WO2002047223A1 - Dispositif laser a semi-conducteur a cavite verticale et a pompage optique - Google Patents

Dispositif laser a semi-conducteur a cavite verticale et a pompage optique Download PDF

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Publication number
WO2002047223A1
WO2002047223A1 PCT/GB2001/005387 GB0105387W WO0247223A1 WO 2002047223 A1 WO2002047223 A1 WO 2002047223A1 GB 0105387 W GB0105387 W GB 0105387W WO 0247223 A1 WO0247223 A1 WO 0247223A1
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Prior art keywords
laser
pump
mirror
wavelength
cavity
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PCT/GB2001/005387
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English (en)
Inventor
Arnaud Garnache-Creuillot
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University Of Southampton
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Priority to AU2002220897A priority Critical patent/AU2002220897A1/en
Publication of WO2002047223A1 publication Critical patent/WO2002047223A1/fr

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    • 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
    • H01S5/18—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities
    • H01S5/183—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities having only vertical cavities, e.g. vertical cavity surface-emitting lasers [VCSEL]
    • H01S5/18361—Structure of the reflectors, e.g. hybrid mirrors
    • 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
    • H01S5/10—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
    • H01S5/14—External cavity lasers
    • H01S5/141—External cavity lasers using a wavelength selective device, e.g. a grating or etalon
    • 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
    • H01S5/18—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities
    • H01S5/183—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities having only vertical cavities, e.g. vertical cavity surface-emitting lasers [VCSEL]
    • H01S5/18383—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities having only vertical cavities, e.g. vertical cavity surface-emitting lasers [VCSEL] with periodic active regions at nodes or maxima of light intensity

Definitions

  • the invention relates generally to semiconductor lasers and in particular to vertical external cavity surface-emitting semiconductor lasers.
  • Compact lasers with output powers of at least Watt-level with good spatial beam profiles have applications including optical communications, high-density optical storage, laser radar, materials processing and laser absorption spectroscopy.
  • High optical power and diffraction-limited circular laser-beam profiles enable beam propagation over large distances and focusing of high power into small areas.
  • the vertical-cavity surface-emitting laser is a known type of electrically pumped semiconductor micro-cavity laser that offers the advantages of high-speed, dynamic, single-longitudinal-mode operation; output in a circular astigmatism-free beam; and good electrical to optical power conversion efficiency.
  • the VCSEL micro-cavity is formed from a multiple quantum well (QW) active region placed between multi-layer "Bragg stack" mirrors disposed at the front and the back of a semiconductor chip.
  • QW quantum well
  • the NCSEL devices require a highly reflecting back mirror and a front mirror of lower reflectivity. In practical terms the NCSEL is limited because it has low output power and cannot deliver more than about 3mW in a diffraction-limited beam.
  • the diffraction limited beam is typically achieved using small ( ⁇ 6 ⁇ m) diameter NCSEL devices resulting in a disadvantageous ⁇ large beam divergence (6° half-angle).
  • a further disadvantage of the NCSEL is that the line- width of the laser output is -10 MHz which is broader than is desirable for practical applications.
  • the disadvantages of the VCSEL have been partially overcome by increasing the size of the laser cavity which is achieved by replacing the front multi-layer Bragg mirror by an external concave mirror. This results in a structure known as a vertical- external-cavity surface-emitting laser (NECSEL).
  • NECSEL vertical- external-cavity surface-emitting laser
  • the cavity length is typically in the range from ⁇ m (10 "6 m) to cm (10 "2 m).
  • the external cavity enables production of a diffraction-limited beam output at high (Watt-level) power; reduces the laser line- width in single mode operation; and allows the incorporation of intra-cavity elements.
  • the replacement of the front Bragg stack mirror by an external concave mirror allows the VECSEL to be designed to operate at wavelengths where the reflectivity of the Bragg stack mirrors is low, for example, at around 1.5 ⁇ m.
  • VECSELs can be optically pumped rather than electrically pumped to create optically pumped semiconductor (OPS) VECSELs which combine the advantageous features of diode-pumped solid state lasers and VCSELS.
  • OPS VECSELs typically use a commercial multimode laser diode pump which is focussed onto the semiconductor chip. The diode pump generates optical power, a group of QWs provide gain and the external mirror controls the output modes of the laser.
  • the use of optical pumping means that a large optical mode area can be used for high power operation which reduces susceptibility to optical damage and gives low beam divergence. Since optically pumped laser devices can be made electrically insulating they are less likely optically lossy and are simpler to fabricate.
  • OPS VECSELS offer the advantage that the laser medium has a broad (>40nm) pump bandwidth. This ensures efficient absorption of the spectrally broad pump-diode light, eliminates sensitivity to pump- diode and wavelength variation and also eliminates the requirement for pump-diode lasers with tight wavelength specifications.
