Showing papers on "Comb generator published in 2017"
22 Sep 2017
TL;DR: In this article, a microwave photonic intensity differentiator based on a Kerr optical comb generated by a compact integrated micro-ring resonator (MRR) is proposed and experimentally demonstrated.
Abstract: We propose and experimentally demonstrate a microwave photonic intensity differentiator based on a Kerr optical comb generated by a compact integrated micro-ring resonator (MRR). The on-chip Kerr optical comb, containing a large number of comb lines, serves as a high-performance multi-wavelength source for implementing a transversal filter, which will greatly reduce the cost, size, and complexity of the system. Moreover, owing to the compactness of the integrated MRR, frequency spacings of up to 200-GHz can be achieved, enabling a potential operation bandwidth of over 100 GHz. By programming and shaping individual comb lines according to calculated tap weights, a reconfigurable intensity differentiator with variable differentiation orders can be realized. The operation principle is theoretically analyzed, and experimental demonstrations of the first-, second-, and third-order differentiation functions based on this principle are presented. The radio frequency amplitude and phase responses of multi-order intensity differentiations are characterized, and system demonstrations of real-time differentiations for a Gaussian input signal are also performed. The experimental results show good agreement with theory, confirming the effectiveness of our approach.
157 citations
TL;DR: A demonstration of a III-V-on-Si comb laser that can function as a compact, low-cost frequency comb generator after frequency stabilization and the use of low-loss passive silicon waveguides enables the integration of a long laser cavity, which enables the laser to be locked in the passive mode at a record-low 1 GHz repetition rate.
Abstract: Optical frequency combs emerge as a promising technology that enables highly sensitive, near-real-time spectroscopy with a high resolution The currently available comb generators are mostly based on bulky and high-cost femtosecond lasers for dense comb generation (line spacing in the range of 100 MHz to 1 GHz) However, their integrated and low-cost counterparts, which are integrated semiconductor mode-locked lasers, are limited by their large comb spacing, small number of lines and broad optical linewidth In this study, we report a demonstration of a III-V-on-Si comb laser that can function as a compact, low-cost frequency comb generator after frequency stabilization The use of low-loss passive silicon waveguides enables the integration of a long laser cavity, which enables the laser to be locked in the passive mode at a record-low 1 GHz repetition rate The 12-nm 10-dB output optical spectrum and the notably small optical mode spacing results in a dense optical comb that consists of over 1400 equally spaced optical lines The sub-kHz 10-dB radio frequency linewidth and the narrow longitudinal mode linewidth (<400 kHz) indicate notably stable mode-locking Such integrated dense comb lasers are very promising, for example, for high-resolution and real-time spectroscopy applications
133 citations
TL;DR: In this article, the authors report the characterization of a quantum cascade laser frequency comb with an optical power of 1.05 µm at λ∼8.2 µm.
Abstract: In this work, we report the characterization of a quantum cascade laser frequency comb with an optical power of 1.05 W at λ∼8.2 μm. A 4.5 mm long device has a high reflectivity coating on the back facet as well as a top cladding designed to lower the group velocity dispersion and is operated at 258 K. Very strong (more than 60 dB) narrow beatnotes are shown, and frequency comb operation is obtained on a bandwidth of 85 cm−1 in a very large range of light-versus current characteristics. A bandwidth of 82 cm−1 has a power per mode of more than 1 mW and an average power per mode of 4.1 mW. Finally, a multi-heterodyne spectrum with 215 lines covering an optical bandwidth of more than 70 cm−1 measured with lasers showing similar performances is presented with very good line separation.
70 citations
TL;DR: In this paper, the authors used a 12 subcarrier comb generator, each of which is modulated by a quadrature-amplitude modulation (QAM) signal and achieved a 1.08 Tbps error free data rate with 3.6 b/s/Hz spectral efficiency.
