Gain-saturated Semiconductor Optical Amplifier Research Articles

Non-orthogonal PS-OOK transmission for FSO communications

This paper proposes a non-orthogonal polarization shift on-off keying (NOPS-OOK) transmission for free-space optical (FSO) communication. At the transmitter end, NOPS-OOK signal is modulated with the non-orthogonal polarizations of bits ‘1’ and ‘0’ characteristics employing a single Mach-Zehnder modulator (MZM). At the receiver end, NOPS-OOK signal is detected using the cascaded polarization-insensitive and gain saturated semiconductor optical amplifier (SOA) and sloped-linear polarizer (SLP) with the polarization perpendicular to bit ‘0.’ The proposed technique is verified in experiments. The experimental results showed that the bit-error-rate (BER) performance of the proposed technique was close to the orthogonal polarization shift OOK (OPS-OOK) signal transmission.

Investigation of amplitude and phase evolution of a short-pulse propagating through a gain saturated semiconductor optical amplifier

Investigation of amplitude and phase evolution of a short-pulse propagating through a gain saturated semiconductor optical amplifier

An effective and universal intensity noise suppression technique for single-frequency fiber lasers at 1.5 μm

We report on an effective and universal technique to fulfill intensity noise suppression for single-frequency fiber lasers (SFFLs) at 1.5 μm. Utilizing a gain-saturated semiconductor optical amplifier and the effective filtering of amplified spontaneous emission, the resultant relative intensity noises of three diverse SFFLs are maintained at −155 dB Hz−1; which is only <0.9 dB from the shot noise limit in the frequency range from 100 kHz to 50 MHz. Refering to the three paradigmatic experimental results, this technology, as a promising external solution of noise suppression, can be modularized to promote the application of SFFLs.

Enhancement of SOA-Based Scintillation Mitigation by PS-OOK Transmission in FSO Communication

This paper proposes an enhancement of semiconductor optical amplifier (SOA)-based scintillation mitigation by polarization shift on-off keying (PS-OOK) transmission in free-space optical (FSO) communication. The scintillation effect is a critical issue in a vertical FSO link. The issue of the extinction ratio (ER) degradation of the received OOK signal caused by the high dynamic gain frequency of the SOA limits the performance of the turbulence-induced scintillation effect mitigation using a gain-saturated and polarization-independent SOA. Therefore, a PS-OOK signal, which has the characteristics of orthogonal polarization of bits “1” and “0,” is transmitted at the transmitter end and a linear polarizer is deployed after the gain saturated SOA at the receiver end. Based on the polarization orthogonality of PS-OOK, the performance of the scintillation-effect suppression is significantly improved by the mitigation of the ER degradation by the blocking of the polarization of bit “0” of the received optical PS-OOK signal using the linear polarizer. The proposed scheme is experimentally verified utilizing the Mach-Zehnder modulator (MZM)-based fading simulator accommodated various turbulence channels. The experimental results illustrate that the scintillation effect is effectively suppressed by the proposed technique compared to the SOA-based conventional single-polarized OOK detection and balanced PS-OOK detection.

Low-Noise Repetition-Rate Multiplication by Injection Locking and Gain- Saturated Amplification

Low-noise repetition-rate multiplication of optical pulses is demonstrated through harmonic injection locking of a mode-locked laser and gain-saturated amplification by a semiconductor optical amplifier (SOA). The approach employs strong optical injection for lowering the repetition-rate phase noise, followed by gain-saturated SOA for suppression of pulse intensity irregularities. In this way, we can achieve low phase noise level and high side-mode suppression ratio (SMSR) at the same time. Experimentally, we show repetition-rate multiplication of a 250-MHz commercial mode-locked laser to 1-GHz repetition-rate, with 3% modulation depth, 33-dB SMSR, and 14-fs absolute rms timing jitter (when integrated from 10 kHz to 10 MHz offset frequency).

Performance enhancement of gain saturated SOA based free space optical link using dual-wavelength transmission

This paper proposes the dual-wavelength transmission technique for improving the performance of the gain-saturated semiconductor optical amplifier (SOA)-based free-space optical (FSO) communication link. When the gain saturated SOA is used to suppress turbulence-induced scintillation, extinction ratio (ER) degradation effect occurs owing to the high-dynamic gain frequency characteristics for intensity modulation and direct detection (IM/DD) system. The proposed method uses small-spacing dual-wavelength (signal and supplemental wavelengths) transmission to compensate ER degradation by mitigating the gain difference between the bits ‘1’ and ‘0’. Regarding the supplemental wavelength, continuous wave (CW) with various average powers and differential signal (DS) transmissions are experimentally investigated. The proposed technique is evaluated under various turbulence channel strengths. The experimental results show that the bit-error rate (BER) performance is significantly improved via effective ER degradation compensation and scintillation suppression.

