OSA's Digital Library

Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 16, Iss. 18 — Sep. 1, 2008
  • pp: 14227–14232
« Show journal navigation

Interference cancellation technique of optical AND gate receiver using optical thyristor

Tae-Gu Kang  »View Author Affiliations


Optics Express, Vol. 16, Issue 18, pp. 14227-14232 (2008)
http://dx.doi.org/10.1364/OE.16.014227


View Full Text Article

Acrobat PDF (166 KB)





Browse Journals / Lookup Meetings

Browse by Journal and Year


   


Lookup Conference Papers

Close Browse Journals / Lookup Meetings

Article Tools

Share
Citations

Abstract

We demonstrate an interference cancellation technique of optical AND gate receiver using optical thyristor for fiber-optic code division multiple access (FO-CDMA) systems. In particular, we fabricate the optical thyristor operating as optical hard-limiter and evaluate that the optical AND gate receiver using fabricated optical thyristor excludes the peaks of side-lobe and cross-correlation result in the system performance degradation. It found that the optical AND gate receiver using optical thyristor excludes the intensity of interference signal resulting in that the peaks of side-lobe and cross-correlation can be fully eliminated for any two users. Therefore, the optical AND gate receiver using optical thyristor is shown to be effective to accommodate more simultaneous users.

© 2008 Optical Society of America

1. Introduction

The success of optical signal processing based on fiber optic delay elements in optical sensors and optical computing has prompted an intense interest in their use in all-optical communications networks [1

1. P. Azmi, M. Nasiri-Kenar, and J. A. Salehi, “Internally Channel-Coded Framed Time-Hopping Fiber-Optic CDMA Communications,” J. Lightwave Technol. 23, 3702–3707 (2005). [CrossRef]

]. Like other spread spectrum systems, the FO-CDMA receiver suffers from interferences of other simultaneous users, which is called multiple-access interference (MAI). Because the FO-CDMA is interference limited system, the number of simultaneous users is much less than the number of subscribers. Many schemes have been proposed to increase the number of simultaneous users [2

2. E. S. Shivaleela, A. Selvarajan, and T. Srinivas, “Two-Dimensional Optical Orthogonal Codes for Fiber-Optic CDMA Networks,” J. Lightwave Technol. 23, 647–654 (2005). [CrossRef]

, 3

3. H. M. H. Shalaby, “Performance analysis of an optical CDMA random access protocol,” J. Lightwave Technol. 22, 1233–1241 (2004). [CrossRef]

]. Among various optical CDMA techniques introduced to date, FO-CDMA using optical orthogonal codes, and their possible variations, has received much attention due to their simple structure and compatibility with today’s intensity modulation/direct-detection fiber-optic transmission system [4

4. A. Keshavarzian and J. A. Salehi, “Optical Orthogonal Code Acquisition in Fiber-Optic CDMA Systems via the Simple Serial-Search Method,” IEEE Trans. Commun. 50, 473–483 (2002). [CrossRef]

-6

6. F. R. K. Chung, J. A. Salehi, and V. K. Wei, “Optical orthogonal codes: Design, analysis, and applications,” IEEE Trans. Inform. Theory IT-35, 595–604 (1989). [CrossRef]

].

Furthermore, the auto-correlation of each sequence exhibits a narrow main-lobe and adequately small side-lobes, and the cross-correlation between any two sequences always remains small. Also, the peaks of side-lobe and cross-correlation are designed to be constant by adjusting the length of optical delay line (ODL). However, optical receivers with conventional structure present the peaks of side-lobe and cross-correlation according to time delay when optical decoder detects the desired signal from encoded optical signal. These peaks degrade the system performance and make it difficult to detect desired signal [7

7. J. A. Salehi, “Optical CDMA via Temporal Code”, IEEE Trans. Commun. 40, 1162–1170 (1992). [CrossRef]

,11

11. C. C. Chang, H. P. Sardesai, and A. M. Weiner, “Code-Division Multiple-Access Encoding and Decoding of Femtosecond Optical Pulses over a 2.5-km Fiber Link,” IEEE Photon. Technol. Lett. 10, 171–173 (1998). [CrossRef]

]. If the peaks of side-lobe and cross-correlation can be minimized or eliminated, the system performance of FO-CDMA can be much improved. Figure 1 shows the optical AND gate receiver using optical thyristor for FO-CDMA system. The optical AND gate receiver using optical thyristor reduces drastically the intensities of interference signals. Therefore, we analyze the correlation properties of the FO-CDMA system with the optical AND gate receiver using optical thyristor, and found that the superior performance with increased optical codes can be obtained.