Abstract: In contrast to traditional free space optical (FSO) systems, the new generation is aimed to be transparent to optical fiber where protocols, high signal bandwidths, and high data rates over fiber are all maintained. In this paper, we experimentally demonstrate a high speed outdoor full-optical FSO communication system over 100 m link. We first describe the design of our transmitter, which consists of a comb generator and a flexible multiformat transmitter. Our measurements are performed in arid desert area under a light dust storm. In this environment, we use a 12 subcarrier comb generator, each of which is modulated by a quadrature-amplitude modulation (QAM) signal. We achieved a 1.08 Tbps error free data rate with 3.6 b/s/Hz spectral efficiency. We place long optical fiber rolls in the transmitter side and the receiver side to mimic real FSO deployments. Furthermore, we investigated the effect of receiver misalignment in outdoor conditions and the effect of background noise. We find that full-optical FSO system is sensitive to the misalignment effect. However, the background noise has negligible effect. Finally, we find that solar heating of the transceiver causes collimator deviation, which requires using a cooling unit or auto tracking system.
63 citations
TL;DR: Optical frequency comb lines with poor carrier to noise ratio (CNR) are significantly improved by Brillouin amplification using its extreme narrow bandwidth gain to suppress out of band noise, enabling higher quality signal modulation.
Abstract: Optical frequency comb lines with poor carrier to noise ratio (CNR) are significantly improved by Brillouin amplification using its extreme narrow bandwidth gain to suppress out of band noise, enabling higher quality signal modulation. Its application to spectral lines of narrow 10 GHz pitch and poor CNR is shown to suppress the otherwise strong phase distortion caused by poor CNR after encoding with 96 Gb/s DP-64-QAM signals and restore the bit error rate (BER) to below the limit for standard forward error correction (FEC). This is also achieved with the required frequency shifted optical pump for amplification obtained by seeding it from the comb itself, sparing the need for lasers and frequency locking. Simultaneous CNR improvement for 38 comb lines is also achieved with BER restored to below the FEC limit, enabled by a multi-line pump that is pre-dispersed to suppress its spectral distortion from the Kerr effect in the gain medium. Carrier performance at minimum BER shows minimal noise impact from the Brillouin amplifier itself. The results highlight the unique advantage of Brillouin gain for phase sensitive communications in transforming otherwise noisy spectral lines into useful high quality signal carriers.
41 citations
TL;DR: It is demonstrated for the first time the stabilization of the fceo of such a PM Yb system with an in-loop fractional frequency stability scaled to an optical frequency of low 10-19 at 1 second averaging time, offering a great potential for applications in optical atomic clock metrology.
Abstract: We report the implementation of a self-referenced optical frequency comb generated by a passively mode-locked all polarization maintaining (PM) Yb fiber laser based on a nonlinear amplifying loop mirror (NALM). After spectral broadening the optical spectrum spans from 650 nm to 1400 nm, allowing for the generation of an optical octave and carrier envelope offset frequency (fceo) stabilization through a conventional f-2f interferometer. We demonstrate for the first time the stabilization of the fceo of such a PM Yb system with an in-loop fractional frequency stability scaled to an optical frequency of low 10-19 at 1 second averaging time, offering a great potential for applications in optical atomic clock metrology.
40 citations
TL;DR: A single-measurement sweep-free distributed Brillouin optical time domain analyzer (BOTDA) sensor based on phase detection based onphase detection is proposed and experimentally demonstrated employing digital optical frequency comb (DOFC) probe signal.
Abstract: A single-measurement sweep-free distributed Brillouin optical time domain analyzer (BOTDA) sensor based on phase detection is proposed and experimentally demonstrated employing digital optical frequency comb (DOFC) probe signal. Brillouin Phase Spectrum (BPS) of DOFC probe induced by Brillouin interaction is measured using coherent detection in a single acquisition, without any frequency scanning and data averaging. Single-measurement BOTDA sensor based on BPS in 10km long fiber is demonstrated with a response time of 100 μs, which is limited only by the fiber length. The spatial resolution is 51.2m, determined by the duration of DOFC. And the Brillouin frequency shift (BFS) uncertainty is estimated to be~1.5 MHz at the end of fiber under test (FUT). Benefiting from the fast response time, dynamic measurement up to 1 kHz vibration frequency has been demonstrated.
