4-phase sequences with near-optimum correlation properties

Abstract

We performed encoding-decoding and associated transmission experiments at 40 Gb/s. A trace of the encoded pulse, shown in Figure 5(b), is obtained using a fast photodiode and a sampling oscilloscope (detection bandwidth: ϳ55 GHz). Obviously, the phase characteristics of the encoded trace cannot be detected through square-law detection; however, reshaping of the initial pulses [Fig. 5(a)] to a pattern of similar duration to that of the design code is clearly observed. The encoded pattern was decoded using the matched SSFBG. The corresponding oscilloscope trace for the decoded pulse is presented in Figure 5(c), which clearly shows that short, distinct pulses are reformed. This result confirms that good code-recognition quality can be obtained by using the SSFBGs. Figure 5(d) shows the trace for the decoded pulse under unmatched case Q 2 :Q* 1 ; short pulses are not reformed.We examined the decoded pulses using the SHG intensity autocorrelator (Ͻ100-fs resolution), in order to assess the duration of the resultant correlation signal. The results of the SHG autocorrelation measurements of the pattern-recognition pulse are shown in Figure 6. The trace we obtained is compared to the theoretical intensity-autocorrelation function of the decoded signal under single-channel operation. The agreement between the calculated and measured traces for the single-channel encoding/decoding process Q 1 :Q* 1 is seen to be excellent. We confirmed that the actual width of the peak for the process Q 1 :Q* 1 was 5.2 ps, which is in good agreement with our theoretical calculation of 4.9 ps.The results of Figures 5 and 6 validate the effectivity of the quaternary-phase coding and decoding of short pulse and illuminate that high-speed all-optical encoding and decoding at 40 Gb/s can be achieved by using three-chip, 240-Gchip/s SSFBGs. CONCLUSIONIn conclusion, we have designed and fabricated a three-chip, 240-Gchip/s encoder/decoder. The encoder/decoder consists of a superstructured fiber Bragg grating (SSFBG). Also, we have experimentally demonstrated 40-Gb/s quaternary-phase encoding and decoding using SSFBGs. The experimental results, building on the effectivity of high-rate all-optical encoder/decoder, show that SSFBG technology represents a promising technology for optical-pulse processing. The high-quality quaternary-pulse encoding and decoding may find use in a variety of all-optical network implementations, including both OCDM and packet-switched networks. Any practical system will, of course, require longer codes in order to accommodate more users, and we are currently actively investigating this issue. ACKNOWLEDGMENT INTRODUCTIONRecently, several terabit optical-transmission systems (including that in [1]) have been demonstrated, yet they are not extraordinary issues any more. This is because, as the transmission speed and capacity have increased, the required signal-processing speed at each switching node has exceeded the physical limit of the electronic components. In order to overcome such an obstacle, alloptical packet switch...

A 16-Channel Reconfigurable OCDMA/DWDM System Using Continuous Phase-Shift SSFBGs

“…We have also employed a code-reconfigurable device for decoding based on the thermo-optic effect that allowed us to dynamically address the decoded sequence. All gratings carry 31-chip, 40-Gchip/s quaternary phase codes chosen from the FamilyA code sequences that offer optimal correlation characteristics [13]. The chip length for these gratings is 2.5 mm (25-ps chip duration), resulting in a total grating length of 77.5 mm.…”

Universal Hash Functions from Exponential Sums over Finite Fields and Galois Rings

“…be the p a d i c expansion of f (2). Such an t:xpansion can be derived from a padic expansion of the coefficients of f(z).…”

A family of quadriphase sequences of period 4(2 n − 1) with low correlation and large linear span

“…In the late 1980s, the optimal family A of quadriphase sequences with period 2 n − 1 and family size 2 n + 1 was found [1,14]. The sequences in the family A are analogous to the m-sequences over Galois fields due to the similarity between Galois rings and Galois fields.…”

“…The sequences in the family A are analogous to the m-sequences over Galois fields due to the similarity between Galois rings and Galois fields. By interleaving two sequences in A, two optimal families B [1] and C [18] of quadriphase sequences can be obtained, and the corresponding period and family size of both B and C are 2(2 n − 1) and 2 n−1 , respectively. Using a generalized quadratic form, Tang, Udaya and Fan generalized the family A and proposed a new family of quadriphase sequences with low correlation [15].…”