Terahertz wave generation from ring-Airy beam induced plasmas and remote detection by terahertz-radiation-enhanced-emission-of-fluorescence: a review

Kang LIU, Pingjie HUANG, Xi-Cheng ZHANG

Front. Optoelectron. ›› 2019, Vol. 12 ›› Issue (2) : 117-147.

PDF(3810 KB)
Front. Optoelectron. All Journals
PDF(3810 KB)
Front. Optoelectron. ›› 2019, Vol. 12 ›› Issue (2) : 117-147. DOI: 10.1007/s12200-018-0860-7
REVIEW ARTICLE
REVIEW ARTICLE

Terahertz wave generation from ring-Airy beam induced plasmas and remote detection by terahertz-radiation-enhanced-emission-of-fluorescence: a review

Author information +
History +

Abstract

With the increasing demands for remote spectroscopy in many fields ranging from homeland security to environmental monitoring, terahertz (THz) spectroscopy has drawn a significant amount of attention because of its capability to acquire chemical spectral signatures non-invasively. However, advanced THz remote sensing techniques are obstructed by quite a few factors, such as THz waves being strongly absorbed by water vapor in the ambient air, difficulty to generate intense broadband coherent THz source remotely, and hard to transmit THz waveform information remotely without losing the signal to noise ratio, etc. In this review, after introducing different THz air-photonics techniques to overcome the difficulties of THz remote sensing, we focus mainly on theoretical and experimental methods to improve THz generation and detection performance for the purpose of remote sensing through tailoring the generation and detection media, air-plasma.

For the THz generation part, auto-focusing ring-Airy beam was introduced to enhance the THz wave generation yield from two-color laser induced air plasma. By artificially modulated exotic wave packets, it is exhibited that abruptly auto-focusing beam induced air-plasma can give an up to 5.3-time-enhanced THz wave pulse energy compared to normal Gaussian beam induced plasma under the same conditions. At the same time, a red shift on the THz emission spectrum is also observed. A simulation using an interference model to qualitatively describe these behaviors has be developed.

For the THz detection part, the results of THz remote sensing at 30 m using THz-radiation-enhanced-emission-of-fluorescence (THz-REEF) technique are demonstrated, which greatly improved from the 10 m demonstration last reported. The THz-REEF technique in the counter-propagation geometry was explored, which is proved to be more practical for stand-off detections than co-propagation geometry. We found that in the counter-propagating geometry the maximum amplitude of the REEF signal is comparable to that in the co-propagating case, whereas the time resolved REEF trace significantly changes. By performing the study with different plasmas, we observed that in the counter-propagating geometry the shape of the REEF trace depends strongly on the plasma length and electron density. A new theoretical model suggesting that the densest volume of the plasma does not contribute to the fluorescence enhancement is proposed to reproduce the experimental measurements.

Our results further the understanding of the THz-plasma interaction and highlight the potential of THz-REEF technique in the plasma detection applications.

Keywords

ultrafast terahertz (THz) techniques / THz air-photonics / ring-Airy beams / THz-radiation-enhanced-emission-of-fluorescence (THz-REEF) of air-plasma in co-propagation geometry / THz-REEF of air-plasma in counter-propagation geometry

Cite this article

Download citation ▾
Kang LIU, Pingjie HUANG, Xi-Cheng ZHANG. Terahertz wave generation from ring-Airy beam induced plasmas and remote detection by terahertz-radiation-enhanced-emission-of-fluorescence: a review. Front. Optoelectron., 2019, 12(2): 117‒147 https://doi.org/10.1007/s12200-018-0860-7

1 Introduction

Next-generation optical networks are expected to improve capacity and flexibility by dynamic wavelength switching/routing operation due to the more efficient optimization of the network resources [1,2]. The ability to perform such operation directly in optical domain can significantly reduce the number of opto/electrical and electro/optical conversions in the routing nodes. Therefore, it is very attractive in terms of latency reducing, data rate and modulation formats transparency, and potentially low-power operation thanks to photonic integration. These features become even more appealing as the transceiver complexity increases when advanced modulation formats are deployed in the transmission systems. Indeed, besides on-off keying (OOK) modulation format, pure phase and other advanced formats involving phase modulation start to play a major role in optical communication systems thanks to their higher robustness to transmission impairments [3] and to the emerging of coherent systems. For this reason, novel schemes that allow all-optical processing of phase signals can provide useful advanced functionalities in the development of all-optical network scenario. Particularly, in wavelength division multiplexed (WDM) networks, efficient wavelength conversion would provide an essential functionality for releasing a data stream at a specific wavelength from a network resource, and make the original wavelength available for new data. The wavelength converted data then can be conveniently routed onto a different wavelength path. Two separate devices would be normally required for this add/drop operation in order to release the output fiber from the original input wavelength (space deflection) and transfer the signal information to a new output wavelength (wavelength conversion).
Many different all-optical systems implementing ultra-fast switching and/or wavelength conversion operations have been demonstrated in the past several years. These schemes exploited nonlinear phenomena taking places in semiconductor optical amplifiers (SOAs) [4-7], highly nonlinear fibers (HNLF) [8-10] or periodically-poled lithium niobate (PPLN) waveguides [11,12]. The main drawback of HNLFs is that they cannot be integrated by any means. PPLNs, on the other hand, are suitable only for hybrid integration, and have some constraints on their optical bandwidth. Furthermore, their quasi-phase matching band changes its central frequency with the working temperature; hence PPLN needs a constant temperature control. SOA is a highly non-linear optical device, which has been largely studied and exploited in the last decades. Like PPLN, SOA needs temperature stability, but it presents some advantages: it has a very large bandwidth, regardless of the temperature, and can be easily integrated; its only main limitation is switching speed, but recent works demonstrated that quantum dot (QD)-SOAs are suitable for all-optical, ultra-fast signal processing [13].
The SOA in Mach-Zehnder configuration has been proven to be a high versatile device for all-optical signal processing applications, and able to implement several functional blocks which are expected to boost the development of next-generation transparent optical networks. In recent years, the SOA-Mach-Zehnder interferometer (SOA-MZI) has been exploited for realizing a number of different operations with various modulation formats in a broad range of applications including: space switches [14], wavelength conversion [1518], all-optical regeneration [1923], and logical operations [2426]. The ability to perform such a large number of operations makes the SOA-MZI a valuable tool for the development of future transparent, flexible optical communications systems in which the routing core elements will be operated more and more at purely photonic level. Able to operate as burst/packet router, ultra-fast high-performance all-optical switches and wavelength converters based on SOA-MZI can be conveniently exploited as in several noteworthy experiments reported. Up to now, however, SOA-MZIs have been usually employed in combination with other devices implementing add/drop functionalities. For instance, some SOA-MZIs have been employed as mere wavelength converters, integrated in a larger structure to perform label-based optical burst switching in general multi-protocol label switched (GMPLS) networks [27]; in another case, five SOA-MZIs have been combined to form a unique structure for signal regeneration, wavelength conversion and 40∶10 Gb/s demultiplexing [28]. A SOA-MZI has been also used in a two-section hybrid multi-granular switch comprising a micro-electro-mechanical systems (MEMS)-based switch and a SOA-MZI based switch [29], but the latter had a switching time of 1 ns, too long compared to the bit duration of typical employed bit rates.
In this article, we review an advanced scheme based on a single multi-quantum well (MQW) SOA-MZI photonic circuit, which is capable of simultaneously performing selective space deflection and wavelength conversion of a burst of data in presence of an optical gate control signal. Experiments with OOK and differential binary phase shift keying (DPSK) signals at 10 and 40 Gb/s have been carried out without any bit loss at the switched burst boundaries for both cases. The scheme operates entirely in the optical domain, thus enabling ultra-fast dynamic add/drop operation for WDM systems and packet-switched networks. By performing simultaneously the two different operations in a single step, namely data erasing and wavelength conversion at photonic level, the scheme allows to reduce the overall latency of the switch, and to minimize the number of active elements. Furthermore, the performances of the node can potentially be increased by avoiding the penalties introduced by two cascaded switches. In addition, the SOA-MZI architecture offers the possibility of handling different modulation formats; it is bit-rate transparent and thanks to the SOA broad gain spectrum, widely tunable in wavelength.

