Showing papers by "Yasuharu Suematsu published in 1979"
581 citations
TL;DR: In this paper, the authors investigated the origin, qualitative, and quantitative properties of low frequency noise appearing in the light output of the laser diode, which is strongly coupled to optical fibers.
Abstract: This paper describes the theoretical investigation of the origin, qualitative, and quantitative properties of the low frequency noise appearing in the light output of the laser diode, which is strongly coupled to optical fibers. This kind of noise has caused serious problems for reliable optical communications, especially for analog-modulation systems. It is shown that there are two different phenomena which generate such noise. One of them is the double cavity state, and the other is the external light injection state. The cause of our noise considered in the double cavity state is the phase variation due to the variation of the equivalent length between the laser and the reflection point generated by mechanical vibrations. On the other hand, the cause in the external light injection state is the random generations of locking and unlocking states due to the frequency variation (or mode jumping) caused by the variation of the internal temperature of the laser diode. We conclude from our theory that an effective method to reduce such noise is to operate the laser diode at well above the threshold current. The complete elimination will be attained by use of the optical isolator inserted between the laser diode and the transmission lines.
158 citations
TL;DR: A condition for single longitudinal mode operation (SMO) of index-guided injection lasers is given theoretically and supported by experiment in this article, where the transverse higher modes must be cut off by using a narrow-width index-guiding waveguide.
Abstract: A condition for single longitudinal mode operation (SMO, for short) of index-guided injection lasers is given theoretically and supported by experiment. For SMO, the transverse higher modes must be cut off by using a narrow-width index-guiding waveguide. Inclusion of the spontaneous emission into the lasing field must be reduced by using a thinner active region. In terms of the impurity concentration of the active region, the undoped case is the most stable for temperature variation. A heavily doped active region may also produce SMO. The thermal resistance must be reduced to increase temperature stability. MO with a fixed lasing wavelength is experimentally obtained by temperature control up to an injection current of twice threshold.
102 citations
TL;DR: In this paper, a two phase solution growth technique was applied with low cooling rate of 0.08°C/min, which gave 0.13 µm thick active layer by reducing the concentration of Zn dopant, whereas the normal V-I characteristic was kept.
Abstract: Low threshold current density (100) GaInAsP/InP DH lasers emitting at 1.3 µm with thin active layer were studied experimentally and theoretically. The two phase solution growth technique was applied with low cooling rate of 0.08°C/min, which gave 0.05 µm thick uniform active layer. The threshold current density was minimized down to 770 A/cm2 with 0.13 µm thick active layer by reducing the concentration of Zn dopant, whereas the normal V–I characteristic was kept. The residual internal and the external absorption losses of the active layer were estimated to be about 70 cm-1 and 30 cm-1, respectively, in order to know the theoretical threshold limit. The narrowest beam divergence obtained was 23° for the active layer 0.05 µm thick. Both the threshold current density dependence on the thickness of the active layer and the beam divergence were in good agreement with the theory which was calculated by using the relative refractive index difference of 8.7%. A narrow stripe laser with undoped thin active layer had a tendency to emit in a single longitudinal mode.
50 citations
34 citations
TL;DR: In this paper, a new theory of injection lasers is given by taking account of the electronic intraband relaxation with the density matrix method, and gain saturations of lasing modes at band to band and band to impurity level transitions are theoretically given.
Abstract: A new theory of injection lasers is given by taking account of the electronic intraband relaxation with the density matrix method. "Band tail" of the gain profile in nondoped crystal is explained with this relaxation. Gain saturations of lasing modes at band to band and band to impurity level transitions are theoretically given. In the case of band to band transition with k-selection rule, a small excess gain suppression affects the lasing behaviour. At the band to impurity level transition with no k-selection rule, the excess gain suppression disappears. The former effect corresponds to the "inhomogeneous gain profile", and the latter to the "homogeneous gain profile". Theoretical calculations are in good agreement with experiments. As an extention of this theory, a condition of single longitudinal mode oscillation is shown.
28 citations
TL;DR: In this paper, a new GaInAsP/InP injection laser with buried heterostructure fabricated by single-step epitaxial growth on a mesa substrate is reported.
Abstract: A new GaInAsP/InP injection laser with buried heterostructure fabricated by single-step epitaxial growth on a mesa substrate is reported. Single longitudinal-mode operation up to 1.4 times the threshold current Ith and linear light-output/current characteristics up to 3Ith are observed at 1.27 ?m.
24 citations
TL;DR: In this article, GaInAsP/InP distributed Bragg reflector (DBR) with a first-order grating was demonstrated experimentally for the first time at a wavelength of 13 μm, single longitudinal mode oscillation was obtained at low temperature, and the temperature dependence of the lasing wavelength was 07-08 A/deg.
