Two novel orthogonal modulation schemes, in which a modified duobinary return-to-zero (MD-RZ) signal was generated as a label for optical switching network, were proposed. In one scheme, a non-return-to-zero differential phase shift keying (NRZ-DPSK) signal was generated as a payload, while in another scheme, a non-return-to-zero differential quadrature phase shift keying (NRZ-DQPSK) format payload was introduced. A simple method, in which the clock was extracted and recovered from label signals, was adopted. The spectra of two optical packet signals in the back-to-back label switching systems with 2.5 Gbit/s label and 10 Gbit/s payload, respectively, are compared. It is shown that the optical packet signal with a larger duty cycle label has higher spectral efficiency. In the back-to-back system, 2.5 Gbit/s MD-RZ labels with different duty cycles can be directly measured by a conventional binary intensity modulation direct detection (IM-DD) receiver. The MD-RZ labels of two optical packet signals can avoid the eye diagram distortion for long-distance transmission if the dispersion can be compensated. When the input power is beyond 18 dBm, the eye-opening penalty of MD-RZ label with a larger duty cycle is more robust in the label-detecting path.