Digital coherent imager on a silicon photonic chip

Digital coherent imager on a silicon photonic chip | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Digital coherent imager on a silicon photonic chip Volkan Gurses, Debjit Sarkar, Aroutin Khachaturian, Reza Fatemi, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9466036/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 6 You are reading this latest preprint version Abstract Digital signal processing has driven much of the capacity growth in coherent fiber-optic communications, but its use in free-space coherent imagers and sensors has so far been limited. We report a 128-element silicon photonic coherent imager with a fully parallelized readout that performs beamforming in the digital domain at 1550 nm. The photonic integrated circuit consists of an array of grating coupler antennas, each routed to its own balanced coherent receiver, with a common on-chip local oscillator delivered to all 128 receivers through a 1:128 binary splitter tree. Because every channel is digitized independently, we recover the per-channel amplitude and phase without on-chip phase shifters and reconstruct coherent images by computing the array factor in software. Using 6 of the 128 elements, we obtain digitally reconstructed beams with an average half-power beamwidth of 1.67 ◦ and a field-of-view of 8.30 ◦ for illumination angles between −4 ◦ and +4 ◦ . Across the full array, the median common-mode rejection ratio is 27 dB and the median signal-to-noise ratio is 22 dB. The extracted channel phases show sub-degree noise, indicating that the coherent detection and digital processing chain are working as intended. The architecture removes the need for on-chip phase shifters and points toward a practical route to large-format, high-resolution coherent imagers for free-space sensing, ranging, and optical communications. On-chip optical sensor arrays and imagers underpin a range of free-space applications, including light detection and ranging (LiDAR) 1, 2 , optical coherence tomography (OCT) 3 , free-space optical communications 4 , and holographic projection 5 . Silicon photonic optical phased arrays (OPAs) are particularly attractive for these applications because they are built in standard complementary metal-oxide-semiconductor (CMOS) processes and can therefore be scaled to large element counts 6, 7 . OPA-based beam steering 8 , coherent imaging 9 , and three-dimensional sensing 10 have all been demonstrated. Most OPA systems to date rely on on-chip thermo-optic or electro-optic phase shifters to set the phase at each element for beamforming and beamsteering. As the element count grows, the power dissipated by the phase shifters, the thermal crosstalk between neighbors, and the calibration effort all increase 11 . Radio-frequency (RF) and millimeter-wave phased arrays avoid these issues by digitizing each element independently and forming the beam in software 12, 13 . Digital beamforming makes it possible to form multiple beams from the same data, null interferers adaptively, and compensate for array non-idealities, all without reconfiguring any hardware. Coherent fiber-optic communications have followed a similar trajectory. Digital signal processing (DSP) has been responsible for much of the capacity growth over the past decade, handling impairment compensation, carrier recovery, and equalization in the digital domain 14–17 . High-speed analog-to-digital converters combined with DSP have become standard in coherent transceivers. Applying these ideas—digital beamforming in particular—to free-space coherent imagers has received much less attention. In this paper, we demonstrate digital beamforming on a 128-element silicon photonic coherent imager at 1550 nm. The photonic integrated circuit (PIC) uses a fully parallelized readout: the output of every channel’s coherent receiver is routed off-chip for amplification, digitization, and processing. No on-chip phase shifters are used. Per-channel amplitude and phase are extracted in software and combined to reconstruct coherent images of the scene. Using 6 of the 128 elements, we obtain digitally reconstructed beams with a half-power beamwidth of 1.67 ◦ and a field-of-view of 8.30 ◦ . For the full array, we report the common-mode rejection ratio (CMRR) and signal-to-noise ratio (SNR) distributions, and quantify the phase extraction noise. The architecture shows that digital beamforming is a practical approach for OPA receivers and offers a route to higher element counts for free-space coherent imaging, sensing, and optical communications. Physical sciences/Engineering Physical sciences/Optics and photonics Physical sciences/Physics Full Text Additional Declarations Competing interest reported. A.K. and A.H. are shareholders of HEPT Lab, Inc. All other authors declare no competing interests. Cite Share Download PDF Status: Under Review Version 1 posted Reviewers