38 citations
TL;DR: An integrated heterodyne optical phase-locked loop was designed and demonstrated with an indium phosphide based photonic integrated circuit and commercial off-the-shelf electronic components.
Abstract: An integrated heterodyne optical phase-locked loop was designed and demonstrated with an indium phosphide based photonic integrated circuit and commercial off-the-shelf electronic components. As an input reference, a stable microresonator-based optical frequency comb with a 50-dB span of 25 nm (~3 THz) around 1550 nm, having a spacing of ~26 GHz, was used. A widely-tunable on-chip sampled-grating distributed-Bragg-reflector laser is offset locked across multiple comb lines. An arbitrary frequency synthesis between the comb lines is demonstrated by tuning the RF offset source, and better than 100Hz tuning resolution with ± 5 Hz accuracy is obtained. Frequency switching of the on-chip laser to a point more than two dozen comb lines away (~5.6 nm) and simultaneous locking to the corresponding nearest comb line is also achieved in a time ~200 ns. A low residual phase noise of the optical phase-locking system is successfully achieved, as experimentally verified by the value of -80 dBc/Hz at an offset of as low as 200 Hz.
32 citations
TL;DR: In this article, a fully stabilized mid-infrared optical frequency comb spanning from 2.9 to 3.4 µm is described, which is based on half-harmonic generation in a femtosecond optical parametric oscillator.
Abstract: A fully stabilized mid-infrared optical frequency comb spanning from 2.9 to 3.4 µm is described in this article. The comb is based on half-harmonic generation in a femtosecond optical parametric oscillator, which transfers the high phase coherence of a fully stabilized near-infrared Er-doped fiber laser comb to the mid-infrared region. The method is simple, as no phase-locked loops or reference lasers are needed. Precise locking of optical frequencies of the mid-infrared comb to the pump comb is experimentally verified at sub-20 mHz level, which corresponds to a fractional statistical uncertainty of 2 × 10−16 at the center frequency of the mid-infrared comb. The fully stabilized mid-infrared comb is an ideal tool for high-precision molecular spectroscopy, as well as for optical frequency metrology in the mid-infrared region, which is difficult to access with other stabilized frequency comb techniques.
28 citations
TL;DR: The high power efficiency and narrow beatnote linewidth will greatly expand the applications of quantum cascade laser frequency combs including high-precision remote sensing and spectroscopy.
Abstract: An efficient mid-infrared frequency comb source is of great interest to high speed, high resolution spectroscopy and metrology. Here we demonstrate a mid-IR quantum cascade laser frequency comb with a high power output and narrow beatnote linewidth at room temperature. The active region was designed with a strong-coupling between the injector and the upper lasing level for high internal quantum efficiency and a broadband gain. The group velocity dispersion was engineered for efficient, broadband mode-locking via four wave mixing. The comb device exhibits a narrow intermode beatnote linewidth of 50.5 Hz and a maximum wall-plug efficiency of 6.5% covering a spectral coverage of 110 cm-1 at λ ~ 8 μm. The efficiency is improved by a factor of 6 compared with previous demonstrations. The high power efficiency and narrow beatnote linewidth will greatly expand the applications of quantum cascade laser frequency combs including high-precision remote sensing and spectroscopy.
27 citations
TL;DR: This Letter proposes a straightforward and efficient method for electro-optic frequency comb generation with a small line spacing and a large span, based on two-stage modulation and sets up an easily established mutually coherent hybrid dual-comb interferometer, which is used to measure the absorption and dispersion profiles of the molecular transition of H13CN.
Abstract: An electro-optic frequency comb enables frequency-agile comb-based spectroscopy without using sophisticated phase-locking electronics. Nevertheless, dense electro-optic frequency combs over broad spans have yet to be developed. In this Letter, we propose a straightforward and efficient method for electro-optic frequency comb generation with a small line spacing and a large span. This method is based on two-stage modulation: generating an 18 GHz line-spacing comb at the first stage and a 250 MHz line-spacing comb at the second stage. After generating an electro-optic frequency comb covering 1500 lines, we set up an easily established mutually coherent hybrid dual-comb interferometer, which combines the generated electro-optic frequency comb and a free-running mode-locked laser. As a proof of concept, this hybrid dual-comb interferometer is used to measure the absorption and dispersion profiles of the molecular transition of H13CN with a spectral resolution of 250 MHz.
