Tunable optical comb generation based on carrier-suppressed intensity modulation and phase modulation

<正>An approach to generate a flat optical comb with tunable comb spacing and adjustable comb number is proposed.In the proposed approach,a Mach-Zehnder modulator(MZM),being biased to generate two carrier-suppressed first-order sidebands,is cascaded with a phase modulator.The two optical sidebands are then sent to the phase modulator to generate two identical,but frequency-shifted phase-modulated spectra.Thanks to the complementary nature of the two adjacent comb lines in the phase-modulated spectra,the overlapping of the two spectra would lead to the generation of a flat optical comb.Since only the phase modulation index or the microwave power is needed to be adjusted,the system is easy to be implemented with tunable comb spacing and adjustable comb number.Numerical simulations are performed,and the approach is verified by an experiment.     

Flat-top optical frequency comb generation based on optical fiber-loop modulation with external injection

An optical frequency comb generation scheme using time-to-frequency conversion and optical fiber-loop modulation is proposed and demonstrated experimentally. Flat-top optical pulse train from an intensity modulator is injected into a fiber loop, which includes a phase modulator and an amplifier and is cyclically modulated by the phase modulator, to generate abundant optical comb lines. A total of 110 comb lines with 3-dB spectral power variation and 10-GHz frequency spacing are obtained. The proposed scheme is relatively simple and uses only one intensity modulator and one phase modulator.     

Frequency comb generation using femtosecond pulses and cross-phase modulation in optical fiber at arbitrary center frequencies

A technique is presented for generating optical frequency combs centered at arbitrary wavelengths by use of cross-phase modulation (XPM) between a femtosecond pulse train and a cw laser beam by copropagating these signals through an optical fiber. We report results from use of this method to place a 90-MHz frequency comb on an iodine-stabilized Nd:YAG laser at 1064 nm and on a frequency-doubled Nd:YVO(4) laser at 532 nm. XPM is verified to be the comb-generating process, and the width of the frequency comb is measured and compared with theory. The spacing of the frequency comb is compared with the femtosecond source, and a frequency measurement with this comb is demonstrated.     

Wideband optical comb generation using an injection-locked feedback loop

This paper presents a novel circuit for wideband optical comb generation which will be useful in DWDM applications. The injection-locked feedback loop broadens the bandwidth of the optical comb. The injection-locked laser diodes perform amplification, bandpass filtering as well as laser RIN suppression. Several hundred GHz bandwidth optical comb can be generated by this circuit within a reasonable power envelope.     

All optical arbitrary waveform generation by optical frequency comb based on cascading intensity modulation

We propose and experimentally demonstrate an all optical arbitrary waveform generation by optical frequency comb (OFC) based on cascading intensity modulation. By selecting spectral lines of interest from OFC through optical filters, 10 GHz, 20 GHz, and 60 GHz sinusoidal signals with low phase noise and more complex waveforms, including ultra-short pulse, half-wave cosine, and single frequency modulated MMW signals, are generated easily.     

Frequency comb generation and carrier-envelope phase control in femtosecond optical parametric oscillators

We describe progress in the measurement and control of the carrier-envelope phase-slip frequencies of pulses generated by a femtosecond optical parametric oscillator. Example applications of such control are presented and include the generation of a frequency comb spanning nearly three optical octaves, and the creation of a train of 30-fs pulses via coherent pulse synthesis. Future prospects for frequency combs based on femtosecond optical parametric oscillators are discussed.     

Optical frequency comb generation using a quasi-velocity-matched Fabry-Perot phase modulator

We report about the optical frequency comb generation by means of a bulk type phase modulator with periodic domain inversion. The phase modulator operates as a quasi-velocity-matched electro-optical phase modulator having high modulation efficiency. It is possible to generate a broadband optical frequency comb by using the modulator installed into an Fabry-Perot resonator. In this experiment, we made the quasi-velocity-matched phase modulator and then used it to generate the efficient optical frequency comb. From this result, we could confirm operation characteristics of the optical frequency comb and the utility of the phase modulator respectively.     

Accuracy of optical frequency comb generation in optical fiber

We evaluated the accuracy of an optical frequency comb in optical fibers by measuring the frequency shift after a sideband from an electro-optic modulator had passed through the fiber. We found that a frequency drift of a few hertz was due largely to a variation in the ambient temperature that corresponded to an increase in the square root of the Allan variance to 0.66 Hz.     

低相噪光学频率梳

光学频率梳是光钟的重要组成部分,相噪是光梳的基本特性。文章从光梳相噪的描述方法入手,对光学频率梳相噪产生的几种常见来源及相噪抑制技术进行了综述,详细介绍了业已实现的几种低相噪光学频率梳。文末展望了未来低相噪光学频率梳的发展新趋势。     

Asymptotic formalism for ultraflat optical frequency comb generation using a Mach-Zehnder modulator

We theoretically prove that a conventional Mach-Zehnder modulator can generate an optical frequency comb with excellent spectral flatness. The modulator is asymmetrically dual driven by large amplitude sinusoidal signals with different amplitudes. The driving condition to obtain spectral flatness is analytically derived and optimized, yielding a simple formula. This formula also predicts the conversion efficiency and bandwidth of the generated frequency comb.     

