JP2015138849A - Wavelength multiplex transmitter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wavelength multiplex transmitter which compensates loss of light beam caused by an EA modulator of a high frequency without increasing the current amount per unit length of DFB semiconductor laser.SOLUTION: "123" represents a wavelength multiplex transmitter module, "122" represents a wavelength multiplex transmitter that is one semiconductor chip, and "121" represents an optical fiber. The semiconductor chip 122 consists of four DFB semiconductor lasers 101 to 104, four electric field absorption (EA) type optical modulators 105 to 108, and one multi mode interference (MMI) type four to one optical multiplexer 113. In other words, the semiconductor chip 122 has four EA-DFBs on which DFB semiconductor lasers and EA modulators are integrated. The optical multiplexer 113 has a multiplex ratio of optical output from the DFB semiconductor laser 101 with the shortest wavelength, the ratio being larger than that of optical output from DFB semiconductor lasers 102 to 104 corresponding to lane1 to 3.

Description

  The present invention relates to a wavelength division multiplexing transmitter, and more specifically, wavelength division multiplexing transmission in which a plurality of output lights emitted from a plurality of electroabsorption (EA) modulator integrated semiconductor lasers having different wavelengths are bundled into one waveguide by an optical multiplexer. Related to the vessel.

  Development of 100 Gigabit Ethernet (100 GbE) is advancing as one of the standards constituting the next-generation ultrahigh-speed network (see Non-Patent Document 1). In particular, 100GBASE-LR4 and 100GBASE-ER4 that exchange data between medium and long-distance buildings (-10 km) and remote buildings (-40 km) are promising. In the above-mentioned standard, four wavelengths (for example, 1294.53 to 1296.59 nm, 1299.02 to 1301.09 nm, 1303.54 to 1305.63 nm, and 1308.09 to 1310.19 nm) are defined. ), A LAN-WDM method is used in which 25 Gb / s (or 28 Gb / s) data is placed on each of the data and then superimposed to generate a 100 Gb / s signal.

  FIG. 5 shows the configuration of a conventional wavelength division multiplexing transmitter module used at 100 GbE. Reference numeral 323 denotes a wavelength multiplexing transmitter module, 322 denotes a wavelength multiplexing transmitter which is one semiconductor chip, and 321 denotes an optical fiber. The semiconductor chip 322 includes four DFB semiconductor lasers 301-304, four electroabsorption (EA) type optical modulators 305-308, and one multimode interference (MMI) type four-to-one optical multiplexer 313. . In other words, the semiconductor chip 322 includes four EA-DFBs in which a DFB semiconductor laser and an EA modulator are integrated. Reference numerals 309 to 312 denote input waveguides of the MMI type four-to-one optical multiplexer 313, and 314 denotes an output waveguide of the optical multiplexer 313.

  Each of the DFB semiconductor lasers 301 to 304 outputs continuous light, and the laser oscillation wavelength bands of the DFB semiconductor lasers 301 to 304 are 1294.53 to 1296.59 nm, 1299.02 to 1301.09 nm, and 1303.54-1305. .63 nm and 1300.009-1310.19 nm. In general, the four wavelength bands are referred to as lane 0, lane 1, lane 2, and lane 3 from the short wavelength side.

  The EA light modulators 305 to 308 have absorption layers of the same composition, and the continuous light of the DFB semiconductor laser 301 to 304 is 25 Gb / s or 28 Gb / s according to the electric inputs of different electric signals (25 Gb / s or 28 Gb / s). s modulated signal light. The modulated signal lights output from the EA optical modulators 305-308 are output to the waveguides 309-312, respectively.

  The MMI optical multiplexer 313 multiplexes four modulated signal lights having different wavelengths and outputs them to the output waveguide 314 as wavelength multiplexed light bundled together. The wavelength multiplexed light bundled into one is diffused light 315 and emitted into the space, converted into parallel light 317 by the lens 316, passed through the isolator 318, and made into convergent light 320 by the second lens 319. The light is collected and coupled to the fiber 321.

  Although not shown in the drawing, the wavelength multiplexing optical transmitter module 323 includes a temperature sensor (for example, thermistor) of the semiconductor chip 322, a Peltier element for temperature control, a DFB semiconductor laser 301-304, and an EA type in addition to the above. A DC power supply is provided for supplying power to the optical modulators 305-308. It also has a modulator driver and high-frequency line termination resistor for driving the EA type modulators 305 to 308, and a signal line and control circuit for controlling the amplitude, bias voltage, and electrical cross point of the modulator driver. Further, an electrical signal waveform shaping circuit, a clock extraction circuit, and a circuit that suppresses the influence of power supply voltage fluctuations may be provided in front of the modulator driver.

  As the EA type optical modulators 305 to 308, InGaAlAs-based tensile strain quantum wells that have an excellent extinction ratio and are effective in suppressing hole pileup are used. As the output waveguides 309-312 and 314, ridge type waveguides embedded with a low dielectric constant BCB are used in order to secure a high frequency band. As the MMI optical multiplexer 313, a high-mesa waveguide with strong optical confinement and small radiation loss is used.

