Bound soliton pulses in a passively mode-locked fibre ring laser

The bound solitons in a passively mode-locked fibre ring laser are observed and their formation mechanism is summarized in this paper. In order to obtain stable bound solitons, a strong CW laser field at the centre of the soliton spectral is necessary to suppress and synchronize the random soliton phase variations.

Observation of 550 MHz passively harmonic mode-locked pulses at L-band in an Er-doped fiber laser using carbon nanotubes film

We demonstrate a passively harmonic mode-locked（PHML） fiber laser operating at the L-band using carbon nanotubes polyvinyl alcohol（CNTs-PVA） film. Under suitable pump power and an appropriate setting of the polarization controller（PC）, the 54^（th） harmonic pulses at the L-band are generated with the side mode suppression ratio（SMSR） better than 44 dB and a repetition frequency of 503.37 MHz. Further increasing the pump power leads to a higher frequency of 550 MHz with compromised stability of 38.5 dB SMSR. To the best of our knowledge, this is the first demonstration on the generation of L-band PHML pulses from an Er-doped fiber laser based on CNTs.

Passive Quenching Electronics for Geiger Mode 4H-SiC Avalanche Photodiodes

We design and fabricate 4H-SiC UV avalanche photodiodes （APDs） ~qth positive beveled mesa, which exhibit low leakage current and high avalanche gain when working in the Geiger mode. The single photon counting performance of the SiC APDs is studied by using a passive-quenching circuit. A new method to determine the exact breakdown voltage of the APD is proposed based on the initial emergence of photon count pulses. The photon count rate and dark count rate of the APD are also evaluated as a function of quenching resistance.

Low threshold high stability passively mode-locked laser performance of a disordered crystal:Nd^(3+):Gd_(0.5)Y_(2.5)Al_5O_(12)

A stable passively mode-locked laser of Nd^3＋：Gd0.5Y2.5Al5O12（Nd：GYAG） disordered crystal is experimentally investigated both using Z-type and W-type cavities with a semiconductor saturable absorbed mirror.The continuous-wave mode-locked threshold of the absorbed pump power is just 1.8 W.The maximum average output power is 210 mW,which is obtained at the absorbed pump power of 2.3 W.The pulse width is measured to be11.1 ps assuming a Gaussian shape.

Tunable dual-wavelength passively mode-locked Yb-doped fiber laser using SESAM

In this linear-cavity passively mode-locked laser based on semiconductor saturable absorber mirror, an Ybdoped fiber is shared by two branch cavities as gain medium. These two cavities can respectively output single-wavelength pulse with the wavelength tuning range of 1 009.~1 057.6 nm and 1 011.6-1 052.6 nm by adjusting volume Bragg grating. When two cavities output pulses together, the dual-wavelength pulses with the maximum and minimum wavelength separation of 34.8 and 2.4 nm, respectively, are achieved by net gain equalization method to suppress mode competition at room temperature. The maximum pulse energies of dual-wavelength pulses are 0.47 and 0.33 nJ separately; their repetition rates are 11.39 and 11.41 MHz.

Diode-pumped passively mode-locked femtosecond Yb:(Y_(0.9)La_(0.1) )_2O_3 ceramic laser

We experimentally demonstrate a diode-pumped passively mode-locked femtosecond laser with yb3＋-doped yttrium lanthanum oxide ceramic. Mode-locking is achieved by using a semiconductor saturable absorber mirror, and intraeavity dispersion is compensated by a pair of SF6 prisms. Laser pulses as short as 357 fs at a central wavelength of 1 075 nm are obtained. The maximum average output power is 670 mW under 4.5 W of pumping power with a slope efficiency of 20%. To the best of our knowledge, this is the shortest pulse generated from Yb-doped yttrium lanthanum oxide ceramic lasers with a sub-500 fs pulse duration.

Passively mode-locked Tm,Ho:YVO_4 laser based on a semiconductor saturable absorber mirror

We report the demonstration of passively continuous-wave mode-locking （CWML） of diode-pumped Tm,Ho：YVO4 laser using an InGaAs/GaAs multiple quantum-well （MQW） structure semiconductor as the saturable absorber. Stable mode-locking pulses at the central wavelength of 2 041 nm are obtained. The maximum output power is 151 roW. The pulse duration is 10.5 ps at the repetition rate of 64.3 MHz.

