Universal problem of spectral characterization for element base of microwave photonic means from broad band electrooptic and optical electronic modulators and receivers to narrow band Bragg and Fabry-Perot filters is very actual. The presented modulating and forming devices contain, in a minimal structure, a special laser diode and two modulators, the first of which is calibrated (master) and has a significant impact on the accuracy of modulation and forming in second (functional), and ensuring the operating modes of both modulators affects the complexity of the devices structure. The last one element is photoreceiver with given characteristics as laser diode ones. The purpose of the work is to present developed devices for various implementation with a minimized structure and simple control, which allow achieving results similar to those obtained using complex multi-stage, two-port, dual, parallel, polarization divided Mach-Zehnder modulators, accompanied with acousto-optic and polarization modulators, all of which have become unavailable under the sanctions pressure. Their advantages can become more significant using microminiaturization technologies – combined microwave and photonic, photonic and quantum integrated circuits (PIC), developing in KNRTU-KAI and UUST, especially under the influence of external climatic factors. These aspects are discussed in the report using the examples of instantaneous frequencies measurements, broadband spectral characteristics of modulators and photoreceivers, quantum key distribution systems with frequency coding. Few words are said about sensor networks.
Seven years ago, we proposed the concept of addressed fiber Bragg structures (AFBS), which simultaneously perform the functions of: a complexed sensitive element based on two FBGs (2λ-AFBS) with different Bragg frequencies or FBG with two π-phase shifts (2π-AFBS), the difference frequency of which is the AFBS address and the value of it is invariant to measured physical fields; a two-frequency laser radiation source, which can operate as in reflection, so as transmission mode respectively to structure above, a self-multiplexed set of sensors, if the difference frequency will be unique for each AFBS, enabling their address multiplexing. In this article, we consider the ontology of AFBS, including the parent structures with 2λ- or 2π-components, successor AFBS with three spectral components and various combinations of difference frequencies: symmetrical and asymmetric, performing the functions of the addressing and converting information signals to the low-frequency region at the same time, along with the functions of rejecting collisions caused by the relative movement of structures relative to each other during measurements. The subjects of interrogation of these structures and their calibration are discussed as well as prospects of AFBS further development based on common tasks born by ontology formalization and decisions of applicability tasks.
To achieve a dense and efficient deployment of RRH microcells and easy initialization of their central wavelengths, tunable colorless laser transmitters are included in the ONU of the transport domain of 5G mobile radio access networks, making it easy to tune and control the radiation wavelength using various mechanisms. In the ONU, upstream wavelength control is necessary due to possible errors in setting the center wavelength during initial connection with OLT (BBU), as well as due to wavelength drift due to aging of the laser transmitter. The paper presents a new method of straight (ONU-OLT) dual-frequency wavelength initialization in one of the WDM-PON channels, built on AWG, using the process of determining the maximum amplitude modulation coefficient of the probe radiation components beating envelope as a parameter that indicates tuning to its central wavelength. Using the method makes it possible to increase the signal-to-noise ratio of the initialization channel, its sensitivity, and the accuracy of tuning to the center of the AWG channel in comparison with the known methods using the processes of direct detection of single-frequency probe radiation.
Tuning the wavelength of a colorless laser transmitter, used to build an upstream channel in the WDM-PON transport domain of a 5G mobile radio access network, to the wavelength of the maximum transmission of its multiplexer channel is implemented by a number of regulated and proactive procedures. Part I is a beginning of this article and is devoted to straight initialization. The main attention in the article will be paid to the consideration of reflective type systems. Broadband and single-frequency reflective methods for tuning direct modulation lasers: VSCEL, DFB, DBR, and external modulation lasers: integral module on InP-substrate, with direct detection and heterodyne reception are analyzed, their advantages and disadvantages are determined. The transition to modulation reflectometric methods of tuning on few close frequencies is substantiated, for which two- and three- frequency technologies for multiplexer probing based on EML lasers with scanning are proposed. The use of methods makes it possible to increase the signal-to-noise ratio, sensitivity and accuracy of multiplexer spectral characteristics measurements, and, consequently, the accuracy of tuning the wavelength of a colorless laser transmitter to the central wavelength of one of multiplexer channels.
New approaches are presented to the process of measuring the chromatic dispersion of a high-speed communication channel based on the classical method for determining the ratio of the radio frequency signal power. The power ratio is recorded at the output of two identical photodetectors, one of which is equipped with a Bragg notch filter at the carrier frequency. New approaches are based on preliminary amplitude modulation of an optical carrier with a radio clock signal frequency with the formation of an additional two-, three or four-frequency radiations to determine the shift between the central wavelengths of the communication channel and the Bragg notch filter, and also the use of methods to increase the signal-to-noise ratio of the measurements. The registration of information at the probing frequency or doubled probing frequency allows obtaining a gain in the signal-to-noise ratio of measurements up to 10-13 dB and performing chromatic dispersion measurements at a signal-to-noise ratio at a clock frequency of 3-5 dB. The penalty for using additional probing frequencies is up to 1 dB.
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