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Optics Express

Optics Express

  • Editor: Andrew M. Weiner
  • Vol. 21, Iss. 12 — Jun. 17, 2013
  • pp: 14500–14511
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Broadband on-chip optical non-reciprocity using phase modulators

Christophe Galland, Ran Ding, Nicholas C. Harris, Tom Baehr-Jones, and Michael Hochberg  »View Author Affiliations


Optics Express, Vol. 21, Issue 12, pp. 14500-14511 (2013)
http://dx.doi.org/10.1364/OE.21.014500


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Abstract

Breaking the reciprocity of light propagation in a nanoscale photonic integrated circuit (PIC) is a topic of intense research, fostered by the promises of this technology in areas ranging from experimental research in classical and quantum optics to high-rate telecommunications and data interconnects. In particular, silicon PICs fabricated in processes compatible with the existing complementary metal-oxide-semiconductor (CMOS) infrastructure have attracted remarkable attention. However, a practical solution for integrating optical isolators and circulators within the current CMOS technology remains elusive. Here, we introduce a new non-reciprocal photonic circuit operating with standard single-mode waveguides or optical fibers. Our design exploits a time-dependent index modulation obtained with conventional phase modulators such as the one widely available in silicon photonics platforms. Because it is based on fully balanced interferometers and does not involve resonant structures, our scheme is also intrinsically broadband. Using realistic parameters we calculate an extinction ratio superior to 20dB and insertion loss below 3dB.

© 2013 OSA

1. Introduction

Materials typically used to guide and manipulate light in optical fibers and photonic integrated circuits (PIC) have symmetric permittivity and permeability tensors and in the linear regime light propagation satisfies the Lorentz reciprocity theorem [1

1. S. Fan, R. Baets, A. Petrov, Z. Yu, J. D. Joannopoulos, W. Freude, A. Melloni, M. Popović, M. Vanwolleghem, D. Jalas, M. Eich, M. Krause, H. Renner, E. Brinkmeyer, and C. R. Doerr, “Comment on “Nonreciprocal Light Propagation in a Silicon Photonic Circuit”,” Science 335(6064), 38, author reply 38 (2012). [CrossRef] [PubMed]

]. One way to break reciprocity is to operate in the non-linear regime and harvest bi-stability [2

2. L. Fan, J. Wang, L. T. Varghese, H. Shen, B. Niu, Y. Xuan, A. M. Weiner, and M. Qi, “An All-Silicon Passive Optical Diode,” Science 335(6067), 447–450 (2012). [CrossRef] [PubMed]

]. A more versatile approach is to guide light through a material exhibiting strong magneto-optical effect, which causes a Faraday rotation of the polarization dependent on the propagation direction [3

3. J. Ballato and E. Snitzer, “Fabrication of fibers with high rare-earth concentrations for Faraday isolator applications,” Appl. Opt. 34(30), 6848–6854 (1995). [CrossRef] [PubMed]

5

5. L. Sun, S. Jiang, J. D. Zuegel, and J. R. Marciante, “All-fiber optical isolator based on Faraday rotation in highly terbium-doped fiber,” Opt. Lett. 35(5), 706–708 (2010). [CrossRef] [PubMed]

]. In practice, this effect is used in commercial optical isolators and circulators, which are essential components in today’s fiber-optics systems. For example, protecting lasers from back-scattered light is critical to ensure their integrity and stability. Yet, whereas fiber-optics isolators and circulators relying on the magneto-optic effect have become widely available, a practical solution for PICs has yet to be demonstrated. Obtaining non-reciprocity with the help of magneto-optic materials by constructing a hybrid chip [6

6. R. L. Espinola, T. Izuhara, M.-C. Tsai, R. M. Osgood Jr, and H. Dötsch, “Magneto-optical nonreciprocal phase shift in garnet/silicon-on-insulator waveguides,” Opt. Lett. 29(9), 941–943 (2004). [CrossRef] [PubMed]

, 7

7. L. Bi, J. Hu, P. Jiang, D. H. Kim, G. F. Dionne, L. C. Kimerling, and C. A. Ross, “On-chip optical isolation in monolithically integrated non-reciprocal optical resonators,” Nat. Photonics 5(12), 758–762 (2011). [CrossRef]

] suffers from much increased fabrication complexity. This approach suppresses most benefits of silicon PICs, which rely on their entire fabrication in a CMOS-compatible process that ensures scalability, yield and low cost.