Further Investigation of Intensity Noise Reduction on an Incoherent Light Source using a Gain Saturated Semiconductor Optical Amplifier in a Spectrum-sliced Channel at 2.5 Gb\\s

The “spectrum-slicing” technique, employing incoherent light, has been shown to be a highly practical, cheap and hence very attractive proposal for future all-optical networks. In this study, the use of semiconductor optical amplifier gain saturation for intensity noise reduction on incoherent light is further studied in terms of the Relative-Intensity-Noise (RIN), with a view to obtaining the optimum SOA injection current and input power conditions to achieve the best possible intensity noise reduction, in conjunction with OSNR, BER and Q-factor results. The results reported herein give designers knowledge of the best SOA operating conditions to enhance overall system performance, whilst still obtaining signal gain from the SOA.

Optimum Linewidth of Spectrum-Sliced Incoherent Light Source Using a Gain-Saturated Semiconductor Optical Amplifier

We investigate the optimum linewidth of the spectrum-sliced incoherent light (SSIL) source using a gain-saturated semiconductor optical amplifier (SOA) for the maximum capacity and longest transmission distance. For this purpose, we carry out experimental and simulation studies on the transmission performance of a 10-Gb/s on–off keying signal generated by using the SSIL source over a wide range of the SSIL linewidth. We find out that there are two windows of the linewidth for the high-speed operation of the SSIL source: ultra-narrow (i.e., linewidth $\ll$ receiver bandwidth) and very wide (i.e., linewidth $\gg$ receiver bandwidth). However, when the linewidth of the SSIL source is very wide, the 10-Gb/s signal generated by using this SSIL suffers severely from fiber chromatic dispersion and optical filtering. The simulation results are confirmed by experimental data measured by using an ultranarrow fiber Fabry–Perot filter (bandwidth = 700 MHz) and a bandwidth-tunable optical filter (bandwidth = 20 ∼ 53 GHz). Thus, we can conclude that the optimum linewidth of SSIL for capacity and transmission distance is ultranarrow. We also present a couple of drawbacks of the ultranarrow SSIL source, compared to the conventional wide-linewidth SSIL one, such as a large spectrum-slicing loss, a large SOA input power required for the suppression of excess intensity noise inherent in the incoherent light source, and the susceptibility to in-band crosstalk.

Throughput enhancement of slow adaptive orthogonal frequency division multiple access based passive optical network uplink transmission in 20‐km single fibre loopback link employing channel stabilisation

The authors have proposed and experimentally demonstrated a novel slow adaptive orthogonal frequency division multiple access (OFDMA)-based passive optical network (PON) uplink transmission scheme using a 1-GHz reflective semiconductor optical amplifier operating as an optical network unit (ONU) in combination with Rayleigh backscattering (RB) mitigation in a 20-km single fibre loopback link. This RB mitigation, which can dramatically stabilise the channel state information and enhance the total throughput so that the OFDMA-PON transmitters can operate in the slow adaptive concept and provides beyond 15-Gbit/s uplink transmission, is achieved by employing 10-MHz low-frequency dithering of an optical seed carrier cooperating with a gain-saturated semiconductor optical amplifier at an optical line terminal. In doing so, the proposed scheme could guarantee a 50% total throughput enhancement with a proof-of-concept multiple access scenario for two ONUs, compared to its counterpart that does not apply the RB mitigation technique.

Performance Improvement of Ultranarrow Spectrum Sliced Incoherent Light Using Offset Filtering

We report on the improved bit-error-rate (BER) performance of 12.5-Gb/s ultranarrow spectrum-sliced incoherent light signals by using offset optical filtering. We show that a gain-saturated semiconductor optical amplifier creates a correlation between amplitude and frequency (or chirp) of the incoherent light signals. Offset optical filtering then converts the chirp into amplitude to produce destructive interference with the excess intensity noise inherent in the spectrum-sliced incoherent light signals. The simple offset filtering lowers an error floor by a factor of two near forward-error correction (FEC) threshold, which will greatly improve the corrected BER after FEC decoding.

