光学超宽带脉冲生成与分布：双电极马赫-曾德尔调制器方法
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"使用双电极马赫-曾德尔调制器实现光学超宽脉冲的生成与分布"
本文探讨了一种新颖的方法，用于在光域中生成和分发超宽频（UWB）脉冲。这种方法的核心是利用双电极马赫-曾德尔调制器（DE-MZM）。DE-MZM在四象限点偏置，以实现线性响应。当调制器接收到两个具有相同尖锐参数但不同时间延迟的高斯脉冲输入时，输出的光场强度可以视为这两个脉冲的差。这种配置能够生成近似单周期波形的超宽带信号。
在实验设计中，位于北京交通大学光波技术研究所和电磁兼容性全光网络及先进通信网络国家重点实验室的研究人员，通过调整DE-MZM的输入脉冲特性，如幅度和半高全宽（FWHM），来精确控制生成的UWB脉冲形状和特性。如果输入的高斯脉冲具有不同的幅度，但保持相同的时间延迟，那么可以通过调制器产生具有不同能量分布的UWB信号。相反，如果改变时间延迟，可以调整脉冲的相位关系，从而影响脉冲的宽度和形状。
此外，文章还讨论了DE-MZM的线性特性如何优化UWB脉冲的质量。由于DE-MZM在四象限点的偏置，它可以有效地将两个输入脉冲的不同特征结合在一起，生成具有超宽频率范围的脉冲，这在无线通信、数据传输和雷达系统中具有重要应用价值。DE-MZM的这种操作方式提供了对UWB信号生成的灵活性，使得系统能够适应不同的通信需求和环境条件。
这项工作展示了光学方法在UWB脉冲生成领域的潜力，特别是在提高信号带宽、降低功耗和增强系统性能方面。通过利用双电极马赫-曾德尔调制器的特性，研究人员能够创建出复杂的UWB脉冲序列，这些序列对于实现高速、低功率的光通信系统至关重要。未来的研究可能会进一步探索如何优化这些技术，以实现更高效、更可靠的UWB光通信解决方案。
138 CHINESE OPTICS LETTERS / Vol. 8, No. 2 / February 10, 2010
Optical ultra-wideband pulse generation and distribution
using a dual-electrode Mach-Zehnder modulator
Jing Li (ooo ¬¬¬)
1,2
, Tigang Ning (wwwJJJjjj)
1,2∗
, Li Pei ( www)
1,2
, and Chunhui Qi (ãããSSS¦¦¦)
1,2
1
Institute of Lightwave Technology, Beijing Jiaotong University, Beijing 100044, China
2
Key Lab of All Optical Network and Advanced Telecommunication Network of EMC,
Beijing Jiaotong University, Beijing 100044, China
∗
E-mail: tgning@bjtu.edu.cn
Received April 8, 2009
A novel approach to generate and distribute ultra-wideband (UWB) pulses in optical domain is investigated.
In this proposed scheme, a dual-electrode Mach-Zehnder modulator (DE-MZM) is biased at its quadrature
p oint so as to realize the linear response. Then the intensity of output optical field can be assumed to the
subtraction of two input Gaussian pulses. If the input Gaussian pulses are with the same sharp parameters
but different time delays, a quasi-monocycle-waveform UWB signal can be generated. If the input Gaussian
pulses are with different amplitudes and full-width at half-maximum (FWHM), a quasi-doublet-waveform
UWB signal can be generated. A transmission of the UWB signals through a 25-km single mode fiber is
carried out successfully. The results in both temporal and frequency domains are also presented.
OCIS co des: 060.0060, 060.2330, 060.2360, 060.5625.
doi: 10.3788/COL20100802.0138.
Ultra-wideband (UWB) systems have attracted a lot of
attention in recent years. Their abilities of delivering
high bit rate data, good wall penetration, low power con-
sumption, multi-path, and interference immunity make
them very promising solutions to many communication
problems, such as consumer indoor wireless communica-
tions, medical and military communicatios, etc. In 2002,
the US Federal Communications Commission (FCC) ap-
proved the unlicensed use of the UWB spectrum from 3.1
to 10.6 GHz for indoor communications, with a power
spectral density (PSD) lower than –41.3 dBm/MHz.
Based on the FCC definition, an UWB signal should have
a spectral bandwidth greater than 500 MHz or a frac-
tional bandwidth greater than 20%
[1,2]
. Since the PSD
of UWB signals is limited, the propagation of UWB sig-
nal is limited to several meters. The technology of UWB-
over-fiber can solve the problem by connecting the Center
Station (CS) and Base Station BS with optical fiber, tak-
ing the advantage of low loss, wideband, and immunity
to electromagnetic interference offered by optical fibers.
Another significant advantage of the optical domain is
that it can provide broadband all-optical signal process-
ing.
The choice of the UWB pulse shapes is critical to the
performance of the UWB system. Gaussian monocycle
and doublet pulses have been considered as promising
candidates for UWB communications
[3]
. There are two
different ways to generate UWB signal, one is electrical
scheme
[4,5]
and the other is optical scheme
[6−11]
. It is de-
sirable that the UWB signals can be generated directly
in the optical domain to avoid the costly electrical to op-
tical conversion. Several methods have been proposed to
generate and distribute Gaussian monocycle and doublet
pulses, including the generation of the UWB pulses us-
ing a frequency-shift-keying modulator
[7]
, a nonlinearly
biased Mach-Zehnder modulator
[8]
, a two-tap microwave
delay-line filter with coefficients of (1−1)
[9]
, or an optical
spectrum shaper with frequency-to-time mapping
[10,11]
.
In this letter, a novel approach to generating and dis-
tributing UWB pulses in optical domain is carried out
and proved. In the proposed system the bias voltages of
dual-electrode Mach-Zehnder modulator (DE-MZM) are
V
bias−up
= 0 and V
bias−down
= V
π
/2. Thus a DE-MZM
is biased at its quadrature point, and then the DE-MZM
is operated at the linear region of its transfer function.
The intensity of the output optical field can be assumed
to the subtraction of two input Gaussian pulses. If the
two Gaussian pulses are with different time delays, a
Gaussian quasi-monocycle pulse can be generated; if the
two Gaussian pulses are with different amplitudes and
full-width at half-maximum (FWHM), a Gaussian quasi-
doublet pulse can be generated. By adjusting the pa-
rameters of system, an UWB quasi-monocycle or quasi-
doublet pulse is obtained at the output of a photodiode
(PD). The transmission of the UWB signals through a 25-
km single mode fiber (SMF) is carried out successfully.
Vertification based on the proposed approach are carried
out and the results in b oth temporal and frequency do-
mains are presented.
With a DE-MZM biased at quadrature point, Fig. 1
shows a conceptual diagram of the generation and dis-
tribution of UWB monocycle pulse and UWB doublet
pulse. As can be seen from Fig. 1, the optical field at
the input of the DE-MZM can be written as
E
in
= E
c
exp [jω
c
t + jφ (t)] , (1)
where E
c
denotes the amplitude of the optical field, ω
c
represents the angular frequency of the optical carrier,
and φ (t) is the phase noise of the laser diode. The
DE-MZM is biased at its quadrature point. The elec-
trical driving signals sent into two arms of DE-MZM are
the Gaussian pulses g
1
(t) and g
2
(t). Moreover, the bias
voltages of DE-MZM are V
bias−up
= 0 and V
bias−down
=
V
π
/2. Thus the DE-MZM is operated at the linear region
of its transfer function. The optical field at the output
1671-7694/2010/020138-04
c
° 2010 Chinese Optics Letters
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