Optical system and method for operating an optical device, an optical transmitter

Abstract

The optical device includes a first waveguide, a ring waveguide adjacent to the first waveguide, and heaters coupled to the ring waveguides one by one. A method includes coupling a first light source having a first wavelength to the first waveguide, increasing the current through the heater until the first ring waveguide in the ring waveguide resonates, distributing the first ring optical waveguide to the first wavelength, resetting the current through the heater to the initial current, coupling a second light source having a second wavelength to the first waveguide, where the second wavelength is different from the first wavelength, increasing the current through the heater until the second ring waveguide in the ring waveguide resonates, where the second ring waveguide in the ring waveguide is different from the first ring waveguide in the ring waveguide, and distributing the second ring waveguide in the ring waveguide to the second wavelength. Embodiments of the present application also disclose an optical system and methods for operating an optical device and an optical transmitter.

Description

Technical Field

[0001] Embodiments of the present application relate to optical systems and methods of operating optical devices, optical transmitters. Background Art

[0002] MRM (Micro Ring Modulator or Microring Modulator or Minor Ring Modulator, micro-ring modulator) is very promising for providing high data rates, ultra-low power consumption, and small footprint (or size) for wavelength division multiplexing (WDM), which includes dense wavelength division multiplexing (DWDM). DWDM uses multiple MRMs for different channels, which can further increase the data rate. Some areas of DWDM implementation need improvement, for example, reliably and effectively controlling the resonance frequency of the MRM in a DWDM system. Summary of the Invention

[0003] According to one aspect of embodiments of the present application, a method of operating an optical device is provided, where the optical device includes a first waveguide, a plurality of ring waveguides adjacent to the first waveguide, and a plurality of heaters respectively coupled to the ring waveguides, and each of the plurality of heaters is provided with an initial current. The method includes: coupling a first light source having a first wavelength to the first waveguide; increasing the current through the heater until the first ring waveguide in the ring waveguides resonates, where the first ring waveguide in the ring waveguides is coupled to the first heater in the heaters; allocating the first ring waveguide in the ring waveguides to the first wavelength; resetting the current through the heater or through the heaters excluding the first heater in the heaters to the initial current; coupling a second light source having a second wavelength to the first waveguide, where the second wavelength is different from the first wavelength; increasing the current through the heater or through the heaters excluding the first heater in the heaters until the second ring waveguide in the ring waveguides resonates, where the second ring waveguide in the ring waveguides is different from the first ring waveguide in the ring waveguides; and allocating the second ring waveguide in the ring waveguides to the second wavelength.

[0004] In another aspect according to an embodiment of the present application, a method of operating an optical transmitter is provided. The optical transmitter includes a first waveguide, a plurality of micro-ring modulators (MRMs) adjacent to the first waveguide, and a plurality of heaters coupled to the MRMs in one-to-one correspondence. Each of the plurality of heaters is provided with an initial current. The method includes the following steps: coupling a light source having a wavelength to the first waveguide; increasing the current through each of the heaters until one of the MRMs resonates, where one of the MRMs is coupled to one of the heaters; allocating one of the MRMs to the wavelength; resetting the current through the heater or through the heaters excluding one of the heaters to the initial current; and repeating the steps of coupling, increasing, allocating, and resetting until each of the MRMs is allocated to a different wavelength.

[0005] In yet another aspect according to an embodiment of the present application, an optical system is provided, including: an optical transmitter, where the optical transmitter includes a first waveguide, a plurality of micro-ring modulators (MRMs) disposed adjacent to the first waveguide, and a plurality of heaters coupled to the MRMs in one-to-one correspondence; a plurality of heater controllers coupled to the plurality of heaters in one-to-one correspondence; and an allocation controller configured to perform the following operations: coupling a light source to the first waveguide; instructing the heater controllers to increase the current through the heaters until one of the MRMs resonates, where one of the MRMs is coupled to one of the heaters; and allocating one of the MRMs to the wavelength of the light source. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] When read in conjunction with the accompanying drawings, various aspects of the present invention can be best understood from the following detailed description. It should be emphasized that, in accordance with standard practice in the industry, the various components are not drawn to scale and are for illustrative purposes only. In fact, for the sake of clear discussion, the dimensions of the various components can be arbitrarily increased or decreased.

[0007] Figure 1 A simplified diagram of an optical system with dynamic channel allocation according to an embodiment of the present disclosure is shown.

[0008] Figure 2 Shown according to an embodiment of the present disclosure Figure 1 A simplified diagram of an MRM used in the optical system in

[0009] Figure 3 Shown according to an embodiment of the present disclosure in connection with Figure 1 A simplified top view of a ring waveguide coupled to a heater used in the optical system in

[0010] Figure 4 Shown according to an embodiment of the present disclosure in connection with Figure 1 A simplified cross-sectional view of a ring waveguide coupled to a heater used in the optical system in

[0011] Figure 5 shows a simplified diagram of an optical transmitter of the optical system in Figure 1 accordance with an embodiment of the present disclosure.

[0012] Figure 6 shows a simplified diagram of an optical receiver of the optical system in Figure 1 accordance with an embodiment of the present disclosure.

[0013] Figure 7 shows a flowchart of a method implemented with dynamic channel allocation in the optical system in Figure 1 accordance with an embodiment of the present disclosure.

[0014] Figure 8 shows an example of channel allocation generated by dynamic channel allocation in the optical system in Figure 1 accordance with an embodiment of the present disclosure.

[0015] Figure 9 shows a channel allocation for comparison with the Figure 8 example channel allocation in DETAILED DESCRIPTION

[0016] The following disclosure provides many different embodiments or examples for implementing the present invention. Specific embodiments or examples of components and arrangements are described below to simplify the present invention. Of course, these are merely examples and are not intended to be limiting. For example, in the following description, forming the first component above or on the second component may include embodiments in which the first component and the second component are in direct contact, and may also include embodiments in which additional components may be formed between the first component and the second component, such that the first component and the second component may not be in direct contact. Additionally, the present invention may repeat reference numerals and / or letters in the various examples. This repetition is for simplicity and clarity purposes and does not in itself indicate a relationship between the various embodiments and / or configurations discussed.

