Showing papers on "Comb generator published in 2020"

Performance of chip-scale optical frequency comb generators in coherent WDM communications.

Abstract: Optical frequency combs have the potential to become key building blocks of wavelength-division multiplexing (WDM) communication systems. The strictly equidistant narrow-band spectral lines of a frequency comb can serve either as carriers for parallel WDM transmission or as local-oscillator (LO) tones for parallel coherent reception. When it comes to highly scalable WDM transceivers with compact form factor, chip-sale comb sources are of particular interest, and recent experiments have demonstrated the viability of such devices for high-speed communications with line rates of tens of Tbit/s. However, the output power of chip-scale comb sources is generally lower than that of their conventional discrete-element counterparts, thus requiring additional amplifiers and impairing the optical signal-to-noise ratio (OSNR). In this paper, we investigate the influence of the power and optical carrier-to-noise ratio (OCNR) of the comb lines on the performance of the WDM link. We identify two distinctively different regimes, where the transmission performance is either limited by the comb source or by the link and the associated in-line amplifiers. We further investigate the impact of line-to-line power variations on the achievable OSNR and link capacity using a soliton Kerr frequency comb as a particularly interesting example. We believe that our findings will help to compare different comb generator types and to benchmark them with respect to the achievable transmission performance.

Design of Efficient Resonator-Enhanced Electro-Optic Frequency Comb Generators

Abstract: Resonator-enhanced electro-optic (RE-EO) frequency comb generators produce broad combs by coupling an optical field to a resonator containing a phase modulator driven at a harmonic of the resonator free spectral range (FSR). Recent advances in integration technologies have opened up the possibility of fabricating low-loss, efficient, and tunable ring-based RE-EO comb generators. In this work, we analyze the properties of a canonical ring-based RE-EO comb generator and propose a new dual-ring comb generator to increase comb conversion efficiency, an especially important characteristic for comb-based optical communications systems. After a brief review of RE-EO comb generator properties in the case of resonant operation, i.e., when the optical frequency and the modulation frequency are harmonics of the resonator FSR, we analyze the effect of input optical phase noise and modulation phase noise on the resulting comb. Additionally, we show analytically that in non-resonant operation the optical frequency offset and the modulation frequency offset can be much larger than the linewidth of the resonator, increasing the tolerance to fabrication errors. Then, we develop and validate numerical models to predict the output spectrum in the presence of dispersive waveguides, which cannot be modeled analytically. Using these accurate models, we analyze a dual-ring RE-EO comb generator that uses a small coupling ring to increase the conversion efficiency to 32%, compared to the 1.3% efficiency of a single-ring RE-EO comb generator. We then analyze a point-to-point inter-data center optical link and determine that a dual-ring RE-EO comb generator can support high-capacity coherent links at 20 Tb/s per fiber.

Performance Enhancement of Optical Comb Based Microwave Photonic Filter by Machine Learning Technique

Abstract: Machine learning technique is employed to design a microwave photonic filter (MPF) consisting of an optical comb generator and a phase modulator (PM), to realize centralized management of radio signal delivery in optical networks. The proposed comb generator successfully generates up to 103 optical carriers with adjustable wavelength spacing and number of optical carriers. It exhibits large tunability, flat band response and high tone-to-noise ratio. Thus, the proposed optical comb-based filter is capable to provide flexible tunability with respect to its center frequency and 3-dB bandwidth. In our experimental setup, different wavelength spacing settings and number of optical carriers are fed into the PM for modulation and their corresponding frequency responses are measured by a network analyzer. The experimental data have been analyzed to correlate with the simulation results and theoretical predictions. Besides, a subcarrier multiplexing (SCM) technique can be applied to a multi-user optical system incorporating the proposed filter since its frequency response is varied by the accumulated dispersion. After measuring the characteristic of the proposed filter, a set of frequency responses is collected and fed into the convolutional neural network (CNN) model to obtain the inverse mapping between frequency response to the wavelength spacing and fiber length. As a result, the well-trained model can successfully predict the wavelength spacing and fiber length with high accuracy.

