DNA-based tunable THz oscillator

The intrinsic helix conformation of the DNA strands is known to be the key ingredient of control of the electric current through the molecule by the perpendicular (gate) electric field. We show theoretically that Bloch oscillations in periodic systems with helical conformation are also strongly affected by such lateral field; the oscillation frequency splits into a manifold of several generally non-commensurate frequencies leading to a complicated pattern of the charge motion. For model parameters typical for the DNA the frequency of such oscillations falls in the THz domain, suggesting a possibility to design a DNA-based nano-scale source of THz radiation.     

Widely tunable optical delay generator

We propose and demonstrate a method for quasi storage of light based on periodic spectral filtering realized in the time domain by amplitude modulation using frequency-to-time conversion. The delay can be tuned in a wide range by changing the frequency of an electrical modulation signal. In our experiments, the delay of single 2.5 ps pulses varied by 66 pulse widths. The technique works equally well for more complex optical data packets. Contrary to known approaches, the method has a very large spectral bandwidth and can be implemented by either fiber or integrated solutions using existing technologies. Because of the large bandwidth, fractional delays up to several tens of thousands of pulse widths can be achieved potentially for subpicosecond pulses, which is a tremendous value regarding the implementation simplicity.     

Widely tunable monochromatic THz sources based on phase-matched difference-frequency generation in nonlinear-optical crystals: A novel approach

We review our up-to-date result on the development of widely tunable monochromatic THz sources, implemented based on difference-frequency generation (DFG) in GaSe, ZnGeP₂, and GaP. Using a GaSe crystal, the output wavelength was tuned in the range from 66.5 μm to 5664 μm (from 150 cm^?1 to 1.77 cm^?1) with the highest peak power 389 W. This tuning range is the widest ever produced for a continuously tunable and coherent tabletop THz source. Moreover, the conversion efficiency 0.1% is also the highest ever achieved for a tabletop system. On the other hand, based on DFG in a ZnGeP₂ crystal, the output wavelength was tuned in the ranges 83.1–1642 μm and 80.2–1416 μm for two phase-matching configurations. The output power has reached 134 W so far. Finally, using a GaP crystal, the output wavelength was tuned in the range 71.1–2830 μm, whereas the highest peak power was 15.6 W. The advantage of using GaP over GaSe and ZnGeP₂ is that crystal rotation is no longer required for wavelength tuning. Instead, one just needs to tune the wavelength of one mixing beam within the bandwidth of as narrow as 15.3 nm.     

Widely tunable single-frequency pulsed optical parametric oscillator

The spectral output of a nanosecond dual-cavity doubly resonant optical parametric oscillator has been investigated versus the relative length of the signal and idler cavities. Regions of stable single-frequency operation are determined by use of a type II phase-matched KTP crystal and compared with the predictions of a mode-overlap model. A wide mode-hop-free tuning range is obtained over 40 GHz, limited only by piezoelectric biases. Furthermore, discrete tuning is investigated over the full parametric gain curve. For demonstration purposes, experiments are performed in the domain that is most inclined to multifrequency emission, i.e., near degeneracy.     

Widely tunable extreme UV frequency comb generation

Extreme UV (XUV) frequency comb generation in the wavelength range of 51 to 85 nm is reported based on high-order harmonic generation of two consecutive IR frequency comb pulses that were amplified in an optical parametric chirped pulse amplifier. The versatility of the system is demonstrated by recording direct XUV frequency comb excitation signals in He, Ne, and Ar with visibilities of up to 61%.     

Widely tunable femtosecond fiber optical parametric oscillator

The phase-matching condition in a fiber is discussed. A balance among the different orders of fiber dispersion can be found to achieve a widely tuning modulation instability gain for pumping around the normal dispersion regime. Three coupled nonlinear wave equations are used to simulate the femtosecond fiber optical parametric oscillator. The numerical results show that, through appropriate choice of dispersion, femtosecond pulses with a 180-nm tunable range can be generated when pump wavelength near a fiber’s zero-dispersion wavelength is tuned only 7 nm. Further tuning is limited by the walk-off between the pump and the signal pulses.     