agreed at journal 05 May, 2026 Reviewers invited by journal 05 May, 2026 Editor assigned by journal 29 Apr, 2026 Editor invited by journal 29 Apr, 2026 Submission checks completed at journal 27 Apr, 2026 First submitted to journal 27 Apr, 2026 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-9466036","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":634655763,"identity":"11c10c38-c087-4985-8385-fd13c1785768","order_by":0,"name":"Volkan Gurses","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA0ElEQVRIiWNgGAWjYPACGwYGdiDF2AAkDhCnJY2BgZmZNC2HSdAiH5H7+MOHP+fl+Zv5Dz74uYNBju9GAn4thjfSzSRntt02nHGYmdmw9wyDsSRBLTPS2Jh5G24nMBxmZpNmbGNI3ECEFubPf/6cS5A/zMz+G6ilnqAWeYk0BmkGtgMJBkBbmIFaEgwIaTHgecYm2duWbLjxMLMxkCFhOPPMAwK2tKcxf/jxx05e7njjww8/22zk+Y4TsuUAKl8Cv3KwLQ2E1YyCUTAKRsFIBwANXUMJb0s6JQAAAABJRU5ErkJggg==","orcid":"","institution":"California Institute of Technology","correspondingAuthor":true,"prefix":"","firstName":"Volkan","middleName":"","lastName":"Gurses","suffix":""},{"id":634655765,"identity":"358f527f-c07e-40e3-9d31-741498151236","order_by":1,"name":"Debjit Sarkar","email":"","orcid":"","institution":"California Institute of Technology","correspondingAuthor":false,"prefix":"","firstName":"Debjit","middleName":"","lastName":"Sarkar","suffix":""},{"id":634655767,"identity":"2036a381-d6b8-493f-b4da-2f12f7030185","order_by":2,"name":"Aroutin Khachaturian","email":"","orcid":"","institution":"California Institute of Technology","correspondingAuthor":false,"prefix":"","firstName":"Aroutin","middleName":"","lastName":"Khachaturian","suffix":""},{"id":634655768,"identity":"8a3bd51e-7014-4b98-a7e1-ce3c94955bb5","order_by":3,"name":"Reza Fatemi","email":"","orcid":"","institution":"California Institute of Technology","correspondingAuthor":false,"prefix":"","firstName":"Reza","middleName":"","lastName":"Fatemi","suffix":""},{"id":634655774,"identity":"37f41c66-4a65-4a70-afbe-094057a914be","order_by":4,"name":"Ali Hajimiri","email":"","orcid":"","institution":"California Institute of Technology","correspondingAuthor":false,"prefix":"","firstName":"Ali","middleName":"","lastName":"Hajimiri","suffix":""}],"badges":[],"createdAt":"2026-04-20 03:08:33","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9466036/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9466036/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":109068289,"identity":"c8c28fe9-19aa-4d1a-8d32-a6541cadb6e2","added_by":"auto","created_at":"2026-05-12 10:05:26","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1860723,"visible":true,"origin":"","legend":"","description":"","filename":"Manuscriptv2.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9466036/v1_covered_3d015039-1610-4f95-8b2e-fad705f9dc49.pdf"}],"financialInterests":"Competing interest reported. A.K. and A.H. are shareholders of HEPT Lab, Inc. All other authors declare no competing interests.","formattedTitle":"Digital coherent imager on a silicon photonic chip","fulltext":[],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":false,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":true,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":true,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-9466036/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9466036/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eDigital signal processing has driven much of the capacity growth in coherent fiber-optic communications, but its use in free-space coherent imagers and sensors has so far been limited. We report a 128-element silicon photonic coherent imager with a fully parallelized readout that performs beamforming in the digital domain at 1550 nm. The photonic integrated circuit consists of an array of grating coupler antennas, each routed to its own balanced coherent receiver, with a common on-chip local oscillator delivered to all 128 receivers through a 1:128 binary splitter tree. Because every channel is digitized independently, we recover the per-channel amplitude and phase without on-chip phase shifters and reconstruct coherent images by computing the array factor in software. Using 6 of the 128 elements, we obtain digitally reconstructed beams with an average half-power beamwidth of 1.67\u003csup\u003e◦\u003c/sup\u003e and a field-of-view of 8.30\u003csup\u003e◦\u003c/sup\u003e for illumination angles between −4\u003csup\u003e◦\u003c/sup\u003e and +4\u003csup\u003e◦\u003c/sup\u003e. Across the full array, the median common-mode rejection ratio is 27 dB and the median signal-to-noise ratio is 22 dB. The extracted channel phases show sub-degree noise, indicating that the coherent detection and digital processing chain are working as intended. The architecture removes the need for on-chip phase shifters and points toward a practical route to large-format, high-resolution coherent imagers for free-space sensing, ranging, and optical communications.