High-performance phase locking of wide linewidth semiconductorlasers by combined use of optical injection locking and opticalphase-lock loop

The requirement for narrow linewidth lasers or short-loop propagation delay makes the realization of optical phase-lock loops using semiconductor lasers difficult. Although optical injection locking can provide low phase error variance for wide linewidth lasers, the locking range is restricted by stability considerations. Theoretical and experimental results for a system which combines both techniques so as to overcome these limitations, the optical injection phase-lock loop (OIPLL), are reported. Phase error variance values as low as 0.006 rad ² (500 MHz bandwidth) and locking ranges exceeding 26 GHz were achieved in homodyne OIPLL systems using DFB lasers of summed linewidth 36 MHz, loop propagation delay of 15 ns and injection ratio less than -30 dB. Phase error variance values as low as 0.003 rad² in a bandwidth of 100 MHz, a mean time to cycle slip of 3×10¹⁰ s and SSB noise density of -94 dBc/Hz at 10 kHz offset were obtained for the same lasers in an heterodyne OIPLL configuration with loop propagation delay of 20 ns and injection ratio of -30 dB     

Dispersion effects of FBG filter and optical SSB filtering in DWDM millimeter-wave fiber-radio systems

We study the optical filtering technique for dense wavelength division multiplexing (DWDM) channel allocation of millimeter-wave fiber-radio signals in the optical double-sideband (DSB) format. First, we investigate both theoretically and experimentally the dispersion effect of fiber Bragg grating (FBG) used as the filter on DWDM millimeter-wave optical signal transmissions. This result suggests that the dispersion effect has to be considered in the DWDM channel allocation for millimeter-wave fiber-radio access systems. Next, we propose a DWDM allocation for millimeter-wave fiber-radio systems, which adopts the optical single-sideband (SSB) filtering technique at the receiver side by using a square response of FBG filter. It can realize the minimum WDM channel interval for optical DSB signals, while it enables the optical frequency interleave between the neighboring channels without any serious signal degradation due to the interchannel interference. Then, we experimentally demonstrate the error-free DWDM transmission of two 60-GHz-band, 155.52-Mb/s differential phase-shift keying (DPSK) fiber-radio signals over 25-km-long single-mode fiber (SMF) with the minimum channel interval of 83.6 GHz (=0.68 nm) by using the test-square response FBGs. Finally, we show that based upon the experimental results, in the micro- or pico-cellular DWDM broad-band millimeter-wave fiber-radio access network 1000 antenna base stations (BSs) under the coverage of the single central office (CO) would be feasible by sectorizing the zone.     

Harmonic Millimeter-Wave Generation and Frequency Up-Conversion Using a Passively Mode-Locked Multisection DFB Laser Under External Optical Injection

We demonstrate that a passively mode-locked multisection distributed-feedback (PML-MS DFB) laser can perform both harmonic millimeter-wave generation and harmonic frequency up-conversion under the external optical injection. Optical multiple modes generated by a PML-MS DFB laser produce harmonic millimeter-waves by mode-beating in a photodiode (PD), and the phase quality and stability are enhanced by the injection of external optical signal modulated at f_LO. In addition, if the external optical signal is modulated simultaneously by f_LO and f_IF, the PML-MS DFB laser performs all-optical frequency up-conversion producing sidebands at f_LOplusmnf_IF when detected by a PD. Using this method, we demonstrate generation of stable harmonic millimeter-waves at 30.42 and 60.84 GHz with f_LO of 15.21 GHz, and up-conversion of 10-Mb/s quadrature-phase-shift keying data at 150 MHz f_IF into the 60-GHz band. These functions of a PML-MS DFB laser can be useful for radio-over-fiber applications in which a compact optical source is needed for processing high-frequency radio signals in optical domain     

Optical microwave generation and transmission experiments in the12- and 60-GHz region for wireless communications

Experiments on the optical generation and transmission of millimeter-wave radio signals are reported. The millimeter-wave signals are generated by heterodyning the optical spectral lines of a mode-locked laser (MLL) or of two or more semiconductor lasers at an optic/millimeter-wave converter (OMC). 70-, 140-, and 155-Mb/s data transmission experiments have been carried out successfully in optical single-channel and multichannel systems at radio frequencies of 12 GHz and 58-70 GHz. Bit-error-rate measurements yielded error-free transmission and no error floor was observed. A monolithically integrated tunable optical-signal source was developed and used for generating the millimeter-wave signals. This technology promises a high cost-saving potential for applications in radio-over-fiber systems     

Low detection penalty in an optical DPSK heterodyne system using asaturated optical amplifier as phase modulator

