Wavelength-multiplexed light source with reduced temperature sensitivity

Abstract

The optical distribution network comprises a front-stage optical multiplexer section having a plurality of optical inputs and a plurality of intermediate optical outputs. Each of the plurality of optical inputs of the front-stage optical multiplexer section receives a respective one of a plurality of input optical signals of a different wavelength. The front-stage optical multiplexer section multiplexes a unique subset of the plurality of input optical signals into each of the plurality of intermediate optical outputs. The optical distribution network further comprises an optical coupler section having a plurality of optical inputs respectively optically connected to the plurality of intermediate optical outputs of the front-stage optical multiplexer section. The optical coupler section distributes a portion of each optical signal received at each of the plurality of optical inputs of the optical coupler section to one of the plurality of optical outputs of the optical coupler section.

Description

[Background technology]

[0001] The embodiments disclosed herein relate to optical data communications. Optical data communications systems operate by modulating laser light to encode a digital data pattern. The modulated laser light is transmitted from a sending node to a receiving node through an optical data network. Upon reaching the receiving node, the modulated laser light is demodulated to retrieve the original digital data pattern. The implementation and operation of optical data communications systems therefore depends on having a reliable and efficient laser light source. It is also desirable for the laser light source of an optical data communications system to have a minimal form factor and be designed as efficiently as possible in terms of cost and energy consumption. It is in this context that the embodiments disclosed herein arise. Summary of the Invention

[0002] In an example embodiment, an optical distribution network is disclosed. The optical distribution network comprises a front-stage optical multiplexer section having a plurality of optical inputs and a plurality of intermediate optical outputs. Each of the plurality of optical inputs of the front-stage optical multiplexer section is configured to receive a respective one of a plurality of input optical signals of a different wavelength. The front-stage optical multiplexer section is configured to multiplex a unique subset of the plurality of input optical signals onto each of the plurality of intermediate optical outputs. A unique subset of the plurality of input optical signals multiplexed onto any given one of the plurality of intermediate optical outputs is mutually exclusive with the plurality of input optical signals multiplexed onto other ones of the plurality of intermediate optical outputs. The optical distribution network further comprises an optical coupler section having a plurality of optical inputs respectively optically connected to the plurality of intermediate optical outputs of the front-stage optical multiplexer section. The optical coupler section has a plurality of optical outputs corresponding to the plurality of optical outputs of the optical distribution network. The optical coupler section is configured to distribute a portion of each optical signal received at each of the plurality of optical inputs of the optical coupler section to one of the plurality of optical outputs of the optical coupler section.

[0003] In an example embodiment, a laser module is disclosed. The laser module comprises a laser array comprising a plurality of lasers, each laser of the plurality of lasers configured to generate and output a different one of a plurality of wavelengths of continuous wave laser light. The plurality of lasers are arranged in the laser array such that a sequence of the plurality of wavelengths of the continuous wave laser light is non-monotonic ordered across the laser array. The laser module further comprises an optical distribution network comprising a front-stage optical multiplexer section and an optical coupler section disposed after the front-stage optical multiplexer section with respect to a direction of light propagation through the optical distribution network. The front-stage optical multiplexer section has a plurality of optical inputs optically connected to the plurality of lasers such that the non-monotonic ordering of the sequence of the plurality of wavelengths of the continuous wave laser light across the laser array matches an ordering of wavelength acceptance passbands of the plurality of optical inputs of the front-stage optical multiplexer section. The front-stage optical multiplexer section has a plurality of intermediate optical outputs. The front-end optical multiplexer section is configured to multiplex a unique and mutually exclusive subset of the plurality of wavelengths of the continuous wave laser light into each of the plurality of intermediate optical outputs. The optical coupler section has a plurality of optical inputs optically connected respectively to the plurality of intermediate optical outputs of the front-end optical multiplexer section. The optical coupler section has a plurality of optical outputs respectively corresponding to the plurality of optical outputs of the optical distribution network and each of the plurality of outputs of the laser module. The optical coupler section is configured to distribute a portion of each optical signal received at each of the plurality of optical inputs of the optical coupler section to one of the plurality of optical outputs of the optical coupler section.

[0004] A method for operating a laser module is disclosed. The method comprises operating a plurality of lasers to generate a plurality of input optical signals, each of which is of a different wavelength. The method further comprises communicating a plurality of input optical signals to a plurality of optical inputs of the upstream optical multiplexer section, such that each of the plurality of optical inputs of the upstream optical multiplexer section receives a respective one of the plurality of input optical signals of a different wavelength. The method further comprises operating the upstream optical multiplexer section to multiplex a unique subset of the plurality of input optical signals onto each of the plurality of intermediate optical outputs, such that a unique subset of the plurality of input optical signals multiplexed onto any given one of the plurality of intermediate optical outputs is mutually exclusive with the plurality of input optical signals multiplexed onto other ones of the plurality of intermediate optical outputs. The method further comprises communicating a unique subset of the plurality of input optical signals from the plurality of intermediate optical outputs to a plurality of optical inputs of the optical coupler section, such that a different unique subset of the plurality of input optical signals is communicated to each of the plurality of optical inputs of the optical coupler section, respectively. The method further comprises operating the optical coupler section to distribute a portion of each optical signal received at each of a plurality of optical inputs of the optical coupler section to one of a plurality of optical outputs of the optical coupler section. [Brief description of the drawings]

[0005] [Figure 1A] 1 illustrates an example of an optical power supply for an optical data communication system in accordance with some embodiments.

[0006] [Figure 1B] 1 illustrates how each of the optical fibers of an N-port optical fiber array receives each of multiple wavelengths (λ 1 to λ M ) of CW laser light in accordance with some embodiments.

[0007] [Figure 2A] 1 illustrates an example of an M×1 cascaded MUX network in accordance with some embodiments.

[0008] [Figure 2B] 1 illustrates the relative intensities of CW laser light at different optical wavelengths λ1, λ2, λ3, λ4, λ5, λ6, λ7, and λ8 output from an 8×1 cascaded MUX network in accordance with some embodiments.

[0009] [Figure 2C] FIG. 2 illustrates an M×1 cascaded MUX network (where M=8) optically connected to a laser array in accordance with some embodiments.

[0010] [Figure 2D] 4 illustrates input port optical wavelength acceptance passbands of an MZI (MUX) in a first MZI stage, an MZI (MUX) in a second MZI stage, and an MZI (MUX) in a third MZI stage, according to some embodiments.

[0011] [Diagram 3] 1 illustrates an example of an architecture for an M×N optical distribution network having M optical inputs and N optical inputs, where N is less than M, in accordance with some embodiments.

[0012] [Figure 4A] 4 illustrates an 8×4 optical distribution network, which is an implementation of the M×N optical distribution network of FIG. 3, in accordance with some embodiments.

[0013] [Figure 4B] FIG. 4B illustrates the relative intensities of CW laser light at different optical wavelengths λ1, λ2, λ3, λ4, λ5, λ6, λ7, and λ8 output from the 8×4 optical distribution network of FIG. 4A in accordance with some embodiments.

[0014] [Figure 4C] 4B illustrates the 8×4 optical distribution network of FIG. 4A optically connected to a laser array in accordance with some embodiments.

[0015] [Figure 5A]4 illustrates a system in which a laser array is directly connected to the M×N optical distribution network of FIG. 3 to form a laser module, according to some embodiments.

[0016] [Figure 5B] 5B is a diagram of the system of FIG. 5A showing an M×N optical distribution network in greater detail in accordance with some embodiments.

[0017] [Figure 6A] FIG. 2 illustrates a system in which a laser array is directly coupled to an 8×8 optical distribution network in accordance with some embodiments.

[0018] [Figure 6B] FIG. 1 illustrates the relative intensities of CW laser light at different optical wavelengths λ1, λ2, λ3, λ4, λ5, λ6, λ7, and λ8 provided to the input of an 8×8 optical distribution network and output through the output of the 8×8 optical distribution network in accordance with some embodiments.

[0019] [Figure 7] 4 is a flow chart illustrating a method for operating a laser module in accordance with some embodiments. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] In the following description, numerous specific details are set forth in order to provide an understanding of the embodiments disclosed herein. However, it will be apparent to one of ordinary skill in the art that the embodiments disclosed herein may be practiced without some or all of these specific details. In addition, detailed descriptions of well-known process operations are omitted in order to avoid unnecessarily obscuring the disclosed embodiments.

[0021] High bandwidth, multi-wavelength WDM (wavelength division multiplexing) systems are used to meet the increasing interconnection bandwidth requirements. In some examples of these WDM systems, a remote laser array outputting multiple wavelengths of continuous wave (CW optical) laser light is combined with an optical distribution network to transmit optical power at multiple wavelengths across multiple optical output ports. In some embodiments, the number of optical output ports N is smaller than the number of optical input ports M at a point in the optical train, which necessitates the implementation of an optical multiplexer (MUX) function. In some embodiments, an arrayed waveguide grating or a cascaded Mach-Zehnder interferometer is used to combine (multiplex) multiple (M) wavelengths of light into one optical channel, which is then combined with a 1×N optical splitter to realize an M×N optical distribution network. However, an M×1 optical MUX requires optical filtering with passbands bandwidth-limited by the optical wavelength spacing, which may result in undesirable temperature sensitivity. Disclosed herein are example embodiments of an M optical input by N optical output (M×N) optical (optical) distribution network (where N is less than M) that uses a reduced number of optical MUX stages (compared to an M×1 cascaded optical MUX network) in combination with a star coupler at the output. Compared to using an M×1 optical MUX system followed by a 1×N optical split, the M×N optical distribution network disclosed herein allows for lower temperature sensitivity by allowing for a wider optical MUX passband.

[0022] Also, for a cascaded MUX network, the required sequence of input optical wavelengths typically does not increase or decrease with the order of the input channels. Rather, the sequence of input optical wavelengths is a non-monotonic sequence that must match the input optical wavelength passband of the first optical MUX stage. In various example embodiments disclosed herein, the optical wavelength sequence on the laser array is configured to match the input optical wavelength passband of the first optical MUX stage to allow direct one-to-one coupling of the lasers in the laser array with the input channels of the optical distribution network without the need for any further optical routing or optical crossing. It should be understood that the optical wavelength sequence on the laser array is the order in which the different laser wavelengths occur from laser to adjacently located laser in a single direction across the laser array.

[0023] 1A illustrates an example of an optical power supply 111 for an optical data communication system, in accordance with some embodiments. The optical power supply 111 comprises a laser array 101, an M×N optical distribution network 103, and an optional optical amplification module 105. The laser array 101 comprises a number (M) of lasers 101-1 through 101-M, where M is greater than 1. Each laser 101-1 through 101-M emits light at a different wavelength (λ1 through λ2). M 1 to 104-M of the laser array 101. M) of CW laser light is transmitted from optical outputs 104-1 through 104-M of laser array 101 to corresponding optical inputs 106-1 through 106-M of M×N optical distribution network 103. Optical distribution network 103 routes the CW laser light of each of the M wavelengths generated by the plurality of lasers 101-1 through 101-M to each of the number (N) of optical output ports 107-1 through 107-N of optical distribution network 103. In some embodiments, optional optical amplification module 105 is not present, and multiple wavelengths (λ1 through λ2) of CW laser light are directed to a given one 107-x (where x is any one of 1 through N) of N optical output ports 107-1 through 107-N of optical distribution network 103. M ) CW laser light is transmitted directly to a corresponding one 108-x of N optical outputs 108-1 to 108-N of optical power supply 111 and then to a corresponding one 113-x of N optical fibers 113-1 to 113-N of N-port optical fiber array 113. In some embodiments, optional optical amplifier module 105 is not present and multiple wavelengths (λ1 to λ2) are directed to a given one 107-x of N optical output ports 107-1 to 107-N of optical distribution network 103. M ) is transmitted through optical amplifier module 105 for amplification in route to N optical outputs 108-1 to 108-N of optical power supply 111, and then transmitted to a corresponding one 113-x (where x is an integer from 1 to N) of N optical fibers 113-1 to 113-N of N-port optical fiber array 113. In this manner, optical power supply 111 transmits a plurality of wavelengths (λ1 to λ2) in each of N optical fibers 113-1 to 113-N of N-port optical fiber array 113. M ) CW laser light.

