Stepped-Frequency THz-Wave Signal Generation From a Kerr Microresonator Soliton Comb.

IEEE/OSA Journal of Lightwave Technology


Solving multi-armed bandit problems using a chaotic microresonator comb


Wireless data transmission in the 560-GHz band utilizing terahertz wave generated through photomixing of a pair of distributed feedback lasers injection-locking to a Kerr micro-resonator soliton comb


Carrier conversion from terahertz wave to dual-wavelength near-infrared light for photonic terahertz detection in wireless communication


Terahertz wireless communication in a 560-GHz band using a Kerr micro-resonator soliton comb


Low phase noise THz generation from a ber-referenced Kerr microresonator soliton comb


Thermal control of a Kerr microresonator soliton comb via an optical sideband

We report the thermal control of a dissipative Kerr microresonator soliton comb via an optical sideband generated from an electro-optic modulator. Same as the previous reports using an independent auxiliary laser, our sideband-based (S-B) auxiliary light also enables access to a stable soliton comb and reduces the phase noise of the soliton comb, greatly simplifying the set-up with an auxiliary laser. More importantly, because of the intrinsically high frequency/phase correlation between the pump and S-B auxiliary light, the detuning between the pump and resonance frequency is automatically almost fixed, which allows an 18 times larger "effective" soliton existence range than the conventional method using an independent auxiliary laser, as well as a scanning of the soliton comb of more than 10 GHz without using microheaters.


Amplification and phase noise transfer of a Kerr microresonator soliton comb for low phase noise THz generation with a high signal-to-noise ratio

Optical injection locking is implemented to faithfully transfer the phase noise of a dissipative Kerr microresonator soliton comb in addition to the amplification of the Kerr comb. Unlike Er-doped fiber and semiconductor optical amplifiers, the optical injection locking amplifies the comb mode without degrading the optical signal-to-noise ratio. In addition, we show that the residual phase noise of the optical injection locking is sufficiently small to transfer the relative phase noise of comb modes (equivalent to the repetition frequency) of low phase noise Kerr combs, concluding that the optical injection locking of a Kerr comb can be an effective way to generate low phase noise terahertz (THz) waves with a high signal-to-noise ratio through an optical-to-electronic conversion of the Kerr comb.


Frequency-scanned microresonator soliton comb with tracking of the frequency of all comb modes

Rapid and large scanning of a dissipative Kerr-microresonator soliton comb with characterization of all comb modes along with the separation of the comb modes is imperative for the emerging applications of frequency-scanned soliton combs. However, the scan speed is limited by the gain of feedback systems, and measurement of the frequency shift of all comb modes has not been demonstrated. To overcome the limitation of the feedback, we incorporate feedback with feedforward. With an additional gain of >40 by a feedforward signal, a dissipative Kerr-microresonator soliton comb is scanned by 70 GHz in 500µ, 50 GHz in 125µ, and 25 GHz in 50µ (= 500 THz/s). Furthermore, we propose and demonstrate a method to measure the frequency shift of all comb modes, in which an imbalanced Mach-Zehnder interferometer with two outputs with different wavelengths is used. Because of the two degrees of freedom of optical frequency combs, the measurement at two different wavelengths enables estimation of the frequency shift of all comb modes.


Investigation of the phase noise of a microresonator soliton comb

Optical frequency combs generated from microresonators (especially microresonator soliton combs) have been attracting significant attentions because of the potential to be fully chip-scale. Among various promising applications of soliton combs, coherent optical communications and mm/THz wireless communications require low phase noise of the comb modes and low relative phase noise between the comb modes, respectively. Here, we measure the phase noise of a soliton comb, investigating how the thermorefractive noise of a microresonator influences on the phase noise. We observe the quadratic increase of the phase noise of the comb modes, as the comb mode number, counted from the wavelength of a pump cw laser, increases. In addition, we measure the relative phase noise between the comb modes, showing less influence of the phase noise of pump cw lasers by comparing soliton combs generated from pump cw lasers with low and large phase noise.