[0017] Furthermore, for ease of description, spatial relationship terms such as "below", "beneath", "lower", "above", "upper", etc. may be used herein to describe the relationship of one element or component to another as shown in the figures. In addition to the orientation shown in the figures, spatial relationship terms are intended to include different orientations of the device during use or operation. The device may be positioned otherwise (rotated 90 degrees or in other orientations), and the spatial relationship descriptors used herein may be interpreted accordingly.

[0018] In addition, when a number or a range of numbers is described using terms such as "about", "approximate", etc., taking into account the variations inherent in the manufacturing process as understood by a person of ordinary skill in the art, such terms are intended to include numbers within a reasonable range. For example, based on known manufacturing tolerances associated with the manufactured component (having a characteristic associated with the number), the quantity or range of numbers includes a reasonable range of the described number, such as within + / - 10% of the described number. For example, a material layer with a thickness of "about 5 nm" may include a size range from 4.25 nm to 5.75 nm, where the manufacturing tolerance known to a person of ordinary skill in the art associated with depositing the material layer is + / - 15%.

[0019] The present disclosure relates to optical systems (such as optical data communication systems) and methods of operating optical systems. In particular, the present disclosure relates to methods and systems for multiplexing different wavelengths using MRM in an optical transmitter and for demultiplexing different wavelengths using a ring resonator (RR) in an optical receiver. For simplicity, the present disclosure alternately uses ring modulator (RM) and MRM to refer to a modulator having a ring waveguide with a diameter in the micron range.

[0020] Optical data communication systems operate by modulating a laser to encode a digital data pattern. The modulated laser is transmitted from a transmitting node (e.g., an optical transmitter) to a receiving node (e.g., an optical receiver) through an optical data network. The modulated laser arriving at the receiving node is demodulated to obtain the original digital data pattern. Therefore, the implementation and operation of an optical data communication system depend on having mechanisms for reliably and efficiently transmitting and detecting the laser at different nodes in the optical data network.

[0021] Wavelength division multiplexing (WDM) is widely used to transmit modulated data at different carrier wavelengths over a common optical waveguide. WDM can overcome fiber congestion, which is a potential problem in optical modules that include parallel optical transceivers with one channel per fiber. Specifically, by reducing the number of fibers in each optical module, WDM multiplexing can simplify the optical module, thereby reducing its cost and size.

[0022] In dense wavelength division multiplexing (DWDM), a narrow spacing is used between adjacent wavelengths. This is typically achieved by directly modulating data onto highly stable optical carriers and then combining multiple carriers in a fiber. DWDM allows a large number of channels to be accommodated within a given wavelength range, thereby providing high performance. In DWDM, a variety of optical devices are used, including modulators, multiplexers (such as add filters), demultiplexers (such as drop filters), and switches. To compensate for manufacturing variations, temperature variations, and / or laser wavelength drift, these optical devices are typically phase-tuned to a specific wavelength of a given channel. Depending on the system requirements, a tuning range of at least 180° may be required.

[0023] Ring modulators (including MRMs) are very promising in providing high data rates, ultra-low power consumption, and size. A DWDM system can further increase the data rate by using multiple RMs for different channels in an optical transmitter. Conversely, such a DWDM system can use multiple ring resonators (RRs) for different channels in an optical receiver.

[0024] Due to process variations and different operating environments, RMs and RRs generally do not resonate at their target frequency (or design frequency) when operating in an optical system. One way to correct them is to place a heater (such as a metal heater or a silicon heater) near the ring waveguide of the RM or RR and use the heater to shift the resonance frequency to the target frequency.

[0025] In some methods, the heater is designed to completely cover one free spectral range (FSR) spectrally in a DWDM system. In this method, the worst-case scenario occurs when the frequency offset of the RM or RR is one FSR. In some cases, the required temperature increase to cover one FSR may be unrealistic. For example, for a 5-μm RM or RR, one FSR may be 14 nm, and for a 10-μm RC or RR, one FSR may be 7 nm. If the heater needs to cover one FSR in both cases and the heating efficiency is about 70 pm / K (meaning that as the temperature increases by 1 degree, the spectrum will shift by 70 pm), the required temperature increase will be equal to FSR / (70 pm / K), which is 200 K for a 5-μm RM or RR and 100 K for a 10-μm RC or RR. In a DWDM system, increasing the temperature by 200 K is almost impossible or unrealistic. Additionally, considering that the DWDM system may already be operating at an ambient temperature of 100 °C (~370 K), if the temperature of the RM or RR is increased by another 100 K, serious reliability issues may occur.

[0026] Embodiments of the present disclosure significantly reduce the power consumption of such heaters by allocating and reallocating different wavelengths to different MRMs and / or RRs in a DWDM system. The allocation and reallocation occur during the initialization process of the DWDM system, for example, after each power-on of the DWDM system. In some cases, during different initialization processes of the DWDM system, an RM (or RR) may be allocated to different channels. In one embodiment, the RM or RR is allocated to a channel with a wavelength less than the design wavelength of the RM and RR. Therefore, the required frequency offset is reduced, the heating power consumption is reduced, and the final operating temperature is also reduced.

[0027] Figure 1FIG. 0 shows a simplified schematic diagram of an optical system 100 constructed in accordance with an embodiment of the present disclosure. The optical system 100 may be a WDM system or a DWDM system. The optical system 100 includes an optical transmitter 102, an optical receiver 202, and an optical fiber 150 (and / or other transmission medium) coupled between the optical transmitter 102 and the optical receiver 202. The optical system 100 may include Figure 1 other components not shown in FIG.

