CN115498505A - Wavelength-adjustable laser and laser external cavity - Google Patents

Wavelength-adjustable laser and laser external cavity Download PDF

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Publication number
CN115498505A
CN115498505A CN202211417332.0A CN202211417332A CN115498505A CN 115498505 A CN115498505 A CN 115498505A CN 202211417332 A CN202211417332 A CN 202211417332A CN 115498505 A CN115498505 A CN 115498505A
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wavelength
phase shifter
micro
external cavity
port
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CN115498505B (en
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韩溪林
王耀
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Suzhou Xilian Optical Core Microelectronics Technology Co ltd
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Suzhou Xilian Optical Core Microelectronics Technology Co ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
    • H01S5/14—External cavity lasers
    • H01S5/141—External cavity lasers using a wavelength selective device, e.g. a grating or etalon
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/005—Optical components external to the laser cavity, specially adapted therefor, e.g. for homogenisation or merging of the beams or for manipulating laser pulses, e.g. pulse shaping
    • H01S5/0078—Optical components external to the laser cavity, specially adapted therefor, e.g. for homogenisation or merging of the beams or for manipulating laser pulses, e.g. pulse shaping for frequency filtering
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/02—Structural details or components not essential to laser action
    • H01S5/026—Monolithically integrated components, e.g. waveguides, monitoring photo-detectors, drivers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/06—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium
    • H01S5/065—Mode locking; Mode suppression; Mode selection ; Self pulsating
    • H01S5/0657—Mode locking, i.e. generation of pulses at a frequency corresponding to a roundtrip in the cavity
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
    • Y02D30/00—Reducing energy consumption in communication networks
    • Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks

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  • Physics & Mathematics (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Optics & Photonics (AREA)
  • Optical Integrated Circuits (AREA)
  • Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)

Abstract

The embodiment of the invention discloses a wavelength-adjustable laser and a laser external cavity. The wavelength-adjustable laser external cavity comprises a coupling module, a reflection module and a wavelength locking module, wherein the reflection module comprises a reflection unit and a filtering unit; the external incident beam is coupled into the reflection module from the input end of the coupling module, filtered by the filtering unit after passing through the reflection unit, then passes through the reflection unit, and is output from the output end of the coupling module; the filtering unit comprises a first micro-ring resonator, a first Mach-Zehnder interferometer, a second micro-ring resonator and a phase shifter which are sequentially connected; the wavelength locking module comprises a wavelength locking circuit, and the wavelength locking circuit is used for controlling the phase of the phase shifter so as to lock the optical wavelength of the filtering unit. The embodiment of the invention improves the stability of the heater of the wavelength-tunable laser external cavity and greatly prolongs the service life of the tunable laser.

Description

Wavelength-adjustable laser and laser external cavity
Technical Field
The embodiment of the invention relates to the technical field of optics, in particular to a wavelength-adjustable laser and a laser external cavity.
Background
In long-distance multi-wavelength optical communication and coherent optical communication systems, due to the long transmission distance, a large output optical power, a narrow line width, and a wide tunable range are required. An external cavity laser is an important laser structure, and is a mainstream scheme of a coherent optical communication transmitting end light source due to a low line width and a wide tuning range.
In the prior art, a tunable external cavity laser forms a filter by two cascaded micro-ring resonators, and the resonant frequencies of the two micro-rings are adjusted in a heating manner to match at the center wavelength, so that an output mode is selected.
The tunable laser external cavity formed by cascading the double micro-ring resonators requires a large tuning range of the heater, so that the temperature of the heater is extremely high, and the heater generates phase shift along with the aging of the heater, so that the tunable laser fails.
Disclosure of Invention
The embodiment of the invention provides a wavelength-tunable laser and a laser external cavity, wherein the wavelength-tunable laser external cavity can be used for a wavelength-tunable external cavity laser with narrow line width, high power and wide tuning range, the wavelength-tunable laser external cavity thermal phase shifter has the advantages of prolonged service life and enhanced system reliability.