  • the main requirement for OPS VECSELS is that the pump wavelength should be greater than the bandgap energy of the active region.
  • FIG. 1 is a schematic diagram of a typical OPS-VECSEL.
  • a laser diode pump 10 emits light 15 at a pump wavelength ⁇ p.
  • the light emanating from the laser diode 10 is passed through a lens 20 which focuses a light beam 25 into an "active region" 30B of a VECSEL structure known as a gain mirror 30.
  • the gain mirror 30 has three main layers comprising a multi-layer mirror 30C, the active region 3 OB and an anti-reflection coating 30 A.
  • the multi-layer mirror 30C is a highly reflective Bragg stack.
  • Bragg stacks are composed of layer-pairs, each pair having a layer of high and a layer of low refractive index material. A number of layer-pairs are placed between two homogeneous media which in this case are the substrate and air.
  • the reflectivity R of the Bragg stack is dependent on the refractive index difference between the materials and the number of pairs of alternate layers used. The reflectivity is expressed by the formula:
  • ni and n 2 are the refractive indices of the materials forming each layer-pair, n s and no are the refractive indices of the substrate and incident medium respectively; and N is the number of periods of layer-pairs.
  • This formula shows that if N is fixed, the reflectivity increases when the ratio n ⁇ /n 2 is increased and conversely if n ⁇ /n 2 is fixed , the reflectivity increases with N.
  • the Bragg stack mirror 30C could for example be constructed from pairs of AlAs/GaAs quarter- wave layers. Since this mirror forms the back mirror of the lasing cavity it is designed to be highly reflective at the laser output wavelength ⁇ L . Thus the layers are constructed with an optical thickness of ⁇ /4.
  • the active region 3 OB comprises a multiplicity of quantum wells, which are typically formed by sandwiching one thin low-band-gap material between two higher- band-gap materials. Typically electrons are trapped in the region with the lower band-gap but they have a finite probability of tunnelling through the high-band-gap barriers.
  • the active region absorbs the incoming light 25 from the optical pump. Electrons and holes, which are "carriers", are generated in the active region by the light from the optical pump. These photo-excited carriers diffuse through the active region and are captured by the multiple QWs that provide gain across a predetermined range of wavelengths. The gain is typically inversely proportional to the thickness of the active region.
  • a standing wave is set up in the chip micro-cavity and the length of the active region is arranged so that the maxima of the intra-cavity standing wave coincide with the locations of the QWs.
  • the electrons and holes are confined to the active region by an anti-reflection (AR) coating 30A which separates the active region 3 OB from an air interface in the main laser cavity.
  • the AR coating 30A is designed to have low reflectivity and thus improved transmissivity at ⁇ L which increases the intensity of laser light entering the main laser cavity 45.
  • the AR coating 30A typically has a broadband absorption profile to improve pump light transmission into the semiconductor. This AR coating is formed from a layer of a dielectric material and a confinement layer that is needed to prevent carriers from diffusing to the semiconductor surface.
  • the main laser cavity 45 is bounded by an external concave mirror 50 at the front and by the highly reflective Bragg micro-mirror 30C at the back.
  • the laser can be tuned by adjusting the length of the laser cavity 45.
  • the laser can also be tuned by altering the position of the incident pump light on the gain mirror structure. By exploiting non- uniformities in the gain mirror structure a shift in the reflection wavelength of the Bragg mirror 30C can thus be achieved.
  • the wavelength of the output laser light 55 is determined both by the particular modes of vibration supported in the cavity, which depend on the length of the laser cavity 45, and by the peak wavelength of the effective gain.
  • the gain mirror 30 forms a micro-cavity that must be coupled to the main laser cavity 45.
  • This coupling is as wavelength-insensitive as possible.
  • a wavelength-insensitive coupling also reduces the interplay between optical and thermal effects. Since optical properties such as refractive indices are very sensitive to temperature changes, poor coupling between the micro-cavity and the main laser cavity 45 is disadvantageous as it may result in the output power of the laser device attaining a maximum at a small value of the incident pump power. Thereafter, further increasing the pump power will cause a rapid decrease in the output power of the device which may then switch-off due to "thermal rollover".
  • the gain mirror 30 is attached to a heat-sink 40.
  • the heat-sink may be mounted on a thermoelectric cooler, in which case, fine wavelength tuning can be achieved by changing the gain mirror temperature.
  • a first prior art design for the gain mirror 30 aims to improve pump power absorption in the gain mirror 30 by making the active layer relatively wide (several ⁇ m) and incorporating within it a large number of QWs.
  • the micro-cavity of the gain mirror is typically designed to operate at resonance.
  • the electric field amplitude of the mode in the active region is a maximum at the location of the QWs.
