Semiconductor laser with stable wavelength in burst mode and switching method

Abstract

The application discloses a semiconductor laser with stable wavelength in burst mode, comprising a substrate, and a first laser diode and a second electro-absorption diode vertically integrated; the epitaxial layer of the first laser diode is arranged above the epitaxial layer of the second electro-absorption diode, and the epitaxial layer of the first laser diode and the epitaxial layer of the second electro-absorption diode jointly form a composite waveguide structure; the first laser diode comprises a first laser waveguide active layer, a first laser top electrode and a first laser bottom electrode; the second electro-absorption diode comprises a second electro-absorption waveguide active layer, a second electro-absorption top electrode and a second electro-absorption bottom electrode; the first laser bottom electrode and the second electro-absorption top electrode can be the same physical electrode or separate physical electrodes. The application is to eliminate the wavelength shift during the transmission signal burst.

Description

Technical Field

[0001] This invention relates to the field of semiconductor laser technology, and more particularly to a semiconductor laser with a stable wavelength in burst mode and a switching method thereof. Background Technology

[0002] In a passive optical network (PON) architecture, the optical network unit transmitter operates in burst mode, transmitting optical signals only within a given time interval. Such a PON is called a time-division multiplexing system. To meet the demands for higher speeds and greater capacity, next-generation PON technologies utilize dense wavelength division multiplexing (DWDM), which uses dense wavelength channels within the same optical fiber to increase transmission capacity, while maintaining a time-division multiplexing structure within each channel. Thus, the PON becomes a wavelength division-time division multiplexing (WDM-TDM) passive optical network.

[0003] The burst mode configuration of time-division multiplexing (TDM) presents challenges to the operation of wavelength-division multiplexing (WDM) systems. In burst mode, the laser drive current rises from zero to operating current during the signal burst, causing the laser wavelength to shift at a rate of approximately 0.01 nm / mA after reaching a threshold. This results in the wavelength change of one WDM channel exceeding its bandwidth, leading to optical crosstalk in adjacent channels and severely impairing their transmission performance. Figure 1 As shown, to avoid this situation, current technologies primarily use mechanical shutters or beam refraction systems to prevent light from entering the network system during signal bursts. However, this method has drawbacks such as manufacturing difficulties, high losses, and large size. Meanwhile, a common method for turning lasers on or off is to change their injection current, making it higher or lower than a threshold. Changes in the laser injection current cause changes in its emission wavelength, a phenomenon that can cause crosstalk between adjacent channels in wavelength division multiplexing (WDM) passive optical network systems, generating noise. Summary of the Invention

[0004] The purpose of this invention is to eliminate wavelength shift during bursts of transmitted signals, thereby providing a semiconductor laser with a stable wavelength in burst mode and a switching method thereof.

[0005] To achieve the above objectives, the following technical solution is adopted:

[0006] A semiconductor laser with a stable wavelength in burst mode includes a substrate and a vertically integrated first laser diode and a second electro-absorption diode; the epitaxial layer of the first laser diode is disposed on the epitaxial layer of the second electro-absorption diode, and the epitaxial layers of the first laser diode and the second electro-absorption diode together form a composite waveguide structure.

[0007] The first laser diode includes a first laser waveguide active layer, a first laser top electrode, and a first laser bottom electrode;

[0008] The second electro-absorption diode includes a second electro-absorption waveguide active layer, a second electro-absorption top electrode, and a second electro-absorption bottom electrode;

[0009] The first laser bottom electrode and the second electroabsorption top electrode can be the same physical electrode or separate physical electrodes.

[0010] Furthermore, a negative bias voltage is applied to the second electro-absorption diode to put it in a light absorption state, thereby controlling the intracavity loss of the laser and changing the laser's operating state to on or off.

[0011] Furthermore, when the intracavity loss exceeds the gain that the laser semiconductor can provide, the laser can be controlled to shut down.

[0012] Furthermore, when the intracavity loss is lower than the gain that the laser semiconductor can provide, the laser can be controlled to turn on.

