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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 19, Iss. 27 — Dec. 19, 2011
  • pp: 26645–26650
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Field-driven all-optical wavelength converter using novel InGaAsP/InAlGaAs quantum wells

Tsu-Hsiu Wu, Jui-Pin Wu, and Yi-Jen Chiu  »View Author Affiliations


Optics Express, Vol. 19, Issue 27, pp. 26645-26650 (2011)
http://dx.doi.org/10.1364/OE.19.026645


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Abstract

A new type of semiconductor quantum well (QW) for high-speed all optical wavelength converter (AOWC) is proposed and demonstrated in this work. Based on InGaAsP (well)/InGaAlAs (barrier) multiple QW, large electron band offset ratio relative to heavy hole can be attained to shorten sweep rate of photocarrier driven by electric field, realizing high-speed efficient AOWC through cross absorption modulation (XAM). By such QWs, an optical waveguide with high-speed electrode connection is fabricated. A −3dB bandwidth of 38 GHz with 8V bias in time-varying photocurrent and all optical response is observed. The corresponding sweep time is less than 10ps, consistent with calculated tunneling rate of QW and thus confirming high sweep rate through field-driven tunneling processing. All-optical conversion with error-free 40Gb/s data transmission and −11dB of conversion efficiency in system performance is also attained in this device, suggesting that such AOWC has potential for 100Gb/s application.

© 2011 OSA

1. Introduction

2. Device design and fabrication

Once the pump light is absorbed in QW region, XAM can be operated by blue shift of QW from the generated photocarriers, such as charge screening, band filled effect, or exciton bleaching. The probe light can thus be modulated through QCSE of QW. Therefore, the speed limitation based on XAM in QW will be mostly relied on carrier sweep-out behavior. High sweep rate of photocarrier can set up high screening electric field to drive probe light by QCSE, where three major processing are thermion emission, recombination, and tunneling processing. When the QW device is operated under high reverse bias, due to the low overlap in electron- and hole- wave functions, the probability of recombination can be neglected. Also, by comparing with field-enhanced tunneling processing, thermal emission effect can be neglected due to lower statistical distribution of hot carrier. Hence, the swept-out rate by tunneling processing out of multiple QWs (MQWs) is assumed as the main operation mechanism to recover absorbing state after high pump power excitation [15

15. S. Hojfeldt and J. Mork, “Modeling of carrier dynamics in quantum-well Electroabsorption modulators,” IEEE J. Sel. Top. Quantum Electron. 8(6), 1265–1276 (2002). [CrossRef]

,16

16. T. Otani, T. Miyazaki, and S. Yamamoto, “Optical 3R regenerator using wavelength converters based on Electroabsorption modulator for all-optical network applications,” IEEE Photon. Technol. Lett. 12(4), 431–433 (2000). [CrossRef]

]. Considering a single quantum well case, carrier swept time (τT) through tunneling processing can be represented by Eq. (1) [17

17. L. D. Landau and E. M. Lifshitz, Quantum Mechanics, Non-Relativistic Theory, 3rd ed. 178–181 (1977).

-18

18. A. M. Fox, D. A. B. Miller, G. Livescu, J. E. Cunningham, and W. Y. Jan, “Quantum well carrier sweep out: Relation to Electroabsorption and exciton saturation,” IEEE J. Quantum Electron. 27(10), 2281–2295 (1991). [CrossRef]

]:
1(τT)i=nπ2Lw2miexp[2Lb2mbi[ΔEiEi(n)|e|F(Lw+Lb)2]]
(1)
ΔEgis the band gap difference between well and barrier. ΔEc and ΔEv are band offsets of conduction and valence band respectively. Lw and Lb are widths of quantum well and barrier, where the effective mass is denoted as mi and mbi (i = e or h are for electron or hole), andE(i)(n)is the nth sub-band energy level. F is the electric field in well. Although high external electric field could fasten carrier tunneling processing, conduction electron confinement will then be reduced to deteriorate QCSE. Therefore, band offset ratio and carrier effective mass of conduction and valance bands are main design issues for overall all optical performance. In general semiconductors of bandgaps λ = 1300nm or 1500nm, effective mass of valance-band heavy hole (~0.1 mo) is around one order of magnitude larger than conduction-band electron. Heavy-hole dynamics is thus the key issue responsible for slow carrier sweep rate. Although valance band offset (ΔEv) could be reduced through band gap engineering, the lowered conduction band offset (ΔEc) will inevitably reduce optical modulation efficiency due to reduced QCSE by light conduction-band electron mass. Therefore, as a point view of material design, large band offset ratio (ΔEc/ΔEv) becomes one of the main parameters to get high-speed efficiency AOWC. Large ΔEc/ΔEv could have advantages of allowing high applied electric field to fasten carrier processing while still maintaining significant QCSE [18

