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Communication

Surface-Emitting Lasers with Surface Metastructures

by
Anjin Liu
1,2,*,
Jing Zhang
1,2,
Chenxi Hao
1,2,
Minglu Wang
1,2 and
Wanhua Zheng
1,2,3
1
State Key Laboratory on Integrated Optoelectronics, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China
2
Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, China
3
Key Laboratory of Solid-State Optoelectronics Information Technology, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China
*
Author to whom correspondence should be addressed.
Photonics 2023, 10(5), 509; https://doi.org/10.3390/photonics10050509
Submission received: 23 March 2023 / Revised: 20 April 2023 / Accepted: 25 April 2023 / Published: 27 April 2023
(This article belongs to the Special Issue Nanophotonics Pioneer: Prof. Dr. Dieter Bimberg ‘Green Photonics Networks: From VCSELs to Nanophotonics’)
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Abstract

:
Vertical-cavity surface-emitting lasers (VCSELs) have been widely used in consumer electronics, light detection and ranging, optical interconnects, atomic sensors, and so on. In this paper, a VCSEL with the surface metastructure like one-dimensional high-contrast grating (HCG), based on the HCG-DBR vertical cavity, was first designed and fabricated. The polarization characteristic of the HCG-VCSEL were experimentally studied. The p-doped top 4-pair DBR for the current spreading and the direction shift between the HCG and the elliptical oxide aperture may result in a low orthogonal polarization suppression ratio in the HCG-VCSEL. Then, the Bloch surface wave surface-emitting laser (BSW-SEL), based on the HCG-DBR metastructure, is proposed for single-mode, high-efficiency, and high-power output with a low divergence angle. The mode field and the far field profile of the BSW-SEL are calculated for verification. The surface-emitting lasers with surface metastructures are useful for the sensing applications and optical interconnects.

1. Introduction

Vertical-cavity surface-emitting lasers (VCSELs) have unique features: circular beam, low power consumption, high-speed modulation, and two-dimensional (2D) array configuration [1,2,3,4]. They have been widely used in numerous fields, including light detection and ranging (LiDAR), data communication, face recognition, internet of things, infrared illumination, printing, atomic sensors, and so on [5,6,7,8,9]. As the core structure of a VCSEL, a vertical cavity is typically composed of two low-loss distributed Bragg reflectors (DBRs) with a thickness of several micrometers. To relieve the fabrication challenges of the low-loss DBRs, a kind of surface metastructure called high-contrast grating (HCG) has been used as a highly reflective mirror over a large wavelength range to construct a vertical cavity [10,11,12,13,14]. The HCG has a thickness of a few hundred nanometers, much thinner than an epitaxial DBR. Also, compared with the epitaxial DBR, it is easier to fabricate the highly reflective HCG for the short wave and infrared wavelength ranges.
With a deep understanding of the basic physics of the HCG, VCSELs with HCGs as the top mirrors have been intensively studied. In 2007 the electrically injected 850-nm GaAs-based HCG-VCSEL with single-mode operation and a polarization suppression ratio of 20 dB was first demonstrated [15]. GaAs-based HCG-VCSEL at other wavelength ranges, GaN- and InP-based HCG-VCSELs, have also been realized [16,17,18,19,20,21,22]. In addition, VCSELs with silicon-based HCGs were demonstrated targeting the on-chip light sources [23,24,25]. Besides the single-mode operation and polarization selection output, the HCG-VCSEL can achieve a wide tuning range and shaped beam profile [26,27,28]. Moreover, the HCG-VCSEL is expected to achieve a relaxation resonance frequency of larger than 40 GHz because of the smaller effective mode length, which is very useful for high-speed optical interconnects [18].
For the realization of the HCG-VCSEL, one of the key issues besides the design of the HCG-VCSEL is the fabrication of the highly reflective HCG. HCGs are often based on an oxide layer, being monolithically integrated or air suspended [15,16,17,18,19,20,21,22,23,24,25,26,27,28,29]. Recently we reported 940-nm HCG-VCSEL with a post-supported suspended HCG by simple fabrication [18]. The device achieved single mode operation with a side mode suppression ratio of larger than 43 dB.
The solitary HCG-VCSEL and VCSEL have limited single-mode output power and a large divergence angle, making them not good for sensing applications and optical interconnects. One-dimensional (1D) and 2D photonic crystal surface-emitting lasers (PCSELs) can achieve single mode operation with high power and a low divergence angle based on the 1D and 2D distributed feedback over a large area [30,31,32,33]. Since these PCSELs are based on the first-order diffraction for surface emission, the efficiency of the PCSEL is limited because theoretically the downward radiation (50%) of the first-order diffraction power is lost. Therefore, an extra DBR has been proposed to reflect the downward radiation in the PCSELs, and a slope efficiency of 0.8 W/A is expected with a complex fabrication [31].
In this paper, we first study the polarization characteristics of the HCG-VCSEL. The experimental results indicated that the alignment of the HCG with the oxide aperture may affect the performance of the HCG-VCSEL. Then, based on the HCG-VCSEL structure, we propose a novel surface-emitting laser, called the Bloch surface wave surface-emitting laser (BSW-SEL), with the HCG-DBR metastructure by the distributed feedback effect. The proposed BSW-SEL is expected to achieve single-mode, high-efficiency, and high-power output with a low divergence angle [34].

