Binary-phase shift keying based time-domain index modulation signal detection with low power local oscillator

Traditional photon detectors are operated in the direct detection mode, counting incident photons with a known quantum efficiency. Here, we have investigated a superconducting nanowire single photon detector (SNSPD) operated as a photon counting mixer at telecommunication wavelength around 1.5 μm. This regime of operation combines excellent sensitivity of a photon counting detector with excellent spectral resolution given by the heterodyne technique. Advantageously, we have found that low local oscillator (LO) power of the order of hundreds of femtowatts to a few picowatts is sufficient for clear observation of the incident test signal with the sensitivity approaching the quantum limit. With further optimization, the required LO power could be significantly reduced, which is promising for many practical applications, such as the development of receiver matrices or recording ultralow signals at a level of less-than-one-photon per second. In addition to a traditional NbN-based SNSPD operated with normal incidence coupling, we also use detectors with a travelling wave geometry, where a NbN nanowire is placed on the top of a Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> nanophotonic waveguide. This approach is fully scalable and a large number of devices could be integrated on a single chip.

In order to realize receiver (Rx) photonic integrated circuits (PICs) applicable to 400 Gb/s-class coherent passive optical network (PON) systems, we integrated tunable wavelength f ilters (TWFs), PIN photodiodes (PIN-PDs), and optical 90 degree hybrids (90HBs) into Rx PICs fabricated on a commercial standard silicon photonics (SiPh) platform. As a result of device evaluation, we observed characteristics indicating the potential for application in 400 Gb/s-class coherent PON systems. Subse quently, we prototyped Rx assemblies in which the Rx PIC and a digital signal processing (DSP) chip are mounted. When the Rx assembly received a 60-Gbaud dual-polarization (DP) quadrature phase shift keying (QPSK) 200 Gb/s C-band optical signal after 2 km loopback transmission, we achieved an optical received power of −24 dBm at a bit error ratio (BER) of 2×10−2, which corresponds to the forward error correction (FEC) limit. Based on this result, the Rx assembly is suitable for a PON system with a maximum transmission distance of 20 km and up to 16 terminations. Similarly, when the Rx assembly received a DP 16 quadrature amplitude modulation (QAM) 400 Gb/s optical signal, we achieved an optical received power of −6 dBm at the FEC limit. Although some issues remain, these results suggest the Rx assembly can be applied to 400 Gb/s-class coherent PON systems. In the future, we will improve the Rx characteristics by reducing insertion loss of the Rx PICs and will prototype and evaluate transmitter (Tx) assemblies.

A miniature neon indicator lamp, also known as a Glow Discharge Detector (GDD), costing about 50 cents, was found to be an excellent room temperature THz radiation detector. A proof of concept of 300 GHz heterodyne detection using GDD is demonstrated in this paper. Furthermore, a comparison to direct detection was carried-out and polarization effects on heterodyne detection were investigated. Preliminary results at 300 GHz showed better sensitivity by a factor of 20 with only 56 microwatt local oscillator power using heterodyne compared to direct detection. Further improvement of the detection sensitivity can be achieved if the Local Oscillator (LO) power (Plo) is increased. Effects of orthogonal polarizations of signal and local oscillator powers on heterodyne sensitivity were found to be surprisingly weak. More efficient quasi optical design for heterodyne detection is presented in this study, experimental results showed above 50% better performance compared to conventional ones.

Laser heterodyne radiometer has the advantages of low cost, small size, and high spectral resolution. It can expand the existing ground carbon measurement network, verify satellite observation results, and provide data coverage outside the satellite observation area. Using the existing laser heterodyne radiometer, is presented a prototype of near-infrared laser heterodyne radiometer based on the erbium-doped fiber amplifier that can realize local oscillator power locking. In the laser heterodyne radiometer a distributed feedback semiconductor laser with a center wavelength of 1.603 μm is used as a local oscillator light source. The erbium-doped fiber amplifier is used to enhance the local oscillator power, and the automatic power control circuit is adopted to lock the output optical power of the erbium-doped fiber amplifier. The baseline slope caused by the change of the local oscillator power is eliminated, and the whole layer atmospheric transmittance spectrum without baseline fitting is measured. The instrument performance of a highly integrated laser heterodyne radiometer based on an erbium-doped fiber amplifier is evaluated in detail, and the atmospheric CO&lt;sub&gt;2&lt;/sub&gt; transmittance spectrum is measured in the Science Island (31.9°N, 117.2°E) of Hefei. Six groups of atmospheric CO&lt;sub&gt;2&lt;/sub&gt; transmittance spectra are obtained during the measurement period of one day, which are compared with the simulation results from an atmospheric radiation model, showing that they are consistent with each other. The experimental results show that the application of erbium-doped fiber amplifier can improve the performance of laser heterodyne radiometer, optimize its structure, and provide equipment supplement for realizing unattended long-term atmospheric CO&lt;sub&gt;2&lt;/sub&gt; concentration observation and building a comprehensive carbon observation network.