18. A. M. Fox, D. A. B. Miller, G. Livescu, J. E. Cunningham, and W. Y. Jan, “Quantum well carrier sweep out: Relation to Electroabsorption and exciton saturation,” IEEE J. Quantum Electron. 27(10), 2281–2295 (1991). [CrossRef]

,19

19. D. A. B. Miller, D. S. Chemla, T. C. Damen, A. C. Gossard, W. Wiegmann, T. H. Wood, and C. A. Burrus, “Electric field dependence of optical absorption near the band gap of quantum-well structures,” Phys. Rev. B Condens. Matter 32(2), 1043–1060 (1985). [CrossRef] [PubMed]

].

Based on the results of Fig. 1, strain-compensated P-Q/Al-Q MQWs is grown as active region by a MOCVD system, sandwiched by top p-InP and bottom n-InP layers for AOWC waveguide. Underneath, a passive waveguide is grown for integrating top active waveguide, defining optical spot-size converter (SSC), which is for efficient coupling from a single-mode fiber to the small core of AOWC waveguide. Figure 2
Fig. 2 (left) device picture and (right) the schematic plot of measurement setup. RX is photoreceiver.
shows the fabricated waveguide core. Whole processing is defined by selective undercut-etching active region [21

21. F.-Z. Lin, Y.-J. Chiu, S. A. Tsai, and T.-H. Wu, “Laterally tapered undercut active waveguide fabricated by simple wet etching method for vertical waveguide directional coupler,” Opt. Express 16(11), 7588–7594 (2008). [CrossRef] [PubMed]

]. The finished AOWC waveguide and passive waveguide are 2.5μm and 8μm respectively. The length of EAM region is 100μm. N- and p- metal ohmic contact for biasing AOWC are deposited by evaporating Ni/AuGe/Au and Ti/Au metals. In the two ends of optical waveguide of AOWC, two coplanar waveguides (CPW) are fabricated as the connection lines for receiving high-speed modulated photocurrent as well as biasing AOWC.

3. Experimental results and discussion

In characterizing AOWC, small-signal optical-to-electrical (OE, photocurrent) measurement, is first performed to exam carrier swept rate in MQWs. The measurement setup is shown in the right side of Fig. 2. A time-modulated optical pump power is obtained by a 40Gb/s Mach-Zender modulator (MZM, JDSU 40Gb/s) with a broadband Vector Network Analyzer (VNA). The modulated signal is then amplified by an EDFA and coupled into AOWC for exciting photocurrent. The pump light is TE-polarized centered at 1530nm. After the light is converted into photocarriers, as shown in Fig. 2, CPW line is used as current collector. By VNA, the final OE response is extracted. Left side of Fig. 3
Fig. 3 (left) different-bias OE response with frequency. The dash curve is simulated curve. (right) OO response.
shows the normalized OE response. As biasing from 4 to 8 V, −3dB bandwidth drop increases from 10GHz to 38GHz, suggesting the electrical-field enhancement of carrier swept processing. Above 7V, the response is saturated, mainly limited by MZM bandwidth. As photocarrier are swept out of active region, the generated photocurrent will flow out and propagate in the waveguide, may affecting the overall frequency OE response due to the electrodes and circuits connected to AOWC. In order to check this point, VNA is also used to exam electrical properties of waveguide (or S-parameter). The −3dB drop in electrical transmission (S21) is 50GHz which is larger than OE bandwidth, further confirming the speed of received photocarrier is modulator-limited. For further testing high-speed properties of cross optical absorption through carrier swept process, a 1555nm probe light (Fig. 2) is sent to AOWC with 1545nm pump light using co-directional scheme with pump light, performing OO response. After filtering out pump light, the modulated probe light responses is sent into VNA for analysis. As shown in the right side of Fig. 3, the response exhibits the same behavior with OE response for biasing at voltages of higher than 7V; indicating all-optical response based on cross absorption is mainly attributed to high-speed carrier sweep processing. Using distributive photocurrent model, theoretical OE response plotted with dash curve in Fig. 3 can be simulated to fit the experimental results, where the fitted response time is 8ps. Furthermore, the insert of Fig. 3 plots the DC all optical conversion efficiency. −12dB DC conversion efficiency at bias of 8V with 8dB extinction ratio is obtained in all optical modulation. Large QCSE still exists in such high electric field, implying that large electron confinement in conduction band. By accompanying with OE and OO conversion, it indicates that large band offset ratio using P-Q/Al-Q MQW could be operated at 10ps regime of response time.

