Cross-gain Modulation Research Articles

Simulations of an all-optical flip-flop with a reset pulse frequency exceeding operating frequency

An all-optical flip-flop based on a nonlinear multi-section DFB semiconductor laser structure is proposed. Holding beam is not required for device's operation. A section of the DFB structure is detuned to prevent lasing in the “OFF” state, and it is accompanied with a negative nonlinear coefficient that is due to partial absorption of photons at Urbach tail. At a high light intensity in the structure the nonlinear coefficient reduces the detuning, and the device is in lasing state; “ON” state. The device is reset by an optical pulse at a shorter wavelength through cross gain modulation. The reset pulse is absorbed in a middle section in the device before reaching the detuned nonlinear section. The switching times between the states are in nanoseconds time scale.

Dark Pulse Laser With Tunable Width Based on SOA and Feedback

We demonstrate a dark pulse optical fiber laser with tunable widths based on semiconductor optical amplifier and feedback. In the case of different feedback lengths, by adjusting the polarization controller, dark pulses with a frequency repetition of 13.3 MHz and widths vary from 4.29 to 15.15 ns are generated. Dark pulses are produced by the interaction of birefringence, large normal dispersion, cross-phase modulation, and cross-gain modulation in semiconductor optical amplifier.

Photonic generation of filter-free ultrawideband monocycle and doublet signal using single semiconductor optical amplifier in counter-propagation scheme

We propose and demonstrate a flexible and filter-free method to generate ultrawideband monocycle and doublet pulses utilizing cross-gain modulation in a semiconductor optical amplifier. The counter-propagation scheme and UWB-over-fiber technology is implemented by exploiting dispersion-induced pulse broadening effect in a single-mode fiber. Owing to the counter-propagation scheme, the pump and probe light can be the same wavelength, which could provide the system better dispersion performance.

UWB doublet signal generation and modulation based on DFB laser under optical pulses injection

In this paper, a novel scheme to generate ultra-wideband (UWB) doublet signals based on the cross-gain modulation (XGM) effect in the DFB lasers is proposed and experimentally demonstrated, the modulation and transmission of the generated UWB doublet signals are also researched. In the proposed system, a gain-switched laser (GSL) is used as a master laser (ML) and the optical pulses from the ML are optically injected into two paralleled DFB lasers, which are used as slave lasers (SL). Then the outputs from the SLs are detected by a balanced photodiode (BPD) to generate the Bi-phased UWB signals. By properly setting the system parameters, UWB signals with various modulation formats such as on–off keying (OOK), pulse amplitude modulation (PAM) as well as the phase-shift keying (PSK) can be generated. In addition, fiber transmission of the modulated UWB signals is also experimentally investigated.

Design and analysis of all-optical half-adder, half-subtractor and 4-bit decoder based on SOA-MZI configuration

In the paper, all-optical Boolean circuits implemented with a semiconductor optical amplifier based Mach–Zehnder interferometer, are simulated and analyzed at 10 Gb/s to extract a simple design rule. Authors propose the novel designs of half-adder, half-subtractor and 4-bit decoder for various results and also discussed the results at different bit rates. In the designs, one data acts as a pump generated through clock wave laser and another acts as a probe from mode lock laser. The designs consist of non-linearity in semiconductor optical amplifier using the cross gain modulation technique. Cross gain modulation refers to data on pump signal modulating the carrier density in semiconductor optical amplifier. At the same time, the gain variation indentation inverts the probe signal after passing through amplifier. Interferometer structure is used to convert the phase modulation into intensity modulation. The paper aims to achieve the goal through simulation and Boolean analysis in terms of gates, to provide simple design rule. Obtained results are very useful in the design of other more complex all-optical circuits that employ the given gates as the basic building block. The extinction ratio is the optimization criteria for all the three circuits at different values of pump power and bit rate of input pulse.