[0028] The optical transmitter 102 includes light sources (such as lasers) (not shown) that emit light at wavelengths λ1, λ2,... λ n n, respectively, where n is the number of channels in the DWDM scheme implemented in the optical system 100. The light at these wavelengths is multiplexed and transmitted through the waveguide 108. As they pass through the waveguide 108, the light at these wavelengths is modulated by the RM 106 (including RM1, RM2,... RMn) through resonance, which will be briefly described below.

[0029] Each RM 106 includes a ring waveguide (or loop waveguide) 106r, as Figure 2 shown. The ring waveguide 106r is adjacent to and spaced apart from the waveguide 108 carrying the multi-wavelength light. When the following equation EQ-1 is satisfied, the ring waveguide 106r resonates.

[0030] 2πn eff R = m1λ (EQ-1)

[0031] In Equation EQ-1, "n eff " is the effective refractive index of the ring waveguide 106r, "R" is the radius of the ring waveguide 106r, "m1" is a natural number, and "λ" is the wavelength of the light that causes the ring waveguide 106r to resonate (referred to as the resonance wavelength). When the ring waveguide 106r resonates, all or most of the light energy at the resonance wavelength λ is absorbed by the ring waveguide 106r and does not pass through the waveguide 108.

[0032] The ring waveguide 106r includes a highly doped p / n junction. For example, in some embodiments, the dopant concentration may be approximately 4e 18 / cm 3 to 7e 18 / cm 3 . The p / n junction is biased or reverse-biased to a bias voltage by a ring modulator driver (RMD) 116 (see Figure 1 ). When the bias voltage changes, the free carrier density in the p / n junction also changes, which in turn changes the effective refractive index n of the ring waveguide 106r effTherefore, by changing the bias voltage, the ring waveguide 106r can be controlled to resonate at the resonant wavelength λ. In other words, by applying a bias voltage to the ring waveguide 106r, the light at the wavelength λ is modulated. In an application, the bias voltage can be in a digital data pattern (i.e., switching between 0 and 1). In Figure 2 In the illustrated embodiment, the p / n junction in the ring waveguide 106r has a height H1 (such as about 200 nm) from the surface of the substrate and a width W1 (such as about 370 nm), and the p-type doped material (such as silicon) and the n-type doped material (such as silicon) have widths W2 (such as about 500 nm) and W3 (such as about 500 nm), respectively.

[0033] Referring to Figure 1 , the optical receiver 202 includes a waveguide 208 for receiving an optical signal (e.g., transmitted by the optical transmitter 102), and the optical signal carries multiple multiplexed and modulated wavelengths. When the optical signal passes through the waveguide 208, the light of different wavelengths is detected in a resonant manner by the RR 206 (including RR1, RR2,... RR n ). The structure of the RR 206 is similar to that of the RM 106, except that the structure of the RR 206 includes a ring waveguide (e.g., a silicon ring) 206r that is not a p / n junction (see Figures 3 - 4 ). The RR 206 also resonates according to the above equation EQ-1. When the RR 206 resonates, the energy of the light at the resonant wavelength λ is absorbed by the RR 206 and coupled to the waveguide 210, which in turn drives the photodetector 212 to convert the optical signal into an electrical signal. Subsequently, the electrical signal is amplified by a transimpedance amplifier (TIA) 214 and processed by other circuits not shown in Figure 1 .

[0034] In an embodiment, the resonant wavelengths of the RM 106 and the RR 206 are designed to match the wavelengths λ1, λ2,... λ n . However, due to variations in the manufacturing process and the operating environment, the actual resonant wavelengths of the RM 106 and the RR 206 may not exactly match the wavelengths λ1, λ2,... λ n or their multiples, and need to be adjusted or corrected to the wavelengths λ1, λ2,... λ n or their multiples. In this embodiment, the resonant wavelengths of the RM 106 and the RR 206 are tuned by heaters 130 and 230 ( Figures 2 - 4 ) coupled to each of the RM 106 and the RR 206.

[0035] Referring to Figure 3 and Figure 4, which shows simplified schematic top and cross-sectional views of portions of an optical transmitter 102 and an optical receiver 202, respectively. The optical transmitter 102 includes a heater 130, and the heater 130 is coupled to the ring waveguide 106r in a one-to-one correspondence. The optical receiver 202 includes a heater 230, and the heater 230 is coupled to the ring waveguide 206r in a one-to-one correspondence. The ring waveguides 106r and 206r are formed on a substrate 101, and the substrate 101 may include a silicon wafer or other suitable material. The ring waveguides 106r and 206r may be formed on the same substrate (e.g., to form an integrated optical transceiver), or may be formed on separate substrates (e.g., to form separate optical transmitters and optical receivers). The heaters 130 and 230 may include metal heaters, silicon heaters, or other suitable heaters. The heaters 130 and 230 are disposed directly above the respective ring waveguides 106r and 206r and are separated from the respective ring waveguides 106r and 206r by a vertical distance D. For example, in one embodiment, the distance D may be in the range of 0.7 μm to 0.9 μm. One or more dielectric materials (such as silicon oxide) may fill the space between the heaters 130 and 230 and the respective ring waveguides 106r and 206r. Each of the heaters 130 and 230 is in a ring shape and is connected to two electrodes 132 that supply current to the heater. The optical transmitter 102 and the optical receiver 202 also include metal wirings (M1 to M x ), metal vias (V0 to V x ) and micro-bumps (U-bump). The electrodes 132 are coupled to some of the micro-bumps through metal wirings and metal vias. In addition, the p / n junction of the ring waveguide 106r is coupled to some of the micro-bumps through metal wirings and metal vias, and these metal wirings and vias are sequentially coupled to RMD116( Figure 1 ).