Optimization of Intensity Noise Reduction from an Incoherent Light Source Using Gain Saturated Semiconductor Optical Amplifier in a Spectrum-sliced Channel at 2.5 Gb\\S

The “spectrum-slicing” technique employing incoherent light has been shown to be a highly practical, cheap and hence very attractive proposal for future all-optical networks. In this study, the use of Semiconductor Optical Amplifier (SOA) gain saturation for intensity noise reduction of incoherent light is studied with a view to obtaining the optimum SOA injection current and input power conditions to achieve the best possible intensity noise reduction-in terms of OSNR, BER, noise power and Q-factor. The results reported herein give designers knowledge of the best SOA operating conditions to enhance overall system performance, while still obtaining signal gain from the SOA.

Generation of 10-GHz duty-cycle tunable square optical pulse in an SOA-based mode-locked fiber laser

We demonstrate the generation of 10-GHz optical square pulses by injecting a picosecond pulse train into an SOA-based mode-locked fiber laser. The novel scheme exploits nonlinear effects and gain saturation phenomenon in the semiconductor optical amplifier (SOA). This technique uses gain-compression dynamics between the input pulses and the generated ones in gain-saturated SOA to form square pulses. The center wavelength of the generated optical square pulse can be tuned from 1530 to 1570 nm by adjusting the center wavelength of the optical band pass filter (OBPF) in the SOA-based mode-locked fiber ring laser. The duty cycle of the output pulse can be tuned from 12.7 to 88.4%, which strongly depends on the input power and intra-cavity power.

Reusing a Data-Erased ASE Carrier in a Weak-Resonant-Cavity Laser Diode for Noise-Suppressed Error-Free Transmission

Under injection-locking with downstream amplified spontaneous emission (ASE) carrier spectrally sliced by a 200-GHz arrayed waveguide grating and amplitude-squeezed by a gain-saturated semiconductor optical amplifier (SOA), the injection-level-dependent extinction ratio (ER) and bit-error-rate (BER) penalty of a weak-resonant-cavity Fabry-Perot laser diode (WRC-FPLD) upstream transmitter are investigated. By fixing the downstream power at -13 dBm, the downstream ASE data is amplitude-squeezed by the gain-saturated SOA to greatly suppress the ER from 12.6 to 2.2 dB, which improves the BER of upstream data carried by the reused ASE in the WRC-FPLD. By reusing the amplitude-squeezed downstream ASE carrier in the upstream WRC-FPLD, such a single ASE-based bidirectional channelized transmission network provides downstream and upstream receiving sensitivities of <;-27.5 and 21.8 dBm, respectively, at a BER of 10-9 after 25 km transmission.

Saturated signal-to-noise ratio of up-stream WRC-FPLD transmitter injection-locked by down-stream data-erased ASE carrier

By controlling the extinction ratio (ER) and overshooting level of the down-stream amplified spontaneous emission (ASE) with a gain-saturation semiconductor optical amplifier (SOA), the down-stream data-erased ASE carrier is re-encoded in an injection-locked weak-resonant-cavity Fabry-Perot laser diode (WRC-FPLD) up-stream transmitter to implement all-ASE based bi-directional WDM-PON system. The effect of ER on the up-stream transmission performance of the down-stream data-erased ASE injection-locked WRC-FPLD is elucidated via the gain-saturation model. It is observed that the communication criterion with a bit-error-rate of <10⁻⁹ at 2.488 Gbit/s can be met only when ER is reduced to <3 dB and overshooting level <-5 dB. The up-stream WRC-FPLD re-encoded ASE data-stream could improve its signal-to-noise ratio (SNR) to 6.4 dB by minimizing the ER and overshooting level of the down-stream data-erased ASE to 2.4 dB and -7.8 dB, respectively, with the gain-saturated SOA. The SNR can also be improved with higher power injecting into the up-stream transmitter until saturation occurs and the optimal window of the ASE injection power is between -7 and -3 dBm.

Characterization and Analysis of Relative Intensity Noise in Broadband Optical Sources for Optical Coherence Tomography

Relative intensity noise (RIN) is one of the most significant factors limiting the sensitivity of an optical coherence tomography (OCT) system. The existing and prevalent theory being used for estimating RIN for various light sources in OCT is questionable, and cannot be applied uniformly for different types of sources. The origin of noise in various sources differs significantly, owing to the different physical nature of photon generation. In this study, we characterize and compare RIN of several OCT light sources including superluminescent diodes (SLDs), an erbium-doped fiber amplifier, multiplexed SLDs, and a continuous-wave laser. We also report a method for reduction of RIN by amplifying the SLD light output by using a gain-saturated semiconductor optical amplifier.

