CN112003648A - Integrated light emitting device - Google Patents
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- H04B10/50—Transmitters
- H04B10/501—Structural aspects
- H04B10/503—Laser transmitters
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/50—Transmitters
- H04B10/516—Details of coding or modulation
- H04B10/54—Intensity modulation
- H04B10/541—Digital intensity or amplitude modulation
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/50—Transmitters
- H04B10/516—Details of coding or modulation
- H04B10/548—Phase or frequency modulation
- H04B10/556—Digital modulation, e.g. differential phase shift keying [DPSK] or frequency shift keying [FSK]
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Abstract
The invention provides an integrated light emitting device, which comprises a laser, a light frequency comb, a wavelength division demultiplexer and a wavelength division multiplexer which are sequentially arranged along the propagation direction of light, wherein the laser is used for generating a light source signal with a single wavelength; the optical frequency comb is used for receiving a single-wavelength light source and processing the signal into a plurality of optical carrier signals with equal wavelength intervals; the wavelength division demultiplexer is used for receiving the optical carrier signals with multiple wavelengths and decomposing the optical carrier signals into multiple paths of sub-optical carrier signals; the wavelength division multiplexer is used for synthesizing the multiple paths of sub-optical carrier signals into one path of optical signal and outputting the optical signal. According to the integrated light emitting device, the light source signal is emitted through the laser, the optical frequency comb receives the light source signal and generates a plurality of carrier signals with equal wavelength intervals to output the optical carrier, the problems of high power consumption and difficult temperature control circuit design caused by excessive light emitters are solved, and the production cost of the light emitting device is reduced.
Description
Technical Field
The invention relates to the technical field of communication, in particular to an integrated light emitting device.
Background
The optical transmission technology with high capacity and low power consumption is an important means for bearing various data communications, and at present, the construction of data centers, 5G communications and backbone networks has the problems of higher and higher signal transmission rate and higher power consumption. Therefore, the optical transmitting chip is required to have multi-channel capability to increase the transmission rate and reduce the power consumption of the chip to reduce the power consumption. The multichannel parallel transmission is an important research direction of future light-emitting chips, and can effectively improve the transmission rate and reduce the size of the chips.
In the related art, the main scheme of the multi-channel light emitting chip is a direct modulation scheme using a vertical cavity surface emitting laser array (VECSEL), or an external modulation scheme where Distributed Feedback (DFB) lasers with different wavelengths form a multi-wavelength light source.
However, the direct modulation scheme using the vertical cavity surface emitting laser array (VECSEL) has problems of low modulation rate, difficulty in integration of optoelectronic chips, and the like. The external modulation scheme of the multi-wavelength light source formed by adopting Distributed Feedback (DFB) lasers with different wavelengths has the defects of high energy consumption and high cost.
Disclosure of Invention
The invention provides an integrated light emitting device, which aims to solve the technical problems of high power consumption and difficult integration of light emitting devices in the related art.
According to the integrated light emitting device of the embodiment of the invention, along the propagation direction of the light, the light emitting device comprises a laser, a light frequency comb, a wavelength division demultiplexer and a wavelength division multiplexer which are arranged in sequence,
the laser is used for generating a single-wavelength light source signal;
the optical frequency comb is used for receiving the light source signal and processing the light source signal into a plurality of output optical carrier signals with equal wavelength intervals;
the wavelength division demultiplexer is used for receiving a plurality of output optical carrier signals with equal wavelength intervals and decomposing the plurality of output optical carrier signals into a plurality of paths of sub-optical carrier signals;
and the wavelength division multiplexer is used for synthesizing the plurality of sub-optical carrier signals into one path of optical signal and outputting the optical signal.
According to the integrated light emitting device provided by the embodiment of the invention, the light source signal is emitted by one laser, the light frequency comb receives the light source signal and generates a plurality of output light carrier signals with equal wavelength intervals, the problems of high power consumption and difficult temperature control circuit design caused by excessive lasers in the traditional light emitting device are solved, and the production cost of the light emitter is reduced.
According to some embodiments of the invention, the optical frequency comb comprises:
the IQ modulation circuit is used for processing the received light source signal into primary modulated light waves with various wavelengths;
a phase modulator for phase adjusting the primary modulated light waves of multiple wavelengths and forming the output optical carrier signals at a plurality of equal wavelength intervals.