TL;DR: The device is fully characterized and generates a comb with frequency spacing ranging from 6 to 10 GHz, good noise properties that include relative intensity noise of <-130 dB/Hz and linewidth of 1.5 MHz, and a high phase correlation between comb lines.
Abstract: We report on an InP photonic integrated circuit for the generation of an externally injected gain switched optical frequency comb. The device is fully characterized and generates a comb with frequency spacing ranging from 6 to 10 GHz, good noise properties that include relative intensity noise of <−130 dB/Hz and linewidth of 1.5 MHz, and a high phase correlation between comb lines. These characteristics, in conjunction with the compactness and cost efficiency of the integrated device, demonstrate the quality of the resultant comb source for numerous applications.
TL;DR: An optical comb source that generates 550 ultra-narrow spectral lines with a spectral linewidth of 1.5-3 kHz, spanning over the C-band, originates from a single-mode Brillouin laser processed with phase modulation, pulse compression, and four-wave mixing.
Abstract: We demonstrate an optical comb source that generates 550 ultra-narrow spectral lines with a spectral linewidth of 1.5–3 kHz, spanning over the C-band. The source originates from a single-mode Brillouin laser processed with phase modulation, pulse compression, and four-wave mixing. As a result, the narrow linewidth of the Brillouin laser improves the phase noise of every spectral line of the frequency comb.
TL;DR: This study focuses on presenting a fully stabilized, self-referenced Yb:fiber frequency comb respectively phase locked to a microwave standard and an optical reference employing the highest, fundamental repetition rate of 750-MHz without additional external amplifiers and compressors.
Abstract: This study focuses on presenting a fully stabilized, self-referenced Yb:fiber frequency comb respectively phase locked to a microwave standard and an optical reference employing the highest, fundamental repetition rate of 750-MHz without additional external amplifiers and compressors. In addition, the challenge of phase locking the carrier envelop offset frequency for this high-repetition-rate fiber frequency comb is separately investigated in two schemes, namely, f-2f self-referencing and an approach of phase locking a beat note between the Yb: fiber frequency comb and a continuous wave laser.
TL;DR: The generation of high-coherence primary Kerr combs with multiple sub-lines by using dual pumps is experimentally generated and the application of a primary comb state in multichannel communications is demonstrated.
Abstract: We experimentally generate high-coherence primary Kerr combs with multiple sub-lines by using dual pumps and demonstrate the application of a primary comb state in multichannel communications. We find that more than 10 primary comb lines can be generated within the spectrum of modulation instability gain in our microring resonator. The generation is also verified by numerical simulations and the measured linewidth confirms the high coherence of the generated primary comb lines. We also demonstrate the high-coherence characteristics in a coherent communication experiment, in which each comb line is encoded with 20 Gbaud quadrature phase-shift-keyed signals.
TL;DR: In this article, a self-starting harmonic frequency comb with a THz repetition rate in a quantum cascade laser has been demonstrated and the mode spacing of the harmonic comb was shown to be uniform to within $5\times 10^{-12}$ parts of the central frequency using multiheterodyne self-detection.
Abstract: Optical frequency combs establish a rigid phase-coherent link between microwave and optical domains and are emerging as high-precision tools in an increasing number of applications. Frequency combs with large intermodal spacing are employed in the field of microwave photonics for radiofrequency arbitrary waveform synthesis and for generation of THz tones of high spectral purity in the future wireless communication networks. We demonstrate for the first time self-starting harmonic frequency comb generation with a THz repetition rate in a quantum cascade laser. The large intermodal spacing caused by the suppression of tens of adjacent cavity modes originates from a parametric contribution to the gain due to temporal modulations of the population inversion in the laser. The mode spacing of the harmonic comb is shown to be uniform to within $5\times 10^{-12}$ parts of the central frequency using multiheterodyne self-detection. This new harmonic comb state extends the range of applications of quantum cascade laser frequency combs.
