Mohammadreza Malekizandi

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.

WDM–TDM NG-PON Power Budget Extension by Utilizing SOA in the Remote Node

Today, even in access networks, data traffic is enormously increasing, a trend that causes existing passive optical network (PON) infrastructures to become bottlenecks in a tele- and data-communication infrastructure, which is aimed to be both broadband and seamless. Thus, two major objectives are considered for next-generation PONs (NG-PONs), i.e., first, bandwidth increase, and second, reach extension to reduce deployment costs. Here, we describe a new reach extension scheme that at the same time allows increasing the number of subscribers in the network. The amplification technique is based on a bidirectional semiconductor optical amplifier (SOA). It is shown that the extender configuration not only meets the bandwidth and budget requirements for NG-PONs but also remarkably improves them. Differential (quadrature) phase-shift keying (D(Q)PSK) signals are investigated in this paper. Hybrid wavelength-division multiplexing/time-division multiplexing (WDM/TDM) transmission up to 120-Gb/s downstream and 40-Gb/s upstream are experimentally demonstrated. The access budget of 33.4 dB is achieved at 10 Gb/s on every WDM channel in case of DPSK enabling a splitting ratio of 1:512 per wavelength. Furthermore, optical power budget of 40 dB is obtained when DQPSK is used, where a splitting ratio of 1024 per wavelength can be supported. Additionally, a cost-efficient chirped managed directly modulated laser scheme is proposed for DPSK signal generation in U.S. scenario enabling a high-power budget performance low-cost transmitter configuration, which appears suitable for NG-PON application. The proposed technique also alleviates nonlinear impairments [specifically, cross-phase modulation (XPM)], which appear in dense WDM transmission.

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.

Generation of UWB Doublet Pulse Based on Directly Modulated Laser and Chromatic Dispersion

An ultra-wideband (UWB) doublet pulse generation technique in the optical domain for UWB-over-fiber systems is presented. Our solution is based on the direct modulation of a semiconductor laser, optical filtering, and chromatic dispersion in a transmission fiber. When the integration of the transmitter in optical access network infrastructure is considered, the transmission length difference, or the difference in accumulated dispersion, is an issue to exactly obtain the desired pulse shape. To solve this problem, we propose to adjust the transmitter operation point, specifically the laser chirp, with respect to the targeted transmission fiber length. Bit error rate measurements prove that doublet pulses can be achieved with fiber length variation from 15 to 40 km of single-mode fiber.

Radio transmission and BER performance of UWB pulse generation based on directly modulated semiconductor laser

Optical UWB pulse generation and wireless propagation through antenna is investigated. Experimental BER results are presented. It is shown due to antenna characteristics monocycle pulse is converted into 3rd-order Gaussian derivative after wireless propagation.

TDM-PON compatible generation of 10 Gbps NRZ and 1.25 Gbps UWB signals by a single light source

A novel and cost-efficient technique is presented to generate non-return-to-zero (NRZ) and ultra-wideband (UWB) signals in different time slots of time division multiplexing-passive optical network (TDM-PON) by using a single chirped controlled semiconductor laser associated with an optical bandpass filter. In this technique, the chirp of the laser is controlled by different bias burst amplitudes (BBA) for different time slots. Through the proper selection of the burst amplitudes, 10 Gbps NRZ and 1.25 Gbps UWB signals are generated in different time slots. Principle of operation is discussed, the complete chirp behavior of the laser is experimentally investigated, data transmission of the generated signals is demonstrated and bit-error-rate (BER) level of 10-9 is achieved.

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.

MEMS-based wavelength and orbital angular momentum demultiplexer for on-chip applications

We demonstrate a new tunable MEMS-based WDM&OAM Fabry-Pérot filter for simultaneous wavelength (WDM) and Orbital Angular Momentum (OAM) (de)multiplexing. The WDM&OAM filter is suitable for dense on-chip integration and dedicated for the next generation of optical interconnects utilizing all three degrees of freedom of the electromagnetic waves: wavelength, polarization, and OAM. The WDM&OAM filter consists of two Distributed Bragg Reflectors (DBRs), (see Fig. 1a, b): a bottom one fixed to the substrate and a movable top MEMS DBR. An applied tuning current, changing the resonator length, extends the top DBR and hence selects the central filter wavelength. A spiral phase mask on the top switches the OAM order by ±1, ±2, etc. For a detailed description of the structure and fabrication of the device, please refer to [1, 2]. The MEMS filter shows a full-width at half-maximum (FWHM) bandwidth of about 0.2 nm and a free spectral range (FSR) of about 126 nm. The phase mask provides sufficient OAM state purity in a 35 nm window around 1550 nm, covering well the whole C-band.

10-Gbps direct on-off-keying modulation across 85-nm continuous tuning range using telecom MEMS-VCSEL

The expansion of cellular networks over the past decades has gone through an astonishing evolution. Due to centralized network functions, splitting of the generation/processing of RF signal in base band units (BBUs) and the baseband-RF conversion in remote radio heads (RRHs) has become inevitable. To systematically overcome the bandwidth and latency issues, a cost-efficient WDM-PON capable of linking a BBU to a multitude of distributed RRHs is of high demand. Such a system is standardized in the G.metro project (ITU-T SG15), where the distributed 10 Gbps transceivers will automatically adjust their wavelengths which is centrally controlled [1]. The biggest challenge up to now was the lack of low-cost wideband tuneable lasers for high-speed transmission. In this work, we have developed a short-cavity, widely-tuneable, electrically-pumped MEMS-VCSEL for high-speed applications. The device operates at 10 Gbps for a continuous tuning range of 85 nm which, to the best of our knowledge, is the record tuning for any 10-Gbps directly modulated laser.