M. A. Ummy

Tunable multi-wavelength SOA based linear cavity dual-output port fiber laser using Lyot-Sagnac loop mirror

We propose and demonstrate a simple dual port tunable from the C- to the L-band multi-wavelength fiber laser based on a SOA designed for C-band operation and fiber loop mirrors. The laser incorporates a polarization maintaining fiber in one of the fiber loop mirrors and delivers multi-wavelength operation at 9 laser lines with a wavelength separation of ~2.8 nm at room temperature. We show that the number of lasing wavelengths increases with the increase of the bias current of the SOA. Wavelength tunability from the C to L-band is achieved by exploiting the gain compression of a SOA. Stable multi-wavelength operation is achieved at room temperature without temperature compensation techniques, with measured power and the wavelength stability within < ±0.5 dB and 
±0.1 nm, respectively.

Dual Sagnac loop mirror SOA-based widely tunable dual-output port fiber laser

A widely tunable (30 nm) fiber laser based on a double Sagnac loop mirror configuration is proposed and demonstrated. A semiconductor optical amplifier (SOA) placed between the two loop mirrors acts as the gain medium. The fiber laser has two output ports with adjustable optical power outputs. Wavelength tunability is obtained through the use of a thin film tunable filter, while optical power adjustability is accomplished by proper adjustment of each of the loop mirror reflectivity via a polarization controller. A total output power of + 9 dBm is measured and the potential for higher output powers is discussed. Optical power stability of better than +/- 0.15 dB is measured for 6 hours.

Switchable dual-wavelength SOA-based fiber laser with continuous tunability over the C-band at room-temperature

We propose and demonstrate a simple compact, inexpensive, SOA-based, dual-wavelength tunable fiber laser, that can potentially be used for photoconductive mixing and generation of waves in the microwave and THz regions. A C-band semiconductor optical amplifier (SOA) is placed inside a linear cavity with two Sagnac loop mirrors at its either ends, which act as both reflectors and output ports. The selectivity of dual wavelengths and the tunability of the wavelength difference (Δλ) between them is accomplished by placing a narrow bandwidth (e.g., 0.3 nm) tunable thin film-based filter and a fiber Bragg grating (with bandwidth 0.28 nm) inside the loop mirror that operates as the output port. A total output power of + 6.9 dBm for the two wavelengths is measured and the potential for higher output powers is discussed. Optical power and wavelength stability are measured at 0.33 dB and 0.014 nm, respectively.

A bow-tie photoconductive antenna using a low-temperature-grown GaAs thin-film on a silicon substrate for terahertz wave generation and detection

This paper presents heterogeneously integrated bow-tie emitter–detector photoconductive antennas (PCAs) based on low-temperature grown-gallium arsenide (LTG-GaAs) thin-film devices on silicon-dioxide/silicon (SiO2/Si) host substrates for integrated terahertz (THz) systems. The LTG-GaAs thin-film devices are fabricated with standard photolithography and thermal evaporation of metal-contact layers of chromium (Cr), nickel (Ni) and gold (Au). They are etched selectively and separated from their growth GaAs substrate. The LTG-GaAs thin-film devices are then heterogeneously integrated on bow-tie antenna electrodes patterned on the surface of a SiO2/Si host substrate for THz emitters and THz detectors. Cost-effective and selective integration of LTG-GaAs thin-film devices on a Si platform is demonstrated. THz radiation from the fabricated THz PCAs is successfully measured using a pump–probe THz time-domain configuration. The THz temporal duration was measured at full width half maximum of 0.36 ps. Its frequency spectrum exhibits a broadband response with a peak resonant frequency of about 0.31 THz. The demonstration illustrates the feasibility of creating heterogeneously integrated THz systems using separately optimized LTG-GaAs devices and Si based electronics.

Engineering an Extended Gain Bandwidth Hybrid Raman—Optical Parametric Amplifier for Next Generation CWDM PON

We describe a model and present simulation results for the optimization of an extended amplification bandwidth hybrid Raman-Optical Parametric amplifier (HROPA) in Tandem configuration. In this configuration, the Raman and Parametric processes are separated and each one takes place in a separate span of fiber, allowing for optimization of amplification gain (e.g., > 20 dB), gain bandwidth (e.g., 170 nm) and gain ripple (e.g., <; 4 dB). We also focus on the potential signal degradation performance due to the generation of idlers within the operational bandwidth. To overcome this limitation, we propose and model a modified HROPA design, which allows for the management and the suppression of idlers in the amplifier. The idler suppression is achieved through partitioning the channels in two sub-bands and using a wavelength-division multiplexed DEMUM/MUX pair to limit/suppress the idlers, as well as crosstalk terms generated in the amplifier. Our study shows that with proper selection of pump wavelength and power and engineering the HROPA with correct filter transfer function, we can achieve error free performance even in the case when significant misalignment of the transmitter wavelength from the center of the coarse WDM channel band exists.