A model established from the rate equations of a near traveling-wave optical amplifier (NTWOA) used as a phase modulator shows that the modulation rate is limited by the carrier lifetime to 500 Mb/s and that the worst-case detection penalty is about 0.7 dB. It is then experimentally demonstrated that close control of the injected light polarization can reduce the detection penalty in a DPSK (differential phase-shift keying) heterodyne system, using an NTWOA phase modulator instead of an LiNbO₃ modulator, to 0.6 dB. This device and a balance receiver have allowed the implementation of 282-Mb/s DPSK link operating at 1.522 μm over 242 km of fiber with a 3-dB margin     

基于直流光注入直调DFB-LD的可调光毫米波信号产生技术

提出了一种基于直流光注入直接调制分布反馈式半导体激光器(DFB-LD)的载波可调的光毫米波生成方案,利用直接调制DFB-LD的输出瞬态波长随驱动电流增大而蓝移的特点,将直流光注入至直调DFB-LD的0码波长附近注入锁定。锁定的直调激光器在1码时输出的蓝移波长与原注入波长相位相干,再通过光电探测器将拍频信号转换为调制的光毫米波信号。实验重点讨论了40GHz光毫米波的产生,同时完成了30、40、50和60GHz光毫米波的可调谐性实验。本文的方案结构简单,无需外调制器和微波本振,载波可调并可产生高至60GHz光毫米波信号,可作为光/无线混合接入中成本节省的光上变频方案。     

Harmonic Signal Generation and Frequency Up-Conversion Using a Hybrid Mode-Locked Multisection DFB Laser

Harmonic signal generation and frequency up-conversion are demonstrated using a hybrid mode-locked multisection distributed-feedback (MS-DFB) laser. Hybrid mode-locking is realized by direct injection of electrical local oscillator (LO) signals into the laser gain control section. The harmonic signals are generated when multiple optical modes produced by the hybrid mode-locked MS-DFB laser are detected in a photodiode (PD). In addition, if data signals at f_IF are applied to the device along with LO signals at fLO, optical sidebands separated from the optical modes by f_IF are generated and harmonic up-converted signals are obtained by mode-beating in PD. Using this method, we demonstrate generation of the third-harmonic millimeter-waves at 30.79 GHz with f_LO at 10.263 GHz, and up-conversion of 12.5-Mb/s 32 quadrature amplitude modulation data at 300-MHz f_IF into 30-GHz band     

Multiplexing of millimeter-wave signals for fiber-radio links by direct modulation of a two-mode locked Fabry-Pe/spl acute/rot laser

In this paper, we introduce generation of multiplexed signals on the millimeter-wave bands for fiber-radio systems where an optical millimeter-wave generator is based on a two-mode locked Fabry-Pe/spl acute/rot (FP) slave laser, whose injection current is directly modulated by a signal source. We qualitatively consider the distortion of the millimeter-wave signals from the FP slave laser. The distortion components on the millimeter-wave bands are induced from the simultaneous modulation of the locked modes and the nonlinear modulation response of the FP laser. Two-tone modulation of the locked FP laser is examined to evaluate the dynamic range of the millimeter-wave signals against the second- and third-order distortion components. We also perform fiber transmission of three 156-Mb/s-BPSK signals on the 60-GHz band to demonstrate fiber-radio down-link systems. The total capacity of the down-link system is discussed. In addition, two methods for multicarrier generation on the millimeter-wave bands are proposed. Multicarrier generators supported by these methods can be used as local signals for up-link millimeter-wave signals. The first method is based on multitone modulation of the FP slave laser. We attempt the down-conversion of a 52-Mb/s ASK signal on the 60-GHz band by using the millimeter-wave local signals. The second method depends on the distorted modulation of the FP slave laser by using a single continuous wave signal where the DC-bias level of the FP laser's injection current is partly under the threshold value. We confirm that five carriers on the 60-GHz band are effectively generated by using the second method. Furthermore, the influences of the chromatic dispersion effects on the millimeter-wave local signals are investigated for both methods.     

Simultaneous all-optical frequency downconversion technique utilizing an SOA-MZI for WDM radio over fiber (RoF) applications

Simultaneous all-optical frequency-downconversion technique utilizing a semiconductor optical amplifier Mach-Zehnder interferometer (SOA-MZI) is experimentally demonstrated, and its application to a wavelength-division-multiplexing (WDM) radio over fiber (RoF) uplink is proposed. The conversion efficiencies from 22.5 (f/sub RF/) to 2.5 GHz (f/sub IF/=f/sub RF/-2f/sub LO/) are in the range from 1.5 to 3 dB for the optical RF wavelength between 1548 and 1558 nm. Error-free simultaneous all-optical frequency downconversion of the two WDM RoF upstream channels that carry 155-Mb/s differential phase-shift keying data at 22.5 GHz to an optical intermediate frequency signal having the frequency of 2.5 GHz with the power penalty less than 0.1 dB at the bit error rate of 10/sup -8/ is achieved.     

