Isolated semiconductor laser, optical transmitting assembly and optical module

Abstract

An isolated semiconductor laser, optical transmitting assembly and optical module, comprising a front DFB laser and a rear DFB laser; wherein the oscillation wavelength of the front DFB laser is, the oscillation wavelength of the rear DFB laser is, and; the rear DFB laser is configured to be driven by a direct current; the front DFB laser is configured to work in a direct current bias superimposed alternating current modulation or only alternating current modulation mode. The present application does not need a traditional magneto-optical isolator, since the oscillation wavelength of the rear DFB laser is less than the oscillation wavelength of the front DFB laser, and the interval is at least 100 nm, the light (wavelength) reflected back from the front end of the laser cannot obtain effective gain in the rear DFB active area oscillating at, and is strongly attenuated, thereby achieving a natural optical isolation effect, significantly reducing the sensitivity of the laser to feedback light, realizing the small size, low cost, high stability of the isolated laser output, and especially suitable for high-speed direct modulation lasers and compact optical transmitting assemblies and optical modules.

Description

Technical Field

[0001] This invention relates to the field of semiconductor light-emitting devices, and more specifically to a method for isolating external feedback light from a semiconductor laser by utilizing the non-reciprocal phenomenon exhibited during transitions between semiconductor energy levels, thereby significantly reducing the impact of external feedback light on the laser. Background Technology

[0002] In practical applications such as fiber optic communication, sensing, and lidar, the output light of semiconductor lasers is often reflected back into the laser cavity by components such as connectors and fiber endfaces. This external optical feedback is a key issue leading to system performance degradation. Therefore, developing semiconductor lasers that can resist such feedback is crucial. Specifically, many characteristics of semiconductor lasers, especially their oscillation stability, are severely affected by external feedback. For typical DFB lasers, when the intensity of external feedback reaches -20dB or higher, the lasing wavelength will drift, the side-mode suppression ratio will deteriorate significantly, and consequently, the output optical power will change. Especially for high-speed direct-modulation DFB lasers, the modulation bandwidth and passband flatness will change, leading to severe degradation of the eye diagram.

[0003] To eliminate the influence of external feedback, DFB direct-modulated lasers operating at modulation rates above 10 Gbps generally require optical isolators. Currently, practical optical isolators are all based on the Faraday effect in magneto-optical crystals, which can only be fabricated into millimeter (mm)-sized micro-optics devices and cannot be monolithically integrated with micrometer (μm)-sized waveguide devices based on semiconductor materials. This leads to a series of bottlenecks such as cost and packaging size for laser devices. Although unidirectional light transmission can be achieved by utilizing the nonlinearity or time-varying properties of materials to disrupt the reciprocity of light, these methods are difficult to directly integrate with semiconductor lasers on a single chip. Using asymmetric transmission or other anti-reflection structure designs can also significantly reduce the impact of external feedback on lasers under specific conditions, and some of these structures can be implemented in the form of waveguides and integrated with the laser. However, ultimately, issues such as cost, thermal stability, and packaging size are still unavoidable.

[0004] Therefore, there is still a lack of effective means to reduce or even eliminate the impact of external feedback on the characteristics of semiconductor lasers at low cost without significantly increasing the package size. Summary of the Invention

[0005] This invention discloses an isolated semiconductor laser based on a dual-segment DFB with energy level non-reciprocity effect, aiming to solve the technical problem of laser performance degradation caused by external feedback light.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: an isolated semiconductor laser, characterized in that it includes: a front-end DFB laser and a back-end DFB laser monolithically integrated on the same substrate;

[0007] Wherein, the lasing wavelength of the front-end DFB laser is The lasing wavelength of the downstream DFB laser is ,and ;

[0008] The rear DFB laser is configured to be driven by a DC current to inject its output laser as an optical pump source into the front DFB laser.

[0009] The front-end DFB laser is configured to operate in a DC bias superimposed AC modulation or AC modulation only mode, and converts the optical pump energy into a modulated optical signal output.

[0010] As a further improvement of the present invention, the rear DFB laser and the front DFB laser are integrated by a docking growth process, so that the two have their own independent active regions and optical feedback structures.

[0011] As a further improvement of the present invention, the front-end DFB laser includes a gain peak wavelength of The first active region; the subsequent DFB laser includes a gain peak wavelength of The second active region;

[0012] Wherein, the first active region and the second active region are one of a quantum dot active region, a quantum well active region, or a bulk material active region, and the parameters of the first active region and the second active region are set differently to satisfy... .

