Broadband Optical Frequency Comb Generation Research Articles

Broadband Optical Frequency Comb Generation Based on a Dual-Pumped Brillouin-Erbium Fiber Laser

Broadband Optical Frequency Comb Generation Based on a Dual-Pumped Brillouin-Erbium Fiber Laser

Flexible broadband optical frequency comb generation assisted by injection locking of semiconductor laser

A broadband optical frequency comb (OFC) generator is proposed and experimentally demonstrated. Based on the injection locking process in a semiconductor laser diode, multiple coherent carriers with large intervals can be generated, which are further combined to give a much broader OFC through the electro-optical modulation (EOM) technique. The corresponding theoretical analysis and simulation have been given in detail. In the experimental demonstration, an OFC with 9 comb lines can be generated on a single carrier by the cascaded MZMs with a multi-harmonic RF drive signal. After tripling the number of carriers, the number of the comb lines becomes 27. By properly adjusting the carrier’s interval and drive signal frequency, the generated OFC shows great flexibility on spacing and the number of comb lines, where a 27-line OFC with FSR of 5 GHz and 6.5 GHz have been demonstrated respectively. In addition, by increasing the number of RF sources, the OFC with up to 43 comb lines can be generated in this system. Compared with the traditional OFC generation implemented by the EOM technique on a single optical carrier, three times optical spectrum extension or the number of comb lines increasing can be achieved. The Multi-carrier broaden spectrum method retains all the advantages of EOM-based OFC generation and overcomes its disadvantages, such as limited spectrum width and the number of comb lines. It provides a new idea for broadband OFC generation.

Broadband optical frequency comb generation based on single electro-absorption modulation driven by radio frequency coupled signals

Broadband optical frequency comb (OFC) generation based on a single electro-absorption modulator (EAM) is proposed. The EAM is driven by a radio frequency (RF) multi-frequency signal generated by a multiplication coupler composed of an electrical power splitter and an arithmetic circuit. Thus the number of comb-lines of the generated OFC can be increased. A complete theoretical model of OFC generation by an EAM driven by nth power of the RF source is established, and the performance of the OFC is analyzed by using OptiSystem software. The results show that, the number of comb-lines of the OFC is positively correlated with the number of multiplication of the RF source signal. The frequency spacing of the comb-lines is twice the frequency of the RF source signal and is tunable by adjusting the frequency of the RF source signal. Increasing chirp factor and modulation index of EAM could increase the number of comb-lines of the generated OFC. The amplitude of the RF source signal had little impact on the flatness of the OFC and the average OFC power. The scheme developed is not only simple and low-cost, but also can produce a large number of comb-lines.Graphical

Design of Broadband Flat Optical Frequency Comb Based on Cascaded Sign-Alternated Dispersion Tellurite Microstructure Fiber.

We designed a tellurite microstructure fiber (TMF) and proposed a broadband optical frequency comb generation scheme that was based on electro-optical modulation and cascaded sign-alternated dispersion TMF (CSAD-TMF). In addition, the influence of different nonlinear effects, the ultrashort pulse evolution in the CSAD-TMF with the anomalous dispersion (AD) zones and the normal dispersion (ND) zones were analyzed based on the generalized nonlinear Schrodinger equations (GNLSE) modelling. According to the simulations, when the input seed comb had a repetition rate of 20 GHz and had an input pulse peak power of 30 W, the generation scheme could generate optical frequency combs with a 6 dB spectral bandwidth spanning over 170 nm centered at 1550 nm. Furthermore, the generated combs showed good coherence in performance over the whole 6 dB spectral bandwidth. The highly coherent optical frequency combs can be used as high-repetition-rate, multi-wavelength light sources for various integrated microwave photonics and ultrafast optical signal processing applications.