  • This gain mirror design does increase the absorbed laser pump power but has the disadvantage of increased temperature sensitivity as a direct result of its narrow spectral window of operation.
  • a second prior art design for the gain mirror 30 is described in the research paper "Diode-pumped broadband Vertical-External-Cavity surface Emitting semiconductor laser: Application to high sensitivity intracavity laser absorption spectroscopy", A. Garnache et al., JOSA B, September 2000[1].
  • This design increases the spectral bandwidth of the coupling between the active region 30B and the main laser cavity 45 by using an AR coating 30A that is narrow-band and by designing the micro-cavity of the gain mirror so that it operates at anti-resonance. It has used an active region which is thinner than for the first prior art design.
  • the narrow-band AR coating is essentially a Bragg stack comprising a multiplicity of dielectric layers.
  • the reflection at the gain mirror interface with the air i.e. at the interface of AR coating 30A with the air in the laser cavity
  • the reflection at the interface between the layers in the active zone is significantly larger than the reflection at the interface between the layers in the active zone.
  • the space between the surface of the AR coating at the air interface and the highly reflective Bragg stack 30C at the opposite end of the gain mirror acts as a sub-cavity.
  • the sub-cavity works at anti-resonance at the design wavelength ⁇ _, hence the sub-cavity length is not a multiple of ⁇ _J4.
  • the narrow-band response of the AR stack 30A results in a resonance condition being set up at some other wavelength ⁇ R , where the sub-cavity length is a multiple of XR/2.
  • the effective gain is proportional to the product of the material gain produced by the QWs in the active region and the modulus squared of the electric field
  • the AR-stack bandwidth is designed to approximately match the free spectral range (FSR) between the two sub-cavity modes i.e. the mode associated with ⁇ _J4 and the mode associated with R/2.
  • FSR free spectral range
  • the gain mirror has a filter profile with a shape like a top-hat and it is considerably broader than the single-peak curve characteristic of the intrinsic gain bandwidth.
  • the resonance at X R is absent because the region between the highly reflective Bragg mirror 30C and the surface of the AR coating 30 A at the air interface looks like a single optical layer. In this case reflections at the air interface will be present at any wavelength and not restricted to a narrow band. The absence of the resonance due to reflection at the air interface means that the effective gain bandwidth will be narrower for the first prior art design than for the second prior art design.
  • the second prior art design for the gain mirror 30 has the advantage that it increases the gain bandwidth and hence improves the coupling between the microcavity and the main laser cavity in the region of the spectrum close to the laser wavelength ⁇ ⁇ _ .
  • this design has the disadvantage that the incoming laser diode pump energy is inefficiently converted into laser output.
  • the multilayer structure of the AR coating is specially designed to provide good coupling between the microcavity and the main laser cavity at wavelengths close to the laser wavelength L . As a consequence, the AR coating is more reflective (typically 30% or greater) at the pump wavelength ⁇ P than it would be in the case of the first prior art design.
  • the active region of the second prior art design is narrow has the disadvantage that a relatively small proportion of the laser diode pump light entering the active region is absorbed there.
  • the wasted fraction of light (around 50%) is dissipated as heat which can cause a decrease in the output power due to thermal rollover.
  • the invention provides a vertical cavity laser device comprising: a multi-layer laser structure having a pump light receiving face for receiving incident pump light at a pump wavelength, and a semiconductor gain region operable to provide optical gain at a laser emission wavelength in response to the pump light; two laser cavity mirrors disposed about the multi-layer laser structure so as to define a laser cavity wherein each laser cavity mirror is operable to reflect light at the laser emission wavelength; and a pump mirror disposed behind the gain region so as to reflect pump light back through the gain region for at least a second pass.
  • Embodiments of the invention provide a gain with a broad spectral bandwidth that improves the coupling of the micro-cavity to the main laser cavity at the laser wavelength and, in addition, they provide improved efficiency of conversion of pump laser light to laser output.
  • the gain region can preferably be a multi-layered structure, for example a quantum well structure as in previously proposed VECSELs.
  • FIG. 1 is a schematic diagram of an OPS VECSEL
  • Figure 2A is a schematic diagram of a gain mirror structure according to a first embodiment of the invention.
  • Figure 2B is a schematic diagram of a gain mirror structure according to a second embodiment of the invention.