In some embodiments of the present invention, an electro-optical modulator is disposed between the wavelength division demultiplexer and the wavelength division multiplexer, and the electro-optical modulator is configured to modulate each of the sub-optical carrier signals according to a preset modulation format.
According to some embodiments of the invention, the electro-optic modulator employs an L-type PN junction.
In some embodiments of the present invention, the method for implanting ions into an L-shaped PN junction includes:
making for forming P++The photoresist protective layer of the first carrier region, P-type ions are injected into the first carrier region and reach a preset concentration;
is made for formingN++The photoresist protective layer of the second carrier region, injecting N-type ions into the second carrier region and reaching a preset concentration;
manufacturing a photoresist protective layer for a P-type low-concentration doped third carrier sub-region, and injecting P-type ions into the third carrier sub-region;
arranging a fourth carrier region above the third carrier region, and injecting N-type ions into the fourth carrier region;
and manufacturing a photoresist protective layer for an N-type low-concentration doped fifth carrier region, injecting N-type ions into the fifth carrier region, and communicating the N-type ions in the fourth carrier region and the fifth carrier region.
In some embodiments of the invention, the light emitter further comprises: a waveguide fiber coupler for coupling the optical signal to an optical fiber.
According to some embodiments of the invention, the wavelength division multiplexer and the wavelength division demultiplexer each comprise a mach-zehnder interferometer and a phase shifter for temperature effect compensation.
In some embodiments of the invention, the phase shifter applies a voltage using segmented electrodes.
In some embodiments of the invention, the laser is coupled to the waveguide of the optical frequency comb by a flip-chip bonding process.
According to some embodiments of the present invention, the optical frequency comb, the wavelength division multiplexer, and the wavelength division demultiplexer are formed on a silicon-on-insulator (SOI) wafer using a silicon photofabrication process.
Drawings
FIG. 1 is a schematic view showing a structure of a light emitter in the related art;
FIG. 2 is a schematic diagram of another light emitter in the related art;
FIG. 3 is a schematic diagram of the structure of an integrated light emitting device according to an embodiment of the present invention;
FIG. 4 is a schematic diagram of a structure of an optical frequency comb according to an embodiment of the present invention;
FIG. 5 is a cross-sectional view of a MZI modulator body portion waveguide according to an embodiment of the present invention;
FIG. 6 is a schematic view of an ion implantation process of an L-shaped PN junction according to an embodiment of the present invention;
FIG. 7 is a schematic diagram illustrating simulation of modulation efficiency of an L-shaped PN junction according to an embodiment of the present invention;
FIG. 8 is a schematic cross-sectional view of a phase shifter waveguide according to an embodiment of the present invention;
FIG. 9 is a schematic cross-sectional view of an electro-optic modulator according to an embodiment of the present invention;
FIG. 10 is a schematic diagram of an optical frequency comb output simulation according to an embodiment of the present invention;
FIG. 11 is a schematic diagram of an MZI structure according to an embodiment of the present invention;
FIG. 12 is a schematic diagram of a transmission spectrum of an unequal-arm MZI structure according to an embodiment of the present invention;
FIG. 13 is a diagram illustrating a phase shifter according to an embodiment of the present invention employing segmented electrode energization;
FIG. 14 is a 4-channel silicon fundamental wavelength division multiplexer according to an embodiment of the present invention;
FIG. 15 is a schematic diagram of a 4-channel wavelength division multiplexer transmission line according to an embodiment of the present invention;
fig. 16 is a schematic structural diagram of a silicon-based electro-optic modulator with an MCRR structure according to an embodiment of the present invention;
FIG. 17 is a diagram illustrating normalized output spectra of MCRR and MZI in accordance with an embodiment of the present invention;
FIG. 18 is a schematic diagram of a silicon-based electro-optic modulator according to an embodiment of the present invention;
fig. 19 is a schematic structural diagram of a silicon fundamental wavelength division multiplexer according to an embodiment of the present invention.
Detailed Description
To further explain the technical means and effects of the present invention adopted to achieve the intended purpose, the present invention will be described in detail with reference to the accompanying drawings and preferred embodiments.
As shown in FIG. 1, which is a technical solution of a multi-channel light emitting chip adopting an external modulation structure in the related art, N (N ≧ 2) lasers are used as light sources, the wavelengths of the lasers are different, and the wavelength intervals are consistent. The light output by each laser is modulated by the modulator in the respective channel, so as to realize modulation formats such as OOK, PAM, QPSK or QAM. The output signals of the N channels are synthesized into one path for output after wavelength division multiplexing.
