新型光学包：NRZ标签与双二进制DCS-RZ载波抑制

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"一种新型的光包结构被提出，它采用了非归零（NRZ）标签和双二进制载波抑制归零（DCS-RZ）的有效载荷，适用于光分组交换网络。NRZ标签后跟着带有一定保护时间的DCS-RZ有效载荷。低速率的NRZ标签的频谱位于光学载波频率附近，而由于DCS-RZ调制，高速率DCS-RZ有效载荷的部分对应频谱被抑制。在交换节点，通过光学带通或-notch滤波器分别实现标签或有效载荷的简单提取。该方案的可行性通过Virtual Photonics Inc. (VPI)设计的著名光子学设计平台的仿真得到验证。" 这篇摘要讨论了光通信领域中光分组交换的一种创新技术，即使用NRZ编码的标签和DCS-RZ编码的有效载荷。NRZ是一种二进制编码方式，信号在每个时钟周期内保持非零状态，以表示1或0。而DCS-RZ则是一种在载波上引入负冲以抑制归零的调制方法，可以降低功耗并改善信噪比。文章指出，NRZ标签的频谱与部分被抑制的DCS-RZ有效载荷的频谱重叠，这种设计使得在光分组交换网络中，可以通过选择性地过滤特定频率来识别和提取标签或有效载荷。保护时间的引入是为了确保标签和有效载荷之间的正确分离，避免干扰。在光交换节点，利用光学滤波技术可以有效地实现这一过程。光学带通滤波器允许特定频率范围的光通过，因此可用于提取NRZ标签，因为它的频谱特性比较独特。而-notch滤波器则能消除特定频率，因此适合用于剔除标签，保留DCS-RZ有效载荷。通过VPI公司的光子学设计平台进行的仿真验证了这种方法的可行性。这种新型光包格式有望提高光分组交换网络的效率和灵活性，同时减少错误检测和数据处理的复杂性。这一技术对于未来高速、大容量的光通信网络具有重要意义，因为它可以优化网络资源的利用，并且简化光信号处理步骤。

96 CHINESE OPTICS LETTERS / Vol. 6, No. 2 / February 10, 2008

Novel optical packet with non-return-to-zero label and

duobinary carrier-suppressed return-to-zero payload

Kun Qiu (

¤¤¤

&&&

) and Yun Ling (

'''



)

Key Laboratory of Broadband Optical Fiber Transmission and Communication Networks,

University of Electronic Science and Technology of China, Chengdu 610054

Received June 29, 2007

A novel p acket format with non-return-to-zero (NRZ) label and duobinary carrier-suppressed return-to-zero

(DCS-RZ) payload is proposed for optical packet switching networks. NRZ label is followed by DCS-RZ

payload with a certain guard time. The spectra of the low-rate NRZ label locate around the optical carrier

frequency where some parts of the corresponding spectra of the high-rate DCS- RZ payload have been

suppressed due to DCS-RZ modulation. At the switching node, the label or payload extraction can b e

realized simply through an optical bandpass or notch filter respectively. The feasibility of the scheme

is verified by the simulation on the famous p hotonic design platform designed by Virtual Ph otonics Inc.

(VPI). The effects of optical filter bandwidth on the received signal quality are discussed by analyzing bit

error rate (BER) and contrast ratio performances.

OCIS codes: 060.0060, 060.2330, 060.4080, 060.4230.

Optical packet switching, which provides the smallest

switching granularity and avoids the electronic bottle-

neck, has been one of the hottest research areas on the

next-generation optical networks

[1]

. For the convenience

of separating optical label and payload signals which will

be sent to control unit and optical switch matrix respec-

tively, several optical packet formats have been proposed,

including bit-serial label

[2−4]

, subcarrier multiplexing

(SCM) label

[5,6]

, optical code (OC) label

[7]

, orthogonal-

modulated label

[8]

and so on. For separating the label

and payload, bit-serial label or OC label requires accu-

rate timing to control optical gate or 1 ×2 optical switch.

Orthogonal-modulated label, such as differential phase-

shift keying (DPSK) label and amplitude-shift-keying

(ASK) payload, requires to decrease the extinction ratio

of payload to guarantee the correct detection of DPSK

label. In addition, a wavelength conversion module is

adopted to suppress the old DPSK label. The scheme of

SCM label is the easiest method to realize the separation

of label and payload by using optical filter, compared

with other schemes. But the linear modulation of high-

frequency subcarrrier imposes many great difficulties

and the highest bit-rate of payload is limited by the

subcarrier frequency. In this paper, a novel packet for-

mat with non-return-to-zero (NRZ) label and duobinary

carrier-suppressed return-to-zero (DCS-RZ) payload will

be introduced and the separation of label and payload

can be realized by using optical filters.

DCS-RZ modulation suppresses the optical carrier fre-

quency completely and reduces the signal bandwidth to

the same as the NRZ modulation. DCS-RZ signal can

enhance the nonlinearity and chromatic dispersion tol-

erance in the fiber transmission

[9]

. So the high bit-rate

payload with DCS-RZ modulation can enhance the fiber

transmission length. Another important characteristic of

DCS-RZ payload is the notch-shaped spectrum around

the optical carrier frequency. If the low bit-rate label is

modulated with NRZ format on the same optical wave-

length, the spectra of NRZ label will locate around the

optical carrier frequency. NRZ modulation of the label

guarantees the smallest bandwidth and decreases the in-

terference between the label and payload caused by their

spectral overlap. The spectral separation of NRZ label

and DCS-RZ payload makes it possible to extract the

label or payload by using an optical filter.

According to the introduction of the packet format

with NRZ label and DCS-RZ payload, the module of

optical packet generation consists of NRZ label genera-

tion and DCS-RZ payload generation. Figure 1 shows

Fig. 1. Schematic diagram of the simulation system.

1671-7694/2008/020096-04

 2008 Chinese Optics Letters

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