Photonic coherent detection array

Abstract

To provide a coherent detection array and a multiplexed method for reading a signal of the coherent detection array.SOLUTION: A coherent detection array may be mounted onto a photonic integrated circuit (PIC). The coherent detection array may contain a plurality of coherent detection units coupled to a connection waveguide and an electric conduction path, and the electric conduction path may function as a reading channel for multiplying an electric signal. A detection unit can be constructed by containing a free space-waveguide coupling device, an optical coupling device, and an optical detection device. The coherent detection array enables a multiplying method capable of activating a high free level of the coherent detection array. Those method may contain one that can be made by a local oscillator, and one that is related to a characteristic and a response of a construction element of a PIC-type detection array.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] Cross-reference to related applications This application claims the benefit of U.S. Provisional Patent Application No. 62 / 889,065, filed Aug. 20, 2019, which is incorporated herein by reference in its entirety.

[0002] The present invention relates to optical coherent detection, and in particular to detector arrays for optical coherent detection. [Background technology]

[0003] Optical coherent detection, also known as optical heterodyne detection, can measure both the electric field amplitude and phase of an optical signal relative to a reference optical signal, usually called a local oscillator (LO), whereas direct optical detection measures only the optical intensity of the optical signal. The advantages of coherent detection include low shot noise optical amplification, rejection of background light, and providing additional information through phase.

[0004] A detector array is an array of detector units that utilizes spatial parallelism to rapidly acquire the signals of a scene, and when used at the focal plane of an imaging system, it is called a focal plane array (FPA). Conventional detector array technologies, such as CCD and CMOS image sensors, only operate in direct optical detection mode. To realize parallel spatial coherent detection, the direct detector array needs to be in an interferometric configuration, which requires free-space bulk optics to coherently combine the signal light and LO on the detector array. However, such a configuration is not only bulky, but also has the problem that the spatial mode matching of the incident signal light to the LO beam affects the efficiency of coherent detection.

[0005] Coherent detector arrays based on photonic integrated circuit (PIC) technology greatly simplify coherent imaging systems by performing optical interference on a photonic chip, and the mode matching problem is logically solved since the signal light and the LO light usually appear in the same waveguide mode. A known form of coherent detector array based on PIC is the nanophotonic coherent imager (NCI), described in Non-Patent Document 1 [Firooz Aflatouni, Behrooz Abiri, Angad Rekhi, and Ali Hajimiri, "Nanophotonic coherent imager," Optics Express 23, 5117-5125 (2015)]. In NCI, the coherent detector array is configured such that the optical antenna (grating coupler) of each detector pixel is individually connected by a waveguide to a directional coupler and a photodetector outside the detection area. The pixel pitch of the NCI increases linearly with the number of pixels to ensure space for the waveguide, and therefore the size of the PIC chip increases quadratically with the number of pixels. Therefore, where size and cost are important, the NCI approach may be limited to a few pixels.

[0006] In addition, for certain coherent detection applications where real-time detection is useful, it is desirable for the coherent detection array to operate at high frame rates. These applications include frequency modulated continuous wave (FMCW) light detection and ranging (LIDAR) and optical coherence tomography (OCT). Recent high-pixel direct detection arrays achieve high frame rates by equipping each column or pixel of the pixel array with an analog-to-digital circuit (ADC) for parallel readout and conversion. However, these detector arrays require pixel signals to be transferred row by row to a horizontal register of a column address circuit. Modern CMOS-based direct detection arrays use frame storage, which allows them to operate at very high sampling rates, but the frame storage circuitry severely limits the number of pixels in the detector array. In general, existing coherent or direct detection array designs and their operation have a trade-off between pixel count and frame rate. Summary of the Invention [Problem to be solved by the invention]

[0007] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention describe a coherent detection array implemented on a photonic integrated circuit (PIC) and a multiplexing method for readout of the coherent detection signals that exploits the properties of the detection array. [Means for solving the problem]

[0008] The coherent detection array may include multiple coherent detection units coupled with connecting waveguides and electrical conductive paths, and local oscillator (LO) light is introduced into the coherent detection units via the connecting waveguides. The detection units may be configured to include a free-space-waveguide coupler that receives signal light incident on the detection units from a medium including, but not limited to, free space, an optical coupler that mixes the signal light and the LO light, and an optical detector that measures the mixed signal-LO light. The electrical conductive path serves as a readout channel for multiplexing the electrical signal, and the readout channel can facilitate stacking of detection units and scalability of the coherent detection array without the need for complex waveguide routing or optical switching. The coherent detection array also enables multiplexing methods that take advantage of the high degree of flexibility of the coherent detection array. Some of these methods are enabled by local oscillators, while others are related to the properties and responses of the components of the PIC-type detection array. Due to the scalable design of coherent detection arrays and the multiplexing methods applicable to them, coherent detection arrays are capable of simultaneously achieving high pixel count and high frame rate operation. [Brief description of the drawings]

[0009] Those skilled in the art will appreciate that the drawings are primarily for illustrative purposes and are not intended to limit the scope of the inventive subject matter described herein. The drawings are not necessarily to scale, and in some cases, various aspects of the inventive subject matter disclosed herein may be shown exaggerated or enlarged in the drawings to facilitate an understanding of different features.

[0010] [Figure 1] 2 shows an example of the configuration of a coherent detection unit according to a first preferred embodiment of the present invention employing two photodetectors. [Diagram 2] 2 shows an example of the configuration of a coherent detection array according to a second preferred embodiment of the present invention in which the embodiment of FIG. 1 is adopted. [Diagram 3]3 is a variation of FIG. 2 in which one or more electrodes of the photodetectors of the coherent detection unit are connected by electrical conductive paths that cross different columns instead of across different rows.

[0011] [Figure 4] 13 shows another example of the configuration of the coherent detection unit according to the third preferred embodiment of the present invention, in which a single photodetector is employed. [Diagram 5] FIG. 5 is a variation of FIG. 4 in which one or more waveguides and / or optical couplers are removed to simplify the detection unit.

[0012] [Figure 6] 4 shows an example of the configuration of a coherent detection array according to a fourth preferred embodiment of the present invention in which a single photodetector is adopted in each detection unit. [Figure 7] 6, in which one or more electrodes of the photodetectors of a detection unit are connected by electrical conductive paths that cross different columns instead of across different rows. [Figure 8] 7 is a second modification of FIG. 6 in which the embodiment of FIG. 5 is adopted. [Figure 9] 6 in which the changes to FIG. 6 according to both FIG. 7 and FIG. 8 are incorporated.

[0013] [Figure 10] 1 shows an example of a configuration of a coherent detection unit according to a fifth preferred embodiment of the present invention, in which two polarizations of input light are separately detected by the detection unit, where the input light is coupled to the detection unit via a polarization-splitting free-space-to-waveguide coupler, and a single photodetector is employed for detection of each polarization. [Figure 11] FIG. 11 is a first variation of FIG. 10 using a single local oscillator to interfere two polarizations of the input light. [Figure 12] FIG. 11 is a second variation of FIG. 10 in which one or more waveguides are omitted to simplify the coherent detection unit. [Figure 13]11 and 12. A third variation incorporating the changes to FIG. 10 according to both FIG.

[0014] [Figure 14] 10 shows an example of a configuration of a coherent detection array according to a sixth preferred embodiment of the present invention, in which two polarizations of input light are detected separately by the detection units of the array. [Figure 15] 15 is a first variation of FIG. 14 in which one or more electrodes of the photodetectors of the detection unit are connected by electrical conductive paths that cross different rows instead of across different rows. [Figure 16] 14 in which the embodiment of FIG. 11 is adopted. [Figure 17] 15 and 16. FIG. 16 is a third variation of FIG. 14 incorporating the changes to FIG. [Figure 18] 14 in which the embodiment of FIG. 12 is adopted. [Figure 19] FIG. 14 is a fifth variant of FIG. 14 incorporating the changes to FIG. 14 according to FIGS. 15 and 18. [Figure 20] 14 in which the embodiment of FIG. 13 is adopted. [Figure 21] 14 incorporating the changes to FIG. 14 according to both FIG. 15 and FIG. 20.

[0015] [Figure 22] 13 is another example of a configuration of a coherent detection unit according to a seventh preferred embodiment of the present invention, in which two polarizations of the input light are detected separately in the detection unit, in which the input light is coupled to the detection unit via a polarization-splitting free-space-waveguide coupler, and two photodetectors are employed for detection of each polarization. [Diagram 23] 23 is a variation of FIG. 22 in which a single local oscillator source is used to interfere two polarizations of the input light.

[0016] [Figure 24]22 shows another example of the configuration of a coherent detection array according to the eighth preferred embodiment of the present invention, in which two polarizations of the input light are detected separately by the detection units of the array. 23 shows a coherent detection array in which the embodiment of FIG. 22 is adopted. [Diagram 25] 25 is a first variation of FIG. 24 in which one or more electrodes of the photodetectors of a detection unit are connected by electrical conductive paths that cross different columns instead of across different rows. [Figure 26] 24 in which the embodiment of FIG. 23 is adopted. [Figure 27] 25 and 26. FIG. 26 is a third variation of FIG. 24 incorporating the changes to FIG.

[0017] [Figure 28] 1 shows a conceptual diagram of a coherent detection device comprising a coherent detection array, an optical input circuit, an electrical multiplexing circuit, and an electrical readout circuit.

[0018] [Figure 29] 29A and 29B are graphs showing the concept of one embodiment of the multiplexing method using a local oscillator in a coherent detection array of the present invention. Fig. 29A is a graph showing an example of a frequency spectrum obtained by combining photocurrents or signals of connected detection units in a coherent detection array that does not use a frequency offset in the local oscillator. Fig. 29B is a graph showing an example of a frequency spectrum obtained by combining photocurrents or signals of connected detection units in a coherent detection array that applies a frequency offset to the local oscillator.

[0019] [Diagram 30]30A to 30C are graphs showing the concept of one embodiment of a multiplexing method using the photodetector responsivity of a coherent detection array of the present invention. FIG. 30A is a graph showing an example of a frequency spectrum obtained by combining the photocurrent or signal of the connected detection units in a coherent detection array in which the photodetector responsivity is not modulated. FIG. 30B is a graph showing an example of a frequency spectrum obtained by combining the photocurrent or signal of the connected detection units in a coherent detection array in which the photodetector responsivity is modulated. FIG. 30C is a graph showing an example of a frequency spectrum obtained by combining the difference between the photocurrent or signal of the connected detection units in a coherent detection array of a balanced configuration in which the photodetector responsivity is modulated. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] To realize a coherent detector array with a high pixel count, it is desirable for the array pixel design to be scalable without extra complexity. In addition, in conventional detector array designs, time- and space-division multiplexing signal readout methods are commonly used, but there is a trade-off between pixel count and frame rate. Therefore, a high degree of freedom in signal multiplexing is desirable.

[0021] This technique provides a coherent detection array approach that allows for high scalability of pixel counts, and adds a high degree of freedom in the array in addition to the degrees of freedom in the time and space domains to be used, allowing multiplexing of signals during readout. Here, the pixels of the coherent detection array are referred to as coherent detection units or simply detection units of the coherent detection array.

[0022] To achieve scalability for high pixel count designs, the coherent detection array is configured to perform light interference and detection at pixels, i.e., coherent detection units. In some aspects, the coherent detection array may be implemented on a photonic chip using PIC technology, and each detection unit of the coherent detection array may be configured to include a waveguide that introduces LO light into the unit, a free space-waveguide coupler that couples signal light into the PIC chip, an optical coupler that mixes the LO light and the signal light, and an on-chip photodetector that measures the mixed light. Each detection unit may be connected by a waveguide and an electrical conductive path to form a coherent detection array, allowing signal readout of each detection unit by a multiplexing method.

[0023] In signal multiplexing, a large degree of freedom can be divided into optical and electrical domains: those realized by local oscillators and those related to the properties and response of the components of the PIC-type coherent detection array.

[0024] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings, showing the design of a coherent detection unit, a coherent detection array and a multiplexing method. Coherent detection unit and coherent focal plane array First Preferred Embodiment

[0025] A coherent detection unit 100 according to the preferred embodiment will now be described with reference to FIG. 1, which shows a plan view of the coherent detection unit 100. The coherent detection unit 100 shown in FIG. 1 is configured to include a free space-waveguide coupler 11, optical couplers 12-1 and 12-2, waveguides 13-1, 13-2, 13-3, 13-4, and 13-5, photodetectors 14-1 and 14-2, and electrodes 15-1, 15-2, 15-3, and 15-4. The coherent detection unit 100 may also be configured to include additional components, such as one or more modulators and / or heaters, which may be used to modulate or change the characteristics of the coherent detection unit. These additional components are not shown in FIG. 1. The coherent detection unit 100 may be integrated on a substrate 16 using optical waveguide technology.

[0026] The waveguide 13-1 transmits the local oscillator light E LO,in One end (input end) where the local oscillator light E LO,out The optical coupler 12-1 is an optical waveguide having an end (output end) through which the local oscillator light E LO,in A portion of the local oscillator light may be split from the waveguide 13-1 to the waveguide 13-2. The waveguide 13-2 may pass the local oscillator light to the optical coupler 12-2. The optical coupler 12-1 may include, but is not limited to, a Y-junction, a directional coupler, and a multimode interferometer.

[0027] The free space-waveguide coupler 11 couples the signal light E Sig,in is a portion that can be coupled to the coherent detection unit 100. Sig,in The light may be incident normal or oblique to the plane of the photonic chip on which the free space-waveguide coupler 11 is implemented. Light received by the free space-waveguide coupler 11 can flow through the waveguide 13-3 to the optical coupler 12-2. The free space-waveguide coupler 11 is generally an optical antenna that couples light from free space or a medium to the photonic chip. Free space-waveguide couplers include, but are not limited to, grating couplers commonly used in PIC designs, and novel photonic micro / nanostructures.

[0028] The optical coupler 12-2 is a coupler having waveguides 13-2 and 13-3 as input ports and waveguides 13-4 and 13-5 as output ports. The local oscillator light from the input waveguide 13-2 and the signal light from the input waveguide 13-3 can be mixed and interfered with in the optical coupler 12-2. The optical coupler 12-2 is configured such that the light of the input waveguide 13-2 is divided between the output waveguides 13-4 and 13-5 at a certain ratio, and similarly, the light of the input waveguide 13-3 is divided between the output waveguides 13-4 and 13-5 at a certain ratio. The ratio may or may not be fixed, and may or may not depend on the characteristics of the light input to the optical coupler (such as, but not limited to, wavelength), the characteristics and conditions of the optical coupler (such as, but not limited to, temperature), and other unspecified factors. The optical coupler 12-2 may be, but is not limited to, a directional coupler and a multimode interferometer.

[0029] In some aspects, such as a balanced configuration in which optical coupler 12-2 is a 50 / 50 coupler, the light in input waveguide 13-2 may be split equally in magnitude between output waveguides 13-4, 13-5, and the light in input waveguide 13-3 may be split equally in magnitude between output waveguides 13-4, 13-5.

[0030] The photodetector 14-1 detects light input from the waveguide 13-4. When the photodetector 14-1 detects the light from the waveguide 13-4, a photocurrent may be generated and flow to the electrodes 15-1 and 15-2. Similarly, the photodetector 14-2 detects the light input from the waveguide 13-5. When the photodetector 14-2 detects the light from the waveguide 13-5, a photocurrent may be generated and flow to the electrodes 15-3 and 15-4. In some aspects, one of the electrodes 15-1 and 15-2 may represent an anode, and the other electrode may represent a cathode. Similarly, one of the electrodes 15-3 and 15-4 may represent an anode, and the other electrode may represent a cathode.

