Showing papers on "Injection locking published in 2022"

Using Transitional Points in the Optical Injection Locking Behavior of a Semiconductor Laser to Extract Its Dimensionless Operating Parameters

Abstract: The complete set of intrinsic dimensionless parameters of a packaged and fiber-pigtailed distributed feedback (DFB) semiconductor laser are extracted from the non-linear operational stability boundaries of the optical-injection-locking (OIL) architecture. Specifically, this procedure is done by relating the intrinsic parameters to the injection ratios corresponding to the Hopf bifurcation points at zero detuning, as well as the detuning of the Hopf-Saddle-Node point. The bifurcation points of the injected laser's operational space are found by coupling its output into a high-resolution optical spectrum analyzer. This is enabled by establishing a 30 dB side mode suppression ratio between the central mode and Period 1 oscillations to define the boundaries of Stable Locking. Along with the laser's threshold current and free-running relaxation oscillation frequencies, performing these measurements over a range of pumping values allows for the calculation of the laser's linewidth enhancement factor, irrespective of the device packaging. Utilizing a high pump approximation, the remaining dimensionless parameters are extracted after obtaining the photon lifetime. Using this approach, the operational capabilities of an arbitrarily-packaged laser can be determined, allowing for the analysis of an injected laser's operational space for a variety high-frequency and dynamical applications.

Dual-laser self-injection locking to an integrated microresonator

Abstract: Diode laser self-injection locking (SIL) to a whispering gallery mode of a high quality factor resonator is a widely used method for laser linewidth narrowing and high-frequency noise suppression. SIL has already been used for the demonstration of ultra-low-noise photonic microwave oscillators and soliton microcomb generation and has a wide range of possible applications. Up to date, SIL was demonstrated only with a single laser. However, multi-frequency and narrow-linewidth laser sources are in high demand for modern telecommunication systems, quantum technologies, and microwave photonics. Here we experimentally demonstrate the dual-laser SIL of two multifrequency laser diodes to different modes of an integrated Si3N4 microresonator. Simultaneous spectrum collapse of both lasers, as well as linewidth narrowing and high-frequency noise suppression , as well as strong nonlinear interaction of the two fields with each other, are observed. Locking both lasers to the same mode results in a simultaneous frequency and phase stabilization and coherent addition of their outputs. Additionally, we provide a comprehensive dual-SIL theory and investigate the influence of lasers on each other caused by nonlinear effects in the microresonator.

Using Transitional Points in the Optical Injection Locking Behavior of a Semiconductor Laser to Extract Its Dimensionless Operating Parameters

Abstract: The complete set of intrinsic dimensionless parameters of a packaged and fiber-pigtailed distributed feedback (DFB) semiconductor laser are extracted from the non-linear operational stability boundaries of the optical-injection-locking (OIL) architecture. Specifically, this procedure is done by relating the intrinsic parameters to the injection ratios corresponding to the Hopf bifurcation points at zero detuning, as well as the detuning of the Hopf-Saddle-Node point. The bifurcation points of the injected laser's operational space are found by coupling its output into a high-resolution optical spectrum analyzer. This is enabled by establishing a 30 dB side mode suppression ratio between the central mode and Period 1 oscillations to define the boundaries of Stable Locking. Along with the laser's threshold current and free-running relaxation oscillation frequencies, performing these measurements over a range of pumping values allows for the calculation of the laser's linewidth enhancement factor, irrespective of the device packaging. Utilizing a high pump approximation, the remaining dimensionless parameters are extracted after obtaining the photon lifetime. Using this approach, the operational capabilities of an arbitrarily-packaged laser can be determined, allowing for the analysis of an injected laser's operational space for a variety high-frequency and dynamical applications.