[0024] In some embodiments, each of the optical fibers 113-1 to 113-N of the N-port optical fiber array 113 receives optical signals at multiple wavelengths (λ1 to λN) from the optical power supply 111. M) to corresponding optical supply ports 115-1 through 115-N on the electro-optic chip 102. In this manner, the N-port optical fiber array 113 is connected to route M wavelengths (λ1 through λ M ) CW laser light to each of N optical feed ports 115-1 through 115-N on the electro-optical chip 102. In some embodiments, the electro-optical chip 102 is a CMOS (complementary metal oxide semiconductor) and / or SOI (silicon-on-insulator) photonic / electronic chip that transmits and receives data in an optical data communication system. In some embodiments, the electro-optical chip 102 is a TeraPHY™ chip from Ayar Labs, Inc. of Santa Clara, Calif., as described in U.S. patent application Ser. No. 17 / 184,537.

[0025] FIG. 1B illustrates an N-port optical fiber array 113, in accordance with some embodiments, in which each of the optical fibers 113-1 through 113-N of the N-port optical fiber array 113 is configured to transmit multiple wavelengths (λ1 through λ2). M ) is received. In some embodiments, the CW laser light of multiple wavelengths (λ1 to λ M ) is transmitted through each of the optical fibers 113-1 through 113-N of the N-port optical fiber array 113 at substantially equal intensity (optical power level). The laser array 101 comprises a number (M) of CW optical output channels, where each of the M laser output channels has a unique optical wavelength (λ1 through λ M An optical distribution network 103 is implemented to distribute optical power from each of the M laser output channels of the laser array 101 to each of the N optical output ports 107-1 through 107-N of the optical distribution network 103.

[0026] In some embodiments, for an M×N optical distribution network 103 where the number N of optical output ports 107-1 through 107-N is less than the number M of CW optical output channels of the laser array 101, the M×N optical distribution network 103 comprises at least one stage of an optical wavelength multiplexer (MUX). In some embodiments, optical wavelength multiplexing is implemented by using a series of cascaded Mach-Zehnder Interferometers (MZIs), where each MZI can multiplex two wavelengths of light incident on two MZI input ports into one of the MZI output ports. In some embodiments, a cascaded MZI system is used to achieve M×1 multiplexing, where M=2 n where n is an integer. In this type of cascaded MZI system, the last MZI stage of the cascaded MZI system has a free spectral range (FSR) approximately equal to the optical wavelength spacing, where the FSR of the MZI is doubled for each preceding stage of the cascaded MZI system. In some embodiments, this type of cascaded MZI system is used to implement WDM in optical data communication applications. The MZIs in the cascaded MZI system described above function as optical wavelength MUXes. However, in various embodiments, it is not necessary to utilize MZIs as MUXes in the M×N optical distribution network 103. For example, in some embodiments, instead of using MZIs as MUX devices, the M×N optical distribution network 103 may be implemented using essentially any other type of optical MUX device (e.g., ring-based add / drop filters, grating-based add / drop filters, directional couplers, and / or integrated dichroic filters, among others).

[0027] For an M×N optical distribution network 103 implementing a cascaded MUX network, the optical wavelength sequence of the optical input ports 106-1 to 106-M may not be monotonically increasing or decreasing, and the optical wavelength sequence of the optical input ports 106-1 to 106-M should be adjusted to match the allowable optical wavelength passband of the MUX device. For example, when using an MZI as a MUX in the M×N optical distribution network 103, the first MZI stage has an FSR equal to the optical wavelength spacing M multiplied by the optical wavelength spacing and a half FSR shift in the transfer function of the two input ports of the first MZI stage. Thus, the two optical wavelengths entering the two input ports of each MZI are selected such that the two optical wavelengths are separated by the wavelength spacing multiplied by M / 2. Accordingly, disclosed herein are embodiments for an improved optical power supply 111 configured such that the optical wavelength sequence of the laser array 101 meets the input optical wavelength passband sequence requirements of the cascaded MUX networks in the M×N optical distribution network 103 to enable one-to-one coupling of each physical laser channel of the laser array 101 to a corresponding physical input channel (106-1 to 106-N) of the cascaded MUX networks in the M×N optical distribution network 103.

[0028] To implement the M×N optical distribution network 103 directly using the above-mentioned cascaded MUX network, a 1×N optical power splitter is placed after the M×1 MUX. One drawback of this approach is that the last MUX stage in the M×1 wavelength optical combiner requires a tolerance passband that is substantially narrower than the optical wavelength interval. Since the spectral response of any material with a non-zero thermo-optic coefficient shifts with temperature, a narrower optical wavelength passband will increase the temperature sensitivity of the insertion loss of the M×N optical distribution network 103. For example, in an MZI-based 8×1 optical combiner, the last MZI should have an FSR approximately equal to the optical wavelength interval, which will result in an optical wavelength passband that is substantially narrower than the optical wavelength interval. If the peak of the optical wavelength passband of the MUX (e.g., MZI) in the first MUX (MZI) stage is nominally aligned with the input optical wavelength of the laser, a shift in the peak of the optical wavelength passband of the MUX (e.g., MZI) in the first MUX (MZI) stage due to a shift in temperature will lead to a reduction in the output optical power of the M×N optical distribution network 103.

[0029] Embodiments are disclosed herein for an M×N optical distribution network (where N is less than M) with a reduced number of MUX stages compared to an M×1 optical distribution network. Also, in various embodiments, the M×N optical distribution network disclosed herein comprises an optical star coupler implemented to distribute light from a plurality of intermediate optical outputs of a reduced MUX front-end network to N optical output ports of the M×N optical distribution network. In these embodiments, the reduced MUX front-end network is an M×O front-end network, where O is less than or equal to N (1 < O ≦ N), and each of the O output ports of the M×O front-end network transmits a unique set of optical wavelengths. In these embodiments, an O×N star coupler is optically connected to the O output ports of the M×O front-end network to complete the formation of the M×N optical distribution network, where each of the N optical outputs of the M×N optical distribution network transmits all M CW laser light input wavelengths. Compared to an M×N optical distribution network implemented using an M×1 cascaded MUX network following a 1×N network, an M×N optical distribution network implemented using an M×O front-end network followed by an O×N star coupler is implemented using fewer functional stages, and thus provides lower optical insertion loss, which corresponds to fewer optical components per path for realizing the M×N CW laser light distribution function. Also, compared to an M×N optical distribution network implemented using an M×1 cascaded MUX network following a 1×N network, an M×N optical distribution network implemented using an M×O front-end network followed by an O×N star coupler has a wider FSR for the front MUX stage and thus can support a wider CW laser light input wavelength passband, reducing temperature sensitivity. The wider CW laser light input wavelength passband provides lower variation in optical insertion loss when the MUX spectrum is shifted due to a change in temperature.

[0030] FIG. 2A illustrates an example of an M×1 cascaded MUX network 200, in accordance with some embodiments. Specifically, FIG. 2A illustrates an 8×1 wavelength combiner based on cascaded MZI stages 201-1, 201-2, and 201-3. MZI stage 201-1 includes four MZIs 203-1, 203-2, 203-3, and 203-4. MZI stage 201-2 includes two MZIs 205-1 and 205-2. MZI stage 201-3 includes one MZI 207. MZIs 203-1, 203-2, 203-3, 203-4, 205-1, 205-2, and 207 function as a two-to-one optical multiplexer (MUX). Thus, the 8×1 cascaded MUX network 200 comprises seven two-to-one optical multiplexers MUX1, MUX2, MUX3, MUX4, MUX5, MUX6, and MUX7 in the form of MZIs 203-1, 203-2, 203-3, 203-4, 205-1, 205-2, and 207, respectively.

[0031] The MZI 203-1 has two optical inputs 203i1-1 and 203i2-1 that receive CW laser light input wavelengths λ6 and λ2, respectively. The two optical inputs 203i1-1 and 203i2-1 correspond to input channels 1 and 2, respectively, of the M×1 cascaded MUX network 200. The MZI 203-1 has an optical output 203o-1. The MZI 203-1 is configured to multiplex the two CW laser light input wavelengths λ6 and λ2 onto one optical output 203o-1.

[0032] The MZI 203-2 has two optical inputs 203i1-2 and 203i2-2 that receive CW laser light input wavelengths λ4 and λ8, respectively. The four optical inputs 203i1-2 and 203i2-2 correspond to input channels 3 and 4, respectively, of the M×1 cascaded MUX network 200. The MZI 203-2 has an optical output 203o-2. The MZI 203-2 is configured to multiplex the two CW laser light input wavelengths λ4 and λ8 onto one optical output 203o-2.

[0033] The MZI 203-3 has two optical inputs 203i1-3 and 203i2-3 that receive CW laser light input wavelengths λ1 and λ5, respectively. The two optical inputs 203i1-3 and 203i2-3 correspond to input channels 5 and 6, respectively, of the M×1 cascaded MUX network 200. The MZI 203-3 has an optical output 203o-3. The MZI 203-3 is configured to multiplex the two CW laser light input wavelengths λ1 and λ5 onto one optical output 203o-3.

[0034] The MZI 203-4 has two optical inputs 203i1-4 and 203i2-4 that receive CW laser light input wavelengths λ3 and λ7, respectively. The two optical inputs 203i1-4 and 203i2-4 correspond to input channels 7 and 8, respectively, of the M×1 cascaded MUX network 200. The MZI 203-4 has an optical output 203o-4. The MZI 203-4 is configured to multiplex the two CW laser light input wavelengths λ3 and λ7 onto one optical output 203o-4.

[0035] MZI 205-1 has two optical inputs 205i1-1 and 205i2-1 optically connected to the optical outputs 203o-1 and 203o-2 of the corresponding MZIs 203-1 and 203-2, respectively. Thus, CW laser light input wavelengths λ2 and λ6 are delivered to optical input 205i1-1, and CW laser light input wavelengths λ4 and λ8 are delivered to optical input 205i2-1. MZI 205-1 has an optical output 205o-1. MZI 205-1 is configured to combine four CW laser light input wavelengths λ2, λ4, λ6, and λ8 onto one optical output 205o-1.

[0036] MZI 205-2 has two optical inputs 205i1-2 and 205i2-2 optically connected to optical outputs 203o-3 and 203o-4 of corresponding MZIs 203-3 and 203o-4, respectively. Thus, CW laser light input wavelengths λ1 and λ5 are transmitted to optical input 205i1-2, and CW laser light input wavelengths λ3 and λ7 are transmitted to optical input 205i2-2. MZI 205-2 has an optical output 205o-2. MZI 205-2 is configured to combine four CW laser light input wavelengths λ1, λ3, λ5, and λ7 onto one optical output 205o-2.

[0037] The MZI 207 has two optical inputs 207i1 and 207i2 optically connected to the optical outputs 205o-1 and 205o-2 of the corresponding MZIs 205-1 and 205-2, respectively. Thus, the CW laser light input wavelengths λ2, λ4, λ6, and λ8 are transmitted to the optical input 207i1, and the CW laser light input wavelengths λ1, λ3, λ5, and λ7 are transmitted to the optical input 207i2. The MZI 207 has an optical output 207o. The MZI 207 is configured to combine eight CW laser light input wavelengths λ1, λ2, λ3, λ4, λ5, λ6, λ7, and λ8 onto one optical output 207o.

[0038] The architecture of the M×1 cascaded MUX network 200 can be expanded by adding an additional MZI stage on the front-end side (channel input side, i.e., on the left side), so that the number of channel inputs (M) can be increased by 2 for any n. n (i.e., M=2 n ), where (n) is the number of MZI stages (an integer). In the example 8×1 wavelength combiner of FIG. 2A, the integer number of MZI stages (n) is equal to 3, so (M) is equal to 8.

[0039] The difference in optical path length in the MZIs in each successive MZI stage 201-1, 201-2, and 201-3 is approximately doubled to reduce the FSR in each successive MZI stage by approximately 2. For example, the optical path length in a given one of the MZIs 205-1 and 205-2 in the second MZI stage 201-2 is approximately twice the optical path length in a given one of the MZIs 203-1, 203-2, 203-4, and 203-5 in the first MZI stage 201-1, so that the FSR in the second MZI stage 201-2 is approximately half the FSR in the first MZI stage 201-1. Similarly, the optical path length in MZI 207 in the third MZI stage 201-3 is approximately twice the optical path length in a given one of MZIs 205-1 and 205-2 in the second MZI stage 201-2, so the FSR in the third MZI stage 201-3 is approximately half the FSR in the second MZI stage 201-2. The increase in optical path length in the MZIs of successive MZI stages is shown in FIG. 2A for MZIs 203-1, 203-2, 203-3, 203-4, 205-1, 205-2, and 207, but is not to scale.