[0031] In some aspects, each photocurrent generated by the photodetectors 14-1, 14-2 can include a direct component and a cross component, and a noise component may also be present. The direct component is proportional to the average intensity of the signal light and the local oscillator light. The cross component is the product of the electric fields of the signal light and the local oscillator light, i.e., <E LO,in (t)E Sig,in (t)〉, where t represents time and 〈·〉 represents time averaging over a duration inversely proportional to the bandwidth of the photodetector. For simplicity of explanation, a noise component may be included in the direct component of the photocurrent.

[0032] In some aspects, the cross component may represent a beating of the signal light with the local oscillator light, with a beat frequency equal to the sum or difference of the frequencies of the signal light and the local oscillator light. The sum beat frequency is typically very high, so the corresponding photocurrent component may be averaged in time or suppressed by the finite response of the photodetector. The difference beat frequency is typically an intermediate frequency, so the corresponding photocurrent component may be resolved in time for further processing.

[0033] In some aspects, such as a balanced configuration where optical coupler 12-2 is a 50 / 50 coupler, by taking the difference of the photocurrents due to photodetectors 14-1, 14-2, the direct components of the photocurrents are cancelled out except for possible residual noise components, while the cross components of the photocurrents may be added according to the phase difference between the cross components of the photocurrents due to photodetectors 14-1, 14-2.

[0034] In another aspect, the photocurrent generated by the photodetectors 14-1, 14-2 may be modulated by modulating the responsivity of the photodetectors. Second Preferred Embodiment

[0035] Two examples of coherent detection arrays 200, 210 according to the presently preferred embodiments are described with reference to FIGS.

[0036] FIG. 2 illustrates a plan view of a coherent detection array 200. The coherent detection array 200 is configured to include multiple units of the coherent detection unit 100 according to the embodiment shown in FIG. 1. In some aspects, the coherent detection array 200 may include other embodiments of the coherent detection unit. In some aspects, the coherent detection array 200 may be configured by linking multiple units of the coherent detection unit 100 in a linear configuration. In other aspects, embodiments of the coherent detection array may be configured by linking multiple units of the coherent detection unit 100 in a geometric shape other than a linear configuration. The coherent detection array 200 may be integrated on the substrate 26 using optical waveguide technology.

[0037] In some aspects of the linear configuration, the coherent detection array may be configured with M rows and N columns of M×N coherent detection units, where M and N are positive integers. As an example, the embodiment of the coherent detection array 200 shown in FIG. 2 includes 12 coherent detection units 100-1, 100-2, 100-3, 100-4, 100-5, 100-6, 100-7, 100-8, 100-9, 100-10, 100-11, 100-12, all of which are coherent detection units 100 arranged in a 3-row, 4-column format.

[0038] Each row of the coherent detection array 200 can be configured by connecting a series of coherent detection units 100 using the waveguide 13-1 (see FIG. 1). In some aspects, the coherent detection array according to the preferred embodiment is configured such that the output end of the waveguide 13-1 of the coherent detection unit 100 is connected to the input end of the waveguide 13-1 of the next coherent detection unit 100, thereby reducing the transmitted LO light E LO,out Next, the input LO light E LO,inTherefore, the set of waveguides 13-1 in a row constitutes the connecting waveguides for that row and is also called the row coding waveguide for that row to indicate the role of the waveguide. The LO light of the connecting waveguides can be coupled to the connected coherent detection unit 100 via optical couplers 12-1 (see Figures 1 and 2). In such a configuration, the detection units in the same row of the coherent detection array may share the same local oscillator light, and each unit in the row taps a portion of the local oscillator light from the connecting waveguide. The proportion of the local oscillator light split by different coherent detection units in a row may be the same or different.

[0039] The connecting waveguides may connect a single row of coherent detection units, or may connect two or more rows of coherent detection units. The connecting waveguides do not have to connect all the coherent detection units in a single row. Depending on the configuration and arrangement of the coherent detection units in the coherent detection array, a row may or may not be a straight line.

[0040] Referring to FIG. 2, the row coding waveguides 21-1, 21-2, and 21-3 each transmit a local oscillator light E LO,in m (corresponding to m=1, 2, 3) can be introduced into one end, and the local oscillator light E LO,out mand the other end through which the optical fibers (corresponding to m=1, 2, 3) can be transmitted. For a coherent detection array with M rows, the index m ranges from 1 to M. In FIG. 2, the locally oscillating light of the row-coded waveguide 21-1 is coupled to the coherent detection units 100-1, 100-2, 100-3, 100-4 via the optical coupler 12-1. Similarly, the locally oscillating light of the row-coded waveguide 21-2 is coupled to the coherent detection units 100-5, 100-6, 100-7, 100-8 via the optical coupler 12-1, and the locally oscillating light of the row-coded waveguide 21-3 is coupled to the coherent detection units 100-9, 100-10, 100-11, 100-12 via the optical coupler 12-1. The optical couplers 12-1 of the coherent detection units 100-1, 100-2, 100-3, 100-4, 100-5, 100-6, 100-7, 100-8, 100-9, 100-10, 100-11, 100-12 can split the same or different percentages of light into the units by appropriate design of the optical couplers 12-1.

[0041] Local oscillator light E LO,in m (m=1, 2, ..., M, where M is the number of rows in the coherent detection array, and M=3 in the example of FIG. 2 ) may have the same or different optical frequencies, the same or different magnitudes (including zero amplitude), and the same or different relative phases. Also, the local oscillator light E LO,in m may be irradiated at the same or different times and for the same or different durations. LO,in m may be introduced to the array of coherent detection units from the same or different light sources. The light sources may be on-chip light sources or external light sources outside the photonic chip. These light sources may be controlled by several optical switches and networks located on the photonic substrate 26, either in the same location or not in the same location as the coherent detection array. The light sources and the optical switch network are not shown in FIG. 2.

[0042] In some aspects, to form a multiplexed readable detector array, multiple rows of coherent detector units may be serially connected by electrical conductive paths, also called column readout wiring, and the coherent detector units of each column of the detector array may share the same electrical outlet that is connected to readout circuitry located at the periphery of the coherent detector array. These electrical conductive paths may function as readout channels for multiplexing. For simplicity of nomenclature, the electrical conductive paths will also be referred to as wiring in the following.

[0043] The electrical conductive path connecting the coherent detection units may connect a single row of coherent detection units or may connect two or more rows of coherent detection units. The electrical conductive path may not connect all the coherent detection units in a single row. A row may or may not be a straight line, depending on the configuration and arrangement of the coherent detection units in the coherent detection array.

[0044] In some aspects, the coherent detection array according to the preferred embodiment shown in FIG. 2 may be configured such that for each column of coherent detection units, the electrode 15-1 of the photodetector 14-1 is connected to a column readout wiring, the electrode 15-3 of the photodetector 14-2 is connected to a column readout wiring, and the electrode 15-2 of the photodetector 14-1 and the electrode 15-4 of the photodetector 14-2 are connected to a common column readout wiring. In other aspects, the electrode 15-2 of the photodetector 14-1 and the electrode 15-4 of the photodetector 14-2 may be connected to separate column readout wirings instead of a common column readout wiring. The electrical signals obtained from the detection units connected to the same electrical conduction path are integrated (summed or subtracted depending on the sign or direction of the signal) and transmitted collectively to an output terminal that may be connected to a peripheral readout circuit. The peripheral readout circuit of the coherent detection array is not shown in FIG. 2.

[0045] The embodiment of the coherent detection array 200 in Fig. 2 shows a configuration with three rows, each row containing four coherent detection units 100, with the electrodes of the photodetectors on four different rows being connected by column readout wiring. For the coherent detection units 100-1, 100-5, and 100-9 in the first column shown in Fig. 2, the electrode 15-1 of the photodetector 14-1 is connected to the column readout wiring 22-1, the electrode 15-3 of the photodetector 14-2 is connected to the column readout wiring 23-1, and the electrodes 15-2 of the photodetector 14-1 and 15-4 of the photodetector 14-2 are connected to the column readout wiring 24-1. The current at the output end of column readout wiring 22-1 is the sum of the photocurrents from photodetector 14-1, the current at the output end of column readout wiring 23-1 is the sum of the photocurrents from photodetector 14-2, and the current at the output end of column readout wiring 24-1 is the sum or difference of the photocurrents from photodetectors 14-1 and 14-2 depending on the direction of the photocurrents.

[0046] Similarly, for the second column of coherent detection units 100-2, 100-6, and 100-10, electrode 15-1 of photodetector 14-1 is connected to column readout wiring 22-2, electrode 15-3 of photodetector 14-2 is connected to column readout wiring 23-2, and electrode 15-2 of photodetector 14-1 and electrode 15-4 of photodetector 14-2 are connected to column readout wiring 24-2. The current at the output end of column readout wiring 22-2 is the sum of the photocurrents from photodetector 14-1, the current at the output end of column readout wiring 23-2 is the sum of the photocurrents from photodetector 14-2, and the current at the output end of column readout wiring 24-2 is the sum or difference of the photocurrents from photodetectors 14-1 and 14-2 depending on the direction of the photocurrents.

[0047] Similarly, for the third column of coherent detection units 100-3, 100-7, and 100-11, the electrode 15-1 of the photodetector 14-1 is connected to the column readout wiring 22-3, the electrode 15-3 of the photodetector 14-2 is connected to the column readout wiring 23-3, and the electrodes 15-2 of the photodetector 14-1 and 15-4 of the photodetector 14-2 are connected to the column readout wiring 24-3. The current at the output end of the column readout wiring 22-3 is the sum of the photocurrents from the photodetector 14-1, the current at the output end of the column readout wiring 23-3 is the sum of the photocurrents from the photodetector 14-2, and the current at the output end of the column readout wiring 24-3 is the sum or difference of the photocurrents from the photodetectors 14-1 and 14-2 depending on the direction of the photocurrents.

[0048] Similarly, for the fourth column of coherent detection units 100-4, 100-8, and 100-12, electrode 15-1 of photodetector 14-1 is connected to column readout wiring 22-4, electrode 15-3 of photodetector 14-2 is connected to column readout wiring 23-4, and electrode 15-2 of photodetector 14-1 and electrode 15-4 of photodetector 14-2 are connected to column readout wiring 24-4. The current at the output end of column readout wiring 22-4 is the sum of the photocurrents from photodetector 14-1, the current at the output end of column readout wiring 23-4 is the sum of the photocurrents from photodetector 14-2, and the current at the output end of column readout wiring 24-4 is the sum or difference of the photocurrents from photodetectors 14-1 and 14-2 depending on the direction of the photocurrents.

[0049] In FIG. 2, pad Pa is an output terminal of a column readout line which can be connected to a peripheral readout circuit.

[0050] In Figure 2, the coherent detection units of the coherent detection array can be considered as being grouped into four different subsets (columns) by electrical conductive paths, i.e., column readout wiring, with each coherent detection unit of the array being included in a single subset grouped by an electrical conductive path. Alternatively, the coherent detection units of the coherent detection array can be considered as being grouped into three different subsets (rows) by connecting waveguides, i.e., row coding waveguides, with each coherent detection unit being included in a single subset grouped by a connecting waveguide. Each coherent detection unit of the coherent detection array can be defined by a row coding waveguide and a column readout wiring. Variations of the second preferred embodiment

[0051] 3 shows a plan view of a coherent detection array 210. The coherent detection array 210 is a variation of the coherent detection array according to the embodiment shown in FIG. 2. Similar to the coherent detection array 200, the coherent detection array 210 can be configured to include multiple units of the coherent detection unit 100 according to the embodiment shown in FIG. 1. Each row of the coherent detection array 210 can be configured by connecting a series of coherent detection units 100 using a waveguide 13-1 (see FIG. 1). Multiple rows of coherent detection units 100 may be connected in series by electrical conductive paths to form a detection array. As an example, the embodiment of the coherent detection array 210 shown in FIG. 3 includes twelve coherent detection units 100-1, 100-2, 100-3, 100-4, 100-5, 100-6, 100-7, 100-8, 100-9, 100-10, 100-11, 100-12, all of which are coherent detection units 100 arranged in a configuration of three rows and four columns.

[0052] Similar to the coherent detection array 200, the coherent detection array 210 of the preferred embodiment may be configured such that for each column of coherent detection units, either electrode 15-1 or electrode 15-2 of photodetector 14-1 is connected to a column readout wiring, and similarly, either electrode 15-3 or electrode 15-4 of photodetector 14-2 is connected to a column readout wiring.

[0053] Unlike the coherent detection array 200, the coherent detection array 210 according to the preferred embodiment may be configured such that other electrodes of the photodetectors of the coherent detection units are connected across different columns by electrical conductive paths, also referred to as row coding wiring, instead of across different rows by column readout wiring. In some aspects, for each row of coherent detection units of the coherent detection array 210, either electrode 15-1 or electrode 15-2 of the photodetector 14-1 may be connected to a row coding wiring, and similarly, either electrode 15-3 or electrode 15-4 of the photodetector 14-2 may be connected to a row coding wiring. In other aspects, the two row coding wirings may be merged into a common wiring instead of separate wiring. The row coding wiring may be utilized to multiplex the signals of the coherent detection array with similar or different roles as the row coding waveguides of the detection array.

[0054] With reference to the coherent detection array 210 shown in Fig. 3, in the first column of coherent detection units 100-1, 100-5, and 100-9, the electrode 15-1 of the photodetector 14-1 is connected to the column readout wiring 22-1, and the electrode 15-3 of the photodetector 14-2 is connected to the column readout wiring 23-1.

[0055] Similarly, for the coherent detection units 100-2, 100-6, and 100-10 in the second column, the electrode 15-1 of the photodetector 14-1 is connected to the column readout wiring 22-2, and the electrode 15-3 of the photodetector 14-2 is connected to the column readout wiring 23-2.

[0056] Similarly, for the coherent detection units 100-3, 100-7, and 100-11 in the third column, the electrode 15-1 of the photodetector 14-1 is connected to the column readout wiring 22-3, and the electrode 15-3 of the photodetector 14-2 is connected to the column readout wiring 23-3.

[0057] Similarly, for the coherent detection units 100-4, 100-8, and 100-12 in the fourth column, the electrode 15-1 of the photodetector 14-1 is connected to the column readout wiring 22-4, and the electrode 15-3 of the photodetector 14-2 is connected to the column readout wiring 23-4.

[0058] On the other hand, for the coherent detection units 100-1, 100-2, 100-3, and 100-4 in the first row of the coherent detection array 210, electrode 15-2 of photodetector 14-1 is connected to row coding wiring 27-1, and electrode 15-4 of photodetector 14-2 is connected to row coding wiring 28-1.

[0059] Similarly, for the coherent detection units 100-5, 100-6, 100-7, and 100-8 in the second row, electrode 15-2 of photodetector 14-1 is connected to row coding wiring 27-2, and electrode 15-4 of photodetector 14-2 is connected to row coding wiring 28-2.

[0060] Similarly, for the coherent detection units 100-9, 100-10, 100-11, and 100-12 in the third row, electrode 15-2 of photodetector 14-1 is connected to row coding wiring 27-3, and electrode 15-4 of photodetector 14-2 is connected to row coding wiring 28-3.

[0061] The pads Pa in FIG. 3 are terminals of column readout wiring and row coding wiring that can be connected to peripheral electrical circuitry.

[0062] In FIG. 3, the coherent detection units of the coherent detection array can be considered as being grouped into four different subsets (columns) by some electrical conductive paths, i.e., column readout wiring, and grouped into three different subsets (rows) by other electrical conductive paths, i.e., row coding wiring, with each coherent detection unit of the array being included in two subsets (column 1 and row 1) grouped by electrical conductive paths. Each coherent detection unit of the coherent detection array may be addressed by a row coding wiring and a column readout wiring. Alternatively, the coherent detection units of the coherent detection array can be considered as being grouped into three different subsets (rows) by connecting waveguides, i.e., row coding waveguides, with each coherent detection unit being included in a single subset grouped by a connecting waveguide. Each coherent detection unit of the coherent detection array may be addressed by a row coding waveguide and a column readout wiring. Third Preferred Embodiment

[0063] Two examples of coherent detection units 300, 310 according to the present preferred embodiment will now be described with reference to FIGS.

