Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
2001-05-08
2003-11-11
Schwartz, Jordan M. (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C359S247000, C359S245000
Reexamination Certificate
active
06646775
ABSTRACT:
BACKGROUND OF THE INVENTION
(a) Field of the Invention
The present invention relates to a light source integrated with a modulator and a module for optical communication, and especially to the structure for the light source integrated with the modulator and suitable for a light source for long distance trunk used in wavelength division multiplexing (WDM).
(b) Description of the Related Art
As a light source for long distance trunk used in WDM, a module is put into practice which includes a distributed feedback semiconductor laser (DFB-LD) and a field absorbing modulator (MOD) on a single semiconductor substrate. This type of light source can realizes the transmission speed as high as 2.5 Gb/s and has been vigorously researched.
A resistance to distribution or an ability of transmitting long-distance signals in the DFB-LD is the most important parameter exhibiting element performance. The selection of products having no defect therein is currently conducted by measuring the resistance to distribution or the power penalty after the transmission of each element. It is an important subject to increase the yield of the selection for decreasing the cost of the light source.
Murotani et al. reported the dependency of the single mode yield of the DFB/MOD module having an asymmetrical &lgr;/4 phase shifter (a structure obtained by moving the &lgr;/4 phase shift region of the diffraction grating from the central position of the DFB-LD, hereinafter referred to as “asymmetrical &lgr;/4-D-FB/MOD”) on a &kgr;L value of a diffraction grating in the DFB-LD in the Electronics Society Meeting (C-4-15, p242) held in September 1999 by the Institute of Electronics, Information and Communication Engineers.
As shown in
FIG. 1
, the single mode yield rapidly decreases with the increase of the &kgr;L in the asymmetrical &lgr;/4-DFB/MOD module. Conventional publications including the above publication describe neither the yield of the power source integrated with the modulator separately from the single mode yield, nor the optimum structure regarding determination of the facet reflection rate and of the &kgr;L. The optimum structure has not been conventionally established by considering the dependency of the diffraction grating on the &kgr;L value and the dependency of the modulator on the facet reflection rate.
SUMMARY OF THE INVENTION
In view of the foregoing, an object of the present invention is to increase the yield of obtaining DFB/MOD module having no defect by considering the dependency of the &kgr;L value of the diffraction grating on the single mode yield and the transmission yield and the dependency of the modulator on the facet reflection rate.
The present invention provides an optical device including: a substrate; a distributed feedback (DFB) semiconductor laser formed on the substrate and including a diffraction grating having an asymmetrical &lgr;/4 phase shift region, the diffraction grating extending along an optical axis of the DFB semiconductor laser; and a field absorbing modulator integrated with the DFB semiconductor laser on the substrate for modulating a light wave emitted from the DFB semiconductor laser, the modulator having a facet reflection rate between 0.01 and 0.02% at an output end thereof, the diffraction grating having a &kgr;L value between 1.4 and 1.7.
In another aspect of the present invention, the facet reflection rate of the output end of the modulator is in a range between 0.02 and 0.03%, and the &kgr;L value of the diffraction grating is between 1.2 and 1.3.
In a further aspect of the present invention, the facet reflection rate of the output end of the modulator is in a range between 0.03 and 0.05%, and the &kgr;L value of the diffraction grating is between 1.3 and 1-4.
In a still further aspect of the present invention, the facet reflection rate of the output end of the modulator is in a range between 0.05 and 0.1%, and the &kgr;L value of the diffraction grating is between 1.4 and 1.7.
In accordance with the present invention, the proper combinations of the &kgr;L value of the diffraction grating and the reflection rate of the output facet of the modulator of the DFB semiconductor laser can fabricate the source for integrating the modulator having the excellent quality with a higher yield and lower cost.
The above and other objects, features and advantages of the present invention will be more apparent from the following description.
REFERENCES:
patent: 4873691 (1989-10-01), Uomi et al.
patent: 2001/0005391 (2001-06-01), Sakata
patent: 2001/0019568 (2001-09-01), Sakata
M. Yamaguchi et al., “Requirements for Modular-Integrated DFB LD's for Penalty-Free 2.5-Gb/s Transmission”, Journal of Lightwave Technology, vol. 13, No. 10, (Oct. 1995), pp. 1948-1954 with Abstract.
Y. Kotaki et al., “Analysis of Static and Dynamic Wavelength Shifts in Modulator Integrated DFB Lasers”, Proceedings of the European Conference on Optical Communications, (Sep. 12, 1993), pp. 381-384 with Abstract.
O. Sahlen, “Optimization of DFB Lasers Integrated with Franz-Keldysh Absorption Modulators”, Journal of Lightwave Technology, vol. 12, No. 6, (Jun. 1, 1994), pp. 969-976 with Abstract.
M. Aoki et al., New Transmission Simulation of EA-Modulator Integrated DFB-Lasers Considering the Facet Reflection-Induced Chirp, IEEE Phontonics Technology Letters, vol. 9, No. 3, (Mar. 1997), pp. 380-382 with Abstract.
J. Hashimoto et al., “Influence of Facet Reflection on the Performance of a DFB Laser Integrated with an Optical Amplifier/Modulator”, IEEE Journal of Quantum Electronics, vol. 28, No. 3, (Mar. 1992), pp. 594-603 with Abstract.
NEC Corporation
Schwartz Jordan M.
Shultz Jessica
Sughrue & Mion, PLLC
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