Rapid ultrafine-tunable optical delay line at the 1.55-mum wavelength

A fast, ultrafine-tunable delay line at 1550 nm is demonstrated by use of acousto-optic pulse shaping. Delays of up to 30 ps can be achieved without any optical readjustment. The delay is linear to the rf center frequency applied to the acousto-optic modulator and is fully electronic. It takes only 3micros to switch between different time slots, irrespective of the time separation in the tuning range of 30 ps; for a smaller tuning range the tuning speed can be faster. The tuning resolution and range depend on the choice of system parameters. The pulse energy can be regulated by rf power.     

6.3 GHz Linearly Tuning Single-Frequency Nd:YVO<Subscript>4</Subscript> Laser

We propose a linearly frequency-tuning single-frequency Nd:YVO₄ laser. We achieve a single-frequency tuning operation with a tuning range of 6.3 GHz and a maximum power of 0.5 W at 1,064 nm by tilting a thin coated etalon and changing the voltage applied to an RTP crystal in a synchronous way. The laser is linearly tuned with a standard frequency variation of ～190 MHz. We estimate the average tuning speed to be 0.81 GHz/s. The tuning range obtained is more than three times the longitudinal mode spacing of the laser resonator.     

Dual-frequency Brillouin fiber laser for optical generation of tunable low-noise radio frequency/microwave frequency

We demonstrate a new approach, i.e., a cw dual-frequency Brillouin fiber laser pumped by two independent single-frequency Er-doped fiber lasers, for the generation of tunable low-noise rf/microwave optical signals. Its inherent features of both linewidth narrowing effect in a Brillouin fiber cavity and common mode noise cancellation between two laser modes sharing a common cavity allow us to achieve high frequency stability without using a supercavity. Beat frequency of the dual-frequency Brillouin fiber laser can be tuned from tens of megahertz up to 100 GHz by thermally tuning the wavelengths of the two pump lasers with tuning sensitivity of approximately 1.4 GHz/ degrees C. Allan variance measurements show the beat signals have the hertz-level frequency stability.     

Research on tunable local laser used in ground-to-satellite coherent laser communication

In order to realize homodyne reception and Doppler frequency shift tracking in ground-to-satellite coherent laser communication, a local laser is experimentally demonstrated in this Letter. It is realized based on modulationsideband injection locking, and has a 10 GHz tuning range, a 1 THz/s tuning rate, a 5 k Hz linewidth, and 16 m W of output power. When applied to a Costas loop in a coherent laser communication system, the local laser can achieve ?5 GHz Doppler frequency shift tracking with a 20 MHz/s frequency shift rate, which is sufficient for the ground-to-satellite coherent laser communication.     

External-cavity lasers based on a volume holographic grating at normal incidence for spectroscopy in the visible range

We present two external-cavity diode lasers that utilize a volume holographic grating as the frequency selective feedback element. By using the grating at normal incidence, it is possible to design simple and compact external-cavity diode lasers that have sufficient tunability for molecular spectroscopy. The first design utilizes a long-cavity designed for narrow linewidth and good long-term stability. The laser operates near 635 nm and it has a PZT-controlled tuning range of 28 GHz and a 1-s linewidth of 900 kHz. The second design utilizes a grating attached very close to the laser diode, making the laser compact, robust and easy to operate. The short external-cavity laser operates near 658 nm and it has a linewidth of 30 MHz. Continuous and mode-hop free tuning range of 145 GHz can be obtained by using a simple temperature tuning method.     

Development of 1.3GHz high-T-c rf SQUID

A new high-T_c (HT_c) rf SQUID working at around 1.3GHz has been developed to avoid electromagnetic interference such as growing mobile communication jamming. This new system works in a frequency range from 1.23 to 1.42GHz (centred at 1.3GHz), which is not occupied by commercial communication. The sensor used in the 1.3GHz rf SQUID is made of a HT_c coplanar superconducting resonator and a large-area HT_c superconducting film concentrator. We have achieved in the 1.3GHz HT_c rf SQUID system a minimal flux noise of 2.5×10^{-5}Φ_0/\sqrt{Hz} and a magnetic field sensitivity of 38fT/\sqrt{Hz} in white noise range, respectively. The effective area of the concentrator fabricated on a 15×15mm^2 substrate is 1.35mm^2. It is shown that the 1.3GHz rf SQUID system has a high field sensitivity. Design and implementation of 1.3GHz HT_c rf SQUID offers a promising direction of rf SQUID development for higher working frequency ranges.     

