Noise Carrier Research Articles

Improvement of optical noise in optical-injection-locked quantum dot lasers epitaxially grown on silicon by reducing external carrier noise

Abstract This study theoretically investigates the impact of external carrier noise from pumping sources on the optical noise of epitaxial quantum dot (QD) lasers on silicon. The findings indicate that the spectral linewidth and relative intensity noise (RIN) of silicon-based QD lasers using a quiet pump are significantly reduced. At 5.5 times the threshold current, the spectral linewidth decreases from 337.2 kHz to 213.2 kHz, and the RIN decreases from −141.3 dB Hz−1 to −168.8 dB Hz−1. This reduction is attributed to the lower external carrier noise level of the quiet pump, which also suppresses the spectral linewidth rebroadening effect at a high bias current. Moreover, when external optical injection locking is applied, the spectral linewidth further decreases to 24 kHz at an injection ratio of −70 dB and to 1.8 mHz at 0 dB. The RIN also slightly decreases to −172.4 dB Hz−1 with an injection ratio of 10. These results demonstrate that using a quiet pump is an effective and manageable strategy for significantly reducing both the spectral linewidth and RIN of QD lasers, thereby facilitating their application in next-generation photonic integrated circuits, continuous-variable quantum key distribution, quantum computing and ultra-precise quantum sensing.

Intensity noise reduction in quantum dot comb laser by lower external carrier fluctuations.

This work investigates the impact of carrier noise induced by an external current source on the linewidth enhancement factor (LEF) and relative intensity noise (RIN) of a 100 GHz quantum dot fourth-order colliding-pulse mode-locked laser (MLL), driven by a normal pump with Gaussian-distributed carrier sequences and a quiet pump with sub-Poissonian-distributed carrier sequences. The results indicate that under a normal pump, the LEFs are approximately zero for reverse saturable absorber (SA) bias voltages ranging from 0 to 2.5 V, and the laser achieves a RIN as low as -156 dB/Hz. When using a quiet pump, both the LEF and RIN are reduced across all SA bias conditions, particularly at low reverse SA bias voltages. Specifically, the LEF decreases by up to 0.58 at 0 V, and the average RIN spectrum is reduced by more than 3 dB at the same voltage. This work provides a straightforward approach for the development and optimization of multi-channel light sources for dense wavelength division multiplexing (DWDM) technologies with low optical noise.

PSYCHOACOUSTICS-WEB: A free online tool for the estimation of auditory thresholds

PSYCHOACOUSTICS-WEB is an online tool written in JavaScript and PHP that enables the estimation of auditory sensory thresholds via adaptive threshold tracking. The toolbox implements the transformed up-down methods proposed by Levitt (Journal of the Acoustical Society of America, 49, 467-477, (1971) for a set of classic psychoacoustical tasks: frequency, intensity, and duration discrimination of pure tones; duration discrimination and gap detection of noise; and amplitude modulation detection with noise carriers. The toolbox can be used through a common web browser; it works with both fixed and mobile devices, and requires no programming skills. PSYCHOACOUSTICS-WEB is suitable for laboratory, classroom, and online testing and is designed for two main types of users: an occasional user and, above all, an experimenter using the toolbox for their own research. This latter user can create a personal account, customise existing experiments, and share them in the form of direct links to further users (e.g., the participants of a hypothetical experiment). Finally, because data storage is centralised, the toolbox offers the potential for creating a database of auditory skills.

Neurometric amplitude modulation detection in the inferior colliculus of Young and Aged rats

Amplitude modulation is an important acoustic cue for sound discrimination, and humans and animals are able to detect small modulation depths behaviorally. In the inferior colliculus (IC), both firing rate and phase-locking may be used to detect amplitude modulation. How neural representations that detect modulation change with age are poorly understood, including the extent to which age-related changes may be attributed to the inherited properties of ascending inputs to IC neurons. Here, simultaneous measures of local field potentials (LFPs) and single-unit responses were made from the inferior colliculus of Young and Aged rats using both noise and tone carriers in response to sinusoidally amplitude-modulated sounds of varying depths. We found that Young units had higher firing rates than Aged for noise carriers, whereas Aged units had higher phase-locking (vector strength), especially for tone carriers. Sustained LFPs were larger in Young animals for modulation frequencies 8–16 Hz and comparable at higher modulation frequencies. Onset LFP amplitudes were much larger in Young animals and were correlated with the evoked firing rates, while LFP onset latencies were shorter in Aged animals. Unit neurometric thresholds by synchrony or firing rate measures did not differ significantly across age and were comparable to behavioral thresholds in previous studies whereas LFP thresholds were lower than behavior.