Future passive optical network (PON) systems supporting more than 50 Gb/s/λ present a challenge for the use of intensity modulation direct detection (IM-DD). Since coherent technology improves the receiver sensitivity over that of IM-DD, it is a promising candidate for 100 Gb/s or higher PON systems. Introducing hardware-efficient signal processing technologies tailored to PON systems will help render coherent technology suitable for PON systems. We here review hardware-efficient signal processing technologies suitable for PON systems. We introduce two types of simplified adaptive equalization (AEQ), one which sacrifices differential group delay compensation (DGDC), and another which sacrifices some chromatic dispersion compensation but does provide DGDC. Transmission experiments on a 100 Gb/s/λ-based coherent wavelength division multiplexing (WDM) PON system showed that simplified AEQ without DGDC and with DGDC exhibited only 0.2 and 1.4 dB penalty, respectively, compared with conventional DSP. The additional penalty due to the maximum possible cumulative DGD was evaluated by numerical simulation. Conventional AEQ and the simplified AEQ with DGDC showed negligible penalty, but the simplified AEQ without DGDC showed a 1.4 dB penalty. We also introduce simplified carrier phase recovery (CPR) with interpolarization phase offset estimation, and this showed the same performance as the conventional DSP, in both experiment and simulation. Taking these results into account, 100 Gb/s/λ-based coherent WDM PON systems with the simplified AEQs in combination with the simplified CPR were shown to be able to support the loss budget required for eight ONU splits over an 80 km span of single mode fiber.

The impact of local oscillator intensity noise on the performance of an optical phase diversity FSK receiver using a delay-and-multiplying discriminator is analyzed for both Gaussian approximation and exact non-Gaussian statistics. The bit error rate (BER) is expressed in terms of Q-function using Gaussian approximation. Also, an exact equation for BER is derived by a non-Gaussian approach. Given data rate, frequency deviation, discriminator delay, composite laser linewidth, bandwidth ratio of pre- and post-detection lowpass filters, local oscillator relative intensity noise (RIN), and receiver thermal noise, the received signal power (sensitivity) can be calculated with respect to given local oscillator power for a specified BER. Both Gaussian and non-Gaussian numerical results show that there exists an optimal local oscillator power to achieve maximum sensitivity for RIN -150 dB/Hz, -135 dB/Hz, and -125 dB/Hz, respectively, at a BER of 10/sup -9/ The deviation of sensitivity between Gaussian and non-Gaussian (exact) results is shown to be within 1 dB for the illustrated examples, when the product of frequency deviation and discriminator delay is equal to 0.25. If this product is far away from 0.25, the performance is greatly degraded as seen from the exact calculations and the deviation due to Gaussian approximation also becomes very significant.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Silicon technologies for HF applications have been proven for more than two decades, and technologies have greatly evolved. Whether CMOS or BiCMOS technologies, the unique combination of radio frequency, baseband, and digital functions allow a very high level of integration. While it is possible to achieve fully integrated transceivers, the major advantages of these silicon technologies lie mainly in their unparalleled performance in the field of frequency synthesis and frequency conversion. We propose in this paper a review of the major results obtained on these RF components since the beginning of the 2000s, also considering the impact of the technology node. The back-end of line (BEOL) process on which depends the quality of microwave monolithic integrated circuits (MMICs) is briefly presented in the introductory part. If circuit performances are tightly bound to the active devices (i.e., the heterojunction bipolar transistor SiGe HBT or CMOS transistor), passive elements (i.e., quality factor of inductors and varactors, losses of transmission, or interconnection lines) as well as the definition of the substrate also play a major role. The core of the article is oriented toward the noise of synthesized signals and frequency conversion. Frequency synthesis is presented through the analog design of a voltage-controlled oscillator (VCO) or through the direct digital frequency synthesis (DDFS), for which respective figures of merit are presented and discussed in a second section. The spectral purity of the oscillators being decisive in the definition of the throughput of a link is approached through the comparison of different figures of merit (FoM) for a set of circuits achievements over the selected period. If the realization of free oscillators is closely bound to the phase-locked loop (PLL)-type control loop for VCOs, the DDFS solution provides more direct and more flexible alternative at first sight. Therefore, these two solutions are analyzed collectively. Finally, the oscillator integrated in the transmitter or receiver supplies the needed LO (local oscillator) power to the frequency mixer in the frequency conversion module: henceforth, the third part of this study focuses on high-frequency mixer realizations. We thus consider this LO power in some advanced figure of merit mentioned in the second section. The design trade-off of the mixer is presented in an approach combining LO (conversion gain, channel isolation, and phase noise) and RF (HF noise figure and channel isolation) constraints. The final section provides a summary of the results and trends mentioned in the paper.

