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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 20, Iss. 10 — May. 7, 2012
  • pp: 11037–11045
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Single silicon wire waveguide based delay line interferometer for DPSK demodulation

Rai Kou, Hidetaka Nishi, Tai Tsuchizawa, Hiroshi Fukuda, Hiroyuki Shinojima, and Koji Yamada  »View Author Affiliations


Optics Express, Vol. 20, Issue 10, pp. 11037-11045 (2012)
http://dx.doi.org/10.1364/OE.20.011037


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Abstract

We experimentally demonstrate a high-quality phase shift keying demodulator based on a silicon photonic wire waveguide. Since the birefringence of the waveguide generates extremely huge differential group delay, an ultra-compact and high-extinction-ratio delay line interferometer is devised in TE and TM modes. We firstly calculated and simulated the requirements for propagation length and waveguide’s dimensions. Then, we measured the interference spectrum, eye pattern, bit error rate, and temperature dependence to ascertain its feasibility for DPSK demodulation. For a 2.8 cm-long wire waveguide, a free spectral range of 9.6 GHz and an error-free DPSK demodulation around 10 Gb/s are obtained.

© 2012 OSA

1. Introduction

Various advanced modulation formats, such as multilevel phase shift keying (M-PSK) [1

1. A. H. Gnauck and P. J. Winzer, “Optical phase-shift-keyed transmission,” J. Lightwave Technol. 23(1), 115–130 (2005). [CrossRef]

,2

2. P. J. Winzer and R. J. Essiambre, “Advanced modulation formats for high-capacity optical transport networks,” J. Lightwave Technol. 24(12), 4711–4728 (2006). [CrossRef]

], multilevel quadrature amplitude modulation (M-QAM) [3

3. M. Nakazawa, S. Okamoto, T. Omiya, K. Kasai, and M. Yoshida, “256-QAM (64 Gb/s) coherent optical transmission over 160 km with an optical bandwidth of 5.4 GHz,” IEEE Photon. Technol. Lett. 22(3), 185–187 (2010). [CrossRef]

], and orthogonal frequency division multiplexing (OFDM) [4

4. A. Sano, E. Yamada, H. Masuda, E. Yamazaki, T. Kobayashi, E. Yoshida, Y. Miyamoto, R. Kudo, K. Ishihara, and Y. Takatori, “No-guard-interval coherent optical OFDM for 100-Gb/s long-haul WDM transmission,” J. Lightwave Technol. 27(16), 3705–3714 (2009). [CrossRef]

,5

5. S. L. Jansen, I. Morita, T. C. W. Schenk, N. Takeda, and H. Tanaka, “Coherent optical 25.8-Gb/s OFDM transmission over 4160-km SSMAF,” J. Lightwave Technol. 26(1), 6–15 (2008). [CrossRef]

], have captured attention in optical telecommunications fields, not only for high-capacity transmission applications but also for middle- and short- reach applications [6

6. J. J. Yu, M. F. Huang, D. Y. Qian, L. Chen, and G. K. Chang, “Centralized lightwave WDM-PON employing 16-QAM intensity modulated OFDM downstream and OOK modulated upstream signals,” IEEE Photon. Technol. Lett. 20(18), 1545–1547 (2008). [CrossRef]

,7

7. C. W. Chow, C. H. Yeh, C. H. Wang, F. Y. Shih, C. L. Pan, and S. Chi, “WDM extended reach passive optical networks using OFDM-QAM,” Opt. Express 16(16), 12096–12101 (2008). [CrossRef] [PubMed]

]. These formats promise great improvements of bandwidth utilization efficiency and the optical signal to noise ratio (OSNR) in comparison with the traditional on-off-keying (OOK) format. Particularly, quadrature phase shift keying (QPSK) and dual-polarization QPSK (DP-QPSK) have attracted a great deal of attention, because standardization and many major development projects for practical applications are underway. Methods for detecting PSK signals can generally be separated into two types: coherent detection and direct detection. Coherent detection provides a great improvement of the OSNR by mixing a local oscillator light into the transmitted signal light and very effective compensations for signal degradations due to chromatic dispersion (CD) and polarization mode dispersion (PMD) on the transmission line. However, a digital signal processing (DSP) unit is necessary to exploit the full potential of coherent detection. This makes these systems costly and complex, and also results in high power consumption and overheating. Thus, direct detection with delay line interferometers (DLIs) is a reasonable method for achieving M-PSK transmission, especially in metro and access networks. Previously reported DLIs have mostly been constructed from free-space optics with a Michelson interferometer [8

