Buried Heterostructure Lasers Research Articles

Theoretical analysis of the buried heterostructure laser for stable dual-wavelength generation

Stable dual-wavelength emission from a laser is desirable for microwave signal generation using the optical heterodyning method. As both optical wavelengths are generated from the same cavity, the phase noise of the generated microwave signal is minimized. In this work, we exploit the inherent birefringence in the buried heterostructure semiconductor laser to generate dual polarized modes. We carefully analyze the mode competition between various modes in the cavity and propose the desirable gain modification conditions for stable dual mode oscillations when the laser is operating near the threshold. We show that the required asymmetry in the gain for two stable modes can be obtained from the mode confinement factors and facet losses. We also show the applicability of our results to a homogeneously broadened multimode laser.

Slotted surface gratings fabricated by selective area growth of the p-InP cladding layer for BH lasers.

In this paper, we present a novel, to our knowledge, method for the fabrication of slotted surface gratings for buried heterostructure (BH) lasers. In the device fabrication process, SiO2 strips needed for InP current blocking layer growth are reused for the formation of slot grating pattern masks. In the following growth of the p-InP cladding layer, because the slot areas are covered by SiO2, the InP material is grown selectively in only the areas outside the slot areas, forming slots of the surface gratings in the p-InP layer at the same time as the cladding layer growth. Single longitude mode BH lasers having slotted surface gratings have been fabricated successfully, and the spectra show higher than 40 dB side mode suppression ratio (SMSR). The adoption of the method helps to simply the device fabrication and thus lower the device fabrication cost notably.

Single-mode InGaAsP/InP BH lasers based on high-order slotted surface gratings.

A single-mode InGaAsP/InP buried heterostructure (BH) laser based on high-order slotted surface gratings has been fabricated. The introduction of surface slotted grating can simplify the fabrication process of single-mode BH lasers notably. The laser shows a good single-mode emission performance, with larger than 30 dB side-mode suppression ratio (SMSR) when the current is between 200 and 400 mA. Calculations show that the gain coupling mechanism plays a key role for the slot grating to select the emission wavelength. The linewidth of the laser is measured. The fitted Gaussian and Lorentzian linewidths are 1500 and 550 kHz, respectively.

Improvement of Power and Efficiency of High-Mesa Semi-Insulating InP: Fe Buried Heterostructure Lasers with Wide Bandgap Layers

High-mesa semi-insulating buried heterostructure (SIBH) lasers with InP: Fe have great potential in high-speed and high-power scenarios, but the leakage current problem under high current injections has always limited their application. In order to solve the issue of low output power and low efficiency for high-mesa SIBH lasers, the mechanism of leakage current generation in InP-based semi-insulating (SI) layers at high injection levels was analyzed through numerical simulation. The deterioration of the device performance is due to the hole current-induced electron leakage current, which results from the reduction of the potential barrier and Fe-Zn interdiffusion. Thus, lasers with wide bandgap layers of InAlAs and ZnCdSe were employed for current blocking, the power and wall-plug efficiency of which were improved by more than 36% and 5%, respectively. For the first time, a SIBH laser based on lattice-matched ZnCdSe barrier layers is proposed, which shows good output performance and high reliability. The introduction of the wide bandgap layer in the SIBH structure establishes potential barriers to confine both carrier leakages at high injection levels, which realizes the high-power and high-efficiency operation of the laser.

Room Temperature, Continuous Wave Quantum Cascade Laser Grown Directly on a Si Wafer

We report the room temperature demonstration of a high power, continuous wave, LWIR quantum cascade laser grown directly on a Si substrate. A new wafer, based on a high efficiency, strain-balanced laser core was processed into a lateral injection buried heterostructure laser geometry. A pulsed efficiency of 11.1% was demonstrated at room temperature, with an emission wavelength of 8.35 μm. With low fidelity, epilayer-up packaging, CW emission up to 343 K was also demonstrated, with a maximum output power of >0.7 W near room temperature.