\u003c/p\u003e\n\u003cp\u003eOn-chip optical sensor arrays and imagers underpin a range of free-space applications, including light detection and ranging (LiDAR)\u003csup\u003e1, 2\u003c/sup\u003e, optical coherence tomography (OCT)\u003csup\u003e3\u003c/sup\u003e, free-space optical communications\u003csup\u003e4\u003c/sup\u003e, and holographic projection\u003csup\u003e5\u003c/sup\u003e. Silicon photonic optical phased arrays (OPAs) are particularly attractive for these applications because they are built in standard complementary metal-oxide-semiconductor (CMOS) processes and can therefore be scaled to large element counts\u003csup\u003e6, 7\u003c/sup\u003e. OPA-based beam steering\u003csup\u003e8\u003c/sup\u003e, coherent imaging\u003csup\u003e9\u003c/sup\u003e, and three-dimensional sensing\u003csup\u003e10\u003c/sup\u003e have all been demonstrated.\u003c/p\u003e\n\u003cp\u003eMost OPA systems to date rely on on-chip thermo-optic or electro-optic phase shifters to set the phase at each element for beamforming and beamsteering. As the element count grows, the power dissipated by the phase shifters, the thermal crosstalk between neighbors, and the calibration effort all increase\u003csup\u003e11\u003c/sup\u003e. Radio-frequency (RF) and millimeter-wave phased arrays avoid these issues by digitizing each element independently and forming the beam in software\u003csup\u003e12, 13\u003c/sup\u003e. Digital beamforming makes it possible to form multiple beams from the same data, null interferers adaptively, and compensate for array non-idealities, all without reconfiguring any hardware.\u003c/p\u003e\n\u003cp\u003eCoherent fiber-optic communications have followed a similar trajectory. Digital signal processing (DSP) has been responsible for much of the capacity growth over the past decade, handling impairment compensation, carrier recovery, and equalization in the digital domain\u003csup\u003e14–17\u003c/sup\u003e. High-speed analog-to-digital converters combined with DSP have become standard in coherent transceivers. Applying these ideas—digital beamforming in particular—to free-space coherent imagers has received much less attention.\u003c/p\u003e\n\u003cp\u003eIn this paper, we demonstrate digital beamforming on a 128-element silicon photonic coherent imager at 1550 nm. The photonic integrated circuit (PIC) uses a fully parallelized readout: the output of every channel’s coherent receiver is routed off-chip for amplification, digitization, and processing. No on-chip phase shifters are used. Per-channel amplitude and phase are extracted in software and combined to reconstruct coherent images of the scene. Using 6 of the 128 elements, we obtain digitally reconstructed beams with a half-power beamwidth of 1.67\u003csup\u003e◦\u003c/sup\u003e and a field-of-view of 8.30\u003csup\u003e◦\u003c/sup\u003e. For the full array, we report the common-mode rejection ratio (CMRR) and signal-to-noise ratio (SNR) distributions, and quantify the phase extraction noise. The architecture shows that digital beamforming is a practical approach for OPA receivers and offers a route to higher element counts for free-space coherent imaging, sensing, and optical communications.\u003c/p\u003e","manuscriptTitle":"Digital coherent imager on a silicon photonic chip","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-05-12 07:34:55","doi":"10.21203/rs.3.rs-9466036/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"170357174407972654888340759722767521394","date":"2026-05-05T08:53:23+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-05-05T06:58:36+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-04-29T10:08:21+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2026-04-29T09:34:53+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-04-27T18:30:02+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2026-04-27T18:29:00+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"95ae04be-6102-4b5c-bffc-2d7b350e053b","owner":[],"postedDate":"May 12th, 2026","published":true,"recentEditorialEvents":[{"type":"reviewerAgreed","content":"170357174407972654888340759722767521394","date":"2026-05-05T08:53:23+00:00","index":25,"fulltext":""},{"type":"reviewersInvited","content":"10","date":"2026-05-05T06:58:36+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-04-29T10:08:21+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2026-04-29T09:34:53+00:00","index":"","fulltext":""}],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[{"id":67539031,"name":"Physical sciences/Engineering"},{"id":67539032,"name":"Physical sciences/Optics and photonics"},{"id":67539033,"name":"Physical sciences/Physics"}],"tags":[],"updatedAt":"2026-05-12T07:34:55+00:00","versionOfRecord":[],"versionCreatedAt":"2026-05-12 07:34:55","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9466036","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9466036","identity":"rs-9466036","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}