2. HCG-VCSEL

The schematics of the HCG-VCSEL are shown in Figure 1. The epitaxial structure of the HCG-VCSEL at 940-nm wavelength range can be referred to in [18]. The epitaxial structure includes a bottom 38.5-pair Al0.12Ga0.88As/Al0.9Ga0.1As DBR, a λ-cavity, p-doped top Al0.12Ga0.88As/Al0.9Ga0.1As DBR with a 30-nm Al0.98Ga0.02As layer, a lattice-matched Ga0.51In0.49P sacrificial layer with a thickness of three-quarter wavelength for the air layer beneath the HCG, and a top GaAs layer for the HCG. The cavity consists of three 8-nm In0.13Ga0.87As quantum wells (QWs) surrounded by 8-nm Al0.3Ga0.7As barriers.
To investigate the impact of the p-doped top DBR on the performance of the HCG-VCSEL, the current density profiles in the active regions with 4-pair and 1-pair top DBRs are calculated. As shown in Figure 2 calculated by the finite-element method, compared with the HCG-VCSEL with a 1-pair top DBR, the current density in the center of the active region is larger for the HCG-VCSEL with a 4-pair top DBR. It is worth noting that the current density in the active region is less uniform when the oxide aperture becomes elliptical. The enhanced current density in the center of the active region with a 4-pair top DBR is due to the current spreading effect, which is good for the uniform current injection across the oxide aperture. Increasing the pair number of the DBR can further enhance the current density uniformity. However, this lowers the necessity of introducing the HCG and increases the cost and the difficulty of the wafer epitaxy. Additionally, the thicker top DBR can lower the polarization performance of the HCG-VCSEL. Thus, in the wafer design the 4-pair top DBR is adopted.
The period Λ of the HCG is 648 nm, and the thickness of the GaAs-based HCG is 140 nm. The designed GaAs-based HCG has a polarization-dependent reflectivity of greater than 99.5% from 870 nm to 1000 nm for the transverse electric (TE, electric field parallel to the grating bar) polarization, and the reflectivity is less than 1% at 940-nm wavelength range for the transverse magnetic (TM, electric field perpendicular to the grating bar) polarization, as shown in Figure 3, and this was calculated by rigorous coupled wave analysis. The 4-pair p-doped top Al0.12Ga0.88As/Al0.9Ga0.1As DBR for current spreading together with the HCG as the top mirror is beneficial to achieving a higher reflectivity. As shown in Figure 3, for the top mirror composed of the HCG, the air layer beneath the HCG, and the 4-pair top DBR, the reflectivity band with a reflectivity of larger than 99.5% is larger than that of the solitary TE HCG, and the reflectivity at the 940-nm wavelength range is also larger than that of the TM HCG. This indicates that the 4-pair DBR for current spreading can reduce the reflectivity difference between the reflectivity of the TE polarization and that of the TM polarization, which may affect the polarization characteristic of the HCG-VCSEL. However, we find that 4-pair top DBR can help to achieve a reflectivity of larger than 99.5% for the top mirror even when the solitary HCG with a larger airgap width has a reflectivity of less than 99.5% at 940-nm wavelength range, as shown in Figure 4. This indicates that the duty cycle (a/Λ) tolerance of the HCG is large, and thus very helpful for the realization of the HCG-VCSEL.
To fabricate the HCG-VCSEL, the Ti/Pt/Au p-contact is firstly formed by the lift-off process. Then the top GaAs layer is removed and the GaInP layer is selectively etched to form the mesa. Next, an inductively coupled plasma (ICP) etching is used to etch the top Al0.12Ga0.88As/Al0.9Ga0.1As DBR, cavity region, and 3 pairs of the bottom DBR to expose the 30-nm Al0.98Ga0.02As layer. The Al0.98Ga0.02As layer is then oxidized to form an oxide aperture in a water vapor atmosphere at 420 degrees. The oxidation aperture is checked by an infrared camera system after oxidation. An infrared microscope image is shown in Figure 5a. The dashed ellipse in Figure 5a indicates the profile of the oxidation edge. Because the oxidation results in the reflectivity change of the oxidized region of the mesa, there is a color difference between the regions inside the dashed ellipse and outside the dashed ellipse in Figure 5a. The profile of the oxidation edge is elliptic because the oxidation rate of the Al0.98Ga0.02As layer depends on the crystallographic orientation [35]. The ellipticity of the oxide aperture can be enhanced as the mesa size is increased. Finally, the Au/Ge/Ni/Au n-contact is deposited at the back of the substrate, and is annealed at 425 degrees.