Balanced-mixer receivers for optical systems, first proposed by Oliver,1 have been shown to be useful in suppressing local oscillator (LO) excess intensty noise.2 Furthermore, such a receiver requires less local oscillator power than does a conventional single-detector receiver. This latter advantage is particularly important for high-bit-rate optical heterodyne systems, since receiver thermal noise increases rapidly in typical PINFET front ends as the intermediate frequency is increased. Hence, to ensure that LO shot noise dominates thermal noise (as desired for maximum sensitivity), LO power must be increased at high speeds. With the limited ouput power available from present semiconductor lasers, sufficient LO power is difficult to obtain for speeds of Gbit/s and Intermediate frequenices near 2 GHz.

A field programmable gate array (FPGA)-based physical layer phase-encryption technique suitable for applications in high-speed passive optical networks is presented. The physical layer ciphering technique is based on a combination of multilevel phase shift keying (PSK) modulation and binary differential PSK. A mathematical model of the system is first derived and numerical simulations are obtained using Mathematica. Expressions for the probability of error for both a legitimate and eavesdropping receiver are derived and evaluated numerically. The results from experimental implementation using high-speed phase modulators and FPGAs are also given to further prove the efficacy of the presented technique. The macroscopic cryptography technique offers completely opaque communication over trans-oceanic distances, gigabit date rates and multiple wavelengths.

This paper deals with the design considerations, fabrication process, and performance of coplanar waveguide (CPW) heterojunction FET (HJFET) down- and up-converter monolithic microwave integrated circuits (MMIC's) for V-band wireless system applications. To realize a mixer featuring a simple structure with inherently isolated ports, and yet permitting independent port matching and low local oscillator (LO) power operation, a concept is utilized by treating the HJFET as a three-port device in which the LO signal is injected through the source terminal, the RF (or IF) signal through the gate terminal, and the IF (or RF) signal is extracted from the drain terminal. The down-converter chip incorporates an image-rejection filter and a source-injection mixer. The up-converter chip incorporates a source-injection mixer and an output RF filter. With an LO power and frequency of 7 dBm and 60.4 GHz, both converters can operate at any IF frequency within 0.5-2 GHz, with a corresponding conversion gain within -7 to -12 dB, primarily dominated by the related filter's insertion loss. Chip size is 3.3 mm/spl times/2 mm for the down-converter, and 3.5 mm/spl times/1.8 mm for the up-converter.

A miniature neon indicator lamp, also known as a Glow Discharge Detector (GDD), costing about 50 cents, was found to be an excellent room temperature THz radiation detector. Polarization effects on heterodyne detection were investigated in this work. In heterodyne detection, because of the dot product relationship between signal electric field (ES) and local oscillator (LO) electric field (Elo), optimal operation of heterodyne detection is obtained when ES and Elo are of the same polarization. Preliminary results at 300 GHz showed better sensitivity by a factor of 20 with only 56 microwatt local oscillator power using heterodyne compared to direct detection. Further improvement of the detection sensitivity can be achieved if the LO power (Plo) is increased. In this work investigation of polarization effects in heterodyne detection using neon indicator lamp GDD was carried-out. Experimental results of heterodyne detection at 300 GHz showed that an intermediate frequency (IF) signal was obtained for orthogonal polarization of the LO and signal, in contradiction to the theory. Also, our latest imaging results using Glow Discharge Detector at millimeter wavelengths will be shown in this work.

