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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 18, Iss. 17 — Aug. 16, 2010
  • pp: 17729–17735
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Novel directional coupled waveguide photodiode–concept and preliminary results

Meredith N. Draa, Jeffrey Bloch, Dingbo Chen, David C. Scott, Nong Chen, Steven Bo Chen, Xucai Yu, William S. Chang, and Paul K. L. Yu  »View Author Affiliations


Optics Express, Vol. 18, Issue 17, pp. 17729-17735 (2010)
http://dx.doi.org/10.1364/OE.18.017729


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Abstract

A novel photodiode is presented using a directional coupler incorporated with a UTC style photodiode with 0.88A/W responsivity and 35dBm OIP3 at 25mA. The device responsivity is characterized at various photocurrents up to 10mA and the OIP3 is measured up to 25mA and 10GHz. Additionally, the device capacitance is measured and used to model the capacitance limited OIP3 of the device. The failure of the device was compared to a traditional waveguide photodiode showing burnout no longer occurs at the front of the device and demonstrated the potential of the new design to control the photocurrent density profile for a waveguide style photodiode.

© 2010 OSA

1. Introduction

2. Device design

Conventional waveguide directional couplers and multimode interference couplers are based on the interference in quasi-symmetrical waveguide structures that have a small number of modes. Although their power transfer and the interference process are well controlled, and the structure can be analyzed by techniques such as coupled mode or super-mode analyses, a UTC detector placed on top of low-mode coupler cannot be used to absorb a uniform and small fraction of incident power for three reasons. (1) The optical power in coupled low-mode waveguides is oscillatory, where even distribution is desired. (2) Only a limited total power can be handled in low-mode waveguides without saturation because of their small cross section. (3) The UTC detector is a major perturbation of the waveguide coupler. In order to detect a very large incident power without saturation in the UTC detector, only a very small uniform fraction of incident power should be absorbed in the absorber. For these reasons, a novel DCPD design which consists of a UTC structure on top of a very large multimode waveguide was conceived. Figure 1a
Fig. 1 (a) Tapered DCPD device geometry. (b) DCPD layer structure, with bandgap, wavelength (in μm), dopant, carrier concentration (in cm−3) and thickness.
shows the first design. It includes an input transitional waveguide, 50μm long, which transfers the incident optical radiation into desired modes. A 90μm propagation section of 8μm wide waveguide is used to control the input optical radiation pattern at the beginning of the DCPD. The active region (UTC layers) is 200μm long and 2μm wide. After the first 40μm, the width of the optical waveguide is tapered, so the distribution of absorbed power can be more uniform. The UTC on top of a highly multimode waveguide presents a highly asymmetrical total waveguide structure which cannot be analyzed analytically. Simulation techniques such as BeamProp and Fimmwave were used to first find the modes excited in the complex asymmetric structure. A few selected dominant modes were then used to analyze their interferences. These interference patterns will contribute to the actual radiation that may be excited by the incident radiation. Since the actual excited modes of the structure are much more complex, this preliminary result is used only as a guide to vary the dimensions and indices of the DCPD. Various proposed structures excited by incident radiation are then simulated to seek dimensional and index variation which yields uniform and low fractional absorbed power. Figure 2a
Fig. 2 (a) Simulation of DCPD and WGPD power absorption along the device and (b) simulation of varying fiber position in x or y direction in units of microns, with the original case from (a) at coordinates (0,0).
illustrates the simulated absorbed power per μm length. Contrary to the conventional waveguide PD, the absorption is fairly uniform, with an average of less than 1% of the incident power along the device. Note that the simulated absorbed power per unit length will vary slightly, depending on the specific combination of modes excited by incident radiation determined by the relative position of the fiber. In order to assess the sensitivity of fiber position to the absorption profile in the present input coupling waveguide design, we simulated cases for ± 0.5µm in both the x and y directions from the ideal position that was shown in Fig. 2a. In Fig. 2b we see that changes of 0.5µm in either the x or y direction result in different absorption profiles that will lead to changes in the overall responsivity.