In order to further test system performance of AOWC by P-Q/Al-Q MQW, a large signal with non-return-to-zero (NRZ) 40Gb/s pattern is used. The experiment follows the setup of small-signal OO conversion, except that an EDFA and an electrical amplifier (Picosecond 5882 40Gb/s Amplifier) are placed behind filter and receiver (RX, U2T XPVD 2120R). Device insertion loss is −12.5dB, including coupling loss and propagation loss. The input average optical power of pump signal and DC probe power was set as 3dBm and 0dBm. A pseudo random bit string (PRBS) with pattern length of 231-1 with bit rate of 40Gb/s is used for digital pulse train. The back-to-back and converted eyes of AOWC are measured and plotted in Fig. 4
Fig. 4 (left) eye diagram of pump signal and converted signal, (right) the corresponding bit error rate.
, where back-to-back eye is directly measured after MZM with amplification. As shown, eye pattern exhibits the similar behaviors with back-to-back eye pattern. Extracted from eye pattern, AC conversion efficiency is −11dB. And optical signal-to-noise ratios (OSNR, Q value) are extracted as 5.9 and 5.5 for pump and converted signal. And the AC extinction ratios of 5dB (pump) and 5.6dB (converted signal) are observed, where the enhancement is mainly from the nonlinear transfer function of XAM (inserted plot of Fig. 3). The noise from EDFA and electrical amplifier could limit AC extinction ratio and OSNR performance. No error floor of bit error rate test (BERT) and less than 0.5dB loss budge in 10-9 BER are observed in high-speed data transmission. 40Gb/s transmission without pattern dependence in such AOWC is realized, indicating material structure of P-Q/Al-Q MQW can have capability to get speed as well as efficient XAM in system performance.

4. Conclusion

In this work, a high band-offset ratio of quantum well, namely InGaAsP/InGaAlAs (P-Q/Al-Q), is first employed as high-speed all optical wavelength converter (AOWC) through cross absorption modulation (XAM) effect. Using P-Q and Al-Q as well and barrier material, high band-offset ratio of electron to hole can be realized to enhance the field-driven tunneling rate of heavy hole for at high electric field while still sustaining large quantum confine Stark effect (QCSE) in electron. Using high-speed microwave coplanar waveguides (CPW) as connection lines, an optical waveguide based on P-Q/Al-Q material is fabricated as a high-speed AOWC. By driving voltage of 8V, −3dB bandwidth 38GHz of photocurrent is directly detected from CPW line of AOWC, limited by modulator. Same bandwidth of all optical conversion is also observed, confirming high-speed sweep processing of photocarrier as well as cross-absorption modulation can be realized in such QW. By fitting photocarrier response through distributive photocurrent model, less than 10ps response of all-optical conversion is suggested. A successful 40Gb/s data transmission is also demonstrated in this device.

Acknowledgments

The authors would like to thank the financial supports from the National Science Council, Taiwan (NSC99-2221-E-110-029-MY3) and “Aim for the Top University Plan Taiwan” (97C030133). The wafer and high-speed instrument supports from Land Mark Optoelectronics Corporation and Professor H. Taga in NSYSU are also of great help.

References and links

1.

M. Onishi, T. Okuno, T. Kashiwada, S. Ishikawa, N. Akasaka, and M. Nishimura, “Highly nonlinear dispersion-shifted fibers and their application to broadband wavelength converter,” Opt. Fiber Technol. 4(2), 204–214 (1998). [CrossRef]

2.