2 Operating principle for OOK signals

The device operation can be generally described as a selective wavelength shifter as depicted in Fig. 1. In the absence of any control signal, input data at λin are normally let through without wavelength conversion. Whereas, when an optical control gate is applied, they are transferred at a new wavelength λnew. Thus, selective wavelength shifting of the input data depending on the control signal state is performed. However, in practical implementation, the original data without the dropped burst and the wavelength-converted data burst are available at two different fibers, which would be desirable in some practical cases. Clearly, by recollecting the two output fibers, the selective wavelength shifting operation schematically depicted in Fig. 1, is obtained.
Fig.1 Generic operation of wavelength shifter

Full size|PPT slide

The scheme for the implementation of the selective wavelength shifter for OOK signals is shown in Fig. 2. As illustrated in the figure, a data signal at wavelength λdata, comprising a continuous wave (CW) stream of OOK modulated bits, is split into two paths and synchronously applied to two ports IN 1 and P 1 of a SOA-MZI. In particular, the IN 1 port is a common port for the two SOAs in the interferometer arms, whereas the signal entering the P 1 port, only enters SOA 1 in the upper branch. The power levels of two replica of the data signal are independently adjusted such that the weakest replica, which acts as data probe in the device, is applied to the common port IN 1, whereas the stronger one, the data pump, is applied to the control port P 1. Similarly, a gate signal at wavelength λgate is generated and simultaneously applied to the IN 2, P 2 and P 3 ports of the SOA-MZI. In particular, the gate signal entering port IN 2 acts as a probe signal, whereas the copies entering ports P 2 and P 3 act as pump signals solely in SOA 1 and SOA 2, respectively. The input gate replicas entering ports IN 2 (the gate probe) and P 2 (gate pump 1) are synchronized in the SOA-MZI so that they crosses SOA 2 at the same time, whereas the gate signal entering port P 3 (gate pump 2) is slightly delayed with respect to gate pump 1, and its power level is lower than that of gate pump 1. Finally, a CW holding beam at wavelength λHB, is coupled together with the data probe signal to enters port IN, in order to speed up the response time of both SOA 1 and SOA 2 [30].
Fig.2 Operation principle of improved scheme for 40 Gb/s OOK operations

Full size|PPT slide

The operation principle can be explained as follows. By acting on the phase shifters (PSs) placed in the interferometer arms and on the SOA currents, the device is initially biased so that, in absence of any pump signal, the probe data would experience destructive interference at OUT 1. In normal operation, however, the data probe and data pump signals are always simultaneously applied to the SOA-MZI. In this way, when the gate pumps are switched off, a phase shift in the upper arm of the interferometer is produced by the marks in the data pump as effect of carrier depletion in SOA 1. The power level of the data pump signal can then be chosen such that the induced phase shift in SOA 1 cases constructive interference to occur for the data probe at OUT 1. Thus, in absence of gating signals, input data are normally presented at OUT 1, where they are retrieved at the device output by means of an optical filter centered at λdata (pass-through data). When the gate signal turns high, gate probe, gate pump 1, and gate pump 2 signals enter the device from their respective inputs. In particular, the power levels of gate pump 1 and gate pump 2 are such to restore the original gain/phase balance between the two interferometer arms set by the initial bias condition. The weaker delayed gate pump 2 plays an important role for 40 Gb/s applications, since it cancels out the slow part of the phase transient induced by the onset/release of gate pump 1 in SOA 2, as explained in Ref. [15]. In this way, sharp-edged selective cancellation of the data signal at OUT 1 is obtained, which is required for operation with high data rates. It should be noted that the gate pump 2 signal is thus typically not required for operation at 10 Gb/s [31,32]. The gate pump 2 signal could be also avoided for higher data rates if faster SOAs, optimized for high-speed operation were employed in the SOA-MZI [18]. Because of the device symmetry, the initial bias settings of the device are such that the gate probe signal entering from IN 2 would also experience total destructive interference at OUT 2 if no pump signal were applied. This condition is broken by the gate pump 1 and the gate pump 2 signals that make gate probe light at λgate to appear at OUT 2. However, with a proper choice of the data pump power level, the initial condition of destructive interference at OUT 2 for the gate probe light entering from IN 2 can be restored again by the marks in the data pump signal. This results in transferring the input data pattern onto the gate signal at OUT 2 with inverted logic. An optical band-pass filter, tuned at λgate at OUT 2 can thus be used to select this inverted replica of the gated data (the wavelength-shifted signal). Clearly, the wavelength-shifted signal is presented at OUT 2 only when the original signal data are suppressed at OUT 1.
The working principle of the scheme is also illustrated in Fig. 3. Here, the normalized transmission characteristics of the SOA-MZI relating the power at OUT 1 and OUT 2 to the power at IN 1 and IN 2, respectively, are reported as a function of the phase difference Δϕ between the interferometer’s arms for the case of a perfectly balanced device. In the figure we assume, for sake of simplicity, that the shape of the output/input power characteristic does not change with applied power (i.e., only a phase shift is induced in the SOAs by the pumps). We also neglect the effect of gate pump 2, as it only affects the operation of the device during the transients [15]. At OUT 1 (OUT 2), the effect of data (gate) pump is then to push the working point for the data (gate) probe from the initial low-transmission point A (A′), to the high-transmission point B (B′), so that data (gate) are output from OUT 1 (OUT 2). On the other hand, the gate (data) pump pulls back the data (gate) probe to the low-transmission point A (A′), so that data (gate) probe is cancelled in correspondence of the gate (data) pump signal. This, at the same time, cancels data in correspondence of the gate, and creates an inverted copy of the data at the gate probe wavelength.
Fig.3 Graphical description of operation, illustrating effect of pump signals on switched probes