Recently, the first electrically driven non-reciprocal device in a silicon PIC was reported [8

8. H. Lira, Z. Yu, S. Fan, and M. Lipson, “Electrically Driven Nonreciprocity Induced by Interband Photonic Transition on a Silicon Chip,” Phys. Rev. Lett. 109(3), 033901 (2012). [CrossRef] [PubMed]

], based on the concept of interband photonic transitions developed earlier by Yu and Fan [9

9. Z. Yu and S. Fan, “Complete optical isolation created by indirect interband photonic transitions,” Nat. Photonics 3(2), 91–94 (2009). [CrossRef]

, 10

10. K. Fang, Z. Yu, and S. Fan, “Photonic Aharonov-Bohm Effect Based on Dynamic Modulation,” Phys. Rev. Lett. 108(15), 153901 (2012). [CrossRef] [PubMed]

] (an idea similar to the one already used for non-reciprocal mode-conversion in optical fibers [11

11. I. K. Hwang, S. H. Yun, and B. Y. Kim, “All-fiber-optic nonreciprocal modulator,” Opt. Lett. 22(8), 507–509 (1997). [CrossRef] [PubMed]

]). In this device, a traveling-wave radio-frequency (RF) signal induced a time-varying and spatially non-homogeneous modulation of the refractive index in a silicon waveguide specially engineered to support two TE modes with opposite symmetries and different propagation constants and wavevectors. While the concept is elegant and no hybrid technology is needed, the implementation is so far prohibitively complicated, and the fabricated device exhibited >70dB insertion loss [8

8. H. Lira, Z. Yu, S. Fan, and M. Lipson, “Electrically Driven Nonreciprocity Induced by Interband Photonic Transition on a Silicon Chip,” Phys. Rev. Lett. 109(3), 033901 (2012). [CrossRef] [PubMed]

].

It is therefore intriguing to ask whether a simpler scheme, relying only on existing components that can be readily fabricated in a CMOS process, can be exploited to obtain non-reciprocal light propagation in a monolithic silicon PIC. Others have shown interesting progress in this direction by employing two “tandem” phase modulators to imprint a non-reciprocal frequency shift [12

12. C. R. Doerr, N. Dupuis, and L. Zhang, “Optical isolator using two tandem phase modulators,” Opt. Lett. 36(21), 4293–4295 (2011). [CrossRef] [PubMed]

]. Two limitations of this scheme are its intrinsic narrow-band operation and its modest extinction ratio of 10.8dB. Passive resonant structures can be employed to enhance intrinsic silicon non-linearities [2

2. L. Fan, J. Wang, L. T. Varghese, H. Shen, B. Niu, Y. Xuan, A. M. Weiner, and M. Qi, “An All-Silicon Passive Optical Diode,” Science 335(6067), 447–450 (2012). [CrossRef] [PubMed]

], but this approach also suffers from narrow optical bandwidth and the performance intrinsically depends on the input light power. Finally, non-reciprocal light modulation can be achieved in traveling-wave modulators, at the cost of very long devices operating at very high-speed, and with only modest extinction ratio [13

13. L. Xu and H. K. Tsang, “Nonreciprocal Optical Modulation for Colorless Integrated Optical Transceivers in Passive Optical Networks,” Opt. Commun. Netw. 2(3), 131–136 (2010). [CrossRef]

].

2. Single-stage non-reciprocal modulator

2.1 System design

The design schematized in Fig. 1(a)
Fig. 1 (a) Schematic of the proposed design. MMI: multimode interferometer. The waveguide length of the optical delay is Lopt = T/4 c/ng. (b) Conceptualization of the device as a non-reciprocal modulator. (c) Computed behavior for a cosine (left panels) and a bandwidth-limited square wave (right panels) as modulator drive signals. The waveforms are shown in the upper panels. In the lower panels, we plot the transmission coefficients from port 1 to 2 (solid black line), 2 to 1 (solid red line), 1 to 0 (dashed grey line) and 2 to 3 (dashed blue line). We note that the device is symmetric under the simultaneous permutation 1↔3 and 0↔2. For the simulations we used the following parameters: MMI loss = 0.1dB [21, 22]; waveguide loss = 0.3dB/cm [23]; total waveguide length = 8 mm; dynamic loss = 2dB / π phase shift (see section 5.2).
consists of two Mach-Zehnder modulators (MZMs) driven by delayed versions of the same RF signal and separated by an optical delay line introducing a quarter-period retardation in the signal driving MZM a (left-hand side) with respect to MZM b (right-hand side). (An alternative and equivalent design based on a four-stage modulator is presented in section 5.3.) We note that tunable RF delay lines capable of 100ps delay with little distortion on 10Gb/s data stream can readily be implemented in a standard CMOS circuit [18