Fig. 1. The block diagram of AND gate receiver using optical thyristor

2. Optical thyristor operating as optical hard-limiter

An optical thyristor with a very thin layer and PnpN hetrojunction is an optical device with fast switching speed as shown in Fig. 2. When the light is given to the optical thyristor in OFF state, current-voltage characteristic curve moves from C1 to C2 or C3 according to input light intensity. The C1 is the I-V curve without optical input, and other curves (C2, C3) are the I-V curves with optical inputs. At this time, the optical thyristor still remains in OFF state by the light moving the current-voltage (I-V) curve to C2, but the optical thyristor turns into ON state by the light moving the I-V curve to C3. Accordingly, the operating point changes from S1 (OFF-state) to S2 (ON-state), and the optical thyristor emits the light of constant intensity [9

9. K. D. Choquette, R. P. Schneider, K. L. Lear, and K. M. Geib, “Low threshold voltage vertical-cavity lasers fabricated by selective oxidation,” Electron. Lett. 30, 2043–2044 (1994). [CrossRef]

]. This emission results from the external voltage (VD) and resistor. Moreover, because the light intensity emitted is constant regardless of applied light intensity, it can serve as an optical hard-limiter which is applicable to FO-CDMA system. Among these optical thyristors, the PnpN optical thyristor has more increased optical sensitivity and faster operation than conventional optical thyristor. Therefore, PnpN optical thyristor can be used as the optical hard-limiter.

Fig. 2. Typical S-shape I-V characteristics of an optical thyristor operating as optical hard-limiter

The vertical-cavity laser (VCL)-depleted optical thyristor (DOT) shown in Fig. 1 was grown on n-GaAs substrates by metal organic chemical vapor deposition (MOCVD). These devices have a PnpN triple junction structure with two distributed Bragg reflector (DBR) mirrors consisting of Al0.9Ga0.1As/Al0.16Ga0.84As layers with linearly graded transition layers. The alloy composition grading allows reduction in the series resistance of the devices. The cavity space between the top and the bottom mirrors is 4λ, where λ is the emission wavelength in the semiconductor medium. This device structure allows either electrical or optical switching from the OFF state to the ON state. During the ON state the VCL-DOT has low impedance and emits laser light. To increase the efficiency of optical emission, an undoped multiple quantum well layer has been incorporated as the active layer of the VCL-DOT. The active region also acts as an absorption region for optically switching the VCL-DOT. Although the active region is thin, enhancement of absorption is expected because of multi-reflection by the two DBR mirrors. The designed parameters such as doping concentration and layer thickness of the each active layer were simulated using a finite difference method. The top ohmic contact was fabricated using a lift-off process of Ti-Au (20 nm/150 nm), and the bottom was contacted with AuGe-Ni-Au (40 nm/20 nm/150 nm) located on the substrate. To pattern the devices, reactive ion etching was used to etch square mesas ranging in size from 30X30 to 60X60 µm with a size variation of 0.5 um. The VCL-DOTs are then placed in a wet thermal oxidation furnace to laterally oxidize the current confinement layer and anneal the ohmic contacts.