Observation of amplitude squeezing in a constant-current-driven distributed feedback quantum dot laser with optical feedback

We illustrate the generation of single-mode amplitude squeezing in a distributed feedback quantum dot laser driven by a constant-current pump. Achieving broadband amplitude squeezing of 1.7 dB over a 10 GHz range at room temperature is realized by suppressing carrier noise and implementing optical feedback. The noise-corrected squeezing level reached 5.1 dB. Furthermore, the examination of the zero-delay second-order correlation function demonstrates the robust feedback stability of the amplitude-squeezed state in the quantum dot laser compared to a reference quantum well laser. This investigation lays the groundwork for future advancements in integrated optical quantum chips.

Comparison of spectral resolution and spectro-temporal modulation sensitivity well above and near the hearing threshold

Spectral resolution and spectro-temporal modulation (STM) sensitivity both show a correlation with speech reception thresholds in noise. Both are also sensitive to the difficulties resulting from sensorineural hearing loss; however, the relationship between the two is not fully understood. The present study investigated the potential relationship between spectral resolution and STM sensitivity and the impact of presentation level in young, normal hearing listeners. Four noise carriers were tested with the two broader bandwidths and two 1-octave wide bandwidths: 200–6400 Hz, 1250–5000 Hz, 1250–2500 Hz, & 2500–5000 Hz. Presentation levels were 70 dB SPL and 20 dB SL relative to the individual’s pure-tone frequency-shaped noise carrier threshold. Spectral resolution was tested using a phase reversal paradigm, also known as a spectral ripple discrimination task, with thresholds measured in cycles per octave. Spectral, temporal, and STM sensitivity were each tested using a depth detection task, with thresholds measured in dB. On a test-by-test case, results were aligned with past studies that included a single test. The results show that both sensitivities are distinct at a low presentation level close to individual hearing thresholds, and a mixed relationship between both measures indicate that spectral resolution may only be one contributor to STM sensitivity.

Impact of external carrier noise on the linewidth enhancement factor of a quantum dot distributed feedback laser.

This paper demonstrates that the linewidth enhancement factor of quantum dot lasers is influenced by the external carrier transport issued from different external current sources. A model combining the rate equation and semi-classical carrier noise is used to investigate the different mechanisms leading to the above phenomenon in the context of a quantum dot distributed feedback laser. Meanwhile, the linewidth enhancement factor extracted from the optical phase modulation method shows dramatic differences when the quantum dot laser is driven by different noise-level pumps. Furthermore, the influence of external carrier noise on the frequency noise in the vicinity of the laser's threshold current directly affects the magnitude of the linewidth enhancement factor. Simulations also investigate how the external carrier transport impacts the frequency noise and the spectral linewidth of the QD laser. Overall, we believe that these results are of paramount importance for the development of on-chip integrated ultra-low noise oscillators producing light at or below the shot-noise level.

Non-cooperative underwater acoustic MFSK time-frequency representation optimization method based on sparse reconstruction

The performance of the traditional non-cooperative underwater acoustic (UWA) multiple frequency shift key (MFSK) recognition and parameter estimation method based on time-frequency representation (TFR) is affected by TFR energy divergence. Herein, a sparse TFR estimation model for UWA MFSK is presented. The model exploits the properties of MFSK TFR element sparsity and row sparsity, which can effectively reduce the impact of the channel and does not require any a priori information. To achieve better TFR performance, we propose an inversion fitting method that can effectively improve the frequency resolution, while keeping the time resolution unchanged. Simulation and experimental results show that the Peak Signal to Noise Ratio (PSNR) of the proposed method reaches 21dB with the increase of Signal to Noise Ratio (SNR), indicating that the proposed method has high carrier frequency reconstruction and noise suppression performance. The proposed method can continuously reduce the value of Average Carrier Frequency Offset (ACFO) under inversion fitting method, indicating that inversion fitting method can further reduce the energy divergence and improve frequency resolution.

RIN Reduction in Gain-Switched InAs-InP(113)B Quantum Dot Laser Based on Multi-Population Rate Equations

For the first time, relative intensity noise (RIN) of an InAs-InP(113)B quantum dot (Q-Dot) laser is examined theoretically under the gain-switching condition with the application of a Gaussian pulse beam (GPB) to excited state (Exs) of the laser. The multi-population rate equations considering nonlinear gain are solved by the Runge–Kutta method. Noises are added to rate equations as Langevin noise sources and a different method is applied here for the addition of these noise sources to equations. In this method, new rate equations are defined to eliminate the cross-correlations between the noise sources to make them independent and simulate with independent white Gaussian random variables. Obtained results showed that RIN decreases with the increasing ac peak current and the increasing inhomogeneous broadening. It was also observed that further RIN reduction of about 30 dB/Hz and gain-switched short pulses with a high power due to Exs emission being obtained with the application of GPB to Exs of the laser. Moreover, it was demonstrated that while carrier noise generated from Exs and ground state (Grs) affect the RIN spectrum, there is no effect of wetting layer (Wly) carrier noise.