[0064] FIG. 4 shows a plan view of the coherent detection unit 300. The coherent detection unit 300 shown in FIG. 4 is configured to include a free space-waveguide coupler 31, optical couplers 32-1, 32-2, waveguides 33-1, 33-2, 33-3, 33-4, a photodetector 34, and electrodes 35-1, 35-2. The coherent detection unit 300 may also be configured to include additional components, such as one or more modulators and / or heaters, which may be used to modulate or change the characteristics of the coherent detection unit. These additional components are not shown in FIG. 4. The coherent detection unit 300 may be integrated on a substrate 36 using optical waveguide technology.

[0065] The coherent detection unit 300 is an improved version of the coherent detection unit 100 shown in Figure 1. The coherent detection unit 300 may be understood with reference to the coherent detection unit 100 according to the embodiment shown in Figure 1 in conjunction with the following description.

[0066] The essential difference between the two embodiments of the coherent detection unit shown in Figures 1 and 4 is that one photodetector 34 is used in the coherent detection unit 300 instead of the two photodetectors 14-1, 14-2 of the coherent detection unit 100. Also, the optical coupler 32-2 of the coherent detection unit 300 is a coupler with waveguides 33-2, 33-3 as input ports and a waveguide 33-4 as an output port. The optical coupler 32-2 may be realized as a 2x2 directional coupler with a suitably terminated free output port, a Y-junction, or other form of light mixing with at least two input ports and one output port.

[0067] In some aspects, the photocurrent generated by the photodetector 34 may include a direct component that varies slowly in time and a cross component that varies rapidly in time, and a noise component may also be present. If only one photodetector is used in the coherent detection unit 300, it may be necessary to filter the photocurrent generated by the photodetector 34 with an appropriate filter to suppress the direct component of the photocurrent. The filter may or may not be located in the detection unit. The filter is not shown in FIG. 4. Variations of the Third Preferred Embodiment

[0068] 5 shows a plan view of a coherent detection unit 310. The coherent detection unit 310 shown in FIG. 5 is a modified example of the coherent detection unit 300 according to the embodiment shown in FIG.

[0069] The coherent detection unit 310 shown in FIG. 5 is similar to the coherent detection unit 300 shown in FIG. 4, but is essentially different in that the waveguide 33-2 is omitted for simplification, and the optical couplers 32-1 and 32-2 are integrated into a single optical coupler 32-3. The optical coupler 32-3 of the coherent detection 310 in FIG. 5 serves the role of both the optical couplers 32-1 and 32-2 of the coherent detection unit 300 in FIG. 4. For the coherent detection unit 310, the optical coupler 32-3 can directly mix the local oscillator light in the waveguide 33-1 and the signal light in the waveguide 33-3. The mixed light can be transmitted to the waveguide 33-4, the output segment of the waveguide 33-1.

[0070] In some aspects, optical coupler 32-3 of coherent detection unit 310 may be configured to transmit a majority portion of the signal light from waveguide 33-3 to waveguide 33-4 and transmit a minor portion of the signal light from waveguide 33-3 to an output segment of waveguide 33-1. An example optical splitting ratio for optical coupler 32-3 is 999:1. Fourth Preferred Embodiment

[0071] Four examples of coherent detection arrays 400, 410, 420, 430 according to the presently preferred embodiments will now be described with reference to FIGS.

[0072] FIG. 6 illustrates a plan view of a coherent detection array 400. The coherent detection array 400 is configured to include multiple units of the coherent detection unit 300 according to the embodiment shown in FIG. 4. In some aspects, the coherent detection array 400 may include other embodiments of the coherent detection unit. In some aspects, the coherent detection array 400 may be configured by linking multiple units of the coherent detection unit 300 in a linear configuration. In other aspects, embodiments of the coherent detection array may be configured by linking multiple units of the coherent detection unit 300 in a geometric shape other than a linear configuration. The coherent detection array 400 may be integrated on the substrate 46 using optical waveguide technology.

[0073] The coherent detection array 400 shown in FIG. 6 is similar to the coherent detection array 200 shown in FIG. 2, but is essentially different in that the coherent detection unit 300 according to the embodiment shown in FIG. 4 is adopted as a constituent unit of the detection array instead of the coherent detection unit 100 used in the coherent detection unit 200. In some aspects of the linear configuration, the coherent detection array may be configured with M rows and N columns of M×N coherent detection units. As an example, the embodiment of the coherent detection array 400 shown in FIG. 6 includes 12 coherent detection units 300-1, 300-2, 300-3, 300-4, 300-5, 300-6, 300-7, 300-8, 300-9, 300-10, 300-11, 300-12, all of which are coherent detection units 300 arranged in a 3-row, 4-column format.

[0074] The coherent detection array 400 may be understood with reference to the embodiment of the coherent detection array 200 shown in FIG. 2, in conjunction with the following description.

[0075] Each row of the coherent detection array 400 can be configured by connecting a series of coherent detection units 300 using the waveguide 33-1 (see FIG. 4). In some aspects, the coherent detection array according to the preferred embodiment is configured such that the output end of the waveguide 33-1 of the coherent detection unit 300 is connected to the input end of the waveguide 33-1 of the next coherent detection unit 300, thereby reducing the transmitted LO light E of the detection unit. LO,out Next, the input LO light E LO,in The set of waveguides 33-1 in a row constitutes the connecting waveguides for that row, also called the row coding waveguides for that row. The LO light of the connecting waveguides can be coupled via optical couplers 32-1 to the connected coherent detection unit 300 (see Figures 4 and 6).

[0076] For the coherent detection array 400 shown in Figure 6, the row coding waveguides are waveguides 41-1, 41-2, and 41-3. The LO light of row coding waveguide 41-1 is coupled to coherent detection units 300-1, 300-2, 300-3, and 300-4 via optical coupler 32-1. Similarly, the LO light of row coding waveguide 41-2 is coupled to coherent detection units 300-5, 300-6, 300-7, and 300-8 via optical coupler 32-1, and the LO light of row coding waveguide 41-3 is coupled to coherent detection units 300-9, 300-10, 300-11, and 300-12 via optical coupler 32-1. The optical couplers 32-1 of the coherent detection units 300-1, 300-2, 300-3, 300-4, 300-5, 300-6, 300-7, 300-8, 300-9, 300-10, 300-11, 300-12 may split the same or different percentages of light to the units by appropriate design of the optical couplers 32-1.

[0077] Multiple rows of coherent detection units can be connected in series by electrical conductive paths, also called column readout wires. The coherent detection units connected by each column readout wire may share the same electrical outlet, which may be connected to readout circuitry located at the periphery of the coherent detection array. In some aspects, the coherent detection array according to the preferred embodiment can be configured such that for each column of coherent detection units, the electrode 35-1 of the photodetector 34 is connected to a column readout wire, and similarly, the electrode 35-2 of the photodetector 34 is connected to a column readout wire.

[0078] 6, the electrode 35-1 of the photodetector 34 is connected to the column readout wiring 42-1, and the electrode 35-2 of the photodetector 34 is connected to the column readout wiring 43-1. Similarly, the electrode 35-1 of the photodetector 34 is connected to the column readout wiring 42-2, and the electrode 35-2 of the photodetector 34 is connected to the column readout wiring 43-2, for the coherent detection units 300-2, 300-6, and 300-10 of the second column. Similarly, the electrode 35-1 of the photodetector 34 is connected to the column readout wiring 42-3, and the electrode 35-2 of the photodetector 34 is connected to the column readout wiring 43-3, for the coherent detection units 300-3, 300-7, and 300-11 of the third column. Similarly, for the coherent detection units 300-4, 300-8, and 300-12 in the fourth column, the electrode 35-1 of the photodetector 34 is connected to the column readout wiring 42-4, and the electrode 35-2 of the photodetector 34 is connected to the column readout wiring 43-4.

[0079] As in FIG. 2, pads Pa in FIG. 6 are output terminals of column readout wiring that can be connected to peripheral readout circuits. First Variant of the Fourth Preferred Embodiment

[0080] FIG. 7 shows a plan view of a coherent detection array 410. The coherent detection array 410 is a variation of the coherent detection array 400 according to the embodiment shown in FIG. 6. Similar to the coherent detection array 400, the coherent detection array 410 can be configured to include multiple units of the coherent detection unit 300 according to the embodiment shown in FIG. 4. Each row of the coherent detection array 410 can be configured by connecting a series of coherent detection units 300 using a waveguide 33-1 (see FIG. 4). Multiple rows of coherent detection units 300 may be connected in series by electrical conductive paths to form a detection array. As an example, the embodiment of the coherent detection array 410 shown in FIG. 7 includes twelve coherent detection units 300-1, 300-2, 300-3, 300-4, 300-5, 300-6, 300-7, 300-8, 300-9, 300-10, 300-11, 300-12, all of which are coherent detection units 300 arranged in a configuration of three rows and four columns.

[0081] Similar to the coherent detection array 400, the coherent detection array 410 of the preferred embodiment may be configured such that for each column of coherent detection units, either electrode 35-1 or electrode 35-2 of the photodetector 34 is connected to a column readout wiring.

[0082] Unlike the coherent detection array 400, the coherent detection array 410 according to the preferred embodiment may be configured such that other electrodes of the photodetectors of the coherent detection units are connected across different columns by electrical conductive paths, also called row-coding wiring, instead of across different rows by column readout wiring. For each row of the coherent detection array 300 of the coherent detection unit 410, either the electrode 35-1 or the electrode 35-2 of the photodetector 34 may be connected to a row-coding wiring.

[0083] 7, the electrodes 35-2 of the photodetectors 34 of the coherent detection units 300-1, 300-5, and 300-9 in the first column are connected to the column readout wiring 43-1. Similarly, the electrodes 35-2 of the photodetectors 34 of the coherent detection units 300-2, 300-6, and 300-10 in the second column are connected to the column readout wiring 43-2, the electrodes 35-2 of the photodetectors 34 of the coherent detection units 300-3, 300-7, and 300-11 in the third column are connected to the column readout wiring 43-3, and the electrodes 35-2 of the photodetectors 34 of the coherent detection units 300-4, 300-8, and 300-12 in the fourth column are connected to the column readout wiring 43-4.

[0084] On the other hand, the electrodes 35-1 of the photodetectors 34 of the coherent detection units 300-1, 300-2, 300-3, and 300-4 in the first row are connected to row coding wiring 44-1. Similarly, the electrodes 35-1 of the photodetectors 34 of the coherent detection units 300-5, 300-6, 300-7, and 300-8 in the second row are connected to row coding wiring 44-2, and the electrodes 35-1 of the photodetectors 34 of the coherent detection units 300-9, 300-10, 300-11, and 300-12 in the third row are connected to row coding wiring 44-3.

[0085] The pads Pa in FIG. 7 are terminals of column readout wiring and row coding wiring that can be connected to peripheral electrical circuitry. Second Variant of the Fourth Preferred Embodiment

[0086] 8 shows a plan view of a coherent detection array 420. The coherent detection array 420 is another variation of the embodiment of the coherent detection array 400 shown in FIG.

[0087] The coherent detection array 420 shown in FIG. 8 is similar to the coherent detection array 400 according to the embodiment shown in FIG. 6, but is essentially different in that the coherent detection unit 310 according to the embodiment shown in FIG. 5 is adopted as a constituent unit of the detection array instead of the coherent detection unit 300 used in the coherent detection array 400. In some aspects of the linear configuration, the coherent detection array may be configured with M rows and N columns of M×N coherent detection units. As an example, the embodiment of the coherent detection array 420 shown in FIG. 8 includes 12 coherent detection units 310-1, 310-2, 310-3, 310-4, 310-5, 310-6, 310-7, 310-8, 310-9, 310-10, 310-11, 310-12, all of which are coherent detection 310 units arranged in a form of 3 rows and 4 columns. Third Variant of the Fourth Preferred Embodiment

[0088] 9 shows a plan view of a coherent detection array 430. The coherent detection array 430 is another variation of the coherent 400 detection array embodiment shown in FIG.

[0089] The coherent detection array 430 combines modifications made to the coherent detection array 400 in accordance with the coherent detection array 410 of Figure 7 and the coherent detection array 420 of Figure 8. The coherent detection array 430 may be understood with reference to the coherent detection arrays 410, 420 according to the embodiments shown in Figures 7 and 8, in conjunction with the following description.

[0090] On the other hand, like the coherent detection array 420, the coherent detection array 430 employs the coherent detection unit 310 according to the embodiment shown in Fig. 5 as a constituent unit of the detection array, instead of the coherent detection unit 300 used in the coherent detection arrays 400, 410. On the other hand, like the coherent detection array 410, the coherent detection array 430 can be configured such that either the electrode 35-1 or the electrode 35-2 of the photodetector 34 of the coherent detection unit 310 of each column of the detection array is connected to a row readout wiring that crosses the row of that column, and the other electrode of the photodetector 34 of the coherent detection unit 310 of each row of the detection array is connected to a row coding wiring that crosses the column of that row.

[0091] 9, the electrodes 35-2 of the photodetectors 34 of the coherent detection units 310-1, 310-5, and 310-9 in the first column are connected to the column readout wiring 43-1. Similarly, the electrodes 35-2 of the photodetectors 34 of the coherent detection units 310-2, 310-6, and 310-10 in the second column are connected to the column readout wiring 43-2, the electrodes 35-2 of the photodetectors 34 of the coherent detection units 310-3, 310-7, and 310-11 in the third column are connected to the column readout wiring 43-3, and the electrodes 35-2 of the photodetectors 34 of the coherent detection units 310-4, 310-8, and 310-12 in the fourth column are connected to the column readout wiring 43-4.

[0092] On the other hand, the electrodes 35-1 of the photodetectors 34 of the coherent detection units 310-1, 310-2, 310-3, and 310-4 in the first row are connected to row coding wiring 44-1. Similarly, the electrodes 35-1 of the photodetectors 34 of the coherent detection units 310-5, 310-6, 310-7, and 310-8 in the second row are connected to row coding wiring 44-2, and the electrodes 35-1 of the photodetectors 34 of the coherent detection units 310-9, 310-10, 310-11, and 310-12 in the third row are connected to row coding wiring 44-3. Fifth Preferred Embodiment

[0093] Four examples of coherent detection units 500, 510, 520, 530 according to the present preferred embodiment will now be described with reference to Figs.

[0094] FIG. 10 shows a plan view of a coherent detection unit 500. The coherent detection unit 500 shown in FIG. 10 is configured to include a polarization-separating free space-waveguide coupler 51, optical couplers 52-1, 52-2, 52-3, 52-4, waveguides 53-1, 53-2, 53-3, 53-4, 53-5, 53-6, 53-7, 53-8, photodetectors 54-1, 54-2, and electrodes 55-1, 55-2, 55-3, 55-4. The coherent detection unit 500 may also be configured to include additional components, such as one or more modulators and / or heaters, which may be used to modulate or change the properties of the coherent detection unit. These additional components are not shown in FIG. 10. The coherent detection unit 500 may be integrated on a substrate 56 using optical waveguide technology.

[0095] The coherent detection unit 500 is an improved version of the coherent detection unit 300 shown in FIG. 4. The coherent detection unit 500 is configured to detect an input signal light, which may be multiplexed with polarization in the x- and y-directions. The x- and y-directions are an example of an orthogonal basis of polarization defined by the design of the polarization-splitting free-space-to-waveguide coupler 51 so that the two polarization components may be measured separately. The coherent detection unit 500 may be understood with reference to the embodiment of the coherent detection unit 300 shown in FIG. 4 in conjunction with the following description.

