Infrared heterodyne detection

Heterodyne experiments have been performed in the middle infrared region of the electromagnetic spectrum using the CO2laser as a radiation source. Theoretically optimum operation has been achieved at kHz heterodyne frequencies using photoconductive Ge:Cu detectors operated at 4°K, and at kHz and MHz frequencies using Pb1-xSnxSe photovoltaic detectors at 77°K. In accordance with the theory, the minimum detectable power observed is a factor of 2/η greater than the theoretically perfect quantum counter, hvΔf. The coefficient 2/η varies from 5 to 25 for the detectors investigated in this study. A comparison is made between photoconductive and photodiode detectors for heterodyne use in the infrared, and it is concluded that both are useful. Heterodyne detection at 10.6 µm is expected to be useful for communications applications, infrared radar, and heterodyne spectroscopy. It has particular significance because of the high radiation power available from the CO2laser, and because of the 8 to 14 µm atmospheric window.     

基于AlGaN/GaN HEMT太赫兹探测器的340 GHz无线通信接收前端

利用天线耦合AlGaN/GaN HEMT太赫兹探测器的自混频和外差混频效应,分别设计并测试了340 GHz频段直接检波式和外差混频式接收机前端。通过接收机信噪比的测量和接收功率的定标,得到了两种接收机的等效噪声功率。直接检波模式下探测器的响应度约为20 mA/W,直接检波模式和外差混频模式下接收机的等效噪声功率分别约为?64.6 dBm/Hz1/2和?114.79 dBm/Hz。在相同的载波功率和接收信号带宽条件下,当本振太赫兹波功率大于?7 dBm时,外差混频接收的信噪比优于直接检波的信噪比。当本振功率大于0 dBm时,外差混频接收机表现出优良的解调特性,其信噪比高出直接检波接收机的信噪比10 dB以上。     

Minimally cooled heterojunction laser heterodyne detectors in metalorganic vapor phase epitaxially grown Hg1-xCdxTe

By taking advantage of Auger suppression techniques, the leakage currents of room temperature infrared detectors operating in the LWIR band can be greatly reduced. At present, these detectors suffer from large 1/f noise and hence the improvement in the detectivity resulting from the reduced leakage currents can only be realized at high frequencies. However, this is not a problem for heterodyne systems which employ intermediate frequencies above 40 MHz. A thermo-electrically cooled Auger suppressed infrared detector operated at 260K has been studied as a heterodyne detector. The device was operated with the application of sufficient local oscillator power to double its dark current (about 0.3 mW) and a NEP of 2 x 10^-19 W Hz⁻¹ was deduced from heterodyne measurements. The frequency response is presently limited by a combination of the detector capacitance and the series resistance to about 70 MHz and ways to reduce this series resistance are considered.     

Narrowband heterodyne reception using unstabilized sources

Source power for laboratory-type experiments is often limited at millimeter and submillimeter wavelengths. This requires the use of sensitive receiving equipment. Cooled square-law detectors and narrowband heterodyne detectors are examples. We have developed a coherent mechanical frequency shifter, which makes possible narrowband heterodyne detection without the need for highly frequency stable sources. Identical frequency and phase fluctuations of the transmit and local oscillator signals derived from one source are eliminated at the intermediate frequency. The widely tunable frequency shifter, designed for a 637GHz scale-model radar, was tested in a 140GHz non-radar configuration. We investigated the receiver's minimum coherently resolvable bandwidth and its sensitivity. Several types of sources were compared for the effect of local oscillator amplitude noise on receiver sensitivity at low intermediate frequency.     

Printed circuit antennas with integrated FET detectors formillimeter-wave quasi optics

Planar twin dipole microstrip antennas with integrated FET detectors which provide antenna patterns suitable for millimeter-wave quasioptical applications are discussed. The circuits are suitable for use as individual elements of an imaging array. A 63-GHz heterodyne mixer using such a circuit produced a system noise temperature of 7900 K     

Photodetectors for optical communication systems

The characteristics of high-sensitivity photodetectors suitable for wide bandwidth optical communication systems are summarized. Photodiodes, photomultipliers, and photoconductive detectors for wavelengths from 0.3 µm to 10.6 µm are covered. The use of internal current gain by means of avalanche and electron multiplication and by means of optical heterodyne detection to increase sensitivity of high speed photodetectors is discussed. The application to visible and infrared laser communication systems is reviewed.     

Heterodyne Spatial Tracking System for Optical Space Communication

Design considerations for an optical spatial tracking system for both coherent and noncoherent heterodyne detection are addressed. Heterodyne detection systems are much less susceptible to background radiation and device noise than conventional direct detection systems. In addition, the angle discriminator profile in a heterodyne detection system can be tailored via the local oscillator spatial distribution. An optimal LO distribution is described and its performance is compared to some Suboptimal distributions. It is shown that an ideal quadrant detector can achieve near optimal performance, since the LO effectively acts like a continuum of detectors. Cramer-Rao tracking bounds and other performance criteria are given under the conservative assumption that the angular process to be tracked is a single-pole process. The method used is directly applicable to other types of angular processes. Experimental verification of some of the basic concepts is presented.     