According to an aspect of the present invention, there is provided a wavelength tunable laser external cavity, including a coupling module, a reflection module and a wavelength locking module, where the reflection module includes a reflection unit and a filtering unit;
the coupling module is connected with the reflection unit, the reflection unit is connected with the filtering unit, external incident beams are coupled into the reflection module from the input end of the coupling module, filtered by the filtering unit after passing through the reflection unit, then pass through the reflection unit, and are output from the output end of the coupling module;
the filtering unit comprises a first micro-ring resonator, a first Mach-Zehnder interferometer and a second micro-ring resonator which are sequentially connected along the transmission direction of the light beam; the filtering unit further comprises a phase shifter; the phase shifter comprises a first phase shifter arranged on the first micro-ring resonator, a second phase shifter arranged on the first Mach-Zehnder interferometer and a third phase shifter arranged on the second micro-ring resonator;
the wavelength locking module comprises a wavelength locking circuit, the wavelength locking circuit is connected with the phase shifter, and the wavelength locking circuit is used for controlling the phase of the phase shifter so as to lock the optical wavelength of the filtering unit.
Optionally, the phase shifter further includes a fourth phase shifter disposed on the reflection unit, and the fourth phase shifter is configured to control a wavelength of the incident light beam.
Optionally, the filtering unit further includes:
a first photodetector connected to the first micro-ring resonator;
a second photodetector connected to the first Mach-Zehnder interferometer;
a third photodetector connected to the second microring resonator.
Optionally, the reflection unit includes a directional coupler or a second mach-zehnder interferometer;
the input port of the reflection unit is connected with the coupling module, the input port of the first micro-ring resonator is connected with the transmission port of the reflection unit, the transmission port of the first micro-ring resonator is connected with the first photoelectric detector, the filtering port of the first micro-ring resonator is connected with the input port of the first Mach-Zehnder interferometer, the transmission port or the filtering port of the first Mach-Zehnder interferometer is connected with the input port of the second micro-ring resonator, the filtering port or the filtering port of the first Mach-Zehnder interferometer is connected with the second photoelectric detector, the transmission port of the second micro-ring resonator is connected with the third photoelectric detector, the filtering port of the second micro-ring resonator is connected with the filtering port of the reflection unit, and the loading port of the reflection unit is connected with the coupling module.
Optionally, the coupling module includes a coupling input end and a coupling output end, and the wavelength locking module further includes a beam splitter; the input port of the reflection unit is connected with the coupling input end, the loading port of the reflection unit is connected with the input end of the beam splitter, the first output end of the beam splitter is connected with the coupling output end, and the second output end of the beam splitter is connected with the wavelength locking circuit.
Optionally, the coupling input end and the coupling output end include an end-face coupler or a grating coupler.
Optionally, the wavelength tunable laser external cavity is formed based on a silicon-on-insulator and silicon nitride integrated semiconductor process, wherein the waveguide is a silicon nitride waveguide.
Optionally, the phase shifter includes a thermal phase shifter, and the thermal phase shifter includes a silicon substrate, a silicon dioxide layer, a silicon nitride waveguide layer, an isolation layer, and an electrical heating layer, which are sequentially stacked.
Optionally, the thermal phase shifter includes a heat insulation groove for removing a portion of the silicon substrate to block heat generated by the electric heating layer from dissipating along the silicon substrate. According to another aspect of the present invention, there is provided a wavelength tunable laser, including a gain chip and the above wavelength tunable laser external cavity;
the seed light beam generated by the gain chip is coupled into the wavelength-adjustable laser external cavity and is modulated by the wavelength-adjustable laser external cavity to output a laser light beam with adjustable wavelength.
Optionally, the tunable laser further includes a semiconductor amplifier disposed at an output end of the external cavity of the wavelength tunable laser.