TL;DR: It is found that the common mode and differential phases are uncorrelated, and for the first time for a QDLFC that the intrinsic differential-mode phase (IDMP) between adjacent subcarriers is substantially the same for all subcarrier pairs.
Abstract: We measure, simultaneously, the phases of a large set of comb lines from a passively mode locked, InAs/InP, quantum dot laser frequency comb (QDLFC) by comparing the lines to a stable comb reference using multi-heterodyne coherent detection. Simultaneity permits the separation of differential and common mode phase noise and a straightforward determination of the wavelength corresponding to the minimum width of the comb line. We find that the common mode and differential phases are uncorrelated, and measure for the first time for a QDLFC that the intrinsic differential-mode phase (IDMP) between adjacent subcarriers is substantially the same for all subcarrier pairs. The latter observation supports an interpretation of 4.4ps as the standard deviation of IDMP on a 200µs time interval for this laser.
TL;DR: An investigation of an InP quantum-well-based integrated extended cavity passively mode-locked laser which shows extra broad frequency comb generation and the coherence between the longitudinal modes in the wide comb is demonstrated.
Abstract: We present an investigation of an InP quantum-well-based integrated extended cavity passively mode-locked laser which shows extra broad frequency comb generation. The ring laser was characterized in frequency and time domains for a range of the current levels injected in the semiconductor optical amplifier. The study showed an increase of the bandwidth to over 40 nm at the -20 dB level. The coherence between the longitudinal modes in the wide comb is demonstrated by the characterization of a spectrally filtered signal in time and RF domains. The relative time delay across the optical comb was measured.
TL;DR: This work addresses comb spectrum processing on an integrated platform, pointing towards a device-compact solution for optical clock multipliers (frequency comb filters) which have diverse applications ranging from photonic-based RF spectrum scanners and photonic radars to GHz-granularity WDM switches and LIDARs.
Abstract: We report a photonic integrated circuit implementation of an optical clock multiplier, or equivalently an optical frequency comb filter. The circuit comprises a novel topology of a ring-resonator-assisted asymmetrical Mach-Zehnder interferometer in a Sagnac loop, providing a reconfigurable comb filter with sub-GHz selectivity and low complexity. A proof-of-concept device is fabricated in a high-index-contrast stoichiometric silicon nitride (Si3N4/SiO2) waveguide, featuring low loss, small size, and large bandwidth. In the experiment, we show a very narrow passband for filters of this kind, i.e. a −3-dB bandwidth of 0.6 GHz and a −20-dB passband of 1.2 GHz at a frequency interval of 12.5 GHz. As an application example, this particular filter shape enables successful demonstrations of five-fold repetition rate multiplication of optical clock signals, i.e. from 2.5 Gpulses/s to 12.5 Gpulses/s and from 10 Gpulses/s to 50 Gpulses/s. This work addresses comb spectrum processing on an integrated platform, pointing towards a device-compact solution for optical clock multipliers (frequency comb filters) which have diverse applications ranging from photonic-based RF spectrum scanners and photonic radars to GHz-granularity WDM switches and LIDARs.
TL;DR: In this paper, three-wave mixing is used to tune a broadband near infrared frequency comb into the mid-infrared using nonlinear spectral holography or quasi-periodic modulation.
Abstract: New methods to frequency down-convert a broadband near infrared frequency comb into the mid-infrared by three-wave mixing are studied. Modulation of the second-order nonlinear coefficient based on the concepts of either nonlinear spectral holography or quasi-periodic modulation enables us to obtain different spectral shapes of the mid-infrared comb. It includes flat and broadband single-band or dual-band spectra, or a shape that exhibits two or even three sharp peaks at chosen frequencies. The methods we present can be used to tailor the frequency comb spectra to selected molecular absorption lines in the mid-infrared.
