Abstract:
An external cavity laser tuner. One embodiment constructed according to principles of the invention includes a cantilever interposed between the laser cavity mirrors or operating as a mirror. Another embodiment constructed according to principles of the invention includes a torsional mirror interposed between the laser cavity mirrors or operating as a mirror. A further embodiment constructed according to principles of the invention includes a torsional filter interposed between the laser cavity mirrors. An additional embodiment constructed according to principles of the invention includes an electrooptic prism interposed between the laser cavity mirrors.

Description:
REFERENCE TO EARLIER APPLICATION 
     This Application claims the benefit of United States Provisional Application No. 60/099,556, filed Sep. 9, 1998, by P. Tayebati, entitled Compact External Cavity Tunable Lasers Using Hybrid Integration With Micromachined And Electrooptic Tunable Elements. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to lasers, and more specifically to tuning external cavity lasers. 
     BACKGROUND OF THE INVENTION 
     Lasers are well known in the art. A laser typically comprises a front mirrored end and a rear mirrored end which are disposed so as to establish a reflective cavity therebetween. An active, or gain, region is disposed between the two mirrored ends. The gain region is constructed so that when the gain medium is appropriately stimulated, it will emit light. The rear mirror typically is substantially fully reflective at the wavelengths of interest, and the front mirror typically is partially reflective at the wavelengths of interest so as to allow a beam of laser light to be emitted therefrom. 
     A laser may be tuned to emit light at wavelengths of interest. Tuning the laser promotes emission of light at a desired wavelength. Tuning typically involves absorbing or scattering light outside the desired wavelength. 
     SUMMARY OF THE INVENTION 
     The invention is an external cavity laser tuner. 
     One embodiment constructed according to the principles of the invention includes a cantilever interposed between the laser cavity mirrors or operating as a mirror. 
     Another embodiment constructed according to the principles of the invention includes a torsional mirror interposed between the laser cavity mirrors or operating as a mirror. 
     A further embodiment constructed according to the principles of the invention includes a torsional filter interposed between the laser cavity mirrors. 
     An additional embodiment constructed according to principles of the invention includes an electrooptic prism interposed between the laser cavity mirrors. 
     These and other features of the invention will be appreciated more readily in view of the drawings and detailed description below. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is described in detail below with reference to the following drawings, throughout which similar reference characters denote corresponding features consistently, wherein: 
     FIG. 1 is a schematic representation of an external cavity laser including an embodiment of a laser tuner constructed according to principles of the invention; 
     FIG. 2 is a schematic representation of an external cavity laser including another embodiment of a laser tuner constructed according to principles of the invention; 
     FIG. 3 is a top perspective view of the laser tuner of FIGS. 1 and 2; 
     FIG. 4 is a schematic representation of an external cavity laser including a further embodiment of a laser tuner constructed according to principles of the invention; 
     FIG. 5 is a schematic representation of an external cavity laser including an additional embodiment of a laser tuner constructed according to principles of the invention; 
     FIGS. 6 and 7 are perspective views of the laser tuner of FIGS. 4 and 5, showing articulation thereof; 
     FIG. 8 is a schematic representation of an external cavity laser including yet another embodiment of a laser tuner constructed according to principles of the invention; 
     FIG. 9 is a perspective view of the laser tuner of FIG. 8; 
     FIG. 10 is a schematic representation of an external cavity laser including yet a further embodiment of a laser tuner constructed according to principles of the invention; 
     FIG. 11 is a schematic representation of an external cavity laser including yet an additional embodiment of a laser tuner constructed according to principles of the invention; and 
     FIGS. 12 and 13 are schematic representations of the laser tuner of FIGS. 10 and 11, showing different voltage-related tuning characteristics thereof. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention is an external cavity laser tuner. The four embodiments of a tuner for tuning a diode laser system integrate micro-electromechanical components and electrooptic components with a semiconductor gain medium. 
     1. Tunable External Cavity Laser Diode Using A Micromachined Cantilever. 
     Referring to FIG. 1, a tunable external cavity laser is shown including a micro-electromechanical cantilever. The laser includes a semiconductor optical amplifier (SOA)  1 ; a beam shaping lens system  2 ; an appropriate waveplate  3 ; the microelectromechanical or microelectromagnetic cantilever  4 ; a diffraction grating  5 ; and a collimating lens  6 . 
     This embodiment of an external cavity tunable laser employs an antireflection-coated SOA  1  as a gain medium. Light introduced into the SOA excites the atomic structure of the SOA which intensifies the energy level of light directed therethrough. Alternatively, electrical energy may be introduced into the SOA for intensifying the energy level of the light. 
     The lens  2  shapes the emerging emission from the SOA  1  and directs the beam onto a waveplate  3 . The waveplate  3  polarizes the beam. 
     From the waveplate  3 , the light beam is focused onto a micromachined beam steering cantilever  4 . The output beam then is collimated with a lens  6  and projected onto a diffraction grating  5 . 
     The foregoing elements are arranged in a geometry that retro-reflects some wavelength of light back into the SOA. 
     Referring to FIG. 3, the cantilever  4  has a length ranging from 100 μm to 500 μm and a width ranging from 50 μm to 300 μm. The cantilever  4  is tuned electrostatically or electromagnetically in ways known in the art of micromechanical technology. By tuning the angle A 1  of the cantilever relative to a reference line R 1 , a different wavelength of light is generated by the cavity. 
     In FIG. 2 a variant of the tunable laser is shown in which an antireflection-coated SOA  1  again is the gain medium. A lens  2  and a waveplate  3  shape and polarize the emerging emission from the SOA. The output beam is collimated and projected onto a diffraction grating  5 . The diffracted light then is focused with the collimating lens  6  onto a micromachined beam steering cantilever  4 , as described above. 
