Tuning system for external cavity diode laser
First Claim
1. In a tunable diode laser having an external cavity including a collimating lens, a rotatable mirror for reflecting a selected wavelength from a diffraction grating back into the laser, means for simultaneous rotation and linear translation of said mirror comprising:
- a. a pivot axis, for rotation of said mirror, positioned at the intersection of the bisectors of the angles created by the normals to the mirror planes at the points of intersection between said minor for first, second and third positions of said mirror;
b. the first said position representing the angular position which reflects a first desired wavelength, diffracted by said diffraction grating, in the tuning rang of said system, and a first lineal position corresponding to an optical distance for said lasers and cavity representing a first integral number of half wavelengths at said first desired wavelength;
c. the second said position representing the angular position which reflects a second desired wavelength, the nominal center wavelength of said system, diffracted by said diffraction grating and a second lineal position corresponding to the optical distance for said laser and said cavity representing said first integral number of half wavelengths at said nominal center wavelength of said system;
d. the third said position representing the angular position which reflects a third desired wavelength, on the opposite side of said nominal center wavelength form said first desired wavelength and within the tuning range of said system, diffracted by said diffraction grating and a third lineal position corresponding to the optical distance for said laser and cavity representing said first integral number of half wavelengths at said third wavelength; and
,e. said first, second and third lineal positions including distance corrections to the actual physical length corresponding to the length and indices of refraction of the window of said diode laser and a distance correction corresponding to the thickness and indices of refraction of the lens.
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Abstract
A tunable external cavity semiconductor laser is provided with a semiconductor laser diode, a diffraction grating and a movable mirror. The diode laser is positioned to illuminate a diffraction grating and a movable mirror is positioned to reflect a selected wavelength back into the cavity. The mirror is mounted on a pivot so positioned to provide simultaneous rotation and linear translation. The pivot point is selected so as to provide an internal cavity length which is exactly an integral number of half wavelengths at three different wavelengths and an exceptionally close (within 1/1000 of one wavelength) match at all other wavelengths within the tuning range. Significantly, the pivot point calculation takes into account the effect of the dispersion of the laser and other optical elements in the system on the cavity length. These elements are usually a small part of the physical length of the cavity, but their greater dispersion makes their contribution to the number of half wavelengths in the resonant cavity very significant.
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Citations
18 Claims
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1. In a tunable diode laser having an external cavity including a collimating lens, a rotatable mirror for reflecting a selected wavelength from a diffraction grating back into the laser, means for simultaneous rotation and linear translation of said mirror comprising:
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a. a pivot axis, for rotation of said mirror, positioned at the intersection of the bisectors of the angles created by the normals to the mirror planes at the points of intersection between said minor for first, second and third positions of said mirror; b. the first said position representing the angular position which reflects a first desired wavelength, diffracted by said diffraction grating, in the tuning rang of said system, and a first lineal position corresponding to an optical distance for said lasers and cavity representing a first integral number of half wavelengths at said first desired wavelength; c. the second said position representing the angular position which reflects a second desired wavelength, the nominal center wavelength of said system, diffracted by said diffraction grating and a second lineal position corresponding to the optical distance for said laser and said cavity representing said first integral number of half wavelengths at said nominal center wavelength of said system; d. the third said position representing the angular position which reflects a third desired wavelength, on the opposite side of said nominal center wavelength form said first desired wavelength and within the tuning range of said system, diffracted by said diffraction grating and a third lineal position corresponding to the optical distance for said laser and cavity representing said first integral number of half wavelengths at said third wavelength; and
,e. said first, second and third lineal positions including distance corrections to the actual physical length corresponding to the length and indices of refraction of the window of said diode laser and a distance correction corresponding to the thickness and indices of refraction of the lens. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. In an external cavity tunable laser system having a laser, having a laser, a diffraction grating and a rotatable mirror positionable to reflect a beam diffracted by said diffraction grating at a selected angle, corresponding to the diffraction angle of a selected wavelength, back into said laser, the improvement comprising:
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a. pivot means for said mirror; b. the axis of rotation of said pivot means positioned at the line of intersection of the bisectors of the angles created by the normals to the plane of said mirror at three different angular positions of said mirror representing the diffraction angle from said grating of three different wavelengths; c. said normals passing through their corresponding mirror planes at the points of intersection between said mirror planes at said three different angular positions; d. said three different angular positions of said mirror corresponding to the angular position which reflects three different wavelengths within the tuning range of said laser and a lineal position representing an integral number of half wavelengths within said cavity at said three different wavelengths; and
,e. one of said three different wavelengths is the nominal center wavelength of the system. - View Dependent Claims (11, 12, 13)
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14. An external cavity tunable laser system comprising:
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a. a base member; b. diffraction grating means mounted on said base member; c. diode laser means mounted on said base member and having an output beam positioned to strike said grating at a grazing angle; d. mirror means for reflecting a diffracted beam from said grating back onto said grating and thence back into said laser; e. mirror mounting means providing for simultaneous lineal and rotational movement of said mirror about an axis of rotation corresponding to the line of intersection of the bisectors of the angles created by the normals to the plane of said mirror at three different positions of said mirror, said normals passing through their corresponding mirror planes at the points of intersection between said mirror planes at said three different angular positions, each of said three different angular positions of said mirror providing an integral number of half wavelengths within said cavity at a selected wavelength, calculated according to the general formula;
space="preserve" listing-type="equation">Opl=Ph1+C,where; Opl=the optical length of the tuning cavity Phl=the physical length of the tuning cavity C=a correction for the wavelength-dependent indices of refraction of the optical elements of the system. - View Dependent Claims (15, 16, 17, 18)
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Specification