Antti T. Aho

High-power temperature-stable GaInNAs distributed Bragg reflector laser emitting at 1180 nm.

We report a single-mode 1180 nm distributed Bragg reflector (DBR) laser diode with a high output power of 340 mW. For the fabrication, we employed novel nanoimprint lithography that ensures cost-effective, large-area, conformal patterning and does not require regrowth. The output characteristics exhibited outstanding temperature insensitivity with a power drop of only 30% for an increase of the mount temperature from 20°C to 80°C. The high temperature stability was achieved by using GaInNAs/GaAs quantum wells (QWs), which exhibit improved carrier confinement compared to standard InGaAs/GaAs QWs. The corresponding characteristic temperatures were T0=110  K and T1=160  K. Moreover, we used a large detuning between the peak wavelength of the material gain at room temperature and the lasing wavelength determined by the DBR. In addition to good temperature characteristics, GaInNAs/GaAs QWs exhibit relatively low lattice strain with direct impact on improving the lifetime of laser diodes at this challenging wavelength range. The single-mode laser emission could be tuned by changing the mount temperature (0.1 nm/°C) or the drive current (0.5 pm/mA). The laser showed no degradation in a room-temperature lifetime test at 900 mA drive current. These compact and efficient 1180 nm laser diodes are instrumental for the development of compact frequency-doubled yellow-orange lasers, which have important applications in medicine and spectroscopy.

High power (60 mW) GaSb-based 1.9 μm superluminescent diode with cavity suppression element

The characteristics and the fabrication of a 1.9 μm superluminescent diode utilizing a cavity suppression element are reported. The strong suppression of reflections allows the device to reach high gain without any sign of lasing modes. The high gain enables strong amplified spontaneous emission and output power up to 60 mW in a single transverse mode. At high gain, the spectrum is centered around 1.9 μm and the full width at half maximum is as large as 60 nm. The power and spectral characteristics pave the way for demonstrating compact and efficient light sources for spectroscopy. In particular, the light source meets requirements for coupling to silicon waveguides and fills a need for leveraging to mid-IR applications photonics integration circuit concepts exploiting hybrid integration to silicon technology.

GaSb superluminescent diodes with broadband emission at 2.55 μm

We report the development of superluminescent diodes (SLDs) emitting mW-level output power in a broad spectrum centered at a wavelength of 2.55 μm. The emitting structure consists of two compressively strained GaInAsSb/GaSb-quantum wells placed within a lattice-matched AlGaAsSb waveguide. An average output power of more than 3 mW and a peak power of 38 mW are demonstrated at room temperature under pulsed operation. A cavity suppression element is used to prevent lasing at high current injection allowing emission in a broad spectrum with a full width at half maximum (FWHM) of 124 nm. The measured far-field of the SLD confirms a good beam quality at different currents. These devices open further development possibilities in the field of spectroscopy, enabling, for example, detection of complex molecules and mixtures of gases that manifest a complex absorption spectrum over a broad spectral range.

High-power 1550 nm tapered DBR laser diodes for LIDAR applications

Pulsed operation characteristics of a high-power 1550 nm tapered distributed Bragg Reflector (DBR) laser diode are described. The development targets applications such as LIDAR and range finding, which require eye-safe, coherent light sources with a high peak-power. In particular, we employ a regrowth-free technique and AlGaInAs/InP gain structure, and demonstrate a peak power of about 1.6 W (drive-current limited) and a CW power of 560 mW at room temperature.

Spectral Characteristics of Narrow-Linewidth High-Power 1180 nm DBR Laser With Surface Gratings

We report narrow-linewidth 1180-nm GaInNAs/GaAs distributed Bragg reflector lasers reaching up to ~500-mW continuous-wave output power at room temperature. The lasers employ surface gratings, which avoided the problematic regrowth and enabled a high side-mode suppression ratio over a relatively large mode-hop-free tuning range. The wavelength tuning rates of 0.1 nm/°C and 1 pm/mA were obtained by changing the mount temperature and the drive current, respectively. The lasers exhibit a narrow emission linewidth (<;250 kHz) even at high output power levels. The side-mode suppression ratio is relatively independent of the power level and remains higher than 50 dB even in the vicinity of the roll-off point. An outstanding temperature stability is provided by good carrier confinement in the GaInNAs/GaAs quantum well. A 2000 h burn-in with constant 1.5 A bias at 20 °C improved the output characteristics slightly and did not reveal any failure among the tested components.

High-power 1550 nm tapered DBR lasers fabricated using soft UV-nano-imprint lithography

Paper reports the DBR-RWG surface grating design, the fabrication process, and the output characteristics of tapered DBR laser diodes for the applications, like for example LIDAR and range finding, that require eye-safe high-power single-mode coherent light sources. The fabricated regrowth-free DBR AlGaInAs/InP lasers exhibited a CW output power as high as 560 mW in single-mode operation at room temperature. At maximum output power the SMSR was 38 dB, proving the excellent behavior of the surface gratings. The tapered section enabled scaling the maximum CW power at room temperature from 125 mW to 560 mW, by increasing its length from 0.5 mm to 4.0 mm. The paper discusses the limitations and performance variation associated to the power scaling by using the tapered section length as a scaling parameter.