Full size|PPT slide

The switching time of the interferometer structure is affected by the dynamics of the two SOAs. The gain recovery of the SOAs has been characterized, to be about 80 ps (Fig. 4(a)). The corresponding phase dynamics are then expected to operate on the same scale. This value is suitable for 10 Gb/s operation without bit loss, but at 40 Gb/s, being the recovery time longer than the bit time, it can affect the signal introducing unwanted pattern effects. This can be counteracted by using an additional holding beam. The role of the holding beam at λHB, which is injected together with the input signal with a proper power level, is to reduce the effective carrier lifetime in the SOAs, decreasing in this way the gain recovery time of the two SOAs [30]. Clearly, also the 10 Gb/s wavelength-converted data benefit by the presence of the assist light. Figure 4 also shows the different behavior of the wavelength conversion operation, with and without the holding beam for a bit rate of 10 Gb/s. In particular, Fig. 4(b)) reports the eye diagram of the output wavelength-converted signal in absence of the holding beam, whereas Fig. 4(c)) shows the same signal in the presence of the holding beam. As shown by the traces, the eye opening is sensibly increased in presence of the holding beam, due to a steeper rising front with respect to the case in which the holding beam is turned off. Furthermore, for obtaining proper operation at 40 Gb/s without any bit loss, the second gate pump, as already anticipated, has also been required. This two-pump push-pull configuration, in which the gate pump 2 is properly delayed and attenuated with respect to pump 1, speeds up the interferometer response [15], thus providing sharpen transients of the switched bursts. In this way, data loss can be avoided even at data rates exceeding the intrinsic response of carriers’ density restoration in the SOAs.
Fig.4 Gain recovery dynamics of SOAs. ( a) Gain recovery time; (b) eye diagram of wavelength-shifted output data without holding beam; (c) eye diagram of wavelength-shifted output data with holding beam

Full size|PPT slide

3 Experimental results with OOK signals

To demonstrate the scheme operation, we generated in two separate experiments: a 10 and 40 Gb/s non return to zero (NRZ) continuous stream of OOK data by driving a Mach-Zehnder intensity modulator (MZ-IM) with a pseudo-random-bit-sequence (PRBS) provided by a pattern generator. A squared gate/control signal with variable length was also produced using a waveform generator and a MZ-IM. In the case of 10 Gb/s data rate, the rising and falling time of the gating signal edges were measured to be about 35 ps, whereas at 40 Gb/s data rate, rising and falling time of about 10 ps for the gate signal have been obtained by employing a 40 GHz bandwidth MZ-IM. Signal wavelengths were λdata = 1554 nm and λgate = 1557 nm for the data and control signal, respectively. Both signals were split to generate the various probes and pump replicas, as described before. Each probe and pump signal was synchronized at the respective SOA-MZI input ports by means of optical delay lines. As previously explained, in the 40 Gb/s case, two gate pump signals have been employed simultaneously to speed-up the switching time of the device. In particular, the gate pump 2 signal entered port P 3 of the SOA-MZI with about 15 ps of delay with respect to the input time of gate pump 1 at port P 2 [33]. The oscilloscope traces of the input/output signals for the case of data at 10 and 40 Gb/s are shown in Figs. 4 and Fig. 5, respectively.
In the case of 10 Gb/s data, a 400 ns long gate signal with 40% duty-cycle has been used. For proper operation, the two SOAs in the interferometer arms were symmetrically driven and the pump powers were chosen to induce the proper amount of phase modulation in the two interferometer arms. The corresponding average input power levels at the SOA-MZI were -6, 0, -4.5 and 4 dBm for data probe, data pump, gate probe and gate pump, respectively, whereas the HB power level is set to 3 dBm. The two SOAs in the MZI were equally biased with a current of 300 mA.
For the 10 Gb/s experiment, Figs. 5(a) and 5(b) show the input data and control signals, respectively. The pass-through signal from port OUT 1 at λdata is shown in Fig. 5(d), whereas the wavelength converted signal at λgate at OUT 2 is depicted in Fig. 5(c). Details of the rising and falling edges of both output signals in switching operation are reported in Figs. 5(e) and 5(f). Rising and falling times of the shifted signal and falling time of the pass-through signal are set by the transient times of the control gate, which are close to the transients of the input data (about 35 ps, as measured on a 40 GHz sampling oscilloscope), whereas the rising time of the pass-through data are related to the carrier recovery time in SOA 1 when only the holding beam is present in the amplifier. As can be observed in Figs. 5(e) and 5(f), these dynamics do not affect noticeably the eye opening of the boundary bits. It is worth noting that a good extinction ratio of the data in the pass-through and shifted signal, as well as high suppression of the pass-through signal (which was estimated to be more than 15 dB from the oscilloscope traces) when the control gate is in the ON state, can be observed. The amplified spontaneous emission (ASE) power from the SOAs at the outputs of both the pass-band band filters in absence of input gate/probe signals was measured to be below -25 dBm. This value should ensure low noise loading in the network in absence of signals at the switch output.
Fig.5 Oscilloscope traces of input/output signals in the case of data at 10 Gb/s. (a) Input data; (b) gate signal; (c)wavelength-shifted output; (d) pass-through output; (e, f)transient edges of the output signals

Full size|PPT slide

The results relative to the 40 Gb/s experiment are shown in Fig. 6. In this case, a squared-wave gate signal having a period of 1 ns and 40% duty-cycle has been exploited. The corresponding average input power levels at the SOA-MZI were -9.3, 0, -7, 1.5 and -4.5 dBm for data probe, data pump, control probe and control pumps 1 and 2, respectively. The holding beam was set at 3 dBm. The two SOAs in the MZI were equally biased with a current of 380 mA. In particular, Figs. 6(a) and 6(b) show the input data and gate signals, respectively. The wavelength converted signal at λgate is shown in Fig. 6(c), whereas the pass-through signal at λdata is shown in Fig. 6(d). In Figs. 6(e) and 6(f), the details of the trailing and falling edges of both pass-through and wavelength-converted signals are reported. As shown, the speed-up in the phase response of the two interferometer arms, obtained by means of the push-pull configuration for the gate pump, produces a switching time shorter than bit duration, allowing in practice no bit loss for the 40 Gb/s bursts.
Fig.6 Oscilloscope traces of input/output signals in the case of data at 40 Gb/s. (a) Input data; (b)gate signal; (c) pass-through output; (d) wavelength-shifted output; (e, f)transient edges of the output signals