  The size of the semiconductor chip 322 is 2,000 × 2,600 μm, the resonant length of the four DFB semiconductor lasers 301-304 is 400 μm, and the waveguide length between the DFB semiconductor laser 301-304 and the EA modulator 305-308 is set. The element length of 50 μm and the EA type optical modulators 305 to 308 is set to 150 μm.

  The wavelength division multiplex transmitter module 323 is obtained by mounting the manufactured semiconductor chip 322 in an ultra-small package of 12 mm × 20 mm. When operated at 100 Gbit / s at 40 ° C., 40 km error-free transmission over a single mode fiber is possible. Is possible. As these results show, the wavelength division multiplexing transmitter module 323 has sufficient performance as a transceiver for future generations of 100 GbE.

  FIG. 6 shows a configuration of a conventional integrated wavelength multiplexing transmitter module used at 100 GbE. Reference numeral 432 denotes a wavelength division multiplexing transmitter module, reference numerals 430 and 431 denote semiconductor chips, and wavelength division multiplexing transmitters 429 denote optical fibers.

  The semiconductor chip 430 includes two DFB semiconductor lasers 401-402, two electroabsorption (EA) type optical modulators 405-406, one multimode interference (MMI) type two-to-one optical multiplexer 413, and a waveguide. 409-410, 415. That is, the semiconductor chip 430 includes two EA-DFBs in which a DFB semiconductor laser and an EA modulator are integrated. Here, 409 to 410 are input waveguides of the MMI type two-to-one optical multiplexer 413, and 415 is an output waveguide of the optical multiplexer 413.

  Each of the DFB semiconductor lasers 401 to 402 outputs continuous light, and the laser oscillation wavelength bands of the DFB semiconductor lasers 401 and 402 are 1294.53 to 1296.59 nm and 1299.02 to 1301.09 nm.

  The EA light modulators 405 to 406 have absorption layers of the same composition, and the continuous light of the DFB semiconductor laser 401-402 is 25 Gb / s or 28 Gb / s according to the electric inputs of different electric signals (25 Gb / s or 28 Gb / s). s modulated signal light. The modulated signal lights output from the EA optical modulators 405-406 are output to the waveguides 409-410, respectively.

  The basic configuration of the semiconductor chip 431 is the same as that of the semiconductor chip 430, such as a DFB semiconductor laser 403-404 that outputs continuous light, an EA optical modulator 407-408 having an absorption layer of the same composition, and one multimode interference (MMI). It comprises a two-to-one type optical multiplexer 414 and output waveguides 411-412, 416. On the other hand, the laser oscillation wavelength bands of the DFB semiconductor lasers 403 to 404 are 1303.54 to 1305.63 nm and 1308.09 to 1310.19 nm, respectively.

  The MMI optical multiplexers 413-414 respectively combine two modulated signal lights having different wavelengths, and output them to the output waveguides 415-416 as wavelength multiplexed light bundled together. The wavelength multiplexed light bundled into one is diffused light 417-418 and emitted to the space, and is converted into parallel light 421-422 by the lenses 419-420.

  The parallel light 421 changes its path at right angles by the mirror 423, changes its polarization by 90 ° by the half-wave plate 424, and further changes its path at right angles by the polarization filter 425 and enters the isolator 426. On the other hand, since the polarization of the parallel light 422 is not changed by the half-wave plate, it passes through the polarization filter and enters the isolator 426. In other words, the polarization filter 425 combines the two wavelength multiplexed lights into a wavelength poly-multiplexed light.

  The parallel lights 421 to 422 that have passed through the isolator 426 are converged by the lens 427 into convergent light 428 and are coupled to the fiber 429.

  The sizes of the semiconductor chips 430 and 431 are 1500 × 1,000 μm, the resonance length of the four DFB semiconductor lasers 401 to 404 is 400 μm, and the size of the wavelength multiplexing transmitter module 432 including the LC receptacle is 8. 7 mm × 29 mm. The wavelength division multiplexing transmitter module 432 is capable of an error-free operation of 40 km when operated at 100 Gbit / s at 40 ° C.

  FIG. 7 shows a cross-sectional view of a semiconductor chip on which a DFB semiconductor laser, an EA modulator, and an optical multiplexer are formed. Reference numeral 501 denotes an n electrode, 502 denotes an n-InP substrate, 503 denotes an n-InP clad layer, 504 denotes an active layer of the DFB semiconductor laser, and 505 denotes a guide layer of the DFB semiconductor laser. In 505, a diffraction grating is formed by EB (electron beam) drawing. Reference numeral 506 denotes a p-InP clad layer, and 507 denotes an electrode of a DFB semiconductor laser. Further, reference numeral 508 denotes an absorption layer of the EA modulator, 509 denotes an electrode of the EA modulator, 510 denotes a core layer of a waveguide (or an optical multiplexer), and 511 denotes non-doped InP.

  In the central portion of the DFB semiconductor laser, a quarter wavelength phase shift 512 is provided by shifting the phase of the diffraction grating by a quarter wavelength in order to realize a single mode of the oscillation wavelength. In one semiconductor chip, the composition of the active layer 504 is the same, and the wavelength is changed by changing the pitch of the diffraction grating. Further, the composition of the absorption layer 508 of the EA modulator is the same in one semiconductor chip.