[0013] Furthermore, in burst mode, the first laser diode remains in a driven state, i.e., constant current injection; the burst signal controls the voltage applied between the top and bottom electrodes of the second electroabsorption diode, i.e., controls the laser cavity loss, thereby changing the laser's operating state from off to on.

[0014] Furthermore, in burst mode, the pump state of the first laser diode remains unchanged, thereby maintaining a stable emission wavelength.

[0015] A method for switching on and off a semiconductor laser with a stable wavelength in burst mode is also provided. The method includes the semiconductor laser described above. In burst mode, a negative bias voltage is applied to the second electro-absorption diode to put it in a light absorption state, thereby controlling the intracavity loss of the laser and changing the laser's operating state to on or off.

[0016] By adopting the above solution, the beneficial effects of the present invention are:

[0017] This invention achieves laser switching on and off by controlling the optical cavity loss, rather than by changing the injection current. That is, the injection current remains constant when the laser is on and off, thus eliminating any significant changes in the emission wavelength. Simultaneously, this invention simplifies optical blocking in wavelength division multiplexing (WDM) passive optical network systems, simplifies component design and manufacturing, increases yield, and most importantly, improves the laser switching speed. This switching speed is a key parameter in WDM-TDM systems and is one that current methods cannot achieve. Attached Figure Description

[0018] Figure 1 A diagram illustrating crosstalk caused by burst mode operation in a wavelength division multiplexing system;

[0019] Figure 2 This is a schematic diagram of the laser structure of the present invention;

[0020] Figure 3 In one embodiment of the present invention, a graph showing the change in composite optical mode loss with the applied bias voltage of the electro-absorption diode is provided.

[0021] The following are explanations of the labels in the attached diagram:

[0022] 1—Substrate; 2—Composite waveguide structure;

[0023] 3—First laser waveguide active layer; 4—First laser top electrode;

[0024] 5—First laser bottom electrode; 6—Second electrically absorbing waveguide active layer;

[0025] 7—Second electroabsorption bottom electrode. Detailed Implementation

[0026] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0027] Reference Figures 2 to 3 As shown, the present invention provides a semiconductor laser with a stable wavelength in burst mode, comprising a substrate 1, and a vertically integrated first laser diode and a second electro-absorption diode; the epitaxial layer of the first laser diode is disposed on the epitaxial layer of the second electro-absorption diode, and the epitaxial layers of the first laser diode and the second electro-absorption diode together form a composite waveguide structure 2; the first laser diode includes a first laser waveguide active layer 3, a first laser top electrode 4, and a first laser bottom electrode 5; the second electro-absorption diode includes a second electro-absorption waveguide active layer 6, a second electro-absorption top electrode, and a second electro-absorption bottom electrode; the first laser bottom electrode 5 and the second electro-absorption top electrode can be the same physical electrode or separate physical electrodes.

[0028] Specifically, a negative bias voltage is applied to the second electro-absorption diode to put it in a light absorption state, thereby controlling the intracavity loss of the laser and changing the laser's operating state to on or off. That is, when the intracavity loss exceeds the gain that the laser semiconductor can provide, the laser can be controlled to be off, and when the intracavity loss is lower than the gain that the laser semiconductor can provide, the laser can be controlled to be on.

[0029] Meanwhile, in burst mode, the first laser diode remains in a driven state, i.e., constant current injection; the burst signal controls the voltage applied between the top and bottom electrodes of the second electroabsorption diode, i.e., controls the laser cavity loss and thus changes the laser operating state from off to on; in burst mode, the pump state of the first laser diode remains unchanged, thereby maintaining a stable emission wavelength.

[0030] In one embodiment, the first laser diode and the second electroabsorption diode are active pin diodes that are vertically integrated with each other. That is, the epitaxial layer of a conventional laser diode (LD) is arranged on the epitaxial layer of an electroabsorption diode. The laser injection current flows between the first laser top electrode 4 and the first laser bottom electrode 5 to provide gain for the laser diode to generate light. The bias voltage applied between the first laser bottom electrode 5 and the second electroabsorption bottom electrode 7 controls the light absorption introduced therein, and further controls the cavity loss of the laser.

