Gain-saturated Reflective Semiconductor Optical Amplifier Research Articles

Mitigation of scintillation in FSO communication using a temporally and spatially incoherent spectrum-sliced light source.

We propose and demonstrate a temporally and spatially incoherent spectrum-sliced light source for scintillation mitigation in free-space optical (FSO) communications. For the temporal incoherence, we utilize the spectrum-sliced incoherent light (SSIL) modulated by gain-saturated reflective semiconductor optical amplifiers for data modulation and the suppression of excess intensity noise inherent in a narrowband incoherent light source. We then employ offset launching from a single-mode fiber to a multi-mode fiber to add the spatial incoherence to the SSIL source. The experimental demonstration shows that this temporally and spatially incoherent light is effective in mitigating scintillation. For example, this light source reduces the transmitter power required to achieve a bit-error ratio of 10-3 by ∼6 dB in comparison with the laser source. This is an ∼3 dB larger reduction in the transmitter power than the reduction achieved by a temporally incoherent light source.

Mitigation of Scintillation in FSOC Using RSOA-Based Spectrum-Sliced Incoherent Light

We propose and experimentally demonstrate the mitigation of adverse effects of scintillation using a spectrum-sliced incoherent light source based on gain-saturated reflective semiconductor optical amplifiers (RSOAs). This incoherent light source, originally developed for the cost-effective realization of wavelength-division-multiplexed passive optical networks, employs RSOAs for both data modulation and the suppression of large excess intensity noise inherent in incoherent light sources. We show through experiment that this incoherent light source is effective in suppressing the power fluctuations induced by scintillation when compared to a coherent light source, and thus improves the receiver sensitivity of free-space optical communication systems under weak atmospheric turbulence.

Colorless WRC-FPLDs Subject to Gain-Saturated RSOA Feedback for WDM-PONs

A directly modulated, colorless, weak-resonant-cavity Fabry–Perot laser diode (WRC-FPLD)-based transmitter is, for the first time, proposed and experimentally demonstrated for wavelength-division multiplexed passive optical networks (WDM-PONs). The transmitter utilizes optical gain-saturated reflective semiconductor optical amplifier (RSOA)-induced feedback and is free from external optical injection. Experimental investigations are undertaken of the impact of RSOA-feedback dynamic mechanisms on directly modulated output optical signals and corresponding colorless transmission performances for various system architectures. It is shown that the coherent-like optical source produced by the proposed transmitter architecture offers an output wavelength tunable range as large as 65 nm with side-mode suppression ratios (SMSRs) of >37 dB. In simple 25-km single-mode fiber intensity modulation and direct detection WDM-PON systems, the colorless transmission of directly modulated 7.5-Gb/s optical orthogonal frequency-division multiplexed signals is experimentally achieved over a wavelength tunable range of 35 nm, during which $2.3\times 10^{-3}$ are also experimentally obtainable.

Colorless Long-Reach Duplex WDM-PON With Rayleigh Backscattering Noise Mitigation Using Orthogonal Codes

We propose and experimentally demonstrate a novel colorless full-duplex passive optical network (PON) access architecture. Utilizing orthogonal codes and correlation receiving methods, the novel PON can mitigate the optical beat interference (OBI) noise induced by Rayleigh backscattering (RB). A pair of electrical orthogonal codes is generated and modulated at the same wavelength in the optical line terminal (OLT). Then, modulated optical signals are transmitted from the OLT to the optical network units (ONUs). One of the codes is for downstream signal coding, and the other is used as the upstream seed. In the ONU, the upstream signal is remodulated without erasing the downstream signal. Neither extra centralized continuous wave (CW) light sources nor gain-saturated reflective semiconductor optical amplifier is required. By using these orthogonal codes, the spectral overlap between upstream signal and downstream signal in the full-duplex system is reduced, which can mitigate the OBI noise significantly. The performance of transmission and power margin is investigated through the experiments with different transmission distances. The remodulated upstream signals are recovered by correlation algorithm in the OLT. By correlation algorithm, we can get coding gain, which is important in long-reach transmissions. Because of coding gain and the OBI noise mitigation, a link power margin of 4-10 dB can be achieved for 5 Gb/s downstream and 1.25 Gb/s upstream, when the transmission distance is from 20 to 70 km.

Centrally controlled self-healing wavelength division multiplexing passive optical network based on optical carrier suppression technique

We proposed and demonstrated a centrally controlled and self-healing wavelength division multiplexing passive optical network with colorless optical network units (ONUs) based on optical carrier suppression technique. By switching the affected data in the OCS signal sideband to an alternate protection path, only one optical switch is provisioned at the optical line terminal, which is controlled by a logic control circuit upon monitoring of power outage on the working path. The proposed scheme can reliably protect against both distribution and feeder fiber failures. Moreover, gain-saturated reflective semiconductor optical amplifiers are used as colorless transmitters in ONUs. The protection scheme feasibility and system performances are experimentally verified with 10 Gb/s downstream and 1.25 Gb/s upstream data in both working and protection modes. The protection switching time was measured to be around 1 ms.

