Hooman A. Davani

Tuneable VCSEL aiming for the application in interconnects and short haul systems

Widely tunable vertical cavity surface emitting lasers (VCSEL) are of high interest for optical communications, gas spectroscopy and fiber-Bragg-grating measurements. In this paper we present tunable VCSEL operating at wavelength around 850 nm and 1550 nm with tuning ranges up to 20 nm and 76 nm respectively. The first versions of VCSEL operating at 1550 nm with 76 nm tuning range and an output power of 1.3mW were not designed for high speed modulation, but for applications where only stable continious tuning is essential (e.g. gas sensing). The next step was the design of non tunable VCSEL showing high speed modulation frequencies of 10 GHz with side mode supression ratios beyond 50 dB. The latest version of these devices show record output powers of 6.7mW at 20 °C and 3mW at 80 °C. The emphasis of our present and future work lies on the combination of both technologies. The tunable VCSEL operating in the 850 nm-region reaches a modulation bandwidth of 5.5GHz with an output power of 0.8mW.

Widely tunable high-speed bulk-micromachined short-wavelength MEMS-VCSEL

We present the first results of a high-speed bulk-micromachined tunable vertical-cavity surface-emitting laser (VCSEL) operating near 850nm using a half-symmetric resonator with a movable curved microelectromechanical system (MEMS) membrane.

Polarization investigation of a tunable high-speed short-wavelength bulk-micromachined MEMS-VCSEL

We report the investigation of the state of polarization (SOP) of a tunable vertical-cavity surface-emitting laser (VCSEL) operating near 850 nm with a mode-hop free single-mode tuning range of about 12 nm and an amplitude modulation bandwidth of about 5 GHz. In addition, the effect of a sub-wavelength grating on the device and its influence on the polarization stability and polarization switching has been investigated. The VCSEL with an integrated sub-wavelength grating shows a stable SOP with a polarization mode suppression ratio (PMSR) more than 35 dB during the tuning.

Surface micromachined MEMS tunable VCSEL at 1550 nm with > 70 nm single mode tuning

We present surface micro-machined tunable vertical-cavity surface-emitting lasers (VCSELs) operating around 1550nm with tuning ranges up to 100nm and side mode suppression ratios beyond 40 dB. The output power reaches 3.5mW at 1555 nm. The electro-thermal and the electro-statical actuation of a micro electro-mechanical system (MEMS) movable distributed Bragg reflector (DBR) membrane increases/decreases the cavity length which shifts the resonant wavelength of the cavity to higher/lower values. The wavelength is modulated with 200 Hz/120 kHz. Both tuning mechanisms can be used simultaneously within the same device. The newly developed surface micro-machining technology uses competitive dielectric materials for the MEMS, deposited with low temperature plasma enhanced chemical vapor deposition (PECVD), which is cost effective and capable for on wafer mass production.

Tuning dynamics of a > 70 nm continuously tunable MEMS-VCSEL with a hybrid curved mirror

Long-wavelength tunable vertical-cavity surface-emitting lasers (VCSEL) are an attractive tool for many applications, as optical fiber communications and spectroscopy. Large and continuous wavelength tuning and tuning speed are two important attributes of MEMS-VCSEL. They are essential for e.g. wavelength modulation spectroscopy techniques in gas sensing. The MEMS-VCSEL combines an InP-based cavity incorporating 7 InGaAlAs quantum wells, a buried tunnel junction (BTJ = 12 µm) [1] and a concave MEMS-DBR which can be electro-thermally actuated for wavelength tuning. An anti-reflection coating is put on top to eliminate the phase coupling limitation and to enable an extension of the tuning range at expense of slightly reduced optical output power [2]. To achieve a further extension of the tuning range, a new MEMS-DBR has been developed. The MEMS-DBR is a hybrid mirror composed of semiconductor (3.5 pairs) AlGaAs/GaAs and dielectric (8 pairs) SiO/SiN layers. The hybrid mirror combines the advantages of both materials. Due to a high refractive index contrast between SiO/SiN, the mirror has a high theoretical reflectivity of 99.8% and a large stop bandwidth of 224 nm defined by a reflectivity larger than 98.0 %. To enable electro-thermal actuation of the MEMS-DBR, the semiconductor layers are doped with silicon which enables a heating current to flow through the suspension beams of the membrane. The length of the air-gap, which is included in the cavity, increases due to the thermal expansion thus the wavelength can be tuned. The concave bending of the membrane is caused by an implemented compressive mechanical stress gradient inside the layers (In-doping). The membrane parameters are as follow: Ø=190 µm, beam width=58 µm, -length=150 µm, radius of curvature R=4.1 mm, air-gap=6.8 µm. More information on the device structure and technology as well as semiconductor and dielectric MEMS-DBRs can be found in [1–3].

1.55 μm high-speed MEMS-tunable VCSEL

We present a micro electro-mechanical system (MEMS) tunable vertical-cavity surface-emitting laser (VCSEL) emitting around 1.55 μm with single-mode output power of >2.5mW and high side-mode suppression-ratio (SMSR) of >50dB over the entire tuning range of >50nm. The small-signal modulation technique (S21) has been used to study intrinsic and parasitic influences on the modulation response of the device. Additionally, the static characteristics as well as electrical and thermal design of the device are discussed with respect to its high-speed modulation behavior. The tunable laser shows 3-dB direct modulation frequencies above 6.4 GHz.

Widely electro thermal tunable bulk-micromachined MEMS-VCSEL operating around 850nm

We present a tunable MEMS-VCSEL operating around 850 nm wavelength with the highest reported continuous tuning range of 37 nm achieved with semiconductor DBRs. The electro thermal tuning speed of the device reaches 700 Hz.

Mechanical properties of a movable micro-mirror membrane for electrostatically tunable optical filters and vertical-cavity surface-emitting lasers

Wavelength-tunable vertical-cavity surface-emitting lasers (VCSEL) with a central wavelenght at 1.55µm can be used e.g. for gas sensing applications. A VCSEL is an ideal laser source because of its inherent longitudinal singlemode behaviour, low power consumption, compactness and high-speed modulation capability.