基于平面光波导谐振腔的可调谐光电振荡器

提出了一种基于平面光波导谐振腔的可调谐光电振荡器.该振荡器中,相位调制器串联光波导谐振腔,取代了传统系统中的强度调制器、长光纤和滤波器.由于光学谐振腔对光子频率和相位敏感,调节激光器改变输出光的波长,不仅可以调制光的强度,还可以对微波光子进行选频输出.当光子在波导腔中发生谐振时,产生很强的延时特性,可以取代传统系统中的长光纤.整个光电振荡器系统体积为长29.5cm、宽21cm、高7cm.实验中,改变0.1pm的光子波长,能够产生步长为12.535.5 MHz的调谐,调谐范围达2 GHz,且系统能够产生10 GHz的微波信号,在中心频率为10 GHz处其相位噪声为-109.7dBc/Hz@10kHz.该研究为光电振荡器的小型化和实用化提供了一种新的思路.     

Development of 1.3GHz high-T-c rf SQUID

A new high-T_c (HT_c) rf SQUID working at around 1.3GHz has been developed to avoid electromagnetic interference such as growing mobile communication jamming. This new system works in a frequency range from 1.23 to 1.42GHz (centred at 1.3GHz), which is not occupied by commercial communication. The sensor used in the 1.3GHz rf SQUID is made of a HT_c coplanar superconducting resonator and a large-area HT_c superconducting film concentrator. We have achieved in the 1.3GHz HT_c rf SQUID system a minimal flux noise of 2.5×10^{-5}Φ_0/\sqrt{Hz} and a magnetic field sensitivity of 38fT/\sqrt{Hz} in white noise range, respectively. The effective area of the concentrator fabricated on a 15×15mm^2 substrate is 1.35mm^2. It is shown that the 1.3GHz rf SQUID system has a high field sensitivity. Design and implementation of 1.3GHz HT_c rf SQUID offers a promising direction of rf SQUID development for higher working frequency ranges.     

Novel photonic approach to microwave frequency measurement using tunable group delay line

A photonic approach for measuring microwave frequency over a wide bandwidth is proposed.An optic group delay line composed of several magneto-optical switches and a 1.6-km single-mode fiber is used as a tunable dispersive medium in the measurement setup.A minimum frequency accuracy of 80 MHz in the range of 1-20 GHz is achieved experimentally.     

Frequency dependence of the radio frequency collapse effect

A systematic study of the dependence of the radio frequency (rf) collapse effect on the frequency of the rf field which induces the fast relaxation of the hyperfine field was performed for Permalloy and amorphous Fe₄₅Ni₃₀Si₁₀B₁₅ alloy. The rf collapse was studied for the frequency range of 12 MHz to 64 MHz. The results show that the rf collapse appears gradually in both materials as the rf field frequency exceeds the Larmor frequency what is in agreement with the model predictions.     

二极管激光泵浦Nd：YVO4激光器的频率调谐特性研究

用加热法和压电陶瓷ＰＺＴ调腔的方法，实现二极管激光泵浦的单频运转１０６４ｎｍ２％Ｎｄ：ＹＶＯ４激光器调谐。调谐范围４７．４ＧＨｚ，增益峰漂移引起的激光频率温度系数２ｖ／２Ｔ＝－１．０４ＧＨｚ／℃，压电陶瓷调谐系数１５０ＭＨｚ／Ｖ。研究了加热影响件性能的情况。     

Bandwidth tunable high-Tc superconducting filter

We have developed a high-T_c superconducting band-pass filter, whose center frequency and bandwidth can be tuned independently, with steep attenuation at both lower and higher band edges. This tunable filter is composed of two different types of band-pass filters, one with steep attenuation at the lower band edge and the other with steep attenuation at the higher band edge. Two filters are connected in series and each filter is covered with additional dielectric plates, respectively. The tuning characteristics of the entire filter can be controlled by adjusting the distances between the dielectric plates and the substrate. The entire filter was fabricated monolithically on a 30-mm-wide and 60-mm-long LaAlO₃ substrate. A center frequency of 1.93 GHz, a 3 dB bandwidth of 20 MHz, and an attenuation of 30 dB, 1.0 MHz apart from both band edges, were obtained for the entire filter. Then, a sapphire plate was set above each of two filters, and a center frequency tuning of 10 MHz and a bandwidth tuning of 5 MHz were obtained by adjusting the distances between the substrate and the sapphire plates.     

Response of metal-insulator-metal point contact diodes to visible laser light

Video response and mixing behaviour of metal-insulator-metal point contact diodes have been investigated for visible laser light. Thermally enhanced tunneling is shown to dominate the dc detection behavior of those diodes, while mixing of frequencies being more than several MHz apart is a more complex phenomenon involving thermal, field-and photo-assisted tunneling. In further experiments the potential of point contact diodes for optical heterodyne spectroscopy was examined. Two green laser lines of 122 GHz frequency difference were mixed with the second harmonic of an appropriate microwave frequency, generated simultaneously on the diode. The modestS/N ratio achieved has to be assigned to the different behaviour of metal-insulator-metal diodes in the visible and rf range.     