[0040] 2B illustrates the relative intensities of CW laser light at different optical wavelengths λ1, λ2, λ3, λ4, λ5, λ6, λ7, and λ8 output from the 8×1 cascaded MUX network 200 according to some embodiments. With reference to FIG. 2A, it is noted that the CW laser light wavelengths λ1, λ2, λ3, λ4, λ5, λ6, λ7, and λ8 are not in the order of the input channel positions. The CW laser light wavelength input sequence is adjusted to λ6, λ2, λ4, λ8, λ1, λ5, λ3, λ7 for input channels 1-8, respectively, to match the input allowable wavelengths of MZI (MUX) 203-1, 203-2, 203-3, and 203-4 in the first MZI stage 201-1.

[0041] In some embodiments, the M×1 (M=8) cascaded MZI system 200 is implemented as a multiplexer / demultiplexer (MUX / DEMUX) in a WDM system. In some embodiments, the output 207o of the M×1 cascaded MUX network 200 is optically connected to a 1×N optical splitter to form an M×N optical distribution network, where M is 8. In some embodiments, any M×1 cascaded MUX network similar to the M×1 cascaded MUX network 200 (where M=2 n (n is an integer) has an optical output optically connected to the optical input of the 1×N optical splitter to form an M×N optical distribution network.

[0042] 2C illustrates an M×1 cascaded MUX network 200 (where M=8) optically connected to laser array 101 according to some embodiments. Lasers 1-8 are tuned to output respective CW laser light wavelengths λ6, λ2, λ4, λ8, λ1, λ5, λ3, λ7 for respective input channels 1-8. In this manner, the CW laser light input wavelengths are set to match the MUX allowed wavelengths of respective corresponding MZI inputs 203i1-1, 203i2-1, 203i1-2, 203i2-2, 203i1-3, 203i2-3, 203i1-4, and 203i2-4 of MZI stage 201-1. The laser array 101 is configured to have a CW laser light wavelength sequence that matches an input wavelength sequence of a first MUX stage (MZI stage 201-1) of a MUX network of the M×1 cascaded MUX network 200 to which the laser array 101 is optically connected. The CW laser light wavelength sequence of the laser array 101 is a non-monotonic wavelength sequence. Regardless of the number (M) of outputs of the laser array 101, the CW laser light wavelength sequence of the laser array 101 is configured to match an allowed wavelength sequence of the first MUX stage (MZI stage 201-1) of the M×1 cascaded MUX network 200 to which the laser array 101 is optically connected. In this manner, the number (M) of outputs of the laser array 101 and the number of channel inputs of the M×1 cascaded MUX network 200 can be increased or decreased.

[0043] 2D illustrates the input port optical wavelength acceptance passbands of MZI (MUX) 203-1, 203-2, 203-3, 203-4 in the first MZI stage 201-1, MZI (MUX) 205-1, 205-2 in the second MZI stage 201-2, and MZI (MUX) 207 in the third MZI stage 201-3, according to some embodiments. FIG. 2D illustrates that the optical bandwidth of the acceptance passbands decreases as each subsequent MZI stage 201-2 and 201-3 progresses in a direction from the CW light source of the laser array 101 toward the third MZI stage 201-3. In the final (third) MZI stage 201-3, the width of each of the wavelength acceptance passbands is limited by the channel-to-channel wavelength separation requirements. During the manufacturing process of M×1 (M=8) cascaded MUX network 200, variations or deviations from target values ​​may occur in the physical properties of the optical components in M×1 (M=8) cascaded MUX network 200. For example, processing variations may lead to variations or deviations in the optical refractive index of the waveguide material and / or the dimensions of the patterned structures, which in turn may lead to wavelength shifts in the wavelength acceptance passbands of MZIs (MUXs) 203-1, 203-2, 203-3, 203-4, 205-1, 205-2, and 207. Also, because MZI(MUX) 203-1, 203-2, 203-3, 203-4, 205-1, 205-2, and 207 are formed of materials having non-zero thermo-optic coefficients, a change in temperature of M×1 cascaded MUX network 200 leads to a shift in the wavelength acceptance passbands of MZI(MUX) 203-1, 203-2, 203-3, 203-4, 205-1, 205-2, and 207. As the wavelength acceptance passbands of MZI(MUX) 203-1, 203-2, 203-3, 203-4, 205-1, 205-2, and 207 are shifted relative to the input wavelengths (λ1, λ2, λ3, λ4, λ5, λ6, λ7, and λ8), narrower wavelength acceptance passbands result in greater modulation of optical output power than wider wavelength acceptance passbands. For this reason, the leading MZI(MUX) stage in M×1 cascaded MUX network 200 (the MZI(MUX) stage closer to laser array 101) is less sensitive to manufacturing process variations and has lower temperature sensitivity.Also, because the wavelength acceptance passband narrows with each subsequent MZI(MUX) stage proceeding in a direction from the laser array 101 toward the last MZI(MUX) stage, removal of one or more MZI(MUX) stages beginning with the last MZI(MUX) stage and continuing in a direction toward the laser array 101 reduces the temperature sensitivity, where the last MZI(MUX) stage is the MZI(MUX) stage furthest from the laser array 101. For example, the third MZI(MUX) stage 201-3 is the last MZI(MUX) stage in the M×1 (M=8) cascaded MUX network 200.

[0044] FIG. 3 illustrates an example of an architecture for an M×N optical distribution network 300 (where N is less than M) having M optical inputs and N optical inputs, according to some embodiments. The M×N optical distribution network 300 comprises a front-end or first optical MUX section 313 followed by an optical coupler section 315. The front-end optical MUX section 313 comprises a number (P) of MUX stages 301-1 through 301-P, where P is an integer greater than zero. The first MUX stage 301-1 is optically connected to a number (M) of optical input channels. In some embodiments, each of the M optical input channels carries M different optical wavelengths (λ1 through λ2) such that each of the M optical input channels carries a different optical wavelength than the others of the M optical input channels. M ) to transmit CW laser light of one unique wavelength from a set of MUX stages 301-1 through 301-P. S ) two-to-one MUXes 303-SY, where S is the number of MUX stages 301-S counting from the location of the M optical input channels toward the front-end MUX section 313, and Y is a number ranging from 1 to K. S K1 is the identification number of the MUX in the MUX stage 301-S counted up to M, and M is the number of optical input channels. For example, the first MUX stage 301-1 (S=1) has K1=(M / 2 1) two-to-one MUXes 303-1-Y, where Y ranges from 1 to K1. The second MUX stage 301-2 (S=2) has K2=(M / 2 2 ) two-to-one MUXes 303-2-Y, where Y ranges from 1 to K2. The third MUX stage 301-3 (S=3) has K3=(M / 2 3 ) two-to-one MUXes 303-3-Y, where Y ranges from 1 to K3, and so on. The Pth (last) MUX stage 301-P (S=P) of the pre-mux section 313 has K P =(M / 2 P ) two-to-one MUX303-PY, where Y ranges from 1 to K P Each of the MUXes 303-SY includes a first optical input 303i1-SY, a second optical input 303i2-SY, and an optical output 303o-SY.

[0045] Each of the MUXes 303-SY of the MUX stages 301-1 to 301-P is configured to receive a first set of one or more different wavelengths of CW laser light on a corresponding first optical input 303i1-SY and a second set of one or more different wavelengths of CW laser light on a corresponding second optical input 303i2-SY, where the first and second sets of one or more different wavelengths of CW laser light are mutually exclusive of each other. Each MUX 303-SY is also configured to output a third set of the multiple different wavelengths of CW laser light onto a corresponding common (single) optical output 303o-SY. The third set of the multiple different wavelengths of CW laser light transmitted through the optical output 303o-SY includes each of the different wavelengths of CW laser light of the first and second sets of one or more different wavelengths of CW laser light received at the corresponding first optical input 303i1-SY and the corresponding second optical input 303i2-SY, respectively. The last MUX stage 301-P of the front-end optical MUX section 313 comprises a number (O) of MUXes 303-P-1 through 303-P-O, where O is (M / 2 P ), i.e., O=(M / 2 P), M is the number of optical input channels, and P is the number of optical MUX stages in front-end optical MUX section 313. Thus, MUXes 303-P-1 through 303-PO of the last MUX stage 301-P of front-end optical MUX section 313 collectively have a number (O) of optical outputs 305-1 through 305-O. The O optical outputs 305-1 through 305-O of front-end optical MUX section 313 are referred to as O intermediate optical output ports of M×N optical distribution network 300.

[0046] The O optical outputs 305-1 through 305-O are optically connected to corresponding O optical inputs 309-1 through 309-O in an O×N star coupler 307 in an optical coupler section 315 following a front-end optical MUX section 313 in the M×N optical distribution network 300. Each of the O optical outputs 305-1 through 305-O conveys a unique set of multiple wavelengths of CW laser light to a corresponding one of the O optical inputs 309-1 through 309-O of the O×N star coupler 307 such that any one of the O optical inputs 309-1 through 309-O receives a set of CW laser light wavelengths that is mutually exclusive with respect to any other one of the O optical inputs 309-1 through 309-O. The O×N star coupler 307 is configured to transmit each of the CW laser light wavelengths received at each of the O optical inputs 309-1 to 309-O to each of the N optical outputs 311-1 to 311-N of the O×N star coupler 307. In this manner, each of the N optical outputs 311-1 to 311-N transmits all M wavelengths of CW laser light received across all O optical inputs 309-1 to 309-O, which transmits all M wavelengths of light (λ1 to λ2) received at optical input channels 1 to M. M )

[0047] As described above, in the M×N optical distribution network 300, M unique wavelengths (λ1 to λ M) channels are routed into a network of P MUX stages 301-1 to 301-P, where P is equal to or greater than one. The sequence of M optical wavelengths conveyed through the M optical input channels does not necessarily match the optical input channel sequence. More specifically, the values ​​of the M optical wavelengths conveyed through the M optical input channels do not necessarily monotonically increase or decrease with optical input channel number. After the P MUX stages 301-1 to 301-P, the M optical wavelengths are multiplexed into O intermediate optical output ports 305-1 to 305-O, where each of the O intermediate optical output ports 305-1 to 305-O conveys a unique and mutually exclusive subset of the M input wavelengths. The light conveyed through the O intermediate optical output ports 305-1 to 305-O is then multiplexed into N optical outputs 311-1 to 311-N, each of which conveys a unique and mutually exclusive subset of the M optical wavelengths (λ1 to λ2) received across the M optical input channels. M ), to N optical outputs 311-1 through 311-N by O×N star coupler 307. Thus, M×N optical distribution network 300 comprises an M×O cascaded MUX network (front-end optical MUX section 313) having O intermediate optical output ports 305-1 through 305-O, where O is greater than 1, and each of the O intermediate optical output ports 305-1 through 305-O carries a unique subset of the M input optical wavelengths. Also within M×N optical distribution network 300, the M×O cascaded MUX network (front-end optical MUX section 313) is followed by an O×N star coupler 307 (optical coupler section 315), where N is greater than or equal to O.

[0048] It should be appreciated that, in comparison to an M×1 cascaded MUX network (such as the M×1 cascaded MUX network 200 shown in FIG. 2A ), the M×N optical distribution network 300 of FIG. 3 implements a reduced number of MUX stages 301-1 through 301-P because the number O of intermediate optical outputs 305-1 through 305-O is greater than one and an O×N star coupler 307 is implemented to combine light received through the O intermediate optical outputs 305-1 through 305-O and distribute the combined light to each of the N optical outputs 311-1 through 311-N. The reduced number of MUX stages 301-1 through 301-P facilitates meeting manufacturing tolerances within a given chip footprint and correspondingly provides more reliable optical transmission throughout the M×N optical distribution network 300. It should also be appreciated that, compared to an M×1 cascaded MUX network (such as the M×1 cascaded MUX network 200 shown in FIG. 2A ), the M×N optical distribution network 300 of FIG. 3 has a number O of intermediate optical output ports 305-1 through 305-O greater than 1, is less sensitive to manufacturing process variations, and is less sensitive to thermal shifts. This reduced sensitivity to manufacturing process variations and thermal shifts in the M×N optical distribution network 300 is provided by removing one or more of the end-position MUX stages 301-(P+) that would otherwise be present in the M×1 cascaded MUX network, where P+ represents the collective count of one or more end-position MUX stages 301-(P+) that are replaced by an O×N star coupler 307 to achieve the M×N optical distribution network 300. Therefore, compared to an M×1 cascaded MUX network (such as the M×1 cascaded MUX network 200 shown in FIG. 2A ), the optical transmission performance of the M×N optical distribution network 200 of FIG. 3 is less sensitive to variations in temperature of the M×N optical distribution network 300.