[0096] The coherent detection unit 500 is configured by combining coherent detection subunits 301, 302 (see FIG. 10) similar to the coherent detection unit 300, but uses a polarization-separating free space-waveguide coupler 51 instead of the free space-waveguide coupler 31 of the coherent detection unit 300. The coherent detection subunit 301 is configured to include the polarization-separating free space-waveguide coupler 51, optical couplers 52-1, 52-2, waveguides 53-1, 53-2, 53-3, 53-4, a photodetector 54-1, and electrodes 55-1, 55-2. The coherent detection subunit 302 is configured to include an identical polarization-splitting free-space-to-waveguide coupler 51, optical couplers 52-3 and 52-4, waveguides 53-5, 53-6, 53-7, and 53-8, photodetector 54-2, and electrodes 55-3 and 55-4. In this configuration, the polarization-splitting free-space-to-waveguide coupler 51 is a common component of the two coherent detection subunits 301, 302.

[0097] In FIG. 10, the waveguide 53-1 transmits the local oscillator light E LO,in x and a local oscillator light E LO,out x The waveguide 53-5 has an end through which the local oscillator light E LO,in y is introduced into one end, and the local oscillator light E LO,out y and the other end through which E LO,in x and E LO,in y (The corresponding E LO,out x and E LO,out y ) may appear in the waveguides 53-1, 53-5 as identical guided modes, i.e., the fundamental TE mode that is commonly considered in photonic integrated circuits for optimal propagation and coupling efficiency. In other aspects, in terms of properties such as amplitude, frequency and phase, E LO,in x E LO,in y may be the same as or different from.

[0098] The coherent detection unit 500 detects the signal light E, which may contain multiplexed x- and y-polarizations, using a polarization-splitting free-space-to-waveguide coupler 51. Sig,in Receives signal light ESig,in may be received and separated into x- and y-polarized light by the polarization-splitting free space-waveguide coupler 51. On the one hand, the x-polarized light is conveyed to the coherent detection subunit 301 via the waveguide 53-3, and when detected by the photodetector 54-1, a photocurrent may be generated at the electrodes 55-1, 55-2. On the other hand, the y-polarized light is conveyed to the coherent detection subunit 302 via the waveguide 53-7, and when detected by the photodetector 54-2, a photocurrent may be generated at the electrodes 55-3, 55-4.

[0099] In some aspects, the photocurrent generated by each photodetector 54-1, 54-2 may include a direct component that varies slowly in time and a cross component that varies rapidly in time, and a noise component may also be present. Because the coherent detection unit 500 uses one photodetector per polarization, the photocurrent generated by the photodetectors 54-1, 54-2 may need to be filtered with an appropriate filter to suppress the direct component of the photocurrent. The filter may or may not be located in the detection unit. The filter is not shown in FIG. 10. First Variant of the Fifth Preferred Embodiment

[0100] 11 shows a plan view of a coherent detection unit 510. The coherent detection unit 510 shown in FIG. 11 is a modified example of the coherent detection unit 500 according to the embodiment shown in FIG.

[0101] 11 is similar to the coherent detection unit 500 of FIG. 10, except that the optical coupler 52-3 is moved to the waveguide 53-1 to couple the same local oscillator light from the waveguide 53-1 into the waveguide 53-6 that is coupled into the waveguide 53-2. In this way, the x-polarized and y-polarized components of the signal light coupled into the detection unit 510 are the same local oscillator light E LO,in The waveguide 53-5 may be omitted if necessary. Second Variant of the Fifth Preferred Embodiment

[0102] 12 shows a plan view of a coherent detection unit 520. The coherent detection unit 520 shown in FIG. 12 is another modified example of the coherent detection unit 500 according to the embodiment shown in FIG.

[0103] The coherent detection unit 520 shown in Fig. 12 is similar to the coherent detection unit shown in Fig. 10, but the coherent detection unit 520 is composed of a combination of coherent detection sub-units 311 and 312. These are similar to the coherent detection sub-units 301 and 302 in Fig. 10, but are essentially different in that, for simplification, the waveguides 53-2 and 53-6 are omitted, the optical couplers 52-1 and 52-2 are integrated into the optical coupler 52-5, and the optical couplers 52-3 and 52-4 are integrated into the optical coupler 52-6.

[0104] The optical coupler 52-5 of the coherent detection unit 520 of FIG. 12 serves as both the optical couplers 52-1 and 52-2 of the coherent detection unit 500 of FIG. 10, and similarly, the optical coupler 52-6 of the coherent detection unit 520 serves as both the optical couplers 52-3 and 52-4 of the coherent detection unit 500. In the coherent detection unit 520, the optical coupler 52-5 can directly mix the local oscillator light of the waveguide 53-1 with the signal light of the waveguide 53-3. The mixed light may be transmitted to the waveguide 53-4 and the output segment of the waveguide 53-1. Similarly, the optical coupler 52-6 may directly mix the local oscillator light of the waveguide 53-5 with the signal light of the waveguide 53-7. The mixed light may be transmitted to the waveguide 53-8 and the output segment of the waveguide 53-5.

[0105] In some aspects, optical coupler 52-5 of coherent detection unit 520 may be configured to transmit a majority portion of the signal light from waveguide 53-3 to waveguide 53-4 and a minor portion of the signal light from waveguide 53-3 to an output segment of waveguide 53-1. Similarly, optical coupler 52-6 of coherent detection unit 520 may be configured to transmit a majority portion of the signal light from waveguide 53-7 to waveguide 53-8 and a minor portion of the signal light from waveguide 53-7 to an output segment of waveguide 53-5. An example optical splitting ratio for optical couplers 52-5, 52-6 is 999:1. Third Variant of the Fifth Preferred Embodiment

[0106] 13 shows a plan view of a coherent detection unit 530. The coherent detection unit 530 shown in FIG. 13 is another modified example of the coherent detection unit 500 according to the embodiment shown in FIG.

[0107] The coherent detection unit 530 is a combination of modifications made to the coherent detection unit 500 according to the coherent detection unit 510 of Figure 11 and the coherent detection unit 520 of Figure 12. The coherent detection unit 530 may be understood with reference to the coherent detection units 510, 520 according to the embodiments shown in Figures 11 and 12, together with the following description.

[0108] On the other hand, similar to the coherent detection unit 520, the coherent detection unit 530 integrates the optical couplers 52-1 and 52-2 into a single optical coupler 52-5 and omits the waveguide 53-2 from the coherent detection unit 500 for simplicity (see FIG. 10). On the other hand, similar to the coherent detection unit 510, the coherent detection unit 530 moves the optical coupler 52-3 to the waveguide 53-1 to couple the same local oscillator light from the waveguide 53-1 to the waveguide 53-6 that is coupled to the waveguide 53-4. In this way, the x-polarized and y-polarized components of the signal light coupled to the detection unit 530 are the same local oscillator light E LO,inThe waveguide 53-5 may be omitted if necessary. Sixth Preferred Embodiment

[0109] Eight examples of coherent detection arrays 600, 610, 620, 630, 640, 650, 660, 670 according to the presently preferred embodiments will now be described with reference to Figures 14, 15, 16, 17, 18, 19, 20 and 21.

[0110] FIG. 14 illustrates a plan view of a coherent detection array 600. The coherent detection array 600 is configured to include multiple units of the coherent detection unit 500 according to the embodiment shown in FIG. 10. In some aspects, the coherent detection array 600 may include other embodiments of the coherent detection unit. In some aspects, the coherent detection array 600 may be configured by linking multiple units of the coherent detection unit 500 in a linear configuration. In other aspects, embodiments of the coherent detection array may be configured by linking multiple units of the coherent detection unit 500 in a geometric shape other than a linear configuration. The coherent detection array 600 may be integrated on the substrate 66 using optical waveguide technology.

[0111] The coherent detection array 600 shown in FIG. 14 is similar to the coherent detection array 200 shown in FIG. 2, but is essentially different in that the coherent detection unit 500 according to the embodiment shown in FIG. 10 is adopted as a component unit of the detection array instead of the coherent detection unit 100 used in the coherent detection array 200. In some aspects of the linear configuration, the coherent detection array may be configured with M rows and N columns of M×N coherent detection units. As an example, the embodiment of the coherent detection array 600 shown in FIG. 14 includes 12 coherent detection units 500-1, 500-2, 500-3, 500-4, 500-5, 500-6, 500-7, 500-8, 500-9, 500-10, 500-11, 500-12, all of which are coherent detection units 500 arranged in a form of 3 rows and 4 columns.

[0112] The coherent detection array 600 may be understood with reference to the embodiment of the coherent detection array 200 shown in FIG. 2, in conjunction with the following description.

[0113] In some aspects of the coherent detection unit 500 configured to detect incoming signal light that may be multiplexed with polarization in the x and y directions, each row of the coherent detection array 600 may be configured to include a row-coded waveguide for x-polarization and a row-coded waveguide for y-polarization, with separate LO light being introduced into each row-coded waveguide. The series of waveguides 53-1, 53-5 of a row of connected coherent detection units 500 of the coherent detection array 600 constitutes the row-coded waveguide for that row (see Figures 10 and 14). The LO light of the row-coded waveguide for x-polarization may be coupled to the connected coherent detection unit 500 via optical coupler 52-1, and the LO light of the row-coded waveguide for y-polarization may be coupled to the connected coherent detection unit 500 via optical coupler 52-3 (see Figures 10 and 14).

[0114] The electric field of the LO light introduced into the row-encoded waveguide of the coherent detector array is E LO,in mx and E LO,in my (m=1, 2, ..., M, where M is the number of rows in the detector array.) The corresponding transmitted LO field from the waveguide is E LO,out mx and E LO,out my The LO electric field E for different m LO,in mx and E LO,in my may have the same or different optical frequencies, the same or different magnitudes, and the same or different relative phases.

[0115] For the coherent detector array 600 shown in FIG. LO,in 1x and E LO,in 1y are introduced into the row coding waveguides 61-1 and 61-2 in the first row, respectively, and the LO electric field E LO,in 2x and E LO,in 2y are introduced into the row-encoded waveguides 61-3 and 61-4 in the second row, respectively, and the LO electric field E LO,in 3x and ELO,in 3y are introduced into the row coding waveguides 61-5 and 61-6 in the third row, respectively.

[0116] In some aspects, the coherent detection array according to the present preferred embodiment may be configured such that, for each column of coherent detection units, the electrodes 55-1 and 55-2 of the photodetector 54-1 and the electrodes 55-3 and 55-4 of the photodetector 54-2 are connected to separate column readout wiring. In other aspects, either the electrodes 55-1 or 55-2 of the photodetector 54-1 and either the electrodes 55-3 or 55-4 of the photodetector 54-2 may be connected to a common column readout wiring instead of separate column readout wiring.

[0117] 14, the electrodes 55-1 and 55-2 of the photodetector 54-1 are connected to the column readout wirings 62-1 and 63-1, respectively, and the electrodes 55-3 and 55-4 of the photodetector 54-2 are connected to the column readout wirings 64-1 and 65-1, respectively. Similarly, the electrodes 55-1 and 55-2 of the photodetector 54-1 are connected to the column readout wirings 62-2 and 63-2, respectively, and the electrodes 55-3 and 55-4 of the photodetector 54-2 are connected to the column readout wirings 64-2 and 65-2, respectively, for the coherent detection units 500-2, 500-6, and 500-10 of the second column. Similarly, for the coherent detection units 500-3, 500-7, and 500-11 in the third column, the electrodes 55-1 and 55-2 of the photodetector 54-1 are connected to the column readout wirings 62-3 and 63-3, respectively, and the electrodes 55-3 and 55-4 of the photodetector 54-2 are connected to the column readout wirings 64-3 and 65-3, respectively. Similarly, for the coherent detection units 500-4, 500-8, and 500-12 in the fourth column, the electrodes 55-1 and 55-2 of the photodetector 54-1 are connected to the column readout wirings 62-4 and 63-4, respectively, and the electrodes 55-3 and 55-4 of the photodetector 54-2 are connected to the column readout wirings 64-4 and 65-4, respectively.

[0118] As in FIG. 2, pads Pa in FIG. 14 are output terminals of column readout wiring that can be connected to peripheral readout circuits. First Variation of the Sixth Preferred Embodiment

[0119] FIG. 15 shows a plan view of a coherent detection array 610. The coherent detection array 610 is a variation of the coherent detection array 600 according to the embodiment shown in FIG. 14. Similar to the coherent detection array 600, the coherent detection array 610 can be configured to include multiple units of the coherent detection unit 500 according to the embodiment shown in FIG. 10. Each row of the coherent detection array 610 can be configured by connecting a series of coherent detection units 500 using a waveguide 53-1 (see FIG. 10). Multiple rows of coherent detection units 500 may be connected in series by electrical conductive paths to form a detection array. As an example, the embodiment of a coherent detection array 610 shown in FIG. 15 includes twelve coherent detection units 500-1, 500-2, 500-3, 500-4, 500-5, 500-6, 500-7, 500-8, 500-9, 500-10, 500-11, 500-12, all of which are coherent detection units 500 arranged in a configuration of three rows and four columns.

[0120] Similar to the coherent detection array 600, the coherent detection array 610 of the preferred embodiment may be configured such that, for each column of coherent detection units, either electrode 55-1 or electrode 55-2 of photodetector 54-1 is connected to a column readout wiring, and similarly, either electrode 55-3 or electrode 55-4 of photodetector 54-2 is connected to a column readout wiring.

[0121] Unlike the coherent detection unit 600, the coherent detection array 610 according to the preferred embodiment may be configured such that other electrodes of the photodetectors of the coherent detection unit are connected across different columns by row-coding wiring instead of across different rows by column readout wiring. For each row of the coherent detection unit 500 of the coherent detection array 610, either the electrode 55-1 or the electrode 55-2 of the photodetector 54-1 may be connected to a row-coding wiring, and similarly, either the electrode 55-3 or the electrode 55-4 of the photodetector 54-2 may be connected to a row-coding wiring. In some aspects, some row-coding wiring may be merged to simplify the layout.

[0122] Referring to the coherent detection array 600 shown in Fig. 15, in the first column of coherent detection units 500-1, 500-5, and 500-9, the electrode 55-2 of the photodetector 54-1 is connected to the column readout wiring 63-1, and the electrode 55-3 of the photodetector 54-2 is connected to the column readout wiring 64-1.

[0123] Similarly, for the coherent detection units 500-2, 500-6, and 500-10 in the second column, the electrode 55-2 of the photodetector 54-1 is connected to the column readout wiring 63-2, and the electrode 55-3 of the photodetector 54-2 is connected to the column readout wiring 64-2.

[0124] Similarly, for the coherent detection units 500-3, 500-7, and 500-11 in the third column, the electrode 55-2 of the photodetector 54-1 is connected to the column readout wiring 63-3, and the electrode 55-3 of the photodetector 54-2 is connected to the column readout wiring 64-3.

[0125] Similarly, for the coherent detection units 500-4, 500-8, and 500-12 in the fourth column, the electrode 55-2 of the photodetector 54-1 is connected to the column readout wiring 63-4, and the electrode 55-3 of the photodetector 54-2 is connected to the column readout wiring 64-4.

[0126] On the other hand, for the coherent detection units 500-1, 500-2, 500-3, and 500-4 in the first row, the electrode 55-1 of the photodetector 54-1 is connected to a row coding wiring 67-1, and the electrode 55-4 of the photodetector 54-2 is connected to a row coding wiring 68-1.

[0127] Similarly, for the coherent detection units 500-5, 500-6, 500-7, and 500-8 in the second row, electrode 55-1 of photodetector 54-1 is connected to row coding wiring 67-2, and electrode 55-4 of photodetector 54-2 is connected to row coding wiring 68-2.

[0128] Similarly, for the coherent detection units 500-9, 500-10, 500-11, and 500-12 in the third row, electrode 55-1 of photodetector 54-1 is connected to row coding wiring 67-3, and electrode 55-4 of photodetector 54-2 is connected to row coding wiring 68-3.

[0129] The pads Pa in FIG. 15 are terminals of column readout wiring and row coding wiring that can be connected to peripheral electrical circuitry. Second Variant of the Sixth Preferred Embodiment

[0130] 16 shows a plan view of a coherent detection array 620. The coherent detection array 620 is another variation of the coherent detection array 600 according to the embodiment shown in FIG.