  • Figure 3 is a band-energy diagram for a DP VECSEL according to a first embodiment of the invention
  • Figure 4 is a table that specifies the design parameters of the DP VECSEL of the first embodiment of the invention
  • Figure 5 is the mathematically predicted behaviour of the anti-reflection coating according to the first embodiment of the invention
  • Figure 6 shows the predicted behaviour of reflectivity and the modulus squared of the electric field in the quantum wells as a function of wavelength for the first embodiment of the invention
  • Figure 7 shows the predicted behaviour of the Bragg reflectivity of the highly reflective mirror of the first embodiment of the invention
  • Figure 8 shows the predicted value modulus squared of the electric field across the whole DP VECSEL structure according to the first embodiment of the invention
  • Figure 9 shows an experimental set-up suitable for both the first embodiment and the second embodiment of the invention
  • Figure 10 shows experimental results for reflectivity as a function of wavelength for the whole gain-mirror structure according to the first embodiment of the invention
  • Figure 11 shows experimental results for reflectivity as a function of wavelength for the anti-reflection coating according to the first embodiment of the invention
  • Figure 12 shows experimental results for the reflectivity and the photoluminescence as functions of wavelength for the epitaxial VECSEL structure according to the first embodiment of the invention
  • Figure 13 shows experimental results for output power as a function of input power according to the first embodiment of the invention
  • Figure 14 shows experimental results for differential quantum efficiency and wavelength functions of incident pump power according to the first embodiment of the invention
  • Figure 15 is a band gap energy diagram for a CEP VECSEL according to a second embodiment of the invention.
  • Figure 16 is a table that specifies the parameters of the CEP VECSEL of the second embodiment of the invention.
  • Figure 17 is the mathematically predicted behaviour of the highly reflective Bragg mirror according to the second embodiment of the invention.
  • Figure 18 shows the predicted behaviour of the anti-reflection coating of the second embodiment of the invention
  • Figure 19 shows the predicted reflectivity and transmissivity in the whole structure as a function of wavelength according to the second embodiment of the invention
  • Figure 20 shows the predicted behaviour of reflectivity and the modulus squared of the electric field in the active region in the region of the laser emission wavelength for the second embodiment of the invention.
  • Figure 21 shows the predicted behaviour of reflectivity and the modulus squared of the electric field in the active region in the region of the pump wavelength for the second embodiment of the invention.
  • Figure 2 illustrates schematically two alternative constructions for the gain mirror according to embodiments of the invention.
  • Figure 2A illustrates a "double pass pumping" gain mirror structure 100. This modifies in two ways the gain mirror of the second prior-art design.
  • the basic components as already described above are the multi-layer anti-reflection coating 30A which has high transmittance at the laser wavelength, the active region 3 OB including QWs, and the Bragg stack mirror 30C which is highly reflective (HR) at the laser wavelength.
  • the first modification is the addition of an AR multi-layer structure that has high transmissivity and low reflectivity at the pump wavelength. This modification results in a dual-wavelength
  • This first modification serves to reduce reflection loss of the pump light at the air interface.
  • the second modification included in the double pump pass pumping gain mirror is the addition of a further Bragg stack mirror 60 that is highly reflective at the pump wavelength.
  • This additional mirror 60 is located behind the mirror 30C and serves to reflect pump light that has made a single pass through the active region, directing it back for a second pass through the micro-cavity.
  • This modification serves to double the effective absorption path that the active region presents to the pump laser light.
  • the two highly reflective mirrors 60 and 30C are substantially non- absorbent to either the pump or the laser light because these mirrors have large energy band-gaps.
  • This gain mirror structure will promote a more uniform distribution of electron and hole carriers amongst the QWs in the active region 3 OB. Note that this structure allows optical pumping from a single direction only such that the pump light is incident on the side of the gain mirror with the AR coating.
  • a "cavity-enhanced pumping" gain mirror structure 200 is shown in Figure 2B.
  • the gain mirror of the second prior-art design comprising a mirror 30C highly reflective at ⁇ ]_ .
  • a thin active region 30B and an anti-reflection stack 30A with high transmissivity at ⁇ i is modified by adding a first additional mirror 80 and a second additional mirror 90, with one on either side of three-layer gain mirror structure (30A, 30B, 30C).
  • the reflectivity of the first additional mirrors 80 is close to 100% and the reflectivity of additional mirror 90 is around 30%.
  • the reflectivity of the first additional mirror 80 could be in the range from 50%) to 100% while the reflectivity of the second additional mirror 90 could be in the range from 10%) to 60%>.
  • These two additional mirrors 80 and 90 define an optical cavity inside the multi-layer structure that is designed to operate resonantly at the pump wavelength.
  • the outer cavity is designed so that the separation in wavelength between the resonant peaks is small.
  • the cavity has low finesse and the resonance, which is centred on the pump wavelength, is spectrally broad.
  • This cavity enhanced pumping structure for the gain mirror reduces the reflectivity at the pump wavelength and the cavity formed by the additional mirrors 80 and 90 promotes multiple passes of the pump light through the active region.