To fabricate the post-supported HCG, electron beam lithography (EBL, Raith 150) is used to define the grating pattern with the polymethyl methacrylate (PMMA) electron resist. The grating pattern with the PMMA mask is transferred to the top GaAs layer by the ICP etching. The GaInP layer beneath the etched top GaAs layer is selectively removed by the HCl solution. Two nanoscale posts beneath the HCG can be realized to support the air-suspended HCG without critical point drying for the HCG release [36]. The scanning electron microscope (SEM) image of the fabricated HCG-VCSEL is shown in Figure 5b.
The power-current (L-I) curves of the HCG-VCSELs are measured on-wafer with a home-built probing system. The measurement system is remote-controlled and includes a Keithley 2401 source meter, a calibrated integrating sphere/photo detector system from Labsphere Inc., a thermoelectric cooler (TEC) to control the temperature, and a charge coupled device (CCD) camera. The orthogonal polarization suppression ratio (OPSR) of the HCG-VCSEL is measured by the system shown in Figure 6. The source meter provides injection current, and the TEC controls the temperature of the holder at 25 °C. The emitting light from the HCG-VCSEL that was placed on the holder passes through the objective lens and the beam splitter (BS) to the Glan-Thomson polarizer, and then enters the photodetector (PD). The TE and TM L-I curves of the HCG-VCSEL are measured by rotating the polarizer. The OPSR can be expressed thus:
OPSR = 10 log ( P TE / P TM )
where PTE and PTM are the powers of TE and TM polarizations, respectively.
Figure 7 shows the LI curves and the OPSR curve of the HCG-VCSEL with a mesa diameter of 87 μm and an HCG size of 8 μm × 8 μm. The black solid line represents the total power emitting from the HCG-VCSEL. The blue dotted line and green short-dash dotted line are the power curves of the TE and TM polarizations, respectively. The red dashed line is the calculated OPSRs according to Equation (1). The sum of the TE- and TM- polarization powers is lower than the power measured without polarizer shown in Figure 7a because of the coupling losses in the system in Figure 6. The period of the HCG is 648 nm, and the airgap of the HCG is about 380 nm. The size of the oxide aperture is about 4.5 μm × 7 μm. The threshold current of the HCG-VCSEL is about 0.68 mA. Below the threshold current, the HCG-VCSEL has relatively strong spontaneous emission, which may be due to the low reflectivity of the top mirror under the TM polarization. The output power of the HCG-VCSEL is about 0.8 mW at 5 mA. A smaller threshold current can be realized by reducing the oxide aperture and reasonably increasing the HCG size [37]. The output power can also be enhanced by increasing the HCG size and optimizing the top mirror. On the other hand, the fabrication process of the HCG can be further optimized to reduce extra losses, which can lead to a larger output power. The power OPSR is currently about 9 dB: less than the reported result in [10]. We also measure the spectra of the two orthogonal polarizations, and the spectral OPSR is 19.5 dB at 1.2 mA. The spectral OPSR is larger than the power OPSR, because all the power of the spontaneous emission and the suppressed modes are included by the photodiode when the power is measured [38].
To understand the polarization characteristics, we measure the near field image, typically as shown in Figure 7a. In the near field image, the emission is within the elliptical oxide aperture, which is partly due to the large mesa for easy probe measurement. As we know, the VCSEL with an asymmetric oxide aperture always has a polarization selection [39,40]. In our HCG-VCSEL, the HCG together with the top 4-pair DBR is a TE-polarized mirror. The HCG bars are along the crystallographic orientation [01–1]. The angle shift between the TE direction of the HCG and the major axis (along [0–10]) of the elliptical oxide aperture is about 50 degrees. The elliptical oxide aperture can introduce a polarization selectivity of a VCSEL, whereas the HCG also has a polarization selectivity. The direction shift between the HCG and the elliptical oxide aperture may result in a low OPSR. The HCG-VCSEL with a symmetric oxide aperture or with the HCG specifically aligned with the asymmetric oxide aperture [41], may achieve a high OPSR, which will be very good for the sensing applications and optical interconnects.
The linewidth of the VCSEL is an important parameter in applications. The linewidth of the HCG-VCSEL can be broadened by the Brownian motion of the suspended HCG [42]. The linewidth of our HCG-VCSEL is expected to be less than that of the reported HCG-VCSEL, because there are two posts to support the suspended HCG and reduce the Brownian motion of the HCG. The linewidth of our HCG-VCSEL will be measured and reported elsewhere.

