Performance evaluation of (D)APSK modulated coherent optical OFDM system

Performance of amplitude and phase shift keying (APSK) modulated coherent optical orthogonal frequency division multiplexing (CO-OFDM) with and without differential encoding is investigated. Numerical simulations based on 40 Gbit/s single-channel and 5 ^* 40 Gbit/s wavelength division multiplexing transmission are performed, and the impacts of amplified spontaneous emission noise, laser linewidth, chromatic dispersion, and fiber nonlinearity on the system performance are analyzed. The results show that compared with conventional 16 quadrature amplitude modulation (QAM) modulated optical OFDM signal, although 16(D)APSK modulated optical OFDM signal has a lower tolerance towards amplified spontaneous emission (ASE) noise, it has a higher tolerance towards fiber nonlinearity such as self-phase modulation (SPM) and cross-phase modulation (XPM): the optimal launch power and the corresponding Q² factor of 16(D)APSK modulated OFDM signal are respectively 2 dB and 0.5 dB higher than 16QAM modulated optical OFDM signal after 640 km transmission, both in single-channel and WDM CO-OFDM systems. Although the accumulated CD decreases the peak-to-average power ratio (PAPR) during transmission, 16(D)APSK modulated OFDM signal will still remain an advantage compared with 16QAM modulated OFDM signal up to 1000 km single-channel transmission, meanwhile relaxing the needs for training symbols and pilot subcarriers and consequently increase the spectral efficiency.     

Full-duplex fiber-wireless link with 40 Gbit/s 16-QAM signals for alternative wired and wireless accesses based on homodyne/heterodyne coherent detection

A novel full-duplex fiber-wireless link with 40 Gbit/s 16-ary quadrature amplitude modulation (QAM) signals is proposed to provide alternative wired and wireless accesses for the user terminals. In the central station (CS), the downstream signal for wired and wireless accesses is beared onto the CW laser source via an optical I/Q modulator to realize the QAM modulation. At the hybrid optical network unit (HONU), a tunable laser is used to provide coherent optical local oscillator for homo-/heterodyne beating to coherently down-convert the baseband optical signal to the baseband electrical one for wired access or to the mm-wave one for wireless access according to the requirement of the user terminals. Simultaneously, the lightwave from the tunable laser is also used as the uplink optical carrier for either wired or wireless access, and is modulated colorlessly by the baseband or mm-wave signal of the uplink alternatively. After filtering, only one tone carrying the uplink signal is transmitted back to the CS even for the wireless access. The theoretical analysis and simulation results show that our proposed full-duplex link for the alternative wired and wireless accesses maintains good performance even when the transmission link with standard single mode fiber (SSMF) is extended to 30 km.     

Optical design and analysis of CWDM upstream TWDM PON for NG-PON2

For passively reach-extended next-generation passive optical networks (NG-PONs), we propose an asymmetric hybrid PON architecture and wavelength plan for using eight 2.5 Gbit/s coarse wavelength division multiplexing (CWDM) in the upstream direction and eight 10 Gbit/s dense wavelength division multiplexing (DWDM) in the downstream direction, called Cu-TWDM PON. The power budget feasibilities, the optical path losses, and the dispersion power penalties in the CWDM upstream wavelengths are precisely investigated in terms of related specifications required to enhance the network coverage to over 40 km with single-mode fibers (SMFs) based on ITU-T G.652.A and B and Corning’s SMF-28e, as the worst-case and the practical-case feasibilities, respectively. We also report on 10 Gbit/s and 2.5 Gbit/s transmission experiments up to 60 km for the downstream and upstream links. Based on the analyses and experimental results, we provide guidelines for the physical media dependent layer specification of Cu-TWDM PON for NG-PON applications.     