  • the design equation that gives a relationship between the reflectivities of the first and second additional mirrors 80 and 90 is:
  • Rl ⁇ p is the reflectivity of the first additional mirror 80
  • R2 ⁇ p is the reflectivity of the second additional mirror 90
  • ⁇ p is the absorption coefficient at ⁇ p
  • w is the thickness of the absorber in the active region.
  • the active region of the cavity enhanced gain mirror can be made thinner than the active region for the double-pass pumping structure 100.
  • Both of the gain mirrors illustrated in Figure 2 should allow the OPS-VECSEL to be pumped optically with efficiency greater than 0.9x( ⁇ p/ ⁇ L ). This can be achieved without increasing the length of the active region.
  • the quantum efficiency can be improved by keeping the optical pump photon energy close to the laser photon energy. The improved efficiency reduces heating of the gain mirror.
  • the multi-layer structure of the anti-reflection coating and the high and medium reflectivity Bragg stack mirrors can be grown in a single fabrication process known as "epitaxy" where the layers are grown on top of each other such that the crystal orientation of the upper layer is determined by the crystal orientation of the base layer.
  • the multi-layer structures can be fabricated as composites formed by depositing additional layers on epitaxially grown structures.
  • the structures are designed for their optical properties alone and they are electrically insulating.
  • the multi-layered structures of the Bragg mirrors and of the anti-reflection coatings are generally periodic structures comprising layers of optical thickness ⁇ /4.
  • Such layered structures are suitable for the growth of GaAs.
  • the multi-layered structures could also be non-periodic structures comprising dielectric layers with differing thicknesses. Any multi-layered structure with the reflectivity in the region of ⁇ i, and ⁇ p properties in accordance with the invention would suffice.
  • Figure 3 is a band-gap energy diagram for an embodiment of the double pass pumping structure 100 (DP VECSEL).
  • the optical pump light 505 enters the gain mirror through the composite AR layer 535 and passes through the active region 30B where a proportion of the pump energy is absorbed.
  • the pump light that is not absorbed in the active layer will pass through the HR layer 525 designed to reflect at ⁇ L and will be reflected by the distributed Bragg reflector (DBR) 545 such that it passes back through the active region for a second time.
  • DBR distributed Bragg reflector
  • the gain mirror is formed on a gallium arsenide (GaAs) substrate 590 whose band-energy is smaller than that of the pump laser but larger than that of the main laser.
  • the active region 3 OB comprises six QWs 500 formed from very thin layers of indium gallium arsenide (InGaAs).
  • the QWs 500 are arranged in a (2+1+1+2) formation and are separated by layers of GaAs.
  • the optical depth of the active region is 5.1 times ⁇ j/2. This value of 5.1 takes account of the phase-shift of the laser light due to reflection at the multi-layer AR stack 535.
  • the structure is designed to be anti-resonant at the laser wavelength, which means that there is a node at the air/semiconductor interface.
  • the quantum wells are placed at the anti-nodes of the intra-cavity standing wave 570 as shown.
  • the Bragg stack 545 which has high reflectivity at ⁇ p comprises eight pairs of layers 510. Each pair 510 consists of an Aln. ⁇ Gao. 9 As layer of optical thickness ⁇ p/4 and an AlAs layer of optical thickness ⁇ p/4. The band-energy of AlAs is higher than that of the Alo . ⁇ Gao. 9 As so a series of potential wells is formed.
  • the HR mirror 525 adjacent to the HR mirror 545 comprises twenty-seven pairs 520, each of which comprises a layer of AlAs and a layer of AlGaAs. Each layer has an optical thickness of ⁇ _J4. A single additional ⁇ _ 4 layer 521 of AlAs is situated adjacent to these twenty-seven pairs and to the active region.
  • the value ⁇ is the appropriate value so that the multi-layer structure has low reflectivity at both of the wavelengths ⁇ i and ⁇ p.
  • the design equation that gives the appropriate wavelength ⁇ ow that specifies the optical depths of a multi-layer structure which provides high reflectivity in dual wavelength (DW) bands centred on ⁇ i and ⁇ p is: A p ⁇ L
  • the AR coating 535 consists of a unit 530 comprising a pair of ⁇ 14 layers of AlAs and AlGaAs which is repeated twice, a single ⁇ 14 layer 531 of AlAs, a ⁇ /2 layer 540 of AlGaAs and an AlAs/AlGaAs/AlAs triplet 550 of ⁇ " /4 layers.
  • Figure 4 is a table that specifies the composition of each of the multi-layer structures corresponding to the band gap diagram of Figure 3 and specifies the spacings or material thickness of each layer required to obtain the appropriate optical thickness.
  • the optical thickness is given by the product of the layer spacing and the refractive index of the respective layer.
  • the refractive indices at 1050nm are given by Table 1 below.
  • Figures 5 to 8 are predictions obtained from mathematical models of the DP VECSEL structure of Figure 3.