10-GHz broadband optical frequency comb generation at 1550/1310 nm

The generation of high-repetition rate (frep ≥ 10 GHz) ultra-broadband optical frequency combs (OFCs) at 1550 nm and 1310 nm is investigated by seeding two types of highly nonlinear fibers (HNLFs) with 10 GHz picosecond pulses at the pump wavelength of 1550 nm. When pumped near the zero dispersion wavelength (ZDW) in the normal dispersion region of a HNLF, 10 GHz flat-topped OFC with 43 nm bandwidth within 5 dB power variation is generated by self-phase modulation (SPM)-based OFC spectral broadening at 26.5 dBm pump power, and 291 fs pulse trains with 10 GHz repetition rate are obtained at 18 dBm pump power without complicated pulse shaping methods. Furthermore, when pumped in the abnormal dispersion region of a HNLF, OFCs with dispersive waves around 1310 nm are studied using a common HNLF and fluorotellurite fibers, which maintain the good coherence of the pump light at 1550 nm. At the same time, sufficient tunability of the generated dispersive waves is achieved when tuning the pump power or ZDW.

Graphene-decorated microfiber knot as a broadband resonator for ultrahigh-repetition-rate pulse fiber lasers

Searching for an ultrahigh-repetition-rate pulse on the order of hundreds of gigahertz (GHz) is still a challenging task in the ultrafast laser community. Recently, high-quality silicon/silica-based resonators were exploited to generate a high-repetition-rate pulse based on the filter-driven four-wave mixing effect in fiber lasers. However, despite their great performance, the silicon/silica-based resonators still have some drawbacks, such as single waveband operation and low coupling efficiency between the fiber and resonators. To overcome these drawbacks, herein we proposed an all-fiber broadband resonator fabricated by depositing the graphene onto a microfiber knot. As a proof-of-concept experiment, the graphene-deposited broadband microfiber knot resonator (MKR) was applied to Er- and Yb-doped fiber lasers operating at two different wavebands, respectively, to efficiently generate hundreds-of-GHz-repetition-rate pulses. Such a graphene-deposited broadband MKR could open some new applications in ultrafast laser technology, broadband optical frequency comb generation, and other related fields of photonics.

Deuterated silicon nitride photonic devices for broadband optical frequency comb generation.

We report and characterize low-temperature, plasma-deposited deuterated silicon nitride films for nonlinear integrated photonics. With a peak processing temperature less than 300°C, it is back-end compatible with complementary metal-oxide semiconductor substrates. We achieve microresonators with a quality factor of up to 1.6×106 at 1552nm and >1.2×106 throughout λ=1510-1600 nm, without annealing or stress management (film thickness of 920nm). We then demonstrate the immediate utility of this platform in nonlinear photonics by generating a 1THz free-spectral-range, 900nm bandwidth modulation-instability microresonator Kerr comb and octave-spanning, supercontinuum-broadened spectra.

Broadband optical frequency comb generator based on driving N-cascaded modulators by Gaussian-shaped waveform

A new approach for realizing a wideband optical frequency comb (OFC) generator based on driving cascaded modulators by a Gaussian-shaped waveform, is proposed and numerically demonstrated. The setup includes N-cascaded MZMs, a single Gaussian-shaped waveform generator, and N-1 electrical time delayer. The first MZM is driven directly by a Gaussian-shaped waveform, while delayed replicas of the Gaussian-shaped waveform drive the other MZMs. An analytical model that describes the proposed OFC generator is provided to study the effect of number and chirp factor of cascaded MZM as well as pulse width on output spectrum. Optical frequency combs at frequency spacing of 1 GHz are generated by applying Gaussian-shaped waveform at pulse widths ranging from 200 to 400 ps. Our results reveal that, the number of comb lines is inversely proportional to the pulse width and directly proportional to both number and chirp factor of cascaded MZMs. At pulse width of 200 ps and chirp factor of 4, 67 frequency lines can be measured at output spectrum of two-cascaded MZMs setup. Whereas, increasing the number of cascaded stages to 3, 4, and 5, the optical spectra counts 89, 109 and 123 frequency lines; respectively. When the delay time is optimized, 61 comb lines can be achieved with power fluctuations of less than 1 dB for five-cascaded MZMs setup.