     As with the embodiment of FIG. 1, the elements are arranged in a geometry that retro-reflects some wavelength of light back into the SOA. Also, by tuning the angle A 1  of the cantilever  4  relative to a reference line R 1 , a different wavelength of light is generated by the cavity. 
     2. Tunable External Cavity Laser Diode Using A Microelectromechanical Torsion Mirror. 
     Referring to FIG. 4, a tunable external cavity laser is shown including a microelectromechanical or mircroelectromagnetic torsion mirror. The device includes a semiconductor optical amplifier (SOA)  1 ; a beam shaping lens system  2 ; an appropriate waveplates  3 ; a diffraction grating  5 ; a collimating lens  6 ; and the torsion mirror  7 . 
     This embodiment of an external cavity tunable laser employs an antireflection-coated SOA  1  as a gain medium. 
     The lens  2  shapes the emerging emission from the SOA  1  and directs the beam onto a waveplate  3 . The waveplate  3  polarizes the beam. 
     From the waveplate  3 , the light beam is focused onto a micromachined beam-steering torsion mirror  7 . The output beam then is collimated using a lens  6  and projected onto a diffraction grating  5 . 
     The foregoing elements are arranged in a geometry that retro-reflects some wavelength of light back into the SOA. 
     Referring to FIGS. 6 and 7, the mirror has dimensions ranging from 10 μm to 500 μm. The mirror has torsion arms with lengths ranging from 10 μm to 300 μm. 
     The torsion mirror is tuned electrostatically or electromagnetically in ways known in the art of micromechanical technology. By tuning the angle A 2  of the torsion mirror relative to a reference line R 2 , a different wavelength of light is generated by the cavity. 
     In FIG. 5 a variant of the tunable laser is shown including an antireflection-coated SOA  1  as a gain medium. A lens  2  and a waveplate  3  shape the beam and polarization of the emerging emission from the SOA. The output beam is collimated and projected onto a diffraction grating  5 . The diffracted light is focused, using a lens  6 , onto a micromachined beam-steering torsion mirror  7 , as described above. 
     As with the embodiment of FIG. 4, the elements are arranged in a geometry that retro-reflects some wavelength of light back into the SOA. Also, by tuning the angle A 2  of the torsion mirror relative to a reference line R 2 , a different wavelength of light is generated by the cavity. 
     3. Tunable External Cavity Laser Diode Using A Tunable Microelectromechanical Torsion Filter. 
     Referring to FIG. 8, an external cavity tunable laser is shown including a microelectromechanical or mircroelectromagnetic torsion Fabry-Perot filter. The device includes a semiconductor optical amplifier (SOA)  1 ; a beam-shaping lens system  2 ; the torsion Fabry-Perot filter  3 ; a collimating lens  4 ; and a mirror  5 . 
     This embodiment of an external cavity tunable laser employs an antireflection-coated SOA  1  as a gain medium. 
     The lens  2  shapes the profile of the emerging emission from the SOA  1 . The light then is focused onto a micromachined torsion filter  3 . The output beam is collimated and returned to the SOA with a lens  4  and a mirror  5 . 
     Referring to FIG. 9, the filter has a dimension ranging from 10 μm to 500 μm. The filter has torsion arms with lengths ranging from 10 μm to 300 μm. The filter area is a multicavity or single cavity filter deposited with standard methods. 
     The torsion filter is tuned electrostatically or electromagnetically in ways known in the art of micromechanical technology. By tuning the torsion filter, the angle A 3  of the torsion filter is adjusted relative to a reference line R 3 . The transmission wavelength of the Fabry-Perot filter is modified correspondingly and a different wavelength of light generated by the laser cavity. 
     The torsion filter is independently an innovative technology claimed by the inventor. 
     4. Tunable External Cavity Laser Diode Using An Electrooptic Prism. 
     Referring to FIG. 10, an external cavity laser is shown including an electrooptic prism. The device includes a semiconductor optical amplifier (SOA)  1 ; a beam-shaping lens system  2 ; an appropriate waveplate  3 ; a diffraction grating  5 ; a collimating lens  6 ; a beam-stirring electrooptic prism  9 ; and a mirror  10 . 
     This embodiment of an external cavity tunable laser employs an antireflection-coated SOA  1  as a gain medium. The lens  2  and waveplate  3  shape the beam and polarization of the emerging emission from the SOA. The light then is collimated and projected onto the diffraction grating  5 . The diffracted light is focused onto a beam-steering electrooptic prism  9  using the lens  6  and projected onto a combination of mirror  10  and lens. 
     The device is configured with a geometry that retro-reflects some wavelength of light back into SOA causing laser oscillations. 
     Referring to FIGS. 12 and 13, the electrooptic prism  9  is tuned by applying a voltage across the prism  9 . Altering the voltage alters the index of refraction of the prism  9  which stirs the exiting beam. Tuning the angle of the beam promotes different wavelengths of light in cavity. 
     The electrooptic prism  9  may be constructed from linear or quadratic electrooptic crystals or materials. 
     In FIG. 11 a variant of the tunable laser is shown in which an antireflection-coated SOA  1  is used as a gain medium. A lens  2  and a waveplate  3  shape the beam and polarization of the emerging emission from the SOA. The output beam then is focused and incident onto one side of an electrooptic prism  9 . The refracted light is collimated with the lens  6  onto a diffraction grating  5 . 
     As with the foregoing embodiment, the device is configured with a geometry which retroreflects the diffracted light. Also, tuning the angle of the beam promotes different wavelengths of light in cavity. 
     The invention is not limited to the foregoing, but encompasses all improvements and substitutions consistent with the principles of the invention.