Field of View Increase for Optical Heterodyne Receivers

The field of view of optical heterodyne systems are usually limited by a simple criterion- namely, that A_RΩ_R ? λ², where A_R is an effective aperture, Ω_R the corresponding field of view and λ the optical wavelength. This paper will demonstrate that with a simple change of systems geometry and the possible use of array detectors, this severe restriction can be alleviated considerably and, in some cases, eliminated. Both coherent sources and thermal radiation sources are considered. This might suggest that heterodyne systems that were eliminated in the past because of that criterion alone, could turn out to be, not only possible, but even advantageous compared to other techniques.     

本振功率对目标微动激光平衡外差探测的影响研究

面向远距离目标微多普勒效应的探测,建立了本振光功率变化对激光平衡外差探测回波信噪比影响的数学模型,并进行了仿真分析。通过搭建的1 550 nm激光平衡外差探测实验平台测试了由于本振功率变化对于目标微多普勒特征提取效果的影响。研究结果表明,对于平衡外差探测,由于两光电探测器量子效率不可能完全匹配,考虑到散粒噪声、热噪声和本振相对强度噪声的影响,将存在一个最佳本振功率值使探测信噪比达到最大。当选取该本振功率进行探测时,获得的目标微多普勒特征可读性更强,提取误差更小。     

RF-based electron beam timing measurement with sub-10fs resolution

Time of flight measurements of a relativistic electron beam have been performed and have demonstrated a resolution below 10fs. The electronics consisted of a heterodyne receiver incorporating an array of analogue phase detectors in order to reduce noise. The performance of the system makes it suitable for the challenging requirements of intra-pulse train timing measurements in a future linear collider.     

The Application of Superconducting Tunnel Junction Detectors to Astronomy

Detectors based on the superconducting-insulating-superconducting (SIS) junction long ago surpassed Schottky-diode semiconductor detectors as the most sensitive heterodyne mixers in the millimeter and submillimeter (far-infrared) wavelength range. Other novel superconducting device configurations have been applied as direct detectors. Though still in the early stages of development, and yet to find widespread application, they have demonstrated advantages over traditional semiconductor detectors in specialized situations. Exciting progress has been made in recent years in developing the superconducting tunnel junctions (STJ) as a photon detector for optical and near-optical wavelengths, where silicon CCD's are currently dominant. I examine some of the areas in which the properties of STJ detectors may best match the instrument capabilities that astronomical observations require, and discuss the implications of the intrinsic spectral resolution of the STJ. This capability will enable a significant increase in observing efficiency, once the technology matures, that should justify increased complexity of cryogenic systems, particularly for instruments to be used on the next generation of large ground-based telescopes.     

Polarisation-diversity receiver for coherent FSK communications

A polarisation-insensitive optical heterodyne receiver, in which two signals with orthogonal polarisations are independently detected and demodulated, and subsequently combined, has been demonstrated for FSK-modulated signals at 50 Mbit/s with a sensitivity of ?55.5 dBm (Pe=10?9). The receiver uses the entire received signal and local oscillator signal with only one photodiode in each branch. Differences between the two PINFET detectors result in a ±ldBm sensitivity variation for all polarisation states of the received signal.     

The optical response of epitaxial lift-off HEMT's to 140 GHz

We present measurements on the optical frequency response of epitaxial lift-off (ELO) 1.0-μm InP high-electron mobility transistors (HEMTs) to 140 GHz using electrooptic sampling and heterodyne techniques. Our picosecond sampling measurements established that the lift-off devices exhibited substantial optical response to 140 GHz. Heterodyne measurements made at 60 and 94 GHz later confirmed these findings. A novel three wave mixing technique was used to extend the heterodyne bandwidth to 130 GHz. In these experiments, millimeter waves were generated in our optically driven HEMT's and launched into waveguides. These lift off devices can be major additions to future millimeter wave integrated optoelectronic systems either as high frequency optical detectors or as optically driven tunable millimeter wave sources     

Photocounting array receivers for optical communication through the lognormal atmospheric channel--III: Error bound forM-ary equal-energy orthogonal signaling (Corresp.)

A bound on the probability of error is obtained for anM-ary direct-detection optical communications system consisting of an amplitude-stabilized source, a lognormal atmospheric channel, and a photocounting detector array. Equal-energy, equiprobable, orthogonal signaling, and fiat independent fading at all detectors is assumed. The result reduces to that obtained previously in the absence of fading. A comparison is made with the analogous solution for the heterodyne array receiver.     