18. J. Buckwalter and A. Hajimiri, “An Active Analog Delay and the Delay Reference Loop,” Proceedings of the IEEE Radio Frequency Integrated Circuits (RFIC) Symposium, 17–20 (2004). [CrossRef]

] that could be wire- or flip-chip-bonded to the photonic chip. We consider a periodic function F(t): F(t) = F(t + T); with period T = 1/f; also satisfying F(t ± T/2) = -F(t), and normalized to have peak-to-peak amplitude ± 1. Examples of such functions are sine and cosine waves, as well as square waves with 50% duty cycle. An MZM is implemented by modulating the optical phase in each arm of a Mach-Zehnder interferometer. For chirp-free operation, the phase modulators are driven in push-pull mode: the upper arm experiences a phase shift φ(t) while the lower arm is driven symmetrically with a phase shift -φ(t) with respect to a constant offset. In the laboratory time-frame of reference, the optical phase modulations in MZM a and b can be written φa(t) = γ(1 ± F(t-T/4)) and φb(t) = γ(1 ± F(t)), respectively, with γ the effective phase modulation amplitude (in radians) and +/− for the upper/lower arm. By choosing the waveguide length between the two MZMs to be Lopt = T/4 c/ng (ng is the group index and c the speed of light in vacuum) light incoming from the right (ports b1, b2) travels in phase with the RF signal and therefore experiences twice the same modulation in MZMs b and a. On the contrary, for light incoming from the left (portsa1, a2), the modulation functions in MZMs a and b exhibit a π phase shift (i.e. have opposite signs). In this configuration, non-reciprocity is ensured by the presence of two phase-shifted periodic signals. To obtain high-visibility interferences the optical path difference between the two arms of the delay line must be adjustable (see below) and thus resistive heaters shall be used to finely tune their relative index shift [19

19. R. L. Espinola, M. C. Tsai, J. T. Yardley, and R. M. Osgood Jr., “Fast and low-power thermooptic switch on thin silicon-on-insulator,” IEEE Photon. Technol. Lett. 15(10), 1366–1368 (2003). [CrossRef]

]. In the following simulations we will take f = 4 GHz, which for a group index of ng = 4.2 [20

20. E. Dulkeith, F. Xia, L. Schares, W. M. J. Green, and Y. A. Vlasov, “Group index and group velocity dispersion in silicon-on-insulator photonic wires,” Opt. Express 14(9), 3853–3863 (2006). [CrossRef] [PubMed]

] leads to Lopt = 4.46 mm.

2.2 Transfer matrix calculations

2.3 Numerical simulations

We show the simulated behavior of a realistic device in Fig. 1(c), for a phase modulation amplitude γ = π/4 (π/2 peak-to-peak) and two different waveforms (a cosine and a bandwidth-limited square wave). In the calculations we included physically relevant effects such as waveguide loss (0.3dB/cm) [23

23. P. Dong, W. Qian, S. Liao, H. Liang, C.-C. Kung, N.-N. Feng, R. Shafiiha, J. Fong, D. Feng, A. V. Krishnamoorthy, and M. Asghari, “Low loss shallow-ridge silicon waveguides,” Opt. Express 18(14), 14474–14479 (2010). [CrossRef] [PubMed]

] and beam splitter insertion loss (0.1dB) [21

21. Z. Sheng, Z. Wang, C. Qiu, L. Li, A. Pang, A. Wu, X. Wang, S. Zou, and F. Gan, “A Compact and Low-Loss MMI Coupler Fabricated With CMOS Technology,” IEEE Photon J. 4(6), 2272–2277 (2012). [CrossRef]

, 22

22. R. Halir, I. Molina-Fernandez, A. Ortega-Monux, J. G. Wanguemert-Perez, X. Dan-Xia, P. Cheben, and S. Janz, “A Design Procedure for High-Performance, Rib-Waveguide-Based Multimode Interference Couplers in Silicon-on-Insulator,” Lightwave Technology, Journalism 26, 2928–2936 (2008).