[0036] Figure 5 An embodiment of the optical transmitter 102 constructed according to the present disclosure is shown. For simplicity, the illustrated optical transmitter 102 includes 4 channels (corresponding to wavelengths λ1, λ2, λ3, and λ4). However, the disclosed systems and methods are applicable to optical transmitters 102 having any number of channels, such as more than four channels or any number of channels out of four channels. The optical transmitter 102 includes four light sources (such as lasers) 105, and the four light sources emit light at wavelengths λ1, λ2, λ3, and λ4, respectively. The light at wavelengths λ1, λ2, λ3, and λ4 is multiplexed and transmitted through the waveguide 108. The optical transmitter 102 includes four RMs 106, namely RM1, RM2, RM3, and RM4. The four RMs 106 are respectively designed to resonate at wavelengths λ1, λ2, λ3, and λ4. However, due to process variations and operating environment variations, the four RMs 106 may not resonate at wavelengths λ1, λ2, λ3, and λ4.

[0037] The optical transmitter 102 further includes a distribution controller 104 for assigning wavelengths λ1, λ2, λ3, and λ4 to the RMs 106 during system initialization. For example, the ring modulators RM1, RM2, RM3, and RM4 may be assigned wavelengths λ1, λ2, λ3, and λ4 respectively, or wavelengths λ2, λ3, λ4, and λ1 respectively, which will be discussed further with reference to Figure 7 below.

[0038] The optical transmitter 102 also includes a heater 130 coupled to the RM 106 (see Figures 2 - 4 ), and a heater controller 120 coupled to the heater 130 in a one-to-one correspondence. During system initialization, the distribution controller 104 controls the heater controller 120, and the heater controller 120 in turn controls the heater 130. Once the assignment is complete, the heater controller 120 controls the heater 130 to fine-tune (or auto-correct) the resonant wavelength of the RM 106 without the intervention of the distribution controller 104.

[0039] The optical transmitter 102 further includes waveguides 110, a photodetector (such as a photodiode) 112, and a TIA 114. In a one-to-one correspondence, the waveguides 110 are coupled to the RMs 106, and the photodetector 112 is coupled between the waveguide 110 and the TIA 144. The output of the TIA 114 is coupled to the heater controller 120 and the distribution controller 104. Once the RM 106 resonates, the optical signal is coupled to the corresponding waveguide 110. Subsequently, the photodetector 112 converts the optical signal into an electrical signal, which is then amplified by the TIA 114. The distribution controller 104 uses the amplified electrical signal for channel assignment during system initialization, and the heater controller 120 uses the amplified electrical signal for auto-correction during system runtime. The optical transmitter 102 also includes a bus 140 for interconnecting the distribution controller 104 with other components (such as a memory) of the optical transmitter 102. Each heater controller 120 may include a comparator and / or other suitable digital or analog circuits. The optical transmitter 102 also includes an RMD 116 to bias the p / n junction in the RM 106.

[0040] Figure 6An embodiment of an optical receiver 202 constructed in accordance with the present disclosure is shown. For simplicity, the optical receiver 202 shown includes four channels (corresponding to wavelengths λ1, λ2, λ3, and λ4). However, the disclosed systems and methods are applicable to optical receivers 202 having any number of channels, such as more than four channels or multiples of four channels. The optical receiver 202 includes four light sources (such as lasers) 205 that emit light at wavelengths λ1, λ2, λ3, and λ4, respectively. The optical receiver 202 includes a waveguide 208. During system initialization, the waveguide 208 receives optical signals from the light sources 205. During system runtime, the waveguide 208 receives optical signals from optical transmitters such as optical transmitter 102 via optical fiber 150. The optical receiver 202 includes four RRs 206, namely RR1, RR2, RR3, and RR4. The four RRs 206 resonate at wavelengths λ1, λ2, λ3, and λ4, respectively. However, due to process variations and operating environment variations, the four RRs 206 may not resonate at wavelengths λ1, λ2, λ3, and λ4.

[0041] The optical receiver 202 further includes an allocation controller 204 that can allocate wavelengths λ1, λ2, λ3, and λ4 to the RRs 206 during system initialization. For example, the ring resonators RR1, RR2, RR3, and RR4 may be allocated wavelengths λ1, λ2, λ3, and λ4, respectively, or wavelengths λ2, λ3, λ4, and λ1, respectively, which will be further discussed with reference to Figure 7 below.

[0042] The optical receiver 202 further includes heaters 230 coupled to the RRs 206 (see Figures 3 - 4 ) and heater controllers 220 coupled to the heaters 230 in a one-to-one correspondence. During system initialization, the allocation controller 204 controls the heater controllers 220, which in turn control the heaters 230. Once the allocation is complete, the heater controllers 220 control the heaters 230 to fine-tune (or automatically correct) the resonant wavelengths of the RRs 206 without the intervention of the allocation controller 204.

[0043] The optical receiver 202 also includes a waveguide 210, a photodetector (such as a photodiode) 212, and a TIA 214. In a one-to-one correspondence manner, the waveguide 210 is coupled to the RR 206, and the photodetector 212 is coupled between the waveguide 210 and the TIA 214. The output of the TIA 214 is coupled to the heater controller 220 and the allocation controller 204. Once the RR 206 resonates, the optical signal is coupled to the corresponding waveguide 210. Subsequently, the photodetector 212 converts the optical signal into an electrical signal, which is then amplified by the TIA 214. The allocation controller 204 uses the amplified electrical signal for channel allocation during system initialization, and the heater controller 220 uses the amplified electrical signal for automatic correction during system runtime. The optical receiver 202 also includes a bus 240, which is used to interconnect the allocation controller 204 with other components (such as memory) of the optical receiver 202. Each heater controller 220 may include a comparator and / or other suitable digital or analog circuits.

[0044] Each of the allocation controllers 104 and 204 may be implemented in hardware, software, or a combination thereof. Suitable hardware may include one or more general-purpose processor devices, such as a microprocessor, a central processing unit, etc., or one or more dedicated processor devices, such as an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), a digital signal processor (DSP), a network processor, etc. The hardware is configured to execute instructions that perform the operations and steps discussed herein. Suitable software includes any machine code stored in any storage medium (such as RAM or ROM), as well as machine code stored on other devices (such as a floppy disk, a flash memory, or a CD ROM). For example, the software may include source code or object code. In addition, the software also includes any instruction set that can be executed in a client or a server. A combination of software and hardware may also be used to provide enhanced functionality and performance for certain embodiments of the present invention. An example is to directly fabricate software functions into a silicon chip.