Ultraflat and broadband optical frequency comb generator based on cascaded two dual-electrode Mach–Zehnder modulators

A novel scheme for the generation of ultraflat and broadband optical frequency comb (OFC) is proposed based on cascaded two dual-electrode Mach–Zehnder modulators (DE-MZM). The first DE-MZM can generate a four-comb-line OFC, then the OFC is injected into the second DE-MZM as a carrier, which can increase the number of comb lines. Our modified scheme finally can generate a broadband OFC with high flatness by simply modifying the electrical power and the bias voltage of the DE-MZM. Theoretical analysis and simulation results reveal that a 16-comb-line OFC with a frequency spacing that two times the frequency of the RF signal can be obtained. The power fluctuation of the OFC lines is 0.48 dB and the unwanted-mode suppression ratio (UMSR) can reach 16.5 dB. Additionally, whether the bias drift of the DE-MZMs has little influence on the power fluctuation is also analyzed. These results demonstrate the robustness of our scheme and verify its good accuracy and high stability with perfect flatness.

Simple and seamless broadband optical frequency comb generation using an InAs/InP quantum dot laser.

A simple and seamless broadband optical frequency comb (OFC) generator is proposed and experimentally demonstrated using a Fabry-Perot quantum dot mode-locked laser combined with a dual-driven LiNbO₃ Mach-Zehnder modulator driven by a low-power radio frequency (RF) signal. It is experimentally demonstrated that the 10-dB seamless bandwidth of the OFC is 8.2 nm (1.02 THz), which has 62 and 40 comb lines for frequency intervals of 16.56 GHz and 24.84 GHz, respectively. The single-sideband phase noise is as low as -112 and -108 dBc/Hz at an offset of 10 kHz, respectively, for the photodetector-converted 16.56 and 24.84 GHz frequency carriers. Correspondingly, the RF linewidths of the 16.56 GHz and 24.84 GHz carriers are about 251 Hz-263 Hz, respectively. Using a QD laser, an ultra-low phase noise and quasi-tunable broadband OFC generator is obtained easily.

A flat and broadband optical frequency comb with tunable bandwidth and frequency spacing

A flat and broadband optical frequency comb generator based on two cascaded intensity modulators is proposed and experimentally demonstrated. In this scheme, we first use even or odd harmonic sidebands to generate optical frequency comb, so the bandwidth can be improved. By adjusting the power of the microwave signals and the direct current bias applied to the modulators, a flat and broadband optical frequency comb can be achieved. The scheme is relatively simple and adjustable, where the frequencies spacing vary with microwave frequency applied on modulators. 15 and 20 comb lines with the comb flatness within 1dB can be generated. The generated spectrums can meet the requirement of OFDM modulation, and can be used for high capacity optical transmission systems in the future.

Low-noise and broadband optical frequency comb generation based on an optoelectronic oscillator

A novel scheme to generate broadband high-repetition-rate optical frequency combs and low phase noise microwave signals simultaneously is proposed and experimentally demonstrated. By incorporating an optical frequency comb generator in an optoelectronic oscillator loop, more than 200 lines are generated for a 25 GHz optical frequency comb, and the single-sideband phase noise is as low as -122 dBc/Hz at 10 kHz offset for the 25 GHz microwave signal. 10 and 20 GHz optical frequency combs and microwave signals are also generated. Unlike the microwave frequency synthesizer, the phase noise of the microwave signals generated by this new scheme is frequency independent.

Frequency comb assisted diode laser spectroscopy for measurement of microcavity dispersion

While being invented for precision measurement of single atomic transitions, frequency combs have also become a versatile tool for broadband spectroscopy in the last years. In this paper we present a novel and simple approach for broadband spectroscopy, combining the accuracy of an optical fiber-laser-based frequency comb with the ease-of-use of a tunable external cavity diode laser. This scheme enables broadband and fast spectroscopy of microresonator modes and allows for precise measurements of their dispersion, which is an important precondition for broadband optical frequency comb generation that has recently been demonstrated in these devices. Moreover, we find excellent agreement of measured microresonator dispersion with predicted values from finite element simulations and we show that tailoring microresonator dispersion can be achieved by adjusting their geometrical properties.

Broadband optical frequency comb generation with a phase-modulated parametric oscillator

We introduce a novel broadband optical frequency comb generator consisting of a parametric oscillator with an intracavity electro-optic phase modulator. The parametric oscillator is pumped by 532-nm light and produces near-degenerate signal and idler fields. The modulator generates a comb structure about both the signal and the idler. Coupling between the two families of modes results in a dispersion-limited comb that spans 20 nm (5.3 THz). A signal-to-noise ratio of >30 dB in a 300-kHz bandwidth is observed in the beat frequency between individual comb elements and a reference laser.