Showing papers on "Chirp published in 2013"
TL;DR: Broadband and narrowband chirp excitations are utilized to address the need to both test at multiple frequencies and achieve a high signal-to-noise ratio to minimize acquisition time.
204 citations
TL;DR: In this paper, a buckled spring-mass architecture is proposed to convert the energy of the dynamic mass to electrical energy in the piezoelectric materials as efficiently as possible.
Abstract: Bistable vibration energy harvesters are attracting more and more interest because of their capability to scavenge energy over a large frequency band. The bistable effect is usually based on magnetic interaction or buckled beams. This paper presents a novel architecture based on amplified piezoelectric structures. This buckled spring‐mass architecture allows the energy of the dynamic mass to be converted into electrical energy in the piezoelectric materials as efficiently as possible. Modeling and design are performed and a normalized expression of the harvester behavior is given. Chirp and band-limited noise excitations are used to evaluate the proposed harvester’s performances. Simulation and experimental results are in good agreement. A method of using a spectrum plot for investigating the interwell motion is presented. The effect of the electric load impedance matching strategy is also studied. Results and comparisons with the literature show that the proposed device combines a large bandwidth and a high power density. (Some figures may appear in colour only in the online journal)
141 citations
TL;DR: The modulation and the demodulation processing in regard to typical spaceborne SAR receive signals are introduced and verified by a simulation for the case of pointlike targets.
Abstract: In this letter, we present a new waveform technique for the use of multiple transmitters in synthetic aperture radar (SAR) data acquisition. This approach is based on the principle of the orthogonal-frequency-division-multiplexing technique. Unlike multiple subband approaches, the proposed scheme allows the generation of multiple orthogonal waveforms on common spectral support and thereby enables to exploit the full bandwidth for each waveform. This letter introduces the modulation and the demodulation processing in regard to typical spaceborne SAR receive signals. The proposed processing techniques are verified by a simulation for the case of pointlike targets.
138 citations
TL;DR: It is shown that, although the total width of the x-ray bursts spans femtosecond time scales, the pulse exhibits a zeptosecond structure due to the interference of high harmonic emission from multiple reencounters of the electron wave packet with the ion.
Abstract: We demonstrate theoretically that the temporal structure of high harmonic x-ray pulses generated with midinfrared lasers differs substantially from those generated with near-infrared pulses, especially at high photon energies. In particular, we show that, although the total width of the x-ray bursts spans femtosecond time scales, the pulse exhibits a zeptosecond structure due to the interference of high harmonic emission from multiple reencounters of the electron wave packet with the ion. Properly filtered and without any compensation of the chirp, regular subattosecond keV waveforms can be produced.
132 citations
TL;DR: In this article, a tacho-less order tracking method is established for any speed variations including large speed variation such as run-up or run-down process of machinery, where a Chirplet-based approach is proposed to estimate the instantaneous frequency of a certain harmonic of rotating frequency.
129 citations
TL;DR: This is the first integrated 77-GHz automotive radar transceiver with the feature of anti-interference, and the proposed frequency-hopping random chirp FMCW technique reconfigures the chirP sweep frequency and time every cycle to result in noise-like frequency response for mutual interference after the received signal is down-converted and demodulated.
Abstract: This paper presents a 77-GHz long-range automotive radar transceiver with the function of reducing mutual interference. The proposed frequency-hopping random chirp FMCW technique reconfigures the chirp sweep frequency and time every cycle to result in noise-like frequency response for mutual interference after the received signal is down-converted and demodulated. Thus, the false alarm rate can be reduced significantly. The transceiver IC is fully integrated in TSMC 1P9M 65-nm digital CMOS technology. The chip including pads occupies a silicon area of 1.03 mm × 0.94 mm. The transceiver consumes totally 275 mW of power, and the measured transmitting power and receiver noise figure are 6.4 dBm and 14.8 dB, respectively. To the authors' knowledge, this is the first integrated 77-GHz automotive radar transceiver with the feature of anti-interference.
95 citations
TL;DR: A new distributed angle estimation method for localization in wireless sensor networks (WSNs) under multipath propagation environment is proposed using a two-antenna anchor that can emit two linear chirp waves simultaneously and the angle of departure of the emitted waves is estimated at each receiving node via frequency measurement of the local received signal strength indication (RSSI) signal.