基于40 nm CMOS工艺的毫米波注入锁定分频器

设计了一款应用于60 GHz频率综合器的二分频注入锁定分频器。通过优化射频注入和直流偏置网络,降低了注入信号损耗,提高了注入效率;通过优化注入管和交叉管尺寸、减小寄生电容、降低振荡摆幅,提高了注入效率,降低了功耗;电磁仿真毫米波段电感,建立集总等效电路模型,实现了高感值、低串联电阻的差分电感的设计,提高了锁定范围。电路设计采用SMIC 40 nm 1P6M RF CMOS工艺,芯片核心面积为0.016 mm²。仿真结果表明,在0.8 V电源电压下,电路功耗为5.5 mW,工作频率范围为55.2~61.2 GHz,注入锁定范围为6.0 GHz,满足低功耗和宽锁定范围的要求,适用于毫米波段锁相环频率综合器。     

Simultaneous electrooptical upconversion, remote oscillatorgeneration, and air transmission of multiple optical WDM channels for a60-GHz high-capacity indoor system

The system concept and data transmission experiments for a mobile broad-band communication system at 60 GHz are presented in this paper. Dense wavelength division multiplexing (DWDM) is advantageously applied for simultaneous electrooptical upconversion of all optical channels carrying individual intermediate-frequency signals by means of a single external modulator. Thus, simple, but flexible, millimetric signal generation is obtained. Using this concept, data transmission experiments at 60 GHz have been carried out. Furthermore, the transponder noise performance is analyzed. Results of coded and uncoded 512-carrier orthogonal frequency division multiplex transmission with 50-Mb/s (subcarrier modulation quaternary phase-shift keying), 100 Mb/s (subcarrier modulation 16-quadrature amplitude modulation) as well as single-carrier modulation at 156 Mb/s utilizing three operational DWDM channels are presented. Uplink and downlink transmission has been realized. The significant performance improvement due to the application of coding is demonstrated in some experiments and line-of-sight transmission is compared to nonline-of-sight transmission. Low bit error rates, employing realistic air link conditions, have been obtained in all experiments     

Indirect Subharmonic Optical Injection Locking of a Millimeter-Wave IMPATT Oscillator

Large aperture phased-array antennas operating at millimeter-wave frequencies are designed for space-based communications and imaging. Array elements are composed of active transmit-receive (T/R) modules that are phase and frequency synchronized to a reference signal at the central processing unit by a fiber-optic (FO) distribution network. The implementation of FO links, synchronizing the millimeter-wave Iocal oscillators (LO's), imposes a great challenge. This paper presents results of indirect optical injection locking of a free-running 38-GHz (Ka-band) IMPATT oscillator over the Iocking range of 2-132 MHz, depending on the injected power level (amplifier gain). In the experiment, the nonlinearity of both the laser diode and the IMPATT oscillator is exploited to achieve 12th subharmonic injection locking. The overall system FM noise degradation of the reference signal is 16 dB at 500-Hz offset. The FM noise degradation is dominated by the theoretical limit of 20 log N, where N is the frequency multiplication factor used in subharmonic injection locking. Methods by which optical injection locking may be extended into 60 and 90 GHz are demonstrated.     

High-speed, burst-mode, packet-capable optical receiver andinstantaneous clock recovery for optical bus operation

This paper describes an enhanced performance version of a high-speed burst-mode compatible optical receiver and its application to 622-Mb/s optical bus operation in conjunction with an instantaneous clock recovery scheme. The receiver is fabricated in a 12 GHz f_t silicon bipolar technology and consists of a differential transimpedance amplifier with an auto-threshold level controller and a high-speed quantizer. Using an InGaAs avalanche photodiode, the typical burst mode sensitivity is around -34 dBm (10^-9 BER) at bit rates up to 1.5 Gb/s with a dynamic range of 26 db for both pseudorandom and burst signals. The results using a laser beam modulated by a high-speed external modulator indicate that the receiver can be operated at bit rates higher than 2 Gb/s. With a worst-case self-resetting time <50 ns for the threshold control circuit, the receiver is usable for optical packet communication where data signals with varying optical power are employed. This receiver was demonstrated in a 622-Mb/s optical bus application where the clock signal was recovered from the packet data signal using a novel high-speed CMOS instantaneous clock recovery IC     

5 Gbit/s direct optical DPSK modulation of a 1530-nm DFB laser

5 Gb/s direct optical differential-phase-shift-keying (DPSK) modulation of a 1530-nm distributed feedback (DFB) laser is demonstrated using injection current modulation with a bipolar signal format. Delay demodulation is performed using an interferometer with a delay time T equal to the duration of one bit. The input and differentially encoded nonreturn to zero (NRZ) signals are shown. The bipolar modulation current signal is basically the time derivative of the NRZ signal. There was no degradation of the optical DPSK signal due to thermal frequency modulation of the laser. The direct DPSK modulation technique avoids the insertion loss and systems complexity of external DPSK modulators     