  Although the conventional wavelength division multiplexing optical transmitter module shown in FIG. 5 and the conventional integrated wavelength division multiplexing transmitter module shown in FIG. 6 are useful, the short wavelength modulation signal light and the long wavelength modulation are made with the same semiconductor chip. There is a drawback in that signal light is present, and the light intensity of a short wavelength is weaker by about 1 dB than the light intensity of a long wavelength. The reason will be described below.

  The absorption layer of the EA modulator has a multi-quantum-well structure, and utilizes a quantum Stark (QCSE) effect that shifts the absorption edge of light by applying a voltage.

  FIG. 8A shows the absorption curve of the absorption layer and the oscillation wavelength of the DFB semiconductor laser when no voltage is applied to the EA modulator, and FIG. 8B shows the voltage applied to the EA modulator. The absorption curve of the absorption layer and the oscillation wavelength of the DFB semiconductor laser are shown. FIG. 8C shows a digital signal generated depending on whether or not voltage is applied to the EA modulator. When no voltage is applied to the EA modulator, the absorption curve of the absorption layer does not depend on the oscillation wavelength of the DFB semiconductor laser, as shown in FIG. It becomes a state. On the other hand, when a voltage is applied to the EA modulator, as shown in FIG. 8B, the absorption edge is shifted and the absorption curve is applied to the oscillation wavelength of the DFB semiconductor laser, so that the light is absorbed and the light is turned off. Become. In this way, depending on whether or not voltage is applied to the EA modulator, as shown in FIG. 8C, a digital signal for turning on and off the light can be generated.

  Here, as described above, the composition of the EA modulator is the same in the same chip, that is, the movement of the absorption curve of the EA modulator is constant even if a plurality of EA-DFBs are present in the same chip. On the other hand, since the oscillation wavelengths of the plurality of EA-DFBs are different, the voltage applied to the EA modulator is adjusted to match the optimum modulation condition. Typically, the voltage applied to the EA modulator is 0.1 V (off) /2.1 V (on) for lane 0, 0.3 V / 2.3 V for lane 1, and 0.5 V / 2 for lane 2. .5V and lane3 are about 0.7V / 2.7V, and fine adjustment of about ± 0.2V is performed.

  However, even if the modulation conditions of each lane are adjusted, it is actually difficult to achieve an optimal state that is completely equivalent to all the lanes. FIG. 8D shows how the on-state absorption curves are applied to the two wavelengths when the oscillation wavelength is a short wavelength and when the oscillation wavelength is a long wavelength. Since it is in the ON state, the long wave is completely separated from the absorption curve, but the short wave is partially covered by the absorption curve.

  For this reason, in general, the shortest wave lane 0 has a large optical loss in the ON state with respect to the longer wave lane 1 to lane 3, and the modulated signal light of lane 0 has a light intensity of about 1 dB lower than other lanes. Further, in order to reduce the light loss due to the EA modulator, it is necessary to adjust the voltage to decrease. However, as described above, the off voltage of lane 0 is typically about 0.1 V, and is ± 0.2 V. There is not enough room to make fine adjustments.

  Therefore, conventionally, in order to compensate for the light loss caused by the lane 0 EA modulator, the output of the lane 0 DFB semiconductor laser is increased. FIG. 9 shows optical outputs of lanes 0, 2, and 3 in a typical wavelength multiplexing optical transmitter. The typical optical output is about 1 mW (average optical output during modulation at 45 ° C.), and the injection current of a typical DFB semiconductor laser is 100 mA, but lane 0 reduces the optical output by 1 dB (0.79 times). It has become. Therefore, to ensure the same optical output, the lane 0 injection current is set to 125 mA. By increasing the injection current from 100 mA to 125 mA, the optical output of the DFB semiconductor laser is 1.27 times, and the optical output of lane 0 is equivalent to the optical output of lanes 2 and 3.

Tsuyoshi Fujisawa, Ji Kanazawa, Hiroyuki Ishii, Yasuhiro Kawaguchi, Nobuhiro Nuoya, Aki Ohki, Kiyoto Takahata, Ryuzo Iga, Fumiyoshi Kano, Hiromi Ohashi, "Monolithic Integrated Light Source for Next Generation 100GbE Transceivers" IEICE , November 2011, OCS2011-68, OPE2011-106, LQE2011-10, pp.77-80 T. Ohyama, A. Ohki, K. Takahata, T. Ito, N. Nunoya, T. Fujisawa, R. Iga, and H. Sanjoh., “Compact 100GbE transmitter optical sub-assembly using polarization beam combiner”, The 10th conference on Lasers and Electro-Optics Pacific Rim, and The 18th OptoElectronics and Communications Conference / Photonics in Switching 2013, CLEO-PR & OECC / PS 2013, Kyoto, Japan, MK1-4

  However, increasing the drive current of the DFB semiconductor laser by 1.25 times only for lane 0 means that the operating current density in the active layer of the DFB semiconductor laser (or simply, the current amount per unit length of the DFB semiconductor laser) is 1. I will increase it 25 times. In general, it is known that the degradation rate of the DFB semiconductor laser has a correlation with the operating current density. However, in lane 0, the amount of heat generated in the active layer increases as the operating current density increases, and the degradation is accelerated compared to lanes 2 and 3. Is done.