14 May 2017
TL;DR: In this paper, an optical frequency comb with five lines having <0.86 dB intensity deviation and 10 GHz spacing was obtained using a silicon microring modulator and a microric resonator filter with only 3.6 Vpp driving voltage.
Abstract: An optical frequency comb with five lines having <0.86 dB intensity deviation and 10 GHz spacing is experimentally obtained using a silicon microring modulator and a microring resonator filter with only 3.6 Vpp driving voltage.
TL;DR: A compact, maintenance-free acetylene-stabilized fiber laser with a sub-kHz short-term linewidth and an Allan deviation below 3×10-13 for integration times above 1 s is developed.
Abstract: We demonstrate a significant improvement in the performance of a fiber-based frequency comb when a GPS-disciplined Rb clock is replaced with an acetylene-stabilized laser as the frequency reference. We have developed a compact, maintenance-free acetylene-stabilized fiber laser with a sub-kHz short-term linewidth and an Allan deviation below 3×10-13 for integration times above 1 s. Switching the comb reference from the Rb clock to the acetylene-stabilized laser improves both comb tooth linewidth and Allan deviation by about two orders of magnitude. Furthermore, long-term measurements of the acetylene-stabilized laser frequency with reference to the GPS-disciplined clock indicate a potential relative frequency uncertainty of 2 × 10-12.
TL;DR: A setup for high-resolution two-photon spectroscopy using a mid-infrared continuous wave optical parametric oscillator (CW-OPO) and a near-inf infrared diode laser as the excitation sources, both of which are locked to fully stabilized optical frequency combs.
Abstract: We report a setup for high-resolution two-photon spectroscopy using a mid-infrared continuous wave optical parametric oscillator (CW-OPO) and a near-infrared diode laser as the excitation sources, both of which are locked to fully stabilized optical frequency combs. The diode laser is directly locked to a commercial near-infrared optical frequency comb using an optical phase-locked loop. The near-infrared frequency comb is also used to synchronously pump a degenerate femtosecond optical parametric oscillator to produce a fully stabilized mid-infrared frequency comb. The beat frequency between the mid-infrared comb and the CW-OPO is then stabilized through frequency locking. We used the setup to measure a double resonant two-photon transition to a symmetric vibrational state of acetylene with a sub-Doppler resolution and high signal-to-noise ratio.
TL;DR: It is found that the cavity-induced phase noise suppression is strongest for high-order comb tones, e.g., reaching up to 40 dB for the 100th comb tone at high offset frequencies.
Abstract: We investigate for the first time, to the best of our knowledge, both theoretically and experimentally, how the phase noise of the radio frequency (RF) drive signal affects the phase noise of the individual tones of a Fabry–Perot (F–P) modulator-based optical frequency comb. We observe that the expected deleterious effect of the RF drive signal phase noise on the comb output is partially suppressed due to the filtering characteristics of the F–P cavity. We found that the cavity-induced phase noise suppression is strongest for high-order comb tones, e.g., reaching up to 40 dB for the 100th comb tone at high offset frequencies. The phase noise suppression becomes even stronger for low RF-drive powers, or when the seed laser does not resonate in the F–P cavity. For both cases, we observe up to a 10 dB increase in phase noise suppression. We also evaluate the timing jitter improvement obtained, thanks to the cavity-induced phase noise reduction. The timing jitter (integrated from 2.5 MHz to 2.5 GHz) decreased by a factor of 7 for the beat signal obtained between two comb tones that are 100 tones apart (in comparison with the timing jitter obtained in a cavity-less comb generator).
19 Mar 2017
TL;DR: The correlation properties of the phase noise between pairs of comb lines are determined for a quantum-dot frequency comb source laser through simultaneous measurements of the in-phase and quadrature components for each of the comb lines.
Abstract: The correlation properties of the phase noise between pairs of comb lines are determined for a quantum-dot frequency comb source laser through simultaneous measurements of the in-phase and quadrature components for each of the comb lines.
