INVITED PAPER
Special Section on Photonic Technologies for Access NetworksOptical Feedback-Tolerant Gain-Coupled DFB Lasers for
Isolator-Free Modules in the Access Networks
Koji NAKAMURA†a), Satoshi MIYAMURA†, and Hiroki YAEGASHI†, Nonmembers
SUMMARY Passive optical network topology has been widely adopted in access networks due to its low-cost and yet flexible network structure. To further promote the passive optical networks, the cost reduction of optical modules is critical. Relatively expensive combination of a conventional index-coupled distributed feedback laser diode (IC-DFB-LD) and an opti-cal isolator is commonly used for passive optiopti-cal networks with transmis-sion distance more than 30 km. Although gain-coupled DFB-LDs (GC-DFB-LD) have been widely investigated in the hope of eliminating the isolator in optical modules, their limited output power keeps them from practical use in passive optical networks. In this paper, we describe the de-velopment of 1.31μm and 1.49 μm GC-DFB-LDs with high output power and optical feed back tolerance for isolator-free optical modules in ac-cess networks. The relative intensity noise (RIN) degradation was well suppressed below−120 dB/Hz at −8 dB optical feedback in the tempera-tures range from 0◦C to 85◦C from both 1.31μm and 1.49 μm GC-DFB-LDs. Optical feedback tolerance of 1.31μm and 1.49 μm GC-DFB-LDs were improved by more than 6 dB and 4 dB as compared with conventional IC-DFB-LDs. Dispersion power penalty after over 30 km transmission at 1.25 Gbps were achieved less than 0.3 dB and 0.7 dB under−15 dB opti-cal feedback conditions. The proposed 1.31μm GC-DFB-LD prototypes experimentally demonstrated 14 mW output power with over 5,000-hour operation at 85◦C. Our devices are found to fully complying IEEE 802.3ah standard and seem to be promising for the low-cost optical modules in long-reach access network applications. The details of the device structure as well as transmission experiments are also reported.
key words: gain coupled distributed feedback lasers, relative intensity noise, optical isolators, optical feedback semiconductor lasers
1. Introduction
Passive optical network (PON) is a very cost-effective net-work topology since many subscribers share the common single-mode optical fiber connected to an optical line ter-minal (OLT). The addition of subscribers is easily realized by connecting the optical fiber at a coupler near by the sub-scribers. The above advantages make PON an attractive can-didate to realize low-cost and yet flexible access networks.
PONs have been proposed and implemented in a num-ber of standards. The ITU-T/FSAN-based first-generation asynchronous transfer mode (ATM)-PON (A-PON) and broadband PON (B-PON) are ATM-based systems. The gigabit-PON (G-PON, successor of B-PON) supports both ATM and other traffic protocol by using time division mul-tiplexing (TDM) and generic framing procedure. Ethernet-PON (E-Ethernet-PON) handles information traffic based on Ethernet protocol and provides sufficient bandwidth for emerging
ser-Manuscript received November 9, 2009. Manuscript revised February 19, 2010.
†The authors are with Oki Electric Industry Co., Ltd., Warabi-shi, 335-8510 Japan.
a) E-mail: [email protected] DOI: 10.1587/transele.E93.C.1165
vices, such as Internet Protocol (IP) TV, video-on-demand (VoD), IP telephone, video conferencing.
All PONs are single-channel systems consisting of a single upstream wavelength channel of 1.31μm and a sin-gle downstream wavelength channel of 1.49μm. Given the exponentially increasing number of subscribers and ever in-creasing data traffic demand, the transmission bit rate of PONs are likely to be upgraded in the very near future.
