{"id":426891,"date":"2025-03-26T07:59:38","date_gmt":"2025-03-26T07:59:38","guid":{"rendered":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/abnormal-gradients-in-multi-port-power-optimization-of-2x3-mmi-using-lumopt\/"},"modified":"2025-03-26T16:25:15","modified_gmt":"2025-03-26T16:25:15","slug":"abnormal-gradients-in-multi-port-power-optimization-of-2x3-mmi-using-lumopt","status":"publish","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/abnormal-gradients-in-multi-port-power-optimization-of-2x3-mmi-using-lumopt\/","title":{"rendered":"Abnormal gradients in multi – port power optimization of 2×3 MMI using Lumopt"},"content":{"rendered":"

<p><p>We’ve written the following code to attempt the inverse design of a 2×3 MMI device using Lumopt. The goal is to achieve equal power at the three output ports when two mode light sources enter through two input ports respectively. However, we’ve noticed that the actual FOM curve doesn’t trend towards a gradual reduction in insertion loss. Why is this the case? Could you please provide me with professional advice and assistance? Thank you!<br><br>def runSim(params, eps_bg, eps_wg, x_pos, y_pos, size_x, size_y, filter_R, working_dir, beta):<br><br>######## DEFINE GEOMETRY ########<br>geometry = TopologyOptimization2D(params=params, eps_min=eps_bg, eps_max=eps_wg, x=x_pos, y=y_pos, z=0, filter_R=filter_R, beta=beta)<br><br>######## DEFINE FIGURE OF MERIT FOR EACH OUTPUT WAVEGUIDE ########<br><span class=”ps-stream-hashtag”>#fom1<\/span><\/a> = ModeMatch(monitor_name = ‘fom_1’, mode_number = ‘Fundamental TE mode’, direction = ‘Forward’, norm_p = 2, target_fom=1\/3)<br><span class=”ps-stream-hashtag”>#fom2<\/span><\/a> = ModeMatch(monitor_name = ‘fom_2’, mode_number = ‘Fundamental TE mode’, direction = ‘Forward’, norm_p = 2, target_fom=1\/3)<br><span class=”ps-stream-hashtag”>#fom3<\/span><\/a> = ModeMatch(monitor_name = ‘fom_3’, mode_number = ‘Fundamental TE mode’, direction = ‘Forward’, norm_p = 2, target_fom=1\/3)<br>fom1 = ModeMatch(monitor_name=’fom_1′, mode_number=’Fundamental TE mode’, direction=’Forward’, norm_p=2, target_T_fwd=lambda wl: 1\/3 * np.ones(wl.size))<br>fom2 = ModeMatch(monitor_name=’fom_2′, mode_number=’Fundamental TE mode’, direction=’Forward’, norm_p=2, target_T_fwd=lambda wl: 1\/3 * np.ones(wl.size))<br>fom3 = ModeMatch(monitor_name=’fom_3′, mode_number=’Fundamental TE mode’, direction=’Forward’, norm_p=2, target_T_fwd=lambda wl: 1\/3 * np.ones(wl.size))<br><br>######## DEFINE OPTIMIZATION ALGORITHM ########<br>optimizer1 = ScipyOptimizers(max_iter=400, method=’L-BFGS-B’, pgtol=1e-6, ftol=1e-5, scale_initial_gradient_to=0.25)<br>optimizer2 = ScipyOptimizers(max_iter=400, method=’L-BFGS-B’, pgtol=1e-6, ftol=1e-5, scale_initial_gradient_to=0.25)<br>optimizer3 = ScipyOptimizers(max_iter=400, method=’L-BFGS-B’, pgtol=1e-6, ftol=1e-5, scale_initial_gradient_to=0.25)<br>optimizer4 = ScipyOptimizers(max_iter=400, method=’L-BFGS-B’, pgtol=1e-6, ftol=1e-5, scale_initial_gradient_to=0.25)<br>optimizer5 = ScipyOptimizers(max_iter=400, method=’L-BFGS-B’, pgtol=1e-6, ftol=1e-5, scale_initial_gradient_to=0.25)<br>optimizer6 = ScipyOptimizers(max_iter=400, method=’L-BFGS-B’, pgtol=1e-6, ftol=1e-5, scale_initial_gradient_to=0.25)<br><br><br>######## DEFINE SETUP SCRIPT AND INDIVIDUAL OPTIMIZERS ########<br>script1 = load_from_lsf(‘E:\/CHH\/Mixer with lumopt\/2×3 MMI Mixer input1 bend 6×6.lsf’)<br>script2 = load_from_lsf(‘E:\/CHH\/Mixer with lumopt\/2×3 MMI Mixer input2 bend 6×6.lsf’)<br># script1 = script.replace(‘opt_size_x=36e-6′,’opt_size_x={:1.6g}’.format(size_x))<br># script1 = script.replace(‘opt_size_y=6e-6′,’opt_size_y={:1.6g}’.format(size_y))<br><br>wavelengths = Wavelengths(start = 1550e-9, stop = 1550e-9, points = 1)<br>opt1 = Optimization(base_script=script1, wavelengths = wavelengths, fom=fom1, geometry=geometry, optimizer=optimizer1,<br>use_deps=False, hide_fdtd_cad=True, plot_history=False, store_all_simulations=False, save_global_index=True)<br>opt2 = Optimization(base_script=script1, wavelengths = wavelengths, fom=fom2, geometry=geometry, optimizer=optimizer2,<br>use_deps=False, hide_fdtd_cad=True, plot_history=False, store_all_simulations=False, save_global_index=False)<br>opt3 = Optimization(base_script=script1, wavelengths = wavelengths, fom=fom3, geometry=geometry, optimizer=optimizer3,<br>use_deps=False, hide_fdtd_cad=True, plot_history=False, store_all_simulations=False, save_global_index=False)<br>opt4 = Optimization(base_script=script2, wavelengths=wavelengths, fom=fom1, geometry=geometry, optimizer=optimizer4,<br>use_deps=False, hide_fdtd_cad=True, plot_history=False, store_all_simulations=False, save_global_index=True)<br>opt5 = Optimization(base_script=script2, wavelengths=wavelengths, fom=fom2, geometry=geometry, optimizer=optimizer5,<br>use_deps=False, hide_fdtd_cad=True, plot_history=False, store_all_simulations=False, save_global_index=False)<br>opt6 = Optimization(base_script=script2, wavelengths=wavelengths, fom=fom3, geometry=geometry, optimizer=optimizer6,<br>use_deps=False, hide_fdtd_cad=True, plot_history=False, store_all_simulations=False, save_global_index=False)<br><br>######## PUT EVERYTHING TOGETHER AND RUN ########<br>weights = [0.5, 0.5, 0.5, 0.5, 0.5, 0.5]<br>opT = [opt1, opt2, opt3, opt4, opt5, opt6]<br>opt = SuperOptimization(optimizations=opT,weights=weights)<br>opt.run(working_dir=working_dir)<br><br><br>if __name__ == ‘__main__’:<br>size_x = 12000<br>size_y = 6000<br>filter_R = 200e-9<br><br>x_points=int(size_x\/20)+1<br>y_points=int(size_y\/20)+1<br>eps_wg = 2.8**2<br>eps_bg = 1.44**2<br>x_pos = np.linspace(-size_x\/2*1e-9,size_x\/2*1e-9,x_points)<br>y_pos = np.linspace(-size_y\/2*1e-9,size_y\/2*1e-9,y_points)<br><br>## We need to pick an initial condition. Many different options:<br># params = 0.5*np.ones((x_points,y_points)) #< Start with the domain filled with (eps_wg+eps_bg)\/2<br><span class=”ps-stream-hashtag”>#params<\/span><\/a> = np.ones((x_points,y_points)) #< Start with the domain filled with eps_wg<br><span class=”ps-stream-hashtag”>#params<\/span><\/a> = np.zeros((x_points,y_points)) #< Start with the domain filled with eps_bg<br>params = None #< Use the structure defined in the project file as initial condition<br><br>working_dir = ‘2x3_MMI_Mixer_2scripts_x{:04d}_y{:04d}_f{:04d}’.format(size_x,size_y,int(filter_R*1e9))<br>runSim(params, eps_bg, eps_wg, x_pos, y_pos, size_x*1e-9, size_y*1e-9, filter_R, working_dir=working_dir, beta=1)\"NONE\"<\/p><\/p><\/p>\n","protected":false},"template":"","class_list":["post-426891","topic","type-topic","status-publish","hentry","topic-tag-lumopt-1","topic-tag-mmi-2"],"aioseo_notices":[],"acf":[],"custom_fields":[{"0":{"_bbp_forum_id":["27833"],"_bbp_topic_id":["426891"],"_bbp_author_ip":["2408:8453:618:aead:7023:7e55:7142:7b1d"],"_bbp_last_reply_id":["427515"],"_bbp_last_active_id":["427515"],"_bbp_last_active_time":["2025-04-01 10:29:11"],"_bbp_reply_count":["3"],"_bbp_reply_count_hidden":["0"],"_bbp_voice_count":["3"],"_bbp_engagement":["520400","473055","294329"],"_btv_view_count":["259"],"_bbp_topic_status":["unanswered"],"_edit_last":["473055"],"_bbp_revision_log":["a:1:{i:426999;a:2:{s:6:\"author\";i:473055;s:6:\"reason\";s:0:\"\";}}"],"_bbp_subscription":["473055","294329","520400"]},"test":"longchdtu-dk"}],"_links":{"self":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics\/426891","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics"}],"about":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/types\/topic"}],"version-history":[{"count":1,"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics\/426891\/revisions"}],"predecessor-version":[{"id":426999,"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics\/426891\/revisions\/426999"}],"wp:attachment":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/media?parent=426891"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}