  Since the optical output of lane 1 is typically 0.4 dB down (0.91 times) compared to lanes 2 and 3, the optical output of the DFB semiconductor laser is increased by 1 by raising the injection current of lane 1 to 110 mA. .11 times. Therefore, the deterioration of the DFB semiconductor laser is advanced in lane 1 as compared with lanes 2 and 3.

  Such variations in the degradation of the DFB semiconductor laser are also present in the configuration shown in FIG. In the wavelength division multiplexing transmitter module shown in FIG. 6, there are two semiconductor chips (wavelength division multiplexing transmitters), and lane 0 is lower than lane 1 and lane 2 is lower than lane 3, typically 0.4 dB output is low (0 .91 times). That is, it is necessary to increase the optical output of the DFB semiconductor laser by 1.11 times by increasing the injection current of lane 0 and lane 2 to 110 mA.

  That is, in the lane where the oscillation wavelength of the DFB semiconductor laser is short wave, the loss of light by the EA modulator in the on state is larger than that in the long wave, and it is necessary to increase the drive current of the DFB semiconductor laser to compensate for it. there were. For this reason, the amount of current per unit length of a lane DFB semiconductor laser having a short oscillation wavelength has increased, and variations have occurred in the degradation of the DFB semiconductor laser depending on the oscillation wavelength.

  As described above, there is a problem that it is difficult to use all the DFB semiconductor lasers in the same manner due to variations in the deterioration rates of the plurality of DFB semiconductor lasers formed in the same wavelength division multiplexing transmitter module.

  The present invention has been made in view of such a problem, and an object of the present invention is to reduce light loss by an EA modulator in a lane in a short wave without increasing the amount of current per unit length of the DFB semiconductor laser. It is an object of the present invention to provide a wavelength multiplexing transmitter that compensates for the above.

  In order to solve the above problems, the present invention provides a wavelength multiplexing transmitter, a plurality of semiconductor lasers having different oscillation wavelengths, and a plurality of electroabsorption optical modulators connected to each of the plurality of semiconductor lasers. And a multiplexer that multiplexes the signal light emitted from the plurality of electroabsorption optical modulators, and the multiplexer is connected to the semiconductor laser having the shortest oscillation wavelength. The coupling efficiency of the signal light emitted from the type optical modulator is larger than the coupling efficiency of the signal light emitted from the electroabsorption optical modulator connected to the other semiconductor laser.

  According to a second aspect of the present invention, in the wavelength division multiplexing transmitter according to the first aspect, the coupling efficiency for each wavelength of the multiplexer is larger as the wavelength is shorter.

  According to a third aspect of the present invention, in the wavelength division multiplexing transmitter according to the first or second aspect, the plurality of semiconductor lasers, the plurality of electroabsorption optical modulators, and the multiplexer are all a single semiconductor. It is formed on a chip.

  According to a fourth aspect of the present invention, in the wavelength division multiplexing transmitter according to the first or second aspect, the multiplexer is a plurality of first multiplexers connected to the plurality of electroabsorption optical modulators. And a second multiplexer that combines the signal light emitted from the plurality of first multiplexers, the plurality of semiconductor lasers, the plurality of electroabsorption optical modulators, and the plurality of The first multiplexer is formed on a plurality of semiconductor chips.

  According to a fifth aspect of the present invention, in the wavelength division multiplexing transmitter according to the fourth aspect, the second multiplexer is a polarization multiplexing type multiplexer.

  According to the present invention, it is possible to compensate for a light loss caused by an EA modulator in a lane in a short wave without increasing the amount of current per unit length of the DFB semiconductor laser.

It is a figure which shows the structure of the wavelength division multiplexing transmitter which concerns on Embodiment 1 of this invention. It is a figure which shows the structure of the optical multiplexer which consists of a directional coupler which concerns on Embodiment 1 of this invention. It is a figure which shows the structure of the Mach-Zehnder type | mold optical multiplexer which concerns on Embodiment 1 of this invention. It is a figure which shows the structure of the wavelength division multiplexing transmitter which concerns on Embodiment 2 of this invention. It is a figure which shows the structure of the conventional wavelength division multiplexing transmitter module used by 100 GbE. It is a figure which shows the structure of the conventional integrated wavelength division multiplexing module used by 100 GbE. It is sectional drawing of the semiconductor chip in which the DFB semiconductor laser, the EA modulator, and the optical multiplexer were formed. (A) shows the absorption curve of the absorption layer when no voltage is applied to the EA modulator and the oscillation wavelength of the DFB semiconductor laser, and (b) shows the absorption layer when the voltage is applied to the EA modulator. An absorption curve and an oscillation wavelength of the DFB semiconductor laser are shown, (c) shows a digital signal generated by the presence or absence of voltage application to the EA modulator, and (d) shows a case where the oscillation wavelength is short and a long wavelength. The case shows how the on-state absorption curves are applied to these two wavelengths. It is a figure which shows the optical output of lane0, 2 and 3 in a typical wavelength multiplexing optical transmitter.