A PAPR reduction technique using Hadamard transform combined with clipping and filtering based on DCT/IDCT for IM/DD optical OFDM systems

In Intensity Modulator/Direct Detection (IM/DD) optical OFDM systems, the high peak-to-power average ratio (PAPR) will cause signal impairments through the nonlinearity of modulator and fiber. In this paper, a joint PAPR reduction technique based on Hadamard transformation and clipping and filtering using DCT/IDCT transform has been proposed for mitigating the impairments in IM/DD optical OFDM system. We then experimentally evaluated the effect of PAPR reduction on the bit error rate (BER) performance and the results show the effectiveness of the proposed technique. At a bit error rate (BER) of 1 × 10⁻³, the receiver sensitivity of the proposed 2.5 Gb/s IM/DD optical OFDM system after 100-km standard single-mode fiber transmission has been improved by 0.8 dB, 1.3 dB and 3.1 dB for a launch power of 6.4 dBm, 8 dBm and 10 dBm respectively when compared with the classical system.     

A sub-sampling 4.25 GS/s 3-bit flash ADC with asymmetric spatial filter response

A sub-sampling 3-bit 4.25 GS/s flash ADC with a novel averaging termination technique—asymmetric spatial filter response—in 0.13 um CMOS for impulse radio ultra-wideband (IR-UWB) receiver is presented. In this design, a track and hold (T/H) circuit with self-biased buffer is used to compensate the degradation in amplitude when frequency increases to giga Hz. Averaging termination technique using asymmetric spatial filter response is proposed to relieve the termination offset of the flash ADC. A revised encoder scheme is adopted to solve the problem of different propagation delay. The measurement results reveal that the SFDR and SNDR of the ADC are 26.3 dB and 18.4 dB, respectively, even the input signal frequency is 4.2 GHz. INL and DNL are measured improved to 0.11LSB and 0.18LSB, respectively, when asymmetric spatial filter is used. The power of ADC is 63 mW and the active area is 0.49×0.72 mm². The ADC achieves a figure of merit (FoM) of 2.2 pJ/conversion-step.     

A Regenerative Prescaled Clock Recovery for High-Bit-Rate OTDM Systems

A regenerative prescaled clock recovery device based on an optoelectronic version of the Miller divider has been tested in high-bit-rate OTDM systems. Tests at 4 × 2.5 and 4 × 10 Gbit/s have been performed to characterize the locking range and the frequency response of the device. The timing jitter of the recovered signal in the case of the 4 × 10 Gbit/s OTDM system does not exceed 0.5 ps. Finally, a comparison of two bit-error-rate measurements (with and without the clock recovery system) were carried out for the 4 × 10 Gbit/s OTDM system. The relevant penalty for each channel is negligible, while the maximum received power difference among the four channels at a bit error rate value of 10 ^− 10 is around 0.7 dB.     

Demonstrations of 10 and 40 Gbps upstream transmissions using 1.2 GHz RSOA-based ONU in long-reach access networks

Carrier-distributed long-reach passive optical network (LR-PON) is a promising candidate for future access networks. In this work, we analyze and compare the 4 × 2.5 Gb/s and 4 × 10 Gb/s upstream traffics in a carrier-distributed LR-PON using four wavelength-multiplexed 2.5 Gb/s on–off keying (OOK) and 10 Gb/s optical orthogonal frequency division multiplexing-quadrature amplitude modulation (OFDM-QAM) signals. Four commercial 1.2 GHz bandwidth reflective semiconductor optical amplifiers (RSOAs) are used in each optical networking unit (ONU) for the generation of the upstream signal. Due to the limited bandwidth of the RSOA, only up to 2.5 Gb/s upstream OOK signal can be generated. However, by using the spectral efficient modulation, such as OFDM-QAM, 10 Gb/s data rate can be achieved. 20, 50 and 75 km fiber transmissions are also compared using the two different kinds of modulation respectively.     

Bidirectional and simultaneous transmission of baseband and wireless signals over RSOA based WDM radio-over-fiber passive optical network using incoherent light injection technique

Reflective semiconductor optical amplifier (RSOA) based wavelength division multiplexed radio-over-fiber passive optical network (WDM−RoF−PON) has been proposed and demonstrated, to transmit 2.5 Gbps baseband (BB) and 1.25 Gbps wireless data in downstream and 1 Gbps BB data signal in upstream over 25-km single-mode fiber (SMF), and wireless downstream signal over 25-km SMF as well as 5.2 m free space in air. In the downstream, 2.5 Gbps BB data and 1.25 Gbps wireless data are modulated using single-electrode Mach–Zehnder modulator (SD-MZM) based on double-sideband with optical carrier suppression (DSBCS) scheme and simultaneously transmitted by incoherent light injection technique and employing fiber Bragg grating (FBG) at the base station. RSOA is utilized at the user end to reuse the carrier for uplink transmission. High receiver sensitivity, low bit-error-rate (BER) and excellent eye-diagram, eye height are achieved in our proposed network system and the results affirm the acceptability of proposed RSOA based WDM−RoF−PON.     