An on-chip III-V-semiconductor-on-silicon laser frequency comb for gas-phase molecular spectroscopy in real-time

Abstract: Frequency combs, spectra of evenly-spaced narrow phase-coherent laser lines, have revolutionized precision measurements On-chip frequency comb generators hold much promise for fully-integrated instruments of time and frequency metrology While outstanding developments are being reported with Kerr, quantum cascade and microring electro-optic combs, the field of high-resolution multiplexed gas-phase spectroscopy has remained inaccessible to such devices, because of their large line spacing, their small number of usable comb lines, the intensity variations between their comb lines, and their limited photonic integrability Here we identify a path to broadband gas-phase spectroscopy on a chip We design a low-noise III-V-on-silicon comb generator on a photonic chip, that emits a flat-top spectrum of 1400 lines at a repetition frequency of 10 GHz, a feature never approached by other ultra-miniaturized comb synthesizers With dual-comb spectroscopy, our near-infrared electrically-pumped laser records high-resolution (1 GHz) sensitive multiplexed spectra with resolved comb lines, in times as short as 5 microseconds Isotope-resolved 12C/13C detection in carbon monoxide is performed within 1 millisecond With further developments, entire high-resolution spectroscopy laboratories-on-a-chip may be manufactured at the wafer scale In environmental sensing, broad networks of spectrometers could be densely field-deployed to simultaneously monitor, in real time, sources and sinks of greenhouse gases, industrial pollution or noxious emissions of motor vehicles

Phase calibration and uncertainty evaluation for a RF comb generator

Abstract: In this paper, we present calibration and uncertainty evaluation methods for the phase of a radio-frequency comb generator using a calibrated sampling oscilloscope. In addition, we present many sol...

Ultrafast electro-optic laser

Abstract: An ultrafast electro-optic laser makes a stabilized comb and includes: a comb generator that produces a frequency comb; a dielectric resonant oscillator; a phase modulator in communication with the dielectric resonant oscillator; an intensity modulator in communication with the phase modulator; an optical tailor in communication with the comb generator and that produces tailored light; a filter cavity in communication with the intensity modulator; a pulse shaper in communication with the filter cavity; a highly nonlinear fiber and compressor in communication with the pulse shaper; an interferometer in communication with the optical tailor and that produces a difference frequency from the tailored light; and an electrical stabilizer in communication with the interferometer and the comb generator and that produces the stabilization signal with a stabilized local oscillator cavity that produces a stabilized local oscillator signal that is converted into the stabilization signal and communicated to the dielectric resonant oscillator.

Chip-based frequency combs for wavelength-division multiplexing applications

Abstract: Optical frequency combs have the potential to become key building blocks of optical communication subsystems. In general, a frequency comb consists of a multitude of narrowband spectral lines that are strictly equidistant in frequency and that can serve both as carriers for massively parallel data transmission and as local oscillator tones for coherent reception. Recent experiments have demonstrated the viability of various comb generator concepts for communication applications. These comb generators must offer low phase noise and line spacings of several tens of gigahertz while being amenable to chip-scale integration into compact transceiver assemblies. Among the various approaches, so-called Kerr frequency combs stand out as a particularly promising option. Kerr comb generators exploit broadband parametric gain in Kerr-nonlinear microresonators and allow the providing of tens or even hundreds of tones from a single device. This chapter will describe advances regarding different types of chip-scale frequency comb sources and their use in optical communications with a special emphasis on high-performance Kerr frequency combs.

High-Resolution Dual-Comb Gas-Phase Spectroscopy with a Mode-Locked Laser on a Photonic Chip

Abstract: An integrated III-V-on-silicon mode-locked laser enables the first on-chip comb generator of 1.0-GHz line-spacing for direct interrogation of gas-phase narrow rovibrational transitions in molecules. Its flat-top spectrum empowers real-time multiplexed spectroscopy without any scanning elements.

Using an extracavity acousto-optic frequency modulator to stabilize the offset frequency of the fiber optical comb generator

Abstract: A fiber optical frequency comb generator stabilized to an optical frequency standard based on a single ytterbium ion (171Yb+) was created. An extracavity acousto-optic frequency modulator (AOFM) was used to stabilize the comb offset frequency. It allowed increasing the bandwidth of the feedback loop that stabilizes the offset frequency to several tens of kilohertz. The stabilization of the entire frequencies was achieved using an intracavity electro-optic modulator (EOM) based on a KTP crystal. This approach made it possible to minimize the noise that stabilization systems contribute to the output frequencies of the comb generator.

