An improved self-reference photonic sampling method is proposed to measure the frequency response of photodiode (PD) chips. In the proposed scheme, the uneven response of the Mode-Locked Laser Source (MLLS) is eliminated by using the half-frequency photonic sampling measurements. The microwave de-embedding under short-open-load-device termination is used to realize on-chip de-embedding of the adapter network connected to the receiver of the microwave network analyzer in terms of the transmission loss and the impedance mismatch. The proposed on-chip measurement method is free of any extra electro-optical transducer standard, and an accurate measurement can still be realized without an impedance match.
An approach to measuring high-frequency responses of electro-absorption modulated lasers (EMLs) is proposed based on fixed low-frequency pilot analysis. The fixed low-frequency pilot is inserted into the microwave driving signal loaded on the EML through amplitude modulation. Then, the high-frequency response of EML can be obtained by extracting and analyzing the pilot (kHz level) after photodetection, thereby realizing the low-frequency detection for EML measurement. Moreover, the method is independent of the responsivity fluctuation of the photodetector due to the fixed frequency analysis and enables the self-calibrated frequency response measurement of high-speed EML.
A simple and novel method is proposed for the self-calibrated measurement of high-speed photodetectors (PDs) based on photonic sampling by using a mode-locked laser (MLL). Through the photonic sampling measurements, the uneven response of the MLL can be determined. The prominent advantage of the proposed method lies that the self-reference extraction of the frequency response of the PD can be achieve without the need of any extra electrical/optical transducer standard. In the experiment, a commercial PD is measured by using a MLL with the repetition frequency of 21.936 MHz. The measurement results fit in with the conventional electro-optic frequency sweep measurement.
A slowly-varying-envelope photonic sampling method is proposed for hyperfine and ultra-wideband frequency response measurement of high-speed photodetectors (PDs). The measuring frequency range of PD is firstly divided into several segments by the repetition frequency fr of a mode-locked laser diode (MLLD), and the hyperfine frequency response measurement of the PD in every segment is then achieved by applying a slowly-varying-envelope microwave modulation sweeping up to fr/2, which is also independent of the uneven responses of the MLLD and the Mach-Zehnder modulator (MZM). Finally, through carefully choosing the joint-frequency of photonic sampling, the ultra-wideband frequency response of the PD can be obtained with the help of seamlessly stitching different segments. Most importantly, the frequency response of the PD at any frequency can be measured by subtly changing the frequency of photonic sampling from DC to fr/2. Moreover, the measuring frequency range of the PD can be extended by 2(n+1)-fold relative to the modulation frequency range of the MZM, where the microwave frequency swept up to fr/2 enables the measuring frequency range up to (n+1)fr.
An approach to measuring ultra-wideband frequency responses of high-speed photodetectors (PDs) is proposed based on low-speed photonic sampling. The optical frequency comb lines of a mode-locked laser diode (MLLD) can be used as the ultra-wideband and scalable optical stimulus of PD. The relative frequency response of PD can be extracted by analyzing the frequency components at comb lines of the MLLD. Thereinto, the uneven response of the MLLD can be eliminated through the specific frequency photonic sampling, thereby realizing the self-referenced and ultra-wideband measurement of PD. Moreover, the measuring frequency range is 2M-fold expanded with respect to the operating range of the microwave modulation frequency.
Electroabsorption-modulated laser (EML) is integrated by distributed feedback (DFB) laser and electro-absorption modulator (EAM). Microwave interaction in the EML has been observed to limit modulation performance especially in high frequency region. In this work, the EML is investigated as a three-port network with two electrical inputs and one optical output. Scattering matrix of the device was derived theoretically and obtained experimentally. Thus, microwave equivalent circuit model of the EML can be established and microwave interaction between the DFB laser and the EAM was successfully extracted. The results reveal that microwave interaction within an integrated EML contains both electrical isolation and optical coupling. The electrical isolation is bidirectional while the optical coupling is directional, which aggravates the performance of the EML. This result can provide a reference for further device optimization design.
A novel laser phase noise measurement method based on self-homodyne structure with a Faraday rotating mirror (FRM) and an optical coherent receiver is proposed and experimentally demonstrated. The proposed method is simple in structure and easy to operate. Compared with the ordinary phase noise measurement system of self-homodyne optical coherent receiver, the length of the required delay fiber is halved and the polarization of the optical signal is more stable. Experimental results show that the proposed method can accurately characterize the phase noise and the linewidth of the laser under test, which are consistent with those obtained by the conventional self-homodyne method.