A planar waveguide optical discrete Fourier transformer design for 160 Gb/s all-optical OFDM systems

A cost-effective all-optical discrete Fourier transformer (ODFT) is designed based on a silicon planar lightwave circuit (PLC), which can be applied to all-optical orthogonal frequency division multiplexing (OFDM) transmission systems and can be achieved by current techniques. It consists of 2 × 2 directional couplers, phase shifters and optical delay lines. Metal-film heaters are used as phase shifters, according to the thermooptic effect of SiO₂. Based on the ODFT, a 160 Gb/s OFDM system is set up. Simulation results show excellent bit error rate (BER) and optical signal-to-noise ratio (OSNR) performances after 400 km transmission.     

Transmission of 112 Gb/s dual-carrier DQPSK signal over 10 Gb/s-based WDM optical links

The 112 Gb/s dual-carrier differential quadrature phase shift keying (DC-DQPSK) optical transceiver, which does not need digital signal processing and coherent detection, is proposed for cost-effective 100G transport solution. In this paper, we describe upgrade schemes of 10 Gb/s-based WDM optical links by adopting 112 Gb/s DC-DQPSK transceiver, while the dispersion of the optical links is compensated 100% at each span. Method of introducing the DC-DQPSK signal into single grid of 100 GHz spaced WDM link is demonstrated. Performance sufficient for error-free operation after forward error correction is achieved over 640 km standard single mode fiber (SSMF) link. In another method, we experimentally investigate the transmission performance with co-propagating 10.7 Gb/s on-off-keying (OOK) signals over 1000 km of SSMF when the dual carriers occupy two channel grids separately. Excellent tolerance to the nonlinearities impacted by the OOK signals and low optical signal-to-noise ratio requirement are verified to demonstrate superior transmission performance in 10 Gb/s-based WDM links.     

All-optical clock extraction from 40-Gbit/s NRZ data using cascaded long-period fiber grating

All-optical clock extraction from a 40-Gbit/s NRZ input signal is demonstrated using a cascaded long-period fiber grating (CLPG) and a mode-locked fiber ring laser. The CLPG has a Mach–Zehnder configuration with two arms along the core and cladding regions. Using the difference in propagation delay between two arms, the non-return-to-zero (NRZ) signal is converted to the pseudo-return-to-zero (PRZ) signal. To obtain repetitive pulses as a clock signal from the PRZ signal, a ring laser with a semiconductor optical amplifier (SOA) is used. Subsequently, the measured carrier-to-noise ratio (CNR) of the PRZ and clock signals are enhanced up to 30 dB and 31 dB, respectively, compared to that of the original NRZ signal. Also, the clock signal centered at 40 GHz has a low timing jitter of <1.3 ps. It is expected that this method can be applied to high speed fiber-optic systems of >40 Gbit/s due to its small time delay between the core and cladding regions.     

Numerical design of a 100 W, 38 dB gain,W-band multi-section serpentine waveguide vacuum electronic TWT

The serpentine waveguide circuit is a robust beam-wave interaction circuit for W-band TWTs. Here presented the electromagnetic properties and design methodology for W-band multi-section SWG traveling wave tube. Cold-test (in absence of electron beam) numerical design performed theoretically and further optimized/validated with standard simulation code to predict the dispersion, interaction impedance, ohmic-loss and small-signal gain. Numerical simulation for the quarter wave transformer couplers with SWG circuit geometry shown the return-loss less than −20 dB for the 5% frequency band. Later, in systematic manner, hot-test (in presence of electron beam) numerical design performed for multi-section TWT by using standard particle-in-cell 3-D simulation code. The three section, 60 periods SWG TWT predicted peak radiation power 130 W at target frequency 94 GHz, 39.5 dB saturated gain, 5.3% instantaneous 3-dB frequency bandwidth, and 6.5% electronic efficiency.     