A Novel Thresholder Based on XGM Effect in a DFB Laser Combined With External Optical Filtering

A novel thresholder based on cross-gain modulation (XGM) effect in a distributed-feedback (DFB) semiconductor laser combined with offset optical filtering is proposed and demonstrated. To the best of our knowledge, this is the first XGM effect-based thresholder that is operated by optical injection of a DFB laser. In this scheme, a DFB laser without an isolator is the key component, which costs less than the nonlinear devices required in other schemes. The spectrum output from the DFB laser can be broadened after the pulses injected to the laser cavity, which is induced by the XGM effect. Only the correct codes that have enough peak power will be able to broaden the spectrum of the DFB laser, while the low-power noise cannot. By offset filtering the broadened parts of the optical spectrum, the correct optical pulse is acquired, while the undesired noise is diminished. In this scheme, an injection power of 7 dBm is enough to generate the XGM effect, which is much lower than most of the existing schemes. In addition, as the DFB laser is used as the pump laser as well as the nonlinear medium, this scheme is more compact and low cost compared with the schemes proposed before.

10 Gbps Externally Modulated XGM Based Wavelength Conversion Using SOA

This paper proposes a method for All Optical Wavelength Conversion using semiconductor optical amplifier at 10Gbps. The system is demonstrated for Cross Gain Modulation (XGM) process of SOA, which is the simplest wavelength conversion technique that takes the advantage of non linear gain suppression mechanism in SOA. The system performances are analyzed using Q factor and Extinction Ratio of the eye diagram. The input pump power is varied from 2 dBm to 5 dBm; also the extinction ratio of Mach-Zehnder modulator is varied from 30 dBm to 60 dBm. Maximum Q Factor of 11.86dB is obtained for a maximum output signal power 23.94 dBm. Minimum Q Factor obtained is 7.58dB for a minimum output signal power 23.15 dBm. The extinction ratio falls from 18.56dB to 16.63dB as the input conditions are varied.

All-Optical XOR Logic Gates: Insights and Comparisons

Three XOR photonics logic gate configurations namely semiconductor optical amplifier-Mach Zender interferometer cross phase modulation (SOA-MZI XPM), SOA-MZI cross gain modulation (XGM) and terahertz optical asymmetrical demultiplexer (TOAD) XOR are analysed and compared in terms of generated power, optical signal-to-noise ratio (OSNR) values and bit error rate (BER) signal quality. The highest generated power is possessed by the TOAD at 23.5 dBm, the SOA-MZI XPM showed the most extinction ratio or OSNR with 109.6 dB whereas the best BER is recorded in the SOA-MZI XGM at 4.42 x 10-22.

All Optical Wavelength Conversion of Nyquist-WDM Superchannels Using FWM in SOAs

In this paper, the performance of all-optical wavelength conversion (WC) of Nyquist-WDM superchannels is investigated for future implementation in optical networks. We consider advanced modulation formats of DQPSK and 16-QAM for the subchannel modulation format achieving raw bit rates of 448 and 896 Gb/s, respectively. We demonstrate through simulations the WC of Nyquist-WDM superchannel using degenerate and nondegenerate four-wave mixing (FWM) in a semiconductor optical amplifier (SOA). We consider the effects of raised cosine (RC) and root raised cosine (RRC) signal pulse shaping within the wavelength conversion process. We find that the performance of the converted superchannel is severely impaired by crosstalk due to cross-gain modulation of the pump by the superchannel. Optimum performance of the converted superchannel is achieved by setting the detuning between the continuous-wave pump and the central wavelength of the superchannel to be around 200 GHz and using pumps of double the gain saturation power of the SOA with 23 dB pump to signal power ratio.

Photonic Implementation of Spike-Timing-Dependent Plasticity and Learning Algorithms of Biological Neural Systems

The neurobiological learning algorithm, spike-timing-dependent plasticity (STDP), is demonstrated in a simple photonic system using the cooperative nonlinear effects of cross gain modulation and nonlinear polarization rotation, and supervised and unsupervised learning using photonic neuron principles are examined. An STDP-based supervised learning scheme is presented which is capable of mimicking a desirable spike pattern through learning and adaptation. Furthermore, unsupervised learning is illustrated by a principal component analysis system operating under similar learning rules. Finally, a photonic-distributed processing network capable of STDP-based unsupervised learning is theoretically explored.