Optimization of gain bandwidth and gain ripple of a hybrid Raman/parametric amplifier for access network applications.

We describe the mathematical model and present simulation results for the optimization of a hybrid Raman/optical parametric amplifier (HROPA), exhibiting a bandwidth of 170 nm and low ripple that covers the top half of the wavelength plan (e.g., 1441 to 1611 nm) of next generation coarse wavelength division multiplexed passive optical network systems. We show that a critical parameter in the proper amplifier parameter optimization is the inclusion of the fourth-order dispersion coefficient (β(4)). Omission of β(4) can lead to over-estimation or underestimation of the gain bandwidth, and hence its inclusion in the analysis of the HROPA is necessary.

PON ring architectures for truly shared LAN capability and dynamic bandwidth allocation for fiber wireless (FiWi) applications

Due to reduced operational and equipment costs, time division multiplexed (TDM)-based passive Optical Network (PON) access solutions including Gigabit PON (GPON) and Ethernet PON (EPON) have been widely accepted as a viable technology for the implementation of fiber-to-the-x (FTTx) solutions, and are being deployed globally. Users are increasingly requiring more bandwidth for high end applications and at the same time greater mobility. The convergence of fiber and wireless systems is seen as the optimum solution to offer the combination of the fiber capacity and the wireless mobility. PON has been proposed as a backhaul for wireless. Typical architectures are traditionally deployed as tree topologies. However, tree-based topologies have several inherent drawbacks such as inability to support a truly shared Local Area Network (LAN) capability among end users. In this paper, we propose scalable ring-based architectures that offer truly shared LAN capability as well as dynamic bandwidth allocation. These architectures are ring-based as well as hybrid, combination of tree-based and ring-based. These flexible architectures can be used as the back-haul to wireless by incorporating the base stations in the ONU locations. Our proposed hybrid PON ring architecture is scalable to 78 ONUs without the use of any amplifiers and in addition, the basic ring architecture and in turn the hybrid one is transparent to protocols and data rates and hence allows for greater BW flexibility as well as greater number of serviced end-users.

Beam Combining of SOA-Based Bidirectional Tunable Fiber Nested Ring Lasers With Continuous Tunability Over the C-band at Room Temperature

Nested ring cavities are used to develop a simple compact, low-cost semiconductor optical amplifier (SOA)-based bidirectional tunable fiber ring laser source. We propose a bidirectional tunable fiber ring laser structure based on (N > 1) number of SOAs that has a great potential for achieving a high power laser source that uses low-power optical components by coherently coupling the nested ring cavities. A commercial tunable filter is used to deliver a wavelength tuning range of 30 nm. The lasing tunable range can be further changed by using SOAs with operating wavelengths in different regions of the optical spectrum. The output power of the bidirectional fiber ring resonator with three SOAs was around 3.5 times larger than the output of a single SOA fiber ring laser (i.e., 17.7 versus 5.14 mW) at 1550 nm wavelength. The optical signal-to-noise ratio was measured to be up to +49 dB, wavelength stability was ±0.015 nm, and optical power stability was better than ±0.2 dB.

Tunable multi-wavelength SOA based linear cavity fiber laser source for optical communications applications

We propose and demonstrate a simple compact, inexpensive, SOA-based, multi-wavelength tunable (C- to L-band) fiber laser. A C-band design SOA is used, yet multi-wavelength operation either at the C or L-band region is accomplished by exploiting the gain compression phenomena of the SOA. We demonstrate that the wavelength tunability can be achieved either by inserting a variable attenuator inside the cavity of the laser or by changing the reflectivity of the mirrors. We exploit two different kinds of loop mirrors, a Sagnac and a Lyot-Sagnac loop mirror, which perform multiple functions. Stable multi-wavelength operation is achieved at room temperature without temperature compensation techniques, with measured power and the wavelength stability within &#60; ±0.5 dB and ±0.1 nm, respectively.

Dual-output port widely tunable fiber laser based on a SOA dual sagnac loop mirror configuration

Widely tunable (30 nm) fiber laser based on a dual Sagnac loop mirror configuration is demonstrated. Dual output port operation is accomplished by proper adjustment of the loop mirror reflectivity allowing for +9 dBm output power.