3. Results and discussion

We have experimentally investigated the optical AND gate receiver using optical thyristor, which minimizes or eliminates the peaks of side-lobe and cross-correlation result in the system performance degradation. Also, we discuss a means of reducing the effective MAI signals by placing the VCL-DOT in the optical AND gate receiver. Previously, optical receivers with conventional structure present the overlapping signals according to time delay when optical decoder detects the desired signal from encoded optical signals. The overlapping signals in the channel and the peaks of side-lobe due to decoding processing degrade the system performance and make it difficult to detect desired signal [4

4. A. Keshavarzian and J. A. Salehi, “Optical Orthogonal Code Acquisition in Fiber-Optic CDMA Systems via the Simple Serial-Search Method,” IEEE Trans. Commun. 50, 473–483 (2002). [CrossRef]

, 7

7. J. A. Salehi, “Optical CDMA via Temporal Code”, IEEE Trans. Commun. 40, 1162–1170 (1992). [CrossRef]

]. If the overlapping signals in the channel and the peaks of side-lobe due to decoding processing can be eliminated, the performance of FO-CDMA system can be much improved. In this work, we demonstrate the oxidized PnpN VCL-DOT operating as optical hard-limiter in the optical AND gate receiver. In order to exclude the peaks of side-lobe and cross-correlation result in the system performance degradation, VCL-DOTs are placed before and after the ODL, as shown in Fig. 1. The first VCL-DOT placed in the optical AND gate receiver operates the intensities of pulses which are overlapped on the channel by MAI signals, as shown in Fig. 3(a).

Fig. 3. Optical input and the optical output pulses of (a) first and (b) second VCL-DOT placed in the optical AND gate receiver.

Fig. 4. Auto-correlation properties of (a) optical receiver with conventional structure and (b) optical AND gate receiver using optical thyristor when λ=1.

Fig. 5. Cross-correlation properties of (a) optical receiver with conventional structure and (b) optical AND gate receiver using optical thyristor when λ=1.

4. Conclusion

Acknowledgment

This work was supported by the Brain Korea 21 project.

References and links

1.

P. Azmi, M. Nasiri-Kenar, and J. A. Salehi, “Internally Channel-Coded Framed Time-Hopping Fiber-Optic CDMA Communications,” J. Lightwave Technol. 23, 3702–3707 (2005). [CrossRef]

2.

E. S. Shivaleela, A. Selvarajan, and T. Srinivas, “Two-Dimensional Optical Orthogonal Codes for Fiber-Optic CDMA Networks,” J. Lightwave Technol. 23, 647–654 (2005). [CrossRef]

3.

H. M. H. Shalaby, “Performance analysis of an optical CDMA random access protocol,” J. Lightwave Technol. 22, 1233–1241 (2004). [CrossRef]

4.

A. Keshavarzian and J. A. Salehi, “Optical Orthogonal Code Acquisition in Fiber-Optic CDMA Systems via the Simple Serial-Search Method,” IEEE Trans. Commun. 50, 473–483 (2002). [CrossRef]

5.

W. Huang, I. Andonovic, and M. Tur, “Code acquisition in coherent optical pulse CDMA systems utilizing coherent correlation demodulation,” IEEE Trans. Commun. 48, 611–621 (2000) [CrossRef]

6.

F. R. K. Chung, J. A. Salehi, and V. K. Wei, “Optical orthogonal codes: Design, analysis, and applications,” IEEE Trans. Inform. Theory IT-35, 595–604 (1989). [CrossRef]

7.

J. A. Salehi, “Optical CDMA via Temporal Code”, IEEE Trans. Commun. 40, 1162–1170 (1992). [CrossRef]

8.

M. Kuijk, P. L. Heremans, G. Borghs, and R. Vounckx, “Depleted double-heterojunction optical thyristor”, Appl. Phys. Lett. 64, 2073–2075 (1994). [CrossRef]

9.

K. D. Choquette, R. P. Schneider, K. L. Lear, and K. M. Geib, “Low threshold voltage vertical-cavity lasers fabricated by selective oxidation,” Electron. Lett. 30, 2043–2044 (1994). [CrossRef]

10.

T. Numai, M. Sugimoto, I. Ogura, H. Kosaka, and K. Kasahara, “Surface-emitting laser operation in vertical-to-surface transmission electrophotonic devices with a vertical cavity,” Appl. Phys. Lett. 58, 1250–1252 (1991). [CrossRef]

11.

C. C. Chang, H. P. Sardesai, and A. M. Weiner, “Code-Division Multiple-Access Encoding and Decoding of Femtosecond Optical Pulses over a 2.5-km Fiber Link,” IEEE Photon. Technol. Lett. 10, 171–173 (1998). [CrossRef]

12.