Two Polarization Comb Dynamics in VCSELs Subject to Optical Injection

Abstract: Optical frequency comb technologies have received intense attention due to their numerous promising applications ranging from optical communications to optical comb spectroscopy. In this study, we experimentally demonstrate a new approach of broadband comb generation based on the polarization mode competition in single-mode VCSELs. More specifically, we analyze nonlinear dynamics and polarization properties in VCSELs when subject of optical injection from a frequency comb. When varying injection parameters (injection strength and detuning frequency) and comb properties (comb spacing), we unveil several bifurcation sequences enabling the excitation of free-running depressed polarization mode. Interestingly, for some injection parameters, the polarization mode competition induces a single or a two polarization comb with controllable properties (repetition rate and power per line). We also show that the performance of the two polarization combs depends crucially on the injection current and on the injected comb spacing. We explain our experimental findings by utilizing the spin-flip VCSEL model (SFM) supplemented with terms for parallel optical injection of frequency comb. We provide a comparison between parallel and orthogonal optical injection in the VCSEL when varying injection parameters and SFM parameters. We show that orthogonal comb dynamics can be observed in a wide range of parameters, as for example dichroism linear dichroism (γa=−0.1 ns−1 to γa=−0.8 ns−1), injection current (μ=2.29 to μ=5.29) and spin-flip relaxation rate (γs=50 ns−1 to γs=2300 ns−1).

Creating electronic oscillator-based Ising machines without external injection locking

Abstract: Coupled electronic oscillators have recently been explored as a compact, integrated circuit- and room temperature operation-compatible hardware platform to design Ising machines. However, such implementations presently require the injection of an externally generated second-harmonic signal to impose the phase bipartition among the oscillators. In this work, we experimentally demonstrate a new electronic autaptic oscillator (EAO) that uses engineered feedback to eliminate the need for the generation and injection of the external second harmonic signal to minimize the Ising Hamiltonian. Unlike conventional relaxation oscillators that typically decay with a single time constant, the feedback in the EAO is engineered to generate two decay time constants which effectively helps generate the second harmonic signal internally. Using this oscillator design, we show experimentally, that a system of capacitively coupled EAOs exhibits the desired bipartition in the oscillator phases without the need for any external second harmonic injection, and subsequently, demonstrate its application in solving the computationally hard Maximum Cut (MaxCut) problem. Our work not only establishes a new oscillator design aligned to the needs of the oscillator Ising machine but also advances the efforts to creating application specific analog computing platforms.

Injection Locking of Optoelectronic Oscillators With Large Delay

Abstract: The optoelectronic oscillator is a delay line oscillator that leverages optical fiber technology to realize the large delay required for low phase noise systems. Spurious sidemodes are an artifact of the delay line oscillator, yet treatments of injection locking of optoelectronic oscillators have relied on the application of classical injection locking theory valid only for single mode oscillators. The large delay contributed by the optical fiber delay line is accounted for by classical theory only in part through the quality factor Q that captures the round-trip group delay in a neighborhood of the oscillation frequency. This paper presents a new formulation of time delay oscillators subject to injection that describes all the essential features of their dynamics and phase noise. The common assumptions of a single mode oscillator and weak injection are removed. This is important to correctly predict the locking range, the suppression of sidemodes and the phase noise spectrum. The findings of the analysis are validated by experimental measurements provided by an optoelectronic oscillator under injection by an external source.

Active mode lock optoelectronic oscillator based on the simulated Brillouin scattering effect

Abstract: An active mode-locked optoelectronic oscillator (AML-OEO) based on the simulated Brillouin scattering (SBS) effect without an electrical filter is demonstrated here. By using phase modulation and SBS-based selective sideband amplification, the central frequency of the proposed SBS-AML-OEO is easily adjusted by simply changing the pump laser frequency instead of the filters. A microwave frequency comb signal with an adjustable central frequency and fixed bandwidth are generated by injecting a mode-locking external RF synchronizing with the free spectral ranging FSR. In addition, the harmonic SBS-AML-OEO is also achieved by harmonic signal injection. The proposed method reveals a simple solution to tune the central frequency and has the potential to be integrated on a chip since there is no structure changing in the scheme.