Vocal count responses of narwhals to bulk carrier noise in Milne Inlet, Nunavut, Canada

AbstractConcerns were raised about possible behavioral disturbance to narwhals (Monodon monoceros) when exposed to shipping noise in Milne Inlet, Baffin Island, Canada. We deployed passive acoustic recorders in August and September 2018 and 2019, along and adjacent to the nominal shipping corridor. We measured broadband (0.01–25 kHz) sound pressure levels (SPL) after correcting for the auditory weighting function of high frequency cetaceans. Received SPLs and counts of Whistles, Buzzes, and Knocks were compared in a before‐during‐after study of individual bulk carrier transits, relative to periods with no ships. Narwhal call counts were generally lower once bulk carriers were within line‐of‐sight, including when ship noise levels were just above ambient noise levels. Call counts varied both “before” and “after” individual bulk carriers passed by the recorders. There was no evidence of a behavioral threshold SPL below which a response did not occur. We did not observe call count reductions to the same extent in 2019 compared to 2018 as higher ambient noise levels in 2019 likely masked some individual ship noise. There was no evidence of habituation or sensitization to the bulk carrier noise within or between years. Continued acoustic monitoring is recommended, especially if bulk carrier transits increase.

Pulsatile Gaussian-Enveloped Tones (GET) for cochlear-implant simulation

Acoustic simulation of cochlear implants (CIs) allows studies of not only perceptual performance in normal-hearing listeners but also relative contribution of spectral and temporal cues to speech recognition. Different from conventional simulations using continuous sinusoidal or noise carriers, this study employs pulsatile Gaussian-enveloped tones (GETs) to simulate several key features in modern CIs. Subject to the time–frequency uncertainty principle, the GET has a well-defined tradeoff between its duration and bandwidth. In theory, the key pulsatile features of CI electric stimuli could be simulated in the analysis part of a pulsatile acoustic model. We hypothesized that a GET vocoder could transmit speech information similar to actual CIs. In an experiment, 900-Hz/channel pulse trains were directly mapped to 900-Hz GET trains to simulate the maxima selection and amplitude compression of a widely-used n-of-m processing strategy, or the Advanced Combination Encoder. The simulated and actual implant performance of speech-in-noise recognition was similar in terms of the overall trend, absolute mean scores, and standard deviations. The results suggest that the pulsatile GET can serve as an alternative to simulating modern CIs in terms of simulating pulsatile and several other key features of CI stimuli and, more importantly, producing similar speech perception patterns. Investigation is needed to further evaluate the performance of the GET in different acoustic and electric configurations.

Sensitivity Modeling for LiteBIRD

LiteBIRD is a future satellite mission designed to observe the polarization of the cosmic microwave background radiation in order to probe the inflationary universe. LiteBIRD is set to observe the sky using three telescopes with transition-edge sensor bolometers. In this work we estimated the LiteBIRD instrumental sensitivity using its current design. We estimated the detector noise due to the optical loadings using physical optics and ray-tracing simulations. The noise terms associated with thermal carrier and readout noise were modeled in the detector noise calculation. We calculated the observational sensitivities over fifteen bands designed for the LiteBIRD telescopes using assumed observation time efficiency.

Amplitude-modulation forward masking for listeners with and without hearing loss.

Amplitude-modulation (AM) forward masking was measured for listeners with normal hearing and sensorineural hearing loss at 4000 and 1000 Hz, using continuous and noncontinuous masker and signal carriers, respectively. A low-fluctuation noise (LFN) carrier was used for the "continuous carrier" conditions. An unmodulated low-fluctuation noise (U-LFN), an unmodulated Gaussian noise (U-GN), and an amplitude-modulation low-fluctuation noise (AM-LFN) were maskers for the "noncontinuous carrier" conditions. As predicted, U-GN yielded more masking than U-LFN and similar masking to AM-LFN, suggesting that U-GN resulted in AM forward masking. Contrary to predictions, no differences in masked thresholds were observed between listener groups.

Spectrotemporal Modulation Discrimination in Infants With Normal Hearing.