Experimental investigation of photonic microwave switching based on XGM in a SOA

The photonic microwave switching performances based on the cross gain modulation (XGM) effect in a semiconductor optical amplifier (SOA) are experimentally investigated. The influences of the key parameters of the system, such as the optical power of the pump and probe signals, the SOA bias current and the modulation depth are experimentally studied and analyzed to optimize the system performance. Important performances of the linearity, the dynamic range and the polarization sensitivity of the photonic microwave switching system are analyzed and discussed. The channel uniformities are also investigated according to the requirements of the photonic microwave switching applications.

Flexible 16 $\times$ 10-Gb/s All-Optical Broadcast and Multicast TWDM Passive Optical Network

To achieve flexible packet routing in a time wavelength-division multiplexing passive optical network (PON) architecture, most proposed systems use a tunable transceiver in the optical line terminal (OLT). The tunable transceiver is attractive for use in a PON system because it is able to broadcast and multicast packets within the entire PON system, being limited only to a single PON link. The proposed all-optical packet routing (AOPR) module was designed to incorporate a fixed-type wavelength OLT transmitter with a continuous-wave pump probe signal module. The design of the module is based on the ALL-ON method to support all broadcast signals, which replaces the wavelength tuning feature in the tunable OLT transmitter. The proposed architecture was designed using the multicasting cross-gain modulation (XGM) method. In this proposed design, the XGM function of the OLT system becomes a part of the AOPR OLT transmitter. The arrangement of this design aims to generate single or multiple wavelengths in a downstream direction in each OLT PON port. The measurement results revealed that the proposed system can handle a total of 160-Gb/s broadcast downstream bandwidth to serve 16 PON links using $16\lambda$ with a maximum of 2048 users.

Photonic implementation of a neuronal algorithm applicable towards angle of arrival detection and localization.

A photonic system exemplifying the neurobiological learning algorithm, spike timing dependent plasticity (STDP), is experimentally demonstrated using the cooperative effects of cross gain modulation and nonlinear polarization rotation within an SOA. Furthermore, an STDP-based photonic approach towards the measurement of the angle of arrival (AOA) of a microwave signal is developed, and a three-dimensional AOA localization scheme is explored. Measurement accuracies on the order of tens of centimeters, rivaling that of complex positioning systems that utilize a large distribution of measuring units, are achieved for larger distances and with a simpler setup using just three STDP-based AOA units.

A single As2Se3 chalcogenide Highly Non-Linear Fiber (HNLF) based simultaneous all-optical half-adder and half-subtracter

In this article, a novel simultaneous all-optical half-addition and half-subtraction scheme based on exploitation of cross-gain modulation (XGM) and four-wave mixing (FWM) in parametric medium consisting of As2Se3 chalcogenide HNLF capable of operating at 100Gbps bit rate has been demonstrated. The proposed scheme does not require any type of extra assist light sources. XGM & FWM processes have been utilized for the realization of borrow (AB‾ &A‾B) & carry (A.B) outputs, respectively of the proposed all-optical half-addition and half-subtraction module. The sum/difference output of proposed half-adder has been obtained by temporally combining earlier realized borrow (AB‾ &A‾B) signals. Q-factors and extinction ratios (ER) of over 10.5 & 11.3255dB, respectively for XGM based outputs (AB‾ &A‾B) and 10.73 & 17.47dB, respectively for FWM based outputs (A.B) have been achieved.

Adaptive Optical Self-Interference Cancellation Using a Semiconductor Optical Amplifier

We experimentally demonstrate an optical system that uses a semiconductor optical amplifier (SOA) to perform adaptive, analog self-interference cancellation for radio-frequency signals. The system subtracts a known interference signal from a corrupted received signal to recover a weak signal of interest. The SOA uses a combination of slow and fast light and cross-gain modulation to perform precise amplitude and phase matching to cancel the interference. The system achieves 38 dB of cancellation across 60-MHz instantaneous bandwidth and 56 dB of narrowband cancellation, limited by noise. The Nelder-Mead simplex algorithm is used to adaptively minimize the interference power through the control of the semiconductor's bias current and input optical power.