8. X. Liu, A. H. Gnauck, X. Wei, J. Hsieh, C. Y. Ai, and V. Chien, “Athermal optical demodulator for OC-768 DPSK and RZ-DPSK signals,” IEEE Photon. Technol. Lett. 17(12), 2610–2612 (2005). [CrossRef]

], and a low-Δ silica planar lightwave circuit (PLC) or optical fibers with a Mach-Zehnder interferometer [9

9. Y. K. Lize, M. Faucher, E. Jarry, P. Ouellette, E. Villeneuve, A. Wetter, and F. Seguin, “Phase-tunable low-loss, S-, C-, and L-band DPSK and DQPSK demodulator,” IEEE Photon. Technol. Lett. 19(23), 1886–1888 (2007). [CrossRef]

12

12. Y. Sakamaki, K. Hattori, Y. Nasu, T. Hashimoto, Y. Hashizume, T. Mizuno, T. Goh, and H. Takahashi, “One-chip integrated polarisation-multiplexed DQPSK demodulator using silica-based planar lightwave circuit technology,” Electron. Lett. 46(16), 1152–1153 (2010). [CrossRef]

]. Since all of these devices are constructed on the basis of controlling the propagation length between the two arms, the total area is not easy to reduce due to the different direction of the arms. For example, we investigated the areas of commercial differential phase-shift keying (DPSK) demodulators for a bit rate of 10 Gb/s, which are ~5500 and ~500 mm2/ch for free-space-optics and silica PLC-based DLIs, respectively. In recent years, silicon photonics technology has become widely known as a very effective approach to resolve the issues, because the high refractive index contrast enables strong optical confinement and small bend radii with negligible excess loss. As a result, silicon rib-waveguide-based DLIs [13

13. K. Voigt, L. Zimmermann, G. Winzer, T. Mitze, J. Bruns, K. Petermann, B. Huttl, and C. Schubert, “Performance of 40-Gb/s DPSK demodulator in SOI-technology,” IEEE Photon. Technol. Lett. 20(8), 614–616 (2008). [CrossRef]

] and silicon wire waveguide-based dual-bus micro-ring resonator [14

14. L. Zhang, J. Y. Yang, M. Song, Y. Li, B. Zhang, R. G. Beausoleil, and A. E. Willner, “Microring-based modulation and demodulation of DPSK signal,” Opt. Express 15(18), 11564–11569 (2007). [CrossRef] [PubMed]

17

17. Y. Ding, J. Xu, C. Peucheret, M. Pu, L. Liu, J. Seoane, H. Ou, X. Zhang, and D. Huang, “Multi-channel 40 Gbit/s NRZ-DPSK demodulation using a single silicon microring resonator,” J. Lightwave Technol. 29(5), 677–684 (2011). [CrossRef]

], have been shown to successfully work as PSK demodulators. Here we propose a polarization DLI constructed from only a single silicon photonic wire waveguide, the basic idea of which is presented in Ref [18

18. R. Kou, K. Yamada, H. Nishi, T. Tsuchizawa, T. Watanabe, H. Shinojima, and S. Itabashi, “DPSK demodulation with a single silicon photonic nanowire waveguide,” in Proc. IEEE 8th International Conference on Group IV Photonics (GFP 2011), 323–325 (2011).

], which shows potential as a simple, compact and high-quality demodulator. In this paper, we develop the concept to fully understand the basic and advanced characteristics of the device in detail for future telecommunication applications.