[0131] The coherent detection array 620 shown in FIG. 16 is similar to the coherent detection array 600 shown in FIG. 14, but is essentially different in that the coherent detection unit 500 used in the coherent detection array 600 is replaced by the coherent detection unit 510 according to the embodiment shown in FIG. 11 as a constituent unit of the detection array. In some aspects of the linear configuration, the coherent detection array may be configured with M rows and N columns of M×N coherent detection units. As an example, the embodiment of the coherent detection array 620 shown in FIG. 16 includes 12 coherent detection units 510-1, 510-2, 510-3, 510-4, 510-5, 510-6, 510-7, 510-8, 510-9, 510-10, 510-11, 510-12, all of which are coherent detection units 510 arranged in a 3-row, 4-column format.

[0132] When the coherent detection unit 510 is used, the row-coded waveguides for x-polarization and y-polarization are integrated into one, and the same local oscillator light E LO,in m (m=1, 2, ..., M, where M is the number of rows) may be used for the two polarizations.

[0133] For the coherent detection array 620 shown in FIG. LO,in 1 is introduced into the row coding waveguide 61-1 in the first row, and the LO light E LO,in 2 is introduced into the row-encoded waveguide 61-3 in the second row, and the LO light E LO,in 3 is introduced into the row coding waveguide 61-5 of the third row. Third Variant of the Sixth Preferred Embodiment

[0134] 17 shows a plan view of a coherent detection array 630. The coherent detection array 630 is another variation of the coherent detection array 600 according to the embodiment shown in FIG.

[0135] The coherent detection array 630 combines modifications made to the coherent detection array 600 according to the coherent detection array 610 of Figure 15 and the coherent detection array 620 of Figure 16. The coherent detection array 630 may be understood with reference to the coherent detection arrays 610, 620 according to the embodiments shown in Figures 15 and 16, in conjunction with the following description.

[0136] On the other hand, similar to the coherent detection array 620, the coherent detection array 630 adopts a coherent detection unit 510 according to the embodiment shown in FIG. 11 as a constituent unit of the detection array instead of the coherent detection unit 500 used in the coherent detection arrays 600 and 610.

[0137] When the coherent detection unit 510 is used, the row-coded waveguides for x-polarization and y-polarization are integrated into one, and the same local oscillator light E LO,in m (m=1, 2, ..., M, where M is the number of rows) may be used for the two polarizations.

[0138] For the coherent detection array 630 shown in FIG. LO,in 1 is introduced into the row coding waveguide 61-1 in the first row, and the LO light E LO,in 2 is introduced into the row-encoded waveguide 61-3 in the second row, and the LO light E LO,in 3 is introduced into the row coding waveguide 61-5 of the third row.

[0139] On the other hand, similar to the coherent detection array 610, the coherent detection array 630 may be configured such that for each column of coherent detection units 510 of the detection array, either electrode 55-1 or electrode 55-2 of photodetector 54-1 is connected to a column readout wiring across the row of that column, and either electrode 55-3 or electrode 55-4 of photodetector 54-2 is connected to a column readout wiring across the row of that column, while the other electrodes of photodetectors 54-1, 54-2 of the coherent detection units 510 of each row of the detection array may be connected to row coding wiring across the columns of that row, or to a common row coding wiring.

[0140] Please refer to the coherent detection array 630 shown in Fig. 17. On the other hand, for the coherent detection units 510-1, 510-5, and 510-9 in the first column, the electrode 55-2 of the photodetector 54-1 is connected to the column readout wiring 63-1, and the electrode 55-3 of the photodetector 54-2 is connected to the column readout wiring 64-1.

[0141] Similarly, for the coherent detection units 510-2, 510-6, and 510-10 in the second column, the electrode 55-2 of the photodetector 54-1 is connected to the column readout wiring 63-2, and the electrode 55-3 of the photodetector 54-2 is connected to the column readout wiring 64-2.

[0142] Similarly, for the coherent detection units 510-3, 510-7, and 510-11 in the third column, the electrode 55-2 of the photodetector 54-1 is connected to the column readout wiring 63-3, and the electrode 55-3 of the photodetector 54-2 is connected to the column readout wiring 64-3.

[0143] Similarly, for the coherent detection units 510-4, 510-8, and 510-12 in the fourth column, the electrode 55-2 of the photodetector 54-1 is connected to the column readout wiring 63-4, and the electrode 55-3 of the photodetector 54-2 is connected to the column readout wiring 64-4.

[0144] On the other hand, for the coherent detection units 510-1, 510-2, 510-3, and 510-4 in the first row, the electrode 55-1 of the photodetector 54-1 is connected to a row coding wiring 67-1, and the electrode 55-4 of the photodetector 54-2 is connected to a row coding wiring 68-1.

[0145] Similarly, for the coherent detection units 510-5, 510-6, 0-751, and 510-8 in the second row, electrode 55-1 of photodetector 54-1 is connected to row coding wiring 67-2, and electrode 55-4 of photodetector 54-2 is connected to row coding wiring 68-2.

[0146] Similarly, for the coherent detection units 510-9, 510-10, 510-11, and 510-12 in the third row, electrode 55-1 of photodetector 54-1 is connected to row coding wiring 67-3, and electrode 55-4 of photodetector 54-2 is connected to row coding wiring 68-3. Fourth Variant of the Sixth Preferred Embodiment

[0147] 18 shows a plan view of a coherent detection array 640. The coherent detection array 640 is another variation of the coherent detection array 600 embodiment shown in FIG.

[0148] The coherent detection array 640 shown in FIG. 18 is similar to the coherent detection array 600 shown in FIG. 14, but is essentially different in that the coherent detection unit 520 according to the embodiment shown in FIG. 12 is adopted as a constituent unit of the detection array instead of the coherent detection unit 500 used in the coherent detection array 600. In some aspects of the linear configuration, the coherent detection array may be configured with M rows and N columns of M×N coherent detection units. As an example, the embodiment of the coherent detection array 640 shown in FIG. 18 includes 12 coherent detection units 520-1, 520-2, 520-3, 520-4, 520-5, 520-6, 520-7, 520-8, 520-9, 520-10, 520-11, 520-12, all of which are coherent detection units 520 arranged in a 3-row, 4-column format. Fifth Variation of the Sixth Preferred Embodiment

[0149] 19 shows a plan view of a coherent detection array 650. The coherent detection array 650 is another variation of the coherent detection array 600 embodiment shown in FIG.

[0150] The coherent detection array 650 combines modifications made to the coherent detection array 600 in accordance with the coherent detection array 610 of Figure 15 and the coherent detection array 640 of Figure 18. The coherent detection array 650 may be understood with reference to the coherent detection arrays 610, 640 shown in Figures 15 and 18, in conjunction with the following description.

[0151] On the other hand, like the coherent detection array 640, the coherent detection array 650 employs a coherent detection unit 520 according to the embodiment shown in FIG. 12 as a constituent unit of the detection array, instead of the coherent detection unit 500 used in the coherent detection arrays 600 and 610.

[0152] On the other hand, similar to the coherent detection array 610, the coherent detection array 650 may be configured such that for each column of coherent detection units 520 of the detection array, either electrode 55-1 or electrode 55-2 of photodetector 54-1 is connected to a column readout wiring across the row of that column, and either electrode 55-3 or electrode 55-4 of photodetector 54-2 is connected to a column readout wiring across the row of that column. Meanwhile, the other electrodes of photodetectors 54-1, 54-2 of the coherent detection units 520 of each row of the detection array may be connected to a row readout wiring across the column of that row, or to a common row readout wiring.

[0153] Please refer to the coherent detection array 650 shown in Fig. 19. On the other hand, for the coherent detection units 520-1, 520-5, and 520-9 in the first column, the electrode 55-2 of the photodetector 54-1 is connected to the column readout wiring 63-1, and the electrode 55-3 of the photodetector 54-2 is connected to the column readout wiring 64-1.

[0154] Similarly, for the coherent detection units 520-2, 520-6, and 520-10 in the second column, the electrode 55-2 of the photodetector 54-1 is connected to the column readout wiring 63-2, and the electrode 55-3 of the photodetector 54-2 is connected to the column readout wiring 64-2.

[0155] Similarly, for the coherent detection units 520-3, 520-7, and 520-11 in the third column, the electrode 55-2 of the photodetector 54-1 is connected to the column readout wiring 63-3, and the electrode 55-3 of the photodetector 54-2 is connected to the column readout wiring 64-3.

[0156] Similarly, for the coherent detection units 520-4, 520-8, and 520-12 in the fourth column, the electrode 55-2 of the photodetector 54-1 is connected to the column readout wiring 63-4, and the electrode 55-3 of the photodetector 54-2 is connected to the column readout wiring 64-4.

[0157] On the other hand, for the coherent detection units 520-1, 520-2, 520-3, and 520-4 in the first row, the electrode 55-1 of the photodetector 54-1 is connected to a row coding wiring 67-1, and the electrode 55-4 of the photodetector 54-2 is connected to a row coding wiring 68-1.

[0158] Similarly, for the coherent detection units 520-5, 520-6, 520-7, and 520-8 in the second row, electrode 55-1 of photodetector 54-1 is connected to row coding wiring 67-2, and electrode 55-4 of photodetector 54-2 is connected to row coding wiring 68-2.

[0159] Similarly, for the coherent detection units 520-9, 520-10, 520-11, and 520-12 in the third row, electrode 55-1 of photodetector 54-1 is connected to row coding wiring 67-3, and electrode 55-4 of photodetector 54-2 is connected to row coding wiring 68-3. Sixth Variation of the Sixth Preferred Embodiment

[0160] 20 shows a plan view of a coherent detection array 660. The coherent detection array 660 is another variation of the coherent detection array 600 according to the embodiment shown in FIG.

[0161] The coherent detection array 660 shown in FIG. 20 is similar to the coherent detection array 600 shown in FIG. 14, but is essentially different in that the coherent detection unit 530 according to the embodiment shown in FIG. 13 is adopted as a constituent unit of the detection array instead of the coherent detection unit 500 used in the coherent detection array 600. In some aspects of the linear configuration, the coherent detection array may be configured with M rows and N columns of M×N coherent detection units. As an example, the embodiment of the coherent detection array 660 shown in FIG. 20 includes 12 coherent detection units 530-1, 530-2, 530-3, 530-4, 530-5, 530-6, 530-7, 530-8, 530-9, 530-10, 530-11, 530-12, all of which are coherent detection units 530 arranged in a form of 3 rows and 4 columns.

[0162] When a coherent detection unit 530 is used, the row-coded waveguides for x-polarization and y-polarization are integrated into one, and the same local oscillator light E LO,in m (m=1, 2, ..., M, where M is the number of rows) may be used for the two polarizations.

[0163] For the coherent detection array 660 shown in FIG. LO,in 1 is introduced into the row coding waveguide 61-1 in the first row, and the LO light E LO,in 2 is introduced into the row-encoded waveguide 61-3 in the second row, and the LO light E LO,in 3 is introduced into the row coding waveguide 61-5 of the third row. Seventh Variation of the Sixth Preferred Embodiment

[0164] 21 shows a plan view of a coherent detection array 670. The coherent detection array 670 is another variation of the coherent detection array 600 embodiment shown in FIG.

[0165] The coherent detection array 670 combines modifications made to the coherent detection array 600 according to the coherent detection array 610 of Figure 15 and the coherent detection array 660 of Figure 20. The coherent detection array 670 may be understood with reference to the coherent detection arrays 610, 660 according to the embodiments shown in Figures 15 and 20, together with the following description.

[0166] On the other hand, like the coherent detection array 660, the coherent detection array 670 employs a coherent detection unit 530 according to the embodiment shown in FIG. 13 as a constituent unit of the detection array, instead of the coherent detection unit 500 used in the coherent detection arrays 600 and 610.

[0167] When a coherent detection unit 530 is used, the row-coded waveguides for x-polarization and y-polarization are integrated into one, and the same local oscillator light E LO,in m (m=1, 2, ..., M, where M is the number of rows) may be used for the two polarizations.

[0168] For the coherent detection array 670 shown in FIG. LO,in 1 is introduced into the row coding waveguide 61-1 in the first row, and the LO light E LO,in 2 is introduced into the row-encoded waveguide 61-3 in the second row, and the LO light E LO,in 3 is introduced into the row coding waveguide 61-5 of the third row.

[0169] On the other hand, similar to the coherent detection array 610, the coherent detection array 670 may be configured such that for each column of coherent detection units 530 of the detection array, either electrode 55-1 or electrode 55-2 of photodetector 54-1 is connected to a column readout wiring across the row of that column, and either electrode 55-3 or electrode 55-4 of photodetector 54-2 is connected to a column readout wiring across the row of that column, while the other electrodes of photodetectors 54-1, 54-2 of the coherent detection units 530 of each row of the detection array may be connected to row coding wiring across the columns of that row, or to a common row coding wiring.

[0170] Please refer to the coherent detection array 670 shown in Fig. 21. On the other hand, for the coherent detection units 530-1, 530-5, and 530-9 in the first column, the electrode 55-2 of the photodetector 54-1 is connected to the column readout wiring 63-1, and the electrode 55-3 of the photodetector 54-2 is connected to the column readout wiring 64-1.

[0171] Similarly, for the coherent detection units 530-2, 530-6, and 530-10 in the second column, the electrode 55-2 of the photodetector 54-1 is connected to the column readout wiring 63-2, and the electrode 55-3 of the photodetector 54-2 is connected to the column readout wiring 64-2.

[0172] Similarly, for the coherent detection units 530-3, 530-7, and 530-11 in the third column, the electrode 55-2 of the photodetector 54-1 is connected to the column readout wiring 63-3, and the electrode 55-3 of the photodetector 54-2 is connected to the column readout wiring 64-3.

[0173] Similarly, for the coherent detection units 530-4, 530-8, and 530-12 in the fourth column, the electrode 55-2 of the photodetector 54-1 is connected to the column readout wiring 63-4, and the electrode 55-3 of the photodetector 54-2 is connected to the column readout wiring 64-4.

[0174] On the other hand, for the coherent detection units 530-1, 530-2, 530-3, and 530-4 in the first row, the electrode 55-1 of the photodetector 54-1 is connected to a row coding wiring 67-1, and the electrode 55-4 of the photodetector 54-2 is connected to a row coding wiring 68-1.

[0175] Similarly, for the coherent detection units 530-5, 530-6, 530-7, and 530-8 in the second row, electrode 55-1 of photodetector 54-1 is connected to row coding wiring 67-2, and electrode 55-4 of photodetector 54-2 is connected to row coding wiring 68-2.

[0176] Similarly, for the coherent detection units 530-9, 530-10, 530-11, and 530-12 in the third row, the electrode 55-1 of the photodetector 54-1 is connected to a row coding wiring 67-3, and the electrode 55-4 of the photodetector 54-2 is connected to a row coding wiring 68-3. Seventh Preferred Embodiment

[0177] Two examples of coherent detection units 700, 710 according to the presently preferred embodiment will now be described with reference to Figs.

[0178] 22 shows a plan view of a coherent detection unit 700. The coherent detection unit 700 shown in FIG. 22 can be configured to include a polarization-separating free space-waveguide coupler 71, optical couplers 72-1, 72-2, 72-3, 72-4, waveguides 73-1, 73-2, 73-3, 73-4, 73-5, 73-6, 73-7, 73-8, 73-9, 73-10, photodetectors 74-1, 74-2, 74-3, 74-4, and electrodes 75-1, 75-2, 75-3, 75-4, 75-5, 75-6, 75-7, 75-8. The coherent detection unit 700 may also be configured to include additional components, such as one or more modulators and / or heaters, which may be used to modulate or change the characteristics of the coherent detection unit. These additional components are not shown in Figure 22. The coherent detection unit 700 may be integrated on the substrate 76 using optical waveguide technology.