Full size|PPT slide

Results of bit error rate (BER) measurements are shown in Figs. 7 and 8 for data at 10 and 40 Gb/s respectively, relative to a 211-1 long PRBS (limited by the gate duration that we used in the experiments). Input/output eye diagrams, corresponding to error-free operation, are also illustrated in the insets of the figures. At 10 Gb/s as shown in Fig. 6, the pass-through data looks almost immune to pattern effects, due to the self-switching mechanism, which results in a negligible power penalty of about 0.2 dB (at a BER of 10-9). On the other hand, the eye diagram of the wavelength converted signal shows a slower transient in its leading edge, corresponding to the falling edge of the data pump, because of carriers’ dynamics in SOA 2. For this signal, a power penalty of about 0.85 dB was measured at BER= 10-9. Also in the case of 40 Gb/s experiment, the eye-diagrams and bit-error rate measurements reported in Fig. 8, show that the pass-through data are almost unaffected by the switch, showing a negligible power penalty of about 0.3 dB. On the other side, whereas the wavelength converted signal is only slightly distorted by the wavelength conversion process, corresponding in a larger power penalty for the wavelength-converted data, which has been measured to be about 1.4 dB.
Fig.7 BER measurements results (a) and input/output eye diagrams (b) at 10 Gb/s. The extinction ratio is 12.5, 12.1, and 11.8 dB for the input, pass-through and shifted eye diagram, respectively

Full size|PPT slide

Fig.8 BER measurements results (a) and input/output eye diagrams (b) at 40 Gb/s. The extinction ratio is 12, 11.4 and 9.8 dB for the input, pass-through and shifted eye diagram, respectively

Full size|PPT slide

4 Operating principle for PSK signals

The proposed scheme allowing to perform simultaneous switch and wavelength conversion operation in a single SOA-MZI can be suitably modified for dynamic wavelength routing and add/drop operations of PSK signals [34]. The corresponding operation principle of the modified scheme is illustrated in Fig. 9. As shown in Fig. 9, a DPSK data signal at wavelength λdata is simultaneously applied to two ports of a SOA-MZI: similarly to the previous OOK case, one replica of the input data, acting as a probe signal for both SOAs, is applied to the port IN 1 whereas the other replica, acting as a data pump solely in SOA 2, is applied to port P 1 of the device. The two SOAs inside the MZI are driven with different bias current values, so that the interferometer is initially unbalanced, and the PSs placed on the interferometer’s arms are set in such a way that the data probe signal entering IN 1 would experience partial destructive interference at OUT 1, if no other signal is applied to the device. In normal operation, however, the data probe and pump signals always enter simultaneously the device. In particular, the pump power level is such to induce a phase shift in SOA 2 leading to constructive interference at OUT 1 for the probe signal, hence maximizing its transmission. Thus, in absence of the gate signal, the output data probe is normally let through OUT 1 of the device (pass-through data in the figure). When a gate signal at λgate with an appropriate power level is input to the device from IN 2, two effects occur inside the SOA-MZI. First, the gain of the two SOAs is significantly reduced with a consequent decrease of the data probe power at the output of SOA 1 and SOA 2 to approximately the same level. The second effect is an induced extra phase shift in both SOAs. However, since SOA 1 is operating in the small-signal gain regime before the gate signal enters the device, the corresponding pump-induced phase shift in SOA 1 is larger than that occurring in SOA 2, which is already operating in a partially saturated regime due to the presence of pump data. For a given suitable level of unbalance in the SOAs driving currents and of saturation in SOA 2, it is then possible to impress a π phase difference between the two data probe fields emerging from SOA 1 and SOA 2 by properly adjusting the gate signal power level. As the amplitude of the data probe fields leaving the highly saturated SOA 1 and SOA 2 is also equalized, this reflects into total destructive interference at OUT 1, leading to a strong suppression of the pass-through data probe in correspondence of the gate signal. At the same time, the gate and data pump signals nonlinearly interact inside SOA 2, giving rise to several four wave mixing (FWM) components; in particular, one of the two first-order generated FWM components is the complex conjugated replica of the data signal. This wavelength converted replica of the data signal at λFWM (wavelength-shifted data in Fig. 9) thus appears at OUT 2 port of the device only when the pass-through data are cancelled at OUT 1, and can be selected by means of a bandpass optical filter tuned at λFWM. The FWM complex conjugate operation preserves anyway the input DPSK data encoding.
Fig.9 Operation principle of modified proposed scheme for 40 Gb/s PSK operations

Full size|PPT slide

Also in this case, we can explain the principle of operation by considering the SOA-MZI transfer characteristic under the different operating conditions. This is schematically illustrated in Fig. 10, where the data probe output power (at OUT 1) is plotted as a function of the phase difference in the interferometer arms, Δϕ. In the figure it is shown that, when only the data probe enters the device, the SOA-MZI is suitably biased at the point named A′. The effect of applying a data pump is a new output characteristic and a phase shift in SOA 2 that moves the working point to the point named A in the figure. This is the working point on OUT 1 power characteristic when both the data pump and probe signals are injected into the device. When the gate signal at λgate is input to the device from IN 2 with an appropriate power level, two effects occur inside the SOA-MZI. First, the amplifiers gain is significantly reduced so that the data probe power at the output of both SOAs decreases to approximately the same level. The second effect is an induced extra phase shift in both SOAs. However, since SOA 1 is in the small-signal gain regime before the gate enters the device, the corresponding pump-induced phase shift is larger than that occurring in SOA 2, which is already partially saturated by the pump data.
Fig.10 Graphical description of SOA-MZI switch for pass-trough/data erasing operation

Full size|PPT slide

5 Experimental results with PSK signals

In two separate experiments, we generated a continuous stream of 10 and 40 Gb/s DPSK modulated optical data and a gate signal. The gate signal was a 500 ns long squared signal with a duty-cycle of 50%. Data and gate wavelengths were fixed at λdata = 1554.2 nm and λgate = 1552.9 nm, respectively. The data stream was split into two paths to generate the probe and pump replicas; the data probe and pump signals were then synchronized at the respective SOA-MZI inputs by means of delay lines. Driving currents of SOA 1 and SOA 2 were 380 and 420 mA, respectively. In the 10 Gb/s experiment, power levels at the SOA-MZI input ports were -4, 8 and 13 dBm for data probe, data pump, and control gate signals, respectively, whereas in the 40 Gb/s experiment power levels at the SOA-MZI input ports were -4, 10.6 and 15.7 dBm for data probe, data pump, and control gate signals, respectively.
The corresponding optical spectra at SOA 2 output are shown in Fig. 11. The FWM-generated signals at λFWM = 1551.6 nm show an output OSNR (on 0.1 nm resolution bandwidth) of around 30 dB in both cases. The oscilloscope traces of the input/output signals corresponding to the 10 and 40 Gb/s cases are shown in Fig. 12. From the top to the bottom, the input data, the control gate, the pass-through data, the wavelength-shifted data, and the transients of the demodulated switched bursts (including also the 40 Gb/s case), are reported. A complete cancellation of the data burst in the pass-through signal can be observed (more than 15 dB calculated from the oscilloscope traces) when the control gate is in the ON state. The details of the rising and falling edges of switched output signals, shown in Figs. 12(e) to 12(h), confirm that the switching dynamics are fast enough to prevent any bit loss at the boundaries after demodulation with standard 1-bit delay interferometer for both 10 and 40 Gb/s modulated data. The input/output demodulated eye diagrams, as well as BER measurements, are reported in Fig. 13 for both the 10 and 40 Gb/s experiments.
Fig.11 Output spectra from SOA 2 with 10 (a) and 40 Gb/s (b) DPSK modulated data (res.: 0.1 nm)

