Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
  • H01S5/00—Semiconductor lasers
  • H01S5/30—Structure or shape of the active region; Materials used for the active region
  • H01S5/34—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers
  • H01S5/3401—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers having no PN junction, e.g. unipolar lasers, intersubband lasers, quantum cascade lasers
  • H01S5/3402—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers having no PN junction, e.g. unipolar lasers, intersubband lasers, quantum cascade lasers intersubband lasers, e.g. transitions within the conduction or valence bands
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
  • B82Y20/00—Nanooptics, e.g. quantum optics or photonic crystals
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
  • H01S5/00—Semiconductor lasers
  • H01S5/04—Processes or apparatus for excitation, e.g. pumping, e.g. by electron beams
  • H01S5/041—Optical pumping
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
  • H01S5/00—Semiconductor lasers
  • H01S5/06—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium
  • H01S5/0607—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium by varying physical parameters other than the potential of the electrodes, e.g. by an electric or magnetic field, mechanical deformation, pressure, light, temperature
  • H01S5/0608—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium by varying physical parameters other than the potential of the electrodes, e.g. by an electric or magnetic field, mechanical deformation, pressure, light, temperature controlled by light, e.g. optical switch
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
  • H01S5/00—Semiconductor lasers
  • H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
  • H01S5/12—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region the resonator having a periodic structure, e.g. in distributed feedback [DFB] lasers
  • H01S5/1228—DFB lasers with a complex coupled grating, e.g. gain or loss coupling