Self-Injection-Locked Optoelectronic Oscillator Based on Frequency Conversion Filtering

Abstract: The multi-mode noise is an important issue for the optoelectronic oscillator (OEO) in generating a spectrally pure microwave. Especially in oscillators with low phase noise, increasing the cavity length to improve the phase noise performance will make the mode interval smaller, which is more likely to cause multi-mode noise. Here, we proposed a low phase noise and high side-mode suppression ratio self-injection-locked OEO based on frequency conversion filtering. We theoretically and experimentally studied the influence of the phase noise of the external microwave source on the proposed OEO and, as a comparison, the conventional injection-locked OEO. The results show that, compared with the traditional injection-locked OEO, the proposed OEO is less sensitive to the phase noise of the external microwave source. Under the same experimental conditions, the proposed OEO achieved the same side-mode suppression ratio and the phase noise is reduced by 30 dB at 10 kHz offset from the 10-GHz carrier compared with the conventional injection-locked OEO.

A 208-GHz Injection Locking Doubler Chain With 3.2% PAE and 2.9-mW Output Power in CMOS Technology

Abstract: This letter presents an injection locking doubler chain centered at 208 GHz in 65-nm CMOS technology. The doubler chain consists of a doubler and two injection locking oscillators (ILOs). The doubler uses push–push topology to generate wideband second-harmonic output. Both ILOs are based on T-embedding network oscillator for high gain and high efficiency. The measured injection locking range is 188.4–225.6 GHz with the input injection power less than 0 dBm. The peak output power with the minimum injection input is 4.6 dBm (2.9 mW), and the 3-dB bandwidth is 200–220 GHz (9.5%). The power consumption is 83 mW under 1.2-V supply, and the peak power-added efficiency (PAE) reaches 3.2% at 211 GHz. Moreover, the total size of the chip excluding pads is 530 $\mu \text{m}\,\,\times200\,\,\mu \text{m}$ . To the best of the author’s knowledge, this work demonstrates the highest PAE among CMOS doubler chains in similar frequency ranges reported by far.

Enhanced frequency-modulated continuous-wave generation by injection-locking period-one oscillation in a semiconductor laser with an intensity modulated comb.

Abstract: We report on an enhanced photonic generation of frequency-modulated continuous-wave (FMCW) signals by injection-locking a semiconductor laser operating in period-one (P1) nonlinear dynamic with an intensity modulated electro-optic frequency comb. When the cavity mode is injection-locked with respect to any of the comb modes, through linearly sweeping the frequency of the injected comb mode while synchronously modulating the injected intensity, the center wavelength of the cavity mode can be tuned following the injected comb mode. This way, it allows maintaining the phase-locking between the cavity mode and comb mode even if beyond the original locking bandwidth of the cavity mode, since it is tuned accordingly. It thus leads to the generation of FMCW signal with efficient phase noise suppression and improved achievable sweep range compared with the limited original injection-locking bandwidth. Such injection enhanced phase-locking is investigated and a demonstration with the injection of -4th order comb mode has realized photonic FMCW generation with enhanced sweep range and suppressed phase noise. Thanks to the flexibility in sweep parameters, this method can also be readily applied for the generation of arbitrary waveforms.

Analysis of Injection-Locked Ring Oscillators for Quadrature Clock Generation in Wireline or Optical Transceivers

Abstract: Injection-locked ring oscillators (ILROs) are widely used for quadrature clock generators (QCG) in multi-lane wireline or optical transceivers because of their low power, low area, and technology scalability. However, locking a four-stage I/Q oscillator with a two-phase injection signal generates imbalances in amplitude and phase, resulting in I/Q phase errors and degraded jitter performance. This paper proposes a modified frequency-domain analysis with amplitude constraint for even-phase ILROs. Combining theoretical derivations with simulation results in 28nm CMOS technology, the behaviors of ring oscillators with partial injection and ILRO-based QCG are discussed and concluded.

Frequency Comb and Injection Locking Based Mutual Protections in Coherent Optical Access Network

Abstract: A P2MP coherent network features mutual protection between adjacent networks, and remote delivery of optical carriers that are injection locked to an optical frequency comb is proposed. System functionality and performance has been verified experimentally. © 2022 The Author(s)

A Divide-by-Three ILFD With Second Harmonic Enhancement

Abstract: This letter presents a low-voltage divide-by-three injection-locked frequency divider (ILFD) with a second harmonic enhancement technique. The injection current generated from the extra divide-by-two injection path is enhanced compared with the former work, thus the larger locking range (LR). Fabricated in the CMOS 65-nm technology, the core circuit consumes 5.18 mW from a 0.6-V power supply. Under 0 dBm signal injection, the measured largest LR achieves 19.03% ranging from 23.30 to 28.20 GHz without frequency tuning. By using a varactor, the bandwidth can range from 23.30 to 31.02 GHz, which can be used as the first stage frequency division in the phase-locked loop (PLL) of the 5G transceiver.