In North America, the majority of PON deployments are based on ITU-T/FSAN-group B-PON and are slowly migrating toward G-PON. While in Asia (mainly Japan and Korea), IEEE-based gigabit Ethernet (GE)-PON has been deployed. Both G-PON and GE-PON services are, based on best effort/TDM and require relatively high transmission bit rate up to 1 Gbps. GE-PON system is divided into PX-10 and PX-20 according the transmission distance of PX-10 km and 20 km, respectively. Fabry-Perot laser diodes (FP-LDs) and distributed-feedback laser diodes (DFB-LDs) are used as light sources for PX-10 and PX-20, respectively. Al-though low-cost FP-LD is ideal for PON applications, its relatively poor transmission characteristics limit its use for PX-10 only [1]–[4].
To further encourage the adaptation of PX-20 system, the cost reduction of DFB-LD is crucial. In order to reduce the optical module cost, uncooled DFB-LDs have been de-veloped for the temperature range between−40◦C and over 85◦C [5]–[7]. However, conventional index coupled DFB-LDs (IC-DFB-LD) are sensitive to the external optical feed-back and require additional optical isolator (ISO) to shut out reflection return light for stable operation.
Since PON system has many optical fiber end facets that generate optical reflections, DFB-LDs with optical re-flection tolerance are critically needed to improve the rela-tive intensity noise (RIN) characteristics for the reliable net-work operation [8]–[10].
The Gain-coupled laser diodes (GC-DFB-LD) have been recognized to have robust RIN characteristics against optical feedback [11]. The optical modules without ISOs are very cost-effective because the ISO is an especially ex-pensive device in the optical module. While the RIN char-acteristics were improved, the output optical power level of GC-DFB-LD is not high enough to be used for PON appli-cations [12], [13].
In this paper, we successfully demonstrate the GC-DFB-LDs with improved optical output power and high op-tical feedback tolerance complying to the standard defined in IEEE 802.3ah [14]. In the next chapter, we will report the Copyright c 2010 The Institute of Electronics, Information and Communication Engineers
terminals (OLTs) are also discussed in chapter 3.
2. Device Structure and Characteristics of GC-DFB-LD for ONU
2.1 Device Structures and Characteristics
Figure 1 shows the schematic diagram of a GC-DFB-LD with buried hetero structure grown by three-step metal or-ganic vapor phase epitaxy (MOVPE) growths. The 1.3 μm-strain compensated multiple quantum wells (SC-MQW) consists of a 30-nm thick InGaAsP (λg = 1.3 μm) wave-guide layer for optical absorption and 10 periods of 0.8% compressive strained InGaAsP (λg =1.4 μm) quantum wells with 0.4% tensile strained InGaAsP (λg = 1.1 μm) barriers, sandwiched between 25-nm thick lattice matched InGaAsP (λg = 1.1 μm) as separated confinement layers. The device length was a 350μm. The antireflection (AR) coating was deposited on the front facet, while the high-reflection (HR) coating was provided on the rear facet for high slope effi-ciency characteristic. The grating pattern on n-InP substrate was formed by interference exposure lithography and wet chemical etching. The grating depth was optimized to con-trol the coupling coefficient (κ). The κ of the GC-DFB-LDs were calculated from oscillation spectra wave forms in con-dition of under threshold current [15], [16]. The estimated κ and κgain/κindexof the GC-DFB-LD were around 40 cm−1
and 2%, respectively.
Figure 2 shows the temperature dependence of the out-put power characteristics as a function of injected current under the CW operation for the temperatures between 0◦C and 90◦C. The threshold currents and the slope e fficien-cies were 4.5 mA and 0.44 W/A at 25◦C, and 19.2 mA and
0.20 W/A at 85◦C, respectively. The characteristic temper-ature and the degradation in the slope efficiency were es-timated to be 44 K and −3.4 dB, respectively. We fabri-cated the GC-DFB-LD sample that has similar optical out-put characteristics as conventional IC-DFB-LD by optimiz-ing the waveguide layer for optical absorption, MQW struc-tures and the mesa width of BH structure [17]. Stable sin-gle mode operation maintaining side mode suppression ratio (SMSR) exceeding 40 dB was experimentally demonstrated over 15 mW of the output power at the temperature up to 90◦C. We confirmed that the most of the GC-DFB-LDs were
Fig. 1 Schematic structure of GC-DFB-LD.
expected to contribute to the stability of the single mode op-eration.