[0049] In the optical distribution network 300, each of the multiple optical inputs (303i1-1-m and 303i2-1-m, where m is from 1 to (M / 2)) of the front-stage optical multiplexer section 313 is a different wavelength (λ1 to λ M) to receive each of the plurality of input optical signals. The front-end optical multiplexer section 313 is configured to multiplex a unique subset of the plurality of input optical signals onto each of the plurality of intermediate optical outputs (305-1 through 305-O). The unique subset of the plurality of input optical signals multiplexed onto any given one of the plurality of intermediate optical outputs (305-1 through 305-O) is mutually exclusive of the plurality of input optical signals multiplexed onto other ones of the plurality of intermediate optical outputs (305-1 through 305-O). The optical coupler section 315 is configured to distribute a portion of each optical signal received at each of the plurality of optical inputs (309-1 through 309-O) of the optical coupler section 315 to one of the plurality of optical outputs (311-1 through 311-N) of the optical coupler section 315. In some embodiments, the optical coupler section 315 is implemented as a free space optical star coupler. In some embodiments, the optical coupler section 315 is implemented as a network of 2x2 optical couplers.

[0050] The upstream optical multiplexer section 313 includes a number (P) of optical multiplexer stages (301-1 to 301-P). The number (P) is equal to a first value divided by the logarithm of 2, where the first value is the logarithm of a second value, and the second value is equal to a number (M) of a plurality of optical inputs (303i1-1-m and 303i2-1-m, where m is 1 to (M / 2)) of the upstream optical multiplexer section 313 divided by a number (O) of a plurality of intermediate optical outputs (305-1 to 305-O) of the upstream optical multiplexer section 313. Each of the number (P) of optical multiplexer stages (301-1 to 301-P) has a number of inputs (303i1-1-m and 303i2-1-m) of the upstream optical multiplexer section 313, and a number (O) of intermediate optical outputs (305-1 to 305-O) of the upstream optical multiplexer section 313. S The optical multiplexer 303-SY includes two-to-one optical multiplexers 303-SY, where (S) is a given integer sequence number of the number (P) of optical multiplexer stages (301-1 to 301-P) counting from the first stage of the number (P) of optical multiplexer stages (301-1 to 301-P) to the last stage of the number (P) of optical multiplexer stages (301-1 to 301-P), and Y is an integer number ranging from 1 to (M / 2 P) are multiplexer numbers. The first stage of the number (P) of optical multiplexer stages (301-1 to 301-P) has optical inputs optically connected to M number of optical inputs (M) (303i1-1-m and 303i2-1-m, where m is 1 to (M / 2)) of the upstream optical multiplexer section 313. The last stage of the number (P) of optical multiplexer stages (301-1 to 301-P) has optical outputs optically connected to O number of intermediate optical outputs (305-1 to 305-O) of the upstream optical multiplexer section 313. The number (K S ) is a number (M) of optical inputs (303i1-1-m and 303i2-1-m, where m is 1 to (M / 2)) of the front-stage optical multiplexer section 313. S It's equal to divided by the value that is equal to.

[0051] Number (K S Each of the two-to-one optical multiplexers 303-SY has a first optical input, a second optical input, and an optical output. S Each of the (K1) two-to-one optical multiplexers 303-SY is configured to multiplex optical signals received at its first and second optical inputs onto its optical output. Each of the (K1) two-to-one optical multiplexers in a first optical multiplexer stage of the number (P) optical multiplexer stages is configured to have a first optical wavelength passband for the first optical input and a second optical wavelength passband for the second optical input, where the second optical wavelength passband is different from the first optical wavelength passband. In some embodiments, the first optical wavelength passband and the second optical wavelength passband correspond to discontinuous channel wavelengths of a continuous wave laser light input to the optical distribution network.

[0052] 4A illustrates an 8×4 optical distribution network 300A, which is an implementation of the M×N optical distribution network 300 of FIG. 3, according to some embodiments. The 8×4 optical distribution network 300A includes a front-end optical MUX section 313A with one MUX stage 301-P (where P=1). The 8×4 optical distribution network 300A further includes an optical coupler section 315A with a 4×4 star coupler 307A. In the 8×4 optical distribution network 300A, the number of optical input channels M is 8 (channel 1 to channel 8), the number of MUX stages P is 1 (303-P, where P=1), the number of intermediate optical outputs O is 4 (305-1 to 305-4), and the number of optical outputs N is 4 (311-1 to 311-4). In this manner, the 8×4 optical distribution network 300A is configured to transmit each of the eight different CW laser light wavelengths received across the eight input channels to each of the four optical outputs 311-1, 311-2, 311-3, and 311-4 of the 8×4 optical distribution network 300A.

[0053] MUX stage 301-P (which is the first and last MUX stage) in 8×4 optical distribution network 300A comprises four two-to-one MUXs 303-P-1, 303-P-2, 303-P-3, and 303-P-4. In some embodiments, each of MUXes 303-P-1 through 303-P-4 is implemented as an MZI. Each of the four MUXs 303-P-1 through 303-P-4 has a respective first optical input 303i1-Px, a respective second optical input 303i2-Px, and a respective optical output 305-x, where x is an integer number of a given one of MUXes 303-P-1 through 303-P-4. The order of the CW optical wavelengths of the eight optical input channels (channel 1 to channel 8) is λ6, λ2, λ4, λ8, λ1, λ5, λ3, and λ7, respectively, so as to match the MUX allowable wavelengths of MUXs 303-P-1 to 303-P-4. Thus, the first MUX 303-P-1 multiplexes the optical wavelengths λ2 and λ6 onto the optical output 305-1. The second MUX 303-P-2 multiplexes the optical wavelengths λ4 and λ8 onto the optical output 305-2. The third MUX 303-P-3 multiplexes the optical wavelengths λ1 and λ5 onto the optical output 305-3. And the fourth MUX 303-P-4 multiplexes the optical wavelengths λ3 and λ7 onto the optical output 305-4. Thus, the two optical wavelengths on each of optical outputs 305-1 through 305-4 are separated from each other by an optical wavelength spacing of four channel-to-channel.

[0054] The 4×4 star coupler 307A includes a first 2×2 optical coupler 401, a second 2×2 optical coupler 402, a third 2×2 optical coupler 403, and a fourth 2×2 optical coupler 404. The first 2×2 optical coupler 401 has a first optical input 309-1 optically connected to an optical output 305-1 of the first MUX 303-P-1, and a second optical input 309-2 optically connected to an optical output 305-2 of the second MUX 303-P-2. Thus, the first 2×2 optical coupler 401 receives two CW laser optical wavelengths λ2 and λ6 at the first optical input 309-1, and two CW laser optical wavelengths λ4 and λ8 at the second optical input 309-2. The first 2x2 optical coupler 401 has a first optical output 401o1 and a second optical output 401o2. The first 2x2 optical coupler 401 is configured to multiplex all optical wavelengths received at the first optical input 309-1 and the second optical input 309-2 onto each of the two optical outputs 401o1 and 401o2. In this manner, each of the four CW laser optical wavelengths λ2, λ4, λ6, and λ8 are output through each of the first optical output 401o1 and the second optical output 401o2.

[0055] The second 2x2 optical coupler 402 has a first optical input 309-3 optically connected to the optical output 305-3 of the third MUX 303-P-3 and a second optical input 309-4 optically connected to the optical output 305-4 of the fourth MUX 303-P-4. Thus, the second 2x2 optical coupler 402 receives two CW laser optical wavelengths λ1 and λ5 at the first optical input 309-3 and two CW laser optical wavelengths λ3 and λ7 at the second optical input 309-4. The second 2x2 optical coupler 402 has a first optical output 402o1 and a second optical output 402o2. The second 2x2 optical coupler 402 is configured to couple all of the CW laser optical wavelengths received at the first optical input 309-3 and the second optical input 309-4 onto each of the two optical outputs 402o1 and 402o2. In this manner, each of the four CW laser light wavelengths λ1, λ3, λ5, and λ7 is output through each of first optical output 402o1 and second optical output 402o2.

[0056] The third 2×2 optical coupler 403 has a first optical input 403i1 optically connected to the first optical output 401o1 of the first 2×2 optical coupler 401, and a second optical input 403i2 optically connected to the first optical output 402o1 of the second 2×2 optical coupler 402. Thus, the third 2×2 optical coupler 403 receives four CW laser optical wavelengths λ2, λ4, λ6, and λ8 at the first optical input 403i1, and receives four CW laser optical wavelengths λ1, λ3, λ5, and λ7 at the second optical input 403i2. The third 2×2 optical coupler 403 has a first optical output 311-1 and a second optical output 311-2. The third 2×2 optical coupler 403 is configured to multiplex all of the CW laser optical wavelengths received at the first optical input 403i1 and the second optical input 403i2 onto each of the two optical outputs 311-1 and 311-2. In this manner, each of the eight CW laser optical wavelengths λ1, λ2, λ3, λ4, λ5, λ6, λ7, and λ8 are output through each of the first optical output 311-1 and the second optical output 311-2 of the third 2×2 optical coupler 403.

[0057] The fourth 2×2 optical coupler 404 has a first optical input 404i1 optically connected to the second optical output 401o2 of the first 2×2 optical coupler 401, and a second optical input 404i2 optically connected to the second optical output 402o2 of the second 2×2 optical coupler 402. Thus, the fourth 2×2 optical coupler 404 receives the four CW laser optical wavelengths λ2, λ4, λ6, and λ8 at the first optical input 404i1, and receives the four CW laser optical wavelengths λ1, λ3, λ5, and λ7 at the second optical input 404i2. The fourth 4×2 optical coupler 404 has a first optical output 311-3 and a second optical output 311-4. The fourth 2×2 optical coupler 404 is configured to multiplex all of the CW laser optical wavelengths received at the first optical input 404i1 and the second optical input 404i2 onto each of the two optical outputs 311-3 and 311-4. In this manner, each of the eight CW laser optical wavelengths λ1, λ2, λ3, λ4, λ5, λ6, λ7, and λ8 are output through each of the first optical output 311-3 and the second optical output 311-4 of the fourth 2×2 optical coupler 404.

[0058] An optical waveguide crossover 409 is implemented in the 4×4 star coupler 307A to provide an optical connection between the second optical output 401o2 of the first 2×2 optical coupler 401 and the first optical input 404i1 of the fourth 2×2 optical coupler 404, and to provide an optical connection between the first optical output 402o1 of the second 2×2 optical coupler 402 and the second optical input 403i2 of the third 2×2 optical coupler 403. The optical waveguide crossover 409 is configured to ensure that light traveling from the second optical output 401o2 of the first 2×2 optical coupler 401 to the first optical input 404i1 of the fourth 2×2 optical coupler 404 is not interfered with by light traveling from the first optical output 402o1 of the second 2×2 optical coupler 402 to the second optical input 403i2 of the third 2×2 optical coupler 403, and vice versa.

[0059] 4B illustrates the relative intensities of CW laser light at different optical wavelengths λ1, λ2, λ3, λ4, λ5, λ6, λ7, and λ8 output from the 8×4 optical distribution network 300A of FIG. 4A, according to some embodiments. With reference to FIG. 4A, it is noted that the input optical wavelengths λ1, λ2, λ3, λ4, λ5, λ6, λ7, and λ8 are not in the order of the input channel positions. The input optical wavelength input sequence is adjusted to λ6, λ2, λ4, λ8, λ1, λ5, λ3, λ7 for input channels 1-8, respectively, to match the input allowed wavelengths of MUXes 303-P-1-303-P-4 in the first (and last) MUX stage 301-P.

[0060] 4C illustrates the 8×4 optical distribution network 300A of FIG. 4A optically connected to the laser array 101 according to some embodiments. Lasers 1-8 are tuned to output CW laser optical wavelengths λ6, λ2, λ4, λ8, λ1, λ5, λ3, λ7 for input channels 1-8, respectively. In this manner, the sequence of CW laser optical wavelengths across the laser array 101 from laser 1 to laser 8 is set to substantially coincide with the peaks of the input optical wavelength acceptance passbands of the respective optical inputs 303i1-1, 303i2-1, 303i1-2, 303i2-2, 303i1-3, 303i2-3, 303i1-4, and 303i2-4 of the MUXes 303-1-303-4 in the first MUX stage 301-P (P=1) of the front-end optical MUX section 313A of the 8×4 optical distribution network 300A.