Frequency-modulated microwave signal generation by dual-wavelength-injection period-one laser dynamics.

Abstract: In this Letter, dual-wavelength-injection period-one (P1) laser dynamics is proposed for the first time, to the best of our knowledge, to generate frequency-modulated microwave signals. By injecting light with two different wavelengths into a slave laser to excite P1 dynamics, the P1 oscillation frequency can be modulated without external control of the optical injection strength. The system is compact and stable. The frequency and bandwidth of the generated microwave signals can be easily adjusted by tuning the injection parameters. Through both simulations and experiments, the properties of the proposed dual-wavelength injection P1 oscillation are revealed, and the feasibility of the frequency-modulated microwave signal generation is verified. We believe that the proposed dual-wavelength injection P1 oscillation is an extension of laser dynamics theory, and the signal generation method is a promising solution for generating broadband frequency-modulated signals with good tunability.

Broadband Terahertz Quantum Cascade Laser Dual‐Comb Sources under Off‐Resonant Microwave Injection

Abstract: Broadband dual-comb spectroscopy has attracted increasing interests due to its unique advantages in high spectral resolution, fast detection, and so on. Although the dual-comb technique is relatively mature in the infrared wavelengths, it is, currently, not commercially capable of practical applications in the terahertz regime due to the lack of high performance broadband terahertz dual-comb sources. In the terahertz frequency range, the electrically pumped quantum cascade laser (QCL) is a suitable candidate for the dual-comb operation. However, free running terahertz QCL dual-comb sources normally show limited optical bandwidths ($\sim$100-200 GHz). Although the resonant microwave injection locking has been widely used to broaden the emission spectra of terahertz QCLs by modulating the laser drive current at the cavity round-trip frequency, it is hard to be employed to broaden the dual-comb bandwidths due to the large phase noise induced by the resonant injection and non-ideal microwave circuits. Therefore, it is challenging to obtain broadband terahertz dual-comb sources that can fully exploits the laser gain bandwidth. Here, we employ an off-resonant microwave injection to significantly broaden the dual-comb bandwidth of a terahertz QCL dual-comb source emitting around 4.2 THz. The measured optical dual-comb bandwidth is broadened from 147 GHz in free running to $>$450 GHz under the off-resonant injection. The broadened dual-comb bandwidth is experimentally proved by the transmission measurements of a filter and a GaAs etalon. By performing a simple numerical analysis based on a rate equation model, we explain that the broadband dual-comb operation under the off-resonant microwave injection could be resulted from a wider lasing bandwidth and a higher degree of phase matching.

Nonlinear Analysis of an Injection-Locked Oscillator Coupled to an External Resonator

Abstract: This work investigates an injection-locked power oscillator inductively coupled to an external resonator for wireless power transfer. The system allows a high transfer efficiency, while ensuring a constant oscillation frequency versus the coupling factor, unlike free-running implementations. An analytical formulation provides insight into the impact of the coupling factor on the locked-operation ranges. Two types of qualitative behavior, delimited by a codimension-two bifurcation, are distinguished. The investigation is extended to a Class-E oscillator at 13.56 MHz, analyzed with a new harmonic balance (HB) method that provides the family of locked-solution curves in a single simulation. Very good agreement is obtained with the measurement results.

All-optical, tunable, V- and W-band microwave generation using semiconductor lasers at period-one nonlinear dynamics with asymmetric mutual injection stabilization.

Abstract: This study investigates an optically injected semiconductor laser operating at period-one nonlinear dynamics for all-optical microwave generation. A novel, to the best of our knowledge, all-optical stabilization scheme is proposed to greatly enhance the spectral purity of such generated microwaves, which sends a small fraction of the injected laser output back to the injecting laser, not the injected laser itself. Mutual injection with highly different injection power between the two lasers, i.e., highly asymmetric mutual injection, is thus formed. As a result, the microwave linewidth is reduced by up to at least 85 times, the phase noise variance is improved by up to at least 750 times, and a side-peak suppression ratio of more than 44 dB is achieved. Microwave generation that is tunable up to at least 110 GHz with a 3-dB linewidth down to below 2 kHz is realized.