Full size|PPT slide

Fig.12 Oscilloscope traces of input/output signals in the case of DPSK modulated data. (a) Input data; (b) gate signal; (c) pass-through output; (d) wavelength-shifted output; (e, f) transient edges of the output signals at 10 Gb/s; (g, h) transient edges of the output signals at 40 Gb/s

Full size|PPT slide

The BER of demodulated data eye diagrams was measured to be about 11 dB for all the input/output signals in both the 10 and 40 Gb/s experiments. The results of BER measurements with a 211-1 long PRBS (limited by gate duration) confirmed the effectiveness of the proposed technique, as shown in Fig. 13. Almost negligible power penalty (at BER= 10-9) with respect to the input data for both the pass-through (0.5 dB) and wavelength-shifted data (0.2 dB) was observed at 10 Gb/s, whereas a power penalty (at BER= 10-9) of about 1 and 1.5 dB for the pass-through and shifted data, respectively, was observed at 40 Gb/s. By using orthogonal double-pump FWM [35], flat conversion efficiency over a fair portion of the SOA gain spectrum could be easily achieved, enabling wide-band conversion range operation. Alternatively, FWM architecture with two parallel pumps can be implemented to make the scheme operation transparent to input data wavelength and polarization [36].
Fig.13 (a) BER measurements for input (IN), pass-trough (PT) and wavelength-shifted (WS) data at 10 and 40 Gb/s; (b) eye diagrams of input/output demodulated data at 10 Gb/s; (c) eye diagrams of input/output demodulated data at 40 Gb/s

Full size|PPT slide

6 Conclusions

We propose novel and effective methods enabling all-optical switching, by means of simultaneous data erasing and wavelength conversion of a burst of data selected by an optical gate signal. The presented scheme is suitable for high-speed dynamic wavelength routing and/or add/drop operation in WDM networks. All the solutions operate entirely in the photonic domain and are based on a single integrated SOA-MZI, which can in principle operate with OOK and any constant-envelope advanced phase-modulated signal, like M-ary PSK. The device enables wide-band conversion operation over the entire C band [32] and it can be transparent to input data wavelength and polarization. Reduced power penalty as well as faster operation up to 40 Gb/s have been obtained.