Quantum-well laser diodes operating at 1.28um monolithically integrated on Ge substrate (Conference Presentation)

Here we demonstrate for the first time a GaInNAsSb/GaAs quantum well based laser diode with emission beyond 1.25 µm that is monolithically integrated on an artificial Ge substrate. Molecular beam epitaxy grown GaInNAsSb quantum wells enable gain from silicon transparency wavelength up to 1.55µm. Proposed material system paves the way for silicon photonics with high density monolithically integrated temperature insensitive gain elements (and electro-absorption in case of modulators). Compared with QD gain structures monolithically integrated on Ge/Si demonstrated earlier QW-based material system important advantages in single pass gain enabling the realization of devices with very short lengths and volume. Moreover, GaInNAsSb/GaAs QWs can exhibit efficient uncooled operation at temperatures as high as 80°C reducing the energy consumption imposed by active cooling of PICs. Presentation demonstrates low threshold (sub-25mA) directly modulated laser diodes using a short cavity (250µm) enabled by the high gain. Bandwidth characteristics of the material is studied with relative intensity noise (RIN) measurement. Hakki-Paoli measurement show gain up to 68 1/cm from a short gain element of 250µm in length. Preliminary burn-in results show that lasers operate hundreds of hours without any sign of degradation contributed by the close lattice matching between III-V and Ge.

High power GaSb superluminescent diodes with broadband emission around 2.55 µm (Conference Presentation)

Most of the environmental gases like H2S, C2H2, CH4, CO(2), N2O and H2O have strong absorption lines within 2-3 µm wavelength range. Detection of these gases requires a spectrally broad, compact, efficient, cost-effective, and high output power light source. Such choice of parameters can be offered by high brightness and broadband superluminescent diodes (SLD). Here we report the development of GaSb-based high power broadband superluminescent diodes (SLDs) emitting around 2.55 μm. The active region consists of two GaInAsSb/GaSb quantum wells. To enable high gain and high output power we adopted a long ridge waveguide (RWG) geometry, i.e. 2.5 mm. The width (5µm) and etching depth (1800 nm) of waveguide was chosen to operate device in single transverse mode. Lasing inside the cavity was suppressed by tilting the waveguide 8° with respect to cavity facets. Recently developed cavity suppression element [1] was employed to further suppress the spectral modulations and smoothen out the spectrum. For operation at long wavelengths, we employed a pulsed driving scheme with sub-µs pulse injection to address temperature dependent non-radiative Auger recombination. Devices have demonstrated an average output power of more than 3 mW and peak power over 15 mW at room temperature (RT). The maximum full-width at half-maximum (FWHM) of spectrum was ~124 nm, corresponding to 1200 mA drive current. This is the highest power reported to date for 2.55 µm SLDs. For comparison, SLD at 1.90µm emitted a continuous wave (CW) output power up to 60 mW and FWHM of ~ 60 nm [1]. Integration of this high brightness, broadband light sources with SOI-waveguides enables realization of a compact multiple gas sensor in this wavelength range [2]. [1] N. Zia, J. Viheriala, R. Koskinen, A. Aho, S. Suomalainen, and M. Guina, “High power (60 mW) GaSb-based 1.9 μm superluminescent diode with cavity suppression element,” Appl. Phys. Lett., vol. 109, no. 23, p. 231102, 2016. [2] P. Karioja, T. Alajoki et al, “Multi-wavelength mid-IR light source for gas sensing”, Proc. SPIE 10110, 2017.

Low loss GaInNAs/GaAs gain waveguides with U-bend geometry for single-facet coupling in hybrid photonic integration

We report a low loss U-bend waveguide for realization of GaAs-based gain elements employed in hybrid photonic integration. This architecture allows us to position the input and output ports of the gain waveguide on the same facet and thus alleviates the geometrical constrains in hybrid integration, i.e., the need for precise alignment with silicon photonic waveguides on both ends of the III–V chip. As an exemplary demonstration, we report the loss and gain characteristics of GaInNAs/GaAs U-bend waveguides operating at 1.3 μm. In particular, we demonstrate a bending loss as low as 1.1 dB for an 83 μm bending radius. Efficient laser diode operation is also demonstrated.We report a low loss U-bend waveguide for realization of GaAs-based gain elements employed in hybrid photonic integration. This architecture allows us to position the input and output ports of the gain waveguide on the same facet and thus alleviates the geometrical constrains in hybrid integration, i.e., the need for precise alignment with silicon photonic waveguides on both ends of the III–V chip. As an exemplary demonstration, we report the loss and gain characteristics of GaInNAs/GaAs U-bend waveguides operating at 1.3 μm. In particular, we demonstrate a bending loss as low as 1.1 dB for an 83 μm bending radius. Efficient laser diode operation is also demonstrated.

Performance and lifetime of high-power narrow-linewidth 1180 nm GaInNAs DBR-LDs

We report the highest power narrow spectrum 1180 nm distributed Bragg reflector (DBR) laser diodes prepared using GaInNAs quantum wells as a gain material. In particular, we demonstrate a CW output power up to 560 mW from Ridge Waveguide (RWG)-DBR laser diodes and up to 2.75W for Tapered DBR-LDs. The demonstration targets applications in second harmonic generation (SHG) for generating high brightness yellow radiation. RWG-DBR LDs are optimal light sources for waveguide SHG-crystals allowing high efficiency coupling to single mode WG embedded in the SHG-crystal. On the other hand, tapered DBR-LDs provide a power level that suitable for bulk SHG-crystals that can withstand more IR-light and alleviate the need for waveguide alignment. To reach the 1180 nm range we have developed high-quality GaInNAs quantum wells embedded in GaAs waveguide, a material system that has been in the past recognized for poor reliability in laser operation. In our case, preliminary lifetime test for GaInNAs RWG-DBR LDs showed no signs of degradation in a room-temperature operation for over 2000hours under high current driving at 1500 mA drive-current. The DBR section was defined using nanoimprint-lithography as described in [1].