According to the technical scheme, each channel needs one laser as a light source, and the number of the lasers is increased along with the increase of the number of the channels, so that the following problems are brought: the laser is a high-energy-consumption device, the power consumption of the whole chip is increased along with the increase of the number of the lasers, the use cost is increased, and the requirement on heat dissipation is improved; if the heat dissipation treatment of the chip is not well done, the temperature of the device can be increased, the wavelength of the laser can be changed due to the increased temperature, the wavelength deviates from the channel of the wavelength division multiplexer, and the performance of the device is reduced; the laser needs a driving circuit and a temperature feedback control circuit to ensure the constancy of output power and wavelength, and along with the increase of the lasers, the circuit design also becomes complex, and the design cost of subsequent circuits is increased.
Fig. 2 shows a technical solution of a multi-channel optical transmitting chip using a direct modulation structure in the related art. The light source adopts a vertical cavity surface emitting laser array (VCSEL), the array can realize simultaneous output of a plurality of light sources on one chip, a driving electric signal is loaded on the laser, intensity modulation is carried out on the output light intensity of the laser by changing the size of the driving signal, and OOK and PAM equal-amplitude modulation formats are realized.
The technical scheme has the following disadvantages: different from a semiconductor laser which emits light at the edge of a waveguide, the light emitted by the vertical cavity surface emitting laser is perpendicular to the surface of a resonant cavity and is directly emitted to an upper space, and is difficult to integrate with other photoelectronic devices such as a wavelength division multiplexer, an optical switch and the like, so that the integration level of a photoelectronic chip is limited. Because the laser is directly modulated, the modulation rate is not very high at present. In addition, the scheme can only perform amplitude modulation on light, and cannot realize high-order modulation such as QPSK, QAM and the like, so that the application in high-speed transmission is limited.
Based on the above-described drawbacks of the related art, the present invention is an integrated light emitting device. As shown in fig. 3, the light emitting device according to the embodiment of the present invention includes a laser, an optical frequency comb, a wavelength division demultiplexer, and a wavelength division multiplexer, which are sequentially arranged in a propagation direction of a light.
The laser is used for generating a single-wavelength light source signal, and the optical frequency comb is used for receiving the light source signal and processing the light source signal into a plurality of output optical carrier signals with equal wavelength intervals. That is, a single-wavelength light source signal generated by the laser is transmitted to the optical frequency comb, and the single-wavelength light source signal is processed by the optical frequency comb to obtain a plurality of output optical carrier signals with equal wavelength intervals.
The wavelength division demultiplexer is used for receiving a plurality of output optical carrier signals with equal wavelength intervals and decomposing the output optical carrier signals with the equal wavelength intervals into a plurality of paths of sub-optical carrier signals, and the wavelength division multiplexer is used for synthesizing the plurality of paths of sub-optical carrier signals into one path of optical signal and outputting the optical signal.
According to the integrated light emitting device provided by the embodiment of the invention, a single-wavelength light source signal is emitted by one laser, the light frequency comb receives the light source signal and generates a plurality of output light carrier signals with equal wavelength intervals, the problems of high power consumption and difficult temperature control circuit design caused by excessive lasers in the traditional light emitting device are solved, and the production cost of the light emitter is reduced.
According to some embodiments of the invention, as shown in fig. 3, the optical frequency comb comprises: the device comprises an IQ modulation circuit and a phase modulator, wherein the IQ modulation circuit is used for processing a received light source signal into primary modulated light waves with multiple wavelengths. The phase modulator is used for adjusting the phase of the primary modulated light waves with multiple wavelengths and forming a plurality of output optical carrier signals with equal wavelength intervals.
It should be noted that the I path and the Q path of the IQ modulator may be respectively composed of mach-zehnder interference structure (MZI) modulators based on a carrier dispersion effect. The phase difference between the I path and the Q path is pi, and the phase difference is realized by a thermal resistance-based waveguide phase shifter.
The IQ modulator also includes a traveling wave electrode for loading microwave signals, a DC electrode for loading bias voltage, and a phase shifter electrode. The phase modulator is composed of a silicon-based straight waveguide based on a carrier dispersion effect and a driving electrode. After single-wavelength light output by one laser is modulated by an IQ modulator, the frequency spectrum of output light comprises a carrier, a fundamental frequency and multiple harmonics, a prototype of a frequency comb is formed, and a sufficient number of tooth lines with equal frequency intervals are generated by modulation of a phase modulator, so that a complete frequency comb is formed and used as an optical carrier of each channel behind.