25-GHz-Spaced DWDM-PON With Mitigated Rayleigh Backscattering and Back-Reflection Effects

A novel 25-GHz-spaced dense wavelength-division multiplexing passive optical network (DWDM-PON) is proposed to improve the utilization of wavelength resource and mitigate the Rayleigh backscattering (RB) and back-reflection effects. A colorless optical network unit (ONU) is realized by remodulating the downstream (DS) signal via a gain-saturated reflective semiconductor optical amplifier (RSOA). Due to the simple interconnecting architecture at the remote node (RN), the DS and upstream (US) signals in each feed fiber (FF) are carried on different channels. Therefore, the RB and back-reflection effects are significantly reduced. The feasibility and merits of the proposed system are experimentally demonstrated with the error-free transmission of 10-Gb/s DS and 1.25-Gb/s US signals over a 25-km single-mode fiber.

Mutually Injection-Locked Tunable Laser Based on GS-RSOAs for L-Band Generation

We propose a mutually injection-locked tunable (MILT) laser for L-band generation based on arrayed waveguide grating and gain-saturated reflective semiconductor optical amplifiers. The laser generates a 3-dB bandwidth less than 0.05 nm and a high and uniform sidemode suppression ratio (SMSR >;52 dB, ΔSMSR >;3 dB) over 40 L-band wavelengths. Using an MILT laser greatly reduced the phase noise, which is measured to be -107.83 dBc/Hz at a frequency of 10-kHz offset from the center. Furthermore, the 1.25-Gb/s directly modulated transmission performance of the MILT laser shows that there is a power penalty of ~ 0.2 dB over a 20-km single mode fiber.

Ultranarrow Spectrum-Sliced Incoherent Light Source for 10-Gb/s WDM PON

We report on the use of an ultranarrow ( ~0.01 nm) spectrum-sliced incoherent light source for transmission of 10-Gb/s nonreturn-to-zero signals over 20-km dispersion-uncompensated standard single-mode fiber and 0.2-nm-bandwidth optical band-pass filter. A wideband amplified spontaneous emission is first generated using an erbium-doped fiber amplifier and then spectrum-sliced by an ultranarrow fiber Fabry-Perot filter (3-dB bandwidth: ~0.006 nm). The spectrum-sliced light is intensity-smoothed by using a gain-saturated reflective semiconductor optical amplifier and then modulated at 10.7 or 12.5 Gb/s, assuming forward error correction (FEC) with 7% or 25% overheads, respectively. Thanks to the narrow linewidth of the source, we are able to retain the intensity smoothing after the transmission, achieving uncorrected bit-error ratios better than 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> and 3 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> at 10.7 and 12.5 Gb/s, respectively. We discuss the applicability of the proposed light source to wavelength-division-multiplexed passive optical networks and the choice of FEC codes for the proposed scheme.

Cost-effective centralized automatic protection switching scheme for reliable wavelength division multiplexing passive optical network

A simple, cost-effective, centrally controlled, self-protection, colorless wavelength division multiplexing passive optical network is proposed. By using an optical switch at the optical line terminal and an N×N arrayed waveguide grating at a remote node, it can provide 1∶1 protection for downstream traffic and 1+1 protection for upstream data, respectively. The scheme feasibility is verified with 1.25 Gb/s for upstream and 2.5 Gb/s for downstream data rates based on gain-saturated reflective semiconductor optical amplifier, in both normal working and protection modes. The network performance in terms of complexity and availability is also evaluated.

A new cross-protection dual-WDM-PON architecture with carrier-reuse colorless ONUs

This paper proposes a new cross-protection colorless dual-WDM-PON architecture. The proposed protection scheme can provide 1+1 downstream protection and 1:1 upstream protection against both feeder fiber and distribution fiber failures by using the fiber links and AWGs of the neighboring WDM-PON. Wavelength is reused for the down- and up-stream transmissions in dual-WDM-PONs where gain-saturated reflective semi-conductor optical amplifiers (RSOAs) are employed as colorless transmitters in ONUs. The number of extra protection fibers is minimized and wavelength is much more efficiently utilized compared with other protection schemes. The feasibility and operation of the proposed dual-WDM-PON architecture are experimentally verified with 1.25Gb/s for upstream and 2.5Gb/s for downstream over 20km single mode fiber transmission in both working and protection modes.