Characterization of a Josephson Junction Comb Generator

Abstract: We present a new type of microwave frequency combs with a potentially calculable pulse shape. The device is an array of 1500 Josephson junctions (JJs) connected in series along a transmission line. The pulse generation is based on the nonlinearity of the JJs. A large-signal network analyzer and a cryogenic probe station are used to characterize the pulses in the frequency domain up to 50 GHz. We compare the measured data to simulations that use the resistively and capacitively shunted JJ model. The amplitude stability of the demonstrated comb generator is better than 0.5 dB per 0.1 dB input drive variation within the operating range. Finally, we observe qualitative agreement between the measured and simulated power spectrum dependence on the input power, and discuss possible improvements to the system model.

Consideration to Terminating Condition of Mains Cable for Radiated Emission Measurement Caused by Different Disturbance Sources

Abstract: Very high frequency (VHF)-line impedance stabilization network (VHF-LISN), which is defined as the termination device for mains cable of equipment under test to specify the input impedance of each line at the mains power supply outlet, can improve correlation between test sites that perform radiated emission measurement. Balanced and unbalanced types of VHF-LISN are currently under proposal with International Special Committee on Radio Interference (CISPR) as a device for prescribing the terminating condition of the power supply cable. Simulation analysis with common mode (CM)/differential mode (DM) signal sources was performed to investigate the emission characteristics with the two types of termination devices under several measurement arrangements that used two-wire and three-wire mains cables. Furthermore, to confirm the validity of the simulation analysis, measurement of a versatile comb-generator-operated by ac mains was performed under the same test arrangement and two types of termination devices. Quasi CM/DM signal from an ac-operated comb generator was injected back into the mains cable of the same comb generator. This article explains how we ascertained the radiated emission characteristics with each termination device, and provides guidance for their appropriate usage.

Multi-channel system of quantum key distribution with frequency coding based on the AMPM-PMAM electro-optical scheme

Abstract: In this paper, we propose the option of constructing a multi-channel system of quantum key distribution with frequency coding based on the AMPM-PMAM electro-optical scheme, using a Comb generator, multiplexer and demultiplexer to form a set of parallel quantum subchannels. The AMPM-PMAM work of the QKD system is based on the modulation conversion of the photon carrier based on the Ilyin-Morozov method and its one- and two-modulator implementations. The application of this scheme will significantly increase the transmission speed of the quantum key, allow the use of several levels of cryptographic protection, reduce the likelihood of achieving a positive result in PNS attacks of Eve (illegal subscriber) by eliminating the carrier from the structure of the signal transmitted through the quantum key distribution channel, and splitting information about key to different independent quantum channels.

Low-phase noise microwave frequency comb generator with adjustable comb pitch

Abstract: The invention discloses a low-phase noise microwave frequency comb generator with an adjustable comb pitch. A continuous light signal generated by a laser enters an intensity modulator, and a modulation signal generated after modulation of a microwave source enters the intensity modulator to modulate the continuous light generated by the laser and then divides the continuous light into N paths oflight; optical injection locking is performed, namely different harmonic components are locked by using N DFB lasers, and the harmonic components enter corresponding photoelectric detectors respectively through an optical delay line and a long optical fiber in sequence to generate different beat frequency signals so as to generate frequency doubling microwave signals with different multiples; andeach path of microwave signal is fed back to the light intensity modulator after being amplified and filtered respectively, so that N mutually independent injection locking photoelectric oscillation loops are formed, and finally, the output of the microwave frequency comb is realized. All outputs have a fixed phase relationship, and the phase noise is very low. And the output of multi-frequency-point signals with unequal frequency intervals can be realized by adjusting each path of DFB laser.

Integrated electro-optic frequency comb generator

Abstract: An integrated electro-optic frequency comb generator based on ultralow loss integrated, e.g. thin-film lithium niobate, platform, which enables low power consumption comb generation spanning over a wider range of optical frequencies. The comb generator includes an intensity modulator, and at least one phase modulator, which provides a powerful technique to generate a broad high power comb, without using an optical resonator. A compact integrated electro-optic modulator based frequency comb generator, provides the benefits of integrated, e.g. lithium niobate, platform including low waveguide loss, high electro-optic modulation efficiency, small bending radius and flexible microwave design.