300-GHz-band wireless communication using a low phase noise photonic source

International Journal of Microwave and Wireless Technologies


Continuous scanning of a dissipative Kerr-microresonator soliton comb for broadband, high-resolution spectroscopy

Dissipative Kerr-microresonator soliton combs (hereafter called soliton combs) are promising to realize chip-scale integration of full soliton comb systems providing high precision, broad spectral coverage, and a coherent link to the micro/mm/THz domain with diverse applications coming on line all the time. However, the large soliton comb spacing hampers some applications. For example, for spectroscopic applications, there are simply not enough comb lines available to sufficiently cover almost any relevant absorption features. Here, we overcome this limitation by scanning the comb mode spacing by employing Pound-Drever-Hall locking and a microheater on the microresonator, showing continuous scanning of the soliton comb modes across nearly the full free-spectral range of the microresonator without losing soliton operation, while spectral features with a bandwidth as small as 5 MHz are resolved.


Generation of a microresonator soliton comb via current modulation of a DFB laser


Frequency-modulated continuous-wave LIDAR (FMCW LIDAR) has been widely used for both scientific and industrial tools. Here, in this report, a new class of LIDAR technique based on an optical frequency comb, named frequency-modulated comb LIDAR (FMcomb LIDAR), is proposed. Instead of using one carrier such as FMCW LIDAR, the multiple carriers from an optical frequency comb are used in FMcomb LIDAR. Because of the correlation between comb modes, each frequency-scanned comb mode can be coherently stitched, thus allowing for a resolution equivalent to scanning by many comb modes while scanning only by the comb mode spacing. In a proof-of-concept experiment, three comb modes from an electro-optic frequency comb (EO comb) are coherently stitched, showing Fourier-transform limited resolution (defined as FWHM linewidth) of 10 ps (i.e., 1.5 mm in air) for about 65 ns delay. The obtained resolution is three-times higher than that of conventional FMCW LIDAR when the same scan range is considered.


Control of Kerr-microresonator optical frequency comb by a dual-parallel Mach-Zehnder interferometer

A technique to integrate key functions of a Kerr-microresonator optical frequency comb into one device, i.e., a dual-parallel Mach-Zehnder interferometer (DP-MZI), is proposed. In the technique, a DP-MZI enables the control of carrier envelope offset frequency (f), as well as repetition frequency (f), in addition to generating a stable dissipative Kerr soliton. In experiments, influences on f and f by pump frequency and power modulation via a DP-MZI are investigated, followed by a demonstration of long-term full stabilization of a microresonator soliton comb to a fiber-based optical frequency comb. As another example demonstration, timing jitter of a microresonator soliton comb is significantly suppressed by referencing to a fiber through a two-wavelength delayed self-heterodyne interferometer (TWDI).


Low-noise millimeter-wave synthesis from a dual-wavelength fiber Brillouin cavity

In this Letter, a photonic system is proposed to generate millimeter waves with low phase noise and ultra-high frequency stability. By locking two free-running CW lasers to the same fiber cavity whose free-spectral range is actively stabilized, millimeter waves can be synthesized in a wide frequency range with fine-tuning capability. Exploiting the spectral narrowing effect of stimulated Brillouin scattering, the generated millimeter waves exhibit low phase noise that does not scale up as the frequency increases. In the experimental demonstration, up to ∼300 GHz millimeter waves are generated, with a phase noise of <-90 dBc/Hz at 10 kHz offset limited by the local oscillator and an in-loop 60 min frequency RMS drift of 0.43 mHz. The output frequency of the system can be readily increased to sub-THz region by replacing one of the pump CW lasers.


A photonic frequency discriminator based on a two wavelength delayed self-heterodyne interferometer for low phase noise tunable micro/mm wave synthesis

Low phase noise frequency synthesizers are of paramount interest in many areas of micro-mm wave technology, encompassing for example advanced wireless communication, radar, radio-astronomy, and precision instrumentation. Although this broad research field is not bereft of methods for the generation of either low phase noise micro- or mm waves, no universal system applicable to low phase noise generation for micro and mm waves has yet been demonstrated. Here we propose a new photonic frequency discriminator based on a two wavelength delayed self-heterodyne interferometer which is compatible with such an objective. The photonic frequency discriminator can be a reference both for micro and mm waves to lower their phase noise. As a proof-of-concept, we demonstrate a low phase noise tunable OEO (6-18 GHz) and locking of a heterodyne beat between two cw lasers (10-400 GHz) with low relative phase noise. The required components for the photonic frequency discriminator are off-the-shelf and can be readily assembled. We believe this new type of photonic frequency discriminator will enable a new generation of universal precision tunable sources for the X, K, V, W and mm-bands and beyond.