Abstract: In this paper, we design a new distributed angle estimation method for localization in wireless sensor networks (WSNs) under multipath propagation environment. We employ a two-antenna anchor that can emit two linear chirp waves simultaneously, and propose to estimate the angle of departure (AOD) of the emitted waves at each receiving node via frequency measurement of the local received signal strength indication (RSSI) signal. An improved estimation method is further proposed where multiple parallel arrays are adopted to provide the space diversity. The proposed methods rely only on radio transceivers and do not require frequency synchronization or precise time synchronization between the transceivers. More importantly, the angle is estimated at each sensor in a completely distributed manner. The performance analysis is derived and simulations are presented to corroborate the proposed studies.
95 citations
TL;DR: This letter proposes a practical approach to mitigate the range ambiguities in high-PRF SAR by using the orthogonal frequency-division multiplexing (OFDM) waveform diversity, which has a large time–bandwidth product.
Abstract: Range-ambiguity suppression is a technical challenge for high-pulse-repetition-frequency (PRF) synthetic aperture radar (SAR). This letter proposes a practical approach to mitigate the range ambiguities in high-PRF SAR by using the orthogonal frequency-division multiplexing (OFDM) waveform diversity. The system scheme, waveform design, and range-ambiguity-to-signal-ratio performance are detailed. The approach eliminates the ambiguities, instead of just suppressing them like other techniques. The proposed OFDM chirp diverse waveform has a large time–bandwidth product. It is validated by computer-simulation results. Although OFDM radar has received much attention in recent years, there appears to be little work done in applying OFDM concepts to mitigate high-PRF radar range ambiguities, as is the subject of this letter.
95 citations
TL;DR: It is demonstrated the possibility of running a single-pass free electron laser in a dynamical regime, which can be exploited to perform two-color pump-probe experiments in the vacuum ultraviolet or x-ray domain, using the free-electron laser emission both as a pump and as a probe.
Abstract: We demonstrate the possibility of running a single-pass free electron laser (FEL) in a dynamical regime, which can be exploited to perform two-color pump-probe experiments in the vacuum ultraviolet or x-ray domain, using the free-electron laser emission both as a pump and as a probe. The studied regime is induced by triggering the free-electron laser process with a powerful laser pulse, carrying a significant and adjustable frequency chirp. As a result, the output FEL radiation is split in two pulses, separated in time (as previously observed by different authors), and having different central wavelengths. We show that both the spectral and temporal distances between FEL pulses can be independently controlled. We also provide a theoretical description of this phenomenon, which is found in good agreement with experiments performed on the FERMI@Elettra free-electron laser.
91 citations
17 Mar 2013
TL;DR: In this article, the authors suggest a chirp signal and describe its advantages over other signals, and demonstrate the effectiveness of this approach in online impedance measurement in three-phase AC systems.
Abstract: Impedance defined in synchronous coordinates is a useful tool to predict and evaluate stability of three-phase AC systems. For online impedance measurement in AC systems, the widely used frequency sweep method takes a long time and may not be practical in systems where the operating point cannot be maintained for a long time. A wide bandwidth signal could be used to significantly reduce the measurement time. This paper suggests a chirp signal and describes its advantages over other signals. Experimental results demonstrate the effectiveness of this approach.
84 citations
TL;DR: A new architecture for high-speed compressed sensing using chirp processing with ultrafast laser pulses, presently applied to the measurement of sparse-frequency microwave signals, is demonstrated.
Abstract: We demonstrate a new architecture for high-speed compressed sensing using chirp processing with ultrafast laser pulses, presently applied to the measurement of sparse-frequency microwave signals. We spectrally encode highly chirped ultrafast laser pulses with pseudorandom bit sequences such that every laser pulse acquires a unique spectral pattern. The pulses are partially compressed in time, extending the effective sampling rate beyond the electronic limit, and then modulated with a sparse microwave signal. Finally the pulses are fully compressed and detected, effectively integrating the measurement. We achieve 100 usable features per pattern allowing for 100 points in the reconstructed microwave spectra and experimentally demonstrate reconstruction of two- and three-tone microwave signals spanning from 900 MHz to 14.76 GHz. These spectra are reconstructed by measuring the energy of only 23 to 38 consecutive laser pulses acquired in a single shot with a 500 MHz real-time oscilloscope.
TL;DR: In this paper, a couple mode theory is proposed to interpret and estimate the observed effects of sound wave concentration on a chirped sonic crystal, which is related to a progressive slowing down of the sound wave as it propagates along the material.