2. Principle and numerical estimation

First, we describe the conventional demodulation principle with free-space optics, a PLC, and other structures, for PSK formats using DLI(s). A 1-bit time slot of the modulation rate ΔΤ is expressed as
ΔT=ng(Larm1Larm2)c
(1)
where ng is the group refractive index of propagation media, L is the length of the optical path, and c is the speed of light in a vacuum. The lengths of one or both arms, Larm1 and Larm2, are modified to obtain 1-bit delay. Since the difference between Larm1 and Larm2 indicates a centimetres-long optical path in different directions, this type of DLI is very hard to downsize. For example, when the optical-path difference of ~2 cm for 10-Gb/s demodulation with a silica waveguide is required, the whole area per channel can be estimated as the squared value: ~4 cm2. Although a folded waveguide structure could be used to resolve this issue, the excess loss due to the bending-radius limitation should be carefully considered, even if the confinement geometry has a high contrast index such as over 1%. On the other hand, a DLI made of a single silicon photonic wire waveguide is expressed as
ΔT=(ng,TEng,TM)Lc
(2)
where ng of TE and TM modes has different group refractive indices ng,TE and ng,TM. The reason for using this principle to make a DLI is that a very large group refractive index difference between two polarization modes (known as the B value in fiber optics fields or the origin of differential group delay (DGD) in time axis) can be easily obtained from a silicon photonic wire waveguide by confinement factors difference. The B value is generally close to zero or quite small in a silica waveguide or fiber. For instance, it is ~10−4 even in stress-induced polarization maintaining fiber (PMF). However, the value for a silicon photonic wire waveguide is >1000 times greater than that for PMF. Therefore, an extremely simple DLI that is just in a straight line and very short.

In the device design, we calculated the group refractive indices using the film mode matching method [19

19. A. Sv Sudbo, “Film mode matching: a versatile numerical method for vector mode field calculations in dielectric waveguides,” J. Opt. A, Pure Appl. Opt. 2, 211–233 (1993).

]. To obtain larger B value, the cross-sectional dimension of the waveguide should be designed with a relatively high aspect ratio, such as ~2:1. When the designed core width and core thickness are 460 and 200 nm and the BOX thickness is 3 μm, B is expected to be 1.274. Figure 1
Fig. 1 Calculated mode profiles of a silicon waveguide with dimensions of 460 nm × 200 nm for the TE mode (left) and TM mode (right).
shows the calculated mode profiles, where the group refractive indices are 4.218 for the TE mode and 2.944 for the TM mode. According to the Eq. (2), the required length for 10- and 40-Gb/s DPSK demodulation is estimated to be approximately 2.4 and 0.6 cm, respectively.

3. Basic device characterization

The silicon waveguide and spot size converters (SSCs) with an inverse taper [20

20. T. Shoji, T. Tsuchizawa, T. Watanabe, K. Yamada, and H. Morita, “Low loss mode size converter from 0.3 μm square Si wire waveguides to singlemode fibres,” Electron. Lett. 38(25), 1669–1670 (2002). [CrossRef]

] were fabricated from a conventional SOI wafer. SiO2/SiOx was deposited by electron cyclotron resonance-chemical vapor deposition (ECR-CVD), and the structure was defined by reactive ion etching (RIE) of the SiO2/SiOx and by ECR-RIE of silicon. With our recent improvement and optimization of the fabrication processes, the propagation loss of TE and TM mode can be suppressed to around 1 dB/cm in a silicon waveguide, even if the dimensions are 400 nm × 200 nm. The fabrication process is described in more detail in Refs [21

21. T. Tsuchizawa, K. Yamada, H. Fukuda, T. Watanabe, J. Takahashi, M. Takahashi, T. Shoji, E. Tamechika, S. Itabashi, and H. Morita, “Microphotonics devices based on silicon microfabrication technology,” IEEE J. Sel. Top. Quantum Electron. 11(1), 232–240 (2005). [CrossRef]

,22

22. T. Tsuchizawa, K. Yamada, T. Watanabe, S. Park, H. Nishi, R. Kou, H. Shinojima, and S. Itabashi, “Monolithic integration of silicon-, germanium-, and silica-based optical devices for telecommunications applications,” IEEE J. Sel. Top. Quantum Electron. 17(3), 516–525 (2011). [CrossRef]

].

For the basic optical characterizations, we used 3-μm thermally expanded core (TEC) fiber to couple a C-band amplified spontaneous emission (ASE) light source into the silicon waveguide with SSCs. The propagation loss and coupling loss were measured as 1.2 dB/cm and 0.75 dB/facet for the TE mode and 0.7 dB/cm and 0.7 dB/facet for the TM mode. The extinction ratio (ER) of the polarization interference calculated from these measurement results is over 20 dB even in a 2.4-cm-long waveguide for 10-Gb/s demodulation.