Development of a Hand Exoskeleton System for Index Finger Rehabilitation

In order to overcome the drawbacks of traditional rehabilitation method,the robot-aided rehabilitation has been widely investigated for the recent years.And the hand rehabilitation robot,as one of the hot research fields,remains many challenging issues to be investigated.This paper presents a new hand exoskeleton system with some novel characteristics.Firstly,both active and passive rehabilitative motions are realized.Secondly,the device is elaborately designed and brings advantages in many aspects.For example,joint motion is accomplished by a parallelogram mechanism and high level motion control is therefore made very simple without the need of complicated kinematics.The adjustable joint limit design ensures that the actual joint angles don＇t exceed the joint range of motion（ROM） and thus the patient safety is guaranteed.This design can fit to the different patients with different joint ROM as well as to the dynamically changing ROM for individual patient.The device can also accommodate to some extent variety of hand sizes.Thirdly,the proposed control strategy simultaneously realizes the position control and force control with the motor driver which only works in force control mode.Meanwhile,the system resistance compensation is preliminary realized and the resisting force is effectively reduced.Some experiments were conducted to verify the proposed system.Experimentally collected data show that the achieved ROM is close to that of a healthy hand and the range of phalange length（ROPL） covers the size of a typical hand,satisfying the size need of regular hand rehabilitation.In order to evaluate the performance when it works as a haptic device in active mode,the equivalent moment of inertia（MOI） of the device was calculated.The results prove that the device has low inertia which is critical in order to obtain good backdrivability.The experiments also show that in the active mode the virtual interactive force is successfully feedback to the finger and the resistance is reduced by one-third;for the passive control mode,the desired trajectory is realized satisfactorily.

Compact high-power mode-locked Nd:YVO_4 picosecond laser using multiple-pass cavity

A stable self-starting mode-locked Nd：YVO4 laser with a Herriott-type multiple-pass cavity （MPC） oper- ating at 1 064 nm is demonstrated. An in-band 880-nm laser diode is used as an end-pump and a semi- conductor saturable absorber mirror （SESAM） is used for passive mode locking （ML） and providing pulse durations of 14 ps. At a pump power of 26.4 W, the maximum average output power is as high as 10.5 W at a repetition rate of 22 MHz, which corresponds to a single pulse energy of 0.48 #J. Optical-to-optical conversion efficiency is as high as 39.8~ at the maximum output power with a slope efficiency of 55.2%.

Highly efficient reduced graphene oxide mode-locked Nd:GGG laser

We report, for the first time to our knowledge, a diode-end-pumped passively mode-locked（ML） Nd-doped gadolinium gallium garnet laser based on a chemically reduced graphene oxide（RGO） saturable absorber mirror. The ML laser gives a pulse duration of 15.1 ps under the maximum average output power of 1.44 W, corresponding to a slope efficiency of 21.1%. The single-pulse energy and peak power are 21.6 n J and 1.43 k W, respectively. The results indicate that our RGO saturable absorber has promising prospects for applications in high-power and high-efficiency ultrafast lasers.

Dissipative soliton operation in diode pumped ultrafast Yb:GdYSiO_5 oscillator

We demonstrate the dissipative soliton mode locking in a diode pumped Yb：GdYSiO^（Yb：GYSO） laser operating in the positive dispersion regime. We obtain stable passively mode-locked pulses with strong positive chirp and with very steep spectral edges. The central wavelength is 1050 nm with bandwidth of about 4 nm, autocorrelation trace shown the typical pulse duration is about 3.5 ps. We obtain the maximum average power of 558 mW for a 3.3-W absorbed pump power, with 22% slope efficiency, and a 78-MHz pulse repetition frequency.

Ultra-broadband optical spectrum generation from a stretched pulse fiber laser utilizing zero-dispersion fiber

We investigate the effects of a piece of zero-dispersion fiber （ZDF） on the pulse dynamics of a passively mode-locked fiber laser operating in the stretched-pulse regime. Numerical simulation suggests that the proper location and length of ZDF facilitate spectrum broadening and pulse shortening in fiber lasers while maintaining constant net cavity dispersion. A nonlinear polarization evolution mode-locked Er-doped fiber laser with a dispersion map is built based on the simulation. Larger optical spectrum broadening is obtained by inserting a longer ZDF after the active fiber during single-pulse operation, which well agrees with the simulation.

A 5 GHz 7.2 dB NF low power direct conversion receiver front-end with balun LNA

A 5GHz low power direct conversion receiver radio frequency front-end with balun LNA is presented. A hybrid common gate and common source structure balun LNA is adopted, and the capacitive cross-coupling technique is used to reduce the noise contribution of the common source transistor. To obtain low 1/f noise and high linearity, a current mode passive mixer is preferred and realized. A current mode switching scheme can switch between high and low gain modes, and meanwhile it can not only perform good linearity but save power consump- tion at low gain mode. The front-end chip is manufactured on a 0.13-#m CMOS process and occupies an active chip area of 1.2 mm2. It achieves 35 dB conversion gain across 4.9-5.1 GHz, a noise figure of 7.2 dB and an IIP3 of -16.8 dBm, while consuming 28.4 mA from a 1.2 V power supply at high gain mode. Its conversion gain is 13 dB with an IIP3 of 5.2 dBm and consumes 21.5 mA at low gain mode.