[0179] The coherent detection unit 700 is an improved version of the coherent detection unit 100 shown in Fig. 1. The coherent detection unit 700 is configured to detect incident signal light, which may be multiplexed with polarizations in the x and y directions so that the two polarization components can be measured separately. The coherent detection unit 700 may be understood with reference to the embodiment of the coherent detection unit 100 shown in Fig. 1 in conjunction with the following description.

[0180] The coherent detection unit 700 is configured by combining coherent detection subunits 101 and 102 (see FIG. 22). Each is similar to the coherent detection unit 100, but a polarization-separating free space-waveguide coupler 71 is used instead of the free space-waveguide coupler 11 of the coherent detection unit 100. The coherent detection subunit 101 is configured to include the polarization-separating free space-waveguide coupler 71, optical couplers 72-1 and 72-2, waveguides 73-1, 73-2, 73-3, 73-4, and 73-5, photodetectors 74-1 and 74-2, and electrodes 75-1, 75-2, 75-3, and 75-4. The coherent detection subunit 102 is configured to include an identical polarization-splitting free-space-to-waveguide coupler 71, optical couplers 72-3, 72-4, waveguides 73-6, 73-7, 73-8, 73-9, 73-10, photodetectors 74-3, 74-4, and electrodes 75-5, 75-6, 75-7, 75-8. In this configuration, the polarization-splitting free-space-to-waveguide coupler 71 is a common component of the two coherent detection subunits 101, 102.

[0181] In FIG. 22, the waveguide 73-1 transmits the local oscillator light E LO,in x and a local oscillator light E LO,out x The waveguide 73-10 has an end through which the local oscillator light E LO,in y and a local oscillator light E LO,out y and the other end through which the optical fiber can be transmitted.

[0182] The coherent detection unit 700 detects the signal light E, which may contain multiplexed x- and y-polarizations, using a polarization-splitting free-space-to-waveguide coupler 71. Sig,in Receives signal light E Sig,inmay be received by the polarization-splitting free space-waveguide coupler 71 and separated into x- and y-polarized light. On the one hand, the x-polarized light is conveyed to the coherent detection subunit 101 via the waveguide 73-3 and may generate photocurrents at the electrodes 75-1, 75-2, 75-3, and 75-4 when detected by the photodetectors 74-1 and 74-2. On the other hand, the y-polarized light is conveyed to the coherent detection subunit 102 via the waveguide 73-7 and may generate photocurrents at the electrodes 75-5, 75-6, 75-7, and 75-8 when detected by the photodetectors 74-3 and 74-4. Variations of the Seventh Preferred Embodiment

[0183] 23 shows a plan view of a coherent detection unit 710. The coherent detection unit 710 shown in FIG. 23 is a modified example of the coherent detection unit 700 according to the embodiment shown in FIG.

[0184] 23 is similar to the coherent detection unit 700 of FIG. 22, except that the optical coupler 72-3 is moved to the waveguide 73-1 to couple the same local oscillator light from the waveguide 73-1 into the waveguide 73-6 that is coupled into the waveguide 73-2. In this way, the x-polarized and y-polarized components of the signal light coupled into the detection unit 710 are the same local oscillator light E LO,in The waveguide 73-10 may be omitted if necessary. Eighth Preferred Embodiment

[0185] Four examples of coherent detection arrays 800, 810, 820, 830 according to the presently preferred embodiments will now be described with reference to FIGS.

[0186] FIG. 24 illustrates a plan view of a coherent detection array 800. The coherent detection array 800 is configured to include multiple units of the coherent detection unit 700 according to the embodiment shown in FIG. 22. In some aspects, the coherent detection array 800 may include other embodiments of the coherent detection unit. In some aspects, the coherent detection array 800 may be configured by linking multiple units of the coherent detection unit 700 in a linear configuration. In other aspects, embodiments of the coherent detection array may be configured by linking multiple units of the coherent detection unit 700 in a geometric shape other than a linear configuration. The coherent detection array 800 may be integrated on the substrate 86 using optical waveguide technology.

[0187] The coherent detection array 800 shown in FIG. 24 is similar to the coherent detection array 200 shown in FIG. 2, but is essentially different in that the coherent detection unit 700 according to the embodiment shown in FIG. 22 is adopted as a constituent unit of the detection array instead of the coherent detection unit 100 used in the coherent detection array 200. In some aspects of the linear configuration, the coherent detection array may be configured with M rows and N columns of M×N coherent detection units. As an example, the embodiment of the coherent detection array 800 shown in FIG. 24 includes six coherent detection units 700-1, 700-2, 700-3, 700-4, 700-5, 700-6, all of which are coherent detection units 700 arranged in a form of two rows and three columns.

[0188] The coherent detection array 800 may be understood with reference to the embodiment of the coherent detection array 200 shown in FIG. 2, in conjunction with the following description.

[0189] In some aspects of the coherent detection unit 700 configured to detect incoming signal light that may be multiplexed with polarizations in the x and y directions, each row of the coherent detection array 800 may be configured to include a row-coded waveguide for x-polarization and a row-coded waveguide for y-polarization, with separate LO light being introduced into each row-coded waveguide. The series of waveguides 73-1, 73-10 of a row of connected coherent detection units 700 of the coherent detection array 800 constitutes the row-coded waveguide for that row (see Figures 22 and 24). The LO light of the row-coded waveguide for x-polarization may be coupled to the connected coherent detection unit 700 via optical coupler 72-1, and the LO light of the row-coded waveguide for y-polarization may be coupled to the connected coherent detection unit 700 via optical coupler 72-3 (see Figures 22 and 24).

[0190] The electric field of the LO light introduced into the row-encoded waveguide of the coherent detector array is E LO,in mx and E LO,in my (m=1, 2, ..., M, where M is the number of rows in the detector array.) The corresponding transmitted LO field from the waveguide is E LO,out mx and E LO,out my The LO electric field E for different m LO,in mx and E LO,in my may have the same or different optical frequencies, the same or different magnitudes, and the same or different relative phases.

[0191] For the coherent detector array 800 shown in FIG. LO,in 1x and E LO,in 1y are introduced into the row-encoded waveguides 81-1 and 81-2 in the first row, respectively, and the LO electric field E LO,in 2x and E LO,in 2y are introduced into the row coding waveguides 81-3 and 81-4 of the second row, respectively.

[0192] In some aspects, the coherent detection array according to the preferred embodiment may be configured such that, for each column of coherent detection units, the electrodes 75-1 and 75-2 of the photodetector 74-1, the electrodes 75-3 and 75-4 of the photodetector 74-2, the electrodes 75-5 and 75-6 of the photodetector 74-3, and the electrodes 75-7 and 75-8 of the photodetector 74-4 are connected to individual column readout wiring. In other aspects, either the electrode 75-1 or the electrode 75-2 of the photodetector 74-1 and either the electrode 75-3 or the electrode 75-4 of the photodetector 74-2 may be connected to a common column readout wiring instead of individual column readout wiring. Either the electrode 75-5 or the electrode 75-6 of the photodetector 74-3 and either the electrode 75-7 or the electrode 75-8 of the photodetector 74-4 may be connected to a common column readout wiring instead of individual column readout wiring. In a further aspect, some column readout wiring may be consolidated to simplify the layout.

[0193] 24, the electrode 75-1 of the photodetector 74-1 is connected to the column readout wiring 82-1, the electrode 75-3 of the photodetector 74-2 is connected to the column readout wiring 83-1, the electrode 75-5 of the photodetector 74-3 is connected to the column readout wiring 88-1, and the electrode 75-7 of the photodetector 74-4 is connected to the column readout wiring 89-1. The electrode 75-2 of the photodetector 74-1 and the electrode 75-4 of the photodetector 74-2 are connected to a common column readout wiring 84-1, and the electrode 75-6 of the photodetector 74-3 and the electrode 75-8 of the photodetector 74-4 are connected to a common column readout wiring 87-1.

[0194] Similarly, for the second column of coherent detection units 700-2 and 700-5, the electrode 75-1 of the photodetector 74-1 is connected to the column readout wiring 82-2, the electrode 75-3 of the photodetector 74-2 is connected to the column readout wiring 83-2, the electrode 75-5 of the photodetector 74-3 is connected to the column readout wiring 88-2, and the electrode 75-7 of the photodetector 74-4 is connected to the column readout wiring 89-2. Also, the electrode 75-2 of the photodetector 74-1 and the electrode 75-4 of the photodetector 74-2 are connected to a common column readout wiring 84-2, and the electrode 75-6 of the photodetector 74-3 and the electrode 75-8 of the photodetector 74-4 are connected to a common column readout wiring 87-2.

[0195] Similarly, for the third column of coherent detection units 700-3 and 700-6, the electrode 75-1 of the photodetector 74-1 is connected to the column readout wiring 82-3, the electrode 75-3 of the photodetector 74-2 is connected to the column readout wiring 83-3, the electrode 75-5 of the photodetector 74-3 is connected to the column readout wiring 88-3, and the electrode 75-7 of the photodetector 74-4 is connected to the column readout wiring 89-3. Also, the electrode 75-2 of the photodetector 74-1 and the electrode 75-4 of the photodetector 74-2 are connected to a common column readout wiring 84-3, and the electrode 75-6 of the photodetector 74-3 and the electrode 75-8 of the photodetector 74-4 are connected to a common column readout wiring 87-3.

[0196] As in FIG. 2, pads Pa in FIG. 24 are output terminals of column readout wiring that can be connected to peripheral readout circuits. First Variation of the Eighth Preferred Embodiment

[0197] FIG. 25 shows a plan view of a coherent detection array 810. The coherent detection array 810 is a variation of the embodiment of the coherent detection array 800 shown in FIG. 24. Similar to the coherent detection array 800, the coherent detection array 810 can be configured to include multiple units of the coherent detection unit 700 according to the embodiment shown in FIG. 22. Each row of the coherent detection array 810 can be configured by connecting a series of coherent detection units 700 using a waveguide 73-1 (see FIG. 22). Multiple rows of coherent detection units 700 may be connected in series by electrical conductive paths to form a detection array. As an example, the embodiment of the coherent detection array 810 shown in FIG. 25 includes six coherent detection units 700-1, 700-2, 700-3, 700-4, 700-5, 700-6, all of which are coherent detection units 700 arranged in a two-row, three-column format.

[0198] Similar to the coherent detection array 800, the coherent detection array 810 of the preferred embodiment may be configured such that, for each column of coherent detection units, either electrode 75-1 or electrode 75-2 of photodetector 74-1 is connected to a column readout wiring, either electrode 75-3 or electrode 75-4 of photodetector 74-2 is connected to a column readout wiring, either electrode 75-5 or electrode 75-6 of photodetector 74-3 is connected to a column readout wiring, and either electrode 75-7 or electrode 75-8 of photodetector 74-4 is connected to a column readout wiring.

[0199] Unlike the coherent detection array 800, the coherent detection array 810 of the preferred embodiment may be configured such that other electrodes of the photodetectors of the coherent detection units are connected across different columns by row-coding wiring instead of across different rows by column readout wiring. In some aspects, for each row of coherent detection units 700 of the coherent detection array 810, either electrode 75-1 or electrode 75-2 of photodetector 74-1 may be connected to a row-coding wiring, either electrode 75-3 or electrode 75-4 of photodetector 74-2 may be connected to a row-coding wiring, either electrode 75-5 or electrode 75-6 of photodetector 74-3 may be connected to a row-coding wiring, and either electrode 75-7 or electrode 75-8 of photodetector 74-4 may be connected to a row-coding wiring. In other aspects, either electrode 75-1 or electrode 75-2 of photodetector 74-1 and either electrode 75-3 or electrode 75-4 of photodetector 74-2 may be connected to a common row coding wire instead of separate row coding wires, and either electrode 75-5 or electrode 75-6 of photodetector 74-3 and either electrode 75-7 or electrode 75-8 of photodetector 74-4 may be connected to a common row coding wire instead of separate row coding wires. In further aspects, some row coding wires may be merged and / or some column readout wires may be merged to simplify the layout.

[0200] 25, the coherent detection array 810 is shown. On the other hand, for the first column of coherent detection units 700-1 and 700-4, the electrode 75-1 of the photodetector 74-1 is connected to the column readout wiring 82-1, the electrode 75-3 of the photodetector 74-2 is connected to the column readout wiring 83-1, the electrode 75-5 of the photodetector 74-3 is connected to the column readout wiring 88-1, and the electrode 75-7 of the photodetector 74-4 is connected to the column readout wiring 89-1.

[0201] Similarly, for the second row of coherent detection units 700-2 and 700-5, electrode 75-1 of photodetector 74-1 is connected to column readout wiring 82-2, electrode 75-3 of photodetector 74-2 is connected to column readout wiring 83-2, electrode 75-5 of photodetector 74-3 is connected to column readout wiring 88-2, and electrode 75-7 of photodetector 74-4 is connected to column readout wiring 89-2.

[0202] Similarly, for the third column of coherent detection units 700-3 and 700-6, electrode 75-1 of photodetector 74-1 is connected to column readout wiring 82-3, electrode 75-3 of photodetector 74-2 is connected to column readout wiring 83-3, electrode 75-5 of photodetector 74-3 is connected to column readout wiring 88-3, and electrode 75-7 of photodetector 74-4 is connected to column readout wiring 89-3.

[0203] On the other hand, for the coherent detection units 700-1, 700-2, and 700-3 in the first row, electrode 75-2 of photodetector 74-1 and electrode 75-4 of photodetector 74-2 are connected to a common row coding wiring 811-1, and electrode 75-6 of photodetector 74-3 and electrode 75-8 of photodetector 74-4 are connected to a common row coding wiring 812-1.

[0204] Similarly, for the second row of coherent detection units 700-4, 700-5, and 700-6, electrode 75-2 of photodetector 74-1 and electrode 75-4 of photodetector 74-2 are connected to a common row coding wiring 811-2, and electrode 75-6 of photodetector 74-3 and electrode 75-8 of photodetector 74-4 are connected to a common row coding wiring 812-2.

[0205] The pads Pa in FIG. 25 are terminals of column readout wiring and row coding wiring that can be connected to peripheral electrical circuitry. Second Variant of the Eighth Preferred Embodiment

[0206] 26 shows a plan view of a coherent detection array 820. The coherent detection array 820 is another variation of the coherent detection array 800 according to the embodiment shown in FIG.

[0207] The coherent detection array 820 shown in FIG. 26 is similar to the coherent detection array 800 shown in FIG. 24, but is essentially different in that the coherent detection unit 700 used in the coherent detection array 800 is replaced by the coherent detection unit 710 according to the embodiment shown in FIG. 23 as a constituent unit of the detection array. In some aspects of the linear configuration, the coherent detection array may be configured with M rows and N columns of M×N coherent detection units. As an example, the embodiment of the coherent detection array 820 shown in FIG. 26 includes six coherent detection units 710-1, 710-2, 710-3, 710-4, 710-5, 710-6, all of which are coherent detection units 710, arranged in a two-row, three-column format.

[0208] When the coherent detection unit 710 is used, the row-coded waveguides for x-polarization and y-polarization are integrated into one, and the same local oscillator light E LO,in m (m=1, 2, ..., M, where M is the number of rows) may be used for the two polarizations.

[0209] For the coherent detection array 820 shown in FIG. LO,in 1 is introduced into the row coding waveguide 81-1 in the first row, and the LO light E LO,in 2 is introduced into the row coding waveguide 81-3 of the second row. Third Variant of the Eighth Preferred Embodiment

[0210] 27 shows a plan view of a coherent detection array 830. The coherent detection array 830 is another variation of the coherent detection array 800 according to the embodiment shown in FIG.

[0211] The coherent detection array 830 combines modifications made to the coherent detection array 800 according to the coherent detection array 810 of Figure 25 and the coherent detection array 820 of Figure 26. The coherent detection array 830 may be understood with reference to the coherent detection arrays 810, 820 according to the embodiments shown in Figures 25 and 26, in conjunction with the following description.