References

[1]
Zhang X C, Xu J. Introduction to THz Wave Photonics. New York: Springer, 2010
[2]
Zhang X C. Teaching note, 2013
[3]
Fixsen D J, Cheng E S, Gales J M, Mather J C, Shafer R A, Wright E L. The cosmic microwave background spectrum from the full cobefiras data set. Astrophysical Journal, 1996, 473(2): 576–587
CrossRef Google scholar
[4]
Leisawitz D T, Danchi W C, DiPirro M J, Feinberg L D, Gezari D Y, Hagopian M, Langer W D, Mather J C, Moseley S H, Shao M, Silverberg R F, Staquhn J G, Swain M R, Yorke H W, Zhang X L. Scientific motivation and technology requirements for the SPIRIT and SPECS far-infrared/submillimeter space interferometers. In: Proceedings of SPIE 4013, UV, Optical, and IR Space Telescopes and Instruments. International Society for Optics and Photonics, 2000, 36–47
[5]
Phillips T G, Keene J. Submillimeter astronomy (heterodyne spectroscopy). Proceedings of the IEEE, 1992, 80(11): 1662–1678
CrossRef Google scholar
[6]
Majumdar A K. Advanced Free Space Optics (FSO): A Systems Approach. New York: Springer, 2014
[7]
Liu H B, Chen Y, Bastiaans G J, Zhang X C. Detection and identification of explosive RDX by THz diffuse reflection spectroscopy. Optics Express, 2006, 14(1): 415–423
CrossRef Pubmed Google scholar
[8]
Leahy-Hoppa M R, Fitch M J, Zheng X, Hayden L M, Osiander R. Wideband terahertz spectroscopy of explosives. Chemical Physics Letters, 2007, 434(4–6): 227–230
CrossRef Google scholar
[9]
Davies A G, Burnett A D, Fan W, Linfield E H, Cunningham J E. Terahertz spectroscopy of explosives and drugs. Materials Today, 2008, 11(3): 18–26
[10]
Federici J F, Schulkin B, Huang F, Gary D, Barat R, Oliveira F, Zimdars D. Thz imaging and sensing for security applications—explosives, weapons and drugs. Semiconductor Science and Technology, 2005, 20(7): S266–S280
CrossRef Google scholar
[11]
Tonouchi M. Cutting-edge terahertz technology. Nature Photonics, 2007, 1(2): 97–105
CrossRef Google scholar
[12]
Roobottom C A, Mitchell G, Morgan-Hughes G. Radiation-reduction strategies in cardiac computed tomographic angiography. Clinical Radiology, 2010, 65(11): 859–867
CrossRef Pubmed Google scholar
[13]
Alexandrov B S, Gelev V, Bishop A R, Usheva A, Rasmussen K O. DNA breathing dynamics in the presence of a terahertz field. Physics Letters A, 2010, 374(10): 1214–1217
CrossRef Pubmed Google scholar
[14]
Siegel P H, Pikov V. Impact of low intensity millimetre waves on cell functions. Electronics Letters, 2010, 46(26): 70–72
CrossRef Google scholar
[15]
Chen J, Chen Y, Zhao H, Bastiaans G J, Zhang X C. Absorption coefficients of selected explosives and related compounds in the range of 0.1-2.8 THz. Optics Express, 2007, 15(19): 12060–12067
CrossRef Pubmed Google scholar
[16]
Zhang X C, Shkurinov A, Zhang Y. Extreme terahertz science. Nature Photonics, 2017, 11(1): 16–18
CrossRef Google scholar
[17]
Lee Y S. Principles of Terahertz Science and Technology. New York: Springer, 2009
[18]
Auston D H. Picosecond optoelectronic switching and gating in silicon. Applied Physics Letters, 1975, 26(3): 101–103
CrossRef Google scholar
[19]
Tani M, Matsuura S, Sakai K, Nakashima S. Emission characteristics of photoconductive antennas based on low-temperature-grown GaAs and semi-insulating GaAs. Applied Optics, 1997, 36(30): 7853–7859
CrossRef Pubmed Google scholar
[20]
Auston D H, Cheung K P, Smith P R. Picosecond photoconducting hertzian dipoles. Applied Physics Letters, 1984, 45(3): 284–286
CrossRef Google scholar
[21]
Ropagnol X, Khorasaninejad M, Raeiszadeh M, Safavi-Naeini S, Bouvier M, Côté C Y, Laramée A, Reid M, Gauthier M A, Ozaki T. Intense THz Pulses with large ponderomotive potential generated from large aperture photoconductive antennas. Optics Express, 2016, 24(11): 11299–11311
CrossRef Pubmed Google scholar
[22]
Hafez H A, Chai X, Ibrahim A, Mondal S, Férachou D, Ropagnol X, Ozaki T. Intense terahertz radiation and their applications. Journal of Optics, 2016, 18(9): 093004
CrossRef Google scholar
[23]
Boyd R W. Nonlinear Optics. Oxford: Elsevier, 2008
[24]
Kitaeva G Kh. Terahertz generation by means of optical lasers. Laser Physics Letters, 2008, 5(8): 559–576
CrossRef Google scholar
[25]
Reimann K. Table-top sources of ultrashort Thz pulses. Reports on Progress in Physics, 2007, 70(10): 1597–1632
CrossRef Google scholar
[26]
Rice A, Jin Y, Ma X F, Zhang X C, Bliss D, Larkin J, Alexander M. Terahertz optical rectification from<110>zinc-blende crystals. Applied Physics Letters, 1994, 64(11): 1324–1326
CrossRef Google scholar
[27]
Yang K H, Richards P L, Shen Y R. Generation of far-infrared radiation by picosecond light pulses in LiNbO3. Applied Physics Letters, 1971, 19(9): 320–323
CrossRef Google scholar
[28]
Hebling J, Almasi G, Kozma I, Kuhl J. Velocity matching by pulse front tilting for large area THz-pulse generation. Optics Express, 2002, 10(21): 1161–1166
CrossRef Pubmed Google scholar
[29]
Hebling J, Yeh K L, Hoffmann M C, Bartal B, Nelson K A. Generation of high-power terahertz pulses by tilted pulse-front excitation and their application possibilities. Journal of the Optical Society of America B, Optical Physics, 2008, 25(7): B6–B19
CrossRef Google scholar
[30]
Fülöp J A, Pálfalvi L, Klingebiel S, Almási G, Krausz F, Karsch S, Hebling J. Generation of sub-mJ terahertz pulses by optical rectification. Optics Letters, 2012, 37(4): 557–559
CrossRef Pubmed Google scholar
[31]
Hirori H, Doi A, Blanchard F, Tanaka K. Single-cycle terahertz pulses with amplitudes exceeding 1 mV/cm generated by optical rectification in LiNbO3. Applied Physics Letters, 2011, 98(9): 091106
CrossRef Google scholar
[32]
Zhang X C, Ma X F, Jin Y, Lu T M, Boden E P, Phelps P D, Stewart K R, Yakymyshyn C P. Terahertz optical rectification from a nonlinear organic crystal. Applied Physics Letters, 1992, 61(26): 3080–3082
CrossRef Google scholar
[33]
Hauri C P, Ruchert C, Vicario C, Ardana F. Strong-field single-cycle THz pulses generated in an organic crystal. Applied Physics Letters, 2011, 99(16): 161116
CrossRef Google scholar
[34]
Shalaby M, Hauri C P. Demonstration of a low-frequency three-dimensional terahertz bullet with extreme brightness. Nature Communications, 2015, 6(1): 5976
CrossRef Pubmed Google scholar
[35]
Hamster H, Sullivan A, Gordon S, White W, Falcone R W. Subpicosecond, electromagnetic pulses from intense laser-plasma interaction. Physical Review Letters, 1993, 71(17): 2725–2728
CrossRef Pubmed Google scholar
[36]
Cook D J, Hochstrasser R M. Intense terahertz pulses by four-wave rectification in air. Optics Letters, 2000, 25(16): 1210–1212
CrossRef Pubmed Google scholar
[37]
Dai J, Clough B, Ho I C, Lu X, Liu J, Zhang X C. Recent progresses in terahertz wave air photonics. IEEE Transactions on Terahertz Science and Technology, 2011, 1(1): 274–281
CrossRef Google scholar
[38]
Kim K Y, Taylor A J, Glownia J H, Rodriguez G. Coherent control of terahertz supercontinuum generation in ultrafast laser–gas interactions. Nature Photonics, 2008, 2(10): 605–609
CrossRef Google scholar
[39]
Wu Q, Zhang X C. Free-space electro-optic sampling of terahertz beams. Applied Physics Letters, 1995, 67(24): 3523–3525