Abstract: We propose and experimentally demonstrate a mechanism of sound wave concentration based on soft reflections in chirped sonic crystals. The reported controlled field enhancement occurs at around particular (bright) planes in the crystal and is related to a progressive slowing down of the sound wave as it propagates along the material. At these bright planes, a substantial concentration of the energy (with a local increase up to 20 times) was obtained for a linear chirp and for frequencies around the first band gap. A simple couple mode theory is proposed that interprets and estimates the observed effects. Wave concentration energy can be applied to increase the efficiency of detectors and absorbers.
TL;DR: In this article, a 220-GHz homodyne transceiver module is proposed for frequency modulated continuous wave radar applications, which is fabricated on 3-μm-thick GaAs membranes and consists of a Schottky diode based transmitter frequency doubler that simultaneously operates as a subharmonic down-converting mixer.
Abstract: We present a 220-GHz homodyne transceiver module intended for frequency modulated continuous wave radar applications. The RF transceiver circuits are fabricated on 3-μm-thick GaAs membranes, and consist of a Schottky diode based transmitter frequency doubler that simultaneously operates as a sub-harmonic down-converting mixer. Two circuits are used in a balanced configuration to improve the noise performance. The output power is > 3 dBm over a 40-GHz bandwidth (BW) centered at 220 GHz, and the receiver function is characterized by a typical mixer conversion loss of 16 dB. We present radar images at 4-m target distance with up to 60-dB dynamic range using a 30-μs chirp time, and near-BW-limited range resolution. The module is intended for applications in high-resolution real-time 3-D radar imaging, and the unit is therefore designed so that it can be assembled into 1-D or 2-D arrays.
TL;DR: It is demonstrated that a given field envelope produces a unique and unequivocal chirp-scan map and that, under some asymptotic assumptions, both the spectral amplitude and phase of the measured pulse can be retrieved analytically from only two measurements.
Abstract: We investigate a variant of the d-scan technique, an intuitive pulse characterization method for retrieving the spectral phase of ultrashort laser pulses. In this variant a ramp of quadratic spectral phases is applied to the input pulses and the second harmonic spectra of the resulting pulses are measured for each chirp value. We demonstrate that a given field envelope produces a unique and unequivocal chirp-scan map and that, under some asymptotic assumptions, both the spectral amplitude and phase of the measured pulse can be retrieved analytically from only two measurements. An iterative algorithm can exploit the redundancy of the information contained in the chirp-scan map to discard experimental noise, artifacts, calibration errors and improve the reconstruction of both the spectral intensity and phase. This technique is compared to two reference characterization techniques (FROG and SRSI). Finally, we perform d-scan measurements with a simple grating-pair compressor.
TL;DR: This letter presents a novel algorithm to compute the instantaneous frequency (IF) of a multicomponent nonstationary signal using a combination of fractional spectrograms (FS).
Abstract: This letter presents a novel algorithm to compute the instantaneous frequency (IF) of a multicomponent nonstationary signal using a combination of fractional spectrograms (FS). A high resolution time frequency distribution (TFD) is defined by combining FS computed using windows of varying lengths and chirp rates. The IF of individual signal components is then computed by applying a peak detection and component extraction procedure. The mean square error (MSE) of IF estimates computed with the AFS is lower than the MSE of IF estimates obtained from other TFDs for SNR varying from -5 dB to 16 dB.
TL;DR: In this article, a systematic and optimized approach to grating construction is provided, and different apodization techniques are compared where appropriate, where the poling period is varied smoothly, monotonically, and rapidly at the edges of the device.
Abstract: Chirped quasi-phasematching (QPM) optical devices offer the potential for ultrawide bandwidths, high conversion efficiencies, and high amplification factors across the transparency range of QPM media. In order to properly take advantage of these devices, apodization schemes are required. We study apodization in detail for many regimes of interest, including low-gain difference frequency generation (DFG), high-gain optical parametric amplification (OPA), and high-efficiency adiabatic frequency conversion (AFC). Our analysis is also applicable to second-harmonic generation, sum frequency generation, and optical rectification. In each case, a systematic and optimized approach to grating construction is provided, and different apodization techniques are compared where appropriate. We find that nonlinear chirp apodization, where the poling period is varied smoothly, monotonically, and rapidly at the edges of the device, offers the best performance. We consider the full spatial structure of the QPM gratings in our simulations, but utilize the first order QPM approximation to obtain analytical and semi-analytical results. One application of our results is optical parametric chirped pulse amplification; we show that special care must be taken in this case to obtain high gain factors while maintaining a flat gain spectrum.
