Wavelength coverage over 67 nm with a GCSR ... - Semantic Scholar
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Wavelength coverage over 67 nm with a GCSR laser. Tuning characteristics and switching speed. P.-J. Rigole, S. Nilsson, L. Backbom, B. Stblnacke, T. Klinga, E. Berglind, B. Stoltz*, D. J. Blumenthal"", M. Shell"* Laboratory of Photonics and Microwave Engineering, Royal Institute of Technology, Electrum 229, S-164 40 Kista, Sweden * Ericsson Components AB, 16481 Kista, Sweden ** Research Center, Georgia Institute of technology, Atlanta, Georgia 30332
Abstract: Complete wavelength coverage over 67 nm was measured with SMSR better than 25 dB using a Grating assisted codirectional Coupler with Sampled rear Reflector (GCSR) laser. Wavelength switching time for coupler current step was also measured. Introduction: Widely tunable monolithic semiconductor lasers are important for wavelength division multiplexed (WDM) networks and optical measurement systems. Complete wavelength coverage over 40 nm and 62.5 nm has been demonstrated for electrically tuned SSG-DBR lasers[l,2]. The GCSR laser has shown very wide stepwise tuning range (100 nm) [3]. We report here a 67 nm complete wavelength coverage in a GCSR laser. Laser structure: The laser structure is schematically shown in fig. 1 . It consists of a gain section, a coupler section for coarse tuning, a phase tuning section for continuous fine tuning and a reflector (SSGDBR) section for medium tuning. The SEM pictures of the cross section in the different parts of the laser are also shown. The fabrication of the laser is described in [3]. The multi-pitch grating structure is depicted in fig. 2a and fig. 2b shows the calculated reflection comb. CW Tuning measurements: The tuning measurements were made with a gain current of 200 mA and at a fixed heat sink temperature of 20°C. In Fig. 3 are shown the tuning characteristics of the laser when the coupler current and the reflector current are changed simultaneously. The curve was recorded by successively selecting each peak of the comb by adjusting the coupler current and then tune the reflector current while changing the coupler current (linearly relatively to the reflector current) to track the selected peak for maximal transmission of the coupler. For all points the side-mode suppression is better than 25 dB. The total tuning range is around 75 nm limited by reflector bandwidth but the wavelength coverage is 67 nm since the first peak could not be tuned to the start of the next one. Gaps are still observed in the tuning characteristics corresponding to longitudinal mode jumps. These missing wavelengths can be reached by using the phase tuning section of the laser. Access to wavelengths around 1588 nm required a slight adjustment of the gain current. Thus a tuning range between 1535 and 1602 nm is covered. The maximum output power was 4 mW and varies with 13 dB in the tuning range. Dynamic tuning measurements: The time and spectral behaviour of the laser was measured under switching operation of the coupler current. The measurement set-up consists of a digital to analogue circuit with sub nanosecond rise time similar to the one use in [4] to step the coupler current, a tunable optical filter and a detector coupled to a digital oscilloscope. The filter bandwidth was taken to 0.2 nm such as the drift in wavelength due to overshot in current and thermal effects was kept inside it. Fig. 4a shows the time variation of the detector signals corresponding to the optical filter centred at the start and stop wavelengths. The average spectrum under back and forth switching is shown in fig. 4b. The switching time was measured between the disappearance of the start wavelength and the appearance of the stop wavelength. The switching time was from 2 ns for the closest peak and up to 27 ns for a peak distant of 38 nm. This behaviour is explained by the carrier lifetime in the tuning section and is similar to the one observed in DBR lasers [5]. Conclusion: Wavelength coverage over 67 nm with a four-current control was demonstrated. Switching time measurements shows an increasing switching time with increasing wavelength step. The longest switching time measured was 27 ns. This work was supported by the European ACTS BLISS project. References
[l] M. Oberg et al., Journal of Lightwave Technology, Vol. 13, N"9, Sept. 95.
[2] H. Ishii et al., Electronics Letters, Vol. 32, N"5, Feb. 96. [3] P-J Rigole et al., IEEE Photonics Technology Letters, Vol. 7, No 11, Nov. 95. [4]D. J. Blumenthal et al, OFC 96, pp 108-110. [5] L. Zhang and J. Carteldge, IEEE Photonics Technology Letters, Vol. 5, No IO, Oct. 93. 125
Gain 400 um
Coupler Phase tuning Reflector 500u.m 150um 900um
i.
'"'" 600
590
580
Fig. 1 Schematic view of the GCSR laser with SEM pictures of the different cross sections
570
560
1 550
0.8t 540
0.4
M
I
l"""
0
0.2 0.0 -60
-40
-20
0
20
40
20
40
60
Ir Reflector current [mA] Coupler current a Ir
60
AWavelength (nm)
Fig.3 Wavelength coverage versus reflector current. The coupler current is changed simultaneously.
Fig. 2 (a) One sampling period of the SSG-DBR. (b) Calculated reflectivity for 10 As with losses of 5 cm-1.
10 . 00 dB/div Kef2 +Duty 50.0
ss
Ref2 Rise 1.00ns
Refa Fall 2.51ns
I . . .