[0013] As a further improvement of the present invention, the front-end DFB laser includes a lasing wavelength of The first grating region; the subsequent DFB laser includes a lasing wavelength of The second grating region;

[0014] Wherein, the first grating region and the second grating region are any of the following grating forms with a mode selection mechanism: uniform grating, phase-shifting grating, or partial grating. The parameters of the first grating region and the second grating region are set differently to meet the following requirements: ;

[0015] The first grating region and the second grating region are fabricated using a mode-selective grating forming process.

[0016] As a further improvement of the present invention, the first grating region and the second grating region are fabricated by any one or more grating forming processes selected from holographic lithography, EBL lithography, nanoimprint lithography, and deep ultraviolet lithography.

[0017] The downstream DFB laser is configured to be driven by direct current;

[0018] The front-end DFB laser is configured to have a drive current that includes an AC modulation component and may optionally include a DC bias component.

[0019] The DC bias component of the front-end DFB laser is configured to be adjustable to compensate for the total output power when the output power of the rear-end DFB laser is saturated.

[0020] As a further improvement of the present invention, the aforementioned isolated semiconductor laser is characterized in that: an electrical isolation channel is provided between the front-end DFB laser and the rear-end DFB laser to enable the two lasers to be electrically injected separately.

[0021] An optical emitting component comprising an isolated semiconductor laser as described above.

[0022] An optical module comprising an isolated semiconductor laser as described above.

[0023] The beneficial effects of this invention are: this invention eliminates the need for traditional magneto-optical isolators, due to the lasing wavelength of the downstream DFB laser. Smaller than the lasing wavelength of the front-end DFB laser And the light reflected back from the laser front end at intervals of 100nm and above (wavelength is...) Unable to be blasted at The laser gains effective gain in the DFB active region of the rear section, which is then strongly attenuated, achieving a natural optical isolation effect. This significantly reduces the laser's sensitivity to feedback light, enabling miniaturized, low-cost, and highly stable isolated laser output. It is particularly suitable for high-speed direct-modulation lasers and compact optical emission components and modules. Attached Figure Description

[0024] Figure 1 : Schematic diagram of the monolithically integrated dual-segment DFB structure of the device of the present invention along the propagation direction z;

[0025] Figure 2 : The epitaxial layer structure of the device of the present invention in the xz plane along the epitaxial growth direction x and the propagation direction z;

[0026] Figure 3 In the embodiment, the gain spectrum of the first active region and the second active region includes the relationship between the peak wavelength of the gain of the first active region and the second active region, and the relationship between the lasing wavelength of the first grating region and the second grating region.

[0027] Figure 4 : The trend of photogenerated current measured in the front section 101 without injection when different currents are injected into the rear section 102;

[0028] Figure 5 The spectrum measured at the front face 104 of the laser when a 50mA current is injected into the rear section 102 and a 0mA current is injected into the front section 101, without external feedback.

[0029] Figure 6 The spectrum was measured at the front face 104 of the laser when a 50mA current was injected into the rear section 102 and a 0mA current was injected into the front section 101, with an external feedback return loss of -10dB. Detailed Implementation

[0030] The present invention will now be further described with reference to the accompanying drawings.

[0031] Example 1

[0032] like Figure 1 and Figure 2 As shown, the isolated semiconductor laser provided by this invention adopts a monolithically integrated dual-segment DFB structure. A schematic diagram along the propagation direction z is shown below. Figure 1 As shown. The front-end DFB101 is designed to lasing at long wavelengths. The DFB102 in the rear section is designed to be lased at short wavelengths. , Furthermore, the wavelengths of the two segments are at least 100 nm apart. An electrode isolation channel 103 is provided between the two segments. The front end face 104 is designed for wavelength... Antireflective coating, rear end face 105 for wavelength A high-reflectivity film is used. The rear-stage DFB102 operates by injecting DC current through the P-electrode 107 and N-electrode 108, serving as an optical pump source to provide sufficient charge carriers for the front-stage 101, enabling carrier switching. The front-stage DFB101 mainly uses the electrode 106 and N-electrode 108 to load a modulation current, converting the injected light energy into a modulated optical signal output. Because the front-stage DFB operates at a longer wavelength, the corresponding transition energy level has a lower energy. In the lasing state, the switched charge carriers at this lower energy level are in a depleted state. Therefore, the photogenerated charge carriers generated by the absorption of the injected light from the rear-stage DFB will quickly release kinetic energy through collisions with the crystal lattice and relax into the lower transition energy level, maintaining the lasing of the front-stage DFB at the lower energy level, thus keeping it in normal output under modulation. Since the stability of the entire device's lasing state mainly depends on the stable light output provided by the rear-stage DFB lasing, external feedback will not affect the steady-state characteristics of the entire device, such as the stability of the lasing wavelength and side-mode suppression ratio. Thus, the influence of external feedback on laser characteristics can be effectively suppressed.