[0061] FIG. 5A illustrates a system in which a laser array 101 is directly connected to the M×N optical distribution network 300 of FIG. 3 to form a laser module 500, according to some embodiments. FIG. 5B is a diagram of the system of FIG. 5A showing the M×N optical distribution network 300 in more detail, according to some embodiments. In some embodiments, in the systems of FIG. 5A and FIG. 5B, the laser module 500 comprises the M×N optical distribution network 300 and is integrated on a single semiconductor electro-optical chip ("chip"). In this sense, the M×N optical distribution network 300 is a chip-scale M×N optical distribution network 300.

[0062] Laser array 101 comprises M lasers, with lasers 1 through M each tuned to output CW light at a unique wavelength into a corresponding one of M optical input channels (channel 1 through channel M) of M×N optical distribution network 300. In this manner, the set of M lasers outputs M different wavelengths (λ1 through λ M ), each laser is adjusted to collectively output M CW laser beams of different wavelengths (λ1 to λ M) outputting CW laser light of a different wavelength. In some embodiments, each of the M lasers in the laser array 101 is a distributed feedback (DFB) laser.

[0063] In some embodiments, at least one of the M lasers in the laser array 101 is thermally coupled to at least one other of the M lasers in the laser array, such that a temperature change of one of the thermally coupled lasers leads to a temperature change of at least one other of the thermally coupled lasers. In some embodiments, the M lasers in the laser array 101 are thermally coupled together collectively, such that the temperatures of each of the M lasers change / drift together. In some embodiments, each of the M lasers in the laser array 101 is thermally connected to a common thermally conductive substrate / plate 501, such that the temperature of each of the M lasers in the laser array 101 is normalized to an average temperature based on the collective thermal output of the M lasers in the laser array 101, and the temperatures of the M lasers in the laser array 101 drift together in direction and magnitude. In this way, temperature-induced wavelength variations are substantially the same across the M lasers in the laser array 101, which acts to maintain the relative wavelength spacing between the lasers when temperature-induced wavelength variations occur. In some embodiments, multiple lasers (Laser 1 through Laser M) are arranged in laser array 101 such that the sequence of multiple wavelengths of continuous wave laser light (output by Lasers 1 through M) is non-monotonically ordered across laser array 101.

[0064] In some embodiments, the M×N optical distribution network 300 is a photonic integrated circuit (PIC) integrated on a semiconductor electro-optical chip with M optical input channels (channel 1 through channel M) and N optical output channels (output 1 through output N). The M optical input channels (channel 1 through channel M) correspond to optical inputs 303i1-1, 303i2-1-1 through 303i1-1-(M / 2), and 303i2-1-(M / 2), respectively, of MUXes 303-1-1 through 303-1-(M / 2) in a first MUX stage 301-1 of a front-end optical MUX section 313 of the M×N optical distribution network 300. The N optical output channels (output 1 through output N) correspond to N optical outputs 311-1 through 311-N, respectively, of an optical coupler section of the M×N optical distribution network 300. The M×N optical distribution network 300 has N optical output channels (output 1 to output N) each of which is connected to all M different wavelengths (λ1 to λN) output by the laser array 101. M 3. The optical coupler section 315 is configured to distribute light from each of the M optical input channels (channel 1 through channel M) to all N optical output channels (output 1 through output N) to convey a CW laser light of 100 MHz to 100 MHz. The optical coupler section 315 has a plurality of optical outputs (311-1 through 311-N) corresponding to the plurality of optical outputs of the optical distribution network 300 and the plurality of outputs of the laser module 500, respectively.

[0065] In some embodiments, the laser array 101 is optically coupled directly to the M×N optical distribution network 300 without any intermediate light guiding components (such as optical fibers or optical waveguides) such that CW laser light from each of the M lasers in the laser array 101 is transmitted directly to a corresponding one of the M optical input channels (channel 1 through channel M) in the M×N optical distribution network 300 chip. For example, laser 1 transmits CW laser light directly to optical input channel 1, laser 2 transmits CW laser light directly to optical input channel 2, and so on, with laser M transmitting CW laser light directly to optical input channel M. In these embodiments, each of the M lasers in the laser array 101 is optically coupled directly to a corresponding physical optical channel in the M×N optical distribution network 300. It should be understood, however, that in various embodiments, essentially any optical coupling method or technique may be used to optically couple each of the M lasers in the laser array 101 to a corresponding one of the M optical input channels (Channel 1 through Channel M) in the M×N distribution network 300. For example, in some embodiments, the optical coupling of the M lasers in the laser array 101 to the corresponding M optical input channels (Channel 1 through Channel M) in the M×N optical distribution network 300 is done by, by way of example, optical vertical grating coupling, optical edge coupling, and / or lens-based optical coupling, among other techniques.

[0066] In some embodiments, MUXes 303-1-1 through 303-1-(M / 2) in the first MUX stage 301-1 of the front-end optical MUX section 313 of the M×N optical distribution network 300 may require an input optical wavelength sequence that does not vary linearly or monotonically (increase / decrease) with physical optical input channel number. In these embodiments, the wavelengths of the CW laser light output by the M lasers in the laser array 101 are set to substantially coincide with the peaks of the wavelength acceptance passbands of MUXes 303-1-1 through 303-1-(M / 2) in the first MUX stage 301-1 of the front-end optical MUX section 313 of the M×N optical distribution network 300. Specifically, the laser 1 in the laser array 101 is set to output a CW laser light of a wavelength substantially matching a peak of a wavelength acceptance passband of the first optical input 303i1-1-1 of the first MUX 303-1-1 of the first MUX stage 301-1, and the laser 1 is directly optically coupled to the first optical input 303i1-1-1 of the first MUX 303-1-1 of the first MUX stage 301-1. Next, the laser 2 in the laser array 101 is set to output a CW laser light of a wavelength substantially matching a peak of a wavelength acceptance passband of the second optical input 303i2-1-1 of the first MUX 303-1-1 of the first MUX stage 301-1, and the laser 2 is directly optically coupled to the second optical input 303i2-1-1 of the first MUX 303-1-1 of the first MUX stage 301-1. Laser 3 in laser array 101 is then configured to output CW laser light of a wavelength substantially matching a peak of the wavelength acceptance passband of first optical input 303i1-1-2 of second MUX 303-1-2 of first MUX stage 301-1, and laser 3 is directly optically coupled to the first optical input 303i1-1-2 of second MUX 303-1-2 of first MUX stage 301-1. Laser 4 in laser array 101 is then configured to output CW laser light of a wavelength substantially matching a peak of the wavelength acceptance passband of second optical input 303i2-1-2 of second MUX 303-1-2 of first MUX stage 301-1, and laser 4 is directly optically coupled to the second optical input 303i2-1-2 of second MUX 303-1-2 of first MUX stage 301-1, and so on.And finally, laser M in laser array 101 is configured to output CW laser light at a wavelength substantially coinciding with a peak of the wavelength acceptance passband of second optical input 303i2-1-(M / 2) of the last (i.e., (M / 2)th) MUX 303-1-(M / 2) of the first MUX stage 301-1, and laser M is optically coupled directly to the second optical input 303i2-1-(M / 2) of the last MUX 303-1-(M / 2) of the first MUX stage 301-1. In some embodiments, laser array 101 is optically interfaced with optical distribution network 300 such that multiple wavelengths of continuous wave laser light are transmitted from the multiple lasers (Laser 1 through Laser M) to multiple optical inputs (303i1-1, 303i2-1-1 through 303i1-1-(M / 2), 303i2-1-(M / 2)) of front-stage optical multiplexer section 313.

[0067] It should be understood that because the wavelengths of the CW laser light output by the M lasers in laser array 101 are set to substantially coincide with peaks of the wavelength acceptance passbands of MUXes 303-1-1 through 303-1-(M / 2) in first MUX stage 301-1 of front-end optical MUX section 313 of M×N optical distribution network 300, the wavelengths of the CW laser light output by the M lasers in laser array 101 do not have to vary monotonically from laser 1 to laser M in laser array 101. It should be understood, therefore, that laser array 101 is configured differently from a conventional laser array having only laser light output wavelengths that monotonically increase or decrease along a sequence or series of lasers.

[0068] Optically connecting a laser array having only laser light output wavelengths that increase or decrease monotonically along a sequence / series of lasers to an M×N optical distribution network 300 having a non-monotonic input wavelength sequence requires routing crossing optical paths between the laser array 101 and the M×N optical distribution network 300, such as by routing light through optical fibers connected between the laser array 101 and the M×N optical distribution network 300. In some embodiments, the non-monotonic ordering of the sequence of multiple wavelengths of CW laser light across the laser array 101 matches the ordering of the wavelength acceptance passbands of the multiple optical inputs (303i1-1, 303i2-1-1 through 303i1-1-(M / 2), 303i2-1-(M / 2)) of the front-end optical multiplexer section 313. By configuring each of the M lasers in the laser array 101 to output CW light having a particular wavelength that substantially coincides with a peak of a wavelength acceptance passband of a corresponding one of the M optical inputs of the M×N optical distribution network 300, the need to route optical paths across one another can be avoided when optically connecting the laser array 101 to the M×N optical distribution network 300. This is advantageous because routing optical paths across one another can lead to additional optical insertion losses (e.g., as can occur when optical routing is done in a single waveguide layer within an integrated optical chip and accordingly must necessitate the use of optical waveguide crossings that typically have non-zero optical insertion losses).

[0069] In some embodiments, the M×N optical distribution network 300 is implemented with a front-end optical MUX section 313 that includes at least one MUX stage 301-x, where x is an integer from 1 to P, and P is greater than or equal to 1. However, in other embodiments, variations of the M×N optical distribution network 300 are implemented without the front-end optical MUX section 313, and then P is equal to zero. In those embodiments in which P is equal to zero, the number O of intermediate optical output ports 305-1 through 305-O of the M×N optical distribution network 300 effectively becomes the number M of optical input channels (channel 1 through channel M) of the M×N optical distribution network 300. In these embodiments, the front-end optical MUX section 313 is removed from the M×N optical distribution network 300, so that the M optical input channels (channel 1 through channel M) are optically connected to O optical inputs 309-1 through 309-O, respectively, of the optical coupler section 315 of the M×N optical distribution network 300, i.e., the M optical input channels (channel 1 through channel M) are optically connected to O optical inputs, respectively, of the O×N star coupler 307.

[0070] 6A illustrates a system in which the laser array 101 is directly coupled to an 8×8 optical distribution network 600, according to some embodiments. FIG. 6B illustrates the relative intensities of CW laser light at different optical wavelengths λ1, λ2, λ3, λ4, λ5, λ6, λ7, and λ8 provided to inputs 309-1 through 309-8 of the 8×8 optical distribution network 600 and output through outputs 311-1 through 311-8 of the 8×8 optical distribution network 600, according to some embodiments. The 8×8 optical distribution network 600 is implemented as a variation of the M×N optical distribution network 300 of FIG. 3, where P is equal to zero, O is equal to M, M is equal to 8, and N is equal to 8. Thus, since P is equal to zero, the 8×8 optical distribution network 600 does not include a front-end optical MUX section 313. Since there is no front-end optical MUX section 313, there is no first MUX stage 301-1 with MUXes 303-1-1 through 301-1-(M / 2) having different optical input wavelength acceptance passbands. Thus, in the 8×8 optical distribution network 600, the sequence of M lasers across the laser array 101 may be configured to have essentially any ordering / sequence of CW laser optical output wavelengths, including a monotonically increasing order / sequence of CW laser optical output wavelengths across the laser array 101, or any (e.g., non-monotonic varying) order / sequence of CW laser optical output wavelengths across the laser array 101. In some embodiments, the 8×8 optical distribution network 600 is integrated on a semiconductor electro-optical chip.

[0071] The laser array 101 of FIG. 6A comprises eight lasers (laser 1-laser 8), where each of the eight lasers is tuned to output CW laser light of a unique wavelength (λ1-λ8) to each of the eight optical input channels (channel 1-channel 8) of the 8×8 optical distribution network 600. In some embodiments, each of the eight lasers in the laser array 101 is a distributed feedback (DFB) laser. Also, in some embodiments, the eight lasers in the laser array 101 are thermally coupled to each other, such that a temperature change in one of the thermally coupled lasers leads to a temperature change in the other of the thermally coupled lasers. In these embodiments, the eight lasers in the laser array 101 are thermally coupled collectively, such that the temperature of each of the eight lasers changes / drifts together. In some embodiments, each of the eight lasers in the laser array 101 is thermally connected / contacted to a common thermally conductive substrate / plate 501, such that the temperature of each of the eight lasers in the laser array 101 is normalized to an average temperature based on the collective thermal output of the eight lasers in the laser array 101, and the temperatures of the eight lasers in the laser array 101 drift together in direction and magnitude.