Injection-locked fiber laser for tunable millimeter-wave generation

A dual-ring injection-locked fiber laser consisting of a ring of optoelectronic oscillator (OEO) and a ring of fiber laser is proposed and demonstrated for tunable millimeter-wave (mm-wave) generation. The approach combines the advantages of mm-wave generation based on OEOs and fiber lasers, which can generate a high-frequency, low-phase-noise, and a mode-hopping-free mm-wave signal with a large tuning range. A low-phase-noise mm-wave signal with a tunable frequency of 30-50 GHz and a tuning step of 10 GHz is obtained in a proof-of-concept experiment. The tuning range can be as large as 140 GHz if a high bandwidth photodetector is applied.     

All-optical microwave bandpass filter and phase shifter using a broadband optical source and an optical phase modulator

We propose a system that can perform microwave bandpass filtering and phase shifting simultaneously without redundant optical-electrical and electrical-optical conversions. The principle is based on polarization-dependant phase modulation of a broadband optical source and the variable optical carrier time shift method. A single-bandpass microwave photonic filter with a central frequency of 10.8 GHz, a 3-dB bandwidth of 670 MHz, and a 360° phase tuning range is experimentally demonstrated. The capability of our configuration to implement wideband phase shifters is also verified.     

Broadband Brillouin slow light with multiple-longitudinal-mode,tunable pump

We propose and demonstrate broadband Brillouin slow light using a multiple-longitudinal-mode tunable fiber laser as Brillouin pump. A tunable broadband Brillouin pump with a tuning range from 1 520 to 1 555 nm is generated using a fiber ring laser with a semiconductor optical amplifier (SOA) as its gain medium. The pump spectrum consists of a large number of longitudinal modes separated by 6 MHz. The 3-dB bandwidth is about 11.5 GHz, and its fluctuation is less than 100 MHz within the tuning range. An 8-Gb/s data signal can be delayed by up to 83.0 ps (bit error rate < 10 9) at 17-dBm pump power.     

Tunable atomic magnetometer for detection of radio-frequency magnetic fields

We describe an alkali-metal magnetometer for detection of weak magnetic fields in the radio-frequency (rf) range. High sensitivity is achieved by tuning the Zeeman resonance of alkali atoms to the rf frequency and partially suppressing spin-exchange collisions in the alkali-metal vapor. We demonstrate magnetic field sensitivity of 2 fT/Hz(1/2) at a frequency of 99 kHz with a resonance width of 400 Hz. We also derive a simple analytic expression for the fundamental limit on the sensitivity of the rf magnetometer and show that a sensitivity of about 0.01 fT/Hz(1/2) can be achieved in a practical system with a measurement volume of 200 cm3.     

宽带微波馈入对于具有常规磁场构型的ECR离子源性能的提高

As clearly demonstrated at several laboratories,the performances of electron-cyclotron resonance (ECR)ion sources can be enhanced by increasing the physical sizes(volumes)of embedded ECR zones.En- larged ECR zones have been achieved by engineering the central magnetic field region of these sources so they are uniformly-distributed"volumes"in resonance with single-frequency rf power.Alternatively,the number of ECR surfaces in conventional minimum-B geometry sources can be increased by heating their plasmas with multiple,discrete frequency microwave radiation.Broadband rf power offers a simple,low cost and arguably more effective means for increasing the physical sizes of the ECR zones within the latter source type.In this article,theoretical arguments are made in support of the volume effect and the charge-state enhancing ef- fects of broadband microwave radiation(bandwidth:200MHz)plasma heating are demonstrated by comparing the high-charge-states of Ar ion beams,produced by powering a conventional minimum-B geometry,6.4GHz ECR ion source,equipped with a biased disk,with those produced by conventional bandwidth(bandwidth:～1.5MHz)radiation.     

Laser frequency offset locking scheme for high-field imaging of cold atoms

We present a simple and flexible frequency offset locking scheme developed for high-field imaging of ultra-cold atoms which relies on commercially available RF electronics only. The main new ingredient is the use of the sharp amplitude response of a “home-made” RF filter to provide an error signal for locking the lasers. We were able to offset lock two independent diode lasers within a capture range of hundreds of MHz, and with a tuning range of up to 1.4 GHz. The beat-note residual fluctuations for offset locked lasers are below 2 MHz for integration times of several hundreds of seconds.     

Single-frequency 1.25 W monolithic lasers at 1123 nm

Experimental investigation ofd Nd:YAG monolithic nonplanar ring lasers operated at 1123 nm wavelength is presented. Stable single-frequency 1123 nm laser output has been obtained with successful suppression of the strong 1064 nm radiation. Single-frequency output power of 1.25 W is demonstrated with a pump power of 3.98 W at 808 nm, which gives a slope efficiency of 39%. The laser frequency tuning range is over 3 GHz, and the average tuning rate with temperature is -2.6 GHz/ degrees C. A strong iodine absorption line can be covered within the laser frequency tuning range.