In some embodiments of the present invention, as shown in fig. 3, an electro-optical modulator is disposed between the wavelength division demultiplexer and the wavelength division multiplexer, and the electro-optical modulator is configured to modulate each sub-optical carrier signal according to a preset modulation format.
The wavelength division demultiplexer demultiplexes a plurality of output light waves with equal wavelength intervals output by the optical frequency comb according to wavelength, and transmits the output light waves to each sub-channel, an electro-optical modulator is arranged in each sub-channel, and the wavelength division multiplexer multiplexes the decomposed light waves modulated by each channel into one waveguide for output.
The wavelength division multiplexer and the wavelength division demultiplexer are formed by two schemes, wherein one scheme is formed by taking a Mach-Zehnder modulator structure (MZI) as a basic unit, and the other scheme is formed by taking a micro-ring resonant cavity as a basic unit.
The basic unit of the wavelength division multiplexer of the Mach-Zehnder modulator structure (MZI) is an MZI structure. When the two arms of the MZI have a length difference, the output spectral line is sinusoidal. For an N-channel wavelength division multiplexer, a 2 × 2 MZI cascade may be implemented. The two arms of the MZI have phase shifters to correct for shifts in the center wavelength of the channel.
As shown in fig. 19, the wavelength division multiplexer and the wavelength division demultiplexer in the micro-ring resonator structure are formed by a bus waveguide and a plurality of micro-ring resonators, the resonant wavelength of each micro-ring resonator corresponds to the output wavelength of a laser, and a thermo-optic effect phase shifter is arranged on the waveguide of the micro-ring resonators and used for correcting the shift of the resonant wavelength.
In some embodiments of the present invention, the electro-optical modulator is a carrier dispersion type electro-optical modulator, and a carrier depletion type based on a PN structure or a carrier injection type based on a PIN structure may be adopted, and both structures change the carrier concentration in the silicon waveguide by applying power to cause the change of the effective refractive index of the waveguide, thereby playing a role in modulation. The modulator may be an MZI structure, an IQ modulator structure, or an MZI-coupled resonator structure.
According to some embodiments of the present invention, as shown in fig. 5 and 9, the electro-optic modulator may employ an L-shaped PN junction.
As shown in fig. 6, the ion implantation method of the L-type PN junction includes:
s100, preparing for forming P++The P-type ions are injected into the first carrier region to reach a preset concentration;
s200, preparing for forming N++The photoresist protective layer of the second carrier region injects N-type ions into the second carrier region and reaches a preset concentration;
s300, manufacturing a photoresist protective layer for the P-type low-concentration doped third carrier sub-region, and injecting P-type ions into the third carrier sub-region;
s400, arranging a fourth carrier region above the third carrier region, and injecting N-type ions into the fourth carrier region;
s500, manufacturing a photoresist protective layer for the N-type low-concentration doped fifth carrier region, injecting N-type ions into the fifth carrier region, and communicating the N-type ions in the fourth carrier region and the fifth carrier region.
In some embodiments of the invention, the light emitter further comprises: a waveguide fiber coupler for coupling an optical signal to an optical fiber. For example, the decomposed optical waves of each channel are combined into one optical signal by a wavelength division multiplexer, and then coupled with an optical fiber by a grating coupler or a spot-size converter.
According to some embodiments of the invention, the wavelength division multiplexer and the wavelength division demultiplexer each comprise a mach-zehnder interferometer and a phase shifter for temperature effect compensation. Therefore, the transmission spectrum of the Mach-Zehnder element can be adjusted through the phase shifter to compensate for channel center wavelength drift caused by temperature change, and the performance of the optical transmitter is improved. The waveguide structure cross-section of the phase shifter is identical to that shown in fig. 8.
In some embodiments of the invention, the phase shifter applies the voltage using segmented electrodes. It should be noted that, in order to reduce the voltage, a power-up mode of the segmented electrode may be adopted, as shown in fig. 13. When the thermal resistors have the same structure, the adoption of the segmented electrode power-up mode is equivalent to the parallel connection of the thermal resistors divided into a plurality of segments of resistors, so that the resistance value is reduced, the heat generated under the same voltage is larger, and the phase-shifting efficiency is higher.