The GC-DFB-LD was packaged in a TO-CAN coax-ial module without optical ISO. The coupling efficiency be-tween the GC-DFB-LD chip and the optical single mode fiber was estimated to be about 40%. Figure 3 shows a test system setup to evaluate the optical feedback tolerance of the fabricated GC-DFB-LD consisting of a polarization controller (PC), an optical 3-dB coupler, a variable optical attenuator (ATT), a power meter, and an HR terminator.
First we measured the RIN characteristics with optical feedback with various temperatures. The amounts of optical feedback power were monitored by the power meter shown in Fig. 3. The results were compared with those of conven-tional IC-DFB-LDs with the same MQW structures as the GC-DFB-LD. As for the characteristics of our conventional IC-DFB-LD, the threshold currents and the slope e fficien-cies were 5.9 mA and 0.46 W/A at 25◦C, and 22.6 mA and
0.23 W/A at 85◦C, respectively. The module output powers
were set constant at the fiber output power of 4 dBm. Fig-ure 4 shows the dependence of the RIN values at 1.25 GHz with the optical feedback power. For the conventional
IC-Fig. 2 Temperature dependence of CW light-current characteristics from GC-DFB-LD with AR coating.
Fig. 3 System setup to evaluate optical feedback-tolerance of GC-DFB-LD.
Fig. 4 Optical feedback power dependence of RIN at 1.25 GHz of GC-DFB-LD (open circle) and IC-GC-DFB-LD (closed circle) with constant fiber output power at 4 dBm.
Fig. 5 Eye diagrams (a) GC-DFB-LD without OFB at 25◦C, (b) GC-DFB-LD with−15 dB OFB at 25◦C, (c) GC-DFB-LD with−15 dB OFB at 85◦C, and (d) IC DFB-LD with−15 dB OFB at 85◦C.
DFB-LDs, the RIN values degraded over−120 dB/Hz when the optical feedback power exceeded −10 dBm. In con-trast, the RIN degradation of the GC-DFB-LD was well suppressed below−120 dB/Hz in the operating temperature range from 0◦C to 85◦C, even when the optical feedback power was increased up to−4 dBm. This result indicates that the GC-DFB-LD is less sensitive to the optical feed-back by 6 dB in comparison with conventional IC-DFB-LDs. The result also indicates that the RIN value better than −120 dB/Hz can be secured in our GC-DFB-LD even with the optical feedback level of −8 dB. This condition fully complies with the stringent requirement of IEEE802.3ah and experimentally demonstrates that the fabricated GC-DFB-LD without ISO can realize low-cost PX-20 systems.
Fig. 6 Bit-error-rate characteristics under optical feedback at 85◦C: (a) GC-DFB-LD and (b) IC-DFB-LD at 85◦C.
2.2 Transmission Characteristics
We carried out 1.25 Gbps direct modulation experiments with non-return-to-zero (NRZ) signal under 223− 1
pseudo-random bit sequence. The TO-CAN coaxial modules were set on a circuit board with a thin-film 50-Ω resistance in se-ries to match the impedance. The applied modulation volt-age was controlled with the optical output avervolt-age power of 3 dBm and the dynamic extinction ratio of 6 dB. The eye pat-terns were measured using a fourth-order Bessel-Thomason receiver response with fr = 0.9375 GHz. Those results
GC-Fig. 7 The transmission conditions dependence of power penalty: (a) GC-DFB-LD and (b) IC-DFB-LD.
DFB-LD without optical feedback (OFB) at 25◦C, (b) with −15 dB OFB at 25◦C, (c) with−15 dB OFB at 85◦C, and
(d) the IC-DFB-LD with−15 dB OFB at 85◦C. Clear eye opening was maintained with−15 dB OFB at 85◦C.