Switchable wavelength generation by injection-locked fiber laser based on GS-RSOAs

This paper proposes a switchable wavelength fiber laser (SWFL) based on an arrayed waveguide grating (AWG) and a gain-saturated reflective semiconductor optical amplifier (RSOA). The SWFL was experimentally implemented in the C- and L-bands. In order to achieve narrow-linewidth oscillation, the SWFL was driven by bidirectional injection-locked RSOAs. The RSOA was operated in the gain-saturated region, using gain compression properties to obtain uniform power over a wide bandwidth. Based on this configuration, we obtained 40 C-band international telecommunication unit (ITU) wavelengths with 100-GHz channel spacing. The SWFL displayed a narrow 3-dB bandwidth (<0.06 nm), a high and uniform peak power (P max > 0.22 dB, ΔP max < 0.26 dB), and a high and uniform side mode suppression ratio (SMSR > 66 dB, ΔSMSR < 1 dB). The peak-power and wavelength stabilities were ±0.24 dB and ±0.01 nm, respectively, at room temperature over a 1 h period.

Linearization and dispersion tolerable technique for remote access unit in uplink RoF system based on gain-saturated RSOA cascaded EAM

A novel scheme of a remote access unit which is based on an electroabsorption modulator cascaded by a gain-saturated reflective semiconductor optical amplifier is proposed to improve a transmission performance of uplink signal. The cascaded gain-saturated reflective semiconductor optical amplifier plays a role in enhancing linearity of the electroabsorption modulator as well as suppressing dispersion-induced carrier suppression in the uplink transmission using its nonlinear gain property. In the proposed scheme, carrier-to-interference ratio of transmitted 10-GHz band uplink signal was improved by 10.7 dB and the dispersion-induced carrier suppression of 5.65-GHz RF carrier was greatly mitigated by 33.4 dB through the 75.6-km optical link.

Gigabit radio-over-fiber link for converged baseband and millimeter-wave band signal transmission using cascaded injection-locked Fabry-Pérot laser diodes

A novel scheme, for both baseband and millimeter-wave band gigabit data transmission in radio-over-fiber system, is proposed and experimentally demonstrated by using cascaded injection-locked Fabry- Pérot laser diodes. It was able to improve suppression ratio of carrier suppressed signal using the cascaded injection-locking. The suppression ratio improvement of the optical carrier suppressed signal of 20 dB was verified. Applying this mechanism, 60-GHz millimeter-wave carrier of enhanced signal quality could be accomplished. Its peak power and phase noise were obtained as -40 dBm and -103.5 dBm/Hz respectively, which was suitable for 60-GHz data transmission. In addition, a successful bidirectional transmission of 1.25-Gbps wired and wireless data was achieved by adopting remodulation technique using a gain-saturated reflective semiconductor optical amplifier for uplink.

Enhanced Shared-TDD Based Hybrid WDM/TDM-PON with Dynamic Bandwidth Allocation Scheme

Although wavelength division multiplexing-passive optical network (WDM-PON) is known as a high-speed transfer, it creates high channel costs per subscriber and low bandwidth utilization due to the fact that a wavelength is dedicated to each subscriber. Thus, it is imperative to reduce channel costs per subscriber and improve the bandwidth utilization. To achieve these, we first adopt a existing WDM-PON, which uses the bidirectional transmission with a single source for cost-efficiency by employing a gain-saturated reflective semiconductor optical amplifier (RSOA). Secondly, based on the existing WDM-PON, we propose an enhanced hybrid WDM/TDM-PON, which can extend the number of subscribers supported in each wavelength with splitters in the physical layer and a shared-time division duplex (TDD) frame format in the media access control (MAC) layer. Moreover, it can adaptively control the bandwidth through a dynamic bandwidth allocation (DBA) scheme according to the volume of traffic. Compared to the non TDD-based hybrid WDM/TDM-PON, it can reduce channel costs per subscriber from the extended number of subscribers supported in each wavelength. Furthermore, due to the DBA, it can improve the total queueing delay and throughput, and thus increase the bandwidth utilization.

Frequency detuning effects in a loop-back WDM-PON employing gain-saturated RSOAs

We report that, in a loop-back wavelength-division-multiplexed passive optical network link with gain-saturated reflective semiconductor optical amplifiers, the upstream performance is strongly affected not only by the gain saturation but also by the selective spectral filtering caused by the frequency difference between the optical downstream signal and the cascaded filter's passband. We experimentally investigate these effects and propose to use an additional negatively detuned optical filter at an optical network terminal to improve the upstream transmission performance.

Bidirectional WDM-PON based on gain-saturated reflective semiconductor optical amplifiers

We propose a bidirectional wavelength-division-multiplexed passive optical network by employing gain-saturated reflective semiconductor optical amplifiers (RSOAs) for wavelength-independent optical network terminals. The fabricated RSOA module has the input saturation power less than -13 dBm and its saturated gain higher than 13 dB within the C-band for arbitrary polarization states. The upstream signals are generated by remodulating the downstream signals whose modulation amplitude is squeezed through gain-saturated RSOAs. We present experimental results on bidirectional transmission with 1.25 Gb/s for upstream and 2.5 Gb/s for downstream data rates over 20-km transmission distance.