Figures 2(a)
Fig. 2 (a) CAD layout (b) Photograph of the module and microphotograph of monolithically integrated device. (b) Schematic diagram of the setup for measuring the interference spectra.
-2(c) show the CAD layout, photographs of the fiber pigtail module and fabricated device, and a schematic diagram of the setup for measuring the interference spectra. The module contains total 75 silicon photonic wire waveguides (5 parameters of length × 5 waveguides × 3 blocks), and we choose four of them to connect with in/output fiber array blocks by epoxy adhesive. Since group delay comes from the difference between TE and TM modes, the polarization angle of input light should be adjusted to around 45 degrees with reference to the waveguide substrate by a polarization controller (PC). At the output of the module, a second PC is needed to control the polarization in order to match it with the principal axis of the polarization beam splitter (PBS), and then the constructive and destructive signal paths are separated as each polarization. When we aligned the polarization angle of in/output lights, we used optical spectrum analyzer (OSA) to make the ER maximum value. Therefore, the accurate angle would be slightly shifted from just 45 degrees, because the insertion loss for each polarization mode has difference as shown in Table 1

Table 1. Summary of Propagation, Coupling, and Total Insertion Losses for TE and TM Modes at Demodulation Bit Rates of 10 and 40 Gb/s.

table-icon
View This Table
. Using the loss parameters in Table 1, we calculated the theoretical polarization angles of incident light and the tolerance for keeping the ER above 20 dB. For a 2.4 cm-long device (e.g. theoretical length for 10-Gb/s demodulation), the results are 41 degrees and +/−5.5 degrees, respectively. In the experiment, we used 2.8-, 1.6- and 1.15-cm-long silicon photonic wire waveguides to characterize the interference spectra from the constructive port of the PBS. The measurement results for each length around the wavelength of 1550 nm (~193.5 THz) are shown in Fig. 3
Fig. 3 Interference spectrum of normalized transmittance for each DLI. The device lengths are 2.8 (top), 1.6 (middle), and 1.15 cm (bottom), with corresponding FSRs of 9.6, 17.0 and 23.8 GHz, respectively. The different ER for each FSR comes from resolution limit of the OSA (min. resolution: ~2 GHz).
, where free spectral ranges (FSRs) of 9.6, 17.0 and 23.8 GHz and ERs of 12, 16 and 19 dB are obtained, respectively. Note that the factor limiting the observed ER is the measurement equipment: the OSA’s minimum resolution is approximately ~2 GHz. Hence, we expect the actual ER for each DLI is higher than the measured value, especially for the ER of 12 dB with the FSR of 9.6 GHz.

Calculated and measured FSRs for each device length are shown in Fig. 4
Fig. 4 Comparison between calculated and measured FSRs, which are functions of device length of silicon photonic wire waveguides at 1550-nm wavelength.
. The difference between the calculation and measurement is most likely due to structural error. We analyzed the FSR dependence of the fluctuations by simulation to discuss which parameter is dominant. In our fabrication processes, the fluctuations of both the width and thickness are lower than +/−5 nm. As a result, with a 2.4 cm-long device, for example, the FSR shift for +/−5 nm width offset is only + 2 ~-2%, while that for the thickness offset is + 11 ~-14%. The thickness of the SOI layer on a four-inch wafer actually fluctuates a little, which can be observed using a commercial laser interferometer for measuring film thickness. Therefore, the FSR difference between the calculation and measurement could mainly come from the thickness fluctuation. Another possibility is that the SSC on each side which also could cause relatively weak polarization dependence of group velocities, and they are not included in the device length when conducting the calculation.