An 8 bit, 100 kS/s,switch-capacitor DAC SAR ADC for RFID applications

An 8 bit switch-capacitor DAC successive approximation analog to digital converter (SAR-ADC) for sensor-RFID application is presented in this paper. To achieve minimum chip area, maximum simplicity is imposed on capacitive DAC; replacing capacitor bank with only a one switch-capacitor circuit. The regulated dynamic current mirror (RDCM) design is introduced to provide stabilized current. This invariable current from RDCM, charging or discharging the only capacitor in circuit is controlled by pulse width modulated signal to realize switch capacitor DAC. The switch control scheme is built using basic AND gates to generate the control signals for RDCM. Only one capacitor and reduced transistor count in digital part reduces the silicon area occupied by the ADC to only 0.0098 mm². The converter, designed in GPDK 90 nm CMOS, exhibits maximum sampling frequency of 100 kHz & consumes 6.75 µW at 1 V supply. Calculated signal to noise and distortion ratio (SNDR) at 1 V supply and 100 kS/s is 48.68 dB which relates to ENOB of 7.79 bits. The peak values of differential and integral nonlinearity are found to be +0.70/−0.89 LSB and +1.40/−0.10 LSB respectively. Evaluated figure of merit (FOM) is 3.87×10²⁰, which show that the proposed ADC acquires minimal silicon area and has sufficiently low power consumption compared to its counterparts in RFID applications.     

Experimental evaluation of prefiltering for 56 Gbaud DP-QPSK signal transmission in 75 GHz WDM grid

We investigate optical prefiltering for 56 Gbaud (224 Gbit/s) electrical time-division multiplexed (ETDM) dual polarization (DP) quaternary phase shift keying (QPSK) transmission. Different transmitter-side optical filter shapes are tested and their bandwidths are varied. Comparison of studied filter shapes shows an advantage of a pre-emphasis filter. Subsequently, we perform a fiber transmission of the 56 Gbaud DP QPSK signal filtered with the 65 GHz pre-emphasis filter to fit the 75 GHz transmission grid. Bit error rate (BER) of the signal remains below forward error correction (FEC) limit after 300 km of fiber propagation.     

ROF系统中单边带光载OFDM信号传输性能研究

研究了一种光纤无线通信系统中用单边带产生光载波并传输的OFDM-ROF方案.将2Gbit/s的OFDM信号与10GHz的射频信号混频驱动电光调制器,产生单边带调制信号,调制后的信号经光纤传输至基站,通过光电转换后再进行无线传输.实验证实,2Gbit/s的基带OFDM信号在10GHz-ROF系统中通过光纤传输200km后不经无线传输,其功率代价仅为1dB.不经过光纤仅经过8m无线传输后功率代价大约只有0.3 dB.产生的信号既经过200km光纤传输又经过8m无线传输后接收星座图也很好.     

Stable and wavelength-tunable RSOA- and SOA-based fiber ring laser

In this work, we propose and experimentally investigate a wavelength-tunable fiber ring laser architecture by using the reflective semiconductor optical amplifier (RSOA) and semiconductor optical amplifier (SOA). Here, the wavelength tuning range from 1538.03 to 1561.91 nm can be obtained. The measured output power and optical signal to noise ratio (OSNRs) of the proposed fiber laser are between -0.8 and -2.5 dBm and 59.1 and 61.0 dB/0.06 nm, respectively. The power and wavelength stabilities of the proposed laser are also studied. In addition, the proposed laser can be directly modulated at 2.5 Gbit/s quadrature phase shift keying-orthogonal frequency-division multiplexing (QPSK-OFDM) signal and 20–50 km single-mode fiber (SMF) transmissions are achieved within the forward error correction (FEC) limit without dispersion compensation. It could be a cost-effective and promising candidate for the standard-reach and extended-reach wavelength division multiplexed passive optical network (WDM-PON).     