[0045] Figure 7 A flowchart of a method 400 that may be implemented in the allocation controllers 104 and 204 is shown. The method 400 includes operations 402, 404, 406, 408, 410, 414, 416, and 418. The present invention contemplates other operations. Additional operations may be provided before, during, and after the method 400, and for additional embodiments of the method 400, some of the described operations may be moved, replaced, or eliminated. The following describes the method 400 for the operation of the allocation controller 104 in conjunction with Figure 5 to describe. Figure 8 An example channel allocation generated by the method 400 is shown.

[0046] At operation 402, the allocation controller 104 turns off the automatic heater control for all channels in the optical transmitter 102. For example, the allocation controller 104 configures the heater controller 120 to cause the heater controller 120 to ignore the input from the TIA 114. Additionally, each heater 130 is provided with an initial current, such as a current that is substantially zero (0) amperes. As Figure 8 (Lower part) shows, the ring modulators RM1, RM2, RM3, and RM4 are designed to resonate at wavelengths λ1, λ2, λ3, and λ4, respectively.

[0047] At operation 404, the allocation controller 104 configures the light source 105 to emit light at a selected wavelength, such as wavelength λ1 or any one of wavelengths λ1, λ2, λ3, and λ4. For example, the allocation controller 04 may turn on one light source in the light source 105 that emits light at the selected wavelength and turn off the other light sources 105. Then, the light emitted by the selected light source 105 is coupled into the waveguide 108.

[0048] At operation 406, the allocation controller 104 instructs all heater controllers 120 to increase the current supplied to the corresponding heaters 130 by a step ΔI. For example, the step ΔI may be in the range of 1 μA to 5 μA. Alternatively, the allocation controller 104 instructs all heater controllers 120 (excluding any heater controllers 120 corresponding to the RM 106 of the allocated wavelength) to increase the current supplied to the corresponding heaters 130 by a step ΔI.

[0049] At operation 408, the allocation controller 104 checks whether any of the RM 106 are in resonance. For example, if the signal amplitude of the TIA 114 exceeds a specific threshold, it is determined that the corresponding RM 106 is in a resonant state.

[0050] If none of the RM 106 are in resonance, the method 400 returns to operation 406 to further increase the current supplied to the heater 130 and then continues with operation 408. This continues until one of the RM 106 is in resonance. For illustration, assume that RM3 resonates at the selected wavelength λ1. Then, the method 400 proceeds to operation 410.

[0051] At operation 410, the allocation controller 104 allocates the resonant RM 106 at a selected wavelength. For illustration, RM3 is allocated the wavelength λ1, which is different from the designed resonant wavelength λ3. Then, the allocation controller 104 resets all the heater controllers 120 to provide an initial current to the heaters 130. In another embodiment, the allocation controller 104 only resets the heater controllers 120 corresponding to the unallocated RM 106 (RM1, RM2, and RM4 in this illustration) and enables the automatic heater control for the allocated RM 106 (RM3 in this illustration). In an alternative embodiment, the allocation of RM3 has been completed, and RM3 is fine-tuned by the heater controller 120 through an automatic heating control loop having RM3, waveguide 110, photodetector 112, TIA 114, and heater controller 120.

[0052] Then, method 400 proceeds to operation 414 to check if all wavelengths have been allocated. If all wavelengths have been allocated, method 400 continues to operation 416. Otherwise, method 400 continues with operation 404 to select the next wavelength for allocation. For ease of illustration, the next wavelength is λ2. Operation 404 only turns on the light source for wavelength λ2.

[0053] Then, method 400 repeats operations 406 and 408 until one of the RM 106 resonates. For ease of illustration, assume RM4 resonates at the selected wavelength λ2. Then, at operation 410, the allocation controller 104 allocates the wavelength λ2 to RM4. Additionally, the allocation controller 104 resets all the heater controllers 120 to provide an initial current to the heaters 130. In another embodiment, the allocation controller 104 only resets the heater controllers 120 corresponding to the unallocated RM 106 (RM1 and RM2 in this figure) and enables the automatic heater control for the allocated RM 106 (RM3 and RM4 in this figure).

[0054] Then, method 400 performs operations 414, 404, 406, 408, and 410 to allocate the remaining wavelengths to RM 106. For ease of illustration, in the next two loops, wavelengths λ3 and λ4 are allocated to the ring modulators RM1 and RM2, respectively. In the above example, the wavelengths are selected in ascending order, i.e., from λ1 to λ4. Optionally, the wavelengths can be selected in descending order or randomly.

[0055] When all wavelengths have been allocated (operation 414), method 400 proceeds to operation 416. At operation 416, method 400 conveys the channel allocation (i.e., how RM 106 corresponds to wavelengths λ1 to λ4) to the optical receiver that is expected to receive the optical signal from the optical transmitter 102.

[0056] At operation 418, method 400 completes the allocation and may store certain results of the allocation in a memory. For example, method 400 may store the current values at the resonance of RM 106 during the allocation. These values may be used for future allocations to speed up the allocation process. For example, method 400 may store the results of the allocation. Additionally, method 400 may initiate the operation of optical transmitter 102. For example, method 400 may modulate wavelengths λ1 to λ4 by applying electrical signals to RMD 116 respectively, thereby generating modulated optical signals. These modulated optical signals are multiplexed and transmitted through optical fiber 150. During operations 402 to 418, RMD 116 may be set to a fixed bias voltage or a switched bias voltage until optical transmitter 102 starts operating.

[0057] Embodiments of method 400 are also applicable to allocation controller 204 in optical receiver 202. These embodiments are briefly described below with reference to Figures 6 - 8 Briefly describe these embodiments.