  • Figure 5 is a plot of reflectivity against wavelength for the composite AR layer
  • Figure 6 is a plot of the square of the absolute value of the electric field E in the QWs 500 of the active region of the DP VECSEL.
  • the dashed double-peak curve 710 corresponds to a QW on the side of the anti-reflection coating 535 while the solid double-peaked curve 700 corresponds to a QW on the side of the high reflectivity Bragg stack mirror 525.
  • the uppermost solid line 720 is a plot of reflectivity against wavelength for the whole gain mirror structure which has a top-hat shape with a constant value over a broad range of wavelengths centred around 1020 ⁇ m.
  • Figure 7 shows the Bragg reflectivity for the DP VECSEL, which is the squared coefficient of reflectivity for the electric field, as a function of wavelength.
  • the plot is for the pump DBR 545 and the HR mirror 525 part of the gain mirror structure only.
  • Figure 8 shows the spatial distribution of the square of the absolute value of the electric field [ E [ 2 in the gain mirror structure at the laser emission wavelength ⁇ L for the DP VECSEL.
  • the AR coating Since the AR coating has negligible reflectivity at its design wavelength, the energy flux in the air and in the active zone is approximately the same for both the incident and for the reflected wave. As a consequence
  • Figure 9 shows an experimental set-up for implementing the double-pass pumping OPS-VECSEL according to a first embodiment of the invention.
  • the gain mirror structure is mounted on a copper heat-sink 800 using a layer of heat paste 810.
  • the gain mirror structure 820 comprises from bottom to top: the GaAs substrate; the highly reflective Bragg stack mirror; the active region containing from three to six QWs; and the anti-reflection coating.
  • the VECSEL gain mirror structure is fabricated epitaxially.
  • the optical pump source 870 is located about 2.5cm from the active region of the gain mirror.
  • the pump light is incident on the gain mirror at a slight angle and it is focused by a convex lens 830.
  • the external concave mirror 860 of the main laser cavity which acts as an output coupler has a transmissivity of around 1% at the laser wavelength and is located directly above the gain mirror, at a distance of about 2.5cm from the top of the active zone.
  • the laser output is directed through the concave mirror 860.
  • Figures 10 to 14 are experimental results obtained using the set-up of Figure 9.
  • Figure 10 gives the reflectivity as a function of wavelength for seven different values of the displacement d in mm of the incident laser pump light from the centre of the gain mirror structure for the whole VECSEL structure including the Bragg HRs 545and 525, the active region 505 and the AR region 535.
  • Curve 900 corresponds to zero displacement of the pump light incident from the centre of the gain mirror and curve 960 corresponds to a displacement of 17.5mm from the centre.
  • This figure illustrates that if the gain mirror multi-layer structure is designed for ⁇ and ⁇ p at zero displacement, the gain mirror characteristics are effectively blue-shifted to smaller wavelengths by increasing the displacement d.
  • Figure 12 characterises the DP VECSEL structure according to the first embodiment of the invention.
  • the uppermost curve 1020 gives the reflectivity of the gain mirror as a function of wavelength.
  • the middle curve 1010 gives the edge photoluminescence of the gain mirror as a function of wavelength, which was obtained by pumping close to the edge of the wafer.
  • Figure 13 gives the output power P out in mW as a function of Pj n on the chip in
  • This figure illustrates the damage ratio of the gain mirror structure due to high intensity at ⁇ L inside the cavity.
  • Figure 14 gives two parameters as a function of the incident pump power Pj n on the chip in Watts.
  • the lower near-linear curve 1060 shows the variation in the laser wavelength as a function of Pj n .
  • the laser wavelength increases as Pj n increases and ⁇ / ⁇ Pj n - 16 nm/W.
  • Figure 15 is a band-gap energy diagram for the cavity enhanced pumping gain mirror structure (CEP VECSEL) according to a second embodiment of the invention.
  • CEP VECSEL cavity enhanced pumping gain mirror structure
  • each layer of the gain mirror structure corresponding to Figure 15 are specified in the table of Figure 16.
  • the spacings are calculated by dividing the required optical thickness by the refractive index of the layer material.
  • the gain mirror structure of the CEP VECSEL is designed to be anti-resonant as it was for the first embodiment of the invention.
  • the active region for the CEP VECSEL of this second embodiment of the invention is narrower than that for the first embodiment of the DP VECSEL of Figure 3.
  • the active region 3005 of Figure 15 contains six QWS 2010 arranged in three pairs.
  • Each pair of QWs is placed close to a maximum of the intra-cavity standing wave 2050.
  • the highly reflective Bragg stack 3015 is constructed from a repeating unit
  • the HR region 3015 thus has a total of eighty-one layers.