A self-calibrated method is proposed for electrical spectrum measurement of optical frequency comb (OFC) based on segmental electro-optic up-conversion. In the method, every N comb teeth of OFC are divided into one segment in the frequency domain, and M segments are investigated with the measuring frequency range of M×N×fr (fr is the repetition frequency of the OFC). Through symmetric frequency modulation, intra-segment measurement and seamless stitching between different segments are performed. Finally, only a low-frequency microwave source is required to achieve the electrical spectrum measurement of OFC within ultra-wideband frequency range, and the measuring frequency range can be 2M-fold expanded with respect to the modulation frequency rang. Meanwhile, the frequency responses of MachZehnder modulator and photodetector are fully cancelled out, realizing the self-calibrated electrical spectrum measurement of OFC within ultra-wideband frequency range.
In this paper, we propose and numerically investigate a novel method to generate optical frequency comb (OFC) based on mutual injection in a twin-stripe semiconductor laser (a cell array integrating two lasers on one chip in parallel). Because of the existence of optical confinement factors and the small waveguide spacing, considerable lateral coupling or mutual injection occurs between the two paralleling neighbors. The twin-stripe semiconductor laser will be driven into complex nonlinear dynamic states and can be employed to generate OFCs. The proposed mutual-injection-induced OFC generation method does not need any external microwave sources or modulators. Moreover, the compact OFC generator is free of any auxiliary optical passive devices required in the typical master-slave injection configuration. The numerical results show that the mutual-injection-induced OFC can be flexibly adjusted by changing the bias currents and the mutual injection parameters.
A stimulated Brillouin scattering-based Fourier domain mode locking optoelectronic oscillator is proposed and experimentally demonstrated to generate complementary linearly-chirped microwave waveform (LCMW) pairs. The chirped components of the generated LCMW pairs are in C band and Ku band, and their center frequencies can be easily tuned. The generated LCMW pairs have great coherence since pulse compression ratio of each chirped component ids close to the time-bandwidth product (i.e., 10250). What’s important, the generated LCMW pairs have excellent frequency sweep linearity which is better than 1.76%.
In this paper, we propose and numerically investigate a novel scheme to optically generate microwave signal based on mutual injection locking. A twin-stripe semiconductor laser is driven into mutual injection locking state with two phase-locked wavelengths. Microwave signals with low phase noise are achieved. The frequency of the demonstrated microwave signals can be tuned by adjusting detuning frequency between the twin lasers. The results show that our proposed scheme is featured with not only lower phase noise but also better noise tolerance compared with typical master-slave injection configuration.
Photonic down-conversion sampling is a promising technique that can directly and adaptively transfer a high-frequency microwave signal to a low-frequency replica in the first Nyquist zone, thanks to the large bandwidth of the electro-optic modulator and the ultra-short optical pulse train. Therefore, this technique is beneficial to achieving broadband microwave measurement by using a low-speed photodetector together with a low-frequency and narrowband digital (or analog) receiver. In this presentation, we will discuss broadband high-resolution microwave frequency measurement schemes based on low-speed photonic sampling, which are applicable for multi-tone signal. We will also discuss calibration-free microwave characterization of broadband electro-optic modulators based on low-speed photonic sampling, where the microwave response of either a phase modulator or an intensity modulator can be obtained through low-frequency detection.
An approach to characterizing the intrinsic phase response of an optical filter free of additional phase shift from the pigtail or the free space is proposed and experimentally demonstrated. The kernel of this approach is based on the fact that the intrinsic phase response of an optical filter with a minimum phase response has a unique relationship with its magnitude response. Thus, the intrinsic phase response can be obtained through the measurement of the magnitude response only. Most importantly, this method avoids the influence of the fiber pigtail or the free space on the phase response measurement, which cannot be easily calibrated in the traditional single-sideband modulation-based optical vector analyzer. A phase retrieval algorithm based on fast Fourier transform is presented, which can be used to accurately retrieve the intrinsic phase response of an optical filter with either a symmetric magnitude response or an asymmetric one. In the experiment, the intrinsic phase response of an active stimulated-Brillouin-scattering-based optical filter with an asymmetric magnitude response and a phase-shift fiber Bragg grating with pigtails is successfully retrieved from the measured magnitude response using the proposed method.