CrossRef Google scholar
[40]
Nuss M C, Auston D H, Capasso F. Direct subpicosecond measurement of carrier mobility of photoexcited electrons in gallium arsenide. Physical Review Letters, 1987, 58(22): 2355–2358
CrossRef Pubmed Google scholar
[41]
van Exter M, Fattinger C, Grischkowsky D. Terahertz time-domain spectroscopy of water vapor. Optics Letters, 1989, 14(20): 1128–1130
CrossRef Pubmed Google scholar
[42]
Morales G J, Lee Y C. Ponderomotive-force effects in a nonuniform plasma. Physical Review Letters, 1974, 33(17): 1016–1019
CrossRef Google scholar
[43]
Liu K, Buccheri F, Zhang X C. Thz science and technology of micro-plasma. Physics (Chinese Wuli), 2015, 44: 497–502
[44]
Hamster H, Sullivan A, Gordon S, Falcone R W. Short-pulse terahertz radiation from high-intensity-laser-produced plasmas. Physical Review E: Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics, 1994, 49(1): 671–677
CrossRef Pubmed Google scholar
[45]
Löffler T, Jacob F, Roskos H G. Generation of terahertz pulses by photoionization of electrically biased air. Applied Physics Letters, 2000, 77(3): 453–455
CrossRef Google scholar
[46]
D’Amico C, Houard A, Franco M, Prade B, Mysyrowicz A, Couairon A, Tikhonchuk V T. Conical forward THz emission from femtosecond-laser-beam filamentation in air. Physical Review Letters, 2007, 98(23): 235002
CrossRef Pubmed Google scholar
[47]
Amico C D, Houard A, Akturk S, Liu Y, Le Bloas J, Franco M, Prade B, Couairon A, Tikhonchuk V T, Mysyrowicz A. Forward THz radiation emission by femtosecond filamentation in gases: theory and experiment. New Journal of Physics, 2008, 10(1): 013015
CrossRef Google scholar
[48]
Buccheri F, Zhang X C. Terahertz emission from laser induced microplasma in ambient air. Optica, 2015, 2(4): 366–369
CrossRef Google scholar
[49]
Xie X, Dai J, Zhang X C. Coherent control of THz wave generation in ambient air. Physical Review Letters, 2006, 96(7): 075005
CrossRef Pubmed Google scholar
[50]
Kress M, Löffler T, Eden S, Thomson M, Roskos H G. Terahertz-pulse generation by photoionization of air with laser pulses composed of both fundamental and second-harmonic waves. Optics Letters, 2004, 29(10): 1120–1122
CrossRef Pubmed Google scholar
[51]
Clough B, Dai J M, Zhang X C. Laser air photonics: covering the “terahertz gap” and beyond. Zhongguo Wuli Xuekan, 2014, 52(1): 416–430
[52]
Chen Y, Yamaguchi M, Wang M, Zhang X C. Terahertz pulse generation from noble gases. Applied Physics Letters, 2007, 91(25): 251116
CrossRef Google scholar
[53]
Dai J, Liu J, Zhang X C. Terahertz wave air photonics: terahertz wave generation and detection with laser-induced gas plasma. IEEE Journal of Selected Topics in Quantum Electronics, 2011, 17(1): 183–190
CrossRef Google scholar
[54]
Dai J, Karpowicz N, Zhang X C. Coherent polarization control of terahertz waves generated from two-color laser-induced gas plasma. Physical Review Letters, 2009, 103(2): 023001
CrossRef Pubmed Google scholar
[55]
Kim K Y, Glownia J H, Taylor A J, Rodriguez G. Terahertz emission from ultrafast ionizing air in symmetry-broken laser fields. Optics Express, 2007, 15(8): 4577–4584
CrossRef Pubmed Google scholar
[56]
Karpowicz N, Zhang X C. Coherent terahertz echo of tunnel ionization in gases. Physical Review Letters, 2009, 102(9): 093001
CrossRef Pubmed Google scholar
[57]
You Y S, Oh T I, Kim K Y. Off-axis phase-matched terahertz emission from two-color laser-induced plasma filaments. Physical Review Letters, 2012, 109(18): 183902
CrossRef Pubmed Google scholar
[58]
Blank V, Thomson M D, Roskos H G. Spatio-spectral characteristics of ultra-broadband THz emission from two-colour photo excited gas plasmas and their impact for nonlinear spectroscopy. New Journal of Physics, 2013, 15(7): 075023
CrossRef Google scholar
[59]
Manceau J M, Massaouti M, Tzortzakis S. Strong terahertz emission enhancement via femtosecond laser filament concatenation in air. Optics Letters, 2010, 35(14): 2424–2426
CrossRef Pubmed Google scholar
[60]
Liu J, Zhang X C. Terahertz-radiation-enhanced emission of fluorescence from gas plasma. Physical Review Letters, 2009, 103(23): 235002
CrossRef Pubmed Google scholar
[61]
Liu J, Dai J, Chin S L, Zhang X C. Broadband terahertz wave remote sensing using coherent manipulation of fluorescence from asymmetrically ionized gases. Nature Photonics, 2010, 4(9): 627–631
CrossRef Google scholar
[62]
Clough B, Liu J, Zhang X C. Laser-induced photoacoustics influenced by single-cycle terahertz radiation. Optics Letters, 2010, 35(21): 3544–3546
CrossRef Pubmed Google scholar
[63]
Cook D J, Chen J X, Morlino E A, Hochstrasser R M. Terahertz field-induced second-harmonic generation measurements of liquid dynamics. Chemical Physics Letters, 1999, 309(3–4): 221–228
CrossRef Google scholar
[64]
Dai J, Xie X, Zhang X C. Detection of broadband terahertz waves with a laser-induced plasma in gases. Physical Review Letters, 2006, 97(10): 103903
CrossRef Pubmed Google scholar
[65]
Karpowicz N, Dai J, Lu X, Chen Y, Yamaguchi M, Zhao H, Zhang X C, Zhang L, Zhang C, Price-Gallagher M, Fletcher C, Mamer O, Lesimple A, Johnson K. Coherent heterodyne time-domain spectrometry covering the entire “terahertz gap”. Applied Physics Letters, 2008, 92(1): 011131
CrossRef Google scholar
[66]
Clough B, Dai J, Zhang X C. Laser air photonics: beyond the terahertz gap. Materials Today, 2012, 15(1–2): 50–58
CrossRef Google scholar
[67]
Lu X, Karpowicz N, Chen Y, Zhang X C. Systematic study of broadband terahertz gas sensor. Applied Physics Letters, 2008, 93(26): 261106
CrossRef Google scholar
[68]
Zalkovskij M, Zoffmann Bisgaard C, Novitsky A, Malureanu R, Savastru D, Popescu A, Uhd Jepsen P, Lavrinenko A V. Ultrabroadband terahertz spectroscopy of chalcogenide glasses. Applied Physics Letters, 2012, 100(3): 031901
CrossRef Google scholar
[69]
D’Angelo F, Mics Z, Bonn M, Turchinovich D. Ultra-broadband THz time-domain spectroscopy of common polymers using THz air photonics. Optics Express, 2014, 22(10): 12475–12485
CrossRef Pubmed Google scholar
[70]
Yang Y, Mandehgar M, Grischkowsky D R. Broadband THz pulse transmission through the atmosphere. IEEE Transactions on Terahertz Science and Technology, 2011, 1(1): 264–273
CrossRef Google scholar
[71]
Sun X, Buccheri F, Dai J, Zhang X C. Review of THz wave air photonics. In: Proceedings of SPIE 8562, Infrared, Millimeter-Wave, and Terahertz Technologies II. SPIE, 2012, 856202
[72]
Clough B, Liu J, Zhang X C. “All air-plasma” terahertz spectroscopy. Optics Letters, 2011, 36(13): 2399–2401
CrossRef Pubmed Google scholar
[73]
Berry M V, Balazs N L. Nonspreading wave packets. American Journal of Physics, 1979, 47(3): 264–267
CrossRef Google scholar
[74]
Unnikrishnan K, Rau A R P. Uniqueness of the Airy packet in quantum mechanics. American Journal of Physics, 1996, 64(8): 1034–1035
CrossRef Google scholar
[75]
Schiff L I. Quantum Mechanics. Oxford: McGraw-Hill Education (India) Pvt Limited, 1968
[76]
Durnin J. Exact solutions for nondiffracting beams. I. The scalar theory. Journal of the Optical Society of America A, Optics and Image Science, 1987, 4(4): 651–654