Multi-wavelength pulse generation using flattop optical frequency comb and arrayed waveguide grating

A scheme of multi-wavelength pulse generator using optical frequency comb and arrayed waveguide grating (AWG) is proposed and experimentally demonstrated. A flattop optical frequency comb is shaped into multiple narrowband Gaussian spectra by using an AWG which contains a number of Gaussian channels, and then multi-wavelength optical pulses are achieved. In the experiment, six wavelength pulses with full width at half-maximum (FWHM) of 14.6 ps at 10 GHz are obtained, and two wavelength-interleaved pulse trains at 20 GHz and four wavelength-interleaved pulse trains at 40 GHz are demonstrated by using the multi-wavelength optical pulses. This scheme has flexibility because the pulse width, the repetition rate, and time-interval can be readily controlled.     

Broadband second harmonic generation of an optical frequency comb produced by four-wave mixing in highly nonlinear fibers

We demonstrate broadband second harmonic generation of low-energy pulses produced by injecting two single-frequency lasers into a highly nonlinear fiber. Full nonlinear conversion of the corresponding spectra, consisting of broadband (∼200 nm) optical frequency combs at ∼1580 nm, were obtained by using conventional birefringence phase-matching in two BIBO crystals (2-mm and 100-μm long) with a normal incidence configuration. The crystals were not tilted and the pulses were not compressed. This broadband conversion results from the large phase-matching bandwidth of the nonlinear BIBO crystals at ∼1550 nm, but also seems to be a consequence of a fundamental comb with small spectral phase variation.     

Dispersion compensation for terahertz optical frequency comb generation

We demonstrate dispersion compensation in a terahertz-span optical frequency comb generator by use of an intracavity prism pair. With partial compensation of the material dispersion of the lithium niobate modulator, the span of the comb increases from 3.0 to 4.3THz.     

Terahertz optical frequency comb generation with optimized cascaded difference frequency generation

Optical Review - A novel scheme that generates terahertz optical frequency comb (THz OFC) based on optimized cascaded difference frequency generation (OCDFG) with an aperiodically poled lithium...     

Ultrawideband monocycle generation using cross-phase modulation in a semiconductor optical amplifier

We propose a novel scheme to generate ultrawideband (UWB) monocycle pulses based on cross-phase modulation (XPM) of a semiconductor optical amplifier (SOA). The proposed system consists of a SOA and an optical bandpass filter (OBF). Due to the XPM, a continuous wave (CW) probe signal is phase modulated by another optical Gauss pulse in the SOA. The OBF will convert the phase modulation to intensity modulation. A pair of polarity-reversed UWB monocycle pulses is achieved by locating the probe carrier at the positive and negative linear slopes of the OBF. Both cases conform to the UWB definition of the Federal Communications Commission.     

Optoelectronic oscillator using a LiNbO3 phase modulator for self-oscillating frequency comb generation

Optical frequency comb generation by using a novel optoelectronic oscillator (OEO) is proposed and demonstrated with the emphasis placed on self-oscillating operation. In the OEO, a wideband LiNbO3 phase modulator is driven with a large-amplitude radio-frequency (RF) feedback signal to generate a deeply phase-modulated light wave; accordingly, an optical frequency comb with a bandwidth greater than the RF signal is generated by self-oscillation. Although it generates multifrequency components, the OEO exhibits characteristics of a single-mode oscillator. Its operation is stable and self-starting. An optical frequency comb with a 120 GHz bandwidth and 9.95 GHz frequency spacing was successfully generated by self-oscillation at a single frequency.     

Efficient multi-frequency generation of ultrashort light pulses using stimulated Raman scattering and optical parametric amplification

Optical parametric amplification of multi-frequency seed pulses generated in a mixture of compressed hydrogen and methane by stimulated Raman scattering of 1 ps, 1 kHz laser pulses at 395.8 nm has been studied. Efficient generation of spectrally narrow ultrashort pulses with a spatial distribution close to the Gaussian profile of the pump beam was obtained in the visible and near infrared ranges.     

Second harmonic generation in birefringent optical fibers

Second harmonic generation in optical fibers is investigated. A scheme to combine material, modal and geometrical dispersion to achieve phase matching is proposed. Conversion efficiency, as a function of the fiber's parameters and the incoming electric field strength, is computed.     

Generation of flat optical frequency comb by fiber loop modulation

We propose a novel flat optical frequency comb generation system that employs fiber loop modulation and experimentally demonstrate its operation. Generally, when an external laser beam is injected into a fiber loop system including an optical modulator and an amplifying medium, multiple sidebands are generated exponentially. On the other hand, the fiber loop starts mode-locked oscillation at a center frequency to maximize the round-trip gain in the fiber loop from the seeds of the injected laser sidebands. By locking the sidebands from fiber loop modulation with the mode-locked oscillation in the fiber loop, the synchronous spectrum between the mode-locked oscillation and the sidebands can be shaped into a flat spectrum. Thus, a flat optical frequency comb with a flatness of about ±1 dB is obtained in the spectral bandwidth of about 1 THz.     

High-resolution spectroscopy based on optical phase modulator and optical frequency comb

A phase modulation of an optical frequency comb has been applied to measure a fine spectrum in the 1.5 μm wavelength range by the optical heterodyne-detection method. The measurement frequency range covered 25 GHz, which satisfies the frequency interval of the optical frequency comb, with a spectral resolution of 1 MHz.