In some embodiments of the present invention, the laser is coupled to the waveguides of the optical frequency comb by a flip chip process. Therefore, the convenience and reliability of connection between the laser and the optical frequency comb can be improved.
According to some embodiments of the present invention, the optical frequency comb, the wavelength division multiplexer, and the wavelength division demultiplexer each comprise a silicon-based wafer. That is, the optical frequency comb, modulator, and wavelength division multiplexer/demultiplexer may all be fabricated on a silicon-on-insulator (SOI) wafer, with the waveguide structure designed to meet only TE mode transport. It should be noted that the silicon-based chips are adopted for the above devices, so that the integration level of the chips can be improved, and the preparation cost of the devices can be reduced.
An integrated light emitting device according to the present invention is described in detail below in three specific embodiments with reference to the accompanying drawings. It is to be understood that the following description is only exemplary, and not a specific limitation of the invention.
The first embodiment is as follows:
the optical transmitter of the present invention may be a multichannel multiplexing silicon-based optical transmitting chip based on an optical frequency comb, as shown in fig. 3, and mainly includes: the semiconductor laser, silicon-based optical frequency comb, silicon-based fundamental wavelength division multiplexer, wavelength division demultiplexer, silicon-based electro-optic modulator and the electrode for controlling the phase shifter in the power divider drive the traveling wave electrode of the high-speed electro-optic modulator, and the electrode meets impedance matching and phase matching and realizes high-speed and low-power-consumption phase adjustment.
The optical frequency comb, the electro-optical modulator, the wavelength division multiplexer and the wavelength division demultiplexer are all prepared on a silicon-on-insulator (SOI) wafer, and the waveguide structure is designed to only meet TE mode transmission.
As shown in FIG. 4, the first stage of the optical frequency comb is an IQ modulator, and the I path and the Q path are electro-optical modulators of MZI structure, which constitute two arms of a large MZI. The power divider of MZI is composed of a 1 × 2 multimode interferometer structure (MMI), and the combiner and the power divider are the same in structure and opposite in use direction.
FIG. 5 is a cross-sectional view of a main portion waveguide of an MZI modulator, the waveguide structure adopts a ridge waveguide structure, the height of the waveguide is 220nm, the width of the waveguide is 450nm-600nm, and only TE is supported0And (4) conveying the mold. The height of the flat plate layers on the two sides of the waveguide can be set to be 90 nm-60 nm, and high-concentration ion doping is respectively carried out to form N++And P++Region, the edge is 0.4um-1um from the side of the waveguide. RF signal loading on high speed electrode and P++Zone connected, reverse biased voltage Vb1Through the DC electrode and N++The regions are contiguous.
The MZI electro-optic modulator adopts the carrier dispersion effect, changes the effective refractive index of the waveguide by changing the carrier concentration in the waveguide, and plays a role in phase modulation, the larger the overlapping area of the optical mode and the carrier depletion region in the waveguide is, the higher the modulation efficiency is, namely VπThe lower. To achieve more frequency tooth trace at lower driving voltage, half wave voltage V of the modulator is requiredπAs low as possible.
In the present application, an L-shaped PN junction is formed in a waveguide by a five-step ion implantation process, as shown in fig. 6: the first step is to make a P++The photoresist protective layer of the slab region of (1) is subjected to P-type ion implantation so that the concentration of P-type ions in the slab layer is 1020/cm-3. Second step of same procedure for N++Then N-type ion implantation is carried out to make the concentration of the region reach 1020/cm-3. And thirdly, manufacturing a photoresist protective layer for P-type low-concentration doping, and then performing P-type ion implantation. And the fourth step is N-type ion implantation, and a layer of N-type ion region covers the waveguide P-type ion doping region. And fifthly, manufacturing a photoresist protective layer for N-type low-concentration doping, and then performing N-type ion implantation to connect the two N-type regions. The carrier makes drift motion under the action of reverse voltage, so that the modulation with large bandwidth and high speed can be realized, the overlapping area of a depletion region and an optical mode in the waveguide is enlarged, and the modulation efficiency is effectively improvedThe half-wave voltage is reduced.
The simulation result of the phase shifter with 3mm length based on the L-shaped PN junction is shown in FIG. 7, and pi phase shift can be realized under the drive of 3V voltage. The high-speed electrode of the electro-optical modulator adopts a coplanar strip line (CPS) structure, and the structure not only can realize impedance matching with the source end impedance and the terminating resistance and realize traveling wave transmission of a driving signal, but also can realize phase matching between the transmission of RF and the transmission of an optical mode in a waveguide. Thereby increasing the electro-optic bandwidth of the modulator.