Spectral resolution correlates with speech understanding in post-lingually deafened adults with cochlear implants (CIs) and is proposed as a non-linguistic measure of device efficacy in implanted infants. However, spectral resolution develops gradually through adolescence regardless of hearing status. Spectral resolution relies on two different factors that mature at markedly different rates: Resolution of ripple peaks (frequency resolution) matures during infancy whereas sensitivity to across-spectrum intensity modulation (spectral modulation sensitivity) matures by age 12. Investigation of spectral resolution as a clinical measure for implanted infants requires understanding how each factor develops and constrains speech understanding with a CI. This study addresses the limitations of the present literature. First, the paucity of relevant data requires replication and generalization across measures of spectral resolution. Second, criticism that previously used measures of spectral resolution may reflect non-spectral cues needs to be addressed. Third, rigorous behavioral measurement of spectral resolution in individual infants is limited by attrition. To address these limitations, we measured discrimination of spectrally modulated, or rippled, sounds at two modulation depths in normal hearing (NH) infants and adults. Non-spectral cues were limited by constructing stimuli with spectral envelopes that change in phase across time. Pilot testing suggested that dynamic spectral envelope stimuli appeared to hold infants' attention and lengthen habituation time relative to previously used static ripple stimuli. A post-hoc condition was added to ensure that the stimulus noise carrier was not obscuring age differences in spectral resolution. The degree of improvement in discrimination at higher ripple depth represents spectral frequency resolution independent of the overall threshold. It was hypothesized that adults would have better thresholds than infants but both groups would show similar effects of modulation depth. Participants were 53 6- to 7-month-old infants and 23 adults with NH with no risk factors for hearing loss who passed bilateral otoacoustic emissions screening. Stimuli were created from complexes with 33- or 100-tones per octave, amplitude-modulated across frequency and time with constant 5 Hz envelope phase-drift and spectral ripple density from 1 to 20 ripples per octave (RPO). An observer-based, single-interval procedure measured the highest RPO (1 to 19) a listener could discriminate from a 20 RPO stimulus. Age-group and stimulus pure-tone complex were between-subjects variables whereas modulation depth (10 or 20 dB) was within-subjects. Linear-mixed model analysis was used to test for the significance of the main effects and interactions. All adults and 94% of infants provided ripple density thresholds at both modulation depths. The upper range of threshold approached 17 RPO with the 100-tones/octave carrier and 20 dB depth condition. As expected, mean threshold was significantly better with the 100-tones/octave compared with the 33-tones/octave complex, better in adults than in infants, and better at 20 dB than 10 dB modulation depth. None of the interactions reached significance, suggesting that the effect of modulation depth on the threshold was not different for infants or adults. Spectral ripple discrimination can be measured in infants with minimal listener attrition using dynamic ripple stimuli. Results are consistent with previous findings that spectral resolution is immature in infancy due to immature spectral modulation sensitivity rather than frequency resolution.

Optical phase-locked loop phase noise in 5G mm-wave OFDM ARoF systems

The use of millimeter-wave (mm-wave) frequencies is required in order to support the increasing number of connected devices expected from the fifth generation (5G) of mobile communications. Subsequently, the generation of radio-frequency (RF) carriers ranging from 10GHz to 300GHz and their transport through optical distribution network (ODN) is a key element of the future 5G fronthaul. Optically assisted RF carrier generation is one of the most promising solutions to tackle this issue, allowing a wide use of analog radio-over-fiber (ARoF) architectures. However the main limitation of these optical methods is related to the finite coherence of lasers sources, which can dramatically degrade data transmission in analog formats. To mitigate its impact, the use of orthogonal frequency-division multiplexing (OFDM) as the 5G standard allows employing efficient phase noise compensation algorithms. Therefore, in this study, we present an experimental demonstration of a mm-wave generation technique based on an optical phase-locked loop (OPLL) that fulfills the frequency specifications for 5G. Then, an algorithm is introduced that improves data recovery at reception and reduces the impact of a possible high phase noise carrier. Finally, a back-to-back data transmission experiment is performed, demonstrating the efficiency of the algorithm to reach the 5G requirements. These results emphasize the use of OPLLs as a viable solution to generate mm-wave carriers for 5G and beyond.