[0072] In some embodiments, the laser array 101 is directly coupled to the 8×8 optical distribution network 600 without any intermediate light guiding components (such as optical fibers or optical waveguides) such that CW laser light from each of the eight lasers (Laser 1-Laser 8) in the laser array 101 is emitted directly into a corresponding one of the eight optical input channels (Channel 1-Channel M) in the 8×8 optical distribution network 600. However, it should be understood that in various embodiments, essentially any method or technique of coupling light may be used to optically couple each of the eight lasers (Laser 1-Laser 8) in the laser array 101 to a corresponding one of the eight optical input channels (Channel 1-Channel M) in the 8×8 distribution network 600, such as, by way of example, vertical grating optical coupling, optical edge coupling, and / or lens-based optical coupling, among others.

[0073] The 8×8 optical distribution network 600 is configured to distribute light from each of the eight optical input channels (channel 1 through channel 8) to each of the eight optical output channels 311-1 through 311-8 such that each of the eight optical output channels 311-1 through 311-8 carries CW laser light of all eight different wavelengths (λ1 through λ8) output by the laser array 101 and input to the 8×8 optical distribution network 600. The eight optical input channels (channel 1 through channel 8) correspond to optical inputs 309-1 through 309-O, respectively, of the 8×8 optical distribution network 600, where O is 8. The eight optical output channels 311-1 through 311-8 correspond to optical outputs 311-1 through 311-N of the 8×8 optical distribution network 600, where N is 8.

[0074] In the 8x8 optical distribution network 600, the optical coupler section 315 is implemented as an 8x8 star concatenation 307B with twelve 2x2 optical couplers 601-1 to 601-12. The first 2x2 optical coupler 601-1 has a first optical input 601i1-1 optically connected to a first optical input channel (channel 1) and a second optical input 601i2-1 optically connected to a second optical input channel (channel 2). Thus, the first 2x2 optical coupler 601-1 receives the CW laser optical wavelength λ1 at the first optical input 601i1-1 and receives the CW laser optical wavelength λ2 at the second optical input 601i2-1. The first 2x2 optical coupler 601-1 has a first optical output 601o1-1 and a second optical output 601o2-1. The first 2×2 optical coupler 601-1 is configured to couple a CW laser light wavelength λ1 received at the first optical input 601i1-1 and a CW laser light wavelength λ2 received at the second optical input 601i2-1 onto each of the two optical outputs 601o1-1 and 601o2-2. In this manner, each of the two CW laser light wavelengths λ1 and λ2 is output through each of the first optical output 601o1-1 and the second optical output 601o2-1.

[0075] The second 2x2 optical coupler 601-2 has a first optical input 601i1-2 optically connected to a third optical input channel (channel 3) and a second optical input 601i2-2 optically connected to a fourth optical input channel (channel 4). Thus, the second 2x2 optical coupler 601-2 receives the CW laser optical wavelength λ3 at the first optical input 601i1-2 and receives the CW laser optical wavelength λ4 at the second optical input 601i2-2. The second 2x2 optical coupler 601-2 has a first optical output 601o1-2 and a second optical output 601o2-2. The second 2×2 optical coupler 601-2 is configured to couple the CW laser light wavelength λ3 received at the first optical input 601i1-2 and the CW laser light wavelength λ4 received at the second optical input 601i2-2 onto each of the two optical outputs 601o1-2 and 601o2-2. In this manner, each of the two CW laser light wavelengths λ3 and λ4 is output through each of the first optical output 601o1-2 and the second optical output 601o2-2.

[0076] The third 2x2 optical coupler 601-3 has a first optical input 601i1-3 optically connected to a fifth optical input channel (channel 5) and a second optical input 601i2-3 optically connected to a sixth optical input channel (channel 6). Thus, the third 2x2 optical coupler 601-3 receives the CW laser optical wavelength λ5 at the first optical input 601i1-3 and receives the CW laser optical wavelength λ6 at the second optical input 601i2-3. The third 2x2 optical coupler 601-3 has a first optical output 601o1-3 and a second optical output 601o2-3. The third 2×2 optical coupler 601-3 is configured to couple the CW laser light wavelength λ5 received at the first optical input 601i1-3 and the CW laser light wavelength λ6 received at the second optical input 601i2-3 onto each of the two optical outputs 601o1-3 and 601o2-3. In this manner, each of the two CW laser light wavelengths λ5 and λ6 is output through each of the first optical output 601o1-3 and the second optical output 601o2-3.

[0077] The fourth 2x2 optical coupler 601-4 has a first optical input 601i1-4 optically connected to a seventh optical input channel (channel 7) and a second optical input 601i2-4 optically connected to an eighth optical input channel (channel 8). Thus, the fourth 2x2 optical coupler 601-4 receives the CW laser optical wavelength λ7 at the first optical input 601i1-4 and receives the CW laser optical wavelength λ8 at the second optical input 601i2-4. The fourth 2x2 optical coupler 601-4 has a first optical output 601o1-4 and a second optical output 601o2-4. The fourth 2×2 optical coupler 601-4 is configured to couple the CW laser light wavelength λ7 received at the first optical input 601i1-4 and the CW laser light wavelength λ8 received at the second optical input 601i2-4 onto each of the two optical outputs 601o1-4 and 601o2-4. In this manner, each of the two CW laser light wavelengths λ7 and λ8 is output through each of the first optical output 601o1-4 and the second optical output 601o2-4.

[0078] The fifth 2x2 optical coupler 601-5 has a first optical input 601i1-5 optically connected to the first optical output 601o1-1 of the first 2x2 optical coupler 601-1, and a second optical input 601i2-5 optically connected to the first optical output 601o1-2 of the second 2x2 optical coupler 601-2. Thus, the fifth 2x2 optical coupler 601-5 receives two CW laser optical wavelengths λ1 and λ2 at the first optical input 601i1-5, and two CW laser optical wavelengths λ3 and λ4 at the second optical input 601i2-5. The fifth 2x2 optical coupler 601-5 has a first optical output 601o1-5 and a second optical output 601o2-5. The fifth 2×2 optical coupler 601-5 is configured to multiplex all of the CW laser optical wavelengths received at the first optical input 601i1-5 and the second optical input 601i2-5 onto each of the two optical outputs 601o1-5 and 601o2-5. In this manner, each of the four CW laser optical wavelengths λ1, λ2, λ3, and λ4 are output through each of the first optical outputs 601o1-5 and the second optical outputs 601o2-5 of the fifth 2×2 optical coupler 601-5.

[0079] The sixth 2x2 optical coupler 601-6 has a first optical input 601i1-6 optically connected to the first optical output 601o1-3 of the third 2x2 optical coupler 601-3, and a second optical input 601i2-6 optically connected to the first optical output 601o1-4 of the fourth 2x2 optical coupler 601-4. Thus, the sixth 2x2 optical coupler 601-6 receives two CW laser optical wavelengths λ5 and λ6 at the first optical input 601i1-6, and two CW laser optical wavelengths λ7 and λ8 at the second optical input 601i2-6. The sixth 2x2 optical coupler 601-6 has a first optical output 601o1-6 and a second optical output 601o2-6. The sixth 2×2 optical coupler 601-6 is configured to multiplex all of the CW laser optical wavelengths received at the first optical input 601i1-6 and the second optical input 601i2-6 onto each of the two optical outputs 601o1-6 and 601o2-6. In this manner, each of the four CW laser optical wavelengths λ5, λ6, λ7, and λ8 are output through each of the first optical output 601o1-6 and the second optical output 601o2-6 of the sixth 2×2 optical coupler 601-6.

[0080] The seventh 2x2 optical coupler 601-7 has a first optical input 601i1-7 optically connected to the second optical output 601o2-1 of the first 2x2 optical coupler 601-1, and a second optical input 601i2-7 optically connected to the second optical output 601o2-2 of the second 2x2 optical coupler 601-2. Thus, the seventh 2x2 optical coupler 601-7 receives two CW laser optical wavelengths λ1 and λ2 at the first optical input 601i1-7, and receives two CW laser optical wavelengths λ3 and λ4 at the second optical input 601i2-7. The seventh 2x2 optical coupler 601-7 has a first optical output 601o1-7 and a second optical output 601o2-7. The seventh 2×2 optical coupler 601-7 is configured to multiplex all of the CW laser optical wavelengths received at the first optical input 601i1-7 and the second optical input 601i2-7 onto each of the two optical outputs 601o1-7 and 601o2-7. In this manner, each of the four CW laser optical wavelengths λ1, λ2, λ3, and λ4 are output through each of the first optical output 601o1-7 and the second optical output 601o2-7 of the seventh 2×2 optical coupler 601-7.

[0081] The eighth 2x2 optical coupler 601-8 has a first optical input 601i1-8 optically connected to the second optical output 601o2-3 of the third 2x2 optical coupler 601-3, and a second optical input 601i2-8 optically connected to the second optical output 601o2-4 of the fourth 2x2 optical coupler 601-4. Thus, the eighth 2x2 optical coupler 601-8 receives two CW laser optical wavelengths λ5 and λ6 at the first optical input 601i1-8, and two CW laser optical wavelengths λ7 and λ8 at the second optical input 601i2-8. The eighth 2x2 optical coupler 601-8 has a first optical output 601o1-8 and a second optical output 601o2-8. The eighth 2×2 optical coupler 601-8 is configured to multiplex all of the CW laser optical wavelengths received at the first optical input 601i1-8 and the second optical input 601i2-8 onto each of the two optical outputs 601o1-8 and 601o2-8. In this manner, each of the four CW laser optical wavelengths λ5, λ6, λ7, and λ8 are output through each of the first optical outputs 601o1-8 and the second optical outputs 601o2-8 of the eighth 2×2 optical coupler 601-8.

[0082] The 8×8 star coupler 307B includes six optical waveguide crossings 603-1 through 603-6 to enable optical routing between the optical outputs of the 2×2 optical couplers 601-1 through 601-4 and the optical inputs of the 2×2 optical couplers 601-5 through 601-8, as described above. The optical waveguide crossing 603-1 enables optical routing between the first optical output 601o1-2 of the second 2×2 optical coupler 601-2 and the second optical input 601i2-5 of the fifth 2×2 optical coupler 601-5. The optical waveguide crossings 603-2 and 603-4 enable optical routing between the first optical output 601o1-3 of the third 2×2 optical coupler 601-3 and the first optical input 601i1-6 of the sixth 2×2 optical coupler 601-6. Optical waveguide crossings 603-3, 603-5, and 603-6 enable optical routing between a first optical output 601o1-4 of the fourth 2×2 optical coupler 601-4 and a second optical input 601i2-6 of the sixth 2×2 optical coupler 601-6. Optical waveguide crossings 603-1, 603-4, and 603-6 enable optical routing between a second optical output 601o2-1 of the first 2×2 optical coupler 601-1 and a first optical input 601i1-7 of the seventh 2×2 optical coupler 601-7. Optical waveguide crossings 603-2 and 603-5 enable optical routing between a second optical output 601o2-2 of the second 2×2 optical coupler 601-2 and a second optical input 601i2-7 of the seventh 2×2 optical coupler 601-7. The optical waveguide crossover 603-3 enables optical routing between the second optical output 601o2-3 of the third 2×2 optical coupler 601-3 and the first optical input 601i1-8 of the eighth 2×2 optical coupler 601-8. Each of the optical waveguide crossovers 603-1 through 603-6 is configured to ensure that the CW laser light passing through each of the two intersecting optical waveguides does not interfere with each other.

[0083] The ninth 2x2 optical coupler 601-9 has a first optical input 601i1-9 optically connected to a first optical output 601o1-5 of the fifth 2x2 optical coupler 601-5, and a second optical input 601i2-9 optically connected to a first optical output 601o1-6 of the sixth 2x2 optical coupler 601-6. Thus, the ninth 2x2 optical coupler 601-9 receives four CW laser optical wavelengths λ1, λ2, λ3, and λ4 at the first optical input 601i1-9, and receives four CW laser optical wavelengths λ5, λ6, λ7, and λ8 at the second optical input 601i2-9. The ninth 2x2 optical coupler 601-9 has a first optical output 601o1-9 and a second optical output 601o2-9. The ninth 2×2 optical coupler 601-9 is configured to multiplex all optical wavelengths received at the first optical input 601i1-9 and the second optical input 601i2-9 onto each of the two optical outputs 601o1-9 and 601o2-9. In this manner, each of the eight CW laser optical wavelengths λ1, λ2, λ3, λ4, λ5, λ6, λ7, and λ8 are output through each of the first optical outputs 601o1-9 and second optical outputs 601o2-9 of the ninth 2×2 optical coupler 601-9 (corresponding to optical outputs 311-1 and 311-2, respectively, of the 8×8 optical distribution network 600).