Widely tunable ring-cavity tellurite fiber Raman laser

We report a widely tunable ring-cavity tellurite fiber Raman laser covering the S+C+L+U band. A tunable range (1495-1600 nm, limited by the tunable optical bandpass filter) over 100 nm is obtained by using a single-mode tellurite fiber with high Raman gain coefficients (55 W(-1)km(-1)) and large Raman shift (~22.3 THz) as the gain medium. Furthermore, the free-running 1665 nm Raman fiber laser is achieved from the ring cavity by removing the tunable optical bandpass filter, which shows that such a tellurite fiber has potential for constructing a widely tunable fiber Raman laser covering the S+C+L+U band. A high optical signal-to-noise ratio of over 60 dB for almost all of the tunable range is also demonstrated.     

Thermally tunable THz filter made of semiconductors

By using the finite-difference time domain method, the transmission properties of terahertz wave passing through two different periodic subwavelength structures on InSb semiconductor slabs under different temperatures have been investigated. The results show that the peak transmittance increases and the transmittance peak has a blue shift when the temperature is increasing. It is extremely versatile to control the tunable THz filter by varying the temperature.     

宽谱可调谐的全固化Cr:LiSAF激光器

报道了调谐范围达130 nm的的V型腔端面泵浦全固化Cr:LiSAF激光器。研究了V型腔结构的重要参数,优化了腔型设计以提高激光器的效率。激光器自由运转输出时,斜效率最高达39.2%,泵浦阈值最低为32.8 mW。对比分析了双折射滤光片(BF)和棱镜的调谐效果。在腔内插入BF调谐,实现了783~913 nm连续可调谐输出,在840 nm处获得115 mW的最大输出功率,在800~900 nm的区间内,输出功率超过80 mW。用棱镜作为调谐元件,调谐范围达802~887 nm,最大输出功率为6.5 mW。从调谐范围和输出功率看,BF的调谐效果更好。     

Widely tunable Yb-doped laser with all fiber structure

In this paper, an all fiber Yb³⁺-doped fiber ring laser with large tuning range has been reported. A 976 nm laser diode (LD) pumped laser is used as the pump source and high concentration Yb³⁺-doped fiber is adopted as gain medium. Adjusting the polarization controller (PC), a widely tunable range of 20 nm from 1030 to 1050 nm is obtained. The spectral linewidth of the pulse is less than 0.2 nm. Comparing with other fiber laser structures, the fiber laser with an all-fiber structure has higher efficiency and better stability. The laser also has very stable and flat output within the whole tuning range.     

Widely tunable dual-pump parametric amplifiers with photonic crystal fibres

This paper theoretically studies the double-pumped fibre-optical parametric amplifiers （FOPAs） in photonic crystal fibres. Two distinct working regimes of FOPAs are researched, which depend on the dispersion at the central wavelength of the two pumps. Extremely broad tuning range can be obtained when the central pump wavelength is in the normal dispersion regime and is insensitive to the wavelength separation between the two pumps, while the tuning range is narrow in the anomalous dispersion regime and can be significantly enhanced by increasing the wavelength separation. Impacts of higher-order dispersions and temporal walk-off on the gain spectra are also discussed.     

Widely tunable monolithic narrowband grating filter for near-infrared radiation

We propose a monolithic narrowband guided-mode grating filter in fused silica that is widely tunable in the near-IR wavelength region. Based on a recently demonstrated approach for a monolithic reflector comprising an encapsulated grating, we theoretically investigate such a device by means of rigorous modeling aimed at a narrow linewidth. It is demonstrated that upon a spatial variation of the filter's grating period its resonance wavelength can be tuned in a remarkably wide range of near-IR radiation with 800 nm<λ(res)< 1600 nm by translating the laser beam relative to the grating area. The filter performance in terms of linewidth and contrast is essentially preserved over the entire tuning interval.     