High Power, Room Temperature InP-Based Quantum Cascade Laser Grown on Si

We report on the realization of an InP-based long wavelength quantum cascade laser grown on top of a silicon substrate. This demonstration first required the development of an epitaxial template with a smooth surface, which combines two methods of dislocation filtering. Once wafer growth was complete, a lateral injection buried heterostructure laser geometry was employed for efficient current injection and low loss. The laser emits at a wavelength of ~ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10.8~\mu \text{m}$ </tex-math></inline-formula> and is capable of operation above 373 K, with a high peak power (>4 W) at room temperature. Laser threshold behavior with temperature is characterized by a T0 of 178 K. The far field beam shape is single lobed, showing fundamental transverse mode operation.

InAs/InP quantum dash buried heterostructure mode-locked laser for high capacity fiber-wireless integrated 5G new radio fronthaul systems.

We have developed and experimentally demonstrated a highly coherent and low noise InP-based InAs quantum dash (QDash) buried heterostructure (BH) C-band passively mode-locked laser (MLL) with a pulse repetition rate of 25 GHz for fiber-wireless integrated fronthaul 5G new radio (NR) systems. The device features a broadband spectrum providing over 46 equally spaced highly coherent and low noise optical channels with an optical phase noise and integrated relative intensity noise (RIN) over a frequency range of 10 MHz to 20 GHz for each individual channel typically less than 466.5 kHz and -130 dB/Hz, respectively, and an average total output power of ∼50 mW per facet. Moreover, the device exhibits low RF phase noise with measured RF beat-note linewidth down to 3 kHz and estimated timing jitter between any two adjacent channels of 5.5 fs. By using this QDash BH MLL device, we have successfully demonstrated broadband optical heterodyne based radio-over-fiber (RoF) fronthaul wireless links at 5G NR in the underutilized spectrum of around 25 GHz with a total bit rate of 16-Gb/s. The device performance is experimentally evaluated in an end-to-end fiber-wireless system in real-time in terms of error vector magnitude (EVM) and bit error rate (BER) by generating, transmitting and detecting 4-Gbaud 16-QAM RF signals over 0.5-m to 2-m free-space indoor wireless channel through a total length of 25.22 km standard single mode fiber (SSMF) with EVM and BER under 8.4% and 2.9 × 10-5, respectively. The intrinsic characteristics of the device in conjunction with its system transmission performance indicate that QDash BH MLLs can be readily used in fiber-wireless integrated systems of 5G and beyond wireless communication networks.

Beam steering characteristics in high-power quantum-cascade lasers emitting at ∼ 4.6 μm* *Project supported by the National Basic Research Program of China (Grant Nos. 2018YFA0209103 and 2018YFB2200504), the National Natural Science Foundation of China (Grant Nos. 61991430, 61774146, 61790583, 61674144, and 61774150), and the Key Projects of the Chinese Academy of Sciences (Grant Nos. 2018147, YJKYYQ20190002, QYZDJ-SSW-JSC027, and XDB43000000).

A beam steering effect of high-power quantum cascade (QC) lasers emitting at ∼ 4.6 μm was investigated. The continuous wave (CW) output power of an uncoated, 6-mm-long, 7.5-μm-wide buried-heterostructure QC laser at 25 °C was as high as 854.2 mW. The maximum beam steering angle was offset by ± 14.2° from the facet normal (0°) in pulsed mode. The phenomenon was judged explicitly by combining the diffraction limit theory and Fourier transform of the spectra. It was also verified by finite element method software simulation and the calculation of two-dimensional (2D) effective-index model. The observed steering is consistent with a theory for coherence between the two lowest order lateral modes. Therefore, we have established an intrinsic linkage between the spectral instabilities and the beam steering by using the Fourier transform of the spectra, and further presented an extremely valid method to judge the beam steering. The content of this method includes both three equidistant peak positions in the Fourier transform of the spectra and the beam quality located between once the diffraction limit (DL) and twice the DL.