4. DPSK demodulation

Figure 6
Fig. 6 Schematic diagram of the setup for signal pattern observation and BER measurements of DPSK signal. The demodulation part is shown in the dashed box which includes a silicon photonic wire waveguide module, PBS, and a PC on each side of the module.
shows a schematic diagram of the setup for signal pattern observation and bit error rate (BER) measurements for DPSK signal. We used a tunable laser diode (TLD), a pulse pattern generator (PPG), and a zero-chirp LiNbO3 DPSK modulator to generate a non-return-to-zero (NRZ) 10-Gb/s pseudorandom bit stream (PRBS) of length 211-1. The polarization angle of the light was adjusted to around 45 degrees with reference to the waveguide substrate with a polarization controller (PC). To simplify the characterization setup, we carried out this experiment with the fiber pigtail module. A second PC was placed at the output of the module to control the polarization angle, and then a PBS was placed to separate the signals into a constructive or destructive port in accordance with its polarization state. Finally, each signal was coupled into a photo detector (PD) and electrical amplifier to observe the demodulation pattern with a sampling oscilloscope or measure the BER with an error detector. Figures 7(a)
Fig. 7 (a) Electrical output from the PPG. (b) Modulated DPSK optical output from a LiNbO3 modulator. (c) Demodulated optical output from an exit PBS. (d) Eye diagram of demodulated optical output. All patterns were obtained with a modulation bit rate of 10 Gb/s and a wavelength of 1550 nm.
- 7(c) show 10-Gb/s PRBS patterns of electrical output from the PPG, DPSK optical output from the LiNbO3 modulator, and demodulated optical output from the PBS, respectively. Figure 7(d) is the eye diagram of the demodulated signal. Clear eye opening is exhibited. Both demodulated signals [Figs. 7(c) and 7(d)] are observed from the constructive port of the PBS in this measurement. The experiment results in Figs. 7(a)-7(d) are measured with a single-ended PD, in Figs. 8
Fig. 8 BER measurement for word length of PRBS 231-1. OSNR penalty between modulation rate of 9.6 and 10.0 Gb/s is 0.2 dB.
and 9
Fig. 9 Dependence of OSNR requirement for BER of 1 × 10−9 on modulation rates around 10 Gb/s.
are measured with balanced PD as shown in Fig. 6.

Next, we placed several optical components, including a variable optical attenuator, band pass filter, and balanced detector, to the measurement setup to measure BER versus OSNR characteristics of DPSK modulation rate around 10.0 Gb/s with 2.8-cm-long device. Error-free operation was estimated by measuring up to a BER of 10−9 at bit rates of 9.6 and 10.0 Gb/s with PRBS length of 231-1. When comparing with the two bit rates, the OSNR penalty was observed as only 0.2 dB. Finally, we confirmed the modulation rates from 8.8 to 10.8 Gb/s versus the OSNR requirement for a BER of 10−9 using the silicon wire waveguide based demodulator (Fig. 9). With our experiment, 1-dB OSNR penalty tolerance of approximately 1.6 Gb/s (8.8 ~10.4 Gb/s) and the lowest OSNR requirement of around 9.6 Gb/s are observed, respectively. The results correspond approximately to the investigation using conventional DLI as in Ref [1

1. A. H. Gnauck and P. J. Winzer, “Optical phase-shift-keyed transmission,” J. Lightwave Technol. 23(1), 115–130 (2005). [CrossRef]

].

In addition, one of our future conceptions is that epitaxially grown germanium PDs and transimpedance amplifiers can be integrated with compact optical devices such as WDM filter [29

29. H. Nishi, T. Tsuchizawa, R. Kou, H. Shinojima, T. Yamada, H. Kimura, Y. Ishikawa, K. Wada, and K. Yamada, “Monolithic integration of a silica AWG and Ge photodiodes on Si photonic platform for one-chip WDM receiver,” Opt. Express 20(8), 9312–9321 (2012). [CrossRef] [PubMed]

] and this kind of PSK demodulator.

5. Conclusion

Acknowledgments

The authors thank Mr. Toshifumi Watanabe of NTT Advanced Technology for CAD design and fabrication processes, Mr. Takashi Goh of NTT Photonics Laboratories for BER measurement and helpful discussion. They also thank Dr. Shinji Mino of NTT Photonics Laboratories and Dr. Sei-ichi Itabashi and Mr. Shin’ichiro Mutoh of NTT Microsystem Integration Laboratories for encouragement.

References and links

1.

A. H. Gnauck and P. J. Winzer, “Optical phase-shift-keyed transmission,” J. Lightwave Technol. 23(1), 115–130 (2005). [CrossRef]

2.

P. J. Winzer and R. J. Essiambre, “Advanced modulation formats for high-capacity optical transport networks,” J. Lightwave Technol. 24(12), 4711–4728 (2006). [CrossRef]

3.

M. Nakazawa, S. Okamoto, T. Omiya, K. Kasai, and M. Yoshida, “256-QAM (64 Gb/s) coherent optical transmission over 160 km with an optical bandwidth of 5.4 GHz,” IEEE Photon. Technol. Lett. 22(3), 185–187 (2010). [CrossRef]

4.

A. Sano, E. Yamada, H. Masuda, E. Yamazaki, T. Kobayashi, E. Yoshida, Y. Miyamoto, R. Kudo, K. Ishihara, and Y. Takatori, “No-guard-interval coherent optical OFDM for 100-Gb/s long-haul WDM transmission,” J. Lightwave Technol. 27(16), 3705–3714 (2009). [CrossRef]

5.