TL;DR: In this article, an erbium-based offset-free frequency comb using a fiber-coupled acousto-optic modulator is presented, where the offset frequency was stabilized at zero and measured by shifting it from zero.
Abstract: We demonstrate an erbium-based offset-free frequency comb using a fiber-coupled acousto-optic modulator. The comb has two f–2f interferometers; one is for carrier-envelope offset beat detection, and the other is for frequency-shifted offset beat detection. The frequency was shifted by placing the acousto-optic modulator in front of an amplifier and a highly nonlinear fiber for spectral broadening. We confirmed that the offset frequency was stabilized at zero and measured it by shifting it from zero. The Allan deviations of the measured offset frequency were 0.10 and 0.18 Hz with a 1 s averaging time and using feedback and feed-forward stabilization, respectively.
TL;DR: In this paper, a self-oscillating optical frequency comb using a Raman-pumped Brillouin optoelectronic oscillator was demonstrated, and the authors used a 7-line optical comb with 2.7 dB variation of 10.89 GHz spacing with a phase noise of -93 dBc/Hz at 10 kHz offset.
Abstract: We demonstrate the generation of a self-oscillating optical frequency comb using a Raman-pumped Brillouin optoelectronic oscillator. In this scheme, stimulated Brillouin scattering is utilized as a frequency selective component. Due to the narrow gain bandwidth of stimulated Brillouin scattering, which is ~30 MHz in a single mode fiber with about 11 GHz frequency shift, microwave signal with very low phase noise can be generated. Thus, the optical comb driven by this optoelectronic oscillator is highly coherent. In our experiment, a 7-line optical comb with 2.7 dB variation of 10.89 GHz spacing is obtained with a phase noise of -93 dBc/Hz at 10 kHz offset.
TL;DR: In this paper, a tunable ultraflat optical frequency comb generator based on the optoelectronic oscillator (OEO) using a dual-parallel Mach-Zehnder modulator (DPMZM) is proposed and experimentally demonstrated.
Abstract: A tunable ultraflat optical frequency comb generator based on the optoelectronic oscillator (OEO) using a dual-parallel Mach–Zehnder modulator (DPMZM) is proposed and experimentally demonstrated. By incorporating a tunable DPMZM-OEO, five comb lines were generated with frequency spacing from 5 to 12 GHz under a wide central wavelength tuning from 1530 to 1560 nm, and a comb flatness of 0.3 dB is obtained. The corresponding signal generated by the DPMZM-OEO is also measured, and the phase noise of the frequency tunable signals is as low as −125 dBc/Hz at 10-kHz frequency offset.
TL;DR: In this paper, a measurement technique that exploits the high coherent controllability of multi-comb systems was proposed, which corresponds to a generalization of the frequency control between the comb sources.
Abstract: We propose a novel measurement technique that exploits the high coherent controllability of multi-comb systems, which corresponds to a generalization of the frequency control between the comb sources. In this paper, we particularly focus on the arbitrary relative carrier envelope phase (CEP) control through the relative offset frequency of two combs. We successfully demonstrate polarization-modulated comb generation and its coherent detection in the developed system. The proof-of-principle experiment indicates the potential of multi-comb systems, enabling a rapid, precise, and arbitrary coherent modulation method utilized for a wide variety of metrological applications.
TL;DR: In this paper, a monolithic solution to extract efficiently light from terahertz quantum cascade lasers with metal-metal waveguides suitable for broadband frequency comb applications is presented. But the design is optimized for a bandwidth of 400 GHz around a center frequency of 2.5 GHz.
Abstract: We present a monolithic solution to extract efficiently light from terahertz quantum cascade lasers with metal-metal waveguides suitable for broadband frequency comb applications. The design is optimized for a bandwidth of 400 GHz around a center frequency of 2.5 THz. A five-fold increase in total output power is observed compared to standard metal-metal waveguides. The extractor features a single-lobed far-field pattern and increases the frequency comb dynamical range to cover more than 50% of the laser dynamic range. Frequency comb operation up to a spectral bandwidth of 670 GHz is achieved.