Loss budget in single-fiber loopback access networks with ASE light source considering gain compression effect of GS-SOA

This paper estimates the loss budget of wavelength division multiplexing (WDM) single-fiber loopback access networks that employ a broadband amplified spontaneous emission (ASE) light source at the central office (CO) and an optical modulator with optical amplification function in each optical network unit (ONU). This study considers the backreflection lights from two sources, a broadband ASE light from the CO (Reflection-I) and a modulated signal from the ONU (Reflection-II). A gain-saturated semiconductor optical amplifier (GS-SOA) is placed at the ONU to reduce the excess intensity noise of sliced ASE and the spontaneous-spontaneous beat noise caused by Reflection-II; this technique increases the loss budget of the transmission line and removes an optical pre-amplifier from the optical receiver. Experiments clarify that with the gain compression effect of the GS-SOA the loss budget is 22.7dB.

Rational harmonic mode-locking pulse quality of the dark-optical-comb injected semiconductor optical amplifier fiber ring laser

We study the rational harmonic mode-locking (RHML) order dependent pulse shortening force and dynamic chirp characteristics of a gain-saturated semiconductor optical amplifier fiber laser (SOAFL) under dark-optical-comb injection, and discuss the competition between mode-locking mechanisms in the SOAFL at high-gain and strong optical injection condition at higher RHML orders. The evolutions of spectra, mode-locking and continuous lasing powers by measuring the ratio of DC/pulse amplitude and the pulse shortening force (I(pulse)/P(avg)(2) ) are performed to determine the RHML capability of SOAFL. As the rational harmonic order increases up to 20, the spectral linewidth shrinks from 12 to 3 nm, the ratio of DC/pulse amplitude enlarges from 0.025 to 2.4, and the pulse-shortening force reduces from 0.9 to 0.05. At fundamental and highest RHML condition, we characterize the frequency detuning range to realize the mode-locking quality, and measure the dynamic frequency chirp of the RHML-SOAFL to distinguish the linear and nonlinear chirp after dispersion compensation. With increasing RHML order, the pulsewidth is broadened from 4.2 to 26.4 ps with corresponding chirp reducing from 0.7 to 0.2 GHz and linear/nonlinear chirp ratio changes from 4.3 to 1.3, which interprets the high-order chirp becomes dominates at higher RHML orders.

Cross-Gain Compression in Semiconductor Optical Amplifiers

In this paper, we present a novel scheme that exploits cross-gain modulation (XGM) in semiconductor optical amplifiers (SOAs) without overall pattern effects. This technique uses two signals with reversed-intensity modulation and different wavelength to exploit propagation and gain-compression dynamics in gain-saturated SOAs at almost constant overall input power. The resulting cross-gain-compression mechanism between copropagating waves can lead to all-optical waveform reshaping. By using this technique, we experimentally demonstrate enhanced wavelength conversion by XGM and wavelength-preserving noise compression at 10 Gb/s

Loss budget expansion technique using gain-saturated SOA in WDM single-fiber loopback access networks

This paper reduces the impact of backreflection in WDM single-fiber loopback access networks by using a gain-saturated semiconductor optical amplifier (SOA). The backreflection lights from two sources are taken into consideration, the continuous wave (CW) light at the central office (CO) (Reflection-I) and the modulated signal at the optical network unit (ONU) (Reflection-II). A SOA is placed at the ONU to reduce the intensity noise caused by Reflection-II. To investigate the effect by the proposed technique, an experiment creating multiple reflection points is conducted. The results show that a loss budget of 10 dB without SOA can be increased to 16 dB.

All-optical pulse data generation in a semiconductor optical amplifier gain controlled by a reshaped optical clock injection

Wavelength-maintained all-optical pulse data pattern transformation based on a modified cross-gain-modulation architecture in a strongly gain-depleted semiconductor optical amplifier (SOA) is investigated. Under a backward dark-optical-comb injection with 70% duty-cycle reshaping from the received data clock at 10GHz, the incoming optical data stream is transformed into a pulse data stream with duty cycle, rms timing jitter, and conversion gain of 15%, 4ps, and 3dB, respectively. The high-pass filtering effect of the gain-saturated SOA greatly improves the extinction ratio of data stream by 8dB and reduces its bit error rate to 10−12 at −18dBm.