Abstract: GaInAsP/InP distributed Bragg reflector (DBR) lasers with a first-order grating were demonstrated experimentally for the first time at a wavelength of 13 μm Single longitudinal mode oscillation was obtained at low temperature, and the temperature dependence of the lasing wavelength was 07-08 A/deg The equivalent refractive index of GaInAsP at the lasing wavelength of 13 μm was 350 at 186 K
19 citations
18 citations
TL;DR: In this article, an approximate analysis of gain suppression for both band-to-band and bandto-impurity-level transitions with the help of the density matrix method is given.
Abstract: An approximate analysis of the gain suppression is given for both band-to-band and band-to-impurity-level transitions with the help of the density matrix method. The gain-suppression is represented in an explicit form as a function of the injection current. This approximate method is convenient for investigating the characteristics of injection lasers.
17 citations
01 Apr 1979
Journal Article•
TL;DR: In this article, the angles of beam divergence perpendicular to the junction plane have been studied for low-threshold GaInAsP/InP double-heterostructure lasers with a thin active layer emitting at 1.31 μm.
Abstract: The angles of beam divergence perpendicular to the junction plane have been studied for low-threshold GaInAsP/InP double-heterostructure lasers with a thin active layer emitting at 1.31 μm. The narrowest beam divergence obtained was 23° for a laser diode with an active-layer thickness of 0.05 μm. At an active-layer thickness of 0.13 μm, the beam divergence was 40° with a threshold current density of 770 A/cm2.
TL;DR: In this paper, a branching wavelength-selective filter for optical communication systems consisting of a three-dimensional Input waveguide with a grating and an output slab waveguide is analyzed.
Abstract: A branching wavelength-selective filter for optical communication systems consisting of a three-dimensional Input waveguide with a grating and an output slab waveguide is analyzed. It is found that insertion loss occurs due to the radiation of the light from the grating into the substrate. Conditions for lossless operation of the filter are given. Optical branching filters with three-dimensional input waveguides were fabricated by using an electron-beam exposure system. Filtering resolution was measured experimentally and found to agree with theory.
TL;DR: In this paper, a new GaInAsP/InP injection laser with buried heterostructure fabricated by single-step epitaxial growth on a mesa substrate is reported.
Abstract: A new GaInAsP/InP injection laser with buried heterostructure fabricated by single-step epitaxial growth on a mesa substrate is reported. Single longitudinal-mode operation up to 1.4 times the threshold current Ith and linear light-output/current characteristics up to 3Ith are observed at 1.27 ?m.
01 Jan 1979
TL;DR: In this article, a GaJ.nAsP/InP DBR laser with a first-order grating was demonstrated at a wavelength of 1.3 pm, and a single longitudinal mode oscillation was obtained at low temperature and the temperature dependence of the lasing wavelength was 0.7-0.8 A/deg.
Abstract: 701 Abstract-GaInAsPIInP distributed Bragg reflector (DBR) lasers with a first-order grating were demonstrated experimentally for the first time at a wavelength of 1.3 pm. Single longitudinal mode oscillation was obtained at low temperature, and the temperature dependence of the lasing wavelength was 0.7-0.8 A/deg. The equivalent refractive index of GaInAsP at the lasing wavelength of 1.3 pm was 3.50 at 186 K. OUBLE-HETEROSTRUCTURE (DH) GaInAsP/InP lasers (l) -(6) , lasing in a 1.2-1.7 pm wavelength region, are considered to be one of the most promising light sources for low-loss fiber 171 communications. The frequency control and single longitudinal mode oscillation are also very attractive, especially for wavelength multiplexing on single mode fiber systems. With respect to such interest, a GaInAsP/InP DH dis- tributed Bragg reflector (DBR) injection laser with second- order grating was already reported (SI. From the experiments of various types of GaAs distributed reflector lasers (9) -(16) , it was verified that the single longitudinal mode oscillation and the stability of lasing wavelength against the temperature and the injection current level were realized in those lasers (9) , (15), (16). Because the lasing wavelength is about 0.9 pm in GaAs distributed reflector lasers, the form of the grating is mostly limited to the second or third order because of the dif- ficulty of processing. GaAs distributed reflector lasers with first-order gratings were reported only for optically pumped (17) , (18) or injected DFB lasersoperated at low temperatures (I91 . In the case of GaInAsP/InP lasers, the fabrication of a first-order grating is not so difficult because the lasing wave- length is longer. As demonstrated by previous experiments, the refractive index of GaInAsP at a lasing wavelength of 1.24 pm is about 3.5 (8), so that the period of a first-order grating on the GaInAsP is about A = 1800-1900 a, which can be realized in the atmosphere by the interference with the 3250 A line of a He/Cd laser. Use of the first-order grating for distributed reflector lasers will increase the quantum efficiency of the lasers by elimination of the lower order diffraction losses. In this paper, we want to demonstrate GaJ.nAsP/InP DBR lasers with first-order gratings fabricated on the exposed sur-