Quantum-dot Semiconductor Optical Amplifier Research Articles

Desıgn of quantum-dot semiconductor optical amplifiers wıth near-zero linewidth enhancement factor

The linewidth enhancement factor (LWEF) of a semiconductor optical amplifier (SOA) quantifies refractive index fluctuations in the gain medium, which induce phase distortion in the amplified optical signal. Optoelectronic systems employing SOAs with high LWEFs often exhibit poor device stability and beam coherence. Thus, designing SOAs with low LWEF is imperative. Recently, Quantum-Dot (QD) SOAs have emerged as a solution for LWEF suppression due to quantum-confinement effects enabling tunability of the QD carrier density and emission frequency. In this study, we aim to design a composite active region comprised of a host medium and the embodied QDs, to explore the corresponding LWEF variation and propose the ultimate design strategy to achieve near-zero LWEF in QD SOAs for enhancing device stability and beam coherence. Our approach entails modeling the refractive index of the composite active region using effective medium approximation via Maxwell–Garnett mixing formulation. We then extensively tune key SOA parameters, including QD carrier density, QD emission frequency, and the collision-time constant of the carriers to uncover the optimal configuration for minimizing the LWEF. Based on empirical values, we have developed and validated a simple yet effective algorithm that precisely simulates LWEF behavior in response to changes in key QD SOA parameters. This approach offers a straightforward model for estimating LWEF variation, and its corresponding minimization in QD SOAs without requiring complex experimental measurement techniques.

Binary Adder, Subtractor and Parity Checker Based on Optical Logic Gates

We propose schemes for binary adder, subtractor and parity checker using optical logic gates. These schemes could be useful for calculations using optical systems. Utilizing optical logic gates, we can achieve functions of binary adder, subtractor and parity checker of high-speed optical signals. Due to two-photon absorption in the wetting layer, quantum dot-semiconductor optical amplifier Mach-Zehnder interferometer (QD-SOA-MZI) can work as high data rate optical logic gates. The simulated result supports the idea that it is possible to realize all-optical binary adder, subtractor and parity checker at high optical signal rates.

A novel bidirectionally operated chirped quantum-dot based semiconductor optical amplifier using a dual ground state spectrum

Bi-directionally operated amplifiers enabling efficient utilization of transmission wavelengths are promising candidates in densely integrated photonic circuits for future cost-effective, power-efficient optical networks. Here, we demonstrate, for the first time, a broadband semiconductor optical amplifier (SOA) based on a novel chirped multilayered quantum dot (QD) structure, which is suitable for bi-directional amplification via the dual ground state (GS) emission spectrum. The fabricated QD SOA has achieved a maximum 3-dB gain bandwidth of 50 nm while retaining on-chip gain above 20 dB at both GS wavelengths. Under an optimum pumping current of 280 mA, the bi-directionally operated QD SOA has shown around 10 dB receiver sensitivity improvement in ultra-high-speed 100 Gbaud non-return-to-zero and 53.125 Gbaud four-level pulse amplitude modulation data transmission systems.

The effect of doping on the electrons and holes in quantum dot semiconductor optical amplifiers

Abstract The doping effect on the reservoir carrier temperature of the electron and hole in quantum dot optical amplifiers (QD SOAs) has been formalized and modeling, taking into account the most of carrier heating (CH) contributions such as; free carrier absorption, carrier heating time relaxation, interdot relaxation time, occupation probability of dot level, injected current and electron-hole interaction. The theoretical simulation shows the carrier temperature increasing straight forward with increasing the surface density of the donor and accepter which had not studied earlier as the best of our knowledge. It clears that, the surface carrier concentration of donor or acceptor atoms supplying more hot carriers for wetting layer (WL) which is leading an increasing the carrier temperature. In other word, the long life time of carriers from WL to Quantum Dot (QD) states is very high. Consequently, the collision of carriers and nonradiative relaxation are increasing the CH effect. Also, the majority of carrier is responsible on the increasing of electron or hole temperature, so the variation electron temperature in N-type is higher than hole in valence band, while the reverse is done with doping with P-type.

Cross gain modulation in quantum dot semiconductor optical amplifiers under the influence of the Probe

The Pulse effect on the cross-gain modulation (XGM) in the quantum dot (QD) semiconductor optical amplifiers (SOAs) is investigated using the combining of the SOA power with the QD rate equations system. The QDs structure includes three regions: ground state (GS), excited state (ES) and wetting layer (WL). Thus, a set of rate equations for pump and probe signals is introduced for both steady-state and small-signal power values, which are solved numerically. The pulse shape was included in the analysis, for pump and probe signals. The theoretical results showed a good agreement with the experimental results. It was found that decreasing pulse width of pump/probe ratio is efficient to increase XGM efficiency and bandwidth.