Single-Mode Fabry-P&amp;#233;rot Quantum Cascade Lasers at λ~10.5 μm

In this paper, we report a single-mode Fabry-Pérot long wave infrared quantum cascade lasers based on the double phonon resonance active region design. For room temperature CW operation, the wafer with 35 stages was processed into buried heterostructure lasers. For a 4 mm long and 13 μm wide laser with high-reflectivity (HR) coating on the rear facet, continuous wave output power of 43 mW at 288 K and 5 mW at 303 K is obtained with threshold current densities of 2.17 and 2.7 kA/cm2. The lasing wavelength is around 10.5 μm. Single mode emission was observed for this particular device over the whole investigated current and temperature range.

Membrane buried-heterostructure DFB laser with an optically coupled III-V/Si waveguide.

We have developed a membrane buried-heterostructure (BH) distributed feedback (DFB) laser consisting of an optically coupled III-V/Si waveguide and SiN surface grating. A 230-nm-thick membrane III-V layer enables us to construct an optical supermode in a 220-nm-thick Si waveguide and control the optical confinement factor in both the III-V and Si layers by changing Si waveguide width. This makes it possible to use a conventional Si photonics platform because the Si waveguides widely used on it are around 220-nm thick. To fabricate the BH-the key component for constructing a membrane laser with a lateral current-injection structure-we used direct wafer bonding and regrowth by metalorganic vapor phase epitaxy. Light output from the DFB laser is transferred to the Si waveguide through a short inverse-taper InP waveguide. A fiber-chip interface constructed by using inverse-taper Si waveguides and SiOx waveguides provides 2-dB fiber coupling loss. Fiber coupling power of 7.9 mW is obtained with a λ/4-shifted DFB laser with a 500-µm-long cavity. Single-mode lasing with a side-mode suppression ratio of 50 dB and lasing up to 120°C are also demonstrated.

Monolithic Integration of Buried-Heterostructures in a Generic Integrated Photonic Foundry Process

This paper demonstrates the integration of buried-heterostructure (BH) lasers and semiconductor optical amplifiers (SOAs) in a generic photonic foundry platform. The process-flow adaptations necessary for their integration with existing building blocks are presented. BH Fabry–Perot lasers fabricated within the platform are fully characterized and compared with shallow-ridge (SR) lasers already available as a standard building block. SR lasers were fabricated on the same wafer sharing the same layer stack. BH lasers showed a reduction in threshold current of 60% and a reduction in thermal resistance of 40%. The full integration is then validated by the characterization of a compact arrayed waveguide grating laser-based transmitter consisting of eight BH-SOAs and a deep-ridge waveguide. A side-mode suppression ratio of up to 57 dB and a linewidth of 1.5 MHz are achieved.

Buried-Heterostructure Quantum Cascade Lasers Fabricated Using a Sacrificial Layer and a Two-Step Regrowth Process

We report various aspects related to the selective area growth of thick InP:Fe layers by metal organic vapor deposition and their application to buried-heterostructures. In particular, we focus on the development of planar buried-heterostructure-quantum cascade lasers using selective wet chemical etching for ridge mesa preparation and versatile regrowth processes. After describing the optimization of the insulating properties of InP:Fe layers, we expose our approach to circumvent the difficulties inherent to the selective area growth on non-planar structures. By adding an InGaAs/InP layer stack (where, the InGaAs layer is used as a sacrificial layer) on the top of the active region, reproducible regrowths have been successfully carried out with good optical, electrical and crystalline quality. Using this method, buried-heterostructure quantum cascade lasers characterized in TM00 mode, exhibited output powers in the range of 2.5 W and wall plug efficiencies of about 13% at room temperature.