Transmission characteristics under −15 dB optical feedback were measured for 30 km transmission without op-tical isolator. Bit error rates are shown and compared in Fig. 6(a) for GC-DFB-LD at 85◦C and (b) for IC-DFB-LD at 85◦C, respectively. Error free transmissions were success-fully achieved by both GC-DFB-LD and IC-DFB-LD. The dispersion power penalty is defined as the difference in aver-aged received power at 10−12of BER, between back-to-back and after the transmission. In the case of the GC-DFB-LD, the dispersion power penalty after 30 km transmission was less than 0.3 dB under−15 dB external optical feedback at 85◦C. In contrast, the dispersion power penalty of the IC-DFB-LD was 1.1 dB with the same conditions above. The power penalty of the GC-DFB-LD after 30 km transmission was improved as compared with the IC-DFB-LD.
The dispersion power penalties of the eight GC-DFB-LDs and the five IC-DFB-GC-DFB-LDs are plotted with three dif-ferent transmission conditions in Fig. 7. For eight modules of the GC-DFB-LDs, dispersion power penalty were found to be less than 0.3 dB at each temperatures under all con-ditions. The distributed value of dispersion power penalty
Fig. 8 Aging test for GC-DFB-LDs. (a) Long-term aging test under the APC operation at 14 mW and 85◦C, (b) the stability of RIN.
is small and stable. A mean and a standard deviation were 0.16 dB and 0.08 dB, respectively. While a maximum dis-persion power penalty of the five IC-DFB-LDs in all condi-tions was 1.1 dB. A mean and a standard deviation of disper-sion power penalty were 0.63 dB and 0.25 dB, respectively. The reason of the power penalty deterioration for the IC-DFB-LDs at 85◦C is not clearly understood. However, we deduce that the deterioration power penalty of IC-DFB-LD is affected by the instability of the oscillation mode.
A series of long-term aging tests were conduced on the forty-eight GC-DFB-LDs after the burn-in test. Figure 8(a) shows the driving current trace of the aging test at the am-bient temperatures of 85◦C. The lasers were operated at the constant output power level of 14 mW and the operation cur-rents were around 100 mA at 85◦C. We set up the measure-ment at the output of 14 mW, because the optical power of more than 7 dBm is expected from the optical fiber of the module if we assume the coupling efficiency of 40% be-tween the LD chip and the optical fiber. No significant in-crease in the driving current was observed for 5,000 hours of operation at 85◦C, 14 mW. The failure criterion was set at 20% increase in operating current [18]. The lasers with the operating current increase proportional to the aging time have the median life estimated to be around 1.3× 105hours.
Figure 8(b) shows the average value of the fifteen GC-DFB-LDs after randomly chosen (closed circle) and the aver-age value that was added three times the standard deviation (open circle) at the beginning, 2,000 hours and 5,000 hours. Excellent reliabilities are experimentally demonstrated for the GC-DFB-LDs based on our experimental results. 3. Device Structure and Characteristics of
GC-DFB-LD for OLT
3.1 Device Structures and Characteristics
We made a slight modification in the MQW active layers for the 1.49μm GC-DFB-LD for OLT applications as compare to the one already shown in Fig. 9. The 1.49μm-SC-MQW consisting of a 30-nm thick InGaAsP (λg = 1.49 μm) wave-guide layer for optical absorption and ten periods of 0.8% compressive strained InGaAsP quantum wells with 0.4% tensile strained InGaAsP barriers, sandwiched between 25-nm thick lattice matched InGaAsP (λg = 1.1 μm) as sepa-rated confinement layers. The device length is 350μm. The AR coating was deposited on the front facet, while the HR coating was provided on the rear facet.
Figure 10 shows the temperature dependence of the output power to the current characteristics under the CW op-eration at the temperatures between−40◦C and 90◦C. The
Fig. 9 Schematic structure of GC-DFB-LD for OLT.