Research on all-optical half adder based on cross-gain modulation in quantum-dot semiconductor optical amplifier

Research on all-optical half adder based on cross-gain modulation in quantum-dot semiconductor optical amplifier

Experimental study of four-wave mixing based on a quantum dot semiconductor optical amplifier

The article is devoted to the study of four-wave mixing (FWM) in a semiconductor optical amplifier with quantum dots (QD-SOA). Experimental measurements of FWM signals are characterized in nonlinear media of GaAs-based QD-SOA with gain in the 1,550 nm region. Theoretical part of nonlinear effect of FWM is studied and important all-optical communication applications are listed. Experimental studies of a four-wave system are described and an analysis of FWM signals is given for various input powers of pump signals and injection currents. The devices are compared in terms of such parameters as conversion efficiency and signal-to-noise ratio. The results of the study made it possible to reveal the possibility of the effect of FWM signals on useful signals in channels with spectral division multiplexing wavelength division multiplexing (WDM) in the downstream and upstream in a semiconductor optical amplifier. Based on the experimental results, it was concluded that FWM does not affect adjacent channels of WDM signals and does not generate additional optical noise when scaling the WDM gigabit passive optical network (GPON) up to 60 km using semiconductor optical amplifiers (SOAs).

Encryption Using Optical Pseudo-Random Binary Sequence Based on Optical Logic Gate

In this paper, we propose a scheme for high-speed all-optical Pseudo-Random Binary Sequence (PRBS) generator and use it for generating keystream for encryption. This PRBS generator design is based on Linear Feedback Shift Registers (LFSR) and optical XOR and AND gates. The optical logical gates are based on quantum dot-semiconductor optical amplifier Mach-Zehnder interferometer (QD-SOA-MZI). With two photon absorption (TPA) in quantum dot-semiconductor optical amplifier (QD-SOA), this kind of optical logic gates performs well when processing data in an ultra-fast timescale and therefore able to function as high speed PRBS generator. Result shows that it’s possible for this scheme to realize all-optical encryption and decryption at high process rate up to 320 Gb/s. We simulated different ways of generating keystream with schemes such as cascaded generator, parallel generator and alternating step generator. These generators use more than one LFSR. Result shows that the schemes we use can function as stable and complex keystream generators.

Numerical simulation of Tb/s all-optical reconfigurable frequency encoded OR and AND gate using quantum dot semiconductor optical amplifier-based Mach–Zehnder interferometer

Frequency encoded reconfigurable logic gates OR and AND are designed using interferometric switch based on quantum dot semiconductor optical amplifier (QDSOA) and simulated using MATLAB for the first time as far as our knowledge goes. The amplitude modulation (AM) and quality factor ([Formula: see text] are calculated using numerical simulations confirming practical feasibility of the logic gates. This paper also investigates the effect of amplified spontaneous emission (ASE) noise on AM, [Formula: see text] and signal-to-noise ratio (SNR) values. AM below 0.005 dB and [Formula: see text] more than 30[Formula: see text]dB ensure error free operation of the logic gates.

Ultrafast All Optical Parity Generator and Checker based on Quantum Dot Semiconductor Optical Amplifier

This investigation reports all optical parity generators and checkers based on quantum dot semiconductor optical amplifiers at 200 Gb/s. The proposed circuit has been realized by using SOA-MZI configuration with a quantum dot as an active region in SOA. A parity generator consists of three inputs and utilizes 2 XOR logic while a parity checker employs 3 XOR logic with 4 inputs. Cross-phase modulation in SOA has been exploited in the design of XOR logic. MZI configuration converts phase modulation to amplitude modulation to achieve desired boolean equation of XOR. A wide and clear eye diagram has been obtained for the parity generator and checker outputs. The quality factor for the parity generator and checker outputs obtained are 17.2 and 15.1 respectively also the extinction ratio for both outputs are more than 15 dB.

Investigation of four-wave mixing in flared-waveguide quantum-dot semiconductor optical amplifiers

Investigation of four-wave mixing in flared-waveguide quantum-dot semiconductor optical amplifiers

Gain of TlBr/BrCl Quantum Dot Semiconductor Optical Amplifier

This work studies the thallium halogenide TlBr/BrCl quantum dot (QD) semiconductor structure and specifies its optical properties. This QD structure is poorly studied. High gain is obtained, with two peaks at 800 and 3000 n m . Doping is shown to increase the gain by one order. Then, TlBr QD semiconductor optical amplifier (SOA) characteristics are studied. High dB gain is shown mainly at the doped structure, which can be used in various inline applications.

Simulative analysis of 1 Tb/s all-optical half-adder using quantum dot semiconductor optical amplifiers

Abstract All-optical half adder using quantum dot semiconductor optical amplifier is proposed and analyzed using numerical simulations for two different unsaturated gains. Cross gain modulation (XGM) and cross phase modulation (XPM) in Mach–Zehnder interferometer structure generate CARRY and SUM, respectively, of the half adder. The performance of the device is optimized with respect to input pump powers and effect of amplified spontaneous emission (ASE) noise is also investigated. We have found extinction ratio (ER) as high as 16.48 dB for SUM and 12.95 dB for CARRY which ensures efficient performance of the proposed half adder. The quality factor Q is also high (24.58 dB for SUM and 18.47 dB for CARRY). These confirm clear transmissions of the bits with low bit error rate (BER).

