Mohammad Tanvir Haidar

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.

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.

Monolithic integration of VCSELs and PIN photodiodes for bidirectional data communication over standard multimode fibers

We present the monolithic design, fabrication and properties of 850nm wavelength AlGaAs-GaAs-based transceiver chips with a stacked layer structure of a VCSEL and a PIN photodetector. Bidirectional data transmission via a single, two-side butt-coupled multimode fiber (MMF) is thus enabled. The approach aims at a miniaturization of transceiver chips in order to ensure compatibility with standard MMFs with core diameters of 50 and 62.5μm used predominantly in premises networks. These chips are supposed to be well suited for low-cost and compact half- and full-duplex interconnection at Gbit/s data rates over distances of a few hundred meters.

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.

Up to 9Gbit/s data transmission with monolithically integrated VCSELs and PIN photodiodes

With the increasing demand for high-speed optical interconnection in mobile systems like cars and airplanes, vertical-cavity surface-emitting lasers (VCSELs) offer an alternative solution to the well-established red LEDs used in media-oriented systems transport (MOST) networks based on polymer optical fiber [1]. In order to find a compromise between the need for multi-Gbit/s data rates and low system cost, we have previously presented a monolithic integration of VCSELs and metal-semiconductor-metal photodiodes (MSM PDs) for bidirectional data communication over a single butt-coupled multimode fiber (MMF) [2]. Here, for the first time, PIN PDs are used in VCSEL-based 850 nm wavelength range transceiver chips. The devices were miniaturized for use with standard 50 µm core diameter graded-index (GI) MMFs, as shown in Fig. 1 (left). By avoiding resonant signal detection mentioned in a somewhat related approach [3], no temperature control is required neither for MSM nor for PIN PD-based transceiver chips.

7Gbit/s data transmission over 500m multimode fiber with monolithically integrated bidirectional VCSEL-based transceiver chips

We present design, fabrication and operation characteristics of AlGaAs-based transceiver chips with monolithically integrated VCSELs and PIN photodetectors. Up to 7 Gbit/s data transmission over a 500m long standard multimode fiber is demonstrated.

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.

Towards a SFP+ module for WDM applications using an ultra-widely-tunable high-speed MEMS-VCSEL

In this work, we have used a tunable VCSEL for high-speed optical data transmission. To obtain wide tunability, a MEMS-DBR is surface micromachined onto a short-cavity high-speed VCSEL operating at 1550 nm. Ultra-wide continuous tuning is realized with electro-thermal actuation of the MEMS with built-in stress gradient within SiOx/SiNy dielectric layers. The MEMS-VCSEL operates in single-mode with SMSR > 40 dB across the entire tuning range. Quasi-error-free transmission of direct-modulation at record 15 Gbps is reported for 20 nm tuning, showing the potential towards the standard requirements for the SFP+ modules in the tail-ends of the WDM transmission system.

Vortex-MEMS filters for wavelength-selective orbital-angular-momentum beam generation

In this paper an on-chip device capable of wavelength-selective generation of vortex beams is demonstrated. The device is realized by integrating a spiral phase-plate onto a MEMS tunable Fabry-Perot filter. This vortex-MEMS filter, being capable of functioning simultaneously in wavelength and orbital angular momentum (OAM) domains at around 1550 nm, is considered as a compact, robust and cost-effective solution for simultaneous OAM- and WDM optical communications. Experimental spectra for azimuthal orders 1, 2 and 3 show OAM state purity >92% across 30 nm wavelength range. A demonstration of multi-channel transmission is carried out as a proof of concept.