S. L. Jansen, I. Morita, T. C. W. Schenk, N. Takeda, and H. Tanaka, “Coherent optical 25.8-Gb/s OFDM transmission over 4160-km SSMAF,” J. Lightwave Technol. 26(1), 6–15 (2008). [CrossRef]

6.

J. J. Yu, M. F. Huang, D. Y. Qian, L. Chen, and G. K. Chang, “Centralized lightwave WDM-PON employing 16-QAM intensity modulated OFDM downstream and OOK modulated upstream signals,” IEEE Photon. Technol. Lett. 20(18), 1545–1547 (2008). [CrossRef]

7.

C. W. Chow, C. H. Yeh, C. H. Wang, F. Y. Shih, C. L. Pan, and S. Chi, “WDM extended reach passive optical networks using OFDM-QAM,” Opt. Express 16(16), 12096–12101 (2008). [CrossRef] [PubMed]

8.

X. Liu, A. H. Gnauck, X. Wei, J. Hsieh, C. Y. Ai, and V. Chien, “Athermal optical demodulator for OC-768 DPSK and RZ-DPSK signals,” IEEE Photon. Technol. Lett. 17(12), 2610–2612 (2005). [CrossRef]

9.

Y. K. Lize, M. Faucher, E. Jarry, P. Ouellette, E. Villeneuve, A. Wetter, and F. Seguin, “Phase-tunable low-loss, S-, C-, and L-band DPSK and DQPSK demodulator,” IEEE Photon. Technol. Lett. 19(23), 1886–1888 (2007). [CrossRef]

10.

J. Gamet and G. Pandraud, “C- and L-band planar delay interferometer for DPSK decoders,” IEEE Photon. Technol. Lett. 17(6), 1217–1219 (2005). [CrossRef]

11.

Y. Nasu, K. Hattori, T. Saida, Y. Hashizume, and Y. Sakamaki, “Silica-based adaptive-delay DPSK demodulator with a cascaded Mach-Zehnder interferometer configuration,” in Proc. European Conference and Exhibition on Optical Communication (ECOC 2010), 3 pp. (2011).

12.

Y. Sakamaki, K. Hattori, Y. Nasu, T. Hashimoto, Y. Hashizume, T. Mizuno, T. Goh, and H. Takahashi, “One-chip integrated polarisation-multiplexed DQPSK demodulator using silica-based planar lightwave circuit technology,” Electron. Lett. 46(16), 1152–1153 (2010). [CrossRef]

13.

K. Voigt, L. Zimmermann, G. Winzer, T. Mitze, J. Bruns, K. Petermann, B. Huttl, and C. Schubert, “Performance of 40-Gb/s DPSK demodulator in SOI-technology,” IEEE Photon. Technol. Lett. 20(8), 614–616 (2008). [CrossRef]

14.

L. Zhang, J. Y. Yang, M. Song, Y. Li, B. Zhang, R. G. Beausoleil, and A. E. Willner, “Microring-based modulation and demodulation of DPSK signal,” Opt. Express 15(18), 11564–11569 (2007). [CrossRef] [PubMed]

15.

X. Lin, L. Chao, W. Chiyan, and H. Tsang, “Optical differential-phase-shift-keying demodulation using a silicon microring resonator,” IEEE Photon. Technol. Lett. 21(5), 295–297 (2009). [CrossRef]

16.

R. Kou, S. Park, T. Tsuchizawa, H. Fukuda, H. Nishi, H. Shinojima, and K. Yamada, “Phase demodulation of DPSK signals using dual-bus coupled silicon micro-ring resonator,” IEICE Trans. Electron . E95-C, 224–228 (2012).

17.

Y. Ding, J. Xu, C. Peucheret, M. Pu, L. Liu, J. Seoane, H. Ou, X. Zhang, and D. Huang, “Multi-channel 40 Gbit/s NRZ-DPSK demodulation using a single silicon microring resonator,” J. Lightwave Technol. 29(5), 677–684 (2011). [CrossRef]

18.

R. Kou, K. Yamada, H. Nishi, T. Tsuchizawa, T. Watanabe, H. Shinojima, and S. Itabashi, “DPSK demodulation with a single silicon photonic nanowire waveguide,” in Proc. IEEE 8th International Conference on Group IV Photonics (GFP 2011), 323–325 (2011).