Photonics-enabled wideband microwave burst detection

In this Letter, to the best of our knowledge, a novel wideband microwave burst detection system is realized by utilizing photonics-assisted wavelength and time division multiplexing, in conjunction with optical storage. Deploying a coherent electro-optical dual comb and a recirculating optical frequency shifter with ∼1.28 μs round-rip delay, the proof-of-concept experimental system demonstrates the interrogation of ∼1 μs radio frequency (RF) bursts with up to an 8 GHz bandwidth and arbitrary hopping pattern at 1 MHz resolution and a refresh rate of ∼60 kHz using an 80 MHz RF detection unit. The proposed system can be easily upgraded to higher bandwidths and longer burst time apertures with suitable hardware.


Ultra-broadband dual-branch optical frequency comb with 10-18 instability


Fast ultra-wideband microwave spectral scanning utilizing photonic wavelength- and time-division multiplexing

A high-speed ultra-wideband microwave spectral scanning system is proposed and experimentally demonstrated. Utilizing coherent dual electro-optical frequency combs and a recirculating optical frequency shifter, the proposed system realizes wavelength- and time-division multiplexing at the same time, offering flexibility between scan speed and size, weight and power requirements (SWaP). High-speed spectral scanning spanning from ~1 to 8 GHz with ~1.2 MHz spectral resolution is achieved experimentally within 14 µs. The system can be easily scaled to higher bandwidth coverage, faster scanning speed or finer spectral resolution with suitable hardware.


Low noise, self-referenced all polarization maintaining Ytterbium fiber laser frequency comb

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 (f) stabilization through a conventional f-2f interferometer. We demonstrate for the first time the stabilization of the f of such a PM Yb system with an in-loop fractional frequency stability scaled to an optical frequency of low 10 at 1 second averaging time, offering a great potential for applications in optical atomic clock metrology.


Electro-optic comb based real time ultra-high sensitivity phase noise measurement system for high frequency microwaves

Recent progress in ultra low phase noise microwave generation indispensably depends on ultra low phase noise characterization systems. However, achieving high sensitivity currently relies on time consuming averaging via cross correlation, which sometimes even underestimates phase noise because of residual correlations. Moreover, extending high sensitivity phase noise measurements to microwaves beyond 10 GHz is very difficult because of the lack of suitable high frequency microwave components. In this work, we introduce a delayed self-heterodyne method in conjunction with sensitivity enhancement via the use of higher order comb modes from an electro-optic comb for ultra-high sensitivity phase noise measurements. The method obviates the need for any high frequency RF components and has a frequency measurement range limited only by the bandwidth (100 GHz) of current electro-optic modulators. The estimated noise floor is as low as -133 dBc/Hz, -155 dBc/Hz, -170 dBc/Hz and -171 dBc/Hz without cross correlation at 1 kHz, 10 kHz, 100 kHz and 1 MHz Fourier offset frequency for a 10 GHz carrier, respectively. Moreover, since no cross correlation is necessary, RF oscillator phase noise can be directly suppressed via feedback up to 100 kHz frequency offset.


All-polarization-maintaining, single-port Er: fiber comb for high-stability comparison of optical lattice clocks


Low noise electro-optic comb generation by fully stabilizing to a mode-locked fiber comb

A fully stabilized EO comb is demonstrated by phase locking the two degrees of freedom of an EO comb to a low noise mode-locked fiber comb. Division/magnification of residual phase noise of locked beats is observed by measuring an out-of-loop beat. By phase locking the 200 th harmonics of the EO comb and a driving cw frequency to a fiber comb, a record low phase noise EO comb across +/- 200 harmonics (from 1544.8 nm to 1577.3 nm) is demonstrated.