TL;DR: In this paper, a relativistic, three-dimensional numerical model was developed to calculate and quantify the characteristics of emitted radiation when an electron beam interacts with an intense laser pulse.
Abstract: Based on single particle tracking in the framework of classical Thomson scattering with incoherent superposition, we developed a relativistic, three-dimensional numerical model that calculates and quantifies the characteristics of emitted radiation when a relativistic electron beam interacts with an intense laser pulse. This model has been benchmarked against analytical expressions, based on the plane wave approximation to the laser field, derived by Esarey et al. [Phys. Rev. E 48, 3003 (1993)]. For laser pulses of sufficient duration, we find that the scattered radiation spectrum is broadened due to interferences arising from the pulsed nature of the laser. We find that by appropriately chirping the scattering laser pulse, spectral broadening can be minimized, and the peak on-axis brightness of the emitted radiation is increased by a factor of approximately 5.
TL;DR: Based on the heterodyne beating between the pre-chirped optical pulse and the continuous wave light in a wideband photodetector, linearly chirped microwave pulse, which yields a large time-bandwidth product (TBWP) of 106 and high compression ratio of 160, is generated in this experiment.
Abstract: Based on the heterodyne beating between the pre-chirped optical pulse and the continuous wave (CW) light in a wideband photodetector (PD), linearly chirped microwave pulse with time duration of 32ns and bandwidth of 33GHz, which yields a large time-bandwidth product (TBWP) of 106 and high compression ratio of 160, is generated in our experiment Dispersion compensation fiber (DCF) with uniform response across broad bandwidth is used for providing the original linear chirp in our method, which shows the promise to generate linearly chirped microwave pulse with bandwidth of up to THz The flexibility of the center frequency and the stability of the time-frequency performance are demonstrated by generating different types of linearly chirped microwave pulses The range resolution of our generated microwave pulse is also verified by off-line processing
TL;DR: In this paper, the authors theoretically investigate high-order harmonic generation in a spatially inhomogeneous field with mid-infrared driving wavelength and few-cycle duration, and they show that this spatiotemporally synthesized electric field is powerful to control the quantum path; as a result an ultra-broadband supercontinuum with bandwidth over 300 eV can be obtained successfully.
Abstract: We theoretically investigate high-order harmonic generation in a spatially inhomogeneous field with mid-infrared driving wavelength and few-cycle duration. It is found that this spatiotemporally synthesized electric field is powerful to control the quantum path; as a result an ultra-broadband supercontinuum with bandwidth over 300 eV can be obtained successfully. Important characteristics of the attosecond pulse generation, including temporal envelope, harmonic chirp and carrier–envelope phase (CEP) dependence are further discussed. The results show that close-to-Fourier-limit 27 as isolated pulses are straightforwardly filtered from the supercontinuum. Moreover, such short isolated attosecond pulses can be supported by nearly all the CEPs of the laser electric field. This would open a way to obtain broadband isolated attosecond pulses with no need of CEP stabilization of the laser field.
TL;DR: A successful conversion of this energy modulation into a beam density modulation, and the formation of a series of microbunches with a subpicosecond periodicity by means of magnetic optics (chicane) are demonstrated.
Abstract: A strong energy modulation in an electron bunch passing through a dielectric-lined waveguide was recently demonstrated in Antipov et al., Phys. Rev. Lett. 108, 144801 (2012). In this Letter, we demonstrate a successful conversion of this energy modulation into a beam density modulation, and the formation of a series of microbunches with a subpicosecond periodicity by means of magnetic optics (chicane). A strong coherent transition radiation signal produced by the microbunches is obtained and the tunability of its carrier frequency in the 0.68--0.9 THz range by regulating the energy chirp in the incoming electron bunch is demonstrated using infrared interferometry. A tabletop, compact, tunable, and narrowband source of intense THz radiation based on this technology is proposed.
TL;DR: In this paper, a concept for self-aligned formation of the p-n junction which is flexible in the capability to produce a number of device configurations is presented, and experimental results from devices which are formed through such processes are presented with operation up to and beyond 40 Gbit/s.