Fig. 10 Temperature dependence of CWlight-current characteristics from GC-DFB-LD with AR coating.
threshold currents and the slope efficiencies were 4.6 mA and 0.30 W/A at 25◦C, and 16.0 mA and 0.20 W/A at 85◦C,
respectively. The characteristic temperature and the degra-dation in the slope efficiency were estimated to be 45 K and −2.7 dB, respectively. Stable single mode operation main-taining SMSR exceeding 40 dB was obtained with the out-put power of more than 15 mW at the temperature up to 90◦C. The estimated κ and κgain/κindex of the GC-DFB-LD
were around 50 cm−1and 2%, respectively.
Figure 11 shows the optical feedback power depen-dence of the RIN values at 1.25 GHz. As for the char-acteristics of our conventional IC-DFB-LD for OLT, the threshold currents and the slope efficiencies were 7.1 mA and 0.38 W/A at 25◦C, and 26.6 mA and 0.25 W/A at 85◦C,
respectively. For the conventional IC-DFB-LD, the RIN val-ues exceed−120 dB/Hz when the optical feedback power is increased to −8 dBm. In contrast, the RIN degradation of the GC-DFB-LD is well suppressed below−120 dB/Hz at
Fig. 11 Optical feedback power dependence of RIN at 1.25 GHz of GCDFB-LD (open circle) and IC-DFB-LD (closed circle) with constant fiber output power at 4 dBm.
Fig. 12 Eye diagrams (a) GC-DFB-LD without OFB at 25◦C, (b) GC-DFB-LD with−15 dB OFB at 25◦C, (c) GC-DFB-LD with−15 dB OFB at 85◦C, and (d) IC DFB-LD with−15 dB OFB at 85◦C.
Fig. 13 Bit-error-rate characteristics under optical feedback at 85◦C: (a) GC-DFB-LD and (b) IC-DFB-LD.
the operating temperatures from 0◦C to 85◦C, even when the optical feedback power is increased up to−4 dBm. Those results indicate that the GC-DFB-LD is less sensitive to thee optical feedback by 4 dB in comparison with the conven-tional IC-DFB-LD. The results also indicate that the RIN value better than−120 dB/Hz can be secured for the GC-DFB-LD even with the presence of−8 dB-optical feedback. 3.2 Transmission Characteristics
We carried out 1.25 Gbps direct modulation experiments with NRZ signal under 223− 1 pseudo-random bit sequence.
Fig. 14 The dispersion power penalty versus optical feedback power of GCDFB- LD (open circle) and IC-DFB-LD (closed circle), 6 dB extinction ratio for 30 km SMF transmission at 1.25 Gbps as a function of the optical feedback power.
The TO-CAN modules were set on a circuit board with a thin-film 50-Ω resistance in series to match the impedance. The applied modulation voltage was controlled so that the optical output average power of 5 dBm and the dynamic ex-tinction ratio of 6 dB were obtained. Back-to-back eye dia-grams are shown Fig. 12(a) without OFB, (b) with−15 dB OFB at 25◦C, (c) without OFB at 85◦C, and (d) with−15 dB OFB at 85◦C. Clear eye opening was maintained with −15 dB optical feedback at 85◦C. Transmission
characteris-tics under−15 dB OFB were measured for 30 km transmis-sion without ISO. Bit error rates were shown in Fig. 13 (a) for the GC-DFB-LD at 85◦C and (b) for the IC-DFB-LD at 85◦C, respectively. The BER measurement of the GC-DFB-LD shows no error floor up to 10−12, and a small dispersion power penalty for 30 km transmission less than 0.38 dB at 85◦C. On the other hand, the dispersion power penalty of the IC-DFB-LD showed the deterioration of 1.37 dB at 85◦C. Figure 14 shows the dispersion power penalty of 30 km transmission at 1.25 Gbps at 0◦C, 25◦C, and 85◦C as func-tions of optical feedback power with 3.0 dBm average out-put power under direct modulation. These experimental re-sults clearly prove the transmission characteristics improve-ments realized by the 1.49μm GC-DFB-LD.