Definitions

• the field of the invention is that of unipolar semiconductor lasers, which is particularly advantageous for generating wavelengths in the mid-infrared range 4-12 ⁇ m.
• FIG. 1 Such a unipolar laser is produced from a stack of layers of semiconductor materials, of thickness calibrated so as to produce structures with quantum wells having discrete levels of energy.
• This type of laser has already been described in the literature and in particular in the following references: F. Capasso, AY Cho, J. Faist, AL Hutchinson, S. Luryi, C. Sirtori, DL Sivco "Unipolar semiconductor laser" EP 95 302 112.8 .
• Unipolar lasers generally with cascade, involve transitions between discrete levels of energy at the level of the conduction band, that is to say for example between the levels Ei and E 2 illustrated in FIG. 1.
• Energy levels involved in this type of structure thus generate wavelengths in the infrared medium which it is difficult to obtain by other more conventional methods.
• the invention proposes a method for optical control of a unipolar laser.
• This method uses optical beams for controlling wavelengths much shorter than the wavelength of the unipolar laser and therefore of frequency which can be modulated very quickly.
• the subject of the invention is a method for controlling a unipolar semiconductor laser comprising a stack of semiconductor layers so as to create a quantum well structure having in at least one of the semiconductor layers said active layer, at least a first discrete energy level Ei and a second discrete energy level E 2 in the conduction band, so as to create a laser emission, of photonic energy corresponding to the difference in energy levels between said first energy level and said second energy level, under electrical excitation, characterized in that it comprises the optical pumping of said active layer or of another layer of the stack by optical means emitting at least one control beam at a length wave, photonic energy greater than or equal to the band gap of the optically pumped layer.
• semiconductor lasers are lasers having a large number of optical modes as shown in FIG.
• One way of rendering such single-mode lasers is to create at the active layer a diffraction grating whose period fixes the emission wavelength and therefore mode.
• the diffraction grating can be obtained by a grating etched in the structure as illustrated in the article by J. Faist et al. Proceedings of the CLEO conference, 1997.
• the invention proposes to operate the optical control of the unipolar laser with two optical beams capable of interfering with the optically created diffraction grating making it possible to produce a single-mode unipolar laser that is optically controlled and easier to manufacture than that requiring engraving operations.
• the invention also relates to a method of optical control of a unipolar semiconductor laser, characterized in that the optical control means comprise two optical beams of the same wavelength and means for making said beams interfere in the stack of semiconductor layers making up the laser so as to create a network of interference fringes in said stack.
• the network of optical control fringes can be obtained from a single control laser and from means of recombination of said beams, using conventional interference methods.
• FIG. 3 illustrates a first example of an optical control method of a unipolar laser according to the invention
• Figure 4 illustrates the operation of the unipolar laser using the first example of optical control method described in Figure 3;
• FIG. 5 illustrates a second example of an optical control method of a unipolar laser according to the invention
• FIG. 6 illustrates the operation of the unipolar laser using the second example of optical control method described in Figure 5;
• FIG. 7 illustrates a first example of a method according to the invention for rendering a single-pole laser by optical means
• FIG. 8 illustrates a second example of a method according to the invention for making a single-pole laser by optical means
• FIG. 9 illustrates a third example of a method according to the invention making it possible to make a unipolar laser singlemode by optical means
• FIG. 10 illustrates a fourth example of a method according to the invention making it possible to make a unipolar laser singlemode by optical means
• - Figure 11 illustrates a mesa structure of a unipolar semiconductor laser used in the method according to the invention.
• the optical control method of a unipolar semiconductor laser comprises a control laser beam coming to act at the level of the active layer of the quantum structure of the laser or at the level of any layer of the stack of layers. of the laser.
• the wavelength of the control laser beam must be sufficiently low for carriers to be photoinjected above the gap of the semiconductor material forming the layer which it is desired to optically pump into the stack of layers of the unipolar laser.
• the control laser beam emits at a wavelength ⁇ i, associated with a photonic energy h ⁇ i, such as electrons of the valence band BV located on a level of energy E 3 , are injected into the conduction band on the energy level E L
• a photonic energy h ⁇ i such as electrons of the valence band BV located on a level of energy E 3
• the semiconductor laser electrons are brought to the energy level E 2 , then falling to the lower energy level Ei release a photonic energy h ⁇ o corresponding to the emission of the laser at the wavelength ⁇ o associated with the frequency ⁇ 0 .
• Electrons are thus simultaneously brought to the energy level Ei by electrical pumping and optical pumping. This results in a kind of congestion on this energy level and leads to a reduction in the gain of the semiconductor laser.
• FIG. 4 illustrates this type of operation for a structure traversed by a current l 0 where passes from the output power of the laser P 0 (without illumination) to the power Pe (under illumination).
• the control laser beam generates electron-hole pairs in any layer of the stack of layers of the laser, which is not necessarily the active layer. This has the effect of increasing the losses of the laser in this layer by absorption of free carriers, and therefore of decreasing the gain resulting from the laser. The result is therefore the same as in the first variant: By increasing the losses, the net gain of the laser has been decreased, and therefore increased its threshold and decreased its operating power, under control lighting.
• the control laser beam emits at a wavelength ⁇ 2 , associated with a photonic energy h ⁇ 2 , such as electrons of the valence band BV, located on an energy level E 3 is injected into the conduction band on the energy level E 2 .
• the control laser acts as an additional optical pumping which is added to the optical pumping of the unipolar semiconductor laser.
• FIG. 6 The operation of this example of a laser is illustrated in FIG. 6. It appears in particular that in the particular case where the unipolar laser is pumped just below its threshold, the supplement provided by the optical pumping allows the laser to operate, the laser control thus acts as an optical switch of the unipolar laser.
• the wavelength ⁇ u emitted by the unipolar laser is then equal to this period d ⁇ u ⁇ d
• a refractive index of the active layer n 3.3 (classic for ll-V semiconductor materials)
• a tunable unipolar laser is thus obtained, which conventionally is more difficult to obtain in the medium-infrared wavelength range (a few microns).
• Such a laser requires neither a change in operating current, nor a change in temperature, which is a huge advantage for the stability of its performance (in particular the output power), as a function of the wavelength.
• optical devices allowing, from a single optical beam emitted by a control laser, to generate the fringes of illumination.
• These devices include an optical beam separation means into two optical beams and a recombination means according to an interference method.
• FIG. 7 illustrates a first example of a method for optical control of a tunable unipolar laser. This process uses the illumination of the unipolar laser 1, emitting in the direction X, by two optical beams Fi and F 2 coming from a control laser 2 emitting a divergent beam F 0 through a lens 3. More precisely, the incident beam F 0 goes to through a biprism 4 which generates the two interference beams Fi and F 2 .
• FIG. 8 illustrates a second example of an optical control method for a unipolar laser in which the interference is created using two Fresnel mirrors 40 and 41, making an angle between them.
• FIG. 9 illustrates a third example of a method of optical control of a unipolar laser in which the interferences are created two diffraction gratings acting in transmission 42 and 43. It can typically be the same mask locally containing a grating 42 of step di and locally a network 43 of step d 2 .
• FIG. 11 illustrates a structure of a unipolar semiconductor laser in which the emitted light is confined by virtue of an architecture in the form of a mesa, and inside the stack of layers thanks to layers of suitable semiconductor materials.
• the upper electrical contact layer is locally removed over a width of around a few microns. More precisely, FIG. 11 shows an optical opening 10 in the upper contact layer 11.
• the active layer 13 is inserted between different stacks of layers, deposited on the surface of a substrate 12.
• An insulating layer 14 and locally etched allows to transport electrons locally.
• Table 1 refers to all the layers, Table 2 details the active region, Tables 3, 4 and 5 refer to specific stacks determined to obtain the required energy levels. TABLE 1
• GaAs substrate doped n 2-3x10 18 cm -3

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• Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Nanotechnology (AREA)
• Condensed Matter Physics & Semiconductors (AREA)
• General Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Life Sciences & Earth Sciences (AREA)
• Biophysics (AREA)
• Crystallography & Structural Chemistry (AREA)
• Semiconductor Lasers (AREA)

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• 1998
  • 1998-10-13 FR FR9812812A patent/FR2784514B1/fr not_active Expired - Lifetime
• 1999
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  • 1999-10-12 WO PCT/FR1999/002457 patent/WO2000022704A1/fr active Application Filing
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