[0084] The tenth 2×2 optical coupler 601-10 has a first optical input 601i1-10 optically connected to the second optical output 601o2-5 of the fifth 2×2 optical coupler 601-5, and a second optical input 601i2-10 optically connected to the second optical output 601o2-6 of the sixth 2×2 optical coupler 601-6. Thus, the tenth 2×2 optical coupler 601-10 receives four CW laser optical wavelengths λ1, λ2, λ3, and λ4 at the first optical input 601i1-10, and receives four CW laser optical wavelengths λ5, λ6, λ7, and λ8 at the second optical input 601i2-10. The tenth 2×2 optical coupler 601-10 has a first optical output 601o1-10 and a second optical output 601o2-10. The tenth 2×2 optical coupler 601-10 is configured to multiplex all of the CW laser optical wavelengths received at the first optical input 601i1-10 and the second optical input 601i2-10 onto each of the two optical outputs 601o1-10 and 601o2-10. In this manner, each of the eight CW laser optical wavelengths λ1, λ2, λ3, λ4, λ5, λ6, λ7, and λ8 are output through each of the first optical output 601o1-10 and the second optical output 601o2-10 of the tenth 2×2 optical coupler 601-10 (corresponding to the optical outputs 311-3 and 311-4, respectively, of the 8×8 optical distribution network 600).

[0085] The eleventh 2×2 optical coupler 601-11 has a first optical input 601i1-11 optically connected to a first optical output 601o1-7 of the seventh 2×2 optical coupler 601-7, and a second optical input 601i2-11 optically connected to a first optical output 601o1-8 of the eighth 2×2 optical coupler 601-8. Thus, the eleventh 2×2 optical coupler 601-11 receives four CW laser optical wavelengths λ1, λ2, λ3, and λ4 at the first optical input 601i1-11, and receives four CW laser optical wavelengths λ5, λ6, λ7, and λ8 at the second optical input 601i2-11. The eleventh 2×2 optical coupler 601-11 has a first optical output 601o1-11 and a second optical output 601o2-11. The eleventh 2×2 optical coupler 601-11 is configured to multiplex all of the CW laser optical wavelengths received at the first optical input 601i1-11 and the second optical input 601i2-11 onto each of the two optical outputs 601o1-11 and 601o2-11. In this manner, each of the eight CW laser optical wavelengths λ1, λ2, λ3, λ4, λ5, λ6, λ7, and λ8 is output through each of the first optical output 601o1-11 and the second optical output 601o2-11 of the eleventh 2×2 optical coupler 601-11 (corresponding to the optical outputs 311-5 and 311-6, respectively, of the 8×8 optical distribution network 600).

[0086] The twelfth 2x2 optical coupler 601-12 has a first optical input 601i1-12 optically connected to the second optical output 601o2-7 of the seventh 2x2 optical coupler 601-7, and a second optical input 601i2-12 optically connected to the second optical output 601o2-8 of the eighth 2x2 optical coupler 601-8. Thus, the twelfth 2x2 optical coupler 601-12 receives four CW laser optical wavelengths λ1, λ2, λ3, and λ4 at the first optical input 601i1-12, and receives four CW laser optical wavelengths λ5, λ6, λ7, and λ8 at the second optical input 601i2-12. The twelfth 2x2 optical coupler 601-12 has a first optical output 601o1-12 and a second optical output 601o2-12. The twelfth 2×2 optical coupler 601-12 is configured to multiplex all of the CW laser optical wavelengths received at the first optical input 601i1-12 and the second optical input 601i2-12 onto each of the two optical outputs 601o1-12 and 601o2-12. In this manner, each of the eight CW laser optical wavelengths λ1, λ2, λ3, λ4, λ5, λ6, λ7, and λ8 are output through each of the first optical output 601o1-12 and the second optical output 601o2-12 of the twelfth 2×2 optical coupler 601-12 (corresponding to the optical outputs 311-7 and 311-8, respectively, of the 8×8 optical distribution network 600).

[0087] The 8×8 star coupler 307B further comprises two further optical waveguide crossings 603-7 and 603-8 to enable optical routing between the optical outputs of the 2×2 optical couplers 601-5 through 601-8 and the optical inputs of the 2×2 optical couplers 601-9 through 601-12. The optical waveguide crossing 603-7 enables optical routing between a first optical output 601o1-6 of the sixth 2×2 optical coupler 601-6 and a second optical input 601i2-9 of the ninth 2×2 optical coupler 601-9. The optical waveguide crossing 603-3 further enables optical routing between a second optical output 601o2-5 of the fifth 2×2 optical coupler 601-5 and a first optical input 601i1-10 of the tenth 2×2 optical coupler 601-10. The optical waveguide crossover 603-8 enables optical routing between a first optical output 601o1-8 of the eighth 2×2 optical coupler 601-8 and a second optical input 601i2-11 of the eleventh 2×2 optical coupler 601-11. The optical waveguide crossover 603-8 further enables optical routing between a second optical output 601o2-7 of the seventh 2×2 optical coupler 601-7 and a first optical input 601i1-12 of the twelfth 2×2 optical coupler 601-12. Each of the optical waveguide crossovers 603-7 and 603-8 is configured to ensure that the CW laser light passing through each of the two intersecting optical waveguides does not interfere with each other.

[0088] In various embodiments, the optical waveguide intersections 409 and 603-1 through 603-8 referred to herein may be implemented in many different ways, such as, by way of example, those described in the following references:A)Y.Zhang et al.,“A CMOS-Compatible,Low-Loss,and Low-Crosstalk Silicon Waveguide Crossing,”in IEEE Photonics Technology Letters,Vol.25,No.5,pp.422-425,March 1,2013;B)H.Chen et al.,“Low-Loss Multimode-Interference-Based Crossings for Silicon Wire Waveguides,”in IEEE Photonics Technology Letters,Vol.18,No.21,pp.2260-2262,November 1,2006;C)H.Yang et al.,“A Broadband, Low-Crosstalk and Low Polarization Dependent Silicon Nitride Waveguide Crossing Based on the Multimode-Interference,”Optics Communications,Vol.450,pp.28-33,2019;D)P.Sanchis et al.,“Highly Efficient Crossing Structure for Silicon-on-Insulator Waveguides,”Optics Letters,Vol.34,pp.2760-2762,2009;E)W.Bogaerts et al.,“Low-Loss,Low-Cross-Talk Crossings for Silicon-on-Insulator Nanophotonic Waveguides,”Optics Letters,Vol.32,pp.2801-2803,2007;、および、F)C.H.Chen et al.,“Taper-Integrated Multimode-Interference Based Waveguide Crossing Design,”in IEEE Journal of Quantum Electronics,Vol.46,No.11,pp.1656-1661,November 2010。

[0089] 7 is a flow chart illustrating a method for operating the laser module 500 according to some embodiments. The method includes: M The method further comprises a step 701 of operating a plurality of lasers (Laser 1 through Laser M) to generate a plurality of input optical signals of different wavelengths (λ1 through λ2), respectively, for each of a plurality of optical inputs (303i1-1-m and 303i2-1-m, where m is from 1 to (M / 2)) of the front-stage optical multiplexer section 313. M The method further comprises operating 703 the front-end optical multiplexer section 313 to multiplex a unique subset of the plurality of input optical signals onto each of the plurality of intermediate optical outputs (305-1 through 305-O) such that a unique subset of the plurality of input optical signals multiplexed onto any given one of the plurality of intermediate optical outputs (305-1 through 305-O) is mutually exclusive from the plurality of input optical signals multiplexed onto other ones of the plurality of intermediate optical outputs (305-1 through 305-O). The method further comprises the step of communicating 707 a unique subset of the plurality of input optical signals from the plurality of intermediate optical outputs (305-1 through 305-O) to a plurality of optical inputs (309-1 through 309-O) of the optical coupler section 315 such that a different unique subset of the plurality of input optical signals is communicated respectively to each of the plurality of optical inputs (309-1 through 309-O) of the optical coupler section 315. The method further comprises the step of operating 709 the optical coupler section 315 to distribute a portion of each optical signal received at each of the plurality of optical inputs (309-1 through 309-O) of the optical coupler section 315 to one of the plurality of optical outputs (311-1 through 311-O) of the optical coupler section 315. In some embodiments, the optical coupler section 315 is implemented as a free space optical star coupler. In some embodiments, the optical coupler section 315 is implemented as a network of 2×2 optical couplers.

[0090] In some embodiments, the multiple lasers (Laser 1 through Laser M) are arranged in the laser array 101 such that the wavelength sequences of the multiple input optical signals of different wavelengths are non-monotonic ordered across the laser array 101 to match a corresponding non-monotonic ordered sequence of wavelength-tolerance passbands across the multiple optical inputs (303i1-1-m and 303i2-1-m, where m is from 1 to (M / 2)) of the front-stage optical multiplexer section 313. In some embodiments, both the non-monotonic ordering of the wavelength sequences of the multiple input optical signals across the laser array 101 and the corresponding non-monotonic ordering of the wavelength-tolerance passbands across the multiple optical inputs (303i1-1-m and 303i2-1-m, where m is from 1 to (M / 2)) of the front-stage optical multiplexer section 313 are used to determine whether the optical power tolerance at the optical output of the laser module 500 for temperature induced wavelength variations is consistent with the wavelength sequences of the multiple input optical signals across the laser array 101. The monotonic ranking of the inputs of the lasers (303i1-1-m and 303i2-1-m, where m ranges from 1 to (M / 2)) of the upstream optical multiplexer section 313 and the corresponding monotonic ranking of the wavelength acceptance passbands of the multiple optical inputs (303i1-1-m and 303i2-1-m, where m ranges from 1 to (M / 2)) of the upstream optical multiplexer section 313 are collectively defined to be increased for each of the multiple lasers (Laser 1 through Laser M) compared to the tolerance of the optical power at the optical output of the laser module 500 for temperature induced wavelength variations for each of the multiple lasers (Laser 1 through Laser M). The tolerance of the optical power at the optical output of the laser module 500 refers to the tolerable effect of wavelength variations on the output optical power of the laser module 500 for each wavelength at each optical output port of the laser module 500. Temperature induced wavelength variations for each of the multiple lasers (Laser 1 through Laser M) contribute to variations in the output optical power of the laser module 500 for each wavelength at each optical output port of the laser module 500, where the output optical power variations at the optical outputs of the laser module 500 should be maintained within a specified acceptable power tolerance.

[0091] In some embodiments, operating 705 the front-stage optical multiplexer section 313 includes communicating a plurality of input optical signals received at a plurality of optical inputs (303i1-1-m and 303i2-1-m, where m is from 1 to (M / 2)) of the front-stage optical multiplexer section 313 through a number (P) of optical multiplexer stages 301-1 through 301-P, where the number (P) is a factor of two to one. the first value is the logarithm of the second value, and the second value is equal to the number (M) of the multiple optical inputs (303i1-1-m and 303i2-1-m, where m is 1 to (M / 2)) of the upstream optical multiplexer section 313 divided by the number (O) of the multiple intermediate optical outputs (305-1 to 305-O) of the upstream optical multiplexer section 313, i.e., P=[log(M / O) / log(2)].

[0092] In some embodiments, each of the number (P) of optical multiplexer stages (301-1 to 301-P) has K S The optical multiplexer 303-SY includes two-to-one optical multiplexers 303-SY, where S is a given integer sequence number of the P optical multiplexer stages (301-1 to 301-P) counting from the first stage of the P optical multiplexer stages (301-1 to 301-P) to the last stage of the P optical multiplexer stages (301-1 to 301-P), and Y is a number ranging from 1 to (M / 2 P ) are multiplexer numbers. The first stage of the number (P) of optical multiplexer stages (301-1 to 301-P) has optical inputs optically connected to a number (M) of a plurality of optical inputs (M) (303i1-1-m and 303i2-1-m, where m ranges from 1 to (M / 2)) of the upstream optical multiplexer section 313. The last stage of the P of optical multiplexer stages (301-1 to 301-P) has optical outputs optically connected to a number (O) of a plurality of intermediate optical outputs (305-1 to 305-O) of the upstream optical multiplexer section 313. S) is a number (M) of optical inputs (303i1-1-m and 303i2-1-m, where m is 1 to (M / 2)) of the front-stage optical multiplexer section 313. S is equal to the number (K S Each of the two-to-one optical multiplexers 303-SY has a first optical input, a second optical input, and an optical output. The method further comprises: S ) two-to-one optical multiplexers 303-SY.

