Spectrally efficient optical label insertion/extraction technique using an optical single sideband filter

A novel label insertion technique, using an adaptive optical single sideband (OSSB) filter, is experimentally shown. The OSSB filter is used to suppress one of the sidebands of the 40-Gb/s payload signal, and a 2.5-Gb/s intensity modulated signal is inserted as a label in the suppressed sideband. Lower label-payload crosstalk is observed using the OSSB filter compared to the absence of sideband suppression, allowing a reduction of 5 dB in the label power without additional penalty. The enhanced tolerance to group velocity dispersion (GVD) of the payload is experimentally assessed and a 5-dB penalty is observed for 136 ps/nm of accumulated dispersion. Additionally, simulation results show the efficient use of electrical dispersion compensation to improve the GVD tolerance, allowing the doubling of the dispersion tolerance.     

超结构光纤光栅的正交波分复用系统实现方案及接收机串扰分析

解释了超结构光纤光栅(SSFBG)作为脉冲成型滤波器的特性,说明SSFBG能够产生规则的时域矩形光脉冲,在频域上功率谱密度表现为sinc函数的形式.当光波道的频率间隔为码元速率的整数倍时,相邻波长的功率谱零点位于信号波长的中心频率处,频谱正交交叠.研究了一种基于SSFBG的正交波分复用(OWDM)系统,发送端用SSFBG进行脉冲整形,接收端采用窄带滤波器.给出基于理想窄带滤波器和高斯窄带滤波器两种接收机的串扰噪声模型,并得出了仿真结果.结果显示,两种窄带滤波器均可抑制严重的信道串扰,当接收机窄带滤波器通带足够窄时,接收机串扰比信道串扰降低约10 dB;理想窄带滤波器优于高斯窄带滤波器2～5 dB.     

A wavelength-tunable semiconductor amplifier/filter for add/drop multiplexing in WDM networks

Reconfigurable channel drop in a wavelength-division multiplexed system is demonstrated using a packaged semiconductor amplifier/filter. The filter is electrically tunable over 9.0 nm with a 0.9-nm width and is used with an optical circulator to demultiplex three 5.0-Gb/s WDM channels spaced by 2.25 nm. A receiver sensitivity improvement and low optical crosstalk is observed over a dynamic range of nearly 10 dB.     

Rapidly tunable narrowband wavelength filter usingLiNbO3 unbalanced Mach-Zehnder interferometers

We demonstrate a rapidly tunable narrowband wavelength filter using unbalanced Mach-Zehnder interferometers in lithium niobate. It is designed to switch among eight channels spaced 50 GHz apart in optical frequency (approximately 0.4 nm in wavelength) in less than 50 ns. The insertion loss is 19 dB and crosstalk is less than -22 dB. The filter consists of a cascade of three electrooptically tunable unbalanced Mach-Zehnders and a feedback circuit to keep the filter centered on the desired wavelength     

Four-channel tunable optical notch filter using InGaAsP/InPreflection gratings

A new tunable optical notch filter for use in wavelength division multiplexing (WDM) transmission system has been fabricated in the InGaAsP/InP material system for use at 1.55 μm. The device uses tunable reflection gratings in a waveguide to control the channels (4 in this case). Crosstalk levels between 9 dB and 20 dB have been measured, depending on the channel. System experiments at 150 Mb/s show less than 1 dB crosstalk penalty at 10^-9 bit-error rate     

新型Christiansen滤波器的设计

针对一种新提出的新型Christiansen滤波器,进行了理论计算、仿真分析和实验,其功率透射谱和理论数据吻合.结果表明:通过对输出谱、峰值功率、邻道串扰、3 dB带宽以及光阑孔径进行数值分析和比较,设计出峰值损耗低于4 dB,3 dB带宽低于2 nm的器件.并且对比一阶至四阶sinc函数滤波器的仿真功率透射谱发现,越高阶的滤波器,其功率透射谱越理想,性能越好.     