M. Dinu, F. Quochi, and H. Garcia, “Third-order nonlinearities in silicon at telecom wavelengths,” Appl. Phys. Lett. 82(18), 2954–2956 (2003). [CrossRef]

3.

M. N. Sysak, J. W. Raring, J. S. Barton, M. Dummer, A. Tauke-Pedretti, H. N. Poulsen, D. J. Blumenthal, and L. A. Coldren, “Single-chip, widely-tunable 10Gbit.s photocurrent-driven wavelength converter incorporating a monolithically integrated laser transmitter and optical receiver,” Electron. Lett. 42(11), 657–658 (2006). [CrossRef]

4.

M. Hattori, K. Nishimura, R. Inohara, and M. Usami, “Bidirectional data injection operation of hybrid integrated SOA-MZI all-optical wavelength converter,” J. Lightwave Technol. 25(2), 512–519 (2007). [CrossRef]

5.

A. Matsumoto, K. Nishimura, K. Utaka, and M. Usami, “Operational design on high-speed semiconductor optical amplifier with assist light for application to wavelength converters using cross-phase modulation,” IEEE J. Quantum Electron. 42(3), 313–323 (2006). [CrossRef]

6.

J. Wang, A. Marculescu, J. Li, P. Vorreau, S. Tzadok, S. B. Ezra, S. Tsadka, W. Freude, and J. Leuthold, “Pattern effect removal technique for semiconductor-optical-amplifier-based wavelength conversion,” IEEE Photon. Technol. Lett. 19(24), 1955–1957 (2007). [CrossRef]

7.

M. Spyropoulou, N. Pleros, K. Vyrsokinos, D. Apostolopoulos, M. Bougioukos, D. Petrantonakis, A. Miliou, and H. Avramopoulos, “40 Gb/s NRZ wavelength conversion using a differentially-biased SOA-MZI: Theory and experiment,” J. Lightwave Technol. 29(10), 1489–1499 (2011). [CrossRef]

8.

G. Contestabile, N. Calabretta, M. Presi, and E. Ciaramella, “Single and multicast wavelength conversion at 40 Gb/s by means of fast nonlinear polarization switching in an SOA,” IEEE Photon. Technol. Lett. 17(12), 2652–2654 (2005). [CrossRef]

9.

B. E. Olsson and D. J. Blumenthal, “WDM to OTDM multiplexing using an ultrafast all-optical wavelength converter,” IEEE Photon. Technol. Lett. 13(9), 1005–1007 (2001). [CrossRef]

10.

K. K. Chow and C. Shu, “All-optical signal regeneration with wavelength multicasting at 6x10 Gb/s using a single electroabsorption modulator,” Opt. Express 12(13), 3050–3054 (2004). [CrossRef] [PubMed]

11.

J. Yu, Z. Jia, and G. K. Chang, “All-optical mixer based on cross-absorption modulation in electroabsorption modulator,” IEEE Photon. Technol. Lett. 17(11), 2421–2423 (2005). [CrossRef]

12.

H. S. Chung, R. Inohara, K. Nishimura, and M. Usami, “40-Gb/s NRZ wavelength conversion with 3R regeneration using an EA modulator and SOA polarization-discriminating delay interferometer,” IEEE Photon. Technol. Lett. 18(2), 337–339 (2006). [CrossRef]

13.

K. Nishimura, R. Inohara, M. Usami, and S. Akiba, “All-optical wavelength conversion by electroabsorption modulator,” IEEE J. Sel. Top. Quantum Electron. 11(1), 278–284 (2005). [CrossRef]

14.

N. E. Dahdah, J. Decobert, A. Shen, S. Bouchoule, C. Kazmierski, G. Aubin, B.-E. Benkelfat, and A. Ramdane, “New design of InGaAs–InGaAlAs MQW Electroabsorption modulator for high-speed all-optical wavelength conversion,” IEEE Photon. Technol. Lett. 16(10), 2302–2304 (2004). [CrossRef]

15.

S. Hojfeldt and J. Mork, “Modeling of carrier dynamics in quantum-well Electroabsorption modulators,” IEEE J. Sel. Top. Quantum Electron. 8(6), 1265–1276 (2002). [CrossRef]

16.

