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Optics Express

Optics Express

  • Editor: Michael Duncan
  • Vol. 12, Iss. 4 — Feb. 23, 2004
  • pp: 601–608
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Multi-port polarization-independent optical quasi-circulators by using a pair of holographic spatial- and polarization- modules

Jing-Heng Chen, Po-Jen Hsieh, Der-Chin Su, and Jung-Chieh Su  »View Author Affiliations


Optics Express, Vol. 12, Issue 4, pp. 601-608 (2004)
http://dx.doi.org/10.1364/OPEX.12.000601


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Abstract

In this paper we proposed an alternative type of multi-port polarization-independent optical quasi-circulator by using a pair of holographic spatial- and polarization- modules. The prototype is fabricated and experimentally tested. In addition, the operating principles, the characteristics and the performances of this device are discussed. The merits of this design include polarization-independence, compactness, high isolation, low polarization mode dispersion, and easy fabrication. Furthermore, the number of ports can be scaled up easily.

© 2004 Optical Society of America

1. Introduction

2. Principles

Fig. 1. Structure and operation principle of the holographic spatial walk-off polarizer.

In this paper, we propose a new HSPM, which is composed of a pair of HSWPs, a 45° Faraday rotator, and a 45° half-wave plate. The operation characteristic of the HSPM is shown in Fig. 2. For easy understanding, a circle with a bisecting line is used to represent the associated states of polarization (SOP) of the light after propagating through each component. An orthogonal x-z coordinate system with an unit distance L is utilized to characterize the beam propagation direction and the associated spatial location. Symbols ⦶ and ⊖ represent the electric-field polarizations which lie in the planes perpendicular (s-polarization) and parallel (p-polarization) to the paper plane, respectively. The symbol ⊕ represents the light beam that has both s- and p- polarized components.

Fig. 2. Structure and operation characteristics of the holographic spatial- and polarization- module.

In Fig. 2(a), when an unpolarized light is incident along the +z direction on the HSPM, the s- component passes through the first HSWP directly. On the other hand, the p- component passes through this HSWP after two diffractions and two total-reflections. Next, these two orthogonally polarized components pass through FR and H. Their SOPs are rotated a total of 90°, +45° by FR and +45° by H. These two components finally enter the second HSWP and then recombine together at the output with the similar diffraction and total-reflection effects in the first HSWP. Therefore, the outgoing unpolarized light of this HSPM is shifted spatially with a distance L along +x direction. In Fig. 2(b), when an unpolarized light is incident along the -z direction on the HSPM, the s- component passes through the first HSWP directly and the p- component also passes through this HSWP after two diffractions and two total-reflections. Next, these two orthogonally polarized components pass through H and FR. Their SOPs are rotated a total of 0°, -45° by H and +45° by FR. Finally, the s- component passes through the second HSWP straightly; the p- component passes through the second HSWP after two diffractions and two total-reflections more. Therefore, the s- component is transmitted straightly of this HSPM while the p- component is shifted spatially with a distance 2L along -x direction and then transmitted. Based on the same principles, we connect a pair of HSPMs sequentially, their operation characteristic is shown in Fig. 3(a) and (b). In Fig. 3(a), when an unpolarized light is incident along the +z direction on these HSPMs, the outgoing unpolarized light is shifted spatially with a distance 2L along +x direction and then transmitted. In Fig. 3(b), when an unpolarized light is incident along the -z direction on these HSPMs, the s- component is transmitted straightly while the p- component is shifted spatially with a distance 4L along the -x direction and then transmitted.

[xs(2n1)xp(2n1)]=[2(n1)L2(1n)L],(foranoddport)
(1)
[xs(2n)xp(2n)]=[2L2(2n)L].(foranevenport)
(2)
Fig. 3. Structure and operation characteristics of the series connected holographic spatial- and polarization- modules.
Fig. 4. Operation characteristics of the series connected holographic spatial- and polarization- modules when an unpolarized light is shuttled between its two sides.