[0031] Optically, the epitaxial layer of the first laser diode and the epitaxial layer of the second electro-absorption diode together form a composite waveguide structure 2. The optical mode of this composite waveguide is as follows: Figure 2 As shown by the dashed lines, although most modes are confined to the first laser waveguide active layer 3, the tail of the mode extends to the electro-absorption layer. When the electro-absorption diode, i.e. the second electro-absorption diode, is not biased or the bias voltage is 0V, the diode is almost transparent to the laser, which means that the composite optical mode has low loss. However, when the electro-absorption diode is biased at a certain voltage, the diode will produce high loss for the composite optical mode.

[0032] like Figure 3 An exemplary loss curve for the composite optical mode with varying bias of the electro-absorption diode is shown. When the bias voltage is close to 0V, the loss of the electro-absorption diode is negligible, and the laser operates normally in the on state. However, as the bias voltage increases—in one embodiment, at -2.6V—the loss of the electro-absorption diode increases dramatically, and the laser stops operating in the off state. Therefore, during burst mode operation, only an appropriate bias voltage needs to be applied to the electro-absorption diode to switch the laser between on and off states. Since the laser injection current remains at the operating current level, the emission wavelength remains within the operating wavelength range, thus eliminating the problem of introducing unnecessary crosstalk.

[0033] In addition, a method for switching on and off a semiconductor laser with a stable wavelength in burst mode is provided, including the semiconductor laser described above. In burst mode, a negative bias voltage is applied to the second electro-absorption diode to put it in a light absorption state, thereby controlling the intracavity loss of the laser and changing the laser's operating state to on or off.

[0034] As described above, during burst mode operation, the laser can be switched between on and off states simply by applying an appropriate bias voltage to the electro-absorption diode, i.e., the second electro-absorption diode. In one embodiment, the laser can stop working and be in the off state when the bias voltage is -2.6V.

[0035] As can be seen from the above, this invention proposes a method for controlling the switching on and off of a semiconductor laser by changing the bias voltage on a diode formed by an electro-absorbing material. This invention does not require setting up an optical blocking mechanism in the optical path, thereby greatly improving the switching speed of the laser. At the same time, it not only simplifies the device structure, but also realizes the rapid switching of the laser's switching state in burst mode, which is an important improvement to the key operational performance of the module.

[0036] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for switching on and off a semiconductor laser with a stable wavelength in burst mode, comprising a semiconductor laser, characterized in that, The semiconductor laser includes a substrate and a vertically integrated first laser diode and a second electro-absorption diode; the epitaxial layer of the first laser diode is disposed on the epitaxial layer of the second electro-absorption diode, and the epitaxial layers of the first laser diode and the second electro-absorption diode together form a composite waveguide structure. The first laser diode includes a first laser waveguide active layer, a first laser top electrode, and a first laser bottom electrode; The second electro-absorption diode includes a second electro-absorption waveguide active layer, a second electro-absorption top electrode, and a second electro-absorption bottom electrode; The first laser bottom electrode and the second electroabsorption top electrode are the same physical electrode or separate physical electrodes; A negative bias voltage is applied to the second electro-absorption diode to put it in the light absorption state, thereby controlling the intracavity loss of the laser and changing the laser's operating state to on or off. When the intracavity loss exceeds the gain that the laser semiconductor can provide, the laser is controlled to shut down. When the intracavity loss is lower than the gain that the laser semiconductor can provide, the laser is controlled to turn on. In burst mode, the first laser diode remains in a driven state, i.e., constant current injection; the burst signal is used to control the voltage applied between the top and bottom electrodes of the second electro-absorption diode to control the laser cavity loss and thus change the laser's operating state from off to on. Both the first laser diode and the second electro-absorption diode are active pin diodes; the composite optical mode formed by the composite waveguide structure is mainly confined within the active layer of the first laser waveguide, and the tail of the composite optical mode extends into the active layer of the second electro-absorption waveguide.

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