  • the incoming pump light 3050 has energy greater than the band energy of the Al0.osGao. 9 s As of the active region but less than the band energy of the multi-layered structures of the HR region 3015 and of the AR region 3025.
  • the outgoing laser light 3055 at ⁇ L is reflected from the HR region. Since the AR region 3025 has medium reflectivity at ⁇ p, a portion of the pump light will be reflected back through the active region and a further portion will pass through the AR region 3025 and enter the air 3035 of the main laser cavity.
  • Figures 17 to 21 are predictions obtained from mathematical models of the
  • Figure 17 shows the Bragg reflectivity as a function of the wavelength for the
  • Figure 18 shows the Bragg reflectivity as a function of wavelength for the AR region 3025.
  • the solid curve 4010 is the absorption efficiency and the dashed curve 4020 is the reflectivity.
  • Figures 20 and 21 show characteristics of the whole CEP VECSEL gain mirror according to the second embodiment of the invention. Dispersion is taken into account in this mathematical model but absorption is not.
  • Figure 19 gives the reflectivity profile 4030 and the
  • Figure 20 gives the reflectivity profile

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

Abstract

L'invention concerne un dispositif laser à cavité verticale comprenant une structure laser (820) multicouche dotée d'une face de réception (90, 70) de lumière de pompage destinée à recevoir une lumière de pompage incidente à une longueur d'onde de pompage, et d'une région de gain (30B) semi-conductrice destinée à fournir un gain optique à une longueur d'onde d'émission laser en réponse à la lumière de pompage; deux miroirs de cavité laser disposés autour de la structure laser multicouche de façon à définir une cavité laser, chaque miroir de cavité laser fonctionnant de façon à réfléchir la lumière à une longueur d'onde d'émission laser; et un miroir de pompage (60, 80) disposé derrière la région de gain (30B) de façon à réfléchir la lumière de pompage à travers la région de gain (30B) pendant au moins un second passage.
PCT/GB2001/005387 2000-12-08 2001-12-05 Dispositif laser a semi-conducteur a cavite verticale et a pompage optique WO2002047223A1 (fr)

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AU2002220897A AU2002220897A1 (en) 2000-12-08 2001-12-05 Optically pumped vertical cavity semiconductor laser device

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GB0030015A GB2369929A (en) 2000-12-08 2000-12-08 Semiconductor laser device
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JP2004207724A (ja) * 2002-12-20 2004-07-22 Osram Opto Semiconductors Gmbh ヴァーティカルエミッション型半導体レーザー
WO2004086577A2 (fr) * 2003-03-24 2004-10-07 The University Of Strathclyde Perfectionnements dans des dispositifs optiques semiconducteurs a cavite verticale
FR2870051A1 (fr) * 2004-05-04 2005-11-11 Commissariat Energie Atomique Emetteur de rayonnement avec faisceau de pompage incline
EP1608049A1 (fr) * 2004-06-19 2005-12-21 Samsung Electronics Co., Ltd. Source laser à cavité externe avec multiples longueurs d'onde
EP1796232A1 (fr) * 2005-12-09 2007-06-13 Osram Opto Semiconductors GmbH Laser à semi-conducteur à émission verticale à pompage optique et à cavité externe
DE102006002879A1 (de) * 2006-01-20 2007-08-02 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Halbleiteranordnung für einen optisch gepumpten oberflächenemittierenden Halbleiterlaser
US7379488B2 (en) 2004-06-19 2008-05-27 Samsung Electronics Co., Ltd. External cavity dual wavelength laser system
WO2008000243A3 (fr) * 2006-06-30 2008-12-04 Osram Opto Semiconductors Gmbh Corps semi-conducteur à surface émettrice à sens d'émission vertical et longueur d'ondes à émission stabilisée
EP2325955A1 (fr) * 2009-11-23 2011-05-25 Klastech- Karpushko Laser Technologies GmbH Laser pompé de manière optique par une cavité résonnante et son procédé de fonctionnement
EP2710695A4 (fr) * 2011-05-16 2015-07-15 VerLASE TECHNOLOGIES LLC Dispositifs optoélectroniques améliorés par résonateur et leurs procédés de fabrication
DE102014205022A1 (de) 2014-03-18 2015-09-24 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Optisch gepumpter Halbleiter-Scheibenlaser
US9716364B2 (en) 2014-03-18 2017-07-25 Fraunhofer•Gesellschaft Zur Förderung der Angewandten Forschung E.V. Optically pumped semiconductor disk laser