The wavelength-tunable laser external cavity provided by the embodiment of the invention comprises a coupling module, a reflection module and a wavelength locking module, wherein the reflection module comprises a reflection unit and a filtering unit; the filtering unit comprises a first micro-ring resonator, a first Mach-Zehnder interferometer, a second micro-ring resonator and a phase shifter which are sequentially connected along the transmission direction of the light beam, wherein the phase shifter comprises a first phase shifter arranged on the first micro-ring resonator, a second phase shifter arranged on the first Mach-Zehnder interferometer and a third phase shifter arranged on the second micro-ring resonator, and the phase shifter can be a thermal phase shifter; the wavelength locking module comprises a wavelength locking circuit, and the wavelength locking circuit is connected with the phase shifter. An external incident beam is coupled into the reflection module through the input end of the coupling module, filtered by the filtering unit after passing through the reflection unit, passes through the reflection unit again, and the filtered beam is output through the output end of the coupling module; the phase shifter is controlled by the wavelength locking circuit to carry out phase locking so as to lock the output light wavelength of the filtering unit, so that the wavelength-tunable laser external cavity can carry out large-range wavelength tuning, the narrow line width is kept, the wavelength broadening brought by the use of the optical amplifier is compensated, and the target requirements of tunability, narrow line width and high power of the laser are met. And through the structural arrangement of the first micro-ring resonator, the Mach-Zehnder interferometer and the second micro-ring resonator which are sequentially connected, the tuning range of the thermal phase shifter of the micro-ring resonator is effectively reduced, and the service life and the reliability of the micro-ring resonator are enhanced.
It should be understood that the statements in this section do not necessarily identify key or critical features of the embodiments of the present invention, nor do they necessarily limit the scope of the invention. Other features of the present invention will become apparent from the following description.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.
FIG. 1 is a schematic structural diagram of an external cavity of a wavelength tunable laser according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of an external cavity of another wavelength tunable laser according to an embodiment of the present invention;
FIG. 3 is a schematic structural diagram of an external cavity of a wavelength tunable laser according to an embodiment of the present invention;
fig. 4 is a schematic structural diagram of a micro-ring resonator with a thermal phase shifter according to an embodiment of the present invention;
FIG. 5 is a schematic cross-sectional view of a phase shifter according to an embodiment of the present invention;
FIG. 6 is a schematic cross-sectional view of another phase shifter according to an embodiment of the present invention;
FIG. 7 is a schematic diagram of a wavelength tunable laser according to an embodiment of the present invention;
fig. 8 is a schematic structural diagram of another wavelength tunable laser provided in an embodiment of the present invention.
Detailed Description
In order to make the technical solutions of the present invention better understood, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
It should be noted that the terms "first," "second," and the like in the description and claims of the present invention and in the drawings described above are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used is interchangeable under appropriate circumstances such that the embodiments of the invention described herein are capable of operation in sequences other than those illustrated or described herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.
Fig. 1 is a schematic structural diagram of an external cavity of a wavelength tunable laser according to an embodiment of the present invention, where the external cavity of the wavelength tunable laser provided in this embodiment is applicable to a wavelength tunable external cavity laser. As shown in fig. 1, the external cavity 10 of the wavelength tunable laser includes a coupling module 100, a reflection module 200 and a wavelength locking module 300, wherein the reflection module 200 includes a reflection unit 210 and a filtering unit 220.
The coupling module 100 is connected to the reflection unit 210, the reflection unit 210 is connected to the filtering unit 220, an external incident beam a is coupled into the reflection unit 210 from an input end of the coupling module 100, filtered by the filtering unit 220 after passing through the reflection unit 210, and then passes through the reflection unit 210 and is output from an output end of the coupling module 100. In view of the overall effect, the reflection module 200 generates a reflection effect, that is, the external incident light a is incident to the reflection module 200 and is reflected by the reflection module 200 to be output.
The filtering unit 220 includes a first micro-ring resonator 221, a first mach-zehnder interferometer 222, and a second micro-ring resonator 223 that are sequentially connected in the light beam transmission direction. The filtering unit 220 further includes a phase shifter 224, and the phase shifter 224 includes a first phase shifter 2241 disposed at the first micro-ring resonator 221, a second phase shifter 2242 disposed at the first mach-zehnder interferometer 222, and a third phase shifter 2243 disposed at the second micro-ring resonator 223, wherein the filtering effect of the filtering unit 220 is achieved by phase-shifting the different phase shifters, respectively.
The wavelength locking module 300 includes a wavelength locking circuit 310, the wavelength locking circuit 310 is connected to the phase shifter 224, and the wavelength locking circuit 310 is used for controlling the phase of the phase shifter 224 to lock the optical wavelength of the filtering unit 220.