[0033] The epitaxial layer structure of the device of the present invention in the xz plane along the epitaxial growth direction x and along the propagation direction z is as follows: Figure 2 As shown, the front section 101 region, from bottom to top, includes a substrate 201, a first buffer layer 202, a stop etching layer 203, a second buffer layer 204, a first confinement layer 205-1, a first active layer 206-1, a second confinement layer 207-1, a first grating layer 208-1, an upper cladding layer 209, and a top ohmic contact layer 210. The rear section 102 region, from bottom to top, includes a substrate 201, a first buffer layer 202, a stop etching layer 203, a second buffer layer 204, a third confinement layer 205-2, a second active layer 206-2, a fourth confinement layer 207-2, a second grating layer 208-2, an upper cladding layer 209, and a top ohmic contact layer 210.

[0034] The direct modulation distributed feedback laser proposed in this invention has no particular restrictions on the growth material system used. It can be, but is not limited to, InP-AlGaInAs-InGaAsP material system, GaAs-InGaAs-AlGaAs material system, GaAs-(In)GaAsP-(Al)GaInP material system, sapphire-InGaN-AlGaN material system, etc.

[0035] Example 2

[0036] This invention also proposes a method for fabricating a dual-segment DFB isolated semiconductor laser. The laser field confinement and carrier confinement of this invention can be achieved using ridge waveguides or buried heterojunctions. Taking the ridge waveguide method as an example, the fabrication method of the invention includes the following steps:

[0037] Step S1: On the substrate 201, the first buffer layer 202, the stop etching layer 203, the second buffer layer 204, the first confinement layer 205-1, the first active layer 206-1, the second confinement layer 207-1 and the first grating layer 208-1 are epitaxially grown sequentially.

[0038] Step S2: Fabricate the grating with the required period in the first grating layer 208-1, and bury the InP wetting layer.

[0039] Step S3: Mask the front section 101 area, and etch the rear section 102 area downwards to the stop etching layer 203.

[0040] Step S4: In the rear section 102 region, the second buffer layer 204, the third confinement layer 205-2, the second active layer 206-2, the fourth confinement layer 207-2, and the second grating layer 208-2 are sequentially grown.

[0041] Step S5: Fabricate the grating with the required period for the later stage on the second grating layer 208-2;

[0042] Step S6: Continue epitaxial growth of the cladding layer 209 and the ohmic contact layer 210 on the entire wafer;

[0043] Step S7, ridge waveguide etching;

[0044] Step S8, etching electrode isolation channel 103;

[0045] Step S9, dielectric deposition and electrode windowing;

[0046] Step S9: Fabrication of top electrodes 106, 107 and bottom electrode 108.

[0047] Example 3

[0048] In a 10G-PON system, the OLT (Optical Line Terminal) transmitter, operating at a wavelength of 1577nm, uses a DFB laser to perform the critical task of downlink data transmission. Its ability to resist external feedback light is crucial, directly determining the stability and quality of service of the entire access network. This importance stems from the tree-like network structure of PON. The optical signal emitted by the OLT is distributed to multiple users through optical splitters, and each user's connectors, fiber end faces, etc., generate reflected light. These numerous, random reflected lights converge along the fiber path and feed back to the OLT laser. For ordinary DFB lasers, this external feedback can cause a series of serious problems, such as deterioration of the system bit error rate. Feedback light leads to a significant increase in laser intensity noise (RIN), resulting in a decrease in the signal-to-noise ratio at the receiver, thereby increasing the system bit error rate and affecting the reliability of data transmission.

[0049] Specifically, feedback light can interfere with the resonant mode of the laser, potentially causing wavelength drift or mode switching. This not only affects the transmission of this channel but may also interfere with other coexisting PON wavelengths (such as the uplink 1310nm and potentially coexisting GPON 1490nm signals). Current architectures must use separate, magneto-optical isolation components, which are bulky and expensive.