19.

A. Sv Sudbo, “Film mode matching: a versatile numerical method for vector mode field calculations in dielectric waveguides,” J. Opt. A, Pure Appl. Opt. 2, 211–233 (1993).

20.

T. Shoji, T. Tsuchizawa, T. Watanabe, K. Yamada, and H. Morita, “Low loss mode size converter from 0.3 μm square Si wire waveguides to singlemode fibres,” Electron. Lett. 38(25), 1669–1670 (2002). [CrossRef]

21.

T. Tsuchizawa, K. Yamada, H. Fukuda, T. Watanabe, J. Takahashi, M. Takahashi, T. Shoji, E. Tamechika, S. Itabashi, and H. Morita, “Microphotonics devices based on silicon microfabrication technology,” IEEE J. Sel. Top. Quantum Electron. 11(1), 232–240 (2005). [CrossRef]

22.

T. Tsuchizawa, K. Yamada, T. Watanabe, S. Park, H. Nishi, R. Kou, H. Shinojima, and S. Itabashi, “Monolithic integration of silicon-, germanium-, and silica-based optical devices for telecommunications applications,” IEEE J. Sel. Top. Quantum Electron. 17(3), 516–525 (2011). [CrossRef]

23.

G. Cocorullo, F. G. Della Corte, and I. Rendina, “Temperature dependence of the thermo-optic coefficient in crystalline silicon between room temperature and 550 K at the wavelength of 1523 nm,” Appl. Phys. Lett. 74(22), 3338–3340 (1999). [CrossRef]

24.

H. Fukuda, K. Yamada, T. Tsuchizawa, T. Watanabe, H. Shinojima, and S. Itabashi, “Ultrasmall polarization splitter based on silicon wire waveguides,” Opt. Express 14(25), 12401–12408 (2006). [CrossRef] [PubMed]

25.

H. Fukuda, K. Yamada, T. Tsuchizawa, T. Watanabe, H. Shinojima, and S. Itabashi, “Polarization rotator based on silicon wire waveguides,” Opt. Express 16(4), 2628–2635 (2008). [CrossRef] [PubMed]

26.

H. Fukuda, K. Yamada, T. Tsuchizawa, T. Watanabe, H. Shinojima, and S. Itabashi, “Silicon photonic circuit with polarization diversity,” Opt. Express 16(7), 4872–4880 (2008). [CrossRef] [PubMed]

27.

Y. Nasu, Y. Hashizume, Y. Sakamaki, T. Hashimoto, K. Hattori, and Y. Inoue, “Reduction of Polarization Dependence of PLC Mach-Zehnder Interferometer Over Wide Wavelength Range,” J. Lightwave Technol. 27(21), 4814–4820 (2009). [CrossRef]

28.

Y. Nasu, M. Oguma, T. Hashimoto, H. Takahashi, Y. Inoue, H. Kawakami, and E. Yoshida, “Asymmetric half-wave plate configuration of PLC Mach-Zehnder interferometer for polarization insensitive DQPSK demodulator,” J. Lightwave Technol. 27(23), 5348–5355 (2009). [CrossRef]

29.

H. Nishi, T. Tsuchizawa, R. Kou, H. Shinojima, T. Yamada, H. Kimura, Y. Ishikawa, K. Wada, and K. Yamada, “Monolithic integration of a silica AWG and Ge photodiodes on Si photonic platform for one-chip WDM receiver,” Opt. Express 20(8), 9312–9321 (2012). [CrossRef] [PubMed]

OCIS Codes
(060.5060) Fiber optics and optical communications : Phase modulation
(130.3120) Integrated optics : Integrated optics devices
(230.7380) Optical devices : Waveguides, channeled
(070.2615) Fourier optics and signal processing : Frequency filtering

ToC Category:
Integrated Optics

History
Original Manuscript: February 29, 2012
Revised Manuscript: April 19, 2012
Manuscript Accepted: April 23, 2012
Published: April 27, 2012

Citation
Rai Kou, Hidetaka Nishi, Tai Tsuchizawa, Hiroshi Fukuda, Hiroyuki Shinojima, and Koji Yamada, "Single silicon wire waveguide based delay line interferometer for DPSK demodulation," Opt. Express 20, 11037-11045 (2012)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-20-10-11037


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