], and the dynamic loss intrinsically linked to phase modulation using free-carrier dispersion effect [24

24. R. A. Soref and B. R. Bennett, “Electrooptical effects in silicon,” IEEE J. Quantum Electron. 23(1), 123–129 (1987). [CrossRef]

] (see section in section 5.2). Even in the presence of losses, and independent of the signal shape, transmission from port 2 to 1 is exactly zero, demonstrating robust isolation. In contrast, transmission from port 1 to 2 is non-zero, with a maximal value of ~0.74 (or −1.3dB) and a time-averaged value of –3.27dB for a cosine signal. Improved averaged transmission is achieved by driving the modulators with a square-wave. For example, assuming a modulation bandwidth of 5f (Fig. 1(c), right panel), time-averaged insertion loss decreases to 2.17dB.

This first result is by itself remarkable and potentially useful in real systems. For example, the output at port 2 can be directly used as a clock signal, or as an information carrier in return-to-zero encoding schemes. The device can even be used to simultaneously perform the encoding by modulating the amplitude γ. Our system therefore integrates a return-to-zero modulator and a high extinction isolator into a single compact device, making use of only conventional components. We emphasize that the modulation frequency can be chosen arbitrarily, as low as permitted by waveguide propagation loss in the delay line and desired footprint, and as fast as permitted by the modulators and drivers bandwidths.

3. Double-stage isolator

3.1 System design

3.2 Numerical simulations

The simulations in Figs. 2(b)-2(c) demonstrate that this configuration indeed achieves non-modulated transmission of right-to-left propagating light, both in amplitude (Fig. 2(b)) and phase (Fig. 2(c)), with insertion loss of 2.9dB. Extinction is reduced compared to Fig. 1(c) but still better 20dB in the case of square-wave modulation and perfect arm balancing (14dB for cosine modulation). This figure can be further improved by increasing the modulator bandwidth-to-frequency ratio. When the optical paths in the arms of each delay line are not perfectly balanced (modulo 2π), the performances are degraded, as shown by the dashed lines in Figs. 2(b)-2(c) for an optical phase mismatch of π/10 between upper and lower arm in each stage’s delay section.

To estimate the impact of relevant parameters and imperfections on the system, we study two figures of merit: the insertion loss (IL), defined as the time-averaged transmission in the passing direction, and the extinction ratio (ER), equal to the peak transmission value in “blocking” direction divided by the IL. In Fig. 3(a)
Fig. 3 (a) Insertion loss (IL, black curves) and extinction ratio (ER, red curves) as a function of the modulation amplitude γ (in units of π rad), for the single-pass configuration of Fig. 1(a) (solid lines) and the cascaded setting of Fig. 2(a) (dashed lines). (b) Same performances plotted as a function of the optical phase imbalance in the delay line of each device, for a fixed modulation amplitude γ = π/4. Color scheme as in (a).
, we show the dependence of IL and ER on the modulation amplitude for the single-pass and the cascaded configurations; the optimal modulation amplitude in both cases is close to γ = π/4, which yields the lowest IL for single-pass configuration and the highest ER for cascaded configuration.

Figure 3 also reports the sensitivity of the performances on the relative phase difference accumulated in the two arms of the delay line (modulo 2π). Given the thermo-optic coefficient of silicon dnSi/dT = 1.9 x 10−4 K−1 around 1.55µm, we calculate the temperature-dependent phase shift (in rad) per unit length of waveguide to be less than π/4 mm−1K−1. Controlling the phase difference within π/10 can thus be achieved by tuning the temperature over a 0.4 mm section with 1 K accuracy, well within reach of existing technology [25

25. K. Padmaraju, J. Chan, L. Chen, M. Lipson, and K. Bergman, “Thermal stabilization of a microring modulator using feedback control,” Opt. Express 20(27), 27999–28008 (2012). [CrossRef] [PubMed]

]. Yet some feedback circuit may be needed to ensure stable operation.