The wavelength tunable laser external cavity provided by the embodiment of the present invention may be a semiconductor device integrated on a chip, for example, a semiconductor chip formed based on a semiconductor process in which Silicon On Insulator (SOI) and silicon nitride are integrated, where the wavelength tunable laser external cavity includes a silicon nitride (SiN) waveguide. The coupling module 100 includes an input for receiving an incident light beam and an output for outputting a filtered light beam. The connection between the coupling module 100 and the reflection unit 210 may be a direct connection, for example, through an optical waveguide, or an indirect connection, where the reflection unit may include a directional coupler or a mach-zehnder interferometer or a structure composed of a directional coupler, and the specific implementation may be designed according to the actual situation.
The filtering unit 220 and the wavelength locking module 300 work together to realize wavelength adjustment. In one embodiment, the phase shifter 224 may be a thermal phase shifter, and the wavelength locking circuit 310 is a logic circuit for locking the wavelength, and when the temperature of the phase shifter is changed, the operating wavelength of the filtering unit 220 is changed. Specifically, the first phase shifter 2241 controls the resonance wavelength of the first micro-ring resonator 221, the second phase shifter 2242 controls the resonance wavelength of the first mach-zehnder interferometer 222, and the third phase shifter 2243 controls the resonance wavelength of the second micro-ring resonator 223, thereby controlling the output wavelength at a desired wavelength and achieving the optimum value of optical power.
In the existing technical solution using the dual micro-ring resonator, in order to achieve a preset wavelength tuning range, the thermal phase shifter needs to work in a relatively large temperature adjustment range, which may cause a problem that the heater is degraded with time. In this embodiment, the first mach-zehnder interferometer 222 is added between the first micro-ring resonator 221 and the second micro-ring resonator 223 for filtering, so as to filter out unwanted wavelengths, reduce a tunable range, reduce thermal tuning ranges at two micro-rings, and improve the thermal tuning reliability of the double micro-rings. The specific principle is as follows:
assuming that the free spectral regions FSR of the first microring resonator 221 and the second microring resonator 223 are FSR1 and FSR2, respectively, the tunable range is: tuning Range = FSR1 FSR 2/(FSR 1 FSR 2), when two resonance peaks of the micro-ring coincide for the first time, they coincide again after one Tuning Range.
For example, in one embodiment, if two microring resonators are directly connected and both microring resonators have resonance at 1523nm and 1557nm, light generated in the gain chip can resonate at both 1523nm and 1557nm wavelength positions. But because of the tunable laser, if the tunable range is set to 1520nm-1580nm, for example, and the resonance at 1557nm cannot be determined whether it is reached at 1557nm after phase shift by 1523nm via the heater or the resonance itself is generated at 1557 nm. It is therefore necessary to change the tuning range, i.e. to adjust the peak at 1557nm outside the tuning range, so that it is ensured that at most one peak occurs within the same tuning range.
However, this has the problem that for a dual microring resonator, the thermal tuning range is the full tuning range, thus requiring the thermal phase shifter of both microrings to cover the full range and operate in the 1520nm-1580nm range in use. This is because the temperature adjustment range is excessively large (for example, 80 ℃ or even 100 ℃) when the heater is used for the first micro ring resonator 221 and the second micro ring resonator 223, and thus there may occur a problem that the heater is deteriorated with time.
To solve this problem, the present embodiment considers adopting a method of reducing the Tuning Range. The specific implementation mode is as follows: by adding the first mach-zehnder interferometer 222 and making the FSR of the microring resonator small: for example, let the first peak remain around 1520nm and the second peak remain around 1550 nm. The FSRs of the two micro-ring resonators are very small, so that the temperature required for tuning one FSR is also very small, and then the reasonably designed Mach-Zehnder interferometer enables the period of the Mach-Zehnder interferometer to be matched with the double micro-ring resonator, so that when the Mach-Zehnder interferometer is tuned within the range of 1520nm-1550nm, the transmission peak value of the Mach-Zehnder interferometer is always kept consistent with the peak value of the double-ring resonator after being tuned at 1520nm (the wavelength above 1550nm cannot be transmitted through) through thermal tuning. When tuned in the range of 1550nm-1580nm, the peak value of the Mach-Zehnder interferometer is always kept consistent with the peak value of the double-ring resonator tuned at 1550nm (the wavelength below 1550nm cannot be transmitted) through thermal tuning.
