摘要： Lithium Niobate (LN) is a basic material of integrated optics, for example for electro and acousto-optical modulators, switches, diffraction gratings, nonlinear optical wavelength converters and others [1]. LN based ion exchange or Ti-indiffused contact photolithographic techniques are established technologies, however, finite tolerance of optical elements could not respond some modern applications. For example, high-purity suppressed carrier synthesis or high extinction ratio pulse generation for precision measurement systems require additional active trimming electrodes [2] at the device and corresponding servo loop. Recently developed direct laser writing (DLW) of femtosecond/ultrafast laser pulses [3] can be employed to address the problem, but this method is problematic for mass production and suffer from high insertion loss in optical waveguides (typically ~1 dB/cm compared to <0.1 dB/cm for Ti in-diffused waveguides). We have proposed a method that combines low loss of Ti in-diffused technology and passive permanent trimming of DLW. Moreover, the implementation of the proposed technique is based on very cheap commercially available equipment that makes it very attractive. This is a micro-machining of a thin loading metal film on the top of a waveguide. It is based on dependence of plazmon polariton excitation efficiency on the thickness of metal film. Titanium loading film by thickness of 10 nm adds addition insertion losses (~ 1 dB/mm) and changes effective refractive index of the waveguide (~ 10-6(cid:121)10-5). The loading film was deposited in zones of the integrated optical chip which were most sensitive to its influence such as X-type direction coupler and Y-branch. The film thickness of several nanometres allows rather low laser intensity could be used for local ablation. The simple semiconductor pump laser (978 nm) for erbium doped fiber optic amplifier was used. The output fiber was exploited as a probe. The tip of the fiber was positioned close to the integrated optical chip surface. For laser power of 500 mW the intensity on the tip of the output single mode fiber was about 1 kW/mm2. The integrated optical chip was attached to a precise 3-axis translation stage that allowed flexible manipulation of the loading film micro-machining. Monitoring of optical signals (1550 nm) on the output of integrated optical chip provided possibilities on-line control of the trimming. To demonstrate the efficiency of the proposed method the adjustment of extinction ratio ER (relation of maximum transmitted optical power to its minimum) of Mach-Zehnder modulator was performed. ER is critically dependent on precise power balance in both arms of the interferometers. We demonstrate increase in ER in 17 dB (from 30 to 47 dB). Our findings can potentially be applied in modulators for quantum key distribution, precise sensing, high fidelity signal processing and others.