JPH053365A - Distributed feedback laser - Google Patents

Abstract

PURPOSE:To suppress the occurrence of a jitter in a transmission waveform by utilizing a thermal effect. CONSTITUTION:Resistance layers 10 and 11 are provided on both sides of an active layer 8 and clad layers 7 and 9 which are main constituents of the conventional distributed feedback laser, with current blocking layers 7 and 9 being respectively put between layers 7-9 and layers 10 and 11 the negative logic signal Q<-> of a main signal Q for light emission is injected into the resistance layer sections 10 and 11. Therefore, the temperature variation of the laser active layer 8 caused by changes in data pattern can be eliminated and the variation of oscillating center wavelength can be suppressed by utilizing a thermal effect.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser, and more particularly to a distributed feedback laser which oscillates in a single axis mode.

[0002]

2. Description of the Related Art In a conventional distributed feedback laser, a clad layer 9, an active layer 8, a clad layer 7 and a cap layer 6 are formed on a substrate 12 as shown in FIG.
3 is provided. A diffraction grating 14 is formed in the clad layer 9, and both end faces are coated with antireflection films 15 and 16.

When the metal electrode 1 is connected to the negative electrode and the metal electrode 13 is connected to the positive electrode, electrons are injected from the metal electrode 1 and holes are injected from the metal electrode 13, so that the electrons go to the positive electrode side and the holes go to the negative electrode side.

However, the electrons are confined in the active layer 8 due to the potential barrier between the active layer 8 and the cladding layer 9, and the holes also enter the active layer 8 due to the potential barrier between the active layer 8 and the cladding layer 7. Be trapped. Thus, the electrons and holes trapped in the active layer 8 are recombined to generate light. Further, since the refractive index n of the active layer 8 is larger than that of the cladding layers 7 and 9, the generated light is also confined in the active layer 8. The generated light is reflected by the diffraction grating 14 having a grating period of Λ, and when the diffraction order is m, only the light of wavelength λ ₀ satisfying the condition of the following formula 1 is selectively lased (semiconductor laser and application See Hiroo Yonezu Technology). Furthermore, the antireflection films 15 and 16 on both end surfaces
To prevent the Fabry-Perot mode from oscillating,
The reflectance of both end faces is reduced.

[0005]

[Equation 1]

[0006]

The problem in the case of performing data transmission using this conventional distributed feedback laser will be described with an example.

FIG. 7 is a block diagram of a data transmission system. Data Q is input to the distributed feedback laser. The distributed feedback laser 20 outputs an optical signal corresponding to the data, and the optical signal is input to the optical fiber 18, transmitted, and reproduced by the optical receiver 19.

At this time, it is assumed that the mark ratio of the data Q changes with time as shown in FIG. When the mark ratio changes, the temporal average value of carriers injected into the laser changes. When the number of injected carriers increases, the amount of heat generated by the laser increases, and the physical size and refractive index of the laser chip increase. Therefore, the oscillation wavelength λ _{0 of the} laser shifts to the long wavelength side according to Equation 1. That is, the relationship between the mark ratio and the oscillation wavelength is shown in FIG. 9, and the oscillation wavelength λ ₀ also changes according to the change in the mark ratio. When such an optical signal is transmitted through an optical fiber, due to the chromatic dispersion of the optical fiber,
The group velocity of the optical signal changes with the fluctuation of the oscillation wavelength.
As described above, there is a problem that the optical signal wavelength shown in (a) causes phase jitter as shown in (b) and the transmission characteristics deteriorate.

The present invention solves the above-mentioned problems of the prior art, and provides a distributed feedback laser in which phase jitter does not occur even when a signal whose mark ratio changes with time is transmitted to an optical fiber having chromatic dispersion. It is provided.

[0010]

A distributed feedback laser according to the present invention comprises an active layer for lasing on a distributed feedback substrate which oscillates in a single axis mode, a clad layer for confining carriers and light in the active layer, and A first metal electrode for inputting a current signal of 1, a cap layer for reducing a contact resistance with the metal electrode, and a diffraction grating for selecting only a specific wavelength of light generated in the active layer In a distributed feedback laser having antireflection films for suppressing Fabry-Perot mode oscillation on both end faces, a current blocking layer having relatively good thermal conductivity is provided outside both sides of the active layer, the cladding layer, and the cap layer. A resistance layer for passing a second current signal is provided in thermal contact with the outside in order, and second and third metal electrodes for inputting the second sub-current are further provided in the resistance layer. Characteristic distribution Type laser is obtained.

Further, according to the present invention, the current amplitudes of the first current signal and the second current signal are determined by the heat generation of the distributed feedback laser by the first current signal and the resistance layer by the second current signal. The distributed feedback laser described above is obtained, characterized in that the heat generation of the above is adjusted so as to be substantially equal at the same mark ratio of the signal.

Further, according to the present invention, the second current signal has a negative logic relationship with the first main current signal.
The distributed feedback laser described above or before that can be obtained.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view of one embodiment of the distributed feedback laser of the present invention. On the substrate 12, an active layer 8 for laser oscillation, clad layers 7 and 9 for confining carriers and light in the active layer 8, a metal electrode 2 for inputting a current signal Q,
Cap layer 6 for reducing the contact resistance with the metal electrode 2
And a diffraction grating 14 that selects only a certain wavelength of the light generated in the active layer 8 is formed.