  Hereinafter, embodiments of the present invention will be described in detail.

(Embodiment 1)
FIG. 1 shows a configuration of a wavelength division multiplexing transmitter according to Embodiment 1 of the present invention. Reference numeral 123 denotes a wavelength multiplexing transmitter module, 122 denotes a wavelength multiplexing transmitter which is one semiconductor chip, and 121 denotes an optical fiber. The semiconductor chip 122 includes four DFB semiconductor lasers 101-104, four electroabsorption (EA) type optical modulators 105-108, and one 4-to-1 optical multiplexer 113. That is, the semiconductor chip 122 includes four EA-DFBs in which a DFB semiconductor laser and an EA modulator are integrated. 109-112 is an input waveguide of the 4-to-1 optical multiplexer 113, and 114 is an output waveguide of the optical multiplexer 113.

  All of the DFB semiconductor lasers 101-104 output continuous light, and the laser oscillation wavelength bands of the DFB semiconductor lasers 101-104 are 1294.53 to 1296.59 nm, 1308.09 to 1310.109 nm, and 1299.02-11301, respectively. .09nm, 1303.54-1305.63nm.

  The EA optical modulator 105-108 has an absorption layer of the same composition, and the continuous light of the DFB semiconductor laser 101-104 is 25 Gb / s or 28 Gb / s according to the electric input of different electric signals (25 Gb / s or 28 Gb / s). s modulated signal light. The modulated signal lights output from the EA optical modulators 105-108 are output to the waveguides 109-112, respectively.

  The optical multiplexer 113 multiplexes four modulated signal lights having different wavelengths and outputs them to the waveguide 114 as wavelength multiplexed light bundled together. The wavelength multiplexed light bundled into one is diffused light 115 and emitted into the space, converted into parallel light 117 by the first lens 116, passed through the isolator 118, and converged light 120 by the second lens 119. And condensed and coupled to the fiber 121.

  Although not shown in the figure, the wavelength multiplexing optical transmitter module 123 includes a temperature sensor (for example, thermistor) of the semiconductor chip 122, a Peltier element for temperature control, a DFB semiconductor laser 101-104, and an EA type. A DC power supply is provided for supplying power to the optical modulators 105-108. It also has a modulator driver / high-frequency line termination resistor for driving the EA type modulator 105-108, and a signal line and control circuit for controlling the amplitude / bias voltage / electrical cross point of the modulator driver. Further, an electrical signal waveform shaping circuit, a clock extraction circuit, and a circuit that suppresses the influence of power supply voltage fluctuations may be provided in front of the modulator driver.

  As the EA type optical modulator 105-108, an InGaAlAs tensile strain quantum well that has an excellent extinction ratio and is effective in suppressing the pile-up of holes is used. As the output waveguides 109-112 and 114, ridge type waveguides embedded with a low dielectric constant BCB are used in order to secure a high frequency band. As the optical multiplexer 113, a high-mesa waveguide with strong light confinement and small radiation loss is used.

  The size of the semiconductor chip 122 is 2,000 × 2,600 μm, the waveguide length between the DFB semiconductor laser 101-104 and the EA modulator 105-108 is 50 μm, and the element length of the EA type optical modulator 105-108 is set. 150 μm.

  The wavelength division multiplexing transmitter module 123 is obtained by mounting the manufactured semiconductor chip 122 in an ultra-small package of 12 mm × 20 mm, and when operated at 100 Gbit / s at 40 ° C., 40 km error-free transmission over a single mode fiber. Achieved. As these results show, the wavelength division multiplexing transmitter module 123 has sufficient performance as a transceiver for future generations of 100 GbE.

  In the conventional wavelength multiplexing transmitter shown in FIG. 5, the element lengths (or resonance lengths) of the DFB semiconductor lasers 301 to 304 are the same, typically 400 μm. Therefore, as shown in FIG. 9, lane2-3 has a current of 100 mA and the optical output reaches 1 mW, whereas lane0 needs to flow 125 mA, and the amount of current per unit length of the DFB semiconductor laser increases. There was a problem.

  On the other hand, in the first embodiment of the present invention, the ratio of multiplexing in the optical multiplexer 113 is adjusted for each wavelength, that is, the optical output from the shortest wavelength DFB semiconductor laser 101 corresponds to lane1-3. The light intensity for each wavelength of the multiplexed light output from the optical multiplexer 113 is made uniform by increasing the ratio of multiplexing than the optical output from the lasers 102-104.

  FIG. 2 shows a configuration of an optical multiplexer including the directional coupler according to Embodiment 1 of the present invention. The optical multiplexer 113 includes three directional couplers 151-153. The directional coupler 151 combines the optical outputs output from lane0 and lane1, the directional coupler 152 combines the optical outputs output from lane2 and lane3, and the directional coupler 153 is the directional coupler. 151 and the directional coupler 152 multiplex the optical outputs output from one of the output ends. The light output output from one output terminal of the directional coupler 153 becomes the combined light of the optical multiplexer 113. The directional coupler can adjust the branching ratio by designing the coupling length L.