[0212] On the other hand, like the coherent detection array 820, the coherent detection array 830 adopts the coherent detection unit 710 of the embodiment shown in FIG. 23 as a constituent unit of the detection array instead of the coherent detection unit 700 used in the coherent detection arrays 800 and 810.

[0213] When the coherent detection unit 710 is used, the row-coded waveguides for x-polarization and y-polarization are integrated into one, and the same local oscillator light E LO,in m (m=1, 2, ..., M, where M is the number of rows) may be used for the two polarizations.

[0214] For the coherent detection array 830 shown in FIG. LO,in 1 is introduced into the row coding waveguide 81-1 in the first row, and the LO light E LO,in 2 is introduced into the row coding waveguide 81-3 of the second row.

[0215] On the other hand, similar to the coherent detection array 810, the coherent detection array 830 may be configured such that for the coherent detection units 710 in each column of the detection array, either the electrode 75-1 or the electrode 75-2 of the photodetector 74-1 is connected to a column readout wiring, either the electrode 75-3 or the electrode 75-4 of the photodetector 74-2 is connected to a column readout wiring, either the electrode 75-5 or the electrode 75-6 of the photodetector 74-3 is connected to a column readout wiring, and either the electrode 75-7 or the electrode 75-8 of the photodetector 74-4 is connected to a column readout wiring. Meanwhile, the other electrodes of the photodetectors 74-1, 74-2, 74-3, 74-4 of the coherent detection units 710 in each row of the detection array may be connected to row coding wiring that crosses the columns of that row. In some aspects, some row coding wiring may be merged and / or some column readout wiring may be merged to simplify the layout.

[0216] Refer to the coherent detection array 830 shown in Fig. 27. On the other hand, for the first column of coherent detection units 710-1 and 710-4, the electrode 75-1 of the photodetector 74-1 is connected to the column readout wiring 82-1, the electrode 75-3 of the photodetector 74-2 is connected to the column readout wiring 83-1, the electrode 75-5 of the photodetector 74-3 is connected to the column readout wiring 88-1, and the electrode 75-7 of the photodetector 74-4 is connected to the column readout wiring 89-1.

[0217] Similarly, for the second row of coherent detection units 710-2 and 710-5, electrode 75-1 of photodetector 74-1 is connected to column readout wiring 82-2, electrode 75-3 of photodetector 74-2 is connected to column readout wiring 83-2, electrode 75-5 of photodetector 74-3 is connected to column readout wiring 88-2, and electrode 75-7 of photodetector 74-4 is connected to column readout wiring 89-2.

[0218] Similarly, for the third column of coherent detection units 710-3 and 710-6, electrode 75-1 of photodetector 74-1 is connected to column readout wiring 82-3, electrode 75-3 of photodetector 74-2 is connected to column readout wiring 83-3, electrode 75-5 of photodetector 74-3 is connected to column readout wiring 88-3, and electrode 75-7 of photodetector 74-4 is connected to column readout wiring 89-3.

[0219] On the other hand, for the coherent detection units 710-1, 0-271, and 710-3 in the first row, electrode 75-2 of photodetector 74-1 and electrode 75-4 of photodetector 74-2 are connected to a common row coding wiring 811-1, and electrode 75-6 of photodetector 74-3 and electrode 75-8 of photodetector 74-4 are connected to a common row coding wiring 812-1.

[0220] Similarly, for the second row of coherent detection units 710-4, 710-5, and 710-6, electrode 75-2 of photodetector 74-1 and electrode 75-4 of photodetector 74-2 are connected to a common row coding wiring 811-2, and electrode 75-6 of photodetector 74-3 and electrode 75-8 of photodetector 74-4 are connected to a common row coding wiring 812-2. Multiplexing method

[0221] In the following, a signal multiplexing method that may be applied to the coherent detection array of the present invention will be described. In some aspects, the signal multiplexing method may be applied to the configuration embodiment of the coherent detection array of the present invention. In other aspects, the signal multiplexing method may be applied to other detection array configurations and designs not mentioned.

[0222] Signal multiplexing methods include those that exploit the high degree of flexibility of coherent detector arrays. These multiplexing methods can be categorized into optical and electrical domains. These methods may include those realized by local oscillators and those related to the properties and responses of the components of PIC-type detector arrays.

[0223] Multiplexing in the optical domain can involve the manipulation of the local oscillator and optical waveguide properties of the detector array. Multiplexing via LO is possible by controlling the amplitude, frequency and phase of the LO light at each detector unit or group of detector units of the detector array. The generated photocurrents can be multiplexed to form a multiplexed electrical readout signal. Also, the amplitude, frequency and phase of the LO of the detector units may be modulated in time so that the multiplexed electrical readout signal varies in time accordingly.

[0224] Multiplexing through the detector array's waveguides can be achieved by electrically, thermally, or optically controlling the refractive index of the detector array's waveguides. Electrical control of the refractive index of the waveguide can include using the electro-optic (EO) effect. Thermal control of the refractive index of the waveguide can include using the thermo-optic (TO) effect. Optical control of the refractive index of the waveguide can include using nonlinear optical effects such as cross-phase modulation (XPM). In some aspects, manipulation of the refractive index of the waveguide can be applied to a waveguide through which a local oscillator light is guided. This can provide effects similar to those of manipulating the amplitude, frequency, and phase of the LO. In other aspects, manipulation of the refractive index of the waveguide can be applied to a waveguide through which a signal light is guided.

[0225] Multiplexing in the electrical domain can include manipulating the electrical response or characteristics of the components of the detection units of the coherent detection array, such as the responsivity of the photodetectors. Multiplexing based on the responsivity of the photodetectors can be achieved by controlling the amplitude, frequency and phase of the voltage applied to the photodetectors in each detection unit or group of detection units of the detection array. Photodetectors whose responsivity varies with applied voltage include self-mixing detectors, such as those described in [William C. Ruff, John D. Bruno, Stephen W. Kennerly, Ken Ritter, Paul H. Shen, Barry L. Stann, Michael R. Stead, Zoltan G. Sztankay, Mary S. Tobin, "Self-mixing detector candidates for an FM / cw ladar architecture," Proc. SPIE 4035, Laser Radar Technology and Applications V, (5 September 2000)]. The modulated photocurrents from different coherent detection units can be multiplexed to form a multiplexed electrical readout signal. Also, the amplitude, frequency and phase of the voltage applied to the photodetectors of the detection unit may be modulated in time, so that the multiplexed electrical read-out signal varies in time accordingly.

[0226] Any combination of time division multiplexing, space division multiplexing, LO-based multiplexing, waveguide-based multiplexing and photodetector responsivity-based multiplexing may or may not be simultaneously applied to the coherent detection array. Signal post-processing may be applied to the multiplexed electrical readout signal to extract information about the signal light measured at the detection unit.

[0227] 28 shows a conceptual diagram of a coherent detection device including a coherent detection array 91, an optical input circuit 92, an electrical multiplexing circuit 93, and an electrical readout circuit 94. In this device, any combination of a time division multiplexing method, a space division multiplexing method, a multiplexing method using LO, a multiplexing method using the waveguide of the detection array, and a multiplexing method using the response of the photodetector may be applied.

[0228] For the embodiments of the coherent detection array of the present invention shown in Figures 2, 3, 6, 7, 8, 9, 14, 15, 16, 17, 18, 19, 20, 21, 24, 25, 26 and 27, the current at the output of the column readout wire of the nth column of the coherent detection array is proportional to the following equation:

number

[0229] Below, we describe embodiments of multiplexing methods that exploit the high degrees of freedom in the optical and electrical domains for coherent detection afforded by manipulation of the LO and photodetector responsivities. Local oscillator multiplexing method

[0230] In the following, the principles and embodiments of a multiplexing method using a local oscillator are described, utilizing the design of the coherent detection array of the present invention.

[0231] In some aspects, multiplexing for signal readout can be achieved by manipulating the LO. In such a situation, the responsivity R of the photodetector (m,n) can be treated as being independent of time or varying slowly with time. Next, the cross component of the current in Eq. (1), LO,in(m) (t)E Sig,in(m,n) (t) may be extracted by suppressing the direct component with an appropriate filter, if it varies more slowly than the cross component, or by taking the difference between the photocurrents due to the photodetectors in the case of the embodiments of the coherent detection array shown in Figures 2, 3, 24, 25, 26 and 27 in which a balanced configuration is implemented. The cross component of the current at the output of the nth column readout wire of the coherent detection array is proportional to

number

[0232] In some aspects, the above method for signal multiplexing may be implemented by controlling the local oscillator light in consideration of equation (2) and selecting the rows of the coherent detection array one by one in a sequential or non-sequential manner to read out all the rows in M ​​steps. In other aspects, the multiplexing may be performed by simultaneously injecting non-zero local oscillator light into a subset of the rows of the coherent detection array. Furthermore, the local oscillator light may be injected into different subsets of the rows of the coherent detection array at different times. Also, the electrical signals at the output ends of the column readout wiring of different columns of the detection array may be multiplexed using an existing common readout method to output to an external circuit. Furthermore, signal post-processing may be applied to extract the information of the signal light.

[0233] Two other examples of embodiments of multiplexing methods based on the frequency or amplitude of the LO are described below. It is understood that the examples are non-exhaustive. In some aspects, other multiplexing schemes may be used to utilize any combination of amplitude, frequency, and phase of the local oscillator light. Multiplexing method based on local oscillator frequency offset - Patents.com

[0234] In the following, one embodiment of a multiplexing method using local oscillator frequencies is described.

[0235] In some aspects, local oscillator light having different optical frequencies may be introduced into different rows of a coherent detection array to multiplex the currents in the column readout wiring according to equation (2). In this regard, different terms in the sum in equation (2) indicate different beat frequencies, and signal processing may be applied to demultiplex the information in the different rows.

[0236] The application of the multiplexing method using different LO frequencies to coherent detection extends FMCW-LIDAR (see non-patent document [A. Dieckmann, "FMCW-LIDAR with tunable twin-guide laser diode," Electronics Letters 30, 308-309 (1994)]) to realize omnidirectional simultaneous 3D FMCW-LIDAR. A 3D FMCW-LIDAR is realized by using an all-around irradiating probe laser with a linear frequency chirp modulated at the center frequency f0, with a frequency tuning range B and a sweep period T. s For example, let us take the case of applying 3D FMCW-LIDAR to a target during the period. In the coherent detection array, the m-th row of local oscillator light E LO,in m f0 to Ω m (m=1, ... ,M. When the n-th column readout line is frequency offset by n, the cross component of the FMCW photocurrent at the output of the n-th column readout line is proportional to

number

number

[0237] 29A and 29B show schematic examples of the spectrum of the cross components of the FMCW photocurrent with and without LO frequency offset, respectively. Only positive frequencies are shown since the signals of interest are purely real. FIG. 29A shows an example of the spectrum with no frequency offset, and Eq. (3)(Ω m Consider an example of a photocurrent consisting of signals from three detection units in one column (e.g., detection units 1, 2, and 3 in the first, second, and third rows of the first column). Both detection units 1 and 3 have a ΔT S / B, i.e., τ 11 = τ 31 = ΔT S A detection unit 2 detects the signal from the probe beam of A / B with a round trip time τ 21 =Δ'T S 29A. The signal from the probe beam at frequency Δ is detected by the LO of each of the detection units 1, 2, and 3. For the sake of explanation, it is assumed that the signals at the three detection units have the same amplitude and phase. Since the round trip times of detection units 1 and 3 are the same, the photocurrents from detection units 1 and 3 are added together. Therefore, as depicted in FIG. 29A, the amplitude of the photocurrent at frequency Δ is twice the amplitude of the photocurrent at frequency Δ'. Also, since the photocurrents from the three detection units are added together, it is not possible to distinguish their respective contributions from the summed photocurrent. FIG. 29B shows the case where a frequency offset Ω is applied to the LO of each of the detection units 1, 2, and 3. m The example of the spectrum when m=1, 2, 3 is applied is shown. The frequencies of the photocurrents from the three detection units are separated into different bands, and together with the contributions of the detection units, the round trip time information of the probe beam at the detection units can be determined individually. Multiplexing method based on compressed sensing

[0238] In the following, one embodiment of a multiplexing method using local oscillator amplitude will be described.

[0239] In some aspects, the selection of the row subset of the coherent detection array and the signal post-processing may be based on the method of compressed sensing (CS) (see DL Donoho, "Compressed sensing," IEEE Transactions on Information Theory 52, 1289 (2000)). In order to explain the principle of the multiplexing method, the following description assumes that the incident signal light is a continuous wave (CW) signal, but the method is generally valid for any incident signal light.

[0240] In some embodiments of the CS method, the incident signal light is measured K times, where each measurement is ... ,K's duration T k According to equation (2), the cross component of the current at the output end of the column readout wiring of the nth column of the coherent detection array during the kth measurement is proportional to the following equation:

number

[0241] In the following, the principles of a multiplexing method utilizing the characteristics of photodetectors and an embodiment thereof will be described, taking advantage of the design of the coherent detection array of the present invention.

[0242] In some aspects, multiplexing through manipulation of the characteristics of the photodetectors may be implemented in the coherent detection array embodiments shown in Figures 3, 7, 9, 15, 17, 19, 21, 25, and 27 in which row coding wiring is implemented. In that case, the responsivity of the photodetectors may be expressed as R (m,n) f (m) (t) ensures that the time dependence of the responsivity is the same across the rows of the detector units of the coherent detector array, and the coefficient R (m,n) can explain the variation in responsivity between different photodetectors of different detection units. The function f (m) (t) can be controlled in time by changing the voltage applied to the photodetector in the mth row of the detector array. According to equation (1), the current at the output of the column readout wiring in the nth column of the coherent detector array is written as follows:

number

[0243] In some aspects, the function f (m) (t) can be used to provide a frequency offset for multiplexing the output signals in a manner similar to the local oscillator frequency offset based multiplexing method described by equation (3). As an example, the local oscillator frequency offset can be set to zero and the response is f (m) (t)=C m +A m cos2πΩ m Consider the application to an omnidirectional simultaneous 3D FMCW-LIDAR with a form of t. In this case, equation (5) can be written as

number

number

number

[0244] On the other hand, the baseband current in equation (7) corresponds to a signal component that is not subject to multiplexing due to the temporal modulation of the photodetector responsivity.

[0245] On the other hand, similar to the situation described by equation (3), the sum of the band-shift currents according to equation (8) in the different rows of the detector array is proportional to the modulation frequency Ω of the photodetector responsivity. m The modulation frequency Ω m If is sufficiently large, the distance information τ mnThe FMCW photocurrent components, including , may be shifted to different frequency bands. As a result, frequency modulation applied to the photodetector responsivity can be used to select a subset of rows of a coherent detection array and demultiplex the row signal information, similar to the multiplexing method with LO frequency offset.

[0246] Unlike the situation described by equation (3), the distance information of the band shift current is m The average power term P shifted around 0(m,n) It may appear as two sidebands around the edge, so more advanced signal post-processing may be required to extract such information.

[0247] Figures 30A-30C show schematic examples of the spectrum of the FMCW photocurrent when the responsivity of the photodetector is modulated with a sine wave. The same conditions and parameters as in Figures 29A and 29B are considered. The signals of interest are purely real, so only positive frequencies are shown. Figure 30A shows an example of the spectrum without modulation, while A m = 0. FIG. 30A shows the average power P 0(m,n) FIG. 30B shows that the photodetectors of the detection units 1, 2, and 3 are connected to a frequency Ω m 29B. The spectrum is shown when sinusoidal modulation is applied with m=1, 2, 3. The photocurrent frequencies from the three detection units show a more complex pattern than that shown in FIG. 29B, but are separated into clear bands. FIG. 30C shows the average power P in equations (5), (7), and (8) obtained by taking the difference in photocurrents by the photodetectors for the balanced configuration of the coherent detection array embodiments shown in FIG. 2, FIG. 3, FIG. 24, FIG. 25, FIG. 26, and FIG. 27. 0(m,n) We show a situation in which terms including References Other publications

[0248] Firooz Aflatouni, Behrooz Abiri, Angad Rekhi, and Ali Hajimiri, "Nanophotonic coherent imager," Optics Express 23, 5117-5125 (2015).

