A misalignment compensating optical sensor (222), that is operable to receive excitation light (30) having a range of input propagation angles .omega.. The sensor (222) has a variable reflected propagation angle .theta..sub.0i reflective surface (227) and a sensing waveguide (228). The shape of the reflective surface (227) is selected to maximize the amount of the excitation light (30) it reflects into the sensing waveguide (227) despite misalignment errors between the sensor (222) and the source (58) of excitation light (30). The sensor may also have a lens portion (160) for focusing the excitation light (30) onto the reflective surface (227), and/or a lens portion (174) for collimating the output of signal recovery light (32) from the waveguide (228). An iterative method may be used for designing any particular lens portion (160, 174).