3. Measurement and results

In measuring the responsivity, the highest value was first obtained, which was 0.88A/W at 4V and 10mA. Each photocurrent case is normalized using the responsivity value at 2V, 0.8A/W, 0.81A/W and 0.88A/W for 0.1mA, 1mA and 10mA cases respectively. The responsivity has less variation versus electric field as current increases. The largest increase in normalized responsivity occurs at very low current (0.1mA). It has been suggested that the low electric field impact ionization coefficient leads to this electric field or voltage dependent responsivity [9

9. A. Hastings, D. A. Tulchinsky, and K. J. Williams, “Photodetector nonlinearities due to voltage dependent responsivity,” IEEE Photon. Technol. Lett. 21(21), 1642–1644 (2009). [CrossRef]

]. The DCPD contains InGaAsP in the depletion region which has an electron ionization coefficient relevant at fields greater than 200kV/cm [10

10. N. Shamir and D. Ritter, “Low electric field hole impact ionization coefficients in GaInAs and GaInAsP,” IEEE Electron Device Lett. 21(11), 509–511 (2000). [CrossRef]

]. At high fields, impact ionization causes excess carriers to be created resulting in an increase in responsivity and unwanted nonlinearities [9

9. A. Hastings, D. A. Tulchinsky, and K. J. Williams, “Photodetector nonlinearities due to voltage dependent responsivity,” IEEE Photon. Technol. Lett. 21(21), 1642–1644 (2009). [CrossRef]

]. In Fig. 3 the effect is seen at higher electric fields for the 0.1mA and 1mA case, where there should be little device heating. As the photocurrent increases, so does the device temperature. Investigations into nonlinearities of responsivity as a function of voltage have suggested the presence of impact ionization and Franz Keldysh effects, both of which are dependent on temperature [11

11. H. Pan, Z. Li, A. Beling, and J. C. Campbell, “Measurement and modeling of high-linearity modified uni-traveling carrier photodiode with highly-doped absorber,” Opt. Express 17(22), 20221–20226 (2009), http://www.opticsinfobase.org/abstract.cfm?uri=oe-17-22-20221. [CrossRef] [PubMed]

]. At 10mA we were unable to measure past 175kV/cm as the device would fail due to power dissipation limitations. Additionally, the dark current was measured as a function of reverse bias voltage in Fig. 3 (inset) to determine if this contributed to the increase in responsivity at 0.1mA. The device begins to break down around 14V (350kV/cm electric field), but the dark current is ~225nA, which is more than an order of magnitude less than the change in photocurrent measured at 0.1mA as bias is increased. We conclude that up to 175kV/cm the device shows less dependence on bias voltage at higher photocurrent, where this behavior may be due to the ionization coefficient effects that have been suggested before [9

9. A. Hastings, D. A. Tulchinsky, and K. J. Williams, “Photodetector nonlinearities due to voltage dependent responsivity,” IEEE Photon. Technol. Lett. 21(21), 1642–1644 (2009). [CrossRef]

].

Finally, OIP3 was measured versus frequency from 1 to 10GHz at 10mA and 4V bias voltage as shown in Fig. 6
Fig. 6 OIP3 versus frequency at 20mA and 4V bias voltage with modeled OIP3 curve (black) based on C(V) measurement at 5MHz (inset).
. OIP3 remains relatively flat up to 10GHz. Note that from the electrical point of view, the device length is much less than the microwave wavelength up to 10 GHz. Therefore the bandwidth is limited by the RC constant of lumped element circuits, which was measured to be 10GHz. The capacitance was measured as a function of voltage and plotted in the inset of Fig. 6 at 5MHz. Using the model outlined in [17

17. H. Jiang and P. K. L. Yu, “Equivalent circuit analysis of harmonic distortions in photodiode,” IEEE Photon. Technol. Lett. 10(11), 1608–1610 (1998). [CrossRef]

], we plotted the calculated capacitance limited OIP3 for the device, which is plotted in Fig. 6. We can see from this that the data follows the calculated limit at frequencies above 6GHz.

