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
  • H01S5/06—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium
  • H01S5/062—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium by varying the potential of the electrodes
  • H01S5/0625—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium by varying the potential of the electrodes in multi-section lasers
• • 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
  • H01S5/16—Window-type lasers, i.e. with a region of non-absorbing material between the active region and the reflecting surface
• • 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
  • H01S5/02—Structural details or components not essential to laser action
  • H01S5/028—Coatings ; Treatment of the laser facets, e.g. etching, passivation layers or reflecting layers
  • H01S5/0287—Facet reflectivity
• • 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
  • H01S5/042—Electrical excitation ; Circuits therefor
  • H01S5/0425—Electrodes, e.g. characterised by the structure
  • H01S5/04254—Electrodes, e.g. characterised by the structure characterised by the shape

Definitions

• the present invention relates to a multi-region semiconductor laser (1) developed to reduce the temperature of the laser output facet.
• semiconductor lasers also called as diode lasers
• diode lasers can be exemplified as telecommunication systems, fiber-optic communication, material processing, and high-power laser systems.
• catastrophic optical damage on the output facet of lasers occurs commonly in the state of the art.
• the catastrophic optical mirror damage (COMD) occurs mainly due to the output facet heating, which results from optical absorption on the facet, non-radiative losses, and self-heating of the device. All these parameters also depend on the laser output power and current density of the laser source.
• Standard high-power semiconductor lasers are comprised of a single cavity that operates at high currents (10-20A) and generates high powers (10-20W) .
• said lasers comprise high electro-optic power conversion efficiencies ( >% 60 )
• the power that is not converted into light constitutes a very high thermal load on the laser chip. This increases the cavity temperature of the laser and more importantly the temperature of the laser output facet that exhibits the greatest susceptibility to failure, thereby causing the catastrophic mirror damage.
• SUBSTITUTE SHEETS (RULE 26) operating output power and lifetime of these devices. This problem constitutes greater importance for high-power semiconductor lasers requiring high currents compared to the other lasers. Since fiber and direct-diode laser systems comprise so many of such lasers, the catastrophic optical damage on the individual chip affects the performance and cost of these systems significantly.
• thermal runaway [1] which starts when the laser output facet reaches the critical temperature (T c ) .
• T c critical temperature
• Thermal runaway process cannot be stopped for the laser once the critical temperature is reached and it leads to a device failure with a significant or total loss of the laser output power .
• Al-free laser structures with low surface recombination velocity are developed to increase the optical strength of the laser output facet against COMD.
• Lasers with large optical cavity structures are implemented to reduce the optical intensity on the laser output facet and hence enhancing its optical strength by increasing the power level for COMD.
• Two-step growth based nonabsorbing mirror structures decrease the absorption of the output light by means of shifting or eliminating quantum wells.
• Another study conducted in the state of art within this scope is to form laser output facets by cleaving them in a vacuum environment, coating the mirror to decrease the number of point defects by preventing facet oxidation .
• Defects are formed on said facets during the cleaving process and they cause optical absorption.
• Facet passivation techniques are implemented to improve the optical strength of the facet against COMD.
• the laser is cleaved in the air environment, it is cleaned in a vacuum environment by means of plasma and facet is passivated with hydrogenated amorphous silicon.
• Semiconductor laser facets are passivated by implementing such a method in the patent document "US6618409".
• US5144634 after the laser is cleaned in a vacuum environment, it is passivated by a thin film of Silicon, Germanium or Antimony.
• Another method employed in the state of art to reduce the output facet temperature is the unpumped window method.
• forming an unpumped window next to the facet (10-50pm) of the laser prevents the electrical current injection near facet and ensures to minimize non-radiative surface recombination, thus decreasing the facet temperature.
• Methods such as a dielectric layer, implantation, semiconductor layers, and patterned contact metals have been employed for the current blocking.
• US6373875" relates to a development carried out to decrease the temperature of the output facet and hence increase of the semiconductor laser lifetime by using an unpumped window.
• forming an unpumped window causes optical absorption losses and its length is limited.
• Another method for increasing the optical strength of the laser facet against COMD is the transparent window technique.
• the patent application "US4845725A” can be presented as an example of the transparent window method.
• the quantum well profile can be modified by the diffusion of impurity atoms to form a transparent window.
• Such a window is obtained by increasing the energy bandgap near the laser output window.
• This method has disadvantages such as unintended wavelength shift of the laser region and introduced impurity atoms causing absorption and limiting the length of the window (1-20 pm) .
• the patent application "US7567603" relates to a semiconductor laser, wherein said two methods are implemented together.
• partial current region is added to this combination so as to reduce the current near the output facet even further and to increase facet strength against COMD.
• the above-mentioned methods are approaches applied near the laser output facet and intended to reduce or eliminate possible non-radiative recombination or optical absorption on the facet to retard or avoid the COMD in semiconductor lasers.
• Temperature is one of the main reasons triggering the COMD and the methods discussed above reduce the temperature increase resulting from the non-radiative recombination or absorption and the problems that may result therefrom.
• the self-heating resulting from the limited electrical-to- optical conversion efficiency of the laser contributes significantly to the heating of the laser output facet and said methods do not address this heating mechanism.