Widely tunable Raman ring laser using highly nonlinear fiber

An all-optical widely tunable Raman fiber laser has been realized by incorporating a highly nonlinear fiber in a ring cavity. By feedback a portion of Raman Stokes wave back into the highly nonlinear gain medium, a Raman fiber laser is generated. We found that the lasing wavelength of Raman fiber laser can be tuned from 1537 to 1568 nm with peak power fluctuation within 1 dB, giving a total wavelength tunability of 31 nm. The optical signal-to-noise ratio is found to be wavelength dependent, and the highest optical signal-to-noise ratio of about 59 dB is recorded. The lasing threshold of the Raman fiber laser with this configuration is found to be as low as 300 mW.     

Widely tunable optical parametric oscillator with electrical wavelength control

A LiNbO(3) optical parametric oscillator (OPO) pumped at 930nm shows a wide phase-matching curve. Each pulse produced by the OPO has a very broad natural linewidth, from 1480 to 1800 nm for the signal and from 1950 to 2550 nm for the idler. The emission wavelength is controlled thanks to an electrically tunable Fabry-Perot interferometer inserted into the OPO cavity. The signal wavelength is electrically tuned in the range 1450-1850nm without crystal rotation.     

Widely tunable mid-IR difference-frequency generation based on fiber lasers

A wide tuning technique for mid-IR difference-frequency generation (DFG) with uniform grating periodically poled LiNbO(3) (PPLN) is presented. Based on the dispersion property of the PPLN, the quasi-phase matching (QPM) band for the pump can evolve to two separate bands, and the spacing between them can be increased with the decrease of the crystal temperature. Two such separate QPM bands can be used for increasing the idler tuning range when the crystal temperature is set to adapt the pump tuning. With the technique, an idler tuning range of 690nm is experimentally achieved with fiber laser fundamental lights.     

Widely tunable dual-pump parametric amplifiers with photonic crystal fibres

This paper theoretically studies the double-pumped fibre-optical parametric amplifiers (FOPAs) in photonic crystal fibres. Two distinct working regimes of FOPAs are researched, which depend on the dispersion at the central wavelength of the two pumps. Extremely broad tuning range can be obtained when the central pump wavelength is in the normal dispersion regime and is insensitive to the wavelength separation between the two pumps, while the tuning range is narrow in the anomalous dispersion regime and can be significantly enhanced by increasing the wavelength separation. Impacts of higher-order dispersions and temporal walk-off on the gain spectra are also discussed.     

Extension of tunable far-infrared spectroscopy to 7.9THz

We generated tunable far-infrared radiation by mixing CO(2) -laser,(15)NH(3) -laser, and microwave radiations in a W-Co metal-insulator-metal diode. We used this far-infrared radiation to measure accurately the torsion-rotation transitions of CH(3)OH in the 6-8-THz region.     

Widely tunable photonic crystal fiber Fabry-Perot optical parametric oscillator

We present a widely tunable low-threshold chi(3) optical parametric oscillator. The oscillator cavity is formed by butt coupling dichroic mirrors to either end of a highly nonlinear index-guiding photonic crystal fiber. This yields a singly resonant Fabry-Perot oscillator with a high feedback fraction for the resonant parametric sideband. The tuning range of the output parametric sideband stretches from 23 to 164 THz above the pump frequency. The threshold power of the oscillator is only 15 W.     

Widely and continuously tunable optical parametric generator infrared laser

The experimental results of a high efficiency infrared laser are demonstrated on a quasi phase matched optical parametric generator in PPMgLN (5% MgO doping) pumped by a 1064 nm Nd:YAG laser. A broad continuous signal spectrum 1.56?C1.67 ??m are obtained by tuning the crystal temperature from 20°C to 200°C. When the average pump power is 1.82 W with about 70 ns pulse duration operating at a repetition rate of 10 kHz, the maximum total output power of the PPMgLN OPG is about 323.58 mW consisting of 210 mW of 1.639 ??m signal radiation and 113.58 mW of 3.02 ??m idler radiation.