4. Conclusion

A novel DCPD device has been presented. The device exhibits a maximum responsivity of 0.88A/W and OIP3 of 35dBm at 4V and 25mA. The device linearity was measured over a range of frequencies and photocurrents. The design allows for coupling that reduces the front facet current density. Simulation results indicate that absorption per unit length in UTC detector could even be much lower than the 1% incident power reported here. The smaller the fraction of absorbed power per unit length, the larger is the total power that can be detected without saturation. A smaller fraction of the absorbed power implies a much longer length will be required to achieve a responsivity 0.8A/W and higher. Higher bandwidth (>10GHz) can still be achieved for a longer DCPD, if the UTC detector is a microwave transmission line. This implies that, with proper design, the power handling capacity of DCPD can be very large, without limiting bandwidth.

Acknowledgements

This work was supported in part by DARPA/SPAWAR program N66001-03-8938 TDL46, DARPA TROPHY and STTR programs all under Dr. Ron Esman.

References and links

1.

D. C. Scott, T. A. Vang, J. Elliott, D. Forbes, J. Lacey, K. Everett, F. Alvarez, R. Johnson, A. Krispin, J. Brock, L. Lembo, H. Jiang, D. S. Shin, J. T. Zhu, and P. K. L. Yu, “Measurement of IP3 in p-i-n photodetectors and proposed performance requirements for RF fiber-optic links,” IEEE Photon. Technol. Lett. 12(4), 422–424 (2000). [CrossRef]

2.

H. Jiang and P. K. L. Yu, “Waveguide integrated photodiode for analog fiber-optic links,” IEEE Trans. Microw. Theory Tech. 48(12), 2604–2610 (2000). [CrossRef]

3.

T. Ohno, H. Fukano, Y. Muramoto, T. Ishibashi, T. Yoshimatsu, and Y. Doi, “Measurement of intermodulation distortion in a unitraveling-carrier refracting-facet photodiode and a p-i-n refracting facet photodiode,” IEEE Photon. Technol. Lett. 14(3), 375–377 (2002). [CrossRef]

4.

J. Klamkin, Y.-C. Chang, A. Ramaswamy, L. A. Johansson, J. E. Bowers, S. P. DenBaars, and L. A. Coldren, “Output saturation and linearity of waveguide unitraveling-carrier photodiodes,” IEEE J. Quantum Electron. 44(4), 354–359 (2008). [CrossRef]

5.

S. Demiguel, N. Li, X. Li, X. Zheng, J. Kim, J. C. Campbell, H. Lu, and A. Anselm, “Very high-responsivity evanescently coupled photodiodes integrating a short planar multimode waveguide for high-speed applications,” IEEE Photon. Technol. Lett. 15(12), 1761–1763 (2003). [CrossRef]

6.

A. Umbach, D. Trommer, R. Steingruber, A. Seeger, W. Ebert, and G. Unterborsch, “Ultrafast, high-power 1.55µm side-illuminated photodetector with integrated spot size converter,” in Optical Fiber Communication conference, 2000 OSA Technical Digest Series (Optical Society of America, 2000), paper FG2–1.

7.

M. N. Draa, J. Bloch, D. C. Scott, N. Chen, S. B. Chen, W. S. C. Chang, and P. K. L. Yu, “Behaviors of the third order intercept point for p-i-n waveguide photodiodes,” Opt. Express 17(16), 14389–14394 (2009), http://www.opticsinfobase.org/abstract.cfm?uri=oe-17-16-14389. [CrossRef] [PubMed]

8.

H. Pan, A. Beling, and J. C. Campbell, “High-linearity uni-traveling-carrier photodiodes,” IEEE Photon. Technol. Lett. 21(24), 1855–1857 (2009). [CrossRef]

9.

A. Hastings, D. A. Tulchinsky, and K. J. Williams, “Photodetector nonlinearities due to voltage dependent responsivity,” IEEE Photon. Technol. Lett. 21(21), 1642–1644 (2009). [CrossRef]

10.

N. Shamir and D. Ritter, “Low electric field hole impact ionization coefficients in GaInAs and GaInAsP,” IEEE Electron Device Lett. 21(11), 509–511 (2000). [CrossRef]

11.

