RESUMO
We demonstrate for the first time, to the best of our knowledge, reconfigurable and real-time orthogonal time-domain detection of a high-bandwidth Nyquist signal with a low-bandwidth silicon photonics Mach-Zehnder modulator based receiver. As the Nyquist signal has a rectangular bandwidth, it can be multiplexed in the wavelength domain without any guardband as a part of a Nyquist-WDM superchannel. These superchannels can be additionally multiplexed in space and polarization. Thus, the presented demonstration can open a new possibility for the detection of multidimensional parallel data signals with silicon photonics. No external pulse source is needed for the receiver, and frequency-time coherence is used to sample the incoming Nyquist signal with orthogonal sinc-shaped Nyquist pulse sequences. All parameters are completely tunable in the electrical domain. The feasibility of the scheme is demonstrated through a proof-of-concept experiment over the entire C-band (1530 nm-1560 nm), employing a 24 Gbaud Nyquist QPSK signal due to experimental constraints on the transmitter side electronics. However, the silicon Mach-Zehnder modulator with a 3-dB bandwidth of only 16 GHz can process Nyquist signals of 90 GHz optical bandwidth, suggesting a possibility to detect symbol rates up to 90 GBd in an integrated Nyquist receiver.
RESUMO
Increasing demands for data centers, backbone, access, and wireless networks require inventive concepts to transmit and distribute digital or analog signal waveforms. We present a new, extremely simple transceiver concept, fundamentally different from conventional approaches. It does not rely on high-speed electronics and enables transmission of various time multiplexed analog waveforms or digital data signals with the maximum possible symbol rate in the same rectangular optical spectral band B. The aggregate symbol rate of N signal channels corresponds to B or twice the used modulator's electro-optical bandwidth. By a modification of the system, it can be increased to three times the modulator bandwidth. The rectangular spectra can be further multiplexed into wavelength-superchannels without guardbands. To time demultiplex single signal channel, just another intensity modulator and a detector with an electrical bandwidth corresponding to the channel's baseband width (B/(2N)) is required. No optical filter, high-speed signal processing, or unconventional photonic devices are needed; thus, it has the potential to be easily integrated into any platform and provides an economical and energy-efficient solution for future communication networks and microwave photonic links.
RESUMO
Fully autonomous driving, even under bad weather conditions, can be enabled by the use of multiple sensor systems including 5D radar imaging. In order to get three dimensional, high resolution images with Doppler and time tracking of the target, the radar needs to utilize a large number of transmit/receive modules. For proper beam forming, all of them demand synchronization. Here a new concept for the optical distribution of radar signals, comprising low complexity integrated transmitter and receiver chips and a complex central station, will be introduced. Unavoidable temperature drifts due to environmental influences were compensated to maintain a continuous electrical output power. Within a proof-of-concept radar experiment an angular resolution of 1.1° has been achieved.
RESUMO
Source-free all optical sampling, based on the convolution of the signal spectrum with a frequency comb in an electronic-photonic, co-integrated silicon device will be presented for the first time, to the best of our knowledge. The method has the potential to achieve very high precision, requires only low power and can be fully tunable in the electrical domain. Sampling rates of three and four times the RF bandwidths of the photonics and electronics can be achieved. Thus, the presented method might lead to low-footprint, fully-integrated, precise, electrically tunable, photonic ADCs with very high-analog bandwidths for the digital infrastructure of tomorrow.
RESUMO
In this article, we demonstrate the noise reduction and signal to noise ratio (SNR) enhancement in Brillouin optical time-domain analyzers (BOTDA). The results show that, although the main noise contribution comes from the Brillouin interaction itself, a simple low pass filtering on the detected radio frequency (RF) signal reduces remarkably the noise level of the BOTDA traces. The corresponding SNR enhancement depends on the employed cut-off frequency of the low pass filter. Due to the enhancement of the SNR, a mitigation of the standard deviation error of the Brillouin frequency shift (BFS) has been demonstrated. However, RF filters with low cut-off frequency could lead to distortions on the trace signals and therefore detection errors on a non-uniform BFS. The trade-off between the noise reduction and the signal distortion as well as an optimal cut-off frequency are discussed in detail.