A low-distortion BiCMOS seventh-order Bessel filter operating at2.5 V supply

This paper presents the design of a seventh-order continuous-time Bessel filter using a new low-voltage and highly linear BiCMOS transconductor. A high-gain and parasitic-insensitive integrator is obtained by using an active capacitor scheme. The filter has been designed to operate at a 2.5 V supply with a nominal -3 dB cutoff frequency of 600 kHz. It has been fabricated in 1 μm, double-poly 6-GHz BiCMOS process. The inband group delay variation is less than 10 ns. The total harmonic distortion (THD) measured with a 100 kHz input signal is less than -49 dB for a 2 V_pp amplitude and the dynamic range is 77 dB. The filter can be frequency tuned over almost one decade with a gain variation less than 0.2 dB in the passband. A common-mode rejection ratio (CMRR) of 53 dB in the passband is observed, thanks to a careful common-mode control strategy     

1.5 μm phase-controlled distributed feedback wavelength tunableoptical filter

A 1.5-μm phase-controlled distributed feedback wavelength-tunable optical filter is studied. This is the first optical filter which controls the transmissivity (gain) and the transmission wavelength independently. Wavelength tuning range as wide as 43 GHz (3.4 Å) with high constant gain of 27 dB has been achieved. A five-channel wavelength selection with less than -10 dB crosstalk is expected with this filter. This device also operates as a wavelength tunable laser, and the wavelength tuning range as a laser is larger than as a filter. The reason is studied, and it is shown that suppression of the submodes is important to expand the wavelength tuning range     

A time and wavelength division fiber loop distribution system with acousto-optic tunable filters

A time and wavelength division fiber loop distribution system with acousto-optic tunable filters is proposed. This system can provide a large number of 150 Mb/s HDTV channels with a reliable technology. A theoretical analysis by Gaussian beam approximation shows that one system can distribute 320 HDTV channels to 256 subscribers with a minimum wavelength spacing of 2 nm. An experimental 12 channel (4 time division × 3 wavelength division) system with a wavelength spacing of 20 nm in the 1.3 μm region demonstrates a data rate of 1.2 Gb/s with only ?4dB loss and ?20 dB crosstalk at the tunable filter. The experimental loss and crosstalk characteristics agree well with the theoretical analysis.     

FDM-channel selection filter employing an arrayed-waveguide gratingmultiplexer

A novel channel selection filter based on an arrayed-waveguide grating multiplexer is reported for optical frequency-division-multiplexer (FDM) networks. The filter employs fold-back optical paths and optical switches, and can be operated digitally with multiple switches. A 16 channel selection filter employing a silica-based 16×16 multiplexer achieves a 20 GHz bandwidth and a crosstalk of less than 27 dB     

Observation of coherent interchannel interference in themultiwavelength operation of an acoustooptic filter

Wavelength-division multiplexing using acoustically tuned optical filters offers narrow channel spacing, wide tuning range, and the capability for multiple-wavelength switching. It is shown that a coherent source of interference can arise in multiwavelength switching, due to the simultaneous interaction of several acoustic waves with even a single optical channel. Bit-error-rate studies have been performed on an integrated-optic version of the acoustooptic filter and a crosstalk penalty of ~2 dB due to dual channel interference has been observed. The theoretical origin of this crosstalk is described and it is shown that a modest relaxation of channel spacing can effectively eliminate and crosstalk penalty     

A 16-channel frequency selection switch for optical FDMdistribution systems

The performance of a 5-GHz-spaced, 16-channel frequency selection switch (FS-SW) for optical frequency division multiplexing (FDM) distribution systems is described. The silica waveguide-type FS-SW is constructed with four serially connected periodic filters integrated on a silicon chip. The required crosstalk level for each periodic filter of the FS-SW was estimated to be -21.0 dB for a 16-channel FS-SW and 23.6 dB for a 128-channel FS-SW. Crosstalk can be independent of the power coupling ratio of the 3-dB-coupler regions by choosing suitable connecting configurations for the periodic filters. A controller for the switch is also described and the desired channel can be selected successfully from among 16 optical carriers under an average crosstalk level of less than -20 dB     

10-GHz-spaced 1010-channel tandem AWG filter consisting of oneprimary and ten secondary AWGs

A very large channel-count arrayed waveguide grating (AWG) filter with more than 1000 channels is described. It was achieved by cascading a 1-THz-spaced flat-top 1×10 AWG as a primary filter and ten 10-GHz-spaced 1×160 AWGs as secondary filters in a tandem configuration. We achieved good adjacent and accumulated channel crosstalk values ranging from -32 to -25 dB and from -24 and -18 dB, respectively     

Multiple channel operation of integrated acousto-optic tunable filter

Demonstrates an integrated bulk-wave acousto-optic tunable filter (1.0 nm FWHM) in a multiwavelength crosstalk measurement experiment. With 16 channels present, individual channel crosstalk was lower than -15 dB for both single-wavelength and dual-wavelength filtering. The RF drive power for 70% efficiency was 180 mW/wavelength.<>     

Wide tuning range and low operating power AWG-based thermo-opticwavelength tunable filter using polymer waveguides

