Vertical-Cavity Surface-Emitting Lasers (VCSELs) are widely used for optical interconnects, 3D sensing like face recognition, or automotive applications. Conventional VCSELs with top/bottom distributed Bragg reflectors (DBRs) for any wavelength range are costly and bulky, needing precise growth control. High-contrast subwavelength gratings (HCGs) show a near 100% reflectivity across a wide wavelength range, and have a typical thickness of a few hundred nanometers, much thinner than epitaxial DBRs. In addition, HCGs were reported to have the ability to tightly confine the field in the HCG-based vertical cavities, very promising for high-speed devices. Thus HCGs are ideal candidates for mirror replacements, at least at the top, to construct vertical cavities. Currently HCGs are often based on an oxide layer, being monolithically integrated, or air-suspended, and the fabrication of these HCGs is still challenging.
VCSELs at 940 nm have been attracting particular attention for short-wave wavelength division multiplexing and sensing. Here we report for the first time electrically injected 940-nm HCG-VCSELs using post-supported air-suspended HCGs. The HCG-VCSELs are fabricated without critical point drying, and the HCGs can be released with a 100% yield in water or isopropanol. Our first generation HCG-VCSELs achieve already a low threshold current of 0.65 mA, and a large side-mode suppression ratio of 43.6 dB at 25 ℃ under continuous-wave operation. Theoretically, these HCG-VCSELs have a smaller effective mode length of 1.38*(λ/n), than that of conventional VCSELs with λ/2 cavities. The relaxation resonance frequency will increase by 16%. A data rate of 100 Gbps for these HCG-VCSELs is expected for the on-off keying modulation format.
Our present design and fabrication methods of the HCG-VCSELs can be extended to other wavelength ranges.
We experimentally demonstrate for the first time electrically-injected Vertical-Cavity Surface-Emitting Lasers (VCSELs) with post-supported high-contrast gratings (HCGs) at 940 nm. The HCG-VCSELs have two posts to support the air-suspended HCGs, being realized by simple fabrication without critical point drying. The HCGs can be released with a 100% yield in water or isopropanol. The HCG-VCSEL with a 4 μm × 8 μm oxide aperture achieves a low threshold current of 0.65 mA and a large side-mode suppression ratio of 43.6 dB under continuous-wave operation at 25 degrees. Theoretically, the relaxation resonance frequency of the HCG-VCSEL will increase by 16% compared with that of the conventional VCSEL with a λ/2 cavity. The data rate of 100 Gbps in the on-off keying modulation format for the HCG-VCSEL is expected.
Directly modulated semiconductor lasers (DMLs) with surface high-order grating have been designed, fabricated and measured. The output powers under different temperatures were measured, and there are almost no kinks among all the light-power curves. The threshold current is 22 mA with a slope efficiency of 0.21 mW/mA at 25 ℃. The side-mode suppression ratio (SMSR) over 30 dB is achieved. The wavelength red-shifting caused by current-induced heating is at a ratio of 0.03 nm/mA. Small signal response of this kind of lasers with surface high-order grating was measured at 25 ℃ and the -3 dB bandwidth is 11 GHz.
Vertical-cavity surface-emitting lasers (VCSELs) have wide applications in data communication, sensing, and consumer electronics, because they have many advantages, such as circular beam, low power consumption, high modulation speed, low cost, high reliability, and 2D array configuration. Metastructure like high-contrast grating (HCG) has many unique optical properties which can be used to construct novel VCSELs. Here we study the TE-polarization HCG for 940 nm wavelength range and design high-quality HCG-based vertical cavities with heterostructures aiming at HCG-VCSEL. The TE-polarization HCG-VCSEL at 940 nm is finally designed with a Q-factor of ~3.6×105.
High-contrast metastructures like one-dimensional high-contrast gratings (HCGs) are promising to improve the performance of conventional VCSELs, also presenting a basis for new applications. Different from the previous studies where HCGs are always modelled being of infinite size, we studied here the finite-size HCGs, which match the real situation. We observe finite-size HCGs behaving very differently from infinite-size HCGs. The reflectivity of a finitesize HCG strongly depends on the HCG size and the source size. At the same time, the simulation results show, that finite-size HCGs can shape the output beam, and a Gaussian-like reflected wave is typically achieved. Most important the normally incident light is partly redirected to the in-plane direction, showing unidirectional transmission. Monolithically integrated HCG-based optical sensors can be based on this novel effect. An integrable HCG reflector was fabricated with GaInP as the sacrificial layer targeting the application of HCG-VCSEL at 980 nm range. The measured reflectivity agrees well with the calculated reflectivity.
A three-dimensional tapered silicon-based spot-size converter is studied to improve the butt-jointed efficiency between the laser diode and the single-mode silicon waveguide. This kind of the spot-size converter can be fabricated while the ridge waveguide is etched. There is no need to regrow SiN or SiON on silicon. The optimized coupling efficiency between the spot-size converter and laser diode is over 0.8 at the wavelength of 1550 nm. This spot-size converter is useful for silicon photonics.
We designed and analyzed the ring resonators used as external optical cavities for hybrid tunable lasers based on silicon waveguides. The designed double-ring resonators (DRRs) for tunable lasers on silicon can provide a tuning range over 40 nm by micro-heaters, which cover the entire C-band with a high tuning accuracy.
High efficiency 980 nm longitudinal photonic band crystal (PBC) edge emitting laser diodes are designed and fabricated. The calculated results show that eight periods of Al0.1Ga0.9As and Al0.25Ga0.75As layer pairs can reduce the vertical far field divergence to 10.6° full width at half maximum (FWHM). The broad area (BA) lasers show a very high internal quantum efficiency ηi of 98% and low internal loss αi of 1.92 cm-1. Ridge waveguide (RW) lasers with 3 mm cavity length and 5um strip width provide 430 mW stable single transverse mode output at 500 mA injection current with power conversion efficiency (PCE) of 47% under continuous wave (CW) mode. A maximum PCE of 50% is obtained at the 300 mA injection current. A very low vertical far field divergence of 9.4° is obtained at 100 mA injection. At 500 mA injection, the vertical far field divergence increases to 11°, the beam quality factors M2 values are 1.707 in vertical direction and 1.769 in lateral direction.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.