In this paper, we propose and demonstrate a novel generation scheme for the optical frequency comb (OFC), which is pumped by the optical injection and enhanced by the self-recirculating modulation. A directly modulated semiconductor laser under the optical injection is driven into the nonlinear period-one oscillation dynamic, which provides a primary OFC seed source with only several sparse comb lines and poor flatness. An enhanced OFC can be generated by modulating this directly modulated semiconductor laser in a closed loop, wherein the modulating signal is derived from the primary OFC. The performance of the proposed OFC is optimized through controlling the injection parameters and the self-recirculating modulation index.
An optically tunable radio frequency (RF) downconversion scheme is proposed based on an optoelectronic oscillator (OEO) incorporating a tunable microwave photonic filter. The local oscillation (LO) is generated in the OEO, whose frequency is varied through simply tuning the frequency difference between the optical carrier and the reflection notch of a phase-shifted fiber Bragg grating (PS-FBG). The LO and the input RF signal are combined and added to the OEO loop by a single phase modulator. The RF modulation sidebands and one of the LO modulation sidebands are extracted out of the OEO loop by the PS-FBG and sent to a photo-detector to achieve RF downconversion. In the experiment, optically tunable LOs in the frequency range of 6 GHz to 15 GHz are generated, and RF signals in the frequency range of 7 GHz to 16 GHz are successfully down-converted to intermediate frequency band around 1 GHz. The proposed scheme has the potential to cover a frequency range beyond 40 GHz.
An electrical method is proposed for the absolute time-delay characterization of optical delay components based on the frequency-shifted self-heterodyning. The method utilizes the electrical spectrum of the heterodyne products between the delayed optical signal and the frequency-shifted optical carrier, and achieves the intrinsic absolute time-delay measurement from the notch frequencies of the spectrum at microwave region. Moreover, our method enables highresolution and wide range measurement with low-frequency electrical spectrum analysis. The theoretical analysis is supported by experimental results.
Optoelectronic oscillator (OEO) has been considered as the best technique to produce microwave signal with low phase noise. However, due to the electronic bottleneck rooted from frequency selection mechanism based on electrical filter, it is faced with such a dilemma that it is difficult to simultaneously obtain microwave source with broadband tunability and better phase noise performance. Semiconductor laser under optical injection has showed rich nonlinear dynamics and has demonstrated their potential in various domains, such as information encryption and all-optical signal processing. In this paper we propose and investigate a new modulator-free OEO scheme based on an optically injected semiconductor laser with the subharmonic modulation. The performance of the proposed OEO is optimized with respect to the single sideband phase noise, and the tunability of the generated microwave signal is discussed. A generated microwave signal at 11.42 GHz is experimentally demonstrated with the single sideband phase noise of -101.21 dBc/Hz at the offset frequency of 10 kHz.
We demonstrated a self-referenced electrical method for measuring frequency response of high-speed Mach-Zehnder modulators (MZMs) based on two-tone modulation. The modulation index and half-wave voltage can be extracted from the heterodyne ratio of two desired components by properly adjusting bias voltage. The method achieves the electrical domain measurement of the frequency-dependent modulation indices and frequency-dependent half-wave voltages of MZMs without any extra calibration for the responsivity fluctuation in the photodetection. Moreover, it reduces half bandwidth requirements of photodetector and electrical spectrum analyzer by carefully choosing a half frequency relationship of two-tone microwave signals. The consistency between our method and the optical spectrum analysis method verifies the simple but accurate measurement.
A self-calibrated electrical method to measure magnitude response of optical filters is proposed based on dual-frequency-shifted heterodyne. The combined response of optical modulation, filtering, and photodetection is determined from the first frequency-shifted heterodyne, while the reference response of optical modulation and detection is simultaneously obtained from the second frequency-shifted heterodyne, with which the magnitude response of optical filter under test is extracted and self-calibrated. Our method eliminates the extra separate calibration to correct the responsivity fluctuation in the optical modulation and detection. Moreover, it extends double frequency range due to both upper and lower frequency direction measurement at every swept frequency. Magnitude response of optical filter is experimentally measured with our method and compared to that with the conventional method to check its consistency.