  The directional coupler 151 has a coupling length L designed so that the branching ratio is 56:44, and combines the directional coupler 153 with combined light having a light output from lane 0 of 56% and a light output from lane 1 of 44%. Output to. The directional coupler 152 has a coupling length L designed so that the branching ratio is 54:46, and the directional coupler 153 generates a combined light having a light output from lane 0 of 54% and a light output from lane 1 of 46%. Output to. The directional coupler 153 has a coupling length L designed so that the branching ratio is 50.5: 49.5, the light output from the directional coupler 151 is 50.5%, and the Combined light with an optical output of 49.5% is output.

  With this configuration, the combined light output from the optical multiplexer 113 is 1.24 when the light output from the lane 2 is 1, and the light output from the lane 1 is 1.24. The light output from lane 3 is combined at a rate of 1.01. That is, the coupling efficiency of the light output from each lane is in the order of the light output from lane 0, the light output from lane 3, the light output from lane 2, and the light output from lane 1.

Here, the oscillation wavelength of the DFB semiconductor laser 101 corresponding to lane 0 is the shortest wavelength λ _1, and the oscillation wavelength of the DFB semiconductor laser 102 corresponding to lane ₁ is the longest wavelength λ ₄ . Further, the oscillation wavelength of the DFB semiconductor laser 103 corresponding to lane 2 is the third shortest wavelength λ _3, and the oscillation wavelength of the DFB semiconductor laser 104 corresponding to lane ₃ is the second shortest wavelength λ ₂ .

At this time, the light intensity of the light output of wavelength λ ₁ from the shortest wavelength lane 0 is 0.79 times the light output of wavelengths λ ₃ and λ ₄ from lane 1-2 when the optical multiplexer 113 is input. However, when it is output from the optical multiplexer 113, it becomes 0.98 times the optical output of the wavelength λ ₃ combined. The light intensity of the light output of wavelength λ ₄ from the longest wavelength lane 1 is 0.98 times that of the combined output light of wavelength λ ₃ when output from the optical multiplexer 113. The light intensity of the optical output of wavelength λ ₂ from lane ₃ is 0.79 times the optical output of wavelengths λ ₃ and λ ₄ from lane 1-2 when the optical multiplexer 113 is input. the 1.01 times the light output of the multiplexed wavelength lambda ₃ when the output.

  Thereby, even if the current amount per unit length of the DFB semiconductor laser 101-104 is made equal, the light intensity of the light output after being multiplexed by the optical multiplexer 113 becomes substantially equal at all wavelengths. The degradation rates of 101-104 are almost the same.

  As described above, one example of the branching ratio of the directional coupler 151-153 of the optical multiplexer 113 has been described, but these branching ratios are not limited to the above example. If the variation in the light intensity of the light output for each wavelength becomes small, a certain effect is exhibited.

  FIG. 3 shows the configuration of an optical multiplexer comprising a Mach-Zehnder optical multiplexer according to Embodiment 1 of the present invention. In the optical multiplexer 113, the directional coupler 151-153 can be replaced by a Mach-Zehnder optical multiplexer 161-163. The Mach-Zehnder type optical multiplexer 161-163 can adjust the branching ratio in the same manner as the directional coupler by designing the optical path length difference ΔL of the arm waveguide. Each branching ratio is the same as that when the Mach-Zehnder type optical multiplexer 161-163 is used, as well as when the directional coupler 151-153 is used.

  In the present invention, four EA-DFBs and an example of a 4-to-1 optical multiplexer as an optical multiplexer have been described, but the number of EA-DFBs and the number of branches of the multiplexer are not captured above. That is, the number of EA-DFBs may be, for example, 2, 8, 16, or more, and the optical multiplexer may be 2: 1, 8: 1, or 16: 1. The optical multiplexer is not caught by a directional coupler or a Mach-Zehnder optical multiplexer, and may be a Y branch, a dielectric multilayer filter, an arrayed waveguide grating type, or a combination thereof.

Usually, the wavelength of each lane is lane 0: 1294.53-1296.59 nm
lane 1: 130.09-9130.19 nm
lane 2: 1299.02-1301.09 nm
lane 3: 1303.54-1305.63 nm
The modulation rate by the EA modulator is 25 Gb / s or 28 Gb / s, but the present invention is not limited to the above. This is because if the number of EA-DFBs changes, the number of lanes and the interval also change.

  Usually, 25 Gb / s × 4 wavelength = 100 Gb / s is used. For example, 50 Gb / s × 8 wavelength = 400 Gb / s, 25 Gb / s × 16 wavelength = 400 Gb / s, 10 Gb / s × 10 wavelength = 100 Gb / S may be used.

  What is important in the present invention is to make the coupling efficiency of the light output from the short wavelength lane larger than the coupling efficiency of the light output from the long wavelength lane when multiplexing is performed in the optical multiplexer.