3. BSW-SEL

The aforementioned HCG-VCSEL is still in the scope of the VCSEL because the HCG-VCSEL has a vertical cavity with the phase matching condition [34], and it has a limited single-mode output power. We find that when the p-doped top DBR in the HCG-VCSEL structure in Figure 1 is removed and the cavity thickness is reduced without the phase matching condition, the BSW-SEL is formed without a vertical cavity. Figure 8 shows the schematics of the proposed BSW-SEL and the BSW field distribution [34,43].
Figure 9 shows the dispersion diagrams (i.e., the relation between the propagation constant in the x direction (kx) and the eigenfrequency (ω)) of the infinite Al0.92Ga0.08As/GaAs DBR and 5.5-pair Al0.92Ga0.08As/GaAs DBR. The grey regions are the allowed bands, and the white regions are the forbidden bands of the infinite DBR. The dispersion diagram of the infinite structure is calculated by the relation [34,43,44]:
K ( k x , ω ) Λ = a cos [ 0.5 × ( A + D ) ]
where K is the Bloch number, which is a function of kx and ω, Λ is the period of the multilayer structure, and the matrix elements A and D can be found in [43]. When KΛ is a real number, the Bloch wave can propagate in the structure. When KΛ contains imaginary parts, the Bloch wave is an evanescent wave.
The blue lines in Figure 9 are the BSWs of the 5.5-pair DBR, which can be obtained from [34,43,44]:
( A 0 B 0 ) = ( M 11 M 12 M 21 M 22 ) ( A s B s )
where A0 and B0 are the electric field amplitudes on the left and right sides of the incident layer, respectively. As and Bs are the electric field amplitudes on the left and right sides of the terminated layer, respectively. The dispersion relation between kx and ω can be obtained by the M matrix [43]. When the dispersion curve of the confined mode is located below the air light, and within the bandgap of the multilayer periodic structure, the confined mode becomes the BSW. The BSW at 940 nm corresponding to an angular frequency of 2.005 × 1015 rad/s is marked with a red star in Figure 9.
As we know, the DBR has a high reflectivity, and the DBR is used as the mirror for VCSELs. This high reflection characteristic is due to the band gap of the DBR at kx = 0 in the dispersion diagram, as shown in Figure 9. However, the finite-pair DBR breaks the translational symmetry of the infinite DBR, and introduces the BSW. This BSW is located in the band gap. Therefore, the BSW is strongly confined in the surface layer of the finite-pair DBR, as shown in Figure 8. This BSW can have a large overlap with the active region. At the same time, the BSW decays dramatically at both sides of the DBR, leading to a high confinement factor. The high confinement factor is very beneficial for lasing.
As shown in Figure 8, the HCG can be introduced on top of the DBR with imbedded QWs for gain in the surface layer of the finite-pair DBR. Because the HCG has a transverse periodicity, the dispersion curve of the BSW in Figure 8 is folded back to kx = 0 with respect to kx = K/2 (K = 2 × π/Λ) [45,46]. The forward wave and backward wave of the BSW couple with each other at the intersection point of kx = 0, and a band gap occurs as the period of the HCG is smaller than the working wavelength, as shown in Figure 10. The two band-edge modes belong to a symmetric leaky mode and an antisymmetric bound state in the continuum (BIC), respectively [35,47]. The antisymmetric BIC has theoretically an infinite quality (Q) factor, and simultaneously satisfies the momentum conservation and energy conservation. Therefore, there is a vertical momentum component of the antisymmetric BIC for surface emission, as schematically shown in Figure 8.