Room temperature continuous wave operation of quantum cascade laser at λ ~ 9.4 μm * * Project supported by the National Key Research And Development Program (No. 2016YFB0402303), the National Natural Science Foundation of China (Nos. 61435014, 61627822, 61574136, 61774146, 61674144, 61404131), the Key Projects of Chinese Academy of Sciences (Nos. ZDRW-XH-2016-4, QYZDJ-SSW-JSC027), and the Beijing Natural Science Foundation (No.

Continuous wave (CW) operation of long wave infrared (LWIR) quantum cascade lasers (QCLs) is achieved up to a temperature of 303 K. For room temperature CW operation, the wafer with 35 stages was processed into buried heterostructure lasers. For a 2-mm-long and 10-μm-wide laser with high-reflectivity (HR) coating on the rear facet, CW output power of 45 mW at 283 K and 9 mW at 303 K is obtained. The lasing wavelength is around 9.4 μm locating in the LWIR spectrum range.

Quantum cascade lasers transfer-printed on silicon-on-sapphire

We demonstrate coupling of the laser mode into a passive waveguide by transfer-printing fully processed mid-infrared quantum cascade lasers onto a silicon-on-sapphire platform. The laser waveguide mode is coupled into a silicon waveguide via an adiabatic taper. The experimentally achieved coupling efficiency of the taper is estimated to be ∼10%, and theoretical calculations show that coupling efficiency over 75% is achievable by reducing the adhesive layer thickness to below 100 nm. Light coupling to silicon waveguides is confirmed by images taken at the output facet of a 3-mm-long passive Si waveguide with a mid-infrared camera. Our technique enables the development of heterogeneous photonic systems integrated with a wide range of fully processed semiconductor laser devices, including buried-heterostructure lasers, which was not previously possible.

3.36 µm single-mode quantum cascade laser with a dissipation below 250 mW.

We present 3.36 µm buried heterostructure distributed-feedback quantum cascade lasers with a power dissipation at threshold below 250 mW and operation temperatures as high as 130 °C. Threshold values below 20 mA at -10 °C in pulsed operation and 30 mA at -20 °C in continuous-wave operation are reported. Optical power above 130 mW and 13 mW are achieved at -20 °C in pulsed and continuous-wave operation, respectively. Continuous-wave operation occurs until 15 °C. We show single-mode emission in pulsed and continuous-wave operation. Single-mode performance is demonstrated in long pulse (5.56 µs) operation. The laser far-field exhibits a single lobe emission with full-width-half-max of 27 ° × 34 °.

Extended tuning of mid-ir quantum cascade lasers using integrated resistive heaters.

We present single mode quantum cascade lasers including a microscopic heater for spectral emission tuning. Through the use of a buried heater element, the active region temperature can be modified without changing the submount one. Emission frequency tuning in continuous-wave as large as 9 cm(-1) at 1270 cm(-1) and 14 cm(-1) at 2040 cm(-1) are observed, corresponding to an increase of the active region temperatures of ∼ 90 K. Due to the proximity of the heaters to the active region, emission can be modulated at several kHz range and the absence of moving parts guarantees the mechanical stability of the system. This method can be successfully applied to all buried heterostructure lasers, becoming an attractive solution for molecular spectroscopy in the IR. Using the presented devices, molecular absorptions of N(2)O have been measured between 1270 cm(-1) and 1280 cm(-1) and are in agreement with data from the HITRAN database.

Buried‐heterostructure mid‐infrared quantum cascade lasers fabricated by non‐selective regrowth and chemical polishing

A novel fabrication method of buried-heterostructure (BH) mid-infrared quantum cascade lasers (QCLs) by using non-selective regrowth of iron-doped indium phosphide (InP) (Fe:InP), around deeply etched laser ridges, via metal-organic chemical vapour deposition (MOCVD) and planarisation via chemical polishing is reported. Owing to better heat dissipation, the fabricated 4.75 μm emitting QCLs exhibit about three-fold enhancement in maximum output power under continuous-wave operation at room temperature (T = 20°C) compared with that from lasers without the regrown InP. The demonstrated fabrication method provides a more flexible route to realising BH QCLs by removing strict requirements on the etched-ridge sidewall profile, as well as on the physical dimensions of the dielectric mask for the regrowth via MOCVD. The method can be further employed for making large-emitting aperture, closely packed arrays of QCLs, with planarised geometry, for coherent-power scaling.