Mode-locking threshold decrease in fiber laser by heterochromic optical pulse injection

Abstract: A Yb-doped fiber laser mode locked by a nonlinear amplifying loop mirror (NALM) with a figure-9 configuration is experimentally realized. By coupling heterochromic 1580-nm optical pulses into the circular part of the Yb-doped laser oscillator, a new injection-induced Q-switched mode-locking (Q-ML) like transition state is found for the first time to the best of our knowledge. We have investigated the envelope interval and duration of this Q-switched envelope by changing the pump power, injection power, and cavity length detuning. Experimental results have shown the injected pulses serve as a complementary source for establishing mode-locking (ML). As a result, the self-starting ML threshold of the Yb-doped fiber laser is significantly reduced from 355 to 171 mW, which is only half that in the non-injection case. This optical pulse injection assisted ML process is observed with a real-time oscilloscope, revealing stable and consistent buildup dynamics. Our finding may provide a new approach for understanding the buildup dynamics and building mode-locked fiber lasers with low threshold and high consistency.

Injection-locked parity-time-symmetric optoelectronic oscillator with ultra-high sidemode suppression

Abstract: An optoelectronic oscillator (OEO) that combines injection locking and parity-time (PT) symmetry is proposed and demonstrated to generate microwave signals with low phase noise and a high side-mode suppression ratio. In the experiment, a microwave signal at 10 GHz with a phase noise as low as -117.5 dBc/Hz at an offset frequency of 10 kHz is generated. An ultra-high side-mode suppression ratio of 86.33 dB is achieved.

A Continuous K-Band Phase Shifter Based on Injection-Locked Dual Voltage-Controlled Oscillators

Abstract: In this letter, a $K$ -band signal generation phase shifter (SGPS) is implemented using a standard 55-nm complementary metal-oxide semiconductor (CMOS). Its phase shifting is achieved by injecting signal of a voltage-controlled oscillator (VCO) to the other through an injection buffer. Besides continuous phase shift, it can offer a signal source, facilitating multi-phase signal generation in phase array transceivers. Measurement results suggest the prototype implemented in 55-nm CMOS is able to provide a frequency tuning range of 22.5 to 24.8 GHz and minimal output power of 5.2 dBm. It demonstrates a maximal tuning phase of 45.5°.

5G Millimeter-Wave Analog RoF System employing Optical Injection Locking and Direct Modulation of DFB Laser

Abstract: We demonstrate the successful generation of 28.2 and 35.3 GHz mm-wave signals through optical injection locking and direct modulation of a DFB laser. The low phase noise mm-wave signal generated supports 5G compatible OFDM signals.

Strong-feedback regime of self-injection locking and external cavity laser

Abstract: Realization of the coupling of the laser diode to an external reflector may provide efficient suppression of the phase noises and significant stabilization of the laser source. Locking a semiconductor laser to high-quality-factor microresonator was shown to result in a laser linewidth narrowing to sub-Hz level. The straightforward way to get better stabilization and wider locking band is to increase the feedback level. However, most of the theories used to describe the self-injection locking effect assume the weak feedback from the external reflector. Here we develop the more complete theory of the laser -- resonant reflector interaction that allows to describe this effect for the high feedback level as well. We define different possible regimes taking place at different feedback levels (including the so-called external cavity laser regime) and study applicability domains of the previous and proposed models. We show that existing model of the self-injection locking to whispering-gallery mode resonator is a consequence of the considered model in the low-feedback regime. Finally, we check the model in high-feedback limit experimentally and show a good correspondence with the theory.

Independent Optical and Microwave Injection Locking of Kerr Frequency Combs by an Auxiliary Laser

Abstract: We demonstrate experimentally two regimes of coherent injection locking of a Kerr frequency comb to another counter-propagating modulated laser. In disjoint regions, the microcomb locks to either an optical harmonic or the external modulation signal.