Calibrating the Six-Port Reflectometer by Means of Sliding Terminations

The six-port technique promises to have a major impact on the next generation of automatic network analyzers because complex heterodyne methods may be replaced by simple amplitude detectors. This projection, however, is predicated upon the existence or development of calibration techniques which permit one to conveniently and accurately obtain the parameters which characterize the six-port. This paper describes a number of substantial refinements to a previously described procedure which is based upon the use of sliding terminations.     

Effect of device processing on 1/f noise in uncooled, auger-suppressed CdHgTe diodes

Auger suppression reduces the leakage current in uncooled CdHgTe diodes to the point where the shot noise limited D* is significantly higher than for other uncooled detectors. However, Auger-suppressed diodes exhibit high levels of 1/f noise and so applications have initially been in devices operating at high frequency such as CO₂ laser heterodyne detectors. In order to use Auger suppression in imaging devices, we need to reduce the 1/f noise and this paper describes a study of the effects of device processing on noise. We find that although some of the noise is associated with perimeter leakage currents, variations in the surface passivation treatment have little effect on the total noise. However, a post-passivation anneal can reduce the noise in some cases. We also find that CdTe passivated devices are more stable when baked than those passivated with ZnS.     

Quantum limited detection in tunnel junction mixers

A complete quantum generalization of microwave mixer theory is constructed for nonlinear single-particle tunnel junctions. The result represents a unification of the concepts used to describe these "classical" resistive mixers with the language of photon detection. Tunneling devices are predicted to undergo a transition from energy detectors to photon counters when operated at frequencies where the photon energy becomes comparable to the voltage scale of the dc nonlinearity. The small-signal video current response is found to approach one electron for each photon absorbed at high frequencies. In a heterodyne receiver, sufficiently nonlinear tunnel junctions are predicted to be capable of achieving the fundamental quantum noise limit for sensitivity in the detection of electromagnetic radiation. The theory presented here thus provides a framework for systematically extending the techniques of quantum electronics to considerably lower frequencies than are currently being exploited. Recent measurements of heterodyne mixer performance using superconductive tunneling devices are already beginning to approach quantum limited results at microwave and millimeter wave frequencies. Eventual application of tunnel barriers as photon detectors in the submillimeter and infrared spectral regions also appears to be possible, and the fast response times of such devices could give them an advantage over photoconductors even at the higher frequencies. The development of suitable nonlinear tunnel junctions contains the potential to bridge the present gap in quantum detectors between the infrared photon devices and microwave masers.     

Schottky-Barrier Diodes for Submillimeter Heterodyne Detection

The fabrication and packaging techniques which were used to produce high-reliability mixer diodes for millimeter-wave satellite communications systems have been extended to produce Schottky-barrier mixer diodes for use in the submillimeter-wave region from 1 to 0.1 mm. The influence of material and circuit parameters on the performance of Schottky-barrier diodes as heterodyne detectors in the submillimeter-wave region has been considered. The semiconductor material parameters have been optimized and new packaging concepts have been investigated. A new diode package has been developed which incorporates both an integral stripline filter on 0.05-mm-thick quartz and a section of overmoded waveguide. The new package has the advantage of being replaceable in the mixer circuits, and yet it can provide a low-loss interface between the diode package and the mixer circuit. A new surface-oriented device has been developed in which the contact to the Schottky barrier is formed by photolithographic techniques onto the same surface as the ohmic contact. The surface-oriented devices exhibited heterodyne detection into the submillimeter region.     

Phase and amplitude uncertainties in heterodyne detection

The quantum limits on simultaneous phase and squared-amplitude measurements made via optical heterodyne detection on a single-mode radiation field are established. The analysis proceeds from a fully quantum mechanical treatment of heterodyning with ideal photon detectors. A high mean field uncertainty principle is proven for simultaneous phase and squared-amplitude observations under the condition that the signal and image band states are independent, and the image band has zero mean. Operator representations are developed which show that no such principle applies when arbitrary signal/image band dependence is permitted, although the mean observations are no longer functions of the signal field alone. A multimode two-photon coherent state illustrating this behavior at finite energy is exhibited. Potential applications for the resulting improved accuracy measurements are briefly described.     

Millimeter-wave imaging using FET detectors integrated with printed circuit antennas

The application of field effect transistor (FET) detectors integrated with planar twin dipole microstrip antennas to millimeter-wave imaging has been demonstrated. Circuits were configured as practical heterodyne mixers, as elements in a 2×3 element planar focal plane array for imaging, and as receivers in frequency modulated (FM) radars for three-dimensional imaging, at 63 GHz. These experiments show that quasioptical circuits, using conventional present-day FETs and simple printed circuit construction, can be applied usefully in the millimeter-wave region.