RESUMO
Spectral analysis is essential for measuring and monitoring advanced optical communication systems and the characterization of active and passive devices like amplifiers, filters and especially frequency combs. Conventional devices have a limited resolution or tuning range. Therefore, the true spectral shape of the signal remains hidden. In this work, a small part of the signal under test is preselected with help of the polarization pulling effect of stimulated Brillouin scattering where all unwanted spectral components are suppressed. Subsequently, this part is analyzed more deeply through heterodyne detection. Thereby, the local oscillator is generated from a narrow linewidth fiber laser which acts also as pump wave for Brillouin scattering. By scanning the pump wave together with the local oscillator through the signal spectrum, the whole signal is measured. The method is tunable over a broad wavelength range, is not affected by unwanted mixing products and utilizes a conventional narrow bandwidth photo diode. First proof of concept experiments show the measurement of the power spectral density function with a resolution in the attometer or lower kilohertz range at 1550 nm.
RESUMO
The generation of flat, rectangular frequency combs with tunable frequency spacing and bandwidth is demonstrated. Therefore, several lines or sidebands are extracted out of an existing frequency comb, for example a femtosecond fiber laser. Subsequently, these lines are processed via two Mach-Zehnder modulators in order to generate a flat frequency comb with tunable frequency spacing. Optical frequency combs with various spacing and a maximum bandwidth of 260 GHz are generated. However, much higher bandwidth can be reached easily. The overall flatness of the generated combs is within 0.6 dB.
RESUMO
A new implementation of microwave-photonic filters (MPFs) based on tunable optical delay lines is proposed and demonstrated. The variable delay is based on mapping of the spectral components of an incoming waveform onto the time domain, the application of linearly-varying temporal phase offsets, and an inverse mapping back to the frequency domain. The linear phase correction is equivalent to a frequency offset, and realized though suppressed-carrier single-sideband modulation by a radio-frequency sine wave. The variable delay element, controlled by the selected frequency, is used in one arm of a two-tap MPF. In a proof-of-concept experiment, the free spectral range (FSR) of the MPF was varied by over a factor of four: between 1.2 GHz and 5.3 GHz.
RESUMO
The interference between two spectral lines of the frequency comb of a fiber femtosecond laser is used to generate millimeter-wave and terahertz tones. The two lines are selected by stimulated Brillouin scattering (SBS) amplification. All other modes are strongly rejected based on polarization discrimination, using the polarization-pulling effect that is associated with SBS. The inherent high spectral quality of a femtosecond fiber laser comb allows generation of millimeter- and terahertz waves with linewidths below 1 Hz, and a phase noise of -105 dBc/Hz at 10 kHz offset. The generation, free-space transmission and detection of continuous waves at 1 THz are demonstrated as well. Lastly, the generated millimeter-wave carriers are modulated by 40 Gbit/s data. The entire system consists of a fiber laser and standard equipment of optical telecommunications. Besides metrology, spectroscopy and astronomy, the method can be utilized for the emergent field of wireless millimeter-wave and THz-communications at ultra-high data rates.
RESUMO
The requirements for higher data rates in optical communication systems lead to the use of more efficient modulation formats. In the networks the all optical synchronization and storage of these signals is still a major challenge in order to enable higher transmittable data rates and reduce the energy consumption. In this contribution we show for the first time, to the best of our knowledge, the tunable storage of phase modulated optical data packets with up to 60 pulse widths. This opens the way to the optical storage of data packets modulated with highly efficient modulation formats.
RESUMO
A fully electrically tunable microwave photonic filter is realized by the implementation of delay lines based on frequency-time conversion. The frequency response and free spectral range (FSR) of the filter can be engineered by a simple electrical tuning of the delay lines. The method has the capability of being integrated on a silicon photonic platform. In the experiment, a 2-tap tunable microwave photonic filter with a 3-dB bandwidth of 2.55 GHz, a FSR of 4.016 GHz, a FSR maximum tuning range from -354 MHz to 354 MHz and a full FSR translation range is achieved.
Assuntos
Filtração/instrumentação , Refratometria/instrumentação , Ressonância de Plasmônio de Superfície/instrumentação , Telecomunicações/instrumentação , Desenho Assistido por Computador , Desenho de Equipamento , Análise de Falha de Equipamento , Micro-Ondas , FótonsRESUMO
High-resolution, wide-bandwidth optical spectrum analysis is essential to the measuring and monitoring of advanced optical, millimeter-wave, and terahertz communication systems, sensing applications and device characterization. One category of high-resolution spectrum analyzers reconstructs the power spectral density of a signal under test by scanning a Brillouin gain line across its spectral extent. In this work, we enhance both the resolution and the optical rejection ratio of such Brillouin-based spectrometers using a combination of two techniques. First, two Brillouin loss lines are superimposed upon a central Brillouin gain to reduce its bandwidth. Second, the vector attributes of stimulated Brillouin scattering amplification in standard, weakly birefringent fibers are used to change the signal state of polarization, and a judiciously aligned output polarizer discriminates between amplified and un-amplified spectral contents. A frequency resolution of 3 MHz, or eight orders of magnitude below the central optical frequency, is experimentally demonstrated. In addition, a weak spectral component is resolved in the presence of a strong adjacent signal, which is 30 dB stronger and detuned by only 60 MHz. The measurement method involves low-bandwidth direct detection, and does not require heterodyne beating. The measurement range of the proposed method is scalable to cover the C + L bands, depending on the tunable pump source. The accuracy of the measurements requires that the pump frequencies are well calibrated.