[0058] At operation 402, allocation controller 204 turns off the automatic heater control for all channels in optical receiver 202. For example, allocation controller 202 configures heater controller 220 to cause heater controller 220 to ignore the input from TIA 214. Additionally, each heater 230 is provided with an initial current, such as a current that is substantially zero (0) amperes. Ring resonators 206, namely RR1, RR2, RR3, and RR4, are designed to resonate at wavelengths λ1, λ2, λ3, and λ4 respectively.

[0059] At operation 404, allocation controller 204 configures light source 205 to emit light at a selected wavelength, such as wavelength λ1 or any one of wavelengths λ1, λ2, λ3, and λ4. For example, allocation controller 205 may turn on one light source in light source 205 that emits light at the selected wavelength and turn off the other light sources 205. In one embodiment, light source 205 is only used during the initialization of optical receiver 202. For illustration, assume that wavelength λ1 is selected.

[0060] At operation 406, allocation controller 204 instructs all heater controllers 220 to increase the current supplied to the corresponding heaters 230 in steps of ΔI. For example, the step ΔI may be in the range of 1 μA to 5 μA.

[0061] At operation 408, allocation controller 204 checks whether any of the RR 206 are in resonance. For example, if the signal amplitude from TIA 214 exceeds a specific threshold, it is determined that the corresponding RR 206 is in a resonant state.

[0062] If none of the RR 206 are in resonance, method 400 returns to operation 406 to further increase the current supplied to heater 230, and then continues with operation 408. This continues until one of the RR 206 is in resonance. For the sake of illustration, assume that RR3 resonates at the selected wavelength λ1. Then, method 400 proceeds to operation 410.

[0063] At operation 410, distribution controller 204 distributes the resonant RR 206 at the selected wavelength. For illustration, RR3 is assigned the wavelength λ1. Then, distribution controller 204 resets all heater controllers 220 to supply an initial current to heater 230. In another embodiment, distribution controller 204 only resets the heater controllers 220 corresponding to the unassigned RR 206 (RR1, RR2, and RR4 in this illustration), and enables the automatic heater control for the assigned RR 206 (RR3 in this illustration). For example, RR3 is fine-tuned by heater controller 220 through a loop having RR3, waveguide 210, photodetector 212, TIA 214, and heater controller 220.

[0064] Then, method 400 proceeds to operation 414 to check if all wavelengths have been assigned. If all wavelengths have been assigned, method 400 continues to operation 416. Otherwise, method 400 continues to execute operation 404 to start a new assignment.

[0065] In the new assignment, method 400 performs operation 404 such that only the light source 205 at the next selected wavelength (such as wavelength λ2) is turned on. Then, method 400 repeats operations 406 and 408 until one of the RR 206 is in resonance. For the sake of illustration, assume that RR4 resonates at the selected wavelength λ2. Then, at operation 410, distribution controller 204 assigns the wavelength λ2 to RR4. Additionally, distribution controller 202 resets all heater controllers 220 to supply an initial current to heater 230. In another embodiment, distribution controller 204 only resets the heater controllers 220 corresponding to the unassigned RR 206 (RR1 and RR2 in this illustration), and enables the automatic heater control for the assigned RR 206 (RR3 and RR4 in this illustration).

[0066] Then, method 400 proceeds with operations 414, 404, 406, 408, and 410 to assign the remaining wavelengths to the RR 206. For the sake of illustration, in the next two loops, wavelengths λ3 and λ4 are assigned to the ring resonators RR1 and RR2, respectively. In the above example, the wavelengths are selected in ascending order, i.e., from λ1 to λ4. Optionally, the wavelengths can be selected in descending order or randomly.

[0067] When all wavelengths have been allocated (operation 414), method 400 proceeds to operation 416. At operation 416, method 400 conveys the channel allocation (i.e., how RR 206 corresponds to wavelengths λ1 to λ4) to the optical transmitters that are expected to transmit optical signals to the optical receiver 202.

[0068] At operation 418, method 400 completes the allocation and may store some of the results of the allocation in memory. For example, method 400 may store the current values at which RR 206 resonates during the allocation. These values can be used for future allocations to speed up the allocation process. Additionally, method 400 may initiate the operation of the optical receiver 202. For example, method 400 may receive an optical signal having components at wavelengths λ1 to λ4 through the optical fiber 150, and the components at wavelengths λ1 to λ4 are modulated with respective digital data patterns. The optical signal is coupled to RR 206 as it passes through the waveguide 208. RR 206 then resonates at its allocated wavelength, thereby demultiplexing the optical signal into individual optical signals at the allocated wavelengths. The individual optical signals are coupled to the waveguide 210. The electrical signals carried by the individual optical signals are detected by the photodetector 212 and processed by the TIA 214 and other circuitry.

[0069] Although not intended to be limiting, one or more embodiments of the present disclosure provide numerous advantages for optical systems such as DWDM systems. By comparison Figure 8 and Figure 9 in the allocation, some advantages of the present invention can be understood. As shown in the lower half of Figure 8 and Figure 9 , the ring modulators (or ring resonators) are designed to resonate at wavelengths λ1, λ2, λ3, and λ4, respectively. Due to variations in the manufacturing process and different operating environments, the actual resonant frequencies of the ring modulators and ring resonators are offset from their designed values by F shift . In the example shown, the frequency offset F shift is approximately 75% of one FSR (see Figure 9 ). In some cases, the frequency offset F shift may be close to one FSR. As previously mentioned, it may not be possible to use heaters to compensate for such a large frequency offset, or reliability issues may be introduced. Instead, by using the embodiments of the present disclosure, the heater only needs to compensate for a relatively small frequency offset F assign , as shown in Figure 8 . This is because for any selected wavelength, the ring modulator or ring resonator with the actual resonant wavelength closest to the selected wavelength is allocated to the selected wavelength. Therefore, the frequency offset F assign represents the minimum frequency offset that the ring modulator or ring resonator needs for the operation of the resonant optical system. In the example shown in Figure 8 , the frequency offset F assignLess than 25% of an FSR, which is much less than the frequency offset F shift Advantageously, the heater can be made smaller and / or more efficient, and the power consumption of the optical system can be reduced.