By adding the first Mach-Zehnder interferometer, the thermal tuning range of the micro-ring can be effectively reduced (for example, the temperature is reduced to 40 ℃), namely, the heating temperature range of the micro-ring can be reduced, the problem that a heater is aged along with time can be effectively solved, and a tunable laser adjusting scheme with high heating reliability is provided.
According to the technical scheme of the embodiment of the invention, an external incident beam is coupled into an external cavity of the wavelength-adjustable laser through an input end of a coupling module, and the beam filtered by a filtering unit is output through an output end of the coupling module; the phase shifter is controlled by the wavelength locking circuit to carry out phase locking so as to lock the output light wavelength of the filtering unit, so that the wavelength-tunable laser external cavity can carry out large-range wavelength tuning, narrow line width is kept, wavelength broadening brought by the use of the optical amplifier is compensated, and the target requirements of the tunable laser, the narrow line width and high power are met. And through the structural arrangement of the first micro-ring resonator, the first Mach-Zehnder interferometer and the second micro-ring resonator which are sequentially connected, the tuning range of the thermal phase shifter of the micro-ring resonator is effectively reduced, and the service life and the reliability of the tunable laser are enhanced.
Fig. 2 is a schematic structural diagram of an external cavity of another wavelength tunable laser provided in an embodiment of the present invention. As shown in fig. 2, optionally, the phase shifter 224 further includes a fourth phase shifter 2244 disposed on the reflection unit 210, and the fourth phase shifter 2244 is used for controlling the wavelength of the incident light beam.
Specifically, the fourth phase shifter 2244 is connected to the input section of the reflection unit 210, and the fourth phase shifter 2244 functions to control the input light wavelength so that the whole is tuned to the wavelength of the proper operating range. The fourth phase shifter 2244 may also be a thermal phase shifter, and controls the wavelength of the input light under the control of the wavelength locking circuit 310.
Fig. 3 is a schematic structural diagram of an external cavity of another wavelength tunable laser according to an embodiment of the present invention. As shown in fig. 3, optionally, the filtering unit 220 further includes: a first photodetector 225, the first photodetector 225 being connected to the first micro-ring resonator 221; a second photodetector 226, the second photodetector 226 being connected to the first mach-zehnder interferometer 222; and a third photodetector 227, the third photodetector 227 being connected to the second micro-ring resonator 223.
The photoelectric detector is used for realizing the conversion of photoelectric signals and monitoring whether each device works at a proper wavelength. Specifically, the first photodetector 225 and the third photodetector 227 are respectively used to monitor whether the first micro-ring resonator 221 and the second micro-ring resonator 223 reach a resonance state, and if the first micro-ring resonator and the second micro-ring resonator reach the resonance state, the optical powers monitored at the first photodetector 225 and the third photodetector 227 are the minimum; the second photodetector 226 loaded at the first mach-zehnder interferometer 222 is used to monitor the light transmitted through the port or filtered out from the port of the first mach-zehnder interferometer 222, and may further calculate the optical power currently passing through the output port of the first mach-zehnder interferometer 222, so as to obtain the filter characteristic of the first mach-zehnder interferometer 222 at the wavelength. The wavelength locking circuit 310 is a logic circuit for wavelength locking, which controls each phase shifter; controlling the thermal phase shifter function of the reflection unit 210 is to control the input light wavelength so as to tune to a desired wavelength as a whole; the phase shifters controlling the first micro-ring resonator 221, the second micro-ring resonator 223 and the first mach-zehnder interferometer 222 function to control them individually so that the system output light wavelength is at the location where the devices are resonant individually, so that the system is resonant, with the energy at the output wavelength being the highest.
Optionally, the reflection unit 210 includes a directional coupler or a second mach-zehnder interferometer, taking the reflection unit 210 includes a directional coupler as an example, as shown in fig. 3, an input port of the reflection unit 210 is connected to the coupling module 100, an input port of the first micro-ring resonator 221 is connected to a transmission port of the reflection unit 210, a transmission port of the first micro-ring resonator 221 is connected to the first photodetector 225, a filtering port of the first micro-ring resonator 221 is connected to an input port of the first mach-zehnder interferometer 222, a transmission port or a filtering port of the first mach-zehnder interferometer 222 is connected to an input port of the second micro-ring resonator 223, a filtering port or a transmission port of the first mach-zehnder interferometer 222 is connected to the second photodetector 226, a transmission port of the second micro-ring resonator 223 is connected to the third photodetector 227, a filtering port of the second micro-ring resonator 223 is connected to a filtering port of the reflection unit 210, and a loading port of the reflection unit 210 is connected to the coupling module 100.