The principle of the thermal resistance type electro-optical phase shifter is based on the thermo-optical effect of silicon materials, and the effective refractive index of the waveguide can be changed by the change of the temperature of the waveguide, so that the phase adjustment is realized. The structure of the section of the waveguide of the phase shifter is shown in fig. 8, a thermal resistor of titanium nitride is arranged above the waveguide, and the thermal resistor heats after being electrified, so that the temperature of the waveguide below is changed, and the phase adjustment is realized.
The electro-optic phase modulator also adopts an L-shaped PN junction to improve the modulation efficiency, and the waveguide cross-sectional structure is shown in FIG. 9.
The device is now exemplified by a simulation of its function, 20G RF1The signals are loaded on an I-path modulator and a Q-path modulator respectively, and the input power of each path is 19 dBm. Adjusting phase shifter voltage V of a path I modulatorP1The modulator is enabled to work at a quadrature (quadrature point) working point, and the I-path modulation generates a fundamental frequency and odd harmonics; adjusting phase shifter voltage V of Q-way modulatorP2The modulator works at the maximum working point, and the Q-path modulation generates even harmonic; and the I path and the Q path are output in an orthogonal combination way to form a first-stage optical frequency comb. The second stage electro-optic phase modulator loads RF with power of 8dBm and frequency of 10GHz2The signal and phase modulator has the functions of encrypting frequency tooth lines and adjusting the flatness of the tooth lines, and simulation results are shown in fig. 10, 15 tooth lines can be realized, and the flatness is within 6 dB. The number of tooth lines can be increased by increasing the power of the RF, and the flatness of the output can be adjusted by adjusting the phase difference of the RF, the working point of the modulator and the phase difference of the I path and the Q path.
The wavelength division multiplexer and the wavelength division demultiplexer are composed of MZI and a thermal resistance type phase shifter. The MZI structure is shown in FIG. 11, which employs a 2 × 2 power splitter and combiner structureThere is a difference in length between the two arms. The simulation results are shown in FIG. 12, assuming λ is included1And λ2From input port 1 (port)1) Input, after MZI, λ1Slave port 3 (port)3) Output, λ2Slave port 4 (port)4) And outputting the signal to realize the wavelength division demultiplexing function. The wavelength division multiplexing function can exchange input and output. The channel spacing can be obtained by the following equation:
where Δ L represents the arm length difference of MZI, ng is the group refractive index of the waveguide, and λ0Is the channel center wavelength. The larger Δ L, the narrower the channel spacing.
The phase shifter is used for adjusting the transmission spectrum of the MZI to compensate for the channel center wavelength shift caused by temperature change. The waveguide cross-sectional structure of the phase shifter is identical to that of fig. 8, and a power-up manner of the segment electrodes is adopted in order to reduce the voltage, as shown in fig. 13. When the thermal resistors have the same structure, the adoption of the segmented electrode power-up mode is equivalent to the parallel connection of the thermal resistors divided into a plurality of segments of resistors, so that the resistance value is reduced, the heat generated under the same voltage is larger, and the phase-shifting efficiency is higher.
Taking a 4-channel wavelength division multiplexer as an example, the structure is shown in fig. 14, and the wavelength division multiplexer includes three MZIs in total, wherein the first two MZIs constitute the first stage, and the third constitutes the second stage. The arm length difference of the second-stage MZI has a 2-fold relationship with the arm length difference of the first-stage MZI. Optical signals with 4 wavelengths are respectively transmitted from ports in the figure11、port12、port21And port22Enter, from port33One output is synthesized, and the transmission line is shown in fig. 15.
In order to prevent the shift of the wavelength division multiplexer channel caused by the large temperature change and conveniently adjust the central wavelength of the channel, a phase shifter is added to the MZI. The length of the first-stage MZI phase shifter and the length of the second-stage MZI phase shifter are also in a 2-time relation, and under the same voltage, the phase shifting effect of the phase shifter is also in a 2-time relation according to the silicon thermo-optic effect. The anodes and the cathodes of all the phase shifters in each stage are connected, so that the loaded voltages are consistent, and the generated phase shifts are the same. When the temperature influence received by the chip causes the channel wavelength to shift, the voltage of the phase shifter is adjusted to correct. The wavelength division demultiplexer can realize the input and output exchange of the structure.
