Sujoy Paul

10-Gb/s Direct Modulation of Widely Tunable 1550-nm MEMS VCSEL

We demonstrate direct modulation of a widely tunable microelectromechanical system (MEMS) vertical-cavity surface-emitting laser (VCSEL). The wavelength tuning is realized with electrothermal actuation of a SiOx/SiNy-based MEMS distributed Bragg reflector (DBR). The DBR is deposited in a low-temperature plasma-enhanced chemical vapor deposition chamber on a InP-based half-VCSEL by means of surface micromachining. More than 60 nm of mode-hop free continuous tuning with a center wavelength of 1554 nm is achieved. A maximum 3-dB small-signal modulation response (S21) bandwidth of 7.05 GHz is reported. Quasi-error-free operation of a back-to-back link is demonstrated at 10 Gb/s for a record 47-nm tuning range, showing the compatibility of the MEMS tunable VCSEL as a cost-effective optical source in access networks and interconnects.

Simultaneous wavelength and orbital angular momentum demultiplexing using tunable MEMS-based Fabry-Perot filter

In this paper, we experimentally demonstrate simultaneous wavelength and orbital angular momentum (OAM) multiplexing/demultiplexing of 10 Gbit/s data streams using a new on-chip micro-component-tunable MEMS-based Fabry-Perot filter integrated with a spiral phase plate. In the experiment, two wavelengths, each of them carrying two channels with zero and nonzero OAMs, form four independent information channels. In case of spacing between wavelength channels of 0.8 nm and intensity modulation, power penalties relative to the transmission of one channel do not exceed 1.45, 0.79 and 0.46 dB at the hard-decision forward-error correction (HD-FEC) bit-error-rate (BER) limit 3.8 × 10-3 when multiplexing a Gaussian beam and OAM beams of azimuthal orders 1, 2 and 3 respectively. In case of phase modulation, power penalties do not exceed 1.77, 0.54 and 0.79 dB respectively. At the 0.4 nm wavelength grid, maximum power penalties at the HD-FEC BER threshold relative to the 0.8 nm wavelength spacing read 0.83, 0.84 and 1.15 dB when multiplexing a Gaussian beam and OAM beams of 1st, 2nd and 3rd orders respectively. The novelty and impact of the proposed filter design is in providing practical, integrable, cheap, and reliable transformation of OAM states simultaneously with the selection of a particular wavelength in wavelength division multiplexing (WDM). The proposed on-chip device can be useful in future high-capacity optical communications with spatial- and wavelength-division multiplexing, especially for short-range communication links and optical interconnects.

Bidirectional Multimode Fiber Interconnection at Gb/s Data Rates With Monolithically Integrated VCSEL–PIN Transceiver Chips

We present the monolithic design, fabrication, and properties of 850-nm wavelength AlGaAs-GaAs-based transceiver chips for low-cost bidirectional optical data transmission over a butt-coupled standard multimode fiber of a few hundred meter length. The chips with a stacked layer structure of a vertical-cavity surface-emitting laser (VCSEL) and a PIN (p-doped-intrinsic-n-doped) photodetector can well handle data rates of 9 Gb/s in back-to-back mode and 7 Gb/s over a 500-m-long 50-μm core diameter fiber.

Far-field, linewidth and thermal characteristics of a high-speed 1550-nm MEMS tunable VCSEL

We report an electrically pumped 1550 nm MEMS tunable VCSEL with a continuous tuning of 101 nm at 22 °C. The top MEMS-DBR with built-in stress gradient within the dielectric layers is deposited in a low-temperature PECVD chamber on an InP-based half-VCSEL, structured by surface-micromachining and electrothermally actuated for continuous wavelength tuning. With 2.6 mA threshold current, the laser shows maximum CW output power of 3.2 mW at 1560 nm. The MEMS-VCSEL operates in single-mode with SMSR > 39 dB across the entire tuning range. At 36 °C, the tuning range reaches up to 107 nm. The divergence angle of the MEMS-VCSEL is approximately 5.6° for all tuning wavelengths. The intrinsic linewidth of an unpackaged device is 21 MHz. Quasi-error-free operation at 12.5 Gbps using a directly modulated MEMS-VCSEL is reported for a record 60 nm tuning, showing the potential of the so-called colorless source in WDM applications.