All polarization-maintaining Er fiber-based optical frequency combs with nonlinear amplifying loop mirror

A fully stabilized all polarization-maintaining Er frequency comb with a nonlinear amplifying loop mirror with below 0.2 rad carrier-envelope-offset frequency phase noise is demonstrated. The integrated timing jitter is measured as 40 attosecond from 10 kHz to 10 MHz, which is the lowest value of any Er fiber frequency comb to date.


Ultra-low noise all polarization-maintaining Er fiber-based optical frequency combs facilitated with a graphene modulator

High bandwidth carrier phase and repetition rate control are critical for the construction of low phase noise optical frequency combs. Here we demonstrate the use of a graphene modulator for the former and a bulk electro-optic modulator for the latter enabling record low phase noise operation of an Er fiber frequency comb. For applications that do not require carrier phase control, we show that the form factor of a fiber comb can be reduced by adapting a graphene modulator for rapid repetition rate control. Moreover, the whole system demonstration is performed with all-polarization maintaining Er fiber frequency combs, highly suitable for applications in the field.


Dual-Comb Spectroscopy for Fast, Broadband, and Precise Spectroscopy

デュアルコム分光∼FT-IRにかわる高速広帯域精密分光∼

Dual-comb spectroscopy using two frequency combs with slightly different repetition frequencies has been attracting attention as a new spectroscopic tool. Dual-comb spectroscopy can be considered as a Fourier transform spectroscopy without the mechanical delay-stage. Dual-comb spectroscopy has much higher data acquisition rate and frequency resolution, compared with conventional Michelson interferometerbased Fourier transform spectroscopy. In this paper, we introduce the principle of dual-comb spectroscopy and novel way for phase locking between two frequency combs for simple dualcomb system. In addition, the application of dual-comb spectroscopy to FBG strain sensor is described.


Static FBG strain sensor with high resolution and large dynamic range by dual-comb spectroscopy

We demonstrate a fiber Bragg grating (FBG) strain sensor with optical frequency combs. To precisely characterize the optical response of the FBG when strain is applied, dual-comb spectroscopy is used. Highly sensitive dual-comb spectroscopy of the FBG enabled strain measurements with a resolution of 34 nϵ. The optical spectral bandwidth of the measurement exceeds 1 THz. Compared with conventional FBG strain sensor using a continuous-wave laser that requires rather slow frequency scanning with a limited range, the dynamic range and multiplexing capability are significantly improved by using broadband dual-comb spectroscopy.


Injection locking of Yb-fiber based optical frequency comb,

We demonstrated the synchronization of offset and repetition frequency between two independent Yb-doped fiber mode-locked lasers by injection locking. By injecting master-laser pulse-train into slave laser cavity, stability and accuracy of master frequency comb are transferred to slave comb. Passive stabilization of frequency comb offers robust and convenient way to duplicate frequency comb that can be applied to long-distance comb transfer. Injecting master pulse would also help to initiate and stabilize mode-locking of high repetition rate or ultrabroadband frequency combs. Additionally, we also demonstrated even more robust synchronization of combs can be achieved with the help of active stabilization of relative offset frequency difference.


Comb-Resolved Dual-Comb Spectroscopy Stabilized by Free-Running Continuous-Wave Lasers


Self-compensation of third-order dispersion for ultrashort pulse generation demonstrated in an Yb fiber oscillator

Compensation of the intracavity dispersion in the mode-locked oscillator is known to be one of the most important factors for ultrashort pulse generation. However, recent investigations of a Yb-doped fiber mode-locked oscillator revealed that precise third-order dispersion (TOD) compensation is not always necessary for ultrashort pulse generation, owing to the strong nonlinearity that compensates residual TOD without reducing its spectral bandwidth. The origin of the nonlinear TOD compensation has remained unclear. To investigate the process in detail, we studied the pulse evolution inside a 30 fs Yb-doped fiber mode-locked oscillator both experimentally and numerically, and we found that the nonlinear phase shift with a temporally asymmetric pulse shape introduces an appropriate amount of TOD that exactly cancels the residual cavity dispersion.