H. Pan, Z. Li, A. Beling, and J. C. Campbell, “Measurement and modeling of high-linearity modified uni-traveling carrier photodiode with highly-doped absorber,” Opt. Express 17(22), 20221–20226 (2009), http://www.opticsinfobase.org/abstract.cfm?uri=oe-17-22-20221. [CrossRef] [PubMed]

12.

M. N. Draa, J. Ren, D. C. Scott, W. S. C. Chang, and P. K. L. Yu, “Three laser two-tone setup for measurement of photodiode intercept points,” Opt. Express 16(16), 12108–12113 (2008), http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-16-16-12108. [CrossRef] [PubMed]

13.

H. Pan, A. Beling, H. Chen, and J. C. Campbell, “The frequency behavior of the intermodulation distortions of modified uni-traveling-carrier photodiodes based on modulated voltage measurements,” IEEE J. Quantum Electron. 45(3), 273–277 (2009). [CrossRef]

14.

J. Klamkin, A. Ramaswamy, Y.-C. Chang, L. A. Johansson, M. M. Dummer, J. E. Bowers, S. P. DenBaars, and L. A. Coldren, “Uni-traveling-carrier photodiodes with increased output response and low intermodulation distortion,” in Proceedings of IEEE International Topical Meeting on Microwave Photonics (IEEE, 2007), pp. 14–17.

15.

A. Beling, H. Pan, H. Chen, and J. C. Campbell, “Measurement and modeling of high-linearity partially depleted absorber photodiode,” Electron. Lett. 44(24), 1419–1420 (2008). [CrossRef]

16.

D. A. Tulchinsky, J. B. Boos, D. Park, P. G. Goetz, W. S. Rabinovich, and K. J. Williams, “High-current photodetectors as efficient, linear, and high-power RF output stages,” J. Lightwave Technol. 26(4), 408–416 (2008). [CrossRef]

17.

H. Jiang and P. K. L. Yu, “Equivalent circuit analysis of harmonic distortions in photodiode,” IEEE Photon. Technol. Lett. 10(11), 1608–1610 (1998). [CrossRef]

OCIS Codes
(040.5160) Detectors : Photodetectors
(060.5625) Fiber optics and optical communications : Radio frequency photonics

ToC Category:
Detectors

History
Original Manuscript: June 28, 2010
Revised Manuscript: July 24, 2010
Manuscript Accepted: July 26, 2010
Published: August 2, 2010

Citation
Meredith N. Draa, Jeffrey Bloch, Dingbo Chen, David C. Scott, Nong Chen, Steven Bo Chen, Xucai Yu, William S. Chang, and Paul K. L. Yu, "Novel directional coupled waveguide photodiode–concept and preliminary results," Opt. Express 18, 17729-17735 (2010)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-18-17-17729