• the distance between the laser region and laser output facet is quite short, it is not possible to reduce the facet temperature of the laser to levels lower than its cavity/body temperature in any of said methods.
• the invention discloses a semiconductor laser wherein the laser chip is comprised of multi-regions to reduce the heating of the output facet resulting from the self-heat load of the laser region, such that the laser region with high thermal load is separated from the laser output facet to reduce the facet temperature and increase the optical strength of the output facet against the catastrophic optical damage.
• Another object of the invention is to increase the lifetime and reliability of semiconductor lasers by means of a single chip structure, wherein the laser chip is comprised of multi-region.
• Another object of the invention is to make the laser output facet optically stronger by means of a single chip structure in semiconductor lasers, wherein the laser chip is comprised of multi-region, and hence allow the laser to operate at higher powers .
• Another object of the invention is to ensure that the laser cavity region, wherein the laser chip is comprised of multi ⁇ region, operate at currents similar to the standard one-region lasers and generates high powers.
• Another object of the present invention is to operate the transparency region, wherein the laser chip is comprised of multi-regions, at low currents and allow guiding the laser light to the laser output facet.
• Figure 6 For the one-region and two-region lasers, (a) change of active region temperature and (b) laser output power vs. the transparency region current.
• the present invention relates to a multi-region semiconductor laser (1) developed to reduce the temperature of the output facet in semiconductor lasers.
• the heat generated herein is reduced by separating the laser region (1.1) containing a high thermal load from the laser output facet (1.5) by employing a single chip structure, wherein said laser chip is comprised of multi-region, to improve the optical strength of the output facet against the catastrophic optical damage.
• the inventive multi-region semiconductor laser (1) is a single chip comprised of multi-regions.
• the multi-region semiconductor laser (1) comprises the laser region (1.1) in which the laser beam is generated, wherein the other one is the transparency region (1.2) serving as a transparent waveguide to guide the laser beam out of the chip.
• the multi-region semiconductor laser (1) comprises a waveguide (1.3) having the active region generating the laser beam, and two facets, namely high-reflective mirror- coated facet (1.4) and low-reflective mirror-coated facet (1.5) .
• the current given to the laser region is defined as the laser operating current (Ii) and the current given to the transparency region is defined as the transparency region current (I 2 ) .
• the laser region (1.1) in the multi-region semiconductor laser (1) operates at high current and generates high power similar to standard lasers.
• the value of the transparency region current (I 2 ) guiding the laser output to the output facet (1.5) is in the range of 0 ⁇ I 2 ⁇ Ii* (L2/L1) .
• the optimum value of the transparency region current (I 2 ) is less than the laser threshold current of the transparency region and greater than the transparency current.
• the semiconductor laser (1) is comprised of the high-reflective mirror-coated facet (1.4), laser region (1.1), transparency region (1.2) and low-reflective mirror-coated facet (1.5), respectively.
• the laser beam generated in the laser region (1.1) is emitted from the low-reflective mirror-coated facet (1.5) by passing through the transparency region (1.2) . Therefore, the low-reflective mirror-coated facet (1.5) is also called as the laser output facet.
• the output facet (1.5) is separated from the self-heated laser region (1.1) by means of the transparency region (1.2), it may be ensured that the output facet (1.5) is kept at much lower temperatures than the laser region (1.1) . Therefore, the effect of the high thermal load of the laser region (1.1) on the output facet (1.5) can be reduced and the optical strength of said facet against the catastrophic optical damage is increased by means of the invention.
• the fundamental principle of the inventive multi-region semiconductor laser (1) is that the transparency current (I 2 ) of the transparency region (1.2) with a length of L 2 is much lower than the laser operating current (Ii) of the laser region (1.1) with a length of Li.
• the transparency region current (I 2 ) given to the transparency region (1.2) should basically meet the condition of 0 ⁇ I 2 ⁇ Ii* (L 2 /L I ) .
• This current may be controlled by means of employing two different current sources or may be also controlled by both a single current source and the connection of resistance to a current arm leading to the transparency region (1.2) .
• This approach is illustrated in Figure 3.
• other electronic circuit elements may be employed to control the transparency region current (I 2 ) .
• Another element that can be used to control the transparency region current (I 2 ) is the patterned contact structure shown in Figure 4. Methods such as patterned metal contact, dielectric, implantation or current-blocking semiconductor structures may be employed to obtain this patterned structure.
• the thermal-reflectance method is used to compare the facet temperatures of the multi-region semiconductor laser (1) and the standard single region laser.
• Figure 6(a) shows how the temperature of the active region (the highest temperature in the waveguide region) changes with the laser region current (Ii) and transparency region current (I 2 ) in the two-region and one-region semiconductor laser.
• the facet temperature decreases, and this temperature level does not change with the transparency region current (I 2 ) .
• Figure 6(b) when there is no current injection into the transparency region (1.2), there will be a significant loss ( ⁇ 15%) of laser output power due to the absorption losses in the transparency region. After the current injection into the said region, the transparency is formed, and the output power is recovered without any laser power loss .

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• Physics & Mathematics (AREA)
• Condensed Matter Physics & Semiconductors (AREA)
• General Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Optics & Photonics (AREA)
• Semiconductor Lasers (AREA)

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• 2019
  • 2019-05-22 WO PCT/TR2019/050359 patent/WO2019226140A1/en active Application Filing
  • 2019-05-22 CN CN201980035014.8A patent/CN112189284B/zh active Active

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