Abstract: Silicon photonics is poised to revolutionize several data communication applications. The development of high performance optical modulators formed in silicon is essential for the technology to be viable. In this paper, we review our recent work on carrier-depletion silicon Mach-Zehnder-based optical modulators which have formed part of the work within the U.K. Silicon Photonics and HELIOS projects, as well as including some recent new data. A concept for the self-aligned formation of the p-n junction which is flexible in the capability to produce a number of device configurations is presented. This process is the key in having performance repeatability, a high production yield, and large extinction ratios. Experimental results from devices which are formed through such processes are presented with operation up to and beyond 40 Gbit/s. The potential for silicon photonics to fulfill longer haul applications is also explored in the analysis of the chirp produced from these devices and the ability to produce large extinction ratios at high speed. It is shown that the chirp produced with the modulator operated in dual drive configuration is negligible and that an 18-dB dynamic modulation depth is obtainable at a data rate of 10 Gbit/s.
TL;DR: In this paper, a detailed theoretical analysis of the lasing wavelength precision of the DFB laser array based on a reconstruction-equivalent-chirp (REC) technique is presented.
Abstract: A detailed theoretical analysis of the lasing wavelength precision of the DFB laser array based on a reconstruction-equivalent-chirp (REC) technique is presented. Experimental results of the eight-wavelength DFB laser array with equivalent π phase shift (π-EPS) and four-wavelength DFB laser array with equivalent three shifts are also given. High lasing wavelength precision was obtained. This paper demonstrates that the REC technique is a promising way for fabricating the multiwavelength DFB laser array with low cost and high yield.
TL;DR: In this article, a non-linear Lamb wave signal processing strategy aimed at extending the capability of activepassive networks of PZT transducers for defect detection is proposed, which allows to use chirp shaped pulses in actuation, instead of classically applied spiky pulses, requiring thus lower input voltages.
TL;DR: In this paper, a simple and fast method to estimate the fiber dispersion and laser chirp parameters on a dispersive Intensity Modulation and Direct Detection (IM/DD) optical channel is presented.
Abstract: We report on a simple and fast method to estimate the fiber dispersion and laser chirp parameters on a dispersive Intensity Modulation and Direct Detection (IM/DD) optical channel. Based on the general IM/DD small-signal frequency response, we use the Downhill-Simplex algorithm to fit the channel measurement retrieved with a network analyzer to a general mathematical model. The method is proven to be quite efficient for light sources of different natures and with different adiabatic and transient chirp characteristics, including a Distributed Feedback (DFB) laser, an Electroabsorption modulator (EAM) and even a Reflective Semiconductor Optical Amplifier with fiber-Bragg grating (RSOA-FBG).
TL;DR: A Mach-Zehnder modulator is designed based on a hybrid graphene-silicon waveguide and demonstrated it can process signals nearly chirp-free and can potentially be ultrafast as well as CMOS compatible.
Abstract: We present a hybrid graphene–silicon waveguide, which consists of a lateral slot waveguide with three layers of graphene flakes inside. Through a theoretical analysis, an effective index variation for about 0.05 is found in the waveguide by applying a voltage on the graphene. We designed a Mach–Zehnder modulator based on this waveguide and demonstrated it can process signals nearly chirp-free. The calculation shows that the driving voltage is only 1 V even if the length of the arm is shortened to be 43.54 μm. An extinction up to 34.7 dB and a minimum chirp parameter of −0.006 are obtained. Its insertion loss is roughly −1.37 dB. This modulator consumes low power and has a small footprint. It can potentially be ultrafast as well as CMOS compatible.
TL;DR: LFM and NLFM signals were used for the insonation of microbubble populations and the NLFM chirp with a customized window was used as an excitation signal to perform subharmonic imaging in an ultrasound flow phantom.