D. Zaccarin and M. Kavehrad, “An optical CDMA system based on spectral encoding of LED,” IEEE Photon. Technol. Lett. 5, 479–482 (1993). [CrossRef]

OCIS Codes
(060.2330) Fiber optics and optical communications : Fiber optics communications
(070.4550) Fourier optics and signal processing : Correlators
(250.7260) Optoelectronics : Vertical cavity surface emitting lasers
(350.4600) Other areas of optics : Optical engineering

ToC Category:
Fiber Optics and Optical Communications

History
Original Manuscript: June 20, 2008
Revised Manuscript: August 11, 2008
Manuscript Accepted: August 22, 2008
Published: August 27, 2008

Citation
Tae-Gu Kang, "Interference cancellation technique of optical AND gate receiver using optical thyristor," Opt. Express 16, 14227-14232 (2008)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-16-18-14227


Sort:  Author  |  Year  |  Journal  |  Reset  

References

  1. P. Azmi, M. Nasiri-Kenar, and J. A. Salehi, "Internally Channel-Coded Framed Time-Hopping Fiber-Optic CDMA Communications," J. Lightwave Technol. 23, 3702-3707 (2005). [CrossRef]
  2. E. S. Shivaleela, A. Selvarajan, and T. Srinivas, "Two-Dimensional Optical Orthogonal Codes for Fiber-Optic CDMA Networks," J. Lightwave Technol. 23, 647-654 (2005). [CrossRef]
  3. H. M. H. Shalaby, "Performance analysis of an optical CDMA random access protocol," J. Lightwave Technol. 22,1233-1241 (2004). [CrossRef]
  4. A. Keshavarzian and J. A. Salehi, "Optical Orthogonal Code Acquisition in Fiber-Optic CDMA Systems via the Simple Serial-Search Method," IEEE Trans. Commun. 50, 473-483 (2002). [CrossRef]
  5. W. Huang, I. Andonovic, and M. Tur, "Code acquisition in coherent optical pulse CDMA systems utilizing coherent correlation demodulation," IEEE Trans. Commun. 48, 611-621 (2000). [CrossRef]
  6. F. R. K. Chung, J. A. Salehi, and V. K. Wei, "Optical orthogonal codes: Design, analysis, and applications," IEEE Trans. Inform. Theory IT-35, 595-604 (1989). [CrossRef]
  7. J. A. Salehi, "Optical CDMA via Temporal Code," IEEE Trans. Commun. 40, 1162-1170 (1992). [CrossRef]
  8. M. Kuijk, P. L. Heremans, G. Borghs, and R. Vounckx, "Depleted double-heterojunction optical thyristor," Appl. Phys. Lett. 64, 2073-2075 (1994). [CrossRef]
  9. K. D. Choquette, R. P. SchneiderJr., K. L. Lear, and K. M. Geib, "Low threshold voltage vertical-cavity lasers fabricated by selective oxidation," Electron. Lett. 30, 2043-2044 (1994). [CrossRef]
  10. T. Numai, M. Sugimoto, I. Ogura, H. Kosaka, and K. Kasahara, "Surface-emitting laser operation in vertical-to-surface transmission electrophotonic devices with a vertical cavity," Appl. Phys. Lett. 58, 1250-1252 (1991). [CrossRef]
  11. C. C. Chang, H. P. Sardesai, and A. M. Weiner, "Code-Division Multiple-Access Encoding and Decoding of Femtosecond Optical Pulses over a 2.5-km Fiber Link," IEEE Photon. Technol. Lett. 10, 171-173 (1998). [CrossRef]
  12. D. Zaccarin and M. Kavehrad, "An optical CDMA system based on spectral encoding of LED," IEEE Photon. Technol. Lett. 5, 479-482 (1993). [CrossRef]

Cited By

Alert me when this paper is cited

OSA is able to provide readers links to articles that cite this paper by participating in CrossRef's Cited-By Linking service. CrossRef includes content from more than 3000 publishers and societies. In addition to listing OSA journal articles that cite this paper, citing articles from other participating publishers will also be listed.


« Previous Article  |  Next Article »

OSA is a member of CrossRef.

CrossCheck Deposited