4. Conclusion

To conclude, we estimate the expected optical bandwidth. As the system relies on a series of fully balanced interferometers, it is by design wavelength insensitive. Yet, several second-order effects may limit the actual operating wavelength range. Directional couplers usually have limited bandwidth, so we opt for MMIs [21

21. Z. Sheng, Z. Wang, C. Qiu, L. Li, A. Pang, A. Wu, X. Wang, S. Zou, and F. Gan, “A Compact and Low-Loss MMI Coupler Fabricated With CMOS Technology,” IEEE Photon J. 4(6), 2272–2277 (2012). [CrossRef]

, 26

26. L. B. Soldano and E. C. M. Pennings, “Optical multi-mode interference devices based on self-imaging: principles and applications,” J. Lightwave Technol. 13(4), 615–627 (1995). [CrossRef]

] (see Fig. 1(a)), for which uniform splitting ratio over 94 nm have been demonstrated [27

27. S.-H. Jeong and K. Morito, “Optical 90 ° hybrid with broad operating bandwidth of 94 nm,” Opt. Lett. 34(22), 3505–3507 (2009). [CrossRef] [PubMed]

]. Second, due to group velocity dispersion the optical delay between MZM a and b is actually wavelength dependent. Using the dispersion measured in [20

20. E. Dulkeith, F. Xia, L. Schares, W. M. J. Green, and Y. A. Vlasov, “Group index and group velocity dispersion in silicon-on-insulator photonic wires,” Opt. Express 14(9), 3853–3863 (2006). [CrossRef] [PubMed]

] and a waveguide length of 4.5 mm, we estimate a delay variation of less than 1 ps over more than 100 nm bandwidth around 1550 nm. This is much smaller than the modulation period (250 ps here) and has therefore negligible impact on performance (the ratio ~1/250 is independent of the particular modulation frequency). This variation could be further reduced by tailoring the dispersion [28

28. A. C. Turner, C. Manolatou, B. S. Schmidt, M. Lipson, M. A. Foster, J. E. Sharping, and A. L. Gaeta, “Tailored anomalous group-velocity dispersion in silicon channel waveguides,” Opt. Express 14(10), 4357–4362 (2006). [CrossRef] [PubMed]

]. The limiting factor may eventually come from the wavelength dependence of the plasma dispersion effect [24

24. R. A. Soref and B. R. Bennett, “Electrooptical effects in silicon,” IEEE J. Quantum Electron. 23(1), 123–129 (1987). [CrossRef]

], but this too could be easily compensated for by tuning the modulation amplitude γ.

5. Appendices

5.1 Transfer matrix calculations

Our model can be used to study all relevant optical effects in the linear regime, as well as arbitrary RF signals (including bandwidth limitation, by appropriate choice of the function F(t)), and of course the impact of non-ideal physical implementation such as MZ arm imbalance, asymmetric splitting ratios, etc.

5.2 Dynamic loss and free carrier modulation

5.3 Alternative proposal

We propose a second scheme pictured in Fig 4
Fig. 4 Schematics of the two designs and their use as optical circulators. (a) Design discussed in the main text (Fig. 1(a)). (b) Alternative design discussed here. (c) “Wiring” of design (a) to be used as a non-reciprocal modulator. (d) Same for design (b). The two designs are equivalent after reversing the light propagation direction and switching the “thru” and “cross” ports.
. Here, a single MZI is built with four phase modulators in each arm, pair-wise driven in push-pull mode by the signal F(t). Again, the electric signal is delayed from right to left by a quarter-period between each successive pair of modulators, and an optical path length Lopt = T/4c/ng is introduced to ensure that light launched from the right keeps a fixed relationship with the phase of the electric drive, thus experiencing a total optical phase modulation φ(t)=4γ(1±F(t)). Light propagating from left to right sees a π retardation in the electric signal between each successive modulator, thus accumulating a zero net phase shift relative to the other arm:Δφ(t)=2γ(F(t)+F(tπ/Ω))=0. The transfer matrices for this configuration are therefore:

S=i(sin(4γF(t))cos(4γF(t))cos(4γF(t))sin(4γF(t)))andS=i(0110)

We now recall the transfer matrices obtained for the design of Fig. 1(a):
T=(cos(2γF(t))sin(2γF(t))sin(2γF(t))cos(2γF(t)))andT=(1001)
We see that as far as the optical field intensity is concerned, the two designs perform the exact same function, after swapping both the roles of the “cross” and “thru” ports and the propagation direction. The two designs also have the same modulation efficiency and phase shift requirement, since the factor multiplying γ scales with the number of phase modulators in each scheme. While the first design requires two additional beam splitters, it features three-times shorter optical and RF delay lines, yielding lower optical losses, electrical signal attenuation and electronics complexity. For the sake of simplicity, we performed our analysis in the main text based on the first design, but simulations where made with this alternative design yielding similar results.