Optionally, the coupling module 100 may include a coupling input end 101 and a coupling output end 102, and the wavelength locking module 300 may further include a beam splitter 320, where the beam splitter 320 is schematically illustrated in fig. 3 as a directional coupler for guiding part of the coupled-out light into the wavelength locking circuit 310. In other embodiments, the beam splitter 320 may also be a device having a beam splitting function, such as a mach-zehnder interferometer, and may be selected according to actual situations in specific implementation.
As shown in fig. 3, an input port of the reflection unit 210 is connected to the coupling input port 101, a load port of the reflection unit 210 is connected to an input port of the beam splitter 320, a first output port (a transmission port of the directional coupler) of the beam splitter 320 is connected to the coupling output port 102, and a second output port (a filtering port of the directional coupler) of the beam splitter 320 is connected to the wavelength locking circuit 310.
In one embodiment of the present invention, after the light enters the waveguide, the phase is shifted by the fourth phase shifter, and the light passing through the phase shifter is transmitted to the reflection unit (the first directional coupler), which is used for constructing a reflector loop instead of the mirror scheme; besides, the light can be split according to a certain proportion, so that the reflectivity of the external cavity can be adjusted. The four ports of the directional coupler are named as follows: 1-input port, 2-pass-through port, 3-filter-out port, 4-load port.
The four ports of the microring resonator are named as follows: 1-input port, 2-pass-through port, 3-filter-out port, 4-load port. With continued reference to fig. 3, the input port of the reflection unit 210 is connected to the fourth phase shifter 2244, the transmission port of the reflection unit 210 is connected to the input port of the first micro-ring resonator 221, the filtering-out port of the reflection unit 210 is connected to the filtering-out port of the second micro-ring resonator 223, and the loading port of the reflection unit 210 is connected to the input port of the beam splitter 320 (second directional coupler).
The micro-ring resonator is provided with a thermal phase shifter, the thermal phase shifter can be placed at one section or two sections of the micro-ring, or a waveguide connected with an input port of the micro-ring or a waveguide connected with a filtering port, and the thermal phase shifter can be designed according to actual conditions in specific implementation. Fig. 4 is a schematic structural diagram of a microring resonator with a thermal phase shifter according to an embodiment of the present invention, and fig. 4 schematically illustrates the thermal phase shifter disposed on two segments of the microring.
The transmission port of the first microring resonator 221 is connected to the first photodetector 225, and the filtering-out port of the first microring resonator 221 is connected to the input port of the first mach-zehnder interferometer 222 through a long waveguide. The first mach-zehnder interferometer 222 types include, but are not limited to: a directional coupler type Mach-Zehnder interferometer, a multimode interferometer type Mach-Zehnder interferometer, a Y-beam splitter type Mach-Zehnder interferometer. Taking a directional coupler type mach-zehnder interferometer as an example, four ports thereof are named as follows: 1-input port, 2-pass-through port, 3-filter-out port, 4-load port.
The Mach-Zehnder interferometer is of an unequal arm type, and one arm is provided with a thermal phase shifter. After the filtering and phase shifting of the mach-zehnder interferometer, the light is output through the filtering port or the transmission port of the mach-zehnder interferometer, and the unused mach-zehnder interferometer is connected to the second photodetector 226 through the transmission port or the filtering port. The output light is output through a filtering output port or a transmission port and then is connected to an input port of the second micro-ring resonator 223, the transmission port of the second micro-ring resonator 223 is connected to the third photodetector 227, and is filtered and phase-shifted in the second micro-ring resonator 223, and finally, the light is output from the filtering port and finally returns to the filtering port of the reflection unit 210.
The load port of the reflection unit 210 is connected to the input port of the beam splitter 320 and the filter-out port of the beam splitter 320 is connected to the wavelength locking circuit 310.