It is obvious that if some polarization-beam splitters (PBSs), and reflection prisms (RPs) are introduced appropriately at the corresponding positions of the s- and p- components, we can obtain a multi-port optical quasi-circulator. Shown in Fig. 5 is an optical quasi-circulator with 2n-ports consisting of a pair of HSPMs, PBSs, and RPs. According to equations (1) and (2), the introduced PBSs and RPs at the j-th port are located at (xPBSj, zPBSj) and (xRPj, zRPj), which can be expressed as

[xPBS(2n1)zPBS(2n1)xRP(2n1)zRP(2n1)]=[2(n1)L(2n4)L2(1n)L(2n4)L],(foranoddport)
(3)
[xPBS(2n)zPBS(2n)xRP(2n)zRP(2n)]=[2nL(2n+4)L2(2n)L(2n+4)L],(foranevenport)
(4)

where n is a positive integer. Figure 5(a), (b), (c), and (d) show the routes of port 1→port 2, port 2→port 3, port 3→port 4, and port (2n-1)→port 2n, respectively. In these figures, symbols ⍁ and ⊿ represent a PBS and a RP. Other propagation routes can be obtained based on the similar principle.

Fig. 5. Structure and operation principles of the proposed multi-port optical quasi-circulator.

However, in the design of Fig. 5, the optical path of the p- component is larger than that of the s- component. This optical path difference might cause polarization mode dispersion (PMD) to blur the transmission signal. Therefore, in order to solve the PMD problem, we change the original optical guiding paths in Fig. 5, and introduce two different guiding modules composed of PBSs and RPs for the odd and even ports, respectively, as shown in Fig. 6. The designs of these two guiding modules with specifications (Length×Width) of (4n-3)L×0.31(n-1)L and (4n-4)L×0.31(n-1)L for an odd and an even port are shown in Fig. 7(a) and (b), respectively. These guiding modules are located at (xMj, zMj) which can be expressed as

[xM(2n1)zM(2n1)]=[2(1n)L(2n4)L],(foranoddport)
(5)
[xM(2n)zM(2n)]=[2nL(2n+4)L],(foranevenport)
(6)

where n is a positive integer larger than 1. The coordinate in equation (5) corresponds to the center of the RP (in red color) in the odd-port guiding module; the coordinate in equation (6) corresponds to the center of the PBS (in green color) in the even-port guiding module. When the guiding modules are appropriately introduced, the optical path differences between the s- and p- components can be reduced to zero. Therefore, the PMD problem can be solved. Fig. 6(a), (b), (c), and (d) show the routes of port 1→port 2, port 2→port 3, port 3→port 4, and port (2n-1)→port 2n, respectively. Other propagation routes can be obtained based on the similar principle.

Fig. 6. Structure and operation principles of the proposed multi-port optical quasi-circulator without polarization mode dispersion.
Fig. 7. PBSs and RPs guiding modules for (a) the odd ports; (b) the even ports.

3. Experimental results and discussions

The characteristic parameters of this prototype device can be estimated from that of each component. The diffraction efficiencies of HSWPs, as mentioned above, are measured to be ηs=3% and ηp=90%. The transmittances of FR and H, which are commercial devices, are listed to be 0.95 and 0.97, respectively. Thus, the associated losses and isolation values of this optical quasi-circulator can be estimated, as shown in Table 1(a). In order to confirm the validity of this estimation, we have measured the insertion losses of the device. The measured values are correspondent well with the estimated values. If our fabricated HSWPs are anti-reflection coated and are under accurate fabrication processes, the reflection losses should be decreased to 0.1%, and the diffraction efficiencies may reach theoretical values [13

13. B. J. Chang, Optical information storage, Proc. SPIE , vol. 177, 71–81 (1979). [CrossRef]

], i.e., ηs≒0% and ηp≒100%. Under these two improved conditions, the performance of this 6-port optical quasi-circulator can be enhanced greatly, and the associated parameters are calculated and listed in Table 1(b) with ηs<1% and ηp>99%. In addition, the bandwidth of the HSWP at 1300nm central wavelength is 20nm. It should also be possible to design the central wavelength to be at 1550 nm wavelength range.