4. Conclusion
We have proposed and experimentally demonstrated low cost isolator-free 1.31μm and 1.49 μm GC-DFB-LD optical modules for the ONU and OLT of GE-PON (PX20) Access Network applications. Experimental results of the 1.3μm and the 1.49μm GC-DFB-LD proved their performance tol-erance against external optical feedback, while exhibiting a low threshold current less than 20 mA and a slope efficiency as high as 0.20 W/A at 85◦C. The optical feedback
toler-ance of the 1.31μm and the 1.49 μm GC-DFB-LDs were improved more than 6 dB and 4 dB compared with that of the conventional IC-DFB-LD under −15 dB optical feed-back condition. The transmission penalties over 30 km sin-gle mode optical fiber were found to be less than 0.3 dB and
0.7 dB under−15 dB optical feedback at 85◦C, respectively. The 1.31μm GC-DFB-LD also achieved high stable opera-tion at a constant output power of 14 mW, over 5,000 hour at 85◦C. The fabrication process of the proposed GC-DFB-LD is suitable for the low cost chip production We believe the newly proposed GC-DFB-LDs are promising candidates for the low-cost, isolator-free optical modules in the long reach PON applications.
References
[1] H. Sasaki, M. Uekawa, Y. Maeno, K. Kotani, D. Shimura, R. Sekikawa, and T. Takamori, “A low-cost micro-BOSA using Si mi-crolens integrated on Si optical bench for PON application,” Proc. Optical Fiber Conference, Paper OWL6, 2006.
[2] D. Shimura, R. Sekikawa, K. Kotani, M. Uekawa, Y. Maeno, K. Aoyama, H. Sasaki, T. Takamori, K. Masuko, and S. Nakaya, “Bidi-rectional Optical Subassembly with orealigned silicon microlens and laser diode,” IEEE Photonics Technol. Lett., vol.18, no.16, pp.1738– 1740, 2006.
[3] A. Ohki, S. Fukushima, M. Sugo, K. Kato, and Y. Akatsu, “Novel TO-BOSA for FTTH using new optical path alignment technology,” Proc. Optical Fiber Conference, Paper OMK6, 2007.
[4] M. Iwase, “Passive alignment optical modules using high precision plastic package and silicon optical bench technologies,” OECC2002 10C1-1, p.134, 2002.
[5] K. Nakahara, T. Tsuchiya, T. Kitatani, K. Shinoda, T. Taniguchi, S. Fujisaki, T. Kikawa, E. Nomoto, F. Hamano, M. Sawada, and T. Yuasa, “1.3μm InGaAlAs directly modulated MQW RWG DFB lasers operating over 10 Gb/s and 100◦C,” Proc. Optical Fiber Con-ference, Paper ThD1, 2004.
[6] S. Shirai, Y. Tatsuoka, C. Watatani, T. Ota, K. Takagi, T. Aoyagi, E. Omura, and N. Tomita, “120◦C uncooled operation of direct modu-lated 1.3μm AlGaInAs-MQW DFB laser diodes for 10 Gb/s telecom applications,” Proc. Optical Fiber Conference, Paper ThD2, 2004. [7] T. Okuda, Y. Muroya, S. Ishikawa, R. Kobayashi, K.
Tsu-ruoka, Y. Ohsawa, and T. Nakamura, “Low-operation-current and highly-reliable 1.3μm AlGaInAs strain compensated MQW-BH-DFB lasers for 100◦C, 10-Gb/s operation,” Proc. Optical Fiber Con-ference, Paper ThD3, 2004.
[8] R. Hui, M. Kavehrad, and T. Makino, “External feedback sensitivity of partly gain-coupled DFB semiconductor lasers,” IEEE Photonics Technol. Lett., vol.6, no.8, pp.897–899, 1994.