Optionally, the coupling input end 101 and the coupling output end 102 include end-face couplers or grating couplers.
By adopting the end face coupler or the grating coupler, the coupling efficiency and the working bandwidth can be improved, and the subsequent tuning efficiency is further improved.
Optionally, the wavelength tunable laser external cavity is formed based on a silicon-on-insulator and silicon nitride integrated semiconductor process, wherein the waveguide is a silicon nitride waveguide.
Specifically, silicon nitride has the characteristics of low waveguide loss, small refractive index difference, large process tolerance and the like, so that the silicon nitride is widely applied to an external cavity laser.
Optionally, fig. 5 is a schematic cross-sectional structural view of a phase shifter according to an embodiment of the present invention. As shown in fig. 5, the phase shifter includes a thermal phase shifter including a silicon substrate 401, a silicon oxide layer 402, a silicon nitride waveguide layer 403, an isolation layer 404, and an electric heating layer 405, which are sequentially stacked.
Specifically, electrical heating layer 405 may include, but is not limited to, a metal layer 4051 and a tantalum nitride/titanium nitride layer 4052. Fig. 6 is a schematic cross-sectional view of another phase shifter according to an embodiment of the present invention. As shown in fig. 6, the thermal phase shifter further includes a thermal insulation groove 406 for removing a portion of the silicon substrate 401 to prevent heat generated by the electric heating layer 405 from dissipating along the silicon substrate 401, and the thermal insulation can be effectively performed by using a grooving process, so that the interference resistance during the adjustment process of the thermal phase shifter is enhanced, and the thermal tuning efficiency is improved.
The embodiment of the invention particularly describes a composition and a connection mode of the wavelength-tunable laser external cavity, systematically describes a working mode of the wavelength-tunable laser external cavity, improves the reliability of a heater at a micro-ring in the wavelength-tunable laser external cavity, reduces the waveguide loss and improves the tuning efficiency.
Fig. 7 is a schematic diagram of a wavelength tunable laser according to an embodiment of the present invention. As shown in fig. 7, the wavelength tunable laser provided in this embodiment includes:
the gain chip 20 and any one of the wavelength tunable laser external cavities 10 provided in the above embodiments; the seed beam generated by the gain chip 20 is coupled into the wavelength-tunable laser external cavity 10, and is modulated by the wavelength-tunable laser external cavity 10 to output a laser beam with tunable wavelength.
Wherein the gain chip 20 may be used as an external cavity semiconductor laser optical gain medium. In the embodiment of the invention, the left side of the gain chip 20 can be plated with a high reflection film, and the right side can be plated with an anti-reflection film. The embodiment of the present invention does not limit this.
Specifically, the light beam passes through the gain chip 20, and is coupled into the wavelength tunable laser external cavity 10 to the maximum extent and tuned, and the light beam with the wavelength in the appropriate range is output. The gain chip 20 is adopted to make the light source utilized to the maximum extent, improve the utilization rate of the light source and enhance the performance of the laser at the same time.
Fig. 8 is a schematic structural diagram of another wavelength tunable laser provided in an embodiment of the present invention. As shown in fig. 8, the wavelength tunable laser optionally further includes a semiconductor amplifier 30 disposed at the output of the external cavity 10 of the wavelength tunable laser.
The semiconductor amplifier 30 may be a device that amplifies an optical signal. The semiconductor amplifier 30 has characteristics of high gain and high output power. Can be used for improving data transmission power and expanding transmission distance.
The tunable laser provided by the embodiment of the invention has a small structure, can be tuned in a large range, keeps a narrow line width, and enables the output power of the laser to be extremely high by adding the semiconductor optical amplifier, so that the target requirements of the tunable laser, the narrow line width and the high power are met. And aiming at the heater, a semiconductor grooving process is adopted, so that the thermal tuning efficiency is improved, and when a filtering system is designed, a Mach-Zehnder interferometer is purposefully added into the original double-micro-ring structure, so that the tuning range of the thermal phase shifter of the micro-ring resonator is effectively reduced, namely the service life and the reliability of the thermal phase shifter of the micro-ring resonator are enhanced.