Comparison of semi-insulating InAlAs and InP:Fe for InP-based buried-heterostructure QCLs

In a previous work [Flores et al., J. Cryst. Growth 398 (2014) 40] [3] we demonstrated the advantages of using a thin InAlAs spacer layer in the fabrication of buried-heterostructure quantum-cascade lasers (QCLs), as it improves the morphology of the interface between the laser core and the InP:Fe lateral cladding. In this paper we investigate aspects of InAlAs, which are relevant for its role as insulating lateral cladding of the laser sidewalls: carrier traps, electrical resistivity, and functionality as a sole lateral cladding. We find that a thin InAlAs spacer layer not only improves the regrowth interface morphology, but also eliminates interface-related shallow electronic states, thus improving the electrical resistivity of the interface. We further find that bulk InAlAs grown by gas-source molecular-beam epitaxy as well as InP:Fe are semi-insulating at room temperature, with specific resistivities of 3×107Ωcm and 2×108Ωcm, respectively. Both materials have also a high thermal activation energy for electrical conductivity (0.79eV and 0.68eV, respectively). In order to compare the performance of InP:Fe and InAlAs as a lateral cladding, lasers were fabricated from the same QCL wafer with differing stripe insulation materials. The resulting lasers differ mainly by the lateral insulation material: SiO2, InP:Fe (with InAlAs spacer), and pure InAlAs. All devices show a similar performance and similar temperature dependence, indicating insulating properties of InAlAs adequate for application in lateral regrowth of buried-heterostructure QCLs.

An experimental study of noise in mid-infrared quantum cascade lasers of different designs

We present an experimental study of noise in mid-infrared quantum cascade lasers (QCLs) of different designs. By quantifying the high degree of correlation occurring between fluctuations of the optical frequency and voltage between the QCL terminals, we show that electrical noise is a powerful and simple mean to study noise in QCLs. Based on this outcome, we investigated the electrical noise in a large set of 22 QCLs emitting in the range of 7.6–8 μm and consisting of both ridge-waveguide and buried-heterostructure (BH) lasers with different geometrical designs and operation parameters. From a statistical data processing based on an analysis of variance, we assessed that ridge-waveguide lasers have a lower noise than BH lasers. Our physical interpretation is that additional current leakages or spare injection channels occur at the interface between the active region and the lateral insulator in the BH geometry, which induces some extra noise. In addition, Schottky-type contacts occurring at the interface between the n-doped regions and the lateral insulator, i.e., iron-doped InP, are also believed to be a potential source of additional noise in some BH lasers, as observed from the slight reduction in the integrated voltage noise observed at the laser threshold in several BH-QCLs.

Stable growth of ruthenium doped InP at the current blocking layer for buried-heterostructure lasers

We report on the stable growth of ruthenium doped InP (Ru-InP) and its application in optical communication devices, grown by metal-organic vapor phase epitaxy. Ru-InP has semi-insulating characteristics for both n- and p-InP. The resistivity of the p/Ru/p-InP structure was 2×107Ωcm for a Ru concentration of 5×1017cm−3 in Ru-InP with a Ru-InP thickness greater than 1.0μm. However, the resistivity was very low when the Ru-InP thickness was less than 1.0μm. We investigated the Zn diffusion from p-InP to Ru-InP and found two Zn diffusion fronts in Ru-InP. Each diffusion front had a correlation with the Ru and Zn concentrations. By optimizing the current blocking layers in the Ru-InP and Zn-InP layers in buried-heterostructure lasers (BH-lasers), an output power over 10mW was realized for laser diodes, even when they were operated at 95°C.