[0050] This invention can be applied to the design of 10G rate 1577nm direct-modulation lasers to avoid the need for external, separate optical isolation components. The dual-segment structure is shown in Table 1. The gain spectra of the first active layer 206-1 and the second active layer 206-2 are shown below. Figure 3 As shown, the wavelengths are 1582nm and 1480nm respectively; the lasing wavelengths selected by the first grating layer 208-1 and the second grating layer 208-1 are 1577nm and 1475nm respectively. Figure 4The trend of photogenerated current measured in the front section 101 without injection when different currents are injected into the rear section 102 indicates that the light in the rear section 102 is absorbed by the front section, that is, the optical pump provides effective charge carriers for the front section 101. Figure 5 The spectrum was measured at the front face 104 of the laser when a 50mA current was injected into region 102 of the rear section and a 0mA current was injected into region 101 of the front section. It can be seen that although there is no carrier injection in the front section, when the pump of the short-wavelength light source at the rear section is large enough, carrier flipping can be achieved in the front section, realizing lasing of the 1577nm laser in the front section. Figure 5 The results show that, without external feedback, the side-mode suppression ratio is 38dB and the main-mode -20dB linewidth is 0.072nm. Figure 6 Is this device in Figure 5 The spectrum was measured at the laser front face 104 under the same operating conditions, but with external feedback and a -10dB return loss. It can be seen that the side-mode suppression ratio and principal mode linewidth of the lasing spectrum are almost unaffected.

[0051]

[0052] Table 1 Material and structural parameters of isolated semiconductor lasers

[0053] In summary, the isolated semiconductor laser based on the dual-segment DFB with non-reciprocal energy level effect provided by this invention can significantly reduce the sensitivity of the laser to feedback light without the need for a traditional magneto-optical isolator, and achieves miniaturized, low-cost, and highly stable isolated laser output. It is especially suitable for high-speed direct-modulation lasers and compact optical emitting components and optical modules.

[0054] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. An isolated semiconductor laser, characterized in that, include: A front-end DFB laser and a back-end DFB laser are monolithically integrated on the same substrate; Wherein, the lasing wavelength of the front-end DFB laser is The lasing wavelength of the downstream DFB laser is ,and ; The rear DFB laser is configured to be driven by a DC current to inject its output laser as an optical pump source into the front DFB laser. The front-end DFB laser is configured to operate in a DC bias superimposed AC modulation or AC modulation only mode, and converts optical pump energy into a modulated optical signal output.

2. The isolated semiconductor laser according to claim 1, characterized in that: The rear DFB laser and the front DFB laser are integrated using a docking growth process, so that each has its own independent active region and optical feedback structure.

3. The isolated semiconductor laser according to claim 2, characterized in that: The front-end DFB laser includes a gain peak wavelength of The first active region; The downstream DFB laser includes a gain peak wavelength of The second active region; Wherein, the first active region and the second active region are one of a quantum dot active region, a quantum well active region, or a bulk material active region, and the parameters of the first active region and the second active region are set differently to satisfy... .

4. The isolated semiconductor laser according to claim 2, characterized in that: The front-end DFB laser includes a lasing wavelength of The first grating region; the subsequent DFB laser includes a lasing wavelength of The second grating region; Wherein, the first grating region and the second grating region are any of the following grating forms with a mode selection mechanism: uniform grating, phase-shifting grating, or partial grating. The parameters of the first grating region and the second grating region are set differently to meet the following requirements: .

5. The isolated semiconductor laser according to claim 4, characterized in that: The first grating region and the second grating region are fabricated by any one or more grating forming processes selected from holographic lithography, EBL lithography, nanoimprint lithography, and deep ultraviolet lithography.

6. The isolated semiconductor laser according to claim 1, characterized in that: The downstream DFB laser is configured to be driven by direct current; The front-end DFB laser is configured to have a drive current that includes an AC modulation component and may optionally include a DC bias component. The DC bias component of the front-end DFB laser is configured to be adjustable to compensate for the total output power when the output power of the rear-end DFB laser is saturated.

7. The isolated semiconductor laser according to claim 1, characterized in that: An electrically isolated channel is provided between the front-end DFB laser and the rear-end DFB laser to enable separate electrical injection of the two laser segments.

8. A light-emitting component, characterized in that, It includes an isolated semiconductor laser as described in any one of claims 1 to 7.

9. An optical module, characterized in that, It includes an isolated semiconductor laser as described in any one of claims 1 to 7.

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