 374-381.
Castracane James
Gutin Mikhail A.
Arroyo Teresa M.
InterScience, Inc.
Menefee James
Simkulet Michelle D.
Yablon Jay R.
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