Table 1. Associated losses and isolation valuesa (in Decibels) of a 6-port quasi-circulator with wavelength 1300nm by using (a) our fabricated HSWPs; and (b) ideal HSWPs with anti-reflection coatings and diffraction efficiencies of ηs<1% and ηp>99%.

table-icon
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In order to solve the PMD problem, we appropriately introduce two different guiding modules composed of PBSs and RPs for the odd and even ports, respectively. However, if we want to fabricate more compact modules, these guiding devices should become smaller simultaneously. The result will increase the difficulty of device assembling. Expediently, we can increase the beam splitting distance L (L=2t tan θd) [2

2. J. H. Chen et al. “Holographic spatial walk-off polarizer and its application to a 4-port polarization-independent optical circulator,” Opt. Express 11, 2001–2006 (2003), http://www.opticsexpress.org/abstract.cfm?URI=OPEX-11-17-2001. [CrossRef] [PubMed]

] by increasing the thickness of the substrate to reduce the assembling difficulty. Another reliable method is to operate this device beginning with a high number port.

4. Conclusions

An alternative type of multi-port polarization-independent optical quasi-circulator by using a pair of holographic spatial- and polarization- modules (HSPMs) has been proposed. In order to demonstrate the feasibility, the prototype of a 6-port optical quasi-circulator operating at a wavelength of 1300nm was assembled. In addition, the operating principles and the performance of the proposed optical quasi-circulator have been described. This design has advantages of polarization-independence, compactness, high isolation, low polarization mode dispersion, and easy fabrication. Furthermore, the number of ports can be scaled up easily.

Acknowledgments

This research were supported partially by grants from the National Science Council of ROC under contract No. NSC-92-2215-E-009-052, and the Lee & MTI Center for Networking at the National Chiao Tung University, Taiwan, R. O. C.

References and links

1.

J. Hecht, Understanding fiber optics (Prentice Hall, New Jersey, 2002), Chap. 14.

2.

J. H. Chen et al. “Holographic spatial walk-off polarizer and its application to a 4-port polarization-independent optical circulator,” Opt. Express 11, 2001–2006 (2003), http://www.opticsexpress.org/abstract.cfm?URI=OPEX-11-17-2001. [CrossRef] [PubMed]

3.

N. Sugimoto et al. “Waveguide polarization-independent optical circulator,” IEEE Photon. Technol. Lett. 11, 355–357 (1999). [CrossRef]

4.

L. D. Wang, “High-isolation polarization-independent optical quasi-circulator with a simple structure,” Opt. Lett. 23, 549–551 (1998). [CrossRef]

5.

M. Koga, “Compact quartzless optical quasi-circulator,” Electron. Lett. 30, 1438–1440 (1994). [CrossRef]

6.

Y. K. Chen et al. “Low-crosstalk and compact optical add-drop multiplexer using a multiport circulator and fiber Bragg gratings,” IEEE Photon. Technol. Lett. 12, 1394–1396 (2000). [CrossRef]

7.

A. V. Tran et al. “A bidirectional optical add-drop multiplexer with gain using multiport circulators, fiber Bragg gratings, and a single unidirectional optical amplifier,” IEEE Photon. Technol. Lett. 15, 975–977 (2003). [CrossRef]

8.

D. K. Mynbaev and L. L. Scheiner, Fiber-optic communications technology (Prentice Hall, New Jersey, 2001), Chap. 6.

9.

Y. Sato and K. Aoyama, “OTDR in optical transmission systems using Er-doped fiber amplifiers containing optical circulators,” IEEE Photon. Technol. Lett. 3, 1001–1003 (1991). [CrossRef]

10.