Two types of polymer thermo-optic wavelength tunable filter (TOWTF) have been developed, each with a pair of triangular phase shifters. One filter is designed for a large-scale WDM system (32 channels, 0.8 nm spacing), the other for a small-scale WDM system (10 channels, 0.8 nm spacing). The arrayed waveguide number is optimised thus reducing the operating power required by the filters. Moreover, both filters operated with a low crosstalk of <-25 dB     

A 1.3/1.55-μm wavelength-division multiplexing optical moduleusing a planar lightwave circuit for full duplex operation

We developed a hybrid integrated optical module for 1.3/1.55-μm wavelength-division multiplexing (WDM) full-duplex operation. The optical circuit was designed to suppress the optical and electrical crosstalk using a wavelength division multiplexing filter, and an optical crosstalk of -43 dB and an electrical crosstalk of -105 dB were achieved with a separation between the transmitter laser diode and the receiver photodiode of more than 9 mm. We used the optical circuit design to fabricate an optical module with a bare chip preamplifier in a package. This module exhibited a full duplex operation of 156 Mbit/s with a minimum sensitivity of -35.2 dBm at a bit error rate of 10^-10     

Four-wave mixing between pump and signal in a distributed Raman amplifier

We observed experimentally four-wave mixing (FWM) between a 14xx-nm pump and a 15xx-nm signal in a forward-pumped distributed Raman amplifier (DRA) over 50 km of nonzero dispersion-shifted fiber with a zero dispersion wavelength of 1497 nm. The 100-mW pump Fabry-Perot (FP) spectra centered at 1440, 1450, and 1460 nm are reproduced via FWM around the single-wavelength probe signal around 1558, 1548, and 1538 nm, respectively. The suppression of DRA gain by about 2-3 dB was experimentally observed with peak FWM at minimum phase mismatching between two 14xx-nm FP pump wavelengths and two 15xx-nm signal wavelengths. This DRA gain suppression, together with the reproduced pump FP spectrum at 15xx-nm signal band, may limit the usefulness of the forward-pumped DRA, generating spectrally nonuniform FWM-induced noise floors and crosstalk in wavelength-division-multiplexed fiber-optic transmission systems.     

An Analytic Approach to Random Phase Error and Its Impact on the Performance and Design of Arrayed-Waveguide Gratings

Random phase error due to fabrication process causes the filter response of arrayed-waveguide grating (AWG) to degrade, especially in terms of crosstalk. In the side-lobe region, which is critical to the channel crosstalk performance, each instantiation of the random phase error can yield a significantly different filter transmission than that of the average for that level of phase error. In this report, the statistical behavior of the AWG filter transmission in the side-lobe region is studied analytically. Both the distribution of random side-lobe level at a given wavelength and an upper bound of the outage probability for side-lobe maxima are given in a simple closed form. Accordingly, a crosstalk margin needs to be allocated to ensure a given fabrication yield and this is shown to depend on the fractional bandwidth of the AWG filter. For filter shapes that are close to Gaussian, this crosstalk margin can be 8 dB or more above the average crosstalk level, for small fractional bandwidth of about 1% and fabrication yields of 80% or higher. These relations should be useful to AWG designers particularly when the underlying fabrication process is susceptible to nonnegligible random phase errors.     

Fiber four-wave mixing in multi-amplifier systems with nonuniformchromatic dispersion

Fiber fiber-wave mixing (FWM) is studied for multichannel multi-amplifier systems composed of short fibers with different zero-dispersion wavelength. An analytical expression describing FWM in these systems is derived. Using the expression, crosstalk is calculated for various combinations of fiber lengths, which are selected according to a random function, and allowable fiber input power is evaluated. The results show that the allowable input power for nonuniform dispersion is larger than that for uniform dispersion by several dB, depending on system conditions     

A reconfigurable thin-film filter-based 2 /spl times/ 2 add-drop fiber-optic switch structure

A reconfigurable 2 /spl times/ 2 add-drop fiber-optic switch structure is proposed by incorporating the independent mechanical control and alignment of an off-the-shelf thin-film filter with a reflective optical element. Cascading several 2 /spl times/ 2 add-drop switches gives a low-cost polarization-independent wavelength routing system with the limitation in optical loss that can be compensated by using optical amplifiers. The experimental result indicates a measured average optical loss of <1.30 dB at the center wavelength. In addition, the measured optical coherent crosstalk values at the center wavelength are -15 and -22 dB when the thin-film filter and the mirror are in the optical path, respectively. A very low polarization-dependent loss of <0.07 dB is also investigated.