[0015] on opposite sides of each layer, the current signal Q is negative logic data of the current signal Q ^-. While (typically place the bar at the top of the Q, since the printing can not be used to place on the right shoulder in the drawings The metal electrodes 1 and 3 for inputting) are input, the resistance layers 10 and 11 for generating heat by the injected current, and the current signals Q and Q ⁻ are separated. The current blocking layers 4 and 5 are formed.

Below the substrate 12, the metal electrodes 2 and 1,
A common metal electrode 13 is formed on the both ends of the laser chip, and antireflection films 15 and 16 are formed on both end surfaces of the laser chip in order to suppress oscillation in the Fabry-Pro mode.

FIG. 2 shows an example in which the laser of the present invention is used in a data transmission system. In the laser 17 of the present invention, the signal data Q to be transmitted is input to the Q input, and the negative logic data Q ⁻ of the data Q is input to the Q ⁻ input. The data Q is converted into an optical signal, transmitted through the optical fiber 18, and reproduced by the optical receiver 19. Data Q ^- is not any further possible simply by heating the resistor pair 10, 11.

FIG. 3 shows the change over time in the mark ratio of the data Q and the data Q ⁻ , and the mark ratio of the data Q is 1 /.
Be varied from 2 to 1/3, data Q ^- mark rate of 1
Since it changes from / 2 to 2/3, the mark ratio of the current signal injected into the laser is always 1. Therefore, by adjusting the current amplitudes of the data Q and the data Q ⁻ so that the heat generation of the laser due to the data Q becomes almost equal to the heat generation of the resistance layers 10 and 11 due to the data Q ⁻ , the mark ratio varies. Even so, the temperature of the laser 17 of the present invention is kept constant. That is, as shown in FIG. 4, the oscillation wavelength of the laser 17 of the present invention is constant regardless of the mark rate. Therefore, even if the laser of the present invention is used to transmit a data signal whose mark ratio fluctuates with time through an optical fiber having wavelength dispersion, as shown in FIG. 5, the optical waveform shown in FIG. The transmission waveform is as shown in b), the phase jitter does not increase, and the transmission characteristics do not deteriorate.

[0019]

As described above, according to the present invention, a resistance layer is provided on both sides of a conventional distributed feedback laser, and a data current signal having a constant relationship with a data signal injected into a laser oscillation region is injected therein. By doing so, even if a signal whose mark rate fluctuates with time is transmitted through an optical fiber having wavelength dispersion, there is an effect that phase jitter does not occur.

[Brief description of drawings]

FIG. 1 is a front view and a side view of a distributed feedback laser of the present invention.

FIG. 2 is a diagram showing an example of use of the laser of the present invention.

FIG. 3 is a signal waveform diagram of the signal shown in FIG.

FIG. 4 is a diagram showing an example of a relationship between a mark ratio of an applied signal of a laser of the present invention and an oscillation wavelength.

5 is a diagram showing optical waveforms before and after the optical fiber transmission in FIG.

FIG. 6 is a front view and a side view of a conventional distributed feedback laser.

FIG. 7 is a diagram showing an example of use of a conventional laser.

FIG. 8 is a signal waveform diagram of the signal shown in FIG.

FIG. 9 is a diagram showing an example of a relationship between a mark ratio of an applied signal of a conventional laser and an oscillation wavelength.

10 is an optical wavelength diagram before and after the optical fiber transmission in FIG.

[Explanation of symbols]

1,2,3 metal electrodes 4,5 Current blocking layer 6 Cap layer 7 Clad layer 8 Active layer 9 Clad layer 10,11 Resistance layer 12 substrates 13 metal electrodes 14 diffraction grating 15,16 Anti-reflection film 17 Distributed feedback laser 18 optical fiber 19 Optical receiver 20 Distributed feedback laser 21 Phase jitter

Claims (3)

[Claims] 1. A contact between an active layer for laser oscillation, a clad layer for confining carriers and light in the active layer, a first metal electrode for inputting a first current signal, and a contact with the metal electrode on a substrate. A distributed feedback laser having a cap layer for reducing resistance, a diffraction grating for selecting only a specific wavelength of light generated in the active layer, and an antireflection film for suppressing Fabry-Perot mode oscillation on both end faces. In the above, a current blocking layer having a relatively good thermal conductivity and a resistance layer for flowing a second current signal are thermally adhered to the outside on both sides of the active layer, the clad layer and the cap layer in order. A distributed feedback laser, wherein the distributed feedback laser is provided, and further comprises second and third metal electrodes for inputting the second sub-current to the resistance layer. 2. A mark ratio in which the first current signal and the current amplitudes of the current signals are the same when the heat of the distributed feedback laser due to the first current signal and the heat of the resistance layer due to the second current signal are the same signal. 2. The distributed feedback laser according to claim 1, wherein the distributed feedback laser is adjusted so that 3. The distributed feedback laser according to claim 1 or 2, wherein the second current signal has a negative logic relationship with the first main current signal.