L
I.OOp
M5.00ns C h 4 f
f
1.96 V
5.00ns
Fig.4 (a) Switching recorded in the time domain for 2 close peaks. (b) Average spectrum under switching 126
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I
Wavelength coverage over 67 nm with a GCSR laser. Tuning characteristics and switching speed. P.-J. Rigole, S. Nilsson, L. Backbom, B. Stblnacke, T. Klinga, E. Berglind, B. Stoltz*, D. J. Blumenthal"", M. Shell"* Laboratory of Photonics and Microwave Engineering, Royal Institute of Technology, Electrum 229, S-164 40 Kista, Sweden * Ericsson Components AB, 16481 Kista, Sweden ** Research Center, Georgia Institute of technology, Atlanta, Georgia 30332
Abstract: Complete wavelength coverage over 67 nm was measured with SMSR better than 25 dB using a Grating assisted codirectional Coupler with Sampled rear Reflector (GCSR) laser. Wavelength switching time for coupler current step was also measured. Introduction: Widely tunable monolithic semiconductor lasers are important for wavelength division multiplexed (WDM) networks and optical measurement systems. Complete wavelength coverage over 40 nm and 62.5 nm has been demonstrated for electrically tuned SSG-DBR lasers[l,2]. The GCSR laser has shown very wide stepwise tuning range (100 nm) [3]. We report here a 67 nm complete wavelength coverage in a GCSR laser. Laser structure: The laser structure is schematically shown in fig. 1 . It consists of a gain section, a coupler section for coarse tuning, a phase tuning section for continuous fine tuning and a reflector (SSGDBR) section for medium tuning. The SEM pictures of the cross section in the different parts of the laser are also shown. The fabrication of the laser is described in [3]. The multi-pitch grating structure is depicted in fig. 2a and fig. 2b shows the calculated reflection comb. CW Tuning measurements: The tuning measurements were made with a gain current of 200 mA and at a fixed heat sink temperature of 20°C. In Fig. 3 are shown the tuning characteristics of the laser when the coupler current and the reflector current are changed simultaneously. The curve was recorded by successively selecting each peak of the comb by adjusting the coupler current and then tune the reflector current while changing the coupler current (linearly relatively to the reflector current) to track the selected peak for maximal transmission of the coupler. For all points the side-mode suppression is better than 25 dB. The total tuning range is around 75 nm limited by reflector bandwidth but the wavelength coverage is 67 nm since the first peak could not be tuned to the start of the next one. Gaps are still observed in the tuning characteristics corresponding to longitudinal mode jumps. These missing wavelengths can be reached by using the phase tuning section of the laser. Access to wavelengths around 1588 nm required a slight adjustment of the gain current. Thus a tuning range between 1535 and 1602 nm is covered. The maximum output power was 4 mW and varies with 13 dB in the tuning range. Dynamic tuning measurements: The time and spectral behaviour of the laser was measured under switching operation of the coupler current. The measurement set-up consists of a digital to analogue circuit with sub nanosecond rise time similar to the one use in [4] to step the coupler current, a tunable optical filter and a detector coupled to a digital oscilloscope. The filter bandwidth was taken to 0.2 nm such as the drift in wavelength due to overshot in current and thermal effects was kept inside it. Fig. 4a shows the time variation of the detector signals corresponding to the optical filter centred at the start and stop wavelengths. The average spectrum under back and forth switching is shown in fig. 4b. The switching time was measured between the disappearance of the start wavelength and the appearance of the stop wavelength. The switching time was from 2 ns for the closest peak and up to 27 ns for a peak distant of 38 nm. This behaviour is explained by the carrier lifetime in the tuning section and is similar to the one observed in DBR lasers [5]. Conclusion: Wavelength coverage over 67 nm with a four-current control was demonstrated. Switching time measurements shows an increasing switching time with increasing wavelength step. The longest switching time measured was 27 ns. This work was supported by the European ACTS BLISS project. References
[l] M. Oberg et al., Journal of Lightwave Technology, Vol. 13, N"9, Sept. 95.
[2] H. Ishii et al., Electronics Letters, Vol. 32, N"5, Feb. 96. [3] P-J Rigole et al., IEEE Photonics Technology Letters, Vol. 7, No 11, Nov. 95. [4]D. J. Blumenthal et al, OFC 96, pp 108-110. [5] L. Zhang and J. Carteldge, IEEE Photonics Technology Letters, Vol. 5, No IO, Oct. 93. 125
Gain 400 um
Coupler Phase tuning Reflector 500u.m 150um 900um
i.
'"'" 600
590
580
Fig. 1 Schematic view of the GCSR laser with SEM pictures of the different cross sections
570
560
1 550
0.8t 540
0.4
M
I
l"""
0
0.2 0.0 -60
-40
-20
0
20
40
20
40
60
Ir Reflector current [mA] Coupler current a Ir
60
AWavelength (nm)
Fig.3 Wavelength coverage versus reflector current. The coupler current is changed simultaneously.
Fig. 2 (a) One sampling period of the SSG-DBR. (b) Calculated reflectivity for 10 As with losses of 5 cm-1.
10 . 00 dB/div Kef2 +Duty 50.0
ss
Ref2 Rise 1.00ns
Refa Fall 2.51ns
I . . .
L
I.OOp
M5.00ns C h 4 f
f
1.96 V
5.00ns
Fig.4 (a) Switching recorded in the time domain for 2 close peaks. (b) Average spectrum under switching 126
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