Mutually modulated cross-gain modulation with a considerable modulation wavenumber-interaction length product.

An extended theory of the mutually modulated cross-gain modulation was developed to make it valid under considerable modulated wavenumber-interaction length product. Parametric analysis of the extended theory shows that, in the modulated probe beam out of the gain medium, the spectral sensitivity of the first harmonic wave is associated with its amplitude. The larger the sensitivity is, the smaller the amplitude will be. An effective method was provided to monitor and achieve high spectral sensitivity at a pre-selected frequency detuning in practice. The validity of the extended theory was confirmed by a sensing experiment in a piece of ∼10-km fiber with 10 kHz modulation frequency, in which a fast light propagation with a sensitivity of 0.592 mrad/kHz was achieved.

Investigation of a cross‐gain modulation in a semiconductor optical amplifier based on a quantum dot‐in‐a‐well structure

The authors theoretically investigated the cross-gain modulation and the related cross-phase modulation in a travelling wave quantum dot-in-a-well (QDWELL) semiconductor optical amplifier (SOA). They show that the strong enough pumping wave with an optical power in the range of 1 mW up to several milliwatts synchronises the carrier dynamics in the QDWELL SOA, increasing its operation rate to the frequency of 240 Gb/s and decreasing the patterning effect and chirp.

Implementation of optical logic gates at 160Gbps using nonlinear effect of single SOA

Abstract This paper come across with the design of all optical logic gates OR, AND, NOT, NOR, XNOR and NOT at ultra high speed by using SOA (semiconductor optical amplifier). All logic gates are obtained by principle of XGM (cross gain modulation) and FWM (four wave mixing) in SOA at 160 Gbps. The OR, AND, NOR logics of two data sources are obtained by using additional pump signal, while XNOR logic is obtain by using two data sources with combined effect of four wave mixing and cross gain modulation. The NOT is obtained by using a pump signal along with the one data source with cross gain modulation effect. Thus realization of these logics at 160 Gbps will lead to revolutionary growth in optical signal processing for various high speed operation applications.

Numerical simulation of a novel all-optical flip-flop based on a chirped nonlinear distributed feedback semiconductor laser structure using GPGPU computing

A novel all-optical flip-flop based on a chirped nonlinear distributed feedback laser structure is proposed. The flip-flop does not require a holding beam. The optical gain is provided by a current injection into an active layer. The nonlinear wave-guiding layer consists of a chirped phase shifted grating accompanied with a negative nonlinear refractive index coefficient that increases in magnitude along the wave-guide. In the ‘OFF’ state, the chirped grating does not provide the required optical feedback to start lasing. An optical pulse switches the device ‘ON’ by reducing the chirp due to the negative nonlinear refractive index coefficient. The reduced chirp grating provides enough feedback to sustain a laser mode. The device is switched ‘OFF’ by cross gain modulation. GPGPU computing allows for long simulation time of multiple SET–RESET operations. The ‘ON/OFF’ transitions delays are in nanoseconds time scale.

A Simultaneous Variable Optical Weight and Delay in a Semiconductor Optical Amplifier for Microwave Photonics

In this paper, we demonstrate how a single semiconductor optical amplifier can serve as a simultaneous variable optical weight and tunable optical delay for microwave photonics. The device weight, or power transmission, and delay can be controlled simultaneously and independently from each other by varying the input optical power and the semiconductor bias current. The dual functionality is achieved by combining the effects of slow and fast light with cross-gain modulation in the semiconductor. We experimentally demonstrate a tunable delay range of 100 ps and RF gain range of $-$ 6 to +3 dB for a 600-MHz microwave signal and show how the weight and delay of the device can be separately tuned. The delay range and bandwidth of the device are limited by the semiconductor carrier lifetime and characteristic of slow and fast light. As a simultaneous optical weight and delay, as well as a wavelength converter, a semiconductor optical amplifier operating in this manner can be a compact and versatile element in microwave photonics, radio-over-fiber, and general analog optical signal processing.