(Embodiment 2)
FIG. 4 shows a configuration of a wavelength division multiplexing transmitter according to Embodiment 2 of the present invention. Reference numeral 232 denotes a wavelength multiplexing transmitter module, 230 and 231 denote wavelength division multiplexing transmitters that are semiconductor chips, and 229 denotes an optical fiber.

  The semiconductor chip 230 includes two DFB semiconductor lasers 201-202, two electroabsorption (EA) type optical modulators 205-206, one two-to-one optical multiplexer 213, and waveguides 209-210, 215. That is, the semiconductor chip 230 includes two EA-DFBs in which a DFB semiconductor laser and an EA modulator are integrated. Here, 209 to 210 are input waveguides of the 2-to-1 optical multiplexer 213, and 215 is an output waveguide of the optical multiplexer 213.

  Each of the DFB semiconductor lasers 201 to 202 outputs continuous light, and the laser oscillation wavelength bands of the DFB semiconductor lasers 201 and 202 are 1294.53 to 1296.59 nm and 1299.02 to 1301.09 nm.

  The EA light modulator 205-206 has an absorption layer of the same composition, and the continuous light of the DFB semiconductor laser 201-202 is 25 Gb / s or 28 Gb / s according to the electric input of different electric signals (25 Gb / s or 28 Gb / s). s modulated signal light. The modulated signal lights output from the EA optical modulators 205-206 are output to the waveguides 209-210, respectively.

  The basic structure of the semiconductor chip 231 is the same as that of the semiconductor chip 230. The DFB semiconductor laser 203-204 that outputs continuous light, the EA optical modulator 207-208 having an absorption layer of the same composition, and one two-to-one optical multiplexing. Device 214 and output waveguides 211-212, 216. On the other hand, the laser oscillation wavelength bands of the DFB semiconductor lasers 203-204 are 1303.54-1305.63 nm and 1308.09-1310.19 nm, respectively.

  The optical multiplexers 213-214 respectively combine two modulated signal lights having different wavelengths, and output them to the output waveguides 215-216 as wavelength multiplexed light bundled together. The wavelength multiplexed light bundled into one is diffused light 217 to 218 and emitted to the space, and is converted into parallel light 221 to 222 by the lens 219-220.

  The parallel light 221 changes its path at a right angle by the mirror 223, changes its polarization by 90 ° by the half-wave plate 224, and further changes its path at a right angle by the polarization filter 225 and enters the isolator 226. On the other hand, since the polarization of the parallel light 222 is not changed by the half-wave plate, it passes through the polarization filter and enters the isolator 226. In other words, the two wavelength multiplexed lights are combined by the polarization filter 225 to become wavelength multiplexed light.

  The parallel light 221-222 that has passed through the isolator 226 is converged by the lens 227 to be converged light 228 and coupled to the fiber 229.

  The size of each of the semiconductor chips 230 and 231 is 1,500 × 1,000 μm, and the size of the wavelength multiplexing transmitter module 232 including the LC receptacle is 8.7 mm × 29 mm. The wavelength division multiplex transmitter module 232 is capable of 40 km error-free operation when operated at 100 Gbit / s at 40 ° C.

  In the conventional wavelength division multiplexing transmitter of FIG. 6, the element length (or resonance length) of the DFB semiconductor laser 201-204 is the same, typically 400 μm. Therefore, while lanes 1 and 3 have a current of 100 mA and the optical output reaches 1 mW, it is necessary to pass 110 mA to lanes 0 and 2, which increases the amount of current per unit length of the DFB semiconductor laser. .

  On the other hand, in the second embodiment of the present invention, the ratio of multiplexing in the optical multiplexers 213 and 214 is adjusted for each wavelength, that is, the optical output from the DFB semiconductor lasers 201 and 203 corresponding to the short wavelengths lane 0 and 2. Are increased in proportion to the light output from the DFB semiconductor lasers 202 and 204 corresponding to lanes 1 and 3, so that the light intensity for each wavelength of the combined light output from the optical multiplexers 213 and 214 is made uniform. Yes.

  As in the first embodiment, the optical multiplexers 213 and 214 can be directional couplers or Mach-Zehnder optical multiplexers. The optical multiplexers 213 and 214 are designed to have a branching ratio of 52:48, and output combined light having a light output from lanes 0 and 2 of 52% and a light output from lanes 1 and 3 of 48%.

  With such a configuration, the combined light output from the optical multiplexer 213 is obtained by combining the output light from lane 0 at a rate of 1.08, where the optical output from lane 1 is 1. Similarly, the combined light output from the optical combiner 214 is obtained by combining the output light from lane 3 at a rate of 1.08, where the light output from lane 2 is 1. That is, the coupling efficiency of the light output from each lane is such that the light output from lane 0 is greater than the light output from lane 1, and the light output from lane 2 is greater than the light output from lane 3.

At this time, the optical intensity of the optical output of wavelength λ ₁ from the short wavelength lane 0 is 0.91 times the optical output of wavelength λ ₂ from lane 1 when the optical multiplexer 213 is input. the 0.99 times the light output of the multiplexed wavelengths lambda ₂ when the output from. Similarly, the optical intensity of the optical output of wavelength λ ₃ from the short wavelength lane 2 is 0.91 times the optical output of wavelength λ ₄ from lane 3 when the optical multiplexer 214 is input. the 0.99 times the light output of the multiplexed wavelength lambda ₄ when the output from.