A multipath mitigation algorithm for GNSS signals based on the steepest descent approach

Multipath interference seriously degrades the performance of Global Navigation Satellite System (GNSS) positioning in an urban canyon. Most current multipath mitigation algorithms suffer from heavy computational load or need external assistance. We propose a multipath mitigation algorithm based on the steepest descent approach, which has the merits of less computational load and no need for external aid. A new ranging code tracking loop is designed based on the steepest descent method, which can save an early branch or a late branch compared with the narrow-spacing correlation method. The power of the Non-Line-of-Sight (NLOS) signal is weaker than that of the Line-of-Sight (LOS) signal when the LOS signal is not obstructed and with a relatively high Carrier Noise Ratio (CNR). The peak position in the X-axis of the ranging code autocorrelation function does not move with the NLOS interference. Meanwhile, the cost function is designed according to this phenomenon. The results demonstrate that the proposed algorithm outperforms the narrow-spacing correlation and the Multipath Estimated Delay Locked Loop (MEDLL) in terms of the code multipath mitigation and computation time. The Standard Deviation (STD) of the tracking error with the proposed algorithm is less than 0.016 chips. Moreover, the computation time of the proposed algorithm in a software defined receiver is shortened by 24.21% compared with the narrow-spacing correlation.

Thermal noise of hot carriers under natural sunlight

The efficiency of hot carrier solar cells strongly depends on the attainable carrier temperature in the absorber material. Measurements of hot carrier temperature under natural concentrated sunlight were performed at thin films of graphite, bismuth and PbTe, cooled through AlN ceramic substrate. The carrier temperature was assessed by magnitude of thermal noise voltage of charge carriers in the frequency range between 300 and 20,000 Hz according to Nyquist formula. Noise measurement equipment was calibrated in a range of sample impedances by using heated metal film resistors. We found that the carrier temperature in graphite films can exceed 600 °C under up to 15,000× suns and is much higher than the estimated lattice temperature in the film under the given cooling conditions. Secondary electron micrographs illustrate a good mechanical contact between the graphite film and the AlN substrate. We found also distinct heating of charge carriers in PbTe up to about 100 °C. Contrary to that, no measurable carrier heating above the lattice temperature was detected in bismuth films. Johnson noise thermometry demonstrates potential in identification of attractive candidate materials for absorbers in hot carrier solar cells.

Generation of ultra-low jitter radio frequency phase pulses by a phase-locked oscillator.

We demonstrate a novel, to the best of our knowledge, method for mode locking of an oscillator, which is based on the injection of a strong sinusoidal signal from an external source into the cavity. The oscillator generates a low phase noise carrier signal with a train of ultra-low jitter, short 2π phase pulses at a repetition period equal to the cavity round-trip time. Both the carrier signal and phase pulses are phase-locked to the external source. We demonstrate the effect in an optoelectronic oscillator that generates a train of short phase pulses at a high carrier frequency with the broadband spectrum of a dense RF frequency comb. The phase pulses can be converted to short, ultra-low jitter intensity RF pulses by beating the oscillator signal with the external source, used for locking.

Electrophysiological responses to change in spectral ripple envelope phase in normal-hearing infants

Spectral resolution plays an important role in understanding speech in noisy real-world listening environments. Spectral ripple discrimination is one method used to measure spectral resolution that has been shown to correlate with open-set speech understanding in adults and children who use cochlear implants. In this study, we investigate the feasibility of obtaining an electrophysiological measure of spectral ripple discrimination in very young infants. Spectral ripple stimuli were constructed from two concatenated 1-s noise carriers consisting of 2555 random phase pure tone frequency components between 100–5000 Hz, with a spectral envelope sinusoidally modulated at 1-ripple-per-ocatave with peak-to-trough depth of 20 dB. The starting phase of the first half of the stimulus varied randomly while the starting phase of the second half was “inverted”, shifted by 90-deg, relative to the first. Infants were presented with 150 repetitions of these stimuli at 80 or 65 dBA in sound field while undergoing 32-channel electroencephalography (EEG) recording. Our preliminary analyses show that an acoustic change response can be recorded in awake infants between 2 and 4 months of age in response to a spectral ripple inversion. These preliminary results suggest the potential utility of EEG in the measurement of spectral resolution in very young infants, warranting further investigation.

Speech intelligibility and talker gender classification with noise-vocoded and tone-vocoded speech.

Vocoded speech provides less spectral information than natural, unprocessed speech, negatively affecting listener performance on speech intelligibility and talker gender classification tasks. In this study, young normal-hearing participants listened to noise-vocoded and tone-vocoded (i.e., sinewave-vocoded) sentences containing 1, 2, 4, 8, 16, or 32 channels, as well as non-vocoded sentences, and reported the words heard as well as the gender of the talker. Overall, performance was significantly better with tone-vocoded than noise-vocoded speech for both tasks. Within the talker gender classification task, biases in performance were observed for lower numbers of channels, especially when using the noise carrier.