Temperature characteristics of surface micromachined MEMS-VCSEL with large tuning range

Several Applications for tunable laser diodes have strict constraints in terms of overall power consumption. Furthermore, the implementation in harsh environments with large temperature fluctuations is necessary. Due to the constraint in power consumption, the application of active cooling might not be an option. For this reason we investigate the temperature characteristics of an electrically pumped MEMS-VCSEL with wide continuous wavelength tuning. For the first time, a mode hop free single mode (side mode suppression ratio (SMSR) > 40dB) tuning range of 45nm at 70°C is demonstrated with a MEMS-VCSEL. An increase of the tuning range from 85nm at 20°C to 92nm at 40°C is measured and explained. In contrast to fixed wavelength VCSEL, the investigated device shows a negative temperature induced wavelength shift of -4.5nmK(-1), which is caused by the MEMS-mirror. At 1560nm, the fibre-coupled optical output power is above 0.6mW over the entire temperature range between 20°C to 70°C and shows a maximum of > 3mW at 20°C.

Single-Fiber Bidirectional Optical Data Links with Monolithic Transceiver Chips

We report the monolithic integration, fabrication, and electrooptical properties of AlGaAs-GaAs-based transceiver (TRx) chips for 850 nm wavelength optical links with data rates of multiple Gbit/s. Using a single butt-coupled multimode fiber (MMF), low-cost bidirectional communication in half- and even full-duplex mode is demonstrated. Two design concepts are presented, based on a vertical-cavity surface-emitting laser (VCSEL) and a monolithically integrated p-doped-intrinsic-n-doped (PIN) or metal-semiconductor-metal (MSM) photodetector. Whereas the VCSEL-PIN photodiode (PD) chips are used for high-speed bidirectional data transmission over 62.5 and 50 μm core diameter MMFs, MSM TRx chips are employed for 100 or 200 μm large-area fibers. Such a monolithic transceiver design based on a well-established material system and avoiding the use of external fiber coupling optics is well suited for inexpensive and compact optical interconnects over distances of a few hundred meters. Standard MMF networks can thus be upgraded using high-speed VCSEL-PIN transceiver chips which are capable to handle data rates of up to 10 Gbit/s.

Far-field emission characteristics and linewidth measurements of surface micro-machined MEMS tunable VCSELs

In this paper, we demonstrate for the first time the far-field experimental results and the linewidth characteris- tics for widely tunable surface-micromachined micro-electro-mechanical system (MEMS) vertical-cavity surface- emitting lasers (VCSELs) operating at 1550 nm. The fundamental Gaussian mode emission is confirmed by optimizing the radius of curvature of top distributed Bragg reflector (DBR) membrane and by choosing an ap- propriate diameter of circular buried tunnel junctions (BTJs) so that only the fundamental Gaussian mode can sustain. For these VCSELs, a mode-hop free continuous tuning over 100 nm has already been demonstrated, which is achieved by electro-thermal tuning of the MEMS mirror. The fiber-coupled optical power of 2mW over the entire tuning range has been reported. The singlemode laser emission has more than 40 dB of side-mode suppression ratio (SMSR). The smallest linewidth achieved with these of MEMS tunable VCSELs is 98MHz which is one order of magnitude higher than that of fixed-wavelength VCSELs.

Ultra wide mode-hop free tuning around 1550-NM telecom wavelength using high-speed MEMS-VCSELS

We report ultra-wide tuning of a 1550 nm BCB based high-speed MEMS-VCSEL. The MEMS is electrothermally actuated for a continuous tuning of 101 nm. Maximum output power and minimum threshold current is 3.2 mW and 2.6 mA, respectively.

High speed surface micromachined MEMS tunable VCSEL for telecom wavelengths

We report direct modulation of a widely tunable surface micromachined MEMS VCSEL. The MEMS is electro-thermally actuated for tuning the emission wavelength over 60 nm with a center wavelength of 1554 nm. Error-free transmission is achieved at 10 Gbit/s for 47 nm tuning range.

Tunable MEMS-VCSEL with >140-nm tuning range using tuning range using SiO2/SiC-based MEMS-DBR

With the use of SiO2/SiC based movable MEMS-DBR, the continuous tuning range of electrically pumped MEMS-VCSEL can be extended to > 140 nm. The high refractive index contrast of Δn > 1 between SiO2 and SiC reduces the needed number of layers (11 layers) and broadens the spectral width of the reflectivity (448nm for R > 99.5 %) by more than a factor of two compared to the material system SiO2/Si3N4 (23 layers / 216nm for R > 99.5 %), which has been used for the current world record continuous tuning range of 100nm of an electrically pumped MEMS-VCSEL. The smaller number of needed DBR-layers enables a significant reduction of the overall mirror thickness, which enables a further miniaturization of the device and thus an increase of the free spectral range (FSR), the ultimate limit for continuous wavelength tuning. In this paper we evaluate the performance advantages of using SiO2/SiC based MEMS-DBR for tunable VCSEL by using Transfer-matrix method simulations.