This proposed BSW-SEL with 1D or 2D periodicity has unique features compared with the 2D PCSEL [30,31] and 1D PCSEL (i.e., second-order distributed feedback laser) [32,33]. The 1D and 2D PCSELs works with the guided mode of a waveguide, whereas the BSW-SEL works with a BSW located in the band gap at kx > 0 of the dispersion of the DBR in Figure 9. The BSW-SEL works at the BIC formed by the band folding of the BSW of the finite-pair DBR, whereas the PCSEL works with the index-guided mode. Because the specifically designed finite-pair DBR can simultaneously serve as a mirror to reflect the diffractive light escaping downward, the BSW-SEL can realize a high-efficiency output. Therefore, the BSW-SEL can be expected to achieve a large-area, single-mode operation with a high efficiency and a low divergence angle [34].
On the other hand, the proposed BSW-SEL is different from the tilted cavity laser (TCL) [48,49,50,51]. The TCL consists of a resonant cavity and at least one multilayer interference reflector. It is based on the resonant modes of the multilayer structure. The resonant modes are revealed in the optical reflectivity spectra at tilted incidence of light, and the resonant modes are well confined in the cavity [48,49,50,51]. However, the BSW-SEL is designed based on the BSW of the single multilayer structure. The BSW field is strongly confined in the interface between the air side and the multilayer structure, and decays exponentially in the multilayer structure and the air side. The vertical surface emission of the BSW-SEL is realized by introducing an HCG above the multilayer structure.
To conceptually verify the BSW-SEL with 1D HCG as shown in Figure 8, the field distribution of the resonant mode (i.e., BIC) of the BSW-SEL designed at 940 nm wavelength range is calculated by the finite-element method, as shown in Figure 11a. Due to the limited computational resource, the horizontal (along x direction) calculation domain of the finite-size BSW-SEL structure is 50 μm. Along the x direction, a standing wave is formed by the distributed feedback effect like in the 1D second-order distributed feedback laser [32,33,52,53,54]. In the z direction, considerable light is diffracted upward for surface emission, and at the bottom side the field is decayed because of the BSW in the finite-pair DBR and the reflection of the finite-pair DBR, resulting in less diffracted light emitting downward. The far field pattern (FFP) of the surface-emitting resonant mode in Figure 11a is calculated and shown in Figure 11b. The FFP is two-lobed, and there is a null around 0 degree because the resonant mode is with antisymmetric property [32,33,52,53,54]. The divergence angle can be further reduced by increasing the size, and a single-lobed FFP can also be achieved with a phase-shift HCG structure [55,56].
As aforementioned, the DBR in the BSW-SEL can serve as a reflector to block the downward diffracted light, leading to a larger slope efficiency. In addition, the output power of BSW-SEL can be improved by optimizing the distance between the HCG and the active region to control the coupling strength between the band-edge mode and the active region. Furthermore, the oxide aperture can be introduced in the BSW-SEL to provide current confinement. By optimizing the structure of the HCG, a lower divergence angle of the FFP can be obtained. These show the promise of the large-area, single-mode, high-efficiency, high-power (1D and 2D HCG) surface-emitting laser with a low divergence angle.