Abstract: Subharmonic generation from ultrasound contrast agents depends on the spectral and temporal properties of the excitation signal. The subharmonic response can be improved by using wideband and long-duration signals. However, for sinusoidal tone-burst excitation, the effective bandwidth of the signal is inversely proportional to the signal duration. Linear frequency-modulated (LFM) and nonlinear frequencymodulated (NLFM) chirp excitations allow independent control over the signal bandwidth and duration; therefore, in this study LFM and NLFM signals were used for the insonation of microbubble populations. The amplitude modulation of the excitation waveform was achieved by applying different window functions. A customized window was designed for the NLFM chirp excitation by focusing on reducing the spectral leakage at the subharmonic frequency and increasing the subharmonic generation from microbubbles. Subharmonic scattering from a microbubble population was measured for various excitation signals and window functions. At a peak negative pressure of 600 kPa, the generated subharmonic energy by ultrasound contrast agents was 15.4 dB more for NLFM chirp excitation with 40% fractional bandwidth when compared with tone-burst excitation. For this reason, the NLFM chirp with a customized window was used as an excitation signal to perform subharmonic imaging in an ultrasound flow phantom. Results showed that the NLFM waveform with a customized window improved the subharmonic contrast by 4.35 ± 0.42 dB on average over a Hann-windowed LFM excitation.
TL;DR: A full-band Adaptive Harmonic Model (aHM) is described along with detailed descriptions of its corresponding algorithms for the estimation of harmonics up to the Nyquist frequency and formal listening tests show that the speech reconstructed using aHM is nearly indistinguishable from the original speech.
Abstract: Voice models often use frequency limits to split the speech spectrum into two or more voiced/unvoiced frequency bands. However, from the voice production, the amplitude spectrum of the voiced source decreases smoothly without any abrupt frequency limit. Accordingly, multiband models struggle to estimate these limits and, as a consequence, artifacts can degrade the perceived quality. Using a linear frequency basis adapted to the non-stationarities of the speech signal, the Fan Chirp Transformation (FChT) have demonstrated harmonicity at frequencies higher than usually observed from the DFT which motivates a full-band modeling. The previously proposed Adaptive Quasi-Harmonic model (aQHM) offers even more flexibility than the FChT by using a non-linear frequency basis. In the current paper, exploiting the properties of aQHM, we describe a full-band Adaptive Harmonic Model (aHM) along with detailed descriptions of its corresponding algorithms for the estimation of harmonics up to the Nyquist frequency. Formal listening tests show that the speech reconstructed using aHM is nearly indistinguishable from the original speech. Experiments with synthetic signals also show that the proposed aHM globally outperforms previous sinusoidal and harmonic models in terms of precision in estimating the sinusoidal parameters. As a perspective, such a precision is interesting for building higher level models upon the sinusoidal parameters, like spectral envelopes for speech synthesis.
TL;DR: A direct measurement of the Wigner distribution of complex photon states in an anharmonic oscillator--a superconducting phase circuit, biased in the small anharmonicity regime is demonstrated.
Abstract: The analysis of wave-packet dynamics may be greatly simplified when viewed in phase space. While harmonic oscillators are often used as a convenient platform to study wave packets, arbitrary state preparation in these systems is more challenging. Here, we demonstrate a direct measurement of the Wigner distribution of complex photon states in an anharmonic oscillator—a superconducting phase circuit, biased in the small anharmonicity regime. We apply our method on nondispersive wave packets to explicitly show phase locking in states prepared by a frequency chirp. This method requires a simple calibration, and is easily applicable in our system out to the fifth level.
TL;DR: This research considers an advanced pulse compression noise (APCN) radar waveform possessing salient features from linear-FM (LFM) and noise waveforms and demonstrates the low probability of interception (LPI) characteristic of the APCN waveform for different κ values.
Abstract: This research considers an advanced pulse compression noise (APCN) radar waveform possessing salient features from linear-FM (LFM) and noise waveforms. A cross-correlation model considering several chirp waveform profiles is used to simulate the output of a passive electronic intelligence (ELINT) intercept-receiver. By doing so we are able to demonstrate the low probability of interception (LPI) characteristic of the APCN waveform for different κ values.
TL;DR: In this paper, the bound states of one kind of dissipative solitons in a single-pulse mode-locked fiber laser were observed and it was shown that the separation between the bounded pulses in such soliton molecules increases with the pump power, and also varies with the settings of polarization controllers.
Abstract: Though normal-dispersion mode-locked fiber lasers generally work on a single-pulse regime due to the large chirp of the pulses, we observe bound states of one kind of dissipative solitons in the laser. The separation between the bounded pulses in such soliton molecules increases with the pump power, and also varies with the settings of polarization controllers, which is consistent with other kinds of bounded pulses such as solitons. Our study indicates that the bound state of pulses is an intrinsic feature of mode-locked lasers and is independent of pulse profiles, stimulated by overdriving of mode-locking mechanisms.