[0249] William C. Ruff, John D. Bruno, Stephen W. Kennerly, Ken Ritter, Paul H. Shen, Barry L. Stann, Michael R. Stead, Zoltan G. Sztankay, Mary S. Tobin, "Self-mixing detector candidates for an FM / cw ladar architecture," Proc. SPIE 4035, Laser Radar Technology and Applications V, (5 September 2000).

[0250] A. Dieckmann, "FMCW-LIDAR with tunable twin-guide laser diode," Electronics Letters 30, 308-309 (1994).

[0251] D. L. Donoho, "Compressed sensing," IEEE Transactions on Information Theory 52, 1289 (2000).

Claims

1. 1. A coherent detection apparatus comprising: an array of coherent detection units; Here, each coherent detection unit has a free space-to-waveguide coupler for receiving the signal light; a first waveguide for guiding local oscillator light, the first waveguide being optically coupled to the free space-waveguide coupler via a first optical coupler; one or more photodetectors optically coupled to the first optical coupler to receive photons from the first optical coupler; one or more connecting waveguides optically coupled to the coherent detection units via a plurality of second optical couplers; wherein each connecting waveguide is optically coupled to at least a first subset of the coherent detection units, and each coherent detection unit of the first subset of the coherent detection units is optically coupled to a selected one of the connecting waveguides and to the first waveguide of each of the coherent detection units via one of the second optical couplers; one or more electrical conductive paths electrically coupled to the plurality of coherent detection units; wherein each electrical conductive path is electrically coupled to at least a second subset of the coherent detection units, and each coherent detection unit of the second subset of coherent detection units is electrically coupled to a selected one of the electrical conductive paths via the one or more photodetectors of each coherent detection unit; an electrical circuit electrically coupled to the electrical conductive path; the electrical conductive path functions as the readout channel for multiplexing electrical signals output from the photodetectors to which the readout channel is coupled; the electrical circuit is configured to extract information about the cross-components of the multiplexed electrical signal by recognizing that a selected group of coherent detection units of the read channel primarily contributes to the cross-components of the multiplexed electrical signal of the read channel; A coherent detection apparatus, wherein the cross component is related to the product of the electric fields of the signal light and the local oscillator signal transmitted to the coherent detection unit.

2. 2. The coherent detection apparatus of claim 1, the free space-to-waveguide couplers of at least some of the coherent detection units are polarization-separating free space-to-waveguide couplers; Each of the coherent detection units including the polarization-separating free space-waveguide coupler further comprises: a second waveguide for guiding local oscillator light; wherein the second waveguide is optically coupled to the polarization-splitting free-space-to-waveguide coupler via a third optical coupler; A coherent detection apparatus including one or more photodetectors optically coupled to the third optical coupler and configured to receive photons from the third optical coupler.

3. 3. The coherent detection apparatus according to claim 2, a coherent detection apparatus, wherein for each of the coherent detection units including the polarization-separating free space-waveguide coupler, the first waveguide and the second waveguide are optically coupled to one of the connecting waveguides via one or more of the second optical couplers.

4. 3. The coherent detection apparatus according to claim 2, a first optical coupler for coupling the first waveguide to a second optical coupler and the second optical coupler for coupling the second waveguide to a second optical coupler;

5. 1. A coherent detection apparatus comprising: an array of coherent detection units; Here, each coherent detection unit has a free space-to-waveguide coupler for receiving the signal light; a first optical coupler optically coupled to the free space-to-waveguide coupler; one or more photodetectors optically coupled to the first optical coupler to receive photons from the first optical coupler; one or more connecting waveguides optically coupled to the coherent detection units; wherein each connecting waveguide is optically coupled to at least a first subset of the coherent detection units, and each coherent detection unit of the first subset of coherent detection units is optically coupled directly to the first optical coupler of each of the coherent detection units; one or more electrical conductive paths electrically coupled to the plurality of coherent detection units; wherein each electrical conductive path is electrically coupled to at least a second subset of the coherent detection units, and each coherent detection unit of the second subset of coherent detection units is electrically coupled to a selected one of the electrical conductive paths via the one or more photodetectors of each of the coherent detection units; an electrical circuit electrically coupled to the electrical conductive path; the electrical conductive path functions as the readout channel for multiplexing electrical signals output from the photodetectors to which it is coupled; the electrical circuit is configured to extract information about the cross-components of the multiplexed electrical signal by recognizing that a selected group of coherent detection units of the read channel primarily contributes to the cross-components of the multiplexed electrical signal of the read channel; A coherent detection apparatus, wherein the cross component is related to the product of the electric fields of the signal light and the local oscillator signal transmitted to the coherent detection unit.

6. 6. The coherent detection apparatus according to claim 5, the free space-to-waveguide couplers of at least some of the coherent detection units are polarization-separating free space-to-waveguide couplers; Each of the coherent detection units including the polarization-separating free space-waveguide coupler further comprises: a second optical coupler optically coupled to the polarization-splitting free-space-to-waveguide coupler; A coherent detection apparatus including one or more photodetectors optically coupled to the second optical coupler and configured to receive photons from the second optical coupler.

7. 7. The coherent detection apparatus according to claim 6, A coherent detection apparatus, wherein for each of the coherent detection units including the polarization-separating free space-waveguide coupler, the first optical coupler and the second optical coupler are directly optically coupled to one of the connecting waveguides.

8. 7. The coherent detection apparatus according to claim 6, A coherent detection apparatus, wherein for each of the coherent detection units including the polarization-separating free space-waveguide couplers, the first optical coupler is directly optically coupled to one of the connecting waveguides, and the second optical coupler is directly optically coupled to the other of the connecting waveguides.

9. 7. The coherent detection apparatus according to claim 6, further comprising a plurality of third optical couplers; Each of the coherent detection units including the polarization-separating free space-waveguide coupler further comprises: a waveguide optically coupled to the second optical coupler; A coherent detection apparatus, wherein for each of the coherent detection units including the polarization-separating free space-waveguide coupler, the first optical coupler is directly optically coupled to one of the connecting waveguides, and the waveguide of each of the coherent detection units is optically coupled to the same one of the connecting waveguides via one or more of the third optical couplers.

10. 7. The coherent detection apparatus according to claim 6, further comprising a plurality of third optical couplers; Each of the coherent detection units including the polarization-separating free space-waveguide coupler further comprises: a waveguide optically coupled to the second optical coupler; A coherent detection apparatus, wherein for each of the coherent detection units including the polarization-separating free space-waveguide coupler, the first optical coupler is optically coupled directly to one of the connecting waveguides, and the waveguide of each of the coherent detection units is optically coupled to another of the connecting waveguides via one or more of the third optical couplers.

11. A method for optical coherent detection and signal readout using a coherent detection device, comprising the steps of: coupling the signal light into a first subset of coherent detection units of the coherent detection apparatus; introducing one or more local oscillator signals into a second subset of the coherent detection units; where the coherent detection units of the second subset are optically coupled to a first common connection waveguide for transmitting the local oscillator signals, and where each coherent detection unit of the second subset is electrically coupled to a different read channel, and the first subset overlaps with the second subset to define a first intersection set including at least one of the coherent detection units; registering first information relating to the second subset of coherent detection devices; wherein the first information comprises positions of the coherent detection units of the second subset and physical characteristics of the local oscillator signal introduced into the second subset, the physical characteristics comprising at least one of an amplitude, a frequency, a relative phase, an application time and a duration of the local oscillator signal; performing optical mixing of the signal light and the local oscillation signal in an optical coupler of the coherent detection unit; detecting the mixed optical signal output from the optical coupler of the coherent detection unit by a photodetector of the coherent detection unit, and generating an electrical signal containing information of the mixed optical signal; combining the electrical signals into one or more combined electrical signals for readout; where each combined electrical signal is combined with the electrical signals generated by the photodetectors of the coherent detection unit coupled to a common readout channel; for each coherent detection unit of the first cross set, extracting from the combined electrical signal second information relating to cross components of the electrical signal of each of the coherent detection units individually by using the first information relating to the second subset to ascertain the second information; the cross component is related to the product of the electric fields of the signal light and the local oscillator signal transmitted to each of the coherent detection units; The method, wherein recognizing the second information includes recognizing that only one coherent detection unit of the second subset contributes primarily to the cross component of the combined electrical signal of the common read channel.

12. 12. The method of claim 11, The method further comprising filtering a direct component of the electrical signal generated by the photodetector of the coherent detection unit using high pass filtering.

13. 12. The method of claim 11, The method further includes a step of filtering a direct component of the electrical signal generated by the photodetectors of the coherent detection unit by subtracting signals from at least some pairs of photodetectors of the coherent detection unit, wherein a balanced configuration is implemented for each of the coherent detection units.

14. 12. The method of claim 11, The method further comprises repeating the steps of introducing the local oscillator signal into the second subset, registering the first information, performing the optical mixing, detecting the mixed optical signal, combining the electrical signals, and extracting the second information a plurality of times, where in each iteration the second subset is modified to include a coherent detection unit optically coupled to a second common connecting waveguide, the second common connecting waveguide being different from the first common connecting waveguide.

15. 15. The method of claim 14, The method further includes, within the repeating step, modifying the first subset to include a coherent detection unit, such that the intersection set of the first subset and the second subset includes at least one coherent detection unit.

16. 12. The method of claim 11, The method further includes the steps of: introducing one or more local oscillator signals into a third subset group of coherent detection units; wherein the coherent detection units of each of the third subsets are optically coupled to a common connecting waveguide and each coherent detection unit of each of the third subsets is electrically coupled to a different readout channel, the second subset being one of the third subsets, and a second intersection set being defined by the first subset overlapping a union of the third subsets; registering third information relating to the third subset of coherent detection devices; wherein the third information comprises positions of the coherent detection units of the third subset and physical characteristics of the local oscillator signal introduced into the third subset, the physical characteristics comprising at least one of an amplitude, a frequency, a relative phase, an application time and a duration of the local oscillator signal, the third information comprising the first information; coupling the coherent detection units to a plurality of common read channels; where each of the common read channels is electrically coupled to only one coherent detection unit of each of the third subsets; repeating the steps of introducing the local oscillator signal into the third subset, the step of registering the third information, the step of optically mixing, the step of detecting the optical signal, and the step of combining the electrical signal a number of times; where in each iteration, the group of the third subsets is changed to a different group of the third subsets including a different combination of the coherent detection units optically coupled to a common connecting waveguide so as to satisfy the application condition of a compressive sensing method; said step of introducing said local oscillator signal into said group of said third subset comprises the step of introducing said local oscillator signal exhibiting some common physical characteristics into said group of said third subset, said common physical characteristics comprising at least one of a same frequency and an amplitude following a same distribution; The repeating step further comprises recording the combined electrical signal; The method, wherein the step of extracting the second information for the first intersection set and the second intersection set is performed by additionally introducing the third information and applying a signal reconstruction algorithm corresponding to the compressed sensing method, and recognizing the second information includes recognizing that only one coherent detection unit of each of the third subsets primarily contributes to the cross component of the combined electrical signal of each of the common readout channels.

17. 12. The method of claim 11, The method further includes the steps of: introducing one or more local oscillator signals into a third subset group of the coherent detection units; wherein the coherent detection units of each of the third subsets are optically coupled to a common connecting waveguide and each coherent detection unit of each of the third subsets is electrically coupled to a different read channel, the second subset being one of the third subsets, and a second intersection set being defined by the first subset overlapping the connections of the third subset; registering third information relating to the third subset of coherent detection devices; wherein the third information comprises positions of the coherent detection units of the third subset and physical characteristics of the local oscillator signal introduced into the third subset, the physical characteristics comprising at least one of an amplitude, a frequency, a relative phase, an application time and a duration of the local oscillator signal, the third information comprising the first information; coupling the coherent detection units to a plurality of common read channels, where each common read channel is electrically coupled to only one coherent detection unit of each of the third subsets; the group includes at least two of the third subsets; said step of introducing said local oscillator signals into said third subset includes the step of introducing said local oscillator signals into said third subset having frequencies that differ from one another by a finite frequency offset; one said local oscillator signal is introduced into one said third subset, and into different ones of said third subsets local oscillator signals having different frequency offsets are introduced, said frequency offsets being selected such that for coherent detection units belonging to different ones of said third subsets the electrical signals generated by the photodetectors of these coherent detection units are shifted to different frequency bands; The method, wherein the step of extracting the second information for the first intersection set and the second intersection set is performed by additionally incorporating the third information and recognizing that only one coherent detection unit of each of the third subsets primarily contributes to the cross component of the combined electrical signal of each of the common readout channels.

18. 12. The method of claim 11, The method further includes the steps of: introducing one or more local oscillator signals into a third subset group of the coherent detection units; wherein the coherent detection units of each of the third subsets are optically coupled to a common connecting waveguide and each coherent detection unit of each of the third subsets is electrically coupled to a different read channel, the second subset being one of the third subsets, and a second intersection set being defined by the first subset overlapping the connections of the third subset; registering third information relating to the third subset of coherent detection devices; wherein the third information comprises positions of the coherent detection units of the third subset and physical characteristics of the local oscillator signal introduced into the third subset, the physical characteristics comprising at least one of an amplitude, a frequency, a relative phase, an application time and a duration of the local oscillator signal, the third information comprising the first information; coupling the coherent detection units to a plurality of common readout channels; where each common readout channel is electrically coupled to only one coherent detection unit of each of the third subsets; registering fourth information about the location of a fourth subset of the coherent detection units; where the fourth subset includes at least a portion of the coherent detection units, and the first subset, the third subset and the fourth subset include at least a common coherent detection unit; turning on the photodetectors of the fourth subset with an electrical multiplexing circuit; turning off, by the electrical multiplexing circuitry, the photodetectors of the coherent detection units not included in the fourth subset; The method, wherein the step of extracting the second information is performed by additionally incorporating the third information and the fourth information for the coherent detection units included in the first intersection set and the second intersection set that also belong to the fourth subset.

19. 20. The method of claim 18, Further comprising the steps of: dividing the coherent detection units of the fourth subset into a plurality of groups; wherein the responsivity of the photodetectors of the coherent detection units of each group is modulated in the same manner by the electrical multiplexing circuit; electrically coupling each coherent detection unit of the fourth subset to one or more readout channels; where each of the readout channels is electrically coupled to one or more coherent detection units of different ones of the groups, without being coupled to more than one coherent detection unit from any one of the groups; modulating the responsivities of the photodetectors of different groups of coherent detection units at mutually different frequencies with a finite frequency offset; where the frequency offset is selected such that, for those coherent detection units coupled to a common read-out channel, the electrical signals generated by the photodetectors of these coherent detection units are shifted to different frequency bands; The step of extracting the second information is performed by recognizing that the cross component of the combined electrical signal of each of the readout channels is mainly contributed by the coherent detection units of the fourth subset whose photodetectors generate electrical signals shifted to different frequency bands; The method of claim 1, wherein the step of extracting the second information is performed by incorporating fifth information related to the modulated responsivity of the photodetector, the fifth information including a modulation frequency and amplitude of the responsivity.

20. 2. The coherent detection apparatus of claim 1, A coherent detection apparatus, wherein when the group of coherent detection units comprises a plurality of coherent detection units, each coherent detection unit of the group contributes to the cross component with a signal function that makes the contribution of each coherent detection unit uniquely distinguishable from the cross component.

21. 6. The coherent detection apparatus according to claim 5, A coherent detection apparatus, wherein when the group of coherent detection units comprises a plurality of coherent detection units, each coherent detection unit of the group contributes to the cross component with a signal function that makes the contribution of each coherent detection unit uniquely distinguishable from the cross component.

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