  As a result, even if the current amount per unit length of the DFB semiconductor laser 201-204 is made equal, the light intensities of the optical outputs after being combined by the optical multiplexers 213 and 214 are substantially equal at all wavelengths. The degradation rates of the semiconductor lasers 201-204 are almost the same.

  The branching ratio of the optical multiplexers 213 and 214 is not limited to the above example. If variation in light intensity of light output for each wavelength is reduced, a certain effect is exhibited.

  In the present invention, an example is described in which two EA-DFBs and two semiconductor chips each composed of a 2-to-1 optical multiplexer are integrated as an optical multiplexer. However, the number of EA-DFBs and the number of branching multiplexers are described. Is not caught by the above. That is, four EA-DFBs and two semiconductor chips each composed of a 4-to-1 optical multiplexer may be integrated as an optical multiplexer, for a total of 8 wavelengths. When eight EA-DFBs and two semiconductor chips each consisting of an 8-to-1 optical multiplexer are integrated as an optical multiplexer, the wavelength is 16 wavelengths.

  The optical multiplexer is not caught by a directional coupler or a Mach-Zehnder optical multiplexer, and may be a Y branch, a dielectric multilayer filter, an arrayed waveguide grating type, or a combination thereof.

Usually, the wavelength of each lane is lane 0 1294.53-1296.59 nm
lane1 1299.02-1301.09nm
lane2 1303.54-1305.63nm
lane3 1308.009-130.10.19nm
The modulation rate by the EA modulator is 25 Gb / s or 28 Gb / s, but the present invention is not limited to the above. This is because if the number of EA-DFBs changes, the number of lanes and the interval also change.

  Usually, 25 Gb / s × 4 wavelength = 100 Gb / s is used. For example, 50 Gb / s × 8 wavelength = 400 Gb / s, 25 Gb / s × 16 wavelength = 400 Gb / s, 10 Gb / s × 10 wavelength = 100 Gb / S may be used.

  The important thing in the present invention is to make the coupling efficiency of the light output from the lane having the short wavelength larger than the coupling efficiency of the light output from the lane having the long wavelength when multiplexing is performed in the optical multiplexer.

101-104, 201-204, 301-304, 401-404 DFB semiconductor laser 105-108, 205-208, 305-308, 405-408 EA optical modulator 109-112, 114, 209-212, 215, 309 -312, 314, 409-412, 415 Waveguide 113, 213, 214, 313, 413, 414 Optical multiplexer 115, 217, 218, 315, 417, 418 Diffused light 116, 119, 219, 220, 227, 316 319, 419, 420, 427, lens 117, 221, 222, 317, 421, 422 parallel light 118, 226, 318, 426 isolator 120, 228, 320, 428 convergent light 121, 229, 321, 429 fiber 122, 230, 231, 322, 430 431 Semiconductor chip 123, 232, 323, 432 Wavelength multiplexing transmitter module 151-153 Directional coupler 161-163 Mach-Zehnder type optical multiplexer 223, 423 Mirror 224, 424 Half-wave plate 225, 425 Polarization filter 501 n Electrode 502 n-InP substrate 503 n-InP clad layer 504 active layer 505 guide layer 506 p-InP clad layer 507 DFB semiconductor laser electrode 508 EA modulator absorption layer 509 EA modulator electrode 510 core layer 511 InP
512 quarter-wave phase shift

Claims (5)

A plurality of semiconductor lasers having different oscillation wavelengths;
A plurality of electroabsorption optical modulators connected to each of the plurality of semiconductor lasers;
A multiplexer that multiplexes the signal light emitted from the plurality of electroabsorption optical modulators;
With
The multiplexer is configured such that the coupling efficiency of the signal light emitted from the electroabsorption optical modulator connected to the semiconductor laser having the shortest oscillation wavelength is the electroabsorption optical light connected to the other semiconductor laser. A wavelength division multiplexing transmitter characterized by being larger than the coupling efficiency of signal light emitted from a modulator.   The wavelength division multiplexing transmitter according to claim 1, wherein the coupling efficiency for each wavelength of the multiplexer is larger as the wavelength is shorter.   3. The wavelength division multiplexing transmitter according to claim 1, wherein the plurality of semiconductor lasers, the plurality of electroabsorption optical modulators, and the multiplexer are all formed on a single semiconductor chip. . The multiplexer combines a plurality of first multiplexers connected to the plurality of electroabsorption optical modulators and a signal light emitted from the plurality of first multiplexers. Consisting of
3. The wavelength according to claim 1, wherein the plurality of semiconductor lasers, the plurality of electroabsorption optical modulators, and the plurality of first multiplexers are formed on a plurality of semiconductor chips. Multiple transmitter.   5. The wavelength division multiplexing transmitter according to claim 4, wherein the second multiplexer is a polarization multiplexing type multiplexer.

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