Assuntos
Tecnologia de Fibra Óptica/instrumentação , Refratometria/instrumentação , Telecomunicações/instrumentação , Desenho Assistido por Computador , Desenho de Equipamento , Análise de Falha de Equipamento , Luz , Espalhamento de RadiaçãoRESUMO
We investigate the gain bandwidth of stimulated Brillouin scattering (SBS) in multistage systems. As we will show, the bandwidth is reduced significantly by the number of stages, which can increase the distortions in cascaded slow-light systems, for instance. However, other applications, which are limited by the minimum bandwidth achievable with SBS, can benefit from the reduced bandwidth. Since the peak value of the SBS gain spectrum is not reduced by this method, the reduced bandwidth can drastically enhance the performance of many different applications, such as the quasi-light storage (QLS). The minimum bandwidth of 10.3 MHz for a one-stage system was reduced down to 5.8 MHz for three stages. With this reduced bandwidth, we achieved a storage time advancement of the QLS method by 60%.
RESUMO
In this Letter, we propose a novel method based on the inhomogeneous Brillouin gain saturation to reduce the gain bandwidth significantly below its natural value. Based on our first experiments, we report a decrease of the bandwidth in a standard single mode fiber down to 3 MHz.
RESUMO
We present a simple method for the stimulated Brillouin scattering (SBS) gain bandwidth reduction in an optical fiber. We were able to reduce the natural bandwidth of 20 MHz to around 3.4 MHz by a superposition of the gain with two losses produced by the same source. This reduced bandwidth can drastically enhance the performance of many different applications which up to now were limited by the minimum of the natural SBS bandwidth.
Assuntos
Fibras Ópticas , Refratometria/instrumentação , Desenho Assistido por Computador , Desenho de Equipamento , Análise de Falha de Equipamento , Luz , Espalhamento de RadiaçãoRESUMO
The quasi-light-storage (QLS) is a method for the variable and almost distortion free storage of optical data which is based on stimulated Brillouin scattering (SBS). The natural gain bandwidth of SBS limits the storage time of this method to up to 100 ns. We overcome this limit by the superposition of the SBS gain bandwidth with two losses. With this narrowed gain bandwidth, we were able to enhance the storage time for the QLS by 40%.
RESUMO
This article describes a new approach to cancel the pulse broadening in a cascaded slow-light system. With the help of a simple experimental setup a method with significant potential to achieve a high pulse delay at almost zero pulse broadening is shown. Since the pulse reshaping is done inside a single delaying segment, this method can be used in connection with any other Brillouin based slow-light system.
Assuntos
Modelos Teóricos , Refratometria/métodos , Simulação por Computador , Luz , Espalhamento de RadiaçãoRESUMO
We show a method for distortion-free quasi storage of light which is based on the coherence between the spectrum and the time representation of pulse sequences. The whole system can be considered as a black box that stores the light until it will be extracted. In the experiment we delayed several 5 bit patterns with bit durations of 500ps up to 38ns. The delay can be tuned in fine and coarse range. The method works in the entire transparency range of optical fibers and only uses standard components of optical telecommunications. Hence, it can easily be integrated into existing systems.
RESUMO
A novel method for the achievement of zero-broadening in a SBS based slow-light system is discussed in theory and demonstrated experimentally. The system is realized just with a single broadened Brillouin gain. It is shown, that if the gain bandwidth is much broader than the initial pulse width, the output pulse width decreases with increasing pump power. A compression of approximately 90 % of the initial pulse width was achieved in simulation and experiment.
RESUMO
We propose a delay line configuration to increase the time delay performance of multiple-pump-line Brillouin-based slow light systems. It consists of several short fibers interconnected by filters to block degrading spectral components. Three different delay line configurations are investigated experimentally with an optimized Brillouin spectrum composed of a superposition of a gain with two losses. An increase of the maximum time delay by 12% is reported, which is limited by the insufficient filter slew rates. We believe that the enhancement could be much higher by using filters with an improved slew rate performance.