J. Liu and R. T. Chen, “Path-reversed substrate-guided-wave optical interconnects for wavelength-division demultiplexing,” Appl. Opt. 38, 3046–3052 (1999) [CrossRef]

11.

R. Shechter, Y. Amitai, and A. A. Friesem, “Compact wavelength division multiplexers and demultiplexers,” Appl. Opt. 41, 1256–1261 (2002). [CrossRef] [PubMed]

12.

H. Kogelnik, “Coupled wave theory for thick hologram gratings,” Bell Syst. Tech. J. 48, 2909–2947 (1969).

13.

B. J. Chang, Optical information storage, Proc. SPIE , vol. 177, 71–81 (1979). [CrossRef]

OCIS Codes
(060.4510) Fiber optics and optical communications : Optical communications
(090.2890) Holography : Holographic optical elements
(260.5430) Physical optics : Polarization

ToC Category:
Research Papers

History
Original Manuscript: January 6, 2004
Revised Manuscript: February 7, 2004
Published: February 23, 2004

Citation
Jing-Heng Chen, Po-Jen Hsieh, Der-Chin Su, and Jung-Chieh Su, "Multi-port polarization-independent optical quasi-circulators by using a pair of holographic spatial- and polarization- modules," Opt. Express 12, 601-608 (2004)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-12-4-601


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References

  1. J. Hecht, Understanding fiber optics (Prentice Hall, New Jersey, 2002), Chap. 14.
  2. J. H. Chen et al. �??Holographic spatial walk-off polarizer and its application to a 4-port polarization-independent optical circulator,�?? Opt. Express 11, 2001-2006 (2003), <a href="http://www.opticsexpress.org/abstract.cfm?URI=OPEX-11-17-2001.">http://www.opticsexpress.org/abstract.cfm?URI=OPEX-11-17-2001.</a> [CrossRef] [PubMed]
  3. N. Sugimoto et al. �??Waveguide polarization-independent optical circulator,�?? IEEE Photon. Technol. Lett. 11, 355-357 (1999). [CrossRef]
  4. L. D. Wang, �??High-isolation polarization-independent optical quasi-circulator with a simple structure,�?? Opt. Lett. 23, 549-551 (1998). [CrossRef]
  5. M. Koga, �??Compact quartzless optical quasi-circulator,�?? Electron. Lett. 30, 1438-1440 (1994). [CrossRef]
  6. Y. K. Chen et al. �??Low-crosstalk and compact optical add-drop multiplexer using a multiport circulator and fiber Bragg gratings,�?? IEEE Photon. Technol. Lett. 12, 1394-1396 (2000). [CrossRef]
  7. A. V. Tran et al. �??A bidirectional optical add-drop multiplexer with gain using multiport circulators, fiber Bragg gratings, and a single unidirectional optical amplifier,�?? IEEE Photon. Technol. Lett. 15, 975-977 (2003). [CrossRef]
  8. D. K. Mynbaev, and L. L. Scheiner, Fiber-optic communications technology (Prentice Hall, New Jersey, 2001), Chap. 6.
  9. Y. Sato and K. Aoyama, �??OTDR in optical transmission systems using Er-doped fiber amplifiers containing optical circulators,�?? IEEE Photon. Technol. Lett. 3, 1001-1003 (1991). [CrossRef]
  10. J. Liu and R. T. Chen, �??Path-reversed substrate-guided-wave optical interconnects for wavelength-division demultiplexing,�?? Appl. Opt. 38, 3046-3052 (1999). [CrossRef]
  11. R. Shechter, Y. Amitai, and A. A. Friesem, �??Compact wavelength division multiplexers and demultiplexers,�?? Appl. Opt. 41, 1256-1261 (2002). [CrossRef] [PubMed]
  12. H. Kogelnik, �??Coupled wave theory for thick hologram gratings,�?? Bell Syst. Tech. J. 48, 2909-2947 (1969).
  13. B. J. Chang, Optical information storage, Proc. SPIE, vol. 177, 71-81 (1979). [CrossRef]

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