[9] M. Gotoda, T. Nishimura, K. Matsumoto, T. Aoyagi, and K. Yoshiara, “Highly external optical feedback-tolerant 1.49-μm single-mode lasers with partially corrugated gratings,” IEEE J. Sel. Top. Quantum Electron., vol.15, no.3, pp.612–617, May/June 2009. [10] Y. Hugng, K. Shiba, Y. Muroya, N. Suzuki, and T. Okuda, “Isolator-free 2.5 Gb/s, 45 km transmission characteristics in partially corru-gated waveguide laser diodes from−40◦C to 80◦C under−14 dB external optical feedback,” Proc. Optical Fiber Conference, Paper WH6-1, 1999.
[11] Y. Nakano, Y. Deguchi, K. Ikeda, Y. Luo, and K. Tada, “Reduc-tion of excess intensity noise induced bu external reflec“Reduc-tion in a gain-coupled distributed feedback semiconductor,” IEEE J. Quan-tum Electron., vol.27, no.6, pp.1732–1735, 1991.
[12] H. Lu, C. Blaauw, and T. Makino, “High-temperature single-mode operation of 1.3-μm strained MQW gain-coupled DFB lasers,” IEEE Photonics Technol. Lett., vol.7, no.6, pp.611–613, 1995.
[13] Y. Luo, Y. Nakano, K. Tada, T. Inoue, H. Hosomatsu, and H. Iwaoka, “Fabrication and characteristics of gain-coupled distributed feed-back semiconductor lasers with a corrugated active layer,” IEEE J. Quantum Electron., vol.27, pp.1724–1731, 1991.
[14] K. Nakamura, S. Miyamura, R. Sekikawa, D. Shimura, S. Nakaya, T. Ori, H. Yaegashi, and Y. Ogawa, “Optical feedback-tolerant 1.3μm
gain-coupled DFB lasers for isolatore-free micro-BOSA modules,” Proc. Optical Fiber Conference, Paper OMK5, 2007.
[15] T. Nakura and Y. Nakano, “LAPAREX-An automatic parameter ex-traction program for gain- and index-coupled distributed feedback semiconductor lasers, and its application to observation of chang-ing couplchang-ing coefficients with currents,” IEICE Trans. Electron., vol.E83-C, no.3, pp.488–495, March 2000.
[16] http://www.ee.t.u-tokyo.ac.jp/˜nakano/lab/research/LAPAR EX/ index.html
[17] H. Lu, C. Blaauw, B. Benyon, G.P. Li, and T. Makino, “High-power and high-speed performance of 1.3-μm strained MQW gain-coupled DFB lasers,” IEEE J. Sel. Top. Quantum Electron., vol.1, no.2, pp.375–381, 1995.
[18] S. Matsumoto, M. Fukuda, K. Sato, Y. Itaya, and M. Yamamoto, “Highly reliable 1.55μm GaInAsP laser diode buried with semi-insulating iron-doped InP,” Electron. Lett., vol.30, pp.1395–1306, 1994.
Koji Nakamura received the B.E. and M.E. degrees in Electrical Engineering from Meiji University in 1990 and 1992, respectively. In 1992, he joined the Research and Develop-ment Laboratories, Oki Electric Industry Co., Ltd., Tokyo, Japan, where he has been engaged in research and development of III-V epitax-ial growth technology, semiconductor lasers and optical devices for optical communication sys-tems.
Satoshi Miyamura received the B.E. and M.E. degrees in Electrical and Computer Engi-neering and Computer Science from Kanazawa University in 2002 and 2004, respectively. In 2004, he joined the Research and Development Laboratories, Oki Electric Industry Co., Ltd., Tokyo, Japan, where he has been engaged in re-search and development of semiconductor lasers and optical devices for optical communication systems.
Hiroki Yaegashi received B.S. and M.S. degrees in applied physics from Tohoku Univer-sity, Japan, in 1987 and 1989 respectively. In 1989, he joined Oki Electric Industry Co., Ltd., Japan, where he has been engaged in research and development of semiconductor waveguide devices and laser diodes for Optical communi-cation systems. He is member of the Japan So-ciety of Applied Physics.