DE102008038961B4 (de) 2008-08-13 2019-09-19 Osram Opto Semiconductors Gmbh Oberflächenemittierender Halbleiterlaserchip, Laseranordnung mit einem oberflächenemittierenden Halbleiterlaserchip sowie Verfahren zur Herstellung eines oberflächenemittierenden Halbleiterlaserchips

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JP4690647B2 (ja) * 2002-12-20 2011-06-01 オスラム オプト セミコンダクターズ ゲゼルシャフト ミット ベシュレンクテル ハフツング ヴァーティカルエミッション型半導体レーザー
JP2004207724A (ja) * 2002-12-20 2004-07-22 Osram Opto Semiconductors Gmbh ヴァーティカルエミッション型半導体レーザー
WO2004086577A2 (fr) * 2003-03-24 2004-10-07 The University Of Strathclyde Perfectionnements dans des dispositifs optiques semiconducteurs a cavite verticale
WO2004086577A3 (fr) * 2003-03-24 2005-02-17 Univ Strathclyde Perfectionnements dans des dispositifs optiques semiconducteurs a cavite verticale
FR2870051A1 (fr) * 2004-05-04 2005-11-11 Commissariat Energie Atomique Emetteur de rayonnement avec faisceau de pompage incline
WO2005109584A2 (fr) * 2004-05-04 2005-11-17 Commissariat A L'energie Atomique Emetteur de rayonnement avec faisceau de pompage incline
WO2005109584A3 (fr) * 2004-05-04 2006-06-29 Commissariat Energie Atomique Emetteur de rayonnement avec faisceau de pompage incline
US7379488B2 (en) 2004-06-19 2008-05-27 Samsung Electronics Co., Ltd. External cavity dual wavelength laser system
EP1608049A1 (fr) * 2004-06-19 2005-12-21 Samsung Electronics Co., Ltd. Source laser à cavité externe avec multiples longueurs d'onde
JP2006005361A (ja) * 2004-06-19 2006-01-05 Samsung Electronics Co Ltd 複数の波長を発生させる半導体レーザ装置及び半導体レーザ装置用のレーザポンピング素子
EP1796232A1 (fr) * 2005-12-09 2007-06-13 Osram Opto Semiconductors GmbH Laser à semi-conducteur à émission verticale à pompage optique et à cavité externe
DE102006002879B4 (de) * 2006-01-20 2008-11-13 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Halbleiteranordnung für einen optisch gepumpten oberflächenemittierenden Halbleiterlaser
WO2007087959A1 (fr) * 2006-01-20 2007-08-09 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Dispositif à semi-conducteur conçu pour un laser à semi-conducteur à pompage optique et émission par la surface
DE102006002879A1 (de) * 2006-01-20 2007-08-02 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Halbleiteranordnung für einen optisch gepumpten oberflächenemittierenden Halbleiterlaser
WO2008000243A3 (fr) * 2006-06-30 2008-12-04 Osram Opto Semiconductors Gmbh Corps semi-conducteur à surface émettrice à sens d'émission vertical et longueur d'ondes à émission stabilisée
US8208512B2 (en) 2006-06-30 2012-06-26 Osram Opto Semiconductors Gmbh Surface emitting semiconductor body with vertical emission direction and stabilized emission wavelength
DE102008038961B4 (de) 2008-08-13 2019-09-19 Osram Opto Semiconductors Gmbh Oberflächenemittierender Halbleiterlaserchip, Laseranordnung mit einem oberflächenemittierenden Halbleiterlaserchip sowie Verfahren zur Herstellung eines oberflächenemittierenden Halbleiterlaserchips
DE102008038961B9 (de) 2008-08-13 2019-12-05 Osram Opto Semiconductors Gmbh Oberflächenemittierender Halbleiterlaserchip, Laseranordnung mit einem oberflächenemittierenden Halbleiterlaserchip sowie Verfahren zur Herstellung eines oberflächenemittierenden Halbleiterlaserchips
EP2325955A1 (fr) * 2009-11-23 2011-05-25 Klastech- Karpushko Laser Technologies GmbH Laser pompé de manière optique par une cavité résonnante et son procédé de fonctionnement
EP2710695A4 (fr) * 2011-05-16 2015-07-15 VerLASE TECHNOLOGIES LLC Dispositifs optoélectroniques améliorés par résonateur et leurs procédés de fabrication
US9354366B2 (en) 2011-05-16 2016-05-31 VerLASE TECHNOLOGIES LLC Resonator-enhanced optoelectronic devices and methods of making same
DE102014205022A1 (de) 2014-03-18 2015-09-24 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Optisch gepumpter Halbleiter-Scheibenlaser
EP2940807A1 (fr) 2014-03-18 2015-11-04 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Laser à disque à semi-conducteur pompé optiquement
US9716364B2 (en) 2014-03-18 2017-07-25 Fraunhofer•Gesellschaft Zur Förderung der Angewandten Forschung E.V. Optically pumped semiconductor disk laser

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GB2369929A (en) 2002-06-12
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