2NThe wavelength division multiplexer of the channel is realized by continuing to cascade 2 x 2 MZIs. Ensuring that the arm length difference of each MZI is in a 2-time relation with the arm length difference of the MZIs of two adjacent stages, and ensuring that the length of the phase shifter is in a 2-time relation; the anodes of all MZIs of each stage are connected and the cathodes are connected.
The silicon-based electro-optical modulator in the present application adopts an MZI structure coupled with a micro ring resonator structure (MCRR for short), as shown in fig. 16. Light slave port1Port input, modulated and passed through port3And (6) outputting the port. Port (Port)2And Port4The resonant cavity structure is formed by connecting a bent waveguide. The waveguide section of the MZI structure is the same as that in FIG. 5, the structure of the phase shifter is the same as that in FIG. 8, the high-speed electric signal is loaded on the traveling wave electrode of the MZI, the reverse bias voltage is loaded on the direct current electrode, and the phase shifter is used for adjusting the working point of the modulator. The modulation mechanism is consistent with the electro-optic modulator in the optical frequency comb. According to the Fano resonance (Fano resonance) principle, resonant light in the resonant cavity interferes with coherent non-resonant light in the MZI, and the output spectrum of the interference is in a specific asymmetric shape at a resonant wavelength. Under the same half-wave voltage, the normalized output spectrum is shown in fig. 17, and it can be seen that compared with the spectrum of MZI, the MCRR spectrum can realize the rapid linear change of amplitude under the smaller voltage drive, and the high linear intensity modulation of low voltage can be realized by using the spectrum characteristic, so that the drive voltage is reduced, and the energy consumption is reduced.
The waveguide coupler in the application adopts a Spot Size Converter (SSC) to match the size of an optical mode in a silicon-based waveguide with the size of a spot size of output light of a laser, and adopts a silicon-based waveguide grating as a coupler of the waveguide and an optical fiber.
In order to increase the modulation speed, the traveling wave electrode needs to be optimally designed, and besides the characteristic impedance of the electrode meets the impedance matching (including 50 Ω, 75 Ω, 100 Ω and the like) with the input end, the effective refractive index of the traveling wave electrode is the same as the group refractive index of the waveguide, so as to realize phase matching.
The dc electrode should have sufficient width and thickness to prevent the electrode from being burned out by a large current. The direct current electrode wiring is perpendicular to the traveling wave electrode as much as possible, and the influence of high-frequency electromagnetic interference on direct current level is reduced.
In summary, the light emitter provided by the present application has the following beneficial effects:
the optical frequency comb, the wavelength division multiplexer, the wavelength division demultiplexer, the modulator and the waveguide coupler of the whole chip are prepared by a silicon optical process, and the all-silicon-based chip can improve the integration level of the chip and reduce the preparation cost of devices; the optical frequency comb is adopted to realize the generation of multi-wavelength carrier waves, only one laser is needed, the number of the lasers is reduced, and therefore the power consumption of a light source driving circuit is reduced, and the design of a driving and temperature control circuit is simplified; the modulator adopts an L-shaped PN junction, and compared with the traditional PN junction, the modulator can improve the overlapping area of an optical mode and a carrier depletion region in a waveguide, increase the modulation efficiency of the modulator and reduce half-wave voltage; the silicon-based optical frequency comb is composed of a silicon-based IQ modulator and a silicon-based phase modulator, and can realize enough frequency tooth trace under lower driving power; the phase shifter in the wavelength division multiplexing and wavelength division demultiplexing devices performs phase shift by adopting a segmented electrode power-up mode, so that the adjusting voltage can be reduced.
Example two:
as shown in fig. 18, unlike the first embodiment, the silicon-based electro-optical modulator in the present embodiment is composed of an IQ modulator, which is identical to the IQ modulator in fig. 4. Vs1And Vs2The driving signals are loaded on the I-path modulator and the Q-path modulator respectively under the same clock. Vp1And Vp2The phase-shifting voltage of the phase shifters is adjusted for the paths I and Q, so that the modulators of the paths I and Q work at the orthogonal working point. Regulating Vp3The phase of the I path signal is orthogonal to that of the Q path signal. The modulator can realize high-order code type modulation such as QPSK, QAM16 and the like. The other structures and the obtained effects in this embodiment are the same as those in the first embodiment.