[0070] In one exemplary aspect, the present invention relates to a method of operating an optical device, where the optical device includes a first waveguide, a plurality of ring waveguides adjacent to the first waveguide, and a plurality of heaters coupled to the ring waveguides one-to-one, and each of the plurality of heaters is provided with an initial current. The method includes coupling a first light source having a first wavelength to the first waveguide, and increasing the current through the heater until a first ring waveguide in the ring waveguides resonates, where the first ring waveguide in the ring waveguides is coupled to a first heater in the heaters. The method further includes allocating the first ring waveguide in the ring waveguides to the first wavelength, and resetting the current through the heater or through the heaters excluding the first heater in the heaters to the initial current. The method further includes coupling a second light source having a second wavelength to the first waveguide, where the second wavelength is different from the first wavelength. The method further includes increasing the current through the heater or through the heaters excluding the first heater in the heaters until a second ring waveguide in the ring waveguides resonates, where the second ring waveguide in the ring waveguides is different from the first ring waveguide in the ring waveguides, and allocating the second ring waveguide in the ring waveguides to the second wavelength.

[0071] In one embodiment of the method, the initial current is substantially zero amperes. In one embodiment, the optical device includes a plurality of heater control loops configured to control the plurality of heaters one-to-one, and the method further includes disabling the heater control loops before coupling the first light source, and enabling one of the heater control loops corresponding to the first heater in the heaters after allocating the first ring waveguide in the ring waveguides to the first wavelength.

[0072] In one embodiment of the method, the plurality of ring waveguides includes four or more ring waveguides. In another embodiment, the optical device includes an optical transmitter, and each of the ring waveguides is part of a micro-ring modulator. In another embodiment, after allocating the second ring waveguide in the ring waveguides to the second wavelength, the method further includes modulating the first wavelength by applying a first electrical signal to the first ring waveguide in the ring waveguides to generate a modulated first optical signal; modulating the second wavelength by applying a second electrical signal to the second ring waveguide in the ring waveguides to generate a modulated second optical signal; and multiplexing the modulated first optical signal and the modulated second optical signal into a transmitted optical signal.

[0073] In one embodiment of the method, the optical device includes an optical receiver, and each of the ring waveguides is part of a ring resonator. In another embodiment, after allocating a second ring waveguide in the ring waveguides to a second wavelength, the method further includes receiving an optical signal having a first component at a first wavelength and a second component at a second wavelength; coupling the optical signal to a plurality of ring waveguides; and demultiplexing the optical signal into a first optical signal through a first ring waveguide in the ring waveguides and demultiplexing the optical signal into a second optical signal through a second ring waveguide in the ring waveguides.

[0074] In another exemplary aspect, the present invention relates to a method of operating an optical transmitter, wherein the optical transmitter includes a first waveguide, a plurality of micro-ring modulators (MRMs) adjacent to the first waveguide, and a plurality of heaters coupled to the MRMs one-to-one, and each of the plurality of heaters is provided with an initial current. The method includes the following steps: coupling a light source having a wavelength to the first waveguide; increasing the current through each of the heaters until one of the MRMs resonates, wherein one of the MRMs is coupled to one of the heaters; allocating one of the MRMs to the wavelength; resetting the current through the heater or through the heaters excluding one of the heaters to the initial current; and repeating the steps of coupling, increasing, allocating, and resetting until each of the MRMs is allocated to a different wavelength.

[0075] In one embodiment, before the coupling step, the method further includes turning off the automatic heater control loop of each of the plurality of heaters. In another embodiment, the MRM includes a multiple of four MRMs. In yet another embodiment, the method further includes biasing each of the MRMs to a fixed bias voltage during the steps of coupling, increasing, allocating, resetting, and repeating.

[0076] In one embodiment, the method further includes applying a switching electrical signal to each of the MRMs during the steps of coupling, increasing, allocating, resetting, and repeating. In another embodiment, the method further includes storing the current value through each of the heaters that causes the corresponding MRM to resonate during the step of increasing the current. In yet another embodiment, the steps of coupling, increasing, allocating, resetting, and repeating are performed during the initialization process of the optical transmitter.

[0077] In another exemplary aspect, the present invention relates to an optical system including an optical transmitter, where the optical transmitter includes a first waveguide, a plurality of micro-ring modulators (MRMs) disposed adjacent to the first waveguide, and a plurality of heaters coupled to the MRMs in a one-to-one correspondence. The system further includes: a plurality of heater controllers coupled to the plurality of heaters in a one-to-one correspondence; and a distribution controller configured to: couple a light source to the first waveguide; instruct the heater controllers to increase the current through the heaters until one of the MRMs resonates, where one of the MRMs is coupled to one of the heaters; and assign one of the MRMs to the wavelength of the light source.

[0078] In one embodiment of the optical system, the distribution controller is further configured to: reset the current through the heaters or through a heater excluding one of the heaters to an initial current; and repeat the steps of coupling, instructing, and resetting until each of the MRMs is assigned to a different wavelength. In another embodiment, the distribution controller is further configured to store the result of assigning the MRMs to different wavelengths.

[0079] In one embodiment of the optical system, the optical transmitter further includes a plurality of ring modulator drivers (RMDs) coupled to the MRMs in a one-to-one correspondence. In another embodiment of the system, the optical transmitter further includes a plurality of photodetectors, each of the photodetectors being coupled between one of the MRMs and a corresponding one of the heater controllers.