The above-described embodiments should not be construed as limiting the scope of the invention. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions may be made, depending on design requirements and other factors. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (11)

1. The external cavity of the wavelength-tunable laser is characterized by comprising a coupling module, a reflection module and a wavelength locking module, wherein the reflection module comprises a reflection unit and a filtering unit;
the coupling module is connected with the reflection unit, the reflection unit is connected with the filtering unit, external incident beams are coupled into the reflection module from the input end of the coupling module, filtered by the filtering unit after passing through the reflection unit, then pass through the reflection unit, and are output from the output end of the coupling module;
the filtering unit comprises a first micro-ring resonator, a first Mach-Zehnder interferometer and a second micro-ring resonator which are sequentially connected along the transmission direction of the light beam; the filtering unit further comprises a phase shifter; the phase shifter comprises a first phase shifter arranged on the first micro-ring resonator, a second phase shifter arranged on the first Mach-Zehnder interferometer and a third phase shifter arranged on the second micro-ring resonator;
the wavelength locking module comprises a wavelength locking circuit, the wavelength locking circuit is connected with the phase shifter, and the wavelength locking circuit is used for controlling the phase of the phase shifter so as to lock the optical wavelength of the filtering unit.
2. The wavelength tunable laser external cavity according to claim 1, wherein the phase shifter further comprises a fourth phase shifter disposed in the reflection unit, the fourth phase shifter being configured to control the wavelength of the incident light beam.
3. The wavelength tunable laser external cavity according to claim 1, wherein the filter unit further comprises:
a first photodetector connected to the first micro-ring resonator;
a second photodetector connected to the first Mach-Zehnder interferometer;
a third photodetector connected to the second microring resonator.
4. The wavelength tunable laser external cavity according to claim 3, wherein the reflection unit comprises a directional coupler or a second Mach-Zehnder interferometer;
the input port of the reflection unit is connected with the coupling module, the input port of the first micro-ring resonator is connected with the transmission port of the reflection unit, the transmission port of the first micro-ring resonator is connected with the first photoelectric detector, the filtering port of the first micro-ring resonator is connected with the input port of the first Mach-Zehnder interferometer, the transmission port or the filtering port of the first Mach-Zehnder interferometer is connected with the input port of the second micro-ring resonator, the filtering port or the transmission port of the first Mach-Zehnder interferometer is connected with the second photoelectric detector, the transmission port of the second micro-ring resonator is connected with the third photoelectric detector, the filtering port of the second micro-ring resonator is connected with the filtering port of the reflection unit, and the loading port of the reflection unit is connected with the coupling module.
5. The wavelength tunable laser external cavity according to claim 1, wherein the coupling module comprises a coupling input and a coupling output, the wavelength locking module further comprising a beam splitter; the input port of the reflection unit is connected with the coupling input end, the loading port of the reflection unit is connected with the input end of the beam splitter, the first output end of the beam splitter is connected with the coupling output end, and the second output end of the beam splitter is connected with the wavelength locking circuit.
6. The wavelength tunable laser external cavity according to claim 5, wherein the coupling-in end and the coupling-out end comprise end couplers or grating couplers.
7. The wavelength tunable laser external cavity according to claim 1, wherein the wavelength tunable laser external cavity is formed based on a silicon-on-insulator and silicon nitride integrated semiconductor process, wherein the waveguide is a silicon nitride waveguide.
8. The wavelength tunable laser external cavity according to claim 7, wherein the phase shifter comprises a thermal phase shifter comprising a silicon substrate, a silicon dioxide layer, a silicon nitride waveguide layer, an isolation layer, and an electrical heating layer, which are sequentially stacked.
9. The external wavelength tunable laser cavity according to claim 8, wherein the thermal phase shifter comprises a thermal insulation trench for removing a portion of the silicon substrate to block heat generated by the electrical heating layer from dissipating along the silicon substrate.
10. A wavelength-tunable laser is characterized in that the laser comprises a gain chip and the wavelength-tunable laser external cavity as claimed in any one of claims 1 to 9;
the seed light beam generated by the gain chip is coupled into the external cavity of the wavelength-adjustable laser, and the laser light beam with adjustable wavelength is output after being modulated by the external cavity of the wavelength-adjustable laser.
11. The wavelength tunable laser of claim 10, further comprising a semiconductor amplifier disposed at an output of the external cavity of the wavelength tunable laser.
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