A wide locking range and low Voltage CMOS direct injection-locked frequency divider

A low voltage and wide locking range injection-locked frequency divider using a standard 0.18-/spl mu/m complementary metal oxide semiconductor (CMOS) process is presented. The wide locking range and the low-voltage operation are performed by adding an injection nMOS between the differential outputs of the divider that contains on-chip transformers which result in positive feedback loops to swing the output signals above the supply and below the ground potential. This dual-swing capability maximizes the carrier power and achieves low-voltage performance. The measurement results show that at the supply voltage of 0.75-V, the divider free-running frequency is 2.02 GHz, and at the incident power of 0 dBm the locking range is about 1.49 GHz (36.88%), from the incident frequency 3.27 to 4.64GHz.     

Influence of laser phase on 400-Mbit/s coherent optical DPSK system

The influence of laser phase noise on a 400-Mb/s optical DPSK (differential phase-shift keying) system is experimentally investigated with linewidths ranging from 1.2 MHz to 8 MHz. This range corresponds to linewidth to bit rate ratios ϵ of 0.33-2%. The system performance with these nonzero linewidths is evaluated against a negligible linewidth performance baseline. The sensitivity degradation at a bit error rate of 10^-9 increases from 1.8 to 7 dB as ϵ is increased from 0.33-1%. When ϵ is increased beyond 1%, bit error rate floors higher than 10^-9 develop. These findings agree well with the existing theories and allow the generalization of these results to other bit rates, as well as establishing practical criteria for lasers to be used in DPSK systems     

Wavelength shift keying modulation up to 35 Gb/s with wavelength tone reuse to multiplex two 40 Gb/s DPSK signals

Fast optical frequency shift keying or wavelength shift keying (WSK) modulation offers advantageous features for applications in long haul communications and in optical labeling for packet routing. This includes simple demodulation by optical filtering and constant amplitude envelope providing tolerance to fiber nonlinear effects during transmission. In this paper we report on the generation of WSK signals up to 35 Gb/s with reuse of the wavelength tones for polarization multiplexing two independent 40 Gb/s DPSK signals. Transmission over a 50 km fiber link of the resultant three channel signal is also reported.     

Optical Tandem Single-Sideband-Based WDM Interface for Millimeter-Wave Fiber-Radio Multisector Antenna Base Station

We propose and demonstrate a spectrally efficient wavelength division multiplexed (WDM) optical interface for millimeter-wave radio access networks with the capability of being integrated within a standard 100-GHz WDM infrastructure. The proposed WDM optical interface is realized by the use of a multiport optical circulator in conjunction with fiber Bragg grating filters. The interface supports demultiplexing of wavelength-interleaved optical tandem single-sideband modulated signals for a millimeter-wave fiber radio backbone with a sectorized antenna interface at the remote base station. The functionality of the interface is verified experimentally for RF signals at 29 and 31.6 GHz with 155-Mb/s binary phase-shift keying data. The effects of optical impairments on the transmission performance of WDM channels are experimentally analyzed. The experimental results demonstrate that the WDM optical interface performs efficiently with very low channel impairments due to optical crosstalk.      

Erbium-doped fiber amplifier cascade for multichannel coherentoptical transmission

The requirements and practicalities of amplifier cascades for multichannel coherent transmission are discussed. A four-amplifier cascade which maintains an overall noise figure of less than 13 dB across a 20-nm optical bandwidth for total input powers up to -10 dBm is described. A potential capacity of 100 wavelength division multiplexing channels is demonstrated in a 300-km 622-Mb/s DPSK (differential phase shift keying) coherent transmission experiment     

一种基于相位调制器的40 GHz OFDM-ROF系统实验研究

实验研究了一种基于相位调制器(PM)并级联强度调制器(IM)实现40 GHz毫米波传输正交频分复用(OFDM)信号的光纤无线通信(ROF)系统。在中心站,采用20 GHz的射频(RF)信号驱动PM,调节驱动信号的强度,使输出的信号经光纤布拉格光栅(FBG)滤除中心载波后再送入IM。2.5 Gbit/s的OFDM信号直接调制在光毫米波上,经过50 km标准的单模光纤(SSMF)传输到基站。在基站,光调制信号经光电转换器(PD)转换成电调制信号,再与RF信号混频,恢复出基带OFDM信号。实验结果表明,在无色散补偿、误码率(BER)为10-3的条件下,下行链路中2.5 Gbit/s的OFDM信号经光纤传输50 km后,其功率代价小于1 dB,而且信号的星座图依然较好。