In order to give an intuitive understanding of the second device operation, we consider an ideal square-wave signal (no bandwidth limitation) and split each period into 4 equal time intervals Δti, i = 1..4 (see Fig. 5
Fig. 5 Driving 4 phase modulators with a retarded square-wave signal.
) with the convention Δti+4 = Δti, i any integer. We denote the phase shift applied on the upper (resp. lower) arm by modulator number j at time i by the matrix element φij. (resp. -φij). With this notation, light traveling from left to right accumulates a phase shift in the upper/lower arm of φ+/=±k=0.3φi+k,j+k (with the convention φi,j+4 = φi,j). This corresponds to summing over the diagonals of the square matrix φij (i,j=1..4). For light traveling in “backward” direction (from right to left here), the accumulated phase shift writes: φ+/=±k=0.3φi+k,jk, corresponding to a sum over the anti-diagonals. With this insight, it is readily seen that the following matrix
φi,j=π8(++++++++)
always leads to a null phase shift in the forward direction, while backward propagating light experiences ± π/2 optical phase shift per arm, corresponding to the condition for destructive interference in cross-arm transmission.

Using this matrix approach, it is easy to see that 4 modulation sections is the minimum number to achieve optical isolation with this scheme.

Acknowledgment

The authors would like to thank Gernot Pomrenke, of the Air Force Office of Scientific Research, for his support under the OPSIS (FA9550-10-1-0439) PECASE (FA9550-10-1-0053) and STTR (FA9550-12-C-0079) programs, and would like to thank Mario Paniccia and Justin Rattner, of Intel, for their support of the OpSIS program. Professor Hochberg would like to acknowledge support from the Singapore Ministry of Education ACRF grant R-263-000-A09-133.

References and links

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S. Fan, R. Baets, A. Petrov, Z. Yu, J. D. Joannopoulos, W. Freude, A. Melloni, M. Popović, M. Vanwolleghem, D. Jalas, M. Eich, M. Krause, H. Renner, E. Brinkmeyer, and C. R. Doerr, “Comment on “Nonreciprocal Light Propagation in a Silicon Photonic Circuit”,” Science 335(6064), 38, author reply 38 (2012). [CrossRef] [PubMed]

2.

L. Fan, J. Wang, L. T. Varghese, H. Shen, B. Niu, Y. Xuan, A. M. Weiner, and M. Qi, “An All-Silicon Passive Optical Diode,” Science 335(6067), 447–450 (2012). [CrossRef] [PubMed]

3.

J. Ballato and E. Snitzer, “Fabrication of fibers with high rare-earth concentrations for Faraday isolator applications,” Appl. Opt. 34(30), 6848–6854 (1995). [CrossRef] [PubMed]

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A. E. Turner, R. L. Gunshor, and S. Datta, “New class of materials for optical isolators,” Appl. Opt. 22(20), 3152–3154 (1983). [CrossRef] [PubMed]

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L. Sun, S. Jiang, J. D. Zuegel, and J. R. Marciante, “All-fiber optical isolator based on Faraday rotation in highly terbium-doped fiber,” Opt. Lett. 35(5), 706–708 (2010). [CrossRef] [PubMed]

6.

R. L. Espinola, T. Izuhara, M.-C. Tsai, R. M. Osgood Jr, and H. Dötsch, “Magneto-optical nonreciprocal phase shift in garnet/silicon-on-insulator waveguides,” Opt. Lett. 29(9), 941–943 (2004). [CrossRef] [PubMed]

7.

L. Bi, J. Hu, P. Jiang, D. H. Kim, G. F. Dionne, L. C. Kimerling, and C. A. Ross, “On-chip optical isolation in monolithically integrated non-reciprocal optical resonators,” Nat. Photonics 5(12), 758–762 (2011). [CrossRef]

8.

H. Lira, Z. Yu, S. Fan, and M. Lipson, “Electrically Driven Nonreciprocity Induced by Interband Photonic Transition on a Silicon Chip,” Phys. Rev. Lett. 109(3), 033901 (2012). [CrossRef] [PubMed]

9.