An electrical method is proposed for the microwave characterization of dual-drive Mach–Zehnder modulators based on heterodyne mixing. The proposed method utilizes the heterodyne products between the two-tone modulated optical sidebands and frequency-shifted optical carrier, and achieves calibration-free and bias-drift-free microwave measurement of dual-drive Mach–Zehnder modulators with high resolution electrical-domain techniques. Our method avoids the extra calibration for the photodetector and reduces half the bandwidth requirement for the photodetector and the electrical spectrum analyzer through carefully choosing a half frequency relationship of the two-tone modulation. Moreover, our measurement avoids the bias drifting problem due to the insensitivity to the bias phase of the modulator under test. The frequency-dependent modulation depths and half-wave voltages are measured for a commercial dual-drive Mach–Zehnder modulator with our method, which agree well with the results obtained by the conventional optical spectrum analysis method.
We investigate the phase modulation to intensity modulation conversion in dispersive fibers for measuring frequency
responses of electro-optic phase modulators, and demonstrate two typical measurements with cascade path and fold-back
path. The measured results achieve an uncertainty of less than 2.8% within 20 GHz. Our measurements show stable and
repeatable results because the optical carrier and its phase-modulated sidebands are affected by the same fiber
impairments. The proposed method requires only dispersive fibers and works without any small-signal assumption,
which is applicable for swept frequency measurement at different driving levels and operating wavelengths.
We numerically and experimentally investigate and compare the performance of a Fabry-Perot laser diode (FP-LD)
under both strong- and weak-injection in detail. The numerical simulation results prove that the optically injection-locked
semiconductor laser will become stable in the injection-locking region under the above two conditions.
Nonetheless, the former can achieve stability faster than the latter whatever the frequency detuning is. The dynamic
injection-locking map and the property of side-mode suppression ratio (SMSR) for the optically injection-locked FP-LD
are experimentally obtained, and associated experiment phenomena are observed and qualitatively discussed for both
conditions. Our experiments show that quite different dynamics occur in the two conditions, with weak-injection
arrangement offering overall benefits in terms of more complicated dynamics and potential application.
All-optical sampling attracts considerable attention due to its crucial applications in high-speed optical analog-to-digital conversion. We successfully demonstrated an all-optical sampling scheme using nonlinear polarization rotation in a single semiconductor optical amplifier at 40 GSa/s and 160 GSa/s, respectively. The scheme requires only a single semiconductor optical amplifier and has low power consumption, which shows much potential for the high-speed optical analog-to-digital conversion.
All-optical sampling attracts considerable attention due to its crucial applications in high-speed optical analog-to-digital conversion. We present an all-optical sampling scheme using a single semiconductor optical amplifier. In the experiment, 40 GSa/s all-optical sampling for 2.5 GHz analog optical signal is successfully demonstrated with commercially available fiber-pigtailed components. The all-optical sampling shows a fundamental conversion efficiency of 1.35 and a total harmonic distortion of 2.01% at the operating power of 5 mW. Our scheme requires only one semiconductor optical amplifier and has low power consumption, which shows much potential for the high-speed optical analog-to-digital conversion.
KEYWORDS: Polarization, Picosecond phenomena, Semiconductor optical amplifiers, Distortion, Beam splitters, Ultrafast phenomena, All optical signal processing, Signal attenuation, Signal processing, Refractive index
A scheme for improving the self-induced polarization rotation (SPR) in a semiconductor optical amplifier (SOA) based on holding beam injection is proposed. Gain recovery of TE and TM modes can be largely accelerated through an appropriate holding beam injection, with which the response of SPR in the SOA for ultrafast signal can be speeded up. Holding beam injection is employed in SPR-based optical power equalization as an example of validation, in which the distortion of RZ (return-to-zero)and the overshoot of NRZ (non-return-to-zero) signal are largely suppressed, and the extension ratio are improved by 10 dB and 7 dB, respectively.
An all-optical power equalization based on nonlinear polarization rotation in a single semiconductor optical amplifier
(SOA) is proposed for waveform distortion reduction. Simulations have been done for the degraded data signals to
demonstrate the feasibility of the proposed scheme. The primarily simulated results indicated that the switching power is
less than 10 mW. The all-optical power equalization mentioned in this paper has promoting potential to improve the
signal quality and needs low optical power. Our approach has a simple configuration and allows for photonic integration,
which can be constructed by commercially available components.
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