An LP/CBP reconfigurable analog baseband circuit for software-defined radio receivers in 65 nm CMOS

A low pass (LP) and complex band pass (CBP) reconfigurable analog baseband circuit for software-defined radio (SDR) receivers is presented. It achieves 1–15 MHz LP bandwidth, 2–8 MHz CBP bandwidth and 0–36 dB gain range with 1 dB step. Nulling-resistor Miller feed-forward (NRMFF) differential-mode compensation, passive left half-plane (LHP) zero common-mode compensation and Quasi-Floating Gate (QFG) technique are proposed to improve the high frequency performance and driving capability of the embedded fully differential operational amplifier (Op-Amp). The analog baseband circuit has been implemented in 65 nm CMOS. It achieves 15.2 dB m/27.1 dB m IB/OB-IIP3, −2 dB m IP1dB and 71 dB m IIP2 while consuming 3.6–9.1 mW from a 1.2 V power supply and 0.75 mm² chip area.     

A 1.8 V 3 GS/s 7-bit time-interleaved Quasi C-2C SAR ADC using voltage-comparator time-information

This paper presents a 7-bit 15 × interleaved SAR ADC that operates up to 3 GS/s, using 180 nm CMOS technology. The ADC utilizes the transient information of a dynamic SAR voltage-comparator to resolve 2 bits per clock cycle, using a time-comparator block. Thus, only 5 clock cycles are needed to resolve 7 bits. This results in speed improvement of about 60%, compared to conventional ADC. Also, an improved Quasi C-2 C DAC structure with reduced internal node swing and reduced switching activity are utilized, which decreases the power consumption of DAC up to 65%. We employ the above techniques in designing a 7-bit SAR ADC, in which 3 bits are resolved with time-comparator blocks and 4 bits are resolved with a voltage-comparator. To calibrate the proposed time-comparator block, a calibration process is proposed. ADS simulation of the ADC illustrates an ENOB (Effective Number of Bits) > 6.5-bit and SFDR (Spur Free Dynamic Range) = −52.8 dBc for a single SAR converter with sampling at 200 MS/s. For the time-interleaved SAR ADC with 15 single SAR converters, ENOB is 6.15-bit and SFDR = −45 dBc with sampling at 3 GS/s up to Nyquist frequency. This ADC consumes 150 mW at 1.8 V supply and achieves a Figure-of-Merit (FoM) of 700 fJ/conv-step.     

A 24 W Ku band GaN based power amplifier with 9.1 dB linear gain

A Ku-band power amplifier is successfully developed with a single chip 4.8 mm AlGaN/GaN high electron mobility transistors (HEMTs). The AlGaN/GaN HEMTs device, achieved by E-beam lithography г-gate process, exhibited a gate-drain reverse breakdown voltage of larger than 100 V, a cutoff frequency of f_T=30 GHz and a maximum available gain of 13 dB at 14 GHz. The pulsed condition (100 μs pulse period and 10% duty cycle) was used to test the power characteristic of the power amplifier. At the frequency of 13.9 GHz, the developed GaN HEMTs power amplifier delivers a 43.8 dBm (24 W) saturated output power with 9.1 dB linear gain and 34.6% maximum power-added efficiency (PAE) with a drain voltage of 30 V. To our best knowledge, it is the state-of-the-art result ever reported for internal-matched 4.8 mm single chip GaN HEMTs power amplifier at Ku-band.     

A low-voltage low-power CMOS transmitter front-end using current mode approach for 2.4 GHz wireless communications

This paper presents a low-voltage low-power transmitter front-end using current mode approach for 2.4 GHz wireless communication applications, which is fabricated in a chartered 0.18 μm CMOS technology. The direct up-conversion is implemented with a current mode mixer employing a novel input driver stage, which can significantly improve the linearity and consume a small amount of DC current. The driver amplifier utilizes a transimpedance amplifier as the first stage and employs an inter-stage capacitive cross-coupling technique, which enhances the power conversion gain as well as high linearity. The measured results show that at 2.4 GHz, the transmitter front-end provides 15.5 dB of power conversion gain, output P?1 dB of 3 dBm, and the output-referred third-order intercept point (OIP3) of 13.8 dBm, while drawing only 6 mA from the transmitter front-end under a supply voltage of 1.2 V. The chip area including the testing pads is only 0.9 mm×1.1 mm.