Dynamic power and chirp measurements of a quantum dash semiconductor optical amplifier amplified picosecond pulses using a linear pulse characterization technique

Quantum Dash (QDash) SOAs are of interest as an alternative to quantum dot SOAs, since they have some dot-like properties and are easier to fabricate such as to operate in the 1550 nm region, albeit with longer gain recovery times in the range of hundreds of picoseconds. QDash-SOAs are promising core component is optical subsystems for applications in next generation coherent communications and optical signal processing, which often involve pulse amplification. It is of interest to measure both the dynamic power, phase and associated chirp and thereby the spectrum of typical QDash-SOA amplified pulses. Non-linear measurement techniques are appropriate for pulsewidths less than 5 ps but have low sensitivity for wider pulsewidths often encountered in practice. This paper describes the use of a modified linear pulse characterization technique to measure the dynamic power and phase of the identical pulses of a QDash-SOA amplified 20 GHz repetition rate 19 ps pulsewidth pulse train. The pulse chirp and power from which the pulse chirp and pulse train power spectrum is calculated. The amplified pulse structure is strongly dependent on the amplifier gain and the input pulse shape and energy.

Two-Photon Absorption Effect on Pseudorandom Bit Sequence for High-Speed Operation

Study of two-photon absorption (TPA) has been carried out for all-optical logic operation based on quantum-dot semiconductor optical amplifier (QD-SOA). XOR gate, AND gate and pseudo-random bit sequence (PRBS) were all modeled with the TPA effect on the existing rate equation. Inclusion of TPA induced pumping has increased the output Q-factor (quality). The output result demonstrates that the quality of the output is dependent on the input pulse width and the operation speed. The PRBS system modeled with TPA shows that it can operate at 250 Gb/s and 320 Gb/s and increase in pulse width decrease the Q-factor.

Multichannel random signal generation in optical fiber-based ring laser with quantum-dot semiconductor optical amplifier

Random signal generation in a ring resonator laser is achieved with quantum-dot semiconductor optical amplifiers. The lasing spectra were obtained over a wide range of wavelengths, and the individual longitudinal modes acted as the channels for random number generation.

Alternative method of implementation of all-optical NOR and NAND gates using quantum-dot semiconductor optical amplifiers in non-interferometer structure

Abstract Present communication deals with the design and analysis of all-optical NOR and NAND gates using Quantum dot Semiconductor Optical Amplifiers (QDSOA). The design uses no interferometer structure but cross gain modulation is utilized for operation. The structures are simple and simulations at a rate of 1 Tb/s are processed. For unsaturated gain 30 dB, the logic gates show high values of ER (29.82 dB, 16.93 dB), CR (29.6 dB, 21.33 dB), and Q (25.4 dB, 13.2 dB). This ensures practical feasibility and high quality of the proposed gates.

Non-MZI all-optical XOR gate using cross-gain modulation in quantum dot semiconductor optical amplifier at 2 Tb/s without filter

Non-MZI all-optical XOR gate using cross-gain modulation in quantum dot semiconductor optical amplifier at 2 Tb/s without filter

Polarization diversity scheme for reach extension of WDM/TDM gigabit passive optical network up to 60 km using quantum dot semiconductor optical amplifiers

Gigabit passive optical networks (GPON) are the most advanced technology. The data transfer rate is 2.5 Gbps for downstream and 1.25 Gbps for upstreams. But this network architecture has a limited physical network length of 20 km. This is due to the high budgetary losses of the network. This restriction of access makes the network difficult to access for subscribers located far from the facilities of the telecom operator, and coverage of remote settlements is quite costly (cost of design work, fiber, laying of fiber-optic cable), thereby complicating the elimination of the digital divide between the city, the suburbs and the countryside. To solve this problem, it is proposed to use quantum dot semiconductor optical amplifiers (QD-SOA), which will expand the GPON reach up to 60 km, which is the limit for the logical length under the current protocols. Quantum dot semiconductor optical amplifiers are promising devices for optical communication technology, but for commercial use they have one disadvantage. They are polarization sensitive. In this paper the authors constructed a polarization diversity scheme to avoid polarization sensitivity of QD-SOAs.

All-optical switchable logic gate using a single QD-SOA for RZ-BPSK signal inputs

In this paper, we propose an all-optical switchable logic gate using a single quantum-dot semiconductor optical amplifier (QD-SOA). This logic gate has switching functions for logical operators, and for the number of inputs. The multifunctionality of the proposed circuit is achieved by introducing the phase-shift keying signal. This gate is constructed using a single QD-SOA, single optical bandpass filter, single 3-dB coupler, and single power combiner. The final output is a return-to-zero on—off keying signal. Based on numerical simulations, we illustrate that both the logical operators and the number of inputs can be controlled with external signals. In addition, we demonstrate the effect of the amplified spontaneous emission noise on the extinction ratio (ER) and the quality factor (Q-factor). Further, we evaluate the phase error tolerance of the proposed configuration in terms of the ER and Q-factor. The results show that switching of the logical operators does not affect the quality of the output signal; further, the values of the Q-factor in the three-input operation are better than those obtained with the two-input operation. The proposed configuration has several advantages such as uniform quality, low circuit complexity, and multifunctionality.