Example three:
as shown in fig. 19, unlike the first embodiment, in this embodiment, there is a thermo-optic phase shifter in the micro-ring resonator in each channel of the silicon fundamental wavelength division multiplexer, and the thermo-optic effect of silicon can be used to adjust the resonance point, align the resonance wavelength with the input wavelength, and transmit the light into the bus waveguide to realize wavelength division multiplexing. Wavelength division demultiplexing can be realized by switching input and output. The other structures and the obtained effects in this embodiment are the same as those in the first embodiment.
In addition, the optical transmitter provided by the application can also use a pulse mode-locked laser and a micro-ring resonant cavity of a silicon nitride material to form an optical frequency comb. The modulator can also adopt a PN junction structure or a PIN junction structure to realize the modulation effect, and the thermal resistance type waveguide phase shifter can also adopt doped silicon to form a thermal resistance.
While the invention has been described in connection with specific embodiments thereof, it is to be understood that it is intended by the appended drawings and description that the invention may be embodied in other specific forms without departing from the spirit or scope of the invention.
Claims (10)
1. An integrated light emitting device is characterized in that along the propagation direction of light, the light emitting device comprises a laser, a light frequency comb, a wavelength division demultiplexer and a wavelength division multiplexer which are arranged in sequence;
the laser is used for generating a single-wavelength light source signal;
the optical frequency comb is used for receiving the light source signal and processing the light source signal into a plurality of output optical carrier signals with equal wavelength intervals;
the wavelength division demultiplexer is used for receiving a plurality of output optical carrier signals with equal wavelength intervals and decomposing the plurality of output optical carrier signals into a plurality of paths of sub-optical carrier signals; and the wavelength division multiplexer is used for synthesizing the plurality of paths of sub-optical wave signals into one path of optical signal and outputting the optical signal.
2. The integrated light emitting device of claim 1, wherein the optical frequency comb comprises:
the IQ modulation circuit is used for processing the received light source signal into primary modulated light waves with various wavelengths;
a phase modulator for phase adjusting the primary modulated light waves of multiple wavelengths and forming the output optical carrier signals at a plurality of equal wavelength intervals.
3. The integrated optical transmitter device according to claim 1, wherein an electro-optical modulator is disposed between the wavelength division demultiplexer and the wavelength division multiplexer, and the electro-optical modulator is configured to modulate each of the sub-optical carrier signals according to a preset modulation format.
4. The integrated light emitting device of claim 3, wherein the electro-optic modulator employs an L-shaped PN junction.
5. The integrated light emitting device of claim 4, wherein the method for implanting ions into the L-shaped PN junction comprises:
making for forming P++The photoresist protective layer of the first carrier region, P-type ions are injected into the first carrier region and reach a preset concentration;
fabrication for forming N++The photoresist protective layer of the second carrier region, injecting N-type ions into the second carrier region and reaching a preset concentration;
manufacturing a photoresist protective layer for a P-type low-concentration doped third carrier sub-region, and injecting P-type ions into the third carrier sub-region;
arranging a fourth carrier region above the third carrier region, and injecting N-type ions into the fourth carrier region;
and manufacturing a photoresist protective layer for an N-type low-concentration doped fifth carrier region, injecting N-type ions into the fifth carrier region, and communicating the N-type ions in the fourth carrier region and the fifth carrier region.
6. The integrated light emitting device of claim 1, wherein the light emitter further comprises: a waveguide fiber coupler for coupling the optical signal to an optical fiber.
7. The integrated optical transmit device of claim 1, wherein the wavelength division multiplexer and the wavelength division demultiplexer each comprise a mach-zehnder interferometer and a phase shifter for temperature effect compensation.
8. The integrated light emitting device of claim 7, wherein the phase shifter applies a voltage using segmented electrodes.
9. The integrated light emitting device of claim 1, wherein the laser is coupled to the waveguide of the optical frequency comb by a flip-chip bonding process.
10. The integrated optical transmission device of any one of claims 1-9, wherein the optical frequency comb, the wavelength division multiplexer, and the wavelength division demultiplexer are all formed on a silicon-on-insulator (SOI) wafer using silicon photofabrication.
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| CN114167555A (en) * | 2021-10-12 | 2022-03-11 | 之江实验室 | A 6.4 Tbps silicon-based optical engine transceiver chip assembly for high-speed optical communication |
| CN117240368A (en) * | 2023-11-16 | 2023-12-15 | 鹏城实验室 | Optical domain spectrum synthesis system and optical domain spectrum synthesis method |
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