Injection Locking Properties of an Dual Laser Source for mm-Wave Communications

Abstract: We for the first time, the optical injection locking (OIL) to a frequency comb of a hybrid $\text{{InP-Si}}_{3}\text{{N}}_{4}$ dual laser source for high-purity mm-wave generation through optical heterodyning. Key performance parameters of the comb line demultiplexing functionality provided by this source under OIL – such as adjacent-comb-line side mode suppression ratio (SMSR) and locking range – are reported. It is also shown that the amount of free-running drift exhibited by the hybrid lasers (which should be as little as possible to keep them within the locking range) can be minimized by reducing the amount of bias level applied to the heater-based phase actuators present in such lasers. According to the measured drift, locking range and SMSR, these lasers have potential to achieve continuous locking with SMSR levels of more than 45 dB at comb line separations higher than 9 GHz. Successful carrier generation at 93 GHz is demonstrated by locking the two lasers to an optical frequency comb achieving an ultra-stable International Telecommunication Union (ITU)-compliant signal. Both real-time and DSP-aided data transmissions are demonstrated at this frequency achieving data rates of 12.5 and 28 Gbit/s, respectively.

Frequency Stability Transfer in Passive Mode-Locked Quantum-Dash Laser Diode Using Optical Injection Locking

Abstract: In this paper, we present an experimental study of the metrological stabilization of a solid-state frequency comb for embedded metrology applications. The comb is a passively mode-locked laser diode based on InGaAs/InP Quantum-dash structure emitting optical lines into a 9 nm bandwidth centered at 1.55 $\mu$m with a repetition rate of 10.09 GHz. The frequency stabilization is achieved by optical injection locking of the comb with an external cavity laser diode referenced onto a metrological frequency standard. One observes the transfer of the spectral purity from the injection laser to the neighbouring modes of the injected one as well as the transfer of stability to the adjacent modes. The measurement of the long term stability highlights a frequency noise with random walk behavior specific of the passive mode locking process. Demonstration of sidebands of the injection laser at the repetition frequency of the comb also makes it possible to propose a transfer mechanism and to consider a complete stabilization of the frequency comb at a metrological stability level.

An ultra-wideband injection-locked frequency divider with a multi-order resonator and the passive injection-boosted technique

Abstract: This paper presents an ultra-wideband injection-locked frequencydivider(ILFD)designwhichisapplicabletoamulti-applicationssystem.Atransformer-basedmulti-orderresonatorisutilizedintheILFDtoattainaflatphaseresponse.Thepassiveinjection-boostedtechniqueisproposedtoincreasetheinjectionsignalamplitudeandthuswidenthelockingrange.Withtheinjection-boostedtechniqueandthemulti-orderresonator,theproposedILFDdemonstratesameasuredlockingrangeof50GHz,covering48GHzto98GHz.Thedividerdesignedina40-nmprocessconsumesaDCpowerof11.2mWexcludingbuffersandoccupiesacoresizeof0.38

A 0.021mm² 65nm CMOS 2.5GHz Digital Injection-Locked Clock Multiplier with Injection Pulse Shaping Achieving −79dBc Reference Spur and 0.496mW/GHz Power Efficiency

Abstract: The digital injection-locked clock multiplier (ILCM) using ring oscillators (ROs) is a superior choice for clock generation due to its ease of scaling, compact area, and prominent jitter performance. However, the periodic phase realignment in an ILCM can cause a deterministic phase error in the injection moment, which generates an extremely poor reference spur (e.g., −50dBc). Several digital calibration techniques [1]–[5] have been introduced to reduce the reference spur. The key is to first detect sources of non-idealities (e.g., imperfect injection timing, frequency drift, and slope modulation), and then to enable a specific calibrator to correct each error source. Unfortunately, there are many non-idealities that can affect the injection performance, such as supply ripples, charge injection of the switches, and clock feedthrough, making it impractical to employ multiple calibration loops to simultaneously mitigate each of them. On the other hand, conventional phase-error-detection schemes [2]–[3], [5] suffer from the timing race between the calibration loop and the injection, and hence elaborate timing control is required to extract errors. This timing-control logic is sensitive to process, voltage, and temperature (PVT) variations, leading to inadequate mitigation of the reference spurious power.