CrossRef Google scholar
[77]
Durnin J, Miceli J Jr, Eberly J H. Diffraction-free beams. Physical Review Letters, 1987, 58(15): 1499–1501
CrossRef Pubmed Google scholar
[78]
McGloin D, Dholakia K. Bessel beams: diffraction in a new light. Contemporary Physics, 2005, 46(1): 15–28
CrossRef Google scholar
[79]
Gutiérrez-Vega J C, Iturbe-Castillo M D, Chávez-Cerda S. Alternative formulation for invariant optical fields: Mathieu beams. Optics Letters, 2000, 25(20): 1493–1495
CrossRef Pubmed Google scholar
[80]
Bandres M A, Gutiérrez-Vega J C. Ince-Gaussian beams. Optics Letters, 2004, 29(2): 144–146
CrossRef Pubmed Google scholar
[81]
Siviloglou G A, Christodoulides D N. Accelerating finite energy Airy beams. Optics Letters, 2007, 32(8): 979–981
CrossRef Pubmed Google scholar
[82]
Siviloglou G A, Broky J, Dogariu A, Christodoulides D N. Observation of accelerating Airy beams. Physical Review Letters, 2007, 99(21): 213901
CrossRef Pubmed Google scholar
[83]
Abdollahpour D, Suntsov S, Papazoglou D G, Tzortzakis S. Spatiotemporal Airy light bullets in the linear and nonlinear regimes. Physical Review Letters, 2010, 105(25): 253901
CrossRef Pubmed Google scholar
[84]
Chong A, Renninger W H, Christodoulides D N, Wise F W. Airy–Bessel wave packets as versatile linear light bullets. Nature Photonics, 2010, 4(2): 103–106
CrossRef Google scholar
[85]
Papazoglou D G, Efremidis N K, Christodoulides D N, Tzortzakis S. Observation of abruptly auto focusing waves. Optics Letters, 2011, 6(10): 1842–1844
Pubmed
[86]
Efremidis N K, Christodoulides D N. Abruptly autofocusing waves. Optics Letters, 2010, 35(23): 4045–4047
CrossRef Pubmed Google scholar
[87]
PapazoglouD G. Personal communication, 2015
[88]
Chremmos I, Efremidis N K, Christodoulides D N. Pre-engineered abruptly autofocusing beams. Optics Letters, 2011, 36(10): 1890–1892
CrossRef Pubmed Google scholar
[89]
Liu K, Koulouklidis A D, Papazoglou D G, Tzortzakis S, Zhang X C. Enhanced terahertz wave emission from air-plasma tailored by abruptly autofocusing laser beams. Optica, 2016, 3(6): 605–608
CrossRef Google scholar
[90]
Koulouklidis A D, Papazoglou D G, Fedorov V Y, Tzortzakis S. Phase memory preserving harmonics from abruptly autofocusing beams. Physical Review Letters, 2017, 119(22): 223901
CrossRef Google scholar
[91]
Papazoglou D G, Fedorov V Y, Tzortzakis S. Janus waves. Optics Letters, 2016, 41(20): 4656–4659
CrossRef Pubmed Google scholar
[92]
Panagiotopoulos P, Papazoglou D G, Couairon A, Tzortzakis S. Sharply autofocused ring-Airy beams transforming into non-linear intense light bullets. Nature Communications, 2013, 4(1): 2622
CrossRef Pubmed Google scholar
[93]
Polynkin P, Kolesik M, Roberts A, Faccio D, Di Trapani P, Moloney J. Generation of extended plasma channels in air using femtosecond Bessel beams. Optics Express, 2008, 16(20): 15733–15740
CrossRef Pubmed Google scholar
[94]
Polynkin P, Kolesik M, Moloney J V, Siviloglou G A, Christodoulides D N. Curved plasma channel generation using ultraintense Airy beams. Science, 2009, 324(5924): 229–232
CrossRef Pubmed Google scholar
[95]
Scheller M, Mills M S, Miri M A, Cheng W, Moloney J V, Kolesik M, Polynkin P, Christodoulides D N. Externally refuelled optical filaments. Nature Photonics, 2014, 8(4): 297–301
[96]
Matsubara E, Nagai M, Ashida M. Ultrabroadband coherent electric field from far infrared to 200 THz using air plasma induced by 10 fs pulses. Applied Physics Letters, 2012, 101(1): 011105
CrossRef Google scholar
[97]
Manceau J M, Averchi A, Bonaretti F, Faccio D, Di Trapani P, Couairon A, Tzortzakis S. Terahertz pulse emission optimization from tailored femtosecond laser pulse filamentation in air. Optics Letters, 2009, 34(14): 2165–2167
CrossRef Pubmed Google scholar
[98]
Zhao J, Guo L, Chu W, Zeng B, Gao H, Cheng Y, Liu W. Simple method to enhance terahertz radiation from femtosecond laser filament array with a step phase plate. Optics Letters, 2015, 40(16): 3838–3841
CrossRef Pubmed Google scholar
[99]
Chu X. Evolution of an Airy beam in turbulence. Optics Letters, 2011, 36(14): 2701–2703
CrossRef Pubmed Google scholar
[100]
Dolev I, Kaminer I, Shapira A, Segev M, Arie A. Experimental observation of self-accelerating beams in quadratic nonlinear media. Physical Review Letters, 2012, 108(11): 113903
CrossRef Google scholar
[101]
Dai J, Zhang X C. Terahertz wave generation from thin metal films excited by asymmetrical optical fields. Optics Letters, 2014, 39(4): 777–780
CrossRef Pubmed Google scholar
[102]
Roskos H G, Thomson M D, Kreß M, Löffler T. Broadband THz emission from gas plasmas induced by femtosecond optical pulses: From fundamentals to applications. Laser & Photonics Reviews, 2007, 1(4): 349–368
CrossRef Google scholar
[103]
Oh T I, You Y S, Jhajj N, Rosenthal E W, Milchberg H M, Kim K Y. Scaling and saturation of high-power terahertz radiation generation in two-color laser filamentation. Applied Physics Letters, 2013, 102(20): 201113
CrossRef Google scholar
[104]
Gorodetsky A, Koulouklidis A D, Massaouti M, Tzortzakis S. Physics of the conical broadband terahertz emission from two-color laser-induced plasma filaments. Physical Review A., 2014, 89(3): 033838
CrossRef Google scholar
[105]
Talebpour A, Petit S, Chin S L. Re-focusing during the propagation of a focused femtosecond Ti:sapphire laser pulse in air. Optics Communications, 1999, 171(4–6): 285–290
CrossRef Google scholar
[106]
Clough B, Karpowicz N, Zhang X C. Modulation of electron trajectories inside a filament for single-scan coherent terahertz wave detection. Applied Physics Letters, 2012, 100(12): 121105
CrossRef Google scholar
[107]
Buccheri F, Liu K, Zhang X C. Terahertz radiation enhanced emission of fluorescence from elongated plasmas and microplasmas in the counter-propagating geometry. Applied Physics Letters, 2017, 111(9): 091103
CrossRef Google scholar
[108]
Martin F, Mawassi R, Vidal F, Gallimberti I, Comtois D, Pepin H, Kieffer J C, Mercure H P. Spectroscopic study of ultrashort pulse laser breakdown plasmas in air. Applied Spectroscopy, 2002, 56(11): 1444–1452
CrossRef Google scholar
[109]
Liu J, Zhang X C. Enhancement of laser-induced fluorescence by intense terahertz pulses in gases. IEEE Journal of Selected Topics in Quantum Electronics, 2011, 17(1): 229–236
CrossRef Google scholar
[110]
Liu J, Dai J, Zhang X C. Ultrafast broadband terahertz waveform measurement utilizing ultraviolet plasma photoemission. Journal of the Optical Society of America B, Optical Physics, 2011, 28(4): 796–804
CrossRef Google scholar

Acknowledgements

This research was sponsored by the Army Research Office and was accomplished under Grant Nos. US ARMY W911NF-14-1-0343, W911NF-16-1-0436, and W911NF-17-1-0428. And we would like to appreciate the National Natural Science Foundation of China (NSFC) for supporting Pingjie Huang (Grant Nos. 61473255 and 61873234).

RIGHTS & PERMISSIONS

2018 Higher Education Press and Springer-Verlag GmbH Germany, part of Springer Nature
AI Summary AI Mindmap
PDF(3810 KB)

Accesses

Citations

Detail

Sections
Recommended

/