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References

  1. D. C. Scott, T. A. Vang, J. Elliott, D. Forbes, J. Lacey, K. Everett, F. Alvarez, R. Johnson, A. Krispin, J. Brock, L. Lembo, H. Jiang, D. S. Shin, J. T. Zhu, and P. K. L. Yu, “Measurement of IP3 in p-i-n photodetectors and proposed performance requirements for RF fiber-optic links,” IEEE Photon. Technol. Lett. 12(4), 422–424 (2000). [CrossRef]
  2. H. Jiang and P. K. L. Yu, “Waveguide integrated photodiode for analog fiber-optic links,” IEEE Trans. Microw. Theory Tech. 48(12), 2604–2610 (2000). [CrossRef]
  3. T. Ohno, H. Fukano, Y. Muramoto, T. Ishibashi, T. Yoshimatsu, and Y. Doi, “Measurement of intermodulation distortion in a unitraveling-carrier refracting-facet photodiode and a p-i-n refracting facet photodiode,” IEEE Photon. Technol. Lett. 14(3), 375–377 (2002). [CrossRef]
  4. J. Klamkin, Y.-C. Chang, A. Ramaswamy, L. A. Johansson, J. E. Bowers, S. P. DenBaars, and L. A. Coldren, “Output saturation and linearity of waveguide unitraveling-carrier photodiodes,” IEEE J. Quantum Electron. 44(4), 354–359 (2008). [CrossRef]
  5. S. Demiguel, N. Li, X. Li, X. Zheng, J. Kim, J. C. Campbell, H. Lu, and A. Anselm, “Very high-responsivity evanescently coupled photodiodes integrating a short planar multimode waveguide for high-speed applications,” IEEE Photon. Technol. Lett. 15(12), 1761–1763 (2003). [CrossRef]
  6. A. Umbach, D. Trommer, R. Steingruber, A. Seeger, W. Ebert, and G. Unterborsch, “Ultrafast, high-power 1.55µm side-illuminated photodetector with integrated spot size converter,” in Optical Fiber Communication conference, 2000 OSA Technical Digest Series (Optical Society of America, 2000), paper FG2–1.
  7. M. N. Draa, J. Bloch, D. C. Scott, N. Chen, S. B. Chen, W. S. C. Chang, and P. K. L. Yu, “Behaviors of the third order intercept point for p-i-n waveguide photodiodes,” Opt. Express 17(16), 14389–14394 (2009), http://www.opticsinfobase.org/abstract.cfm?uri=oe-17-16-14389 . [CrossRef] [PubMed]
  8. H. Pan, A. Beling, and J. C. Campbell, “High-linearity uni-traveling-carrier photodiodes,” IEEE Photon. Technol. Lett. 21(24), 1855–1857 (2009). [CrossRef]
  9. A. Hastings, D. A. Tulchinsky, and K. J. Williams, “Photodetector nonlinearities due to voltage dependent responsivity,” IEEE Photon. Technol. Lett. 21(21), 1642–1644 (2009). [CrossRef]
  10. N. Shamir and D. Ritter, “Low electric field hole impact ionization coefficients in GaInAs and GaInAsP,” IEEE Electron Device Lett. 21(11), 509–511 (2000). [CrossRef]
  11. H. Pan, Z. Li, A. Beling, and J. C. Campbell, “Measurement and modeling of high-linearity modified uni-traveling carrier photodiode with highly-doped absorber,” Opt. Express 17(22), 20221–20226 (2009), http://www.opticsinfobase.org/abstract.cfm?uri=oe-17-22-20221 . [CrossRef] [PubMed]
  12. M. N. Draa, J. Ren, D. C. Scott, W. S. C. Chang, and P. K. L. Yu, “Three laser two-tone setup for measurement of photodiode intercept points,” Opt. Express 16(16), 12108–12113 (2008), http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-16-16-12108 . [CrossRef] [PubMed]
  13. H. Pan, A. Beling, H. Chen, and J. C. Campbell, “The frequency behavior of the intermodulation distortions of modified uni-traveling-carrier photodiodes based on modulated voltage measurements,” IEEE J. Quantum Electron. 45(3), 273–277 (2009). [CrossRef]
  14. J. Klamkin, A. Ramaswamy, Y.-C. Chang, L. A. Johansson, M. M. Dummer, J. E. Bowers, S. P. DenBaars, and L. A. Coldren, “Uni-traveling-carrier photodiodes with increased output response and low intermodulation distortion,” in Proceedings of IEEE International Topical Meeting on Microwave Photonics (IEEE, 2007), pp. 14–17.
  15. A. Beling, H. Pan, H. Chen, and J. C. Campbell, “Measurement and modeling of high-linearity partially depleted absorber photodiode,” Electron. Lett. 44(24), 1419–1420 (2008). [CrossRef]
  16. D. A. Tulchinsky, J. B. Boos, D. Park, P. G. Goetz, W. S. Rabinovich, and K. J. Williams, “High-current photodetectors as efficient, linear, and high-power RF output stages,” J. Lightwave Technol. 26(4), 408–416 (2008). [CrossRef]
  17. H. Jiang and P. K. L. Yu, “Equivalent circuit analysis of harmonic distortions in photodiode,” IEEE Photon. Technol. Lett. 10(11), 1608–1610 (1998). [CrossRef]

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