[0093] The above description of the embodiments is for illustrative and descriptive purposes and is not intended to be exhaustive or limiting. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment and, where applicable, can be substituted and utilized in selected embodiments unless otherwise shown or described. Thus, one or more features from one or more embodiments disclosed herein can be combined with one or more features from one or more other embodiments disclosed herein to form another embodiment that is not explicitly disclosed herein but is implicitly disclosed herein. This other embodiment may also be modified in many ways. Such variations of the embodiments are not considered departures from the present disclosure, and all such variations and modifications of the embodiments are intended to be included within the scope of the disclosure provided herein.

[0094] Although some method steps may be described in a particular order herein, it should be understood that other housekeeping steps may be performed between method steps, and / or method steps may be coordinated to be performed at slightly different times or simultaneously, or distributed into a system that permits process steps to be performed at various intervals related to the process, so long as the processing of the method steps is performed in a manner such that the method is successfully performed.

[0095] Although the present embodiments have been described in some detail for ease of understanding, it will be apparent that certain changes and modifications may be made within the scope of the appended claims. Accordingly, the embodiments disclosed herein are considered to be illustrative and not restrictive, and therefore should not be limited to only the details set forth herein, but may be modified within the scope and equivalents of the appended claims.

Claims

1. 1. An optical distribution network comprising: a front-stage optical multiplexer section having a plurality of optical inputs and a plurality of intermediate optical outputs, each of the plurality of optical inputs of the front-stage optical multiplexer section configured to receive a respective one of a plurality of input optical signals of different wavelengths, the front-stage optical multiplexer section configured to multiplex a unique subset of the plurality of input optical signals onto each of the plurality of intermediate optical outputs, each unique subset of the plurality of input optical signals multiplexed onto any one of the plurality of intermediate optical outputs being mutually exclusive with each of the plurality of input optical signals multiplexed onto any other of the plurality of intermediate optical outputs; an optical coupler section having a plurality of optical inputs optically connected respectively to the plurality of intermediate optical outputs of the upstream optical multiplexer section, the optical coupler section having a plurality of optical outputs corresponding to the plurality of optical outputs of the optical distribution network, the optical coupler section being configured to distribute a portion of each optical signal received at each of the plurality of optical inputs of the optical coupler section to one of the plurality of optical outputs of the optical coupler section.

2. 2. The optical distribution network of claim 1, wherein the upstream optical multiplexer section comprises a number (P) of optical multiplexer stages, the number (P) being equal to a first value divided by the logarithm of two, the first value being the logarithm of a second value, and the second value being equal to a number (M) of the plurality of optical inputs of the upstream optical multiplexer section divided by a number (O) of the plurality of intermediate optical outputs of the upstream optical multiplexer section.

3. 3. The optical distribution network of claim 2, wherein each of said number (P) of optical multiplexer stages comprises a number (K Ｓ (S) is a given integer sequence number of the number (P) of optical multiplexer stages, counting from a first stage of the number (P) of optical multiplexer stages to a last stage of the number (P) of optical multiplexer stages, the first stage of the number (P) of optical multiplexer stages having an optical input optically connected to the number (M) of the plurality of optical inputs of the previous optical multiplexer section, the last stage of the number (P) of optical multiplexer stages having an optical output optically connected to the number (O) of the plurality of intermediate optical outputs of the previous optical multiplexer section, and the number (K Ｓ ) is a function of dividing the number (M) of the plurality of optical inputs of the front-stage optical multiplexer section by 2 Ｓ equal to divided by equal to the optical distribution network.

4. 4. The optical distribution network of claim 3, wherein the number (K Ｓ Each of the (K) two-to-one optical multiplexers has a first optical input, a second optical input, and an optical output, Ｓ 1. An optical distribution network comprising:

5. 5. The optical distribution network of claim 4, wherein a number (K) of optical multiplexer stages in a first optical multiplexer stage of said number (P) of optical multiplexer stages １ 1. An optical distribution network comprising:

6. 6. The optical distribution network of claim 5, wherein the first optical wavelength passband and the second optical wavelength passband correspond to discontinuous channel wavelengths of continuous wave laser light input into the optical distribution network.

7. 10. The optical distribution network of claim 1, wherein the optical coupler section is implemented as a free space optical star coupler.

8. 2. The optical distribution network of claim 1, wherein the optical coupler section is implemented as a network of 2x2 optical couplers.

9. 1. A laser module comprising: a laser array comprising a plurality of lasers, each laser of the plurality of lasers configured to generate and output continuous wave laser light at a different one of a plurality of wavelengths, the plurality of lasers being arranged in the laser array such that a sequence of the plurality of wavelengths of continuous wave laser light is non-monotonically ordered across the laser array; an optical distribution network comprising: a front-stage optical multiplexer section; and an optical coupler section disposed after the front-stage optical multiplexer section with respect to a direction of propagation of light through the optical distribution network, the front-stage optical multiplexer section having a plurality of optical inputs optically connected to the plurality of lasers such that the non-monotonic ordering of the sequence of the plurality of wavelengths of continuous wave laser light across the laser array matches an ordering of wavelength acceptance passbands of the plurality of optical inputs of the front-stage optical multiplexer section, the front-stage optical multiplexer section having a plurality of intermediate optical outputs, a laser module, the optical coupler section being configured to multiplex a unique and mutually exclusive subset of the plurality of wavelengths of continuous wave laser light onto each of the plurality of intermediate optical outputs, the optical coupler section having a plurality of optical inputs optically connected respectively to the plurality of intermediate optical outputs of the upstream optical multiplexer section, the optical coupler section having a plurality of optical outputs respectively corresponding to a plurality of optical outputs of the optical distribution network and each of a plurality of outputs of the laser module, the optical coupler section being configured to distribute a portion of each optical signal received at each of the plurality of optical inputs of the optical coupler section to a respective one of the plurality of optical outputs of the optical coupler section.

10. 10. The laser module of claim 9, wherein the plurality of lasers are in thermal contact with a common thermally conductive substrate.

11. 10. The laser module of claim 9, wherein the laser array is optically interfaced with the optical distribution network such that the multiple wavelengths of continuous wave laser light are transmitted from the multiple lasers to the multiple optical inputs of the front-stage optical multiplexer section.

12. 10. The laser module of claim 9, wherein the upstream optical multiplexer section comprises a number (P) of optical multiplexer stages, the number (P) being equal to a first value divided by the logarithm of two, the first value being the logarithm of a second value, and the second value being equal to a number (M) of the plurality of optical inputs of the upstream optical multiplexer section divided by a number (O) of the plurality of intermediate optical outputs of the upstream optical multiplexer section.

13. 13. The laser module of claim 12, wherein each of the number (P) of optical multiplexer stages is a number (K Ｓ wherein S is a given integer sequence number of the number (P) of optical multiplexer stages, counting from a first stage of the number (P) of optical multiplexer stages to a last stage of the number (P) of optical multiplexer stages, the first stage of the number (P) of optical multiplexer stages having an optical input optically connected to the number (M) of the plurality of optical inputs of the previous optical multiplexer section, the last stage of the number (P) of optical multiplexer stages having an optical output optically connected to the number (O) of the plurality of intermediate optical outputs of the previous optical multiplexer section, and the number (K Ｓ ) is a function of dividing the number (M) of the plurality of optical inputs of the front-stage optical multiplexer section by 2 Ｓ Equal to the laser module divided by the value equal to.

14. 14. The laser module of claim 13, wherein the number (K Ｓ Each of the (K) two-to-one optical multiplexers has a first optical input, a second optical input, and an optical output, Ｓ ) each of the two-to-one optical multiplexers configured to multiplex optical signals received at its first and second optical inputs onto its optical output.

15. 15. The laser module of claim 14, wherein a number (K) of optical multiplexer stages in the first optical multiplexer stage of the number (P) of optical multiplexer stages １ 1. A laser module comprising: a first optical multiplexer having a first optical wavelength passband for its first optical input and a second optical wavelength passband for its second optical input, the second optical wavelength passband being different from the first optical wavelength passband.

16. 1. A method for operating a laser module, comprising: operating a plurality of lasers to generate a plurality of input optical signals, each of the input optical signals having a different wavelength; communicating the plurality of input optical signals to a plurality of optical inputs of the front-stage optical multiplexer section such that each of the plurality of optical inputs of the front-stage optical multiplexer section receives a respective one of the plurality of input optical signals of the different wavelengths; operating the front-stage optical multiplexer section to multiplex a unique subset of the plurality of input optical signals onto each of the plurality of intermediate optical outputs such that a unique subset of the plurality of input optical signals multiplexed onto any given one of the plurality of intermediate optical outputs is mutually exclusive with the plurality of input optical signals multiplexed onto any other of the plurality of intermediate optical outputs; communicating a distinct subset of the plurality of input optical signals from the plurality of intermediate optical outputs to a plurality of optical inputs of the optical coupler section such that a distinct distinct subset of the plurality of input optical signals is respectively communicated to each of a plurality of optical inputs of the optical coupler section; operating the optical coupler section to distribute a portion of each optical signal received at each of the plurality of optical inputs of the optical coupler section to one of a plurality of optical outputs of the optical coupler section; A method comprising:

17. 17. The method of claim 16, wherein the plurality of lasers are arranged in a laser array such that a wavelength sequence of the plurality of input optical signals of different wavelengths is non-monotonic ordered across the laser array to match a corresponding non-monotonic ordered sequence of wavelength acceptance passbands across the plurality of optical inputs of the front-stage optical multiplexer section.

18. 18. The method of claim 17, wherein both the non-monotonic ordering of the wavelength sequences of the multiple input optical signals across the laser array and the corresponding non-monotonic ordering of wavelength-tolerance passbands across the multiple optical inputs of the front-stage optical multiplexer section are collectively defined such that a tolerance of optical power at the multiple optical outputs of the optical coupler section to temperature-induced wavelength variations is increased for each of the multiple lasers compared to the tolerance of optical power at the multiple optical outputs of the optical coupler section to temperature-induced wavelength variations for each of the multiple lasers associated with both the monotonic ordering of the wavelength sequences of the multiple input optical signals across the laser array and the corresponding monotonic ordering of wavelength-tolerance passbands across the multiple optical inputs of the front-stage optical multiplexer section.

19. 17. The method of claim 16, wherein operating the upstream optical multiplexer section includes transmitting the plurality of input optical signals received at the plurality of optical inputs of the upstream optical multiplexer section through a number (P) of optical multiplexer stages, the number (P) being equal to a first value divided by the logarithm of two, the first value being the logarithm of a second value, and the second value being equal to a number (M) of the plurality of optical inputs of the upstream optical multiplexer section divided by a number (O) of the plurality of intermediate optical outputs of the upstream optical multiplexer section.

20. 20. The method of claim 19, wherein each of the number (P) of optical multiplexer stages comprises a number (K Ｓ wherein S is a given integer sequence number of the number (P) of optical multiplexer stages, counting from a first stage of the number (P) of optical multiplexer stages to a last stage of the number (P) of optical multiplexer stages, the first stage of the number (P) of optical multiplexer stages having an optical input optically connected to the number (M) of the plurality of optical inputs of the previous optical multiplexer section, the last stage of the number (P) of optical multiplexer stages having an optical output optically connected to the number (O) of the plurality of intermediate optical outputs of the previous optical multiplexer section, and the number (K Ｓ ) is a function of dividing the number (M) of the plurality of optical inputs of the front-stage optical multiplexer section by 2 Ｓ A method that is equal to a value divided by a value that is equal to a value.

21. 21. The method of claim 20, wherein the number (K Ｓ Each of the number (K) of two-to-one optical multiplexers has a first optical input, a second optical input, and an optical output, and the method further comprises: Ｓ 2. A method comprising: operating each of the two-to-one optical multiplexers to multiplex optical signals received at its first and second optical inputs onto its optical output.

22. 20. The method of claim 16, wherein the optical coupler section is implemented as a free space optical star coupler.

23. 17. The method of claim 16, wherein the optical coupler section is implemented as a network of 2x2 optical couplers.

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