T. Otani, T. Miyazaki, and S. Yamamoto, “Optical 3R regenerator using wavelength converters based on Electroabsorption modulator for all-optical network applications,” IEEE Photon. Technol. Lett. 12(4), 431–433 (2000). [CrossRef]

17.

L. D. Landau and E. M. Lifshitz, Quantum Mechanics, Non-Relativistic Theory, 3rd ed. 178–181 (1977).

18.

A. M. Fox, D. A. B. Miller, G. Livescu, J. E. Cunningham, and W. Y. Jan, “Quantum well carrier sweep out: Relation to Electroabsorption and exciton saturation,” IEEE J. Quantum Electron. 27(10), 2281–2295 (1991). [CrossRef]

19.

D. A. B. Miller, D. S. Chemla, T. C. Damen, A. C. Gossard, W. Wiegmann, T. H. Wood, and C. A. Burrus, “Electric field dependence of optical absorption near the band gap of quantum-well structures,” Phys. Rev. B Condens. Matter 32(2), 1043–1060 (1985). [CrossRef] [PubMed]

20.

J. Minch, S. H. Park, T. Keating, and S. L. Chuang, “Theory and experiment of In1-xGaxAsyP1-y and In1-x-yGaxAlyAs long-wavelength strained quantum-well lasers,” IEEE J. Quantum Electron. 35, 771–782 (1999). [CrossRef]

21.

F.-Z. Lin, Y.-J. Chiu, S. A. Tsai, and T.-H. Wu, “Laterally tapered undercut active waveguide fabricated by simple wet etching method for vertical waveguide directional coupler,” Opt. Express 16(11), 7588–7594 (2008). [CrossRef] [PubMed]

OCIS Codes
(230.1150) Optical devices : All-optical devices
(230.4205) Optical devices : Multiple quantum well (MQW) modulators
(130.7405) Integrated optics : Wavelength conversion devices

ToC Category:
Optical Devices

History
Original Manuscript: October 5, 2011
Revised Manuscript: November 18, 2011
Manuscript Accepted: November 20, 2011
Published: December 14, 2011

Citation
Tsu-Hsiu Wu, Jui-Pin Wu, and Yi-Jen Chiu, "Field-driven all-optical wavelength converter using novel InGaAsP/InAlGaAs quantum wells," Opt. Express 19, 26645-26650 (2011)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-19-27-26645