Gigabit-capable Passive Optical Network (PON) systems, such as GPON (standardized in ITU-T Rec. G.984 series) and 1G-EPON (IEEE 802.3ah, now part of IEEE 802.3-2008) have been standardized and are now being mass-deployed in various markets around the world. With the continuous increase in bandwidth demand generated by consumer and business applications, the need for a new, higher capacity access architecture is more than obvious. Therefore, one of the principal requirements for next-generation PON (ngPON) is to provide a substantial increase of the bandwidth available to end-subscribers, when compared with GPON and 1G-EPON. Additionally, considering the Capital Expenditure (CAPEX) investment made for deploying gigabit-capable PON systems, ngPON must be able to protect the investment of the legacy networks by ensuring a subscriber seamless migration from GPON/1G-EPON to ngPON. ngPON systems are currently under standardization in two Standard Development Organizations (SDOs), i.e. 10G-EPON in IEEE, as part of P802.3av, and NG-PON in FSAN/ITU-T. The IEEE P802.3av standard focuses only on extensions to the existing 1G-EPON specifications in order to support 10Gbit/s operation, including symmetric and asymmetric data-rates. On the other hand, NG-PON recommendations cover the complete system, starting from Physical Medium Dependent (PMD), followed by framing and medium access, and ending with security and service provisioning mechanisms. NG-PON systems are divided into two major groups, i.e. NG-PON1 and NG-PON2, based on their characteristics of co-existence with legacy GPON systems. Other SDOs focus on operational, architectural, and management aspects of the existing and future PON systems, e.g. BroadBand Forum (BBF, former DSL Forum).

We propose a filter bank multi-carriers (FBMC) passive optical network (PON) system based on 2-D multiple probabilistic shaping (MPS) distribution to achieve flexible and adjustable access bit-rates. The proposed PON can assign different probabilistic shaping schemes to different time-slots and subcarriers, thus improving the system flexibility and adjustability in both the time and frequency domains. Carrier-less amplitude and phase modulation are adopted to achieve the implementation of the intensity-modulation and direct-modulation applied in our proposed PON system. Moreover, for the first time, an experiment demonstrating MPS FBMC signal transmission over a 25-km standard single mode fiber in PON system is successfully carried out to verify the favorable performance. The bit error rate performance of different MPS time-slots at bit-rates of 23.665, 20.663, 17.666, and 15.481 Gbit/s are investigated. The received optical powers at the threshold for hard-decision forward error correction are −16.13, −16.94, −17.85, and −18.81 dBm, respectively. These experiment results indicate that our proposed MPS FBMC PON system can be flexible and adjustable in acquiring different and dynamic access bit-rates, which suggests a prospective solution for the next generation passive optical network.

In this paper, we present a multiband double sideband-suppressed carrier (DSB-SC) modulated radio over intersatellite optical wireless communication (IsOWC) link with coherent homodyne detection. The proposed system can provide the transparent transport of multiband radio frequency (RF) signals with higher linearity and better receiver sensitivity than the intensity modulated with direct detection (IM/DD) scheme. The full system model and the exactly analytical expression of signal to noise and distortion ratio (SNDR) are derived considering the third-order intermodulation product and amplifier spontaneous emission (ASE) noise. The finite extinction ratio (ER) of Mach-Zehnder Modulator (MZM) and the saturation property of erbium doped fiber amplifier (EDFA) are also considered. Numerical results of SNDR with various numbers of subchannels and ERs are given. Results indicate that the optimal modulation index exists to maximize the SNDR and the power of local oscillator (LO) carrier should be within an appropriate range.

The detection of CO2 based on coherent different absorption LiDAR (CDIAL) requires high signal-to-noise ratio (SNR). To improve the SNR and reduce the inversion error of CO2, a coherent differential absorption LiDAR based on Golay coding is proposed and the corresponding decoding method is also studied. The coding gain of SNR in traditional atmospheric backscattering signal detection is also analyzed when the pulse code technology is used. The variations of coding gain with the power of local oscillator (LO), the code length and the splitting ratio of 3 dB coupler are discussed. The higher the local oscillator power is and the more the beam splitting ratio deviates from 50%, the lower the coding gains. In addition, there are optimal code lengths in practical systems. The influence of thermal noise on the detection system decreases when the LO power grows, and there is optimal LO power which is only related to the system noise characteristics. The optimal LO power decreases with respect to single pulse detection after pulse coding, but the SNR is still higher than the traditional single pulse detection. When the splitting ratio of the 3 dB coupler is 0.495, the optimal LO power in coded system is 0.93 mW. The effective detection ranges of CO2 increase when the pulses are coded, and in the pulse accumulations of 104~1010, the improvement ratios of effective detection range are higher than 15%.