4. Conclusions

In this paper we introduce the HCG to replace part of the top DBR to form the HCG-VCSEL at 940 nm. The HCG-VCSEL is designed, fabricated, and measured. The 4-pair top DBR for current spreading can reduce the reflectivity difference between the reflectivity of the TE polarization and that of the TM polarization, and leads to a large duty cycle (a/Λ) tolerance of the HCG, making it very good for the realization of the HCG-VCSEL. In our experiments, the power OPSR of the HCG-VCSEL is currently about 9 dB, due to the direction shift between the HCG and the elliptical oxide aperture. The polarization characteristic of the HCG-VCSEL can be improved by specifically aligning the HCG with a symmetric oxide aperture; this is our future work. The performance of the HCG-VCSEL will be improved by reducing the self-heating effect [57,58,59,60].
The HCG-VCSEL structure with the HCG-DBR vertical cavity structure can be reduced to the BSW-SEL structure based on the HCG-DBR metastructure without the phase matching condition. The BSW-SEL works with the antisymmetric high-Q BIC for surface emission based on the momentum conservation and energy conservation. Since the specifically designed finite-pair DBR can simultaneously serve as a mirror to reflect the diffractive light escaping downward, the BSW-SEL can realize a high-efficiency output, compared with the PCSEL. The BSW-SEL is expected to achieve a large-area, single-mode operation with a high efficiency and a high beam quality.
The surface-emitting lasers with surface metastructures provide the flexibility to control the mode characteristics, enhance the modulation bandwidth and beam quality, and improve the output power and efficiency. The surface-emitting lasers with surface metastructures are useful light sources for various applications including LiDAR, three-dimensional sensing, and optical interconnects.

Author Contributions

Conceptualization, A.L.; methodology, A.L.; validation, A.L. and J.Z.; formal analysis, A.L., J.Z., C.H. and M.W.; investigation, A.L., J.Z., C.H. and M.W.; data curation, A.L., J.Z., C.H. and M.W.; writing—original draft preparation, A.L.; writing—review and editing, A.L., J.Z., C.H., M.W. and W.Z.; supervision, A.L.; project administration, A.L.; funding acquisition, A.L. and W.Z. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded in part by National Natural Science Foundation of China, grant number 62275243 and 62075209; Beijing Natural Science Foundation, grant number Z200006.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Acknowledgments