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References

  1. M. Onishi, T. Okuno, T. Kashiwada, S. Ishikawa, N. Akasaka, and M. Nishimura, “Highly nonlinear dispersion-shifted fibers and their application to broadband wavelength converter,” Opt. Fiber Technol.4(2), 204–214 (1998). [CrossRef]
  2. M. Dinu, F. Quochi, and H. Garcia, “Third-order nonlinearities in silicon at telecom wavelengths,” Appl. Phys. Lett.82(18), 2954–2956 (2003). [CrossRef]
  3. M. N. Sysak, J. W. Raring, J. S. Barton, M. Dummer, A. Tauke-Pedretti, H. N. Poulsen, D. J. Blumenthal, and L. A. Coldren, “Single-chip, widely-tunable 10Gbit.s photocurrent-driven wavelength converter incorporating a monolithically integrated laser transmitter and optical receiver,” Electron. Lett.42(11), 657–658 (2006). [CrossRef]
  4. M. Hattori, K. Nishimura, R. Inohara, and M. Usami, “Bidirectional data injection operation of hybrid integrated SOA-MZI all-optical wavelength converter,” J. Lightwave Technol.25(2), 512–519 (2007). [CrossRef]
  5. A. Matsumoto, K. Nishimura, K. Utaka, and M. Usami, “Operational design on high-speed semiconductor optical amplifier with assist light for application to wavelength converters using cross-phase modulation,” IEEE J. Quantum Electron.42(3), 313–323 (2006). [CrossRef]
  6. J. Wang, A. Marculescu, J. Li, P. Vorreau, S. Tzadok, S. B. Ezra, S. Tsadka, W. Freude, and J. Leuthold, “Pattern effect removal technique for semiconductor-optical-amplifier-based wavelength conversion,” IEEE Photon. Technol. Lett.19(24), 1955–1957 (2007). [CrossRef]
  7. M. Spyropoulou, N. Pleros, K. Vyrsokinos, D. Apostolopoulos, M. Bougioukos, D. Petrantonakis, A. Miliou, and H. Avramopoulos, “40 Gb/s NRZ wavelength conversion using a differentially-biased SOA-MZI: Theory and experiment,” J. Lightwave Technol.29(10), 1489–1499 (2011). [CrossRef]
  8. G. Contestabile, N. Calabretta, M. Presi, and E. Ciaramella, “Single and multicast wavelength conversion at 40 Gb/s by means of fast nonlinear polarization switching in an SOA,” IEEE Photon. Technol. Lett.17(12), 2652–2654 (2005). [CrossRef]
  9. B. E. Olsson and D. J. Blumenthal, “WDM to OTDM multiplexing using an ultrafast all-optical wavelength converter,” IEEE Photon. Technol. Lett.13(9), 1005–1007 (2001). [CrossRef]
  10. K. K. Chow and C. Shu, “All-optical signal regeneration with wavelength multicasting at 6x10 Gb/s using a single electroabsorption modulator,” Opt. Express12(13), 3050–3054 (2004). [CrossRef] [PubMed]
  11. J. Yu, Z. Jia, and G. K. Chang, “All-optical mixer based on cross-absorption modulation in electroabsorption modulator,” IEEE Photon. Technol. Lett.17(11), 2421–2423 (2005). [CrossRef]
  12. H. S. Chung, R. Inohara, K. Nishimura, and M. Usami, “40-Gb/s NRZ wavelength conversion with 3R regeneration using an EA modulator and SOA polarization-discriminating delay interferometer,” IEEE Photon. Technol. Lett.18(2), 337–339 (2006). [CrossRef]
  13. K. Nishimura, R. Inohara, M. Usami, and S. Akiba, “All-optical wavelength conversion by electroabsorption modulator,” IEEE J. Sel. Top. Quantum Electron.11(1), 278–284 (2005). [CrossRef]
  14. N. E. Dahdah, J. Decobert, A. Shen, S. Bouchoule, C. Kazmierski, G. Aubin, B.-E. Benkelfat, and A. Ramdane, “New design of InGaAs–InGaAlAs MQW Electroabsorption modulator for high-speed all-optical wavelength conversion,” IEEE Photon. Technol. Lett.16(10), 2302–2304 (2004). [CrossRef]
  15. S. Hojfeldt and J. Mork, “Modeling of carrier dynamics in quantum-well Electroabsorption modulators,” IEEE J. Sel. Top. Quantum Electron.8(6), 1265–1276 (2002). [CrossRef]
  16. T. Otani, T. Miyazaki, and S. Yamamoto, “Optical 3R regenerator using wavelength converters based on Electroabsorption modulator for all-optical network applications,” IEEE Photon. Technol. Lett.12(4), 431–433 (2000). [CrossRef]
  17. L. D. Landau and E. M. Lifshitz, Quantum Mechanics, Non-Relativistic Theory, 3rd ed. 178–181 (1977).
  18. A. M. Fox, D. A. B. Miller, G. Livescu, J. E. Cunningham, and W. Y. Jan, “Quantum well carrier sweep out: Relation to Electroabsorption and exciton saturation,” IEEE J. Quantum Electron.27(10), 2281–2295 (1991). [CrossRef]
  19. D. A. B. Miller, D. S. Chemla, T. C. Damen, A. C. Gossard, W. Wiegmann, T. H. Wood, and C. A. Burrus, “Electric field dependence of optical absorption near the band gap of quantum-well structures,” Phys. Rev. B Condens. Matter32(2), 1043–1060 (1985). [CrossRef] [PubMed]
  20. J. Minch, S. H. Park, T. Keating, and S. L. Chuang, “Theory and experiment of In1-xGaxAsyP1-y and In1-x-yGaxAlyAs long-wavelength strained quantum-well lasers,” IEEE J. Quantum Electron.35, 771–782 (1999). [CrossRef]
  21. F.-Z. Lin, Y.-J. Chiu, S. A. Tsai, and T.-H. Wu, “Laterally tapered undercut active waveguide fabricated by simple wet etching method for vertical waveguide directional coupler,” Opt. Express16(11), 7588–7594 (2008). [CrossRef] [PubMed]

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