[0080] The foregoing outlines the features of several embodiments so that those skilled in the art may better understand the various aspects of the present disclosure. Those skilled in the art should understand that they can readily use the present disclosure as a basis for designing or modifying other processes and structures for achieving the same purposes and / or achieving the same advantages as the embodiments described herein. Those skilled in the art should also recognize that such equivalent structures do not depart from the spirit and scope of the present invention, and that they may make various changes, substitutions, and alterations to the present invention without departing from the spirit and scope of the present invention.

Claims

1. A method of operating an optical device, wherein, The optical device includes a first waveguide, a plurality of ring waveguides adjacent to the first waveguide, and a plurality of heaters respectively coupled to the ring waveguides, wherein each of the plurality of heaters is provided with an initial current. The method includes: Coupling a first light source having a first wavelength to the first waveguide; Increasing the current through the heater until the first ring waveguide in the ring waveguides resonates, wherein the first ring waveguide in the ring waveguides is coupled to a first heater among the heaters; Allocating the first ring waveguide in the ring waveguides to the first wavelength; Resetting the current through the heater or through the heaters excluding the first heater among the heaters to the initial current; Coupling a second light source having a second wavelength to the first waveguide, wherein the second wavelength is different from the first wavelength; Increasing the current through the heater or through the heaters excluding the first heater among the heaters until a second ring waveguide in the ring waveguides resonates, wherein the second ring waveguide in the ring waveguides is different from the first ring waveguide in the ring waveguides; and Allocating the second ring waveguide in the ring waveguides to the second wavelength.

2. The method according to claim 1, wherein The initial current is zero amperes.

3. The method according to claim 1, wherein The optical device includes a plurality of heater control loops configured to control the plurality of heaters respectively. The method further includes: Disabling the heater control loops before coupling the first light source; and Enabling one of the heater control loops corresponding to the first heater among the heaters after allocating the first ring waveguide in the ring waveguides to the first wavelength.

4. The method according to claim 1, wherein The plurality of ring waveguides include four or more ring waveguides.

5. The method according to claim 1, wherein The optical device includes an optical transmitter, and each of the ring waveguides is part of a microring modulator.

6. According to the method of claim 5, after allocating the second ring waveguide in the ring waveguides to the second wavelength, the method further includes: Modulating the first wavelength by applying a first electrical signal to the first ring waveguide in the ring waveguides, thereby generating a modulated first optical signal; Modulating the second wavelength by applying a second electrical signal to the second ring waveguide in the ring waveguides, thereby generating a modulated second optical signal; And Multiplexing the modulated first optical signal and the modulated second optical signal into a transmitted optical signal.

7. The method according to claim 1, wherein, The optical device includes an optical receiver, and each of the ring waveguides is part of a ring resonator.

8. According to the method of claim 7, after allocating the second ring waveguide in the ring waveguides to the second wavelength, the method further includes: Receiving an optical signal having a first component at a first wavelength and a second component at a second wavelength; Coupling the optical signal to the plurality of ring waveguides; And Demultiplex the optical signal into a first optical signal through a first ring waveguide in the ring waveguide, and demultiplex the optical signal into a second optical signal through a second ring waveguide in the ring waveguide.

9. A method of operating an optical transmitter, wherein, The optical transmitter includes a first waveguide, a plurality of micro-ring modulators adjacent to the first waveguide, and a plurality of heaters coupled to the micro-ring modulators one-to-one, wherein each of the plurality of heaters is provided with an initial current, and the method includes the following steps: Couple a light source having a wavelength to the first waveguide; Increase the current through each of the heaters until one of the micro-ring modulators resonates, wherein one of the micro-ring modulators is coupled to one of the heaters; Allocate one of the micro-ring modulators to the wavelength; Reset the current through the heater or the heaters excluding the one heater to the initial current; and Repeat the steps of coupling, increasing, allocating, and resetting until each of the micro-ring modulators is allocated to a different wavelength.

10. The method according to claim 9, further comprising, before the coupling step: Turn off the automatic heater control loop of each of the plurality of heaters.

11. The method according to claim 9, wherein, The micro-ring modulator includes a multiple of four micro-ring modulators.

12. The method according to claim 9, further comprising: During the steps of coupling, increasing, allocating, resetting, and repeating, bias each of the micro-ring modulators to a fixed bias voltage.

13. The method according to claim 9, further comprising: During the steps of coupling, increasing, allocating, resetting, and repeating, apply a switching electrical signal to each of the micro-ring modulators.

14. The method according to claim 9, further comprising: During the step of increasing the current, store the current value through each of the heaters that causes the corresponding micro-ring modulator to resonate.

15. The method according to claim 9, wherein, The steps of coupling, increasing, allocating, resetting, and repeating are performed during the initialization process of the optical transmitter.

16. An optical system, comprising: An optical transmitter, wherein the optical transmitter includes a first waveguide, a plurality of micro-ring modulators disposed adjacent to the first waveguide, and a plurality of heaters coupled to the micro-ring modulators one-to-one; A plurality of heater controllers, coupled to the plurality of heaters one-to-one; and An allocation controller configured to perform: Couple a light source to the first waveguide; Instruct the heater controller to increase the current through the heater until one of the micro-ring modulators resonates, wherein one of the micro-ring modulators is coupled to one of the heaters; and Allocate the one of the micro-ring modulators to the wavelength of the light source.

17. The optical system according to claim 16, wherein, The allocation controller is further configured to perform: Reset the current through the heater or the heaters excluding the one heater to the initial current; and Repeat the steps of coupling, instructing, and resetting until each of the micro-ring modulators is allocated to a different wavelength.

18. The optical system according to claim 17, wherein, The allocation controller is further configured to perform: Store the result of allocating the micro-ring modulators to the different wavelengths.

19. The optical system according to claim 16, wherein, The optical transmitter further includes a plurality of ring modulator drivers, and the plurality of ring modulator drivers are coupled to the micro-ring modulators in a one-to-one correspondence.

20. The optical system according to claim 16, wherein The optical transmitter further includes a plurality of photodetectors, and each of the photodetectors is coupled between one of the micro-ring modulators and a corresponding one of the heater controllers.

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