The authors would like to thank Chao Peng in Peking University for stimulating discussions.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Schematics of the HCG-VCSEL. Λ is the period of the HCG, a is the bar width of the HCG, and d is the gap width between the grating bars.
Figure 1. Schematics of the HCG-VCSEL. Λ is the period of the HCG, a is the bar width of the HCG, and d is the gap width between the grating bars.
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Figure 2. Calculated normalized current density profiles in the active regions of the HCG-VCSELs with a 6-μm active diameter and 4-pair and 1-pair top Al0.12Ga0.88As/Al0.9Ga0.1As DBRs.
Figure 2. Calculated normalized current density profiles in the active regions of the HCG-VCSELs with a 6-μm active diameter and 4-pair and 1-pair top Al0.12Ga0.88As/Al0.9Ga0.1As DBRs.
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Figure 3. Reflectivity spectra of the designed HCG with a bar width of 222 nm and the top mirror composed of the designed HCG, the air layer beneath the HCG, and the top 4-pair DBR.
Figure 3. Reflectivity spectra of the designed HCG with a bar width of 222 nm and the top mirror composed of the designed HCG, the air layer beneath the HCG, and the top 4-pair DBR.
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Figure 4. (a) TE and (c) TM reflectivity spectra of the HCG with different gap widths d; (b) TE and (d) TM reflectivity spectra of the top mirror composed of the designed HCG, the air layer beneath the HCG, and the top 4-pair DBR, under different gap widths d for the HCG.
Figure 4. (a) TE and (c) TM reflectivity spectra of the HCG with different gap widths d; (b) TE and (d) TM reflectivity spectra of the top mirror composed of the designed HCG, the air layer beneath the HCG, and the top 4-pair DBR, under different gap widths d for the HCG.
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Figure 5. (a) Infrared microscope image of the mesa after oxidation before the introduction of the grating pattern. The dashed ellipse indicates the profile of the oxidation edge; (b) SEM image of the fabricated HCG-VCSEL.
Figure 5. (a) Infrared microscope image of the mesa after oxidation before the introduction of the grating pattern. The dashed ellipse indicates the profile of the oxidation edge; (b) SEM image of the fabricated HCG-VCSEL.
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Figure 6. Schematics of the polarization measurement system. The blue dotted line represents the emitting light of the HCG-VCSEL.
Figure 6. Schematics of the polarization measurement system. The blue dotted line represents the emitting light of the HCG-VCSEL.
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Figure 7. (a) Power-current (LI) curves and OPSR of the HCG-VCSEL; The inset is the near field pattern at 2 mA; The size of the oxide aperture is about 4.5 μm × 7 μm; (b) Spectra of the fabricated HCG-VCSEL.
Figure 7. (a) Power-current (LI) curves and OPSR of the HCG-VCSEL; The inset is the near field pattern at 2 mA; The size of the oxide aperture is about 4.5 μm × 7 μm; (b) Spectra of the fabricated HCG-VCSEL.
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Figure 8. Schematics of the BSW-SEL with 1D HCG. The BSW field distribution in the z direction is shown.
Figure 8. Schematics of the BSW-SEL with 1D HCG. The BSW field distribution in the z direction is shown.
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Figure 9. Dispersion diagrams of the infinite DBR and 5.5-pair DBR. The line composed of light red stars (*) is the light line of the Al0.92Ga0.08As layer. The line composed of light green circles (○) is the light line of the GaAs layer.
Figure 9. Dispersion diagrams of the infinite DBR and 5.5-pair DBR. The line composed of light red stars (*) is the light line of the Al0.92Ga0.08As layer. The line composed of light green circles (○) is the light line of the GaAs layer.
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Figure 10. Dispersion diagram of the BSW-SEL structure in the first Brillouin zone.
Figure 10. Dispersion diagram of the BSW-SEL structure in the first Brillouin zone.
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Figure 11. (a) Field distribution of the resonant mode (938.5 nm) of the BSW-SEL; (b) calculated far field pattern of the BSW-SEL.
Figure 11. (a) Field distribution of the resonant mode (938.5 nm) of the BSW-SEL; (b) calculated far field pattern of the BSW-SEL.
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Liu, A.; Zhang, J.; Hao, C.; Wang, M.; Zheng, W. Surface-Emitting Lasers with Surface Metastructures. Photonics 2023, 10, 509. https://doi.org/10.3390/photonics10050509

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Liu A, Zhang J, Hao C, Wang M, Zheng W. Surface-Emitting Lasers with Surface Metastructures. Photonics. 2023; 10(5):509. https://doi.org/10.3390/photonics10050509

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Liu, Anjin, Jing Zhang, Chenxi Hao, Minglu Wang, and Wanhua Zheng. 2023. "Surface-Emitting Lasers with Surface Metastructures" Photonics 10, no. 5: 509. https://doi.org/10.3390/photonics10050509

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