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K. Fang, Z. Yu, and S. Fan, “Photonic Aharonov-Bohm Effect Based on Dynamic Modulation,” Phys. Rev. Lett. 108(15), 153901 (2012). [CrossRef] [PubMed]

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C. R. Doerr, N. Dupuis, and L. Zhang, “Optical isolator using two tandem phase modulators,” Opt. Lett. 36(21), 4293–4295 (2011). [CrossRef] [PubMed]

13.

L. Xu and H. K. Tsang, “Nonreciprocal Optical Modulation for Colorless Integrated Optical Transceivers in Passive Optical Networks,” Opt. Commun. Netw. 2(3), 131–136 (2010). [CrossRef]

14.

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R. L. Espinola, M. C. Tsai, J. T. Yardley, and R. M. Osgood Jr., “Fast and low-power thermooptic switch on thin silicon-on-insulator,” IEEE Photon. Technol. Lett. 15(10), 1366–1368 (2003). [CrossRef]

20.

E. Dulkeith, F. Xia, L. Schares, W. M. J. Green, and Y. A. Vlasov, “Group index and group velocity dispersion in silicon-on-insulator photonic wires,” Opt. Express 14(9), 3853–3863 (2006). [CrossRef] [PubMed]

21.

Z. Sheng, Z. Wang, C. Qiu, L. Li, A. Pang, A. Wu, X. Wang, S. Zou, and F. Gan, “A Compact and Low-Loss MMI Coupler Fabricated With CMOS Technology,” IEEE Photon J. 4(6), 2272–2277 (2012). [CrossRef]

22.

R. Halir, I. Molina-Fernandez, A. Ortega-Monux, J. G. Wanguemert-Perez, X. Dan-Xia, P. Cheben, and S. Janz, “A Design Procedure for High-Performance, Rib-Waveguide-Based Multimode Interference Couplers in Silicon-on-Insulator,” Lightwave Technology, Journalism 26, 2928–2936 (2008).

23.

P. Dong, W. Qian, S. Liao, H. Liang, C.-C. Kung, N.-N. Feng, R. Shafiiha, J. Fong, D. Feng, A. V. Krishnamoorthy, and M. Asghari, “Low loss shallow-ridge silicon waveguides,” Opt. Express 18(14), 14474–14479 (2010). [CrossRef] [PubMed]

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R. A. Soref and B. R. Bennett, “Electrooptical effects in silicon,” IEEE J. Quantum Electron. 23(1), 123–129 (1987). [CrossRef]

25.

K. Padmaraju, J. Chan, L. Chen, M. Lipson, and K. Bergman, “Thermal stabilization of a microring modulator using feedback control,” Opt. Express 20(27), 27999–28008 (2012). [CrossRef] [PubMed]

26.

L. B. Soldano and E. C. M. Pennings, “Optical multi-mode interference devices based on self-imaging: principles and applications,” J. Lightwave Technol. 13(4), 615–627 (1995). [CrossRef]

27.

S.-H. Jeong and K. Morito, “Optical 90 ° hybrid with broad operating bandwidth of 94 nm,” Opt. Lett. 34(22), 3505–3507 (2009). [CrossRef] [PubMed]

28.

A. C. Turner, C. Manolatou, B. S. Schmidt, M. Lipson, M. A. Foster, J. E. Sharping, and A. L. Gaeta, “Tailored anomalous group-velocity dispersion in silicon channel waveguides,” Opt. Express 14(10), 4357–4362 (2006). [CrossRef] [PubMed]

OCIS Codes
(130.0250) Integrated optics : Optoelectronics
(130.3120) Integrated optics : Integrated optics devices
(230.3120) Optical devices : Integrated optics devices
(230.3240) Optical devices : Isolators
(130.4110) Integrated optics : Modulators

ToC Category:
Integrated Optics

History
Original Manuscript: May 16, 2013
Manuscript Accepted: May 29, 2013
Published: June 11, 2013

Citation
Christophe Galland, Ran Ding, Nicholas C. Harris, Tom Baehr-Jones, and Michael Hochberg, "Broadband on-chip optical non-reciprocity using phase modulators," Opt. Express 21, 14500-14511 (2013)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-21-12-14500


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